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We propose inkjet-printed high-speed and transparent temperature sensors based on the thermoelectric effect for direct monitoring of the photothermal effect. They consist of highly transparent organic thermoelectric materials that allow excellent biocompatibility and sub-ms temporal resolution, simultaneously. Our transparent thermoelectric temperature sensors can be used to advance various photothermal biomedical applications.

A thin-film transistor (TFT) with a color filter function achieved by designing periodic nanohole arrays in the metal electrodes was studied. Since this metal electrode is not opaque but transparen...

The effect of ultraviolet/Ozone (UV/O3)-assisted annealing process on the structural, chemical, and electrical properties of sol-gel-processed SnO2 films is investigated in this study. Via the UV/O3-assisted annealing processes, mixed-phase SnO2 films composed of amorphous SnO2 and polycrystalline SnO were obtained. Furthermore, the XPS spectra indicate an increase in the SnO2/SnO ratio and a substantial decrease in the number of -OH groups (serving as trap sites). This results in an increase in the conductivity and field-effect mobility of the films. The field-effect mobility of the UV/Ozone-assisted 300 °C-annealed SnO2 thin film transistor (TFT) increases considerably (by ~500×), yielding a device with a field-effect mobility of 3.09 cm2/Vs. In addition, flexible SnO2 TFTs with Al2O3 insulator and Au gate on Polyimide substrate fabricated via gate electrode engineering shows a decreased conduction bandgap offset, compared to the SnO2 TFTs on SiO2, and enhancement mode operation properties (normally off at zero gate voltage) with a field-effect mobility of 1.87 cm2/Vs.

Microelectrode arrays (MEAs) have been extensively used to measure extracellular spike activity from cultured neurons using multiple electrodes embedded in a planar glass substrate. This system has been implemented to investigate drug effects by detecting pharmacological perturbation reflected in spontaneous network activity. By configuring multiple wells in an MEA, a high-throughput electrophysiological assay has become available, speeding up drug tests. Despite its merits in acquiring massive amounts of electrophysiological data, the high cost and the bulky size of commercial multi-well MEA systems and most importantly its lack of customizability prevent potential users from fully implementing the system in drug experiments. In this work, we have developed a microelectrode array based drug testing platform by incorporating a custom-made compact 256-channel multi-well MEA in a standard microscope slide and commercial application-specific integrated circuit (ASIC) chip based recording system. We arranged 256 electrodes in 16 wells to maximize data collection from a single chip. The multi-well MEA in this work has a more compact design with reduced chip size compared to previously reported multi-well MEAs. Four synaptic modulators (NMDA, AMPA, bicuculline (BIC) and ATP) were applied to a multi-well MEA and neural spike activity was analyzed to study their neurophysiological effects on cultured neurons. Analyzing various neuropharmacological compounds has become much more accessible by utilizing commercially available digital amplifier chips and customizing a user-preferred analog-front-end interface design with additional benefits in reduced platform size and cost.

Thermoplasmonic effect-based neural stimulation has been suggested as an alternative optical neural stimulation technology without genetic modification. Integration of near-infrared light with plasmonic gold nanoparticles has been demonstrated as a neuromodulation tool on in vitro neuronal network models. In order to further test the validity of the thermoplasmonic neural stimulation across multiple biological models (in vitro, ex vivo, and in vivo) avoiding genetic modification in optical neuromodulation, versatile engineering approaches to apply the thermoplasmonic effect would be required. In this work, we developed a gold nanorod attached optical fiber technology for the localized neural stimulation based on a thermoplasmonic effect. A simple fabrication process was developed for efficient nanoparticle coating on commercial optical fibers. The thermoplasmonic optical fiber proved that it can locally modulate the neural activity in vitro. Lastly, we simulated the spatiotemporal temperature change by the thermoplasmonic optical fiber and analyzed its applicability to in vivo animal models.

Sol–gel processed ultrathin nanostructured SnO2 thin-film transistors were successfully fabricated on a SiO2/Si substrate without using a self-aligned monolayer or high- ${k}$ insulator, which may be unsuitable techniques for the commercial fabrication of complementary metal–oxide–semiconductors. The highest extracted field mobility was approximately 100 cm2/V $\cdot$ s. In addition, by controlling the SnO2 film thickness, we successfully increased the on/off current ratio to ~107. The electrical performance of the proposed transistors is sufficient for high-resolution liquid crystal or organic light-emitting diode displays, which require a high field-effect mobility (>10 cm2/V $\cdot$ s) and high on/off current ratio (>106). Ultrathin SnO2 is also a promising rare-metal-free starting matrix for ternary and quaternary alloys, showing promising electric properties.

