Novel gas sensors based on thin film bulk acoustic resonators

The paper describes the application of thin film bulk acoustic resonators (TFBAR) with an operating frequency around 2 GHz as gas sensors. The sensor consists of a solidly mounted thin film ZnO resonator fabricated on a silicon substrate covered with a gas sensitive polymer receptor. The sensitivity of the device for vapors and gases, like humidity or carbon dioxide, has been measured. The TFBAR sensitivity is up to two orders of magnitude higher compared to conventional quartz microbalance sensors. The sensitivity for a given target gas depends in a nonlinear way on the receptor thickness. Furthermore, the characteristics of the sensitivity versus receptor-thickness curve depends significantly on the target gas and allows a discrimination between gases. The TFBAR-gas sensor performance and the novel observation of a thickness dependent selectivity of receptor material are discussed.