We report the aqueous-solution-processed Ni-doped In2O3 (NixIn2–xO3, NiInO) thin-film transistors (TFTs) for the first time. The effect of Ni doping on In2O3 microstructure, oxygen defects, and the electron transport properties are investigated by extensive characterization techniques. Analyses indicate that the oxygen vacancies in NiInO are suppressed as the Ni-doping concentration increases, leading to a lower off-state current and a positive shift in threshold voltage. The optimized NiInO TFTs exhibit a high mobility of 17.71 cm2/(V s), on/off current ratio > 106, threshold voltage of 4.21 V, and superior bias stress stability. The success of Ni doping could be attributed to the small ion radius of Ni, large Lewis acid value, and strong Ni–O bond strength. Therefore, the fabricated NiInO TFT provides a bright path for the development of high-performance oxide TFTs.

High-Performance Thin-Film Transistors with Aqueous Solution-Processed NiInO Channel Layer

In this paper, solution-processed ZrO2 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 ( $\mu$ ) decreases from 48.8 to 32.7 cm2 $\cdot \text {V}^{-{1}}\text{s}^{-{1}}$ 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.

Effect of La Addition on the Electrical Characteristics and Stability of Solution-Processed LaInO Thin-Film Transistors With High- ${k}$ ZrO2 Gate Insulator

Thin-film transistors (TFTs) based on solution-derived metal oxides hold great potential in emerging low-cost large-area printed electronics. Despite recent impressive progress, these device performances are far behind those of their corresponding vacuum-based counterparts, impeding their future commercialization. In this work, we designed and created high-performance TFTs based on a nanometer-thick (down to 5 nm) crystalline In–Sm–O channel via aqueous solution processing, with a performance comparable to those of existing vacuum-processed metal oxides. The microstructural, chemical, optical, and electrical properties of the ultra-thin In–Sm–O samples as a function of Sm doping content (0–10%) were comprehensively investigated. The In–Sm–O TFTs (5% Sm) on SiO2/Si dielectrics demonstrated state-of-the-art performance, including a high mobility of 21.51 ± 1.33 cm2 V−1 s−1, subthreshold swing of 0.66 ± 0.06 V per decade, threshold voltage of 2.14 ± 0.44 V, on/off current ratio >108, and remarkable bias stress stability. The success of In–Sm–O was attributed to the high quality of the crystalline In2O3 matrix, the ideal nature of Sm dopant in suppressing oxygen vacancies, as well as the ultrathin and atomically smooth nature of the channel layer. Therefore, the aqueous solution-processed ultra-thin In–Sm–O channel is expected to enable the realization of future low-cost, large-area, and high-performance green electronics.

High-mobility nanometer-thick crystalline In–Sm–O thin-film transistors via aqueous solution processing

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. As the Ga (Y) content in the In1.0GaxOy (In1.0YxOy) channel material was increased to x = 0.1 the mobility of the MOTFTs degrades by a factor of 4. Thereby the temperature stress stability is clearly enhanced by increasing doping concentration: the onset voltage shift is reduced by a factor of 3 for both In1.0Ga0.1Oy and In1.0Y0.1Oy films compared to that in indium-oxide TFTs. Also the stability during negative bias stress (NBS) is improved since the strong oxygen binders Ga and Y prevent the desorption of oxygen at the surface. In contrast, the onset voltage shift during positive bias stress (PBS) of doped metal oxide TFTs is higher ΔVon = 12 V for InGaO (100 : 10) TFTs and ΔVon = 15 V for InYO ((100 : 10) TFTs) compared to that of intrinsic indium oxide TFTs (ΔVon = 6 V), which could be attributed to the generation of flat trap states at the dielectric/semiconductor interface. Doping with Ga and Y significantly enhances the temperature and NBS stability of TFTs and simultaneously degrades the performance.

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

High Performance Indium Dysprosium Oxide Thin-Film Transistors Grown from Aqueous Solution

Y3+ (0, 6, 12, or 20 mol%)-doped In2O3 (YInO; YIO) thin films were fabricated by the sol–gel spin-coating technique, and they were used as the active layer of thin-film transistor (TFT) devices. The YIO-TFTs operate in the n-channel enhancement mode and exhibit a well-defined pinch-off and saturation region. The Y3+ (12 mol%)-doped In2O3 TFT possesses the optimal performance, and its field-effect mobility in the saturated regime, threshold voltage, on–off ratio, and S factor are 0.95 cm2 V−1 s−1, 6.74 V, 1.55 × 105, and 2.37 V decade−1, respectively. The yttrium ion can act as the carrier suppressor to reduce the carrier concentration of In2O3 thin film because of its lower electronegativity (1.22) and standard electrode potential (−2.372 V). The carrier concentrations and conductivities of In2O3 thin films decrease from 2.5 × 1014 to 3.8 × 1011 cm−3, and 14.3 to 1.5 × 10−4 S m−1, respectively, with the increase of Y3+ doping concentrations from 0 to 12 mol%. In addition, the Y3+ (12 mol%)-doped In2O3 thin film also possesses the minimal surface roughness (4.19 nm) and lowest trap states (1.07 × 1013). Therefore, by Y3+ doping the electrical properties of In2O3 thin films can be improved to match the basic requirement of the TFT devices.

Improvement of electrical characteristics in the solution‐processed nanocrystalline indium oxide thin‐film transistors depending on yttrium doping concentration

The present invention provides a transistor and method for making the same. The transistor has an yttrium-doped indium oxide transparent conductive thin-film which is so fabricated with the method to reduce the formation of oxygen vacancies, suppress carrier concentration effectively, and decrease maximum defect density and thus suitable to be applied to the transistor.

Hsin-Yun Fan

Papers

Improvement of electrical characteristics in the solution‐processed nanocrystalline indium oxide thin‐film transistors depending on yttrium doping concentration

Yttrium-doped Indium Oxide Transparent Conductive Thin-Film Transistor and Method for Making Same