Solution-processed Indium Gallium Zinc Oxide Research Articles

Aqueous electrolyte-gated solution-processed metal oxide transistors for direct cellular interfaces.

Biocompatible field-effect-transistor-based biosensors have drawn attention for the development of next-generation human-friendly electronics. High-performance electronic devices must achieve low-voltage operation, long-term operational stability, and biocompatibility. Herein, we propose an electrolyte-gated thin-film transistor made of large-area solution-processed indium-gallium-zinc oxide (IGZO) semiconductors capable of directly interacting with live cells at physiological conditions. The fabricated transistors exhibit good electrical performance operating under sub-0.5 V conditions with high on-/off-current ratios (>107) and transconductance (>1.0 mS) over an extended operational lifetime. Furthermore, we verified the biocompatibility of the IGZO surface to various types of mammalian cells in terms of cell viability, proliferation, morphology, and drug responsiveness. Finally, the prolonged stable operation of electrolyte-gated transistor devices directly integrated with live cells provides the proof-of-concept for solution-processed metal oxide material-based direct cellular interfaces.

Field-Effect Mobility Extraction of Solution-Processed InGaZnO Thin-Film Transistors Considering Dielectric Dispersion Behavior of AlOx Gate Insulator

We investigated the effect of the dielectric dispersion behavior of solution-processed aluminum oxide (AlOx) on the field-effect mobility estimation of the solution-processed indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs). In the metal–insulator–metal (MIM) structure, solution-processed AlOx dielectric film annealed at 350 °C showed dielectric dispersion behavior, which was attributed to the electric double layer (EDL) due to the mobile ions, such as a hydrogen ion (H+) or a hydroxyl group (OH–). The annealing process at a higher temperature of 500 °C reduced the number of mobile ions in the AlOx film and removed the dielectric dispersion behavior in the MIM structure. However, solution-processed IGZO TFTs using the AlOx annealed at 500 °C as gate insulator showed dielectric dispersion-related behavior. We found that the chemical reaction to form a solution-processed IGZO layer supplied the mobile ions to the AlOx film, resulting in the EDL and dielectric dispersion phenomenon. Therefore, the dielectric dispersion should be investigated in the metal–insulator–semiconductor–metal structure, although the dispersive behavior does not occur in the MIM structure. Furthermore, the field-effect mobility (μFE) of solution-processed IGZO TFTs was 35.6 and 17.5 cm2/V·s with and without consideration of the dielectric dispersion behavior. The μFE was overestimated by 203% without regard to the dielectric dispersion. Consequently, the dielectric dispersion should be considered to estimate the accurate μFE of solution-processed IGZO TFTs with solution-processed AlOx as the gate insulator layer.

Effect of Back-Channel Surface on Reliability of Solution-Processed In0.51Ga0.15Zn0.34O Thin-Film Transistors with Thin Active Layer.

We have investigated the degradation mechanism of solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors. The threshold voltage shift (ΔVth) followed a linear function under negative gate bias stress (NBS), while it showed a stretched-exponential behavior under positive gate bias stress. The slope of ΔVth for stress time was rarely changed with variations below 0.3 mV/s. The thickness of the fabricated IGZO layer (In0.51Ga0.15Zn0.34O) was approximately 10 nm. The Debye length (LD) was larger than IGZO thickness (tIGZO) due to the fully depleted active layer under NBS. Therefore, the degradation phenomenon under NBS was related to the adsorption at back-channel surface. The back-channel surface could be affected by the gate bias under NBS, and the molecules adsorbed at the IGZO layer were positively charged and induced extra electrons by NBS. We verified that the number of positively charged adsorbates had a proportional relationship with the ΔVth based on the two-dimensional technology computer-aided design (TCAD) simulation. Furthermore, we investigated the degradation phenomenon with the ΔVth equation regarding the adsorbates, and the result confirmed that the adsorption process could cause the linear ΔVth. We experimentally confirmed the effect of back-channel surface by comparing the ΔVth between different atmospheric conditions and LD. Consequently, the reaction at the back-channel surface should be considered to develop the metal-oxide semiconductor devices.

