Slide vật liệu nano và màng mỏng microfkuidic devices

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Microfluidic Devices

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Thuy. N.T. Nguyen

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Contents

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Sensor

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Pump
Valve
Mixer
Channel
Reactor

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Introduction
Components of microfluidic devices

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Structure of Microfluidic device
Design Structure and Fabrication

Application
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Introduction

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• Total analysis system (TAS): was first introduced in
1980s for analysis in chemical as well as biochemica

l.
• Micro total analysis system (µTAS): was first develop
ed in 1990s. µTAS combines microfluidics, mechanic
al actuators, and transducers for complete analysis i
n micro chip.
• Now µTAS was broaden to synthesize and other app
lication. In general, it was known as Microfluidic devi
ce or Lab on a chip devices.

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Microvalve

Depend on the strength of fl
ow, we have stiffness of flap
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• Passive valve (check valve): no actuation for

control, unidirectional flow.

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flow

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• Active valve: require an actuator to provide a
mechanical action. The actuation include
piezoelectric,
electrostatic,
electromagnetic,
pneumatic, thermopneumatic actuation, bistable,
phase-change.
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Microvalve

Electric: static, piezo

Magnetic
Thermal expansion
Ultrasonic

Design

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Flow rate (velocity, dimension) 
size of valve  stiffness of memb
rane relate to material, dimension
 deflection  applied force  c
hoice the actuation.

Actuator

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Controller

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Actuation

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In micro fluidic:

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membrane

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Membrane: silicon or glass ( often 50 µm thickness, 2mm x 2mm), sometimes poly
mer.
Glass/silicon were wet etching by HF/KOH or dry etching. Then they were anodic
bonding.
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Bistable valve
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Micropump

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Micro pumps are used for pumping fluid into
micro channel.
Classified micropumps

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• Mechanical pump (reciprocate or rotary)
• Non mechanical pumps (pressure driven, electro
kinetic flow, diffuser/nozzle…).
• Valve pumping action / Valveless pumping action.

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Valveless pumping action
Principle working

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Diffuser/Nozzle pumps

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Schematic of diffuser pump

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Bernoulli: (static pressure) + (dynamic pressur
e) x (pressure loss coefficient)= const

 Pd 

d

2
Diffusion action

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2

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vd

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So ξ is high, the energy of flow decrease fast
 Pn 

vn

2

2

n

Nozzle action
If ξn is greater ξd, pumping action
will occur.

ΔPd , ΔPn : pressure across the
diffuser, nozzle

ξd, ξn : pressure loss coefficient
Vd, Vn: mean velocities
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J. Micromech. Microeng. 12 (2002) 420-424

PZT: 6x6 mm2, 250 um thickness
(PZT-5H plate from Morgan Matroc Ltd)

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Si membrane: 7mm x 7mm x 70um

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Valve

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0.6 mm

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12mm

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Bonding

PZT glued with Si m

embrane by conduct
ive epoxy

12mm

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Pump connect power

Test with ethanol, pump rate maxim

um 1500 µl/min at 2.5kHz, with bac
kpressure 1000 Pa.
Real measurement difference simul
ation because of:
- hydrodynamic phenomena

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Flow transport by pressure/electrickinetic

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Pressure driven flow: parabolic profile velocity due to visc
osity.

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Electric-osmotic flow have band broadening due
to induced pressure gradient.

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Profile pressure

 RT

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D 

Journal of Colloid and Interface
Science 275 (2004) 670–678

2

2

2F z c

 eo 

 o
4 

R: universal gas constant

T: absolute temperature
F: Faraday constant

z: charge number

Schematic of electric d
ouble layer model

v eo   eo E

c: concentration
ε: dielectric constant
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Characteristics of fluid in micro scale

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Affected Force: capillary force (because of surface tension) inst
ead of inertia in macro flow.

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F cap  2  r  cos 

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Viscosity is significant effect.
High interface to volume ratio: interaction between liquid an surf
ace wall is strong  high fluidic resistance. The smaller channel si
ze, the bigger fluidic resistance.

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With circular cross s
ection

resis



8 L

R

R: channel radius

L: channel length

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η: viscosity

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Mixer and channel
Mixer: to attain a homogeneous of two solutions in as little time as

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possible.

• Passive mixer: only base on diffusion (internal energy).

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• Active mixer: use external energy to induce turbulence.

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Mixer and channel

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How to improve the mixing?
Passive mixer:

Reduce diffusion distance  reduce time according to Einstein-Smoluchowski equation.

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Split channel into an array of smaller channels  to increase the contact areas.

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Form groove across the channel or block for change direction flow  induce turbulence.

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x 

2 Dt

t: diffusion time
D: diffusion coefficient

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E-S equation

x: diffusion distance

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Active mixer:
Applied voltage across the mixing chamber.
Used pump to make bubble.

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Sensor
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In microfluidic, we need to measure
Flow rate (pressure, velocity)  mechanical sensor (Piezoresistive or cap
acitive)
Temperature of flow  temperature sensor
Concentration of solution  optical sensor

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Piezoresistive pressure sensor
pressure

(resistor)

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Sensitive element

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(membrane)
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Elastic element

Polysilicon (0.5um) was d
Wheatstone bridge
eposited, doped.

Voltage

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Micro Total Analysis System (μ_TAS)

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 To design a µ_TAS, we must answer for What is purpose o
f device? Which is the fluid concern?

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 Whether in chemical or in biology, device must be inert or c
ompatible with fluid.

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reactor

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preparation

Mixer /

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Sample

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Common components of µ_TAS

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Injection (discrete/ co
ntinuous)

Filter

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Separation

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Detection

Electrophoresis

Mechanical

Chromatography

Electrical

Mass spectrocopy

optical
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