http://photonics.intec.ugent.bePhotonics Research Group
Si basedSi based Waveguide and Waveguide and
Surface Plasmon Sensors Surface Plasmon Sensors
Peter Debackere, Dirk Taillaert, Katrien De Vos, Stijn Scheerlinck, Peter Bienstman, Roel Baets
Photonics Research Group
INTEC – IMEC
Ghent University
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VisionLab-on-ChipLab-on-Chip
Miniaturize and integrate optical sensorsMiniaturize and integrate optical sensors
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Lab on ChipBenefits
Compactness allows high integration
Massive parallelisation allows high throughput and multiparameter analysis.
Low fabrication cost can lead to cost effective (even disposable) chips
Biosensors : low fluid volume consumption
Challenges Novel technology, not yet fully developed
Scaling down detection principles
Biosensors: Physical effects: e. g. capillary forces
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Silicon-on-InsulatorHigh Index ContrastHigh Index Contrast
100
m
10
m1
m
Guide and confine light on extremely small scale
Sensitivity increases with decreasing waveguide thickness and increasing index contrast
Cavities:
High Q factors, very small dimensions: Large Free Spectral Range (FSR)
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Silicon-on-Insulator
Deep UV lithography (248 nm)
Standard Reactive Ion Etching
Very high performance and reproducibility
Easy integration with CMOS and/or microfluidics
Wafer-scale processes
Very high throughput
Fabrication using standard CMOS processing stepsFabrication using standard CMOS processing steps
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Silicon-on-InsulatorSimulation : Price per Chip calculated for CMOS research fabSimulation : Price per Chip calculated for CMOS research fab
wafer 300 €
mask(2) 25000 €
deep etch
Litho 1000 € /lot
Etch 1000 € /lot
Strip 1000 € /lot
shallow etch
Litho 1000 € /lot
Etch 1000 € /lot
Strip 1000 € /lot
dicing 100 € /wafer
number of chips/wafer (10 mm2) 12500
number of wafers/lot 23
100.000 chips 0.402 €/chip
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Silicon-on-Insulator
High integration allowing multiparameter analysis
High throughput fabrication, thus low fabrication cost
High sensitivity for low fluid volumes
Integration with microfluidics
High reprocibility
Lab-on-Chip ChecklistLab-on-Chip Checklist
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Active Research CommunitySOI Lab on a Chip
Silicon Photonics Crystal Structures for Sensing
PM Fauchet
Mach-Zehnder sensing in SiNLab-on-Chip Platform based on Highly Sensitive Nanophotonic Si
Biosensors for Single Nucleotide DNA Testing
J Sanchez del Rio
Fast, Ultrasensitive Virus Detection using a Young Interferometer Sensor
Aurel Ymeti
Integrated Surface Plasmon Sensor Low-Index-ContrastSPR Sensor based on combined sensing of Modal, Phase and
Amplitude Changes
P Levy et al
Long-range Surface Plasmon SensorLong-range Surface Plasmon Waveguides and Devices in Lithium-
Niobate
P Berini
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Focus Areas
Label-free and multi-parameter detection of biomolecules
BiosensorsBiosensors
Refractive index sensing of
appropriately functionalized surfaces
DNA, mRNA, proteins, sugars, as well as
enzymatic activities (proteases, kinase,
DNAses)
Waveguide sensors,
Microring Cavities
Surface Plasmon Sensors
Strain sensorStrain sensor
Measure strain in different in-plane directions, long term, immune from electromagnetic
interference
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Overview• Introduction
• Biosensors
• Label-Free Biosensor: Ringresonator Theory
Measurements: Bulk sensing
Measurements: Surface sensing
• Label-Free Biosensor: Surface Plasmon Interferometer Theory
Simulation: Intensity Measurement Mode
Simulation: Wavelength Interrogation Mode
Measurements
•Strain Sensor
•Conclusions
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BiosensorsWaveguide sensors :Microring CavitiesWaveguide sensors :Microring Cavities
Surface Plasmon SensorSurface Plasmon Sensor
• Evanescent field sensing
• Technology and principle well understood