Self-Aligned Double Injection-Function TFT for Deep Sub-Micrometer Channels’ Length—Application to Solution-Processed Indium Gallium Zinc Oxide

We propose and demonstrate self-aligned Double Injection Function Thin Film Transistor (DIF-TFT) architecture that mitigates short channel effects in 200 nm channel on non-scaled insulator (100 nm SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). In this conceptual design, a combination of ohmic-like injection contact and a high injection-barrier metal allows maintaining the high ON currents while suppressing drain-induced barrier lowering (DIBL) effects. Using an industrial 2-D device simulator (Sentaurus), we propose two methods to realize the DIF concept. We use one of them to demonstrate, experimentally, a DIF-TFT based on solution-processed indium gallium zinc oxide (IGZO). Using molybdenum as the ohmic contact and platinum as the high injection barrier, we compare three transistors’ source-contacts: ohmic, Schottky, and DIF. The fabricated DIF-TFT exhibits saturation at sub 1 V drain bias with only about a factor of 2 loss in ON current compared to the ohmic contact.

Novel Method for Fabricating Visible-Light Phototransistors Based on a Homojunction-Porous IGZO Thin Film Using Mechano-Chemical Treatment.

A homojunction-structured oxide phototransistor based on a mechano-chemically treated indium-gallium-zinc oxide (IGZO) absorption layer is reported. Through this novel and facile mechano-chemical treatment, mechanical removal of the cellophane adhesive tape induces reactive radicals and organic compounds on the sputtered IGZO film surface. Surface modification, following the mechano-chemical treatment, caused porous sites in the solution-processed IGZO film, which can give rise to a homojunction-porous IGZO (HPI) layer and generate sub-gap states from oxygen-related defects. These intentionally generated sub-gap states played a key role in photoelectron generation under illumination with relatively long-wavelength visible light despite the wide band gap of IGZO (>3.0 eV). Compared with conventional IGZO phototransistors, our HPI phototransistor displayed outstanding optoelectronic characteristics and sensitivity; we measured a threshold voltage (Vth) shift from 3.64 to -6.27 V and an on/off current ratio shift from 4.21 × 1010 to 4.92 × 102 under illumination with a 532 nm green light of 10 mW/mm2 intensity and calculated a photosensitivity of 1.16 × 108. The remarkable optoelectronic characteristics and high optical transparency suggest optical sensor applications.

Enhancement of the Retention Characteristics in Solution-Processed Ferroelectric Memory Transistor with Dual-Gate Structure.

We demonstrated the enhancement of the retention characteristics in solution-processed ferroelectric memory transistors. For enhanced retention characteristics, solution-processed Indium Gallium Zinc Oxide (InGaZnO) semiconductor is used as an active layer in a dual-gate structure to achieve high memory on-current and low memory off-current respectively. In our dual-gate oxide ferroelectric thin-film transistor (DG Ox-FeTFT), while conventional TFT characteristic is observed during bottom-gate sweeping, large hysteresis is exhibited during top-gate sweeping with high memory on-current due to the high mobility of the InGaZnO. The voltage applied to the counter bottom-gate electrode causes variations in the turn-on voltage position, which controlled the memory on- and off-current in retention characteristics. Specifically, due to the full depletion of semiconductor by the high negative counter gate bias, the memory off-current in reading operation is dramatically reduced by 10⁴. The application of a high negative counter field to the dual-gate solution-processed ferroelectric memory gives a high memory on- and off-current ratio useful for the production of high performance multi-bit memory devices.

Study on dielectric properties of PVP and Al2O3 thin films and their implementation in low-temperature solution-processed IGZO-based thin-film transistors

In the present work, we investigated the dielectric properties of solution-processed Poly-(4-vinylphenol) (PVP), and atomic layer deposited (ALD) alumina (Al2O3) thin films. Later, we integrate these dielectric materials into a thin-film transistor (TFT) device fabricated on a glass substrate using solution-processed indium gallium zinc oxide (IGZO) as a semiconductor. Both PVP and Al2O3 films show good dielectric behavior with minimum leakage and capacitance densities of 7.0 nF/cm2 and $$1.034 \times {10}^{-7}$$ F/cm2, respectively. A bottom source/drain top-gate transistor based on PVP as gate insulator operates in the linear region and demonstrates highly negative threshold voltage values beyond − 40 V. On the other hand, the bottom-gate top source/drain transistor based on Al2O3 gate dielectric demonstrates good saturation behavior with saturation current and saturation mobility of $$4.16 \times {10}^{-4}$$ A and 2.203 cm2/Vs, respectively. Further, using the photochemical activation method, the processing temperature of IGZO thin films is reduced to 325 °C from 400 °C. Low-temperature processed IGZO TFTs also show good saturation behavior with low positive threshold voltage values. However, it is achieved at the expense of saturation mobility which decreases to 0.557 cm2/Vs. Our study presents the possibility of producing organic–inorganic hybrid low-cost, and high-performance devices for upcoming flexible electronics.

