High‐Performance Flexible Electronics Fabricated Using a Surface Energy‐Directed Assembly Process on Ultrathin Polyimide Substrates

Solution-based processes are emerging in the fabrication of flexible electronics owing to their cost-effectiveness, low-temperature processing capabilities, and vacuum-free operations. Currently, printing techniques, as the most widely used solution-based processes, suffer from low resolution and poor pattern fidelity. Although surface energy-directed assembly (SEDA) process enables unparalleled resolution and fidelity, multilayer fabrication and application on flexible substrates are rarely attempted. Here, a SEDA process is used for fabricating metal oxide thin film transistors (TFTs) on ultrathin and flexible polyimide (PI) substrates with a thickness of ≈35 µm. Comprehensive procedures to render PI substrates hydrophobic as well as to homogenize the hydrophobicity of the PI substrates and as-assembled layers are developed. All-solution-processed flexible TFTs are constructed by assembling indium oxide semiconducting channels, indium tin oxide source/drain electrodes, aluminum oxide gate dielectric layers, and indium tin oxide gate electrodes ordinally. The metal oxide TFTs exhibit excellent electrical properties with an average mobility of 22.01 cm² V^-1 s^-1 and stable operation under mechanical strain. Flexible inverters with a high voltage gain of 78 and a high dynamic operation frequency of up to 1 kHz are also constructed, representing new opportunities of the SEDA process for the fabrication of next-generation flexible electronics.