Mechanically Flexible Vertical Thin-Film Transistor with Sub-Micrometer Channel Length Using ZnO Channel and ZeocoatTM Spacer on Ultra-Thin Polyimide Substrate

A mechanically flexible vertical-channel thin film transistor (VTFT) with a channel length of 200 nm was fabricated on a 1.2-μm-thick polyimide substrate. The vertical gate-stack was prepared by forming all the layers by atomic layer deposition except for the source and drain electrodes. The ZeocoatTM thin film was introduced as a spacer instead of the previous one containing fluorine ions. The transfer characteristics of the fabricated flexible VTFT achieved an ION/IOFF of 1.4×104 after the post annealing process at 150 °C. The shifts in threshold voltage under positive and negative bias stresses were estimated to be +2.5 and −3.5 V for 104 s, respectively. The flexible VTFTs were successfully delaminated from the carrier glass via a laser lift-off process and evaluated under mechanically strained conditions at various radius of curvatures (Rc’s). There were no significant changes in the device characteristics even at an Rc of 1 mm.