A Resonant Gas Sensor With Functional Composite Stress Generator

A bridge resonator consisting of a microbeam and a functional composite membrane is proposed in this work for gas detection. The gas molecules adsorbed onto the membrane will generate an axis compressive stress on the micro clamped–clamped beam to decrease the bending stiffness by expanding the designed silicon slits structure, as well as increase the effective mass of the resonator. The resonant frequency shift of the proposed sensor is thus greater than those based only on mass change or stiffness change, showing higher gas sensitivity. The bridge structure of the sensor was successfully fabricated for experimental study. To explore the response of the proposed sensor to humidity, various relative humidities (RHs) produced in a designed measuring system are applied to a test chamber. The evaluation results showed that the resonant frequency of the sensor decreases with the increase of humidity. Significantly, there is an apparent linear relationship between resonant frequency and RH of 28 Hz per 1% RH with negligible deviations and the linear goodness of fit can reach 99.65% when the RH is lower than 12%. The results indicate a high sensing resolution of 0.5% and high repeatability. Besides, the detection of $\text{H}_{{2}}\text{S}$ gas with a low concentration of 5 ppm is demonstrated by this proposed resonant gas sensor. With the proper selection of the functional membrane, an array of sensors is potential to be applied in detecting various volatile gas components in human breath and in atmosphere.