Solution-processed metal-oxide thin-film transistors (TFTs) are considered as one of the most favorable devices for next-generation, large-area flexible electronics. In this paper, we demonstrate the excellent material properties of lanthanum−zinc oxide (LaZnO) thin films deposited by spray pyrolysis and their application to TFTs. The threshold voltage of the LaZnO TFTs shifts toward positive gate voltage, and the mobility decreases with increasing lanthanum ratio in ZnO from 0 to 20%. The purification of the LaZnO precursor (P-LaZnO) further improves the device performance. The P-LaZnO TFT exhibits a field-effect mobility of 22.43 cm 2 V −1 s −1 , zero hysteresis voltage, and negligible threshold voltage V TH shift under positive bias temperature stress. The enhancement in the electrical properties is due to a decrease in grain size, smooth surface roughness, and reduction in the trap density in the LaZnO film. X-ray photoelectron spectroscopy (XPS) results confirm the presence of La in the TFT channel and at/near the interface of the LaZnO and ZrO x gate insulator, leading to fewer interfacial traps. The flexible P-LaZnO TFT fabricated on the polyimide substrate exhibits a mobility of 17.64 cm 2 V −1 s −1 and a negligible V TH shift under bias stress. Also, the inverter made of LZO TFTs is working well with a voltage gain of 17.74 (V/V) at 4 V. Therefore, the LaZnO TFT is a promising device for next-generation flexible displays.

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Metal-oxide thin-film transistors (TFT) fabricated by spray pyrolysis are of increasing interest because of its simple process and scalability. A bottleneck issue is to get a bubble-free and dense material. We studied the effect of ammonium acetate (AA) addition in the oxide precursor solution on the performance of spray-coated ZnO TFTs. AA acts as a stabilizer, which increases the solubility of the solution and enhances the film quality by reducing the defects. With AA addition in ZnO precursor, the films are coffee ring free with high mass density and better grain orientation. The ZnO TFT with AA exhibit a remarkable improvement of its device performance such as saturation mobility increasing from 5.12 to 41.53 cm 2 V −1 s −1 , the subthreshold swing decreasing from 340 to 162 mV/dec and on/ off current ratio increasing from ~10 5 to 10 8. Additionally, the TFTs show excellent stability with a low threshold voltage shift of 0.1 V under gate bias stress. Therefore, the addition of AA is a promising approach to achieve high-performance ZnO TFTs for low-cost manufacturing of displays.

A high‐k, zirconium‐aluminum‐oxide (ZAO) gate insulator (GI) using low‐cost spray pyrolysis technique for large area and low power electronics is demonstrated. The high‐quality spray‐pyrolyzed ZAO GI is obtained with subsequent oxidation by eco‐friendly Ar/O2 plasma treatment. Analyses reveal that only one cycle Ar/O2 plasma treatment significantly enhances the thin‐film and dielectric properties of ZAO, exhibiting improved mass density (4.16 g cm−3), smooth surface roughness (0.32 nm), low leakage current density (2.26 × 10−6 A cm−2), high breakdown electric field (5.15 MV cm−1), and negligible frequency‐dependent capacitance. Hysteresis free, amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistors (TFTs) with ZAO GI exhibit a field‐effect mobility of 15.04 cm2 V−1 s−1, threshold voltage of 1.46 V, subthreshold swing of 115 mV dec−1, ION/IOFF ratio of 7.54 × 108, and negligible positive bias stress. The highly reliable a‐IGZO TFTs performances are achieved due to the significant reduction of oxygen‐related defects at the dielectric/semiconductor interface. The TFT inverter and an eleven‐stage ring oscillator have been demonstrated with ZAO/a‐IGZO TFTs, exhibiting a high voltage gain of 58, oscillation frequency of 2.43 MHz, and signal propagation delay of 18.7 ns at a supply voltage of 6 V, confirming the benefit of spray‐pyrolyzed high‐k ZAO dielectric for low power displays.

