Interconnection and Packaging for 2D Capacitive Micromachined Ultrasonic Transducer Arrays Based on Through-Wafer Trench Isolation

A new process for connecting elements of a 2D capacitive micromachined ultrasonic transducer (CMUT) array to flip-chip bond pads on the back side of the transducer array is presented. Array elements are isolated from one another by trenches etched into the highly conductive silicon substrate using deep reactive ion etching (DRIE). Gold is deposited on the back side of the array to create the flip-chip bond pads. The array is then flip-chip bonded to an integrated circuit that comprises the front-end circuitry for the transducer and provides mechanical support for the isolated array elements. Because the interconnects are fabricated after the CMUT membranes, this technique is suitable for CMUT arrays regardless of the fabrication techniques used to form the membranes.