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Aerosol jet printing (AJP) offers a unique solution to fabrication challenges for microelectronic devices due to its microscopic feature resolution, rapid prototyping capabilities, and ability to print on curved surfaces. However, AJP is challenged by a complex set of interrelated process parameters which must be carefully adjusted to achieve desired print properties. A series of studies were conducted to investigate the effects of AJP parameters on properties of silver nanoparticle ink flexible electronics, and to definean optimized set of parameters to achieve desired performance metrics. Specimens were characterized via optical microscopy, profilometry, electrical testing, static bend testing, and focused ion beam sectioning. It was found that silver nanoparticle ink retained chemical and particle size properties over a period of ~25 weeks. The effects of sintering parameters were investigated and it was determined that 175 °C marks a threshold sintering temperature below which prints did not conduct, but above, print conductance increasedand microstructure showed densification and grain growth. A 65°C platen temperature was found to mitigate both spreading and excessive drying of ink. The effects of individual AJP process parameters on deposition thickness and conductance were evaluated. Finally, an orthogonal array optimization study was conducted to arrive upon a set of optimized printing parameters including aerosol and sheath gas flow, atomizer voltage, print speed, and platen temperature. Findings can be applicable to future works seeking to hasten the adaptation of aerosol jet printing to specific applications.

The hybridization of direct write (DW) and additive manufacturing (AM) technologies to create additively manufactured electronics (AME) has enabled the integration of electrical functionality to form multifunctional AM components. Current work in AME has demonstrated the integration of conductive traces into and onto geometries and form factors that are not possible through traditional electronics packaging processes. This has largely been accomplished by using AM and DW technology to deposit conductive inks to form interconnects on the surface of AM substrates or within multimaterial AM geometries. However, the requisite thermal post-processing and high resistivity of the conductive inks and the limitations in thermal and dielectric performance of printable substrates commonly used in AME restrict the capabilities of these parts. This thesis proposes an alternative process for the conformal deposition of low resistivity traces on additively manufactured all-aromatic polyimides (AM-PI) without the use of conductive inks. This is accomplished through the selective patterning of laser induced graphene (LIG), a porous 3D graphene fabricated via laser irradiation, onto the AM-PI. While the resultant LIG is conductive, its resistivity is further reduced by the electrodeposition of copper (Cu-LIG). In this thesis, the synthesis of LIG on AM-PI, thermally post processed to 240℃, 300℃, and 450℃, is demonstrated and characterized through sheet resistance measurements and Raman spectroscopy. AM-PI post-processed to 300℃ demonstrated the lowest resistivity LIG formation (13.8 Ω/square). The resistivity of Cu-LIG is compared to an industry standard silver ink (Micromax CB028) used in direct write hybrid manufacturing applications. Cu-LIG was found to have a measured resistivity (1.39e-7 Ω·m), two orders of magnitude lower than the measured resistivity of the CB028 silver ink (1.62e-5 Ω·m). Additionally, the current capacity of the Cu-LIG was demonstrated and Joule heating of the material was observed via IR thermography. Cu-LIG demonstrated no failure of conductive trace or substrate under 5A of current for 2 minutes, heating to a maximum recorded temperature of 76.3℃. Several multifunctional components were fabricated as case studies to further validate the process. Several small passive electronic devices (e.g., a heater and an interdigitated capacitor) are fabricated to demonstrate selective deposition of complex copper traces. The fabrication of an Archimedes spiral on a hemispherical substrate via Cu-LIG is completed to demonstrate the ability to use the process to fabricate conformal conductive traces. An LED circuit is fabricated on a face-center cubic AM-PI lattice which demonstrates multi-planar fabrication on geometrically complex 3D printed substrates.

The persistent demand for flexible and wearable electronic components in healthcare, aerospace, media, and transit applications has led to a significant shift from traditional electronics processes to printed electronics. Printed electronics are anticipated to establish itself as the industry's dominant force due to their enhanced flexibility, rapid prototyping capabilities, and seamless integration with everyday objects. They are cost-effective and have the scalable option for large-scale production because additive manufacturing techniques are used. Among the various printing methods available, inkjet printing has recently gained popularity for printing electronics, especially capacitors that require precise and complex structures on different substrates. Inkjet printing relies on micro dispensing additive technology, where liquid phase materials are dispensed using the drop on demand (DOD) technique with conductive nanoparticle inks. Researchers have made several attempts to fabricate fully inkjet-printed composite capacitors and have discovered that the permittivity value of the composite increases compared to a polymer. This suggests that using composites as the dielectric material in a capacitor can potentially increase the capacitance value. However, despite the discussion on various composite dielectric materials, there is a scarcity of information on the use of BaTiO3/SU-8 dielectric materials for capacitor applications. To address this gap, the objective of this study is to formulate BaTiO3/SU-8 ink suitable for inkjet printing and develop a printing process for layered metal insulator metal (MIM) structures. The formulated BaTiO3/SU-8 ink is employed to print the dielectric material, while nano silver ink is used for the two electrodes, enabling the fabrication of the capacitor in a single step. The study takes into account volume and speed jetting parameters as well as waveform to achieve optimal and uniform liquid phase material inkjet printing on the substrates. The thickness of the printed layers is measured using a profilometer, and the sheet resistance of the inkjet printed nano silver conductive ink is evaluated using a four-point probe. Furthermore, the dielectric properties of the printed composite are characterized by measuring the capacitance value. The main goal of this paper is to provide insights into the formulation of BaTiO3/SU-8 dielectric materials and understand the processes involved in the fabrication of a full inkjet printed composite MIM capacitor. Additionally, the experimental results will be compared with theoretical models of BaTiO3/SU-8 dielectric developed by our research group. The successful development of inkjet printed composite MIM capacitors using BaTiO3/SU-8 dielectric materials has the potential to revolutionize the field of printed electronics. The ability to print capacitors with higher capacitance values and complex structures on flexible substrates opens up new possibilities for the integration of electronics into various applications. This research makes a valuable contribution to the expanding knowledge base in the field of inkjet printing for electronics, laying the foundation for future advancements in flexible and wearable electronic devices.

Lead halide perovskite nanocrystals (LHP NCs) exhibit interesting and exceptional optical properties such as near-unity photoluminescence (PL) quantum yield and narrow PL emission line widths. As a result, LHP NCs have demonstrated promising potential in an array of optoelectronic devices such as photovoltaics (PVs), light-emitting diodes (LEDs), optical detectors, and lasers. For CsPbI₃ NCs in particular, one of the major obstacles to their commercial success is structural instability of the perovskite phase, which must be managed. Here, a closer look is taken at the PL emission of CsPbI₃ NC films and how it is affected by light and environmental conditions. The thermal phase stability of CsPbI₃ and the impact of surface area and composition are also investigated. Light-induced changes in photophysical and electronic properties in LHPs can affect their performance in device applications. It is revealed that light excitation induces a slow, reversible enhancement in PL lifetime and intensity in films of perovskite-phase CsPbI₃ NCs. Placing the films under vacuum or nitrogen for several minutes was also found to increase the PL lifetime and intensity. A model of slow, humidity and light-sensitive surface states in CsPbI₃ NCs is proposed. Perovskite-phase CsPbI₃ nanocrystals convert to the optically inactive δ-phase at elevated temperature. Alloying with Br was found to improve the phase stability when the films were relatively thin. Films of mixed-halide CsPbI₂.₅Br₀.₅ nanocrystals less than 30 nm thick showed no conversion to the δ-phase even after 1 hour of heating at 250°C, while thicker films still reverted to the δ-phase after heating. These results show that compositional changes and film thickness can have a significant, cumulative effect on the stability of perovskite nanocrystal films. The role of surface area/energy in CsPbI₃ nanocrystal stability is discussed. CsPbI₃ NC-based solar cells were successfully fabricated. This inspired collaborative work on the development of printable, conductive metal-organic decomposition (MOD) inks, which could play a role in the contacts of perovskite PV for low-cost, flexible, and low-temperature applications. Early development and characterization of a screen-printable, air-curable Ni-based MOD ink is detailed. Current performance of this ink is limited by residual carbon contamination, which is a focus of further development.

Multifunctional composites have gained significant interest as they enable the integration of sensing and communication capabilities into structural, lightweight composites. Researchers have explored additive manufacturing processes for creating these structures through selective patterning of electrically conductive materials onto composites. Thus far, multifunctional composite performance has been limited by the conductivity of functional materials used, and the methods of integration have resulted in compromises to both structural and functional performance. Integration methods have also imposed limitations on part geometry due to an inability to adequately deposit conductive material over concave surfaces. Proposed methods of integrating functional devices within composites have been shown to negatively affect their mechanical performance. This work presents a novel method for integrating printed electronics onto the interior surfaces of closed, complex continuous fiber composite structures via the transfer of selectively printed conductive inks from additively manufactured sacrificial tooling to the composite surface. The process is demonstrated by creating multifunctional composites via embossing printed electronics onto structural composites without negatively affecting the mechanical performance of the structure. Additionally, this process expands the ability to pattern devices onto complex surfaces and demonstrates that the transferred functionality is well integrated (adhered) with the composite surface. The process is further validated through the successful completion of two separate case studies. The first is the integration of a functioning strain gauge onto an S-glass/epoxy composite, while a second process demonstration shows a composite surface featuring a band stop filter at the X-band, otherwise known as a frequency selective surface (FSS), to show the process' suitability for high performance, aerospace grade multifunctional composites.

Flexible electronics, as an emerging field, has gained tremendous attention over the past few years with the advancement in areas such as two-dimensional (2D) materials fabrication and transfer printing techniques. Mechanical peeling, where thin film materials or printed patterns are transferred from a donor substrate to a target substrate, is demonstrated to be a promising and key operation to transfer 2D material or fabricating complex flexible electronic devices, and it is shown that in many cases performing the mechanical peeling process at a desired peeling condition is needed for high quality product. However, despite the promise of mechanical peeling techniques, studies on scaling up the process and enabling the process in a high-volume manufacturing setting are lacking. In this study, a R2R mechanical peeling process that enables continuous and high-throughput transfer of 2D materials and printed electronics has been developed. The system allows for speed and tension control and is used for performing 2D materials transfer. A system model of the R2R process is derived by integrating the peeling process with the R2R system dynamics. The proposed model provides fundamental understanding of the physics involved in the process, including the interactions between peeling front and the roller dynamics. The model can be effectively used for control design and simulation. The success of the R2R peeling process is dependent on the peeling front geometry and its stability during the peeling process. A real-time supervisory control strategy is developed to enable the peeling angle control in a R2R mechanical peeling process. The supervisory control strategy utilizes a peeling front model to estimate the peeling speed and the adhesion energy between the donor substrate and the material to be transferred. The information is used to generate reference signals for the web tension controllers at the regulatory level to adjust the web tensions in order to achieve desired peeling angles. The proposed control strategy is demonstrated with both simulation and experimental results. To reject periodic disturbances originating from rotating roller shafts and adhesion energy changes in the laminate, a model-based repetitive controller is developed and demonstrated.

