Micromachined piezoelectric ultrasonic transducer based on dome-shaped diaphragm supported by flat square diaphragm

This paper reports a microfabricated ultrasonic transducer based on a piezoelectrically actuated dome-shaped diaphragm supported at the center of a flat square diaphragm. The dome-shaped diaphragm is fabricated by silicon isotropic wet etching while the whole diaphragm including the flat square diaphragm is released by KOH etching with a novel dicing-based front-to-back alignment method. Shadow masks are used for patterned film depositions on 3D dome diaphragm. With 30 Vpp drive voltage, the transducer produces sound pressure level (SPL) as high as 88.21 dB between 10 and 40 kHz when measured at 5 mm away in an open field. The linearity of the sound output as a function of input voltage is measured to be very good. In addition, post-process laser cutting was utilized to form a cantilever-like diaphragm structure, which boosted the maximum SPL to 95.12 dB without degrading the linearity.