MEMS: Invention to Market
• Invention->Market
– Creation of a new market is slow.
• Market->Invention (easier)
– What is the existing competition?
– Impact – will it take over the market?
• Manufacturing
• Sales
• Modeling as in this course: Analysis of options,
performance, price. Planning of R+D, business plan.
Device Categories
• Technology Demonstrations
– Test device concept
– Test fabrication technology
– Small # of devices/low yield ok
• Research Tools
– Small # of devices, often custom.
• Commercial Products
– Large # of devices, high yield, low cost, packaging
all critical.
Transducers, Sensors, and Actuators
• Transducers: Generally convert one form of
energy to another. (Not generally conserving
energy.)
– Could be a sensor or an actuator.
• Sensors measure something and provide an
output signal. Usually electrical, but
sometimes optical or mechanical.
• Actuators move something. (But what would
an LED be?)
Domains
• Thermal (temperature, heat, heat flow)
• Mechanical (force, pressure, velocity,
acceleration, position)
• Chemical (concentration, composition, reaction
rate)
• Magnetic (magnetic field intensity,
magnetization)
• Radient (intensity, wavelength, polarization,
phase)
• Electrical (voltage, current, charge, resistance)
Examples of Sensors and Actuators
• Position Sensors
– Resistive strain sensor. (dimensions change, R=rl/A)
– Piezoresistive strain sensor. (dimensions and r
change)
Sensitivity measured by the gauge factor
GF=relative resistance change/strain=(DR/R)/(DL/L)=DR/eR
GF=~2 for metals (mostly geometry, some piezoresistance)
GF=~100 for semiconductors (piezoresistive)
– Piezoelectric materials (Curies, 1880)
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Electric field <-> strain (deformation)
Polarization <-> stress
Sensor/Actuator
In your watch, Quartz (but this is changing!! (Si Time))
Also pyroelectric materials have
temperature<->polarization.
• Magnetostrictive Actuators
– Materials expand/contract with magnetic field
– Similar to piezoelectric effect
– Terfenol-D Tb0.27Dy0.73Fe1.9 -> strain of 2X10-3 or 0.2%.
• Permanent magnetic materials
– Micromirror, microrelay, micromotor
N
S
B
• RF MEMS – Switching or changing capacitance
or building micromachined RF components.
Also ink jets!
• Biological Actuators – Future, nano, research
stage.
• Biomedical Sensors and Actuators
– Neural probes
– Artificial retinas
– Hearing prosthetics (in use)
– Living cells as sensors (chips for culturing and
measuring cell properties (see Kovaks, for
example)
• Chemical Actuators – Electrochemical
actuators using polypyrrole.
• Chemical Sensors – many types!
– Chemireisistors (organic and inorganic)
– Chemicapacitors
– Micromachined Calorimeter (combustible gasses
or explosive particles)
– Micro hot plate (R(T) for several materials.
– Chem FETs
• Can do the same thing with many ion sensitive
membranes.
Pd – Sensitive to hydrogen at 10 ppm
Problem: Drift
• Pumps
– Mechanical
– Electrophoretic/Electroosmotic, used in
separations of DNA and protein fragments.
V
mobile +ions
immobile -ions
Neutrals dragged along by
mobile ions. Flow nearly
constant velocity across
channel.
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• Optical Transducers
– MANY types!
– Overlap between commercial electronics and MEMS.
– Thermal (Bolometers)
• Light heats element, causes resistance change.
– Fabry Perot etalon type devices (interference) for changing
reflection. Like microspectrometer shown previously.
– E-ink displays (MEMS?)
– Thermocouple
– Golay cell
• Light -> heat -> expanding gas -> moves something -> signal.
– Spectrometers
– Diffractive sensors.
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Preview of a case study (or project).
Capacitive Accelerometer, p. 497, Senturia.
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Fabrication Technology – sets limits on structures.
Lumped element modeling in different domains.
Capacitive transducer/actuator
Elasticity, contact mechanics, stiction
Structures – springs/beams.
Fluids – squeeze film damping
Electronics, feedback
System dynamics
Noise