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1-2 MEMS: Design and Fabrication

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approximately 10 26 m, and the extent of the observable universe, which is of the order of 10 m (15 billion
light years); neither geocentric nor heliocentric, but rather egocentric universe. But humans have always
striven to explore, build, and control the extremes of length and time scales. In the voyages to Lilliput and
Brobdingnag of Gulliver’s Travels, Jonathan Swift (1726) speculates on the remarkable possibilities which
1
diminution or magnification of physical dimensions provides. The Great Pyramid of Khufu was originally
147m high when completed around 2600 B.C., while the Empire State Building constructed in 1931 is
presently — after the addition of a television antenna mast in 1950 — 449m high. At the other end of the
spectrum of manmade artifacts, a dime is slightly less than 2cm in diameter. Watchmakers have practiced
the art of miniaturization since the 13th century. The invention of the microscope in the 17th century
opened the way for direct observation of microbes and plant and animal cells. Smaller things were man-
made in the latter half of the 20th century. The transistor — invented in 1947 — in today’s integrated
2
circuits has a size of 0.18 micron (180 nanometers) in production and approaches 10 nm in research lab-
oratories using electron beams. But what about the miniaturization of mechanical parts — machines —
envisioned by Feynman (1961) in his legendary speech quoted above?
Manufacturing processes that can create extremely small machines have been developed in recent years
(Angell et al.,1983; Gabriel et al.,1988,1992; O’Connor,1992; Gravesen et al.,1993; Bryzek et al.,1994; Gabriel,
1995; Ashley, 1996; Ho and Tai, 1996, 1998; Hogan, 1996; Ouellette, 1996, 2003; Paula, 1996; Robinson et al.,
1996a, 1996b; Tien, 1997; Amato, 1998; Busch-Vishniac, 1998; Kovacs, 1998; Knight, 1999; Epstein, 2000;
O’Connor and Hutchinson, 2000; Goldin et al., 2000; Chalmers, 2001; Tang and Lee, 2001; Nguyen and
Wereley, 2002; Karniadakis and Beskok, 2002; Madou, 2002; DeGaspari, 2003; Ehrenman, 2004; Sharke, 2004;
Stone et al., 2004; Squires and Quake, 2005). Electrostatic, magnetic, electromagnetic, pneumatic and thermal
actuators, motors, valves, gears, cantilevers, diaphragms, and tweezers of less than 100µm size have been fab-
ricated. These have been used as sensors for pressure, temperature, mass flow, velocity, sound, and chemical
composition, as actuators for linear and angular motions, and as simple components for complex systems,
such as lab-on-a-chip, robots, micro-heat-engines and micro heat pumps (Lipkin, 1993; Garcia and
Sniegowski, 1993, 1995; Sniegowski and Garcia, 1996; Epstein and Senturia, 1997; Epstein et al., 1997; Pekola
et al., 2004; Squires and Quake, 2005).
Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than
1mm but more than 1 micron, that combine electrical and mechanical components, and that are fabricated
using integrated circuit batch-processing technologies. The books by Kovacs (1998) and Madou (2002)
provide excellent sources for microfabrication technology. Current manufacturing techniques for MEMS
include surface silicon micromachining; bulk silicon micromachining; lithography, electrodeposition, and
plastic molding (or, in its original German, Lithographie Galvanoformung Abformung, LIGA); and electrodis-
charge machining (EDM). As indicated in Figure 1.1, MEMS are more than four orders of magnitude larger
than the diameter of the hydrogen atom, but about four orders of magnitude smaller than the traditional
manmade artifacts. Microdevices can have characteristic lengths smaller than the diameter of a human hair.
Nanodevices (some say NEMS) further push the envelope of electromechanical miniaturization (Roco, 2001;
Lemay et al., 2001; Feder, 2004).
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The famed physicist Richard P. Feynman delivered a mere two, albeit profound, lectures on electro-
mechanical miniaturization: “There’s Plenty of Room at the Bottom,” quoted above, and “Infinitesimal
Machinery,” presented at the Jet Propulsion Laboratory on February 23, 1983. He could not see a lot of use
for micromachines, lamenting in 1959 that “(small but movable machines) may or may not be useful, but
they surely would be fun to make,”and 24 years later said,“There is no use for these machines, so I still don’t

1 Gulliver’s Travels were originally designed to form part of a satire on the abuse of human learning. At the heart of
the story is a radical critique of human nature in which subtle ironic techniques work to part the reader from any
comfortable preconceptions and challenge him to rethink from first principles his notions of man.
2
The smallest feature on a microchip is defined by its smallest linewidth, which in turn is related to the wavelength
of light employed in the basic lithographic process used to create the chip.
3 Both talks have been reprinted in the Journal of Microelectromechanical Systems, vol. 1, no. 1, pp. 60–66, 1992, and
vol. 2, no. 1, pp. 4–14, 1993.

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