Effects of channel thickness on electrical properties and stability of zinc tin oxide thin-film transistors

Abstract

We investigated the effects of channel thickness (tch) on the electrical properties and the bias stress-induced instability of zinc tin oxide (ZTO, Zn : Sn = 4 : 1) thin-film transistors (TFTs). With increasing tch, the electrical properties of the TFTs showed a trend: threshold voltage (Vth) decreased and field-effect mobility (μFE) increased; on the other hand, subthreshold swing and hysteresis characteristics did not show any significant change. The positive bias stress (PBS) test and the following analysis by the stretched-exponential equation revealed that the PBS-induced threshold voltage shift (ΔVth) decreased and the extracted characteristic trapping time (τ) increased with increasing tch. This thickness-dependence of PBS instability cannot be explained by charge trapping/injection model or defect creation model but can be well explained by less ambient effect at the backchannel due to less gate field through a thicker film.