Micromachined capacitive transducer arrays for intravascular ultrasound imaging

We designed, fabricated, and tested ring annular capacitive micromachined ultrasonic transducer (CMUT) arrays for forward looking intravascular ultrasound (IVUS) imaging in the 10-20MHz range. Our fabrication process uses low stress plasma enhanced chemical vapor deposition (PECVD) to form the silicon nitride membrane and provides localized vacuum sealing. The CMUT fabrication requires a maximum process temperature of 250°C enabling post-CMOS CMUT fabrication for electronics integration. Electrical and acoustic characterization results show that the process is repeatable and the response of 40 × 120μm CMUT elements of a lmm diameter array are suitable for IVUS imaging around 16MHz. We also present initial volumetric imaging experiments on different targets using a 32 element CMUT-based forward looking IVUS array and synthetic aperture image reconstruction techniques.