Characterization of Si and SiOx films deposited in very high-frequency excited atmospheric-pressure plasma and their application to bottom-gate thin film transistors

Silicon (Si) and its alloys, such as silicon oxides (SiOx) and silicon nitrides, are indispensable thin film materials for the fabrication of large-area electronic devices. The goal of the present study is to develop a highly efficient deposition technology for good-quality hydrogenated amorphous Si (a-Si), microcrystalline Si (µc-Si), and SiOx films on flexible polymer substrates. For this purpose, we have been using atmospheric-pressure (AP) plasma excited by a 150 MHz very high-frequency (VHF) power. The changes of thickness and structure of the Si and SiOx films in the gas flow direction were studied as a function of distance from the plasma entrance, VHF power density, and gas flow rates. Based on the results, the performance of bottom-gate TFTs with the Si channel and SiOx gate insulator layers being deposited using AP-VHF plasma were examined to test the applicability of the Si and SiOx films to actual TFTs. A TFT with a field-effect mobility of ∼1.7 cm2 V−1s−1 was obtained at a temperature of 120 °C.