Indium Zinc Tin Oxide Thin-film Transistors Research Articles

Amorphous InZnSnO Thin-Film-Transistors Performance Enhancement with Low-Energy Xenon Pulsed-Light Annealing

The electrical characteristics and stability of amorphous indium-zinc-tin oxide (IZTO) thin-film transistors (TFTs) were significantly improved in this study using low-energy Xenon pulsed-light annealing (PLA). In comparison to conventional furnace annealing (FA), PLA treatment significantly reduced the processing temperature and annealing time. Besides, the defect states are obviously reduced from 1.73×1012 cm-2 to 6.53×1011 cm-2 by PLA treatment, resulting in improved device electrical characteristics and enhanced reliability, including improved carrier mobility from 20.08 to 39.61 cm2/V∙s, threshold voltage from 0.82 to 0.24 V, subthreshold swing (S.S.) from 0.54 to 0.24 V/decade, and the ON/OFF current ratio from 2.32×107 to 7.31×108. In addition, the enhanced stability is observed under both positive gate-bias stress (PGBS) of VGS = 30 V and negative gate-bias stress (NGBS) of VGS = –30 V for a stress duration of 3000 s. The threshold voltage shift (ΔVTH) is reduced from 8.31 V to 1.65 V and from –3.93 V to –1.51 V, respectively. This is the first time low-energy PLA was conducted for IZTO TFT performance improvement.

Highly Reliable Implementation of Optimized Multicomponent Oxide Systems Enabled by Machine Learning-Based Synthetic Protocol.

Multicomponent oxide systems are one of the essential building blocks in a broad range of electronic devices. However, due to the complex physical correlation between the cation components and their relations with the system, finding an optimal combination for desired physical and/or chemical properties requires an exhaustive experimental procedure. Here, a machine learning (ML)-based synthetic approach is proposed to explore the optimal combination conditions in a ternary cationic compound indium-zinc-tin oxide (IZTO) semiconductor exhibiting high carrier mobility. In particular, by using support vector regression algorithm with radial basis function kernel, highly accurate mobility prediction can be achieved for multicomponent IZTO semiconductor with a sufficiently small number of train datasets (15-20 data points). With a synergetic combination of solution-based synthetic route for IZTO fabrication enabling a facile control of the composition ratio and tailored ML process for multicomponent system, the prediction of high-performance IZTO thin-film transistors is possible with expected field-effect mobility as high as 13.06 cm2 V-1 s-1 at the In:Zn:Sn ratio of 63:27:10. The ML prediction is successfully translated into the empirical analysis with high accuracy, validating the protocol is reliable and a promising approach to accelerate the optimization process for multicomponent oxide systems.

Electrical Properties of Amorphous Indium Zinc Tin Oxide Thin Film Transistor with Y₂O₃ Gate Dielectric.

High-k Y₂O₃ thin films were investigated as the gate dielectric for amorphous indium zinc tin oxide (IZTO) thin-film transistors (TFTs). Y₂O₃ gate dielectric was deposited by radio frequency magnetron sputtering (RF-MS) under various working pressures and annealing conditions. Amorphous IZTO TFTs with SiO₂ as the gate dielectric showed a high field-effect mobility (μFE) of 19.6 cm²/Vs, threshold voltage (Vth) of 0.75 V, on/off current ratio (Ion/Ioff) of 2.0×106, and subthreshold swing (SS) value of 1.01 V/dec. The IZTO TFT sample device fabricated with the Y₂O₃ gate dielectric showed an improved subthreshold swing value compared to that of the IZTO TFT device with SiO₂ gate dielectric. The IZTO TFT device using the Y₂O₃ gate dielectric deposited at a working pressure of 5 mtorr and annealed at 400 °C in 6 sccm O₂ for 1 hour showed a high μFE of 51.8 cm²/Vs, Vth of -0.26 V, Ion/Ioff of 6.0×10³, and SS value of 0.19 V/dec. With the application of a Y₂O₃ gate dielectric, the Vth shift improved under a positive bias stress (PBS) but was relatively unaffected by negative bias stress (NBS). These shifts were attributed to charge traps within the gate dielectric and/or interfaces between the channel and gate dielectric layer.

