5 장 OLED 1. OLED 의분류및정의 2. OLED 의구조및동작원리 3. 발광재료및특성 4. 디스플레이기술 5. 연구동향및과제 6. 결론, 생각해볼문제 1
1.OLED 의분류및정의 EL 이란? ELD(ElectroLuminiscent Displays)- 전계를인가하거나전류를흘려주었을때발광재료가자체발광하는것 LED(Light Emitting Displays) 와같은뜻으로쓰임 2
유기물 / 고분자 EL 이란? 유기물 / 고분자 ELD는반도체성질을띄는유기물또는공액고분자를발광소재로하여이를두전극사이에끼워놓고전압을가하면전류가발광소재내로흐르면서유기물또는고분자로부터빛이발생되는원리 ( 전기발광이라부른다 ) 를이용하는발광디스플레이이다. 3
유기물 / 고분자 EL 디스플레이특장 기술적측면 1. 발광소자 2. 고휘도 (>10만 cd/m 2 ), 고효율 (>10 lm/w) 3. 낮은구동전압 ; 직류구동 ; 건전지사용가능 4. 색상변화용이 ( 다색화가능 ) 5. 대면적화용이 6. 구부릴수있는소자용이 7. 소자구조간단 ; 제작공정간단 8. 고속응답성 (ms 이하 ) 9. 타분야핵심기술로응용가능 4
유기 EL 의구분 5
발광재료에따른분류 6
유기 EL 과무기 EL 의장단점비교 7
왜 OLED 인가? solid-state 로써내구성우수, 빠른응답속도 자체발광 고휘도, 고효율, 높은대조비, 광시야각, 후면광 (backlight unit) 이불필요 무기 EL 은고전압필요, 대면적화와청색발광어려움 8
OLED 개발동향 1998 1999 2000 2001 2002 유기 EL Pioneer, PM Pioneer 4 Area Color 5.2 PM-OLED OLED Sanyo-Kodak 5.5 AM-OLED CDT-Seiko Epson 2 AM-PLED LG, 8 -Full color Motolora Area color Sony 13 AM-OLED LG, 1.8 Full color SDI 15.1 XGA AM-OLED TMD 17 AM-PLED XGA Toshiba 2.8 Full color Flexible 유기 EL ETRI 2 PM-OLED UDC OLED Pioneer OLED DNP OLED 9
2.OLED 의구조및동작원리 OLED 의기본구조 ( 단층, 다층 ) 10
Multilayer Device Structure( 다층구조 ) + - Electron Injection Electrode(cathode) Electron Transporting Layer(ETL) Emitting Layer(EML) Substrate Hole Transporting Layer(HTL) Light Hole Injection Electrode(anode, ITO) 11
OLED 의기본구조 두께 : 100 ~ 200 nm 전자 LIGHT 양극 ( 투명전극, ITO 유리, 등 ) + 정공 정공수송층 (HTL) 발광층 (EML) + - Exciton 전자수송층 (ETL) - 음극 ( 낮은일함수금속, Ca, Al:Li, Mg:Ag, 등 ) 12
능동유기 EL 의주요기술 그림 5-2 에서능동유기 EL 의주요기술을도식적으로표현하고있다. 유리기판위에반도체를증착하여 TFT 를제작한다. 2.2 능동유기 EL 패널제작을위해화소구동용 TFT 가약 1 백 30 만개필요하며데이터, 스캔구동, DC/DC 변환기등에 30 만개정도의 TFT 가소요된다. Red, Green, Blue 가각각독립증착되며증착된유기 EL 의오염및습도방지를위해봉지기술이필요하다. 13
OLED 의발광원리 Cathode-electron injection Anode-hole injection EML( 발광층 or host) 에서의전자 - 정공의재결합과정을거쳐광이생성 14
Light Emitting diode: I f I r I f >> I r V f + - V r - + hn Band diagram under bias Before V + - Flat-band Injection 15
Schematic representation of various EL mechanisms p n Acceleration Electron moves into p-region Electron injection Impact Excitation EL EL EL Electron-hole Recombination Hole injection Electron-hole Recombination Luminescence Center Intrinsic or High-field EL (Phosphor, Org. Crystal) Semiconductor p-n junction Injection EL Organic / Polymeric LED 16
Schematic Diagram of EL Process Hole Injection Electron Injection h+ e- Anode Cathode Hole Leakeage Current Coulomb Capture (Non-geminate recombination) Electron Leakage Current Exciton Formation Singlet S = 0 Nonrad. ISC T-T Anihil. hn Triplet S = 0 Nonrad. Exciton Decay Ground State 17
