Flexible Thin-Film Transistors with Vertical In-Ga-Zn-O Channel Using Atomic-Layer Deposition on Poly(Ethylene Naphthalate) Substrate

A flexible vertical-channel structure thin-film transistor (VTFT) was proposed and fabricated on poly(ethylene naphthalate) (PEN) substrate. All the layers composing the gate-stack including an In-Ga-Zn-O (IGZO) active channel were prepared by atomic-layer deposition except for source and drain electrodes. A polyimide was introduced as a spacer material and a dry etch process was designed to form the vertical sidewalls. The fabricated flexible IGZO VTFTs exhibited sound transfer characteristics showing the on/off ratio of 1.8×102. The threshold voltage instabilities were estimated to be +6.1 V/-4.5 V under the positive/negative bias stress tests, respectively. The device characteristics did not show any marked degradation even after the substrate delamination and even under the bending state at a curvature radius of 10 mm.