Combinatorial Optimization of Metal-Insulator-Insulator-Metal (MIIM) Diodes With Thickness-Gradient Films via Spatial Atomic Layer Deposition

Metal-insulator-insulator-metal (MIIM) diodes with thickness-gradient films for the insulator layers are fabricated for the first time. Spatially varying atmospheric-pressure chemical vapor deposition is used to deposit ZnO and Al₂O₃ films with orthogonal gradient directions, producing 414 MIIM diodes with 414 different ZnO/Al₂O₃ film-thickness combinations on a single substrate for combinatorial and high-throughput optimization. The nm-scale ZnO/Al₂O₃ films are printed in only 2 min and the entire device fabrication takes 7 h, which is much less than conventional approaches for investigating many insulator-thickness combinations. Rapid identification of the optimal thickness combination is demonstrated; high-performance diodes (asymmetry = 227, nonlinearity = 13.1, and responsivity = 12 A/W) are observed when a trap-assisted tunneling mechanism is dominant for insulator thicknesses of 3.4–4.4 nm (ZnO) and 7.4 nm (Al₂O₃).