Influence of the active layer thickness on the electrical properties of ZnO thin film transistors fabricated by radio frequency magnetron sputtering

We report on the electrical properties of bottom-gate ZnO thin film transistors (TFTs) with different active layer thicknesses. The ZnO active layer films with thickness varied from 20 to 100 nm were deposited by radio frequency (rf) magnetron sputtering on SiO₂/p-Si substrate and annealed at a high temperature of 950 °C. The transistor with 40 nm thick ZnO exhibited the best performance, with a field effect mobility of 27.5 cm²/V s, a threshold voltage of −2.4 V and an on/off ratio of 7×10³.