Indium Oxide Thin-film Transistors Research Articles

Role of gallium and yttrium dopants on the stability and performance of solution processed indium oxide thin-film transistors

We study the effect of gallium and yttrium doping on both the electrical performance and the stability of indium based metal-oxide thin-film transistors (MOTFTs) at varied concentrations.

Improved Negative Bias Stress Stability of Sol-Gel-Processed Mg-Doped In2O3 Thin Film Transistors

We demonstrate sol-gel-processed Mg-doped In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin film transistors (TFTs) with high performance and improved stability. To improve the performance of indium oxide, which is unstable at a high negative threshold voltage, magnesium is used to suppress oxygen vacancy formation. As the Mg doping concentration increases, the oxygen deficiencies and OH impurities decrease, resulting in a positive shift in the threshold voltage and improved stability in negative bias stress environments. In this experiment, Mg-doped (0 to 2 wt%) indium oxide TFTs are fabricated. Indium oxide prepared from a synthesized solution of an indium nitrate hydrate precursor and 2-methoxyethanol has a mobility of 17.2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V s. In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> TFTs doped with 1 wt% Mg also show a high mobility of 11.02 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V s and a noticeable -1.5 V threshold voltage shift under negative bias stress. Our results suggest that the sol-gel-processed Mg-doped In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> TFTs are a promising candidate for use in high-stability and high-performance applications in transparent devices.

Si-doping effect on solution-processed In-O thin-film transistors

In this work, silicon-doped indium oxide thin-film transistors (TFTs) have been fabricated for the first time by a solution processing method. By varying the Si concentration in the In2O3–SiO2 binary oxide structure up to 15 at%, the thicknesses, densities, and crystallinity of the resulting In–Si–O (ISO) thin films were investigated by x-ray reflectivity (XRR) and x-ray diffraction techniques, while the produced TFTs were characterized by a conventional three-probe method. The results of XRR analysis revealed that the increase in the content of Si dopant increased the thickness of the produced film and reduced its density, and that all the Si-doped ISO thin films contained only a single amorphous phase even after annealing at temperatures as high as 800 °C. The manufactured ISO TFTs exhibited a reduction in the absolute value of threshold voltage VT close to 0 V and low current in the off-state, as compared to those of the non-doped indium oxide films, due to the reduced number of oxygen defects, which was consistent with the behavior of ISO TFTs fabricated by a sputtering method. The ISO TFT with a Si content of 3 at% annealed at 400 °C demonstrated the smallest subthreshold swing of 0.5 V/dec, VT of −5 V, mobility of 0.21 cm2 V−1s−1, and on/off current ratio of about 2 × 107.

Performance improvements of tungsten and zinc doped indium oxide thin film transistor by fluorine based double plasma treatment with a high-K gate dielectric

The electrical characteristics and XPS analysis for the amorphous tungsten and zinc doped indium oxide thin film transistor, which was performed with single or double different fluorine based remote plasma treatment, were investigated in this study. A high mobility TFT device with the tungsten doped channel was fabricated in the previous study, but there was an inevitable negative shift for the threshold voltage, which will be a limit for the application of systemic circuit design. Therefore, a double fluorine based remote plasma treatment process is proposed for the high electronegativity of fluorine element and its similar radius as oxygen, which can be used to terminate the donor-like oxygen vacancy. It may induce a positive shift of threshold voltage, while carrier concentration and field effect mobility might be maintained. As a result, the sample with CF4/N2 + O2 plasma treatment exhibits a higher on/off current ratio of ~4.73 × 106, a lower sub-threshold swing value of 0.070 V/decade, and a lower interfacial trap density value of 5.21 × 1011 eV−1 cm−2 than other samples, while there is even a desirable positive shift of threshold voltage and acceptable field effect mobility of 31.2 cm2/Vs. This research proposes an effective approach to improve the reliability characteristic and adjust the inevitable negative shift of threshold voltage without sacrificing the carrier mobility of device.

Water-based processed and alkoxide-based processed indium oxide thin-film transistors at different annealing temperatures**Project supported by the National Natural Science Foundation of China (Grant No. 61675024) and the National Basic Research Program of China (Grant No. 2014CB643600).