Origin of performance improvement in solution-processed indium–gallium–zinc-oxide thin-film transistors having thin active layer and asymmetric dual gate structure

In this paper, we report the electrical characteristics of thin active layer indium–gallium–zinc-oxide thin-film transistors (IGZO TFTs) having an asymmetric dual gate structure. It was observed that the performance of IGZO TFTs significantly improved when the TFT is operated in the dual gate mode though the performance of the top gate mode shows very poor performance of low field-effect mobility and large subthreshold slope. We found that the channel electrons are coupled in the bulk region when the active layer is very thin, and top gate biasing provides additional electrons to the coupled channel region, which improves the electrical performance of dual gate mode IGZO TFTs. Bias stress instability measurements also indicate that dual gate mode IGZO TFTs show better stability compared to the other mode because coupled electrons are mainly formed in the bulk region, which reduce the effect of interfacial defect density of states. Therefore, the improvements of performance of dual gate electrode IGZO TFTs can be realized regardless of the relatively poor performance of the top gate mode.

Effects of lithium doping and ultraviolet photo-patterning on electrical properties of InGaZnO thin film transistors

Alkali metals, such as Li and Na, have been added in solution-processed oxide thin-film transistors (TFTs) because they improved electrical characteristics of the oxide TFTs. In previous research, however, fine-patterning of the alkali metal-doped oxide layers was not performed due to potential performance degradation during photolithography process. In this work, we demonstrate ultraviolet (UV) photo-patterned solution-processed indium gallium zinc oxide (IGZO) TFTs containing various amount of lithium (Li). For patterning of active layer, we applied deep UV (184 nm, 10% and 254 nm, 90%) photo-patterning process. We also investigated the chemical composition and bonding structures of the Li doped IGZO (Li-IGZO) films. It was found that appropriate Li doping on IGZO films can reduce oxygen vacancies and improved the coordination of the metal-oxygen bonding. In addition, Li-IGZO TFTs showed improved mobility and bias stability compared to un-doped counterparts. We believe that this simple patterning process and Li doping can be applied to other types of the high-performance solution-processed oxide TFTs.

Effects of metal content on electrical and physical properties in solution-processed IGZO thin films

The on-current of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) fabricated by solution process with low-temperature post-annealing increases monotonically with the decrease in the Ga content. This trend is different from that of IGZO fabricated by a solution process, which shows the maximum electron mobility at a Ga content of 33%. To clarify its cause, effects of Ga and In contents in solution-processed IGZO post-annealed at a low-temperature on their oxygen deficiency and band structures were investigated with spectroscopic methods such as X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, photoluminescence, and ultraviolet–visible absorption. When the Ga content is low, the oxygen vacancy becomes less abundant. The increase in In content exhibits similar effects on the oxygen vacancy. We have reported that Ga is not oxidized sufficiently at low temperatures, which should cause the generation of oxygen vacancies. By this theory, the above-mentioned decrease in oxygen vacancies can be explained. Furthermore, when these films are actually used as TFT channels, the on-current increases with the decrease in Ga content. From this, in solution-processed IGZO post-annealed at a low temperature, oxygen vacancies mainly act as electron traps that decrease the on-current, rather than acting as donors. In manufacturing flexible devices, even when we decrease the process temperature low enough to suppress the damage to polymer substrates, the devices must maintain good performance. Our results suggest that an optimal metal ratio different from that of a typical vacuum process is necessary to improve the performance of IGZO TFTs fabricated by the low-temperature solution process.

Structure-Property Relation in Organic-Metal Oxide Hybrid Phototransistors.

We report an optoelectronic device consisting of a solution-processed indium gallium zinc oxide (IGZO) thin-film transistor and vacuum-deposited small organic molecules. Depending on the configurations of the organic materials, either bulk heterojunction or planar heterojunction (PHJ), the device assumes the functionality of either a photosensor or a photoinduced memory, respectively. Under λ = 625 nm light illumination, the photosensor shows response and recovery time of ∼50 ms, responsivity of ∼5 mA/W, sensitivity above 104, and a linear response. The mechanism of the photoinduced memory is studied experimentally and verified using a device simulation. We find that the memory is due to long charge retention time at the organic PHJ interface which is stable for over 9 days. It is correlated with the low leakage current found in ordered organic junctions having low subgap tail states. The presented integration of the PHJ with the transistor constitutes a new design of write-once-read-many-times memory device that is likely to be attractive for low-cost applications.

