Control of Threshold Voltage in ZnO/Al₂O₃ Thin-Film Transistors through Al₂O₃ Growth Temperature

Ultra-thin ZnO thin-film transistors with a channel thickness of <10 nm have disadvantages of a high threshold voltage and a low carrier mobility due to a low carrier concentration. Although these issues can be addressed by utilizing the strong reducing power of tri-methyl-aluminum, a method is required to control parameters such as the threshold voltage. Therefore, we fabricated a ZnO/Al2O3 thin-film transistor with a thickness of 6 nm and adjusted the threshold voltage and carrier mobility through the modulation of carrier generation by varying the growth temperature of Al2O3. As the growth temperature of Al2O3 increased, oxygen vacancies generated at the hetero–oxide interface increased, supplying a free carrier into the channel and causing the threshold voltage to shift in the negative direction. The optimized device, a ZnO/Al2O3 thin-film transistor with a growth temperature of 140 °C, exhibited a μsat of 12.26 cm2/V∙s, Vth of 8.16 V, SS of 0.65 V/decade, and ION/OFF of 3.98 × 106. X-ray photoelectron spectroscopy was performed to analyze the properties of ZnO/Al2O3 thin films.