Three-Dimensional Dielectrophoresis Device with Integrated Actuating and Impedance Sensing Michael Beltran Robert Lam Bryan Lochman 12/14/07.

Three-Dimensional Dielectrophoresis Device with

Integrated Actuating and Impedance Sensing

Michael BeltranRobert Lam

Bryan Lochman

12/14/07


Bryan Lochman

12/14/07 Three-Dimensional Dielectrophoresis Device with Integrated Actuating and Impedance Sensing

Lab on a chip

• Lab on a chip technology will reduce the size of complex experimental setups.

• Eliminate large, bulky equipment.

• Move lab experiments to a non-lab environment.

• Especially useful in biological and medical fields for local use.


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Overview

• Device Overview• Theory

– Dielectrophoresis (DEP)– DEP cage actuation– Impedance sensing

• Device Fabrication• Previous Devices• Results

– Parasitic Cages– Particle Concentration

• Recommendations– Micro-scale device


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Device Overview

• 1cm electrode strips

• Induced DEP Cages

• Top conductive sealing layer

• Integrated actuation and sensing

Medoro, G.; Manaresi, N.; Leonardi, A.; Altomare, L.; Tartagni, M.; Guerrieri, R. A Lab-on-a-Chip for Cell Detection and Manipulation. IEEE Sensors Journal, 2003, 3, 317-325


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TheoryDielectrophoresis (DEP)

www-dsv.cea.fr/.../Image/Pascal/biopuces_64.jpg


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• r – radius• E – nonuniform electric field• - permittivity of medium• Re[K] – Clasius-Mossotti Factor where

23 ]Re[2 EKrF m

m

**

**

2 mp

mpK

TheoryDEP – Governing Equation


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• σ = conductivity of electric field

• ω = angular frequency of electric field

• Varying these two variables will alter the permittivity of the particle/medium

j*

TheoryDEP - Permittivity


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• At low frequences:

• At high frequencies:

• Polarization Factor (K) can be switched between positive or negative values

mp

mpK2

mp

mpK

2

TheoryDEP - Clausius-Mossotti


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• Buoyancy Force:

• DEP and Buoyancy:

grF mpB 3

3

4

m

mp gEK

3

2]Re[ 2

TheoryDEP – Vertical Forces

Iliescu, C.; Yu, L.; Xu, G.; Tay, F. A Dielectrophoretic Chip With a 3-D Electric Field Gradient, Journal of Microelectromechanical Systems, 2006, 15, 1506-1513


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• FDEP = volume (~r3)

• Fviscous = surface (~r2)

• Smaller particles will move slower

rF

F

visc

DEP

TheoryDEP – Ratio between DEP, Viscous forces


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• Progressively alternating electrode signals move particles towards target electrode

• Provides better sensing of particles

TheoryDEP – Cage Actuation



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• The DEP Cages are able to move toward a target electrode by moving the counter phase signal to the next electrode closer to the target

TheoryDEP – Cage Actuation



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• To measure the concentration of particles impedance sensing is used• All electrodes are switched to ground except the sensing electrode• The sensing electrode is connected to a transimpedance amplifier

TheoryImpedance Sensing



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• Transfer function of the transimpedance amplifier:

• RM and CM are the resistance and capacitance between the electrode and lid

• RF and CF are the feedback resistance and capacitance

• There are two sensing frequency ranges, low and high, if the same signal is used for both DEP cage formation and sensing

FF

MM

M

F

i

o

CjwR

CjwR

R

Rjw

V

V

1

1)(

TheoryImpedance Sensing – Transfer Function


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• Low Frequency– When w<<1/(RMCM) and w<<1/(RFCF) the sensing equation is:

– The Clausius Mossotti factor at low frequencies,

shows that a particle will only be trapped in the DEP cage if its conductivity is lower than the mediums giving rise to :

– These two equations show the output voltage will decrease with particles at low frequencies

M

F

i

o

R

R

V

V

mp

mpK2

TheoryImpedance Sensing at low frequencies

wopM

wpM RR


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• High Frequency– When w>>1/(RMCM) and w>>1/(RFCF) the sensing equation is:

– The Clausius Mossotti factor at high frequencies,

shows that a particle will only be trapped in the DEP cage if its permittivity is lower than the mediums giving rise to :

– These two equations show the output voltage will decrease with particles at high frequencies

F

M

i

o

C

C

V

V

mp

mpK

2

wopM

wpM CC

TheoryImpedance Sensing at high frequencies


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Original Fabrication

• No MEMS fabrication methods used

• Printed Circuit Board (PCB) techniques used to attach electrodes– Silk screened the

electrode pattern on to a gold clad board

– etched away the uncovered portion

– remove the screened resist



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Similar DEP Devices• CMOS chip for individual cell manipulation

• 102,400 actuation electrodes (20μm x 20μm)• Capability of manipulating 10,000 cells in parallel• Lack of integrated sensing technique

