A first experimental verification of micromachined capacitive Lamb wave transducers

Capacitive Micromachined Ultrasonic Transducers (cMUTs) are generally used to transmit and receive ultrasound in both air and water. These devices can be made on silicon and manufactured using standard CMOS processing techniques. When cMUTs are used in this way, significant effort is made to minimize energy loss into the substrate. If this loss is instead exploited so that the devices are optimized to couple energy into the silicon bulk, Lamb waves and Rayleigh waves are generated with high efficiency. These waves can then be detected using a similar device structure. With this method it is possible to fabricate Lamb wave devices on silicon using conventional integrated circuit processing techniques. This paper discusses the manufacturing and characterization of the first of these devices: a 1 MHz Lamb wave transducer that is fundamentally based on cMUT technology. The characterization of this device demonstrates that the energy coupled into the substrate results in a Lamb Wave where the lowest order anti-symmetric mode (A/sub 0/) is dominant. The insertion loss of this device in air is 43.06 dB.