Si based
Waveguide and
Surface Plasmon Sensors
Peter Debackere, Dirk Taillaert, Katrien De Vos, Stijn Scheerlinck,
Peter Bienstman, Roel Baets
Photonics Research Group
INTEC – IMEC
Ghent University
Photonics Research Group
http://photonics.intec.ugent.be
Vision
Lab-on-Chip
Miniaturize and integrate optical sensors
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Lab on Chip
Benefits

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
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Silicon-on-Insulator
100 m
Guide and confine light on extremely
small scale
1 m
High Index Contrast
Sensitivity increases with decreasing
waveguide thickness and increasing
index contrast
10 m
Cavities:
High Q factors, very small dimensions:
Large Free Spectral Range (FSR)
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Silicon-on-Insulator
Fabrication using standard CMOS processing steps

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
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Silicon-on-Insulator
Simulation : Price per Chip calculated for CMOS research fab
wafer
mask(2)
deep etch
Litho
Etch
Strip
shallow etch
Litho
Etch
Strip
dicing
300 €
25000 €
number of chips/wafer (10 mm2)
number of wafers/lot
12500
23
100.000 chips
0.402 €/chip
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
1000 € /lot
1000 € /lot
1000 € /lot
1000 € /lot
1000 € /lot
1000 € /lot
100 € /wafer
Silicon-on-Insulator
Lab-on-Chip Checklist
High integration allowing
multiparameter analysis
High throughput
fabrication, thus low
fabrication cost
High sensitivity for low
fluid volumes
Integration with
microfluidics
High reprocibility
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Active Research Community
SOI Lab on a Chip
Silicon Photonics Crystal Structures for Sensing
PM Fauchet
Mach-Zehnder sensing in SiN
Lab-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-Contrast
SPR Sensor based on combined sensing of Modal, Phase and
Amplitude Changes
P Levy et al
Long-range Surface Plasmon Sensor
Long-range Surface Plasmon Waveguides and Devices in LithiumNiobate
P Berini
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Focus Areas
Biosensors
Label-free and multi-parameter detection of
biomolecules
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 sensor
Measure strain in different in-plane directions,
long term, immune from electromagnetic
interference
© 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
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Biosensors
Waveguide sensors :Microring Cavities
• Evanescent field sensing
• Technology and principle well understood
• Surface modification and biomolecule
immobilisation are the biggest issues
Surface Plasmon Sensor
• 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
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Theory
resonance 
Incoupling Port
neff D
m
Drop Port
Pass port
flow with biomolecules
matching biomolecule (analyte)
biorecognition element (ligand)
functional monolayer
microring cavity
biosensor
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Theory
Intensity Measurement Mode
• Monochromatic Input, monitor output power as a
function of refractive index
P
• Advantage : real-time interaction registration
• Disadvantage : limited range
Wavelength Interrogation Mode
P
• Broadband input, monitor resonance wavelength as a
function of refractive index
• Advantage: easy to multiplex
• Disadvantage: slower detection method
Sensitivity
Increases with increasing Q factor of the ring
Q
resonance
3dB
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be


Measurement Setup
Light from tunable laser
Light to photodetector
Flow Cell
SiO2
Si
Temperaturecontrol
Results presented here:
Static measurements : zero flow rate
Flow cell dimensions Ø~2mm2
Towards microfluidic setup:
Continuous flow with syringe pump
Flow cell dimensions Ø~100μm2
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Bulk refractive index sensing
• No surface chemistry involved
• Different salt concentrations
resonance wavelength shift [nm]
• Good repeatability (small variations around mean value)
0.35
0.3
Sensitivity
0.25
• shift of 70nm/RIU
• ∆λmin= 5pm
• ∆nmin=1*10-5RIU
0.2
0.15
0.1
0.05
0
1.333
1.334
1.335
1.336
1.337
1.338
refractive index [RIU]
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Surface Chemistry
1. Cleaning and oxidation
2. Silanization: surfaces are dip-coated in APTES solution
3. Coupling of Biotin-LC-NHS
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Surface Sensing
avidin concentration
buffer pH7,4
biotin
Biotin/Avidin
resonator
buffer pH7,4
avidin
biotin
resonator
resonator
0.0045
0.004
0.0035
output [au]
0.003
0.0025
0.002
0.0015
0.001
∆P
0.0005
∆λ
0
1551.80
1551.90
1552.00
1552.10
1552.20
1552.30
1552.40
1552.50
1552.60
wavelength [nm]
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
resonance wavelength shift [nm]
Surface Sensing
Biotin/Avidin
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
5
10
15
20
25
avidin concentration [μg/ml]
•
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
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
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
R

