Post-CMOS processing and DC characterization of a resonant microcantilever for gas sensing

In recent years MEMS based microresonant sensors have been given a lot of attention due to their potential as a platform for the development of many novel physical, chemical, and biological sensors. Monolithic integration of micro device with electronics can not only lower manufacturing cost but also minimize total system size. However, the curling of composite metal-oxide microstructures in the thin-film CMOS-MEMS process, greatly limits the device size. Deep Reactive Ion Etching (DRIE) technologies have advanced significantly in recent years and by alternating passivation and etching cycle, silicon etch process can typically achieve high aspect ratios between 20:1 to 30:1 that can be used to reduce the curling of the structure. In this paper, post-CMOS processing of a microcantilever, designed for CO₂ detection, by using backside DRIE to control the curling and DC characterization of the sensor is reported. In order to estimate the deviation of the parameters from designed values, due to manufacturing tolerance, the DC characteristics of the sensor have also been calculated theoretically. The theoretical value of 1.65 kΩ for piezoresistor and 7.34 kΩ for pick up coil matches with the measured values of 2.15 kΩ and 6.3 kΩ within an error limit of 23% and 16% respectively.