In recent years, photothermal stimulation methods using plasmonic metal nanoparticles have emerged as non-genetic optical techniques in neuromodulation. Although nanoparticle-based photothermal stimulation shows great potential in the excitation and the inhibition of neural activity, the complex synthesis processes of the nanoparticles and the lack of large-area deposition methods can be limiting factors for the development of photothermal neural devices. In this paper, we propose a plasmonic gold nanofilm, fabricated by a standard thermal evaporation process, as a simple and mass-producible photothermal neural interface layer for microelectrode array (MEA) chips. The absorption of the gold nanofilm at near infrared wavelengths is optimized to maximize the photothermal effect by varying the thickness and microstructure of the gold nanofilm. With the optimized conditions, a significantly strong photothermal effect is applied on MEAs without affecting the neural signal recording capability. Finally, primary rat hippocampal neuronal cultures are used to show that the photothermal neural inhibition using the gold nanofilm is as effective as that using the plasmonic nanoparticles. Due to the greater simplicity and versatility of the fabrication process, the plasmonic gold nanofilm can provide a promising solution for the mass production of photothermal platforms.

Optical neuromodulation is a versatile neural stimulation technology that enables highly localized excitatory or inhibitory stimulation of neuronal activities. Photothermal neural stimulation using thermoplasmonic metallic nanoparticles for light to heat conversion has been suggested as an optical neural stimulation technology without genetic modification. Optical fibers implementing the thermoplasmonic effect were recently developed for localized neural stimulation, and the successful demonstration of localized neural stimulation in vitro was reported. However, before photothermal neural stimulation is further applied in the brains of live animals and ultimately in human trials, a safety analysis must carefully be performed for the thermal effect of stimulation in vivo. With the complexity of the physical structure and different thermal properties of the brain and surrounding body, the resulting thermal effect could vary despite the same power of light delivered to the optical fiber. In addition, dynamic thermal properties of the brain such as the daily blood perfusion rate change or metabolic heat generation must also be carefully considered for the precise implementation of photothermal neural stimulation. In this work, an in-depth computational analysis was conducted of the photothermal effects using a thermoplasmonic optical fiber for in vivo neural stimulation. The effects of the experimental design and stimulation protocols on the thermal effect in the brain were analyzed. We believe that the results provide a good experimental guideline for safely conducting photothermal neural stimulation using the thermoplasmonic optical fiber technology.

We realize p-type thin film transistors (TFT) with solution-processed channels using a sol–gel route, based on a copper (II) acetate precursor. The sol–gel process initially produces Cu, which is then oxidized depending on sintering conditions to produce Cu2O and ultimately CuO. These processes are performed at temperatures no higher than 500 °C, and are therefore compatible with standard display glass substrates for use in transparent display applications. To control the film morphology of the sol–gel processed copper oxide layer, additional water was added to the precursor solution. As the water to alkoxide ratio is increased, the degree of hydrolysis increased, thus increasing the grain size of CuO and Cu2O. The resulting p-type CuO and Cu2O TFTs exhibited improved thin film transistor performance, including field effect mobilities of 1.0 × 10− 2 cm2/Vs and 2.0 × 10− 3 cm2/Vs, respectively, and an on/off ratio of approximately 103.

Printed organic thin film transistors (OTFTs) are a key component for the realization of low-cost, flexible electronics applications such as printed RFID tags or flexible displays. In recent years, great advances have been made in developing higher performance organic semiconductors. Many of these new materials show strongly process-dependent performance characteristics. The development of novel processing techniques is thus a key step towards utilizing the full potential of these semiconductor materials. Here we demonstrate a novel directional crystallization technique using a scanned thermal gradient to significantly improve the performance of printed OTFTs. A heat source is translated relative to the sample to induce the crystallization of the semiconductor. This scanned annealing creates a moving thermal gradient and thus develops a moving solvent evaporation gradient. Compared with uniform annealing on a hotplate grain size increases markedly and shows a clear directionality due to the separation of grain nucleation and growth. With this technique, mobility is boosted by about one order of magnitude. Mobilities close to 2 cm2/V s can be achieved. Off-state performance is likewise improved as evidenced by a 3× improvement in subthreshold swing.

