Engineering Interface Defects and Interdiffusion at the Degenerate Conductive In₂O₃/Al₂O₃ Interface for Stable Electrodes in a Saline Solution

A low-temperature Al₂O₃ deposition process provides a simplified method to form a conductive two-dimensional electron gas (2DEG) at the metal oxide/Al₂O₃ heterointerface. However, the impact of key factors of the interface defects and cation interdiffusion on the interface is still not well understood. Furthermore, there is still a blank space in terms of applications that go beyond the understanding of the interface’s electrical conductivity. In this work, we carried out a systematic experimental study by oxygen plasma pretreatment and thermal annealing post-treatment to study the impact of interface defects and cation interdiffusion at the In₂O₃/Al₂O₃ interface on the electrical conductance, respectively. Combining the trends in electrical conductance with the structural characteristics, we found that building a sharp interface with a high concentration of interface defects provides a reliable approach to producing such a conductive interface. After applying this conductive interface as electrodes for fabricating a field-effect transistor (FET) device, we found that this interface electrode exhibited ultrastability in phosphate-buffered saline (PBS), a commonly used biological saline solution. This study provides new insights into the formation of conductive 2DEGs at metal oxide/Al₂O₃ interfaces and lays the foundation for further applications as electrodes in bioelectronic devices.