Low-Concentration Indium Doping in Solution-Processed Zinc Oxide Films for Thin-Film Transistors

Enhancing the Stability and Mobility of TFTs via Indium-Tungsten Oxide and Zinc Oxide Engineered Heterojunction Channels Annealed in Oxygen Ambient

This study demonstrates a significant enhancement in the performance of thin-film transistors (TFTs) in terms of stability and mobility by combining indium-tungsten oxide (IWO) and zinc oxide (ZnO). IWO/ZnO heterojunction structures were fabricated with different channel thickness ratios and annealing environments. The IWO (5 nm)/ZnO (45 nm) TFT, annealed in O2 ambient, exhibited a high mobility of 26.28 cm2/V·s and a maximum drain current of 1.54 μA at a drain voltage of 10 V, outperforming the single-channel ZnO TFT, with values of 3.8 cm2/V·s and 28.08 nA. This mobility enhancement is attributed to the formation of potential wells at the IWO/ZnO junction, resulting in charge accumulation and improved percolation conduction. The engineered heterojunction channel demonstrated superior stability under positive and negative gate bias stresses compared to the single ZnO channel. The analysis of O 1s spectra showed OI, OII, and OIII peaks, confirming the theoretical mechanism. A bias temperature stress test revealed superior charge-trapping time characteristics at temperatures of 25, 55, and 85 °C compared with the single ZnO channel. The proposed IWO/ZnO heterojunction channel overcomes the limitations of the single ZnO channel and presents an attractive approach for developing TFT-based devices having excellent stability and enhanced mobility.

Effects of Iodine Doping on Electrical Characteristics of Solution-Processed Copper Oxide Thin-Film Transistors

In order to implement oxide semiconductor-based complementary circuits, the improvement of the electrical properties of p-type oxide semiconductors and the performance of p-type oxide TFTs is certainly required. In this study, we report the effects of iodine doping on the structural and electrical characteristics of copper oxide (CuO) semiconductor films and the TFT performance. The CuO semiconductor films were fabricated using copper(II) acetate hydrate as a precursor to solution processing, and iodine doping was performed using vapor sublimated from solid iodine. Doped iodine penetrated the CuO film through grain boundaries, thereby inducing tensile stress in the film and increasing the film’s thickness. Iodine doping contributed to the improvement of the electrical properties of the solution-processed CuO semiconductor including increases in Hall mobility and hole-carrier concentration and a decrease in electrical resistivity. The CuO TFTs exhibited a conduction channel formation by holes, that is, p-type operation characteristics, and the TFT performance improved after iodine doping. Iodine doping was also found to be effective in reducing the counterclockwise hysteresis in the transfer characteristics of CuO TFTs. These results are explained by physicochemical reactions in which iodine replaces oxygen vacancies and oxygen atoms through the formation of iodide anions in CuO.

Investigation of the Electrical Characteristics of Bilayer ZnO/In₂O₃ Thin-Film Transistors Fabricated by Solution Processing

Metal-oxide thin-film transistors (TFTs) have been developed as promising candidates for use in various electronic and optoelectronic applications. In this study, we fabricated bilayer zinc oxide (ZnO)/indium oxide (In₂O₃) TFTs by using the sol-gel solution process, and investigated the structural and chemical properties of the bilayer ZnO/In₂O₃ semiconductor and the electrical properties of these transistors. The thermogravimetric analysis results showed that ZnO and In₂O₃ films can be produced by the thermal annealing process at 350 °C. The grazing incidence X-ray diffraction patterns and X-ray photoemission spectroscopy results revealed that the intensity and position of characteristic peaks related to In₂O₃ in the bilayer structure were not affected by the underlying ZnO film. On the other hand, the electrical properties, such as drain current, threshold voltage, and field-effect mobility of the bilayer ZnO/In₂O₃ TFTs obviously improved, compared with those of the single-layer In₂O₃ TFTs. Considering the energy bands of ZnO and In₂O₃, the enhancement in the TFT performance is explained through the electron transport between ZnO and In₂O₃ and the formation of an internal electric field in the bilayer structure. In the negative gate-bias stress experiments, it was found that the internal electric field contributes to the electrical stability of the bilayer ZnO/In₂O₃ TFT by reducing the negative gate-bias-induced field and suppressing the trapping of holes in the TFT channel. Consequently, we suggest that the bilayer structure of solution-processed metal-oxide semiconductors is a viable means of enhancing the TFT performance.

Solution-Processed Gallium-Tin-Based Oxide Semiconductors for Thin-Film Transistors

We investigated the effects of gallium (Ga) and tin (Sn) compositions on the structural and chemical properties of Ga–Sn-mixed (Ga:Sn) oxide films and the electrical properties of Ga:Sn oxide thin-film transistors (TFTs). The thermogravimetric analysis results indicate that solution-processed oxide films can be produced via thermal annealing at 500 °C. The oxygen deficiency ratio in the Ga:Sn oxide film increased from 0.18 (Ga oxide) and 0.30 (Sn oxide) to 0.36, while the X-ray diffraction peaks corresponding to Sn oxide significantly reduced. The Ga:Sn oxide film exhibited smaller grains compared to the nanocrystalline Sn oxide film, while the Ga oxide film exhibited an amorphous morphology. We found that the electrical properties of TFTs significantly improve by mixing Ga and Sn. Here, the optimum weight ratio of the constituents in the mixture of Ga and Sn precursor sols was determined to be 1.0:0.9 (Ga precursor sol:Sn precursor sol) for application in the solution-processed Ga:Sn oxide TFTs. In addition, when the Ga(1.0):Sn(0.9) oxide film was thermally annealed at 900 °C, the field-effect mobility of the TFT was notably enhanced from 0.02 to 1.03 cm²/Vs. Therefore, the mixing concentration ratio and annealing temperature are crucial for the chemical and morphological properties of solution-processed Ga:Sn oxide films and for the TFT performance.