Page 284 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

264 MICROSENSORS

Figure 8.31 Basic types of microaccelerometers: (a) capacitive and (b) piezoresistive. Adapted
from Fatikow and Rembold (1997)

Table 8.12 US market for automotive microaccelerometers in million euros. Adapted from MIRC
(1990)
Application 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
Air bag-cars 21 55 89 88 151 127 129 131 133 135
and vans
ABS a 0 8 8 16 24 31 50 52 54 56
Suspension 0 6 13 18 26 19 19 20 21 22
Total 21 69 110 122 201 177 198 203 208 213
a
Automatic braking system
unit price has fallen from €100 to €9 during this period, so unit sales have dramatically
risen.
The more recent ADXL 250 (Analog Devices) employs a folded flexure structure for
improved linearity and provides two-axis measurement. In contrast, Figure 8.32 shows
the CSEM MS6100 precision low-power capacitive accelerometer (170 uA at 3 V) with
high dynamic stability (2 mg for 2 g sensor) but poor low-temperature stability (typical
offset is 200 ug/°C).
Table 8.13 provides a comparison of the specification of some commercially available
microaccelerometers.
Through increasing the damping and stiffness of the microresonators, it is possible
to increase the dynamic range further; therefore, microaccelerometers are also used in
military applications, such as missile control.