Si based Waveguide and Surface Plasmon Sensors

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

© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be

VisionLab-on-ChipLab-on-Chip

Miniaturize and integrate optical sensorsMiniaturize and integrate optical sensors


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


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)


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


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


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


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


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


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


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



• Biosensors

• Label-Free Biosensor: Ringresonator Theory



• Label-Free Biosensor: Surface Plasmon Interferometer Theory



Measurements

•Strain Sensor

•Conclusions


Theory

Pass port

Incoupling Port

Drop Port

biorecognition element (ligand)matching biomolecule (analyte)

flow with biomolecules

functional monolayermicroring cavity

biosensor

m

Dneffresonance


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


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


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



Surface Chemistry

1. Cleaning and oxidation 2. Silanization: surfaces are dip-coated in APTES solution3. Coupling of Biotin-LC-NHS


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


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



• Label-Free Biosensor: Ringresonator

Theory



• Label-Free Biosensor: Surface Plasmon Interferometer

Theory



Measurements

•Strain Sensor

•Conclusions


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


Theory

Bulky surface plasmon biosensor Fully integrated lab-on-chip solution in Silicon-on-Insulator


Theory : Concept

Si

Si

SiO2

Sample medium

5 μ

m4

μm

1 μ

m.2

2μm

10 μm

Surface Plasmon InterferometerSurface Plasmon Interferometer

Au


Simulation : Intensity Measurement

Constructive InterferenceConstructive Interference


Destructive InterferenceDestructive Interference



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




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



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



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


Sensitivity to adlayersSensitivity to adlayers

6 pm/nm6 pm/nmFor n=1.34 adlayerFor n=1.34 adlayer



Measurement Setup

Top ViewTop View

Side ViewSide View


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

]




Theory




Theory

Sensitivity

Fabrication

Measurements

•Strain Sensor

•Conclusions


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


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


Strain sensorStructure of SOI strain sensor

Si

SiO2

polyimide

SiO2

10µm

2µm

Layer stack Circuit layout


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


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


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/)




Theory




Theory

Sensitivity

Fabrication

Measurements

•Strain Sensor

•Conclusions


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


Acknowledgements

GOA Biosensor Project

IAP Photon

IWT Vlaanderen

FWO Vlaanderen

FOS&S



Alternative (extended) Conclusions


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


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


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


APPENDIX


Si

Si

SiO2

H2OSample medium 54

10.

220

10



Novel ConceptCoupling to SP modesCoupling to SP modes


Novel ConceptMode dispersion gold-clad waveguideMode dispersion gold-clad waveguide

Waveguide mode cutoffWaveguide mode cutoff


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


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


Sensitivity Analysis

Sensitivity to adlayersSensitivity to adlayers

6 pm/nm6 pm/nmFor n=1.34 adlayerFor n=1.34 adlayer



Documents

Si based Waveguide and Surface Plasmon Sensors