Long-Term Operational Stability of Dual-Gated ITO/HfO₂ Field-Effect Transistors via Full Top-Gate Coverage: A Comprehensive Bias-Stress Mapping.

Abstract

Indium tin oxide (ITO) is a promising thin-film semiconductor which could be used in back-end-of-line compatible field-effect transistors (FETs) produced by using monolithic 3D integration. However, these targets cannot be reached without making high-quality gate stacks to enable long-term stable device operation, which currently presents a big challenge. Here, we report fully scalable dual-gated ITO FETs with HfO₂ gate insulators which can turn off at zero gate bias, exhibit an ON/OFF ratio of 10⁷ at 3 V, and achieve high long-term bias stability. Specifically, we demonstrate hysteresis widths and threshold voltage drifts limited to just tens of millivolts over tens of kilosecond sweep and stress times, maintaining this performance under ambient and external light conditions. Furthermore, the ubiquitous negative <i>V</i>_th drift under positive gate bias is suppressed up to 85 °C. These results position our devices among the most stable complementary metal-oxide-semiconductor (CMOS)-compatible thin-film FETs with conventional high-k oxide insulators. This is attributed to the full metal coverage of the top-gate oxide and the fact that the upper defect band of HfO₂ is energetically above the conduction band edge of ITO. Our results suggest that achieving Si-grade reliability in ITO FETs may present a more feasible pathway for the industry compared to other emerging platforms such as MoS₂/HfO₂ devices.