Effect of Mechanical Strain on Hydrogenated Amorphous Silicon Thin-Film Transistors and Compensation Circuits on Flexible Substrates

Abstract

Hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) compensation pixel circuits were fabricated on polyethylene naphthalate substrates at amax-imumtemperature of 170 °C. The typical a-Si:H TFTs showed a field-effect mobility ( $\mu _{\text {FE}}$ ) of 0.8–1.1 cm $^{2}$ /Vs, a threshold voltage ( ${V}_{T}$ ) of 2–3.3 V, a subthreshold swing (SS) of ~0.65 V/decade, and an ON/OFF current ratio of $10^{7}$ – $10^{8}$ . Under DC gate-bias stress without compensation, the TFT drive current decreased by ~50% withoutmechanical strain and ~60% with applied tensile strain. The TFT circuits effectively compensated for the change in the TFT drive current to within 10% of the original drive current value under mechanically strained and unstrained states. The orientation of the TFT within the circuit was found to affect the circuit compensation; TFTs having a channel length perpendicular to the mechanical strain were found to have a 50% higher threshold voltage shift ( $\Delta {V}_{T}$ ) compared to devices parallel to the applied strain.