With the growing popularity of interactive learning, an experiment developing a tangible user interface made of paper was performed. Screen printing was utilized to print conductive traces that would connect to a device that has capacitive touch capabilities. A color mixing program was coded to accompany the tangible interface. It was found that a tangible user interface can be successfully made of paper. Further research with development, construction, and testing of this paper tangible interface was proposed.

Precision agriculture is a set of practices that seek to measure and understand different conditions in space and time across a field, in order to manage water and fertilizer efficiently. Precision agriculture requires high spatial and temporal resolution data, which comes from sensors. However, lack of simple, inexpensive, unobtrusive, low- maintenance sensors that can be widely distributed across a field is a challenge for precision agriculture producers. This thesis describes work towards a network of printed, biodegradable, wireless soil nitrate sensors to meet this need. Sensor nodes consist of potentiometric nitrate sensors, passive UHF-RFID antennas, and a silicon chip to manage power and data communication. Over 95% of the mass of the node is biodegradable.The thesis includes a discussion of each part of the sensor stake. Fabrication techniques for biodegradable substrates, conductors, and encapsulants are discussed. A room-temperature process for printing highly conductive zinc on wood using beeswax encapsulants is a key enabling process. Nitrate sensor operation and development are described, and impacts of using biodegradable materials in nitrate sensors are explored. I show the design, fabrication, and testing of compact RF antennas, and discuss modifications which are required when using biodegradable materials. The printed antennas are integrated with silicon integrated circuits to form passive RFID tags. Requirements and challenges for integrating printed potentiometric sensors with these tags are also discussed. Finally, the impacts of field-deployment are explored. This includes materials lifetime characterization, measuring nitrate sensors in field soils, and validating passive RFID communication in growing crops.

Additive manufacturing strategies, including printing, provide tremendous potential to manufacture low-cost, high-performance electronic devices. While printed electronics have been prepared by a variety of traditional printing strategies including gravure and inkjet printing, these techniques face limitations including low lateral resolution and aspect ratio (feature height/feature width) and difficulty aligning multiple layers of functional materials to build complex electronic devices including diodes and transistors. Previous research in the Francis and Frisbie research groups at the University of Minnesota led to the development of the SCALE (Self-aligned Capillarity-Assisted Lithography for Electronics) process to address these limitations. This process combines high resolution UV micro imprinting of capillary channels and connected ink receiving reservoirs with inkjet printing of electrically functional inks into the reservoirs and spontaneous capillary flow which fills the connected capillary channels with the inks. By creating networks of carefully positioned capillary channels, the complex structures of electronic devices are deposited with higher resolution and layer-to-layer positioning accuracy than achieved with conventional printing methods. These strategies are fully compatible with roll-to-roll production, but this capability hadn’t been demonstrated prior to this work. In this dissertation, a process for roll-to-roll production of the plastic substrates patterned with SCALE capillary channels and reservoirs was developed using low-cost, roll-based imprinting stamps and common sources of air entrapment defects were identified and addressed. Low resistance, high precision metal interconnects were developed and optimized using these patterned plastic substrates. Variables affecting the conductor uniformity, flexibility, and reproducibility were identified and optimized to maximize the useful length and electrical performance of the conductors. This resulted in a fully roll-to-roll compatible manufacturing process for low resistance, flexible metal interconnects. A new, two level capillary channel geometry was developed for conductor fabrication to allow the production of solid metal conductors with flat tops, aspect ratios near 2, and precise feature edges, embedded in the plastic substrates. Finally, a roll-to-roll inkjet printing process was developed for full continuous manufacturing of SCALE devices, and silver SCALE conductors were prepared using this continuous process. This work develops strategies for full roll-to-roll production of SCALE devices and high-performance metal interconnects on patterned plastic substrates.

This research proposes a novel approach to printed electronics manufacturing via molten metal droplet jetting (MMJ). Large scale experimental work is presented to establish suitable jetting parameters for fabrication of high quality conductive electronic traces. Following process optimization, resistivity values as low as 4.49 µΩ-cm for printed 4043 aluminum alloy traces have achieved. This essentially matches the electrical resistivity of the bulk alloy, and it represents a significant improvement over results obtained with printed nanoparticle ink electronics. Electrical resistivity of printed traces that undergo static and cyclical flexing is included in the analysis. The cross-sectional area of traces printed with this approach is orders of magnitude larger than those achieved with nanoparticle inks, hence the traces essentially behave like solid-core metal wire capable of carrying very high currents. The relationship between jetting parameters and the equivalent wire gauge of the uniform printed traces is presented. Early experimental trials revealed the formation of large pinholes inside droplets deposited onto room temperature polyimide substrates. This was hypothesized to be due to the release of adsorbed moisture from the polyimide into the solidifying droplet. Subsequent experiments revealed that heating the polyimide substrate drives off the moisture and eliminates moisture-induced porosity. A multi-physics Ansys process model is also presented to understand behavior of molten metal droplets as they impinge upon a temperature sensitive polymer substrate, spread out, cool down, and solidify. The process model allows the study of many process conditions without expensive and time-consuming physical experimentation.

Different additive manufacturing (AM) methods including fused deposition modeling(FDM) and piezoelectrical drop on demand (DOD) inkjet printing have been used in printedelectronics for easy production, easy integration, better performance, and low cost. Thesemethods have been used in producing everyday smart printed electronics such as conformalantennas (planner and non-planar antennas), sensors, actuators, and solar cells createdon flexible and rigid substrates. The performance of printed electronics strongly dependson printing techniques and printing resolution that enhance their electrical and mechanicalproperties. In this dissertation, 3D and surface printing techniques were used to enhancethe performance of printed electronics devices fabricated on rigid and flexible substrates.First, fused deposition modeling (FDM) technique was used to study the effectof 3D printed heterogeneous substrates on radio frequency response of microstrip patchantennas. Microstrip patch antennas created on acrylonitrile butadiene styrene (ABS) substratesthat were designed by 3D CAD design software (SOLIDWORKS) with dimension50mm x 50mm x 5mm and fabricated with different machine infill densities 25%, 50%,and 75% using FDM 3D printer. Then, 3D X-ray microscope was used to measure theactual volume fraction and construct equivalent simulations for series and parallel equivalentdielectrics constant. The patch antennas were tested for resonant frequency usinga vector network analyzer (VNA) combined with ANSYS-HFSS simulation that was developedbased on the permittivity anisotropy in 3D printed heterogeneous substrates toestimate the bulk permittivity of ABS material and study the effect of varying the dielectricconstant in lateral and thickness direction. Also, microstrip patch antenna with dimension30mm x 25mm, was modeled on polydimethylsiloxane (PDMS) substrate with the samedimension of ABS substrate and analyzed for resonant frequency using Ansoft HFSS andCOMSOL Multiphysics software. Then, COMSOL Multi-physics software was used tostudy the behavior of the microstrip patch antenna under different values of compressionand bending loads to check the feasibility of using the microstrip patch antenna as a passivesensor to detect the strain in the structure wirelessly. Second, piezoelectrical drop ondemand (DOD) inkjet printing was used to print uniform and even high conductive nanosilverink on rigid and flexible substrates. For surface printing, Jetlab 4xl was used to printlines of high conductive nanosilver ink (UTDAg) on semicrystalline polyether ether ketone(PEEK) substrate using fly mode printing with burst. Then, optimal bipolar waveform wasgenerated at proper jetting parameters to generate ideal droplet in term of velocity, size,and uniformity. The ideal droplet was ejected at different drop spacing and stage velocityto print uniform and even lines. Physical and adhesion characteristics of the printed lineswere performed by optical microscopy, scanning electron microscopy, surface profilometry,and soak tests. Also, the effect of high stage velocity printing on the spread behaviorof ejected droplet with different droplet spacing on Kapton substrate was studied by printinglines using two bipolar waveforms. The resistance of printed lines were measured atdifferent curing temperature. Finally, the effect of driving waveforms at different jettingparameters on the size and velocity of generated droplet was investigated using smartink(nanosilver ink) produced by Genes’Ink. A new method was developed to measure the sizeof the generated droplet and recognize weather the droplet has a spherical or an ellipticalshape by using Python programming and the result compared with Aphelion imagingsoftware. Finally, lines printed at three waveform voltages on PEEK and glass substrates.

Chemicals are ubiquitous, from the food we eat to the composition of our own bodies. Different chemicals can give us information about ourselves or our surroundings. For example, chemicals in the body can give information about the state of a person's health, while chemicals in the atmosphere can give information about pollution. Chemical sensors are necessary to gain this information. Electrochemical sensors can use electrical signal output to indicate the presence and amount of chemicals. This is done two ways: amperometric sensors output current, and potentiometric sensors output potential. The magnitude of the signal indicates the amount of chemical present. Printing is useful for fabricating these sensors in flexible form factors and for disposable uses.This thesis discusses the development of several different printed electrochemical sensors. An overview is first given of the developments in printed electrochemical sensors which enabled this work. Printed amperometric sensors for determination of lactate in sweat are optimized for sensing the transition from aerobic to anaerobic metabolism. These sensors are printed to accommodate form factors closely matching that of skin. These sensors have a sensitivity of 4.8 uA/mM and a linear range up to 25 mM lactate. However, an investigation into the selectivity of these sensors determines they are susceptible to interference from the salt present in sweat, making them less useful as sensors and more useful as indicators. Potentiometric sensors are proposed as an alternative for sensing metabolites in sweat, due to their selectivity in sweat. Potentiometric sensors cannot be made for sensing lactate, but ammonium sensors are demonstrated instead for determining levels of carbohydrates and metabolic condition. Potentiometric ammonium sensors show a near-Nernstian response of 57.5 mV/decade +/- 0.3 mV/decade. Sweat is not the only application for printed sensors. Printed potentiometric sensors for nitrate in soil are also demonstrated, where printing enables the use of degradable materials. The nitrate sensors have near-Nernstian sensitivity of -53.3 mV/decade +/- 1.1 mV/decade, and the printed reference developed shows relative insensitivity to nitrate in solution. The work discussed here indicates a step toward distributed networks of sensors.

