A batch fabrication-compatible multifunctional thermal sensor based on thin film thermocouple and thermopile elements

A novel high temperature, multi-functional thermal sensor is presented which is capable of being batch-produced using industry standard microfabrication techniques. The thin film thermocouple and thermopile features were designed to provide both surface temperature and surface heat flux data simultaneously. In addition, its small size allows for installation and usage without significantly disrupting heat or fluid flow from the component of interest. Single crystal sapphire served as the substrate material for its cost effectiveness and high temperature compatibility. Refractory materials tungsten and molybdenum were chosen as the thin film thermocouple/thermopile components, with magnesium oxide acting as a protective coating. All the materials utilized in the sensor have high melting point and comparable coefficients of thermal expansion. Thermal testing of the sensors up to 800 °C determined the thermocouple and thermopile outputs at a variety of temperatures and heat flux conditions. Results showed an increase in thermovoltage with temperature for the thermocouple elements, while the thermopile output increased linearly with applied heat flux. In terms of reliability, the sensor was able to perform continuously for ten hours at 800 °C within an unregulated air environment. Finally, finite element analysis of the sensor was utilized along with experimental test data to gain further insights into its internal temperature distribution and enhance interpretation of the experimental results.