The Effect of Crystalline Aluminum Oxide on Device Performance of Solution-Processed Indium-Gallium-Zinc-Oxide Thin-Film Transistors Operating at Low Voltage.

High dielectric constant (high-k) materials have been extensively investigated for low-voltage operating electronics. In recent years, solution-processed high-k dielectrics have been of technological interests in low fabrication cost, large area process and good film quality, compared to the vacuum-process technology. In this paper, we demonstrate solution-processed aluminum oxide (Al2O3) dielectrics for high performance solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) operating at low voltage. The material and electrical properties of Al2O3 dielectrics fabricated at different post-annealing temperatures were analyzed by atomic force microscopy, scanning electron microscopy, X-ray diffraction and capacitance-voltage measurements. We also investigate the effect of crystalline Al2O3 dielectrics on the device performance of solution-processed IGZO TFTs. It is concluded that improved interfacial characteristics of crystalline Al2O3 dielectrics enhance the device performance of solution-processed IGZO TFTs operating at 3 V.

Solution-Processed Hybrid Ambipolar Thin-Film Transistors Fabricated at Low Temperature

We demonstrate solution-processed hybrid ambipolar thin-film transistors (TFTs) employing a stack structure composed of indium–gallium–zinc-oxide (IGZO) and single-wall carbon nanotube (SWCNT) as an active channel fabricated at low temperature. With an optimized deep-ultraviolet (DUV) photo annealing process for sol–gel based IGZO thin film on SWCNT random networks, the ambipolar transport of both electrons and holes with good electrical characteristics was realized. We also investigate the effect of DUV photo annealing on the material characteristics of solution-processed hybrid stack films and on the device performance of solution-processed hybrid ambipolar TFTs compared to those of samples thermally annealed at 500 °C, which is required for solution-processed high-quality IGZO thin films. The Raman spectra show that DUV photo annealing ensures hole transport in SWCNT random networks of a hybrid stack film, where the intensity of the 2D peak to the G peak was not changed compared to that of pristine SWCNT random networks. We believe that these analytical investigations reveal that DUV photo annealing is a promising method by which to realize hybrid ambipolar SWCNT/IGZO TFTs fabricated at low temperature.

Multi- and single-step in situ microwave annealing as low-thermal-budget techniques for solution-processed indium–gallium–zinc oxide thin films

In this study, low-thermal-budget in situ microwave annealing of solution-processed indium–gallium–zinc oxide (IGZO) thin films was investigated as a potential alternative to the conventional high-thermal-budget annealing process. The low-temperature baking and high-temperature post-deposition annealing of the solution-processed IGZO film were continuously performed using the same microwave equipment, leading to a reduced heat treatment processing time and temperature. We compared the electrical characteristics of IGZO thin film transistors (TFTs) produced using single- and multi-step in situ microwave annealing methods with those of TFTs manufactured via the conventional annealing method and found that the proposed single-step microwave annealing method yielded TFTs with electrical characteristics better than those of the TFTs fabricated using the multi-step and conventional annealing methods. In addition, the reliability was evaluated by conducting positive and negative gate bias stress tests, in which the IGZO TFTs manufactured using the proposed heat treatment method proved superior to those fabricated via the conventional heat treatment method. We investigated the effects of heat treatment on the composition and energy band structures of the IGZO films by performing x-ray photoelectron spectroscopy analysis and found that the proposed in situ microwave annealing method is more effective than the conventional method in solution processing.

Strontium doping effects on the characteristics of solution-processed aluminum oxide dielectric layer and its application to low-voltage-operated indium-gallium-zinc-oxide thin-film transistors

Abstract In this paper, we investigated the strontium doping effects on the electrical and physical characteristics of solution-processed aluminum oxide dielectric layer and its application to low-voltage-operated indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). With an optimized doping concentration of strontium (5 at%) in aluminum oxide (Al 2 O 3 ), an oxide gate dielectric layer having a dielectric constant of ~7 and low leakage current characteristics (~4 × 10 −7 A/cm 2 at 3 MV/cm) could be achieved by a solution process, which are comparably better than those of pristine Al 2 O 3 film. The enhanced dielectric properties from strontium doping can be attributed to the change in the physical properties of Al 2 O 3 film incorporated with strontium, providing charge relaxation of defect states in Al 2 O 3 film. Also, since the strontium is highly reactive with oxygen, the strontium substitution through a doping leads to more strongly bound structure in an Al 2 O 3 film without considerable lattice distortion. Using the strontium-doped aluminum oxide film as a gate dielectric layer, having a thickness less than 10 nm, solution-processed IGZO TFTs operating at ≤ 1 V were demonstrated showing a field-effect mobility of 1.74 ± 1.10 cm 2 /V s and an on-current level of ~10 −5 A.

