MEMS- Micro electro mechanical systems

ME407 MECHATRONICS
SUKESH O P
Assistant Professor
Dept. of Mechanical Engineering
JECC
10/16/2018
1SUKESH O P/ APME/ME407- MR-2018
SUKESH O P/ APME/ME407- MR-2018

ME407 MECHATRONICS
 Course Objectives:
To introduce the features of various sensors used in CNC machines and
robots
To study the fabrication and functioning of MEMS pressure and inertial
sensors
To enable development of hydraulic/pneumatic circuit and PLC
programs for simple applications
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SUKESH O P/ APME/ME407- MR-2018SUKESH O P/ APME/ME407- MR-2018

Expected outcome:
The students will be able to
i. Know the mechanical systems used in mechatronics ii. Integrate
mechanical, electronics, control and computer engineering in the
design of mechatronics systems
ME407 MECHATRONICS
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Expected outcome:
The students will be able to
i. Know the mechanical systems used in mechatronics ii. Integrate
mechanical, electronics, control and computer engineering in the
design of mechatronics systems
ME407 MECHATRONICS
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SYLLABUS
 Introduction to Mechatronics, sensors, Actuators, Micro Electro
Mechanical Systems (MEMS), Mechatronics in Computer Numerical
Control (CNC) machines, Mechatronics in Robotics-Electrical drives,
Force and tactile sensors, Image processing techniques, Case studies
of Mechatronics systems.
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MODULE-III
 Micro Electro Mechanical Systems (MEMS): Fabrication:
Deposition, Lithography, Micromachining methods for
MEMS, Deep Reactive Ion Etching (DRIE) and LIGA processes.
Principle, fabrication and working of MEMS based pressure
sensor, accelerometer and gyroscope
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MEMS
 It is a technology that in its most general form can be defi
ned as miniatured mechanical and electro-mechanical ele
ments that are made using techniques of micromachining.
 Made up of components between 1-100 micrometers in si
ze (i.e., 0.001 to 0.1mm) and MEMS devices range in size
from 20micrometers to millimeter(0.02 to 1.0mm)
 Used for sensing, actuation or are passive micro-structures
 Usually integrated with electronic circuitry for control and
/or information processing
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Components of MEMS
Microelectronics:
• “brain” that receives, processes, and makes decisions
• data comes from microsensors
Microsensors:
• constantly gather data from environment
• pass data to microelectronics for processing
• can monitor mechanical, thermal, biological, chemical
optical, and magnetic readings
Microactuator:
• acts as trigger to activate external device
• microelectronics will tell microactuator to activate device
Microstructures:
• extremely small structures built onto surface of chip
• built right into silicon of MEMS

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Advantages of MEMS
 Better stability and higher accuracy in the performance.
 Miniaturization.
 Integration of sensors and electronics on the same
device.
 Mass fabrication at low cost.
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Applications of MEMS
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Applications of MEMS
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Fabrication of MEMS
 The basic techniques used in the fabrication of
MEMS is deposition of one material over
another material then, patterning using
photolithography and then by etching the
required shape.
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Fabrication of MEMS
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1. Deposition
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PVD
 In PVD deposition technology, the material is removed from the source/
target and is deposited/transferred to the substrate.
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PVD
 Physical vapor deposition ("PVD") consists of a process in which
a material is removed from a target, and deposited on a
surface.
 Techniques to do this include the process of sputtering, in
which an ion beam liberates atoms from a target, allowing
them to move through the intervening space and deposit on
the desired substrate, and evaporation, in which a material is
evaporated from a target using either heat (thermal
evaporation) or an electron beam (e-beam evaporation) in a
vacuum system.
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CVD
 Chemical vapor deposition (CVD) is a deposition method used
to produce high quality, high-performance, solid materials,
typically under vacuum. The process is often used in
the semiconductor industry to produce thin films.
 Chemical deposition techniques include chemical vapor
deposition ("CVD"), in which a stream of source gas reacts on
the substrate to grow the material desired.
 This can be further divided into categories depending on the
details of the technique, for example, LPCVD (Low Pressure
chemical vapor deposition) and PECVD (Plasma-enhanced
chemical vapor deposition).
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2. Patterning
• transfer of a pattern into a material after deposition in order to prepare for
etching .( like printing on a paper).
• techniques include some type of lithography, photolithography is common
LITHOGRAPHY
 Lithography in the MEMS context is typically the transfer of a pattern to a
photosensitive material by selective exposure to a radiation source such as
light.
 A photosensitive material is a material that experiences a change in its
physical properties when exposed to a radiation source.
 If photosensitive material is selectively expose to radiation light (e.g. by
masking some of the radiation) the pattern of the radiation on the material is
transferred to the material exposed and the properties of the exposed and
unexposed regions different.
 This exposed region can then be removed or treated by providing a mask for
the underlying substrate.

