SATHISH_KUMAR_MEMS-COMPLETE-MATERIAL.pdf

INTRODUCTION
TO
MEMS
Prepared by
Mr. L. Sathish Kumar, M.Tech, (Ph.D)
AP, ECE,
SCSVMV.
Prepared by: L.Sathish Kumar, AP, ECE,
SCSVMV UNIVERSITY.
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SYLLABUS OUTLINE
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Basic idea’s about:
• Physics
• Chemistry
• Integrated Circuits (IC)
• Measurement & Instrumentation (MI)
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Unit – 1
INTRODUCTION:
• Introduction & Historical background
• MEMS development
• Overview of Micro fabrication
• Fabrication process flow
• Process selection &
• Design
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Unit – 2
Actuators
Quartz
PZT
PVDF
ZnO
Sensors
Inertia sensor
Pressure sensor
Flow sensor
Tactile sensor
Thermal sensor
Piezoelectric sensor
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Unit – 3
LITHOGRAPHY AND ETCHING TECHNIQUE
• Origin & Overview
• Photolithography
• Sensitivity
• Resolution
• Enhancement technique
• Wet & Dry etching (including comparision)
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Unit – 4
SURFACE MICROMACHINING
• Intro to Micromachining
• Thin films
• Micromachining process – Bulk & Surface
Micromachining
• Comparision between Bulk & Surface
micromachining
• Top-Down & Bottom-Up micromachining
techniques
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Unit – 5
APPLICATIONS
MEMS in
• Automotive market
• Medical & Biomedical
field
• Environmental
monitoring
• Industrial automation
• Tele-communication field
Case-Studies
• Blood pressure(BP)
sensor
• Microphone
• Acceleration sensor
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UNIT – 1
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INTRODUCTION
MEMS or MST??...
• In United States, the technology is known as
microelectromechanical systems (MEMS)
• In Europe, it is called microsystems technology
(MST)
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Intro – Contd.,
• In 1989 - the acronym for “microelectromechanical systems”
(MEMS) introduced
• At the workshop named “Micro Tele-Operated Robotics
Workshop”
• Published in IEEE catalog number of 89TH0249-3
• Professor ‘Roger Howe’ at University of California – first
announced acronym “MEMS”
• National Science Foundation (NSF) funded a set of MEMS
projects under its “Emerging Technologies Initiative” – to
develop
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Intro – contd.,
• The “Defense Advanced Projects Research Agency”
(DARPA) put nearly $200 million into MEMS research
• The rate of filing of MEMS patents has reached over
160 per calendar year in 1997
• The most conservative market studies predict a world
MEMS market in excess of $8 billion in 2003
• Finally - In a phrase, “MEMS” has arrived
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Intro – contd.,
• Dr. Nadim Maluf - put together one of the finest MEMS
primers
• He concentrates mostly on how to design and manufacture
of MEMS
• The past few years have witnessed an increasing maturity
of the MEMS industry and a rapid introduction of new
products
• Market size for MEMS products has doubled in the past 5
years
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Intro – contd.,
• The keyword MEMS in all granted patents in the
United States since 1998 returns nearly 4,000
patents and references
• Added many more illustrations and pictures to
develop the familiarity with the technology
• The emergence of wireless and radio frequency
(RF) as a new market for MEMS technology
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Intro – contd.,
Courtesy of: Engineering &
Science, California Institute
of Technology, Pasadena,
California
The entire page measures a mere 5.9
μm on a side, sufficiently small that
60,000 pages
equivalent to the ‘Encyclopedia
Britannica’ can fit on a pinhead
The work, by T. Newman and R. F. W.
Pease of Stanford University.
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What are MEMS?
(Micro Electro Mechanical System)
• Micro – small size, micro fabricated
structure
• Electro – electrical signal / control
• Mechanical – mechanical functionality
• System – device, structure, system
control
Definition
“Micromachining [also microfabrication,
micromanufacturing] refers to the
fabrication of devices with at least some
of their dimensions in the micrometer
range”

What is MEMS technology?
Why is it Important?
• MEMS is technology of very small devices
• It is a combination of mechanical functions and electrical
functions on the same chip using micro fabrication
technology
• MEMS are made up of components between 1 to 100
micrometres in size
• MEMS device generally ranging size from 20micrometres
to millimetres

Building blocks in MEMS
There are three basic blocks in MEMS technology..
1. DEPOSITION – the ability to deposit thin films of
material on a substrate
2. LITHOGRAPHY – to apply a patterned mask on top of
photolithography imaging
3. ETCHING – to etch the films selectively to the mask
Materials Used – silicon, polymers, metals, ceramics

MEMS Manufacturing
Technology
1. Bulk Micromachining
2. Surface micromachining
3. High Aspect Ratio (HAR) silicon
micromachining Surface
Micromachining
HAR
Micromachinin
g

MEMS Applications
Medical Bio-Field:
• A MEMS is a device that can be implant in the
Human body
• MEMS Surgical tools provide the flexibility &
accuracy to perform surgery
• BioMEMS are used to refer to the science and
technology of operating at the micro scale for
biological & bio-medical applications
In Military & Defence:
• MEMS technology help projectiles to reach
their targets accurately

