S-O5-5
Large-area synthesis of graphene by plasma CVD and its application astransparent conductive films
プラズマCVDによるグラフェン大面積合成からデバイス試作について
Jaeho Kim, Masato Ishihara, Kazuo Tsugawa, Takatoshi Yamada, Yoshinori Koga,
Masataka Hasegawa, and Sumio Iijima
金載浩, 石原正統，津川和夫，山田貴壽，古賀義紀，長谷川雅考，飯島澄男
National Institute of Advanced Industrial Science and Technology (AIST)
Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
産業技術総合研究所 〒305-8565 茨城県つくば市東1-1-1中央第5Graphene is a potential candidate of transparent conductive films (TCFs) as a replacement for ITO
which is a rare metal. We demonstrate a low-temperature and large-area synthesis technique, which isa key technology for the industrial mass production of graphene, for graphene using an advanced
plasma CVD method. The properties of graphene as TCFs make them suitable for practical electricaland optoelectronic applications, which have been demonstrated by the proper operation of a touch
panel fabricated using the films.

Transparent conductive films (TCFs) are required
for electrical and optoelectronic devices and various
other applications. The most widely used TCF is
indium tin oxide (ITO), which is a rare metal. The
development of alternative materials in order toprevent rising costs and supplement an unstablesupply is required. Graphene is a potential
candidate of next-generation TCFs due to their highelectrical conductivity, as well as chemical andphysical stability. To realize practical utilization andindustrialization of graphene, we must develop away that allows the industrial mass production ofgraphene. The synthesis of a large-area graphene on
Cu foils by thermal chemical vapor deposition(CVD) method has been previously proposed [1,2].
However, the method requires a high temperature
CVD reactor of around 1000 ˚C, so that it makes
continuous production difficult. Therefore analternative method to allow a low-temperature andlarge-area synthesis is needed. Plasma CVD is also
expected to be an alternative method because its
high non-equilibrium level and high-density
reactive radicals can permit a low-temperaturesynthesis of materials.
In this work, we developed a plasma CVD
technology for a low-temperature and large-area
synthesis of graphene by utilizing a low-pressure(1-5 Pa) surface wave plasma (SWP) which has
been developed originally. We have succeeded in
the synthesis of a large-area graphene film up to thesize of A3 paper at a low temperature of 300 ˚C [3].
Figure 1 shows a schematic illustration of ourplasma CVD method for the synthesis of grapheneon Cu foils. The SWP apparatus was fabricated byemploying the array configuration of originalgeometry multi-slot antennas.

Fig.1. Schematic illustration of the low-temperature andlarge-area synthesis of graphene using the surface wave
plasma CVD method.

2.45 GHz microwaves introduced into
waveguides produces standing wave, which thentransmit power to the discharge chamber throughthe multi-slot antennas and quartz windows,
exciting localized SWP near the quartz windows.
Uniform plasmas are produced over a CVD area of
60 cm× 40 cm with high-density plasma (~1011cm-3) according to the diffusion phenomena in thebulk plasma region [4].

SWP has relatively low electron temperatures (~2eV) and plasma potentials (~7 V) in the CVD
region even at such a low gas pressure, which are
preferable in the synthesis of carbon materials
because it reduces ion bombardment on thesubstrate in a sheath [4,5].
Figure 2 shows a picture of an A1-size graphenetransparent sheet that was fabricated by connecting
four A3-size sheets which was displayed atNanotech 2011 in Japan.

We have been working on the development ofcontinuous production technologies for theindustrial mass production of graphene using thearray configuration of multi-slot microwave
antennas and roll-to-roll manufacturing method.
Figure 4 shows a schematic illustration ofcontinuous production system of graphene.

Fig.4. Schematic illustration of a roll-to-roll synthesis
system for the industrial mass production of graphene.
Fig.2. Picture of an A1-size graphene-based transparent
film (at Nanotech 2011, Japan).

A test model of an electrostatic capacity-type
touch panel was fabricated by applying thegraphene-based TCFs. Figure 3 shows the process
for fabricating the graphene-based TCFs and apicture of the touch panel. It was confirmed that thetouch panel has sensitivity to be operated by finger
touch.

Plasma processing can be also used to modify thesurface of graphene, to dope functional impurities
into graphene and to etch graphene films to thedesired patterns. Plasma processing techniques will
be a core technology in graphene industries.
Plasma is contributing to green innovation bycreating revolutionary materials such as grapheneand by revolutionizing material processes in thefields of nanotechnology.
This presentation will be concerned withbackground, motivation, and latest experimental
results of our work for the large-area synthesis ofgraphene using the SWP- CVD method.
References[1] X. Li, et. al.: Science 324 (2009) 1312.
[2] S. Bae, et. al.: Nat. Nanotechnol. 5 (2010) 574.
[3] J. Kim, et. al.: Appl. Phys. Lett 98 (2011) 091502.
[4] J. Kim, et. al.: Plasma Source Sci. Technol. 19(2010) 015003.
[5] J. Kim, et. al.: J.Appl. Phys. 101 (2007) 023301.

Fig.3. Schematic illustration of the fabrication process ofgraphene-based TCFs and a picture of the touch panel.