• Surface modification and biomolecule immobilisation are the biggest issues
• Sensing with surface plasmon modes
• Novel technology and principle
• Surface modification and biomolecule immobilisation well understood
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Overview• Introduction
• Biosensors
• Label-Free Biosensor: Ringresonator Theory
Measurements: Bulk sensing
Measurements: Surface sensing
• Label-Free Biosensor: Surface Plasmon Interferometer Theory
Simulation: Intensity Measurement Mode
Simulation: Wavelength Interrogation Mode
Measurements
•Strain Sensor
•Conclusions
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Theory
Pass port
Incoupling Port
Drop Port
biorecognition element (ligand)matching biomolecule (analyte)
flow with biomolecules
functional monolayermicroring cavity
biosensor
m
Dneffresonance
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TheoryIntensity Measurement ModeIntensity Measurement Mode
• Monochromatic Input, monitor output power as a function of refractive index
• Advantage : real-time interaction registration
• Disadvantage : limited range
Wavelength Interrogation ModeWavelength Interrogation Mode
• Broadband input, monitor resonance wavelength as a function of refractive index
• Advantage: easy to multiplex
• Disadvantage: slower detection method
SensitivitySensitivity
Increases with increasing Q factor of the ring
dB
resonanceQ3
P
P
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Measurement Setup
Results presented here:Results presented here:
Static measurements : zero flow rate
Flow cell dimensions Ø~2mm2
Towards microfluidic setup:Towards microfluidic setup:
Continuous flow with syringe pumpFlow cell dimensions Ø~100μm2
SiO2
Light from tunable laser Light to photodetectorFlow Cell
Temperaturecontrol
Si
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Bulk refractive index sensing
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
1.333 1.334 1.335 1.336 1.337 1.338
refractive index [RIU]
reso
nanc
e w
avel
engt
h sh
ift [
nm]
• No surface chemistry involved
• Different salt concentrations
• Good repeatability (small variations around mean value)
• shift of 70nm/RIU• ∆λmin= 5pm• ∆nmin=1*10-5RIU
SensitivitySensitivity
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Surface Chemistry
1. Cleaning and oxidation 2. Silanization: surfaces are dip-coated in APTES solution3. Coupling of Biotin-LC-NHS
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Surface Sensing Biotin/Avidin
resonator
buffer pH7,4
resonator
avidin concentration
biotinavidinbiotin
buffer pH7,4
resonator
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
1551.80 1551.90 1552.00 1552.10 1552.20 1552.30 1552.40 1552.50 1552.60
wavelength [nm]
ou
tpu
t [a
u]
∆λ
∆P
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 5 10 15 20 25
avidin concentration [μg/ml]
reso
nanc
e w
avel
engt
h sh
ift [
nm]
Surface Sensing Biotin/Avidin
• High avidin concentrations: saturation
• Low avidin concentrations: quantitative measurements
• ∆λmin= 5pm 50ng/ml
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Overview• Introduction
• Label-Free Biosensor: Ringresonator
Theory
Measurements: Bulk sensing
Measurements: Surface sensing
• Label-Free Biosensor: Surface Plasmon Interferometer
Theory
Simulation: Intensity Measurement Mode
Simulation: Wavelength Interrogation Mode
Measurements
•Strain Sensor
•Conclusions
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Theory: Surface Plasmons• Evanescent TM polarized electromagnetic waves bound to the surface of a metal
• Benefits for Biosensing High fields near the interface are very sensitive to refractive index changes
Gold is very suitable for biochemistry
From source
To detector
Prism
Gold
R
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Theory
Bulky surface plasmon biosensor Fully integrated lab-on-chip solution in Silicon-on-Insulator
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Theory : Concept
Si
Si
SiO2
Sample medium
5 μ
m4
μm
1 μ
m.2
2μm
10 μm
Surface Plasmon InterferometerSurface Plasmon Interferometer
Au
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Simulation : Intensity Measurement
