−報文−

タッチパネル用新規 In2O3 系透明導電膜材料の開発
秋土原倉池田持裕浩豪

良＊ 1也＊ 1之＊ 1
人＊ 1

Novel In2O3 Based Transparent Conducting Oxide Materialfor Touch Screen
Ryo AKIIKE
Yuya TSUCHIDA
Hiroyuki HARA
Hideto KURAMOCHI

We would like to introduce our novel indium oxide based transparent conducting oxide (TCO). Novel TCO film
showed lower resistivity by lower process temperature, 197 μΩ ·cm at 150℃ , 217 μΩ ·cm at 100℃ respectively.
It can be applied to flexible touch screen (TS) favorably. This development accelerates the investigation of flexible
device, which enable to access to internet easily. Our development will contribute the saving energy on the point ofreduce a process temperature.

temperature has to be suppressed less than glass

1． INTRODUCTION

transition temperature.

In2O3 based transparent conductive oxide film has

Focused on a flexible touch screen, the requirement

been widely applied to electronic devices, flat panelof resistivity is less than 250 μΩ ·cm by less than 150℃

display (FPD), some kinds of photovoltaic devices,(the average of process temperature of PET, PEN = 130

and touch screens. Tin doped In 2 O 3 (ITO) is well℃ 〜 170 ℃ ) [3]. The film thickness is restricted underknown as most acceptable TCO with high conductivity,

50nm not to confirm visually. These properties are hardtransparency and stability. ITO exhibits a low resistivity

to achieve by ITO.

when it deposited on glass substrates with over 200 ℃
process temperature[1] [2].

Recently, flexible devices have become attractive fromthe viewpoint of thinner, light weight. Conventional

In this work, we successfully developed novel In2O3based TCO fulfilled the above-mentioned requirement.
We would like to introduce novel TCO film properties
and their sputtering target.

flexible device is manufactured on polymer materialsubstrate. Hence, TCO is deposited on flexible
polymer substrate instead of glass. Therefore, process＊1

アドバンストマテリアル研究所

2．EXPERIMENTAL
2.1 Preparation of sintered body and sputtering target
Our novel TCO (named USR) consists of In2O3 and27

TOSOH Research & Technology Review Vol.63（2019）the other additives. USR sintered body was preparedby simply resistance heating method reportedelsewhere [4][5]. Commercial powder of In2O3 and theother additives (the purity was over 99.9%) were used

3．RESULTS AND DISCUSSION
3.1

Electrical property

Fig.1 shows temperature dependence of electricalas starting materials. After the sintering, the obtained

resistivity of USR and ITO (In2O3: SnO2 = 97: 3 wt%).

sintered body has more than 99% relative density. AUSR Film resistivity of 217μΩ ·cm can be achieved even

USR sputtering target was fabricated from this sinteredat 100 ℃ . Notably, USR film showed almost samebody by grinding and cutting.

resistivity between 100 ℃ and 150 ℃ . This result
indicates annealing temperature can be suppressed at
100 ℃ . Therefore, many kinds of polymer materials can

2.2 Deposition of USR film
The USR film was deposited on a substrate by DC
magnetron sputtering. The sputtering conditions are

be used as USR’s substrate. USR film is considered as
suitable TCO materials for flexible device.
The detail of an electrical property of USR film after

shown in Table.1.
After deposition, the film samples were annealed at

150℃ post annealing showed 197μΩ·cm (Table.2).

150℃ in a lamp anneal furnace for 60 min with heatingThis resistivity is significant lower value compared with

rate of 50℃ /min under ambient atmosphere.

ITO. Especially, a career mobility of USR exhibit 1.4

The measurement of film properties was investigatedtimes higher value than that of ITO. This relation wasby following methods. Electrical properties were

sustained when the mass of Sn was adjust to that ofmeasured by van der Paw’s method to analyze between

USR’additives (data is not shown).

career density and mobility. Transmission and reflection

For a better understanding the electrical property

spectra of visible wavelength region were measuredof USR film, EBSD measurement was carried out toby spectrometer. The micro crystal structure of film

analyze the micro crystal structure of polycrystalline

was observed by electron back scattering diffraction

films. Fig.2 shows EBSD image of USR and ITO.

