On-chip calibration of Microscale-Thermocouples for Precise Temperature Measurement

Abstract: Precise temperature measurement at micro/nanoscale is crucial across various domains including physical sciences, chemical processes, industrial production, medical diagnosis, weather forecasting, electronics, and biology. Micro/nanoscale thermal mapping requires precise techniques such as thermocouples, resistance-based devices, infrared thermography, optical interferometry, Raman thermometry, and Time domain-thermoreflectance (TDTR) method. Each method has its advantages and limitations, emphasizing the importance of selecting the appropriate technique. Among these methods, micro-thin film thermocouples (TFTCs) offer a compelling solution due to their direct contact-based temperature measurements, minimal surface preparation requirements, lower cost, and robustness against environmental factors. Thermocouples work on the well-established Seebeck effect, where a voltage is generated proportional to the temperature difference between two points. However, at micro/nanoscale, the Seebeck coefficients of thermocouples differ from those in bulk materials, requiring experimental calibration for precise measurements. To address this, we introduce an on-chip characterization platform with a differential temperature measurement setup on a borosilicate glass substrate. This platform utilizes a microheater as a localized heat source to elevate the temperature at the hot junction of the TFTC while maintaining the cold junction at ambient conditions. Numerical simulations are employed to engineer both the microheater and TFTC junction for precise temperature control. The functionality of this platform is validated by fabricating TFTCs using standard fabrication processes and measuring the TFTC response to determine the differential Seebeck coefficient of a Platinum-Chromium TFTC Junction. The calculated sensitivity of Pt/Cr TFTCs using this calibration method is 19.23 +- 0.405 {\mu}V/C.