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SUKESHOP/APME/ME407-MR-2018

LITHOGRAPHY
 Lithography in the MEMS context is typically the transfer of a
pattern to a photosensitive material by selective exposure to a
radiation source such as light.
 A photosensitive material is a material that experiences a
change in its physical properties when exposed to a radiation
source.
 If photosensitive material is selectively expose to radiation light
(e.g. by masking some of the radiation) the pattern of the
radiation on the material is transferred to the material exposed
and the properties of the exposed and unexposed regions
different.
 This exposed region can then be removed or treated by
providing a mask for the underlying substrate.
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 In lithography for micromachining, the photosensitive material
used is typically a photoresist (also called resist, other
photosensitive polymers are also used).
 When resist is exposed to a radiation source of a specific a
wavelength, the chemical resistance of the resist to developer
solution changes. If the resist is placed in a developer solution
after selective exposure to a light source, it will etch away one
of the two regions (exposed or unexposed).
 If the exposed material is etched away by the developer and
the unexposed region is resilient, the material is considered to be
a positive resist. If the exposed material is resilient to the
developer and the unexposed region is etched away, it is
considered to be a negative resist.
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 Few lithography techniques are:
 Ion beam lithography
 Ion track technology
 X-ray lithography
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3. Etching
 Etching is a process which makes it possible to
selectively remove the deposited films or parts of the
substrate in order to prepare a desired patterns,
shapes, features, or structures.
 Etching is used in micro fabrication to chemically
remove layers from the surface of a wafer during
manufacturing.
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 Etching
Wet etching
 Isotropic
 Anisotropic
Dry etching
 Plasma etching
 Reaction ion etching
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Wet etching
 Wet etching removes the material selectively through chemical
reaction.
 The material is immersed in a chemical solution, which reacts and
subsequently dissolves the portion of the material, which is in
contact with the solution.
 Materials not covered by the masks are left undissolved.
 Dipping substrate into chemical solution that selectively removes
material.
 Process provides good selectivity, etching rate of target material
higher that mask material
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Wet etching process fall under three sub-activities.
 Diffusion of the etchant to the surface for removal. The operation
is carried out at room temp. or slightly above, but preferably
below 50C.
 Establishment of reaction b/w the etchant and the material
being removed.
 Diffusion of the reaction by products from the reacted surface.-
cleaning
 The dissolution of material due to chemical reaction may not be
uniform in all directions. This characteristic of etching is called
directionality.
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 Anisotropic materials, the etch rates are not same in all directions.
Anisotropic etching is considerably a highly directional etching process
with different directions.
 The name isotropic material will dissolve uniformly in all directions. In
isotropic etching materials are removed uniformly from all directions and
it is independent of the plane of orientation of the crystal lattice.
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Dry etching
 A dry etching doesnot utilize any liquid chemicals or etchants to
remove materials.
 This etching process is primarily used in surface micromachining
process. The main adv of dry etching are that the process
eliminates handling of dangerous acids and solvents, uses small
amounts of chemicals.
 In dry etching sputter the material using reactive ions or a vapor
etchant.
 Material sputtered or dissolved from substrate with plasma or
gas variations
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Deep Reactive Ion Etching (DRIE)
 In DRIE, the substrate is placed inside a reactor, and several gases are
introduced.
 Chemical part : A plasma is struck in the gas mixture which breaks the
gas molecules into ions. The ions accelerate towards, and react with the
surface of the material being etched, forming another gaseous material.
 Physical part : if the ions have high enough energy, they can knock
atoms out of the material to be etched without a chemical reaction.
 Major techniques are :-
 Cryogenic process
 Bosch process
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 Cryogenic process: low temperature slows down the chemical
reaction that produces isotropic etching. How ever, ions
continuous to bombard upward facing surface and etch them
away. This process produces trenches with highly vertical side
walls.
 Bosch process : also known as pulse (or) time multiplexed
etching. It oscillates repeatedly between two modes to achieve
nearly vertical structure.
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 Relatively new technology.
 Enables very high aspect ratio etches.
 Uses high density plasma to alternately
etch and deposit etch resistant polymer
on sidewalls.
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Micro Machining
 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( ≥ 1mm in size) .
 Micro: fabrication of miniature structures/parts/products that
are not visible with naked eye(1 µm ≤ dimension ≤ 1000 µm in
size).
 Methods of Micro Fabrication: Material deposition & Material
Removal
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Why Micro Machining?
 Present day High-tech Industries, Design requirements are
stringent.
 Extraordinary Properties of Materials (High Strength, High heat
Resistant, High hardness, Corrosion resistant etc).
 Complex 3D Components (Turbine Blades)
 Miniature Features (filters for food processing and textile
industries having few tens of microns as hole diameter and
thousands in number)
 Nano level surface finish on Complex geometries (thousands of
turbulated cooling holes in a turbine blade)
 Making and finishing of micro fluidic channels (in electrically
conducting & non conducting materials, say glass, quartz,
&ceramics)
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Bulk Micromaching
 Bulk and surface micromachining are processes used to
create microstructures on microelectromechanical MEMS
devices.
 While both wet and dry etching techniques are
available to both bulk and surface micromachining,
bulk micromachining typically uses wet etching
techniques while surface micromachining primarily uses
dry etching techniques.
 Bulk micromachining selectively etches the silicon
substrate to create microstructures on MEMS devices.
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Bulk Micromachining
Bulk micromachining involves the removal of part of the
bulk substrate. It is a subtractive process that uses wet
anisotropic etching or a dry etching method such as
reactive ion etching (RIE), to create large pits, grooves
and channels. Materials typically used for wet etching
include silicon and quartz, while dry etching is typically
used with silicon, metals, plastics and ceramics.

