Microfabricated differential-mode gas sensor utilizing temperature compensation

This work presents a microfabricated differential mode capacitive gas sensor utilizing temperature compensation. Typical capacitive cantilever sensors offer promise of both high sensitivity and large measurement range. Unfortunately, functionalized cantilevers form a bimorph system, creating a temperature dependence due to the stress gradient induced by the sensor material mismatch. Taking advantage of the reference cantilever commonly employed in differential-mode capacitive sensing, the design presented herein functionalizes the reference cantilever to match the thermal stresses of the sense cantilever, making the temperature dependence common-mode to remove it from the measurement. A surface micromachined polysilicon hydrogen sensor using 50 nm of palladium on the sense cantilever, and 40 nm of silver on the reference cantilever demonstrates the concept and reduces the temperature induced capacitance error to 4.9 fF/°C compared to 16.6 fF/°C for a bare reference.