Enabling High-Sensitivity Calorimetric Flow Sensor Using Vanadium Dioxide Phase-Change Material With Predictable Hysteretic Behavior

This study proposes a novel high-sensitivity calorimetric flow sensor based on vanadium dioxide (VO2) to meet the growing demand for low-flow detection. The thermoresistive effect characterization results of the fabricated VO2 thin film show a temperature coefficient of resistance (TCR) of $99\boldsymbol {\%}$ /K that is two orders of magnitude higher than that of conventional thermal sensing material, indicating its potential for enhancing the sensitivity of the calorimetric sensor. Notably, it exhibits a nonlinear temperature-dependent hysteretic behavior with the minor resistance-temperature curves nested in the major hysteresis curves, posing a challenge to the practical use of VO2-based sensors. Thus, a comprehensive hysteresis model, utilizing physical model for the major hysteresis loop and modified Preisach models for the minor hysteresis loop, has been established to give an accurate resistance-temperature response, providing a solid basis for the development of high performance sensor based on VO2. The finite element analysis (FEA) confirmed the proposed calorimetric sensor’s superior performance, with a linear range of 0– $0.4~\mu $ L/min and a normalized output sensitivity of 11.08 V/(m/s)/mW, consuming 1.5 times less power than dual-heater configurations. The dual-heater calorimetric sensor achieved a sensitivity of 21.23 V/(m/s)/mW in its CH mode, 18.3 times higher than conventional metal-based sensors. This work advances the understanding of VO2 hysteresis for microflow sensor design and paves the way for nonlinear phase-change material (PCM)-based microfluidic sensors.