3D printing of multifunctional components using two or more materials is a rapidly growing area of research. Metallic alloy inks have been used with various 3D printing techniques to create functional components such as antennas, inductors, resistors, and biocompatible implants. Most of these printing techniques use premixed metallic alloy inks or nanoalloy particles with a fixed composition to fabricate the functional part. Since the properties of alloys vary with changes in the elemental composition, a printing process which could digitally dispense alloy inks having specific desired compositions would enable different functionalities and be highly desirable. Using the binary copper-nickel system as an example, the formation of alloy with metal precursor inks is presented. Since copper and nickel both have a face centered cubic (FCC) structure and show complete miscibility in each other, formation of their nanoalloy is, in theory, relatively easy. By printing metal precursor inks rather than nanoparticle suspensions, problems associated with the nanoparticle inks such as ink stability and nozzle clogging can be avoided. Copper and nickel precursor inks were formulated having rheological properties suitable for inkjet printing. Reduction of metal inks was studied under various conditions. The sintered metal and alloy structures were characterized using thermal analysis, infrared spectroscopy, energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction. Nickel, a ferromagnetic metal, showed novel microstructures such as aligned nanowires and nanowire grids when reduced in the presence of a magnetic field. These microstructures had enhanced anisotropic electrical and magnetic properties along the direction of the nanowire. The reduction of combined ink solutions (copper and nickel) showed formation of a two phase with copper as one phase and a nickel rich alloy as other. These structures demonstrated no change in electrical resistivity when exposed to an oxidation rich environment. To achieve a homogeneous alloy formation, the copper phase and the nickel rich phase were diffused together at high temperatures. Copper nickel alloy inks with ratios Cu30Ni70, Cu50Ni50, and Cu70Ni30 were formulated and reduced at 230 °C and later high temperature diffusion was achieved at 800 °C. The lattice parameter of the alloy phase for the inks with ratio Cu30Ni70 was 3.5533Å, Cu50Ni50 was 3.5658 Å, and Cu70Ni30 was 3.5921 Å. Using Vegard’s law, the composition of the alloy phases for the three samples were estimated to be Cu32Ni68, Cu46Ni54, and Cu75Ni25. This formation of the desired alloy composition can open the door to numerous applications in biomedical and electronics sectors, among others

With the impending development of the Internet of Things (IOT) and wearable technology, the consumer electronics market is subject to enhanced demand for flexible circuits. Printing of electronic inks is regarded as a promising route to realize low-cost, high-throughput manufacturing of flexible electronic devices for a variety of novel applications. Roll-to-roll printing, in particular, can significantly improve the throughput and further reduce production costs. Although several printing techniques, such as inkjet printing, aerosol jet printing and gravure printing, are compatible with roll-to-roll processing, there are several key technical challenges when making flexible circuits with excellent electrical performance and high yield by roll-to-roll printing. First, materials registration is a significant challenge when building multi-layer devices by printing on a moving web. Misalignment of different material layers may degrade device performance or cause electrical shorts. Patterning small features less than 10 μm is another technical challenge for printed electronics. These two challenges limit the industrial application of roll-to-roll printing. To address these two challenges, a novel method termed SCALE (Self-aligned, Capillarity-Assisted Lithography for Electronics) has been developed to fabricate multiple components of integrated circuits. SCALE utilizes micro-imprinting to create a complex network of circular ink receivers and small capillary channels on the top surface of a plastic substrate. When inks are printed into the receivers by a drop-on-demand inkjet printhead, they spontaneously flow under capillary forces into all the capillary channels connected to the receivers. Film deposition occurs upon drying of the inks. Different films can be layered on top of one another by delivering each ink sequentially into receivers with overlapping ink receivers or capillary channels. Since receivers have diameters on the order of 100 μm, the precision required to deliver ink is substantially relaxed. Consequently, this process is more suitable for printing on a moving web and more compatible with high-throughput, roll-to-roll processing. In this thesis, fabrication of fully-printed resistors and low-pass RC filters via this self-aligned strategy is presented. Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was used as the resistive material, and silver was used for the electrodes. Using SCALE, fully inkjet-printed, self-aligned resistors were achieved with resistance values ranging over five orders of magnitude while keeping the overall dimensions of the devices constant. SCALE was then employed to build low-pass RC (resistor-capacitor) filters with cutoff frequency from 0.4 - 27 kHz and excellent operational stability. Self-aligned, fully printed diodes on plastic substrates were also demonstrated using SCALE in this thesis. A new pattern design for devices in a vertically stacked structure is reported, which incorporated flow control structures to realize better control of ink flows and to improve device yield. Printed diodes exhibited outstanding rectification ratios (>1E4) and excellent stability against repeated bending. Overall, the work in this thesis expands the potential of self-aligned inkjet printing for producing fully printed electronic circuits.

Abstract: Skin-adhesive electrodes – more preferably, integrated electronic systems with embedded signal processing and transmittance – that can be worn comfortably on a patient have irreplaceable importance in healthcare. For example, surface electromyography (sEMG) is a non-invasive electrodiagnostic medical technique to detect, record, and interpret electric activity of groups of muscles from skin surface right above them. If skin-adhesive sEMG electrodes can be integrated with wireless data processing and transmittance system in a compact and wearable format, these devices can provide unprecedented opportunities for applications such as posture monitoring for rehab medicine, swallowing self-coaching, and muscle fatigue detector. However, there are stringent demands for form factors that are specific for the target locations in body, such as required level of flexibility, foldability and stretchability. The conversion of electronics into such advanced form factors has been arising the current challenges in the skin-adhesive electronic systems, such as poor reusability, complicated fabrication methods, and poor connection between soft and hard components in the electronics system. In this thesis, we have explored the potential solutions to solve these problems.Overall, this thesis is divided into two themes. In the first theme, we developed a versatile technology with capability of rapid, simple, customizable fabrication of flexible printed circuit boards (Flex-PCBs) and sensors. A simple and cost-effective wax-printing technique to pattern flexible interconnects allowed the system-level integration of sensing, processing, power, and wireless communication units. The flexible circuitry with reusable adhesive can follow the contour of curvilinear skin topology, thus allow enhanced wearability for skin-adhesive electronic systems. In the second theme, we developed textile-based electronics, also known as 'e-textiles', which offer stretchability and comfort for patients. A stretchable conductive silver ink was developed for ink-jet printing to pattern stretchable circuits on nano-textiles. The deep permeation of ink into nano-textiles resulted in stable adhesion, mechanically and electrically strengthen. With our custom-developed electronic circuits, we demonstrated a sEMG system with wireless data emission.

A transistor is an electrical circuit element which acts as a switch, can tune the current in an electrical circuit, and can amplify input signals. Fast switching with low-operating voltage and high amplification are desired characteristics for transistors but are not readily achieved by printed electronics. Electrolyte-gated transistors (EGTs) are a specific class of transistors with an electrolyte as the gate dielectric. Using electrolyte as the gate dielectric enables low-operating voltage, high amplification (gain), and relaxed fabrication requirements. Electrolytes have a huge capacitance which is thickness independent thanks to the formation of electrical double layers (EDL) at the interfaces of the electrolyte with the electrodes. Ion gel is a type of electrolyte consisting of an ionic liquid and a triblock copolymer. The polymer is responsible for providing mechanical integrity, whereas the ionic liquid is responsible for the gating mechanism with great electrical, physical, chemical, and electrochemical properties. Ion gels pave the way for miniaturizing EGTs and their use in printed electronics. Despite all the promising properties of printed EGTs including low-operating voltage, ease of printing, flexibility, and low-toxicity, fast EGTs have not yet been demonstrated. Similarly, higher EGT gain is also required to improve the sensitivity and computational power of devices. In this thesis, the EGT working principles have been investigated, as well as the effects of EGT architectures, materials, components, printing resolution, and precision on the EGT operating speed and gain. New architectures have been designed to produce fast and high-performance EGTs. Modification of EGT architectures and components enabled us to achieve 5 MHz operation with an order of magnitude increase in gain and amplification. In order to fabricate different architectures, a variety of techniques including inkjet, aerosol-jet, and screen printing have been employed. Screen-printed, UV-cured ion gels with a line width resolution of 10 µm have been demonstrated. In conclusion, in this thesis, the performance of printed ion gel-based electrolyte-gated transistors has been investigated and improved by relating the device dynamic and static characteristics to its material components and architecture.

Advancements in manufacturing for printed electronics have brought with it a demand for printed, rechargeable batteries capable of powering these devices. This research aims to meet this demand by characterizing and optimizing components and performance of a printed, rechargeable Zn-MnO2 cell with an ionic liquid gel polymer electrolyte.The cathode and anode are comprised of manganese dioxide (MnO2) and zinc (Zn) respectively. The ionic liquids 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]+[OTf]-) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM]+[OTf]-) with the dissolved salt zinc trifluoromethanesulfonate (Zn(OTf)2) are used as the electrolyte. These nonaqueous electrolytes have been shown to enable rechargeable zinc chemistries as well as compatibility with solution-cast polymer membranes to form gel polymer electrolytes (GPEs). When combined with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) that is dissolved in n-methyl-2-pyrrolidone, a printable separator membrane capable of ionic conductance is produced. This separator membrane can then be incorporated into a layer-by-layer additive manufacturing process to produce a fully printed battery.To produce consistent fully printed cells and to prevent catastrophic cell degradation and failure, additional variables must be considered and optimized. The printed electrode composition must be optimized for surface profile, rheology, and electric conductivity in order to enable uniform and dense separator layers. The ionic liquid electrolyte composition and gel polymer electrolyte morphology must be controlled in order to optimize mass transport and reaction kinetics. Furthermore, the mass transport and kinetic properties of Zn deposition and dissolution in ionic liquid electrolytes and gel polymer electrolytes must be characterized and understood. To characterize these aspects, battery components were produced via stencil casting, doctor blade coating, and solution casting. Electrochemical properties were characterized by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Physical and electric properties were characterized by rheometry, profilometry, four point probe resistivity, and scanning electron microscopy. Cell performance was characterized by galvanostatic and potentiostatic cycle life testing and pulsed current discharging, and differential capacity analysis was performed for further insights.Ball milling and mechanical sieving was found to be an effective method to improve printed electrode surface profile, reducing waviness and roughness each by a factor of 4 compared to unoptimized electrodes while retaining similar conductivity. Zn deposition and dissolution were found to be kinetically (rather than mass transport) limited and therefore quasireversible in both ionic liquids. Zn2+ diffusivity ranged from 1.42-3.38e-9 cm2/s in [BMIM]+[OTf]- electrolytes and from 1.64-4.87e-9 cm2/s in [EMIM]+[OTf]- electrolytes, decreasing with higher concentrations of Zn(Otf)2 salt. [EMIM]+[OTf]- electrolytes were found to provide higher Zn diffusivity, ionic conductivity, and redox kinetics, but were also more prone to forming electrical shorts through the GPE and offered lower discharge capacities than [BMIM]+[OTf]- electrolytes. The polymer structure in the GPE was found to be highly dependent on processing temperature and pressure.Fully printed cells were produced that prevented catastrophic cell failure from delamination of the cathode, resulting in at least a 20x improvement in cycle life compared to mechanically assembled cells. Average discharge capacities for fully printed cells ranged from 1.8-3.6 mAh/cm3, and cells were cycled at least 200 times without catastrophic failure. Critical cell failure mechanisms including phase transformations of MnO2 and deposition of Zn within poor GPE microstructures were identified. Finally, printed cells were discharged under a pulsed current discharge regime typical of those found in Internet of Things devices for 650 cycles without signs of degradation.This research has successfully produced and characterized fully printed, rechargeable, Zn-MnO2 cells with an ionic liquid gel polymer electrolyte for printed electronics and the Internet of Things. The results presented herein seek to further understanding of Zn interactions with ionic liquid gel polymer electrolytes and additive manufacturing methods for printed energy storage devices.

