RESUMEN
Oxide thin film thermocouples (TFTCs) are widely used in high-temperature environment measurements and have the advantages of good stability and high thermoelectric voltage. However, different annealing processes affect the performance of TFTCs. This paper studied the impact of different annealing times on the cyclic characteristics of ceramic oxide thin film thermocouples. ITO/In2O3 TFTCs were prepared on alumina ceramics by a screen printing method, and the samples were annealed at different times. The microstructure of the ITO film was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that when the annealing temperature is fixed, the stability of the thermocouple is worst when it is annealed for 2 h. Extending the annealing time can improve the properties of the film, increase the density, slow down oxidation, and enhance the thermal stability of the thermocouple. The thermal cycle test results show that the sample can reach five temperature rise and fall cycles, more than 50 h, and can meet the needs of stable measurement in high temperature and harsh environments.
RESUMEN
Tungsten-rhenium thin film thermocouples (TFTCs) are well suited for the surface temperature monitoring of hot components due to their small size, rapid response and low cost. In this study, a tungsten-rhenium TFTC with SiC protective film on all parts except the pads was fabricated by a microelectromechanical system (MEMS) process. During the low to medium temperature (-40 °C to 500 °C) repeatability test phase, the thermal voltage from the TFTC agreed well with that of the standard tungsten-rhenium thermocouple. However, during the high temperature test phase, the TFTC lost electronic response at around 620 °C. Failure analysis of the TFTC tested at 620 °C was performed by microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), laser scanning confocal microscope (LSCM) and statistics. The results showed that the pads were oxidized without the protective layer, the number of oxidized protrusions distributed in this TFTC from the pad to the node decreases more and more slowly and the size of the oxidized protrusions also becomes smaller and smaller. This demonstrates the presence of horizontal oxidation diffusion in TFTCs, further illustrating the importance of pad protection and provides a direction for the subsequent structural optimization and the extension of the service life of TFTCs and other sensors.
