Performance improvement of multilayered ZnO/SnO2 thin-film transistors by varying supercycles and growth temperatures

The performance of conventional ZnSnO (ZTO) amorphous oxide semiconductor thin-film transistors deposited by atomic layer deposition was optimized at annealing temperatures greater than 500 °C, which is higher than the application temperature of flexible substrates (400 °C). Therefore, we deposited a ZTO thin film as a multilayered ZnO/SnO₂ structure to lower the process temperature to below 400 °C. To optimize the performance of the device with a multilayered structure, we examined the effects of cycles and growth temperatures. Finally, after performing 6 supercycles with 10 cycles of ZnO and 20 cycles of SnO₂, at a growth temperature of 180 °C and annealing at 350 °C for 1 h, the device achieved a saturation carrier mobility of 8.09 cm²/V·s, threshold voltage of 1.6 V, subthreshold swing of 0.58 V/dec, and on–off current ratio of 2.63 × 10⁷. The optimized multilayer-structured device performed better than the ZTO device annealed at 350 °C for 1 h, and even outperformed the device annealed at 500 °C for 1 h. X-ray photoelectron spectroscopy analysis was also conducted to analyze the properties of conventional ZTO and multilayered ZnO/SnO₂ thin films.