Design of oxide-based tunnel FETs using amorphous IGZO and p-type oxide semiconductors

Abstract

Thin-film transistors based on oxide semiconductors, such as amorphous InGaZnO4 (a-IGZO), are widely used in edge devices owing to their low power consumption. However, the fundamental limitation of the subthreshold swing (SS) hinders both high-speed response and further reduction in power consumption. In this study, we focus on the concept of the tunnel field-effect transistor (TFET), which can significantly reduce SS, and explore its application to a-IGZO-based transistors. To design the a-IGZO based TFETs, we experimentally determined the band diagrams of a-IGZO/SnO and a-IGZO/Nb-doped Bi2WO6 (Nb:BWO), considering depletion layers, using photoemission spectroscopy. Both heterojunctions exhibited type II band alignment, with the energy barriers between the conduction band minimum of a-IGZO and valence band maximum of SnO or Nb:BWO being 0.57 ± 0.05 and 1.72 ± 0.05 eV, respectively. Simulations based on these band diagrams demonstrated the on-off switching behavior of the a-IGZO/SnO TFET only, achieving a minimum SS value of 48 mV/dec with a 3 mm-thick a-IGZO, assuming an ideal interface. These results suggest that optimizing junction properties and material selection plays a crucial role in the realization of a-IGZO-based TFETs for enhanced energy efficiency in electronic devices.