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Automotive Sensors: MEMS
Chris Mosser
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Outline Introduce MEMS Applications Automotive Specific Information
Fabrication Packaging
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What are MEMS? Micro(small) Electro(electric components/functionality)
Micro(small) Electro(electric components/functionality) Mechanical(mechanical components/functionality) Systems(integrated, system-like functionality)
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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
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Why MEMS Small Typically .1-100um feature size Red Blood Cells ~ 10um
Red Blood Cells ~ 10um Human Hair thickness ~ 50um
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Why MEMS Low cost, High yield Use existing IC fabrication technology
Made primarily on Silicon Wafers
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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
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Typical Applications Accelerometers Magnetometers Microphones
Micro-Fluidics RF-MEMS Bridge to Nanotechnology
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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
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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
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Who Developed It Two groups Delco Electronics Group(General Motors)
Used piezoresistive sensing Ford Used capacitive sensing
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Piezoresistive Sensors
Use the piezoresistive effect Applied stress changes resistivity of material Diaphragm with two embedded piezoresisters Source: IMG(UF)
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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
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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
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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)
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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
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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
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Automotive MEMS Summary
Precision Engineering By V. C. Venkatesh, Sudin Izman
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Thank You
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References Application of MEMS Technology in Automotive Sensors and Actuators, David Eddy and Douglas Spanks
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