Ion gels are a versatile class of functional materials. Combining the excellent electrical properties such as high ionic conductivity and capacitance of the ionic liquid (IL) and the mechanical integrity of the polymer, the composite materials have led to a variety of applications such as electrolyte-gated transistors (EGTs), electroluminescent, and electrochromic soft materials. This thesis is built up from previous research on the electrical and mechanical properties of the ABA triblock polymer-based ion gels and continues to improve properties of the materials for electrochemical device applications. In the first part of the thesis work, the objective is to improve the existing ABA triblock polymer systems with poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA) as the IL-solvating midblock by combining the merit of the low Tg from PEO and hydrophobicity from PMMA into one system. As a result, poly(styrene-b-ethyl acrylate-b-styrene) (SEAS) triblock polymer was developed. The ion gels made with SEAS demonstrate similarly high ionic conductivity as the PEO-based ion gels, which are significantly improved from those of the PMMA-based ion gels. By shortening the midblock size of the triblock polymer, a synergistic improvement of both the ionic conductivity and the modulus can be achieved. Additionally, the EGTs made by SEAS-based ion gels demonstrate superior stability under humidity compared with EGTs made by SOS-based ion gels. In the following two projects of the thesis work, the polymer platform changes from petroleum-based polymers with hydrocarbon backbones to renewable aliphatic polyesters with the potential aim of EGTs in biocompatible applications. To achieve the ion gels, both physical and chemical crosslinked-systems have been explored. The physically crosslinked ABA aliphatic polyester triblock ion gels demonstrate good mechanical integrity and can be successfully printed under similar conditions as the previous systems, and demonstrate improved ionic conductivity from the PMMA-based ion gels. In addition, the resulting ion gels also demonstrate efficient hydrolytic degradation under basic condition. In a different approach, chemically crosslinked poly(lactide) (PLA)-based ion gels can be synthesized from a facile one-pot method. Owing to a smaller volume fraction in ion-insulating domain, the ion gel demonstrates an excellent ionic conductivity at low polymer concentration. Meanwhile, the ion gel also possesses a high toughness owing to the chemical crosslinks. The thin chemically crosslinked PLA-ion gels can be laminated onto EGTs via a cut-and-stick method. On the other hand, the bulk ion gel demonstrates a good electromechanical response with high electromechanical sensitivity with the applied strain and a low hysteresis between stretching and unstretching.

Printed electronic fabrication processes have received much attention in recent years due to its potential applications in creating affordable, flexible, low-waste, and diverse electronic devices. The Fujifilm DMP-2830, a compact inkjet material deposition system new to the electronics fabrication labs at Ohio University, is explored and optimized in this thesis by printing two silver nanoparticle inks on glass, photopaper, and PET substrates. A systematic approach toward the characterization of the two nano-inks and common substrates as well as test devices is provided to develop useful fabrication recipes for future users of the DMP-2830. Various designs of resistors, capacitors, and inductors are fabricated on glass, photopaper and PET. For each test device, effects of process and geometric parameter changes were studied. Two sensor applications were also demonstrated to indicate the potential of inkjet printed sensors for future research. The first sensor was a resistive bend sensor to sense motion/deformation, and the second was a capacitive wax microfluidic sensor with a novel printed fabrication approach. It is believed that the methods employed in the characterization of nano-inks and devices in this thesis can be emulated by other materials and substrates in the future when the DMP-2830 is utilized to print a wide range of advanced sensors and devices.

[RESEARCH] QUESTION: How can the principles of temporary and the ephemeral be employed by design in the critical redesign of consumer technological artefacts? OBJECTIVES: - Develop a taxonomy of ephemerality in design, print and technology. - Establish an understanding of the role and function of the ephemeral in the design of products, with emphasis on electronic products. - Establish an applied level of understanding about product design and sustainable products. - Investigate printed electronics and define the key application parameters, including functionality, lifetime (shelf and operation), stability, and homogeneity. Further investigate issues of sustainability in the printing industry and the electronic industry. - Establish and understand current user perception towards sustainability and durability in relation to technological artefacts. - Research and Develop a body of critical design approaches and strategies that result in critical design concepts that aim to provoke and transform people’s perceptions of the durable and sustainable dimensions of consumer technological products. - Develop a suite of experimental prototypes by employing printed electronics and communicate strategies to test the central proposition of this project. - Evaluate the efficacy of the design concepts developed in response to perceptions towards sustainability and durability in relation to technological artefacts. - Synthesise, illustrate and communicate the outcomes and present in conjunction with the prototypes at an Exhibition. This project’s aim is to develop design strategies that explore the potential of the ephemeral and the temporary in the context of consumer electronic artefacts, by implementing printed electronics in the service of sustainable futures. This research-led design project will establish the current perceptions users have towards sustainability and durability in relation to information consumer technology (ICT) objects. The ambition is to create critical and speculative artefacts, that make consumers stop for a moment to reassess their habits and behaviours when utilizing ICT and their attitude towards sustainability. This project will make a valuable contribution to the print and ICT market. Furthermore, it will push boundaries of the way ICT can be used, advocate sustainable ideas, with the potential of recycling, upcycling or biodegrading after its use.

Wearable medical sensors that can monitor biosignals have the potential to transform healthcare - they encourage healthy living by providing individuals feedback on personal vital signs and enable facile implementation of both in-hospital and in-home health monitoring. To date, fabrication of wearable medical sensors heavily relies on conventional semiconductor vacuum-processing, which is expensive and has limited large-area scalability. Taking advantage of the unique manufacturing capabilities of printed electronics, we can now design wearables that are soft, lightweight, and skin-like. These soft and conformable sensors significantly improve the signal-to-noise ratio (SNR) by establishing high-fidelity sensor-skin interfaces. This thesis presents a review of existing literature on flexible and wearable health monitoring devices, discusses different printing techniques for fabricating wearable medical sensors, and highlights two sensing modalities: bioelectronic and biophotonic. For bioelectronic sensing, the design and fabrication of flexible and inkjet-printed gold electrode arrays are demonstrated, which are implemented in a smart bandage for early-detection of pressure ulcers. Also, the efficacy of the electrodes is demonstrated on conformal surfaces and on the skin to record electrocardiography (ECG) and electromyography (EMG) signals. For biophotonic sensing, an all-organic optoelectronic sensor is demonstrated for transmission-mode pulse oximetry, which accurately measures pulse rate and oxygenation. Since transmission-mode pulse oximetry can only be performed at the extremities of the body and requires a pulsatile arterial blood signal - printed, organic, reflection-mode oximeters are reported. The design, sensing methodology, and fabrication of a flexible and printed sensor array composed of organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) are shown, which senses reflected light from tissue to determine the oxygen saturation. The sensor is implemented to measure oxygen saturation on different parts of the body and to create 2D oxygenation maps of adult forearms under pressure-cuff-induced ischemia. Finally, a key enabling technology for wearables - flexible hybrid electronics (FHE) is presented. The implementation of FHE in an integrated multi-sensor platform is discussed, where soft sensors are interfaced with hard silicon-based integrated circuits for wearable health monitoring.

Ubiquitous low-cost sensing remains fundamental to next generation energy, environmental, and industrial situational awareness. Intelligent decision systems of the future require a continuous feed of measurements from a diverse portfolio of sensors. Applications in a variety of areas will undoubtedly rely on different parameters to be measured, but can such sensors be printed? Can such sensors take interesting forms – including transparency? Sensors explored in this dissertation are fundamental to envisioned intelligent decision systems of the future.Flexible in both form and ease of deployment, unpowered printable sensors have the potential to change industry in a profound way. This dissertation will explore the design, production, and implications of these devices. Highly discriminative low-cost sensors are needed for remote and continuous monitoring of a variety of applications within the broad field of “energy”. Challenges remain for low-cost continuous monitoring of physical and chemical parameters for applications in electrical generation, transmission, and distribution. Associated equipment generates greenhouse gas (GHG) emissions and often generalized air pollution (nitrogen oxides, sulfur oxides or particulates). Taking a broader view of energy, there are leaks from hydraulic fracturing sites that should be measured and monitored for environmental considerations. Printable low-cost sensors could support portable systems for detection, quantification, and continuous monitoring. Current methods for detection and measurements of physical and chemical parameters fail to offer cost-effective remote or/and continuous monitoring of these parameters.The area of printed electronics – printed sensors – forms the core of this dissertation research topic, however, the implications of this research are far reaching. There are technological and fundamental science and engineering questions that need to be answered in order to determine if printed electronic sensors – including transparent sensors – are a viable candidate for use in the general area of energy science applications. The parameters of interest simply within “energy applications“ - or expanded to industrial settings - stretch from physical parameters (temperature, humidity, etc.) to environmental parameters (including the aforementioned chemicals) to electromagnetic parameters associated with the electric grid’s operation. The product of this dissertation is to determine if printed sensors – including transparent sensors – will provide continuous and ubiquitous sensing for energy applications.

Printed electronics and microfluidics are two emerging and developing technologies with the common attractive feature of scalability. Advancements in fabrication capabilities have evolved research questions from, “What can we build?” to, “What should we build?”. This work focuses on the combination of these two technologies and their application to biosensing. The motivating theme is to understand how integrated, functional materials interact, elucidate the underlying molecular phenomena, then utilize the emergent advantages to address the outstanding limitations of conventional biosensing strategies. Printed electronics have recently been applied to biological detection with a variety of techniques1 while microfluidics, since their inception, have been used to handle biological fluids.2 The work presented here outlines a patented sensing strategy based off Floating-Gate Transistors (FGTs). The FGT design physically separates the electronic materials and biological fluids and thus bypasses various compatibility obstacles limiting other next-generation sensor technologies.3 The specific changes in interfacial properties that lead to robust signal transduction are derived empirically.4 This is followed by a mechanistic investigation into the molecular origin of sensor operation when FGTs are used in biomolecular detection. Finally, the versatility and scalability engendered by facile prototyping of FGTs is exemplified by successful iterations to DNA,3 ricin,5 and gluten proteins. The first proof-of-principle experiments incorporated printed electronics with an elementary biological system of DNA oligonucleotides. The results successfully demonstrated the potential of FGTs but failed to solidify their concrete value. Systematic investigation into the complex dynamics at the interface of chemically functionalized electrodes and electrolytes uncovered the most attractive features of the FGT technology. The chemistry was tuned with molecules that range in complexity from simple, short-chain alkyl-thiols to reversible protein-protein interactions. The observed responses with well-controlled systems were generalized to real systems like protein capture in food matrices (e.g. ricin in milk, orange juice). The resulting versatility originated from the label-free, electronic sensing mechanism and opened a range of possibilities for FGTs’ impact. The fundamental insights into interfacial dynamics, device operation, and biomolecular interactions were made possible by the advancements in the materials science and fabrication techniques underlying the presented results. Future avenues of development are hypothesized along with the most promising strategies. The continued elucidation of the physical mechanism and engineering upgrades justify the proposed strategies and inspire the continued effort to fully realize the potential of FGT biosensors.

