The current trend is the integration of multiple sensors, supporting processors and communication functions— usually wired but occasionally wireless, as in the case of TPMS.
Often, however, the integration is achieved via system-in-package technology rather than monolithically, for reasons of cost as well as yield optimization.
"The trend is to engage in a level of integration in sensor modules; two MEMS and two signal conditioning ICs are tending to become one to two MEMS devices and one ASIC," said ST's Ferraresi.
The trend toward combo accelerometer and gyroscope sensors for electronic stability control started in 2010 at companies such as Bosch and VTI Technologies, said Robin. "For stability control, you need dual-axis gyroscopes, and then there are applications in navigation, electronic parking, braking and hill start assist," he said. Companies are also starting to use three-axis accelerometers for flexibility in mounting; the three-axis devices' mounting position does not affect their performance.
The need for integration can be seen in TPMS modules, which in addition to the MEMS pressure sensor include a signal conditioning ASIC, microcontroller, RF chip and battery. The requirements are prompting research into the possibilities of piezoelectric-based energy harvesting as a means of powering a low-power module, and monolithic integration could play a key role in the power savings. Another effort, notably pursued by Bosch, is to produce a generalized 2plus1 inertial sensor module with a microcontroller that can be characterized for different automotive applications in software.
No fabless here
While the availability of some foundry MEMS manufacturing is supporting the creation of fabless MEMS device startups, those companies tend to address the consumer markets which have lower requirements for product reliability and longevity.
For the automotive market, MEMS suppliers continue to be integrated device manufacturers, including tier one subsystem makers such as Bosch or Denso and chip IDMs such as Analog Devices, Freescale, Infineon Technologies and Panasonic. “We do not think that will change, as automotive fabs have to be qualified by customers,” said Robin.
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