Enhanced high temperature thermal stability of In2O3-IHFO thin film thermocouples using composite protective layers

In₂O₃-IHFO (7 wt% hafnium-doped In₂O₃) thin-film thermocouples were fabricated on alumina substrates using pulsed laser deposition. A composite protective layer consisting of alumina and nano-silica was subsequently applied to enhance thermal stability. Cross-sectional analysis revealed a uniform, dense and well-defined film structure. Thermoelectric testing demonstrated that the protective layer effectively mitigates film volatilization at high temperatures, significantly enhancing thermocouple stability and performance at high temperatures. The maximum operating temperature reached 1550°C (hot junction), with excellent repeatability (≤2.4 %) in thermal cycling tests. The 9-hour high-temperature endurance test exhibits remarkable stability. These findings highlight a promising protective strategy for thin-film applications in extreme environments.