Page 23 - An Introduction to Microelectromechanical Systems Engineering

2 MEMS: A Technology from Lilliput

might be able to play tennis again. With his remote control, he turned on the projec-
tion screen television and slowly drifted back into light sleep.
This short fictional story illustrates how technology can touch our daily lives in
so many different ways. The role of miniature devices and systems is not immediately
apparent here because they are embedded deep within the application they enable.
The circumstances of this story call for such devices on many separate occasions. The
miniature yaw-rate sensor in the vehicle stability system ensured that the ambulance
did not skid on the icy highway. In the event of an accident, the crash acceleration
sensor guaranteed the airbags would deploy just in time to protect the passengers.
The silicon manifold absolute pressure (MAP) sensor in the engine compartment
helped the engine electronic control unit maintain at the location’s high altitude the
proper proportions in the mixture of air and fuel. As the vehicle was safely traveling,
equally advanced technology in the rear of the ambulance saved Mr. Avon’s life. The
modern blood pressure sensor clipped onto his arm allowed the paramedic to moni-
tor blood pressure and cardiac output. The microneedles in the adhesive patch
ensured the immediate delivery of medication to the minute blood vessels under the
skin, while a miniature electronic valve guaranteed the exact dosage. The next day, as
the patient lay in his bed writing his thoughts in his diary, the microaccelerometer in
the electronic quill recognized the motion of his hand and translated his handwriting
into text. Another small accelerometer embedded in his pacemaker would enable him
to play tennis again. He also could write and draw at will because the storage capac-
ity of his disk drive was enormous, thanks to miniature read and write heads. And
finally, as the patient went to sleep, an array of micromirrors projected a pleasant
high-definition television image onto a suspended screen.
Many of the miniature devices listed in this story, in particular the pressure,
acceleration, and yaw-rate microsensors and the micromirror display, already exist
as commercial products. Ongoing efforts at many companies and laboratories
throughout the world promise to deliver, in the not-too-distant future, new and
sophisticated miniature components and microsystems. It is not surprising, then,
that there is widespread belief in the technology’s potential to penetrate in the future
far-reaching applications and markets.

What Are MEMS—or MST?

In the United States, the technology is known as microelectromechanical systems
(MEMS); in Europe, it is called microsystems technology (MST). A question asking
for a more specific definition is certain to generate a broad collection of replies with
few common characteristics other than “miniature.” But such apparent divergence
in the responses merely reflects the diversity of applications this technology enables,
rather than a lack of commonality. MEMS is simultaneously a toolbox, a physical
product, and a methodology, all in one:

• It is a portfolio of techniques and processes to design and create miniature
systems.
• It is a physical product often specialized and unique to a final application—
one can seldom buy a generic MEMS product at the neighborhood electronics
store.