microactuators and sensors for microfluidics and lab on a
TRANSCRIPT
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Microactuators and Sensors for Microfluidics and Lab on a Chip applications
Massood Tabib-AzarCase Western Reserve University
Cleveland, Ohio 44106
Partially supported by grants from NIST, WPAFB, and SRC
Slides 20-56 are contributed by Michael Ramsey (Oak Ridge)
General reference: Nanoelectromechanics in Engineering and Biology, by M. P. Hughes
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Functional Elements
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FIB Milled Nanochannels in SiO2Membranes
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Addressable Ion Channel Arrays
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Electric Double Layer
Charged particle
--
----
----
Positively charge layer withWell-defined thickness (Stern layer)
Ionic diffuse layer
(Gouy-Chapman Model)
--- +
Inner Helmholtz layer
- charges
Outer Helmholtz layer
IHP OHP
ExponentialLinear
Φ
Distance
(potential)
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Electrokinetic Forces
Caused by interaction between dipole and electric field
AC/DCElectro-orientation
Caused by dipole lag in traveling E-field
ACTraveling wave DEP
Caused by dipole lag in rotating E-field (Torque=Dd X E)
ACElectrorotation
Caused by interaction between double layer charges and tangential E-field
AC/DCElectro-osmosis
Caused by induced dipole in field gradient (Qd. E)
AC/DCDielectrophoresis
(DEP)
Caused by charge in E-field (QE)DCElectrophoresis
Origin (Force)AC or DCForce
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Electrokinetic Transport
ep: electrophoresis
eo: electroosmosis
η: viscosity
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• Negative dielectrophoresis
• Positive dielectrophoresis
• Brownian motion, dielectrophoretic, and electro-osmotic balance
Electro-osmotic force
Electrodes
ElectrodesPositive dielectrophoretic force
Negative dielectrophoretic forcearises when εreal becomes negative
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Existing Tools• Scanning local probe microscopy offers
nearly atomic resolution:– Scanning tunneling microscopy (STM) ~1Å
– Atomic force microscopy (AFM) ~ 10Å
– AFM-related techniques >10Å
• Magnetic force microscopy (MFM)
• Scanning capacitance microscopy (SCM)
– Near-field scanning optical microscopy (NSOM) ~ 50Å
Frequency Gap
SLPM NSOMDC-1GHz 100 THzSurfacelocalized
Surface localized
Signal penetrationCommercial tools do not exist
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Atomic Force Microscopy (AFM) of Cells
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Approach
Frequency Gap
SLPM NSOMDC-1GHz 100 THzSurfacelocalized
Surface localized
Signal penetration140 GHz
Scanning Evanescent Microwave Probe (SEMP) Non-ionizing
Sub-surface sensitiveNearly atomic resolution
Conductivity and permittivity informationCompatible with AFM and NSOM
HyperspectralComponents are commercially available
Non-contact and does not require conducting sample
Challenging
Atomic Force Microscopy(AFM)
Near-Field ScanningOptical Microscope
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Traveling wave imaging
Constructed ImageIncident E&M
Lens or image forming device
Detector Array
E&M: electromagnetic wave
Object
Resolution ~ Wavelength of incident E&M (λ)Advantage: One shot imaging
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d
Decaying, or Evanescent Wave Imaging
Sample
Waveguide
d << λ
E&M (λ,f)
Decaying Fields Scan in z-direction
Monitor Amplitude and Phase as a function of “z”
Resolution ~ d<< λ Disadvantage: Point by point imaging
λ: wavelength of E&Md: diameter of the waveguide opening
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Region
Scanning Evanescent Microwave Microscopy
• Evanescent fields are produced at the tip of a resonator
• Interaction between evanescent microwave field and sample
• Monitoring the resonance change of the probe resonator
λ /2
Active Probe
|E|
b
Sam
ple
tipMicrostripline waveguide
S11
AirRef
lect
ion
Coe
ffic
ien
t
Frequency (GHz)
Sample sample
Probe
Resonator structure
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S11 Spectra of Human Molar Enamel
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.1 1 10 100 1000 10000 100000Sheet resistance in ohm/sq.
