Oxide-based Thin-film Transistors Research Articles

High-mobility and high-reliability Zn-incorporated amorphous In2O3-based thin-film transistors

Polycrystalline indium oxide-based thin film transistors (In2O3 TFTs) have attracted considerable attention because of high field effect mobility (μ FE ∼ 100 cm2 V−1 s−1). However, In2O3 TFTs exhibit poor reliability owing to the adsorption and/or desorption of gas molecules at the grain boundaries. The incorporation of Zn suppresses the crystallization of In2O3. Herein, we systematically studied the effect of Zn incorporation into In2O3 TFTs. The crystallization of In2O3 was suppressed when the Zn concentration ranged from 25% to 68%. Amorphous InZnO (IZO) TFTs with 25% Zn exhibited the highest μ FE of 41 cm2 V−1 s−1 and excellent reliability. In contrast, polycrystalline IZO TFTs showed a low μ FE <12 cm2 V−1 s−1 due to the formation of grain boundaries, and poor reliability after positive gate bias, mostly due to electron trapping at the polycrystalline/insulator interface. These results render an approach to realize In2O3 TFTs that show reasonably high μ FE and excellent reliability.

Transparent and flexible zinc oxide-based thin-film diodes and thin-film transistors: A review

Electronics today has evolved significantly, including its application in transparent and flexible devices. Flexible electronics offers new product concepts, including low production cost, low energy consumption, and sustainable and environmentally friendly materials. This concept leads to the development of novel materials that realize today’s requirements. Incorporating optically transparent and flexible thin-film-based devices into the electronic circuitry helps in maintaining high conductivity along with achieving the similar electronic behavior of the conventional electronic gadgets. Thin-film diodes (TFDs) and thin-film transistors (TFTs) are the core materials to be incorporated as building blocks for flexible devices. Among them, oxide-based thin films have been marked to be significant because of their efficient electrical performance, low temperature processing, and device flexibility. The present article reviews the concepts and application of zinc oxide (ZnO) as the semiconducting material for flexible thin-film devices. We also review flexible and transparent TFDs and TFTs that are based prominently on ZnO as the semiconducting material. Furthermore, the present issues have also been addressed.

Performance and reliability improvement of all-solution processed indium zinc oxide thin-film transistor by UV irradiation treatment

Developing a low-temperature fabrication strategy for amorphous oxide semiconductors, such as amorphous indium zinc oxide (a-IZO) channel layers, for use in flexible oxide-based thin-film transistors (TFTs) is essential. In this work, high-performance and highly stable all-solution processed a-IZO TFTs were achieved by varying the duration of a photo-assisted combination treatment (UV combination treatment), which combines UV irradiation with a low heating temperature (115 °C) in an all-solution processed approach. From the experimental results, UV irradiation can activate the IZO source, drain, and gate electrodes which induces TFT switching. X-ray photoelectron spectroscopy analysis revealed oxygen vacancy (V o) generation after the UV combination treatment which increased the carrier concentration and improved the conductivity of IZO. All-solution processed a-IZO TFTs with high performance and stability, high mobility (µ) up to 17.45 cm2 V−1 s−1, threshold voltage (Vth) = −1.2 V, and subthreshold swing (SS) = 0.64 V dec−1, were obtained at a low temperature of 115 °C for 90 min treatment time. The stability behavior of self-aligned top-gate, top-contact a-IZO TFT fabricated by UV combination treatment was investigated under positive bias stress (PBS) and negative bias stress (NBS) with the smallest ΔV th of 2.4 V and 0.5 V for PBS and NBS, respectively. Our work shows that better stability indicated by the smaller ΔV th is achieved due to reduction of interface trap density and moisture-related impurities, in particular on the activated electrode area. As a result, it can be inferred that UV combination treatment is a simple and promising method to enhance the electrical and stability performance of a-IZO TFTs even with the low-temperature process, which is useful for flexible devices.

