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.

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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