CEC340 MEMS DESIGN LTPC2023

COURSE OBJECTIVES:
 To understand the basic electrical and mechanical concepts of MEMS design
 To understand the design aspects of electrostatic sensors and actuators
 To understand the design aspects of thermal sensors and actuators
 To understand the design aspects of piezoelectric sensors and actuators
 To understand the design aspects of magnetic sensors and actuators

UNIT I ESSENTIAL ELECTRIC AND MECHANICAL CONCEPTS 6

Conductivity of semiconductors, Crystal planes and orientations, stress and strain, flexural beam bending analysis under simple
loading conditions, Dynamic system, resonant frequency and quality factor
UNIT II ELECTRO STATIC SESNING AND ACTUATION 6
Parallel plate capacitor, Applications of parallel plate capacitors- inertial sensor, pressure sensor, flow sensor, tactile sensor,
parallel plate actuators, interdigitated finger capacitors, applications of comb drive devices.
UNIT III THERMAL SENSING AND ACTUATION 6
Fundamentals of thermal transfer, Sensors and actuators based on thermal expansion, Themal couples, Thermal resistors,
Applications- Infrared sensors, flow sensors, Inertial sensors, other sensors
UNIT IV PIEZOELECTRIC SENSING AND ACTUATION 6
Mathematical description of piezoelectric effects, Cantilever piezoelectric actuator model, properties of piezoelectric materials –
Quartz, PZT,PVDF, ZnO , Applications – Acoustic sensors, Tactile sensors
UNIT V MAGNETIC SENSING AND ACTUATION 6
Concepts and principles- magnetization and nomenclatures, principles of micromagnetic actuators, fabrication of micro magnetic
components- deposition, design and fabrication of magnetic coil, MEMS magnetic actuators
30 PERIODS

PRACTICAL EXERCISES: 30 PERIODS

1. Design and simulation of piezoelectric cantilever
2. Design and simulation of thermo couples
3. Design and simulation of comb drive actuators

COURSE OUTCOMES:
Upon completion of this course, the students will be able to
CO1: Understand the basics of MEMS design aspects.
CO2: Apply the knowledge in the development of electro static sensors and actuators.
CO3: Apply the knowledge in the development of thermal sensors and actuators.
CO4: Apply the knowledge in the development of piezoelectric sensors and actuators.
CO5: Apply the knowledge in the development of magnetic sensors and actuators.
TOTAL:60PERIODS

TEXTBOOKS
1.Chang Liu, “Foundations of MEMS”, Pearson education India limited, 2006
REFERENCES
1. Murty B.S, Shankar P, Raj B, Rath, B.B, Murday J, Textbook of Nanoscience and Nanotechnology, Springer publishing, 2013.
2. Sergey Edward Lyshevski, “MEMS and NEMS: Systems, Devices, and Structures”, CRC Press, 2002
3. Tai Ran Hsu, MEMS and Microsystems Design and Manufacture, Tata Mcgraw Hill, 2002
4. Vinod Kumar Khanna Nanosensors: Physical, Chemical, and Biological, CRC press,2012
Points to Remember
1. What do you mean by micro fabrication?
Micro fabrication or MEMS fabrication defines a series of techniques that can modify a substrate
material in an additive or subtractive manner to convert a thin, generally planar, substrate into a
complex structure of multiple materials through the interaction of microscopic features
2. What are the principles of micro fabrication?
The major concepts and principles of micro fabrication are microlithography, doping, thin films,
etching, bonding, and polishing.
3. What is photolithography in micro fabrication?
Photolithography is one of the most important and easiest methods of micro fabrication, and is used
to create detailed patterns in a material. In this method, a shape or pattern can be etched through
selective exposure of a light sensitive polymer to ultraviolet light

4. What is the difference between MEMS and IC?

integrated circuit, is a small electronic device MEMS stands for microelectromechanical
made out of a semiconductor material. It may systems. MEMS devices are typically tiny
contain multiple interconnected components integrated devices or systems that combine
such as transistors, capacitors, resistors, and electrical and mechanical components. They
diodes. ICs are used in a wide range of often include components such as sensors,
electronic devices, from simple actuators, and microstructures, and are used in
microcontrollers to complex microprocessors applications such as accelerometers,
gyroscopes, pressure sensors, and inkjet printer
heads.

ICs focus on electronic components MEMS focus on combining electrical and

mechanical components in a small scale.