MEMS Applications – Contd.,
• Inertial Sensors
• Micromachined Pressure Sensors: Devices,
Interface Circuits, and Performance Limits
• Surface Micromachined Devices
• Microactuators
• Sensors and Actuators for Turbulent Flows
• Microrobotics
• Microscale Vacuum Pumps
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MEMS Applications – Contd.,
• Microscale Vacuum Pumps
• Nonlinear Electrokinetic Devices
• Microdroplet Generators
• Micro Heat Pipes and Micro Heat Spreaders
• Microchannel Heat Sinks
• Flow Control
• Reactive Control for Skin-Friction Reduction
• MEMS Autonomous Control
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Technological Breakthrough
Micro-engineering field - major breakthroughs in
almost all area’s like:
IT,
computers,
medicine,
health,
manufacturing,
transportation,
energy,
avionics,
security & many more fields.
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Contd.,
• The synthesis, design and optimization processes
are evolutionary in nature & they start with a
given set of requirements and specifications.
• Different criteria are used to synthesize and
design micro-transducers (micro scale
actuators and sensors) like:
Behavior,
Physical properties,
Operating principles, and
Performance.
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Contd.,
• physics-based synthesis is performed first in
order to start design at
the system-level,
subsystem-level,
component-level,
device-level &
structure- level.
• At each level of the design hierarchy, the system
performance in the behavioral domain is used to
evaluate. Prepared by: L.Sathish Kumar, AP, ECE,
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Contd.,
• ICs can be designed as the stand-alone MEMS
microelectronic components
• Performance requirements derived from desired
systems
functionality,
operating envelope,
affordability,
reliability, and
other requirements.
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Contd.,
• Integrating hardware (actuators–sensors–
ICs) with system:
intelligence,
control,
decision-making,
signal processing,
data acquisition, etc.
• New multidisciplinary developments areas
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Contd.,
Back-bone of nervous system and high-level
functional diagram
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Micromachining
• Micromachining is the underlying foundation
of MEMS fabrication
• Micromachining is the set of design and fabrication
tools that precisely form structures and elements at
a micro-scale.
• Creating micro features or surface characteristics.
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Micromachining Techniques
Photolithography
Etching
Silicon Micromachining
LIGA
Mechanical Micromachining
Xenon Difluoride dry phase etching
Electro-Discharge Micromachining
Laser Micromachining
Focused Ion Beam Micromachining
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MEMS Solutions..
• MEMS solution becomes attractive if it enables a
new function or provides significant cost
reduction or both.
In Medical application – need – high
performance
In Automotive application – need – low cost
reliability is always a dictated requirement
• A key element to cost competitiveness is batch
fabrication. Prepared by: L.Sathish Kumar, AP, ECE,
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To reach real-time Market..
• Demonstration of the first micro-machined
accelerometer took place in 1979 at Stanford
University. Yet it took nearly 15 years before it
became accepted as a device of choice for
automotive airbag safety systems
• In the process - it was designed and
redesigned, tested, and qualified in the
laboratory and in the field before it began
gaining the confidence of automotive suppliers.
• It takes 5 to 15 years before new technologies
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Materials for MEMS
• Using silicon, glass, ceramics, polymers, and
compound semiconductors made of group
III and V elements, as well as a variety of
metals including titanium and tungsten.
• But, Silicon remains the material of choice
for MEMS.
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Why Silicon?
• Silicon is one of very few materials that is
economically manufactured in single-crystal
substrates
• silicon is an elastic and robust material
whose characteristics have been very well
studied and documented
• Ultrapure, electronic-grade silicon wafers
available for the integrated circuit industry
are common today in MEMS
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Contd.,
• Silicon as an element exists with three different
microstructures: polycrystalline, amorphous &
crystalline.
• Polycrystalline or simply - “polysilicon” and
“amorphous silicon” are usually deposited as
thin films with typical thicknesses below 5μm.
• Crystalline silicon substrates are commercially
available as circular wafers with 100-mm (4-in)
and 150-mm (6-in) diameters.
• crystalline silicon is by far the most common
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Material - Physical Effects
Three physical effects commonly used in the
operation of micro-machined sensors and
actuators are:
1. Piezoresistivity - change in the electrical
resistivity of a semiconductor or metal when
mechanical strain is applied.
2. Piezoelectricity - electricity produced by
mechanical pressure on certain crystals.
3. Thermoelectricity - direct conversion of
temperature differences to electric voltage
and vice versa via a thermocouple. A
thermoelectric device creates a voltage when
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How MEMS made?
 How does one go about fabricating a device no
larger than an ant?
• The tools found in a standard machine shop -
tools such as lathes, milling machines, band
saws and CNCs have grown vastly in
sophistication and precision.
• At exceedingly high speed (~60,000 rpm or
greater) some of these machines are capable of
producing features in the sub-millimeter range,
and so-called “micromilling” is becoming a
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Contd.,
• The first MEMS, and indeed the bulk of
MEMS today, are fabricated using
techniques borrowed and adapted from
integrated circuit (IC) fabrication and
semiconductor processing.
• IC techniques create structures on thin, flat
substrates (usually silicon) in a series of
layered processes.
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Fabrication…
• Fabrication of products deals with making of machines,
structures or process equipment by casting, forming,
welding, machining & assembling.
• Classified into: Macro & Micro
• Macro: fabrication of structures/parts/products that
are measurable/observable by naked eye (greaterthan
1mm in size)
•
• Micro: fabrication of miniature
structures/parts/products that are not visible with
naked eye (microm in size)
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Methods of Micro Fabrication
• Material Deposition
• Material Removal (etching)
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WEEK-02-DAY-01 (18-08-2020)
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Introduction - Fabrication
• Manufacturing processes that can create
extremely small machines have been
developed in recent years.
• Electrostatic, magnetic, electromagnetic,
pneumatic and thermal actuators, motors,
valves, gears, cantilevers, diaphragms, and
tweezers of less than 100μm size have been
fabricated.
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• These have been used as sensors for pressure,
temperature, mass flow, velocity, sound, and
chemical composition, as actuators for linear
and angular motions and as simple
components for complex systems, such as lab-
on-a-chip, robots, micro-heat-engines and
micro heat pumps.
• Devices that have characteristic length of less
than 1mm but more than 1 micron, that
combine electrical and mechanical
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• Current manufacturing techniques for MEMS
include surface silicon micromachining, bulk
silicon micromachining, lithography, electro-
deposition, and plastic molding and electro-
discharge machining (EDM).
• making small machines with movable &
controllable parts.
• MEMS are finding increased applications in a
variety of industrial and medical fields with a
potential worldwide market.
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Applications
• Accelerometers for automobile airbags
• Keyless entry systems
• Dense arrays of micro-mirrors for high
definition optical displays
• Scanning electron microscope tips to image
single atoms
• Micro heat exchangers for cooling of
electronic circuits
• Reactors for separating biological cells
• Blood analyzers & Many more
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Microducts
Microducts are used in
• infrared detectors
• diode lasers
• miniature gas chromatographs &
• high-frequency fluidic control systems
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MEMS Fabrication
• The first MEMS are fabricated using
techniques borrowed and adapted from
integrated circuit (IC) fabrication and
semiconductor processing.
• Such techniques create structures on thin, flat
substrates (usually silicon) in a series of
layered processes.
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Example: MEMS Pressure Sensor
BULK MICROMACHINING
• Start with a thin silicon substrate, called a
wafer, typically measuring 200-400 µm thick.
• Then a thin layer of silicon dioxide (SiO2) is
then “grown” on the wafer.
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• Next, a thin layer of photosensitive material
called photoresist, or simply resist, is
deposited on the SiO2 layer in a process called
spinning.
• Then a transparent plate with selective
opaque regions called a mask is then brought
in close proximity to the wafer.
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• On the regions of the photoresist that make contact
with the UV light, the resist undergoes a
photochemical process in which it hardens and
becomes less soluble.
{This is true for a negative resist. If a positive resist were used, then the exposed
regions would become more soluble}
• The unexposed resist is removed by using a chemical
called a developer, leaving a portion of the SiO2 layer
exposed.
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• The result is a window through the resist to the
SiO2. This exposed region is then chemically
etched with buffered hydrofluoric (HF) acid.
• The presence of the photoresist on certain
regions, however, protects the SiO2 beneath it
from being etched.
• Another chemical process, the remaining
photoresist is stripped from the wafer leaving the
patterned SiO2.
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• The substrate itself is now etched using a
potassium hydroxide (KOH) solution.
• Unlike the previous etching process, however, the
KOH-Si reaction proceeds at different rates in
different spatial directions due to the crystalline
structure of the silicon substrate and its
orientation.
• Such a direction dependent etching process is
known as anisotropic etching.
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STEPS IN A TYPICAL BULK
MICROMACHINING PROCESS
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• In bulk micromachining the substrate itself
becomes part of the structure for the MEMS
device.
• In another technique called surface
micromachining, the structure of the MEMS
consists of layers of material built on top of
the substrate.
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SURFACE MICROMACHINING
• First, a polymer known as polyimide is
selectively deposited on the silicon substrate.
• The polyimide itself will not form any
structural part of the cantilever, but rather is a
temporary layer used to build around.
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• Such a temporary layer is called a sacrificial layer.
• Next a thin film of aluminum is deposited via physical
vapor deposition (PVD) on the sacrificial layer.
• The polyimide is then chemically removed in a
process called release.
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STEPS IN A TYPICAL SURFACE
MICROMACHINING PROCESS
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Micro-fabrication process
• Si Wafer Fabrication
• IC fabrication
 Deposition
 Spin coating
 PVD – Physical Vapor Deposition
 CVD – Chemical Vapor Deposition
 Lithography (Pattern transfer)
 Removal (Mostly etching process)
 Wet / Dry etching
 Plasma etching
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• One of the most important techniques
employed in microfabrication is the addition
of a thin layer of material to an underlying
layer.
• Additive techniques include those occurring
via chemical reaction with an existing layer.
• The addition of impurities to a material in
order to alter its properties, a practice known
as doping. Prepared by: L.Sathish Kumar, AP, ECE,
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Silicon substrate
• In MEMS and microfabrication we start with a
thin, flat piece of material onto which (or into
which – or both!) we create structures.
• This thin, flat piece of material is known as the
substrate, the most common of which in MEMS is
crystalline silicon.
• Silicon’s physical and chemical properties make it
a versatile material in accomplishing structural,
mechanical and electrical tasks in the fabrication
of a MEMS. Prepared by: L.Sathish Kumar, AP, ECE,
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• Almost, all crystalline silicon substrates are
formed using a process call the Czochralski
method.
• Silicon Wafer: Obtained from single crystel
Ingots.
• Single Crystal: All the basic units
(atoms/molecules) are arranged in a uniform
manner throughout the material.
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• Natural Crystal: Diamond, Ruby, etc., formed
by millions of years under the earth pressure
and temperature.
• Man-Made Crystal: Si, Ge & many other
technologically important materials as well as
engineered quantum structures.
“Man-made crystal is called “Crystal Growth”
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Example: 2013 – smart mobile
• MEMS devices in 2013:
 IMU Combo
 Magnetometer
 MEMS Microphones
 Pressure sensor
 Humidity + Temperature sensor
 BAW filters & duplexers
 Antenna tunner
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Example: 2018 – smart mobile
• MEMS devices in 2018:
 9-axis combo
 Pressure + Humidity + Temperature (Combo)
 More Mics
 Silicon timing for XO / TCXO / 32kHz clock
 Antenna switching
 Gas / Biochemical sensors
 Auto-focus
 MEMS mirrors
 Micro-speakers
 Touchscreen
 IR sensor
 Joystick
 Radiation Sensor
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MEMS Company’s
• ST Microelectronics
• Knowles Acoustics
• Avago
• AKM
• Bosch sensortec
• InvenSense
• TriQuint
• AAC Acoustics
• Kionix
• Yamaha
• ADI
• Goertek
• Memsic
• Alps Electric
• Freescale
• Gettop
• Epcos
• Fujitsu
• Qualcomm
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MEMS Design Process
MEMS product placement can be improved and development time can be
systematically shortened through the use of structured
design methods.
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Recent Trend in MEMS Design
Process
• Timelines from initial development through product release
for some successful MEMS commercial products have been
getting shorter as MEMS technologies have matured.
• Companies can no longer afford such long development
times.
• MEMS development time can be systematically shortened
through the use of structured design methods.
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Design Process and Design
Methods
• Methods through case studies.
• Methods that described to shorten
development time.
• Timelines of some of the earliest MEMS
technologies from initial reports, typically
based on academic research, to launch as a
mature commercial product.
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MEMS Product Time-Line
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Product & Company Name’s
• Piezoresistive silicon strain gauges were introduced in the
late 1950s by Kulite Semiconductor.
• Bell Lab’s first license of patents on semiconductor
piezoresistance reported in 1954.
• Digital pressure sensor by Freescale incorporates
calibration and compensation in a paired ASIC.
• Inkjet cartridge by Hewlett Packard uses integrated
circuitry in the nozzle region of thermal inkjet chip to
control droplet size and placement.
• Accelerometers by Freescale provide on-axis stability.
• Digital micro-mirror for digital light projection by Texas
Instruments led a revolution in optical MEMS and light
switching products.
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Product & Company Name’s – Contd.,
• Microfluidic chips by Caliper integrate sampling,
separations, and analysis.
• Film Bulk Acoustic Resonators (FBAR) by Avago
Technologies revolutionized electronic filter design
for the handset market.
• Micromachined MM3 electronic stability program
(ESP) gyroscopic sensor cluster by Bosch enables
consumer and automotive orientation sensing.
• Several time points of developments in the IC
industry that advanced piezoresistive MEMS design.
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Development Sequence
• Recent material and process developments in the
integrated circuits (IC) will have an equivalent impact
in MEMS industry.
• Many ensuing MEMS developments track
technological advances in the IC industry and the
development of micromachining.
• For example - advances in polysilicon, metals, and
surface micromachining also enabled rapid advances
in MEMS products.
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Development Sequence – Contd.,
• Subsequent advances in dry etching created
opportunities for smaller devices, denser packing
on a wafer, and the large aspect ratios needed for
channels or multi-axis devices.
• Silicon-on-insulator (SOI) wafer processes
enabled thinner membranes of high-quality
single crystal silicon (SCS).
• Follow-on products must reach market quickly if
they are to compete with existing products and
build or maintain market share with new designs.
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DESIGN PROCESS
• Design process begins with defining product
requirements.
• Requirements are determined through
interviews and surveys of customers & users,
as well as reviews of competitive products,
and are defined in terms of customer
specifications.
• Quantitative metrics for the specifications are
needed to measure and compare product
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• Designers should take care to build in test
structures and checkpoints in the process to
more accurately evaluate process-dimensional
tolerances and resulting material properties of
fabricated structures.
• Overall performance of the device or system
should be carefully considered with signal
conditioning and systems integration.
• Commercial products use both CMOS integrated
signal conditioning on the same chip as the
MEMS structures and ASICs in multichip modules
for signal conditioning.
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Product Definition Phase
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The product definition phase begins with defining and understanding the
customer(s) and market.

