Improvement of Strained Negative Bias Temperature Instability in Flexible LTPS TFTs by a Stress-Release Design

In this study, the negative bias temperature instability (NBTI) under mechanical strain conditions of low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) with a stress-release structure was investigated. With both electrical and mechanical stresses simultaneously applied, more significant degradation behaviors will be observed in standard TFT devices because mechanical stress makes it easier to generate strain in Si-H bonds, thus benefiting the process of electrochemical reaction. By employing a stress-release shape in the poly channel, mechanical stress, which mainly accumulates at the width edge of the poly-Si/SiO2 interface, is moved away from the main channel; thus, fewer strained Si-H bonds can participate in the electrochemical reaction compared to the standard structure. Therefore, the degradation of devices under strained NBTI is effectively mitigated, such that the reliability of the devices is enhanced. These observations were obtained using electrical characteristics and extraction of the trap state distribution.