Improved Long-Term Stability of Low-Temperature Polysilicon Thin-Film Transistors by Using a Tandem Gate Insulator with an Atomic Layer of Deposited Silicon Dioxide

Abstract

In this study, we report a substantial improvement in the long-term stability of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) with a tandem gate insulator composed of silicon dioxide (SiO₂) deposited by using atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD). Negative-bias temperature instability (NBTI) tests showed that threshold-voltage (ΔVth) shifts were significantly smaller than when only a plasma-enhanced chemical vapor deposition (PECVD) structure was used. We believe that the unique stoichiometric characteristics and the reduction in the interfacial trap density (Dit) produced by the SiO₂ gate insulator that had been fabricated using ALD enhanced the long-term stability of the LTPS TFTs. These results suggest a tandem structure gate insulator with high-quality ALD-based SiO₂ thin film can provide an important improvement in the characteristics of the p-channel LTPS TFTs required for advanced active matrix organic light-emitting diodes (AMOLEDs) applications.