Effects of substrate temperature on performance of calcium-doped zinc oxide TFTs

In this reported work, high-performance fully transparent bottom-gate-type calcium-doped zinc oxide thin-film transistors (Ca-ZnO TFTs) have been successfully fabricated on glass substrate. The effects of substrate temperature during active layer deposition on the electrical properties of Ca-ZnO TFTs were investigated and an optimum condition (substrate temperature: 100°C) was achieved. The optimised thin-film transistors (TFTs) exhibit excellent electrical properties, with an off-state current (I_off) of 1.31 × 10^-12 A, an I_on/I_off current ratio of 3.015 × 10⁸, a saturation mobility (μ_sat) of 25 cm²/Vs and a threshold voltage (V_t) of 4.24 V. The variation trend of V_t, the I_on/I_off current ratio and μ_sat against substrate temperatures is analysed in detail. The experimental results suggest that the performance of Ca-ZnO TFTs can be improved effectively by optimum substrate temperature.