micro-electro-mechanical-systems-based-sensors-160120195338.pdf
- 1. MICRO-ELECTRO-MECHANICAL SYSTEMS(MEMS) BASED TRANSDUCERS o Introduction to MEMS technology o Overview of features and structures of MEMS based Sensors and actuators. o and their Applications Amjad
- 2. Introduction to MEMS transducers MEMS or Micro-Electro-Mechanical Systems are also known as smart matters. They are miniaturized mechanical and electromechanical devices. MEMS are embedded in semiconductor chips using micro-fabrication techniques. Why are they important? It generates continued sustained improvement e.g. functionality of small microphones, cameras, electrical signal filters etc. Generates new kinds of products such as multi-axis inertial motion sensors.
- 3. History and current state ■ The origins of what we now know as micro-electromechanical system (MEMS) technology can arguably be traced back to 1 April 1954, when a paper by Smith (1954), then at the Bell Telephone Laboratories, was published in Physical Review. ■ Roots were laid by Richard Feynman while delivering a speech at Caltech in 1959 “There is plenty of room at the bottom.” ■ From 1960s through 1990s development took place at linear pace. ■ Hit inflation point in 2000s and sustained considerable momentum into the 2010s.
- 4. Future of MEMS The developments in the MEMS include, Trillions of sensors. Incorporation of heterogeneous sensors Improvement on wafer-level packaging technology Integration with advanced CMOS circuitry Local environmental monitoring devices and deployment in wearables. MEMS reliant drones and other small personal robots.
- 5. Why choose MEMS? ■ Small size and light weight. ■ Enhanced performance and reliability. ■ Low cost Applications ■ Automotive systems ■ Automated manufacturing ■ Health care ■ Instrumentation ■ Consumer products ■ Aerospace
- 6. Types of MEMS devices Typical MEMS Devices; Sensors In the broadest definition, a sensor is an object whose purpose is to detect events or changes in its environment, and then provide a corresponding output. This category includes: > Pressure Sensors > Accelerometers > Gyroscopes Actuators Converts energy into motion or mechanical energy. Actuator is a motor that actuates or moves something. Actuators include: > High Aspect Ratio Electrostatic Resonators > Thermal Actuators > Magnetic Actuators > Comb-drives Comb drive actuator
- 7. MEMS based SENSORS ■ MEMS sensors can be defined as the combination of micro-sensors and electronic devices integrated on a single chip. ■ That package is a bit like processors, but it includes all the mobile parts of the device. Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS technology. ■ MEMS researchers and developers have demonstrated an extremely large number of microsensors for almost every sensing modality including temperature, pressure, inertial forces, chemical species, magnetic fields, radiation, etc. ■ The micromachined version of a sensor usually outperforms a sensor made using the most precise macroscale level machining techniques.
- 8. How do they work? ■ Input samples may be: a) motion of a solid b) pressurized liquids or gases, c) biological and chemical substances. ■ Major sensing technologies that can be applied in the MEMS form include the following: • piezoresistive • capacitive • resonant • thermoelectric ■ Piezoresistive sensors dominate pressure, acceleration, and force applications. Typically, four piezoresistors are connected into a Wheatstone bridge configuration to reduce temperature errors.
- 9. Applications of MEMS sensors ■ Biotechnology DNA amplification and identification, biochips for detection of hazardous chemical and biological agents and drug screening. ■ Communications Electrical components such as inductors and tunable capacitors can be improved significantly compared to their integrated counterparts if they are made using MEMS and Nanotechnology. ■ Inertial Sensing MEMS accelerometers have displaced conventional accelerometers for crash air- bag deployment systems in automobiles. ■ Medicine The first and by far the most successful application of MEMS in medicine are MEMS pressure sensors, which have been in use for several decades to monitor patient’s vital signs and used in eye surgery to control vacuum level.
- 10. Accelerometer ■ Accelerometer measures proper acceleration ("g-force"). which is the acceleration it experiences relative to freefall and is the acceleration felt by people and objects. ■ Modern accelerometers are often small micro electro- mechanical systems (MEMS), and are indeed the simplest MEMS devices possible. They can be made using >) Piezo-electric effect >) By sensing capacitive changes >) For very high sensitivities Quantum Tunneling is also used How are they made?
- 11. Features of capacitive interface ■ Can operate as both sensor and actuator. ■ Independent of base material. ■ Relies on the variation of capacitance. Structure of MEMS Accelerometer ■ They consist of MEMS structures suspended by poly-silicon springs above the substrate in a manner that proof mass(body of sensor) is capable of moving in both X and Y axes. ■ 32 sets of radical fingers around four sides of proof mass. ■ Fingers are placed between the plates that are fixed to the substrate. ■ Each finger and pair of fixed plate represents a capacitor.
