Photo-Cross-Linked Polyimide Dielectric for Mechanically Reliable High-Performance Flexible Metal Oxide Thin-Film Transistors

A critical challenge in flexible high-performance thin-film transistors (TFTs) is ensuring the reliability of the dielectric layer with a high-mobility semiconductor, which must maintain its insulating properties while withstanding repeated mechanical deformation. In this study, we investigate photo-cross-linkable photosensitive polyimide (PSPI), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride-3,5-diaminobenzyl cinnamate (6FDA/DABC), as a dielectric material in oxide TFTs using zinc tin oxide or indium gallium zinc oxide as the channel materials. The photo-cross-linked PSPI dielectric exhibited a high areal capacitance of 17.5 nF cm^-2 at 1 kHz, an ultralow leakage current density of 10^-10 A cm^-2 at 2 MV cm^-1, and a breakdown field exceeding 6.7 MV cm^-1 under static conditions. Under repeated mechanical stress, the dielectric maintained its low leakage current and structural integrity after 10,000 bending cycles, ensuring a stable electrical performance. The photo-cross-linked PSPI and zinc tin oxide-based TFT device demonstrated excellent electrical characteristics, achieving a high mobility of 15.5 cm² V^-1·s^-1, an on/off current ratio of 1.5 × 10⁹, and good electrical stability under positive and negative bias stress, confirming its potential for high-performance, flexible TFT applications.