A new breed of automotive applications may be on the horizon for microelectromechanical systems (MEMS) sensors, thanks to an anticipated rise in their production over the next four years.
MEMS sensors, already used for yaw detection in vehicle electronic stability control (ESC) systems, may soon migrate to bigger numbers in rollover detection, tire pressure monitoring, parking brakes and a variety of other automotive applications that involve inertial measurement. Moreover, many engineers believe the MEMS sensor applications could be integrated into fewer modules, thus driving costs down for manufacturers.
“The auto industry is thinking that there may be multiple systems that need to draw on inertial measurements,” says Dave Monk, MEMS automotive product manager for Freescale Semiconductor, a manufacturer of the sensors. “Electronic stability control could use it; airbags could use it; even suspension systems could use it.”
The impetus for MEMS' changing role is its sudden popularity in electronic stability control. After auto industry studies revealed a few years ago that widespread use of ESC could save up to 9,500 lives a year in the U.S. alone, the National Highway Traffic Safety Administration (NHTSA) mandated the technology be implemented on new light vehicles. An NHTSA law calls for 55 percent of new vehicles to include ESC starting on Sept. 1, 2008, with the numbers gradually reaching 100 percent by 2012.
Industry analysts say those rising numbers will have a significant impact on the automotive market. A recent study by iSuppli Corp., a market intelligence firm, indicated implementation of ESC systems would double between 2007 and 2012. As a result, the study says, sales of MEMS sensors for ESC would soar to $715 million by 2012, up from $378 million in 2006.
Cost is Key
For users of the sensors, the bottom line could be a significant drop in price. As production volume has escalated over the past five years, gyroscopic MEMS sensors have plummeted in price from approximately $30 to about one-third of that today.
“This component last year was on average closer to $11-$12 as a result of increased competition from companies new to the ESC supply chain like Panasonic, which will shake the tree with a lower-priced, no frills gyroscope that benefits from economies of scale,” Richard Dixon of iSuppli wrote in an e-mail.
Freescale recently did its part to drive costs down, rolling out a high aspect ratio MEMS (HARMEMS) low-g sensor. The new sensor will operate in the area below 10g and will offer the sensitivity and range of so-called low-g sensors, but will use a microelectronic manufacturing process that keeps costs below those of conventional low-g devices, Freescale says.
One of the goals for the Freescale device and those made by other manufacturers is to promote integration. Systron Donner Automotive, for example, last year introduced the Micro-Gyro, a MEMS-based system that uses a double-ended tuning fork for angular rate-sensing precision. The “gyro on a chip,” as the company calls it, can withstand high under-hood temperatures, thus eliminating the need for complex passenger compartment mounting.
Similarly, Bosch Automotive's DRS MM3 is a sensor cluster that uses a flexible construction technique that allows for detection of angular velocity and acceleration for different paths of force within a vehicle. It can be applied to so-called “active steering” and “hill-hold” parking brakes, as well as in ESC.
For automakers and tier-one suppliers, the development of such MEMS sensors opens the door to system integration. Most automakers would like to integrate their airbag sensors with their stability control, for example, as a way of reducing complexity and cutting costs. Moreover, most are looking at the possibility of measuring angular velocity about the vehicle's roll- and pitch-axes. Roll stability control would be a particular help for SUVs and other vehicles with a high center of gravity, while pitch control could work with active suspension systems. Engineers have also talked about using existing dual-axis sensors in the parking brake, where they could provide stability when a vehicle is stopped, or re-starting, on an incline.
“We firmly believe the technology trends will go toward integration of multiple sensors into a single package,” Monk says.
Still, the ability to integrate may hinge, not on technology, but on corporate structure. Many automakers rigidly organize their engineering departments, placing ESC in the braking division and airbags, for example, in a safety group. To integrate electronics and make use of common sensors, most companies are looking for ways to break down the barriers.
“We're seeing a trend to make these organizations work together,” says Francois Gilly, automotive inertial sensor product marketer for Freescale. “The carmakers are starting to ask, 'Why not merge ESC and airbags together?'”
As yet, no one knows whether automakers will ultimately create large six degree-of-freedom inertial measurement systems capable of controlling ESC, airbags, parking brakes and other automotive systems. Suppliers, however, are preparing for that possibility. The new breed of sensors, they say, is capable of integrating six degrees of freedom into a single package.
“Today you don't see many combined sensors,” Monk says. “But five years from now, you'll see more inertial axes — more degrees of freedom — combined together.”