For People, Society and the Earth

The Atmosphere Dependence of Annealing for AnodeYujiro Hayashi, Rie Mori Yoshinori Shirai, Shozo Komiyama, Ichiro Shiono, Shoubin Zhang

Mitsubishi Materials Corporation Sanda Plant, Sanda-shi, Hyogoken, 669-1339, Japan, TEL +81-79-568-2307, E-mail : yuhayash@mmc.co.jp

II. Introduction

III. Experimental

V. Conclusion

OLED has been developed owing to its expectation to become popular as displays forboth smartphones and tablet devices. Common structure of OLED is the top emissionstructure. In this structure, light is extracted from the top of the light-emitting element.Light can be extracted not only from light-emitting elements, but also from thesubstrate side because the anode is a reflective electrode film. Anode reflects light fromthe light-emitting element and enhances the efficiency of light extraction. The ITO / Ag/ ITO structure is often used as an anode of OLED because Ag has high reflectivity andITO is a transparent electrode. This anode needs some characteristics such asreflectivity, electric characteristic, and processability. In order to satisfy thesecharacteristics, anode is often composed of ITO and Ag stacked layer because Ag hashigh reflectivity and ITO is good transparent conductive oxide.The stacked layer is fabricated by sputtering. In this study, it was found out that the

process affects the reflectivity. High power is required to enforce the light at lowreflectivity. It shortens the life of light emitting material. Therefore, reflectivity is veryimportant characteristic for OLED anode. Our objective is finding out why it occurs.

Reference : Proceedings of International Display Workshops Volume 24, Paper No. OLED3-3, Page 715-717

I. AbstractThe influence of annealing atmosphere on the optical characteristic ofITO and Ag alloy stacked layer was evaluated for the anode of OLED. Itwas found that the reflectivity was improved by anneal in N2, and thedegree of improvement differed according to the type of Ag alloy.

IV. Results and Discussions

© 2017 The Institute of Image Information and Television Engineers

and The Society for Information Display

Deposit ITO with pure Ag or Mitsubishi Materials Corporation‘s Ag alloyfilm structure: Glass substrate/ ITO(10nm)/Ag alloy(100nm)/ITO(10nm)

size of sputtering target: 152.4mmφ×6mmtsputtering condition

Evaluation: spectrophotometer, AFM, TEM

Annealing in various atmosphere(N2, air, mixture of N2 and dry air; N2=0～100%) by infrared heating furnace

condition: 250℃, 1hr

ITO pure Ag and Ag alloy

power DC66W DC250W

sputter gas Ar+O2 (O2=2%) Ar

gas pressure 0.67Pa 0.3Pa

The sample annealed in N2 had higher reflectivity than the sample annealed in air.

Reflectivity spectrum of the sample annealed in various atmosphere

70

75

80

85

90

95

100

400 500 600 700

Refl

ecti

vit

y (

%)

Wavelength (nm)

as depo.

annealed in N2

annealed in air

Brief image of atmosphere control system

N2

tank

Dry air

tank

infrared heating furnace

Rotarypump Dry air: 79% N2+ 21%O2

switchingM.F.C. M.F.C.

content rate of dry air dependence on average reflectivity (400-700nm) The reflectivity dropped even in 10% dry air mixture.

10% dry air ≒ 2% O2

95.2

95.4

95.6

95.8

96.0

96.2

96.4

-10 0 10 20 30 40 50 60 70 80 90 100110

Avera

ge r

eflectivity b

etw

een

400-7

00nm

(%)

dry air content rate. (%)

The atmosphere during annealing didn’t have any effect on the surface roughness.

as depo. annealed in N2 annealed in air

AFM image

Ra(nm) 1.02 1.04 1.02

as depo. annealed in air annealed in N2

TEM image

electron diffractionpattern of top ITO

crystallinity of ITOamorphous(partially crystal)

crystal crystal

Ag

ITO

Ag

ITO

Ag

ITO

The atmosphere during annealing didn’t have any effect on the crystallinity and orientation of ITO.

0

2

4

6

8

10

12

14

16

400 500 600 700

Ref

lect

ivit

y (%

)

Wavelength (nm)

as depo.

annealed in air

annealed in N280

82

84

86

88

90

92

94

400 500 600 700

Tran

smit

tan

ce(%

)

Wavelength (nm)

as depo.

annealed in air

annealed in N2

Reflectivity spectrum Transmittance spectrum

The sample annealed in N2 had high transmittance and low reflectivity in short wavelength region.

Substrate

ITO(10nm)

80

85

90

95

100

400 500 600 700

Ref

lect

ivit

y (%

)

Wavelength (nm)

Pure Ag annealed in N2

Pure Ag annealed in air80

85

90

95

100

400 500 600 700

Ref

lect

ivit

y (%

)

Wavelength (nm)

Alloy A annealed in N2

Alloy A annealed in air

80

85

90

95

100

400 500 600 700

Ref

lect

ivit

y (%

)

Wavelength (nm)

Alloy B annealed in N2

Alloy B annealed in air

Range average reflectivity

400-450nm 500-550nm 600-650nm

Pure Ag N2＞air N2≧air N2≒air

Alloy A N2＞air N2≧air N2≒air

Alloy B N2＞air N2＜air N2＜air

Alloy B had different trend from other alloys.

1) The case of pure Ag

3) The case of Ag alloy

Linear analysis of Alloy B after annealing by TEM-EDS (actual data)

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10

ato

m%

(n

orm

aliz

ed)

Position(nm)

as depo.top ITOAlloy B

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10

ato

m%

(n

orm

aliz

ed)

Position(nm)

in airtop ITOAlloy B

annealingin air

1) Purifying Ag to decrease the additive element 2) Oxidation of additive element3) Blocking Ag’s diffusion

93949596979899

100

-10 0 10 20 30 40

Ave

rage

ref

lect

ivit

y b

etw

een

6

00

-65

0n

m(%

)

dry air content rate (%)

Pure Ag Ag alloy A Ag alloy B

・The suitable atmosphere during annealing differs in Ag alloy.

8485868788899091

-10 0 10 20 30 40

Ave

rage

ref

lect

ivit

y b

etw

een

4

00

-45

0n

m(%

)

dry air content rate (%)

Pure Ag Ag alloy A Ag alloy B

The effect of ITO mainly contributes.The effect of additive element mainly contributes in alloy B.

・The atmosphere during annealing affects the reflectivity of anode.・For pure Ag, the sample annealed in N2 had higher reflectivity than the sample annealed in air.・Even little amount of O2 in the atmosphere decreases reflectivity compare to 100% N2 atmosphere.・The atmosphere during annealing seemed to change the optical characteristic of ITO.

2) The optical characteristic of ITO single layer

Pure Ag(100nm)

Substrate

ITO(10nm)

Ag alloy(100nm)

Substrate

ITO(10nm)

The illustration of linear analysis (considerable possibility)

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10

ato

m%

(no

rmal

ized

)

Position(nm)

in air Ag In additive element O

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10

ato

m%

(no

rmal

ized

)

Position(nm)

in N2 Ag In additive element O

top ITOAlloy B top ITOAlloy B