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Stretchable conductive films were obtained by screen printing and thermal treatment of a homogenous ink comprising a thermally reducible silver formate complex, an acrylate monomer, and a radical i...

A study to characterize surface and structural properties of 3D-printed metal substrates for multilayer inkjet-printing is presented. Such substrates can enable and alleviate the fabrication of smart and functional packages, implants or spare parts. For the characterization, a multilayer structure composed of an insulating layer and a superposed conductive layer is inkjet-printed onto the various 3D-printed metallic substrates. The printing is done using equivalent settings for all substrates. The characterization is based on microscopic and Focused Ion Beam (FIB) images, as well as profilometer and contact angle measurements of the substrates. Furthermore, microscopic images and four-point-probe resistance- and profilometer measurements are carried out, to gain insight into the quality of the multilayer print. We show the diversity in surface and structural properties of 3D-printed substrates, also for those fabricated using the same process. Also, the 3D-printed samples exhibit different wettability properties than metals processed using standard processes. Finally, we can also demonstrate the suitability of selected substrates for inkjet-printing.

A new fabrication technique based on the combined printing of Ag-nanoparticles and dielectric material was developed. The processing, composed of inkjet printing and intense pulsed light sintering/curing, enables a fast, controllable and highly-adaptable structuring of 3D conductor/insulator structures on various types of substrates including ones with low-temperature stability and flexible ones. With this process the classical vias of the multi-layer structure are replaced by a direct connection between the layers achieved by an absence of insulation material at designated areas providing a fast and efficient method for multilayer prototyping. For testing and demonstration a multilayer planar coil structure was fabricated with an overall thickness of 30 µm on the PET substrate. The electromagnetic properties of the structures were successfully tested and verified by comparing several experiments to finite element method simulations. The theoretical simulations show an excellent match with experimental measurements of several structures thus giving confidence in the reliability of the proposed process.

A continuous-flow, coil-type photoelectrocatalytic microreactor for the degradation of caffeine was designed, assembled and characterized. Its main components are the photocatalytically active anode and the cathode coils, which are wrapped around a silica-glass rod and placed into a UV-transparent housing. The anode coil was prepared by anodic oxidation of the titanium coil, which leads to the formation of vertically aligned, titanium dioxide, nanotube arrays that exhibit a high photocatalytic activity and are rigidly attached to the titanium wire. The photocatalytic, electrocatalytic and photoelectrocatalytic activities of the assembled microreactor were measured systematically while changing the main parameters that affect the device’s efficiency. The most significant change in the microreactor’s design in terms of efficiency was to place the cathode coils on both sides of the anode coil, which resulted in the shortest time for complete degradation of the caffeine. When an applied anodic bias potential of 4 V was used in the most efficient microreactor design, 1 mL of the 40 mg/L caffeine was fully decomposed in 55 min.

The trend toward heterogeneous integration of optoelectronic, electronic, and micromechanical components favors three-dimensional (3D) integration in which the components are not arranged side-by-side but rather in vertical stacks. This presents a particular challenge due to the fact that the stacked components have different geometric dimensions, and their contact surfaces are also dissimilar. Therefore, an intermediate substrate, the so-called interposer, with different formats (i.e., flip-chip, wire-bond, and hybrid flip-chip/wire bond) comes into play. Currently, the interposers are mainly made of silicon or glass, which incur huge additional costs to the packaged components. In this study, the unique advantages of additive manufacturing (AM) are exploited to realize organic interposers. The proposed interposers provide easy signal probing and flexible die-to-board integration in lower costs without any lithography process, drilling, plating, or any waste. Accordingly, the two state-of-the-art 3D printers (i.e., a monomaterial 3D printer and a bimaterial 3D printer) were utilized for the manufacturing of the interposer parts. The complementary circuitry for vias and through-holes was facilitated by also additive technologies, i.e., 2D-inkjet printing and microdispensing. Moreover, and to manifest the unique possibilities within AM for the next generation of interposers, two examples for 3D-printed interposers with incorporated added-features, i.e., pillars for flip-chip bonding and cavities for face-up die-attachment were realized. The assemblies were consequently assessed by electrical examinations. Conclusively, the main opportunities and challenges toward the full implementation of AM technology for the fabrication of organic interposers with added-features such as integrated multipurpose vias were discussed. Based on the results obtained from this study, it was found that bimaterial 3D printer was more efficient and powerful for the construction of interposers.

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, three substrates (acrylate, ceramics, and copper) are prepared. To determine the resulting material properties of these substrates, profilometer, contact angle, scanning electron microscope (SEM), and focused ion beam (FIB) measurements are done. The achievable printing resolution and suitable drop volume for each substrate are, then, found through the drop size tests. Then, layers of insulating and conductive ink are inkjet printed alternately to fabricate the target sensor structures. After each printing step, the respective layers are individually treated by photonic curing. The parameters used for the curing of each layer are adapted depending on the printed ink, as well as on the surface properties of the respective substrate. To confirm the resulting conductivity and to determine the quality of the printed surface, four-point probe and profilometer measurements are done. Finally, a measurement set-up and results achieved by such an all-printed sensor system are shown to demonstrate the achievable quality.

