Coating Thickness Controls Crystallinity and Enables Homoepitaxial Growth of Ultra‐Thin‐Channel Blade‐Coated In2O3 Transistors

Abstract

AbstractScalable, solution‐deposited metal oxide (MO) thin films could enable low‐cost, flexible, large‐area electronics; however, the poor morphology of the typically polycrystalline films limits performance. It is demonstrated that optimized coating thickness leads to high‐quality crystalline films in blade‐coated indium oxide (In2O3) ultra‐thin‐film (8 nm) transistors (TFTs). TFTs are fabricated with total channel thickness ranging from 2 to 16 nm via varied multistep processes. Transport in channels fabricated from sequential, thin (≤4 nm) coatings significantly exceeds that from thicker coatings. A marked change is found in the In2O3 crystal texture with coating thickness. Single, thin coatings ≤4 nm produce smooth films with strong (111) texture while thicker coatings are rougher and exhibit little texture. Sequential thin coatings exhibit homoepitaxy. In addition to the improved transport due to the smooth, aligned films, it is found that deposition of sequential thin layers leads to the highest mobility, with either In2O3 or ZnO as the overcoat. This suggests defects at the air interface of the initial thin films limit performance. Optimizing coating thickness and sequence, it is demonstrated 8 nm thick channel In2O3 TFTs exhibiting percolation conduction with an impressive average saturation electron mobility (μsat) of (36.1 ± 0.9) cm2 V−1 s−1 (best‐performing device of 58.0 cm2 V−1 s−1).