Scheme of EL Process Cathode Anode Electron Hole Conduction Band (LUMO) Valence Band (HOMO) h re c j g Electron-Hole Capture; Exciton h F f Singlet Exciton Triplet Exciton Light Emission Heat Dissipation h e h ext Light Output Internal Decay 18
제조공정 19
Patterning for Pixel formation( 패터닝 ) ITO Patterning : Photo-mask, Photo-lithography Cathode Patterning 1. Simple patterning : Shadow mask 2. High resolution Patterning 1. Cathode separator 형성 Prevention of shorts 1. ITO Patterning Angular Evaporation 2. Vertical shadow mask 2. 발광층형성 3. Organic Deposition 3. Cathode 형성 4. Oblique Cathode Deposition 20
제조공정 - 패키징 현재는흡습제사용한금속캔을유기 ELD 뒷면부착 - 무게부피문제등.. 보호층형성방법연구중 : PE-CVD 등 21
3. 발광재료및특성 22
Aspects in Emissive Material 1. Color tuning 2. Color Purity 3. Quantum Efficiency : Photoluminescence 4. Stability 23
단분자 ELD 장점 - 낮은구동전압과비교적큰휘도 단점 - 지속적인발광이나안정성, 양자효율면에서문제점 24
Emissive Materials : Polymers vs Small molecules 1. No essential difference in molecular design concept 2. Emission mechanism is very similar 3. Big difference in processing and durability of devices Polymers : spin-coating, about 5,000 hours Small molecules : vacuum-deposition, ~10,000 hours 25
Advantages of Small Molecules: 1. Molecular Design and synthesis of materials are easy : Color tuning and high fluorescence efficiency 2. Fabrication of multiple layer structures are easy : High Quantum efficiency 3. Simplified understanding of phenomena Disadvantages : 1. Insufficient stability of vacuum deposited films 2. Lack of thermal and mechanical durabilities 26
Organic ELD Functional Molecules Metal Complexes: 배위자자신이강한형광성을갖는것 ( 넓은선폭 ) 배위자로부터의에너지전이에의해금속이온자신이발광하는것 : ( 예 ; Tb, Eu, Dy 등 ) ; 선폭이좁음 ( 단색성우수 ) N O Al O N O N O O N N Zn N N O N O Be O N O Lumophore molecules: CH CH N N O N N O N N Eg; p-p* gap 27
Energy Levels and Band Gap Benzene sp 2 (s) + p z (p) bonding p-orbitals LUMO HOMO + - - + + + - - + + + + + + + - - - + + + - + + + + + + - - - - High p-electron density at para-position Poly(p-phenylene) Energy Band Structure Band Gap E g 28
HOMO-LUMO gap of organic molecules 1 E g N 29
발광재료에요구되는특성 유기물발광층으로요구되는특성 고체상태에서양자효율이클것 전자또는정공이동도가클것 진공증착이가능할것 균일한박막이형성될것 막구성이안정할것 적당한 HOMO, LUMO 준위를가질것 30
Doping in OLEDs Color tuning eg. Red emission from DCJTB or DCM2 doped Alq3 Enhance lumious efficiency Doping either fluorescent or phosphorescent dyes Improve the device stability longer lifetime, less voltage increase during operation eg. Alq3-based OLEDs doped with rubrene, quinacridone derivatives, etc. Energy transfer to dopant Direct charge carrier Trapping at dopant 31
Light (arb. units) 디스플레이공학 OLEDs doped with DCM N O Al O N N O Alq3 NC H 3 C o CN DCM CH 3 N CH 3 0.15 0.10 310 K 290 K 250 K 200 K 150 K 100 K 50 K 17 K undoped 0.05 0.00 500 600 700 Wavelength (nm) 800 32
