Table of contents
ABSTRACT . i
ACKNOWLEDGMENTS ii
Table of contents iv
List of figures vi
List of tables viii
CHAPTER 1. INTRODUCTION 1
1.1 Piezoelectricity 2
1.1.1 Piezoelectric effect 2
1.1.2 Lead zirconate titanate (PZT) . 3
1.2 Piezoelectric MEMS inkjet print head . 5
1.3 Numerical simulation 7
1.3.1 Role of numerical simulation 7
1.3.2 General principle of numerical simulation . 8
1.3.3 Numerical simulations of piezoelectric MEMS inkjet with CFD-ACE+ 9
1.4 References . 10
CHAPTER 2. NUMERICAL AND EXPERIMENTAL STUDY ON ACTUATOR PERFORMANCE
OF PIEZOELECTRIC MEMS INKJET PRINT HEAD 11
2.1 Introduction . 12
2.2 Modeling and simulation settings 13
2.3 Experimental procedure . 16
2.4 Results and discussion . 17
2.4.1 Performance characteristics of PIPH actuator in air . 17
2.4.2 Performance characteristics of PIPH actuator in liquid 18
2.5 Conclusion . 20
2.6 References . 21
CHAPTER 3. SIMULATION OF MICRODROP GENERATION IN PIEZOELETRIC MEMS
INKJET PRINT HEAD 26
3.1 Introduction . 27
3.2 Modeling and simulation settings 27
3.3 Results and discussion . 29
3.3.1 Microdrop generation process . 29
3.3.2 Effect of actuating characteristics . 29
3.3.3 Effect of fluid properties . 30
3.3.4 Effect of geometrical parameters 32
3.4. Conclusion 32
3.5 References . 34
CHAPTER 4. FABRICATION AND CHARACTERIZATION OF PIEZOELECTRIC MEMS
INKJET PRINT HEAD 38
4.1 Introduction . 39
4.2 Experiments . 39
4.3 Results and discussion . 41
4.4 Conclusion . 42
4.5 Rerefences . 44
CHAPTER 5. CONCLUSION AND SUGGESTION . 50
5.1 Conclusion . 50
5.2 Suggestion (new design) 50
Appendix A. Python Source Script for simulation of microdroplet generation (effects of
driving characteristics and fluid properties) . 52
Appendix B. Pattern conditions for fabrication of Inkjetver2 . 54
Appendix C. Dry etching conditions . 55
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al frequency.
With membrane size of 300 um, the numerical and experimental values of the
maximum displacement rate were ca. 0.053 um/V and ca. 0.059 um/V, respectively (Fig.
2-3). The simulation was also extended for various sizes of PIPH actuator membrane
(i.e., 500um, 600um). Fig. 2-4(a) indicated the relationship between the maximum
displacement of PIPH actuator membrane and thickness ratio of PZT to support layer at
an applied voltage of 5V (thickness of support layer was fixed of 2.3 um). Increasing
PZT thickness makes the PZT actuation strain increased and the stiffness of PIPH
actuator membrane, thus, also increased, which decreased its displacement. Total
actuation strain of PIPH actuator membrane finally depends on the competition between
them. Therefore, maximum displacement of PIPH actuator membrane slightly increased
from thickness ratio of 0.2 to 0.5 (corresponding to PZT thickness of 0.5 um to 1.15 um)
and then decreased with thicker PZT film. According to Gere & Timoshenko, the
maximum displacement of a pure bending membrane (with width a and Young’ s
modulus E) under uniform load, P, can be expressed as [18]
18
3
4
max Et
Paαδ = with α = 0.0138 (7)
Therefore, with the maximum displacement δmax produced by PIPH actuator membrane,
the maximum force can be inferred approximately as
2
3
max
max a
EtF α
δ= (8)
Figure 2-4(b) shows the relationship between the maximum force, the maximum
displacement of PIPH actuator membrane and its width at applied voltage of 10V. Both
actuator membranes with PZT thickness of 0.5 um and 1 um exhibited the similar
values of maximum displacement and the parabolic dependence upon the width ( αmax ~
a2). However, the maximum force was enhanced significantly (i.e., 1.75 times) in case
of the PZT thickness of 1 um. In addition, the maximum force reached the saturated
values at membrane width of ca. 600 um. This marks a notice in selecting optimized
sizes of PIPH actuator membrane which can produce both high maximum displacement
and maximum force so that the highest value of the maximum work can be obtained.
Finally, the fundamental frequency of PIPH actuator membrane (width of 300um) was
predicted using FEMLABTM software and compared with an experimental result
monitored by HP4194A impedance analyzer. Its simulation and experimental values
were ca. 379 kHz and ca. 328 kHz, respectively (Fig.2-5).
2.4.2 Performance characteristics of PIPH actuator in liquid
Amount of the fluid ejected through the nozzle is determined not only by the
maximum actuation displacement, maximum actuation force of the membrane and the
behavior of the fluid inside the system, but also by the deflection shape of the
membrane [4]. The displacement of the membrane is due to the shear stress applied by
the actuator and by the pressure of the fluid. This pressure was solved from Navier-
Stokes equations by setting the membrane displacement as one of its boundary
conditions. Therefore, the behavior of the PIPH is a set of electrical-mechanical-fluid
couplings.
19
When the fluid-membrane interaction was considered, the maximum displacement
slightly reduced (i.e., 0.049 um/V (in liquid-interaction) vs 0.053 um/V (in air)). The
maximum force, thus, also reduced in accordance to equation (8). The maximum
displacements of PIPH actuator membrane at various driving frequencies are listed in
Table 2-4. And typical deflection shapes are shown in Fig.2-6. At low frequencies (100
Hz-25 kHz), the deflections were not sensitive to the driven frequency. The PIPH
actuator membrane bends in one direction and it has only one peak (Fig.2-6 (a,b)). The
maximum displacements in these cases were 0.245 ~ 0.267 μm. At higher frequencies
(25 kHz-100 kHz), the deflections increased with the frequency and were different
between bend-up and bend down modes. Moreover, because of the membrane-fluid
interaction, the membrane deflection shape was changed at frequencies above 100 kHz.
The deflection shape of PIPH actuator membrane was sophisticated and exhibited two
or more peaks (Fig.2-6 (c,d)). The appearance of the deflection peaks becomes one of
the disadvantages for the PIPH actuator performance. The behavior of fluid inside the
chamber, thus, also changed unexpectedly. Below 125 kHz, outlet flow rate increased
with increasing the frequency. The response of fluid and the vibration of membrane
were in phase. The ratio between backflow and net flow reached the minimum value of
ca. 3% at driving frequency of 25 kHz. Above 125 kHz, the response of fluid and
vibration of membrane were out of phase (Fig.2-7(a)). This frequency is considered as a
resonance frequency of the PIPH actuator membrane in liquid. And the experimental
result showed the resonance frequency of membrane in liquid was ca. 90 kHz (Fig.2-
7(b)). Both numerical and experimental resonance frequencies of membrane in liquid
were about 3 times smaller than those of membrane in air. The driving frequency of
PIPH actuator must be smaller than this resonance frequency of membrane in liquid.
