Putting cars in to motion: Page 3 of 5

April 03, 2014 //By Jari Nieminen, Murata
Putting cars in to motion
MEMS sensors are increasingly providing a crucial element in closed-loop automotive control systems.
with traditional IC fabrication, allowing simpler active circuit integration. However both also have their associated drawbacks and the difference between the two has, in recent times, become less distinct with the evolution of MEMS manufacturing technology.

This is evident in the proprietary 3D MEMS technology developed by Murata; a combination of bulk and surface micro-machining. This technology offers many benefits: formed from a single crystal the silicon is uniquely suited to being a MEMS substrate, with no plastic deformation up to 70,000g. It also allows direct capacitive sensing of deflection, without loss, giving a highly accurate and stable measurement. The ability to create ‘true’ 3D structures supports 3D sensing elements with low temperature dependence and zero point stability, while yielding the highest signal per silicon surface area. It also supports the design of flexible two-chip solutions, such as combining a sensor with an ASIC to create a solution with tuneable sensitivity and frequency response, for use in specific applications.

Advanced Sensing

The sensitivity required is dependent on the given application; an electronic stability control system requires greater sensitivity and offset stability than an airbag system (for example, although as mentioned earlier these two applications would be classified as active and passive safety systems respectively).

As such it is necessary to design sensors with a specific sensitivity, which in this context equates to the correlative quantium.

Figure 1 shows how sensitivity is measured in terms of correlative quantium and quantium change.

For example if sensitivity is 2V/g, 1g acceleration results in a 2V change in the output. Typically, the requirement for MEMS sensors designed for electrically controlled suspension applications will be to have a full range analogue output of 0 to 5V, whereas the accelerometers for electronic stability control systems in use today use mainly digital outputs in the form of a SPI interface.

The combination of mechanical and electrical elements now enables a wider range of application-specific MEMS sensors, such

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