Strain-Attenuating Multilayer Flexible Substrate with High Thermal Endurance for Process Compatibility with Metal Oxide Thin-Film Transistors

Abstract

Thin-film transistors (TFTs) based on oxide semiconductors, represented by indium-gallium-zinc-oxide (IGZO), are widely used in the display industry and are increasingly required to operate in flexible form factors such as wearable devices and foldable displays. Although thin-film amorphous oxide semiconductors are flexible, the brittle layers in the devices are damaged under sharp or repeated bending. Strategies such as ultrathin substrates and neutral-plane engineering can mitigate the strain applied to the devices; however, they constrain the substrate handling or the device architecture. We propose a strain-attenuating substrate in which a low-modulus elastomer, polydimethylsiloxane (PDMS), is entirely encapsulated inside chemically and thermally stable polyimide (PI). The embedded PDMS reduces the strain applied to the substrate surface, and the PI encapsulation provides high thermal endurance for process compatibility with metal oxide TFT fabrication. The IGZO TFTs fabricated directly on the strain-attenuating substrate maintain their electrical characteristics after bending at a radius of 1.5 mm, with a mobility change of –0.03% and a threshold voltage shift of 0.07 V, whereas the TFTs on a conventional PI substrate of the same thickness show a mobility decrease of 74.53% and a threshold voltage shift of 3.84 V.