Summary of maximum displacement and resonant frequency was shown in Table 2-5.
The prediction for actuator membrane with width of 600 um was also given in this table.
The simulation results agree well with experimental ones. This work along with another
work studying microdroplet generation of PIPH (will be reported elsewhere) offers an
effective guideline in designing the PIPH.
20
2.5 Conclusion
Performance characteristics of PIPH actuator have been investigated numerically
and experimentally. The maximum actuation displacement and the maximum actuation
force are basic performance characteristics of a work-producing PIPH actuator. Natural
frequency of actuator membrane was known as a limit of PIPH actuator operating at
dynamic regime. Considering the electro-mechanical-fluid couplings indicated the inter-
dependence between PIPH actuator membrane and fluid, which leads to significant
changes such as the decrease of resonance frequency or the appear of multi-peak
deflection shapes as well as out-of-phase response of ink liquid. The numerical results
agree well with the experimental ones. These results play an important role in selecting
the appropriate design parameters so that characteristics of PIPH actuator can be
optimized.
21
2.6 References
[1] M. Usui, Seiko Epson Corporation, Shiojiri, Nagano, Japan
[2] Hermann Seitz and Joachim Heizl, J.Micromech.Microeng.14(2004) 1140-1147
[3] Steve Temple, Xaar plc, Cambridge
[4] B Fan, G Song and Hussain, Smart Mater.Struct. 14 (2005) 400-405
[5] Vishal Singhal and Suresh V.Garimella, IEEE transactions on advanced packaging,
VOL.28.N0.2, MAY2005
[6] J. KIM, ME608 Final project, Apr.26.2002
[7] J. S. Yahng and S. C. Jeoung, D. S. Choi and D. Cho, J. H. Kim, H. M. Choi and J.
S. Paik, J.Korean Phys. Soc.Vol. 47, No. 6, December 2005, pp. 977_981
[8] K.Y.Lee, E.D.Case, Journal of Materials Science 31(1996)2253-2264.
[9] Jun-Kyu Paik, Sanghun Shin, Sun-Woong Na, Nae-Eung Lee, and Jaichan Lee,
Integrated Ferroelectrics, 69:383-390 (2005).
[10] Frank M.White, Fluid Mechanics, 4th ed. (Mc Graw Hill, 1998).
[11] Joel h. Ferziger et al, Computational Methods for Fluid Dynamics (Springer
Verlag, 1999).
[12] IEEE Standard on Piezoelectricity, ANSI/IEEE Std176-1987
[13] Szilard R, Theory and Analysis of Plates, Classical and Numerical Methods
(Englewood Cliffs, NJ: Prentice-Hall,1974)
[14] CFD-ACE+ Modules Manual version 2004
[15] J. R. Ahn, D. W. Kim, G. Y. Yeom, J. B. Yoo, and J. Lee, Ferroelectrics, 263, 244
(2001).
[16] Jurgen Brunahl, Physics of Piezoelectric Shear Mode Actuators (Stockholm,2003).
[17] J.E.Huber, N.A.Fleck and M.F.Ashby, Proc.Soc.Lond.A (1997)453,2185-2205.
[18] Gere & Timoshenko, Mechanics of Materials, 3rd ed. (PWS-KENT, 1990).
22
Table 2-1. Fluid properties
Property Density (ρL) Dynamic viscosity (μ)
Unit kg m-3 x10-3 kg m-1 s-1
Value 800 2
Table 2-2. Support layer properties
Property Density (ρ) Young’s Modulus (E) Poisson’s ratio (υ)
Unit kg m-3 x109 Pa
Value 3500 212 0.26
Table 2-3. PZT properties (PZT 52/48 )
Piezoelectric coefficients (x10-12 C/N) Density
(kg m-3)
Young’s
Modulus (Pa)
Poisson’s
ratio (υ) d13 d23 d33 d42 d51
7500 1.7 x1011 0.3 93.5 93.5 223 494 494
Table 2-4. The displacement at various driving frequencies (voltage=5V)
Frequency, f (Hz) Max. bend up (μm) Max Bend down (μm)
100 ~ 500 -0.2447 0.245
1k ~ 5k -0.2439 0.2451
10 k ~ 25 k -0.265 0.267
40 k ~50 k -0.296 0.302
100 k -0.371 0.365
125 k -0.416 0.533
200 k -0.595 0.677
Table 2-5. Summary of actuator performance characteristics
Maximum
displacement
(in air)
Maximum
displacement
(in liquid)
Resonance
frequency
(in air)
Resonance
frequency
(in liquid)
Simulation (300 um) 0.053 um/V 0.049 um/V 379 kHz 125 kHz
Experiment (300 um) 0.059 um/V x 328 kHz 90 kHz
Prediction (600 um) 0.240 um/V x ~ 100 kHz ~ 30 kHz
23
Fig. 2-1. Model of a piezoelectric inkjet print head (PIPH) structure: (a) design, (b)
CFD-ACE+ symmetric model with meshing grids.
Fig. 2-2. Flowchart of fabrication process (a) and SEM images (b) of PIPH actuator.
24
Fig. 2-3. Maximum displacement of PIPH actuator membrane (300 um): (a) simulation
and (b) experiment. Simulation was extended with membrane width of 500-600 um.
Fig. 2-4. Dependence of actuator performance on geometrical parameters, (a) maximum
displacement vs. thickness ratio (PZT/support layer) and (b) maximum force (Fmax) and
maximum displacement (δmax) vs. membrane width
Fig. 2-5. Resonance frequency (in air) of PIPH actuator membrane: (a) FEMLAB
simulation and (b) experiment with HP4194A impedance analyzer.
25
Fig. 2-6. Deflection shape of actuator membrane interacting with liquid, dome shape
with one peak at low frequencies (a) & (b), unexpected shape with more than one peak
at higher frequencies (above 125 kHz < 379 kHz - resonance frequency in air ).
Fig. 2-7. Resonance frequency (in liquid) of PIPH actuator membrane: (a) simulation
and (b) experiment.