Printed electronics is emerging as an integral part of the electronic industry due to its low cost fabrication and flexibility of devices against the rigid and expensive technology using silicon. Various methods for printing have existed for a long time with inkjet printing being the most common method used for electronic devices. This thesis explores a new and innovative printed technology using a capillary based microplotting approach implemented via Sonoplot Microplotter II. Unlike the inkjet printing technique which prints in overlapping spots with resolution between 30µm-100µm, the Microplotting approach helps to prints continuous features with a higher resolution as low as 5 ¿¿. Capillary action is used to fill picoliter amount of ink into a micropipette which is used for printing. Thus, the focus of this thesis is the optimization of this new printing technology under various conductions using different conductive inks and on a broad range of substrates and different tip diameters. In addition, passive resistive, capacitive and inductive components were printed to characterize the printing process and operation of electrical devices under different conditions. The applications of this Microplotter was further demonstrated by printing a flexible resistive strain sensor. The procedures involved for the fabrication of micropipettes using a glass puller for different diameter tips attached to the dispenser head is also explained in this thesis.

Aerosol Jet® Printing (AJP) is a direct-write based additive manufacturing process that is capable of printing electronics with fine features and various materials. It eliminates the complex masking process in traditional semiconductor manufacturing, thus enables flexible electronics design and reduces manufacturing cost. However, the quality control of AJP processes is still a challenging problem, primarily due to the lack of understanding of the potential root causes of the quality issues. There is a complex interaction among process setting variables, in situ feature variables, and quality variables in AJP processes. In this research, an ensemble model strategy is proposed to quantify the effect of the process setting variables on the in situ feature variables, and the effect of the in situ feature variables on quality variables in a two-level hierarchical way. By identifying significant in situ feature variables as responses for the process setting variables, as well as predictors for product quality in a joint estimation problem, the proposed models have a hierarchical variable relationship to enable in situ process control for variation reduction and defect mitigation. A real case study is investigated to demonstrate the advantages of the proposed method.

A solid silver – ligand complex, m-oxolato-bis(ethylenediaminesilver(I)) was developed for formulating particle-free conductive inks. The complex has approximately 47% silver content by weight and is soluble in ink-jet compatible polar solvents. Aqueous ink formulations for the inkjet printing was developed to print uniform films on glass and polyimide substrates. When cured, printed films comprising crystalline metallic silver was determined by XRD. Optimized curing conditions were found to be 120°C for less than five minutes, which may be compatible with high throughput printing. Cured films demonstrated better adhesion on polyimide substrates than on glass. This study has improved the state of the art material used for MOD inks and provided a method for printing on a variety of flexible electronic form factors.

Transparent metal oxides are one of the most promising material systems for thin film flexible electronics due to their unique balance of optical transparency and high electron mobility. Rapid progress in the field of solution-processed metal oxides in the last decade has established them as the leading material system for thin film transistors. Fully-integrating metal oxide materials with printing technologies could enable a wide range of applications such as flexible displays, imaging systems, resorbable bioelectronics, and low-power sensors that remain uneconomical or unmanufacturable with incumbent technologies. This thesis contributes materials and methods that can advance the scalable fabrication of transparent thin film transistors by high-speed gravure printing. Through these studies, an understanding of the interactions between ink chemistry, fluid parameters, printed feature formation, and electronic properties is presented.In the past, gravure-printed electronics has been limited to printing organic inks and metal nanoparticles. Here we couple an understanding of the physics of gravure printing on glass with strategies for inorganic sol-gel ink design to extend the scope of high-speed printing to new high-performance inorganic materials including transparent conductive oxides (TCOs). We explore the impact that ink design has on material properties such as crystallinity, conductivity, transparency, and performance under mechanical bending stress, leading to effective co-optimization of patterning and TCO performance. Furthermore, these ink design principles are applied to silver nanowire hybrid sol-gel inks which allow gravure printing of high figure of merit mechanically robust, transparent conducting films using low processing temperatures.Additionally, this thesis will discuss the design and construction of a custom gravure printer for high-speed patterning and accurate registration of printed layers. The novel design allows the decoupling of the individual subprocesses of gravure to allow mechanistic studies of major printing artifacts and improved areal uniformity. A new understanding of the role of gravure contact mechanics in ink transfer and doctoring is presented.This work also develops high-performance materials for scaling down the process temperatures of printed metal oxide devices. Aqueous ink formulations are explored for inkjet printing transparent electrodes and channel materials in transparent thin film transistors. The unique printing physics, electrical contact properties to aqueous semiconductors, and low-temperature processability of these inks are studied to achieve high-resolution printed TCOs at plastic compatible temperatures below 220 °C. Additionally, low-temperature, UV-annealed high-k dielectrics are presented for processing printed metal oxide transistors. High-performance printed transistors are achieved with high operational stability and connections between bias-stress stability and low-temperature processing are studied.

This thesis reports a 100% inkjet printed transistor with a short channel of approximately 1 µm operating at up to 18.21 GHz. The small gap size is achieved through the use of silver inks with different chemical properties to prevent mixing. Semiconducting single walled carbon nanotubes were printed using deposition methodologies for the semiconducting layer. The combination of the short channel and CNT based semiconductors allows for an exceptional experimentally measured on/off ratio of 106. This all inkjet printed transistor potentially allows for the fabrication of devices using roll-to-roll methodologies with no pre or post processing.

Printed electronics processes have the potential to make electronics manufacturing more flexible by providing a wider choice of materials and easier processing steps. In traditional electronics manufacturing techniques, corrosive etching steps limit the choice of materials and also require advanced infrastructure for process implementation. High speed low cost printing processes (e.g. inkjet) can be used, and the printed tracks can then be cured to conductive circuits that meet the needs of electronic devices like radio frequency identification (RFID) tags, sensors, etc. In this work, intense flashes of broad spectrum light from Xenon lamps are used to cure inkjet printed metal nanoparticle inks. This technique is known as photonic curing. Paper, polyethylene terephthalate (PET), and polyimide have been used as substrates with the aim of determining how different substrates affect the behavior of the ink and the photonic curing parameters. A statistical approach was employed for the experiments, and significant control variables determining curing of the ink were identified. Experiments were also conducted to obtain prints conforming to dimensional tolerances. Using the results from the experiments, standard curing parameters for low resistance and good adhesion of the ink were obtained. The results have been statistically validated and used to study the interaction between the control variables and individual effects of each control variable on the response variable.

Printed electronics is a novel microfabrication paradigm that is particularly well suited for fabrication of low-cost, large-area electronics on flexible substrates. Applications include flexible displays, solar cells, RFID tags or sensor networks. Gravure printing is a particularly promising printing technique because it combines high print speed with high resolution patterning. In this thesis, gravure printing for printed electronics is advanced on multiple levels. The gravure process is advanced in terms of tooling and understanding of printing physics as well as its application to substrate preparation and device fabrication.Gravure printing is applied to transform paper into a viable substrate for printed electronics. Paper is very attractive for printed electronics because it is low-cost, biodegradable, lightweight and ubiquitous. However, printing of high-performance electronic devices onto paper has been limited by the large surface roughness and ink absorption of paper. This is overcome here by gravure printing a local smoothing layer and printed organic thin-film transistors (OTFTs) are demonstrated to exhibit performance on-par with device on plastic substrates.If highly-scaled features are to be printed by gravure, traditional gravure roll making techniques are limited in terms of pattern definition and surface finish. Here, a novel fabrication process for gravure rolls is demonstrated utilizing silicon microfabrication. Sub-3μm features are printed at 1m/s. Proximity effects are demonstrated for more complex highly-scaled features. The fluid mechanics of this effect is studied and it is suggested how it can be used to enhance feature quality by employing assist features.Finally, advancements are made to printed organic thin-film transistors as an important technology driver and demonstrator for printed electronics. First, a novel scanned thermal annealing technique is presented that significantly improves the crystallization of an organic semiconductor and electrical performance. Second, transistors are fully gravure printed at a high print speed of 1m/s. By scaling both lateral and thickness dimensions and optimizing the printing processes, good electrical performance, low-voltage operation and low variability is demonstrated.

Emerging wireless and flexible electronic systems such as wearable devices and sensor networks call for a power source that is sustainable, reliable, has high power density, and can be integrated into a flexible package at low cost. These demands can be met using photovoltaic systems, consisting of solar modules for energy harvesting, battery storage to overcome variations in solar module output or load, and often power electronics to regulate voltages and power flows. A great deal of research in recent years has focused on the development of high-performing materials and architectures for individual components such as solar cells and batteries. However, there remains a need for co-design and integration of these components in order to achieve complete power systems optimized for specific applications. To fabricate these systems, printing techniques are of great interest as they can be performed at low temperatures and high speeds and facilitate customization of the components.This thesis discusses the development of printed and flexible photovoltaic power systems, spanning both device-level and system-level design. Photovoltaic cells and multi-cell modules are designed and manufactured using solution-processed organic materials. The use of carbon nanotube films as a flexible, low-cost, solution-processed transparent electrode for photovoltaics is investigated. Then, photovoltaic modules are integrated with batteries into energy harvesting and storage systems with multiple power levels and form factors, optimized to deliver power to loads such as wearable medical sensors. The energy collecting potentials of these systems are evaluated under indoor and outdoor lighting conditions. Designing the solar module maximum power point to match the battery voltage, as well as optimizing load characteristics such as duty cycle, are shown to enable power systems with long-term wireless operation and high efficiency. Finally, screen-printed passive components are developed and demonstrated in a hybrid flexible voltage regulator circuit. In particular, high-quality printed spiral inductors satisfactory for power electronics applications are achieved through optimization of the geometry and fabrication. Overall, the high-performance devices and integrated system designs demonstrated here have the potential for significant impact in the areas of flexible, portable and large-area electronics.