Monolithic Integration of GaN-Based Green Micro-LED and Quasi-Vertical MOSFET Utilizing a Hybrid Tunnel Junction

We demonstrated the monolithic integration of GaN-based driving metal-oxide-semiconductor field effect transistor (MOSFET) on micro-light-emitting diodes (μLEDs) by regrowing a hybrid tunnel junction (TJ) on top of a commercial green LED wafer. The hybrid TJ served not only as the current spreading layer for μLEDs, but the n/p/n structure of the LED + TJ stack could also be utilized for fabricating a quasi-vertical driving MOSFET. The μLED was connected to the MOSFET via the conductive n-GaN layer. By modulating the gate supply voltage, the MOSFET effectively controlled the injection current of the μLED, allowing for precise modulation of its output performance. The integrated 60-μm μLED exhibited a high output power of 0.12 mW (~ 4.2 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) at a current of 0.3 mA (around 10 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) when the MOSFET was modulated with V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> = 5 V and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> = 16 V, demonstrating good μLED performance and comparable driving capability to previous GaN-based MOSFETs and oxide-based thin film transistors. This work provides a new method for GaN FET/LED monolithic integration, which paves the way for potential applications in visible light communication and flexible μLED displays.

Effect of Surface Modification on the Fundamental Electrical Characteristics of Solution-Gated Indium Tin Oxide-Based Thin-Film Transistor Fabricated by One-Step Sputtering.

Our solution-gated indium tin oxide (ITO)-based thin-film transistor (TFT) produced by single-step sputtering has great future potential in bioelectronics. In particular, chemical modifications of the ITO channel surface are expected to contribute to biomolecular recognition with ultrahigh sensitivity owing to a remarkably steep subthreshold slope (SS). In this study, we investigate the effect of a chemical modification of an aptamer as a receptor molecule at the ITO channel surface on the electrical characteristics of the solution-gated TFT. In this case, a SARS-CoV-2 aptamer is immobilized using a spacer molecule on an aryl diazonium monolayer that is electrochemically deposited with a radical scavenger. The monolayer is expected to not only passivate the ITO channel surface but also change the electron density in the ITO channel owing to the reduction reaction of aryl diazonium salts. Indeed, the electrochemical deposition of aryl diazonium salts decreases the leakage current through the ITO channel surface and provides a steep SS, which is near the thermal limit at 300 K, owing to the decrease in depletion layer capacitance. After the aptamer immobilization, the leakage current and SS unexpectedly return close to their original values before the surface modifications. This finding indicates that aptamer molecules should be carefully used because their negative charges would attract cations around the detection interface. Eventually, the solution-gated ITO-based TFT with the SARS-CoV-2 aptamer clearly responds to inactivated SARS-CoV-2 particles owing to the successful surface modification.