Gold
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Theory
Bulky surface plasmon biosensor
Fully integrated lab-on-chip solution in
Silicon-on-Insulator
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Theory : Concept
5 μm
Surface Plasmon Interferometer
Sample medium
SiO2
1 μm .22μm
Si
4 μm
Au
Si
10 μm
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation : Intensity Measurement
Constructive Interference
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation : Intensity Measurement
Destructive Interference
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation : Intensity Measurement
Optimalisation of Design
Si thickness = 160 nm
Length = 10 m
Si thickness = 100 nm
Length = 6.055 m
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation : Intensity Measurement
Sensitivity Analysis
Sensitivity
-5
10
-6
10
10
-7
Change in the refractive
index that causes a drop
or rise in the
transmission of 0.01 dB
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation : Intensity Measurement
Sensitivity Analysis
Comparison
-5
10
-6
10
10
-7
Prism 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
BUT
Dimensions are two
orders of magnitude
smaller
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation: Wavelength Interrogation
Shift of the spectral minimum
Shift of the
spectral
minimum as a
function of the
bulk refractive
index
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Simulation: Wavelength Interrogation
Sensitivity to adlayers
For n=1.34 adlayer
6 pm/nm
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Measurement Setup
Side View
Top View
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Measurement Results
Compared to Theory
Transmission as a function of wavelength
Measurement
-161530
-18
1550
1560
1570
1580
1590
1600
1610
5 μm Au
• Quantitative
Need for a better
fabrication process
O2 toplayer
Transmission as a function of wavelength
Simulation
-22
-11
1480
1500
1520
1540
1560
-12
-24
-13
Transmission [dB]
Transmission (dB)
-20
1540
• Qualitative
Agreement between
experiment and theory
-26
-28
-14
-15
-16
-30
-17
-32
-18
Wavelength (nm)
Wavelength [nm]
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
1580
1600
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 sensor
Introduction :
Electrical resistance gage
Fiber Bragg Gratings (FBG)

Most popular strain gage

More expensive

Moderate long term reliability

Good long term reliability

No absolute measurements

‘Absolute measurements’

2-D strain sensing

Only 1-D strain sensing

Small resistance changes

EMI insensitive
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensor
Try to combine some advantages of electrical resistance
gages and FBGs

Strain e = L/L

typical R = 0.2 W ~ e = 1000e

typical  = 1000 pm ~ e = 1000e
electrical : resistance,
SOI ring or racetrack resonator

Resonance wavelength depends on strain
L neff



L
neff


Wavelength measurement = robust

Wavelength demultiplexing
(large FSR needed)
optical : wavelength
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensor
Structure of SOI strain sensor
Layer stack
Circuit layout
SiO2
2µm
Si
SiO2
polyimide
10µm
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
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
Experimental results : wavelength shift vs beam deflection,
good agreement with theoretical predictions
2
wavelength shift (nm)
0.9
0.8
1
0.7
3
1
0.6
0.5
2
4
0.4
3
0.3
0.2
4
0.1
0
0
1
2
3
4
5
6
7
Uni-axial strain
beam deflection (mm)
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Strain sensor
Experimental results :

Circular resonator : =0.85exx (pm/e)

Racetrack resonator : =0.99exx , =0.63eyy

Sensitivity and cross-sensitivity can be improved by
optimized design
 =1.3exx , =0.3eyy (pm/e)
© 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
Conclusions
Theory & Proof of Bulk
Surface
Design
Principle Sensing Chem
10-5 RIU
Adlayer
sensing
Optimize Multi
para
P: 10ng/ml
: 50ng/ml
 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
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Acknowledgements
GOA Biosensor
Project
IAP Photon
IWT Vlaanderen
FWO Vlaanderen
FOS&S
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Alternative (extended)
Conclusions
Photonics Research Group
http://photonics.intec.ugent.be
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
Conclusions
Silicon-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
Conclusions
Silicon-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

© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
APPENDIX
Photonics Research Group
http://photonics.intec.ugent.be
H2O
10
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
SiO2
1
Si
4
Si
0.220
Sample medium
5
Simulation: Wavelength Interrogation
Novel Concept
Coupling to SP modes
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Novel Concept
Mode dispersion gold-clad waveguide
Waveguide mode cutoff
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
SPR History
Integrated Surface Plasmon Resonance Device
Schematical
Principle
Device
Drawbacks
Setup
Thin metallic layers
H22O
O
H
Sample
medium
•Quite
large
(mm
scale)
Sample medium
• Not suited for high level
Symmetric cladding
Supermodesintegration
•Design limited to low-index
contrast due to phase matching
considerations
Asymmetric cladding
Interface Modes
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Intensity Measurement/ Simulation
Parameters
•
Length of the sensing region
•
Thickness of the Si waveguide
•
Thickness of the Au layer
Limitations
• Position of the minima :
Dip in the transmission curve @ 1.550 micron should be
near n = 1.33
• Maximum Visibility :
Loss along both ‘arms’ has to be equal
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
Sensitivity Analysis
Sensitivity to adlayers
For n=1.34 adlayer
6 pm/nm
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be
© intec 2007 - Photonics Research Group - http://photonics.intec.ugent.be