Dopants : O N N O NC CN NC CN H3C O H3C O N N(CH3)2 Roles of Dopants 1. Color Tuning 2. Higher Quantum efficiency 3. High Durability i) Exciton formation in host -> energy transfer -> dopants excitation -> light emission ii) Recombination in Dopant itself 33
대표적인 host/dopant 발광계 B G Y Or R (Rj)m Alq-family Host L Idemitsu TDK (Ri)n 2 DPVBi H 3 C CH 3 Kodak N O O Al N N O CH 3 modifided N O O Al N N N O O O N Ga N N O N Red shift Alq3 Gaq3 Dopant N Kodak Perylene distyrylbiphenyl Idmitsu 2 O N H H N O quinacridone Pioneer DPT Mitsubishi rubrene Mitsubishi OCH 3 S O BTX Mitsubishi H N N O O S ABTX Mitsubishi NC O CN DCJTB Kodak 34
Effect of Dopants on the EL Spectrum 35
Host Dopant Interaction host Solid State Solvation Effect Bulovic et al., Chem. Phys. Lett. 287, 455 (1998); 308, 317 (1999). 36
Blue OLED I-V Curve 37
Energy transfer 1. Intermolecular energy transfer 1. Forster energy transfer 2. Dexter energy transfer 2. Intramolecular energy transfer Donor Acceptor Forster ~ 100 angstrom Dexter < 10 angstrom 38
Dopant 조건 : 1. 높은발광효율 2. Host 물질보다밴드갭이낮을것 3. Host 물질과 exciplex를형성하지말것 4. 여기-발광사이클동안안정할것 5. Host 물질에분산이잘될것 39
Advantages of Polymers: 1. Stability and durability are much improved 2. Good Processibility using solution or melt processes 3. Possibility of molecular design Disadvantages : 1. Fabrication of multilayer structures is difficult 2. Removal of impurity is difficult 3. Less flexible in molecular design and difficulty in synthesis 40
C C C C C C C : One S Three P orbitals Pz sp 2 : mixing of one s and two p orbitals 120 o s p sp 2 P z Trans-Polyacetylene 41
Analogous to Tight binding model : H H C C H H H H H C H C C H 3 H C C H H H H H C H H C C C 15 H C H H H C C H n-> LUMO Eg; p-p* gap HOMO? HOMO : Highest Occupied Molecular Orbitals <-> Valence band LUMO : Lowest Occupied Molecular Orbitals <-> Conduction band 42
p-p* Energy Gap of Some Common Conjugated Polymers n trans-polyacetylene R 1.5 ev S n R Polythipophene 2.0 R n Polydiacetylene 1.7 S n Poly(3-alkylthiophene) 2.0 n Poly(p-phenylene) 3.0 S n PTV 1.8 OR n PPV 2.5 NH n Polypyrrole 3.1 RO n RO - PPV 2.2 N H n Polyaniline 3.2 43
Positive polaron Negative polaron Positive polaron Negative polaron 44
Carrier Transport Hopping Transport Microscopic Anisotropy : Intrachain transport is faster than interchain transport and Conformational disorders or defects interrupt the 1-D transport Interchain Hopping Low Mobility : m ~ 10-4 - 10-8 cm 2 /Vs for holes due to poor wavefunction overlap (larger hopping distance), increased disorder and trapping much lower m for electrons(at least two order of magnitude smaller) trapping at defect sites due to impurities such as O 2 45
