THERMO-PNEUMATIC AND PIEZOELECTRIC ACTUATION IN MEMS-BASED MICROPUMPS FOR BIOMEDICAL APPLICATIONS

Northwestern University 12/10/07

Outline

Motivation

Thermo-Pneumatic Actuation

Piezoelectric Actuation

Comparison

Summary

Motivation Drug Delivery

Systems (DDS) Implantable Transdermal

Micro Total Analysis System (µ-TAS)“lab on a chip”

Zhang C; Xing D; Li Y. Biotechnology Advances 2007, 25, 483–514

Staples M; Daniel K; Cima M; Langer R. Pharmaceutical Research 2006, 23, 847-863

Thermo-Pneumatic Micropumps

Basic Mechanism1. Resistive heating2. Air expansion3. Membrane deflection

Actuation Chamber

Pumping Chamber

Resistive Heater

Inlet Valve Outlet Valve

Flexible Membrane Trapped Fluid

Stroke Volume (δV)

ε = δV/ V0 = compression ratio

Typical Voltage: 1-20 VTypical Pump Freq: 1-2 Hz

“Dead Volume” (V0)

Improving Efficiency by Modeling1. Resistive heating

ΔH = CpΔT Pwr=U2/R ΔH=∫(Pwr)dt

2. Air expansion Ideal Gas

Law

3. Membrane deflection Spherical

Geometry Plate

Theory

Analytical Models

RC

dUT

p

2T = temperatured = duty ratioτ = pump periodR = resistanceCp = heat capacityU = voltageΔH = enthalpyP = PressureV = air volumeL = chamber radiush = membrane deflectionm= membrane thicknessv =poisson’s ratio

1

11

1

12 T

VP

VV

TTP

hLhV 23

26

324

42 )(

)1(3

7)(

)1(3

16

m

h

m

h

Em

LP

Response to Input Variables

Optimizing Electrical Energy Input (Qualitatively)

Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123–124.

2005 453–458.

Jeong O; Yang S. Sensors and Actuators 83. 2000 249–255

Flow

Nozzle/Diffusers

Yoo, J; Choi Y; Kanga, C; Kim Y. Sensors and Actuators A 139 2007 216–220.

Valve-Less

More Flexible

Choosing Pump Type Selecting Appropriate Flow Rate

(Qualitatively)

Jun D; Sim W; Yang S. Sensors and Actuators A 139 2007 210–212

PERISTALTIC-TYPE: 21.6 µL/min

BUBBLE-TYPE: 0.023 µL/min

Jeong, O; Park, S; Yang S; Pak, J. Sensors and Actuators A 123–124.

2005 453–458.

Microfabrication Cost-Effective Fabrication/Materials

Silicon-

Based

PDMS-Based

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 “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)

Diaphragm pump using cantilever valves. Results in fatigue and variable flow rate over time.

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

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

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) 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) 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 Input Electrical Flow Rate Materials

Jeong 2000Nozzle/Diffuser,

Corrugated Membrane8 V,

40% Duty at 4 Hz14 µL/min Doped Silicon

Jeong 2005Peristaltic,

Flat Membrane20 V,

50 % Duty at 2 Hz21.6 µL/min PDMS, Cr/Au

Jun 2007Surface Tension,

Air Bubble3.5 V

0.023 µL/min,116 nL in 5 min

PDMS, Ti/Al

Van de Pol 1990Check Valves,Flat Membrane

??? V,0.5 Hz

30 µL/min, Silicon

Yoo 2006Nozzle/Diffuser,Flat Membrane

500 mW,1% Duty at 2Hz

0.73 µL/min PDMS, ITO

Yoo 2007Nozzle/Diffuser,Flat Membrane

500 mW,7% Duty at 2Hz

1.05 µL/minPDMS, ITO,

Parafilm

Cui 2007Nozzle/Diffuser,

Piezoelectric Diaphragm60 – 140 V

10 – 100 µL/minSilicon

Koch 1997Cantilever Valve,

Piezoelectric Diaphragm100 – 600 V 10 – 120 µL/min Silicon

Wan 2001Nozzle/Diffuser,

Piezoelectric Diaphragm3 V 900 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

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