Product Design Phase
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The design process is not linear and short loops on
materials and process selection should feed back
frequently through stakeholder design reviews.

History of Design Methodologies
• Key design methods used in product development is Quality
Function Deployment (QFD).
• Mapping the customer requirements to the metrics and
specifications.
• QFD was first used in 1971 in the Kobe shipyard of Mitsubishi Heavy
Industries.
• Demonstrated results of using QFD encouraged others to adopt the
tool & usage became widespread in Japan.
• Through the 1970’s & 80’s, Japanese companies used QFD to
improve the effectiveness of their product development.
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• Xerox and other U.S. companies started to use QFD along
with Design for assembly (DFA).
• QFD is meant to provide guidance in product
development.
 Strategy planning,
 Rapid prototyping,
 Design of experiments &
 Design for assembly,
- to produce an effective development
project.
• QFD needs to human judgment & is not meant to
automate the design process.
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QFD Process – Roadmap
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Brainstorming
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• Idea generation activity involving the key stakeholders in
product definition, development, and implementation.
• Covering multiple topics, such as user requirements,
technical specifications, and design concepts.
• Moderator (project leader) - describes the objective(s) of
the exercise with the key requirements (high-level) for the
product & the moderator ensures all ideas are captured.
• Brainstorming rules the moderator must enforce –
 No idea is a bad idea
 Be creative and take risks
 No criticism allowed

Microphone - Case Study
• Microphones, in the class of acoustic sensors, provided motivation
for Avago Technology’s acoustic sensor project and Knowles SiSonic
MEMS microphone.
• Mic technology - seen large changes in the past few years with the
introduction of MEMS Mic.
• Electret-condenser microphones (ECMs) comprise the majority of
microphones (mic’s) used in consumer electronic devices.
• Typically contain a polymer membrane within a metal case.
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• ECMs could not withstand solder reflow processes due to
their low melting point materials.
• Costly hand insertion was required to mount ECMs on a
board.
• This limitation provided an opportunity for alternative mic
technology to penetrate the cellular handset and other
large audio markets.
Avago Technologies
• Produced more than one billion film bulk acoustic
resonator piezoelectric band pass filters, primarily used in
cell phones.
• FBAR technology - Dominates the cell phone band pass
filter market. Prepared by: L.Sathish Kumar, AP, ECE,
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• The company decided to look for ways to extend the
use of their technology through -
 Finite element analysis,
 Device layout & fabrication,
 Characterization,
 Acoustic modeling,
 Packaging & testing methods
- all have to be developed and implemented.
• Design of each element must be cognizant of the
requirements in order to optimize the product for -
 Performance,
 Cost &
 Fit to market.
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QFD Phase I:
 Focus development efforts on the most important aspects
of the design from a customer perspective, balancing
efforts among the design elements.
 Product development issues and emerge with a technically
and financially successful product.
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Design Process and Methods
• FBAR fabrication process was used as the basis of
the initial microphone process to enable fast
prototyping.
• Initial experiments were being run, QFD Phase-I
were applied to the acoustic sensor.
• The Results were used in three ways:
1. Determine on which aspects of the design
to focus.
2. Determine which design concepts were
likely to be viable to carry forward through
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QFD Phase – I
• Avago mic project, QFD Phase I was used in the Stanford University
Manufacturing Modeling Lab standard format, relating customer
requirements to engineering metrics.
• Matrix is generated – rows: customer desires such as size or ease-
of-use.. & customer requirements are listed in the leftmost column
of the matrix.
• Columns correspond to specific, quantitatively measured
engineering metrics, for example, linear dimension less than 1 mm.
• Engineering metrics are synonymous with product or process
specifications, and are listed in the top row of the matrix.
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• Matrix is filled out with the relative
relationship between each customer
requirement and engineering metric in the
intersecting matrix element.
• The results of QFD Phase I as applied to the
use of the piezoelectric microphones in
cellular handsets, laptops, and other
applications.
• The output of QFD Phase I is used as input for
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Concept Screening (CS)
• The output of Quality Function Deployment (QFD) Phase I is
used as input for Concept Screening (CS).
• Intent of CS is to screen design ideas, providing the
development team insight on which concepts are worth
pursuing.
• Only the three to five most important engineering metrics
from Phase I are utilized in CS.
• Put the chosen engineering metrics in the top row of the CS
matrix.
• Concepts should include physical form as well as materials
and manufacturing process, but should not be to the level
of detailed design. Prepared by: L.Sathish Kumar, AP, ECE,
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Concept Screening (CS) - Steps
1. Analyze the QFD Phase I results to select the 3, 4, or 5
engineering metrics with the highest weightings.
2. Use design and manufacturing team brainstorming,
competitor product information, literature, knowledge of
process capabilities, or whatever other means are
appropriate to create design concepts. 5-to-7 Design
concepts is a good target.
3. Evaluate each concept in comparison to the engineering
metrics. (“–1” if it is likely unable to meet the metric, “0”
if it will likely meet the metric, and “1” if it is likely to
exceed the metric)
4. Sum the scores for the concepts across the engineering
metrics, and record the total score in a column on the
right of the CS matrix.
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Concept Screening (CS) - Steps
5. Analyze the results. The highest ranking concept or
concepts are those most likely to be viable and most
worthwhile to prototype.
6. If there is more than one potential application, repeat
QFD Phase I and CS for each application, keeping the
design concepts constant.
7. Utilize the CS results in determining the viability and
direction of the project.
(NOTE: A comparison of total scores across applications
will highlight how well the technology and design
concepts fit the respective applications)
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CS – for Mic’s
The Design idea concepts are: (The CS results for the application of
piezoelectric mic’s to cellular handsets, laptops)
1. Piezoelectric mic with Deep Reactive Ion Etching (DRIE) backside cavity and
annular electrodes.
2. Piezoelectric mic with Potassium Hydroxide (KOH) backside cavity and
annular electrodes.
3. Piezoelectric mic with DRIE backside cavity and continuous electrodes.
4. Piezoelectric mic with KOH backside cavity and continuous electrodes.
5. Piezoelectric mic with shallow cavity and annular electrodes.
6. Piezoelectric mic with shallow cavity and continuous electrodes.
QFD and CS were performed after the first round of prototyping
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Cell phone – Mic
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Laptop – Mic
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• These concepts were developed by the project
technical team.
• QFD and CS were performed after the first
round of prototyping, so the team was able to
use initial test results in creating potentially
viable design concepts.
• Important aspects of the physical design
layout and function as well as critical
manufacturing process options are
represented in the concepts.
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Analyzing
• In analyzing the outcomes of CS, it is noted that design
concept 1, “Piezoelectric mic with DRIE backside cavity and
annular electrodes” ranked first in all three of the
application areas, although it was tied for first with concept
3, “Piezoelectric mic with DRIE backside cavity and
continuous electrodes” in the laptop.
• Relative ranking of the other concepts shifted depending
upon the application.
• The Result demonstrates that CS can be useful in
distinguishing the viability of concepts in different
application spaces.
• Total scores varied between the application areas, as the
engineering metrics and targets changed.
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Analyzing
• All the piezoelectric design concepts struggle to
meet sensitivity targets, making the total scores
generally lower in cell phone and laptop
applications.
• This insight on technology fit to market is
important to recognize and utilize.
• Outcomes of the QFD I and CS offer clarity
regarding which design concepts are most likely
to succeed so that resources may be assigned
commensurately.
• Score greater than or equal to zero shows a fair
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Results – Avago Mic’s
• Performance results of the Avago mic’s are published – over
the course of the first 8 months of the project, hundreds of
different designs were prototyped.
• These included:
 circular membranes with electrodes covering the
entire membrane surface.
 circular membranes with annular electrodes.
 circular membranes with electrodes restricted to
the center of the membrane.
 circular membranes with combinations of annular
and central electrodes connected in series and
parallel combinations & a variety of cantilevers.
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Mic – Design Options
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Annular Electrodes
Cantilever
Nested Electrodes

