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Open AccessArticle

Fabrication and Characterization of Capacitive Micromachined Ultrasonic Transducers with Low-Temperature Wafer Direct Bonding

by Xiaoqing Wang 1,2, Yude Yu 1,2,* and Jin Ning 2,3
1
State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Engineering Research Center for Semiconductor Integrated Technology, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Academic Editor: Marc Desmulliez
Micromachines 2016, 7(12), 226; https://doi.org/10.3390/mi7120226
Received: 31 October 2016 / Revised: 6 December 2016 / Accepted: 6 December 2016 / Published: 11 December 2016
This paper presents a fabrication method of capacitive micromachined ultrasonic transducers (CMUTs) by wafer direct bonding, which utilizes both the wet chemical and O2plasma activation processes to decrease the bonding temperature to 400 °C. Two key surface properties, the contact angle and surface roughness, are studied in relation to the activation processes, respectively. By optimizing the surface activation parameters, a surface roughness of 0.274 nm and a contact angle of 0° are achieved. The infrared images and static deflection of devices are assessed to prove the good bonding effect. CMUTs having silicon membranes with a radius of 60 μm and a thickness of 2 μm are fabricated. Device properties have been characterized by electrical and acoustic measurements to verify their functionality and thus to validate this low-temperature process. A resonant frequency of 2.06 MHz is obtained by the frequency response measurements. The electrical insertion loss and acoustic signal have been evaluated. This study demonstrates that the CMUT devices can be fabricated by low-temperature wafer direct bonding, which makes it possible to integrate them directly on top of integrated circuit (IC) substrates. View Full-Text
Keywords: capacitive micromachined ultrasonic transducers (CMUTs); low temperature wafer direct bonding; contact angle; surface roughness capacitive micromachined ultrasonic transducers (CMUTs); low temperature wafer direct bonding; contact angle; surface roughness
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Wang, X.; Yu, Y.; Ning, J. Fabrication and Characterization of Capacitive Micromachined Ultrasonic Transducers with Low-Temperature Wafer Direct Bonding. Micromachines 2016, 7, 226.

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