Page 12 - MEMS Mechanical Sensors

CHAPTER 1
Introduction

1.1 Motivation for the Book

As we move into the third millennium, the number of microsensors evident in every-
day life continues to increase. From automotive manifold pressure and air bag sen-
sors to biomedical analysis, the range and variety are vast. It is interesting to note
that pressure sensors and ink-jet nozzles currently account for more than two-thirds
of the overall microtransducer market share. Future predications indicate that the
mechanical microsensor market will continue to expand [1]. One of the main rea-
sons for the growth of microsensors is that the enabling technologies are based on
those used within the integrated circuit (IC) industry. The production cost of a com-
mercial pressure sensor, for example, is around 1 Euro, and this is largely because
the cost of producing ICs is inversely proportional to the volume produced. The
trend in IC technology since the 1960s has been for the number of transistors on a
chip to double every 18 months; this is referred to as Moore’s law. This has pro-
found implications for the electronic systems associated with microsensors. In addi-
tion to the reduction of size there is added functionality and also the possibility of
producing arrays of individual sensor elements on the same chip.
Another feature that has influenced the popularity trend of microsensors is that
many (but certainly not all) are based on silicon (Si). The electrical properties of sili-
con have been studied for many years and are well understood and thoroughly
documented. Silicon also possesses many desirable mechanical properties that make
it an excellent choice for many types of mechanical sensor.
Today there are many companies working in the field of microelectromechani-
cal systems (MEMS). A quick search on the Internet in July 2003 revealed several
hundred in the United States, Europe, and the Far East, including multinational cor-
porations such as TRW Novasensor, Analog Devices, Motorola, Honeywell, Senso-
Nor, Melexis, Infineon, and Mitsubishi, as well as small start-up companies. There
are also many conferences dedicated to the subject. A selection of examples (but by
no means an exhaustive list) is given here:

• Transducers—International Conference on Solid-State Sensors and Actuators
(held biennially and rotating location between Asia, North America, and
Europe);
• Eurosensors (held annually in Europe);
• IEEE Sensors Conference (first held in 2002, annually United States and
Canada);
• Micro Mechanics Europe—MME (held annually in Europe);

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