Study on Stability of Amorphous Silicon Thin-Film Transistors Prepared by Catalytic Chemical Vapor Deposition

Abstract

In this study, we demonstrate the fabrication process and the characteristics of bottom-gate amorphous silicon thin-film transistors (a-Si TFTs) using films all prepared by catalytic chemical vapor deposition (Cat-CVD). A sputtered chromium (Cr) film as a gate-electrode metal is superior to other metals such as aluminum (Al) and titanium (Ti) for stable operation of the TFTs. We investigate the properties of silicon nitride (SiNx) gate insulator films formed by Cat-CVD, particularly atomic compositions and defect densities, to determine their dependence on TFT characteristics and stability. The stability of the Cat-CVD a-Si TFTs are strongly affected by the SiNx film properties because the charge compensation of defects inside SiNx films by injected electrons appears to be a key origin of instability in addition to stability of a-Si itself. The characteristics and stability of TFTs fabricated using an optimized SiNx gate insulator are at least the same in terms of bias and current stresses as those of highly stabilized plasma enhanced CVD (PECVD) TFTs. We also clarify that the threshold voltage shift is suppressed to almost zero after complete injection of electrons into defects in SiNx films.