Piezoelectric Based MEMS Acoustic Sensor for Wide Frequency Applications

This work describes the development of an acoustic sensor based on piezoelectric
ZnO
thin film to be utilized for aero-acoustic measurements. The design of the device was carried out through
CAD
tool
Coventorware
. The backside of the device consists of the microtunnel and diaphragm structures. The
Si
-diaphragm thickness of the device was optimized for high sound pressure level
(SPL)
(upto
180 dB
) using
Coventorware
. A microtunnel connects the cavity, created after diaphragm formation to the outside environment. The designed device has been fabricated using standard
Si
-fabrication technology. Microtunnel and diaphragm structures have been fabricated in a single step using wet etching technique which results in reduced cost as well as fewer number of process steps and increased yield of the device. The front side consists of a piezoelectric sensing layer of
ZnO
sandwiched between two sputter deposited electrode layers of
Au
covered with
PECVD
oxide on a thermally oxidized
Si
-diaphragm. The low cut-off frequency, bandwidth, resonance frequency and flat band sensitivity of the device have been found to be
35.2 Hz
,
15 kHz, 78 kHz
and
136.5

$\pmb \mu $

V/Pa
respectively. The fabricated device can be used for the
SPL
measurement in aircrafts, aerospace and similar applications.