26
CHAPTER 3. SIMULATION OF MICRODROP GENERATION IN
PIEZOELETRIC MEMS INKJET PRINT HEAD
Abstract
The simulation of microdroplet generation in piezoelectric MEMS inkjet print
heads has been performed. The effects of actuating characteristics such as driving
amplitude and frequency of the piezoelectric membrane, fluid characteristics including
surface tension and viscosity, and geometrical parameters were investigated. From the
simulation results, we obtained three regions for the formation of droplet with the
actuating and fluid parameters, i.e., the formation of no-droplet, single droplet and
satellite droplets. The single droplets can be obtained by applying driving voltage
operating high frequencies with small amplitudes. The simulation results also indicated
the competition between cohesive and disruptive forces in generating droplets. And the
relative chamber size, aspect ratio of nozzle, nozzle shapes and the diffuser function
were importantly geometrical parameters influencing on the droplet generation. This
modeling offers a visual description, and an effective guideline to design inkjet print
head structure with high quality printing.
27
3.1 Introduction
Recently, the industrial ink-jet printing technology has been considered as a
next generation process tool which replaces environmentally harmful, time-consuming
and expensive process for the fabrication of precise electronic devices such as flat panel
display (FPD) and various types of micro-devices. One of the most important elements
in an ink-jet printing system is the ink-jet print head used to eject small amounts of fluid
on target surfaces. The ink-jet print head can be classified into continuous-mode and
drop-on-demand mode heads. In a drop-on-demand mode head, a piezoelectric layer or
a thermal actuator component is typically incorporated into ink-jet head structure to
create the dynamic force for ejecting the fluid from a nozzle outlet. Piezoelectric ink-jet
heads normally offer a greater range of ink compatibility than thermal ink-jet heads,
which are limited to water-based inks or require a new design for each different type of
ink solvent [1-7].
Various designs and fabrication techniques of a piezoelectric inkjet print head
have been reported in literatures [4-8]. However, it is necessary to obtain more intensive
understanding of fundamental phenomena and principles in ejection process, which
gives a useful guideline to design an inkjet structure. In order to reduce the
computational demand, the piezoelectric actuator, which gives an actuating force, was
neglected and replaced by a moving wall boundary. This treatment allows us to
concentrate on the interaction between the liquid and surrounding medium at which the
competition between the cohesive and disruptive forces occurs and droplets are
generated. In this study, we have investigated the ejection process of droplets under
various driving characteristics such as displacement amplitude and driving frequency,
and fluid properties, i.e., surface tension and viscosity. We report the formation of fluid
droplets at such various conditions.
3.2 Modeling and simulation settings
In general, an acting function of a moving wall boundary (i.e. piezoelectrically
actuated vibrating diaphragm) causes ink to be ejected from a nozzle or an orifice onto a
surface. It is well expected that physical parameters determine fluidic characteristics of
28
),,( wvuV =r
0=Vr
the ejected ink, such as formation of a single droplet, decrease of satellite droplets or
non-splashing, droplet size and so on. Those characteristics depend on driving force,
fluid properties and geometric parameters of a print head [1, 2, 11]. The simulation is
implemented with a simple piezoelectric inkjet structure consisting of a cylindrical
chamber connected to a cylindrical nozzle. The diameters of chamber and nozzle are
300 μm and 30 μm, respectively. The piezoelectric actuator, which has a “forcing
function” to produce droplets, was replaced by a moving boundary, as shown in Fig. 3-1.
To simplify and reduce computational cost, 2-dimensional section of the inkjet structure
was used in this simulation with orthogonal meshing. The simulation was performed
using CFD-ACE+ package software known as a multiphysics modeling tool. For droplet
generation, air region was added in the model (as shown in Fig. 3-1(b)).
According to the Volume of Fluid (VOF) theory, the liquid volume fraction F is
determined by solving the following passive transport equation (1) along with the
Navier-Stokes equation (2) [9-15].
0=•∇+∂
∂ FV
t
F r
(1)
PVg
Dt
VD ∇−∇+= rr
r
2μρρ
(2)
where is velocity vector, ρL is density and μ is dynamic viscosity of
fluid. Isopropanol was used as an ink fluid in the simulation (ρ=800 kg/cm3, σ=22
mN/m, μ=2 cp). Boundary conditions for the fluid model are non-slip at the fluid-wall
interfaces ( ) and far-field at the outlet where a constant pressure is set to the same
as atmospheric pressure. Moving boundary condition is applied to the upper wall of the
chamber. The movement of the upper wall can be expressed as follow:
y(x,t)=Asin(2πx/2a)sin(2πft) (3)
where A and f are amplitude and vibrating frequency of the driving displacement
produced by piezoelectrically actuated membrane, respectively. a is the radius of the
chamber.
29
Generally, droplet breakup in a flowing stream is governed by its surface tension,
viscous forces, and dynamic pressure [1,2]. The effects of these quantities in terms of
fluid properties and driving characteristics are considered in this simulation.
3.3 Results and discussion
3.3.1 Microdrop generation process
The microdrop generation process was monitored at a driving displacement with
amplitude and frequency of 5 μm and 30 kHz, respectively. At this driving displacement,
a primary droplet is formed within one cycle, i.e., 33.33 μs. Figure 3-2 shows the four
main steps of an ejection cycle including infusion, inversion, ejection and relaxation
[1,4]. During infusion, called fluid jet formation, the displacement starts at zero or
equilibrium state (Fig. 3-2(a)) and begins to increase, reaching a maximum value of 5
μm. This corresponds to the driving plate deflecting downward, drives the fluid into the
inkjet orifice from the chamber and pulls the meniscus into the orifice through the
nozzle. The meniscus grows until approximately 8.3 μs (Fig. 3-2(b)), begins to decrease
in size and deform in shape. This step is called inversion corresponding to the decrease
of displacement from positive to negative value (Fig. 3-2(c)). When the fluid jet is
destabilized enough, the meniscus is broken off and a droplet is formed at 21.75 μs (Fig.
3-2(d)). During relaxation, the flow undergoes viscously-damped oscillations (Fig. 3-
2(e)) and approaches an equilibrium state before the next ejection cycle begins (Fig. 3-
2(f)). The destabilization of the fluid jet depends on the driving displacement, which
produces discrete and free-flying drops or satellite droplets. For example, if clean break
does not occur between the primary droplet and the fluid in the nozzle, satellite droplets
are generated. The formation of satellite droplets needs to be suppressed for accurate
control of ejection process such as the volume of the droplet and time duration of the
droplet formation.