Solution-Processed Yttrium-Doped IZTO Semiconductors for High-Stability Thin Film Transistor Applications

In this article, solution-processed zinc-tin–oxide (ZTO), indium–zinc–tin–oxide (IZTO), and yttrium-doped indium–zinc–tin–oxide (IZTO:Y) thin film transistors (TFTs) were investigated. The results indicate that the field effect mobility of the ZTO TFTs is enhanced by indium doping, whereas leading to the degradation of stability. Y-doping IZTO TFTs were also studied aiming to improve the stability of IZTO TFTs. The IZTO:Y shows a relatively higher transmittance in the visible light region compared to the nondoped IZTO, which could be due to the decrease of shallow defect levels caused by oxygen vacancy in the bandgap. Based on the X-ray photoelectron spectroscopy analysis, the oxygen vacancy concentration of IZTO:Y thin films decreases dramatically from 36.5% to 18.5% with Y incorporation. Moreover, the stability of IZTO:Y TFTs under positive bias stress (PBS) is also significantly improved. The device with 5-mol% Y element shows a low threshold voltage shift of 0.7 V compared to 2.6 V of IZTO TFT. The improvement in stability and electrical properties of IZTO TFTs are attributed to the Y doping, which can suppress the oxygen vacancy defects. Therefore, the high stability and excellent electrical performance of Y-doped IZTO TFTs have shown great application potential in transparent devices.

Structural and electrical properties of high-κ CeTixOy, ErTixOy and YbTixOy gate dielectrics for InZnSnO thin film transistors

The structural properties and electrical characteristics of high–κ CeTixOy, ErTixOy and YbTixOy gate dielectrics for indium–zinc–tin–oxide (IZTO) thin-film transistors (TFTs) were investigated in this paper. We employed X-ray diffraction to determine the material phase and crystallinity, atomic force microscopy to examine the surface morphology of the dielectric films, and X-ray photoelectron spectroscopy to analyze the chemical feature of three films. The IZTO TFT incorporating a YbTixOy gate dielectric exhibited better electrical characteristics, such as a low threshold voltage (VTH) of 0.17 V, a large field-effect mobility of 20.8 cm2/V-s, a high Ion/Ioff ratio of 3 × 108, and a low subthreshold slope of 108 mV/decade, in comparison with those of other dielectrics. This result suggests that the YbTixOy dielectric possesses a smoother surface as well as a lower oxygen vacancy (or defect). Moreover, the VTH stabilities of IZTO TFT devices were investigated for positive bias stress and negative bias stress conditions.

Solution Processed Oxide Thin Film Transistors

We have developed thin-film-transistors (TFTs) manufactured by a solution processing of the gate insulators and the active material. Oxide insulators, such as aluminum oxide, hafnium oxide, or zirconium doped aluminum oxide represent a method to achieve high performance and low power consuming TFTs. Along with amorphous indium gallium zinc oxide ( a-IGZO), other oxide semiconductors have been studied. Solution processing offers the opportunity to test various materials quickly with low capital investment. We studied poly-crystalline materials, such as indium oxide (In2O3), and tin oxide (SnO2), or amorphous oxides such as indium zinc tin oxide (IZTO).We have developed inket-printed TFTs at the maximum process temperature of 300oC. Inkjet-printed polycrystalline InOx TFTs have mobilities of 60cm2/Vs, and were used in unipolar inverters. SnOx TFTs, show a dependence on the solution concentration, and the mobility can reach ~70cm2/Vs. On the other hand, amorphous IZTO TFTs showed the highest mobility of ~100cm2/Vs by the careful control of the inkjet process. References C. Avis and J. Jang, J. Mater. Chem., 21, 10649-10652, 2011C. Avis and J. Jang, Jap. J. Appl. Phys., 2011, 50, 01BG03, 2011C. Avis and Jin Jang, Electrochem. Solid-State Lett., 4, J9-J11, , 2011Y. G. Kim, C. Avis and J. Jang, ECS Solid-State Lett., 1, Q23-Q25, 2012C. Avis, Y. G. Kim, and J. Jang, J. Mater. Chem., 22, 17415–17420, 2012Y. G. Kim, C. Avis, and J. Jang, J. Disp. Tech., accepted, 2014Figure 1: transfer characteristics of IZTO TFT.

