continued 디스플레이 및 조명용 LED 기술분석

Improving picture quality 디스플레이용 LED 개발방향 및 주요기술 Value Up Point? - Picture Quality, ECO, Slim Picture 2,000,000:1 Improving picture quality Color Gamut Contrast Scanning / Local Dimming 色 再現性 (CCFL 72%, LED 78~95%) Contrast 5,000:1 80,000:1 ` LED TV TV Slim(29mm↓) Design CCFL :~ 105mm  Super Slim LED TV : 20mm↓ Slim化 [ '09年 Edge형 LED Model] - CCFL比 消費電力 40% ↓ 實現 Power Consumption Green Size ‘08 '09 ‘10 CCFL Direct LED Edge LED 40” 180W 120W 85W 70W 46” 215W 135W 95W 77W *Hg free CO2 Down * 120Hz 기준 09 Photonic Conference: LED session

주요 기술 ① Chip technology 高휘도,高출력 LED개발 → 저 소비전력 구현 주로 middle Power 이하 Chip 사용 - Mobile @20mA, 대형 display용 @100~300mA 구동 개발 방향 2005年 ~ 2010年 ~ 低출력 백색 LED(@20mA) 50 150 lm/W 高출력 LED(@100~300mA) 150  200 lm/W 以上↑ ◈ 내부양자효율(IQE) 향상 - Epi: 결정성 향상, MQW 구조 최적화 - Chip: 전극구조 최적화 ◈ 외부 추출효율 향상 - Chip : P-GaN roughening, n-GaN &ITO patterning 적용 ※ RG형광체 경우 30% 효율 저하 예상 결정성 향상 Patterned Wafer [Flip, Thin GaN 구조] [EPI up구조] Surface pattering 기판(Al2O3) 사용 - 고 방열 수직 구조 roughening P-GaN 09 Photonic Conference: LED session

Red Green Phosphor with  Wide Color Gamut White LED 주요 기술 ② 형광체 기술 색 재현성↑, 효율 향상 新 형광체 (Red, Green형광체) Red Green Phosphor with Blue LED  Wide Color Gamut White LED Yag, Silicate계열 (1st Gen.) Quantum Dot 재질 (2nd Gen) NTSC 比115% 110 Deep Green쪽으로 확장 Deep Red 쪽으로 확장 색재현성(%) NTSC 比 95% 반치폭(nm) 90 v’ 현재 NTSC 比 78% 60 20 ’09 현재 ‘11 ‘15 년도 u’ 09 Photonic Conference: LED session

Package Design for display 주요 기술 ③ Package Technology -Life Time Package Design for display 구조 관점 설계 인자 재료 관점 설계 인자 열 전달 구조 단순 Lead frame 구조 Molding compound Chip mold Durable to high temp. Highly reflective L/F [변색방지] [열저항 : 30K/W] 열 전달 구조 복잡 Lead frame 구조 Encapsulation Chip mold Highly Reliable Silicone Resistant to UV, high humidity & temp. Lead Frame [변색] [열저항 大 : 80K/W] Thermal Resistance Lead frame contacts PCB directly ~ 40K/W (@ 60mA) 09 Photonic Conference: LED session

조명용 LED의 개발방향 및 주요기술 에너지절감 및 환경보호 / 사용자 친화적 Smart 감성 조명 고효율 및 친환경 ■ Energy Saving 광원 - 백열등 대비 전력소모량 1/7, 수명 13배 - LED 조명 100% 채용시 2.1조원/年 절감 ※ 05年 국내 조명전력 13 TWh 中, 10 TWh 절감 가능 → 원전 10기 생산전력 ■ Design Flexibility - 조명燈 디자인 편의성 → 경박단소 - RGB LED를 통해 Color 표현 용이 - Robust → 충격에 강함 (출처 : 한국 전력 통계 2006, KOPTI) ■ CO2 배출 절감 - 60W 백열등 CO2 배출량 3,714㎏/年 → LED CO2 배출량 511㎏ ■ 고연색 광원 - CRI 95↑가능 → 태양광에 가까운 광원 - RGB 3색 조합 → 1,670만가지 색 표현 (출처 : Toshiba Lightec 보도자료 (’08) ) ■ 수은-Free 광원 - 40W 형광등 수은 25mg (토끼 치사량) → 사람 치사량 : 0.1~0.5g - 국내 형광등 1.7억만개/年 소비 → 4 Ton/年 수은 하천 유입 ■ 안전성 - 저전압 사용으로 인한 안전사고 방지 - 短반응속도 → 백열등 10만분의 1 수준 09 Photonic Conference: LED session

