Micro-Electro-Mechanical Systems (MEMS)

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Micro-Electro-Mechanical Systems (MEMS)
Submitted to Mr.Deepak Basandari
Made By


Rupesh Kumar

10802946

B.Tech
Mechanical
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Table of contents

• 1) Acknowledgement
• 2) Abstract of work undertaken
• 3) Introduction to the problem
• 4) Fabricating MEMS and Nanotechnology
• a) Deposition Processes
• b) Lithography
• c) Etching
• 5) MEMS and Nanotechnology Applications
• 6) Accelerometer
• 7) Usefulness of accelerometers
• 8) Current Challenges
• 9) Reference sites

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Acknowledgement

• 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
  
• 
  
• 
  RUPESH KUMAR
• 
  10802946

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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.

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Introduction to the problem

• 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. 

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Fabricating MEMS and Nanotechnology

• 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.

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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

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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.

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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.

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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
• 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.
• 3) 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.

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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.

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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.

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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.

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Reference sites

• 1) Memx.org
• 2) Google.com