Racing for the MEMS stack


Just ahead of Apple’s launch of the iPhone 4, Carmelo Papa, general manager of STMicroelectronics’ industrial and multisegment sector, was bullish about a new market for the company. He declared that this year would be the dawn of the ‘era of the gyroscope’.

A few days later, Apple CEO Steve Jobs was demonstrating what the combination of an accelerometer and three-axis gyroscope could do in a mobile handset. ST made its own video for the company’s Field Trip, a series of presentations to financial analysts, to show how the gyro and accelerometer combination could be used to navigate through the streets of Venice - using dead reckoning where the signals from GPS satellites cannot be easily seen in narrow streets.

As ST is the only vendor claiming to make an integrated three-axis gyroscope, this is the one that is suspected to be inside the iPhone 4. Teardown experts such as Chipworks and TechInsights believe die markings confirm ST as the manufacturer.

Benedetto Vigna, head of ST’s MEMS division, claimed that the market for gyros in consumer will be three times bigger than that for similar sensors in automotive – where they are more widely used today for stabilisation control – by 2014.

Although the initial demonstrations revolve around games, Vigna said dead-reckoning calculations can make it possible to pinpoint a user’s location inside buildings such as shops and museums, narrowing location-based information to a rack of clothes or a museum exhibit.

Although it does not need all three axes, optical image stabilisation is another use for cameras and phones. Papa said applications for the MEMS gyro can go further, including vibration control in washing machines. “The potential market is huge,” he said.

According to Benedetto Vigna, the decision to make a three-axis gyro was taken quite late in the day in an indication of how integration and fast turnaround are becoming crucial in getting MEMS into high-volume consumer designs. “By the end of last year, we understood that the market was willing to move faster,” said, explaining that the company had been working on a two-axis design.

“On the 21st October, we put the first transistors on the layout. And you are now holding the product,” he said as he handed out tiny 4x4mm packages. “Because of the nimbleness of the team we now have a three-axis gyroscope.”

ST’s aim is to integrate the gyro and accelerometer and other sensors together with analogue processing using a stack of chips. The MEMS can potentially all go on the same die, with the analogue and ultimately microcontroller going underneath in a multichip package.

In contrast to ST, Freescale is in no hurry to develop consumer-level gyroscopes. ST’s Papa claimed his company will see $100m in revenue from its gyroscope MEMS products by the end of this year, with practically zero in sales at the start of this year. Gervais-Ducouret conceded a few million gyroscopes will sell this year but is not expecting such as quick take-off. Freescale is looking to 2012 as the time “we think there will be a booming in terms of the market for gyroscopes,” he added.

“We have been focusing so far on gyroscopes for automotive,” said Stéphane Gervais-Ducouret, director of global marketing for sensors in the consumer market segment of Freescale, adding that power consumption is an issue for this kind of sensor.

Typically, automotive-grade gyroscopes consume more than 10mA per channel but have the benefit of running from a bigger power source. “If you look at the mobile phone, you are looking for less than 1mA,” he said. ST’s current gyro consumes around 2mA per channel.

Where Freescale has put its effort is into integration. “[ST’s offering] is not integrated all in one. It is not integrated to this level,” said Gervais-Ducouret, referring to the inclusion of a microcontroller in the package along with the MEMS-based sensors and analogue conditioning electronics. “The only thing not on the same piece of silicon are the MEMS-based sensors.”

By moving sensor processing into a local microcontroller, Gervais-Ducouret said it’s possible to achieve power savings compared to running those same algorithms on a host applications processor. “It offers customisable power management – you can change the sampling frequency and have auto wakeup and auto-sleep.”

By moving the processing to a dedicated microcontroller, it’s possible to watch for wakeup gestures without forcing the more power-hungry applications processor to run. This can be extended to applications such as pedometers that use readings from the accelerometers to count steps. “It can run all day without waking up the whole phone,” he claimed.

For the first product, which incorporates accelerometers, Freescale has developed a number of packaged routines that will detect different types of user interaction. The idea is that the company can provide these as canned functions that handset and gadget makers can more easily roll into their designs.

Although the two companies see single-package motion and position detectors as the end-point, the companies are starting from different points.