High-Temperature Stability and Enhanced Performance of a-Si:H TFT on Flexible Substrate Due to Improved Interface Quality

Abstract

We have investigated the effect of anneal time on the performance and temperature-dependent stability of low-temperature-fabricated (180°C) hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) on flexible substrates. For TFTs annealed for 48 h, the subthreshold slope and off-current were reduced by a factor of ~3 and by two orders of magnitude, respectively, when compared to unannealed TFTs. Furthermore, longer annealed TFTs showed a significant improvement in their stability when compared to unannealed TFTs. The lifetime values for the 48- and 96-h-annealed TFTs improved by a factor of ~3 compared to unannealed TFTs when the threshold voltage shift is extrapolated to 10 V. Stability at high temperatures with better lifetimes for the longer annealed TFTs is due to improvement in the a-Si:H/SiN <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> interface quality by the reduction of trapped charges inside the insulator. For all the TFTs at a positive gate bias, ΔV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> follows a power law dependence with time, indicating state creation. A low β value (0.6 for unannealed TFTs to 0.37 for 96-h-annealed TFTs) indicates a good-quality a-Si:H channel and/or the a-Si:H/insulator interface after longer anneals.