6F-3 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 3D 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 360deg 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 mum 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 multi- direction viewing capability and miniature size make this device capable of delivering more comprehensive information for internal medical imaging applications.