(Invited) Oxide Electronics and Recent Progress in Bipolar Applications

The discovery of oxide electronics is of increasing importance today as one of the most promising new technologies and manufacturing processes for a variety of electronic and optoelectronic applications such as next-generation displays, batteries, solar cells, memory devices, and photodetectors[1]. The high potential use seen in oxide electronics is due primarily to their high carrier mobilities and their ability to be fabricated at low temperatures[2]. However, since the majority of oxide semiconductors are n-type oxides, current applications are limited to unipolar devices, eventually developing oxide-based bipolar devices such as p-n diodes and complementary metal-oxide semiconductors.We have contributed to a wide range of oxide semiconductors and their electronics and optoelectronic device applications. Particularly, we have demonstrated n-type oxide-based thin film transistors (TFT), integrating In2O3-based n-type oxide semiconductors from binary cation materials to ternary cation species including InZnO, InGaZnO (IGZO), and InAlZnO. We have suggested channel/metallization contact strategies to achieve stable and high TFT performance[3, 4], identified vacancy-based native defect doping mechanisms[5], suggested interfacial buffer layers to promote charge injection capability[6], and established the role of third cation species on the carrier generation and carrier transport[7]. More recently, we have reported facile manufacturing of p-type SnOx through reactive magnetron sputtering from a Sn metal target[8]. The fabricated p-SnOx was found to be devoid of metallic phase of Sn from x-ray photoelectron spectroscopy and demonstrated stable performance in a fully oxide-based p-n heterojunction together with n-InGaZnO. The oxide-based p-n junctions exhibited a high rectification ratio greater than 103 at ±3 V, a low saturation current of ~2x10-10, and a small turn-on voltage of -0.5 V.In this presentation, we review recent achievements and still remaining issues in transition metal oxide semiconductors and their device applications, in particular, bipolar applications including p-n heterostructures and complementary metal-oxide-semiconductor devices as well as single polarity devices such as TFTs and memristors. In addition, the fundamental mechanisms of carrier transport behaviors and doping mechanisms that govern the performance of these oxide-based devices will also be discussed.ACKNOWLEDGMENTThis work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education.REFERENCES[1] K. Nomura et al., Nature, vol. 432, no. 7016, pp. 488-492, Nov 25 2004.[2] D. C. Paine et al., Thin Solid Films, vol. 516, no. 17, pp. 5894-5898, Jul 1 2008.[3] S. Lee et al., Journal of Applied Physics, vol. 109, no. 6, p. 063702, Mar 15 2011, Art. no. 063702.[4] S. Lee et al., Applied Physics Letters, vol. 104, no. 25, p. 252103, 2014.[5] S. Lee et al., Applied Physics Letters, vol. 102, no. 5, p. 052101, Feb 4 2013, Art. no. 052101.[6] M. Liu et al., ACS Applied Electronic Materials, vol. 3, no. 6, pp. 2703-2711, 2021/06/22 2021.[7] A. Reed et al., Journal of Materials Chemistry C, 10.1039/D0TC02655G vol. 8, no. 39, pp. 13798-13810, 2020.[8] D. H. Lee et al., ACS Applied Materials & Interfaces, vol. 13, no. 46, pp. 55676-55686, 2021/11/24 2021.

Interfacial and microstructural changes of the Al2O3/ZnO multilayer films induced by in-situ growth and post-annealing temperatures

Al2O3/ZnO nanolaminates are promising nanocomposites with special properties for the applications of oxide-based thin-film transistors, photoluminescence devices, and pitch grating references. In this study, Al2O3/ZnO nanolaminates were grown at 80 °C, 120 °C, 250 °C by atomic layer deposition, and then post-annealed by furnace annealing at 600 °C, 700 °C, 800 °C respectively. Both the in-situ growth temperature and post-annealing temperature-induced microstructures of Al2O3/ZnO nanolaminates were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). In addition, the interfacial diffusion and solid-state reaction were systematically studied by high-resolution transmission electron microscopy (HRTEM). The films grown at 80 °C and 250 °C show a typical polycrystalline structure, while the film grown at 120 °C possesses an obvious preferred orientation. After post-annealing at 700 °C, the spinel ZnAl2O4 grains are formed at the interface of the Al2O3/ZnO films grown at 80 °C and 250 °C, which indicates the solid-state reaction has occurred, but this phenomenon did not occur for the films grown at 120 °C. The results indicate that the growth temperature not only affects the crystallinity and preferred orientation of the ZnO interlayers, but also the interfacial diffusion and counter-diffusion of atoms, and thereby the solid-state reaction, in the post-annealing process. So, simultaneously controlling the effects of the growth and post-annealing temperatures has great significance for this kind of nanolaminates.