In this study, indium oxide (In2O3) thin-film transistors (TFTs) are fabricated by two kinds of low temperature solution-processed technologies (), i.e., water-based (DIW-based) process and alkoxide-based (2-ME-based) process. The thickness values, crystallization properties, chemical structures, surface roughness values, and optical properties of In2O3 thin-films and the electrical characteristics of In2O3 TFTs are studied at different annealing temperatures. Thermal annealing at higher temperature leads to an increase in the saturation mobility (μsat) and a negative shift in the threshold voltage (VTH). The DIW-based processed In2O3-TFT annealed at 300 °C exhibits excellent device performance, and one annealed at 200 °C exhibits an acceptable μsat of 0.86 cm2/V·s comparable to that of a-Si:H TFTs, whereas the 2-ME-based TFT annealed at 300 °C exhibits an abundant μsat of 1.65 cm2/Vs and one annealed at 200 °C is inactive. The results are attributed to the fact that the DIW-based process induces a higher degree of oxidation and less defect states than the 2-ME-based process at the same temperature. The DIW-based process for fabricating the In2O3 TFT opens the way for the development of nontoxic, low-cost, and low-temperature oxide electronics.

Electrical stability of solution-processed indium oxide thin-film transistors under illumination stress

ABSTRACTWe investigated the variation in the electrical characteristics of solution-processed indium oxide (In2O3) thin-film transistors (TFTs) under monochromatic illumination conditions at different wavelengths of 1240, 800, 600, 500, 400, and 350 nm. In our results, there was no discernible difference between the characteristics of the TFT measured in the dark state and those obtained under light illumination at the wavelengths of 1240 nm and 800 nm. On the other hand, the TFT performance was remarkably changed when light having a wavelength of 600 nm or less was illuminated. It is found that the photon energy, which causes the characteristic degradation in the solution-processed In2O3 TFTs, is much lower than the direct band gap energy of In2O3. Consequently, illumination-induced instability in the performance of solution-processed In2O3 TFTs can be explained with the transition phenomena of neutral oxygen vacancies to ionized ones in the In2O3 semiconductor film.

Effect of La Addition on the Electrical Characteristics and Stability of Solution-Processed LaInO Thin-Film Transistors With High-${k}$ ZrO2Gate Insulator

In this paper, solution-processed ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films are used to be as insulting layers for lanthanum indium oxide (LaInO) thin-film transistors (TFTs) with different La doping contents. The influence of La addition on the electrical properties and stability under bias stress and temperatures stress for LaInO TFTs is investigated in detail. With the improvement of La doping contents, the saturation mobility (μ) decreases from 48.8 to 32.7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> · V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and the threshold voltage (VT) increases from 1.12 to 1.76 V. When La doping concentration is 10 mol%, LaInO TFT has a small subthreshold swing of 0.12 V/dec. Meanwhile, the stability is improved obviously. It is attributed to the strong bonding strength of La-O relative to that of In-O, resulting in the reduction of trap states. X-ray photoelectron spectroscopy shows that the generation of oxygen vacancies can effectively be suppressed by La addition. The calculation of density of states and the measurement of the capacitance-voltage can also further confirm that the density of trap states is decreased by La addition, and thus the stability of LaInO TFTs can get an obvious improvement.

Fully solution-induced high performance indium oxide thin film transistors with ZrO x high-k gate dielectrics.

Solution based deposition has been recently considered as a viable option for low-cost flexible electronics. In this context, research efforts have been increasingly focused on the development of suitable solution-processed materials for oxide based transistors. In this work, we report a fully solution synthesis route, using 2-methoxyethanol as solvent, for the preparation of In2O3 thin films and ZrOx gate dielectrics, as well as the fabrication of In2O3-based TFTs. To verify the possible applications of ZrOx thin films as the gate dielectric in complementary metal oxide semiconductor (CMOS) electronics, fully solution-induced In2O3 TFTs based on ZrO2 dielectrics have been integrated and investigated. The devices, with an optimized annealing temperature of 300 °C, have demonstrated high electrical performance and operational stability at a low voltage of 2 V, including a high μsat of 4.42 cm2 V−1 s−1, low threshold voltage of 0.31 V, threshold voltage shift of 0.15 V under positive bias stress for 7200 s, and large Ion/Ioff of 7.5 × 107, respectively. The as-fabricated In2O3/ZrOx TFTs enable fully solution-derived oxide TFTs for potential application in portable and low-power consumption electronics.

Operational stability of solution-processed indium-oxide thin-film transistors: Environmental condition and electrical stress

We investigate the operational stability of bottom-gate/top-contact-structured indium-oxide (In2O3) thin-film transistors (TFTs) in atmospheric air and under vacuum. Based on the thermogravimetric analysis of the In2O3 precursor solution, we utilize a thermal annealing process at 400 °C for 40 min to prepare the In2O3 films. The results of X-ray photoemission spectroscopy and field-emission scanning electron microscopy show that the electron is the majority carrier in the In2O3 semiconductor film prepared by a spin-coating method and that the film has a polycrystalline morphology with grain boundaries. The fabricated In2O3 TFTs operate in an n-type enhancement mode. When constant drain and gate voltages are applied, these TFTs in atmospheric air exhibit a more acute decay in the drain currents with time compared to that observed under vacuum. In the positive gate-bias stress experiments, a decrease in the field-effect mobility and a positive shift in the threshold voltage are invariably observed both in atmospheric air and under vacuum, but such characteristic variations are also found to be more pronounced for the atmospheric-air case. These results are explained in terms of the electron-trapping phenomenon at the grain boundaries in the In2O3 semiconductor, as well as the electrostatic interactions between electrons and polar water molecules.

