Interdigital Electrode-Integrated Two-Port SAW Resonator for Vapor Sensing: Dual Measurement in a Single Device

We propose a novel interdigital electrode (IDE)-integrated surface acoustic wave (SAW) sensor comprising of a two-port SAW resonator with an IDE fabricated between the interdigital transducers. Further, we demonstrated the device’s dual parameter measurement capability for sensing and discrimination of volatile organic compounds (VOCs) and relative humidity (RH). A graphene oxide (GO) sensing film was electrophoretically deposited on the IDE, which enabled the dual measurement: (a) capacitance changes of the IDE, and (b) changes in resonance frequency of the resonator. Experiments were conducted to record and evaluate these changes under the flow of different concentrations of typical VOCs: ethanol, acetone, ethyl acetate and water vapour (RH). A decrease in resonance frequency was observed for an increase in concentration for all tested vapours. Interestingly, IDE capacitance values were increasing for an increase in moisture concentration (RH) and decreased for an increase in VOC concentrations, even though both cases caused mass loading to the SAW device. As a result, RH changes were easily differentiated from VOC concentration changes using the IDE-integrated SAW resonator. The unique relationship between the resonance frequency shift and capacitance response also allows the proposed sensor to discriminate between typical VOCs owed to its dual-measurement capability.