EM
P ou
tput
in v
olts
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BASE
X positioner
Y positioner
Support Arm
SignalAmplifier
Crystal Detector
Circulator
Feed line
Resonator & Probe
Sample Holder
Z positioner
Fig. Schematic of the experimental setup
WhiteLight
Source LightChopper
Lens
Light
Lock-inAmplifier #1
Support Arm
Motor#2
Motor#1
Step MotorControllers
DataAcquisition
&Computer
Photo-detector
Lock-inAmplifier #2
RF SignalGenerator
FunctionGenerator
Infrared LD
Optical Fiber
Experimental Arrangement
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Sample: YBa2Cu3O7-δ thin film on 2” sapphire wafer
Frequency: 7.5 GHz
Temperature: 300 K
500 µm probe, in non-contact mode
Appl. Phys. Lett. 72, 861 (1998)
SEMP IMAGES: Topography & Sheet Resistance
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SEMP Image of Mold Release De-Bond with Two Bubbles in
Epoxy
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SEMP Integrated with AFM Setup
laser diode
PZT scanner
sample
cantilever
detector
mirror
µWaveMeas.
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What is Impedance Spectroscopy?• Impedance spectroscopy
(performed with an AFM) is used to image embedded structures in a material
• These embedded nanoparticles cannot be detected with traditional AFM topographical probing.
• A.C. signal applied between tip and sample results in a displacement current that is used to detect embedded structures.
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AFM-Compatible SEMP tip
• No cutoff frequency with coaxial geometry
• Shielded to limit Coulomb interactions and increase electric-field resolution
• Orthogonal, simultaneous probing of topography/field
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SEMP-AFM Combined Imaging
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Silicon substrate
Insulator
Metal (shield)
Metal (waveguide)
Heavily-doped Si
Coaxially Shielded Tip
Probe Cross Section
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Mechanical Design
13.58.6066.542.515095.5Resonant frequency (KHz)
0.590.166.421.7321.75.84Spring constant (N/m)
t = 5 μmt = 3 μmt = 5 μmt = 3 μm t = 5 μmt = 3 μm
L = 1000 μm L = 450 μm L = 300 μm W = 50 μm
ρπ 1252.3
20
E
L
tf =
3
3 26
==LtEW
L
EIK
AlLTOsi
AlAlLTOLTOsisi
ttt
tEtEtEE
++++
=AlLTOsi
AlAlLTOLTOsisi
ttt
ttt
++++
=ρρρ
ρ
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Scanning Near-field Microwave Microscope Probe
Thermaloxide
SiSi Al P+ diffusion
LTO
(a) (b)
Three dimensional view of an SNMM probe Cross-section view along a waveguide arm
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Thermal oxidationLithographyOxide etching
Plasma etching tip
Oxidation sharpening Lithography Oxide etchingP+ ion implantation
Microfabrication: Tip Formation
(a)
(b)
Si
Thermal oxide
P+ diffusion
Al
Si
LTO
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Si Tip after Plasma Etching
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Si Tips before and after Oxidation Sharpening
(a) Before oxidation sharpening
(b) After oxidation sharpening
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Metal depositionLithographyMetal etching
LTO deposition
A'A
(c)
(d)
Si
Thermal oxide
P+ diffusion
Al
Si
LTO
Microfabrication: Waveguide
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Top viewafter step (e)
Metal depositionLithographyMetal etchingLithographyLTO etching
(e)
A'A
(f)
Si
Thermal oxide
P+ diffusion
Al
Si
LTO
Microfabrication: Shield Layer
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Microwave Design
S21
S11
S11
S21
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Tip
Waveguide
Aluminum shield
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Released SNMM Probes
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Microfabrication: Tip Exposure
PR coatingTip exposureMetal etchingLTO etching
LithographySi RIE
(g)
(h)
Si
Thermal oxide
P+ diffusion
Al
Si
LTO
Y. Wang and M. Tabib-Azar, “Microfabricated Near-field Scanning Microwave Probes,” Electron Devices Meeting, IEDM '02. Digest. International, IEEE, pp. 905-908 (2002).
