Subthreshold Conduction of Disordered ZnO-Based Thin-Film Transistors

This study presents the disorderedness effects on the subthreshold characteristics of atomically deposited ZnO thin-film transistors (TFTs). Bottom-gate ZnO TFTs show n-type enhancement-mode transfer characteristics but a gate-voltage-dependent, degradable subthreshold swing. The charge-transport characteristics of the disordered semiconductor TFTs are severely affected by the localized trap states. Thus, we posit that the disorderedness factors, which are the interface trap capacitance and the diffusion coefficient of electrons, would result in the degradation. Considering the factors as gate-dependent power laws, we derive the subthreshold current-voltage relationship for disordered semiconductors. Notably, the gate-dependent disorderedness parameters are successfully deduced and consistent with those obtained by the gm/Ids method, which was for the FinFETs. In addition, temperature-dependent current-voltage analyses reveal that the gate-dependent interface traps limit the subthreshold conduction, leading to the diffusion current. Thus, we conclude that the disorderedness factors of the ZnO films lead to the indefinable subthreshold swing of the ZnO TFTs.

Automated summary

This study investigates the effects of disorder on the subthreshold characteristics of atomically deposited ZnO thin-film transistors (TFTs). It is found that the charge-transport characteristics of the disordered TFTs are severely affected by localized trap states, resulting in gate-voltage-dependent degradation. By considering the disorderedness factors as gate-dependent power laws, a subthreshold current-voltage relationship is derived for disordered semiconductors. The disorderedness parameters obtained from this relationship are consistent with those obtained by the gm/Ids method.