Bulk Micromachining- Advantages/Disadvantages
 Can be done much
faster
 Can make high aspect
ratio parts
 Cheaper
 Not easily integrated
with microelectronics
 Part complexity must be
relatively simple
 Part size is limited to
being larger

Surface Micromachining
 Unlike Bulk micromachining, where a silicon substrate (wafer) is
selectively etched to produce structures, surface micromachining
builds microstructures by deposition and etching of different
structural layers on top of the substrate.
 Generally polysilicon is commonly used as one of the layers and
silicon dioxide is used as a sacrificial layer which is removed or
etched out to create the necessary void in the thickness direction.
 The main advantage of this machining process is the possibility
of realizing monolithic microsystems in which the electronic and
the mechanical components(functions) are built in on the same
substrate
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Surface Micromachining
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 Newer than Bulk Micromachining
 Uses single sided wafer processing
 Involves use of sacrificial and structural layers
 Provides more precise dimensional control
 Involves use of sacrificial and structural layers

Surface Micromachining- Applications
 Used in manufacturing of flat panel television screen.
 Used in production of thin solar cells.
 Used in making bimetal cantilever used for monitoring mercury
vapour, moisture, protein conformational changes in antigen
antibody binding.
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Surface Micromachining Advantages/Disadvantages
 Possible to integrate
mechanical and electrical
components on same
substrate
 Can create structures
that Bulk Micromachining
cannot
 Cheaper glass or plastic
substrates can be used
 Mechanical properties of
most thin-films are usually
unknown and must be
measured
 Reproducibility of
mechanical properties can
be difficult
 More expensive

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HIGH-ASPECT-RATIO ICROMACHINING
 High-aspect-ratio micromachining (HARM) is a process
that involves micromachining as a tooling step followed
by injection moulding or embossing and, if required, by
electroforming to replicate microstructures in metal
from moulded parts. It is one of the most attractive
technologies for replicating microstructures at a high
performance-to-cost ratio and includes techniques
known as LIGA.
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LIGA Process
 Developed in Germany in the early 1980s.
 LIGA stands for the German words
 LIthographie (in particular X-ray lithography)
 Galvanoformung (translated electrodeposition or
electroforming)
 Abformtechnik (plastic molding)
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 Popular high aspect ratio micromachining technology
 Primarily non-Silicon basted and requires use of x-ray radiation
 Special mask and x-ray radiation makes process expensive
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Advantages of LIGA
 LIGA is a versatile process – it can produce parts by several
different methods
 High aspect ratios are possible (large heightto-width ratios in
the fabricated part)
 Wide range of part sizes is feasible - heights ranging from
micrometers to centimeters
 Close tolerances are possible
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Disadvantages of LIGA
 LIGA is a very expensive process
 Large quantities of parts are usually required to justify its application
 LIGA uses X-ray exposure
 Human health hazard
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 Principle, fabrication and working of MEMS based pressure sensor,
accelerometer and gyroscope
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Sensors

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MEMS-based accelerometer
 MEMS-based accelerometer with capacitors is typically a
structure that uses two capacitors formed by a moveable plate
held between two fixed plates.
 Under zero net force the two capacitors are equal but a change
in force will cause the moveable plate to shift closer to one of
the fixed plates, increasing the capacitance, and further away
from the other fixed reducing that capacitance.
 This difference in capacitance is detected and amplified to
produce a voltage proportional to the acceleration
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Thank you
End of module 3
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MEMS- Micro electro mechanical systems

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