Microelectromechanical Systems (MEMS) are miniature devices comprising of integrated mechanical (levers, springs, deformable membranes, vibrating structures, etc.) and electrical (resistors, capacitors, inductors, etc.) components designed to work in concert to sense and report on the physical properties of their immediate or local environment, or, when signaled to do so, to perform some kind of controlled physical interaction or actuation with their immediate or local environment

1. MEMS SENSOR
Presented by
MD. FAIZAN AHMAD

2. Outline
MEMS Introduction
Sensor and its type
Applications
References

3. What is MEMS?
 MEMS or Micro-Electro Mechanical System is a
technique of combining Electrical and
Mechanical components together on a chip, to
produce a system of miniature dimensions.
 MEMS is the integration of a number of micro-
components on a single chip which allows the
microsystem to both sense and control the
environment.
 The components are integrated on a single chip
using micro fabrication technologies.

4. What is a Sensor?
 A device used to measure a physical
quantity(such as temperature) and convert it
into an electronic signal of some kind(e.g. a
voltage), without modifying the environment.
 What can be sensed?
Almost Everything!!!
Commonly sensed parameters are:
 Pressure
 Temperature
 Flow rate
 Radiation
 Chemicals
N
S
EW
2 Axis Magnetic
Sensor
2 Axis
Accelerometer
Light Intensity
Sensor
Humidity Sensor
Pressure Sensor
Temperature Sensor

5. But why MEMS for sensors?
Smaller in size
Have lower power consumption
More sensitive to input variations
Cheaper due to mass production
Less invasive than larger devices

6. Type of Sensors
Mechanical
Sensors
• Accelerometers
• Pressure Sensors
• Microphones
• Gyroscopes(Rotation
Rate)
Optical
Sensors
• Direct Sensors (Light
 Electronic Signal)
• Indirect Sensors
(Light 
Intermediate Energy
 Electronic Signal)
• Biological Light
Sensors
Thermal
Sensors
• Thermo mechanical
(Dimension)
• Thermo Resistive
(Resistance)
• Acoustic (Sound)
• Biological
Chemical & Biological
Sensors
• Electronic Nose
• Electronic Tongue

7. Mechanical Sensors
Accelerometers
Pressure Sensors
Microphones
Gyroscopes(Rotation
Rate) ,etc.

8. Accelerometers
Inertial sensor:
Newton’s 1st law (Mass of inertia).
Device used to measure:
Acceleration
Displacement
Force

10. 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

12. Pressure Sensors
 Pressure sensors are required in all walks of life, irrespective of civilian,
defence, aerospace, biomedical, automobile, Oceanography or domestic
applications.
 Among the various devices, pressure sensors using MEMS technology have
received great attention because the pressure sensors find applications in
everyday life involving sensing, monitoring and controlling pressure.
 Pressure sensors are categorized as
a) Absolute Pressure Sensors
b) Gauge Pressure sensors
c) Differential Pressure Sensors

13. a) Absolute Pressure Sensors
Measure the pressure relative to a reference vacuum
encapsulated within the sensor Such devices are used for
atmospheric pressure measurement and as manifold
absolute pressure (MAP) sensors for automobile ignition
and airflow control systems.
Pressure sensors used for cabin pressure control, launch
vehicles, and satellites also belong to this category.

14. Schematic diagram of Absolute Pressure sensor

15. b) Gauge Pressure sensors
Measure pressure relative to atmospheric pressure. One
side of the diaphragm is vented to atmospheric pressure.
Blood pressure (BP), intra-cranial pressure (ICP), gas
cylinder pressure and most of ground-based pressure
measurements are gauge pressure sensors.

16. Schematic diagram of Gauge Pressure sensor

17. c) Differential Pressure Sensors
Measure accurately the difference ΔP between two
pressures P1 and P2 across the diaphragm (with ΔP << P1
or P2 ), and hence need two pressure ports.
They find applications in airplanes used in warfare. They
are also used in high pressure oxidation systems.

