Albert (“Al”) P. Pisano, Ph. D.
Chair, Department of Mechanical EngineeringProfessor of Mechanical Engineering
FANUC Professor of Mechanical SystemsProfessor of Electrical Engineering and Computer Sciences
Director, Berkeley Sensor & Actuator Center(510) 643-7013
[email protected]://www.me.berkeley.edu/faculty/Pisano
The MINOTAUR Project
MIcro and NanO Technologies for AUtomotive Research
Slide 2
Reason for the MINOTAUR Project
Phase 1 Automotive Sensors (completed)New Sensors for Enhanced Driver Information
Phase 2 Automotive Sensors (completed)Sensor Communication with Control Computers
Phase 3 Automotive Sensors (entering)Software Programmable Automotive Experience
The New Paradigm for Automotive Sensors
Slide 3
Reason for the MINOTAUR Project
Reduced Cost & Ease of ManufactureIntroduction of Micro and Nano Technologies
Higher PerformanceEnhanced Sensitivity and Bandwidth
Greater RobustnessThermal, Shock and Chemical Resistance
New Sensor ModesDirect Measurement of DataReduced Use of Computer Models to Guess
New Requirements for Automotive Sensors
Slide 4
Review of Existing Sensors
Cylinder PressureCombustion TemperatureCombustion Flame SpeedEngine Output TorqueWheel Forces on ChassisRoad Forces on WheelsSuspension Forces and Torques
Existing Sensors Do Not Directly Measure Engineering Phemonena
Slide 5
Review of Existing Sensors
Slide 6
Advanced Safety Vehicle (ASV)
Slide 7
Direct Measurement of Forces
MEMS Strain Gauge
COTS RF Transceiver
MEMS Sensor on Wheel Communicates via RF to Transcieveron Chassis
MEMS Strain Gauge
MEMS Sensor on Shock Tower Measures Vertical Forces On Chassis for DSC Application
Slide 8
Projects Overview
SiC TAPS Sensors for
Harsh Environments
NanowireArray Gas Sensors
MEMS REPS Smart
Plate
MINOTAUR Research Projects
MEMS Strain
Sensors
Integration of NEMS Integration of NEMS and MEMS and MEMS
by Localized Growth of by Localized Growth of NanowiresNanowires
Slide 9
steel substrate
sensorFoil gauges are limited in application and size:
Sensitivity limits length to ~1.5 mmRequire complicated & time consuming bonding
MEMS gauges offer solution:Inherently smallCan incorporate bonding structures into deviceIntegration with control, and data analysis CMOS also a possibility.
Example: Auto BearingRoller / Race interaction creates strain field ~100 μm wideThis field dictates fatigue life of the bearing and relates directly to the force on the bearing, allowing for improvements in traction control applications.Require 0.1μЄ resolution at 10kHz bandwidth
~100 μm
~100 μm~500 μstrain
MEMS resonant strain sensor
MEMS Strain Sensors
Slide 10
Sensor Resolution Vs. Bandwidth
Bandwidth [ Hz ]
με [rms]
100 101 102 10310-4
10-3
10-2
10-1
TargetTargetTargetTarget
104
216.8
217
217.2
217.4
217.6
217.8
218
218.2
0 5 10 15 20 25
Measured = 39 Hz/με Calculated = 36 Hz/με
Applied strain [ microstrain,με ]
SWO
frequ
ency
[ kHz
]
216.8
217
217.2
217.4
217.6
217.8
218
218.2
0 5 10 15 20 25
Measured = 39 Hz/με Calculated = 36 Hz/με
Applied strain [ microstrain,με ]
SWO
frequ
ency
[ kHz
]
Measured Strain Sensitivity
On-chip StrainActuator
MEMS Die Photo
AnchorTines
Anchor
MEMS DiETF
Slide 11
Induction bonding is a fast, clean, and inexpensive heating process.Generating an alternating magnetic field induces eddy currents in the metal.Eddy currents cause localized heat generation from Joule heating.Heat profile can be analyzed and controlled to prevent damage to the heat treatment of the steel.
Silicon-to-Steel Induction BondingSilicon-to-Steel Induction Bonding
Slide 12
Pb/Sn layer is then reflownusing infrared heating.Silicon test structures with Ti/Cu layer are cleaned.Test specimen are then exposed to infrared heating for a short period of time (30-60 seconds).The result: silicon bonded to steel!
Si Test Die Spring Steel Test Structure
CopperTitanium
Pb/SnNitride
Steel parallel with bonded silicon under high strain
Silicon test chips bonded to steel
Silicon-to-Steel IR BondingSilicon-to-Steel IR Bonding
Slide 13
P3: Amorphous SiC,
P1: Epitaxial 6H-SiC, (SiC Electronics)
P2: Poly 3C-SiC, (SiC MEMS structures)
6H-SiC Substrate
Silicon Carbide TAPS Sensors
Extreme Environment Sensor600 °C temperature, 300 atm pressure, 150,000 g
shock
Layers of 3 Different Silicon Carbide Materials
Slide 14
Works at high temperature > 600 °C Inherently small
Can incorporate bonding structures into deviceIntegration capability with control logic systemLess susceptibility to fatigue due high fracture
toughness of SiCNano strain resolution in 100 Hz bandwidth at
600 °C SEM image of a SiC double-folded comb-
drive resonator fabricated at UCB
– Works at high temperature applications (600°C) in oxidative environments
– Si based MEMS pressure sensors fails in harsh conditions (>150 °C, oxidation envionments, and very high pressure conditions).
