Digital MEMS mic put on single chip

Portland, Ore. -- Even the whizziest, most cutting-edge digital systems still use microphones that are based on 50-year-old analog electret technologies. The best candidate for a successor is microelectromechanical systems, but so far analog MEMS microphones have been largely relegated to a single market: hearing aids.

Now, all that will change with the announcement this week of an all-digital MEMS microphone--the first to harness standard chip-processing techniques. The single-chip solution from Akustica Inc. offers more than digital outputs that match the digital processor and memories in PCs, PDAs, Bluetooth headsets and cell phones. It also promises to leverage the scaling power of CMOS chips to finally merge this formerly analog component with the mainstream of digital signal processing. Akustica, which is based in Pittsburgh and has 42 employees, will announce the MEMS mic at the Globalpress Electronics Summit, which starts today in Monterey, Calif.

Akustica's one-chip model AKU2000 microphone builds on five years of MEMS development of intellectual property the startup licensed from nearby Carnegie Mellon University. Its inventor is MEMS pioneer Kaigham (Ken) Gabriel, an EE professor at Carnegie Mellon who co-founded Akustica in 2001. Gabriel researched MEMS at AT&T Bell Labs and spent five years managing MEMS development as director of the Electronics Technology Office at the Defense Advanced Research Projects Agency. He now says that Akustica's first product is the first single-chip microphone in the world to use CMOS.

"We have set ourselves apart by becoming the first company to take advantage of standard CMOS processes--most other MEMS applications use chip processes that have had to be customized for that particular product," said Gabriel, who is Akustica's chairman and chief technology officer. "We are a fabless MEMS company, but our designs can use any CMOS line anywhere. Consequently, we have robustness, lots of second sources and, thus, lots of capacity."

Akustica may need that capacity--that is, if analysts are right about the size of the market it plans to serve. From cell phones to voice-over-Internet Protocol (VoIP) to PDAs and PCs, industry analysts variously forecast that the microphone market could grow to nearly 1 billion units during the next decade from at least 82 million units (mostly for hearing aids) in 2005.

For instance, Yole Development (Lyon, France) claims that the silicon microphone market was nearly 100 million units last year and will grow to 800 million units by 2010. "The winning companies deliver devices with small size and easier integration, plus they leverage the benefits of the semiconductor infrastructure in terms of manufacturing and cost structure," said Jean-Christophe Eloy, the founder of Yole Development. "Companies such as Akustica are using this model to pave the way to high-volume applications."

The only other MEMS-based microphones in the market today were designed by Knowles Electronics LLC (Itasca, Ill.) and Sonion MEMS A/S (Roskilde, Denmark). Knowles has sold more than 82 million units of its analog MEMS mic, and Steve Cullen, an independent analyst formerly with In-Stat (Scottsdale, Ariz.), said that about 8 percent of them went into high-end cell phones, a figure he predicts will rise to 20 percent this year.

But this is a two-chip solution--one chip uses a proprietary MEMS process and the other is a standard CMOS chip carrying the electronics. Knowles says it has designed a digital-output MEMS microphone that it plans to deliver later this year; it is based on the same proprietary MEMS process as its current analog MEMS microphone, plus a separate chip with the digital electronics.

Foundry proven
Akustica's single-chip solution, on the other hand, is cast entirely in standard CMOS, requiring only a single post-CMOS processing step to free up its integral microphone diaphragm. The company said the mic has already been proven out at nine foundries using 11 different design rules--everything from an in-expensive 0.6-micron process with an aluminum interconnect to a high-performance 0.18-micron process using a copper interconnect.

"Our technology can be mass-produced in extremely high volumes with the accompanying high yields and repeatability of standard CMOS semiconductor manufacturing," said Davin Yuknis, vice president of marketing at Akustica.

With the goal of hundreds of millions of units in mind, Akustica has priced its MEMS microphone at less than $4 each for 1,000 units, but prices are expected to go as low as $1.50 in high volumes. The low prices signal Akustica's aim to capture a lion's share of the near-billion-unit market looming ahead.