MEMS makeover consumer electronics apps

Motion sensing technologies for mobile and gaming devices come in a variety of flavors, ranging from IR sensors and inertial sensors to combo devices that integrate accelerometers and gyros. Thanks to the Nintendo Wii and Apple iPhone—and the limitless imagination of designers—motion sensing technologies are enabling a host of novel applications.

Yet, there is still a lack of traction for MEMS sensors in mainstream apps.

Move to mainstream
Marlene Bourne, president and principal analyst at Bourne Research, believes technical innovation is no longer enough, nor is small size or low price. She said MEMS suppliers have demonstrated all three, but the most important question is still looming: Where's the value-add? "The early adopters will integrate MEMS sensors into their products, but they're not the mass market. And movement into the mainstream is what will ultimately drive the growth of MEMS sensors. But I don't see that happening anytime soon," said Bourne.

And there is still work to be done to leverage the technology's capabilities.

The Loop TV remote has two buttons and a scroll wheel that uses a Freespace in-air inertial sensor for 3D pointing.

As an example, Sony's Sixaxis controller uses an inertial measurement unit, which combines an accelerometer with a gyro for six-degrees-of-freedom movement, but Bourne argues that since the controller is still a wing design, it does not take full advantage of MEMS sensing capabilities, as the Wii does.

There is also competition from lower-end phones using software like that from GestureTek, which replicates the interactive experience of a MEMS accelerometer. "This is easier, faster and less expensive to integrate into a cellphone than a sensor. So just because a cellphone has screen orientation or interactive gaming, don't assume that a MEMS sensor is behind it," said Bourne.

"The accelerometer will be the enabler for a lot more user interface functions that will be the standard in the future. With a certain motion, you can achieve many types of detection within a few seconds, whether it's by shaking the device in one direction or another, or by tapping the device," said Michelle Kelsey, marketing manager for inertial sensors at Freescale Semiconductor Inc.

Designers of portable devices are always trying to add more features without increasing size, so when it comes to sensors, they are looking for a number of things—fast response, low current consumption and low voltage operation—all in a tiny package.

In addition, designers are looking for higher sensitivity for motion applications, better temperature compensation offset, and more intelligence in the sensor, such as for threshold detection and click or pulse detection, Kelsey said.

Designers also want quick power-on response time and a sleep-mode option, to turn off the accelerometer when motion detection is not needed, said Kelsey.

Small is big
Some of the latest triple-axis accelerometers are ultrasmall for consumer electronics products and suitable for applications such as gaming, HDD protection and security. Some feature quick power-up, zero-g detect for free-fall protection and a self-test function.

STMicroelectronics NV introduced a new generation of "nano" three-axis linear accelerometers last year. The LIS331 family of low-power MEMS sensors provides embedded smart features for miniaturized motion sensing solutions in consumer and industrial applications.

The ST three-axis motion sensors are said to represent a significant step forward in the product's miniaturization. Housed in a 3mm x 3mm x 0.9mm plastic package, the LIS331 accelerometers also deliver very high immunity to vibration and shock survivability up to 10,000g. The "nano" motion sensors are suitable for a wide range of low-g applications.

Freescale's MMA7455L low-g three-axis digital accelerometer features I2C and SPI interfaces.

Freescale also beefed up its MEMS sensor line last year with the introduction of a three-axis digital-output accelerometer that is 77 percent smaller than previous offerings. The device eliminates the need for an ADC and external memory. The company said the MMA7450L is the thinnest available in a 0.8mm thin plastic land grid array.

Analog Devices Inc. also plans to announce its follow-on to the ADXL330 three-axis accelerometer, used in the Wii remote. ADI promises that its next accelerometer will deliver improved performance, low power and lower cost.

Dual-axis devices
InvenSense offers its IDG-1100 dual-axis gyroscopes in a 4mm x 5mm x 1.2mm package. The devices integrate MEMS resonating structures and CMOS electronics at the silicon wafer level. The IDG-1100 gyroscopes are 25 percent smaller than competing products, InvenSense said.

The IDG-1100 targets cost-sensitive and size-constrained portable consumer applications such as digicams and camcorders for image and video stabilization, portable navigation devices for dead reckoning when GPS signals are lost or corrupted, and 3D motion sensing devices such as air mice and A/V remote controls for TV and multimedia centers and game controllers.

Another technology for air mice is an in-air inertial sensor technology for 3D pointing that incorporates a MEMS sensor, DSP and logic. Hillcrest Labs' Freespace technology, while targeting the market for TV remote controls and game controllers, has been designed into Logitech's MX Air rechargeable cordless air mouse for PCs.

This technology is designed to be position-independent or orientation-free. "Even if you turn the device upside down in your hand, if you go left, the cursor will still move left," said Chuck Gritton, chief technology officer for Hillcrest Labs.

Once you move into the GPS space, expect higher complexity—and higher cost. GPS is benefiting from one of the most complex MEMS sensing clusters to date: magnetic compasses. "These not only combine an accelerometer and gyro, but a MEMS magnetic sensor, and more recently, a MEMS pressure sensor as well," said Bourne. "Only a few of the very high-end models have this, and while manufacturers like the dead-reckoning/directional capability, they consider the sensing module too expensive for mass use anytime soon."

Bourne believes the integration of GPS into handsets could be what will really drive the growth of MEMS sensors in cellphones, but that the cost will limit use to a few high-end models for the foreseeable future.

- Gina Roos
eeProductCenter