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 V_pp 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.