Chris Mosser
http://www.d-r-t.com/sensortech.htm
http://news.thomasnet.com/fullstory/463874
Outline
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Introduce MEMS
Applications
Automotive Specific Information
Fabrication
Packaging
What are MEMS?
• Micro(small)
http://eed.gsfc.nasa.gov/562/SA_MEMs.htm
• Electro(electric components/functionality)
http://www.memx.com/
• Mechanical(mechanical components/functionality)
http://www.memx.com/
• Systems(integrated, system-like functionality)
http://www.forbes.com/2008/04/22/mems-apple-nintendo_leadership_clayton_in_jw_0421claytonchristensen_inl_slide.html
Where do you find MEMs?
• Printers
– High DPI inkjets
• Projectors
• Micro-Mirrors from Texas Instruments
• Cell Phones
– Knowles Microphones used in most new cell
phones
• Automobiles
Why MEMS
• Small
– Typically .1-100um feature size
http://singularityhub.com/wp-content/uploads/2008/08/red-blood-cells.bmp
Red Blood Cells ~ 10um
http://www.vendian.org/envelope/dir2/scaling_construct.html
Human Hair thickness ~ 50um
Why MEMS
• Low cost, High yield
– Use existing IC fabrication technology
– Made primarily on Silicon Wafers
http://media-2.web.britannica.com/eb-media/22/78522-004-BB539CA9.jpg
Why MEMS
• Favorable scaling for a lot of applications
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Flow-rate sensors
Electrostatics
Magnetism
Many others
• Not all applications
– Solar Power
– Turbulent Boundary Energy Harvesting
Typical Applications
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Accelerometers
Magnetometers
Microphones
Micro-Fluidics
RF-MEMS
Bridge to Nanotechnology
Automotive MEMS
• MEMS Sensors and Actuators used to
control various elements of the automobile
– Powertrain and Chassis control
• Ex: Manifold Air Temperature
– Comfort and Convenience
• Ex: Air-Temperature Control
– Communications
• Ex: Wireless
Where it Began
• 1979 - First recorded use of MEMs in automobiles
• Federal emission standards required monitoring the air-tofuel ratio of the engine
– Density of air value was needed
• Many different sensor technologies were introduced to
solve this problem
• MAP (manifold absolute pressure) and MAT (manifold air
temperature) sensors were developed using MEMS
• Silicon based MEMS sensors became the device of choice
due to low cost and high yield
http://www.quantummatrix.com.my/v1/content/view/231/59/
MAP Sensor
Who Developed It
• Two groups
– Delco Electronics Group(General Motors)
• Used piezoresistive sensing
– Ford
• Used capacitive sensing
Piezoresistive Sensors
• Use the piezoresistive effect
– Applied stress changes resistivity of material
Source: IMG(UF)
Diaphragm with two embedded piezoresisters
Capacitive Sensors
• Vary two parameters
– Gap
– Overlap area
• Advantages
– Low power
– High accuracy
– Temperature independent
• Important for a lot of automobile applications
– Reciprocal
• Disadvantages
– Parasitic capacitance
– Small signal
http://www.nanoshift.net/Technology.htm
What about Actuators?
• Traditionally only sensors were developed
for automobiles
• Actuators started to become popular as
MEMs development costs decreased
• Popular actuators include
– Microphones
– Fuel injection nozzles
Fabrication
• Use basic IC fabrication
– Masks/layers/CVD/oxidation/etc
• MEMS specific fabrication
– DRIE (Deep reactive ion etch)
– SOI (silicon on insulator)
General MEMS Packaging
• The most important and expensive part of a
MEMS sensor/actuator
– ~45% of the cost of designing a MEMS device is spent
on packaging
• Often times packaging constraints will prevent a
design from being produced
– May require too complex of a package design for
realistic implementation
• Package can greatly change the response of a
device
– Sensitivity/Dynamic Range/etc all effected by package
Automotive MEMS Packaging
• Automotive sensors generally only allowed
to have 3 wires connected to them
– Minimizes cost
• Environment concerns are especially
important in automotive applications
– Engine heat
– High acceleration/deceleration
– Humidity
Automotive MEMS Summary
Precision Engineering
By V. C. Venkatesh, Sudin Izman
Thank You
References
• Application of MEMS Technology in
Automotive Sensors and Actuators, David
Eddy and Douglas Spanks
• http://www.img.ufl.edu/ms/eel5225/html/as
signments.htm