Electroluminescence ; Non-geminate recombination 전기발광기구 음성폴라론 폴라론재결합 - 여기자빌광소멸 양성폴라론 전자주입 e 전자 - 포논커플링 전자 - 포논커플링 LUMO 음극 h n 양극 HOMO 발광분자 1 2 3 4 5 4 3 2 1 h 정공주입 46
색상튜닝전략 재료측면 : - 치환기 - Electronic properties ex) MEH-PPV : red shift : incorporation of unused electron pairs to enhance the p-electron conjugation - Steric effects - Backbone 구조 - Ring structure - Segmentation - Torsional twist due to side group ex) Polythiophene derivatives 47
Effects of substituents 5 4 N N O Al O O N 7 O N Al 2 515 nm HOMO LUMO Group 4-Me 5-Me 5-F 28 5-Cl 22 5-CN 7-nPr Dlmax PL -10nm 31nm 15nm 10nm -3nm 35nm N N N N O N N O Al O Al O N O O N N N N N 440 nm 580 nm 48
OMe n 520 nm ; Green 550 nm ; Yellow n O OC6H13 OC6H13 590 nm ; Orange 620 nm ; Red CN O n OC6H13 CN OC6H13 n 49
Effects of Ring Structure 520 nm ; Green n S n 650 nm ; Red Effects of torsion of backbone S n 650 nm ; Red CH2CH2OCONHCH2COOC4H9 590 nm ; Orange S n 50
Effects of segmentation n 520 nm ; Green Si O O 470 nm ; Blue-green Si n 51
Intensity (Normalized) 디스플레이공학 Spectra of conjugated polymer Si O O Si n 1.2 1.0 0.8 Abs. PL EL 0.6 0.4 0.2 0.0 300 400 500 600 700 Wavelength (nm) 52
EL Intensity 디스플레이공학 Color Purity 25000 20000 PPV 15000 10000 5000 0 400 500 600 700 800 Wavelength (nm) 53
Definition of color purity 54
EL Intensity(a.u.) 디스플레이공학 White light generation A: 10mA/cm 2 B: 20mA/cm 2 C: 200mA/cm 2 C B A 400 500 600 700 Wavelength (nm) ITO/PVK(30wt% PBD; 3mol% TPB; 0.04mol% coumarin6;0.02mol% DCM1;0.015mol% Nile Red)/Mg:Ag 55
발광효율의향상방법 1. 재료 - 형광수율이높은것 ; - 평면성이좋을것 - 사슬간상호작용이적을것 - 여기자속박이잘될것 - 3중항여기자생성확률이낮거나, 일중항여기자로에너지전이가잘될것 56
PL efficiency : Q = h X q h = efficiency of singlet exciton formation q = t/t r ; ratio of radiative decay t -1 = t -1 r + t -1 nr Efficient PL : Necessary but not sufficient condition for EL - PL studies provides good insight - Needs photophysics and photochemistry study 57
효과적인 Exciton Confinement 를위한구조 1. Copolymer OMe m-x OMe n-y OMe x OMe OMe y OMe 2. Long side chain Si Si 3. Disorder in chain - cis, trans-alkene unit - kink in backbone 58
Non-radiative channel; - intersystem crossing - exciton-exciton collisional annihilation - migration to quenching site - deep levels - excimers - exciplexes - chemical defects such as C=O group - contaminants 59
Quantum Efficiency (lm/w) 디스플레이공학 100 10 FL Halogen/R LED Bulb CDT Polymer Pioneer Quinacridone 1 B LED LCD PDP Idemitsu DPVBi Mitsubishi Rubrene Kodak DCM 0.1 400 450 500 550 600 650 W avelength (nm) Q.E. Limit(5%, 5V) Full Color Requirement 60