Result Discussion & View
• Extensive leverage of the FBAR process and infrastructure enabled
fast fabrication of initial prototypes and allowed many iterations of
prototyping in a short time span.
• ‘Dynamic range’ & ‘Total packaged linear dimensions’ were very
important in all application areas, whereas ‘Noise floor, Shock
resistance, Moisture tolerance & Sensitivity” were key in at least
one application.
• Design concept of creating a piezoelectric microphone with a DRIE
backside cavity and annular electrodes came with the highest rank.
• CS results drove realignment of the program to markets that
matched the technology capabilities.
• As development continues, QFD Phase I and CS should be repeated
with refined customer requirements, engineering metrics, and
design concepts. Prepared by: L.Sathish Kumar, AP, ECE,
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• General methodology of QFD I and CS may be utilized for
rapid development of other products and technologies.
• QFD Phase I can be applied to MEMS in the standard
format, and gives insight on the most critical engineering
metrics on which to focus design efforts.
• Concept Screening tool, used to evaluate design concepts
versus critical engineering metrics, can easily be applied to
other MEMS development efforts.
• CS was utilized in the development of a piezoelectric MEMS
microphone, enabling fast iterations of assessing the fit of
the technology and design concepts with various
applications.
• The Avago Mic’s – Case Study - Demonstrated a case of
extending an existing technology to new applications.

KNOWLES – Mic’s
• ‘Knowles’ has been successful in a number of
product areas, including hearing aids.
• Knowles began to develop a MEMS mic as a
defensive strategy to protect their hearing aid
business. Assisted by few steps:
1. Test,
2. Design &
3. Modeling.
(Note: Dr. Loeppert – Development effort)
• This effort ultimately resulted in the Knowles
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Knowles SiSonic Mic
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Knowles SisonicMicrophone
packaged with signal
conditioning chip

• By 1996, Knowles had achieved a working design,
but it was relatively expensive and the hearing
aid market was too small to justify the product
and development costs.
• Knowles decided to switch applications from
hearing aids to consumer products, first targeting
laptops and eventually cellular phones.
• Knowles sales to Motorola exceeded 30 million
by 2009.
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Summary
The methods find use in helping
companies with patented, well-characterized, or
otherwise advantageous materials or technology
knowhow to evaluate new markets and
applications (technology-push) and also help
companies sift through a wider range of
technologies and design options in pursuing a
new product or market (market-pull).
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Materials and Process
Selection
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Materials Selection
• Materials list for MEMS continues to grow, while CMOS
compatible materials and silicon still comprise a large
fraction of commercial products.
• Aid in materials selection based on attributes:
 Mass,
 Stiffness,
 Inertial load,
 Deflection &
 Frequency
- are related to materials properties.
• To obtain detailed materials data, test structures fabricated
in the same process as the device should be evaluated and
results fed back to a design iteration.
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Materials Selection
• Material properties may also be affected by
their processing history, such as:
Pressure,
Temperature,
Deposition method,
Etchant exposure & more.
• MEMS devices consist of primary (structural)
materials and secondary (dielectric,
interconnect) materials.
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The quality of materials data required for design
increases as the design process progresses

Process Chains and Capabilities
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• Designer should consider how to independently
observe and account for these process variables.
• Overall performance of the device should include
typical sensitivity and resolution specifications.
• Also metrics including reliability, cost, yield, and
repeatability, which are difficult to predict at the outset
of the design process but become more apparent
through careful evaluation of test structures and
process steps.
• Design methodologies that will aid the designer in
selecting the best concepts to carry forward through
prototyping and production.

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UNIT – 2
SENSORS AND ACTUATORS
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Roles in the Context of MEMS
Sensors: Detect and monitor physical or
chemical phenomena.
Transducer: A device that converts one form of
energy into another.
Actuators: Transform energy in non mechanical
energy domains into the mechanical domain.
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SENSORS
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Temperature Resistance Voltage Information
Stimulus (s)
Physical
Medium
Sensing
Element
Conditioning Target
Handling
Temperature Resistance Voltage Information
Signal (S)
Devices that measures physical quantities
and convert them into signals which can be read
by instruments.

ACTUATORS
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Signal Processing
& Amplification
Mechanism
Electric Hydraulic
Pneumatic Final Actuation
Element
Actuator
Sensor
Logical
Signal
Devices that actuates or moves something. More
specifically, they converts energy into motion or
mechanical energy.

Classification of Sensors
• In active sensing, have its own source of light or illumination.
• It includes transmitters that send out a signal, a light wavelength or
electrons to be bounced off the target, with data gathered by the
sensor upon their reflection.
• In passive sensing, measure reflected sunlight emitted from the
sun. When the sun shines, passive sensors measure this energy.
• It gather target data through the detection of vibrations, light,
radiation, heat or other phenomena occurring in the subject’s
environment.
(Note: The above two terms are used with the perspective of remote
sensing)
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Active & Passive Sensors
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Classification of Sensors
• In passive sensors, the power required to produce the output is
provided by the sensed physical phenomenon itself. (such as a
thermometer)
• The active sensors require external power source. (such as a strain
gauge)
• Classified again like - Analog or Digital based on the type of output
signal.
• Analogue sensors produce continuous signals that are proportional
to the sensed parameter and typically require analogue-to-digital
conversion before feeding to the digital controller.
• Digital sensors on the other hand produce digital outputs that can
be directly interfaced with the digital controller.
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What makes a good sensor? (MEMS)
• Precision: An ideal sensor produces same output for
same input. It is affected by noise and hysteresis.
• Resolution: The ability to detect small changes in the
measuring parameter.
• Accuracy: It is the combination of precision, resolution
and calibration.
•
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Calibration of Sensors
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• Most sensors are not ideal and are often affected by surrounding noise.
For a color sensor, this could be ambient light, and specular distributions.
• If a sensor is known to be accurate, it can be used to make comparison
with reference readings. This is usually done with respect to certain
standard physical references, such as for a rangefinder we may use a ruler
for calibration.
• Each sensor has a characteristic curve that defines the sensor’s response
to an input.
• The calibration process maps the sensor’s response to an ideal linear
response.
•

