Optimizing Responsiveness and Accuracy of Noncontact Temperature Measurement Based on Thermoreflectance

A noncontact temperature measurement system based on thermoreflectance (TR) with a high signal-to-noise ratio (SNR) without temperature modulation was developed and optimized for responsiveness to achieve high-speed and accurate temperature measurement.The developed system employed a balanced photodetector and lock-in amplifier to measure minute reflectance changes in a Joule-heated Ti thin-film wiring pattern.The response characteristics of the lock-in amplifier were analyzed theoretically using a fourth-order low-pass filter model.The response time was approximately ten times the time constant (TC) of the filter, and SNR was inversely proportional to the square root of TC.Transient temperature measurements demonstrated that the measurement response depends strongly on TC, and a response time of approximately 15 ms with a temperature uncertainty of 3.3 ℃ was achieved by selecting the optimum TC value.The experimentally obtained SNR increased on extending TC to larger than the theoretical prediction, suggesting a complex noise spectrum at high frequencies.