Enhanced high-temperature stability of Indium tin oxide - Indium Oxide thermocouples by two-step annealing

The complex internal structure of the aero-engine and the high-temperature, high-pressure, and high-speed airflow make it difficult to measure the internal temperature. Indium tin oxide (ITO) and In2O3 films have been studied for their application in high-temperature thermocouples and strain gauges. Due to their large Seebeck coefficient and high-temperature stability, ceramic thin-film thermocouples are expected to be used at high-temperature measure. In this paper, ITO-In2O3 thermocouples were fabricated by magnetron sputtering. Besides, the electrical properties of the air-annealed and two-step nitrogen-annealed thermocouples were compared, including the repeatability of thermoelectric response after multiple thermal cycles and the drift rate during the high-temperature duration. The microstructure and electrical conductivity of both the as-deposited and post-annealed ceramic thin films were tested respectively. The result shows that the resitivity and See-beck coefficient of the thin films annealed in nitrogen is reduced, but the stability at high temperature is greatly improved.