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1. DESIGN & FABRICATION OF ELECTROSTATIC
INKJET HEAD USING SILICON
MICROMACHINING TECHNOLOGY

2. Contents:
• Introduction
• Scope
• Objective
• Design & Simulation
• Fabrication
• Experimental Set up
• Conclusion
• References
2

3. INTRODUCTION
• Ink-jet printing technique is very attractive for forming micro-size
patterns for flat panel displays (FPDS),
• Printing circuit board (PCB),
• Semiconductor,
• Biological,
• Optical,
• Sensor devices
• due to its low temperature process, direct writing, and rapid
photolithography process
3

4. • The inkjet printing mechanisms has been used are
• Thermal method
• Piezoelectric method
• Electrostatic method
INTRODUCTION Cont..
4

5. • Thermal and piezoelectric inkjet printing are based on pushing
out the liquid in a chamber through a nozzle by actuators, such
as thermal bubble and piezoelectric actuators.
• Thermal bubble actuator has the heat problem when the array
of nozzle make in a large area
• Piezoelectric actuator is difficult to make droplet smaller than
nozzle size . The head consisting of piezoelectric or a heater
element has the disadvantage of the complex structure
INTRODUCTION Cont..
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6. • Electrostatic inkjet are based on protruding through an orifice
induced by an electric field forms a meniscus called the Taylor
cone.
• Also it can separate from the meniscus tip as fine droplets
much smaller than the orifice diameter.
• Electrostatic inkjet has a greater advantage than piezoelectric
inkjet and thermal inkjet in the ability to eject fine droplets and
in the simplicity of structure
INTRODUCTION Cont..
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7. SCOPE
This paper discusses about the design and fabrication of
optimized geometry structure of Electrostatic Inkjet Head.
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8. Objective
To design and fabricate inkjet heads to achieve an effective
micro dripping ejection, to provide concentrated electric force
on nozzle and pole tip.
DESIGN & SIMULATION
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9. • They designed and fabricated the following electrostatic
inkjet heads,
• electrostatic inkjet heads, hole type
• electrostatic inkjet heads, Pole type
Hole type Inkjet Head Pole type inkjet head
DESIGN & SIMULATION
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10. • This structure consists of
1. Reservoir,
2. Nozzle
3. Conductive pole to concentrate electric field.
DESIGN & SIMULATION Cont…..
Hole type Inkjet Head
Hole type Inkjet Head
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11. Schematic of the proposed Pole type inkjet head
electrostatic inkjet head.
1. This structure consists of glass electrode part
2. Nozzle part with a reservoir.
Fig. 3. The structure of the proposed pole type electrostatic inkjet
head.
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12. Δ .Є Δ.Ф = -þ
Ē= - ΔФWhere
• Ē -electric field vector
•-Ф- electric potential
• Є- permittivity
• þ - charge density
• Micro droplet is formed from the liquid meniscus due the
induced electric field.
• The electric field is obtained by solving the following
governing equations. (These equations are solved by FEM
method)
DESIGN & SIMULATION Cont…
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13. • The inkjet head utilizes electrostatic forces that act between
electrode and nozzle tip.
• The electrostatic forces are created when a voltage is applied
electrode and head bottom.
• The surface of the inkjet head becomes wet with liquid after
applying an electric field.
• Then charged liquid is separated from the inkjet head tip as
fine droplets.
Mechanism of Spray formation
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14. • When the force induced by an electric field on the inkjet head
tip is stronger than the resultant force of
• surface tension,
• ink viscosity and
• conductivity,
• The meniscus called Taylor cone is generated and fine droplets
is separated from the head by Coulomb force.
Mechanism of Spray formation Cont..
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15. Need For Simulation
• In order to verify effect of geometry shape, we simulate
electric field intensity according to the head structure.
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16. Electric Field Simulation of a Hole type inkjet head
when DI water is used
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17. Electric Field Strength Vs. Nozzle height of a Pole type inkjet head
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18. Result of the Electric field simulation of the hole type inkjet head
Electric field simulation of the hole type inkjet head showed
the following results
• The electric field strength increases linearly with increasing
height of the micro nozzle.
• Also, as the height of the nozzle increases, the electric field
along the periphery of the meniscus can be more concentrated.
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19. • In order to find optimal structure and demonstrate
concentration of electrostatic force at the pole edge, pole type
inkjet head is simulated using FEMLAB.
19

