Page 23 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

EVOLUTION OF MEMS 5

sensors was about 700 million euros and that for accelerometers was about 200 million
euros (see Tables 8.10 and 8.11).
As the market for automotive sensors has matured, the price has fallen from €100 to
€10 for a pressure sensor. In addition, the sophistication of the chips has increased and
so has the level of integration. How this has led to the development of 'smart' sensors is
discussed in Chapter 15.

Working definition of the term smart sensor:
'A smart sensor is a sensor that has part or its entire processing element integrated in a
single chip.'

1.3 EVOLUTION OF MEMS

The next ambitious goal is to fabricate monolithic or integrated chips that can not
only sense (with microsensors) but also actuate (with microactuators), that is, to create
a microsystem that encompasses the information-processing triptych. The technology
employed to make such a microsystem is commonly referred to as MST. Figure 1.7
provides an overview of MST together with some of the application areas. Work to
achieve this goal started in the late 1980s, and there has been enormous effort to fabricate
microelectromechanical systems (MEMS) using MST.

Working definition of the term MEMS:
'A MEMS is a device made from extremely small parts (i.e. microparts).'

Early efforts focused upon silicon technology and resulted in a number of successful
micromechanical devices, such as pressure sensors and ink-jet printer nozzles. Yet, these
are, perhaps, more accurately described as devices rather than as MEMS. The reason

Figure 1.7 Overview of microsystems technology and the elements of a MEMS chip. From
Fatikow and Rembold (1997)