A Dual-Frequency Capacitive Micromachined Ultrasonic Transducer (CMUT) for Vapor Detection

This study reports a novel single-chip dual-frequency (10 MHz/14 MHz) CMUT sensor that exhibits promising capabilities of vapor detection and discrimination. The CMUT is fabricated by the nitride-to-oxide wafer bonding process. Graphene oxide nanosheets are used to functionalize the device and make it sensitive to water vapors. Characterization on the electrical impedance reveals that the two resonances of the device can be easily identified with a single frequency sweep. The sensing performance of the device is analyzed by monitoring its resonance shifts as the relative humidity changes. High sensitivity and fast response/recovery have been achieved. More importantly, the sensor can generate two independent frequency responses due to its multi-resonance feature, showing great potential for discrimination of multiple chemical vapors.