Wafer-Bonding Fabricated CMUT Device with Parylene Coating

Area of Science:

• Materials Science
• Electrical Engineering
• Acoustics

Background:

• Capacitive micromachined ultrasound transducer (CMUT) technology has driven advances in medical ultrasound imaging.
• Standard silicon IC fabrication limits CMUT development for low-frequency underwater applications due to difficulties in creating thick membranes.
• Existing CMUT research predominantly focuses on high-frequency medical uses, neglecting low-frequency underwater potential.

Purpose of the Study:

• To propose and fabricate a novel CMUT device suitable for low-frequency underwater imaging applications.
• To overcome fabrication challenges associated with thick membrane structures in standard IC processes.
• To demonstrate the feasibility of CMUTs for underwater acoustic sensing.

Main Methods:

• Fabrication of a CMUT device featuring a 2.83-μm thick silicon membrane using silicon fusion wafer-bonding technology.
• Conformal deposition of a 5-μm thick Parylene-C layer for immersion measurement.
• Characterization of the CMUT's ultrasound transmission, reception, and pulse-echo capabilities.

Main Results:

• The fabricated CMUT successfully transmitted and received ultrasound waves, exhibiting pulse-echo measurement capability.
• The device's ultrasonic emission and reception performance improved with increasing bias voltage, independent of polarity.
• The results validate the CMUT's suitability for low-frequency applications, considering its structure, fabrication, and performance.

Conclusions:

• The developed CMUT technology shows significant potential for advancing underwater ultrasound imaging.
• Silicon fusion wafer-bonding offers a viable method for fabricating thick-membrane CMUTs for low-frequency applications.
• This research opens new avenues for CMUT utilization in diverse underwater acoustic sensing scenarios.