5. What are the methods of fabrication for MEMS?

MEMS fabrication that is based on the silicon-on-glass (SOG) process requires deposition,
patterning, and etching.
6. What is the role of sensors and actuators?
 Sensors monitor physical activity and alert the control center to changes in asset performance
or its environment.
 Actuators receive signals from control modules to perform physical actions such as
manipulating a robotic arm
7. what is tactile sensor
A tactile sensor is a device that measures information arising from physical interaction with its
environment.
Tactile sensors are generally modeled after the biological sense of cutaneous touch which is capable
of detecting stimuli resulting from mechanical stimulation, temperature, and pain
Tactile sensors are used in robotics, computer hardware and security systems.
A common application of tactile sensors is in touchscreen devices on mobile phones and computing.
8. Compare bulk and surface micromachining
Sr Bulk Micromachining Surface Micromachining
No
1 In this mechanical elements are In this it is fabricated by building
fabricated by etching away the layers on layers
unwanted part in silicon wafer
2 This creates structures inside a This creates structures on top of a
substrate substrate
3 Larger structures are made with bulk It is difficult to build larger structures
micromachining
4 Limited to low aspect ratio in Not constraints by thickness of
geometry as surface dimensions are silicon wafer,so high aspect ratio
much greater than depth as height is geometries can be fabricated using
limited by thickness of silicon wafer surface micromachining
5 Straight forward and well documented Complex masking design and
process production

6 Sacrificial layer is not required Etching of sacrificial layer is

required
7 The process is less expensive but The process is expensive but less
material loss is more material loss
8 Mechanical properties are superior Mechanical properties are good

9 Dimensional control is good Dimensional control is better

10 CMOS integration is fair CMOS integration is good

11 It causes a well known phenomenon in It does not causes undercut problem

the micro electronics industry called
undercut
12 Size is small Size is smaller

13 Typically uses wet etching techniques It uses dry etching techniques

14 Suitable for simple geometry such as Suitable for complex geometry such
 thermal sensor,micro machined neuron as micro valves and actuators
wells