Electronic Processes in Molecules 61
2.6eV 3.2eV 2.7eV 3.7eV ITO 4.7eV a-npd 5.7eV Ir(ppy) 3 /CBP 6.3eV BCP Alq3 6.0eV MgAg 6.7eV Ir N 3 Ir(ppy)3 N CBP N CH3 N N BCP CH3 Singlet -> ground state in Ir(ppy) 3 Triplet of CBP -> Dexter energy transfer to triplet of Ir(ppy) 3 -> ground state Singlet -> intersystem crossing to triplet in Ir(ppy) 3 -> ground state 7.5 % external quantum efficiency, 19 lm/w @ 100 cd/m 2 62
Ligand Effects on Emission energy 63
Green, yellow and red phosphors for OLED Mark Thompson, IMID 2001 64
Hybrid Organic/Quantum Dot LED 65
Organic LED 의발전추세 [J. R. Sheats et al., Science 273, 884 (1996) 의자료에최근발전을추가함.] 66
고분자유기 EL 물질의분류표 67
소재관련기술 유기 LED 의주요기판소재인유리와플라스틱의특징비교 68
발광효율 금속일함수 ( ev ) 양자효율 (%) Ca 2.87~3.00 4Χ10-3 In 4.12~4.20 1.6Χ10-4 Ag 4.26~4.74 1.8Χ10-4 Al 4.06~4.41 8Χ10-6 Cu 4.65~4.70 8Χ10-6 Au 5.1~5.47 5Χ10-7 전하수송층을포함한소자의구조 MEH-PPV 로된발광층단층소자에서의음극금속의일함수에따른양자효율의변화 69
4. 디스플레이기술 (1) 색상도향상기술 유기물및고분자의 EL 발광 - 스펙트럼의영역의반촉치매우넓음 넓은스펙트럼 - 선명한색을내지못함 색상도 - 삼원색각각의색순도 (color purity) 가좋아 야함 ( 발광빛의단색성 ) 단색성 - 발광스펙트럼의폭이매우좁아야함 희토류금속을포함유기물 dopant 로사용하여적색의색순도를높임 70
Eu 을포함하는유기물의화학구조 EL 발광스펙트럼 71
마이크로공진기 유전체다층막반사경 - 투명전극과기판에도입 EL 발광소자와구조는같음 ( 다음슬라이드그림참고 ) 색순도를높이기위한발광색의단색성을높임 방향성을가짐 ( 그림 ) 발진공진구조를이용할경우색순도가좋아짐 공진길이를조절 - 발광파장을조절할수있어색상조절도가능 72
마이크로공진기의 발광빛의방향성과 EL spectra 73
(2) 화소제작기술 유기물및고분자발광소자를이용 컬러디스플레이를실현하는방법 Side by side CCM Color filter Microcavity 74
Full-Color 방법 Emitting Layer Color Technology Company 장점 과제 B G R Blue,Green, Red EL Pioneer, NEC 높은발광효율고해상도 고효율 R, B 발광재료미세가공 B G R White EL + C/F for LCD TDK LCD용 Color Filter 사용가능 백색 EL 효율향상 White balance B G R Blue EL + Color Changing Material Idemitsu Kosan 유기층패턴불필요 높은변환효율 CCM 개발 75
Patterning for Pixel formation ITO Patterning : Photo-mask, Photo-lithography Cathode Patterning 1. Simple patterning : Shadow mask 2. High resolution Patterning 1. Cathode separator 형성 Prevention of shorts 1. ITO Patterning Angular Evaporation 2. Vertical shadow mask 2. 발광층형성 3. Organic Deposition 3. Cathode 형성 4. Oblique Cathode Deposition 76
Thin Film Formation Organics : Vacuum deposition 1. In-line Type - Easy to install more chamber - Easy maintenance Loading chamber EV1 EV2 Mask stock chamber Mask change/ alignment chamber EV3 Unload chamber 2. Cluster Type - Easy back and forth process - Parallel process 77
Pixel Patterning Process ITO Stripes Cathode Separator Glass Substrate Substrate Fine Metal Shadow Mask Cathode Stripes Organic layer Source Pioneer Vacuum Deposition 78
Polymers Thin Film Formation Spin Coating Doctor Blade Ink Jet Printing Dipping Roll printing, Micromolding, etc 79
