Automotive Sensors 2u1e

Chris Mosser

http://www.d-r-t.com/sensortech.htm http://news.thomasnet.com/fullstory/463874

Outline • • • • •

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, system­like 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 • Micro­Mirrors from Texas Instruments

• Cell Phones – Knowles Microphones used in most new cell  phones 

• Automobiles

Why MEMS • Small

– Typically .1­100um feature size

http://singularityhub.com/wp-content/s/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 – – – –

Flow­rate sensors Electrostatics Magnetism Many others

• Not all applications – Solar Power – Turbulent Boundary Energy Harvesting

Typical Applications • • • • • •

Accelerometers Magnetometers Microphones Micro­Fluidics RF­MEMS 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: Air­Temperature Control

– Communications  • Ex: Wireless

Where it Began • 1979 ­ First recorded use of MEMs in automobiles • Federal emission standards required monitoring the air­to­ fuel 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 deg 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