Design Con 2015

Sensor footprint: does size matter?

Steve Barraclough, senior director of product management, Bosch Sensortec

August 01, 2014

Steve Barraclough, senior director of product management, Bosch SensortecAugust 01, 2014

The co-author of this article is Lutz Rauscher, Bosch Sensortec.

Up until shortly before publishing this blog was entitled "Trends in MEMS orientation sensor form factor reduction." That was until we ran the draft past a colleague for proof reading, and in her feedback she summarised: "So, what you are really questioning is does size matter, and if so why does it matter?"

Having realized what she had said, and the three of us blushing past the inevitable smirks and associations that the question raises, we settled on this title simply because it questions the basic assumption within MEMS industry community that smaller actually equates to better. Now, for those to which the question conjures up negative connotations, we offer a small apology, but we do hope we will continue to have your attention.

Industry observers will not argue that the explosion in the adoption of motion sensors, principally accelerometers, was enabled by reducing the form factor to the point where the sensors could easily be integrated into mobile applications. Bosch now ships more than three million sensors a day, a large proportion of which are discrete 2 mm x 2 mm accelerometers.

But the roots of the MEMS technology evolution originate in automotive industry where accelerometers were developed to trigger airbag deployment in motor vehicles, a working environment not overly subject to size constraints and in fact there were solid technical reasons not to shrink. A colleague here at Bosch Sensortec who previously worked in the automotive division commented, "None of us believed size reduction of an accelerometer to something smaller than 10 mm x 10 mm was even possible..."

It turned out to be a real challenge, but once the initial hurdles were overcome it became clear that size reduction in this context equated to cost reduction, which eventually drove the sensor footprint down to the point where entry into the mobile space became feasible.

The tipping point for mobile adoption appears to be around 3 mm x 3 mm, a point where cost, size and performance became acceptable for the consumer electronics sector and inertial sensors ubiquitously present in mobiles. That drive for smaller sensors has continued through to today, with Bosch now offering an industry leading accelerometer portfolio with a 2 mm x 2 mm and below footprint.

Customer feedback highlights the advantage: for a typical 80 square millimeters smartphone PCB (available area), moving from a 9 square millimeters to a 4 square millimeters footprint increases placement options by 225%.

A great example are also pressure sensors – being available only in rather large and (maybe even more importantly) thick packages, they have been ignored by the industry for many years. Now being offered in a 2mm by 2.5 square millimeter without sacrificing performance their use has seen 3-digit percentage year-on-year growth rates.

To read more of this external content and to leave a comment, go to "Sensor footprint evolution", on Embedded.com's sister publication, EETimes Europe.

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