Self-ordered, vertically aligned, titanium oxide (TiO2) nanotubes were grown on an electropolished titanium foil by anodic oxidation in a viscous organic electrolyte. We chose two different anodization times to obtain nanotubes of approximately 9 and 17 μm in length. Some of the TiO2 nanotubes were post-treated with TiCl4 or hydrothermally with TiO2 P25. Their structure and morphology were investigated with field-emission scanning electron microscopy (FSEM) and transmission electron microscopy (TEM). To improve the sensitizing of the high-aspect-ratio nanotubes with dye we used a new approach in which the TiO2 arrays were immersed into the dye solution at elevated temperature in an autoclave. The current–voltage characteristics of the assembled DSSCs gave an average energy-conversion efficiency of 5.7% for the untreated nanotubes.

The increasing demand for miniaturization of electronic packages and assemblies necessitates tighter tolerances in dispensing interconnects and robotic control for placement. In fact, due to increasing requirements in regards to cycle time and accuracy of interconnects (i.e. surface mount adhesives), contactless dispensing is constantly gaining acceptance. In this study, inkjet printing of adhesives is proposed as a promising contactless methodology, in which a precise volume control of dispensed material is applicable. Exploiting the drop-on-demand (DOD) process of inkjet printing, the deposition of non-conductive adhesives (NCA) by means of inkjet printer equipped with an industrial inkjet print-head were investigated. Correspondingly, individual droplets of different kinds of NCA were jetted from small diameter vessels directly to a specified position on the substrate to create the bonding patterns for die-attachment. The resulting die-attach was subsequently characterized, in terms of uniformity, thickness and flatness.

An additive manufacturing concept, consisting of 3D photopolymer printing and Ag nanoparticle printing, was investigated for the construction of a microfluidic biosensor based on immobilized cytochrome P450 enzyme. An acylate-type microfluidic chamber composed of two parts, i.e. chamber-housing and chamber-lid was printed with a polyjet 3D printer. A 3-electrode sensor structure was inkjet-printed on the lid using a combination of Ag and graphene printing. The working electrode was covered with carbon nanotubes by drop-casting and immobilized with cytochrome P450 2D6 enzyme. The microfluidic sensor shows a significant response to a test xenobiotic, i.e. dextromethorphan; the cyclic voltammetrical measurements show a corresponding oxidation peak at 0.4 V with around 5 μM detection limit.

Perfluoroalkoxy (PFA) is one of the most promising materials for the fabrication of cheap, solvent resistant and reusable microfluidic chips, which have been recently recognized as effective tools for biocatalytic process development. The application of biocatalysts significantly depends on efficient immobilization of enzymes or cells within the reactor enabling long-term biocatalyst use. Functionalization of PFA microchannels by 3-aminopropyltriethoxysilane (ATPES) and glutaraldehyde was used for rapid preparation of microbioreactors with surface-immobilized cells. X-ray photoelectron spectroscopy and scanning electron microscopy were used to accurately monitor individual treatment steps and to select conditions for cell immobilization. The optimized protocol for Saccharomyces cerevisiae immobilization on PFA microchannel walls comprised ethanol surface pretreatment, 4 h contacting with 10% APTES aqueous solution, 10 min treatment with 1% glutaraldehyde and 20 min contacting with cells in deionized water. The same protocol enabled also immobilization of Escherichia coli, Pseudomonas putida and Bacillus subtilis cells on PFA surface in high densities. Furthermore, the developed procedure has been proved to be very efficient also for surface immobilization of tested cells on other materials that are used for microreactor fabrication, including glass, polystyrene, poly (methyl methacrylate), polycarbonate, and two olefin-based polymers, namely Zeonor® and Topas®.

Photocatalytic phenol dissociation was studied in a microreactor, with a TiO2 layer immobilized on the reactor inner walls. Experiments were conducted for various residence times, initial concentrations, pH values, and UV light irradiation intensities. The intermediates and products (catechol, hydroquinone, and resorcinol) were quantitatively investigated to determine the predominant reaction pathways for the investigated anatase catalyst. A three-dimensional mathematical model was used to simulate the heterogeneous photocatalysis reaction conditions with Langmuir–Hinshelwood mechanism, considering the adsorption/desorption thermodynamic equilibria, and for kinetic parameter estimation via regression analysis. The effectiveness factor, Thiele modulus, and the correction function were calculated to determine the pore diffusion effects. The value of pH had the dramatic effect of lowering the reaction rate due to the competitive adsorption of hydroxide ions and protons on the catalyst surface. A phenol conversion of 79.5% was achieved at the residence time of 7.22 min, but without total mineralization. © 2014 American Institute of Chemical Engineers AIChE J, 61: 572–581, 2015

