Hydrogen-Related Instability of IGZO Field-Effect Transistors

In this article, we report a comprehensive investigation and a deep understanding of the impact of hydrogen evolution on the reliability of indium-gallium-zinc-oxide (IGZO) field-effect transistors (FETs) with HfO $_{\text{2}}$ as the gate dielectric. Our findings reveal that the source/drain (S/D) regions play a pivotal role in the threshold voltage shift ( $\Delta \textit{V}_{\text{th}}\text{)}$ observed under negative bias stress (NBS) conditions, with short channel (SC) devices exhibiting greater susceptibility to S/D effects compared to long channel (LC) devices. These observations are further supported by TCAD simulations. We combined NBS and positive BTI (PBTI) measurements to comprehensively assess the stress and recovery performance of the devices. This has allowed us to distinguish two distinct hydrogen (H) states, namely H $^{\text{P}}$ and H $^{\text{N}}$ , both of which induce a negative $\Delta \textit{V}_{\text{th}}$ as a result of increased channel carrier concentration. This investigation advances our understanding of the fundamental physical mechanisms underlying the bias temperature instability (BTI) degradation in IGZO FET technologies.