3.3.2 Effect of actuating characteristics
The driving displacement includes its amplitude and frequency. Those quantities
will affect the generation time and quality of droplets. Figure 3-3 shows the images of
30
single droplet and satellite droplets at various driving displacements. At the driving
displacements with small driving amplitudes (e.g., 3.5 μm, 30 kHz –Fig. 3-3(a)), a
single droplet is generated. At the driving displacements with large amplitudes and/or
high frequencies, satellite droplets are generated (as typically shown in Fig. 3-3 (b) 3.5
μm, 70 kHz; (c) 4.5 μm, 50 kHz, (d) 5 μm, 30 kHz). In most situations, it is desirable to
eliminate satellite droplets and increase ejection rates (or reduce droplet generation
time). Figure 3-4 indicates the relationship between the time duration for droplet
generation and actuating characteristics, i.e., the amplitude and frequency of the driving
displacement. The droplet generation time decreases when the amplitude and/or
frequency of the driving displacement increase. There exist three regions for the
formation of droplets: no droplets, single droplets and satellite droplets. Droplets can
not be formed at amplitudes below 2.75 μm (Fig. 3-4(a)) or frequencies below 20 kHz
(Fig. 3-4(b)). Close to the boundary between no-droplet and single droplet regions,
several push-pull cycles are required to generate a single droplet (i.e., 19 cycles at a
driving displacement of 3 μm and 30 kHz). It’s clear that there is a strong competition
between cohesive and disruptive forces in this region and cohesive forces are
predominant. Thus it’s required numerous push-pull cycles to accumulate enough
disruptive force. That’s the reason why time duration for droplet generation significantly
increases with smaller driving displacements (i.e., 3 μm - 30 kHz, 2.75 μm- 40 ~ 80
kHz in Fig. 3-4 (a), or 3 μm - 30 kHz, 4 μm - 20 kHz in fig.4 (b)). Far from this
boundary, the number of push-pull cycles for droplet formation decreases significantly
and satellite droplet formation gradually occurs. Figure 3-4(b) indicates that only single
droplet is generated at driving displacements with amplitude of 3 μm and frequencies
above 30 kHz. However, satellite droplets are generated at most frequencies as the
amplitude becomes large above 4 μm. The threshold of droplet ejection obtained from
this simulation provides a guideline in choosing geometric parameters when the inkjet
structure is designed.
3.3.3 Effect of fluid properties
The surface tension of a liquid tends to pull the liquid into a form that exhibits the
31
minimum surface energy, while the stabilizing effect of liquid viscosity tends to
oppose any disturbance in liquid geometry. External forces, such as driving
displacement in this case, acting on the liquid surface may distort the bulk liquid and
promote the disruption [2,3]. Typical viscosity and surface tension of a fluid to be used
in a piezoelectric inkjet device are in range of 0.5-40 cp and 20-70 mN/m, respectively
[1,2]. Figure 3-5 shows the droplet generation time versus fluid properties, e.g., surface
tension and viscosity. The change in the time duration for droplet generation implies the
competition between the cohesive and disruptive forces acting on the liquid surface. The
competition leads to oscillation and perturbation in the liquid. Under favorable
conditions, the oscillation may be amplified to such an extent that the bulk liquid
disintegrates into droplets. For instance, when viscosity and amplitude of the driving
displacement are fixed at 2 cp and 3.5 μm, respectively, the time duration for droplet
generation increases with the surface tension from 20 mN/m to 70 mN/m and decreases
with the frequency, as shown in Fig. 3-5 (a).
The strong competition between surface tension and driving force produced by the
driving displacement is clear at smaller frequencies, such as 40 kHz , 50 kHz and 60
kHz (as shown in Fig. 3-5 (a)). Surface tension is influencing to the time duration of
droplet generation at driving frequencies. Increasing surface tension makes cohesive
forces predominant. Therefore it’s more difficult (required longer time) to generate
droplets with increasing surface tension while fixed driving displacement (i.e.,
increasing surface tension from 30 mN/m to 70 mN/m at fixed driving displacement of
3.5 μm - 30 kHz, or 50 mN/m to70 mN/m at 3.5μm – 40~50 kHz). At a driving
frequency of 40 kHz, it takes 200 μs or 8 cycles to generate a droplet at a surface
tension of 60 mN/m. However, no droplet is generated at a surface tension of 70 mN/m
even after 20 pull-push cycles. On the other hand, the driving displacement becomes
predominant when the driving frequency increases above 70 kHz, at which a droplet is
formed within 1 pull-push cycle irrespective of surface tension. Time duration for
droplet generation also increases linearly with the viscosity. It takes about 1 to 3 pull-
push cycles to form droplets at investigated driving displacements, i.e., amplitude of 5
μm and frequencies of 20 kHz – 40 kHz, as shown in Fig. 3-5 (b). It is also observed
32
that less satellite droplets are generated with increasing the viscosity. Viscosity acts to
dampen the instabilities that lead to satellite formation.
3.3.4 Effect of geometrical parameters
Figure 3-6 shows three types of inkjet structure used to consider the effect of
geometrical parameter. Effects of the relative chamber size X1/X2 (A-type), aspect ratio
d/h (B-type) and diffuser function (C-type) are analyzed. Time duration for droplet
generation reaches the minimum values at relative ratio of 0.3-0.5, as shown in Fig. 3-
7(a). Conical shape of nozzle inlet (B-type) reduces fluidic impedance compared with
cylindrical shape (A-type). Therefore, droplet generation time of B-type is shorter than
that of A-type, i.e., 55 um (B-type) versus 135 um (A-type) at the same driving
characteristics of 2.5 um-30 kHz. It’s also observed that time for droplet generation
decreases with decreasing the aspect ratio (AR=diameter of nozzle/height of nozzle). At
relatively high driving characteristics, B-type and C-type have the same time duration
for microdroplet generation (Fig. 3-7(b)). However, at lower characteristics (i.e., 2 um-
30 kHz), B-type can generate a single droplet after 5 pull-push cycles (165 us) while C-
type generates no-droplet. This can be explained that adding a diffuser into
microchannel makes backflow (flow from chamber to reservoir) increased and thus
decreases the flow moving through nozzle inlet. Among there types of inkjet structures,
B-type with optimized parameters such as relative ratio of 0.5 and conical nozzle shape,
could be selected as a good candidate. Then its three regions of microdroplet generation
are shown in Fig. 3-8. The microdroplet can be generated with applied voltages of 9V-
21V and frequencies above 15 kHz.
3.4. Conclusion
Microdrop generation process and effects of basic forces on the process such as
surface tension, viscous forces, and dynamic pressure, have been investigated. The
correlation of driving displacement and fluid parameters is also analyzed in this
simulation. Four distinct regimes have been identified in an ejection cycle: infusion,
inversion, ejection and relaxation. In order to form droplets, the necessary and enough
condition is that the driving force caused by the driving displacement is larger than the
33
surface tension force and it should be dynamic. The simulation results indicate that the
driving displacement plays an important role to reduce the droplet generation time and
improve droplet quality. The results show three regions divided into no-droplet, single
droplet and satellite droplet regions. The droplet formation requires the following
actuating characteristics: driving displacements with large amplitude and/or frequency.
