Sub-miniature thin film resonators (TFR) operating near 2 GHz are being developed as mass transducers for high- sensitivity vapor detection. The TFR sensor are coated with species selective vapor absorbing polymers to develop pattern response to the target species for detection and identification. Eight member arrays of TFR sensor have been fabricated and tested for the detection of characteristics explosive vapors including trinitrotoluene, dinitrotoluene, and dinitrobenzene. The TFR sensor use aluminum nitride as the active piezoelectric element and have ben fabricated with resonator quality factors greater than 200. Response patterns and sensitivity measurements are being made using pure vapors, water solutions of the target species, and solid contaminated with the target vapor species.
Progress on the development of a miniature mass transducer for low level vapor detection is described. Thin-film bulk acoustic wave resonators (TFRs) are fabricated with AlN as the piezoelectric layer onto an acoustically reflecting solid substrate. Q's of 200 at 2 GHz have been measured. Comparison of the sensitivity of these 2 GHz TFRs with 250 MHz surface acoustic wave resonators is made. A set of TFRs with species selective coatings has the potential of detecting TNT vapor at the sub PPT level. Detection of 5 ppb TNT with a signal to noise of 200:1 is demonstrated.