High-performance tin oxide field-effect transistors deposited by thermal atomic layer deposition

Abstract

In this study, we investigated the impact of annealing ambient on the performance of SnO2-based field-effect transistors (FETs) while adhering to the thermal budget constraint (process temperature < 450 °C). The SnO2 films were deposited by thermal atomic layer deposition (T-ALD). After annealing the films for 2 h at 400 °C, it was observed that annealing in an O2 ambient resulted in a SnO2 film with an excessive number of background carriers, which made it difficult to fully deplete the channel. Conversely, annealing in an N2 ambient led to an unstable channel that could not be effectively modulated, despite having a carrier concentration about an order of magnitude lower than that of the O2-annealed film. Surprisingly, the devices annealed in an air ambient exhibited the best performance. X-ray photo-emission spectroscopy revealed that annealing in O2 ambient resulted in a higher level of oxygen vacancy, while N2 annealing was more effective in creating stoichiometric SnO. The best device performance achieved in this study was observed in a 6-nm thick channel that was annealed in the air. This device exhibited an on/off ratio of 1.2 × 1011, subthreshold swing of 0.4 V/dec., field-effect mobility of 14.6 cm2/V·s, and threshold voltage of 1.1 V, operating in an enhancement mode. These results emphasize the potential of ALD SnO2 channels for high-performance transistors that are compatible with back-end-of-line processes in Si technology.