First-principles study on defects related to the instability of MOSFET and TFT devices

Abstract

The complementary metal-oxide-semiconductor (MOS) technology has been rapidly enhanced for high-performance and low-power devices. According to the international technology roadmap for semiconductors, the conventional MOS structures should be replaced by high-k/metal gate structures with strained channels, ultra-thin body structures with silicon-on-insulator (SOI), and multi-gate structures such as Fin-type field-effect-transistors until 2018. On the other hand, the cathode ray tubes (CRTs) have been replaced by the flat panel displays owing to the thin-film-transistors (TFTs), which exploit the hydrogenated amorphous Si channels. However, in order to implement the transparent and flexible displays for future electronic industries, conventional TFT devices should be significantly improved. For this goal, the amorphous oxide semiconductors such as indium-gallium-zinc oxides have been considered as the promising channel materials in such TFT devices.

However, the device instabilities such as flat band and threshold voltage shifts are problematic for the mass production of future electronic devices based on metal-oxide-semiconductor field-effect-transistors (MOSFETs) or TFTs. In the extensive study of conventional Si-based MOS devices, the origin of such instabilities is attributed to defects and impurities in the oxide or at the interface. Therefore, such new devices on the future roadmap might be hindered by other different types of defects from those in the conventional structures. For several decades, the atomic and electronic structures of defects in a crystal have been successfully studied by first-principles density-functional calculations. Although some experimental works such as x-ray photoemission spectroscopy analyses show several defect properties, theoretical approach in the atomic scale gives more profound insights on such problems. Therefore, in this work, some defect properties related to the instabilities in the MOSFET and TFT devices are system...