9. What is stress,normal stress,shear stress?

 Stress refers to the force applied to a material per unit area.
 Normal stress When a force acts perpendicular to the surface of an object.
 Shear stress -When a force acts parallel to the surface of an object.
10. What is strain, Normal strain,Shear strain?
 Strain is a deformation or change in the shape of the material that results from the applied
force.
 Normal strain measures the deformation, specifically the length change, of a material when a
stress is applied. It's calculated as the change in length divided by the original length.
 Shear strain is produced when the deforming force causes change in the shape of the body. It
is defined as the ratio of the displacement of a layer to its distance from the fixed layer
11. Define Miller index
Miller indices form a notation system in crystallography for lattice planes in crystal (Bravais)
lattices.
12. State Newton’s laws
 Newton’s First Law of Motion Every object in a state of uniform motion tends to remain in
(The Law of Inertia) the state of motion unless an external force is applied to it.
 Newton’s Second Law of Motion The relationship between an object’s mass m, its
acceleration a, and the applied force F is Acceleratio and forces are vectors.The direction of
the force vector is the same as the direction of the acceleration vector.
 Newton’s Third Law of Motion For every action there is an equal and opposite reaction.
13. Define Poission Ratio
 Poisson's ratio is “the ratio of transverse contraction strain to longitudinal extension strain in
the direction of the stretching force.”
 Here, Compressive deformation is considered negative. Tensile deformation is considered
positive
14. What is meant by modulus of elasticity or young’s modules?
It is a fundamental property of materials that measures their stiffness or resistance to elastic
deformation under stress.
15. Explain the types of beams
 A fixed beam is one that is fixed on both ends of the beam with supports.
 A Guided cantilever is a beam whose one end is fixed and the other end is held parallel to its
original position
 Free end Cantilever beams are beams that are constrained at one end and free at the other.
16. What is the purpose of flow sensor in thermal sensing and actuation?
  Thermal flow sensors are utilized to measure the velocity of surrounding fluids and the
direction of flow.
 The working principle of thermal flow sensors is based on the heat transfer between the
sensor heater and the environment, and the thermo resistive effect of the sensor material.
17. What is the purpose of infrared sensor in thermal sensing and actuation?
 An IR sensor can measure the heat of an object as well as detects the motion
 Infrared sensors are sensitive to heat, and a person's blood vessels are warm, so the position
of the blood vessels can be seen. In infrared light, blood vessels under the skin are readily
visible. Many medical units use this technology when they draw blood, but deficiencies
remain.
18. What is the purpose of acoustic sensor in piezoelectric sensing and actuation ?
 Acoustic sensors are used to detect and measure sound waves or acoustic signals in the
environment.
 Piezoelectric materials provide the transduction between electrical and mechanical response
conversion of electrical signal into mechanical acoustic waves and vice versa.
 They find applications in environmental monitoring, industrial condition monitoring, security
and surveillance, healthcare, automotive, robotics, entertainment, and more
19. What is the Purpose of using tactile sensor in piezoelectric sensing and actuation?
Tactile sensing is an essential element of autonomous dexterous robot hand manipulation. It provides
information about forces of interaction and surface properties at points of contact between the robot
fingers and the objects.
20. What is the purpose of tactile sensor?
Tactile sensing enables the detection and measurement of an object's size, shape, weight, texture,
temperature, shear, and response to a change in force stimuli. While some of these criteria can be
detected by advanced vision sensors, in-depth data about these attributes can only be gathered by
tactile sensing.
21. Explore electrostatic sensing and actuation
 Electrostatic sensing:A capacitor is broadly defined as two conductors that can hold opposite
charges.
 It can be used as either a sensor or an actuator. If the distance and relative position between
two conductors change as a result of applied stimulus, the capacitance value would be changed.
 This forms the basis of capacitive (or electrostatic) sensing.
 Electrostatic actuation: if a voltage (or electric field) were applied across two conductors, an
electrostatic force would develop between these two objects.
22. What are the advantages and disadvantages of electrostatic sensing and actuation?
Advantages:
 Simplicity
 Low power
 Fast response
Disadvantages:
  High voltage required for static actuator operation
23. What is the Functions of Interdigited Fringer Capacitance
The Interdigital Capacitor is a Multi-Finger Periodic Structure and it uses Lumped Circuit
Elements For Rf/Microwave Development. This Has Higher Quality Factor Than Gap Capacitor And
Mim Capacitor.The interdigital capacitors use the capacitance that occurs across a narrow gap
between copper conductors.
24. What is inertia sensor?
 The inertial sensor, also known as the inertial navigation system (INS), uses an accelerometer
and gyro to determine spacecraft attitude in relation to the inertial system.
 The accelerometer is used to test the motion acceleration of the carrier, which is then used to
calculate the real-time location of the carrier.
 Inertial sensors have been used for over a century to measure the motion of an object with
respect to an inertial reference frame.
25. What is the Purpose of inertia sensor in electrostatic sensing and actuation?
Inertial sensors are used to transduce inertial force into measurable electrical signals to measure
acceleration, inclination, and vibration of an object.
26. What is a pressure sensor?
 A pressure sensor is a device or instrument which is able to measure the pressure in gases or
liquids.
 In this case, pressure is defined as the amount of force exerted over an area.
 Pressure sensors allow for more specialized maintenance strategies, such as predictive
maintenance.
27. What is the purpose of a flow sensor?
 Flow sensors are devices used for measuring the flow rate or quantity of a moving liquid or
gas
 Flow sensors utilize both mechanical and electrical subsystems to measure changes in the
fluid's physical attributes and calculate its flow.
28. What is purpose of tactile sensor in electrostatic sensing and actuation?
 A tactile sensor acts as a source of information regarding physical contact with the external
world.
 This technology has garnered considerable attention for its potential applications in healthcare
monitoring, skin prosthetics, and bio mimetic robotics.
29. Define Comb drive
 Two sets of electrodes are placed in the same plane parallel to the substrate.
 Generally, one set of finger-like electrode is fixed on chip while a second set is suspended and
free to move in one or more axes.
 Since the interdigitated fingers are shaped like tooth of combs, such configuration is
commonly referred to as the comb-drive device

30. What is the thermal sensor in MEMS?

 The measurement of temperature and heat can be achieved through different principles
The thermal transfer process—through conduction, convection, or radiation, depends on certain
physical variables, such as the spacing between objects, travel velocity of media, and the properties
of materials and media. Many measurement tasks can be achieved, including the sensing of
distance,acceleration,flow speed and materials characteristics.
31. What does a thermal actuator do?
Thermal actuators convert a temperature change into a mechanical force to push/pull, open/close, or
move a load.
32. Define thermal couple
 Two wires made of dissimilar materials joined at one point constitute a thermal couple
33. Define thermo pile
Multiple thermocouples are connected in an end to end fashion