NOVEL PATTERNING TECHNOLOGY USING AIR-PRESSURE
DISPENSER FOR FABRICATING MICRO-FLUIDIC DEVICES
Toshiyuki Horiuchi, Shinichiro Otsuka, Miyu Ozaki, Ryota Ando and Kazunari Hiraki
Tokyo Denki University, 2-2, Kanda-Nishiki-Cho, Chiyoda-Ku, Tokyo, Japan
Keywords: Air-pressure dispenser, Micro-fluidic device, Micro-fluidic mixer, Micro-beaker, Direct writing,
Image reverse, Thick resist, Flow path.
Abstract: A novel method was developed to easily fabricate micro-fluidic devices with a low cost. It will be especially
useful at preliminary research stages. In the new method, inexpensive commercial air-pressure dispenser
was used. Adopting originally developed “wire nozzles”, it was verified that fine resist patterns with widths
down to 50 μm were successfully delineated. However, because patterns have to be delineated connecting
simple line patterns, it was difficult to delineate trench or hole patterns by painting out a large area.
Moreover, sidewalls of the delineated patterns were not sharp. For this reason, easy image-reverse process
was thought out. In the novel process, opaque liquid patterns were delineated using the dispenser on a thick
negative resist film coated on a substrate, and the resist film was exposed to flood exposure light. As a result,
the resist was sensitized except under the opaque liquid patterns. Therefore, trench or hole patterns
corresponding to the opaque liquid pattern shapes were obtained after developing the resist. Replicated thick
resist patterns have sharply-cut sidewalls, and will be durable for micro-fluidic paths or vessels of bio-
devices.
1 INTRODUCTION
Micro-reactors are useful for mixing a small quantity
of bio-medical liquid and chemical reagents. Even
simple micro-beakers without fluid paths are also
effective, because liquids are often sufficiently
mixed by leaving them for a time or shaking
appropriately. For this reason, various methods for
fabricating micro-reactors and micro-beakers are
proposed. Generally speaking, micro-reactor
trenches and micro-beaker holes are separately
fabricated on substrates in advance, and they are
capped or sealed afterwards. It is easiest as the seal
to put lid plates on the trenches and holes and bind
them. If the reactor or beaker materials are elastic,
the trenches and holes are easily but completely
sealed for the practical use. Such structures are
conveniently fabricated by patterning in thick films
of resists such as negative SU-8 (MicroChem)
(Horiuchi, T; Watanabe, H., Hayashi, N., Kitamura,
T., 2010) (Tsai, N. C.; Sue, C. Y., 2006), EPON
(Hexion Specialty Chemicals) (Yang, R.; Soper, S.
A., Wang, W., 2007) and positive poly-methyl-
methacrylate (PMMA) (Nugen, S. R.; Asiello, P. J.,
Connelly, J. T., Baeumner, A. J., 2009) using
lithography, or replicating the lithographically
fabricated resist patterns to plastic materials such as
Poly-dimethyl-siloxane (PDMS) (Lien, K. Y.; Liu, C.
J., Lee, G. B., 2008) (Casquillas, G. V.; Bertholle, F.,
Berre, M., Meance, S., Malaquin, L., Greffet, J. J.,
Chen, Y., 2008).
However, only a few amounts of micro-reactors
and micro-beakers are required at preliminary
research stages. In addition, required pattern sizes
are as large as around 100 μm. Accordingly,
expensive lithography tools such as steppers and
mask aligners are unsuitable from a view point of
costs.
Moreover, to decide the best features, structures
and sizes of the required devices, various candidates
should be compared in the research. However,
reticles and masks are also expensive and it takes at
least a few days to prepare them.
Under these situations, direct writing using a
dispenser is expected as a new patterning technology
for making a breakthrough. Here, a newly developed
process is investigated for fabricating various micro-
fluidic patterns using an air-pressure dispenser with
special nozzle (Otsuka, S; Horiuchi, T., 2010).
114
Horiuchi T., Ohtsuka S., Ozaki M., Ando R. and Hiraki K..
NOVEL PATTERNING TECHNOLOGY USING AIR-PRESSURE DISPENSER FOR FABRICATING MICRO-FLUIDIC DEVICES.
DOI: 10.5220/0003125701140119
In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2011), pages 114-119
ISBN: 978-989-8425-37-9
Copyright
c
 2011 SCITEPRESS (Science and Technology Publications, Lda.)

