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CMOS MEMS: Revolution in Semiconductor Design

The proprietary fabrication processes required for most MEMS devices have limited the growth of traditional MEMS technologies. In contrast, CMOS MEMS, a new approach to building MEMS structures directly inside standard CMOS semiconductor materials, represents a breakthrough in monolithic devices.

Akustica’s CMOS MEMS structures are fabricated from the metal-dielectric layers of the CMOS which are deposited during the standard CMOS processing flow. This contrasts sharply with other MEMS technologies, which are fabricated in films on top of CMOS, making them only CMOS-compatible. Our approach, therefore, enables system engineers to integrate multiple sensors and associated electronics into one common platform, rather than compelling them to build each circuit discretely with a variety of process technologies and packages. Sensors on a single CMOS MEMS die share the same silicon substrate and are intimately connected on chip, which makes their combined performance greater than the sum of their individual performance.

To date, MEMS development strategies that require custom and captive MEMS fabrications process have been the norm. Commercial successes such as Texas Instruments’ Digital Light Processor, for example—have required significant funding, effort and time to bring to market. In order to accelerate and proliferate the commercialization of MEMS, alternative development strategies are needed. This is especially true in consumer electronics, a broad market area ideally suited to small, volume-priced programmable devices that provide intelligence—application and system-level functionality—and sensing in the same device.

Times have changed, however, bringing some good news for designers. CMOS MEMS’ ability to integrate mechanical devices and signal processing on a single chip opens up new doors to smart sensors anywhere and everywhere, including the consumer electronics market.

CMOS MEMS chips soon will become as commonplace as standard CMOS devices. Thanks to widespread CMOS models and simulation tools, they certainly will be as familiar and as easy to use. Leveraging economies of scale, high quality and maturity of the semiconductor industry, CMOS MEMS will offer a cost-effective solution that goes from design to prototype in a matter of weeks.

Dr. Henning Wicht of WTC, an industry research firm specializing in MEMS, predicts that microphones, memory, micro-energy sources and chip coolers are just some of the applications we should see very soon.

Indeed, CMOS MEMS microphones will be among Akustica’s first products. We soon expect MEMS microphones to replace standard Electret Condenser Microphones (ECMs)—a decades-old technology. Akustica will be able to produce microphones with better than four times the uniformity of ECMs, considered ideal for cost-effective microphone array applications in which better-matched microphones improve beam forming and noise cancellation.

Because these microphones are made using standard CMOS technology, new microphone design times align with the rapid design cycles of the consumer-electronics industry in such applications as notebook PCs, mobile phones and digital media systems.

Microphones are only one possibility. CMOS MEMS will enable single-chip integration of all kinds of electro-mechanical sensor structures with analog and digital signal processing functions to produce acoustic, inertial and RF systems on chip. As a result, countless electronic products will be able to hear, speak and sense the world around them.

About the Author

Ken Gabriel is founder and chief technology officer of Akustica, Inc.www.akustica.comin Pittsburgh, PA. He has been recognized by Forbes magazine as a pioneer and leading architect of MEMS technology. Contact him at kgabriel@akustica.com.

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