Electrical characteristics of a-IGZO transistors along the in-plane axis during outward bending

A highly flexible amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistor (TFT) was tested with respect to the in-plane axis location and device architecture in a bending system. Short channel a-IGZO TFTs were fabricated based on the conventional coplanar configuration and the islanded structure on a polyimide (PI) substrate and were then subjected to a cyclic bending of 1 × 105 with varying radii smaller than a few mm. Embedding the devices at a neutral position in bending system allowed them to function well when exposed to the induced mechanical strain, regardless of the difference in the structural geometry. However, placement of the TFTs outside of the neutral surface resulted in a drastic suppression of the strain-induced electrical failure for the island configuration as the distance of the TFTs from the neutral surface increased. By contrast, the conventional structure, when placed outside the neutral surface, showed strongly accelerated device failure as the strain on the TFTs was increased. The electromechanical integrity was maintained for island-structured TFTs under a bending stress with a radius of 1 mm and a position margin of 50 μm away from the neutral surface. The brittle and rigid characteristics of TFT arrays with inorganic components are still considered problematic in terms of being put into practical use in flexible applications; nevertheless, the high flexibility achieved by this structural design and its geometrical characterization along the in-plane axis shows the great potential for a-IGZO TFTs to serve as the functional building blocks of new platform applications, such as rolling or folding displays, by suppressing the mechanical strain in the backplane.