Capacitive Micromachined Transducers

Capacitive micromachined transducers can be easily manufactured in the form of 1-D and 2-D arrays. A typical 2-D transducer array element consists of 72 small silicon nitride membranes suspended over the silicon substrate. The membranes are electrically connected in parallel with an aluminum layer. Each small membrane has a diameter of 36 microns and the membrane thickness is around 0.5micron. Each array element is electrically connected to the backside of the wafer by a through wafer via (seen as the big dark circular region) coated with conductive polysilicon layer. Another wafer containing the signal processing electronics can be easily bonded to the transducer wafer on the backside for electronics integration. Electrical testing of the through wafer vias indicate a 7 Ohm series resistance and a parasitic capacitance down to 2 pF. The transducers are also tested acoustically and they are able to generate displacements of 6 Anstrom/V and detect displacements of 0.18 fm/rt(Hz) around 3 MHz with a non-optimized amplifier. Since capacitive transducers are not resonant devices in immersion, they have a very broadband response. As a transmitter the same transducer generates a constant pressure output up to more than 10MHz whereas the receiver bandwidth and frequency is determined by the electrical termination.

Contact Information

Contributor’s name: B.T. Khuri-Yakub
Institution: Stanford University
Telephone: (650) 723-0718