– Deposition vs. Etching: precise control of diaphragm thickness through deposition gives high resolution
– 1% resolution at baseline of 300 atm up to 600 °C.
SiC Double Ended Tuning Fork Strain GaugeSiC Double Ended Tuning Fork Strain Gauge
SiC Membrane
6H-SiC Substrate
SiC Membrane
6H-SiC Substrate
SiC High-Resolution Strain Gauge
SiC Diaphragm Pressure Sensor
Slide 15
– High material toughness, high band gap, and oxidation resistance.
– Silicon-based accelerometers do not work in high-g, high electromagnetic radiation, and high temperatures (>150°C).
– Successful operation even above 150,000 g’s
– 1g resolution at 600 °C
SiC membrane
Metallization
Piezoresistive elements
Outer resisterInner resister
Compressive Stress
Tensile Stressg-force g-force
Proof mass
SiC membrane
Metallization
Piezoresistive elements
Outer resisterInner resister
Compressive Stress
Tensile Stressg-force g-force
Proof mass
SiC membrane
Metallization
Piezoresistive elements Piezoresistive elements
Outer resisterInner resister
Compressive Stress
Tensile Stressg-force g-force
Outer resisterInner resister
Compressive Stress
Tensile Stressg-force g-force
Proof mass
– Material compatibility.
– Monolithic integration with other sensors and logic circuits due to process compatibility whereas commercial sensors can not be integrated with this chip technology
SiC Substrate
SiC Circular Diaphragm
Metallization
Piezoresistive element (SiC or High Temp. metal)
SiC Accelerometer
SiC High-G Accelerometer
Slide 16
MEMS REPS Smart Plate
Flexible Fuel Delivery
Advanced Auxiliary
Combustion Stability & Characterization
High Specific Power Generation
MEMS Smart Plate
Signature Control
100-250 Watts
Slide 17
Engine Performance Monitoring & Control Sensors
Oxygen Sensor
Knock SensorPressure Sensors
Silicon CarbideWear Plate
Fuel Valve
Fuel Delivery
Temperature Sensors
Crank Shaft Angle Sensor
Slide 18
MEMS Enabled Portable Power
Low cost manufacturing + Low unit cost MEMS High functionality, performance
Electrical Power Shaft Work
17-4 Stainless Steel
Silicon
17-4 Stainless Steel
Silicon
Magnetic Flywheel
MEMS SystemIntegration
Low Cost ProductionLow Part Count
Traditional Materials
Slide 19
Nanowire Array Gas SensorsBackground
FabricationElectrodeposition of metal in
alumina nano-template
Advantages of DesignHigh surface area to volume ratioHigh sensitivityFast response timeLower power requirement than
conventional sensors
Porous anodic alumina template
Tin Oxide (SnO) Nanowires
A. Kolmakov, Y. Zhang, G. Cheng, M Moskovits, Adv. Mater. 2003, 15, 12.
Slide 20
Integration of NEMS and MEMS Localized Growth of Nanowires
Englander, L.Lin UC Berkeley
– Microscale structures serve as the platform for silicon nanowire synthesis resistive heaters/microbridges
– Heat is provided locally rather than globally
– Single crystal silicon & polysilicon structures serve as platforms
– Wirebond individual microbridges to a chip carrier
– Place chip carrier in a converted PECVD vacuum chamber
Slide 21
Integration of NEMS and MEMS Process Schematics Englander, L.Lin UC Berkeley
MEMS bridges are positioned in close proximity to each other
The growth bridge is resistively heated to reach the synthesis temperature
The cold bridge serves to create local electric field to assist in SiNW orientation
SiNW growth ends once contact with cold bridge takes place
E
Cold Bias Hot Growth Bridge Bridge
5μm
gap
E
Cold Bias Hot Growth Bridge Bridge
5μm
gap
Slide 22
Nanowire Array Gas Sensors Oxygen & Hydrogen Sensors
H2 Molecules
PdNi Nanowires Anode
Cathode
Change in resistance of the sensing element in the presence of hydrogen
molecules.
H
H
H
H H
HR R*
– Hydrogen gas molecules change in the electrical resistance of Pd sensing material
Oxygen Ambient Reducing Gas
Depletion O-
+
++
+
+
+
O-
O-
O-
O-
O-
CO2CO2
CO2
CO2
CO2
CO2
e-e-e-
O2 Molecules
Metal-OxideNanowires
Anode
Cathode
Schematic of the principle of operation
– Metal oxide material reacts to oxidizing and reducing gases
– 1/2O2 + e- O-
– CO + O- CO2 + e-
– The small diameter of nanowires allows the surface chemistry to alter the bulk conductivity of the wires.
Oxygen Sensor Hydrogen Sensor
Slide 23
The MINOTAUR Project
New Micro and Nano SensorsNew Manufacturing Methods
Enhanced Sensitivity and BandwidthIncreased Performance for Closed-Loop Control
Thermal, Shock and Chemical ResistanceImproved Sensor Robustness and Lifetime
Direct Sensor Measurement of DataNew Modes of Vehicle Control and Programmability
CONCLUSIONS