Analysis on Mechanical-Strain Induced Bias-Stress Instabilities for the Flexible InGaZnO Thin Film Transistors with Different Channel Geometries

Channel geometry effects on the gate bias-stress instabilities of the flexible amorphous InGaZnO (IGZO) thin film transistors (TFTs) fabricated on ultra-thin polyimide films with a thickness of 1.2 μm were investigated. The flexible IGZO TFT exhibited a saturation mobility of 13.2 cm2/Vs and a subthreshold swing of 0.19 V/dec. Excellent positive bias stress (PBS) stabilities could be successfully obtained at a gate bias of 20 V even under the mechanically-strained conditions. Alternatively, at a higher bias stress of 35 V, the turn-on voltage shifts at a bending radius of 1 mm during the PBS tests were estimated for the TFTs with channel widths of 20 μm and 160 μm to be 0.7 and 4.9 V, respectively. Channel geometry-dependent PBS instability was suggested to originate from the stress concentration along the bending axis, which was verified by the evaluation results measured at various conditions and the TCAD simulations.