mems

1. UNIT 5

2. Contents
 MEMS
 Computer Printer
 VCR
 Fax Machine
 NC machine

3. Introduction
 Micro Electro Mechanical
System(MEMS) is a device where
microsensors and mechanical parts,
along with signal processing circuits are
integrated on a small piece of silicon.
 Mechanical means they are basically the
mechanical part i.e. actuation parts.
MICROSENSOR MICROACTUATOR
MICROSTRUCTURE MICROELECTRONICS
MEMS
•A typical MEMs system consists of a micro sensor which senses the environment and
converts the environment variable into an electrical value.
•The microelectronics processes the electrical signal and the micro actuator accordingly
works to produce a change in the environment.

4. Distinctive features of the MEMS
Miniaturization
• Size is brought
down for both
sensors and
actuators, and they
are integrated
together
Multiplicity
• Multiplicity is
basically the
multiple functions
that are being made
in a system
Microelectronics
• It integrates
microelectronic
control device with
sensors and
actuators.

5. Fabrication of MEMs device
 It involves the basic IC fabrication methods along with the micromachining
process involving the selective removal of silicon or addition of other
structural layers.
Fabrication
methods
Bulk
Micromachining
Surface
Micromachining
Molding( LIGA)
Technique

6. Bulk Micromachining:
Introduction
• Bulk micromachining is a fabrication technique which builds mechanical elements by starting
with a silicon wafer, and then etching away unwanted parts, and being left with useful mechanical
devices.
• Typically, the wafer is photo patterned, leaving a protective layer on the parts of the wafer that
you want to keep.
• The wafer is then submersed into a liquid etchant, like potassium hydroxide, which eats away any
exposed silicon.
Advantage:
• relatively simple and inexpensive fabrication technology
• well suited for applications which do not require much complexity, and which are price sensitive.
• cost less,
• are highly reliable,
• manufacturable,
• there is very good repeatability between devices.
Application:
• Automotibiles
• Medical Application

7. Surface Micromachining:
Introduction
• Surface Micromachining builds devices up from the wafer layer-by-layer. While Bulk
micromachining creates devices by etching into a wafer,
• A typical Surface Micromachining process is a repetitive sequence of depositing thin films on a
wafer, photo patterning the films, and then etching the patterns into the films.
Advantage:
• It is able to create much more complicated devices, capable of sophisticated functionality.
• suitable for applications requiring more sophisticated mechanical elements
Disadvantage:
• Surface Micromachining requires more fabrication steps than Bulk Micromachining, and hence is
more expensive.

8. At the end of the process, the sacrificial material is removed, and
the structural elements are left free to move and function.
The structural material will form the mechanical elements, and
the sacrificial material creates the gaps and spaces between the
mechanical elements.
In order to create moving, functioning machines, these layers are
alternating thin films of a structural material (typically silicon)
and a sacrificial material (typically silicon dioxide).
 For the case of the structural
level being silicon, and the
sacrificial material being silicon
dioxide, the final "release"
process is performed by placing
the wafer in Hydrofluoric Acid.
 The Hydrofluoric Acid quickly
etches away the silicon dioxide,
while leaving the silicon
undisturbed.
 The wafers are typically then
sawn into individual chips, and
the chips packaged in an
appropriate manner for the
given application.

9. LIGA(Lithographie, Galvanoformung, Abformung):
 LIGA is a technology which creates small, but relatively high aspect ratio
devices using x-ray lithography.
 LIGA is a relatively inexpensive fabrication technology, and suitable for
applications requiring higher aspect ratio devices than what is achievable in
Surface Micromachining.

10. The process typically starts with a sheet of
Poly(methyl methacrylate) (PMMA. )
The PMMA is covered with a photomask, and then
exposed to high energy x-rays.
The mask allows parts of the PMMA to be exposed
to the x-rays, while protecting other parts.
The PMMA is then placed in a suitable etchant to
remove the exposed areas, resulting in extremely
precise, microscopic mechanical elements.

11. APPLICATION OF MEMS

12. • (a) pressure sensors, (b) strain gauges, and (c) accerolometer for the
measuring of acceleration and (d) gyroscope for the measurement of
rotation.
• car industry turbine of engine and power plant
• airbag deployment sensor
Microsensors:
• Involves the controlling and directing of the light band.
• MEMS-based Micro-Mirror array is a likely candidate to replace LCD &
LED as the dominant form of display technologies. This is due to the low-
cost and high performance of the micro-mirrors.
• Furthermore, due to the similar processes and facilities used in the
fabrication of the MEMS micro-mirrors, it is relatively easy to incorporate
them with their controlling IC chip onto a single silicon substrate.
• Digital Mirror Device (DMD) The DMD is a projection system based on a
very large array of micromachined mirrors. These mirrors are integrated
with on-chip CMOS microelectronics which control the position and
operation of the mirrors. A number of large screen projection systems
currently on the market use this DMD chip as the heart of the system
Optical and micro-Mirrors:

13. • MEMS have the great potential in (a) the Biomedical Instruments and Analysis, and
(b) Implants and Drug Delivery.
• Miniaturization of surgical and diagnostic instruments are done for reasons like
• (a) cost reduction,
• (b) less intrusive surgical procedures,
• (c) health concerns,
• (d) reducing amount of test sample needed, e.g. blood,
• (e) speed of diagnosis,
• (f) patient recovery time and,
• (g) ease of usage
Biomedical applications
• MEMS-based devices can also be used to make high performance, high precision
switches.
• These switches can be used for directing signals and to switch on or off micro
devices.
• One of the commercialized switches can be found in the Optical industry and was
developed in 1999 by Marxer andSercalo for the directing of signals.
• One of the main advantages of the switch comes from its low rate of signal loss.
Micro and RF Switches

14. Current Challenges
 Some of the obstacles facing organizations in the development of MEMS and
Nanotechnology devices include:
Packaging
•MEMS packaging is more challenging
than IC packaging due to :
•the diversity of MEMS devices and the
requirement that many of these
devices need to be simultaneously in
contact with their environment as well
as protected from the environment.
•Frequently, many MEMS and Nano
device development efforts must
develop a new and specialized
package for the device to meet the
application requirements. As a result,
packaging can often be one of the
single most expensive and time
consuming tasks in an overall product
development program.
Access to Fabrication
•Most organizations who wish to explore
the potential of MEMS and
Nanotechnology have little or no
internal resources for designing,
prototyping, or manufacturing devices,
as well as little to no expertise among
their staff in developing these
technologies. Few organizations will
build their own fabrication facilities or
establish technical development teams
because of the prohibitive cost.
Fabrication Knowledge
Required
•MEMS device developers must have a
high level of fabrication knowledge and
practical experience coupled with a
significant amount of innovative
engineering skill in order to create and
implement successful device designs.
Often the development of even the
most mundane MEMS device requires
very specialized skills. Without this
expertise and knowledge, at best
device development projects can cost
far more and take much longer. At
worst, they can result in failure.

15. NC MACHINE

16.  In a Numerical Control machine, the program is fed to the
machine through magnetic tapes or other such media. The
original NC machines were essentially basic machine tools
which were modified to have motors for movement along
the axes.
 In a Computer Numerical Controlled machine, the
machines are interfaced with computers. This makes them
more versatile in the sense that, suppose a change in
dimension of a part is required. In a NC machine, you
would have had to change the program in the tape and then
feed it to the machine again. But in a CNC machine, you just
change a variable in the computer and your modification is
done.

17.  in NC(numerical control) machine tools the part program is
entered on the program tape in the form of punched holes.
While in cnc machines the part program is entered into computer
using input devices like keyboard, mouse, cd etc.
 In nc machines the tape reader forms the machine control unit.
While in cnc the computer and the controller forms the machine
control unit
 An NC machine is numerically controlled but has no memory
storage and is run off of the "tape" each time the machine cycles.
A CNC machine has memory storage and the program can be
stored in its control.
The NC machine was the fore-runner of the modern machine
tool industry but is seldom used in todays manufacturing industry

18.  Operating is easy in CNC machine because the input is
given by keyboard and mouse whereas in NC machine input
is given on tape and then the tape is inserted in the machine.

19. History
 The first NC machines were built in the 1940s and 1950s,
based on existing tools that were modified with motors that
moved the controls to follow points fed into the system on
punched tape.
 These early servomechanisms were rapidly augmented with
analog and digital computers, creating the modern CNC
machine tools that have revolutionized the
machining processes

20. Description
 Motion is controlled along multiple axes, normally at least two (X and Y), and
a tool spindle that moves in the Z (depth).
 The position of the tool is driven by direct-drive stepper motor or servo
motors in order to provide highly accurate movements, or in older designs,
motors through a series of step down gears.
 Open-loop control works as long as the forces are kept small enough and
speeds are not too great.
 On commercial metal working machines, closed loop controls are standard
and required in order to provide the accuracy, speed,
and repeatability demanded.
 As the controller hardware evolved, the mills themselves also evolved. One
change has been to enclose the entire mechanism in a large box as a safety
measure, often with additional safety interlocks to ensure the operator is far
enough from the working piece for safe operation.
 Most new CNC systems built today are 100% electronically controlled.
 CNC-like systems are now used for any process that can be described as a
series of movements and operations. These include laser cutting, welding,
friction stir welding, ultrasonic welding, flame and plasma cutting, bending,
spinning, hole-punching, pinning, gluing, fabric cutting, sewing, tape and fiber
placement, routing, picking and placing, and sawing.

21. Examples of CNC machines
 Mills
 Lathes
 Plasma cutters
 Electric discharge machining
 Wire EDM
 Water jet cutters