Inkjet printing of thermoplasmonic nanoparticles enables instantaneous, large-area heat pattern generation upon light illumination from distance. By printing multiple metal nanoparticles of different shapes overlaid, we can fabricate multiwavelength thermoplasmonic images, which generate different heat patterns from a single printed image depending on the wavelength choice of light. In this work, we propose a novel multiwavelength thermoplasmonic image printing process that can be used for anticounterfeit technology. With this technology, “printed thermoplasmonic labels” allow fully secured anticounterfeit inspection procedure. Input stimulus of near-infrared or infrared light illumination and output signal reading of thermal patterns can be both completely invisible. Wavelength selective photothermal effect also enables the encryption of the contained information, which adds more complexity and thus higher security.

High performance organic thin-film transistors and inverters operating at MHz frequencies at 10 V are fabricated on plastic with high throughput (printing speed up to 1.0 m/s) using attoliter-scale high-speed gravure printing. The high performance of the devices is achieved using highly scaled gravure printed features (smaller than 5 μm) and optimizing a high mobility organic semiconductor for the short-channel gravure printed devices (>0.5 cm2/V s) to realize record performance levels.

Two-dimensional (2D) materials have been giving a chance to advance high performance electronic technology for next generation nanoelectronics devices. Among 2D materials, molybdenum disulfide (MoS2) is drawing attention due to its relative large bandgap (1.3-1.8 eV) and the 50~200 cm2/V·S range of high carrier mobility at room temperature. In the few early report, multilayer MoS2 could have been much better than single-layer MoS2 because it has larger density of state (DOS) and helps to create multiple conducting channels by field effect, which will lead to boost the current drive of TFTs. At realistic operating temperatures, however, the carrier transport mechanism of these 2D layered MoS2 FETs has not yet been intensively explored for use in electronics. Therefore, we investigate carrier transport and the impact of the operating ambient conditions on back-gated multilayer MoS2 field-effect transistors with a thickness of ~50 nm at their realistic working temperatures and under different ambient conditions (in air and in a vacuum of ~10-5 Torr). Moreover, we examine the quality of the device interface and an energy distribution of carrier trapping/scattering sites through the low-frequency noise (LFN) measurement. A Schottky barrier of ~65 meV was formed between the Ti/Au metal contact and the MoS2 semiconductor and the barrier partially hindered the flow of carriers. However, when the operating temperature increased, the carriers easily overcame the barrier by thermionic emission at defects. This caused Imin to rise as shown in Fig. 1(a) and (b). However, at high VGS (blue region), the drain current decreased slightly as the operating temperatures increased. This is consistent with phonon scattering which is inversely proportional to the operating temperature. Fig. 2(a) shows that VTH shifts toward the negative direction as the temperature increases. This behavior is observed due to an increase in thermally generated carriers, resulting in a shift in the Fermi level in the semiconductor. Additionally, VTH was higher in air than in a vacuum. One possible explanation is that the oxygen and water molecules on the surface of MoS2 semiconductors could be adsorbed from the ambient air, and they could trap the charge carriers from the conduction band. This could make depleted channels and induce a positive threshold voltage shift. Also, the chemisorption on the MoS2 flake created defects and associated increased scattering which causes a reduction in μeff , unlike in a vacuum (Fig. 2(b)). However, thick multilayer MoS2 was less affected by the ambient conditions, because the thickness of the MoS2 layers suppressed interactions with the underlying channel. This fact was also supported negligible effects of ambient conditions on interface quality as determined by sub-threshold slope values (Fig. 2(a)). In Fig. 3 (a), obtained exponent values (γ) from low-frequency noise analysis, 1/fγ, exhibited the increase of γ at low gate bias range due to active slow traps. And the slow traps were filled and thus γ decreased and saturated to near 1 (0.95) as VG increased. In addition, the Hooge’s parameter, αH , was extremely large in the subthreshold region and drastically decreased as the gate bias increased until it matched Vth . This result also supports that the amount of active traps which cause the carrier number fluctuation decreases more significantly below Vth since the increased gate bias fills traps; it agrees with the change of the exponent value aforementioned. It is also interesting fact that the Hooge’s parameter (measured in ambient conditions) during fully ON regime is on the order of 10-2. This value is comparable to that observed in single-layer MoS2 FETs measured under vacuum conditions. This result provides multilayer structures more robust than single-layer for the effect of surface adsorbates in air and is consistent with our previous statement mentioned above.

