S Ahmad

1
Automotive MEMS Microsensors

• S Ahmad
• Central Electronics Engineering Research
  Institute, Pilani
• Workshop onEmbedded System in Automobile
  Industry
• Indian Institute of Technology, Mumbai
• 1st December, 2003

2
Introduction

• Automotive Industry Quest Passenger Car -
  Performance Improvement, Reduced Cost, Enhanced
  Reliability
• Conventional Sensor - MEMS Replacement
• Newer Possible Applications
• Earliest Use - Manifold Absolute Pressure Sensor
  - MAP - 1979
• Silicon Accelerometer - Airbag - 1990s
• Warranty Period - 10Years/ 150,000 Miles

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Introduction

• Improved Fuel Efficiency, Emission and Safety -
  Federal Standards
• Higher Expectations - Performance, Comfort
• Greater Availability - Micro-controller, Memory,
  Display and Enhanced Diagnostics
• Very Harsh Under the Hood Environment High
  Temperature, Shock, Vibration, Humidity,
  Corrosive Media, EMC and RFI
• Military Grade at Lowest Consumer Price

4
Automotive Sensor Global Market Growth
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Automotive Sensor Usage Early Estimate - 1997
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Automotive Industry MEMS Sensors
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Product Evolution Time Schedule
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Top Ten MEMS Markets

• Micro-fluidic Biochip
• Glucose Monitoring MEMS Sensor
• Tire Pressure Sensors
• Hard Disc Drive Heads
• Inkjet Print Head
• Medical Condition Detection Device
• Large Format Print Head
• Automotive Function Enabling Device
• ABS Accelerometer and Gyroscope
• Automobile Mass Airflow SensorVenture
  Development Corporation

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Basic Auto MEMS Requirements

• Crash Sensing - Air Bag Deployment
• Vehicle Dynamic Control
• Rollover Detection System
• Antitheft System
• Electronic Parking Brake System
• Vehicle Navigation System
• Seat Occupancy / Passenger Position
• Climate Control
• Digital Engine Control
• Road Conditions

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Major Growth Areas

• Accelerometer VDC and Airbags
• Pressure Sensor Transmission, Brakes, Diesel
  Fuel Rails, Refrigeration, Tires, Fuel
  Evaporation,Yaw Rates, GPS Backup
• Position Sensor Wheel Speed, Camshaft,
  Crankshaft, Pedal Positions
• Humidity Sensor Cabin Comfort
• Distance Sensor Collision Avoidance

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Airbag Deployment

• Acceleration - Continuously Measured
• Acceleration Exceeds Some Threshold
• Measured Acceleration Curve Integrated
• Large Velocity Change - Airbag Fired
• Steering Wheel and Side Airbag Firing
• Earlier Sensors - Distributed g Switch
• Insufficient Information On/Off Type
• More Expensive , Less Reliable
• MEMS Accelerometer - Far Better
• Gyroscope - ANALOG Devices - Introduced

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Vehicle Dynamic Control

• VDC - Vehicle Skid Control
• Contains Gyroscope, Low g Accelerometer, Wheel
  Speed Sensor
• Yaw Rate Prediction - Speed Measurement
• Gyroscope Measurement - Compared
• Larger Difference - Single Wheel Brake or Torque
  Reduction Applied, Airbag Fired
• Shock / Vibration Tolerant Gyroscopes - Need
• ANALO Devices - iMEMS Gyro Better Device

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Vehicle Rollover Detection

• More Appropriate - Vans, Trucks, Sport Vehicle
• Roll Angle and Rate Measurement - Tripping
• Gyroscope - Roll Rate, Integration - Angle
• Z - Axis Acceleration Additional Accelerometer
• Sideways Sliding Cause Rollover - Curb/Object
• Dual Axes Low g Accelerometer Ideal Solution
• Shock/Vibration Resistant Gyros - Necessary
• Fast Response Time Gyroscope - Essential

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Security - Antitheft

• Vehicle Towing - Popular Type Theft
• Tilt Detection System - Effective Sensor
• Pan European Specification - 30 Tilt over 3
  minute period - i.e. 0.016o tilt per second
• Fluid Tilt Sensor - Possible Use - Limited Tilt
  Range, Parked Car _at_ Large Tilt Angle - Sensor
  Ineffective Harsh Environment - Temperature
  Change,
• Sensor Performance Heavily Impaired
• Low g Accelerometers Ideal Tilt Sensor

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Parking Brake System

• Manual Parking Brake Activation Robust Push or
  Pull Type Operation
• Braking Force Magnitude - No Concern
• Electronic Parking Brake - Button Activation
• Sensor Measures Vehicle InclinationBraking Force
  Requirement DeterminedBrake Applied - Easy
  Operation
• Low g Accelerometers - Ideal Tilt Detection
  Sensor Sometimes Single Sensor Used Both
  Antitheft and Parking Brake Systems

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Vehicle Navigation System

• Standard Feature Luxury Cars
• Global Positioning System Fundamental Part
• GPS - Position and Altitude but No Direction
• Magnetometer Early Direction SensorLarge
  Ferrous Metal Object - Confused Magnetometer
  Performance - Not Reliable
• Compass and GPS Initial StartTravel Direction
  Match - Map Data - DirectionGyroscope - When and
  How Much Car Turned, Directional Data Match - Map
  Data
• Gyroscope - Heading Information, Low g
  Accelerometer Position Data , Integration

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Electronic Engine Control

• Intake Manifold Pressure - Air to Fuel Ratio
• Mass Air Flow Devices - MEMS Version
• Barometric Pressure - Altitude Information Rich
  to Lean Fuel to Air Mixture Decision
• Cylinder Pressure Measurement -
  PerformanceOptimization - Piezoelectric/ Fiber
  Optic Sensor
• Exhaust Gas Re-circulation - Capacitive Pressure
  Sensor Better Solution
• Hydraulic Fluid Pressure - Isolated Diaphragm
  Type Configuration, Sensor ASIC Integration
• Fuel Injection - Silicon Fuel Injection Nozzle

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Sensor Cluster System

• Same Sensor Family - Variety of Measurements
• Accelerometer/Gyros - Sometimes 15 Sensors
• Difficult Integration, Unsafe Operation Fear
• Inertial Measurement Unit - Six Axes Inertial
  Measurements, Proper location Signal Routing
• Additional Stand Alone Sensors - Still Required
• Sensor Cluster Configuration - More Economical
  Solution, Better Micro-controller Utilization

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Commercial Off-the-Shelf MEMS Pressure Sensor
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6H-SiC High g Piezo-resistive Accelerometer
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ARIES Airbag Deployment Test System
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Three Axes MEMS Accelerometer Sandia Laboratories
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Delphi Automotive System Air Bag
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CEERI Developed Sensors
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Piezo-resistive Pressure Sensor - CEERI
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ZnO Piezoelectric Acoustic Sensor - CEERI
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Polysilicon Load Cell - CEERI
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Three Axes Bulk Micro-machined Accelerometer Test
Structure - CEERI
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Sensor Interface ASIC - Schematic
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Sensor Output Without Conditioning
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Corrected Sensor Output
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Universal Signal Conditioner Resistive Bridge
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Intelligent Pressure Sensor Chip
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Capacitive Sensor Interface ASIC
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Conclusions

• Automobile MEMS Sensor - Fast Growing
• Multi Billion Dollar Industry Growth
• Intelligent Sensor Development - Needed
• Interface and Signal Conditioning - Essential
• Hybrid Approach - Initial Stage
• ASICs Use - Commercial ASICS Available
• Sensor Cluster Approach Better Solution
• Already Late Start Sooner Starting Better

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Thank You