Origin of the improved mobility and photo-bias stability in a double-channel metal oxide transistor.

This study examined the performance and photo-bias stability of double-channel ZnSnO/InZnO (ZTO/IZO) thin-film transistors. The field-effect mobility (µFE) and photo-bias stability of the double-channel device were improved by increasing the thickness of the front IZO film (t(int)) compared to the single-ZTO-channel device. A high-mobility (approximately 32.3 cm(2)/Vs) ZTO/IZO transistor with excellent photo-bias stability was obtained from Sn doping of the front IZO layer. First-principles calculations revealed an increase in the formation energy of O vacancy defects in the Sn-doped IZO layer compared to the IZO layer. This observation suggests that the superior photo-bias stability of the double-channel device is due to the effect of Sn doping during thermal annealing. However, these improvements were observed only when t(int) was less than the critical thickness. The rationale for this observation is also discussed based on the oxygen vacancy defect model.