Light-mediated neuromodulation techniques provide great advantages to investigate neuroscience due to its high spatial and temporal resolution. To generate a spatial pattern of neural activity, it is necessary to develop a system for patterned-light illumination to a specific area. Digital micromirror device (DMD) based patterned illumination system have been used for neuromodulation due to its simple configuration and design flexibility. In this paper, we developed a patterned near-infrared (NIR) illumination system for region specific photothermal manipulation of neural activity using NIR-sensitive plasmonic gold nanorods (GNRs). The proposed system had high power transmission efficiency for delivering power density up to 19 W/mm(2). We used a GNR-coated microelectrode array (MEA) to perform biological experiments using E18 rat hippocampal neurons and showed that it was possible to inhibit neural spiking activity of specific area in neural circuits with the patterned NIR illumination. This patterned NIR illumination system can serve as a promising neuromodulation tool to investigate neuroscience in a wide range of physiological and clinical applications. (C) 2017 Optical Society of America

This work employs novel SnO(2) gel-like precursors in conjunction with sol-gel deposited ZrO(2) gate dielectrics to realize high-performance transparent transistors. Representative devices show excellent performance and transparency, and deliver mobility of 103 cm(2) V(-1) s(-1) in saturation at operation voltages as low as 2 V, a sub-threshold swing of only 0.3 V/decade, and /(on) //(off) of 10(4) ~10(5) .

Organic thin film transistors with channel lengths below 20 μm have been fabricated on plastic substrates using a combination of rotogravure and ink-jet printing exclusively. Gravure is utilized to deposit thin, smooth, and narrow metal lines ideal for gate electrodes; a poly(4-vinylphenol) dielectric; and a poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT) semiconductor using a heated roll. A novel fluid guiding technique is used to maintain closely spaced ink-jet printed source and drain (S/D) contacts. Together these printing processes yield aggressively scaled yet easily manufacturable TFTs with operating frequencies of 18 kHz.

An analytical threshold voltage model for double-gate MOSFETs with localized charges is developed. From the 2-D Poisson's equation with parabolic potential approximation, a compact threshold voltage model is derived. The proposed model is then verified with a 2-D device simulator. The model can be used to investigate hot-carrier-induced device degradation for various device dimensions and various charge distributions.

Neural interface plays an important role in monitoring and modulating brain activity. In order to study the neural information processing in vitro, microelectrode array (MEA) platform is used with cell culture or brain slice. To measure neural signals simultaneously from multiple cells for long-term period, extracellular neural recording technique is preferred and subcellular-scale microelectrodes , dense array, and flexible substrates are ideal. In this chapter, we will introduce the state-of-the-art in vitro neural recording technology based on microfabricated electrodes or transistors. MEAs with metal-type microelectrodes are passive types, and MEAs with active electronic components (field-effect transistors or integrated circuits) are active types. The motivation, operation principles, fabrication processes and materials, and current trends are reviewed.

Inkjet printing of precisely defined structures is critical for the realization of a range of printed electronics applications. We develop and demonstrate a methodology to optimize the inkjet printing of two-dimensional, partially wetting films. When printed inks have a positive retreating contact angle, we show that any fixed spacing is ineffective for printing two-dimensional features. With fixed spacing, the bead contact angle begins large, leading to a bulging overflow of its intended footprint. Each additional line reduces the bead contact angle, eventually leading to separation of the bead. We propose a printing scheme that adjusts the line-to-line spacing to maintain a bead's contact angle between its advancing and retreating values as it is printed. Implementing this approach requires an understanding of the two-dimensional bead surface and compensation for evaporation during the print. We derive an analytic equation for the bead's surface with pinned contact lines and use an empirical fit for mass loss due to evaporation. Finally, we demonstrate that enhanced contact angle hysteresis, achieved by preprinting a feature's border, leads to better corner definition.

In this work, we study the optimization of the geometry of inkjet-printed polymer films and develop a simple analytic framework to understand our results and establish limitations on inkjet-printed patterns. We show how drop spacing and ink concentration affect the thickness of a printed film and how hydrostatic conditions with contact angle hysteresis have to be considered to print optimized rectangular features. If advancing and receding contact angle are not taken into account, printed features will either bulge or break up into smaller beads. Thus, we provide a comprehensive analysis of the limits of film formation using regular assemblies of droplets.