Silicon-On-Nothing ScAlN pMUTs

Silicon-On-Nothing ScAlN pMUTs

2021 IEEE International Ultrasonics Symposium (IUS)

10.1109/IUS52206.2021.9593461

http://dx.doi.org/10.1109/ius52206.2021.9593461

David Sze Wai Choong, Daniel Ssu-Han Chen, Duan Jian Goh, Jihang Liu, Sagnik Ghosh, Yul Koh, Jaibir Sharma, Srinivas Merugu, Fabio Quaglia, Marco Ferrera, Alessandro Stuart Savoia, Eldwin Jiaqiang Ng

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). https://doi.org/10.1109/ius52206.2021.9593461

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.

Publisher Copyright

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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Institute of Microelectronics