Electroless-plated Ni pattern with catalyst printing on indium–gallium–zinc oxide surface

Electroless plated metals have been used for wiring and electrodes in the manufacture of electronic devices. To obtain plated patterns, etching and photoresist are generally used. However, through catalyst patterning by printing, we can obtain metal patterns without etching and photoresists by electroless plating. Solution-processed indium–gallium–zinc oxide (IGZO) has received significant attention for showing high performance and ease of preparation in air atmosphere. In this study, we prepared an electroless plated pattern by catalyst printing as electrodes of IGZO TFT. There are few reports on the application of plated metal electrodes prepared by catalyst printing to the source and drain electrodes of IGZO TFT. The prepared IGZO TFT exhibits a typical current–voltage (I–V) curve. The plated electrodes caused many problems such as performance degradation. However, our result showed that the plated metal electrodes can drive IGZO TFT. In addition, we confirm plated metal growth into the catalyst layer by cross sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) of the plated Ni. We discuss the relevance of the measured work function (WF) of the electrode materials and the performance of IGZO TFT.

Accurate Defect Density-of-State Extraction Based on Back-Channel Surface Potential Measurement for Solution-Processed Metal-Oxide Thin-Film Transistors

We report more accurate extraction method of the defect density of states for solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). Since the solution-processed IGZO TFTs have a very thin (~8 nm) active semiconductor layer, their back-channel surface potential should be considered in the field-effect method. If the back-channel surface potential is ignored, deviation between theoretically derived and experimentally measured activation energy data becomes more significant as the thickness of the semiconductor layer decreases in comparison with its Debye length. Dependence of the back-channel surface potential on the applied gate voltages was verified by scanning Kelvin probe microscopy and found to be proportional to the gate voltages. The modified field-effect method provided a more accurate model of the activation energy over the subthreshold region and correspondingly more accurate defect density of states of the IGZO TFTs.

Improvement of TFT Characteristics for Low-Temperature Solution-Processed Oxide Semiconductors with Hydrogen Injection and Oxidation Process

Thin-film transistors (TFTs) using oxide semiconductors have attracted much attention for switching and driving devices in large-screen, high-resolution liquid crystal display (LCD) and organic light-emitting diode (OLED) displays because of their high mobility1-3. As an advanced oxide TFT fabrication method, the solution-process is widely researched due to advantages such as its low process cost, large-scale fabrication capacity, and the simplicity of the process. However, several drawbacks of the solution-process must be addressed for display applications. One of the key points is the trade-off between the processing temperature and the TFT characteristics. From previous research on solution-processed oxide TFTs, it has been reported that low-temperature-processed TFTs are generally inactive below 400 °C due to a lack of metal-oxide-metal bond formation and decomposition of the residual species4,5. However, a low-temperature process is strongly required for application to plastic substrates for flexible displays and flexible electronics devices.In addition, a low-temperature process is important to achieve low fabrication costs. Here, we demonstrate improvement of the TFT characteristics by application of a hydrogen injection and oxidation (HIO) process for low-temperature solution-processed oxide TFTs. From a technical standpoint, we consider that the important factor is how to efficiently decompose the residual species. The solution-processed oxide TFTs exhibit inferior device performance when a few residual species remain. Therefore, a reduction reaction is initiated by a hydrogen injection process to decompose the residual spices. The characteristics of a TFT based on indium gallium zinc oxide (IGZO) were evaluated, such as the field effect mobility and the threshold voltage (Vth) shift under positive and negative bias stress. The maximum temperature for the entire fabrication process was as low as 300 °C. Solution-processed IGZO thin films were fabricated by a spin-coating method onto 200 nm thick thermally oxidized SiO2/n+-Si substrates and annealing at 300 °C for 1 h. The IGZO precursor was prepared from 0.3 M solutions of indium nitrate hydrate (In(NO3)3·xH2O), gallium nitrate hydrate (Ga(NO3)3·xH2O), and zinc nitrate hydrate (Zn(NO3)2·xH2O) in pure water. The composition ratio for In:Ga:Zn was set to 4:1:1. Hydrogen plasma treatment was adopted for the hydrogen injection process with subsequent annealing at 300 °C for 1 h. After fabrication of the IGZO film, the active area of the IGZO film was defined using a conventional photolithography method. Patterned source/drain (S/D) electrodes (Mo) were formed on the IGZO thin films using a shadow mask. Figure 1 shows the transfer characteristics of the IGZO TFT with and without the HIO process. The transfer characteristics of these IGZO TFTs for gate voltages (Vg) ranging from -30 to 30 V were measured at a fixed drain voltage (Vd) of 30 V. After the HIO process for the IGZO TFTs, the field effect mobility was significantly improved from 2.1 cm2/Vs to 4.8 cm2/Vs. Figure 2 shows the results for the threshold voltage shift (ΔVth) under a positive gate bias stress (PBS) of 20 V and a negative gate bias stress (NBS) of -20 V, with and without the HIO process. The stress time was set to 1 h at the maximum. Improvement of the reliability was confirmed: the Vth shift was less than 0.25 V for PBS and -2 V for NBS. The trap sites of any residual species or defect states in active channels were thus efficiently suppressed by the hydrogen injection process. In addition, the oxidation process may enhance the metal-oxide-metal bond formation. In conclusion, the HIO process as a combination of hydrogen reduction reaction and oxidation was demonstrated as effective for the improvement of solution-processed oxide TFTs. Improvement of the TFT characteristics was confirmed in terms of the field effect mobility and the Vthshift under PBS and NBS. Therefore, we consider that this new approach will lead to the development of high-performance solution-processed oxide TFTs in future. 1K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, Nature 432, 488 (2004). 2K. Nomura, H. Ohta, K. Ueda, T. Kamiya, M. Hirano, and H. Hosono, Science 300, 1269 (2003). 3L. Wang, M. Yoon, G. Lu, Y. Yang, A. Facchetti, and T.J. Marks, Nature materials 5, 893 (2006). 4 M. G. Kim, M. G. Kanatzidis, A. Facchetti, and T. J. Marks, Nature materials 5, 382 (2011) 5 S. Jeong, Y. G. Ha, J. Moon, A. Faccchetti, T. J. Marks, Advanced materials 22, 1346 (2010) Figure 1