Sensors & Transducers
• The term transducer is often used synonymously with
sensors.
• Ideally, a sensor is a device that responds to a change
in the physical phenomenon.
• On the other hand, a transducer is a device that
converts one form of energy into another form of
energy.
• Sensors are transducers when they sense one form of
energy input and output in a different form of energy.
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Sensors & Transducers
• According to the Instrument Society of America -
• Sensor - Can be defined as “A device which provides a
usable output in response to a specified measurand”.
• Here, the output is usually an ‘electrical quantity’ and
measurand is a ‘physical quantity, property or condition
which is to be measured’.
• Transducer - It is defined as “An element when subjected to
some physical change experiences a related change or an
element which converts a specified measurand into a
usable output” by using a transduction principle.
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Some Definitions
• Range - The range of a sensor indicates the limits between which
the input can vary. For example, a thermocouple for the
measurement of temperature might have a range of 25-225 °C.
• Span - The span is difference between the maximum and minimum
values of the input. Thus, the abovementioned thermocouple will
have a span of 200 °C.
• Error - Error is the difference between the result of the
measurement and the true value of the quantity being measured. A
sensor might give a displacement reading of 29.8 mm, when the
actual displacement had been 30 mm, then the error is –0.2 mm.
• Sensitivity - Sensitivity of a sensor is defined as the ratio of change
in output value of a sensor to the per unit change in input value
that causes the output change. For example, a general purpose
thermocouple may have a sensitivity of 41 μV/°C.
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Some Definitions
• Dead band/time - The dead band or dead space of a transducer is the
range of input values for which there is no output. The dead time of a
sensor device is the time duration from the application of an input until
the output begins to respond or change.
• Repeatability - It specifies the ability of a sensor to give same output for
repeated applications of same input value. It is usually expressed as a
percentage of the full range output:
Repeatability = (Max – Min) / Full Range * 100
• Response Time - Describes the speed of change in the output on a step-
wise change of the measurand. It is always specified with an indication of
input step and the output range for which the response time is defined.
• Hysteresis - It is an error of a sensor, which is defined as the maximum
difference in output at any measurement value within the sensor’s
specified range when approaching the point first with increasing and then
with decreasing the input parameter.
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Key Issues in The Selection of Sensors
The field of View and Range
Accuracy
Repeatability and Resolution
Responsiveness in the target-domain
Power Consumption
Hardware Reliability
Size
Interpretation Reliability
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Opportunities
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General Sensors
 Resistive
 Capacitive
 Inductive
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Resistive Sensors
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Translational Single-Turn Multi-Turn
• Translational distance from 2 to 500 mm.
• Rotational displacements from 10o to 50o or more.
• Linear and active
Vo = I * R
R = Constant * Length / Area (*L/A)

Capacitive sensors
• The capacitance between two parallel plates of
area A separated by distance d is -
C = ε A/d.
‘ε’ is a constant related to the di-electric
material between both plates.
 Change d (distance)change the capacitance.
• Example: Elevators button switches, calculator
key pads, Position sensing, small dynamic motion.
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Capacitive sensors
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Inductive Sensors
Linear Variable Differential Transformer (LVDT)
• Used to measure pressure, displacement and
force.
• Inductance (L) α Distance and number of
turns.
• Can vary distance and number of turns
mechanically.
• Non linear.
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Stress and Strain
• Stress → Internal resistance to external force
• Strain → Displacement and Deformation due
to external force.
• Stress is linearly related to strain for elastic
materials.
• Strain Gages:
“Mechanical motion → Electricity”
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SENSORS
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Classification
• Based on Power Source - Active & Passive
• Based on Analog & Digital signal
• Based on Range of Measurement
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Linear and Rotational Sensors
• The position sensors produce an electrical output that
is proportional to the displacement they experience.
• 2 types are there: 1. Contact type, &
2. Non-Contact type.
• Contact type sensors such as strain gage, LVDT, RVDT,
tachometer, etc.
• Non-Contact type includes encoders, hall effect,
capacitance, inductance, and interferometer type.
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Linear and Rotational Sensors
• Usually the high-resolution type of sensors such as
 hall effect,
 Fiber optic inductance,
 Capacitance, and
 Strain gage
- are suitable for only very small range (typically from
0.1 mm to 5 mm).
• The differential transformers on the other hand, have a
much larger range with good resolution.
• Interferometer type sensors provide both very high
resolution (in terms of microns) and large range of
measurements (typically up to a meter).
• But, Interferometer type sensors are bulky, expensive, and
requires large set up time.
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• Among many linear displacement sensors, strain gage provides high
resolution at low noise level and is least expensive.
• A typical resistance strain gage consists of resistive foil arranged.
• A typical setup to measure the normal strain of a member loaded in
tension.
• The strain gauge is a passive, resistive transducer which converts
the mechanical elongation & compression into a resistance change.
• This change in resistance takes place due to variation in length and
cross sectional area of the gauge wire, when an external force acts
on it.
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Basic Experimental set-up
• Strain gage 1 is bonded to the loading member whereas strain gage 2 is
bonded to a second member made of same material, but not loaded.
• This arrangement compensates for any temperature effect.
• When the member is loaded, the gage 1 elongates thereby changing the
resistance of the gage.
• The change in resistance is transformed into a change in voltage by the
voltage sensitive wheat-stone bridge circuit.
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Acceleration Sensors
• Measurement of acceleration is important for systems subject to
shock and vibration.
• Although acceleration can be derived from the time history data
obtainable from linear or rotary sensors.
• Accelerometers whose output is directly proportional to the
acceleration is preferred.
• Two common types:
1. seismic mass type &
2. Piezoelectric accelerometer.
• seismic mass type accelerometer is based on the relative motion
between a mass and the supporting structure.
• Seismic mass limits its use to low to medium frequency
applications.
• Piezoelectric accelerometer, however, is compact and more suitable
for high frequency applications.
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Force, Torque, and Pressure Sensors
• Among many type of force/torque sensors, the strain gage
dynamometers and piezoelectric type are most common.
• Both are available to measure force and/or torque either in
one axis or multiple axes.
• The dynamometers make use of mechanical members that
experiences elastic deflection when loaded.
• These types of sensors are limited by their natural
frequency.
• On the other hand, the piezoelectric sensors are
particularly suitable for dynamic loadings in a wide range of
frequencies.
• They provide high stiffness, high resolution over a wide
measurement range, and are compact.
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Flow Sensors
• Flow sensing is relatively a difficult task. The fluid
medium can be liquid, gas, or a mixture of the two.
• Furthermore, the flow could be laminar or turbulent
and can be a time-varying phenomenon.
• The venturi meter and orifice plate restrict the flow and
use the pressure difference to determine the flow rate.
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• The pitot tube pressure probe is another popular method
of measuring flow rate.
• When positioned against the flow, they measure the total
and static pressures.
• The flow velocity and in turn the flow rate can then be
determined.
• The rotameter and the turbine meters when placed in the
flow path, rotate at a speed proportional to the flow rate.
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pitot tube pressure probe

• The electromagnetic flow meters use
noncontact method.
• Magnetic field is applied in the transverse
direction of the flow and the fluid acts as the
conductor to induce voltage proportional to
the flow rate.
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electromagnetic flow meters