However, further high performance of an inkjet head, i.e., short duration time for
droplet generation and high quality droplet (single droplet), needs driving displacements
with relatively small amplitudes and high frequencies. Geometrical parameters
significantly affect to microdroplet generation. Relative ratio of chamber sizes, aspect
ratio and nozzle shape are important parameters which are optimized from this
simulation.
34
3.5 References
[1] Eric R.Lee, Microdrop generation, CRC Press (2003).
[2] Liu, Huimin, Science and Engineering of Droplets - Fundamentals and Applications,
William Andrew Publishing/Noyes (2000).
[3] Nam-Trung Nguyen, Steven T. Wereley, Fundamentals and Applications of
Microfluidics, Artech Hourse, Inc (2002).
[4] Carl D. Meinhart and Hongsheng Zhang, J. Microelectromechanical Systems, 9
(2000).
[5] John Collins, Yung-Chieh Tan, Abraham P.Lee, IMECE,41983 (2003).
[6] MicroFab Technologies, Inc, www.microfab.com.
[7] J.M. Meacham, M.J.Varady, F.L.Degertekin, and A.G.Fedorov, Physics of fluids,
17 (2005).
[8] Steve Temple, Small fast inkdrop emission from a nozzle, Xaar plc, Cambridge.
[9] B Fan, G Song and Hussain, Smart Mater.Struct. 14, 400-405 (2005).
[10] Joel H. Ferziger et al, Computational Methods for Fluid Dynamics, 3rd Edition,
Springer.
[11] Joohan KIM, ME608 Final project (2002).
[12] CFD-ACE+ Modules Manual version (2004).
[13] Sanghun Shin, Jun-kyu Paik, Nae-eung Lee, Jaichan Lee, Jun-shik Park and Hyo-
derk Park, J.Korean Phys. Soc. 46, 292-295 (2005).
[14] Deuk Chul Kwon and N. S. Yoony, J. H. Kim, Y. H. Shin and K. H. Chung,
J.Korean Phys. Soc. 47, 163-166 (2005).
[15] J. S. Yahng and S. C. Jeoung, D. S. Choi and D. Cho, J. H. Kim, H. M. Choi and J.
S. Paik, J.Korean Phys. Soc. 47, 977-981 (2005).
35
Fig. 3-1. Inkjet head geometry, (a) Three dimensional (3D) and (b) 2D symmetric
section in CFD-ACE+.
Fig. 3-2. Microdrop generation process at driving displacement with amplitude of 5 μm
and frequency of 30 kHz.
36
Fig. 3-3. Droplet properties: no-droplet, single droplet and satellite droplets at various
driving displacements (2~5um, 50 kHz).
Fig. 3-4. Time duration for droplet generation at various actuating characteristics: (a)
amplitude and (b) frequency. Droplets are generated in one cycle or several cycles.
Fig. 3-5. Time duration for droplet generation with fluid properties: (a) surface tension
and (b) viscosity. High surface tension or viscosity makes cohesive forces predominant.
Single droplets
Satellitedroplets
Single droplets
Satellitedroplets
37
Fig. 3-6. Geometrical parameters: (a) relative chamber X1/X2, (b) aspect ratio d/h and
(c) diffuser.
Fig. 3-7. Time duration for droplet generation vs.: (a) relative chamber size (A-type) and
(b) aspect ratio (B-type & C-type).
Fig. 3-8. Time duration for droplet generation vs. driving characteristics of the selected
structure (B-type). Microdroplet can be generated at an applied voltage of 9V-21V and
frequency above 15 kHz.
38
CHAPTER 4. FABRICATION AND CHARACTERIZATION OF
PIEZOELECTRIC MEMS INKJET PRINT HEAD
Abstract
This report describes the fabrication and characterization of a piezoelectric
inkjet print head (PIPH) structure, which is integrated with a reservoir, microchannel,
and actuator membrane and fabricated by micro-electro-mechanical-system (MEMS)
processing. Sol-gel derived Pb(Zr0.52Ti0.48)O3 thin film was used as a main component of
the piezoelectric actuator membrane. And an improvement of inkjet structure
(InkjetVer2) was performed with changing the shapes of nozzle inlet and nozzle outlet
(orifice). The mechanical properties, such as maximum displacement and resonance
frequency of actuator membrane, as well as the ink ejection were monitored. This work
helps to verify the simulation results and standardize the fabrication processes.
39
4.1 Introduction
The fabrication of electronic and/ or mechanical structures in micron scale is
typically an expensive process and a wide variety of materials. An alternate approach is
an ink-jet printing technology. Ink-jet printer is capable of depositing ranging from
organic materials at cost-effective process [1-5]. The ink-jet print head is classified into
continuous and drop-on-demand modes. The drop-on-demand printing is further divided
into the followings: thermal, piezoelectric, electrostatic and acoustic actuations. The
thermal ink jet printing is a method whereby ink drops are ejected from a nozzle by the
growth and collapse of a water vapor bubble on the top surface of a small heater located
near the nozzle. The simple design of the thermal ink jet print head and its fabrication
process compatible with semiconductor processing allow the print head to be built at
low cost but limited to water-based inks. As an alternate method, the piezoelectric ink-
jet head typically offer a greater range of ink compatibility than thermal ink-jet head [6].
Moreover, the piezoelectric driving mechanism has several advantages over other
mechanisms, such as high torque, fast response and low power consumption compare to
other mechanisms. The piezoelectric actuating method also includes various
deformation mechanisms such as squeeze, bend, push and shear modes.
In this study, the PIPH structure operating in bend-mode was fabricated using two
silicon wafers. The first one is used to make actuator membrane and ink chamber and
another is used to form nozzle and microchannel. Both of them were bonded by Eutectic
bonding technique. In this fabrication of InkjetVer2, the shapes of nozzle inlet and
nozzle outlet were modified so that the performance of PIPH could be improved
compared with InkjetVer1. In this paper, we describe its fabrication process and
characterization including mechanical properties and ink ejection process.
4.2 Experiments
Figure 4-1 shows the side view of a PIPH structure. It consists of several
components integrated into two bonded silicon wafers, such as actuator membrane, ink
chamber, nozzle, diffuser, microchannel and reservoir. Vibration of actuator membrane
under an AC applied voltage causes a volume difference of ink chamber which directs
40
the fluid flow in microchannel from reservoir. The bending of actuator membrane, of
course, applies pressure to the printing fluid in the chamber, which forces a droplet to be
expelled from nozzle outlet (orifice) under favorable conditions.
The fabrication process of PIPH required 10 masks (as shown in Fig. 4-2). Masks
M1-M6 were used for fabrication of actuator-chamber plate and the rest was used for
fabrication of microchannel-nozzle plate.
