Investigating bias temperature instability and threshold voltage shifts in indium tin oxide (ITO) transistors

Ultrathin amorphous oxide semiconductors are emerging materials being considered for transistors in memory and various back-end-of-line applications, but their stability remains a concern. Here, we report on both positive and negative bias temperature stability of top-gated indium tin oxide (ITO) transistors whose ultrathin, ~4 nm, channel was deposited with three oxygen compositions (10%, 14%, and 18% O2 partial pressure). No correlation between mobility and stability of such ITO transistors is apparent at room temperature, as we achieve highly stable (∼10 mV threshold voltage shift) devices with good mobility (∼38 cm2 V−1 s−1). We also investigate the time-dependent stability of such ITO transistors at elevated temperatures (85 and 120 °C). We discuss the interplay of multiple physical mechanisms and uncover the effect of processing conditions, leading to oxygen-related defects in the channel and gate dielectric, causing the subsequent instability.