Science and Technology on Inorganic Electroluminescence

- past, present, future -

Hiroshi KobayashiProfessor Emeritus，Tottori University

The 2009 Seminar (45 min.)Date: May 8Place: Hong Kong

Outlines

1. Introduction2. Basic Understanding of Thin Film EL

--- Voltage Dependence--- Electron Injection --- Excitation mechanism of luminescent centers

3. Color EL Materials4. Trial for Electroluminescent Display Panel5. Concluding Remarks

1950 1960 1970 1980 1990 2000 2010

1974

SHARP 二重絶縁構造

19741974

SHARP .

1968BellLab.

RE-dopedZnS thin flmRGB

1999 2004

1st Gen.PowderEL

２nd Gen.,ThinFilm EL(ZnS,IIa-Vb)

3rd. Gen.

4th Gen.

1989 SID Int.Symposium

1987

2005

History of Inorganic ELedited by Dr. Miura (Meiji Univ.)

FPD TAIWAN 2004 Business & Technology Forum on June 9 ~ 12

History of OLED products

passive 1999

active 2003

2000 2001

monochrome(for cellular phone)

Tohoku pioneer

Area color(for in-car products)

Tohoku pioneerTDK

Full color(for cellular phone)

SNMD

Full color(for DSC)

SK Display

ed. by K.Yoneda

IntroductionHistory of EL at Tottori University

1. The preparation of TFEL ; host material, EL centers insulating film, electrode. (1969~ )

2. The Understanding of fundamental physics of TFEL, doped with rare-earth luminescence centers. (1970 ~ 1974)

3. The trial of application of thin film electroluminescence to flat panel displays. (1975 ~ )

4. Multicolor thin film electroluminescence. (1975 ~)

5. Multicolor flat panel electroluminescence. (1980 ~ )

6. Thick dielectric film electroluminescence. (1999 ~ )

7. The organic TFEL (1995 ~ )

Sharp (~1974)

Outline1. Introduction2. Basic Understanding of Thin Film EL

1968---1975 Thesis Work Kobayashi1 Voltage Dependence2 Electron Injection 3 Excitation mechanism of luminescent centers

3. Color EL Materials4. Trial for Electroluminescent Display Panel5. New Development of Color EL 6. Concluding Remarks

These results are summarizedin Kobayashi’Thesis Work

(1974,July in Japanese)

Basic Research on Electroluminescence in Rare Earth Doped ZnS Thin Film

Kobayashi Hiroshi

Voltage Dependence

Previous data

Voltage Dependence of Luminance

Our result:L(E，ΔQ)

Previous result:L(ΔQ)

Electron Injection Mechanism 1

Electron Injection Mechanism 2

Excitation of Luminescent Centers

(a) (b) (c)

Excitation Mechanism of EL 1

Donor-AcceptorPairs Cu-Cl

Nd ion

Donor-Acceptor+

Nd ions

Luminescent Centers in ZnS

Direct Impact Excitation of Er3+ 2

Electron Energy Distribution

E low

E high

Outline

1. Introduction2. Basic Understanding of Thin Film EL3. Color EL Materials4. Trial for Electroluminescent Display

Panel5. New Development of EL6. Concluding Remarks

The Spectra of Mn2+

Emission Spectra Re3+,R,G,B

The Spectra of Ce3+

RGB EL Materials

Eu2+ and Ce3+ in CaS,SrS Host Materials

Outlines

1. Introduction2. Basic Understanding of Thin Film EL3. Color EL Materials4. Trial for Electroluminescent Display

Panel5. New Development of EL6. Concluding Remarks

Powder EL Panel ,R,G,B

Strong Cross Talks

Thin Film EL Panel R,G,B

No Cross Talks

The Full Color EL Panel (1989)

white

Filtered RGB

Blue OrangeWhite

Trials for increasing pixels

Thin Film EL Panel ZnS:Mn

LCD LED

Our New TFELTV picture (4-level gray scale)

Scanning lines (~50),taken out from TV 525 lines

Planar (1)

ZnS:Mn monochrome yellow

Planar (2)

iFire Technology (1)

iFire Technology (2)42 inch

Outline

1. Introduction2. Basic Understanding of Thin Film EL3. Color EL Materials4. Trial for Electroluminescent Display

Panel5. Research on Color EL (1990’s ~ )6. Concluding Remarks

Primary Color (RGB)

R G B

Red Phosphor

ZnS:SmCaS:Eu

Ba2ZnS3:Mn(Ca,Sr)Y2S4:Eu

ZnGa2O4:EuZnS:Mn + FilterZnS:Mn + CCM

Green Phosphor

ZnS:Tb

SrGa2S4:EuCaAl2S4:Eu

Blue Phosphor

ZnS:TmSrS:Ce + Filter

CaGa2S4:CeSrGa2S4:CeSrS:Ag,Cu

CaS:PbBaAl2S4:EuBa2SiS4:Ce

Research on Color EL (1990’s ~ )

After Miura, Meiji University

SrCaYSrCaY22SS44:Eu:Eu

CaAlCaAl22SS44:Eu:Eu

BaAlBaAl22SS44:Eu:Eu

Green

Blue

Red

over 150 cd/m2

over 250 cd/m2

over 50 cd/m2

material Luminance@50 Hz

color

Possibility of RGB emission by Eu2+ ion doped IIa-III2-S4 phosphors for full color inorganic EL displays.（Miura et al., Meiji University）

400 450 500 550 600 650 700 750

EL Inte

nsi

ty (

a.u.)

Wavelength (nm)

BlueGreen Red

NTSC

EBU

BaAl2S4:Eu

CaAl2S4:Eu

SrCaY2S4:Eu

MEIJI University

Possibility of RGB (Miura)

　　　　　　iFire Display TM StructureColor By Blue (CBBTM)

ITOdielectric

thick film dielectric

Glass substrate

gold electrode

BaAl2S4:Eu

(0.134,0.080) (0.32, 0.67) (0.660, 0.340)

Lead magnesium niobate based material combined with aPZT

Color filter CCM 4.1 CCM 1.6

2003i-Fire Display Structure

High Luminance DC Inorganic EL device(Chatani & Kuraray co., LTD, 2005 Oct.)

・Luminance: 650,000 cd/m2 (2,000,000 cd/m2 @8 V)

・Applied Voltage: DC 5.5 V(Threshold Voltage: 3V)

・Luminous Efficiency: 10~14 lm/W・Emission Area: 2 mm X 2 mm・Life: 25,000 h (@350,000 cd/m2)

(2.8 Year)

・Current: 97~137 mA・Resistance: ~40 Ω

ZnS Phosphor based Material

e

Eg: 3.6eV

Chatani

EL Spectra of various materials

5 Concluding Remarks

• Blue Inorganic EL of BaAl2S4:Eu • Color change by blue EL panel• A new 600,000 cd/m2 bright inorganic EL

of dc driven at lower than 10 V.

we summarized the present main topics.

These three findings will stimulate again the researches on inorganic EL

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