Light and image sensors are ubiquitous and used in a wide variety of applications ranging from consumer products to healthcare and industrial applications. The signal-to-noise ratio (SNR) from a photodetector element increases with larger photoactive area, which is costly to scale up using silicon wafers and wafer-based microfabrication. On the other hand, the performance of solution-processed photodetectors and transistors is advancing considerably. It is proposed that the printability of these devices on plastic substrates can enable low-cost areal scaling for high SNR light and image sensors.This thesis advances the performance of printed organic thin film transistor (OTFT), pho- todiode (OPD), and phototransistor (OPT) devices optimized for light and image sensing applications by developing novel printing techniques and creating new device architectures. An overview is first given on the essential figures of merit for each of these devices and the state of the art in solution-processed image sensors. A novel surface energy-patterned doc- tor blade coating technique is presented to fabricate OTFTs on flexible substrates over large areas. Using this technique, OTFTs with average mobility and on-off ratios of 0.6 cm^(2)/Vs and 10^(5) are achieved, which is competitive with amorphous silicon TFTs. High performance OPDs are also fabricated using doctor blade coating and screen printing. These printing processes give high device yield and good controllability of photodetector performance, enabling an average specific detectivity of 3.45×10^(13) cm·Hz^(0.5)·W^(-1) that is higher than silicon photo- diodes (10^(12-13)). Finally, organic charge-coupled devices (OCCDs) and a novel OPT device architecture based on an organic heterojunction between a donor-acceptor bulk heterojunction blend and a high mobility semiconductor that allows for a wide absorption spectrum and fast charge transport are discussed. The OPT devices not only exhibit high transistor and photodetector performance, but are also able to integrate photogenerated charge at video frame rates up to 100 frames per second with external quantum efficiencies above 100%. Applications of these devices include screen printed OTFT backplanes, large-area OPDs for pulse oximeter applications, and OPT-based image sensors.

During intaglio (gravure) printing, a blade wipes excess ink from the engraved plate with the object of leaving ink--filled cells defining the image to be printed. That objective is not completely attained. Capillarity draws some ink from the cell into a meniscus connecting the blade to the substrate, and the continuing motion of the engraved plate smears that ink over its surface. That smear behind the cell delivers a feature lacking in sharpness. Even though the smear formation occurs at micron scale, it affects the functionality at the scale of micron size printed electronics. By examining the limit of vanishing capillary number ($Ca$, based on substrate speed), we reduce the problem of determining smear volume to one of hydrostatics. Using numerical solutions of the corresponding free boundary problem for the Stokes equations of motion, we show that the hydrostatic theory provides an upper bound to smear volume for finite $Ca$; as $Ca$ is decreased, smear volume increases. The theory explains why polishing to reduce the tip radius of the blade is an effective way to control smearing. As the motion continues, smear volume under the meniscus is printed as a tail behind the cell extending back toward the blade. In the limit of vanishing $Ca$, an inner and outer analysis of the meniscus printing problem shows that the meniscus rotates around the pinned contact line at the trailing edge of the cell, and the volume under the meniscus is used to coat a film of thickness decreasing linearly in time forming a tail shape. The tail lengthens with decreasing $Ca$, owing to the concomitant increase in smear volume; the opposite is true as $Ca$ approaches $O(1)$. For small $Ca$, it is computationally expensive to use the Stokes solver to show that the physical mechanism of tail formation described by the analysis as $Ca \to 0$ is correct. Lubrication theory, on the other hand, predicts tail formation mechanism closely for contact angles over the blade close to $\uppi/2$, and this motivates us to use the lubrication model for smaller $Ca$. With the continuing motion of substrate, we show the transition from the tip region (squeeze film) to the Landau-Levich film in the form of a tail shape extending back toward the bulk meniscus (static), and this agrees with the physical picture described by the analysis as $Ca \to 0$. The results contribute to the control and understanding of smear formation mechanism during gravure printing of electronics.

As next-generation electronic products emerge, there is a need to create more electronic functionality in compact spaces. One of the techniques to achieve this is by integrating electronic circuitry on mechanical stress bearing parts of electro-mechanical products. Direct-write printing processes like inkjet printing and aerosol jet printing can be used to print conductive inks on conformal surfaces of mechanical components. Advanced curing/sintering processes such as pulsed photonic curing can be used to cure/sinter printed inks to produce conductive traces. However, the use of photonic curing on conformal surfaces introduces two sources of variability into the process, which are the distance and slope between the flash lamps and the conformal substrate. This research studies the effects that distance and slope between the flash lamps and substrate have on the characteristics of the photonically cured material. Screen printed samples of copper nanoparticle ink on paper substrates were photonically cured at various distances and slope settings in a Novacentrix Pusleforge 3300 machine. Analysis of the experimental data reveals that there is significant decrease in the conductivity of the cured copper ink with increase in both the distance and slope between the flash lamps and the substrate. The lowering of conductivity of the coupons with increase in distance was correlated to the reduction in the intensity of pulsed light with distance from the source. Similarly, the lowering of conductivity of the coupons with increase in slope was correlated to the reduction in the intensity of pulsed light with increase in angle between the incident light and the surface normal. A spectrophotometer was used to correlate the lowering of the conductivity of the printed coupon to the reduction in the amount of light absorbed by the coupon surface with increase in the slope from the flash lamps. This research highlights that distance and slope variations are important considerations to achieve uniform electrical properties in conformal printed electronics undergoing photonic curing.

Recently, various novel functional materials and low-cost device fabrication techniques have emerged in the field of thin-film electronics. Active semiconductors in the form of thin-films are one of the critical components in thin-film transistors (TFTs) to achieve high-performance large-area electronics. Semiconducting single-walled carbon nanotubes (SWCNTs) and amorphous zinc tin oxide (ZTO) are considered to be some of the most promising semiconductors for TFTs due to their advantages such as high electrical performance, air-stability, and optical transparency. In this dissertation, SWCNTs and ZTO are employed as p-channel/ambipolar and n-channel semiconductors in TFTs, respectively, and integrated into various circuits through use of the cost-effective inkjet printing technique. High-performance p-channel TFTs are demonstrated by using single-pass inkjet printing of SWCNTs. Dense uniform networks of SWCNTs are formed in the channel of TFTs with single-pass printing after application of UV O3 treatment on the dielectric surface for suitable surface energy modification. By employing these SWCNT TFTs for p-TFTs along with ZTO n-TFTs, high-speed complementary circuits are demonstrated with low power consumption. The material combination of high-performance inkjet printed n- and p-channel semiconductors results in the fastest ring oscillators (ROSCs) among previously reported ROSCs where printed semiconductors were utilized. Furthermore, adding additional top-gate dielectric and top-gate electrode layers on top of the ROSCs can impart new functionalities that can be used to control the oscillation frequency of the ROSCs linearly with applied top-gate bias. Various basic circuits are also demonstrated by using inkjet printed ambipolar semiconductors. SWCNTs and ZTO, employed as p- and n-channel semiconductors for individual TFTs, turn into an ambipolar semiconductor when they are printed in a bilayer heterostructure. The bilayer ambipolar TFTs show high electron and hole mobilities in air, and ROSCs based on the ambipolar TFTs show the fastest oscillation frequency among the best reported ambipolar TFT-based ROSCs. Ambipolar SWCNT circuits are also demonstrated by encapsulating SWCNTs with aluminum oxide (Al2O3) layer deposited by atomic layer deposition (ALD). These ambipolar circuits are realized on flexible plastic substrates with inkjet printed electrodes, and show high operational and environmental stability.

Additive Manufacturing (AM) is a Layered Manufacturing (LM) process where part is fabricated using materials such as metallic powder, plastics etc. with a layer by layer approach. Direct Metal Laser Sintering (DMLS) is capable of fabricating parts from a wide variety of metals and metallic alloys such as titanium, aluminum, steel, cobalt-chromium, etc. However, the major drawbacks associated with the DMLS process are poor part quality due to inherent staircase effect and thermal distortion along with material shrinkage and associated large build time. This dissertation seeks to reduce or eliminate these disadvantages of the AM process by developing an adaptive slicing approach that will also satisfy the Geometric Dimensioning and Tolerances (GD&T) callouts on the part. A virtual manufacturing model is developed for simulating the effect of input process parameters such as slice thickness, part orientation on the part quality manufactured using DMLS process. Even though in most of the research approaches, STL is used as an input file, an effort is made to include JT file format for virtually building parts using AM processes. A k-d tree based adaptive slicing approach has been developed and verified by comparing it with the uniform slicing approach. As existing AM hardware is not capable of handling adaptive slicing as an input parameter, a clustered slicing approach has been developed and presented in the dissertation. A new approach is developed that will calculate the adaptive slices based on the GD&T callouts information available on the part blueprint. To overcome the effect of material shrinkage and thermal deformations error to some extent, it is proposed to modify the STL/CAD file before feeding it to the machine so as to minimize tolerance errors on the design part. Another area explored in this dissertation is Additive Manufacturing (AM) based Printed Electronics (PE). It is an emerging technique where electronic components and interconnects are printed directly on substrates using a layered technique. The direct printing of the electronic components allows large scale and ultra-thin components to be printed on a wide variety of substrates including glass, silicon and plastic. Currently this technology is a labor intensive and manual process with the machine operator using his experience and judgment to slice the CAD file of the part to create 2D layers at different levels. A new file format based on the Constructive Solid Geometry (CSG) technique is proposed in this research. This file format data will not only include CAD data in the form of CSG primitives and Boolean representation but will also include manufacturing information such as toolpath, component material, deposition pattern etc.Finally, a component shape library is proposed for PE components such as resistors, capacitors etc. in AM based PE. Multiple shapes have been proposed for electronic components that can be used in place of conventional component designs having same electrical functionality but occupy less space on the substrate. A toolpath optimization approach for PE has been proposed to minimize the overall time consumed for material deposition.

In printed electronics, electronic inks are patterned onto flexible substrates using roll-to-roll (R2R) compatible graphic printing methods. For applications where large-area, conformal electronics are necessary, printed electronics holds a competitive advantage over rigid, semiconductor circuitry, which does not scale efficiently to large areas. However, in order to fully realize the true potential of printed electronics, several manufacturing hurdles need to be overcome. Firstly, minimum feature sizes produced by graphic printing methods are typically greater than 25 µm, which is at least an order of magnitude higher for dense, high performing electronics. In this thesis, conductive features down to 1.5 µm are demonstrated using a novel inkjet printing-based process. Secondly, high-resolution printed conductors usually have poor current-carrying capacity, especially for longer wires in large-area applications. This thesis explores the fundamentals of aerosol-jet printing and reveals the regime for printing high-resolution lines with excellent current carrying capacity. Additionally, a novel manufacturing process is demonstrated, which can process 2.5 µm wide conductive wires with linear resistances as small as 5 Ω mm-1. Another challenge for printed electronics manufacturing is to deal with topography produced on the substrate surface by printed features. Besides complicating the subsequent use of contact-printing methods, surface topography is a source of poor device yields as well. This thesis describes two novel methodologies of creating topography-free printed surfaces. In the first method, nanometer-level smooth, planarized silver lines are obtained using a transfer printing approach. In the second method, open microchannels, imprinted in plastic substrates, are filled with a controlled amount of metal using liquid-based additive processes, to obtain conductive wires flush with the substrate surface. Finally, this thesis addresses the issue of overlay alignment, which is the most significant challenge of printed electronics manufacturing. Multi-layered electronic devices require alignment of multiple layers of different materials with micron-level tolerances, which is a daunting task to accomplish on deformable, moving substrates in R2R production formats. This thesis describes a novel, self-aligned manufacturing strategy for printed electronics that relies on capillary flow of inkjet-printed inks within open micro-channels. Multi-level trench networks, pre-engineered on the substrate surface, are sequentially filled with different inks which, upon drying, form stacked layers of electronic materials. Using this approach, fully self-aligned fabrication of all the major building blocks of an integrated circuit is demonstrated. Overall, this thesis presents several new manufacturing avenues for realizing high-performing and dense electronics on plastic by R2R processing.

