This document summarizes a thesis defense presentation given by Proyag Datta at Louisiana State University on April 3, 2001. The presentation covered the design, modeling, fabrication, and testing of a thermomechanical microactuator for controlling combustion in a trapped vortex combustor. Key points included the use of a "recurve" architecture utilizing materials with different coefficients of thermal expansion to achieve actuation, analytical and finite element modeling of the design, and development of fabrication processes for the nickel and nickel-iron materials.

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Louisiana State University
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Thesis Defense – April 3, 2001
Design and Fabrication
of a
Thermomechanical Microactuator
Proyag Datta
Department of Mechanical Engineering
Louisiana State University
April 3, 2001
Thesis Defense

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Louisiana State University
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Thesis Defense – April 3, 2001
Acknowlegdements
Project was funded by AFOSR

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Louisiana State University
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Thesis Defense – April 3, 2001
PRESENTATION OUTLINE
• Introduction
• Design and Modeling
• Fabrication Process Developement
• Conclusion

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Louisiana State University
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Thesis Defense – April 3, 2001
INTRODUCTION
Trapped Vortex(TV) Combustors
• Continuous interest towards improving the
performance of aircraft propulsion systems
• Improved fuel efficiency, better specific energy
release, extended life, extended lean flammability
limit and reduced emission of environmental
pollutants
• A Trapped Vortex combustor is a means to
implement a stabilized combustion process in an
engine

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Louisiana State University
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Thesis Defense – April 3, 2001
INTRODUCTION
Concept of ‘Breathing Wall’
• TV-combustors experience thermo-acoustic
instabilities and ‘hot spots’, which lead to
lowered efficiency in the combustor
• Hot spots can be controlled by injecting cooler air
through dilution holes on the combustor walls
• Distributed air injection would
– control local stoichiometry
– lead to uniform temperature distribution
– minimize wall temperature
– minimize NOx formation

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Louisiana State University
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Thesis Defense – April 3, 2001
INTRODUCTION
Schematic of TV Combustor

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Microvalves
• Properties of an ideal valve
– Low leakage
– Low power consumption
– Low dead volume
– Large differential pressure capability
– Insensitivity to particulate contamination
– Low response time
– Potential for linear operation
– Ability to handle fluids of any density/viscosity/chemistry
• Valves are designed for specific conditions of
operation

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Microvalves
• Valves are classified as ‘passive’ or ‘active’
• Passive Valves
– No external power or control
– Usually one-way or check-valves
• Active Valves
– Powered actuation mechanism
– Driving Mechanisms
• Electrostatic
• Piezoelectric
• Magnetic
• Shape Memory
• Pneumatic

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Overview
• Design Criteria
• Recurve Architecture
• Quasistatic Modeling
• Finite Element Analysis
• Dynamic Modeling

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Design Criteria
• Survival at elevated temperatures
• Actuation distance (~500 µm)
• Force Required
• Compactness of design
• Integrable into combustor walls
• Frequency response (>100Hz)
• Rugged design for operation in harsh
environment

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Design Considerations
• Most methods of active actuation fail due to high
temperature (e.g. piezoelectric, magnetic)
• Passive actuation chosen
• Temperature gradient as energy source to drive
the actuator
• Thermal expansion as method of actuation
• Array structure chosen
– Resistant to particulates
– Tailored to meet force and deflection requirements

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Recurve Architecture
• Direct thermal expansion produces insufficient
deflection
• Deflection of a single bimetallic element is
insufficient for the amount of deflection reqd.
• Bimetallic elements cannot be stacked as tip
rotation nullifies deflection
• Recurve architecture suggested by Ervin and Brei
(1998) chosen

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
‘Recurve’ Schematic

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Recurve Architecture
• Basic building block - composite beam made of
two materials with different coefficients of
thermal expansion
• Produces a parallel displacement of the endpoint
relative to the base
• Can be combined into arrays to obtain greater net
deflections or forces
• By reversing positions of high and low CTE
materials, pull type actuators can be fabricated.

