Fabrication and comparison of the properties of SnInZnO and InZnO TFTs processed by using the Sol-gel method

We fabricated InZnO and SnInZnO thin film transistors using the sol-gel process and evaluated the effect of Sn alloying on the electrical properties and the microstructure of the films. We used high-purity indium nitrate hydrate, tin chloride dihydrate, and zinc acetate dihydrate as the precursors, which were dissolved in 2-methoxyethanol at molar ratios of 1:1 and 1:1:1 for InZnO and SnInZnO, respectively. The gel film was deposited onto a highly-doped p-type Si substrate by spin-coating, followed by sintering at 400 °C in air for 1 h. The microstructural observation indicated that the SnInZnO film had an amorphous structure whereas the InZnO film consisted of a mixed amorphous and nanocrystalline structure. For the SnInZnO thin film transisotor (TFT), the threshold voltage, the on/off current ratio, and the saturating mobility were 32.5 V, 1.8 × 10⁵, and 3.12 cm²/Vs, respectively, which were superior to those for the InZnO TFT. Based on the X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses, the enhanced electrical properties were attributed to the improved controllability of the oxygen vacancies and to the amorphous structure afforded by the Sn alloying. Therefore, we conclude that SnInZnO semiconductors fabricated by using the sol-gel process represent a viable alternative to InGaZnO TFTs.