Strategies for Applications of Oxide-Based Thin Film Transistors

Due to the untiring efforts of scientists and researchers on oxide semiconductor materials, processes, and devices, the applications for oxide-based thin film transistors (TFTs) have been researched and promoted on a large scale. With the advantages of relatively high carrier mobility, low off-current, good process compatibility, optical transparency, low cost, and especially flexibility, oxide-based TFTs have already been adapted for not only displays (e.g., liquid crystal display (LCD), organic light emitting diode (OLED), micro-light-emitting diode (Micro-LED), virtual reality/augmented reality (VR/AR) and electronic paper displays (EPD)) but also large-area electronics, analog circuits, and digital circuits. Furthermore, as the requirement of TFT technology increases, low temperature poly-silicon and oxide (LTPO) TFTs, which combine p-type LTPS and n-type oxide TFT on the same substrate, have drawn further interest for realizing the hybrid complementary metal oxide semiconductor (CMOS) circuit. This invited review provides the current progress on applications of oxide-based TFTs. Typical device configurations of TFTs are first described. Then, the strategies to apply oxide-based TFTs for improving the display quality with different compensation technologies and obtaining higher performance integrated circuits are highlighted. Finally, an outlook for the future development of oxide-based TFTs is given.

Ultraviolet-Assisted Low-Thermal-Budget-Driven α-InGaZnO Thin Films for High-Performance Transistors and Logic Circuits.

Developing a low-temperature fabrication strategy of an amorphous InGaZnO (α-IGZO) channel layer is a prerequisite for high-performance oxide-based thin film transistor (TFT) flexible device applications. Herein, an ultraviolet-assisted oxygen ambient rapid thermal annealing method (UV-ORTA), which combines ultraviolet irradiation with rapid annealing treatment in an oxygen atmosphere, was proposed to realize the achievement of high-performance α-IGZO TFTs at low temperature. Experimental results have confirmed that UV-ORTA treatment has the ability to suppress defects and obtain high-quality films similar to high-temperature-annealing-treated samples. α-IGZO/HfAlO TFTs with high-performance and low-voltage operating have been achieved at a low temperature of 180 °C for 200 s, including a high μsat of 23.12 cm2 V-1 S-1, large Ion/off of 1.1 × 108, small subthreshold swing of 0.08 V/decade, and reliable stability under bias stress, respectively. As a demonstration of complex logic applications, a low-voltage resistor-loaded unipolar inverter based on an α-IGZO/HfAlO TFT has been built, demonstrating full swing characteristics and a high gain of 13.8. Low-frequency noise (LFN) characteristics of α-IGZO/HfAlO TFTs have been presented and concluded that the noise source tended to a carrier number fluctuation (ΔN) model from a carrier number and correlated mobility fluctuation (ΔN-Δμ) model. As a result, it can be inferred that the low-temperature UV-ORTA technique to improve α-IGZO thin film quality provides a facile and designable process for the integration of α-IGZO TFTs into a flexible electronic system.

Recent Advances in Metal-Oxide Thin-Film Transistors: Flexible/Stretchable Devices, Integrated Circuits, Biosensors, and Neuromorphic Applications

Thin-film transistors using metal oxides have been investigated extensively because of their high transparency, large area, and mass production of metal oxide semiconductors. Compatibility with conventional semiconductor processes, such as photolithography of the metal oxide offers the possibility to develop integrated circuits on a larger scale. In addition, combinations with other materials have enabled the development of sensor applications or neuromorphic devices in recent years. Here, this paper provides a timely overview of metal-oxide-based thin-film transistors focusing on emerging applications, including flexible/stretchable devices, integrated circuits, biosensors, and neuromorphic devices. This overview also revisits recent efforts on metal oxide-based thin-film transistors developed with high compatibility for integration to newly reported applications.

Improved electrical performance of solution-processed zinc oxide-based thin-film transistors with bilayer structures

A bilayer thin-film transistor (TFT) structure with ZnO and Al-doped ZnO (AZO) was fabricated using a solution process. The film thickness and sintering atmosphere of ZnO and AZO were controlled and then evaluated by measuring their electrical characteristics. By changing the sintering atmosphere, carriers attributed to oxygen vacancies in the thin film increased. Moreover, the ZnO single-layer TFT sintered in N2 exhibited good electrical characteristics. In the ZnO/AZO bilayer TFT laminated with the ZnO sintered in N2 and high-resistance AZO thin films, electrical characteristics, such as the On/Off ratio and subthreshold swing, improved compared to those of the ZnO-TFT. The On/Off ratio of the ZnO/AZO-TFT using the AZO thin film sintered in an O2 atmosphere notably improved to 3.7 × 105 compared to that of the ZnO-TFT (1.7 × 104). In addition, the subthreshold swing in the ZnO/AZO-TFT was 0.36 V/dec, while the field-effect mobility was 2.2 × 10−1 cm2/Vs, thereby exhibiting the best electrical characteristics among the fabricated samples. According to the grazing-incidence X-ray diffraction measurement, the ZnO particle size and crystallinity of the ZnO/AZO bilayer were higher than those of the ZnO single layer. Therefore, improvement of the electrical characteristics was confirmed.

