Overcoming the Surface Instability Bottleneck in High-Mobility Crystalline Indium Oxide Thin-Film Transistors by Yttrium Oxide Stabilization.

Abstract

Monolithic 3D integration of oxide thin-film transistors provides an approach to continue Moore's Law. Crystalline indium oxide (In₂O₃) is particularly attractive owing to its high electron mobility and low contact resistance. However, its practical deployment is hindered by the difficulty of fabricating crystalline In₂O₃ under BEOL-compatible conditions and by the intrinsic instability of surface oxygen. In this work, we demonstrate an atomic-layer-deposition-enabled stabilization strategy that simultaneously achieves high mobility, strong electrostatic control, and exceptional stability in crystalline In₂O₃ transistors. The afforded devices exhibit a high electron mobility of 92.8 cm²/V·s, a positive threshold voltage of 0.67 V, a steep subthreshold swing of 64.5 mV/dec, and fairly small threshold voltage shifts of -5.6 and 18.6 mV under negative- and positive-bias stress, respectively. Furthermore, the devices show good resistance to forming gas annealing, with small threshold voltage shifts and no degradation in subthreshold swing or on-current. This work not only provides valuable insight into the origin of instability for crystalline oxide semiconductors, but also demonstrates a practical fabrication approach at CMOS BEOL-compatible temperatures to achieve both high performance and high stability for oxide transistors, thereby highlighting the high promise of indium oxide transistors for advanced M3D integration.