ee503 - 07 mems

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MICRO-ELECTROMECHANICAL

SYSTEM (MEMS)

Objectives:

Understand the concept of MEMS Understand MEMS applications Understand MEMS fabrication process

Concept of MEMS

Define MEMS ? Micro-Electro-Mechanical Systems

(MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology.

Compare MEMS with microelectronics:

MEMS vs. Integrated Circuits (IC’s)

•One way to look at it:

–IC’s move and sense electrons

–MEMS move and sense mass

•Another:

–IC’s use Semiconductor processing technologies

–MEMS can use a variety of processes including Semiconductor but also Bulk, LIGA, Surface Micromachining…

•Packaging

–IC packaging consists of electrical connections in and out of a sealed environment

–MEMS packaging not only includes input and output of electrical signals, but may also include optical connections, fluidic capillaries, gas channels and openings to the environment. A much greater challenge.

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Scales and dimensions

Advantages of MEMS

1. Very small size, mass, volume2. Very low power consumption3. Low cost4. Easy to integrate into systems or modify5. Small thermal constant6. Can be highly resistant to vibration, shock and radiation7. Batch fabricated in large arrays8. Improved thermal expansion tolerance 9. Parallelism

MEMS applications

MEMS application can be devided into mems based sensor and actuator.

In general terms, sensors are devices that detect and monitor physical or chemical phenomena

Actuator are devices that produce mechanical motion, force, or torque.

Sensing can broadly defined as energy transduction process that result in perception,

Actuation can be defined as energy transduction process that produce actions.

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Difference between actuator and sensor

1. Power/energy transduction• Sensor – from physical property to electrical/optical• Actuator – from electrical/optical to physical/mechanical2. Power density• Sensor – from potentially high power density to relative low

power density (signal level)• Actuator – high power density conversion, use signal level

(low power density) to modulate/control the power conversion

Difference between actuator and sensor

MEMS SENSOR: ACCELEROMETER

“PRINCIPLES OF OPERATION”

Most accelerometers are Micro-Electro-Mechanical Sensors(MEMS). 

The basic principle ofoperation behind the MEMS accelerometer is the displacement of a small proof mass etched into the silicon surface of the integrated circuit and suspended by small beams.

Consistent with Newton's second law of motion (F = ma), as an acceleration is applied to the device, a force develops which displaces the mass. 

The support beams act as a spring, and thefluid (usually air) trapped inside the IC acts as a damper, resulting in a second order lumped physical system.

This is the source of the limited operational bandwidth and non-uniform frequency response of accelerometers.

MEMS SENSOR: PRESSURE SENSOR

Pressure is sensed by mechanical elements such as plates, shells, andtubes that are designed and constructed to deflect when pressure is applied.

This is the basic mechanism converting pressure to physical movement.

Next, this movement must be transduced to obtain an electrical or other output.

Finally, signal conditioning may be needed, depending on the type of sensor and the application

MEMS SENSOR: PRESSURE SENSOR

MEMS SENSOR: GYROSCOPE

Basically the way it works is that a spinning mass will act like a gyroscope. There are two primary characteristics of a gyro:1) Rigidity in space: the gyro has a tendency to resist forces applied to it, it is stable on the axis it spins.

2) Precession: when a force is applied perpendicular to a spinning rotor the rotor will resist the force where it is applied and the force will manifest 90 degrees later in the direction the rotor is spinning.

MEMS SENSOR: GAS FLOW SENSOR

MEMs Thermal Actuator

What is MEMs thermal actuator? Is a micromechanical device that typically generates motion by thermal expansion amplification. A small amount of thermal expansion of one part of the device translates to a large amount of deflection of the overall device

What is MEMs piezoelectric actuator?Is the ability of certain materials to develop an electric charge that is proportional to a direct applied mechanical stress.

MEMs PIEZOELECTRIC Actuator

MEMs magnetic Actuator

Is a device that uses the MEMS process technology To convert an electrical signal (current)into mechanical output (displacement) or the theory of magnetism.

Advantages of magnetic actuator

1. High actuation force and stoke (displacement)

2. Direct, fully linear transduction (in the case of electrodynamics actuation)

3. Bi-directional actuation

4. Contactless remote actuation

5. Low voltage actuation

6. Magnetic Actuation has a potentially high energy density

Mems electrostatic actuator

In industry, it is used in microresonators , switches ,micromirrors , accelerometers and others.

Electrostatic force depends largely on the size of the structures and the distance between electrodes.

The main problem of electrostatic effect is that it decreases with the square of the distance between the two charged bodies.

MEMS applications

What is Microsystem? A microsystem is an engineering system that

contain MEMS components that are designed to perform specific engineering functions. Microsystem generally consists of 3 major components:• processing unit (brain – decision making)• microsensors (input for decision making)• actuators (output or action as a result of

decision making)

MEMS + processing unit = microsystem23

Components of microsystem

Signal transduction

and processing unit

Sensor Actuator

Power supply

Microsystem

25Nanogear and bug

Thermal actuator

26Nano Clutch

MEMS transmission

There Are Three General Approaches To The Fabrication Of MEMS: Molding).

Surface Micromachining, Bulk Micromachining, LIGA (lithography, plating, molding).

BULK MICROMACHINING

Bulk Micromachining, large portions of the substrate are removed to form the desired structure.

Structures with greater heights can be formed because thicker substrates can be used.

The bulk micromachining process is a key fabrication method used for MEMS-based photonic switching in the high-growth optical and wireless markets.

SURFACE MICROMACHINING

Surface micromachining is a process based on the building up of material layers selectively remaining or removed by continued processing.

LIGA

LIGA processes combine IC lithography and electroplating and molding to obtain depth.

Patterns are created in a substrate and then electroplated to create 3D molds.

These molds can be used as the final product, or various materials can be injected into them. This process has two advantages.

Materials other than silicon can be used (e.g. metal, plastic) and devices with very high aspect ratios can be built.

LIGA (step & process)

Process;1,2,3= lithography, 4= plating, 5= molding

The End

Good Luck in Your Final Exam……

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