Thin film bulk acoustic wave resonator (TFBAR) gas sensor

A novel electro-acoustic chemical sensor, based on a TFBAR, is presented. The principle of operation is the same as the well known quartz crystal micro-balance, where the frequency of operation is extended from the limit of a few tens of MHz to several GHz. The larger sensor output signals, associated with higher frequency operation, is a condition used to develop devices with improved sensitivity. TFBARs have been implemented on [001] Si wafers, using Si/sub 3/N/sub 4//AlN membranes, obtained by anisotropic chemical etching from the back side of the Si substrate. The performance of the TFBAR sensor has been tested using a thin Pd chemical interactive membrane deposited on the etched side of the membrane and exposed to different concentrations of hydrogen in nitrogen. Time response upon different cycles of H/sub 2/ adsorption and desorption are reported together with the sensor calibration curve. The operation frequency of the device, in the GHz range, allows it to obtain large responses. The device is robust in construction and miniaturized in size. Time stability, repeatability and sensitivity have been tested and reported.