Enhancement of the electrical characteristics of thin-film transistors with indium–zinc–tin oxide/Ag/indium–zinc–tin oxide multilayer electrodes

Transparent indium–zinc–tin oxide (IZTO)-based thin-film transistors (TFTs) with IZTO/Ag/IZTO multilayer electrodes were fabricated on glass substrates using a tilted dual-target radio-frequency magnetron sputtering system. The IZTO TFTs with IZTO/Ag/IZTO multilayer electrodes exhibited a high optical transmittance in a visible region. The threshold voltage, the mobility, and the on/off-current ratio of the TFTs with IZTO/Ag/IZTO multilayer electrodes were enhanced in comparison with those of the TFTs with ITO electrodes. The source/drain contact resistance of the IZTO TFTs with IZTO/Ag/IZTO multilayer electrodes was smaller than that of the IZTO TFTs with ITO electrodes, resulting in enhancement of their electrical characteristics.

Effect of channel layer thickness on the performance of indium-zinc-tin oxide thin film transistors manufactured by inkjet printing.

We report the fabrication of high field-effect mobility of ∼110 cm(2)/(V s) for inkjet printed indium-zinc-tin oxide (IZTO) thin film transistors (TFTs). It is found that the morphology of IZTO material deposited by inkjet printing depends strongly on its thickness. When the thickness is 35 nm, IZTO is an homogeneous amorphous material and the TFT exhibits mobility over 100 cm(2)/(V s) and on/off current ratio of >10(6). However, when the thickness is 85 nm, IZTO has a two layer structure of homogeneous and heterogeneous materials and thus the TFT exhibited a mobility of ∼20 cm(2)/(V s). When the thickness is 800 nm, the morphology is porous and heterogeneous and thus the on/off current ratio is less than 1 × 10(3) and its mobility is ∼14 cm(2)/(V s). It is concluded therefore that homogeneous amorphous IZTO TFT on Al2O3 gate insulator can show high mobility, which can be achieved by thin layer formation by inkjet printing.

Enhancement of the electrical characteristics of indium–zinc tin-oxide thin-film transistors utilizing dual-channel layers

Thin film transistors (TFTs) with indium–zinc tin-oxide (IZTO) dual-channel layers were fabricated on heavily-doped p-type Si substrates by using a tilted dual-target radio-frequency magnetron sputtering system. The number of oxygen vacancies in the IZTO channel layer decreased with increasing oxygen partial pressure, resulting in a decrease in the conductivity. The threshold voltage (Vth) shifted toward positive gate-source voltage with increasing oxygen partial pressure for the growth of the IZTO layer because of a decrease in the carrier concentration. The Vth, the mobility, the on/off-current ratio, and the subthreshold swing of the dual-channel IZTO TFTs were 3.5 V, 7.1 cm2/V s, 1.3 V/decade, and 8.2 × 106, respectively, which was enhanced by utilizing dual-channel layers consisting of a top channel deposited at a high oxygen partial pressure and a bottom channel deposited at a low oxygen partial pressure.

Effects of Annealing Conditions on the Dielectric Properties of Solution-Processed Al<SUB>2</SUB>O<SUB>3</SUB> Layers for Indium-Zinc-Tin-Oxide Thin-Film Transistors

In this paper, the effects of annealing conditions on the dielectric properties of solution-processed aluminum oxide (Al2O3) layers for indium-zinc-tin-oxide (IZTO) thin-film transistors (TFTs) have been investigated. The dielectric properties of Al2O3 layers such as leakage current density and dielectric strength were largely affected by their annealing conditions. In particular, oxygen partial pressure in rapid thermal annealing, and the temperature profile of hot plate annealing had profound effects on the dielectric properties. From a refractive index analysis, the enhanced dielectric properties of Al2O3 gate dielectrics can be attributed to higher film density depending on the annealing conditions. With the low-temperature-annealed Al2O3 gate dielectric at 350 degrees C, solution-processed IZTO TFTs with a field-effect mobility of approximately 2.2 cm2/Vs were successfully fabricated.

Effects on Annealing Temperature for Solution-Processed IZTO TFTs by Nitrogen Incorporation

The effects on electrical properties of solution-processed indium zinc tin oxide (IZTO) thin film transistors (TFTs) by nitrogen incorporation were investigated as a function of annealing temperature. The nitrogen incorporation was controlled by NH 4 0H addition into a precursor solution of zinc, indium, and tin chlorides. At 600°C annealing, the nitrogen-doped IZTO TFTs showed a field-effect mobility of 5.33 cm 2 /V s with an on/off ratio of 2.05 × 10 7 , By the nitrogen incorporation, the annealing temperature could be lowered to 400°C for the fabrication of TFTs having a field-effect mobility of 0.303 cm 2 /V s. Physical and chemical analyses on films at various annealing temperatures were performed and compared, respectively.