18. Schematic diagram of Differential Pressure sensors

19.  In almost all types of pressure sensors, the basic sensing element is the
diaphragm, which deflects in response to the pressure.
 As the deflections in diaphragm-based sensors are small they cannot be
directly measured. This mechanical deflection or the resulting strain in the
diaphragm is converted ultimately into electrical signals using suitable
transduction mechanisms, namely,
1) Capacitive
2) Piezoresistive or piezo-electric

20. Capacitive Pressure Sensor
 This approach uses the diaphragm as one electrode of a parallel
plate capacitor structure and diaphragm displacement causes a
change in capacitance with respect to a fixed electrode.
 The merits of capacitive pressure sensors are their high sensitivity,
which is practically invariant with temperature.
 An electronic circuit is used to convert the capacitance change into
an electrical output.

21. Schematic representation of pressure sensors
(a) Piezoresistive (b) capacitive (c) Piezoelectric

22. Microphone
 Microphone is transducer that converts acoustic energy into electrical energy. The
microphones are widely used in voice communications devices, hearing aids,
surveillance and military aims, ultrasonic and acoustic distinction under water, noise
and vibration control.

23.  Basically the microphone MEMS sensor is a variable capacitor where the
transduction principle is the coupled capacitance change between a fixed plate
(back plate) and a movable plate (membrane) caused by the incoming wave of
the sound.

24. Gyroscopes
A gyroscope is a device for measuring or maintaining the
orientation, based on the principles of the conservation of
momentum.
It uses vibrating mechanical element to sense the rotation.
Transfer of energy between two vibrating resonator is by
coriolis acceleration.

25. Types of Gyroscope
Spinning Gyroscope
Optical Gyroscope
Vibrating Gyroscope

26.  The rotation of tines causes the Coriolis Force.
 Forces detected through either electrostatic, electromagnetic or piezoelectric.
 Displacements are measured in the Comb drive.

27. Applications of Gyroscope
 Yaw rate sensor for skid control in antilock braking applications for
automobiles.
 Inertial navigation systems.
 Smart cruise control.
 Guiding gun launched munitions.
 Detection of roll over detections.

28. Applications in Medical Science
 Biocavity Laser : This device
distinguishes cancerous from non
cancerous cells thus aiding the surgeons
in operations.
 Smart Pill :
 Implanted in the body
 Automatic drug delivery (on
demand)
 Sight for the blind : MEMS based array
that may be inserted in the retina of a
blind person to provide partial sight

29. Applications in Marine Science
Sensing in marine environment maybe done for
various reasons:
Oil exploration and related applications
Global weather predictions
Monitor water quality for any contamination
Measure parameters detrimental to the “health” of
structures in the sea ( like oil rigs and ships )
Study of aquatic plants and animals
In military operations

30. Applications in Marine Military Operations
 An array of MEMS sensors spread on the ocean floor
could detect the presence of enemy submarines.
 MEMS sensors (pressure sensors, accelerometers etc.)
are being used in anti-torpedo weapons on submarines
and ships.
 MEMS sensors in torpedoes are responsible for
Detonating the torpedo at the right time
Hitting the target in a crowded environment
Prevent any premature explosion

31. References
 X. Wang, J. Engel, C. Liu, J. Micromech. Microeng. 2003, 13, 628.
 Christian A. Zorman, Mehran Mehregany, MEMS Design and Fabrication, 2nd Ed. 2,16.
 Ms. Santoshi Gupta, MEMS and Nanotechnology IJSER, Vol 3, Issue 5,2012
 Stephen Beeby, MEMS Mechanical Sensor, PP. 7
 Lenz, J., Edelstein, A.S., "Magnetic sensors and their applications." IEEE Sensors J. 2006, 6, 631-
649.
 Sinclair M J 2000 A high force low area MEMS thermal actuator Proc. 7th Intersociety Conf. on
Thermal and Thermomechanical Phenomena (Las Vegas, NV) pp 127–32
 R. Ghodssi, P. Lin (2011). MEMS Materials and Processes Handbook. Berlin: Springer.
 Chang, Floy I. (1995).Gas-phase silicon micromachining with xenon difluoride. 2641. pp. 117.