Threshold voltage reliability in flexible amorphous In–Ga–ZnO TFTs under simultaneous electrical and mechanical stress

Abstract

Flexible amorphous In–Ga–ZnO (a-IGZO) thin film transistors (TFTs) have been successfully demonstrated on 50 µm thick freestanding polyimide (PI) with µ sat around 10 cm2 V−1 s−1. In the literature, common characterization of flexible TFTs consist of measuring their electrical response at different bending radius or under positive and negative gate bias stress (PBS and NBS). However, there are few studies where the flexible TFTs have been measured with a simultaneous mechanical and electrical stress. In this work, simultaneous testing under electrical and mechanical stress were carried out with a gate bias stress voltage of ±6 V during 3600 s, and with a tensile bending radius of 1, 2 and 4 mm. a-IGZO TFTs bottom gate-top contacts were fabricated on commercial Kapton HN PI by a complete photolithography process. All the PBS and NBS characteristics presented an abnormal threshold voltage left shift which was mainly explained by the adsorption/desorption of water molecules at the back channel. This V th shift was modeled with the stretched exponential equation. Analyzed TFTs were stable under simultaneous stress until a 4 mm bending radius with electrical parameters V th, subthreshold slope, µ sat and I on/I off in the order of 0.7 V, 340 mV dec−1, 6 cm2 V−1 s−1 and 5 × 108, respectively.