Ink-Jet Multicolor Polymer Display Patterning Red(Rhodamin101/PPV) Blue(Poly(dioctylfluorene) Cathode Green(PPV) PEDT/PSS 80
마이크로가공관련기술 잉크젯프린팅을적용한유기 LED 의제조공정 81
side by -side R, G, B 소자를나란히배열 공정에어려움 82
Organic EL display demonstrated by Pioneer (1998) 83
CCM 청색발광된빛을색변환층이용화소형성 고휘도청색발광소자이용 - 발광된빛을광발광효율이우수한 R,G,B 의색변환층이용 84
Kosan CCM display 85
color filter 백색광을방출하는전계발광소자를컬러필터를이용하여화소형성 86
Microcavity 백색광발광소자로부터나온빛을미세공진구조를이용하여화소형성 컬러필터대신공진구조사용 87
유기 EL 소자의풀칼라구현방식 88
(3) 디스플레이구동방법 메트릭스구동요구 Passive Matrix Active Matrix 89
Passive Matrix Active Matrix 차이 Passive Matrix- 가로, 세로전극이교차 90
Active Matrix-TFT 가화소마다위치 ( 스위치역할 ) 91
Device Structures - AMOLED Metal Cathode Emissive Layer Transparent Anode Translucent Cathode Light Transparent Plate Buffer Layer Al Wiring Light Emissive Layer Metal Anode (a) Bottom emission (b) Top emission 92
Driving the pixels 93
active matrix 94
능동구동소자와수동구동소자의비교 전압모드프로그래밍방식은데이터를쓰는동안화소의저장커패시터에균일한전압을유지하도록하는방식인반면, 전류모드프로그래밍방식은전류를데이터로하여그에해당하는전압치를저장커패시터에인가함으로써 TFT 의특성에상관없이일정한전류를유기 EL 소자에흐르게한다. 95
유기발광디스플레이의구동원리 수동구동방식 (a) 과능동구동방식 (b) 의회로도 구동원리를살펴보면선택신호에따라실렉트전극에신호를인가하면 SW_TFT 가열리고데이터전극에서인가한데이터신호가 SW_TFT 를통과하여 DRV_TFT 와저장커패시터 (Capacitor) 에인가되며 DRV_TFT 가열리면전원공급선 ( 라인 ) 인 power line(vdd) 로부터전류가 DRV_TFT 를통하여유기 EL 소자에인가되어발광하게된다. 데이터신호의크기에따라 DRV_TFT 의열리는정도가달라져서 DRV_TFT 를통하여흐르는전류량을조절하여계조표시를할수있게된다. 96
채널길이에따른저온폴리 TFT 의 ID-VG 특성 [ 그림 5-25] 는능동유기 EL 패널구동을위한 TFT 특성이다. 폭 2um 에따른채널길이변화의특성이다. n/p TFT 특성비를맞추기위해문턱전압과이동도의균형을공정과 ntft LDD 를조정하여최적화한특성이다. 97
능동구동소자와수동구동소자의비교 Source Line Power Line 1 Dat Power Line Gate Line C 1 M 1 VEL M 4 M 1 M 2 C 2 AZ AZB M 3 V 1 M 4 C ST M 3 Data OLED GND Gate Line M 2 OLED GND AZ 1 Dat AZB Scan VEL VSEL 전압모드프로그래밍방식과전류모드프로그래밍방식의보상회로 98
구동 TFT 를보상하기위해사용되는여러가지예 구동 TFT를보상하기위해사용되는전압모드프로그래밍보상회로 : (a) 전압프로그램 (IMID '02), (b) 전압프로그램 (SID '03), (c) 전압프로그램 (Mirror Compensation)(IDW '03), (d) 구동TFT 직접보상 (IDW '03) 99
디지털구동방식 최근에는 (2008 년 ) 유기 EL 디스플레이에서발생하는 TFT 불균일을원천적으로보상할수있는구동방식의대안으로디지털방식이연구되고있다. 2TR 1 캐패시터를사용하는 [ 그림 5-24(b)] 디지털구동방식은 [ 그림 5-28] 에서와같이 TFT 의 on/off 영역을이용한다. 구동 TFT 는 on/off 동작만함으로 TFT 의 Subthreshold 영역의변화에좌우되지않는다. 유기 EL 에전류를공급하는구동 TFT 를완전 OFF 상태와완전 ON 상태만을이용하는디지털방법으로이경우에는 TFT 의특성이불균일하여도그에따른전류량의차이가상대적으로적어서불균일성을해소할수있다. 즉, TFT 특성불균일을보상할수있어전압방식의대안으로떠오르고있다. 계조표현방식으로시분활계조와면적계조방식이있다. 시분할계조표시방식으로화소가켜져있는시간을길게또는짧게조절하여사람의눈에는밝기가다르게보이도록하여계조를표시하는방법이다. 면적계조방식은고개구율이불가능하다. 즉, 하나의화소를여러개의작은단위화소로나누어발광되는단위화소의개수에따라밝기를조절하는면적분할방식이다. 100
디지털구동방식 디지털구동방식구동영역 유기 EL 의응용분야 101
Organic TFT EL Display Variation in threshold voltage and I-V slope causes problems 102
AM 소자와 PM 소자의비교 PM 소자 제조방법간단함 크기, 화소수증가시 RC 지연, 화소간간섭, 소비전력문제점 103