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Behavior of a Recurve Element
3-D solid model of a recurve element shown
in undeformed(Left) and deformed(Right) state

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Recurve Array

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Quasi-static Modeling
• Strain energy based analytical derivation using
Castigliano’s second theorem
• Equations derived for
– Displacement
– Force

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Quasi-static Modeling
• Equation for Recurve
• Moment in bimetallic strip
D
LM
D
L
m
F
n
ez
412
.
23
+=
Δ
( )
IE
h
T
Me
Δ−
+
=
).(
.
12
24
.2 21 αα
ϕ

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Quasi-static Modeling
Force vs Height
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0 100 200 300 400 500 600
Height of Recurve(Micrometers)
BlockingForce(N)
Deflection vs Height
0
10
20
30
40
50
60
0 100 200 300 400 500 600
Height of Recurve(Micrometers)
Deflection
(Micrometers)

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Quasi-static Modeling
Deflection vs Thickness
0
50
100
150
200
250
0 100 200 300
Thickness (Micrometers)
Deflection
(Micrometers)
Force vs Thickness
0.00
0.20
0.40
0.60
0.80
1.00
0 100 200 300
Thickness (Micrometers)
BlockingForce(N)

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Quasi-static Modeling
Deflection vs Length
0
20
40
60
80
100
0 5000 10000 15000
Length (Micrometers)
Deflection
(Micrometers)
Force vs Length
0.00
0.50
1.00
1.50
2.00
2.50
0 5000 10000 15000
Length (Micrometers)
BlockingForce(N)

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling
• 3-D ANSYS model created
• Steady state analysis carried out
• Alternate configurations simulated
• Coupled field analysis carried out
• Sequential Method of analysis used

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling
• Meshed with Solid87 3-D, 10-Node
Tetrahedral elements for thermal analysis
• Uniform steady state temperature attained
• Nodal results read in for structural
analysis
• Elements changed to Solid92, a 10-node
tetrahedral structural solid

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling – Model I
Meshed ANSYS Model - I

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling – Model I
Deflection of Recurve Model- I

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Comparison of Results
Comparison of Deflections Predicted by Analytical Model and ANSYS (Model I)
0
50
100
150
200
250
0 100 200 300 400 500
Temperature (C)
Deflection(micrometers)
Analytic
ANSYS
Error

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling – Model II
Meshed ANSYS Model - II

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling – Model II
Deflection of Recurve Model- II

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Comparison of Results
Comparison of Deflections Predicted by Analytical Model and ANSYS(Model II)
0
100
200
300
400
500
0 100 200 300 400 500
Temperature (C)
Deflection(micrometers)
Analytic
ANSYS
Error

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
ANSYS Modeling-Max Stress
Max Stress predicted
by analytical model
=1.482E-5 kgf/sq µm

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Dynamic Modeling
• Assess the order of dynamic response of the
passive actuator
• Graphical system-modeling tool
• Uniform treatment of various energy domains
• Lumped parameter pseudo bondgraph model of
heat transfer in the recurve elements developed
• Coupled with the mechanical system bond graph
using signal bonds

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Bond Graph
R
..0
Thermal Part
RD
1..
CM2
0..
SET
RD
1..
RC RC
C RS
0.. 1..
C
..0
I
1..
SE
..
R
0..
0
SE
1..
CM1 I
RC RC
C
0..
RS C
1.. 0..
I
..1
SESE
1..
..
R
0..
0
I CM1
..
R
0..
0
CM2
Mechanical Part

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Results

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Results

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Valve Design
‘Push-pull’ valve arrangement

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Louisiana State University
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Thesis Defense – April 3, 2001
DESIGN and MODELING
Valve Design
Recurve Actuator
Buckling
Valve Cover
Motion of
Valve Cover
Motion of
Actuator
Recurve driven buckling valve cover

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Overview
• Ni-Fe Plating
• Mask Fabrication
• Prototype Fabrication
– Multi-layer fabrication process
– Photolithography
– LIGA
– Conventional Machining Processes

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Materials
• Nickel chosen as high CTE material
– High melting point
– High CTE
– Ease of electroplating
• Invar-like Ni-Fe alloy chosen as low CTE
material
– High melting point
– Low CTE

