Hf-doped ZnO transistor with high bias stability and high field-effect mobility by modulation of oxygen vacancies and interfaces

Abstract

ZnO-based thin film transistors (TFTs) with high bias stability are challenging due to the intrinsic defects and overhigh interface trap density. In this work, we fabricated Hf-doped ZnO films with different cycle ratio of Zn/Hf via atomic layer deposition and subsequent annealing treatment. The results show that the cycle ratio of Zn/Hf is optimized to be 10:1, and the corresponding atomic ratio is 2.24%. The threshold voltage and subthreshold swing of the devices are improved as the annealing temperature increases, owning to the decrease of the oxygen vacancies and interface trap density. Furthermore, we developed Hf-doped ZnO TFT with high bias stability by introducing HfO2 intermediate layer between the active layer and SiO2 dielectric layer, and the shift of threshold voltage is as low as -0.273 V, showing high bias stability. Also, the device has the high field-effective mobility of 52.4 cm2/Vs, low subthreshold swing of 0.68 V/dec and high Ion/Ioff of 3.6 × 108. The results indicate a promising fabrication method for high-performance ZnO-based TFTs, which may be applied in logic circuits, radio frequency identification and so on.