• Ultrasonic flow meters measure fluid velocity
by passing high-frequency sound waves
through fluid.
• As the wave travels towards the receivers (R),
its velocity is influenced by the velocity of the
fluid flow due to the doppler effect.
• This can be used for very high flow rates and
can also be used for both upstream and
downstream flow.
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Temperature Sensors
• A variety of devices are available to measure temperature,
the most common of which are thermocouples,
thermistors, resistance temperature detectors (RTD), and
infrared types.
• Thermocouples are the most versatile, inexpensive, and
have a wide range up to 1200‫﮲‬C typically.
• A thermocouple simply consists of two dissimilar metal
wires joined at the ends to create the sensing junction.
• When used in conjunction with a reference junction, the
temperature difference between the reference junction
and the actual temperature shows up as a voltage
potential.
• Thermistors are semiconductor devices whose resistance
changes as the temperature changes.
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• The relationship between the temperature
and the resistance is nonlinear.
• Linear over a wide range and most stable.
• Infrared type sensors use the radiation heat to
sense the temperature from a distance.
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Proximity Sensors (closeness)
• Used to sense the proximity of an object relative
to another object.
• Usually provide a ON or OFF signal indicating the
presence or absence of an object.
• Inductance, capacitance, photoelectric, and hall
effect types are widely used as proximity sensors.
• Inductance proximity sensors consist of a coil
wound around a soft iron core.
• The inductance of the sensor changes when a
ferrous object is in its proximity.
• This change is converted to a voltage-triggered
switch.
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• Capacitance types are similar to inductance
except the proximity of an object changes the gap
and affects the capacitance.
• Photoelectric sensors are normally aligned with
an infrared light source.
• The proximity of a moving object interrupts the
light beam causing the voltage level to change.
• Hall effect voltage is produced when a current-
carrying conductor is exposed to a transverse
magnetic field.
• The voltage is proportional to transverse distance
between the hall effect sensor and an object in its
proximity.
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Selection Criteria
 Range —Difference between the maximum and minimum value of the sensed
parameter
 Resolution —The smallest change the sensor can differentiate
 Accuracy —Difference between the measured value and the true value
 Precision —Ability to reproduce repeatedly with a given accuracy
 Sensitivity —Ratio of change in output to a unit change of the input
 Zero offset —A nonzero value output for no input
 Linearity —Percentage of deviation from the best-fit linear calibration curve
 Zero Drift —The departure of output from zero value over a period of time for no
input
 Response time —The time lag between the input and output
 Bandwidth —Frequency at which the output magnitude drops by 3 dB
 Resonance —The frequency at which the output magnitude peak occurs
 Operating temperature —The range in which the sensor performs as specified
 Dead-band —The range of input for which there is no output
 Signal-to-noise ratio —Ratio between the magnitudes of the signal and the noise
at the output
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Varieties of Sensors
VARIETIES OF SENSORS
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Sampling and Quantization
• The process of the discretization of the domain of the signal being
measured is called sampling, whereas quantization refers to the
discretization of the range.
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SAMPLING: Evaluating the input
signal at discrete units of time,
say 0, T, 2T, ….. nT.
QUANTIZING: Provides
discretized values to the input
on basis of a finite number of
thresholding conditions.
ENCODING: Transforms the
digital data into a digital signal,
comprising of bits 0111011…,
on basis of various schemes.
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• If the sampling rate isn’t high, one can end up with
different signals (aliases) during reconstruction, that fit
the same set of sample points. This is called aliasing,
and is undesirable. For best sampling, the sampling
rate must be >= 2 times the frequency of the signal.
(Nyquist Shannon Sampling Theorem)
• In the case of quantization, selection of fewer levels of
discretization can lead to progressive loss of spatial
detail. Also, contours (artificial boundaries) can start
appearing due to sudden changes in intensity. For
audio signals, this can be heard as noise/distortions.
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Camera
• Vision processing requires a lot of RAM, and
even low resolution cameras may give lots of
data, parsing through which can be difficult.
• Cameras draw in around 0.1 A current, the
current rating of the USB hub to which they
are attached must be checked.
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Inertial Measurement Unit
Consists of three sensors:
• Accelerometer: Used to
measure inertial acceleration.
• Gyroscope :Measures angular
velocity about defined axis.
• Magnetometer : Can be used
along with gyroscope to get
better estimates of robot’s
orientation.
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Photo-resistors
• Light sensitive resistors whose
resistance decreases as the
intensity of light they are
exposed to increases. They are
made of high resistance
semiconductor material.
• When light hits the device, the
photons give electrons energy.
This makes them jump into the
conductive band and thereby
conduct electricity.
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Infrared Sensor
• IR led is led that emits light
in IR region and can't be
seen by the eyes.
• Photodiode is a type of
diode which works in
reverse bias and its
resistance is changed when
subjected to change in light
intensity.
• They are used for colour
detection etc.
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Flex Sensors
• Measure the amount of
deflection caused by
bending, also called bend
sensors.
• The bending must occur
around a radius of
curvature, as by some angle
at a point isn’t effective and
if done by more than 90
deg., may permanently
damage the sensor.
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Ultrasonic Sensor
• These are commonly used for obstacle
detection.
• Works on principle similar to that of Sonar
which consists of time of flight, the Doppler
effect and the attenuation of sound waves.
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Rotary Encoder
• They convert the angular
position of a shaft or axle to
a analog/digital code.
• They may represent the
value in absolute or
incremental terms. The
advantage of absolute
encoders is that they
maintain the information of
the position even when
power is removed, and this
is available immediately on
its application.
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Touch Sensor
• Touch sensors can be defined as switches that
are activated by the touch.
• Examples includes capacitance touch switch,
resistance touch switch, and piezo-touch
switch.
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Thermocouple
• Converts thermal energy into electrical energy
and is used to measure temperature.
• When two dissimilar metal wires are
connected at one end forming a junction, and
that junction is heated, a voltage is generated
across the junction.
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ACTUATORS
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Types of Actuators
In a robot, actuators are used in order to
produce some mechanical movement.
• Electric Electro-mechanical devices
which allow movement through use of
electrically controlled systems of gears.
• Hydraulic Transforms energy stored in
reservoirs into mechanical energy by
means of suitable pumps.
• Pneumatic Uses pneumatic energy
provided by air compressor and
transforms it into mechanical energy by
means of pistons or turbines.
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Actuator Functional Diagram
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Motor Driver
• Microcontrollers, typically, have current rating of 5-10 mA, while
motors draw a supply of 150mA. This means motors can’t be
directly connected to microcontroller.
• For electromechanical actuators, following motor drivers are often
used:
 Simple DC Motors
L298, L293.
 Servo Motors
Already have power cable and
different control cable.
 Stepper Motors
L/R Driver Circuit, Chopper Drive. L298N Stepper Motor Driver
Controller
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Speed Control using PWM
• Pulse Width Modulation (PWM) is scheme in which duty cycle
of square wave output from the microcontroller is varied by
providing a varying average DC output.
• Voltage seen by the load is directly proportional to the
unregulated source voltage.
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Components of a System Hardware
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Data Handling Systems
• Both data about the physical world and control
signals sent to interact with the physical world
are typically "analog" or continuously varying
quantities.
• In order to use the power of digital electronics,
one must convert from analog to digital form on
the experimental measurement end and convert
from digital to analog form on the control or
output end of a laboratory system.
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Data Collection after Control
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Input / Output Devices
Binary Data:
 Contact input interface – input data to computer.
 Contact output interface – output data from computer.
Discrete Data other than Binary:
 Contact input interface – input data to computer.
 Contact output interface – output data from computer.
Pulse Data:
 Pulse counters - input data to computer.
 Pulse generators - output data from computer.
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Applications of MEMS Sensor
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Inertial Sensor
High-performance inertial sensors:
• With regard to the applications.
• We consider all inertial sensors except for the consumer/mobile and
automotive applications.
• We take into account industrial, aerospace, defense applications (even
industrial applications are considered as “high-performance”
applications, as opposed to consumer ones).
• In some cases: consumer-grade MEMS gyroscopes (for instance few °/h
bias stability) are used in industrial applications.
High-End MEMS Inertial Sensors used in Defense, Aerospace & Industrial
Applications.
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Inertial Sensor
• The only parameter which is considered is the bias stability.
• To simplify representation, performance has been divided
into 4 segments:
 >5°/h range
 0.1-5°/h range
 0.01-0.1°/h range
 <0.01°/h range
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Inertial Sensor
>5°/h range:
 Industrial grade (but it doesn’t mean that this is an
industrial application for instance, often missile and bomb
guidance require moderate bias stability and fall in this
category).
 Ability to get data on angular rates / on motion.
0.1-5°/h range:
 Tactical grade.
 possibility to get angles.
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Inertial Sensor
0.01-0.1°/h range:
 Mid-term navigation grade.
 Possibility for mid-term navigation (for GPS outage)
and azimuth detection.
<0.01°/h range:
 High-end navigation & strategic grade.
 ability to navigate.
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Inertial Sensor
• Day to day bias stability is considered for navigation grade;
this is the most significant parameter in characterizing a
navigation system.
• In-run bias stability is used for industrial and tactical grade
because –
• In the past 20 years, MEMS have appeared and delivered
performance in terms of in-run parameters.
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Inertial Sensor
• Use of inertial sensors is now frequently used in
conjunction with GPS, meaning that day-to-day
bias repeatability is no longer significant (for