Passive type 과 Active type 의비교 구동법 Passive type Duty 구동 (Row line 선택시 on) Active type Static 구동 (anytime on) 고휘도고정세화 Row line 수증가에반비례하여휘도감소 Row line 수에한계 ( 현 240 개 ) Row line 수에관계없이고휘도실현가능 소비전력 소형화 Row line 선택시요구휘도 X Row line 수의휘도가필요 고전압구동 구동 IC 를외장 요구휘도의구동전압에서항시발광저전압구동 ( 저소비전력화 ) 구동 IC 를패널상에내장소형화 소자구조 cost 단순매트릭스단순한공정 저온 poly-si 복잡한공정 104
Power Consumption Device Efficiency Display Efficiency Injection Efficiency - ITO surface modification - Interface layers - Low work function metals/alloys Balanced Transport - Selection of HTL and ETL Recombination - Band Offset Quantum Efficiency - Quenching - Doping Heating Effects - ITO tracks - Reverse bias leakage Drive Electronics - Drive waveforms 105
Power Consumption 106
Behaviour of the LED during operation I Voltage Light 0 Time 107
Degradation Processes 1. Intrinsic Degradation - Electrodes : - Cathode : - Corrosion ; O 2, H 2 O - Chemical Rxn with Org. Mater. - Diffusion - Anode : - ITO ; Oxygen Source; Degradation of Org. Layers - In ; diffusion ; Quenching sites - Au ; diffsuion ; formation of shorts - Interfaces : - Interfacial degradation - Chemical Rxn with Org. Layers Dopant ; PPV/ITO, PPV/Ca Covalent bond ; PPV/Al - Uncontrolled formation of oxide layer - Changes in injection - Electrochemical reaction - Delamination of polymer/metal Interfaces - Organic layers : - Morphological changes - Crystallization - Intermixing 108
- Morphological changes - Crystallization - Intermixing - Electrochemical Degradation - Photochemical changes - Bleaching ; Carbonyl; chain scission - Intrinsic Impurities - O 2, H 2 O, ionic,... 2. Extrinsic Degradation - Moisture and Oxygen - Substrate Roughness & Particles - Thickness of Organic Layers - Particles : Substrate/Preparation ; Device Fab.; under Cleanroom - External Heat : Crystallization - Light : UV, Visible - Device preparation condition - Sputtering, evaporation, etc. 109
Metal - Polymer Interfaces ; Al : Covalent Bond PT ; a - linkage carbon PPV ; vinylene carbon interfacial region ; 20-30 A Breaking p - conjugation Interfacial region Anode Polymer Cathode 110
Ca : Doping or Oxide Layer Oxygen-free sample ; Doping by Ca +2 ; Conducting Polymer at Hi-Temp Oxygen-rich sample ; Oxide layer formation Interface region ; 20-30 A Doped region Oxide region Anode Polymer Cathode Anode Polymer Cathode Oxygen - free Oxygen - rich 111
PL intensity EL Intensity 디스플레이공학 Degradation due to photo-oxidation 25000 1.0 0.8 0.6 air458 vac458 air514 20000 15000 0 m in 15 min 30 min 60 min 0.4 10000 0.2 5000 0 100 200 300 400 500 Time(min) 0 400 500 600 700 Wavelength(nm) Generation of carbonyl group which is quenching site under light irradiation n 112
