Molecular and Atomic Layer Deposition of Hybrid Polyimide–Al₂O₃ Gate Dielectrics for Flexible Electronic Devices

Modern information technologies have tremendous demands on flexible electronic devices such as thin-film transistors (TFTs). As the flexible TFT technology continues to advance, the properties of the gate dielectric become a bottleneck for the flexible TFTs to achieve fast switching speed, low operation voltage, and downscaling. The gate dielectric layer should be sufficiently thin, insulating, and flexible, and therefore, hybrid organic–inorganic dielectrics are of great promise for this purpose. In this work, we develop a scalable vapor-phase MLD/ALD technique, which combines molecular layer deposition (MLD) and atomic layer deposition (ALD), to grow a new hybrid polymer–oxide dielectric thin-film material of polyimide (PI) and Al2O3, and demonstrate that the afforded hybrid polyimide–Al2O3 (HPA) films are well suited as the bendable gate dielectrics for flexible electronic applications. We also perform mechanism investigation on the growth of PI and Al2O3 during the MLD/ALD HPA process and find that the growth of PI is strongly affected by the Al2O3 surface and therefore exhibits a two-stage behavior. We further evaluate the electrical and bending performances of the afforded HPA dielectrics and apply the HPA films as the gate dielectrics for flexible carbon-nanotube TFTs. The fabricated TFTs can well withstand 1000-time repetitive bending without an increase in the TFT gate leakage current, which shows the high promise of the HPA dielectrics for flexible electronic applications. Considering that the MLD/ALD fabrication approach is advantageous for high process reproducibility and large-scale compatibility, we envision that the MLD/ALD-prepared HPA dielectrics will have great applications in future complex flexible electronic circuits.