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

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.