Design, Fabrication and Testing of Surface Micromachined CMUTs for Surface and Interface Waves

Abstract

Interdigital CMUTs weredesigned and fabricated in transmit/receive pairs. Each transmitter or receiverhas 20 double-phase finger pairs with 146 micrometer pitch and 3 millimeter aperture.The wave transmission distance between the receiver and transmitter is 9millimeters. Devices were fabricated on the highly doped silicon wafers by thesurface micromachining technology using silicon nitride as the structuralmaterial and chromium as the sacrificial material. Interface (Scholte type)waves were transmitted and received at 100 V bias and 10 V pp 10 MHz 20 periodharmonic burst excitation. The wave propagation velocity in water andisopropanol were measured by the time-of-flight and spectral analysis methods.The last gave 1376 m/s and 1157 m/s phase velocity of the Scholte waves for water andisopropanol, correspondingly. At the same time, CMUT structural resonance inimmersion was 8.9 MHz for water and 9.3 MHz for isopropanol. This led to theconclusion about better informativity of the Scholte type waves.

DOI: http://dx.doi.org/10.5755/j01.eie.22.5.7123