Electromagnets are a crucial component in a wide range of more complex electrical devices due to their ability to turn electrical energy into mechanical energy and vice versa. The trend for electronics becoming smaller and lighter has led to increased interest in using flat, planar electromagnetic coils, which have been shown to perform better at scaled down sizes. The two-dimensional geometry of a planar electromagnetic coil yields itself to be produced by a roll-to-roll additive manufacturing process. The emergence of the printed electronics field, which uses traditional printing processes to pattern functional inks, has led to new methods of mass-producing basic electrical components. The ability to print a planar electromagnetic coil using printed electronics could rival the traditional subtractive and semi-subtractive PCB process of manufacturing. The ability to print lightweight planar electromagnetic coils on flexible substrates could lead to their inclusion into intelligent packaging applications and could have specific use in actuating devices, transformers, and electromagnetic induction applications such as energy harvesting or wireless charging. In attempts to better understand the limitations of printing planar electromagnetic coils, the effect that the design parameters of the planar coils have on the achievable magnetic field strength were researched. A comparison between prototyping methods of digital extrusion and manufacturing scale flexographic printing are presented, discussing consistency in the printed coils and their performance in generating magnetic fields. A method to predict the performance of these planar coils is introduced to allow for design within required needs of an application. Results from the research include a demonstration of a printed coil being used in a flat speaker design, working off of actuating principles.

Aerosol Jet printing is a non-contact process capable of printing nano-ink patterns on conformal and flexible surfaces. Aqueous or solvent nano-inks are pneumatically atomized by the flow of nitrogen gas. The flow of atomizing gas into and out of the cup leads to evaporation and removal of volatile solvent(s). As the solid loading fraction of the ink increases, the rheological changes eventually lead to instabilities in print output. A potential solution to this problem is to moisten the atomizing ink by running it through a bubbler. In this study, neat co-solvent solutions of ethanol and ethylene glycol at 85: 15 and 30:70 mixing ratios were atomized using nitrogen flow rates ranging from 600 to 1000 ccm. It was observed that ethanol, being the more volatile solvent, was depleted from the neat solution. When using a bubbler solvent add-back system, an excessive amount of ethanol was returned to the neat solution. The rate of solvent loss from an ethanol rich neat solution (80%) was higher compared to an ethylene glycol rich neat solution. A mixture of dry and wet (ethanol moistened) nitrogen gas was used to equalize the rate of ethanol evaporation. Ethanol equilibrium in neat solutions with higher ethylene glycol loading (70%) was achieved with a 40-60% wet nitrogen component while neat solutions with higher ethanol loading (85%) were stable with 85 -90% wet nitrogen gas. The results were validated with copper nano ink with similar co-solvent ratios. The solid content of the ink remained constant over four hours of printing when the optimal dry: wet nitrogen gas ratios were used. Copper ink with 85% ethanol being atomized at 1000 ccm exhibited increase in copper loading (3%) despite the dry: wet solvent add back system.

In recent years, much research has been done to explore direct printing methods, such as screen and inkjet printing, as alternatives to the traditional lithographic process. The primary motivation is reduction of the material costs associated with producing common electronic devices. Much of this research has focused on developing inkjet or screen paste formulations that can be printed on a variety of substrates, and which have similar conductivity performance to the materials currently used in the manufacturing of circuit boards and other electronic devices. Very little research has been done to develop a process that would use direct printing methods to manufacture electronic devices in high volumes. This study focuses on developing and optimizing a drying process for conductive copper ink in a high volume manufacturing setting. Using an infrared (IR) dryer, it was determined that conductive copper prints could be dried in seconds or minutes as opposed to tens of minutes or hours that it would take with other drying devices, such as a vacuum oven. In addition, this study also identifies significant parameters that can affect the conductivity of IR dried prints. Using designed experiments and statistical analysis; the dryer parameters were optimized to produce the best conductivity performance for a specific ink formulation and substrate combination. It was determined that for an ethylene glycol, butanol, 1-methoxy 2- propanol ink formulation printed on Kapton, the optimal drying parameters consisted of a dryer height of 4 inches, a temperature setting between 190 - 200°C, and a dry time of 50-65 seconds depending on the printed film thickness as determined by the number of print passes. It is important to note that these parameters are optimized specifically for the ink formulation and substrate used in this study. There is still much research that needs to be done into optimizing the IR dryer for different ink substrate combinations, as well as developing a control system to ensure that prints continuously dry the same way. In addition to the repeatability study, experimenting with the feasibility of using single pass prints with repeatable performance would also be a worthwhile study. A single print pass will reduce cycle time, and will reduce ink consumption when compared with double pass prints.

Printed electronics can lower the cost and increase the ubiquity of electrical components such as batteries, sensors, and telemetry systems. Unfortunately, the advance of printed electronics has been held back by the limited minimum resolution, aspect ratio, and feature fidelity of present printing techniques such as gravure, screen printing and inkjet printing. Templated dry printing offers a solution to these problems by patterning nanoparticle inks into templates before drying.This dissertation shows advancements in two varieties of templated dry nanoprinting. The first, advective micromolding in vapor-permeable templates (AMPT) is a microfluidic approach that uses evaporation-driven mold filling to create submicron features with a 1:1 aspect ratio. We will discuss submicron surface acoustic wave (SAW) resonators made through this process, and the refinement process in the template manufacturing process necessary to make these devices. We also present modeling techniques that can be applied to future AMPT templates.We conclude with a modified templated dry printing that improves throughput and isolated feature patterning by transferring dry-templated features with laser ablation. This method utilizes surface energy-defined templates to pattern features via doctor blade coating. Patterned and dried features can be transferred to a polymer substrate with an Nd:YAG MOPA fiber laser, and printed features can be smaller than the laser beam width.

Pattern printing techniques have advanced rapidly in the last decade, driven by their potential applications in printed electronics. Several printing techniques have realized printed features ≤10 µm, but unfortunately they suffer from disadvantages that prevent their deployment in real applications; in particular, process throughput is a significant concern. Direct gravure printing delivers high throughput and has a proven history of being manufacturing worthy. Unfortunately, it suffers from scalability challenges due to limitations in roll manufacturing and lack of understanding of the relevant printing mechanisms. Gravure printing relies on individual processes namely filling, wiping, transferring and spreading to achieve high quality printing. As gravure printed features are scaled, the associated complexities are increased, and a detailed study of the various processes involved is needed.In this thesis, the various gravure-related fluidic mechanisms are studied using a novel inverse direct gravure printer. The underlying mechanisms of gravure printing are presented. A simple model of gravure printing is proposed. This model demonstrates that individual fluidic processes can be studied separately and a comprehensive understanding of the wiping process in gravure printing is analyzed carefully due to the importance of this process in producing high-fidelity patterns. We report two critical wiping mechanisms that generate drag-out and lubrication residues, which are fundamental scaling limitations for highly-scaled gravure printing. Third, the filling process is investigated, leaded to explanations of air entrapment in gravure cells. In addition, we provide designs and operation conditions for the ultimate reduction of the residues, leading significant scaling of printed features. Printed lines as small as 2 µm are realized at printing speeds as high as ~1 m/s, attesting to the potential of highly-scaled gravure printing.In addition to comprehensive printing mechanism studies, we demonstrate a fabrication process for a high-resolution roll based on advanced microfabrication techniques. The fabrication process incorporates the design guidelines developed previously to deliver the optimized cell geometry and pattern arrangement. Furthermore, electrically functional high-resolution lines are integrated in a fabrication process for fully printed high performance thin film transistors (TFTs). Highly-scaled TFTs demonstrated with channel lengths as small as 3 µm, leading to devices with transition frequency above 1 MHz; this represents a significant advancement over the state of the art.

The layer-by-layer nature of additive manufacturing (AM) allows for access to the entire build volume of a component during manufacture including the internal structure. Voids are accessible during the build process and allow for components to be embedded and sealed with subsequently printed layers. This process, in conjunction with direct write (DW) of conductive materials, enables the direct manufacture of parts featuring embedded electronics, including interconnects and sensors. The scope of previous works in which DW and AM processes are combined has been limited to single material AM processes. The PolyJet process is assessed for hybridization with DW because of its multi-material capabilities. The PolyJet process is capable of simultaneously depositing different materials, including rigid and elastomeric photopolymers, which enables the design of flexible features such as membranes and joints. In this work, extrusion-based DW is integrated with PolyJet AM technology to explore opportunities for embedding conductive materials on rigid and elastomeric polymer substrates. Experiments are conducted to broaden the understanding of how silver-loaded conductive inks behave on PolyJet material surfaces. Traces of DuPont 5021 conductive ink as small as 750?m wide and 28?m tall are deposited on VeroWhite+ and TangoBlack+ PolyJet material using a Nordson EFD high-precision fluid dispenser. Heated drying at 55°C is found to accelerate material drying with no significant effect on the conductor's geometry or conductivity. Contact angles of the conductive ink on PolyJet substrates are measured and exhibit a hydrophilic interaction, indicating good adhesion. Encapsulation is found to negatively impact conductivity of directly written conductors when compared to traces deposited on the surface. Strain sensing components are designed to demonstrate potential and future applications.

Printed electronics using recently developed solution-processed electronic materials and incorporating conventional graphic arts printing presses has been proposed as an emerging technology for low-cost large-area electronic systems on flexible substrates (e.g. disposable RFID tags, flexible displays, and various types of sensors and actuators). For more than a decade, a significant amount of research in printed electronics has been focused on the development of high mobility printable semiconductor materials. Despite the recent achievements of the high mobility semiconductor materials that surpass the performance of amorphous silicon, overall performance of printed transistors on plastic is not adequate for the proposed applications due to the large dimension of the transistors with significant parasitic capacitance, and underperforming semiconductor materials when incorporated with mass-production printing techniques.In this dissertation, we present a highly-scaled direct-gravure printing technique that allows sub-femtoliter scaling of printed inks, resulting in printed features as small as 4 μm while printed at high speed up to 1 m/s. By using this novel printing technique with the optimization of the high mobility organic semiconductors for the printed device fabrication processes, operation of gravure-printed inverters on plastic at frequencies above 1 MHz is achieved, which satisfies the performance requirements for most of the proposed applications. Along with the demonstration, we discuss how accurate pattern generation in various printing systems can be achieved with the knowledge of using contact angle hysteresis.In addition, we discuss experimental results on understanding of the origin of 1/f noise in organic thin-film transistors, which particularly affects the performance of the devices in sensor applications. Based on detailed analysis of observed non-idealities in the 1/f noise with respect to various grain sizes, operation regions, and bias conditions, we found that the trapping/de- trapping of carriers within the semiconductor is the dominant mechanism of the low-frequency noise generation in the organic thin-film transistors.

