Changhee Lee School of Electrical Engineering and Computer Science Seoul National Univ. chlee7@snu.ac.kr PMOLED and AMOLED 김기용박사 ( 엘리아텍 ) 1
PMOLED vs. AMOLED PMOLED 공통전극 (Cathode) AMOLED Scan Line Data Line 구동법 Passive Matrix Display during line time: Duty driving (Row line 선택시점등 ) Source Gate Drain 화소전극 (Anode) Active Matrix Display during frame time Static driving 고휘도고정세화 Row line 수증가에따라높은순간휘도요구 수명, 소비전력에불리 Row line 수의한계 ( 현재 4) Row line 수에관계없이고휘도실현가능, 고해상도가능 저소비전력 순간휘도 =Row line X 휘도고전압구동 요구휘도의구동전압구동저전압구동 소형화 구동 IC 외장 구동회로 Panel 내부내장 소자구조 Cost 권장혁박사 ( 삼성 SDI) Simple process Low cost Low initial investment 저온 poly Si TFT+ 유기 EL 복잡한 Process High Fab. Cost Grey Scale Control: PWM 김기용박사 ( 엘리아텍 ) 3
Grey Scale Control: PAM 김기용박사 ( 엘리아텍 ) 4 PMOLED Driving 김기용박사 ( 엘리아텍 ) 5
AMOLED : Panel Structure Matrix 전극사이에 switching TFT OLED pixel 의독립구동가능 Frame time 동안 emission 가능 EL 구동주파수감소 High resolution, Large size panel 가능 해결과제 : TFT 불균일성및전원 line 저항에의한 voltage drop : 6 AMOLED vs. AMLCD AMOLED AMLCD 김기용박사 ( 엘리아텍 ) 7
AMOLED: Sony PDA CLIE PEG-VZ9 http://www.sony.net/sonyinfo/news/press/49/4-48e/ 8 Sony PDA : OLED vs LCD Reference : Sony s equal level LCD Sony s OLED display display (transmissive / reflective combined type) Display Size 9.7cm (3.8-inch) (same) Number of Dots 48xRGBx3 (HVGA) (same) Dot Pitch 56µm 168µm (same) Number of colors 6,144 colors (same) Brightness 15cd per square meter 55cd per square meter External Dimensions Response Time (at 5ºC, ON) Color Gamut (NTSC* Ratio) Viewing Angle Contrast Ratio (in darkness) 94.7mm(horizontal) 77.mm(vertical).14mm(thickness) (thickness including the panel only and not including the protruding portions) 65.mm(horizontal) 96.5mm(vertical) 3.49mm(thickness) (thickness includes the panel + backlight) ~.1 Mil. sec. ~ 16 Mil. sec. Approx. 1% Approx. 4% Vertical: Approx. 18 degrees Horizontal:Approx.18degrees Vertical: Approx. 13degrees Horizontal: Approx. 15 degrees Approx. 1 : 1 Approx. 1 : 1 http://www.sony.net/sonyinfo/news/press/49/4-48e/ 9
I-V-L characteristics of OLED 1 Driving Technologies for AMOLED White Balance Different data swing range Different size of driving TFT Different illumination time of each colors CCM (Color Changing Media) Different efficiency to luminescence 5 Eff. 15 Red G reen Blue 1 5 Lum. 4 6 8 1 11
TFT Characteristics Transfer Curve Output Curve PMOS NMOS PMOS NMOS Ioff 영역 : V g =V Sub threshold 영역 : V<V g <V th Ion 영역 : V g >V th Linear region WC ox VD I D = μ ( VG VT ) V L Saturation region I D WC ox = μ L FET ( V G V T ) D 1 AMOLED Driving V control Voltage-based Current-based OLED RGB V DD Driving TR I OLED Light Light IOLED Efficiency I OLED 1 = μc ox W L ( V Data V th Active-matrix 방식에서각화소마다 OLED 전류공급원이필요. TFT + 1 Cap 이가장단순한구조 15 OLED ) V GS =V Current Density (ma/cm ) 1 8 6 4 Current Density Luminance OLED 4 6 Voltage (V) 8 4 3 1 1 Luminance (cd/m ) I DS, μa 1 5 ΔV th 15 1 5 5 1 15 V DS, V 13
Brightness Nonuniformity Standard Two Transistor OLED Pixel Four Transistor OLED Pixel Sarnoff 14 AMOLED Pixel Circuit Equivalent OLED Current (I OLED ) by the same V data regardless of TFT 전압구동방식 : 인가된 V data 에의해I OLED 가결정됨 전류구동방식 : 인가된 I data 에의해I OLED 가결정됨 ( 인가된 I data 에의해적절한V gate 값이정해짐 ) 15
AMOLED : Programming Technologies 16 Backplanes for OLEDs COLUMN DRIVERS (DATA VOLTAGE) ROW DRIVERS (PIXEL SELECT SIGNAL) Poly-Si TFT a-si TFT OTFT Type CMOS NMOS PMOS Performance : Mobility Leakage Stability Uniformity Very good OK Good Issue OK for PHOLED Very good OK OK? OK Issue Issue Data Line V DATA Scan Line Power Line V DD C Switching TR OLED RGB Driving TR Light Manufacturability Maturing Excellent N/A # of Interconnercs Data? scan +data scan +data Cost >Medium Medium Low Plastic compatibility Under development Good Excellent M. Hack, IMID 3 17
LTPS vs a-si TFTs LTPS TFT (ELA) Expensive process (~ x a-si TFT) Poor Uniformity Drain Current [A] 1.E- 1.E-3 1.E-4 1.E-5 1.E-6 1.E-7 1.E-8 1.E-9 1.E-1 1.E-11 1.E-1 1.E-13 Max out at 4th Gen Tools 1.E-14 - -15-1 -5 5 1 15 Gate Voltage [V] Source LTPS TFT Interlayer Insulator Gate LDD: n- poly-si Drain Gate Insulator n+ poly-si n+ poly-si Blocking Layer Glass a-si TFT Low mobility (< 1 cm/vs) Operational instability (V th shift) 1.E-4 1.E-5 1.E-6 1.E-7 1.E-8 1.E-9 1.E-1 1.E-11 1.E-1 1.E-13 1.E-14 - -15-1 -5 5 1 15 Source a-si TFT Passivation a-si:h Gate Insulator Gate Glass Drain 18 LTPS non-uniformity Non-uniformity problem of ELA (Excimer Laser Annealed) Poly-Si TFT XeXl (λ=38 nm) ELA: 가장일반적인 Si 박막결정화방법 Laser energy fluctuation non-uniform crystallization non-uniform V TH and μ of poly-si TFTs non-uniform brightness 19
Possibility of a-si TFT Required Compensation of Vth Shifting Small Size High Resolution is very difficult (Low Mobility) Temp. Stability? Threshold voltage shift of a-si TFT Long term bias stress leads to threshold voltage shift (ΔV th ). V T-S hift (V ) 7 6 5 4 3 OLED α I DS t ΔV T = W μ τ C i L Stretched Expo. Model β 1 t ΔV T = ( V V ) G T 1 exp τ 1 3 4 5 6 A. Nathan, IMID 5 I μeff = C α α 1 i 1 W ( V L β GS Stress Time (Hours) V ) α T Power Law Model Source Gate 1 Drain V th a-si:h layer a-sin x :H layers metallization n + μc-si:h layers substrate