Fatigue Effect of Stretchable a-InGaZnO TFT on PI/PDMS Substrate under Repetitive Uni/Biaxial Elongation Stress

We examine the fatigue effects of repeated elongation stress for a fabricated a-IGZO thin-film transistor (TFT) on an island polyimide (PI)/poly(dimethylsiloxane) (PDMS) substrate. The repeated elongation stress evaluation was performed in both a uniaxial direction with 10, 30, and 50% strain and biaxial direction with 10, 20, and 30% strain for 50 000 cycles. The a-IGZO TFTs on the island PI exhibit the following parameters: Vth: −0.91 ± 0.30 V, μsat: 26.3 ± 0.61 cm2/(V s), and SS: 0.40 ± 0.02 V/decade. As a result of the repeated elongation stress in the maximum evaluated elongation (uniaxis: 50% and biaxis: 30%), the subthreshold swing (SS) increased by about 0.20 V/decade in all directions, and the saturation mobility decreased only in the x-axis direction (Δμsat: 26.30 → 21.43 cm2/(V s)). Through XPS analysis and TCAD simulation, it was confirmed that SS deteriorated due to an increase of the oxygen-vacancy-related defects (NGA and NGD) in the IGZO channel layer after repeated elongation stress. The transmission line method (TLM) confirmed that contact resistance increased when stretched only in the x-axis direction. In addition, the positive bias stress (PBS) test showed abnormal behavior including an additional SS-degradation-induced Vth negative shift after repeated elongation stress in all directions. Consequently, the degradation mechanism of both the electrical properties and bias stability for the stretchable a-IGZO TFT was determined after elongation stresses.