Medical Applications of Micro-Electro-Mechanical Systems (MEMS) Technology - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 31

mechanical structures that are implemented using the techniques of micro-
fabrication. The physical dimensions of MEMS devices can vary from over
one millimeter on the higher end of the dimensional scale down to below
one micron. Likewise, the types of MEMS devices can vary from relatively
simple structures in which there are no mechanically moving elements, to
extremely complex and sophisticated electromechanical systems with multi-
ple moving elements controlled by microelectronics integrated onto a single
substrate. Obviously, the one main criterion of MEMS is that there are at least
some elements on the substrate having a mechanical functionality regard-
less of whether any of the elements move.
While the functional elements of MEMS are miniaturized structures, sen-
sors, actuators, and microelectronics, the most notable (and perhaps most
interesting) elements are the microsensors and microactuators. Microsensors
and microactuators are appropriately categorized as “transducers,” which are
defined as devices that convert energy from one form to another. For example,
microsensor devices typically convert a mechanical movement into an electri-
cal signal. Conversely, microactuators typically convert electrical signals into
mechanical movements. Over the past 25+ years MEMS technologists have
created an extremely large number of microsensors for almost every imagin-
able sensing modality, including pressure, temperature, inertial force, chemi-
cal and biological species, magnetic fields, and radiation. Importantly, many
of these micromachined sensors have demonstrated performances exceeding
those of their macroscale equivalents. For example, the micromachined ver-
sion of a pressure transducer will usually outperform a pressure sensor made
using macroscale manufacturing techniques. Not only is the performance
of MEMS devices exceptional, but also their method of production leverages
batch fabrication techniques used in the integrated circuit (IC) industry, which
translates into low per-device production costs, smaller size and weight, and
other benefits as well. Consequently, with MEMS technology it is possible to
not only achieve stellar device performance, but to do so at a relatively low
cost level. Because of the exceptional performance and cost benefits, the com-
mercial markets for microsensor devices are growing at a rapid rate.
In tandem with developments in microsensors, the MEMS research and
development community has also demonstrated a number of microactua-
tors, including microvalves, optical switches, micromirror display arrays,
microresonators, micropumps, microflaps on airfoils, and many others.
Surprisingly, even though these microactuators are extremely small, they
can frequently cause effects at the macroscale level. That is, these tiny actua-
tors can perform mechanical feats far larger than their size would imply. For
example, researchers have located small microactuators on the leading edge
of airfoils of an aircraft and have been able to steer this aircraft using only
these microminiaturized devices [1].
The real potential of MEMS starts to become fulfilled when these minia-
turized sensors, actuators, and structures can all be merged onto a common
silicon substrate along with integrated circuits. This enables the realization of