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Ni-Fe Electroplating
• Electrolyte formulated to electrodeposit an Invar-
like Ni-Fe alloy (64% Fe, 36% Ni)
• Hull cell experiments were carried out to
determine a suitable current density for plating
• 500 µm high, 120 µm X 120 µm cross section
posts were plated as test structures
• EDXRF and WDS on an electron microprobe were
used for analysis of composition

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Ni-Fe Electroplating
Composition of Deposit as a Function of FeCl
Concentration
0
10
20
30
40
50
60
70
80
0.1 0.12 0.14 0.16 0.18
Moles of Ferrous Chloride
PercentageComposition
Ni
Fe

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Ni-Fe Electroplating
Composition along post varies - Microprobe analysis
Ni-Fe Post 490 micron High
(Data points from bottom to top)
0
20
40
60
80
100
120
0 10 20 30 40 50 60
Length along post(in micrometers)
PercentageComposition
Fe
Ni
Total

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Ni-Fe posts
Top view of posts Side view of single post

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Stress in Ni-Fe posts (20 mA/sqcm)

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Stress in Ni-Fe posts (10 mA/sqcm)

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Ni-Fe Electroplating
Polarization Curve
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
40.000
45.000
50.000
55.000
60.000
65.000
70.000
0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900
Negative Potential (V) vs SCE
NegativeCurrentDensity(mA/sqcm)
E0
Ni/Ni
2+
E0
Fe/Fe
2+
Ohmic corrected polarization curve for nickel-iron bath

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Ni-Fe Electroplating - Issues
• Stress generation – cracks, brittleness
• Passivation – required hard is hard to
obtain, plating stops/slows down for no
apparent reason
• Composition varies from top to bottom
• Rusting

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Mask Fabrication – Optical Mask
• Autocad drawings
– Multilayered
• Optical Mask
– Autocad file conversion
– 5x5 inch commercial wafer with Chrome &
Positive resist
– Exposure on MANN 3600 pattern generator
– Development
– Chrome etch
– Resist removal

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Mask Fabrication – Autocad Drawings

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Mask Fabrication – X-Ray Mask
• X-Ray Mask Fabrication
– Glass ring cut by waterjet
– DFP3 graphite cleaned and stuck to glass ring using UV-
cured glue
– 50 A of Chrome and 300 A of gold E-beam deposited
– SU-8 spun on wafer and baked
– Wafer exposed using optical mask
Glass Ring
Evaporated Chrome & Gold
SU-8
DFP-3 Graphite
Glass UV
Chromium Mask
UV Exposure

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Mask Fabrication
– Post-bake and developed
– Gold and chrome etched from around alignment marks
– Plasma ashing to clean wafer
– 20 µm of gold electrodeposited in SU-8 mold
– Mask mounted on standard NIST ring
– Process was used to manufacture two X-Ray masks
Gold and Chrome etched
from around alignment
mark
Gold Plated into pattern
Alignment Mark
Developed Pattern

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Mask on Glass Ring
Gold on Graphite X-Ray mask mounted on glass ring

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Close up on mask
SU-8 structures with gold plated around them

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Alignment Marks on Mask
Complementary alignment marks on mask

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Mask Fabrication - Issues
• Glass surface should be clean & blemish-free
• Alignment marks need not be complementary –
two crosshairs work better
• Distance of alignment marks from structures is
critical
• SU-8 layer sinks into graphite, depending on
graphite density
• SU-8 removal still a problem

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Substrate Preparation
• 4 inch Titanium plate
– Clean with HF for 1 min
– Rinse in DI
• Oxidation
– Sodium Hydroxide and Hydrogen Peroxide
– 65°C for 20 min
• Copper Plating
– Copper Sulphate based bath
– 20mA/sqcm for 30 min
• Hand polished to improve surface
Titanium
Titanium
Titanium Oxide
Copper

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Photolithography
• Spin coat photoresist
– SJR-5740 positive photoresist
– 2000 rpm for 30 sec to give 10
µm thick coat
– Bake at 95 °C for 8 min
• Exposure
– G-line UV-exposure station at
CAMD
– 400 mJ/sqcm
– Only alignment marks
exposed
• Development
– Microposit 354 developer for
8-12 min
Copper
Titanium Oxide
Photoresist
UV Exposed Photoresist