tactical / industrial grade).
• Other parameters may need to be considered as
well, depending on the application.
• Parameters such as angular random walk or scale
factor may be more important than just bias
stability.
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Inertial Sensor
• The high-end inertial is a tough market, between the different
technologies, the different level of integration, at different
performances and the numerous applications of major
markets which lead to a complex description of this broad
market.
• Added to that, as we deal with critical applications (defense &
aerospace), the availability of various data is limited since
many players are reluctant to discuss and disclose information
about these sensitive markets.
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GYRO Technology
• Gyroscope Definition: A gyroscope is a device for
measuring or maintaining orientation, based on
the principles of conservation of angular
momentum.
• Gyroscopes are based on 3 sensing technologies:
1. Mechanical / Vibration based gyroscopes
(Coriolis force)
2. Optical gyroscopes (Sagnac effect)
3. Resonating gyroscopes (Resonating mass)
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Principle of Gyroscope
Whenever a body is rotating in a plane (plane YZ) and a
couple is applied on the rotating body across the axis of rotation
or spin in an another perpendicular plane (plane XY), the
rotating or spinning body starts processing in a third mutually
perpendicular plane (plane XZ).
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Application
• In Aeronautics:
– Remote control flying devices, helicopters, some hovercraft, etc. rely
on gyroscopes to prevent them from flipping over or going into a spin.
• In Spacecraft: for orientation while in space. Also for changing in
direction & altitude.
• In Naval field: To maintain stability as the effect of gyroscopic couple.
(steering; pitching; rolling)
• In Automobile: Used in Racing car industry. (engine act like big
gyroscope) [balancing]
• In Electronics and Gadgets: smart mobile; video game controllers;
computer mouse; presentation mouse; etc.
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GYRO Technology - Types
• 7 types of gyros have been identified:
1. Mechanical / Spinning Mass gyroscopes
2. Electric Suspension (electrostatic) Gyroscopes (ESG)
3. Ring Laser Gyros (RLG)
4. Fiber Optical Gyroscopes (FOG)
5. Hemispherical Resonator Gyroscopes (HRG)
6. Quartz Gyroscopes (non-MEMS)
7. Micro-machined Gyros (MEMS): vibrating quartz or
vibrating silicon
• Old technology is mechanical dynamically tuned gyros also
called dynamically tuned gyros (DTG)
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Gyroscope
• First appearance: Wii Motion Plus accessory, 2009
June.
• First Android smart phone: Nexus S (end of 2010).
•
• Pros:
 Not sensitive to gravity.
• Cons:
 Currently supported only by high-end Android
phones.
 Drift problems.
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• 7 types of gyros have been identified (upto 2019):
1. Mechanical / Spinning Mass gyroscopes
2. Electric Suspension (electrostatic) Gyroscopes (ESG)
3. Ring Laser Gyros (RLG)
4. Fiber Optical Gyroscopes (FOG)
5. Hemispherical Resonator Gyroscopes (HRG)
6. Quartz Gyroscopes (non-MEMS)
7. Micro-machined Gyros (MEMS): vibrating quartz or
vibrating silicon
• Old technology is mechanical - dynamically tuned gyros
(DTG).
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Gyroscope
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Gyroscope – 3 Axes
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Gyroscope Measurement Data
• Measures rotation around 3 axes.
• More exactly: measures rotation speed (angular velocity)
around the axes.
• Get the angle difference:
• Get the absolute angle:
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Parameters – Sample
• Drift:
• Noise:
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Gyro - as Support Sensor
• Because of accumulating error, gyro alone can be rarely used.
• But,
 The gyro has accumulated error but is not sensitive to
gravity.
 The accelerometer has no accumulated error but has the
gravity component problem.
• Sensor fusion: the use of multiple sensors so that they
compensate each other's weaknesses.
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Gyroscopes - Properties
• Gyroscopes have two basic properties:
1. Rigidity &
2. Precession
• RIGIDITY: The axis of rotation (spin axis) of the gyro wheel
tends to remain in a fixed direction in space if no force is
applied to it.
• PRECESSION: The axis of rotation has a tendency to turn at a
right angle to the direction of an applied force.
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Accelerometer-Gyro Fusion
• The easy way
 Use the virtual sensors that calculate gravity and linear
acceleration from multiple sensors.
• The hard way
 Process raw accelerometer and gyroscope data to yield
the motion information you need.
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Virtual Sensors
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Accelerometer-Gyro Fusion
• Remember: accelerometer measures the sum of gravity and
motion acceleration.
• Kills two use cases:
1. If you need device tilt, the motion acceleration
component corrupts the measurement.
2. If you want motion acceleration, it is impossible to
subtract the gravity acceleration in a general case.
• Separate gravity and motion acceleration with the help of the
gyroscope.
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Concept Diagram
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Concept
• Pick a reliable gravity vector measurement (make
sure that there's no motion then).
• If you detect motion, rotate the previous gravity
vector using the gyroscope data and use it as gravity
vector estimation.
• Subtract this gravity vector estimation from the
measured acceleration – this yields the motion
acceleration.
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Updating the Gravity Vector Estimation
• The gravity vector estimation has to be updated time to time
as rotation angle errors accumulate.
• If we detect an acceleration measurement where there is no
motion acceleration, we can take it as new reliable gravity
vector estimation.
• If the absolute value of the accelerometer output is close to
the Earth's gravity, we can assume that there's no motion;
 the gravity vector estimation can be updated with the
current accelerometer output.
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Recognizing motion
• 3D linear acceleration signals are not so intuitive.
• Motion recognition:
 Record acceleration pattern of reference motion and
compare with these references.
 Convert from acceleration domain to something more
intuitive like velocity.
 Accelerometer/gyroscope bias will become linearly
growing drift after you integrate the acceleration signal.
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Walking with Swinging Hand
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Walking with Steady Hand
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MEMS Accelerometer
• MEMS accelerometer are very tiny
electromechanical sensors that gives output in
electronic form (i.e. voltage/current).
• Types of MEMS accelerometers:
Capacitive
Piezoelectric
Piezoresistive
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Capacitive Accelerometer
• In capacitive accelerometer micro-machined silicon material is
used.
• The distance between these materials varies with the
acceleration faced by the accelerometer that causes to
change the capacitance which leads to change output voltage.
• The particular output voltage defines a particular
acceleration.
• Out put can be: Analog or Digital.
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Concept Diagram
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Acceleration Measurement
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Kalman Filter
• Kalman Filter was proposed by Hungarian-American engineer
Rudolf Emil Kalman.
• Kalman Filter is a mathematical estimation algorithm that
involves a wide range of processes and applications.
• The Kalman Filter has main function of combining the
measurement of time series data of the same variables but
from the different sensors and to forecast the state.
• It predicts the state and corrects it.
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Conclusions..
• Each sensor has strengths and weaknesses.
• Combine them and they compensate each other.
• Some sensor fusion is already built-in.
• Motion recognition based on 3D linear acceleration
signal is much more exact than doing the same from
1D signal.
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PRESSURE SENSOR
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Pressure Sensor
• Pressure sensing was one of the first successful applications
for MEMS in automotive and industrial applications.
• MEMS pressure sensor consists of one or more pressure
sensitive diaphragms or membranes and often an integrated
transducer mechanism to translate the mechanical change
into an electrical signal.
• By applying an external pressure, the membrane will deflect
and this deflection will be measured by various physical
principles such as piezoresistive, capacitive, magneto resistive
or optical means.
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Pressure Sensor
• Two different manufacturing processes are used to form the
pressure sensitive membrane or diaphragm.
1. Bulk Micromachining (BMM) &
2. Surface Micromachining (SMM).
• Pressure sensors have been developed that use a wide range
of sensing techniques, from the most common piezoresistive
type to high-performance resonant pressure sensors.
• Miniature high-performance sensors at low cost has opened
up a wide range of applications.
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• Examples include automotive manifold air and tire pressure,
industrial process control, hydraulic systems, microphones,
and intravenous blood pressure measurement.
• Pressure sensor, then looks at silicon diaphragm fabrication
and characterization, applied sensing technologies, and
applications.
• Pressure is defined as a force per unit area, and the standard
SI unit of pressure is N/m2 or Pascal (Pa).
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Block Diagram – Pressure Sensor
• A range of sensing elements designed to deform under
applied pressures can be fabricated using micromachining
techniques, the most common by far being the diaphragm.
• Transduction mechanisms suitable for measuring strain or
displacement.
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Physics of Pressure Sensing
• The pressure at a given point within a static fluid occurs due
to the weight of the fluid above it.
• This pressure acts in all directions, which leads us to
Archimedes’ principle, which states that when a body is
immersed in a fluid it is buoyed up (i.e., appears to lose
weight) by a force equal to the weight of the displaced fluid.
• A – Area; t – Thickness; Pb – Pressure acting upward; Pd – net
pressure (pressure on top face of the block);  This is the
basic principle by which objects float in liquids.
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• If the weight of a displaced liquid exceeds the weight of the
object, then it has positive buoyancy and will float on the
surface.
• If the weight of the object exceeds the weight of the liquid it
will have negative buoyancy and sink.
• Neutral buoyancy is obtained by when the weight of the
object equals the weight of displaced liquid, and therefore Pb
= Pd.
• Objects with neutral buoyancy will remain suspended in the
liquid at whatever depth they are located.
• Submarines, for example, typically operate at neutral
buoyancy and change depth by angling fins and moving
forward.
• Atmospheric pressure is related to the above case.
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• The incompressible nature of liquids enables them to be used
in hydraulic systems.
• Pascal’s principle states that a liquid can transmit an external
pressure applied in one location to other locations within an
enclosed system.
• The distance moved by the larger piston will be less than that
moved by the smaller piston.
• This principle is used in hydraulic car jacks and presses.
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PITOT TUBE
HYDRAULIC FORCE