(EBSD) method.

Although almost all region of polycrystalline films
consist of typical cubic (bixbyite) structure, furtherobservation revealed that trigonal (corundum) type

Table.１

Sputtering conditions

Parameter
Back ground presure (Pa)
Sputtering gas
O2 partial pressure (％)
Power (W/cm2)
Pressure (Pa)
Temperature
Film thickness (nm)In2O3 exists at grain boundary (Both crystal structures

Conditions

can be seen in Fig.3). According to EBSD quantitative－5

analysis of corundum phase, the sum of corundum area

8.5 × 10Ar
0.5
4.5
0.7
Room temperature(without any heating)30of USR is about 5 times larger than that of ITO.
Corundum phase In2O3 is known as In2O3 polymorphtransition from bixbyite phase at high pressure andhigh temperature [6][7]. Karazhanov et al. reported firstprinciple calculation and band structure analysis ofbixbyite and corundum phase In 2O 3. Their analysisResistivity（μΩ・cm）

indicated that calculated effective masses for bixbyite
600

phase are considerable larger than those for corundum

USR
ITO－3wt％

500

Table.２

400300Parameter

200
100110120130

140150Annealing temperature（℃）

Fig.１

28

Electrical properties of USR film(annealing temperature : 150℃）

Temperature dependence of electrical resistivityof USR film (annealing time : 60min)

USR

Resistivity (μΩ・cm)
197
Sheet resistance (Ω/□)
64.0
Mobility (cm2/Vs)
51.0
Career density (-/cm3) 6.04 × 1020
31.2
Film thickness (nm)ITO
(SnO2:3wt%)
331
108
37.1
5.7 × 1020
30.6

東ソー研究・技術報告第 63 巻（2019）8Energy(eV)

6420－2Γ

Cubic
Trigonal

1μm

HNPΓ

NZFL

Γ

8

Energy(eV)

64
20－2
F
Cubic
Trigonal

1μm

Fig.２

Fig.４

EBSD images of USR film (top) and ITO film (bottom)
after annealing (annealing temperature: 150 ℃)

3.2

Γ

Band structure of top: cubic (bixbyite) In2O3 andbottom: trigonal (corundum) In2O3

Optical property

Optical property of USR film was also studied. TCO
for touch screen is required high transparency atvisible wavelength region. Fig.5 shows transmission
spectra of USR and ITO deposited on glass substrate.
Fig.３

Crystal structure of left: cubic (bixbyite: space group=206) In2O3 and right: trigonal (corundum: spacegroup=167) In2O3
In atoms are violet, O atoms are red

Dotted line is the spectrum of glass substrate. Althoughtransparency of USR film was almost same as ITO,
There is a difference around 300 〜 400nm region.
USR film showed a slightly higher transmittance evenin 30nm thickness. This region is considered as bandphase[8]. Band structures of bixbyite and corundum

absorption. Thus it is assumed this difference is caused

In 2 O 3 are shown in Fig.4. The calculations wereby Burstein-Moss effect. As considered Table.2, a[9]performed with VASP package . The cut-off energy
was set to 500nm. Structural optimization has been
performed with PBEGGA[10]

career density supports this assumption.
Fig.6 shows reflectance spectra of USR and ITO

on a G centered 9 × 9 ×

respectively. Both of them showed similar spectra at

9 k grid for corundum phase and 3 × 3 × 3 k grid forvisible wavelength. Therefore, similar anti-reflective

bixbyite phase respectively. After optimization, bandcoating layer can be applied to fabricate a device.

structure was calculated with hybrid function HSE06[11]with AEXX =0.38 and AGGAX=0.62. Fermi level wasband minimum of corundum phase is more dispersive
than that of bixbyite phase.

