Line RC Delay and Mobility issue RC delay (Signal line) RC delay becomes a dominant factor above UHD Mobility (TFT) Line signal decay becomes a serious issue! e e e e e e e 0.5 ~ 1.5 um thick Cu lines required! 1
Line RC Delay issue with higher Resoution RC-Delay of Gate Bus-Line d1 d2 R R C d12000...... C i t = S (RC)i R C Ton Shading R i = 12000 for UD C RC-Delay 2
On the other hand, a-si:h is facing its limitations Next TFT Platform 20 TFT Performance Criteria 15 10 Frame Rate 480Hz 5 Post a-si TFT 20.7 14.8 10.4 7.4 7.4 3.7 60Hz120Hz Gate Time 3.7 Doubling Technology 1.8 1.8 0.9 240Hz 480Hz 240Hz 120Hz 60Hz SD a-si TFT HD FHD UD Super HV (4Kx2K) (8Kx4K) Resolution 3
Approaches to Post a-si TFT Many Approaches for Post a-si Various Approaches to overcome a-si limitations for ① ② ③ Next Gen. LCDs OLED High resolution displays a-si μc-si 1. 2. 3. 4. 5. Microcrystalline Si Metal induced Crystallization (MILC) LTPS Low cost large area LTPS RTA of a-si MIC ELA SLS 0.5um 0.5um 4
Non-Laser Crystallization Approaches Non- laser Crystallization MIC FE-RTA (Viatron) RTA (Metal Induced Crystallization) (Rapid Thermal Annealing) MIC Equipment (Tera) 5
Growth of LTPS for Smart Phone Displays Due to High Resolution, Low power trend of iphone & OLED Extreme Resolution (960X640) iphone 4 Retina LCD 6
Expansion of LTPS LTPS investment to upgrade AMOLED capacity LTPS to upgrade iphone LCD capacity Advanced LTPS Equipments & Process ELA (JSW) Advanced Equipment - G6 Equipments - High throughput Laser Annealing Advanced Process DLS (TCZ) 5 mask PMOS - Reduced Mask step 7 mask CMOS * CMOS for Mobile (Low Power consumption) SLS (JSW) * PMOS for OLED-TV ( Cost issue) 7
LTPS for Gen 5.5/6 Fabrication Advance in Laser Crystallization Methods Advanced ELA (Excimer Laser Annealing) TCZ (Advanced SLS) 750 mm Laser beam width 750 1300 mm 1300 Adv. ELA Laser beam size 750mm 400 um 1300 1500 Adv. SLS(TCZ) 745mm 4 um Crystallization method determines Grain orientation, TFT Performance, throughput 8
Oxide TFT for Next Tablet PC Display New ipad Ultra High Resolution - Lower Power consumption than a-si Next OLED for Tablet PC - LTPS compatible Oxide TFT 9
Can Ox TFT enter Smart Phone Displays? 1 Middle- end Smart Phone 2 Not - So- Narrow Bezel - Integrated Circuit on Panel 3 Advantage over LTPS for in-cell Touch - inherent lower leakage current enables low frame rate driving 10
Can Ox TFT compete with LTPS? 1 High Resolution Tablet LCD with Fine Pattern 2 OLED TV Backplane with LTPS like stability Backplane for μ ~7 cm 2 /Vs μ > 20 cm 2 /Vs μ > 50 cm 2 /Vs XZTO XZnO..?
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19 Demand for High Mobility Oxide TFT 1. Strong demand from Tablet PC - High end Tablet PCs will continue High Resolution - initial production started by Sharp for new ipad - LGD uses IGZO TFT for WOLED production 2. Next Generation LCD - UD - 3D -70 240Hz - Small market, Ox TFT s priority shift to Tablet 294M 70M 70 UD 240 Hz 15M 10 11 15 Super Hi Vision 3D 3. Inexpensive OLED-TV Backplane - can utilize existing a-si line - Manufacturing of Oxide TFT slowly improving Area Vth uniformity Auto Stereoscopic 3D
Oxide TFT for Next Generation LCD-TVs 70 UD 240 Hz 3D Super Hi Vision Auto Stereoscopic 3D 20
Progress in Oxide TFT Backplane New ipad (Sharp Oxide TFT, Production 4Q 12) LGD 55 OLED TV ( Production Feb 13) BOE 65 LCD-TV (March 13 FPD Shanghai) 21
Oxide TFT Advance Oxide TFT Evolution Gen1 μ ~6, 7 cm 2 /Vs Gen2 μ ~ 20 cm 2 /Vs Gen3 μ ~ 50 cm 2 /Vs High mobility Oxide TFT for - High Frame Rate - High Resolution large screen TVs Best Image Quality Active Glass 3D TVs Auto Stereoscopic 3D 22
Higher Mobility Ox TFT How high the mobility can Go? InSnZnO New IGZO IGO, 1017 cm3 m = 30.9 cm2/ V.s m = 24.2 cm2/ V.s m = 39 cm2/ V.s DC sputtered Al2O3 DC sputtered Al2O3 nude TFT IDW 2010, Sony SID 2011, 49.1, Sony Applied Physics Express (2012) Idemitsu Kosan Co., 23
High mobility even in amorphous phase Oxide semiconductor - ionic bond a-si:h - covalent bond Ionic bond has less chance of bond breaking, lower charge trapping and tail state. High mobility Through the overlapped S orbital, it provides the electron pathway High mobility 27
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OLED-TV Backplane Choice PMOS LTPS vs OXIDE TFT White EL RGB EL CF LTPS Oxide TFT Gen 6 Gen 8 Amorphous GIZO ELA LTPS 35
TFT for AMOLED AMOLED : Current driven Device Difficult to supply Uniform current to each pixel V DD V p i EL (Switching TFT) (Current driving TFT) Vth Uniformity over Area 36
Backplane Issues on Large OLED-TV Stable & Uniform TFT Backplane - Uniform Grain size / Uniform Vth - Uniform Ion/Vth to prevent mura Data Line VDD Address Line Protrusions Switching TFT Driving TFT Tiny grains Uniform grains inside channel OLED 37
Short range Uniformity Issues in OLED local V th variations Ids fluctuates Local brightness variations (Mura) in display local V th variation is caused by Non-uniform Crystallization Vth variations in 10 s mv range Detectable by eye I ds I ds K ( V JND V th gs 2K ( V 2% V ) gs 2 th V ) V th L L I I ds ds 1 JND ( V 2 gs th 2 Vth V V V ) th gs th Ids(A) TFT 1 TFT 2 SPC DR (W/L=40/4) #2 2.0 ua 0.E+00-14 -13-12 -11-10 Vgs(V) V DD S D S D 1 2 3 4 5 6 7 8 9 10 11 12 13 14 38
Vth Shift in AMOLED TFT LCD : Voltage driven Device AMOLED : Current driven Device Data Line V DD Address Line Cst CLC Vcom V p i Switching Oxide TFT Negative Vth Shift under Photo Bias stress EL (Switching TFT) Negative Vth Shift under Photo Bias stress (Current driving TFT) Positive Vth Shift under Photo Bias stress 39