Environment-Dependent Bias Stress Stability of P-Type SnO Thin-Film Transistors

We investigate the effects of environmental water and oxygen on the electrical stability of p-type tin monoxide (SnO) thin-film transistors (TFTs). Under negative gate bias stresses, there was a larger threshold voltage shift (
$\Delta V_{\mathrm {th}})$
in the devices that had been exposed to water than that for the devices that remained unexposed. However, under positive gate bias stresses, devices that had been exposed to water exhibited approximately the same
$\Delta V_{\mathrm {th}}$
as what was observed in devices that had not been exposed. This phenomenon is attributed to the generation of residual-water-related hole traps near the valence band edge in SnO TFTs. In addition, we observed that the environmental oxygen partial pressure had very little effect on the electrical stability of p-type SnO TFTs under either negative or positive gate bias stresses. The weak chemisorption of oxygen molecules caused by high ionization energy can be a plausible mechanism for the oxygen insensitivity of negative gate bias-stress-induced instabilities, and the low electron concentration near the exposed back-channel of p-type SnO TFTs can possible explain the oxygen insensitivity of positive gate bias-stress-induced instabilities.