The smallest effective

masses were calculated as 0.12 for corundum phase( Γ→ Z) and 0.18 for bixbyite phase( Γ→ N) respectively.

100Transmittance（％）

set to zero. Our results support ref [8]. The conducting

phase is expected to be higher than that of bixbyite
contribute the enhancement of career mobility.

6040USR
ITO－3wt％
Glass substrate

200

These results mean a career mobility of corundum
phase. Hence corundum phase of USR film may

80400

600

800

1000

1200

Wavelength（nm）

Fig.５

Transmission spectra of USR film and ITO
after annealing (annealing temperature : 150℃)

29

TOSOH Research & Technology Review Vol.63（2019）3.3

at crystal grain boundary compared with ITO film.

Stability

For practical application of USR film, the stability ofThese crystals were considered that they contribute theelectrical property was investigated. The accelerated

improvement of electrical property. Optical property

degradation test with conditions of 85℃ , 85% relativeand stability was almost same as ITO. These aspects

humidity for 1000 hour was carried out. The result isallow us to treat them as if it is ITO.

seen in Fig.7. Y axis means the relative ratio of electricalresistivity between before and after degradation. The
relative ratio after 1000 hour was almost same value
between USR and ITO. This result indicates USR film
has good enough stability as ITO film has so that ITO
can be substituted for USR.

REFERENCES［1］M. Huang, Z. Hameiri, A. G. Aberle, Vacuum., 121,187 (2015)［2］T. Karasawa, Y. Miyata, Thin Solid Films., 223, 135(1993)［3］T. Hayashi,“TOUCH PANEL SAIZENSEN 2013-4．Conclusion

3014”, 105

In summary, we developed novel In 2 O 3 based
TCO“USR”. The sintered body of USR can besynthesized ordinary sintering scheme and fabricateda sputtering target. The film deposition was carried outroom temperature and then annealed under ambient
atmosphere. A high annealing temperature was not［4］M. Muraoka, M. Suzuki, Y. Sawada, J. Mater. Sci.,
33, 5621 (1998)［5］M. Suzuki, M. Muraoka, Y. Sawada, J. Matsushita,
Mater. Sci. Eng. B., 54, 46 (1998)［6］A. Gurlo, P. Kroll, R. Riedel, Chem. Eur. J., 14, 3304
(2008)

necessary, 197 μΩ ·cm can be achieved at 150℃ and［7］B. García-Domene, J. A. Sans, F. J. Manjón, S. V.

217μΩ ·cm can be achieved at 100℃ respectively.

Ovsyannikov, L. S. Dubrovinsky, D. Martinez-USR film has large number of corundum phase In2O3Garcia, O. Gomis, D. Errandonea, H. Moutaabbid,
Y. Le Godec, H. M. Ortiz, A. Muñoz, P. RodríguezHernández, C. Popescu, J. Phys. Chem. C., 119,

Reflectance（％）

10029076 (2015)

80USR
ITO－3wt％

60［8］S. Zh. Karazhanov, P. Ravindran, P. Vajeeston, A.
Ulyashin, T. G. Finstad, and H. Fjellvag, Phys. Rev.

40B., 76, 7, 075129 (2007)20［9］G. Kresse and J. Furthmüller, Phys. Rev. B., 54, 11

0400

600

800

1000

1200Fig.６169, (1996)［10］J. P. Perdew, K. Burke, and M. Ernzerhof, Phys.

Wavelength（nm）

Reflectance spectra of USR film and ITO after
annealing (annealing temperature : 150℃)

Rev. Lett., 77, 3865 (1996)［11］A. V. Krukau , O. A. Vydrov, A. F. Izmaylov, and G.

Relative ratio of resistivities（Rafter/Rbefore）

E. Scuseria, J. Chem. Phys., 125, 224106 (2006)
2.0USR
ITO－3wt％

1.8
1.6
1.4
1.2
1.0
0200

400

600

800

1000

Time（hour）

Fig.７30

Accelerated degradation test of the electricalproperty of USR film.