PRINTED MEMS MEMBRANE ELECTROSTATIC MICROSPEAKERS. Murarka, A., Wang, A., Jean, J., Lang, J., & Bulovic, V. In 2014 Solid-State, Actuators, and Microsystems Workshop Technical Digest, pages 311–314, Hilton Head, South Carolina, USA, May, 2014. Transducer Research Foundation.
PRINTED MEMS MEMBRANE ELECTROSTATIC MICROSPEAKERS [pdf]Paper  doi  abstract   bibtex   
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.

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