Two-dimensional capacitive micromachined ultrasonic transducer (CMUT) arrays for a miniature integrated volumetric ultrasonic imaging system

Xuefeng Zhuang; Ira O. Wygant; David T. Yeh; Amin Nikoozadeh; Omer Oralkan; Arif S. Ergun; Ching-Hsiang Cheng; Yongli Huang; Goksen G. Yaralioglu; Butrus T. Khuri-Yakub

doi:10.1117/12.594702

12 April 2005 Two-dimensional capacitive micromachined ultrasonic transducer (CMUT) arrays for a miniature integrated volumetric ultrasonic imaging system

Xuefeng Zhuang, Ira O. Wygant, David T. Yeh, Amin Nikoozadeh, Omer Oralkan, Arif S. Ergun, Ching-Hsiang Cheng, Yongli Huang, Goksen G. Yaralioglu, Butrus T. Khuri-Yakub

Author Affiliations +

Proceedings Volume 5750, Medical Imaging 2005: Ultrasonic Imaging and Signal Processing; (2005) https://doi.org/10.1117/12.594702
Event: Medical Imaging, 2005, San Diego, California, United States

Abstract

We have designed, fabricated, and characterized two-dimensional 16x16-element capacitive micromachined ultrasonic transducer (CMUT) arrays. The CMUT array elements have a 250-μm pitch, and when tested in immersion, have a 5 MHz center frequency and 99% fractional bandwidth. The fabrication process is based on standard silicon micromachining techniques and therefore has the advantages of high yield, low cost, and ease of integration. The transducers have a Si3N4 membrane and are fabricated on a 400-μm thick silicon substrate. A low parasitic capacitance through-wafer via connects each CMUT element to a flip-chip bond pad on the back side of the wafer. Each through wafer via is 20 μm in diameter and 400 μm deep. The interconnects form metal-insulator-semiconductor (MIS) junctions with the surrounding high-resistivity silicon substrate to establish isolation and to reduce parasitic capacitance. Each through-wafer via has less than 0.06 pF of parasitic capacitance. We have investigated a Au-In flip-chip bonding process to connect the 2D CMUT array to a custom integrated circuit (IC) with transmit and receive electronics. To develop this process, we fabricated fanout structures on silicon, and flip-chip bonded these test dies to a flat surface coated with gold. The average series resistance per bump is about 3 Ohms, and 100% yield is obtained for a total of 30 bumps.

Citation Download Citation

Xuefeng Zhuang, Ira O. Wygant, David T. Yeh, Amin Nikoozadeh, Omer Oralkan, Arif S. Ergun, Ching-Hsiang Cheng, Yongli Huang, Goksen G. Yaralioglu, and Butrus T. Khuri-Yakub "Two-dimensional capacitive micromachined ultrasonic transducer (CMUT) arrays for a miniature integrated volumetric ultrasonic imaging system", Proc. SPIE 5750, Medical Imaging 2005: Ultrasonic Imaging and Signal Processing, (12 April 2005); https://doi.org/10.1117/12.594702

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