Automotive Sensors: MEMS 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) Electro(electric components/functionality) http://eed.gsfc.nasa.gov/562/SA_MEMs.htm Micro(small) Electro(electric components/functionality) Mechanical(mechanical components/functionality) Systems(integrated, system-like functionality) http://www.memx.com/ http://www.memx.com/ http://www.forbes.com/2008/04/22/mems-apple-nintendo_leadership_clayton_in_jw_0421claytonchristensen_inl_slide.html

Where do you find MEMs? Printers Projectors Cell Phones Automobiles 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 Red Blood Cells ~ 10um http://singularityhub.com/wp-content/uploads/2008/08/red-blood-cells.bmp Red Blood Cells ~ 10um Human Hair thickness ~ 50um http://www.vendian.org/envelope/dir2/scaling_construct.html

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 Flow-rate sensors Electrostatics Magnetism Many others Not all applications Solar Power Turbulent Boundary Energy Harvesting

Typical Applications 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-to-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 MAP Sensor http://www.quantummatrix.com.my/v1/content/view/231/59/

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 Diaphragm with two embedded piezoresisters Source: IMG(UF)

Capacitive Sensors Vary two parameters Advantages Disadvantages 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 MEMS specific 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/assignments.htm