2 EFECTIVENESS OF SIMPLE
REACTORS MADE BY RESIST
Micro-flow-paths fabricated by patterning in thick
resist are useful for creating various bio-fluidic
devices such as micro-mixers, reactors and beakers,
if they are suitably capped and sealed.
Very deep trench patterns with 50-400 μm
depths and steep sidewalls perpendicular to the
substrates are certainly formed if the negative resist
SU-8 is used. Besides, the resist patterns have
favourite elasticity to seal the flow paths formed
between the patterns only by capping them with a
flat lid and moderately binding the substrate and the
lid using screws. The elastic resist film also acts a
roll of sealant. For this reason, micro-fluidic devices
are easily fabricated by the composition shown in
Fig. 1, for example (Horiuchi, T., Watanabe, H.,
Hayashi, N., Kitamura, T.2010).

(c)Mixedfluids.
(b)Totaloutlook.
500
μ
m
10mm
Outlet
Inlet

(e)Outlethole.(d)Inletholes.
100μm
Figure 1: Micro-fluidic mixer simply fabricated by sealing
SU-8 flow-paths binding a flat lid with screws.
SU-8 is mainly composed of epoxy resin, and
convenient to use as the material for bio-fluidic
devices because the epoxy resins are chemically
stable and do not react with most of the body fluids.
Micro-fluidic devices are often fabricated by
replicating original SU-8 mould patterns to PDMS.
In the preliminary research stages, however, the
image reverse replication process to PDMS is
annoying, and not always necessary if the original
SU-8 patterns are easily fabricated with a low cost,
because only a few numbers of same micro-fluidic
devices are required in such research levels. In
addition, size parameters such as trench width,
depth, path length and shape are often changed to
find out the best feature of micro-fluidic devices. To
correspond to such situations, a simple and low-cost
fabrication method of micro-fluidic devices was
investigated using an air-pressure dispenser.
3 PATTERN DELINEATION
USING A DISPENSER
Because only a few numbers of same devices are
necessary at the preliminary research stages, photo-
lithography using a high-grade expensive stepper or
a mask aligner is inexpedient. In addition, reticles
and masks are also expensive, and the patterns on
them cannot be revised or changed after once they
are delivered, unless they are fabricated again.
Moreover, turn-around time (TAT) from the pattern
design to delivery is not short. It takes at least three
days to obtain the ordered reticles or masks.
On the other hand, liquid dispenser systems have
been gradually upgraded and inexpensively available.
For this reason, various researches have been
vigorously executed. (Otsuka, S; Horiuchi, T., 2010)
(Fakhfouri, V.; Mermoud, G., Kim, J. Y., Martinoli
A., Brugger, J., 2009) (
Ohigashi, R.; Tsuchiya, K., Mita,
Y. Fujita, H.,
2008) (Ishida, Y.; Sogabe, K., Kai, S.,
Asano, T.
, 2008) (Murata, K., 2003).
Generally speaking, the minimum pattern size
required for a micro-fluidic device is as large as
around 100 μm, and such large patterns can be
possibly delineated using dispenser systems.
In this research, a commercially available air-
pressure dispenser system (Musashi Engineering,
SHOT mini SL) shown in Fig. 2 was used for the
pattern delineation. As a liquid, positive resist
PMER P-LA900PM (Tokyo Ohka Kogyo) with
viscosity of approximately 1500 mPa
ּ
◌s at 22°C was
used at first, and the resist was dispensed controlling
Binding screw
Micro-tube
Hol
Inlet
Outlet
Lid
Ta
pp
ed screw
Resist
(
SU-8
)
Flow
p
at
h
Substrat
NOVEL PATTERNING TECHNOLOGY USING AIR-PRESSURE DISPENSER FOR FABRICATING
MICRO-FLUIDIC DEVICES
115

the pressure by an air-pressure control unit (Musashi
Engineering,
ML-5000XⅡ).

Dispenser
Airpressu
re
Y‐stage
Z‐stage
X‐stage
controller
Y
X
Z
Figure 2: Air-pressure dispenser system used for the
research.
It was difficult to delineate patterns with a width
of around 100 μm when the commercial system was
used as it was. However, applying a new idea, fine
patterns with a uniform width were successfully
delineated. Specifically speaking, a fine wire was
inserted in the dispenser nozzle, and the tip of the
wire was adjusted to slightly stick out of the nozzle,
as shown in Fig. 3. As a result, various fundamental
patterns were successfully delineated.
Figure 4 shows examples of line patterns
delineated on a silicon wafer with a speed v of 10
mm/s, a wire height h of 10 μm and a stick-out
length s of 30 μm. The patterns have very smooth
linear edges, and the widths are almost uniform.
The pattern widths were controllable by
changing the air-pressure for dispensing the resist
and the delineation speed v, which was controlled by
changing the driving speeds of X and Y stages, as
shown in Fig. 5. Because both stages were driven by
pulse motors, the speeds were accurately controlled
by inputting appropriate pulse rate.

