Page 21 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

EVOLUTION OF MICROSENSORS

System boundary

Input signal Output
(measurand) Sensor Processor Actuator signal
(Input transducer) (Output transducer)

Figure 1.3 The information-processing triptych. From Gardner (1994)

1980s that the price-to-performance ratio of both sensors and actuators had fallen woefully
behind processors. Consequently, measurement systems tended to be large and, more
importantly, expensive. Work therefore started to link the microelectronic technologies
and use these to make silicon sensors, the so-called microsensors.

Working definition of the term sensor:

'A microsensor is a sensor that has at least one physical dimension at the submillimeter
level.'
This work was inspired by the vision of microsensors being manufactured in volumes at low
cost and with, if necessary, integrated microelectronic circuitry. Chapters 5 and 6 describe
in some detail the silicon micromachining technologies used today to make microsensors
and microactuators. An overview of the field of microsensors is given in Chapter 8.
Figure 1.4 shows the relative market for ICs and microsensors in the past 10 years.
It is evident that the market for microsensors lags well behind the market for ICs;
nevertheless, it is worth 15 to 20 billion euros. The main cause has been the relatively
stable price-performance (p/p) ratio of sensors and actuators since 1960, as illustrated in
Figure 1.5. This contrasts markedly with the p/p ratio of ICs, which has fallen enormously
between 1960 and 2000 and is now significantly below that for sensors and actuators. As a
consequence of these changes, the cost of a measurement system is, in general, dominated
first by the cost of the microactuator and second by the cost of the microsensor.
However, despite the cost advantages, there are several major technical advantages of
making microsensors with microsystems technology (MST); the main ones are as follows:

300-
250-
I 200-
I 150-
S
100-
50-
0
1990 1992 1994 1996 1998 2000 2002
Year

Figure 1.4 World market for ICs and microsensors from 1990 to 2000. From various sources