Low-Temperature Photochemically Activated Amorphous Indium-Gallium-Zinc Oxide for Highly Stable Room-Temperature Gas Sensors.

We report on highly stable amorphous indium-gallium-zinc oxide (IGZO) gas sensors for ultraviolet (UV)-activated room-temperature detection of volatile organic compounds (VOCs). The IGZO sensors fabricated by a low-temperature photochemical activation process and exhibiting two orders higher photocurrent compared to conventional zinc oxide sensors, allowed high gas sensitivity against various VOCs even at room temperature. From a systematic analysis, it was found that by increasing the UV intensity, the gas sensitivity, response time, and recovery behavior of an IGZO sensor were strongly enhanced. In particular, under an UV intensity of 30 mW cm(-2), the IGZO sensor exhibited gas sensitivity, response time and recovery time of 37%, 37 and 53 s, respectively, against 750 ppm concentration of acetone gas. Moreover, the IGZO gas sensor had an excellent long-term stability showing around 6% variation in gas sensitivity over 70 days. These results strongly support a conclusion that a low-temperature solution-processed amorphous IGZO film can serve as a good candidate for room-temperature VOCs sensors for emerging wearable electronics.

Wafer-Scale Microwire Transistor Array Fabricated via Evaporative Assembly.

One-dimensional (1D) nano/microwires have attracted significant attention as promising building blocks for various electronic and optical device applications. The integration of these elements into functional device networks with controlled alignment and density presents a significant challenge for practical device applications. Here, we demonstrated the fabrication of wafer-scale microwire field-effect transistor (FET) arrays based on well-aligned inorganic semiconductor microwires (indium-gallium-zinc-oxide (IGZO)) and organic polymeric insulator microwires fabricated via a simple and large-area evaporative assembly technique. This microwire fabrication method offers a facile approach to precisely manipulating the channel dimensions of the FETs. The resulting solution-processed monolithic IGZO microwire FETs exhibited a maximum electron mobility of 1.02 cm(2) V(-1) s(-1) and an on/off current ratio of 1 × 10(6). The appropriate choice of the polymeric microwires used to define the channel lengths enabled fine control over the threshold voltages of the devices, which were employed to fabricate high-performance depletion-load inverters. Low-voltage-operated microwire FETs were successfully fabricated on a plastic substrate using a high-capacitance ion gel gate dielectric. The microwire fabrication technique involving evaporative assembly provided a facile, effective, and reliable method for preparing flexible large-area electronics.