Design, fabrication and testing of surface micromachined CMUTs for surface and interface waves

Interdigital CMUTs were designed andfabricated in transmit/receive pairs. Each transmitter or receiver has 20 double-phase finger pairs with 146 micrometer pitch and 3 millimeter aperture. The wave transmission distance between the receiver and transmitter is 9 millimeters. Devices were fabricated on the highly doped silicon wafers by the surface micromachining technology using silicon nitride as the structural material and chromium as the sacrificial material. Interface (Scholte type) waves were transmitted and received at 100 V bias and 10 V pp 10 MHz single period harmonic burst excitation. The wave propagation velocity in water and isopropanol were measured by the spectral analysis methods. It gave us 1380 m/s and 1125 m/s phase velocity of the Scholte waves for water and isopropanol, correspondingly. We explain these reference values as specific to the measurement conditions, which are specific to our measurement conditions and particular CMUT assembly with the microchannel. Index Terms--Acoustic transducers; microfluidics; microelectromechanical devices.