1. ME381 – Final Project Kenneth D’Aquila and Sean Tseng
Thermo-Pneumatic and Piezoelectric Actuation in MEMS-based Micropumps for Biomedical Applications
ME381 – Final Project
Kenneth D’Aquila and Sean Tseng
Northwestern University 12/10/07

2. Outline Motivation Thermo-Pneumatic Actuation Piezoelectric Actuation
Comparison
Summary

3. Motivation Drug Delivery Systems (DDS)
Implantable
Transdermal
Micro Total Analysis System (µ-TAS)
“lab on a chip”
Staples M; Daniel K; Cima M; Langer R. Pharmaceutical Research 2006, 23,
TO DISECT LATER
Factors limiting the capabilities and convenience of
conventional drug administration may include:
long-term treatment
a narrow therapeutic window
a complex dosing schedule
combination therapy
individualized or emergency-based dosing regimen
labile active ingredient
These limitations are being countered as new approaches
emerge for developing drug and medical device combinations
that can
protect labile active ingredients
precisely control drug release kinetics (timing and amount)
deliver multiple doses
eliminate frequent injection
modulate release using integrated sensor feedback.
Innovative delivery devices
have the capability to completely control drug release: doses
may be administered in pulses or continuously for periods of
months to years, or doses may be stored in a device pending
immediate need for emergency administration.
Numerous fluidic applications in such areas as medicine,
chemistry, environmental testing and thermal transport, have
the potential to be scaled down for reasons of simplified
structure, device cost or portability [1]. Microfluidic system
is one of the most important elements for an application to
microchemical analysis systems, such as a micrototal analysis
system (micro-TAS) or a lab-on-a-chip [2]. Miniaturized systems for biochemical
assays significantly reduce cycle times, reagent costs and labor
intensity. This requires the ability to precisely and efficiently
control the transport of reagents and samples throughout
Drug delivery systems (DDS) have huge commercial potential
Maximize drug therapy efficacy
Controls dosage and specifity
Micro-total analysis systems (µ-TAS), also known as “lab on a chip”
Ability to analyze fluid containing DNA, protein, drug molecules, etc.
Cheap and disposable
Zhang C; Xing D; Li Y. Biotechnology Advances 2007, 25, 483–514

4. Thermo-Pneumatic Micropumps
Basic Mechanism
Resistive heating
Air expansion
Membrane deflection
Typical Voltage: V Typical Pump Freq: 1-2 Hz
ε = δV/ V0 = compression ratio
Inlet Valve
Outlet Valve
“Dead Volume” (V0)
Stroke Volume (δV)
Pumping Chamber
Actuation Chamber
Flexible Membrane
Trapped Fluid
Resistive Heater

5. Analytical Models Improving Efficiency by Modeling Resistive heating
ΔH = CpΔT
Pwr=U2/R
ΔH=∫(Pwr)dt
Air expansion
Ideal Gas
Law
Membrane deflection
Spherical
Geometry
Plate
Theory
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

6. Response to Input Variables
Optimizing Electrical Energy Input (Qualitatively)
More Flexible
Jeong O; Yang S. Sensors and Actuators –255
Nozzle/Diffusers
Valve-Less
Flow
Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123– –458.
Yoo, J; Choi Y; Kanga, C; Kim Y. Sensors and Actuators A –220.

7. Choosing Pump Type Selecting Appropriate Flow Rate (Qualitatively)
PERISTALTIC-TYPE: µL/min
BUBBLE-TYPE: µL/min
Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123– –458.
Jun D; Sim W; Yang S. Sensors and Actuators A –212

8. Microfabrication Cost-Effective Fabrication/Materials Silicon-Based
Jeong O; Yang S. Sensors and Actuators –255
PDMS-Based
TO DISECT LATER
Since current microfluidic systems have been fabricated on a silicon wafer,
some disadvantages exist, such as high cost, complex fabrication
procedures and limited controllable range regarding generated
pressure, flow and pumping rates
Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123– –458.

9. Brief History on Piezoelectricity
“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

10. Piezoelectric Fundamentals
PZT unit cell above TCurie (left) and below TCurie (right)
Unit cell on the right deformed tetragonally allowing for piezoelectric effect

11. Tensor Mathematics

12. Tensor Mathematics (Cont’d)

13. 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

14. 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, TRANSDUCERS '97 Chicago., 1997 International Conference on Volume 1,  June 1997 Page(s): vol.1
Diaphragm pump using cantilever valves. Results in fatigue and variable flow rate over time.

15. Microfabrication (Cantilever Valve)
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

16. 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 –390
Valveless diaphragm pump. No moving parts resulting in higher reliability and more consistent flow rate over time.

17. Microfabrication (Valveless)
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

18. Governing Equations
Pressure loss coefficient given by:

19. 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 –390

20. 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

21. Governing Equations (Cont’d)
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

22. 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

23. 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

24. 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

25. Quantitative Comparison
Name
Year
Variant Type
Input Electrical
Flow Rate
Materials
Jeong
2000
Nozzle/Diffuser, Corrugated Membrane
8 V,
40% Duty at 4 Hz
14 µL/min
Doped Silicon
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,
??? V,
0.5 Hz
30 µL/min,
Silicon
Yoo
2006
Nozzle/Diffuser,
500 mW,
1% Duty at 2Hz
0.73 µL/min
PDMS, ITO
7% Duty at 2Hz
1.05 µL/min
PDMS, ITO, Parafilm
Cui
Nozzle/Diffuser, Piezoelectric Diaphragm
60 – 140 V
10 – 100 µL/min
Koch
1997
Cantilever Valve, Piezoelectric Diaphragm
100 – 600 V
10 – 120 µL/min
Wan
2001
3 V
900 µL/min

26. 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

27. Conclusion
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