Transcript Micro-Electro-Mechanical Systems (MEMS)

Micro-Electro-Mechanical
Systems (MEMS)
Submitted to:
Mr.Deepak Basandari
Made By:
Rupesh Kumar
B.Tech Mechanical
Table of contents
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Acknowledgement
Abstract of work undertaken
Introduction to the problem
Fabricating MEMS and Nanotechnology
a) Deposition Processes
b) Lithography
c) Etching
MEMS and Nanotechnology Applications
Accelerometer
Usefulness of accelerometers
Current Challenges
Reference sites
Acknowledgement
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As I began to reflect on magnitude of this project. i was overwhelmed
by guidance and support extended by my teacher, friends and others. i
would acknowledge of H.O.D sir whose constant encouragements
made me believe in myself .i would express my senior incharge CA
department, who has always there in hour of need.
Last but not the least, our heart goes out to our families and our
friends, who cognizance, knowledge and support make to do this
presentable
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RUPESH KUMAR
10802946
Abstract of work undertaken
Micro-Electro-Mechanical Systems (MEMS) is the
integration of mechanical elements, sensors,
actuators, and electronics on a common silicon
substrate through microfabrication technology. While
the electronics are fabricated using integrated circuit
(IC) process sequences (e.g., CMOS, Bipolar, or
BICMOS processes), the micromechanical
components are fabricated using compatible
"micromachining" processes that selectively etch
away parts of the silicon wafer or add new structural
layers to form the mechanical and electromechanical
devices.
Introduction to the problem
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Imagine a machine so small that it is imperceptible to the human
eye. Imagine working machines no bigger than a grain of pollen. Imagine
thousands of these machines batch fabricated on a single piece of silicon,
for just a few pennies each. Imagine a world where gravity and inertia are
no longer important, but atomic forces and surface science dominate.
Imagine a silicon chip with thousands of microscopic mirrors working in
unison, enabling the all optical network and removing the bottlenecks from
the global telecommunications infrastructure. You are now entering the
microdomain, a world occupied by an explosive technology known as
MEMS. A world of challenge and opportunity, where traditional engineering
concepts are turned upside down, and the realm of the "possible" is totally
redefined.
Fabricating MEMS and
Nanotechnology
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MEMS technology is based on a number of tools and methodologies,
which are used to form small structures with dimensions in the
micrometer scale (one millionth of a meter). Significant parts of the
technology has been adopted from integrated circuit (IC) technology.
For instance, almost all devices are build on wafers of silicon, like ICs.
The structures are realized in thin films of materials, like ICs. They are
patterned using photolithographic methods, like ICs. There are
however several processes that are not derived from IC technology,
and as the technology continues to grow the gap with IC technology
also grows.
There are three basic building blocks in MEMS technology, which are
the ability to deposit thin films of material on a substrate, to apply a
patterned mask on top of the films by photolithograpic imaging, and to
etch the films selectively to the mask. A MEMS process is usually a
structured sequence of these operations to form actual devices. Please
follow the links to read more about deposition, lithography and etching.
Deposition Processes
MEMS Thin Film Deposition Processes
One of the basic building blocks in MEMS processing is the ability to deposit thin films of
material. In this text we assume a thin film to have a thickness anywhere between a few
nanometer to about 100 micrometer.
MEMS deposition technology can be classified in two groups:
1. Depositions that happen because of a chemical reaction:
a) Chemical Vapor Deposition (CVD)
b) Electrodeposition
c) Epitaxy
d) Thermal oxidation
These processes exploit the creation of solid materials directly from chemical reactions in
gas and/or liquid compositions or with the substrate material. The solid material is usually
not the only product formed by the reaction. Byproducts can include gases, liquids and
even other solids.
2) Depositions that happen because of a physical reaction:
a) Physical Vapor Deposition (PVD)
b) Casting
Lithography
Various steps involved in Lithography:
1) Pattern Transfer
Lithography in the MEMS context is typically the transfer of a pattern to a photosensitive
material by selective exposure to a radiation source such as light. A photosensitive
material is a material that experiences a change in its physical properties when exposed
to a radiation source. If we selectively expose a photosensitive material to radiation (e.g.
by masking some of the radiation) the pattern of the radiation on the material is
transferred to the material exposed, as the properties of the exposed and unexposed
regions differs.
2) Alignment
In order to make useful devices the patterns for different lithography steps that belong to
a single structure must be aligned to one another. The first pattern transferred to a wafer
usually includes a set of alignment marks, which are high precision features that are
used as the reference when positioning subsequent patterns, to the first pattern.
3) Exposure
The exposure parameters required in order to achieve accurate pattern transfer from the
mask to the photosensitive layer depend primarily on the wavelength of the radiation
source and the dose required to achieve the desired properties change of the
photoresist. Different photoresists exhibit different sensitivities to different wavelengths.
The dose required per unit volume of photoresist for good pattern transfer is somewhat
constant; however, the physics of the exposure process may affect the dose actually
received. For example a highly reflective layer under the photoresist may result in the
material experiencing a higher dose than if the underlying layer is absorptive, as the
photoresist is exposed both by the incident radiation as well as the reflected radiation.
