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MEMS find place GPS, mobile apps

Posted: 04 Jun 2009 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS? sensor? accelerometer? barometer? GPS?

MEMS accelerometers were introduced as devices that sense when hard drives are being dropped and warn them to lock up their heads. Now come the MEMS barometers that are being pitched as a means to increase disk storage capacity. And the MEMS sensor count is rising in scores of products beyond hard drives. The MEMS sensor count is rising in scores of products beyond hard drives.

MEMS sensors are increasingly being integrated into phones, MP3 players, GPS units, mobile Internet devices (MIDs), portable medical scanners and all sorts of greentech products. Indeed, thanks to the pickup in design-ins for MEMS-based motion, elevation and proximity sensors, the sensor market is standing up to the recession, according to some market watchers.

"Sensors are one of few businesses still growing in 200918 percent, according to analysts," said Demetre Kondylis, VP and general manager of Freescale's sensor and actuator solutions division. "We see acceleration, pressure and proximity sensors for consumer electronics as the next high-volume [sensor] market, after automotive."

Freescale had already sold millions of MEMS accelerometers as airbag sensors in high-reliability automotive applications before it entered the consumer electronics market a few years ago with accelerometers for hard drives that can lock up their heads when dropped. Now the company is hawking a companion digital barometric pressure sensor that it says will let hard drive makers optimize head flying heights for maximum information density. The digital pressure sensor debuted June 2 at the Computex expo in Taipei, Taiwan.

"A hard disk can increase its storage capacity by 200 percent by lowering the slider's flight height from 10- to 7nm," said Wayne Chavez, consumer and industrial operations manager of Freescale's sensor and actuator division. "Using our barometric pressure sensor to measure air density, hard disk drive makers can reliably lower slider flight height to 5nm, which increases storage capacity by four times."

Without a measure of air density, hard drive heads can't run at minimum flight height without failing when barometric pressure changes dramatically, such as onboard an airborne plane. Beyond their use in hard drives, barometric pressure sensors can enhance the performance of other consumer devicesfor example, by allowing GPS navigators to dead-reckon inside buildings or when entering tunnels.

Eventually, accelerometers, barometric pressure sensors and possibly other MEMS sensors as well could be integrated into the same package. Today the MEMS element for an accelerometer or a pressure sensor is on a separate chip that's wire bonded to a CMOS die holding the signal conditioning circuitry on an application-specific IC. But in a combo sensor package, a single ASIC could easily serve both an accelerometer and a barometric pressure MEMS elementthat is, if enough consumer electronics devices start integrating both.

"At Freescale, we believe that the day will come when multiple sensors are housed in the same package," said Kondylis. "Consumer electronic device makers are already asking us to look at integrating these capabilities."

Besides measuring air density in hard drives and providing altitude information for GPS units, Freescale's digital pressure sensor is aimed at environmental sensing applications, safety and security sensing of ambient pressure, and health monitoring.

"A novel application one of our customers is working on is a bandage that uses pressure readings to monitor suction, to improve the healing process for deep wounds," said Chavez.

Freescale claims its MPL115A digital barometric pressure sensor consumes 100 times less energy than other solutions5?A while making one measurement per minute and just 1?A in sleep mode. Digital interconnections are made using either an SPI or I?C interface.

- R. Colin Johnson
EE Times

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