Microfabrication of a capacitive micromachined ultrasonic transducer (CMUT) with an internally sealed pivot

We present an unconventional capacitive micromachined ultrasonic transducer in which a vacuum-sealed cavity beneath a diaphragm layer is comprised of an internal beam that pivots and has a first rocking or rotational vibration mode and a second flapping mode of vibration. It is anticipated that the unique structure may find application in biologically-inspired ultrasound sensors that simultaneously detect omnidirectional sound pressure and pressure gradient. Vacuum sealing the cavity in which the pivoting beam resides eliminates squeeze-film damping that would otherwise cause excessive damping and/or stiffness. This paper presents scanning electron micrographs of successfully fabricated and sealed prototypes and dynamic frequency response measurements, which reveal a fundamental rocking mode of vibration at 480 kHz.