The bottom of this cavity is an
insulation layer which can ensure electrical insulation
between the top and bottom electrodes, and prevent
short circuiting caused by the occasional engagement
of the top and bottom electrode; the top of the cavity
is the integration membrane made by SOI top silicon.
When the sensor is operating in water, in order to
avoid the hydrolysis caused by a strong electric field
in the cavity, the vibration must be a vacuum-sealed
cavity. The top and bottom electrodes are deposited
on the membrane and substrate respectively.
Meanwhile, a MEMS capacitive ultrasonic transducer
is composed of many cells which are connected
parallel and distributed in a certain order