A photocatalytic, TiO2-based microreactor is designed and fabricated on a metal-titanium foil. The microchannel is mechanically engraved in the substrate foil, and a double-layered TiO2 anatase film is immobilized on its inner walls with a two-step synthesis, which included anodization and a hydrothermal treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirm the presence of an approximately 10-μm-thick layer of titania nanotubes and anatase nanoparticles. The SEM and transmission electron microscopy (TEM) of the cross sections show a dense interface between the titanium substrate and the TiO2 nanotubes. An additional layer of TiO2-anatase nanoparticles on the top of the film provides a large, photocatalytic surface area. The metal-titanium substrate with a functionalized serpentine channel is sealed with UV-transparent Plexiglas, and four 0.8-mW UV LEDs combined with a power controller on a small printed-circuit board are fixed over the substrate. The photocatalytic activity and the kinetic properties for the degradation of caffeine are provided, and the longer-term stability of the TiO2 film is evaluated. The results show that after 6 months of use and 3600 working cycles the microreactor still exhibits 60% of its initial efficiency.

Rutile (TiO 2 ) nanoparticles were prepared by a low-temperature hydrothermal process from titanium(IV) isopropoxide as a precursor and without any additional calcination step. The particles were characterized with several techniques (XRD, BET, UV–vis spectrometry, TEM/HRTEM/SAED, FT-IR) and their photocatalytic efficiency was evaluated on the degradation of caffeine. The as-prepared rutile particles exhibited a rod-like morphology with a prism body and pyramidal ends. The low-temperature hydrothermal synthesis introduced an amorphous layer that was around 1-nm thick and uniformly covered the surfaces of the particles. The enhanced photocatalytic properties of the particles confirmed the positive impact of the amorphous surface layer in comparison to the fully crystallized surface of commercial rutile particles and to particles that were synthesized using a conventional high-temperature calcination route. The amorphous surface layer seems to enhance the adsorption of both oxygen and caffeine on the surface of the particles and, therefore, improves the photocatalytic activity of the rutile particles. Being the case, the electron transfer to the adsorbed oxygen is more efficient, increasing the life-time of the photogenerated holes, which contributes to the degradation of caffeine via the formation of reactive radicals and/or by direct oxidation.

A novel robust low cost sensor for measuring the concentration of ethylene in air is tested. Ethylene levels are important for agriculture, but traditional measurement methods, are unsuitable for measurements in the field. The proposed measurement system is based on a non-dispersive infrared sensing element that measures the characteristic IR absorption peak of ethylene at 10.54μm. A compact hollow waveguide and custom electronics are used to reach the required sensitivity. Our results show that ethylene gas can be reliably detected down to a concentration of 20ppm.

A great deal of attention has been attracted to the additive manufacturing technique of 3D printing in rapid prototyping of electronic packages. This technique enables fast and reliable production of complex structures with arbitrary configurations and possesses several advantages over the conventional manufacturing methods, such as mechanical machining and laser cutting. In addition, 3D printed packages can be considered as a try-out for the assessment of customized design prior to mass production, which will significantly reduce the expensive machining costs and material waste. This study proposes an innovative approach to construct simple radio frequency identification (RFID) package by integrating a surface acoustic wave (SAW) transponder in a 3D printed housing. On that account, an acrylate-type plastic SAW transponder housing was 3D-printed, and the corresponding wireless antenna and contact pads were produced via ink-jet printing with a silver nanoparticle (NP) ink. The proper functionality of the silver tracks was obtained by sintering the printed NPs using a photonic curing device. A flip-chip configuration has been pursued for connecting the chip pads to the corresponding pads on the housing. The performance of the package has been tested with a wireless reading unit via antenna-bridge for SAW transponders.

Two types of MOx sensor structures, SnO2 and WO3, of different thicknesses were synthesized on top of the interdigitated Au electrodes and used for the measurements of the ethylene gas. The SEM micrographs revealed inhomogeneities of the WO3 layer and the presence of cracks on the edges of Au electrodes which correlates with the lack of reproducibility of the WO3 sensors. Both sensor structures showed a significant sensitivity to ethylene gas: the sensitivities of both MOx-types were higher at higher temperatures which was more evident in the case of SnO2 structure. The SnO2 layer had approximately 5-times higher sensitivity than the WO3 sensor of the same thickness. The saturation (T10) and desaturation (T90) times were shorter for WO3 sensors at lower temperatures while SnO2 was saturated and desaturated faster at higher temperatures. Sensors with thinner active layer possessed higher sensitivities and shorter T10 and T90 times. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.