Constructive InterferenceConstructive Interference
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Destructive InterferenceDestructive Interference
Simulation : Intensity Measurement
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Optimalisation of DesignOptimalisation of Design
Si thickness = 160 nmSi thickness = 160 nm
Length = 10 Length = 10 mm
Si thickness = 100 nmSi thickness = 100 nm
Length = 6.055 Length = 6.055 mm
Simulation : Intensity Measurement
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Simulation : Intensity Measurement
Sensitivity AnalysisSensitivity Analysis
1010-6-6
1010-7-7
1010-5-5Change in the refractive Change in the refractive index that causes a drop index that causes a drop or rise in the or rise in the transmission of 0.01 dBtransmission of 0.01 dB
SensitivitySensitivity
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Sensitivity AnalysisSensitivity Analysis
1010-6-6
1010-7-7
1010-5-5
ComparisonComparisonPrism Coupled SPR 1 x 10-6
Grating Coupled SPR 5 x 10-5
MZI SOI Sensors 7 x 10-6
Integrated SPR LIC 5 x 10-6
BUTBUT
Dimensions are two Dimensions are two orders of magnitude orders of magnitude
smallersmaller
Simulation : Intensity Measurement
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Shift of the spectral minimumShift of the spectral minimum
Shift of the spectral
minimum as a function of the bulk refractive
index
Simulation: Wavelength Interrogation
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Sensitivity to adlayersSensitivity to adlayers
6 pm/nm6 pm/nmFor n=1.34 adlayerFor n=1.34 adlayer
Simulation: Wavelength Interrogation
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Measurement Setup
Top ViewTop View
Side ViewSide View
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Measurement ResultsTransmission as a function of wavelength
Measurement
-32
-30
-28
-26
-24
-22
-20
-18
-161530 1540 1550 1560 1570 1580 1590 1600 1610
Wavelength (nm)
Tran
smis
sion
(dB
)
Compared to TheoryCompared to Theory
• Qualitative Agreement between experiment and theory
• QuantitativeNeed for a better
fabrication process
5 μm Au
O2 toplayer
Transmission as a function of wavelengthSimulation
-18
-17
-16
-15
-14
-13
-12
-11
1480 1500 1520 1540 1560 1580 1600
Wavelength [nm]
Tran
smis
sion
[dB
]
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Overview• Introduction
• Label-Free Biosensor: Ringresonator
Theory
Measurements: Bulk sensing
Measurements: Surface sensing
• Label-Free Biosensor: Surface Plasmon Interferometer
Theory
Sensitivity
Fabrication
Measurements
•Strain Sensor
•Conclusions
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensorIntroduction :
Electrical resistance gage
Most popular strain gage
Moderate long term reliability
No absolute measurements
2-D strain sensing
Small resistance changes
Fiber Bragg Gratings (FBG)
More expensive
Good long term reliability
‘Absolute measurements’
Only 1-D strain sensing
EMI insensitive
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Strain sensorTry to combine some advantages of electrical resistance gages and FBGs
Strain = L/L
typical R = 0.2 ~ = 1000
typical = 1000 pm ~ = 1000
SOI ring or racetrack resonator
Resonance wavelength depends on strain
Wavelength measurement = robust
Wavelength demultiplexing(large FSR needed)
eff
eff
n
n
L
L
electrical : resistance,
optical : wavelength
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensorStructure of SOI strain sensor
Si
SiO2
polyimide
SiO2
10µm
2µm
Layer stack Circuit layout
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Strain sensor Thin foil strain sensor is bonded to Al plate for testing
Bending test : bending the plate results in tensile strain at top surface
Not yet fiber packaged
Photo of measurement setup
Sensor circuit
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensor
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4 5 6 7
beam deflection (mm)
wav
elen
gth
sh
ift
(nm
)
Uni-axial strain
Experimental results : wavelength shift vs beam deflection,
good agreement with theoretical predictions
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensor
