Thermo-Pneumatic and Piezoelectric Actuation in MEMS-based Micropumps for Biomedical Applications

1
Thermo-Pneumatic and Piezoelectric Actuation in
MEMS-based Micropumps for Biomedical Applications

• ME381 Final Project
• Kenneth DAquila 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, 847-863
Zhang C Xing D Li Y. Biotechnology Advances
2007, 25, 483514
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Thermo-Pneumatic Micropumps

• Basic Mechanism
• Resistive heating
• Air expansion
• Membrane deflection

Typical Voltage 1-20 V Typical Pump Freq 1-2
Hz
e dV/ V0 compression ratio
Inlet Valve
Outlet Valve
Dead Volume (V0)
Pumping Chamber
Stroke Volume (dV)
Actuation Chamber
Flexible Membrane
Trapped Fluid
Resistive Heater
5
Analytical Models

• Improving Efficiency by Modeling
• Resistive heating
• ?H Cp?T
• PwrU2/R
• ?H?(Pwr)dt
• Air expansion
• Ideal Gas
• Law
• Membrane deflection
• Spherical
• Geometry
• Plate
• Theory

T temperature d duty ratio t pump period R
resistance Cp heat capacity U voltage ?H
enthalpy P Pressure V air volume L chamber
radius h membrane deflection m
membrane thickness v poissons ratio
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Response to Input Variables

• Optimizing Electrical Energy Input (Qualitatively)

More Flexible
Jeong O Yang S. Sensors and Actuators 83. 2000
249255
Nozzle/Diffusers
Valve-Less
Flow
Yoo, J Choi Y Kanga, C Kim Y. Sensors and
Actuators A 139 2007 216220.
Jeong, O Park, S Yang S Pak, J. Sensors and
Actuators A 123124. 2005 453458.
7
Choosing Pump Type

• Selecting Appropriate Flow Rate (Qualitatively)

PERISTALTIC-TYPE 21.6 µL/min
BUBBLE-TYPE 0.023 µL/min
Jeong, O Park, S Yang S Pak, J. Sensors and
Actuators A 123124. 2005 453458.
Jun D Sim W Yang S. Sensors and Actuators A 139
2007 210212
8
Microfabrication

• Cost-Effective Fabrication/Materials

Silicon-Based
Jeong O Yang S. Sensors and Actuators 83. 2000
249255
PDMS-Based
Jeong, O Park, S Yang S Pak, J. Sensors and
Actuators A 123124. 2005 453458.
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

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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
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Tensor Mathematics
http//www.physikinstrumente.com
12
Tensor Mathematics (Contd)
http//www.physikinstrumente.com
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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, 1997.
TRANSDUCERS '97 Chicago., 1997 International
Conference on Volume 1,  16-19 June 1997
Page(s)353 - 356 vol.1
Diaphragm pump using cantilever valves. Results
in fatigue and variable flow rate over time.
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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 3 2007
377390
Valveless diaphragm pump. No moving parts
resulting in higher reliability and more
consistent flow rate over time.
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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

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Governing Equations

• Pressure loss coefficient given by

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Governing Equations (Contd)
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
377390
20
Governing Equations (Contd)

• The diffuser efficiency is given by
• If the pressure loss coefficient in the nozzle is
  greater, then ?gt1 and there is net flow from the
  inlet

21
Governing Equations (Contd)

• 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

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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
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 15 1999
573-576
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
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 10 100 µL/min Silicon
Koch 1997 Cantilever Valve, Piezoelectric Diaphragm 100 600 V 10 120 µL/min Silicon
Wan 2001 Nozzle/Diffuser, Piezoelectric Diaphragm 3 V 900 µL/min Silicon
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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