Subthreshold Swing Behavior in Amorphous Indium-Gallium-Zinc-Oxide Transistors from Room to Cryogenic Temperatures

TL;DR

This study investigates the temperature-dependent subthreshold swing in amorphous IGZO transistors from room temperature to cryogenic levels, revealing transport mechanisms and limitations at various temperatures.

Contribution

It provides the first comprehensive analysis of SS behavior in amorphous IGZO devices across a wide temperature range, elucidating underlying electron transport mechanisms.

Findings

SS saturation around 40 mV/dec between 200 K and 100 K

High SS exceeding 200 mV/dec at 4 K limited by measurement current range

Electron transport explained by band tail states and VRH model

Abstract

While cryogenic-temperature subthreshold swing (SS) in crystalline semiconductors has been widely studied, a careful study on the temperature-dependent SS in amorphous oxide semiconductors remains lacking. In this paper, a comprehensive analysis of the SS in thin-film transistors with an amorphous indium gallium zinc oxide (IGZO) channel at temperatures from 300 K down to 4 K is presented. Main observations include: 1) At room temperature (300 K), the devices exhibit a SS of 61 mV/dec, and a low interface trap density (<1011 cm-2), among the best reported values for IGZO devices. 2) A SS saturation around 40 mV/dec is observed between 200 K and 100 K. It is well explained by the electron transport via band tail states with exponential decay (Wt) of 13 meV. 3) At deep-cryogenic temperature, SS increase significantly exceeding 200 mV/dec at 4 K. Such high SS values are actually limited by the measurement current range, confirmed by Id-Vg simulations based on the variable range hopping (VRH) model. This work not only elucidates the SS behavior in amorphous IGZO devices but also provides a deep understanding of the physical mechanisms of electron transport in amorphous semiconductors.