Challenges
• New challenges with regard to the passivation of the sensor
and the approaches to protecting the device from
environmental influences to which it necessarily has to be
exposed during operation.
• This is why a larger variety of technologies exists for the
different pressure-sensing fields, for example, low-pressure or
high-pressure range, low or high operating temperature,
gaseous or liquid media, aggressive or nonaggressive ambient.
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Bulk-Micromachined Pressure Sensors
• Predominantly wafers with crystal orientation are etched from the
backside to a predetermined depth, which leaves a remaining membrane
of the desired thickness at the front-side of the wafer.
• Wet etching in KOH solutions is one technology of choice for etching
nearly through the full wafer thickness.
• For membrane thickness control, either a time-determined etch or
etchstop techniques (p+-etchstop, electrochemical etchstop on reversely
polarized pn junction or dielectric etchstop for SOI-wafers) can be applied.
• Sharp transitions may cause early fracture of the sensor membrane under
an overpressure load.
• This is one of the reasons why, as an alternative to wet etching, DRIE of
silicon is becoming more and more popular and expanding over traditional
KOH-dominated application fields.
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• One more advantage of DRIE is that the geometry of the
cavities and thereby of the membranes can be arbitrarily
chosen, irrespective of crystal orientation (for example, round
cavities and membranes instead of squares or rectangles).
• As a disadvantage, no electrochemical nor p+-etchstop exists
for DRIE.
• A third alternative is to use SOI wafers, which provide a
dielectric etchstop at the buried oxide of the SOI-wafer stack.
• A general feature of bulk-micromachined pressure sensors is a
clear separation between front-side and backside processing.
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• As a rule, semiconductor-type process steps are performed on
the wafer frontside, for example, diffusions, oxidation, layer
deposition, and etching, up to a full IC process in the case of
an integrated sensor.
• Again, steps are performed afterward on the backside of the
wafer, following the IC fabrication process, with the finished
frontside being protected by appropriate measures.
• Advantage: compatibility requirements between frontside and
backside processing are weak, since the membrane is always
in between.
• This makes it possible to integrate a full electronic circuit at
the wafer frontside and to perform the KOH or DRIE
micromachining at the wafer backside with a low risk of
interfering with the frontside.
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• Cross section and encapsulation of pressure sensor. Contact with the
outside world is only to the back side of the sensor membrane,
hermetically isolating the front side containing the electronics from the
environment.
• Main disadvantages of this concept are that backside processing is:
1. Non-standard in semiconductor technology.
2. Requiring dedicated equipment and specialized wafer handling.
3. Backside quality and surface finish, together with thickness and
thickness variations of the wafers.
4. Carefully monitored.
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Surface-Micromachined Pressure
Sensors
• Surface micromachining is an additive microstructuring technology
that is based on the deposition or bonding of additional layers onto
the wafer frontside.
• Processing steps take place exclusively on the wafer frontside,
which moves this technology very close to semiconductor
standards.
• Surface-micromachined pressure sensors are fabricated by
depositing the membrane material (in most cases, either poly- or
single-crystalline silicon) over a so-called sacrificial layer, for
example, silicon oxide or porous silicon.
• This sacrificial layer is later removed either by selective etching (for
example, by hydrofluoric acid) through membrane perforations,
which have to be closed by a subsequent deposition process, or by
thermally collapsing the sacrificial layer in the case of porous
silicon.
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Advantages
Advantages of surface-micromachined pressure sensors are:
1. Minimum surface area consumption.
2. Independence from wafer thickness and thickness
variations.
3. No requirements with respect to the backside quality or
surface finish.
4. Since the backside is not processed at all; ease of
mounting the devices.
5. Robustness of the wafers throughout the whole
manufacturing process.
6. Standard processing and handling.
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Disadvantage
• Potential disadvantage of surface micromachined pressure
sensors is the process restrictions resulting from
compatibility requirements between MEMS and non-MEMS
processes performed on the same wafer side.
• Most important is the fact that during sensor operation,
pressure has to be applied to the frontside membrane,
exposing the whole wafer frontside to the medium whose
pressure is to be measured.
• If, sensor application involves only nonaggressive media,
silicone gel coverage is in many applications sufficient to
protect the delicate wafer frontside from humidity and
dust.
• These measures may represent a considerable extra effort
and a severe complication of the sensor device.
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Signal Generation
• The question of how to detect the deflection of the
membrane, i.e., the applied pressure, is not fully
independent from the fabrication technology of the sensor
element.
• Most bulk-micromachined pressure sensors use a
piezoresistive type of detection, which is most appropriate
and easy to realize for this particular technology.
• Also exist for capacitive evaluation of bulk-micromachined
pressure sensors.
• One wafer contains the membranes, and a second wafer
provides the required counter-electrodes opposite to the
membranes.
• Capacitive detection is much simpler with surface-
micromachined pressure sensors.
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Pressure Sensor Specifications
1. Zero/Offset and Pressure Hysteresis of Zero
2. Linearity
- Independent linearity,
- Terminal based linearity,
- Zero-based linearity.
3. Hysteresis
4. Sensitivity
5. Long-Term Drift
6. Temperature Effects
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Pressure Sensor Types
1. Absolute pressure sensors
2. Gauge pressure sensors
3. Differential pressure sensors
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Samples – Pressure Sensor
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FLOWSENSORS
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Introduction
• Flow is defined as the quantity of fluid (gas,
liquid, vapour or sublimate) that passes a
point per unit time.
• It can be presented by a simple equation:
Flow (Q) = quantity/time.
• It is the rate of change of a quantity. It is
either volumetric or mass flow rate.
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Properties Affecting Fluid Flow
• Velocity of Fluid – the fluid speed in the direction of flow.
The fluid velocity depends on the head pressure that is forcing
the fluid through the pipe. The greater head pressure, the
faster fluid will flow.
• Pipe size – the larger the pipe, the greater the potential
flow rate
• Pipe friction – reduces the flow rate through the pipe. Flow
rate of the fluid is slower near walls of the pipe that at the
center.
• Fluid viscosity – its physical resistance to flow.
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• The specific gravity of fluid – at any given operating
condition, the higher fluid’s specific gravity, the lower
its flow rate.
• Fluid condition – the condition of fluid (clear or
dirty) is one of the limitations in flow measurement,
some measuring devices blocked/plugged or eroded
if dirty fluids are used.
• Velocity Profiles – it has major effect on the accuracy
of most flow meters. It can be laminar, transitional or
turbulent flow.
Properties Affecting Fluid Flow
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Importance of Fluid Measurement
• Measuring flow is one of the most important aspects
of process control.
• The most diverse substances are transported and
distributed in piping system.
• The fluid flowing through pipes have different
properties, so different flow measuring devices are
used.
• The maintenance of definite rates of flow is
important for maximum efficiency and
production.
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Types of Flow Meters
1. Differential pressure flow meters
2. Coriolis Flow meter
3. Vortex Flow meter
4. Ultrasonic Flow meter
5. Electromagnetic Flow meter
6. Thermal Flow meter
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1. Differential Pressure Flow Meters
- It works on the principle of partially
obstructing the flow in a pipe. This creates a
difference in the static pressure between the
upstream and downstream side of the device.
- The difference between static pressure
(referred to as differential pressure) is
measured and used to determine the
flowrate.
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q  V2S0
where:
 = ratio of meter diameter to pipe diameter ≈ 0.5 usually
S0 = cross sectional area of orifice
V = bulk velocity through the orifice/venturi or nozzle
C0 = discharge coefficient ≈ 0.61 for Re > 30,000
1 4
V 2 

2pa  pb 
C0
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Some of the most common types of differential
flow meters are:
• orifice flow meter
• venturi flow meter
• nozzle flow meter
• pitot tube flow meter
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Orifice Flow Meters
Orifice plates are the most common type
of Δp meter and are basically a machined
metal plate with a hole, as shown below.
The plate has a sharp upstream edge and
usually a bevelled edge downstream of
the flow.
Upstream face Downstream face
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The components of a typical orifice flow meter installation are:
• Orifice plate and holder
• Differential pressure transmitter
• Flow indicator or recorder
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Advantages and Disadvantages
Advantages
•Lower cost and easy to install
•Smaller physical size
•Flexibility to change throat to pipe diameter ratio to
measure a larger range of flow rates
Disadvantage
•High pressure loss
•Large power consumption in the form of
irrecoverable pressure loss
•Susceptible to erosion or damage
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