Characterization with X-rays of a Large-Area GEMPix Detector with Optical Readout for QA in Hadron Therapy

Quality Assurance (QA) in hadron therapy is crucial to ensure safe and accurate dose delivery to patients. This can be achieved with fast, reliable and high-resolution detectors. In this paper, we present a novel solution that combines a triple Gas Electron Multiplier (GEM) and a highly pixelated readout based on a matrix of organic photodiodes fabricated on top of an oxide-based thin-film transistor backplane. The first LaGEMPix prototype with an active area of 60 × 80 mm2 was developed and characterized using low energy X-rays. The detector comprises a drift gap of 3.5 mm, a triple-GEM stack for electron amplification, and a readout featuring 480 × 640 pixels at a 126 µm pitch. Here, we describe the measurements and results in terms of spatial resolution for various experimental configurations. A comparison with GAFCHROMIC® films and the GEMPix detector used in the charge readout mode was performed to better understand the contribution to the spatial resolution from both the electron diffusion and the isotropic emission of photons. The measurements were compared to Monte Carlo simulations, using the FLUKA code. The simulation predictions are in good agreement with the GEMPix results. Future plans with respect to applications in hadron therapy are discussed.

Egg albumen-based biopolymer electrolyte lateral capacitive coupling thin-film transistors on logical operation

Recently, green electronic products are receiving increasing attention from scientists. Here, biodegradable lateral capacitively coupled electric-double-layer (EDL) oxide-based thin-film transistors (TFTs) were fabricated on a flexible paper substrate. The TFTs exhibit good performance due to the extremely high EDL capacitance of the egg albumen based electrolyte. Good transistor performances against mechanical stress were observed. In the coplanar double-gate structure, the high-low level of the different periods is input to the two gates to realize the logical function ‘AND’ operation. Resistor loaded inverters were built, exhibiting full-swing amplitude and high-voltage gain at low operating voltages, and implementing ‘NOT’ logic function. And the inverters were used to realize the conversion of the noise signal to the two-bit output. Therefore, the proposed lateral capacitively coupled TFTs may have potential applications in low-cost green portable logic computing devices. Laterally capacitively coupled TFTs were fabricated on a paper substrate by using egg albumen solid electrolyte film as a gate dielectric. The TFTs exhibit good performance due to the extremely high EDL capacitance of the egg albumen based electrolyte. AND logic operations and NOT logic functions are implemented on TFTs based on this lateral planar coupling structure. • Thin-film transistors (TFTs) with lateral capacitive coupling are fabricated on a paper substrate using natural egg albumen as gate dielectric. •These egg albumen-based flexible TFTs can implement logic operation functions under low voltage conditions and have excellent noise immunity. •The proton movement mechanism of lateral capacitive coupling in an external electric field is explained in our coplanar-gate structure of TFTs.

Effective encapsulation of ZnO thin film transistors controlled by thermal energy

