Capacitive Micromachined Ultrasonic Transducer Packaging for Forward-looking Ultrasonic Endoscope using Low Temperature Co-fired Ceramic Side Via

Abstract

This paper reports part of a novel packaging method for a capacitive micromachined ultrasonic transducer (CMUT) based ultrasonic endoscope using low temperature co-fired ceramic (LTCC) side via architecture. An annular ring array CMUT device is designed and fabricated for packaging. LTCC is used as a prime wafer for CMUT fabrication and LTCC side via structure is achieved by hexagonal shape dicing of the fabricated CMUT device. A hexagonal shaped polyimide substrate mounted at the backside of the CMUT is used as a base layer for IC integration (flip-chip bonding) and also provides mechanical support to the CMUT. Cr/Au electrodes were patterned on the LTCC side via and polyimide substrate to achieve electrical connection between CMUT arrays and IC circuits. Au bonding pads were successfully completed on the polyimide substrate by electroplating for flip-chip bonding. Flip-chip mounting on the polyimide substrate is described and the electrical resistance of bumps is measured using the 4-probe method. The difference between the measured and calculated resistance is discussed. This method with the indirect connection of CMUT arrays and IC circuits has flexibility for high performance tube-shaped CMUT packaging with small diameters for intravascular imaging.