CMOS resonant beam gas sensing system with on-chip self excitation

We present a single-chip CMOS resonant beam gas sensing system with on-chip self excitation for the detection of volatile organic compounds (VOC). For the first time, a mass-sensitive resonant cantilever is cointegrated with a feedback circuit yielding a sensor system operating in a self-excitation mode. Analyte gases are absorbed by a sensitive layer deposited on the cantilever. The corresponding mass increase leads to a decrease of the beam´s resonance frequency. In this way, concentrations of various VOC´s in synthetic air are measured. The influence of polymer thickness on resonance frequency, quality factor, and vibration amplitude is investigated. The frequency stability and sensitivity of the cantilever sensor is tested and an optimal polymer thickness of 3-4 pm determined. A limit of detection of 0.8 ppm for octane is calculated. This corresponds to a mass resolution of less than 0.4 pg. The on-chip integration of the feedback circuit makes it possible to abandon external driving circuitry. Thus, it drastically reduces the system size and number of components, and facilitates mass production.