Online proceedings - EDA Publishing Association

fibers which define the electric contact of touch sensors were
formed in deformable fabric structure and were easily
changed. Thus, more stable touch sensor has been required.
Moreover, for the fabric type of sensor, copper wires are
relatively hard to weave and more flexible material is
preferable. In this study, we propose large-area and surface
capacitive type of touch sensors for stable sensing
mechanism (figure 1). The sensors detect the induced
capacitances between fibers and human fingers and the gap
between fibers does not affect the sensitivity (figure 2). The
surface capacitance detection method is utilized for iphone
or other portable systems for detecting human input with
fingers. As a sensor structure, we proposes the conductive
polymer of PEDOT:PSS and dielectric film of UV-curable
adhesive are coated on the fibers and the resultant fibers are
woven for forming sensor fabric. Since conductive polymer
has the advantage of high flexibility, it is highly compatible
to fabric. To solve the problem of the conventional MEMS
process on the large area and high cost, a die-coating method
to coat PEDOT:PSS and UV-curable adhesive on fibers is
proposed, as a continuous coating process for long fibers.
The solutions containing PEDOT:PSS and UV curable
adhesive are put in the die and fibers travels through the die,
coating the polymers on the fibers. And finally, coated fibers
are woven with the automatic looming machines. Then, the
fabricated sensor is examined on the sensitivity to sense the
touch input.
11-13 May 2011, Aix-en-Provence, France
Figure 3. Fabrication process of large area touch sensors. (1)
die-coating of PEDOT:PSS layer on nylon fiber, (2) Die-coating of
UV-curable adhesive, (3) Plain weaving of resultant fibers with
automatic looming machines
Ⅱ. SENSOR DESIGN AND FABRICATION PROCESS
Figure 2. Structure of fabric touch sensors and mechanism of surface
capacitance type of touch sensors. Sensors detect capacitance change
between fibers and fingers because human fingers are conductive and
work as an electrode. The capacitor is formed between conductive film
on fibers and human fingers.
The sensor fabrication consists of reel to reel coating process
of conductive and dielectric polymer with die-coating and
weaving the resultant fibers (figure 3). The sensor structure
where conductive polymer and dielectric films is coated
onto the fibers and they are woven as warps and wefts. The
fibers we used are 470 μm-diameter nylon, which is
commercially available fishing line. Conventional fibers are
manufactured with a standard of g/km and are not easy to
apply to certain diameter dies, but fishing line is
manufactured with a standard diameter and it is easy to fit
the diameter of the die to the diameter of the fibers
(Standards of the Japan Fishing Tackle Manufacturers
Association). Conductive polymer of PEDOT:PSS is coated
on the fiber and its thickness is around 300 nm because most
of PEDOT:PSS electrodes are coated with the thickness of
100 nm. The dielectric layer is 10 μm thick UV-adhesive
polymer. The touch sensors’ spatial density is a pitch of 5 cm.
The areas except for the PEDOT:PSS-coated fibers are filled
with 205 μm diameter pristine nylon fibers to retain the
shape of the fabric. The fabricated fibers are woven in the
manner of plain weaving whose structure is simplest. The
fibers are crossed alternately. The method to determine the
pushed point is based on the detection of capacitance
changes of all fibers. After detecting the pushed vertically
placed fiber and horizontally placed fiber, the crossed point
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