Microphones remain focus of piezoelectric MEMS startup

November 02, 2018 // By Peter Clarke
Piezoelectric MEMS have been one of the big successes of recent years as exemplified by the rise of Vesper Technologies Inc. (Boston, MA) with its microphones – Chirp Microsystems with its PMUT sensor for ranging and the emergence of USound GmbH (Graz, Austria), using piezoelectric membranes for audio speakers.

eeNews Europe caught up with Vesper CEO Matt Crowley and asked about the prospects for piezoelectric MEMS and whether the time is right for his company move into adjacent markets.

Crowley pre-empted his comments by saying there was no announcement about Vesper getting into speakers and that the complexity of taking a MEMS transducer concept from technology through to product should not be underestimated. He added that it was right that Vesper, as a small company, should continue to focus on bringing MEMS microphones to market.

"We are big believers in peizoMEMS. We are one of the first [to use the technology] and now we are in mass production," Crowley said. "It is like building a skyscraper. There seems to be a lot of time spent in a big hole making the foundations but once that is done the building shoots up."

Crowley continued: "We do a have roadmap to improve the piezoelectric material. We use aluminium-nitride although we could also use alternative materials. Piezoelectric transducers do follow a scaling law. If you halve the membrane thickness you can cut the membrane area and die size in half. We continue to invest in the process to reduce the membrane thickness although at present we are using PVD [physical vapor deposition] to sputter aluminium-nitride. But other physical deposition techniques will be applied."

Crowley said that atomic layer desposition (ALD) is a more expensive process but with much better control and that should allow thinner membranes, which are typically of the order of micrometers rather than nanometers.

"We are working with Globalfoundries but at all foundries MEMS tends to use lagging process technology both in terms of lithography and deposition," Crowley said. "Aluminum-nitride is a great material and you can use dopants to change characteristics. We are sort of material agnostic. But new materials are going to help increase sensitivity."

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