Figure 4-3(a) shows the fabrication process of actuator-chamber plate. The low-
temperature oxide (LTO) and low-stress SiNx (1.2 µm) layer were deposited on the
double side polished 300 μm-thick p-type (100) 4 inch silicon wafer by low pressure
chemical vapor deposition (LPCVD) system. Then 300 nm-thick LTO layer was
additionally deposited as a buffer layer by plasma enhanced chemical vapor deposition
(PECVD) system for the following deposition process of bottom electrode and PZT thin
film. Thin (200 Å) Ta as an adhesion layer and a Pt (1500 Å) metallic layer as a bottom
electrode were deposited by DC magnetron sputtering at 350 °C. PZT thin film (0.5 um)
was coated on the prepared substrate (Pt/Ta/SiO2/SiNx/SiO2/Si/SiO2/SiNx) by sol-gel
spin coating method with synthesized precursor solution, followed by fast annealing at
650 °C for 2 min in the rapid thermal process (RTP) system [8-9]. The PZT and bottom
electrode layers were etched by the inductively coupled plasma (ICP) etcher. The ashing
process was performed to remove the remaining photoresist after each dry etching
process. The inter layer dielectric (ILD) was incorporated for the insulation between top
and bottom electrode in the PZT capacitor. The silicon dioxide SiO2 layer (3000 Å), as
an ILD, was deposited by PECVD and patterned by RIE. Then, the Ta/Pt thin films
(200 Å/1000 Å) were deposited for the top electrode by DC magnetron sputtering.
In order to form a vertical ink chamber and actuator membrane, the deep-reactive
ion etcher (deep-RIE) was used. The SiNx/SiO2 layer at the bottom side of the actuator
plate was etched in order to make a mask window of the deep-RIE process for the ink
chamber, followed by the deep-RIE.
Figure 4-3(b) shows the fabrication process of the channel-nozzle plate. The
SiNx/Si/SiNx substrate was used for this plate. The nozzle inlet had pyramidal shape and
41
was defined by wet chemical etching with KOH solution (KOH: DI water=6:4, or 35%
wt) at 80 °C [10]. Then the microchannel and diffuser were defined by the deep-RIE
process. The SiNx layer on the bonding surface of the channel-nozzle plate was etched
by RIE in order to expose the Si surface for the eutectic bonding process.
The Ta/Au (200 Å /3000 Å) thin films were used as glue layers between top plate
(actuator-chamber plate) and bottom plate (channel-nozzle plate) and were deposited by
magnetron sputtering/e-beam evaporator on each bonding surface. Both plates were
bonded by EV501 bonder at temperature of 400°C and an uniform force of 3000 N
during 1 hour.
4.3 Results and discussion
Figure 4-4 shows the SEM and optical micrographs of the fabricated PIPH
structure. Multi-layered actuator membrane was stable without structural deformation
due to the film stress or effects of fabrication steps. However, membrane size was
exceeded 10~20% because of the DRIE process of chamber from back side. The nozzle
inlet had pyramidal shape of silicon wet-etching. The structures of reservoir, channel,
diffuser and nozzle outlet were well defined by deep-RIE process.
The electrical properties of the PZT actuator membrane incorporated in the ink-jet
head structure were measured by an impedance analyzer (HP4194A) and Radiant
Technologies testing system (RT66A). The poling process was performed at final step
to recover the PZT properties. After poling at 12V, 120°C, 60 min, PZT properties were
recovered significantly. Figure 4-5(a) shows the polarization-electric field (P-E) loops
of the PZT membrane under applied voltages of 3~12V. The remanent polarization (Pr)
was ca.18µC/cm2 (compared with ca. 20µC/cm2 of initial state). The fundamental
resonant frequency of the PIPH actuator membrane was ca.270 kHz (as shown in Fig. 4-
5(b)). With actuator membrane fabricated by KOH wet-etching, the membrane size was
accurate. And its natural frequency was ca.330 kHz (see chapter 2). In this case PIPH
actuator membrane was over-etched 10-20% by DRIE, its natural frequency of 270 kHz
was reasonable. This is explained based on the relationship between the membrane’s
resonant frequency, f, and its dimension, a, as following:
42
f ~ 1/a2
In order to measure the displacement of the PIPH actuator membrane, a LK-G10-
KEYENCE non-contact laser displacement measurement was used. Figure 4-6 shows
the maximum displacement (bending of the center point) of PIPH membrane actuator
upon applied voltages. With the actuator membrane extended by DRIE process (over-
etched 10-20%), the maximum displacement obtained from the simulation and
experiment was ca. 0.77-0.112 um/V and 0.098 um/V, respectively.
There are 7x12= 84 cells of PIPH integrated on 4-inch silicon wafer. Each cell
consists of four PIPH structures. Cells of PIPH were separated by laser dicing (M2000
laser). Figure 4-7(a) shows an image of a PIPH cell. Electrical and fluidic systems were
prepared for ejection testing as shown in Fig. 4-7(b). Ejection testing was performed
using high speed digital camera system (Fig. 4-8). Ink fluid was supplied by a
micropump which could control an accurate fluid flow. When fluid flow ≠ 0 (i.e., 0.5, 2,
10 ul/min), it was observed that there was liquid expelled from nozzle outlet. This
confirmed that the possibility of the microchanel, having a diffuser with minimum size
of 30 um, and the nozzle, with diameter of 30 um, could make the liquid moved inside
the micro-scale system. When fluid flow =0 (stop the supply of external flow), an AC
voltage with the amplitude of 5-10V and the frequency of 5-40 kHz was applied to the
PIPH actuator membrane. No ejection or droplets of liquid existed. However, a
vibration of the liquid meniscus was observed at the nozzle outlet (Fig. 4-9). This
implied that the operation of PIPH actuator could not create enough work or “dynamic
force” to expel the liquid out of the orifice.
4.4 Conclusion
Piezoelectric inkjet print head was successfully fabricated by MEMS processing.
The piezoelectric properties were maintained after a lot of fabrication steps. The
existence of the motion of PIPH actuator membrane as well as the movement of liquid
inside microchannel of PIPH structure exhibited the reality of the fabrication of
piezoelectric MEMS inkjet. Although the ejection of liquid could not happened with
current design of PIPH (InkjetVer2), the successful fabrication and its good mechanical
43
properties played an important role in confirming the simulation results and
standardizing the process for a new design (InkjetVer3), which promises the possibility
of mircrodroplet generation.
44
4.5 Rerefences
[1] J. Priest, E. Jacobs, C. Smith, Jr., P. DuBois, B. Holt, and B. Hammerschlag, J.
Microcircuits Electron. Packag, 17, 219–227 (1994).
[2] D. J. Hayes,W. R. Cox, and D. B. Wallace, SPIE Micromachining &
Microfabrication Conf, 22–25 (2001).
