Extrinsic Degradation of Flexible Poly-Si Thin-Film Transistors Under Dynamic Bending Stress

In this work, it is demonstrated that the normal degradation of positive threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}{)}$ </tex-math></inline-formula> shift of flexible low-temperature poly-Si (LTPS) thin-film transistors (TFTs) during bending stress, which increases with bending cycles, as well as a similar degradation occurring spontaneously after the removal of mechanical stress, which depends on the idle time, can be unified as the same extrinsic phenomenon. This extrinsic degradation originates from the air ambient and depends on the operation lifetime, including both stress time and idle time. It is in contrast to the intrinsic degradation of negative <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift that occurs under the same bending stress but in a vacuum or an inert condition. A degradation model is proposed, which includes both extrinsic and intrinsic degradation.