Manaresi, N.; Romani, A.; Medoro, G.; Altomare, L.; Leonardi, A.; Tartagni, M.; Guerrieri, R. A CMOS Chip for Individual Cell Manipulation and Detection, IEEE Journal of Solid-State Circuits, 2003, 38, 12:2297-2305


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Similar DEP Devices

• Dielectrophoretic Chip With a 3-D Electric Field Gradient

• Asymmetric 3D electric gradient achieved with specially configured electrodes

• Thick electrodes integrated into vertical wall structures, thin planar electrodes in bottom substrate

• Enhanced vertical DEP force (lower voltages and temperatures)

Iliescu, C.; Yu, L.; Xu, G.; Tay, F. A Dielectrophoretic Chip With a 3-D Electric Field Gradient, Journal of Microelectromechanical Systems, 2006, 15, 1506-1513


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Similar DEP Devices

• MEMS electrostatic particle transportation system

• Electrostatic device capable of transporting particles in air

• Surface modifications performed to reduce adhesive forces

Desai, A.; Lee, S-W.; Tai, Y. A MEMS Electrostatic Particle Transportation System. Sensors and Actuators, 1999, 73, 37-44


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• Parasitic Cages form between the two in-phase electrodes, electrodes 3 and 4 in Figure (a)

• After actuating the DEP cage, a new parasitic cage will form capturing the slow moving particles

(a) (b)

Actuate the DEP Cage

New parasitic DEP Cage

ResultsParasitic Cages



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Parasitic Cages

ResultsParasitic Cages



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Add intermediate step:

• Creates a smaller chance slow moving particles will be trapped in the attraction basin of the parasitic cage

(a) (b) (c)

ResultsParasitic Cages – Minimize effects



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Reduce space between electrodes:

• Space between electrodes is nearly too small for particles to fit

• Only possible using MEMS fabrication techniques due to small spacing

ResultsParasitic Cages – Minimize effects



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ResultsModeling Assumptions

• Cage distribution far too complicated to be modeled at the level of individual particles

Assumptions• Particle cloud within the DEP cage can be

modeled as homogenous• Permittivity and Conductivity depend solely on

the ratio between the volume of microbeads and suspending medium in the cylinder (distilled water).


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ResultsSignal Processing

•Fixed pattern noise (FPN) removed by subtracting initial non-cage reading (a) from cage reading, and then addition of average initial reading.



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ResultsOptical observation

• Polystyrene microbeads, 3.46 µm diameter in H2O.

• 10 Vpp, 100 kHz • 4 Concentration cycles• Raw data on left• Grayscale representation

of data on right



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• Electric field simulation in FEMLAB in a 2-D plane

• Simulation performed for initial concentration and 4 successive concentration cycles

• Resistance translated to voltage output with known current

ResultsPolystyrene Microbeads



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• Experiment repeated with S. cerevisiae yeast cells in 280-mM mannitol.

• Mannitol medium used to prevent overheating due to excessive conductivity

• S. cerevisiae displays pDEP behavior above 200 kHz, electrolysis occurs at less than 30 kHz

• Experiments performed at 100 kHz

ResultsS. cerevisia



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Recommendations

• Base layer of SiO2 with photoresist on Silicon

Micro-fabrication


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Recommendations

• Mask pattern, inverted from intended electrode pattern

Micro-fabrication


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Recommendations

• Exposure to light – removal of photoresist.

Micro-fabrication


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Recommendations

• Dry plasma etching – removal of Silicon Oxide

Micro-fabrication


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Recommendations

• Removal of photoresist with acetone

Micro-fabrication


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Recommendations

• Ion implantation of electrode channels

Micro-fabrication


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Recommendations

• Removal of silicon oxide via plasma etching with CF4

Micro-fabrication


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Recommendations

• Lap polish of wafer to 50μm thickness

Micro-fabrication


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Recommendations

• Growth of SiO2 layers, removal from underside.

Micro-fabrication


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Recommendations

• Spin deposition of photoresist and mask placement

Micro-fabrication


Bryan Lochman


Recommendations

• Exposure to light - removal of photoresist

Micro-fabrication


Bryan Lochman


Recommendations

• Dry plasma etching – removal of Silicon Oxide

Micro-fabrication


Bryan Lochman


Recommendations

• Removal of photoresist with acetone

Micro-fabrication


Bryan Lochman


Recommendations

• <110> wafer KOH through-etching of silicon wafer

Micro-fabrication


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Recommendations

• Removal of silicon oxide via plasma etching with CF4

Micro-fabrication


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Recommendations

• Combination of base electrode layer and reservoir layer

Micro-fabrication


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Recommendations

• Mated with wafer bonding over long electrodes, leaving wire-connection ports exposed

Micro-fabrication


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Recommendations

• Mass production on a silicon wafer• Glass cover with etched microchannel pattern and

common reservoir

Micro-fabrication

Three-Dimensional Dielectrophoresis Device with Integrated Actuating and Impedance Sensing Michael Beltran Robert Lam Bryan Lochman 12/14/07.

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