Capacitive micromachined ultrasonic transducers

Abstract

Ultrasound technology is a powerful tool in medical diagnosis. While piezoelectric ultrasonic transducers are dominant on the marked at present, capacitive transducers cMUT- are being explored as a complementary technology. The cMUT is a device produced by silicon surface micromachining technology and can compete on production cost and other technical aspects. This thesis presents the design of a single element cMUT transducer, and it is shown how the design can be extended to an array. The fabrication processes is suggested. The motivation for choosing the different process steps is partly based on methods developed at NTNU [1] and make new processes to fit the same frame of work. Some of the process steps are new and not tested in this concept. The techniques are however well known from other MEMS-applications.

The first steps of analytic and numeric models are made up to describe the behavior of the transducer. The results for the mechanical modeling are consistent and give confidence to the models. It is shown how an equivalent circuit can describe the lumped model of the cMUT. The suggested method of fabrication is prepared by making a mask layout in L-Edit software.