Transcript Thermo-Pneumatic and Piezoelectric Actuation in MEMS

THERMO-PNEUMATIC AND
PIEZOELECTRIC ACTUATION IN
MEMS-BASED MICROPUMPS
FOR BIOMEDICAL APPLICATIONS
Northwestern University 12/10/07
Outline

Motivation

Thermo-Pneumatic Actuation
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Piezoelectric Actuation

Comparison

Summary
Motivation

Drug Delivery
Systems (DDS)
 Implantable
 Transdermal
Staples M; Daniel K; Cima M; Langer R. Pharmaceutical Research 2006, 23, 847-863

Micro Total
Analysis System
(µ-TAS)
“lab on a chip”
Zhang C; Xing D; Li Y. Biotechnology Advances 2007, 25, 483–514
Thermo-Pneumatic Micropumps

Basic Mechanism
1.
2.
3.
Resistive heating
Air expansion
Membrane deflection
Inlet Valve
Typical Voltage: 1-20 V
Typical Pump Freq: 1-2 Hz
ε = δV/ V0 = compression ratio
Outlet Valve
“Dead Volume” (V0)
Stroke Volume (δV)
Pumping Chamber
Actuation Chamber
Flexible Membrane
Resistive Heater
Trapped Fluid
Analytical Models

Improving Efficiency by Modeling
1.
Resistive heating



2.
Air expansion

3.
ΔH = CpΔT
Pwr=U2/R
ΔH=∫(Pwr)dt
Ideal Gas
Law
 U 2 d
T  
 C R
 p
 T  T1  P1V1

P2  
 V  V1  T1
Membrane deflection


Spherical
Geometry
Plate
Theory




  3   2
V   h    L h
6
2
T = temperature
d = duty ratio
τ = pump period
R = resistance
Cp = heat capacity
U = voltage
ΔH = enthalpy
P = Pressure
V = air volume
L = chamber radius
h = membrane
deflection
m= membrane
thickness
v =poisson’s ratio
P2 L4
16
h
7  h 3

(
)

( )
4
2
Em
3(1  ) m 3(1  ) m
Response to Input Variables

Optimizing Electrical Energy Input (Qualitatively)
Jeong O; Yang S. Sensors and Actuators 83. 2000 249–255
Nozzle/Diffusers
Flow
Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123–124. 2005 453–458
.
Yoo, J; Choi Y; Kanga, C; Kim Y. Sensors and Actuators A 139 2007 216–220.
Choosing Pump Type

Selecting Appropriate Flow Rate (Qualitatively)
PERISTALTIC-TYPE: 21.6 µL/min
Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123–124. 2005 453–458
BUBBLE-TYPE: 0.023 µL/min
.
Jun D; Sim W; Yang S. Sensors and Actuators A 139 2007 210–212
Microfabrication

Cost-Effective Fabrication/Materials
Jeong O; Yang S. Sensors and Actuators 83. 2000 249–255
Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123–124. 2005 453–458
.
Brief History on Piezoelectricity

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“Piezo” is Greek word for pressure
“Piezo effect” discovered in 1880 by Curie bros.
“Inverse piezoelectric effect” proved using
thermodynamics by Lippmann
Difficult mathematics resulted in very few advancements
until World War I, when it was used in sonar to detect
submarines
Much research from WWII and on from USA, Japan
and USSR

Led to lead zirconate titanate (PZT), most used piezoelectric
ceramic today
Piezoelectric Fundamentals

PZT unit cell above TCurie (left) and below TCurie (right)
 Unit
cell on the right deformed tetragonally allowing for
piezoelectric effect
http://www.physikinstrumente.com
Tensor Mathematics
http://www.physikinstrumente.com
Tensor Mathematics (Cont’d)
http://www.physikinstrumente.com
Piezoelectric Actuation Benefits

Unlimited theoretical resolution
 Limited
by noise from electric field, mechanical design,
mounting flaws, etc.
 Sub-nano resolutions still achievable

