An Amorphous Silicon Photo TFT with Si3N4/Al2O3 or HfO2 Double Layered Insulator for Digital Imaging Applications

Abstract

This paper focuses on amorphous silicon photo thin-film transistors with double layered insulator using Si 3 N 4 /Al 2 O 3 or HfO 2 as candidates for the succession of Si 3 N 4 as a traditional insulator in the fabrication of hydrogenated amorphous silicon thin-film transistors. Whether for industry or for research, there is a need to investigate the use of thin gate insulators for these devices to overcome leakage current. Our investigations included direct and transfer characteristics in dark and under illumination, generated photocurrents, external quantum efficiency and responsivity. Performance is evaluated in terms of the dielectric thickness and nature. Improvements in the proposed structures regarding off-current, responsivity and quantum efficiency are achieved via these materials. Comparing with Si 3 N 4 /HfO 2 transistor, the Si 3 N 4 /Al 2 O 3 device shows the lowest off-current. The HfO 2 device presents the highest on-current when illuminated. The generated photocurrent is higher for Si 3 N 4 /HfO 2 transistor revealing a lower amount of trapped charge. Under illumination and for very thin thicknesses, both devices enhance the Si 3 N 4 device off-current and reach Si 3 N 4 single layer dielectric based phototransistor performance. external quantum efficiency and responsivity are higher in HfO 2 devices comparing with Al 2 O 3 devices. The results are promising and may support further investigations in order to develop high k gate insulators for MIS photo thin-film transistors.