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Co-axially Shielded Tip (2)
Y. Wang and M. Tabib-Azar, “Microfabricated Near-field Scanning Microwave Probes,” Transducers '03
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Coaxially shielded tip
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Carbon Nanotubes& Nanospheres
Self-Assembled on Electrodes
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Carbon Nanotubes
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Nano-Device CharacterizationCarbonNanotubes
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AFM Head – Microwave Tip Assembly
SMA
Co-axial cable
SNMM probe
2 mm
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Mechanical Oscillation Spectrum
Measured resonant frequency is 170.92 KHz, and quality factor is 317. The design value is 150 KHz with L = 300μm, W = 50μm, and t = 5μm.
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0.5
0.6
0.7
0.8
0.9
1
1.1
0.96 0.98 1 1.02 1.04
Normalized Frequency
MicrowaveAFM
AFM-Compatible SEMP tip
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ExplorerTM AFM System
8 cm
Scanner head
Sample holder
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-1.00E-07
0.00E+00
1.00E-07
2.00E-07
3.00E-07
4.00E-07
5.00E-07
6.00E-07
7.00E-07
-0.5 -0.25 0 0.25 0.5 0.75 1
Voltage (V)
Cur
rent
(A
)
DC Conductivity between A Waveguide and A Shield
HP 4155B
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-1.00E-01
-8.00E-02
-6.00E-02
-4.00E-02
-2.00E-02
0.00E+00
2.00E-02
4.00E-02
6.00E-02
8.00E-02
1.00E-01
-3 -2 -1 0 1 2 3
Voltage (V)
Cur
rent
(A
)
R = 37 Ohm
DC Conductivity between A Waveguide and An Implanted Tip Region
HP 4155B
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-2 .50E-02
-2.00E-02
-1.50E-02
-1.00E-02
-5.00E-03
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
-1 -0 .5 0 0.5 1Vo ltage (V)
Cu
rre
nt
(A)
DC Conductivity between the Tip and An Au Sample
R = 50 Ohm
HP 4155B
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Microwave Measurement Setup
NetworkAnalyzerHP 8720C
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S11 Measurements in Air and over An Au Sample
-20
-10
0
10
20
30
40
50
0 5 10 15 20
Frequency (GHz)
S11
Mag
nitu
de (
dB)
|S11| + 50dB in air
|S11| + 25dB approachingan Au sample
|S11| difference
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Schematic of the Image Scanning Circuit
1 2
3
Circulator
Lock-in Amplifier
RF Source
BPFPre-amplifier
Crystal detector
SNMM probe
Sample holder
DAQ
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Contact AFM Microwave Image
Simultaneous AFM and Scanning Near-field Microwave Images (2.8 GHz)
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Use microwave AFM to see inside the cell
Microwave AFM amplitude Microwave AFM phase
Cell nuclei
Membrane contrasted
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Significance of Scanning Near-field Microwave Microscope 1.8 GHz)
cells cell nuclei
membranecontrasted
(a) (b) (c)AFM topography SNMM amplitude SNMM phase
Commonly used
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Microwave MicroscopyOf Molecules in Micro-Fluidics
Hydro-electro-dynamic pumps
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Micro-Fluidic: Experimental Arrangement
RF Source
Fluid Reservoir
Fluid
Pump
Modulation Source
PLA
+2
1
3
Excitation resonator sensing resonator
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Detection of Cavitation bubbles using SEMP<0.1 µm Bubbles