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,

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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

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SA30: Modes of Vibration- Model 4 -7SA30: Modes of Vibration- Model 4 -7

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SA30: Modes of Vibration- Model 8 -11SA30: Modes of Vibration- Model 8 -11

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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

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The micromachining process stepsThe micromachining process steps

• Cross sectioned view showing the micromachining process steps in four different stages.

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The Microsystem ASICThe Microsystem ASIC

• ASIC for vibration control and signal output

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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

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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

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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)

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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

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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

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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

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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

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-150

-100

-50

0

50

100

150

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0 100000 200000 300000 400000 500000 600000 700000 800000

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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