Online proceedings - EDA Publishing Association

was the pushed place.
11-13 May 2011, Aix-en-Provence, France
Ⅲ. CHARACTERIZATION OF FABRICATION PROCESS
The die-coating system and weaving system were
characterized. In the die-coating system, we established a
system of die-coating to form PEDOT:PSS and UV-curable
adhesive-coated fibers that conformed to two specifications
including length and film thickness. The system we
developed, consisted of a winding machine to continuously
transfer fibers, a die to coat PEDOT:PSS, and a heater or UV
light to dry the solvent. The system was required to be tested
to check whether it could form fibers that met the
specifications. First, the die’s diameter for defining the film
thickness is needed to be tuned. The thickness of
PEDOT:PSS should be several hundreds of nm while that of
UV-curable adhesive should be several micrometers.
Second, to make fibers that were hundreds of m-long, the
traveling speed of the fiber had to be considered in terms of
throughput. If the traveling speed was as slow as the speed
with sputtering, which is 30–40 centimeters of chamber size
per 4–5 h for one process duration, it took hundreds of
processes and thousands of hours to coat 100 m-long fibers.
Therefore, a traveling speed of several m/min. was required
to complete a long fiber. In fast-speed deposition, a speed
that was too fast did not enable the wet PEDOT:PSS solution
to follow the fiber. The maximum speed to form a uniform
film was defined, tested, and confirmed so that it satisfied
requirements. Finally, long fibers were actually fabricated
under the defined conditions for the diameter of the die and
the maximum traveling speed.
The die-coating system which was used is shown in figure
4. The machine at both sides is a winding machine
(Factory-Automation Electronics Inc.) for moving fibers
from left to right. To prevent fibers from hanging loosely,
they are transferred under a certain tension by using bobbins
with pressure sensors. The machine is operational at speeds
of up to 50 m/min. The machine in the middle has a die and a
heater. The die consists of a PEDOT:PSS or UV-curable
adhesive reservoir and a nozzle for coating them onto the
fibers. Because the die surrounds fibers with a certain gap,
the wet film was coated on all surfaces of the fiber. The die
had holes in the cap and nozzle. The diameter of the hole in
the cap was 1 mm while those on the nozzle, which were
larger than the 470-μm fiber diameter and ranged from 500
to 980 μm were prepared through machining provided by the
Daiichi-Daiya Company. The resultant gap between fibers
and dies ranges from 0-300μm. The film thicknesses of the
wet PEDOT:PSS and UV-curable adhesive are defined by
the gap between the diameter of the nozzle and that of the
fiber. The thickness of PEDOT:PSS was tuned from 0 to 500
nm. The thicknesses were proportional to the gaps, but the
large gaps induce unevenness of the coated PEDOT:PSS
film. Therefore, the thickness below 200 nm is preferable for
offering even film. On the other hand, UV curable polymer
was also coated with die-coating system by changing the
dies diameters. The diameters were chaged form 486 to 680
Figure 4. Die-coating system. The both sides are yarn winding
machines which travel fibers from left to the light. In the middle, dies
and heaters or UV light were placed for coating PEDOT:PSS or UV
curable adhesive. In the photograph, PEDOT:PSS was coated. The
dies consists of coating nozzle and reservoir of the coating solution.
Figure 5. The structure of the dies. The coating film thickness is defined by the
gap between nozzle diameter of dies and the diameter of Nylon fiber. The
coated wet film was dried by heater or UV light and the dried thickness was
reduced by evaporating solvent.
μm. The film thickness were tuned from 0 to 45 μm. The
thickness was enough thick because the required thickness is
5 μm. The thicknesses were larger than that of PEDOT:PSS
because the PEDOT:PSS solution contained 99 % of water
solvent and the solid content of PEDOT:PSS was only 1 %
while the solution of UV-curable polymer contains almost
100% solid content.
Fast throughput for coating PEDOT:PSS films is essential
to make long electrode-coated fibers. For fibers that are
more than 100-m long, a traveling speed of at least several
m/min is required. However, a fast traveling speed induced
unevenness in PEDOT:PSS and UV curable adhesive film,
resulting in defects. Defects in the electrodes were
problematic because insensitive areas were formed in the
sensors. To avoid these defects, the maximum traveling
speed was experimentally evaluated. The PEDOT films
were coated with the 680 μm die by changing traveling
speeds in a range from 5 to 50 m/min. The photos of the
films coated in the different traveling speeds were taken. It
was confirmed that the films were even until the speed of 50
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