Silicon-On-Nothing ScAlN pMUTs

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Silicon-On-Nothing ScAlN pMUTs
Silicon-On-Nothing ScAlN pMUTs
Journal Title:
2021 IEEE International Ultrasonics Symposium (IUS)
Publication Date:
13 November 2021
Choong, D. S. W., Chen, D. S.-H., Goh, D. J., Liu, J., Ghosh, S., Koh, Y., Sharma, J., Merugu, S., Quaglia, F., Ferrera, M., Savoia, A. S., & Ng, E. J. (2021). Silicon-On-Nothing ScAlN pMUTs. 2021 IEEE International Ultrasonics Symposium (IUS).
This work presents a promising microfabrication technique employing the silicon-on-nothing (SON) process to form a 2 μm thick continuous monocrystalline silicon membrane over a vacuum cavity of 1 μm in depth. Utilizing the SON process, high fill-factor piezoelectric micromachined ultrasonic transducer (pMUT) arrays on an 8-inch silicon wafer with cavity widths ranging from 170 μm down to 38 μm have been demonstrated. Devices are designed with 15% scandium-doped aluminum nitride as the piezoelectric layer of the pMUT for both air-coupled and water-coupled applications. The air-coupled pMUTs show a peak displacement frequency from 0.8 to 1.6 MHz with a Q-factor between 120 to 194. The water-coupled pMUT arrays show a transmit pressure measured by a needle hydrophone, in DI water at a distance of 20 mm, ranging between 0.4 to 6.9 kPa/V with peak frequency between 5 to 13.4 MHz and fractional bandwidth 56 to 36%, respectively. The piezoelectric-over-SON process proposed here has the potential to gain traction in low-cost and high-yield pMUT manufacturing.
License type:
Publisher Copyright
Funding Info:
This research / project is supported by the A*STAR - IAF-ICP - Piezo Specialty Lab-in-a-Fab
Grant Reference no. : I1901E0050

This research / project is supported by the A*STAR - Programmatic - Nanosystems at the Edge
Grant Reference no. : A18A4b0055
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