20. Result of the electric field simulation used the DI water as the liquid
solution.
20

21. Result of the Electric field simulation of the hole type inkjet head
• The structure of the nozzle inner diameter = 80 μm
• Thickness, 20 μm
• Pole diameter are, and 40 μm,
• The pole height is 50 μm.
As the result, the concentration of electrostatic force was shown
at the conductive pole edge.
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22. FABRICATION
• Electrostatic inkjet head consist of 2 layers
• Glass top layer
• Silicon bottom layer.
• Fabrication is done using
• thermal-oxidation
• silicon micromachining technique .
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23. Fabrication process Cont…
• SiO₂ layer on silicon wafer.
• Oxide(deep Si etch mask)
patterning and deep Si etching.
• Reservoir patterning on the
bottom silicon wafer.
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24. • Deep Si etching.
• Deep Si etching for pole
formation.
• SiO₂ removal by HF solution.
Fabrication process Cont…
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25. Fig. 7. Fabrication Process : (a) SiO2 layer on silicon wafer, (b)
Oxide(deep Si etch mask) patterning and deep Si etching, (c)
reservoir patterning on the bottom silicon wafer, (d) Deep Si
etching, (e) Deep Si etching for pole formation, (f) SiO2 removal
by the HF solution.
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26. Photomicrograph of Hole & Pole type nozzle
Hole type Nozzle
Pole type Nozzle
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27. SEM Images of Nozzle
Hole type Nozzle
Pole type Nozzle
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28. EXPERIMENTAL SET UP
Fig. 11. The schematic of the experimental system.
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29. • This system consists of
• The head system,
• High speed camera,
• Micro syringe pump,
• Power,
• Computer
EXPERIMENTAL SET UP Cont….
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30. • To visualize droplet ejection. high speed camera (IDT XS-4)
with a micro-zoom lens and a halogen lamp was used
• The high speed camera can image 5000 frames per second at a
512 x 512 resolution with a micro-zoom lens and a LED light
source were used.
• .
EXPERIMENTAL SET UP Cont….
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31. • A high voltage power supply (maximum voltage of 3.0 kV)
was used with a relay switch to control electrostatic field.
• The liquid have been supplied to the nozzle with constant
velocity by micro syringe pump and the voltage has been
provided to the upper electrode
EXPERIMENTAL SET UP Cont….
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32. • The jetting mode depends on
• the applied voltage,
• the flow rate,
• liquid properties such as
• Electric conductivity,
• surface tension,
• and viscosity.
EXPERIMENTAL SET UP Cont….
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33. • To make an experiment on the micro ejection of the
electrostatic inkjet head, the conductive liquid of the mixture
of D2O, SDS, and micelle-suspended Carbon Nano Tube (5
%wt SWNT) solution is used as ink.
• The outer diameter of the nozzle is 50 μm
• The gap between the upper electrode
• The nozzle orifice is set about 800 μm.
• The constant flow rate by a micro pump is kept at
0.1 μl/min.
EXPERIMENTAL SET UP Cont….
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34. Results
• When flow rate is made constant at 0.1µl/min and 1.7KV is
supplied, a droplet 80µm is obtained.
Fig. 12. Images taken with high-speed camera showing eve
micro ejection from nozzle of inkjet head.
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35. • When flow rate is made constant at 0.1µl/min and the supplied
voltage is kept at 2.5 kV. The droplet diameter ejected from the
nozzle tip is measured about 10 μm.
Results Cont……
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36. Conclusion
• This paper discussed about the design and fabrication of the
following electrostatic inkjet heads.
• electrostatic inkjet heads hole type
• electrostatic inkjet pole type
• It was fabricated using thick-thermal oxidation and silicon
micromachining technique such as
• the deep reactive ion etching (DRIE)
• chemical wet etching process.
• The fabrication process used is very simple and reproducible..
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37. REFERENCES
• Design and Fabrication of Electrostatic Inkjet Head using Silicon Micromachining
Technology Youngmin Kim*, Sanguk Son*, Jaeyong Choi*, Doyoung Byun**, and Sukhan
Lee* JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.8,
NO.2, JUNE, 2008
• Yuji Ishida, Kazunori Hakiai, Akiyoshi Baba and Tanemasa Asano, “Electrostatic Inkjet
Patterning Using Si Needle Prepared by Anodization,” Japanese Journal of Applied
Physics, Vol. 44, No. 7B, pp. 5786-5790, July 2005.
• S. Lee, D. Byun, S. J. Han, S. U. Son, Y. J. Kim, H. S. Ko, “Electrostatic Droplet
Formation and Ejection of Colloid,” MHS, July 31, 2004.
• S.U.Son, Y.M.Kim, J.Y.Choi, S.H.Lee, H.S.Ko, and D.Y.Byun, “Fabrication of MEMS
Inkjet Head for Drop-on-Demand Ejection of Electrostatic Force Method,” Trans. KIEE.
Vol.56. August, 2007.
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