Experimental results : Circular resonator : =0.85xx (pm/)
Racetrack resonator=0.99xx , =0.63yy
Sensitivity and cross-sensitivity can be improved by optimized design
=1.3xx , =0.3yy (pm/)
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Overview• Introduction
• Label-Free Biosensor: Ringresonator
Theory
Measurements: Bulk sensing
Measurements: Surface sensing
• Label-Free Biosensor: Surface Plasmon Interferometer
Theory
Sensitivity
Fabrication
Measurements
•Strain Sensor
•Conclusions
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
ConclusionsTheory & Design
Proof of Principle
Bulk Sensing
Surface Chem
Adlayer sensing
Optimize Multi para
10-5 RIU
We have demonstrated new type of optical strain sensor
Thin foil SOI strain gage
Sensitivity comparable to Fiber Bragg Gratings, but can measure strain in different in-plane directions
P: 10ng/ml: 50ng/ml
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Acknowledgements
GOA Biosensor Project
IAP Photon
IWT Vlaanderen
FWO Vlaanderen
FOS&S
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http://photonics.intec.ugent.bePhotonics Research Group
Alternative (extended) Conclusions
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Conclusions
Silicon on Insulator Microring Cavities SOI microrings
Extremely small high Q cavities Fabrication with standard CMOS
processing techniques
Characterization ∆n ~ 10-4 for bulk refractive index
sensing LOD 10ng/ml avidin concentration
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
ConclusionsSilicon-on-Insulator Surface Plasmon Sensors
• Theoretical Surface Plasmon Biosensor based on new
concept
Sensitivity comparable with current integrated SPR devices
Design is very versatile
Two orders of magnitude smaller than current integrated SPR devices
• Experimental Proof-of-Principle
Discrepancy between theoretical predictions and experimental values
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
ConclusionsSilicon-on-Insulator Strain Sensors
We have demonstrated new type of optical strain sensor
Thin foil SOI strain gage
Sensitivity comparable to Fiber Bragg Gratings, but can measure strain in different in-plane directions
http://photonics.intec.ugent.bePhotonics Research Group
APPENDIX
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Si
Si
SiO2
H2OSample medium 54
10.
220
10
Simulation: Wavelength Interrogation
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Novel ConceptCoupling to SP modesCoupling to SP modes
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Novel ConceptMode dispersion gold-clad waveguideMode dispersion gold-clad waveguide
Waveguide mode cutoffWaveguide mode cutoff
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SPR History Integrated Surface Plasmon Resonance Device
PrinciplePrincipleThin metallic layersThin metallic layers
Symmetric claddingSymmetric cladding
SupermodesSupermodes
Asymmetric claddingAsymmetric cladding
Interface ModesInterface Modes
H2OSample medium
Schematical Device SetupSchematical Device Setup
H2OSample medium
DrawbacksDrawbacks
•Quite large (mm scale)Quite large (mm scale)
• Not suited for high level Not suited for high level integrationintegration
•Design limited to low-index Design limited to low-index contrast due to phase matching contrast due to phase matching considerationsconsiderations
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Intensity Measurement/ SimulationParametersParameters
• Length of the sensing regionLength of the sensing region
• Thickness of the Si waveguideThickness of the Si waveguide
• Thickness of the Au layerThickness of the Au layer
LimitationsLimitations
• Position of the minima :Position of the minima :Dip in the transmission curve @ 1.550 micron should be Dip in the transmission curve @ 1.550 micron should be near n = 1.33near n = 1.33
• Maximum Visibility :Maximum Visibility :Loss along both ‘arms’ has to be equalLoss along both ‘arms’ has to be equal
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Sensitivity Analysis
Sensitivity to adlayersSensitivity to adlayers
6 pm/nm6 pm/nmFor n=1.34 adlayerFor n=1.34 adlayer
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be