Electrical properties of low-temperature-compatible p-channel polycrystalline-silicon TFTs using high-κ gate dielectrics

In this paper, we describe a systematic study of the electrical properties of low-temperature-compatible p-channel polycrystalline-silicon thin-film transistors (poly-Si TFTs) using HfO2 and HfSiOx high-kappa gate dielectrics. Because of their larger gate capacitance density, the TFTs containing the high-kappa gate dielectrics exhibited superior device performance in terms of higher I-on/I-off current ratios, lower subthreshold swings (SSs), and lower threshold voltages (V-th), relative to conventional deposited-SiO2, albeit with slightly higher OFF-state currents. The TFTs incorporating HfSiOx as the gate dielectric had ca. 1.73 times the mobility (mu(FE)) relative to that of the deposited-SiO2 TFTs; in contrast, the HfO2 TFTs exhibited inferior mobility. We investigated the mechanism for the mobility degradation in these HfO2 TFTs. The immunity of the HfSiOx TFTs was better than that of the HfO2 TFTs-in terms of their V-th shift, SS degradation, mu(FE) degradation, and drive current deterioration-against negative bias temperature instability stressing. Thus, we believe that HfSiOx, rather than HfO2, is a potential candidate for use as a gate-dielectric material in future high-performance poly-Si TFTs.