Page 9 - Spring 2009

Fig 8. Ray Stata presents operational amplifiers. (Source: Analog Devices)
to be developed as potential breakthrough products. In the mid–1980’s, some ADI engineers began to explore a new technology called MEMS. By 1989 working prototypes of MEMS accelerometers were demonstrated and significant funding was identified to further explore the technology and develop a product for the market.
The core element of a typical MEMS accelerometer is a moving beam “proof mass” structure. This element is typically comprised of two sets of fingers; one set fixed to a solid ground plane on a substrate and the other set attached to a known mass mounted on springs that can move in response to an applied acceleration. Under acceleration there is a change in capaci-
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tics can be created using this flexible technology.
While the full potential of the market opportunity for MEMS accelerometers was not fully clear in the late 1980’s, the market for automotive accelerometers for airbag deploy- ment was identified as one of the most promising opportuni- ties. The incumbent technology used at the time was a ball and tube sensor16 which was a relatively large and expensive solution. In the period from 1991 to 1997, with significant investment two of ADI’s accelerometers were released and began to successfully penetrate the automotive market for airbag deployment. The small size and relatively low cost of MEMS accelerometers helped to fuel the broad adoption of
airbags as standard features in all automobiles.
However, while MEMS was achieving recognition and suc-
cess in the marketplace, there were challenges associated with developing a high yielding stable manufacturing infrastructure
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tance sensed between the fixed and moving beam fingers.
The dimensions of these MEMS structures are in the order of microns, requiring very high precision silicon pho- tolithography and etching process technologies. These devices also need very low-noise electronic circuits to read out extremely small changes in capacitance (in the order of femtofarads). MEMS structures are typically formed from single crystal silicon or from polysilicon deposited at very high temperatures on the surface of a single crystal silicon wafer. Structures with very different mechanical characteris-
stepping in as the acting General Manager of the MEMS divi- sion and leading the business through a critical stage of its
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During this critical period Ray Stata played a key role as the senior management advocate for the technolo- gy. From 1997 to 2000 Mr. Stata championed MEMS at ADI by
A brief history of the evolution of MEMS microphones
Pressure sensors are the earliest example of commercial success of silicon micromachining dating back to the 1960’s and 1970’s. In 1982 Peterson19 comprehensively described the status of micromachining technology in his paper “Silicon as a Mechanical Material.” There was no specific mention of the use of the technology to produce microphones.
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for the technology.
Today, ADI is recognized as one of the leaders in MEMS accelerometers and gyroscopes with products in a broad range of areas, including automotive, industrial and con- sumer markets (see Fig. 9). Who could have imagined that this core MEMS technology designed specifically for air bag deployment in automobiles would find ubiquitous use as a breakthrough enabling technology for the Nintendo Wii? Building on this strong foundation in inertial sensors and on the core business of converters and amplifiers ADI has recently announced a range of high performance MEMS microphones.
development.
described a micro machined silicon microphone based on the piezoelectric effect. The sensing ele- ment was a deflectable diaphragm composed of silicon and zinc
In 1983 Royer et al.
Fig 7. Matt Lorber and Ray Stata circa 1965. (Source: Analog Devices)
Fig 9. ADXL50 MEMS Accelerometer Structure. (Source: Analog Devices)
8 Acoustics Today, April 2009