Critical Role of In ₂ O ₃ Structure and Interface in Threshold Voltage and Mobility of Oxide Semiconductor FETs

This study investigates the electronic and structural properties of In 2 O 3 thin films on SiO 2 and HfO 2 substrates using synchrotron-based X-ray techniques, focusing on how oxygen vacancies (V o ) and hydroxide (−OH) incorporation influence threshold voltage ( V TH ) and field-effect mobility (μ FE ) in field-effect transistors (FETs). This study demonstrates that V o significantly shifts threshold V TH and impacts the device’s electrical performance, aligning with results from TCAD simulations. In 2 O 3 on HfO 2 exhibits fewer V o and greater stability compared to that on SiO 2, enhancing device lifetime. Structurally, In 2 O 3 on HfO 2 has a higher density (6.4 g/cm 3 ) and lower interface roughness than In 2 O 3 on SiO 2 (5.9 g/cm 3 ), where an intermixing layer is present at the In 2 O 3 /SiO 2 interface. These structural differences contribute to a higher μ FE for In 2 O 3 on HfO 2 (48 cm 2 /V·s) compared to SiO 2 (30 cm 2 /V·s). Further annealing at 400 °C can enhance density and interface quality in In 2 O 3 on HfO 2, which improves its mobility to 115 cm 2 /V·s. These findings underscore the critical role of electronic and structural properties of In 2 O 3 and its interface with the dielectric substrate in optimizing the performance and stability of oxide semiconductor FETs.