Electronic Design

MEMS Inertial Sensor Combines Breakthroughs In Performance And Cost

A recent request from Hewlett-Packard piqued my interest, as company representatives wanted to talk to me about a microelectromechanical systems (MEMS) inertial sensor it had developed.

At the end of these briefings, I typically ask for pricing and availability information, so readers will know when the part will be ready to purchase and how much it will cost. But selling this new MEMS sensor as a component directly to design engineers is not what the folks at HP have in mind.

A MEMS BREAKTHROUGH
The inertial MEMS sensing technology leverages the fluidic MEMS that HP developed for its inkjet printer cartridges. Built in HP’s 200-mm inkjet fab, it combines breakthroughs in performance and cost.

Instead of a single wafer, the sensor uses a threewafer stack consisting of cap, rotor, and stator wafers. This enables the creation of a proof mass, which is the mass that moves back and forth under acceleration. The mass is about 1000 times higher than the proof mass of a normal MEMS device. This leads directly to a lower noise floor, which gives the device excellent resolution in the sub-100-ng/vHz range.

The sensor’s novel electrode design uses a better capacitive measurement system than current devices. Instead of a gap-closing capacitive change, the sensor measures a change in the area of the capacitance. According to HP, this gives the sensor a higher dynamic range of greater than 130 dB. It also contributes to low power—less than 50 mW per axis—since the sensor does not have to run in a static mode.

Other sensor features include three axes of sensing on a single chip (X, Y, Z); a bandwidth of zero to 250 Hz, extensible to 10 kHz; and small size on the order of a typical IC package. HP says the cost is what you would expect of a MEMS device, though not as low as automotive levels of pricing.

A CUSTOM ACCELEROMETER PLATFORM
HP is touting this sensing technology as a platform that enables development of custom accelerometers to meet specific application requirements.

“Because this is all manufactured in a MEMS factory, we have the ability to tailor the exact design of any particular accelerometer at a particular industry. So if there is a need for extremely accurate one-axis sensing, we can optimize the design for that,” said Rich Duncombe, a technologist and strategist at HP.

There are myriad target applications for these sensors, especially in sensor networks. Examples include infrastructure health monitoring (think bridges); security/access monitoring of motion, orientation, and biometrics; vibration monitoring, such as in geophysical mapping; and user interfaces.

THE BUSINESS PROPOSITION
As Duncombe describes it, HP is bringing its broad set of capabilities in the IT sector to bear on a growing domain it calls sensing solutions. In the larger industry, HP is an end-to-end provider for decision or business intelligence, which takes advantage of the networking of these revolutionary sensing technologies, whatever that network may be.

An HP end-to-end solution can gather real-time information from that sensing network, offer the storage and computational assets required to efficiently manage that volume of data, and provide the algorithms associated with interpreting that information, giving recipients better and faster decisions to manage whatever domain they are focused on.

Although HP has these end-to-end capabilities, it also feels that there are experts in various elements of the long value chain, and HP is reaching out to them depending on their vertical or industry.

“As the largest IT supplier, we have very deep client relationships. One of the things that we really value about our business is the fact that those clients are able to bring us some very difficult and valuable business problems,” said Duncombe.

“Then we have this end-to-end capability to partner with them, both with our internal capability and with other solution providers, and then bring a solution back to them. From a go-to-market perspective, the sensing solution is an asset that we are bringing to our clients as we help them move their particular businesses or industries forward,” he said.

So HP’s focus is on end-to-end solutions as opposed to a component type of a business model in the MEMS accelerometer space. “We’re not going to be providing MEMS accelerometers as components, but we really are very interested in engaging with design engineers to create solutions and to find out how to create those high-value end-to-end solutions with them,” Duncombe said.

For example, an end-to-end solution may contain a sensing node that is ruggedized with a very specific form factor for a particular vertical application like structural health monitoring. “There may be some of your audience who would be the perfect partner to actually help design and build that particular subsystem,” said Duncombe. “Then our business focus would be to bring that back into some kind of an endto- end solution for managing that infrastructure.”

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