100μm

Substrat
s
h
Resist
Stainless
steelwire

Conventional
nozzle
Figure 3: Newly developed wire nozzle.

100μm
20kPa
40kPa
60kPa
Air
Delineated
80kPa
100kPa
Figure 4: Delineated line patterns.
0
50
100
150
200
250
300
0 50 100 150 200 250
塗
布
圧力
[
kPa
]
線幅
[μm]
描画速度
: 10 mm/s,
塗布高さ
: 30 μm
描画速度
: 15 mm/s,
塗布高さ
: 30 μm
描画速度
: 20 mm/s,
塗布高さ
: 30 μm
v=10mm/s
v=15mm/s
v=25mm/s
h=30μm
s=30μm
0
50
100
150
200
250
300
Patternwidth(μm)
50
100 150 200 2500
Air
p
ressure
(
kPa
)

Figure 5: Pattern width dependence on scan speed and air
pressure.
The width did not almost depend on h and s
especially when low air-pressures were supplied, as
shown in Figs. 6 and 7. The minimum line pattern
width was approximately 50 μm.
Circularly curved patterns are also obtained, as
shown in Fig. 8. Although the fine pattern edges
were slightly waved, almost smooth edges were
obtained for widths of more than 100 μm.
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250
塗布圧力
[kPa]
線幅
[μm]
10μm
30μm
50μm
50
100 150 200 2500
0
100
200
300
400
Airpressure(kPa)
Patternwidth(μm)
h=10μm
h=30μm
h=50μm
v=10mm/s
s=30μm
Figure 6: Pattern width independence on wire height.
BIODEVICES 2011 - International Conference on Biomedical Electronics and Devices
116

0
50
100
150
200
250
300
350
400
0 50 100 150 200 250
塗布圧力
[kPa]
線幅
[μm]
30μm
50μm
70μm
v
=5mm/s
h=10
μ
m
50
100 150 200 2500
Air
p
ressure
(
kPa
)

s=30μm
s=50μm
s=70μm
100
0
200
300
400
Patternwidth(μm)
Figure 7: Pattern width independence on wire length.
(a)150kPa (b) 100kPa
100 μm 
(c)50kPa
Figure 8: Circularly curved patterns delineated with a
speed v of 5 mm/s, a wire length s of 50 μm and a wire
height h of 30μm. The circular radius is 1 mm.
Next, micro-mixer patterns were actually
delineated under the conditions of h=30
μm, s=50 μm
and ν=10 mm/s at the straight parts and 5 mm/s at the
curved parts
. Figure 9 shows the patterns. Not only
the straight parts, but also the curved parts, cross
point, and end points were successfully delineated.
However, cross sectional profiles of delineated
PMER patterns were flat and round, as shown in Fig.
10. Measured thickness broadly distributed, as
shown in Fig. 11. Such patterns were not directly
available for fabricating micro-flow-paths.
(a)Wholeviewofmicro‐reactorpattern.
1mm
1
2
3
Resist
p
attern
Substrate
A
C
B
D
E

(b)Magnifiedviewofimportantparts.
(v)PartE
(i)PartA
(iii)PartC
(ii)PartB
(iv)PartD
1mm
Figure 9: Micro-mixer patterns of resist PMER P-
LA900PM delineated on a copper-clad plastic substrate
using the air-pressure dispenser.
Resist
Substrat
20 μm
Figure 10: Typical cross section of a pattern delineated by
a dispenser.
60μm
Position(μm)
80μm
Width:120μm
5
4
3
2
1
0
Resistthickness(μm)
‐60 ‐20
0
246
8
‐80 ‐40
Figure 11: Thickness distribution of PMER patterns
delineated using the air-pressure dispenser.
Therefore, a new idea should be thought out for
transforming the flat dispenser patterns to steep and
deep SU-8 patterns easily.
4 NEW PATTERNING PROCESS
Figure 12 shows the novel patterning process using
the air-pressure dispenser for fabricating deep
trenches of micro-fluidic mixer and holes of micro-
beakers with vertical sidewalls into films of SU-8.
(b)Patterndelineation
Opaqueliquid
SU‐8
Substrate
(c)Floodexposure
(d)Development
Developer
(e)Patterning ofSU‐8
ThickSU‐8pattern
(a)CoatingofSU‐8
SU‐8
Substrate
UVlight
Figure 12: Newly developed pattern process.
NOVEL PATTERNING TECHNOLOGY USING AIR-PRESSURE DISPENSER FOR FABRICATING
MICRO-FLUIDIC DEVICES
117