Passivation still remains a challenging issue for the oxide-based thin film transistors because it requires thermal treatments at elevated temperatures to recover the original transistor characteristics. Particularly, the threshold voltage encounters a strong reduction due to the extraction of oxygen from the channel layers. This work demonstrates an effective way to reduce the reaction between the metal-organic precursor and the oxygen from the channel layers based on the bond-energy of the Al-O (569 kJ/mol) that is higher than Zn-O (250 kJ/mol). Reducing the growth temperatures of the passivation layers (PVLs) in the conventional process of thermal atomic layer deposition (ALD) leaves the performance of the thin film transistors (TFTs) only slightly varied but within an acceptable range. Among all devices, the TFTs with Al2O3 PVLs deposited at 100 °C by using H2O as oxidant remain a high mobility of 31.2 ± 0.4 cm2 V−1 s−1, a proper threshold voltage of 1.05 ± 0.04 V, a low subthreshold swing 0.17 ± 0.03 V/dec as well as an excellent stability with a small threshold voltage shift of 0.19, −0.03 and −0.12 V under positive bias stress, illumination bias stress and positive bias illumination stress, respectively. This improved stabilities are attributed to the presence of the high-quality PVLs that protect the channels from environmental effects.

A Review on the Recent Advancements in Tin Oxide-Based Thin-Film Transistors for Large-Area Electronics

Amorphous oxide semiconductors have gained significant attention in the past few decades and have emerged as a promising material for thin-film transistors (TFTs) because they offer high carrier mobility (> 10–50 cm2/V s) and uniformity. In particular, amorphous indium-gallium-zinc-oxide (a-IGZO) has been widely employed as an active channel material in TFTs owing to its high mobility. However, indium-based TFTs suffer from stability problems under positive, negative, and illumination bias stress conditions, which limits their applications in flat-panel displays. Moreover, the limited supply of indium and growing demand for high-stability TFTs with better electrical performance has led to the introduction of tin oxide as a promising solution to replace indium in TFTs. This review provides an overview on the progress and recent developments in indium-free tin oxide-based TFTs for large-area electronics, with special emphasis on the sputtering technique. In addition, the source of the dual conductivity of tin oxide is addressed, which will be helpful in designing complementary metal oxide semiconductor devices. The instability problems and approaches to improve the electrical performance of tin oxide TFTs are also discussed.

Controllable liquid water sensitivity of polymer-encapsulated oxide thin-film transistors

We demonstrated the controllable liquid water sensitivity of polymer-encapsulated oxide-based thin-film transistors (OxTFTs). The oxide active channels of the fabricated TFTs were utilized as water-sensitive layers. The OxTFTs were encapsulated with several polymers as water controlling layers (WCLs) to investigate and optimize the water sensitivity. It was found that the surface energy and porosity of the WCL significantly affect the water-dependent electrical characteristics of the OxTFTs. By employing poly(vinylidene-trifluoroethylene) (P(VDF-TrFE)) as a WCL and annealing the chosen polymer properly, we achieved a continuous shift of the threshold voltage even after several hours of direct exposure to the liquid phase of water which is crucial for sensor properties of the OxTFTs. The device using P(VDF-TrFE) as the WCL exhibits long-term stable detection characteristics and repeatability, demonstrating its applicability as a low-cost soil moisture sensor.

Effects of P-Type SnOx Thin-Film Transistors with N₂ and O₂ Ambient Furnace Annealing.

Recently oxide-based thin-film transistors (TFTs) are investigated for emerging applications of the next generation display devices and other electronic circuits (Fortunato, E., et al., 2012. Oxide semiconductor thin-film transistors: A review of recent advances. Advanced Materials, 24, pp.2945-2986). Despite of the great success in n-type oxide semiconductors with high transparency and high field-effect mobility, high performance P-type oxide TFTs are so highly desired that complementary circuits can be realized with low power and high performance (Ou, W.C., et al., 2008. Anomalous P-channel amorphous oxide transistors based on tin oxide and their complementary circuits. Applied Physics Letters, 92, p.122113). There are some oxides such as SnO, CuO, Cu₂O and NiO are regarded as promising P-type semiconductor materials. In this investigation, tin oxide SnOx is fabricated to be active layer for TFTs device, and furnace annealing with several combinations of nitrogen and oxygen ambient is compared to enhance the electrical characteristics of P-type SnOx TFTs (Park, K.S., et al., 2009. High performance solution-processed and lithographically patterned zinc-tin oxide thin-film transistors with good operational stability. Electrochemical and Solid-State Lett., 12, pp.H256-H258). The results show that with N₂+O₂ ambient, 30 minutes furnace annealing, the P-type SnOx TFTs device shows better performance with mobility (μFE) 0.883 cm²/V · S, threshold voltage (VT) -4.63 V, subthreshold swing (SS) 1.15 V/decade, and Ion/Ioff ratio 1.01×10₃.

