EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie1

Sensor and Actuator Technology

Agenda:ClassificationTransduction MechanismsMEMS SystemMEMS Design Methodology MEMS Design Specifications

Reading: Senturia, Ch. 2 pp. 15-28. Next time: Reading: Senturia, Ch. 3 pp. 29-44.

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie2

Classification

TransducerElement that converts one form of energy to another.May include

– sensors (for measurement)– actuators (for doing work)– displays

Microsensor or microactuator a sensor or actuator that is manufactured using microfabricationand micromachining techniques

Other microstructures that neither sense nor actuate.Microchannels, micronozzles, microlenses, etc.

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie3

Transduction Mechanisms

Taken from Smith, R.L. “Sensors”, The Electrical Engineering Handbook, Ed. Richard C. Dorf, Boca Raton, CRC Press LLC, 2000

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie4

Transduction Mechanisms

Motorola’s integrated pressure sensor

Mechanical PiezoelectricityPiezoresistivity

Resistive, capacitive, and

inductive effects

Electrical

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie5

Transduction Mechanisms

JAMES S. HARRIS GROUP at Stanford University

Mechanical

Optical

Photoelasticsystems

(stress-inducedbirefringence)

InterferometersSagnac effectDoppler effect

Tunable VCSELs

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie6

Transduction Mechanisms

• Xie’s group at University of Florida

ThermalThermal expansion

(bimetal strip, liquid-and gas thermometers,

resonant frequency)Radiometer effect

(light mill)

Mechanical

oxide

siliconsubstrate

metal

poly-Sisilicon

mirror

Bimorphactuator

x

z

Cross-sectional View

bimorph actuator

mirror

mirrorbimorph actuators

1mmframe

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie7

MEMS Transducer Systems

Sensors

Actuators

Interface Circuits

Control and

Processing Circuits

Transducers

Power Supply and

Management

I/O Channel and Protocol

OUTSIDE WORLD

USER

Modular MEMS system designSensor designActuator designInterface designPackaging design

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie8

MEMS Transducer Systems

Sensors

Actuators

Interface Circuits

Control and

Processing Circuits

Transducers

Power Supply and

Management

I/O Channel and Protocol

OUTSIDE WORLD

USER

Separate componentsSignal attenuationNoisePackaging

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie9

MEMS Transducer Systems

Sensors

Actuators

Interface Circuits

Control and

Processing Circuits

Transducers

Power Supply and

Management

I/O Channel and Protocol

OUTSIDE WORLD

USER

Integrated sensors

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie10

MEMS Transducer Systems

Sensors

Actuators

Interface Circuits

Control and

Processing Circuits

Transducers

Power Supply and

Management

I/O Channel and Protocol

OUTSIDE WORLD

USER

Integrated microsystems

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie11

MEMS Design Strategy

High-Level Design IssuesMarket, Impact, Competition, Technology, Manufacturing

Ref. Senturia, Microsystem Design, p. 18.

Technology-driven or market-driven?

+++++++++++++++Commercial Products

++++++++++Research Tools+++++

Technology Demonstration

ManufacturingTechnologyCompetitionImpactMarketsCategory

Relative Importance of High-Level Design Issues

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie12

MEMS Design Process

Ref. Senturia, Microsystem Design, p. 18.

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie13

MEMS Design Methodology

Top-down designSystem levelDevice: macromodelsPhysical: numerical modeling, finite-element methodsProcess: TCAD or Technology CAD

Bottom-up verification

System

Device

Verif

icat

ionSim

ulation System

Device

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie14

MEMS Design Methodology

Ref. Senturia, MicrosystemDesign, p. 23.

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie15

MEMS Design Specifications (1)

Definitions: P(t) = physical variable (input)x(t) = sensor excitationy(t) = sensor response (output)

Disturbances

Sensor Interface Circuit Data System

y(t)

x(t)

Pmeas.(t)P(t)

Pmeas.(t) = P(t) ?

Calibrationdetermines the function that relates y(t) to known physical input, P(t)

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie16

MEMS Design Specifications (2)

Full Scale Outputalgebraic difference between upper and lower endpoints of output

Linearitycloseness of calibration curve to a specified straight line (maximum deviation of calibration point from straight line as percent of Full Scale Output)

Offsety(t) under normal excitation and zero applied input, P(t)=0

y(t)

Full scale outputS

offset

P(t)

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie17

MEMS Design Specifications (3)

y(t)

Hysteresis

P(t)

Hysteresismaximum difference in y(t) when the value is approached first with increasing input and second with decreasing input, expressed in percent Full Scale Output

Errordifference between measured P(t) and true value of P(t) (usually indicated as percentage of Full Scale Output)

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie18

MEMS Design Specifications (4)

Sensitivitymagnitude of change of y(t) with respect to change in P(t),

Accuracyratio of Error to Full Scale Output expressed in percent

Repeatabilityagreement between independent measurements made under the identical conditions (maximum difference in output readings given as % of Full Scale Output)

Resolutionsmallest change in P(t) that results in a detectable change in y(t)(called Threshold if increment is from zero)

Frequency Responsechange with frequency, ω=2πf , of output/input magnitude ratio and phase difference for sinusoidally varying input

)()(

tPtyS

∆∆

=

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie19

MEMS Design Specifications (5)

Cross-axis sensitivitysensitivity of sensor to transverse acceleration or other transverse input (also known as transverse sensitivity)

Signal-to-NoiseS/N = y/nrms where y is the output magnitude and nrms is the root-mean-square noise

Selectivityability to measure one input (measurand) in the presence of other inputs

Overload characteristicsmaximum magnitude of input that can be applied to the sensor without changing the sensor response

Stabilityability of sensor to reproduce output for identical input and conditions over time (expressed as percent of Full Scale Output)

EEL5225: Principles of MEMS Transducers 8/27/2003Lecture 2 by Xie20

Homework 1Due: Wednesday , September 3

Problem 1.1 (Textbook)A Library Treasure Hunt: By consulting recent issues of at least two of the following MEMS-oriented journals, locate articles that illustrate (a) accelerometers for human activity monitoring or civil infrastructure security, (b) MEMS optical imaging, (c) MEMS optical switching, (d) MEMS biosensors, (e) RF MEMS, and (f) micro flow sensors. The journals are: IEEE/ASME Journal of Microelectromechanical Systems, Journal of Micromechanics and Microengineering, Sensors and Actuators, Sensors and Materials, Analytical Chemistry, and Biomedical Microdevices. Give full citations of at least two articles for each of the above topics. List the top 2 topics that are most interesting to you. Note: The Marston Science Library has the IEEE/ASME Journal of Microelectromechanical Systems, Sensors and Actuators A: Physical and B: Chemical (hardcopy and electronic), Analytical Chemistry, and Biomedical Microdevices (electronic copy). Also, make sure to take advantage of IEEE Explore.

Problem 1.2 (Textbook)An On-Line Treasure Hunt: By consulting the events calendar at the web site http://www.memsnet.org (or some other MEMS-oriented web site), identify conferences scheduled for the coming year that cover some combination of (a) accelerometers for human activity monitoring or civil infrastructure security, (b) MEMS optical imaging, (c) MEMS optical switching, (d) MEMS biosensors, (e) RF MEMS, and (f) micro flow sensors.