handbook of modern sensors

18.3 Nano-Technology 547
6000-Å layer of Ga 0.47 In 0.53 As can be grown on the InP substrate at 1 atm and 630 ◦ C
with a rate of 1.4 Å/s [3].
18.3 Nano-Technology
Nano-technology today is a somewhat emotional term, more of a wishful thinking
than a real thing. It refers to dimensions of a device comparable with a nanometer
(10 −9 m) scale. In practice, however, most of the subminiature elements have sizes
about 1000 times larger—in a micrometer (10 −6 m) range. Still, the trend is toward
the smallest dimensions as far as the current technology allows.
The present trend in sensor technologies is undoubtedly shifted toward the micro
miniaturization or microsystem technologies, known as MST. A subset of these is
known as micro-electromechanical systems, or MEMS for short. A MEMS device
has electrical and mechanical components, which means there must be at least one
moving or deformable part and that electricity must be part of its operation. Another
subset is called MEOMS, which stands for micro-electro-optical systems.As the name
implies, at least one optical component is part of the device. Most of the sensors that
are fabricated with the use of MEMS or MEOMS are three-dimensional devices with
dimensions on the order of micrometers.
The two constructional technologies of microengineering are microelectronics and
micromachining. Microelectronics, producing electronic circuitry on silicon chips, is a
very well-developed technology. Micromachining is the name for the techniques used
to produce the structures and moving parts of microengineered devices. One of the
main goals of microengineering is to be able to integrate microelectronic circuitry into
micromachined structures, to produce completely integrated systems (microsystems).
Such systems typically have the same advantages of low cost, reliability, and small
size as silicon chips produced in the microelectronics industry.
Presently, there are three micromachining techniques that are in use or are extensively
developed by the industry [4,5]. Silicon micromachining is given the most
prominence, because this is one of the better developed micromachining techniques.
Silicon is the primary substrate material used in the production microelectronic circuitry
and, thus, is the most suitable candidate for the eventual production of microsystems.
The excimer laser is an ultraviolet laser which can be used to micromachine a
number of materials without heating them, unlike many other lasers which remove
material by burning or vaporizing it. The excimer laser lends itself particularly to the
machining of organic materials (polymers, etc).
LIGA 3 is a technique that can be used to produce molds for the fabrication of
micromachined components. Microengineered components can be made from a variety
of materials using this technique, however it does suffer the disadvantage that
the technique currently requires X-rays from a synchrotron source.
3 LIGA-Lithographic Galvanoforming and Abforming is a German acronym for x-ray lithography.