Printed electronics employing solution-processed materials is considered to be the key to realizing low-cost large-area electronic systems, but the performance of printed transistors is not generally adequate for most intended applications due to limited performance of printable semiconductors. In this dissertation, I propose an alternative approach of a printed switch, where the use of semiconductors can be avoided by building mechanical switches with printed metal nanoparticles. I provide the first demonstration of inkjet-printed micro-electro-mechanical (MEM) switches with abrupt switching characteristics, very low on-state resistance (~10 Ohm), and nearly perfect off-state behavior with immeasurable leakage with on/off current ratio of 107. The devices are fabricated using a novel process scheme to build 3-dimensional cantilever structures from solution-processed metallic nanoparticles and sacrificial polymers. These printed MEM switches thus represent a uniquely attractive path for realizing printed electronics. I will also discuss an inkjet-printed microshell encapsulation as a new zero-level packaging technology. Inkjet-printing of silver nanoparticle ink is demonstrated to form porous microshells through which sacrificial oxide can be selectively removed to release MEMS structures. A second inkjet printing process using finer gold nanoparticle ink or polymer is demonstrated to effectively seal the microshells. This inkjet-printed microshell encapsulation technology is successfully applied to a MEM relay, and is demonstrated to mitigate the issue of contact oxidation. Specifically, the stability of the relay ON-state resistance is dramatically improved by more than a factor of 100.

Advances in research and technology are happening now more than ever in the biotechnology industry. Efficient methods for biological processes and better detection and treatment methods are constantly being sought by researchers. Collaboration among different fields of science and technology has brought us one step closer towards achieving this goal in this work. One such technology that has the capability of providing efficient methods and processes for biology is printed electronics. Printed electronics is an attractive paradigm for realization of biological microfluidic systems. The large area of these systems makes printing valuable from a cost perspective. Furthermore, since printing allows for easy integration of disparate materials on the same substrate through spatially-specific deposition, printed electronics is particularly useful for integration of diverse biological microfluidic functionality on the same substrate. While there have been instances of printed transistors and passive components, there have been no demonstrations to date of the critical components required for biological microfluidic applications or lab on a chip (LOC) devices. In this work, for the first time, we present all-printed gold heaters, gold resistive temperature detectors, and electrostatically actuated PDMS microfluidic valves designed for biological microfluidic applications. In addition, work on DNA sensors using printable organic (pentacene) thin film transistors (OTFTs) is also presented for use in LOC devices. Many biological applications require precise control and stability of temperature, which is demonstrated here through the integration of printed heaters and printed RTDs into a microchip bioprocessor system capable of polymerase chain reaction (PCR). Flow rate measurements and dynamic characteristics of printed PDMS valves are also presented to demonstrate the effectiveness of these devices. With the 440 microns wide and 16 microns deep microfluidic channels used in this project, the valve with the thinnest PDMS membrane (55 microns) closed the channel completely (i.e. flow rate = 0) at a pull-in voltage of 250V. This valve closed and opened in approximately 1.5 and 5.5 seconds, respectively. Pentacene surface has also been optimized to arrive at the best sensitivity for DNA immobilization and hybridization, bringing us a step closer in realizing printed OTFT DNA sensors for `tag-free' electrical detection. To summarize the sensor results, thinner films, higher substrate temperature, and higher input current during pentacene evaporation ensured that DNA immobilized in the channel part of the transistor and therefore provided for highest sensitivity of pentacene film to DNA. This work has thus successfully revealed the potential of printed electronics in real-world biological applications and has also paved the way for exciting future research areas for this technology.

Living in a world full of portable electronics, there is great need for energy storage devices. Currently, limitations for storage involve power inefficiencies as well as bulkiness. This is why printable charge storage devices that display good electrochemical performance are needed. It is for this reason that research into the production and packaging of carbon nanotube based super capacitors was carried out. A super capacitor can be built by using high surface area multi-walled carbon nanotubes suspended in an ionic liquid. The two active electrodes are made from a combination of the multi-walled carbon nanotubes and an ionic liquid, ground into a gel, and then formulated into a printable functional ink. The super capacitor is then built upon a conducting carbon foam substrate where the two electrodes are printed and sandwiched on top of a membrane that allows ion-ion transfer without allowing any physical exchange of nanotube particles. The purpose of this research was to find a printing method or technique that produced functional carbon nanotube based electrodes for supercapacitor assembly. This process involved changing printing variables such as the mesh count for the screen, the type of stencil used, and the thickness of the emulsion applied. Other variables altered for this study focused on the ink formulation portion of the testing. These variables included creating a medium that dispersed the carbon nanotubes, chemical carrier agents for the carbon nanotubes and ionic liquid, ionic liquid selection, concentration of the chemical to the bucky gel relationship, temperature used for curing the ink, and the influence of adhesive agents present in the ink. The printed electrodes were assembled with the separator membrane into supercapacitors that were then measured in the electrochemical cell. The charge/discharge curves were used to calculate the current density and specific capacitance of each combination of supercapacitors. Supercapacitors made of printed electrodes that were 40% bucky gel and 60% 1-methyl-2-pyrrolidinone (with the bucky gel as 9.82% multi-walled carbon nanotubes, 88.42% ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate, and 1.76% Teflon¨ binder) were found to perform the best out of all other combinations of electrodes printed on carbon foam substrate. All printed electrodes had measurable results except for those printed on aluminum substrate.

Thin film copper indium gallium selenide (CIGS) solar cells have exhibited single junction power conversion efficiencies above 20% and have been commercialized. The large scale production of CIGS solar cells, however, is hampered by the relatively high cost and poor stoichiometric control of coevaporating tertiary and quaternary semiconductors in high vacuum. To reduce the overall cost of production, CIGS nanocrystals with predetermined stoichiometry and crystal phase were synthesized in solution. Colloidal nanocrystals of CIGS provide a novel route for production of electronic devices. Colloidal nanocrystals combine the well understood device physics of inorganic crystalline semiconductors with the solution processability of amorphous organic semiconductors. This approach reduces the overall cost of CIGS manufacturing and can be used to fabricate solar cells on flexible and light-weight plastic substrates. As deposited CIGS nanocrystal solar cells were fabricated by ambient spray-deposition. Devices with efficiencies of 3.1% under AM1.5 illumination were fabricated. Examining the external and internal quantum efficiency spectrums of the devices reveal that in nanocrystal devices only the space charge region is actively contributing to the extracted photocurrent. The device efficiency of the as-deposited nanocrystal films is presently limited by the small crystalline grains (≈ 15 nm) in the absorber layer and the relatively large interparticle spacing due to the organic capping ligands on the nanocrystal surfaces. Small grains and large interparticle spacing limits high density extraction of electrons and holes from the nanocrystal film. A Mott-Schottky estimation of the space charge region reveals that only 50 nm depth of the nanocrystalline absorber is effectively contributing to the photogenerated current. One strategy to improve charge collection involves increased space charge region for extraction by vertical stacking of diodes. A much longer absorption path for the photons exists in the space charge region with the stacked devices, increasing the probability that the incident radiation is absorbed and then extracted. This method enables an increase in the collected short circuit current. The overall device efficiency, however, suffers with the increased series resistance and shunt conductance of the device. Growth of nanocrystal grains was deemed necessary to achieve power conversion efficiencies comparable to vapor deposited CIGS films. Simple thermal treatment of the nanocrystal layers did not contribute to the growth of the crystalline grain size. At the same time, because of the loss of selenium and increased trap density in the absorber layer, there was a measurable decrease in device efficiency with thermal processing. For increased grain size, the thermal treatment of the absorber layer took place in presence of compensating amounts of selenium vapor. The process of selenization, as it is called, took place at 500°C in a graphite box and led to an increase of the grain size from 15 nm to several microns in diameter. Devices with the increased grain size yielded efficiencies up to 5.1% under AM1.5 radiation. Mott-Schottky analysis of the selenized films revealed a reduction in doping density and a comparable increase in the space-charge region depth with the increased grain size. The increased collection combined with the much higher carrier mobility in the larger grains led to achieved Jsc values greater than 20 mA/cm2. Light beam induced current microscopy (LBIC) maps of the devices with selenized absorber layers revealed significant heterogeneity in photogenerated current. Distribution of current hotspots in the film corresponded with highly selenized regions of the absorber films. In an effort to improve the overall device efficiency, improvements in the selenization process are necessary. It was determined that the selenization procedure is dependent on the selenization temperature and processing environment. Meanwhile, the reactor geometry and nanocrystal inks composition played important roles in determining selenized film morphology and the resulting device efficiency. Further work is necessary to optimize all the parameters to improve device efficiency even further.

A survey was taken of professionals in the printed electronics industry to determine the basic educational requirements the industry had of a student graduating with a degree in graphic communications or printing sciences. A test was conducted of graphic communication seniors graduating in May 2010 to determine their fundamental knowledge of printed electronics. Data obtained from the industry survey was used to determine the relevant components of a basic printed electronics education. The data obtained from the graduating senior examination determined their areas of knowledge of printed electronics. The needs identified from the industry survey were compared to the areas of knowledge of graphic communications graduating seniors. The knowledge deficiencies of graduating students were identified, and analyzed. It was determined that present graphic communications education is insufficient to meet the needs of the printed electronics industry. Further research was proposed to update graphic communication education to meet the needs of the printed electronics industry.

To realize the potential cost savings promised by printed electronics, high-speed, large-volume manufacturing methods must be established. Rotary printing techniques such as those used in the graphic arts are ideal candidates. However, very little research has been done on utilizing these techniques for printed electronics because digital processes such ink-jet printing have offered researchers a low-cost flexible solution for demonstrating the printability of their materials, despite the fact that these processes may be difficult to scale for large-volume manufacturing. In this thesis, gravure, a printing process which offers the highest resolution, highest speed, and largest volume production in the graphic arts is demonstrated as a viable technique for printed electronics. In order to make laboratory-scale research with this technique possible, a custom table-top gravure printing press was designed. This press allows for small amounts of ink to be utilized during a print and enables multi-layer prints with a registration accuracy not seen in conventional gravure printing presses and suitable for printed electronics. With this press, printing processes to deposit functional materials for printed circuits are investigated with a focus on developing process modules to manufacture fully printed organic thin film transistors. Considerable effort is made to establish processes to deposit metallic lines with feature sizes below 20 μm and a total surface roughness below 20 nm, uniform thin films of polymer dielectrics with thicknesses as low as 70 nm, and high performance polymer semiconductors. These processes are then integrated to manufacture capacitors suitable for integrated circuit components and organic thin film transistors with operating frequencies as high as 18 kHz.