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Chapter 9Chapter 9bb:: Example of a Example of a Micromachined DeviceMicromachined Device::The SA30 Crash Sensor from SensoNorThe SA30 Crash Sensor from SensoNor
Picture shows the interior chip assembly of SensoNor’s SA30 Crash Sensor
The course material was developed in INSIGTH II, a project sponsored by the Leonardo da Vinci program of the European Union
Slide 2
Presentation at Transducers ’97, Chicago, USA, June 1997:Presentation at Transducers ’97, Chicago, USA, June 1997:
An Integrated Resonant Accelerometer Microsystem for Automotive ApplicationsAn Integrated Resonant Accelerometer Microsystem for Automotive Applications
Authors: Per Ohlckers*, Reidar Holm*, Henrik Jakobsen*, Terje Kvisteroy*,
Gjermund Kittilsland*, Martin Nese*, Svein M. Nilsen* and Alain Ferber**
* SensoNor asa, ** SINTEF Electronics and Cybernetics,
Slide 3
Outline of presentation: “An Integrated Resonant Accelerometer Outline of presentation: “An Integrated Resonant Accelerometer Microsystem for Automotive Applications”Microsystem for Automotive Applications”
• Background and motivation
• Design and technology evaluations
• Design
• Fabrication process
• ASIC, integrationand packaging
• Results and discussions
• Future work
• Conclusions
Slide 4
Background and motivationBackground and motivation
• SensoNor has a strong market position: ~ 23 million units (medio 1997) accumulated production of our SA20 Crash Sensor
• Growing Market for Automotive Crash Sensors:World Market Estimate of morethan 60 million units per year in year 2000
• Silicon Microsystem Technologycan be used to get improvedperformance at reduced cost
Slide 5
Design and Technology EvaluationDesign and Technology Evaluation
• In a feasibility study we considered:– Piezoresistive element, bulk micromachined
– Capacitive element, bulk or surface micromachined
– Resonating element, bulk or surface micromachinedThermal vibration excitationPiezoresitive vibration detection
• The resonating principle was chosen:– Excellent performance
– Inherent continuous self test function
– Excellent mechanical shock survival versus measurement range
– Low production cost
Slide 6
SA30: Modes of Vibration- Model 4 -7SA30: Modes of Vibration- Model 4 -7
Slide 7
SA30: Modes of Vibration- Model 8 -11SA30: Modes of Vibration- Model 8 -11
Slide 8
SA30 Sensor Die: Beam Deflections and Stresses in Mode 9SA30 Sensor Die: Beam Deflections and Stresses in Mode 9
• Mode 9.• Resonance around 650kHz• Sensitivity: Around 6-7Hz/g
Slide 9
Fabrication ProcessFabrication Process
• Important process steps:– Deep n-diffusion to define
thickness of mass structure
– Epitaxial layer to define thickness of beams
– Buried conductors
– Anisotropic wet etching from back side
– RIE etch from front side to release mass and beam structures
– Triple stack anodic bonding of glass and silicon wafers
Slide 10
The micromachining process stepsThe micromachining process steps
• Cross sectioned view showing the micromachining process steps in four different stages.
Slide 11
The Microsystem ASICThe Microsystem ASIC
• ASIC for vibration control and signal output
Slide 12
Integration and PackagingIntegration and Packaging
• Hybrid integration in surface mount transfer molded epoxy package
Slide 13
Results and Discussions: Thickness Measurements of BeamsResults and Discussions: Thickness Measurements of Beams
• Thickness control with Fourier Transform Infrared Spectroscopy for 56 samples from 5 different batches:Mean: 3.08 micrometer Standard dev: 0.06 micrometer
Slide 14
Results and Discussions: Thickness Measurements of MassResults and Discussions: Thickness Measurements of Mass
• Thickness control with Fourier Transform Infrared Spectroscopy for 21 samples:Mean: 23.2 micrometer Standard dev: 0.1 micrometer
Wafers, target 22 um
0
2
4
6
8
10
23 23,05 23,15 23,25 23,35 23,45 More
Mass thickness
Fre
qu
en
cy
Frequency
Slide 15
SA30 Sensor Die: Measurements of Sensitivity and LinearitySA30 Sensor Die: Measurements of Sensitivity and Linearity
Linearity SA30 model 1800, Sensitivity 10Hz/g
0,0
50,0
100,0
150,0
200,0
250,0
300,0
350,0
400,0
0 5 10 15 20 25 30 35
Aref [g peak]
del
taF
[H
z p
eak]
Modeling: Non-linearity less than 0,1%
Measurements: Less than 0.2-0.3 %(Measurement set up limited)
Slide 16
SA30 Sensor Die: Measurements of Mode Sensitivity and SeparationSA30 Sensor Die: Measurements of Mode Sensitivity and Separation
Amplitude response at +25°CX-axis: Hz y-axis: dB
-140
-120
-100
-80
-60
-40
0 200000 400000 600000 800000
Mode 9
Slide 17
SA30 Sensor Die: Measurements of Mode Phase ShiftSA30 Sensor Die: Measurements of Mode Phase Shift
Phase response at +25°Cx-axis: Hz y-axis: Degrees
-200
-100
0
100
200
0 200000 400000 600000 800000
Mode 9
Slide 18
SA30 Sensor Die: Measurements of Mode Sensitivity and SeparationSA30 Sensor Die: Measurements of Mode Sensitivity and Separation
Amplitude response at +90°Cx-axis: Hz y-axis: dB
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
0 200000 400000 600000 800000
Slide 19
SA30 Sensor Die: Measurements of Mode Phase ShiftSA30 Sensor Die: Measurements of Mode Phase Shift
Phase response at +90°Cx-axis: Hz y-axis: Angular degrees
-200
-150
-100
-50
0
50
100
150
200
0 100000 200000 300000 400000 500000 600000 700000 800000
Slide 20
SA30 Sensor Die: Measurements of Mode Sensitivity and SeparationSA30 Sensor Die: Measurements of Mode Sensitivity and Separation
Amplitude response at -40°Cx-axis: Hz y-axis: dB
-140
-120
-100
-80
-60
-40
0 100000 200000 300000 400000 500000 600000 700000 800000
Slide 21
SA30 Sensor Die: Measurements of Mode Phase ShiftSA30 Sensor Die: Measurements of Mode Phase Shift
Phase response at -40°Cx-axis: Hz y-axis: Angular degrees
-200
-150
-100
-50
0
50
100
150
200
0 100000 200000 300000 400000 500000 600000 700000 800000
Slide 22
Future Work and Manufacturing Future Work and Manufacturing
• New version of the ASIC to be verified• Demonstrate fully operational microsystem• Pilot production• Full scale production: Millions per year
Slide 23
ConclusionsConclusions• Feasibility of chosen design and process technology
demonstrated, using:– An acceleration sensitive resonant structure in silicon– An ASIC for resonance control and signal conditioning– Hybrid integration with surface mount transfer molded
plastic package
• Future work: – Demonstrating
the fully operational microsystem and ramp up of high volume production
Slide 24
Update Primo Year 2000Update Primo Year 2000
• Fully functional devices produced in sample quantities
• However: – ASIC too complex and thereby too expensive,
thereby target cost was not met– Development was too much delayed to make it
for the next generation of air bag systems
• Therefore, SensoNor has at present decided to put ramp up of production on hold