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Pitch-and-yaw MEMS gyro readies for Wii

Posted: 05 May 2009 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS? gyroscope? pitch and yaw MEMS? Wii console?

InvenSense Inc. has launched what is claimed to be the first pitch-and-yaw MEMS gyroscope, that is able to sense the two axes used by remote controls and baton-shaped game controllers like the Wii, creating a new category of 3D motion sensor.

The MEMS gyro chip will be used in the upcoming Wii MotionPlayer accessory.

At least two chips, one mounted in-plane and one mounted vertically, are required to create a pitch-and-yaw sensor, but InvenSense said its ring-shaped mechanical beam enables a completely planar MEMS chip to sense both motions used in Wii-like controllers.

"If you think about what motions you use with a remote control, it's up and down and side to side, which is pitch and yaw. You never roll your wrists in this application, but all the other MEMS gyros are pitch and roll," claimed Joe Virginia, marketing director at InvenSense.

A ring-shaped, two-axis gyro measures two perpendicular directions of angular momentum, unlike an accelerometer that measures its incline.

Typical interface functions controlled by gyros include single-handed scrolling through selections activated by waving a remote to highlight the desired setting, then select it with a sideways motion. A wide variety of more complex hand movements can be programmed for gyros that are impossible for accelerometers, enabling cursor control and menu selection functions that might take a dozen mouse clicks.

"For a MEMS solution to replace an incumbent technology, its either got to be lower priced or its got to do something that has never been done before," said Karen Lightman, managing director of the MEMS Industry Group. InvenSense "is doing something that has never been done before."

The InvenSense MEMS chip uses a cost-saving wafer-scale bonding method during fabrication that was invented by its founder, MEMS pioneer Steve Nasiri. The six-mask bulk silicon fabrication process mounts the MEMS element on one wafer and bonds it on top of a CMOS wafer. The wafer holds its interface electronics, in the process making over 100,000 electrical interconnections between the wafers.

The technique eliminates the need for an additional encapsulating structure for the MEMS elementneeded to protect its moving mechanical parts from contaminationby using the inverted ASIC wafer as its cap. The proprietary eutectic bonding process used to seal the MEMS utilizes aluminum from the CMOS wafer to create a hermetic seal on thousands of MEMS gyros simultaneously.

Wafer-scale bonding, bulk silicon processing and volume orders have been driving down the cost of the InvenSense gyro chips, allowing them to be used in commercial applications like the forthcoming Wii MotionPlus accessory from Nintendo. The Wii accessory uses a pitch-and-roll gyro from InvenSense, combined with other sensors to create the first six-axis motion processing device for consumer applications.

Wii currently uses an accelerometer to sense the tilt of the controller, an unnatural motion to which gamers must adapt. But a gyro senses the natural angular momentum of the arm as it waves the controller up and down and back and forth. Each set of motions have a separate output from the InvenSense chip.

InvenSense's big design win with Nintendo for the Wii MotionPlus plus other design wins in image stabilization for point-and-shoot cameras have driven the cost of its dual-axis gyros down to less than $2 per axis. By comparison, Freescale introduced a three-axis accelerometer this week that cost $1.39 in quantities of 10,000.

The IXZ-500 and IXZ-650 dual-axis MEMS gyroscopes are packaged in a 4mm x 5mm x 1.2mm package with +/-2,000 degrees per second of primary output, the company said.

- R. Colin Johnson
EE Times





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