Solution-Processed La Alloyed ZrOx High-k Dielectric for High-Performance ZnO Thin-Film Transistors

Abstract

We report La alloyed ${ZrO}_{x}$ high- ${k}$ gate insulator (GI) for $ZnO$ thin-film transistors (TFTs) by solution-process. The La concentration in ${ZrO}_{x}$ is varied from 0 to 7.5% for optimum device performance. The atomic force microscopy and X-ray photoelectron spectroscopy analysis of 5% La alloyed ${ZrO}_{x}$ GI show smooth surface with higher metal-oxide (M – O) bonds and reduced defect density in the bulk compared with pristine ${ZrO}_{x}$ . Therefore, $ZnO$ TFT using 5% La alloyed ${ZrO}_{x}$ GI exhibits hysteresis-free device performance, with saturation mobility of $11.58 {cm}^{2}/V\cdot s$ , $I_{ \mathrm{ON}}/I_{ \mathrm{OFF}}$ ratio of $2.67\times 10^{8}$ , threshold voltage of $1.25 V$ , and subthreshold swing of $249 mV/dec$ . We also achieve highly stable ZnO TFTs under positive bias stress using 5% La alloyed ${ZrO}_{x}$ GI.