In the new process, thick SU-8 film is coated on
a substrate at first, as shown in (a). Next, patterns are
delineated using the air-pressure dispenser as shown
in (b). In this step, an opaque liquid such as a black
water colour is used for the material to be dispensed.
It is not necessary that the liquid has sensitivity to
exposure light. In addition, because the negative
image patterns of the micro-fluidic devices are
needed, only the delineation of lines, dots, and some
simple figures is required. Next, the substrate with
the patterns is exposed to flood ultra violet (UV)
light as shown in (c). Because the SU-8 film is
partially covered by the opaque liquid patterns, only
the parts under them are not sensitized to the UV
light. The opaque liquid patterns are removed in the
development process, as shown in (d). Through
these processes, trench or hole patterns of micro-
fluidic devices with steep sidewalls are made of
thick SU-8, as shown in (e).
To confirm the principal feasibility of the novel
process, black watercolour dissolved with water was
used as an opaque liquid. They were blended by 1:1
weight ratio. After delineating line patterns on SU-8
film coated on a silicon wafer, the wafer was baked
in an oven for 20 min at 90°C. Next, it was exposed
to UV light using a UV lamp (Sumita Optical Glass,
LS-140S) for 10 s, and developed for 10 min in the
SU-8 developer. A typical cross section of SU-8
pattern is shown in Fig. 13. It was verified that
approximately 100-μm thick SU-8 patterns with
sharp sidewalls were successfully formed. Although
the opaque liquid and the process conditions have
not been optimized, very good prospects for
fabricating micro-fluidic devices were obtained. The
width of the groove shown in Fig. 13 was
approximately 300 μm, and the minimum width
should be reduced down to less than 100μm
hereafter.
Figure 13: SU-8 patterns converted from the dispenser
pattern using the novel image-reverse process.
Total TAT to fabricate a test micro-fluidic device
using the new method was estimated and compared
with the TAT of when the device was fabricated by
the conventional projection or contact exposure
lithography using a reticle or a mask.
Table 1 shows the typical processing time for the
dispenser method. To print thick SU-8 patterns
directly using projection or contact exposure
lithography, a reticle or a mask has to be prepared in
advance. It takes at least 3 days to obtain a reticle or
a mask after sending the order to a mask maker,
even when the patterns are very simple. On the other
hand, patterning using an air-pressure dispenser is
ready at any time if the flow-path design is finished.
Actually effective patterning to delineate favourable
patterns should be carried out after some trials.
However, the time for delineation is short in most
cases. The flood exposure time is comparable with
the time required for the direct lithographic
patterning. Times for the pre-bake and the post
exposure bake are also almost the same with those
for the direct lithographic patterning.
Accordingly, although the time for delineating
patterns using the dispenser is additionally needed,
total TAT is drastically improved from 4 days to 1
day or approximately 8 hours.
Table 1: Typical processing times for the new method.
Process Time
1 Coating of SU-8 3 min/substrate
2 Pre-bake
Hold for slow heating (65ºC) 20 min
Bake (90ºC) 50 min
Slow cool down 2 hr
3 Patterning trial 1 hr
4 Actual delineation 3-10 min
5 UV flood exposure 10 s
6 Post exposure bake
Hold for slow heating (65ºC) 20 min
Bake (90ºC) 50 min
Slow cool down 2 hr
7 Development and rinse 10+2 min
5 CONCLUSIONS
To promote the development of bio-fluidic devices,
novel technology for easily fabricating micro-mixers
and micro-beakers with a low cost was developed. In
the novel method, micro-fluidic device patterns are
delineated using an inexpensive air-pressure
dispenser. After patterns were delineated using an
opaque liquid on a thick SU-8 film coated on a
substrate, they were exposed to UV light. Because
only the parts of SU-8 behind the opaque liquid
BIODEVICES 2011 - International Conference on Biomedical Electronics and Devices
118

patterns were sheltered from the UV light, they were
dissolved during the development. As a result, SU-8
structures with micro-flow-paths or micro-beaker
holes were obtained. The principal feasibility was
verified by the experiments, and very good prospects
for the practical use were obtained.
As future works, a few subjects should be
resolved. Main subject is the optimization of opaque
liquid material and delineation conditions. Although
fine patterns with a width of down to 50 μm were
successfully delineated using a resist PMER P-
LA900PM, patterns with a large width of 200-300
μm were just delineated using the water paint as an
opaque liquid. Considering the difference of
viscosity, parameters of the wire-nozzle such as wire
and nozzle diameters, and delineation conditions
have to be optimized. After enabling to delineate
patterns finer than 100 μm, practical micro-fluidic
devices will be developed.
ACKNOWLEDGEMENTS
This work was partially executed as a subject of
Frontier Research and Development Center, Tokyo
Denki University, and partially supported by a
Strategic Research Foundation Grant for Private
Universities (S0801023) from Ministry of
Education, Culture, Sport, Science, and Technology,
Japan (MEXT).
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