Origin of bias-stress and illumination instability in low-cost, wide-bandgap amorphous Si-doped tin oxide-based thin-film transistors

This article reports thin-film transistors (TFTs) with a low-cost, environmentally friendly and wide-bandgap amorphous Si-doped tin oxide (a-STO) semiconductor as the channel layer. To realize practical applications, a comprehensive investigation of a-STO TFTs was performed. The underlying carrier transport mechanism of a-STO TFTs analyzed via the temperature dependence of transfer characteristics is trap-limited conduction. The degradation of the a-STO TFTs induced by bias stress and light illumination is discussed. The results may not only provide a deeper understanding of the electrical properties of a-STO TFTs but also form a fundamental perspective for further improvement of the performance of similar devices.

Proton Conducting Perhydropolysilazane-Derived Gate Dielectric for Solution-Processed Metal Oxide-Based Thin-Film Transistors.

Perhydropolysilazane (PHPS), an inorganic polymer composed of Si-N and Si-H, has attracted much attention as a precursor for gate dielectrics of thin-film transistors (TFTs) due to its facile processing even at a relatively low temperature. However, an in-depth understanding of the tunable dielectric behavior of PHPS-derived dielectrics and their effects on TFT device performance is still lacking. In this study, the PHPS-derived dielectric films formed at different annealing temperatures have been used as the gate dielectric layer for solution-processed indium zinc oxide (IZO) TFTs. Notably, the IZO TFTs fabricated on PHPS annealed at 350 °C exhibit mobility as high as 118 cm2 V-1 s-1, which is about 50 times the IZO TFTs made on typical SiO2 dielectrics. The outstanding electrical performance is possible because of the exceptional capacitance of PHPS-derived dielectric caused by the limited hydrolysis reaction of PHPS at a low processing temperature (<400 °C). According to our analysis, the exceptional dielectric behavior is originated from the electric double layer formed by mobile of protons in the low temperature-annealed PHPS dielectrics. Furthermore, proton conduction through the PHPS dielectric occurs through a three-dimensional pathway by a hopping mechanism, which allows uniform polarization of the dielectric even at room temperature, leading to amplified performance of the IZO TFTs.

Research progress of tin oxide-based thin films and thin-film transistors prepared by sol-gel method

Transparent conductive oxide (TCO) films and transparent oxide semiconductor (TOS) films have been widely adopted in solar cells, flat panel displays, smart windows, and transparent flexible electronic devices due to their advantages of high transparency and good conductivity and so on. Most of TCO and TOS films are mainly derived from indium oxide, zinc oxide and tin oxide. Among these materials, the In element is toxic, rare and expensive for indium oxide film, which will cause environmental pollution; zinc oxide film is sensitive to acid or alkali etchants, resulting in a poor formation of film patterning; tin oxide film is not only non-toxic, eco-friendly, and cheap but also has good electrical properties and strong chemical stability. Thus, tin oxide has a great potential for developing the TCO and TOS films. At present, the film is prepared mainly by the vacuum deposition technique. The drawbacks of this technique are complex and expensive equipment system, high energy consumption, complicated process and high-cost production. However, compared with the vacuum deposition technique, the sol-gel method has attracted extensive attention because of its virtues such as simple process and low cost. In this paper, we review the development status and trend of TCO and TOS films. First, the structural characteristics, conductive mechanism, element doping theory and carrier scattering mechanism of tin oxide thin films are introduced. Then the principle of sol-gel method and correlative film fabrication techniques are illustrated. Subsequently, the application and development of tin oxide-based thin films prepared by sol-gel method in n-type transparent conductive films, thin-film transistors and p-type semiconductor films in recent years are described. Finally, current problems and future research directions are also pointed out.