Low-Temperature Solution-Based In2O3 Channel Formation for Thin-Film Transistors Using a Visible Laser-Assisted Combustion Process

This letter reports the low-temperature solution-based fabrication of indium oxide (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) thin-film transistors (TFTs) using a visible laser-assisted urea combustion process. An In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> precursor solution containing a small amount of urea absorbed the photon energy from a blue laser and started the combustion of urea to form a crystallized In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase. Atomic force microscopy and X-ray diffraction showed that both laser radiation and urea combustion together are necessary to convert a dried precursor solution layer to a crystallized In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase. A TFT fabricated from the 0.2-mol% urea-added solution and laser annealed with a 250-J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> energy fluence exhibited superior transfer characteristics compared with the TFTs fabricated either without urea addition or with small energy fluence radiation. Based on these results and considering the price of blue laser diodes, this technique can be an economical solution for the fabrication of oxide semiconductor TFTs on flexible substrates with a low melting point.

Mg Doping to Simultaneously Improve the Electrical Performance and Stability of MgInO Thin-Film Transistors

In this paper, we have fabricated the magnesium-doped indium oxide (MgInO) thin-film transistors (TFTs) by solution process and evaluate the electrical characteristics and stability under temperature stress and positive bias stress. The MgInO TFTs show a decrease of off-state current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> ) and an increase of threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) with the increase of Mg doping concentration. For MgInO TFT with 0.75 mol% Mg doping concentration, it shows an excellent electrical characteristic (the field effect mobility of 13.77 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , the threshold voltage of 2.84 V, and subthreshold swing value of 0.85 V/decade) and a good stability of temperature stress and positive bias stress. The performance enhancement of MgInO TFTs is attributed to the reduced density of states and the lower interface trap density by the optimized Mg doping concentration, which is first verified by the temperature-dependent field effect measurement and capacitance-voltage method.

Solution-processed high-mobility neodymium-substituted indium oxide thin-film transistors formed by facile patterning based on aqueous precursors

Solution-processed neodymium-substituted indium oxide (InNdO) thin-film transistors (TFTs) based on gel-like aqueous precursors were fabricated with a surface-selective deposition technique associated with ultraviolet irradiation. The Nd concentration can be easily tuned by changing the ratio of Nd2O3 to In2O3 precursors. It was found that Nd played roles of suppressing grain growth, suppressing oxygen vacancy formation, and increasing the electrical stability of TFTs. The InNdO TFT with a Nd:In ratio of 0.02:1 exhibited a mobility of as high as 15.6 cm2 V−1 s−1 with improved stability under gate-bias stress.

Solution-processed gadolinium doped indium-oxide thin-film transistors with oxide passivation

We studied the effect of Gd doping on the structural properties of solution processed, crystalline In2O3 for thin-film transistor (TFT) application. With increasing Gd in In2O3 up to 20%, the material structure changes into amorphous phase, and the oxygen vacancy concentration decreases from 15.4 to 8.4%, and M-OH bonds from 33.5 to 23.7%. The field-effect mobility for the Gd doped In2O3 TFTs decreases and threshold voltage shifts to the positive voltage with increasing Gd concentration. In addition, the stability of the solution processed TFTs can also be improved by increasing Gd concentration. As a result, the optimum Gd concentration is found to be ∼5% in In2O3 and the 5% Gd doped In2O3 TFTs with the Y2O3 passivation layer exhibit the linear mobility of 9.74 cm2/V s, the threshold voltage of −0.27 V, the subthreshold swing of 79 mV/dec., and excellent bias stability.

Stability study of indium tungsten oxide thin-film transistors annealed under various ambient conditions

Amorphous tungsten-doped indium oxide thin-film transistors (a-IWO-TFTs) are prepared by RF sputtering and annealed in air, O2, and N2 ambients. The influence of annealing ambient on the electrical characteristics and stability of the a-IWO-TFTs is investigated. It is found that the characteristics and stability are improved in O2 and N2 ambients, which can be explained by the reduction of structural defects and oxygen vacancies. When annealed in O2, the TFT device with saturation mobility of 27.55 cm2 V−1 s−1, threshold voltage of 0.5 V and drain current on-off ratio of 108 is obtained. After an applied VGS of 25 and −25 V for 2000 s in darkness, the values of ΔVth are 4.5 and −0.92 V, respectively.

