Sol-gel derived Hf- and Mg-doped high-performance ZnO thin film transistors

We report high-performance Hf- and Mg-doped ZnO thin film transistors (TFTs) with various doping concentrations and annealing temperatures of 400 and 450 °C fabricated using a sol-gel solution process. The ZnO TFTs doped with 2 at% Hf exhibited high performances with average mobilities of 4.17 and 19.04 cm2V−1s−1 when annealed at 400 and 450 °C, respectively, along with high Ion/Ioff ratios on the order of 106. The Mg-doped ZnO TFTs showed no significant change in the device performance when varying the doping concentration and annealing temperature. The chemical composition was examined using X-ray photoelectron spectroscopy and it was confirmed that the Hf was doped in the ZnO thin films at both annealing temperatures. The improved electrical performance was attributed to an increase in the grain size at the optimized doping concentration.