Selectable frequency CMUT with membrane stand-off structures

A capacitive micromachined ultrasound transducer (CMUT) capable of selectable-frequency operation through membrane stand-off-controlled collapse-mode operation is presented using verified finite element analysis models. One method for fabricating stand-off structures is presented. Finite element analysis (FEA) simulations were verified with respect to a CMUT fabricated at the University of Virginia Microfabrication Laboratory (UVML) with a correlation coefficient of 0.92 and an amplitude error of 4.1% when comparing the time-domain pressure output signals. Stand-off geometry was optimized using an iterative FEA approach. The optimum spans for each of the four sub-membranes as a percent of the total membrane span are 32% for the central sub-membranes and 18% for the lateral sub-membranes. The stand-off CMUT device designed to operate at both 1.5MHz and 40MHz has been shown in simulation to posses comparable bandwidth to each of two conventional, single-frequency CMUTs operating at 1.5MHz and 40MHz, respectively with comparable bandwidth and a reduction in output intensity of 4.0dB and 4.5dB, respectively.