Integrated Ultrasound Imaging Systems Based on Capacitive Micromachined Ultrasonic Transducer Arrays

Abstract

Capacitive micromachined ultrasonic transducers (CMUTs) overcome many limitations of existing ultrasound transducer technologies enabling new applications of ultrasound, especially for medical imaging and treatment. Some of the most important of these advancements are the ability to fabricate transducer arrays with two dimensional geometries and high operating frequencies. Over the past decade, extensive research has been conducted on the fabrication, characterization, and modelling of CMUTs. Current research efforts focus on the integration of CMUTs in systems for new medical imaging tools. This paper briefly reviews CMUT technology and presents imaging results from two CMUT-based imaging systems. The first system is designed for use within a 5-mm endoscopic channel and is based on a two dimensional, 16-element times 16-element, 5-MHz CMUT array. To provide a means of integrating the CMUT array with electronics, each element of the array is connected to a flip-chip bond pad on the back side of the array via a through-wafer interconnect. The array is flip-chip bonded to a custom-designed integrated circuit (IC) that comprises the frontend circuitry for the transducer elements. The array and IC are connected to an FPGA-based data acquisition system that can acquire volumetric imaging data in real time. Volumetric pulse-echo and photoacoustic images obtained with this system are presented. The second system is based on a 64-element, 20-MHz, 2-mm diameter CMUT ring array. This array is also designed for use in catheter-based imaging applications. Ring arrays have the advantage of providing space in the center for a guidewire or other catheter-based instrument. Volumetric images obtained with the ring-array system are also presented