The dose will also vary with resist thickness.
Etching Processes
In order to form a functional MEMS structure on a
substrate, it is necessary to etch the thin films
previously deposited and/or the substrate itself. In
general, there are two classes of etching
processes:
1) Wet etching where the material is dissolved when
immersed in a chemical solution.
2) Dry etching where the material is sputtered or
dissolved using reactive ions or a vapor phase
etchant.
MEMS and Nanotechnology
Applications
There are numerous possible applications for MEMS and Nanotechnology. As a breakthrough technology,
allowing unparalleled synergy between previously unrelated fields such as biology and microelectronics,
many new MEMS and Nanotechnology applications will emerge, expanding beyond that which is currently
identified or known. Here are a few applications of current interest:
1) Biotechnology
MEMS and Nanotechnology is enabling new discoveries in science and engineering such as the
Polymerase Chain Reaction (PCR) microsystems for DNA amplification and identification, micromachined
Scanning Tunneling Microscopes (STMs), biochips for detection of hazardous chemical and biological
agents, and microsystems for high-throughput drug screening and selection.
2) Communications
3)
High frequency circuits will benefit considerably from the advent of the RF-MEMS technology. Electrical
components such as inductors and tunable capacitors can be improved significantly compared to their
integrated counterparts if they are made using MEMS and Nanotechnology. With the integration of such
components, the performance of communication circuits will improve, while the total circuit area, power
consumption and cost will be reduced. In addition, the mechanical switch, as developed by several research
groups, is a key component with huge potential in various microwave circuits. The demonstrated samples of
mechanical switches have quality factors much higher than anything previously available.
Accelerometers
MEMS accelerometers are quickly replacing conventional accelerometers for crash air-bag deployment
systems in automobiles. The conventional approach uses several bulky accelerometers made of discrete
components mounted in the front of the car with separate electronics near the air-bag; this approach costs
over $50 per automobile. MEMS and Nanotechnology has made it possible to integrate the accelerometer
and electronics onto a single silicon chip at a cost between $5 to $10. These MEMS accelerometers are
much smaller, more functional, lighter, more reliable, and are produced for a fraction of the cost of the
conventional macroscale accelerometer elements.
Accelerometer
An accelerometer is an
electromechanical
device that will measure
acceleration forces.
These forces may be
static, like the constant
force of gravity pulling
at your feet, or they
could be dynamic caused by moving or
vibrating the
accelerometer.
Usefulness of accelerometers
By measuring the amount of static acceleration due to gravity, you can find out
the angle the device is tilted at with respect to the earth. By sensing the amount
of dynamic acceleration, you can analyze the way the device is moving.
At first, measuring tilt and acceleration doesn't seem all that exciting. However,
engineers have come up with many ways to make really useful products using
them.
An accelerometer can help your project understand its surroundings better. Is it
driving uphill? Is it going to fall over when it takes another step? Is it flying
horizontally or is it dive bombing your professor? A good programmer can write
code to answer all of these questions using the data provided by an
accelerometer. An accelerometer can help analyze problems in a car engine
using vibration testing, or you could even use one to make a musical instrument.
In the computing world, IBM and Apple have recently started using
accelerometers in their laptops to protect hard drives from damage. If you
accidentally drop the laptop, the accelerometer detects the sudden freefall, and
switches the hard drive off so the heads don't crash on the platters. In a similar
fashion, high g accelerometers are the industry standard way of detecting car
crashes and deploying airbags at just the right time.
Current Challenges
MEMS and Nanotechnology is currently used in low- or medium-volume applications.
Some of the obstacles preventing its wider adoption are:
1) Limited Options
Most companies who wish to explore the potential of MEMS and Nanotechnology have very limited options
for prototyping or manufacturing devices, and have no capability or expertise in microfabrication technology.
Few companies will build their own fabrication facilities because of the high cost. A mechanism giving
smaller organizations responsive and affordable access to MEMS and Nano fabrication is essential.
2)
Packaging
The packaging of MEMS devices and systems needs to improve considerably from its current primitive
state. MEMS packaging is more challenging than IC packaging due to the diversity of MEMS devices and
the requirement that many of these devices be in contact with their environment. Currently almost all MEMS
and Nano development efforts must develop a new and specialized package for each new device. Most
companies find that packaging is the single most expensive and time consuming task in their overall
product development program. As for the components themselves, numerical modeling and simulation tools
for MEMS packaging are virtually non-existent. Approaches which allow designers to select from a catalog
of existing standardized packages for a new MEMS device without compromising performance would be
beneficial.
3) Fabrication Knowledge Required
Currently the designer of a MEMS device requires a high level of fabrication knowledge in order to create a
successful design. Often the development of even the most mundane MEMS device requires a dedicated
research effort to find a suitable process sequence for fabricating it. MEMS device design needs to be
separated from the complexities of the process sequence.
Reference sites
1) Memx.org
2) Google.com
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