Stretchable Oxide Thin-Film Transistors with a Mechanically and Electrically Reliable Wavy Structure for Skin Electronics

A stretchable oxide thin-film transistor (TFT) was fabricated with InGaZnO (IGZO) as an amorphous oxide semiconductor on a submicrometer-thick polyimide (PI) film. It was then attached along the curvature of the human skin. Ultrathin stretchable TFT patches were conformally demodulated for various deformations due to stretching, compressing, twisting, and bending stress on the skin. On the other hand, when the IGZO TFT/PI stack was placed on a prestretched elastomeric tape, it contracted with tensile stress released to form a wavy structure. These wave-formed stretchable TFTs on elastomers could similarly imitate skin wrinkles. In some TFT devices, physical defects such as fine crease occurred due to tens of thousands of stretching and contraction motions, resulting in anomalous humps in current–voltage characteristics. The occurrence of crease was largely dependent on the location of TFTs placed on the plane, valley, peak, and so on of wrinkles on the elastomeric film. A crack eventually developed when the mechanical stress was locally concentrated. Regarding the cause of hump, H 2 O molecules in the air might have penetrated into the microcrack and interacted on IGZO sidewalls to create donor-like defects such as hydroxyl groups and hydrogen interstitials, resulting in the formation of parasitic subchannels in the IGZO TFT. By introducing an organic capping layer on the IGZO active region, it was possible to effectively suppress the occurrence of deformation defects and degradation of electrical properties of TFTs due to long-term mechanical stress. Appropriate thickness control of the capping layer allowed for a neutral plane to exist on the IGZO channel interface, thereby minimizing strain in TFTs regardless of whether the deformation was convex or concave. These stretchable TFTs demonstrated excellent electrical properties and reliability even after tens of thousands of repeated stretching and compressing motions, showing practical applicability to skin electronics.