Effects of moisture on the LED 113
Microscopic images of EL device EL image PL image Optical image 7 6 7 6 7 6 1 8 5 1 8 5 1 8 5 2 3 4 2 3 4 2 3 4 1 488 nm ITO MEH-PPV Al ITO MEH-PPV Al ITO MEH-PPV Al Halogen lamp 114
Voltage (V) 디스플레이공학 Evolution of Dark Spots 10 8 6 4 2 t3 t2 t0 t1 0 0 100 200 300 400 500 600 Time (sec) 115
Origin of Degradation Dark Spots ; Pinhole (a) (b) 1 2 1 2 1 2 (c) (d) 1 2 116
Packaging 117
Encapsulating material for OLED displays Barix is a coating : alternating layers of polymer and ceramic thin films Vitex Systems (Sunnyvale, CA) 10-year device lifetime water vapor and oxygen less than 10-6 g/m 2 /day (at 38 C and 90% RH). 118
Light Technology Performance Light Technology Performance (M. G. Craford et al. in Electroluminescence I edited by G. Mueller, p. 34) Light Technology Average Commercial Efficiency (lm/w) Incandescent 8 22 Halogen 13-39 LEDs (Inorganic) blue 3 7 red, yellow, green 20-30 white (phosphor-converted blue) 5-10 High-pressure mercury 36-60 Metal Halide 68 95 Fluorescent 41-104 High-pressure sodium 46-140 low-pressure sodium 100 200 Organic EL 40-50 Thin Film EL (ZnS:Mn) ~ 5 119
유기 EL 의응용분야 120
AM 유기 EL 의기본화소구조 선택신호구간 M2 정도에따라전류량조절가능 비선택신호구간 - 커패시터에충전된데이터가 M2 에지속적으로인가, 유기소자발광 121
수동구동에비해낮은전압 순간적으로낮은전류인가가능 셀렉트에관계없이한화면시간동안구동가능 저소비전력, 고해상도, 대면적화에유리 TFT 통해전류흘려주는구조 기존의비정질실리콘 - 캐리어이동도낮음 캐리어이동도높은 Poly-Si TFT 채용 122
유기발광디스플레이의연구동향및과제 1 삼성 SDL 2 LG 화학 3 SKC 4 Elia Tec 5 NESS Display 6 Smart Display 7 현대 Display Tech. 8 네오디스플레이 9 LG 전자 10 에이스디지텍 11 삼성정밀유리 주요소재 관련기업 1 2 3 4 5 6 7 8 9 10 11 Assembly 발광재료 발광도핑재료 전자주입 / 음극전극재료 전자수송재료 정공저지재료 정공주입재료 봉지기판 Encapsulation 흡습제 편광판 유리기판 국내소재개발동향 ( 자료 : 전자부품연구원, 유기 EL 부품소재산업동향, 2002. 12.) 주 : 생산, R&D, 판매 123
국외의연구개발동향 국내소재개발동향 (a) CDT (b) Covion (c) emagin 의유기 LED 소자 (d) Philips 의고분자발광소재 124
국외의연구개발동향 TOLED 와 SOLED 의개념도및 FOLED 의모양 125
5. 발전방향 Display Search 예측 126
기술수준및기술로드맵 유기 EL 기술수준비교 구분선진국한국기술격차 ( 년 ) 원천기술보유 90 50 5 신뢰성검사기술 85 70 1.5 소재, 부품자급도 85 50 3 생산기술 85 80 0.5 인적자원 85 75 1 자료 : 한국산업은행, 테크노리포트 종합 선진국한국기술격차 80 50 2 유기 EL 기술로드맵 유기 EL ~2004 2005 2006 2007 2008 2009 ~ 2010 소형급 AM EL 개발 - Pixel 100PPI - 수율 : 50% - 기판사이즈 : 400 400 자료 : 국가과학기술위원회, 국가기술지도 중대형급 AM 유기 EL 개발 - Pixel 200PPI - 수율 : 50% - 기판사이즈 : 730 920 Flexible 유기 EL - Pixel 300PPI - 수율 : 90% - 기판사이즈 : 1,500 1,800 127
IDC 예측 128
21 세기휴대형정보단말 Display 129
앞으로의과제 국가경쟁력면에서중요한분야 발광 mechanism 개발 새로운고분자재료의개발 소자적층구조에효율성향상 소자수명의한계극복 새로운기술과문화와결합 130
6. 생각해볼문제 1. 앞으로의 OLED 시장의확대와제조, 공정기술력들을바탕으로볼때 OLED 가 display 이외의어떠한역할을할수있을것인가? 2. OLED 디스플레이의기본구조와원리에대해서간단히설명하시오 3. 수동구동과능동구동의차이점에대해서간략히설명하시오. 4. OLED 의특징을바탕으로앞으로의 display 시장에서의위치와다른 display 와의차별성에대해서생각해보시오. 131