- 12. Working Calculations ■ Capacitance of capacitor:- ■ Where = A= area of electrodes d=distance between the =permittivity of material separating them ■ For zero acceleration the capacitance of plates remains same. ■ Displacement is approximately proportional to the capacitive difference. ■ The differential capacitance is measured using synchronous modulation/demodulation techniques. ■ Output signals are; * Voltage proportional to acceleration * PWM proportional to acceleration
- 13. Applications of MEMS Accelerometers ■ Personal devices such as media players, gaming devices and smart phones. ■ Camcorders and still cameras. ■ Detecting car crashes and deploying air bags. ■ Controlling and monitoring military and aerospace systems.
- 14. Gyroscopes ■ MEMS gyroscope reliably sense and measure the angular rate of an object using the Coriolis Effect. ■ MEMS gyroscopes are making significant progress towards high performance and low power consumption. ■ When a mass (m) is moving in direction v→ and angular rotation velocity Ω→ is applied, then the mass will experience a force in the direction of the arrow as a result of the Coriolis force. And the resulting physical displacement caused by the Coriolis force is then read from a capacitive sensing structure.
- 15. Features ■ Measure rotation ■ Couple energy from one vibrational axis to another due to Coriolis Effect ■ Two micromachined modes: Open loop vibration and Force-to rebalance mode ■ Vibrating prismatic beams ■ Beam driven in one direction, deflection measured in orthogonal direction How are they made? MEM gyroscopes are printed onto circuit boards using photolithography. Some parts incorporate multiple gyroscopes and accelerometers, to achieve output that has six full degrees of freedom. There are many types, but they all rely on the same principle, that of vibrating objects undergoing rotation.
- 16. Structure Internally, MEMS gyroscopes use lithographically constructed versions of one or more of the mechanisms outlined below: • Tuning forks – This type of gyroscope uses a pair of test masses driven to resonance. Their displacement from the plane of oscillation is measured to produce a signal related to the system's rate of rotation. • Piezoelectric gyroscopes –A piezoelectric material can be induced to vibrate, and lateral motion due to Coriolis force can be measured to produce a signal related to the rate of rotation. • Vibrating wheel gyroscope – A wheel is driven to rotate a fraction of a full turn about its axis. The tilt of the wheel is measured to produce a signal related to the rate of rotation.
- 17. Applications of MEMS Gyroscope ■ Spacecraft orientation The oscillation can be induced and controlled in the vibrating structure gyroscope for the positioning of spacecraft such as Cassini-Huygens. They provide accurate 3 axis positioning of the spacecraft and are highly reliable over the years as they have no moving parts. ■ Automotive These are used to detect error states in yaw compared to a predicted response when connected as an input to electronic stability control systems in conjunction with a steering wheel sensor. ■ Entertainment Game Boys and most modern smartphones use a piezoelectric gyroscope to detect rotational movement. The Sony SIXAXIS PS3 controller uses a single MEMS gyroscope to measure the sixth axis (yaw). ■ Photography Many image stabilization systems on video and still cameras employ vibrating structure gyroscopes. ■ Industrial robotics Epson Robots uses a quartz MEMS gyroscope, called QMEMS, to detect and control vibrations on their robots. This helps the robots position the robot end effector with high precision in high speed and fast-deceleration motion.
- 18. Actuators ■ An actuator is a type of motor that is responsible for moving or controlling a mechanism or system, a device that actuates or moves something. ■ Converts Energy into motion or mechanical energy. MEMS Actuators ■ Also known as micro-actuators, micro-systems or micro- machines. ■ Produced by assembling extremely small functional parts around 1-15 mm.
- 19. Classification of MEMS Actuators ■ Electrostatic: attraction between oppositely charged conductors. ■ Thermal: Displacement due to thermal expansion. ■ Piezoelectric: Displacement is due to strain induced by an electric field. ■ Magnetic: Displacement is due to interaction among various magnetic elements i.e. permanent magnets, external magnetic fields, magnetizable material and current carrying conductor. ■ On the basis of movement micro-actuators are: 1. Translational 2. Rotational
- 20. Features Features of MEMS actuators are: ■ Light weight ■ Conformable ■ Precision device ■ One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere between a few nanometers to about 100 micrometers. ■ Patterning in MEMS is the transfer of a pattern into a material.
- 21. Applications of MEMS Actuators ■ The applications of micro-actuators include: ■ Digital Micro-mirror Device (DMD) chip in a projector based on DLP technology, which has a surface with several hundred thousand micro-mirrors or single micro-scanning- mirrors also called micro-scanners. ■ Optical switching technology, which is used for switching technology and alignment for data communications. ■ Fluid acceleration such as for micro-cooling. ■ Micro-surgical applications. ■ Data reading and recording control. ■ RF signal limiting.
- 22. Thankyou Group members: (BY appearance) ■ Muhammad Ali Amjad D-13-ES-15 ■ Muhammad Shaur D-13-ES-11 ■ Muhammad Mubeen Iqbal D-13-ES-35