Homogeneous double-layer amorphous Si-doped indium oxide thin-film transistors for control of turn-on voltage

We fabricated homogeneous double-layer amorphous Si-doped indium oxide (ISO) thin-film transistors (TFTs) with an insulating ISO cap layer on top of a semiconducting ISO bottom channel layer. The homogeneously stacked ISO TFT exhibited high mobility (19.6 cm2/V s) and normally-off characteristics after annealing in air. It exhibited normally-off characteristics because the ISO insulator suppressed oxygen desorption, which suppressed the formation of oxygen vacancies (VO) in the semiconducting ISO. Furthermore, we investigated the recovery of the double-layer ISO TFT, after a large negative shift in turn-on voltage caused by hydrogen annealing, by treating it with annealing in ozone. The recovery in turn-on voltage indicates that the dense VO in the semiconducting ISO can be partially filled through the insulator ISO. Controlling molecule penetration in the homogeneous double layer is useful for adjusting the properties of TFTs in advanced oxide electronics.

High-Performance, Solution-Processed Indium-Oxide TFTs Using Rapid Flash Lamp Annealing

In this letter, we discuss the temperature distribution of light-illuminated Si substrates with time and the successful fabrication of high-performance, solution-processed indium-oxide thin-film transistors within an annealing time of 2 min using a high-power flash lamp under ambient conditions. The precursor films are completely converted into oxide films within 30 s using flash lamp annealing (FLA). As a result, we obtained the high performance of indium-oxide TFTs with the mobility of impressive 38.9 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the on/off ratio of ~104 for the irradiation time of 2 min and the mobility of 10.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the on/off ratio of ~5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> for the irradiation time of 10 s for three times, which is the highest mobility ever reported using FLA. This result will be helpful for breaking the barrier in the mass production of the next-generation semiconductors.

Low-temperature, solution-processed indium-oxide thin-film transistors fabricated by using an ultraviolet-ozone treatment

For the fabrication of low-temperature solution-processed metal-oxide thin-film transistors (TFTs), alternative annealing processes have recently been studied for reduced fabrication cost and applications to flexible devices. Indium nitrate solution has been proposed as a precursor for the low-temperature solution-processed TFTs. However, due to its high decomposition temperature, achieving a high-performance indium-oxide (In2O3) TFT at temperatures below 200°C is still difficult. In this study, for improved metal-oxide formation in low-temperature solution-processed In2O3 TFT, indium nitrate film was exposed to UV-ozone for 30 min before annealing at 200°C. The smooth scanning electron microscopy (SEM) image of the UV-ozone treated film implies that the indium nitrates are condensed after treatment. In addition, X-ray photoemission spectroscopy (XPS) data suggest that UV-ozone decreases the number of oxygen vacancies and increases the number of metal-oxygen-metal bonds in the indium-oxide films. As a result, high electrical device performance was achieved with an improved Ion/off ratio (∼107) and mobility (1.25 cm2V −1s −1).

Stable and High-Performance Indium Oxide Thin-Film Transistor by Ga Doping

Research on a replacement of amorphous silicon for a thin-film transistor (TFT) and large area electronics has been driven by costly vacuum processed indium–gallium–zinc oxide (IGZO). Even though widely studied, the performances still require improvement, and a wide number of other materials have been tested. While indium–zinc oxide, IGZO, indium–zinc–tin oxide (ZTO), and ZTO have been widely investigated, gallium-doped indium oxide (IGO) has not been under highlight. Here, we report the use of simple and cost effective spin-coated IGO TFT using spin-coated AlO x gate dielectric. We achieved high mobility over 50 cm2/Vs and high stability. The thin films are studied by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, atomic force microscopy, and field-effect measurements. Analyses reveal the strong dependence between crystallinity, mobility, and stability. All TFTs show excellent operation, with champion characteristics for the 10% Ga-doped InO x , revealing a mobility of 52.6 cm2/Vs, ON/OFF ratios of $10^{8}$ , and $V_{\mathrm {TH}}$ variation of <0.1 V during 1 h of stress measurement.

High mobility polycrystalline indium oxide thin-film transistors by means of plasma-enhanced atomic layer deposition

A thin-film transistor with a 5 nm-thick indium oxide active layer deposited by plasma-enhanced atomic layer deposition (PEALD) showed outstanding performance even with a polycrystalline phase.

Facile patterning of amorphous indium oxide thin films based on a gel-like aqueous precursor for low-temperature, high performance thin-film transistors

Facile patterning of chloride-based precursor films for low-temperature, high performance indium oxide thin-film transistors.