Fabrication and assembly of a monolithic 3D CMUT array for Imaging applications

This paper describes a novel architecture for integration of polysilicon capacitive micromachined ultrasonic imager array on a 31) hexagonal silicon platform for simultaneous multi-directional viewing. Integrated with seven CMUT arrays oriented at seven different directions, this three-dimensional hexagonal imager prism is capable of viewing the front direction and 360 degrees side directions concurrently. The seven CMUT-array plates were monolithically fabricated on one silicon substrate using a surface micromachining process. The silicon substrate under the connection areas between the imager plates was then completely etched away using a selective backside deep silicon etching, leaving behind flexible dielectric films for inter-plate connection. In addition to providing mechanical linkage, these dielectric connecting films also support the thin-film electrical interconnects between the imagers on different plates. The seven CMUT arrays were then folded into a miniature prism and glued together using epoxy. Hexagonal imager prisms with width across corner of the hexagon, ranging from 500 mu m to 4 millimeters in width, and 2 to 4 millimeters in length have been prototyped and tested. The CMUT devices behaved consistently before and after the assembly process. This architecture allows one monolithically integrated or flip-chip bonded beam-forming circuit to control all the imagers on this miniature prism and the number of bonding wires can be minimized. The multidirection viewing capability and miniature size make this device capable of delivering more comprehensive information for internal medical imaging applications.