Printed MEMS membrane electrostatic microspeakers

Publication Type:



Solid-State Sensors, Actuators and Microsystems Workshop (Hilton Head), p.311-314 (2014)




We report the fabrication and operation of electrostatic microspeakers formed by contact-transfer of 125-nm-thick gold membranes over cavities
patterned in a micron-thick silicon dioxide (SiO2) layer on a conducting
substrate. Upon electrostatic actuation, the membranes deflect and produce
sound. Additionally, membrane deflection upon pneumatic actuation can be
used to monitor pressure. Our microspeaker fabrication process enables
fabrication of MEMS diaphragms without wet or deep reactive-ion etching,
thus obviating the need for etch-stops and wafer-bonding. It enables
monolithic fabrication of multiple completely-enclosed drum-like
structures with non-perforated membranes to displace air efficiently, in
both individual-transducer and phased-array geometries. The microspeaker
consumes 262 µW of real electric power under broadband actuation in free
field, and outputs 34 dB(SPL/Volt) of acoustic pressure at 10 kHz drive.
The microspeaker sound pressure level increases with frequency at 40
dB/decade. The total thickness of the microspeakers is dominated by the
silicon wafer substrate (~500 μm thick), with the active device thickness
of less than 2 µm. These thin microspeakers have potential applications in
hearing aids, headphones, and large-area phased arrays for directional
sound sources.