been widely used as the active semiconductor materials for the oxide TFTs. For example, amorphous indium-zinc-tin oxide (a-IZTO) as an active layer on high-k dielectric material such as aluminum oxide (AlO x ), [42][43][44] zirconium oxide (ZrO x ), [45][46][47][48] hafnium oxide (HfO x ), [49] zirconium-doped aluminum oxide (ZAO), [50] and lanthanum doped zirconium oxide (LaZrO x ) [51] have been used for solution process. The purpose of using a high-κ gate insulator is for the low voltage driven oxide TFTs.The oxide TFT could be annealed at a higher temperature (>500 °C) [52] to improve its performance and stability, but higher annealing temperature prevents the use of the plastic substrate for the flexible display. [53] Also, various process technologies are developed to improve the film quality, for example, Ar/O 2 plasma treatment, [54] O 2 annealing, [55] and UV ozone treatment. [56] Many of the previous reports have focused on the thin-film quality and lowering fabrication process temperature by using the UV treatment [57] or combustion method. [58] Moreover, to address present-day microelectronics challenges, the synthesis of high-quality semiconductor precursor solution is essential for high performance, oxide TFTs at low processing temperatures.In this study, we report the impact of metal oxide precursor purification on the performance of TFTs. Smooth surface morphology and the high-quality interface between a-IZTO and ZrO x are confirmed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopic (XPS) analysis, respectively. The mobility, ON/OFF current ratio, gate voltage swing (SS), and hysteresis of the purified a-IZTO TFTs are significantly improved compared to the TFTs using unpurified precursor solutions. The hysteresis and positive bias-stress stability of the transfer curve for the purified a-IZTO TFTs are improved as a result of the reduced interface charge trapping. Therefore, the purification of the oxide semiconductor is an essential step for high performance, solution processed oxide TFTs.

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their high optical transparency and high mobility. The undoped InO x and ZnO have a crystalline structure with high carrier concentration. [23] Therefore, many attempts are carried out to improve TFT performance by using multi-component metal-oxides. [24][25][26][27][28][29][30][31][32] IGZO is a widely used metal-oxide because of its amorphous structure and relatively high mobility. [8,32] The mixing of two or more cations with different sizes and ionic charges is tried for amorphous phase with suppressing crystallization and carrier concentration. [24] The incorporation of an appropriate quantity of cations is required to form the substitutional doping and strong chemical bonding with oxygen ions for stable oxide TFTs. [25] The ionic radius and metal-oxygen bonding strength are the most critical parameters to improve the mobility and stability of metal oxide TFTs. To enhance the bias stability of oxide TFT, carrier suppressors such as Ga 3+ , Gd 3+ , La 3+ , Sc 3+ , and Y 3+ can be used. Ga can be a good choice due to its lower ionic radius (62 pm) and relatively strong bonding strength with oxygen (353.5 kJ mol −1 ). [33] The selection of an appropriate percentage of carrier suppressor is a vital parameter to control the carrier concentration. But, excess doping can modify the material structure, which leads to deteriorating device performance. Ga is used for IGZO, indium-gallium oxide (IGO), [26] and indium-gallium-zinc-tin oxide (IGZTO), [27] so that we selected Ga doping in IZTO to improve mobility and stability. The solution-processed alloyed form of the oxide TFTs fabricated using In-Ga-O, [26] indium-zinc oxide (In-Zn-O), [28] indiumzinc-tin oxide (In-Zn-Sn-O), [29] aluminum-doped indium zinc tin oxide (Al-In-Zn-Sn-O), [30] zinc tin oxide (Zn-Sn-O), [31] and indium gallium zinc oxide (In-Ga-Zn-O) [32] as an active channel material have been widely studied for the high performance of the solution based oxide TFTs. To increase mobility, various treatments were carried out such as heat-treatment [34] and plasma-treatment. [35][36][37] In this study, we report the Ar/O2 plasma treatment effect on the performance of Ga-doped IZTO TFT. First, we improve the performance of the a-IZTO TFT by varying the Ga doping ratio from 0 to 20%. It is found that 10% Ga-doped IZTO shows the best performance. To further improve the TFT performance, the Ar/O 2 plasma treatment was carried out. The carbon concentration at the surface of Ga-doped IZTO could be reduced by Ar/O 2 plasma treatment, which is confirmed from the XPS The effects of gallium doping into indium-zinc-tin oxide (IZTO) thin film transistors (TFTs) and Ar/O 2 plasma treatment on the performance of a-IZTO TFT are reported. The Ga doping ratio is varied from 0 to 20%, and it is found that 10% gallium doping in a-IZTO TFT results in a saturation mobility (µs at ) of 11.80 cm 2 V −1 s −1 , a threshold voltage (V th ) of 0.17 V, subthreshold swing (SS) of 94 mV dec −1 , and on/off current ratio (I on /I off ) of 1.21 × 10 7 . Additionally, the performance of 10% G...