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Photolithography
• Nickel plating
– Activation using C-12
– Sulphamate Bath
– 20 mA/sqcm for 20 min
• Strip photoresist
– Acetone
• Oxidation
– Better visibility & adhesion
Copper
Nickel Alignment Marks
Copper
Copper Oxide

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Visible Alignment Marks
Wafer after oxidation – alignment marks visible

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Photolithography - Issues
• Contact printing process – optical mask has to be
cleaned regularly
• Perfect contact essential for good exposures
• Optical mask should have as much clear field as
possible
• Sacrificial electrode essential for controlling
plating into small areas

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA-Process Overview

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA
• Bond PMMA
– 500 µm thick stock PMMA sheet
– MMA based glue
– 20 psi bonding pressure
• Alignment
– X,Y displacement and rotation adjustments
• Exposure
– X-ray exposure on CAMD beamline XRLM3
Copper
PMMA

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA
X, Y - Displacement
Setscrews
Alignment Mark
on Mask
Alignment Mark
on Substrate
Glass
Rotational Displacement
Setscrew
Optical Microscope
Schematic of Alignment ProcessAlignment Jig

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA
• Development
– GG developer
– 20 min in Developer, 40 min in Rinse
– 1 cycle for every 100 µm of PMMA
– Rinse in DI
• Etch Copper Oxide
– Vacuum wafer under etch solution
Exposed PMMA
Copper oxide etched to expose
copper

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA
• Nickel-Iron Electroplating
• Polishing
• Bond 500 µm thick PMMA sheet
• Flycut down to 100 µm above previous layer
Exposed PMMA
Electroplated nickel-iron,
polished down to level
Second layer of PMMA flycut down
to 100 µm

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Post 1st Electroplating
Wafer after electroplating for 1st layer

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image - Post 1st Electroplating
Part of structure after Nickel-Iron electroplating and polishing

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA
• Alignment and 2nd exposure
• Development
• Copper oxide etch
• Nickel electroplating
– Nickel Sulfamate bath
– Current density of 20 mA/sqcm
Second Exposure of PMMA
Nickel plated into exposed PMMA mold
Copper oxide etched to expose
copper

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
LIGA
• Polish Nickel
• Strip PMMA
– Acetone
– Heat & Stir
• Etch Copper
– 50% NH4OH and 50% H202
• Etch Titanium
– HF
Nickel polished down to level
with nickel-iron
PMMA removed using Acetone
Copper oxide and copper etched to
release structures

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Post 2nd Exposure

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Alignment Error

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Post 2nd Electroplating

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Image – Post final polish

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Issues
• Accurate alignment is difficult
• Unpredictable X-ray exposure results
– Mask setting faulty
• Electroplated Ni-Fe has poor mechanical
properties
• Bond strength between Ni & Ni-Fe suspect
• Adhesion on titanium is poor

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Louisiana State University
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Thesis Defense – April 3, 2001
FABRICATION PROCESS
Future Work
• Alignment Issues
– Reduce alignment steps by fabricating alignment marks
with first PMMA layer
– Use better alignment marks
– Use better alignment system
• Ni-Fe plating
– Additives
– Varied pulse times at lower currents
– Better understanding of material properties of
electroplated Ni & Ni-Fe alloy

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Thesis Defense – April 3, 2001
ACKNOWLEDGEMENTS
Dr. Michael Murphy
• Committee Members:
– Dr. Elizabeth J. Podlaha
– Dr. Sumanta Acharya
– Dr. Wajun Wang
• CAMD Staff
– Yohannes Desta
– Zhong Geng Ling
– Kun Lian
– Jost Gottering
– Harish Manohara

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Thesis Defense – April 3, 2001
ACKNOWLEDGEMENTS
• Kevin Zanca
• Abhinav Bhushan
• Kabseog Kim
• John Fuller
• Tracy Morris
• Summer Dann-Johnson
• Dawit Yemane
• Jason Sevin