[3] G. Duthaler, Master’s thesis, Massachusetts Institute of Technology, Cambridge
(1995).
[4] D. J. Hayes, D. B. Wallace, and M. T. Boldman, ISHM. (1992).
[5] D. J. Hayes,W. R. Cox, and M. E. Grove J. Electron. Manufact, 8, 209–216 (1998).
[6] J. Heinzl and C. H. Hertz, Advances in Electronics and Electron Physics, 65, 91–171
(1985).
[7] Jun-Kyu Paik, Sanghun Shin, Sun-Woong Na, Nae-Eung Lee and Jaichan Lee,
Ferroelectrics, 69, 383-390 (2005).
[8] Caroline S. Lee, H.J. Nam, Y.S. Kim, W.H. Jin and J.U. Bu, J. Korean Phys. Soc, 45,
227 (2004).
[9] Sanghun Shin, Jun-kyu Paik, Nae-eung Lee, Jaichan Lee, Jun-shik Park and Hyo-
derk Park, J. Korean Phys. Soc, 46, 292-295 (2005).
[10] Minhee Yun, J. Korean Phys. Soc, 37, 605~610 (2000).
45
Fig. 4-1. Schematic of piezoelectric inkjet print head structure (side view): (a) Inkjet
version 1 and (b) Inkjet version 2 with the modified nozzle shape at locations marked 1
&2.
Fig. 4-2. Masks used for fabrication of PIPH : M1-M6 (wafer 1) and M7- M10 (wafer2).
46
Fig.4-3. Fabrication process flow of PIPH: (a) wafer 1-actuator and chamber and (b)
wafer 2-channel and nozzle. Both wafers are bonded by Eutectic bonding method.
(a) Actuator and chamber (b) Channel and nozzle
47
Fig. 4-4. SEM and optical micrographs of the fabricated PIPH structure.
Fig.4-5. Electrical properties of PIPH actuator membrane: (a) polarization-electric field
(P-E) hysteresis loops at final step (Pr~18 uC/cm2) and (b) fundamental resonant
frequency (membrane size was over-etched 10%-20% (330 ~ 360 um) by DRIE, 300
um-wide membrane fabricated by wet etching had f~ 330 kHz, agreed with f ~ 1/a2).
48
Fig. 4-6. Displacement of PIPH actuator membrane (membrane size was over-etched
10%-20% (330 ~360 um) by DRIE): (a) simulation 0.77~0.112 um/V and (b)
experiment 0.098 um/V.
Fig. 4-5. Preparing for ejection test: (a) 4-inkjet heads on 1 cell and (b) PCB-wire
bonding and tube attachment.
49
Fig. 4-6. Ejection testing by high speed digital camera system.
Fig. 4-7. Meniscus vibration under an applied voltage of 10V-40 kHz.
50
CHAPTER 5. CONCLUSION AND SUGGESTION
5.1 Conclusion
Simulation, fabrication and characterization of piezoelectric MEMS inkjet print
head have been investigated. Total analysis of the PIPH, including actuator performance
characteristics and microdroplet generation, was performed in the simulation work with
the aid of numerical tools (i.e., FEMLAB, CFD-ACE+). Basic performance
characteristics of a work-producing PIPH actuator (i.e., the maximum actuation
displacement, maximum actuation force and limited driving frequency (first resonant
frequency)) were analyzed in details (chapter 2). Microdroplet generation and
influences on it (such as effects of driving characteristics, fluid properties and
geometrical parameters) were also considered carefully (chapter 3). The fabrication of
the PIPH was carried out using MEMS processing. And the characterization of the PIPH
was employed to confirm the simulation results as well as standardize the fabrication
processes (chapter 4). The review of the simulation and fabrication offers a good
guideline and an effective description in designing piezoelectric MEMS inkjet print
head with possibility of droplet generation and high quality printing.
5.2 Suggestion (new design)
Total analysis of the PIPH has been investigated during this thesis. A new design
(InkjetVer3) is suggested as an candidate which promises good performance
characteristics of PIPH actuator and possibility of mirodroplet generation. InkjetVer3
can be fabricated from three silicon wafers. Some main components (with indicated
geometrical parameters) of InkjetVer3 are an actuator membrane with size of 600 um,
two chambers with ratio of relative chamber size of 0.5 (300 um/600 um), a multi-
diffuser microchannel with the minimum size of 30 um, a nozzle with pyramidal inlet
and cylindrical outlet (diameter of 30 um) and a reservoir with size of 600 um. Model of
InkjetVer3 and masks used to its fabrication are shown in Fig. 5-1 and Fig. 5-2,
respectively. Fabrication of InkjetVer3 has been proceeding.
51
Fig. 5-1. Model of InkjetVer3 (3-silicon wafers).
Fig. 5-2. Masks used for fabrication of InkjetVer3.
