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.

We report the effect of purification of ZrO _x precursor on the performance of solution processed amorphous indium-zinc-tin oxide thin-film transistors with a ZrO _x gate insulator, which is processed at the maximum temperature of 300 °C in air. By purification, the saturation mobility (μ _sat ) increases from 2.45 ± 0.83 to 15.42 ± 4.01 cm ² V ^-1 s ^-1 , subthreshold swing decreases from 141.44 ± 14.08 to 87.90 ± 11.05 mV/decade and drain current ON/OFF ratio increases from ~10 ⁷ to ~10 ⁹ . The leakage currents are remarkably reduced by using purified ZrO _x as a gate insulator. The improvement is mainly due to the reduced impurities and less oxygen vacancies in ZrO _x .

The limited choice of materials for large area electronics limits the expansion of applications. Polycrystalline silicon (poly-Si) and indium gallium zinc oxide (IGZO) lead to thin-film transistors (TFTs) with high field-effect mobilities (>10 cm²/Vs) and high current ON/OFF ratios (I_On/I_Off > ~10⁷). But they both require vacuum processing that needs high investments and maintenance costs. Also, IGZO is prone to the scarcity and price of Ga and In. Other oxide semiconductors require the use of at least two cations (commonly chosen among Ga, Sn, Zn, and In) in order to obtain the amorphous phase. To solve these problems, we demonstrated an amorphous oxide material made using one earth-abundant metal: amorphous tin oxide (a-SnO_x). Through XPS, AFM, optical analysis, and Hall effect, we determined that a-SnO_x is a transparent n-type oxide semiconductor, where the SnO₂ phase is predominant over the SnO phase. Used as the active material in TFTs having a bottom-gate, top-contact structure, a high field-effect mobility of ~100 cm²/Vs and an I_On/I_Off ratio of ~10⁸ were achieved. The stability under 1 h of negative positive gate bias stress revealed a Vth shift smaller than 1 V.

Crystalline tin oxide has been investigated for industrial applications since the 1970s. Recently, the amorphous phase of tin oxide has been used in thin film transistors (TFTs) and has demonstrated high performance. For large area electronics, TFTs are well suited, but they are subject to various instabilities due to operating conditions, such as positive or negative bias stress PBS (NBS). Another instability is hysteresis, which can be detrimental in operating circuits. Understanding its origin can help fabricating more reliable TFTs. Here, we report an investigation on the origin of the hysteresis of solution-processed polycrystalline SnO₂ TFTs. We examined the effect of the carrier concentration in the SnO₂ channel region on the hysteresis by varying the curing temperature of the thin film from 200 to 350 °C. Stressing the TFTs characterized further the origin of the hysteresis, and holes trapped in the dielectric are understood to be the main source of the hysteresis. With TFTs showing the smallest hysteresis, we could fabricate inverters and ring oscillators.