A wafer bonded capacitive micromachined underwater transducer

In this work we have designed, fabricated and tested CMUTs as underwater transducers. Single CMUT membranes with different diameters and 380 microns of thickness are fabricated for the demonstration of an underwater CMUT element. The active area of the transducer is fabricated on top of a 3” silicon wafer. The silicon wafer is bonded to a gold electrode coated glass substrate wafer with 10cm in diameter. Thermally grown silicon oxide layer is used as the insulation layer between membrane and substrate electrodes. Electrical contacts and insulation are achieved using epoxy layers. Single CMUT elements are tested in air and in water. Approximately 40% bandwidth is achieved around 25 KHz with a single CMUT cell.