1. Automotive Sensors: MEMS
Chris Mosser

2. Outline Introduce MEMS Applications Automotive Specific Information
Fabrication
Packaging

3. What are MEMS? Micro(small) Electro(electric components/functionality)
Micro(small)
Electro(electric components/functionality)
Mechanical(mechanical components/functionality)
Systems(integrated, system-like functionality)

4. 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

5. Why MEMS Small Typically .1-100um feature size Red Blood Cells ~ 10um
Red Blood Cells ~ 10um
Human Hair thickness ~ 50um

6. Why MEMS Low cost, High yield Use existing IC fabrication technology
Made primarily on Silicon Wafers

7. 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

8. Typical Applications Accelerometers Magnetometers Microphones
Micro-Fluidics
RF-MEMS
Bridge to Nanotechnology

9. 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

10. 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

11. Who Developed It Two groups Delco Electronics Group(General Motors)
Used piezoresistive sensing
Ford
Used capacitive sensing

12. Piezoresistive Sensors
Use the piezoresistive effect
Applied stress changes resistivity of material
Diaphragm with two embedded piezoresisters
Source: IMG(UF)

13. 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

14. 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

15. 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)

16. 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

17. 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

18. Automotive MEMS Summary
Precision Engineering
 By V. C. Venkatesh, Sudin Izman

19. Thank You

20. References
Application of MEMS Technology in Automotive Sensors and Actuators, David Eddy and Douglas Spanks