No moving parts
 No
frictional wear from sliding or rotating parts
Actuation Mechanism (Cantilever Valve)
Koch, M., Harris, N., Evans, A.G.R., White, N.M., Brunnschweiler, A., “A novel micromachined pump based on thick-film piezoelectric
actuation,” Solid State Sensors and Actuators, 1997. TRANSDUCERS '97 Chicago., 1997 International Conference on Volume 1, 1619 June 1997 Page(s):353 - 356 vol.1
Diaphragm pump using cantilever valves. Results in fatigue and variable flow
rate over time.
Microfabrication (Cantilever Valve)
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Made from three silicon wafers (Layers #1 and 2 are identical)
Etched anisotropically using KOH
Cantilevers made by B+ anisotropic etch stop
Layer #3 made with time-controlled KOH anisotropic etch with LPCVD
silicon nitride mask
Wafers are anodically bonded together
Gold cermet printed on, dried and heated
PZT layer printed on, 3 MV/m electric field applied for polarization
Final gold cermet printed on PZT, dried and heated
Actuation Mechanism (Valveless)
Cui, Q. F., Liu, C. L. and Zha, X. F., “Study on a piezoelectric micropump for the
controlled drug delivery system,” Microfluid Nanofluid 3 2007 377–390
Valveless diaphragm pump. No moving parts resulting in higher reliability
and more consistent flow rate over time.
Microfabrication (Valveless)
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Deep Reactive Ion Etching (DRIE) or precision turning
for cylindrical volume
Pump membrane usually from outside supplier
Piezoelectric transducers from supplier but can be
cut to shape with excimer laser machining
Transducers bonded to membrane with conductive
epoxy glue
Diffuser/nozzle are laser micromachined
Inlet/outlet are etched anisotropically with KOH
Governing Equations

Pressure loss coefficient given by:
Governing Equations (Cont’d)
Cui, Q. F., Liu, C. L. and Zha, X. F., “Study on a piezoelectric micropump for the
controlled drug delivery system,” Microfluid Nanofluid 3 2007 377–390
Governing Equations (Cont’d)

The diffuser efficiency is given by:
 If
the pressure loss coefficient in the nozzle is greater,
then η>1 and there is net flow from the inlet
Governing Equations (Cont’d)
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
The transverse deflection of the pump membrane is
given by:
Difficult to solve due to non-steady state flow and
coupling effects between transducer/membrane,
membrane/fluid
Numerical Solution


Eq. 8 is difficult to solve analytically so a numerical
solution must be found
Use Finite Element Analysis and software ANSYS
Mu, Y. H., Hung, Y.P., and Ngoi, K. A., “Optimisation Design of a
Piezoelectric Micropump,” Int J Adv Manuf Technol 15 1999 573-576
Input Variables

Input factors include the following:
 Membrane
material
 Membrane thickness
 Piezoelectric thickness
 Input voltage

Response is maximum membrane deflection
 Area
under deflection is stroke volume
 Analogous to flow rate
Maximum Deflection vs Input
Mu, Y. H., Hung, Y.P., and Ngoi, K. A., “Optimisation Design of a
Piezoelectric Micropump,” Int J Adv Manuf Technol 15 1999 573-576
Quantitative Comparison
Name
Year
Variant Type
Nozzle/Diffuser,
Corrugated Membrane
Input Electrical
8 V,
40% Duty at 4 Hz
Flow Rate
Materials
Jeong
2000
14 µL/min
Doped Silicon
Jeong
2005
Peristaltic,
Flat Membrane
20 V,
50 % Duty at 2 Hz
21.6 µL/min
PDMS, Cr/Au
Jun
2007
Surface Tension,
Air Bubble
3.5 V
0.023 µL/min,
116 nL in 5 min
PDMS, Ti/Al
Van de Pol
1990
Check Valves,
Flat Membrane
??? V,
0.5 Hz
30 µL/min,
Silicon
Yoo
2006
Nozzle/Diffuser,
Flat Membrane
500 mW,
1% Duty at 2Hz
0.73 µL/min
PDMS, ITO
Yoo
2007
Nozzle/Diffuser,
Flat Membrane
500 mW,
7% Duty at 2Hz
1.05 µL/min
PDMS, ITO,
Parafilm
Cui
2007
Nozzle/Diffuser,
Piezoelectric Diaphragm
60 – 140 V
Koch
1997
Cantilever Valve,
Piezoelectric Diaphragm
100 – 600 V
10 – 120 µL/min
Silicon
Wan
2001
Nozzle/Diffuser,
Piezoelectric Diaphragm
3V
900 µL/min
Silicon
10 – 100 µL/min
Silicon
Qualitative Comparison

Piezoelectric actuation
 No
frictional wear
 Very high resolution
 Lots of work already completed and can predict
performance (ANSYS simulations)

Thermo-Pneumatic
 Large
stroke volume but low frequency
 Simple design and easy fabrication
 Warms fluid
Conclusion
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Choosing one type of actuation over another
depends strictly on application
Thermo-Pneumatic has lower flow rate allowing for
more precise dosage
If reliability is more important and high voltage is
allowed, then piezoelectric actuation is better
Simulations using FEA and ANSYS can help
determine performance and appropriateness for
application