52
Appendix A. Python Source Script for simulation of microdroplet generation
(effects of driving characteristics and fluid properties)
# This file was generated by CFD-GEOM
import GPoint
import GCurve
import GSurface
import GLoop
import GEdge
import GFace
import GFilament
import GBlock2D
import GBlock
import GEntity
import GManip
import GGrid
import GUnstruct
import GInterface
# Set Geometric Precision
GEntity.SetPrecision ( 1E-006 ) a = 300
GEntity.CreateParameter (globals (), 'a') b = 360
GEntity.CreateParameter (globals (), 'b') c = 135
GEntity.CreateParameter (globals (), 'c') d = a-2*c
GEntity.CreateParameter (globals (), 'd') e = 226+14
GEntity.CreateParameter (globals (), 'e') f = 1.2*b
GEntity.CreateParameter (globals (), 'f') cgrid=15 dgrid=8 ggrid=25 egrid=20 fgrid=int(egrid*f/b)
geom_point1 = GPoint.Create (0, 0, 0)
geom_point2 = GPoint.Create (a, 0, 0)
geom_point3= GPoint.Create (c, 0, 0)
geom_point4 = GPoint.Create (c+d, 0, 0)
geom_point5 = GPoint.Create (0, b, 0)
geom_point6= GPoint.Create (a, b, 0)
geom_point7= GPoint.Create (c, b, 0)
geom_point8= GPoint.Create (c+d, b, 0)
geom_point9= GPoint.Create (0, b+e, 0)
geom_point10= GPoint.Create (a, b+e, 0)
geom_point11= GPoint.Create (c, b+e, 0)
geom_point12= GPoint.Create (c+d, b+e, 0)
geom_point13 = GPoint.Create (0, b+e+f, 0)
geom_point14 = GPoint.Create (a, b+e+f, 0)
geom_point15 = GPoint.Create (c, b+e+f, 0)
geom_point16 = GPoint.Create (c+d,b+e+f, 0)
geom_curve1 = GCurve.CreateThroughPoints (geom_point1, geom_point3)
geom_curve2 = GCurve.CreateThroughPoints (geom_point3, geom_point4)
geom_curve3 = GCurve.CreateThroughPoints (geom_point4, geom_point2)
geom_curve4 = GCurve.CreateThroughPoints (geom_point2, geom_point6)
geom_curve5 = GCurve.CreateThroughPoints (geom_point6, geom_point8)
geom_curve6 = GCurve.CreateThroughPoints (geom_point8, geom_point7)
geom_curve7 = GCurve.CreateThroughPoints (geom_point7, geom_point5)
geom_curve8 = GCurve.CreateThroughPoints (geom_point5, geom_point1)
53
geom_curve9 = GCurve.CreateThroughPoints (geom_point7, geom_point11)
geom_curve10 = GCurve.CreateThroughPoints (geom_point11, geom_point12)
geom_curve11 = GCurve.CreateThroughPoints (geom_point12, geom_point8)
geom_curve12 = GCurve.CreateThroughPoints (geom_point12, geom_point10)
geom_curve13 = GCurve.CreateThroughPoints (geom_point10, geom_point14)
geom_curve14 = GCurve.CreateThroughPoints (geom_point14, geom_point16)
geom_curve15 = GCurve.CreateThroughPoints (geom_point16, geom_point15)
geom_curve16 = GCurve.CreateThroughPoints (geom_point15, geom_point13)
geom_curve17 = GCurve.CreateThroughPoints (geom_point13, geom_point9)
geom_curve18 = GCurve.CreateThroughPoints (geom_point9, geom_point11)
#d -gird
geom_edge1 = GEdge.CreatePowerLaw (geom_curve2,dgrid, 1.000000, 1)
geom_edge2 = GEdge.CreatePowerLaw (geom_curve6, dgrid, 1.000000, 1)
geom_edge3 = GEdge.CreatePowerLaw (geom_curve10, dgrid, 1.000000, 1)
geom_edge4 = GEdge.CreatePowerLaw (geom_curve15, dgrid, 1.000000, 1)
#c-grid
geom_edge5 = GEdge.CreatePowerLaw (geom_curve1, cgrid, 1.000000, 1)
geom_edge6 = GEdge.CreatePowerLaw (geom_curve3, cgrid, 1.000000, 1)
geom_edge7 = GEdge.CreatePowerLaw (geom_curve7, cgrid, 1.000000, 1)
geom_edge8 = GEdge.CreatePowerLaw (geom_curve5, cgrid, 1.000000, 1)
geom_edge9 = GEdge.CreatePowerLaw (geom_curve12, cgrid, 1.000000, 1)
geom_edge10 = GEdge.CreatePowerLaw (geom_curve18, cgrid, 1.000000, 1)
geom_edge11 = GEdge.CreatePowerLaw (geom_curve14, cgrid, 1.000000, 1)
geom_edge12 = GEdge.CreatePowerLaw (geom_curve16, cgrid, 1.000000, 1)
#b-grid
geom_edge13 = GEdge.CreatePowerLaw (geom_curve8, bgrid, 1.000000, 1)
geom_edge14 = GEdge.CreatePowerLaw (geom_curve4, bgrid, 1.000000, 1)
#e-grid
geom_edge15 = GEdge.CreatePowerLaw (geom_curve9, egrid, 1.000000, 1)
geom_edge16 = GEdge.CreatePowerLaw (geom_curve11, egrid, 1.000000, 1)
#f-grid
geom_edge17 = GEdge.CreatePowerLaw (geom_curve17, fgrid, 1.000000, 1)
geom_edge18 = GEdge.CreatePowerLaw (geom_curve13, fgrid, 1.000000, 1)
#meshing region 1
geom_face1 = GFace.Create
([geom_edge5,geom_edge1,geom_edge6],[geom_edge8,geom_edge2,geom_edge7],geom_edge14,geom_
edge13)
geom_block2d1 = GBlock2D.Create2D (geom_face1)
#meshing region 2
geom_face2 = GFace.Create (geom_edge2,geom_edge15,geom_edge16,geom_edge3)
geom_block2d2 = GBlock2D.Create2D (geom_face2)
#meshing region 3
geom_face3 = GFace.Create ([geom_edge10,geom_edge3,geom_edge9],geom_edge18,[geom_edge11,_
_geom_edge4,geom_edge12],geom_edge17)
geom_block2d3 = GBlock2D.Create2D (geom_face3)
GInterface.DTFWrite_2d ('VOF.DTF')
54
Appendix B. Pattern conditions for fabrication of Inkjetver2
AOE (PZT, BE), RIE (SiNx)
- PR AZ1512 spin coating 500rpm/5’’, 2000 rpm/35’’(~2um)
- Soft bake: oven 110oC, 3 min
- Exposure: 14 sec
- Develop: ~ 1min
- Post bake: oven 110oC, 1 min
Lift-off (Ta/Pt TE, Key 1)
- PR AZ1512 spin coating 500rpm/5’’, 3500 rpm/35’’(~1.5um)
- Soft bake: oven 110oC, 3 min
- MCB : 3 min
- Bake : oven 110oC, 2 min
- Exposure: 14 sec
- Develop: ~ 1min
DRIE (chamber, diff, nozzle)
- PR AZ9260 spin coating 500rpm/5’’,1000rpm/40’’ (15um)
- Bake: hot plate 110oC, 2 min
- Exposure : 12 mW/cm2, 180 sec (STD)
- Develop : AZ500MIF, ~5-6 sec
- Post bake: 1 min (Oven)
55
Appendix C. Dry etching conditions
Advanced Oxidation
Etcher (AOE)
PZT (500 nm) Pt (1500 Å), Ta (200 Å
Gas CF4 – 5 sccm
Ar – 20 sccm
C4F8 – 5 sccm
C2H4 – 10 sccm
He – 15 sccm
Ar – 10 sccm
Power Top power – 1200 W
Bottom power - 400 W
Bias – 400W
Top power – 800 W
Bottom power- 500 W
Bias – 500W
Pressure 5 mTorr 3 mTorr
Time 3 min 10 sec 1 min 20 sec
RIE (SiO2, SiNx) DRIE (Si)
Gas O2 – 4 sccm
CF4CHF3 – 36 sccm
C4F8 - 150 sccm (passivation)
O2 – 30 sccm
SF6 – 300 sccm
He - 9790 mTor (cooling)
Power 190-230 W
(RF generator)
Top power – 1200 W
Bottom power - 400 W
Bias – 400W
Pressure 40 mTor 45 mTor (SF6-O2)
18 mTor (C4F8)
Etching rate 480 Å/min 60 um/min
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