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MEMS devices have been attracting a lot of attention due to their unique
features – small sizes and low power requirement.
The device sizes are very small, usually in the range from 10µm to 1mm.
To compare, a typical MEMS gear is about the size of a red blood cell. An
optical mirror is about the size of the diameter of a human hair. The
thickness of moveable parts in the chips are usually in the order of
microns, therefore, the mass of moveable parts are very small which require
very small force to move.
The miniature feature reduces the size and weight of the
integrated components, which further reduces power consumptions.
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MEMS devices can be utilized in many ways. Roughly
speaking, they can be applied in a conventional application but with much
smaller sizes and power requirement or in a novel way to enable a new
application. Both are finding many applications in our daily life.
MEMS devices can also be divided into two categories:
sensors and actuators. Sensors are to sense the environmental changes such
as pressure, temperature, humidity, vibration, speed, acceleration, force, motion,
shock, rotation, orientation, magnetic fields, electrical fields, chemicals
(CO2, NO, CO…etc), biological agents (anthrax, virus, bacteria
…), and strain … etc. Actuators are to provide motions and changes to the
environments such as acoustic wave generation and processing,
electromagnetic wave generation and processing, optical signal processing,
mechanical manipulation, fluidic management, pumping, picking, cutting,
shuttering, scanning, and imaging …etc.
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There are many ways to make MEMS devices.
Conventional silicon micromachining technique is a
popular approach. It allows monolithic fabrication using the existing
semiconductor such as VLSI or CMOS processes, which reduce manual labor and
fabrication costs. The monolithic feature also allows precise positioning
for components on the chips. The accuracy of alignment can be in
submicrons. The mechanical characteristics of silicon have been well
studied and show great promise for robust and reliable devices.
Surface micromachining build 3-dimensioanl structures by
depositing multiple poly-silicon and sacrificial layers such as SiO2
and releasing the sacrificial layers in the final step.
Other approaches use the similar philosophy – multiple
layers of deposition and etching but different materials. Electroplating of
metals, polymer coating, evaporation of materials, physical embossing and
molding are also parts of the fabrication techniques.
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Miniaturization.
Many medical instrumentations are expensive, bulky,
heavy and require experienced technicians to operate. This is partially due
to the component sizes and the analysis methodology. MEMS can reduce the
component sizes significantly and enable new analysis methods so portable,
highly-sensitive diagnosis tools
would become possible.
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