Biocompatible coatings for CMUTs in a harsh, aqueous environment

The results of coating capacitive micromachined ultrasonic transducer (CMUT) arrays with two different biocompatible materials, parylene-c and polydimethylsiloxane (PDMS), are reported. These materials were characterized for use with CMUTs to enable direct contact transcutaneous and in vivo imaging. A passivation coating is required to provide electrical isolation to the active areas of the device and to protect it from a corrosive environment. It must also provide good mechanical characteristics to void imaging artifacts. The coated devices were compared side by side with uncoated devices for testing in air. The resonant frequency, collapse voltage and crosstalk were sampled. Parylene coated CMUTs were also tested underwater using pulse excitation. The parylene coating provided electrical insulation to the aqueous solution for 14 days. Both coatings showed a decrease in device resonant frequency and an increase in collapse voltage, as expected from the proposed theory.