주요 기술 ① Chip technology Efficiency Droop 감소 기술 광효율 향상 기술 고출력, 고효율 Epi / Chip 개발 Chip 인가 전류 350mA ~ 1A (@~3.4V) : High Power Efficiency Droop 감소 기술 광효율 향상 기술 ※ 정의: 구동 전류 증가에 따라 光효율이 감소하는 현상 ※ 원인: Electron Leakage ※ 접촉저항 감소, 전류 확산  전력 손실↓ 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 5 10 15 20 25 30 35 40 EQE, % Current, A Final Target Droop ※ 반사율 향상, 전반사 감소  광 추출 효율 ↑ 09 Photonic Conference: LED session

주요 기술 ② Phosphor & Color 광효율 향상, 색 재현성↑, 형광체 합성 기술 70% 85% 광효율 향상, 색 재현성↑, 형광체 합성 기술 연색성 ( Color Rendering Index ) Iradiance (W/m2/nm) 1 2 500 1000 1500 2000 (㎚) 태양광 파장 분표 ① 재료 설계 (모체, 부활재) ② 휘도 최적화 (例) Combinatorial Method) ③ 합성, 입도제어, 표면처리 G B R B B R Y G 색 제어 발광 효율 향상 UV [Blue+Y형광체] [UV+RGB형광체] [RGB LEDs] 09 Photonic Conference: LED session

집적(Integration) 기술 : LED Chip + 형광체 + 봉지재 + 렌즈 + 몰드(컵) 주요 기술 ③ Package Technology 집적(Integration) 기술 : LED Chip + 형광체 + 봉지재 + 렌즈 + 몰드(컵) Optical, Thermal, Color Design & Process Tech. Optical Lens Adaption : Durable to high temp. : Highly Optical efficiency With Dome Lens Thermal Management Color Distribution (b) Ceramic PKG (a) L/F Type : Solution For Bull’s Eye effect . : Conformal Phosphor Coating : White Chip solution < Bull’s Eye > : Lowering the power consumption !! : Incrase Life Time !!! 09 Photonic Conference: LED session

Ⅱ Ⅲ Ⅰ 결언: LED 산업기술의 연계성 전방산업 발달 1. 휴대전화 시스템 2. LCD TV 3. 자동차 4. 조명 5. 조선 6. 정보가전 LED 응용(융합) 휴대전화, LCD BLU, 자동차/조선, 정보가전, 농업, 수산업, 항만, 의료, 환경, 정보통신, 군사 LED 조명 실내조명, 실외조명, 도로조명, 건축/디스플레이조명, 광학 기구 설계/제작 LED 제어구동회로 Ⅱ Ⅲ 광원모듈 광원 모듈 조립 패키징 LED 장점 1. 고효율 2. 장수명 3. 초소형, 경량 4. 저전압 구동 5. 저온 광원 6. 점광원 7. Full Color 8. 빠른 반응속도 9. 설치 간단 패키지 공정 Standard, S/V, H/P PKG, Array PKG 형광체 ect. 광소자 LED 칩 공정 다층 박막 성장 (In,Al)GaN(청,녹,UV), InAlGaP(적,황), AlGaAs (적,IR) Ⅰ GaN/sapphire GaN/SiC 기판 Sapphire, GaN, SiC, Si, GaAs 09 Photonic Conference: plenary session

요약 LED 기술개요 백색 LED 설계/제작 기술 - 에피, 칩, 패키지 효율 향상 방안 디스플레이 및 조명용 LED 기술분석 결언

History of HEMT - An idea of using heterostructure, proposed by W. Shockley - High mobility of 2D gas, predicted by Esaki & Tsu, 1969 Advancement of Epitaxial Growth Techniques, MBE  (atomically flat interface, abrupt doping profile, high crystal quality) - 2D gas, experimentally proven by Dingle et al., 1978 - AlGaAs/GaAs HEMT, fabricated by Mimura et al., 1980 - HET (Hot Electron Transistor), Heiblum et al., 1981 - RHET (Resonant Tunneling HET), Yokoyama et al., 1985 HEMT 관련: Semiconductor & semimetals, Vol. 30

Temperature dependence of ‘e’ mobility for high purity GaAs with n = 2.7 x 1013 cm-3 ‘e’ mobility of GaAs=4800cm2/Vsec @RT It becomes as great as 300,000 @40K due to the decrease of polar-optical and iezoelectric-acoustic phonon scattering. Below 40K, it decreases steeply to ~ 9000 But, the problem is low conductivity of u-GaAs. If increasing doping, mobility @40K ~@RT due to impurity scattering. Need for semiconductor materials with both high mobility and high carrier concentration  modulation-doped superlattice, proposed by Esaki and Tsu A key technology for the success of HEMT is (Si dopint is abrupt doping profile, low diffusion) HEMT 관련: Semiconductor & semimetals, Vol. 30

Modulation Doping spacer HEMT 관련: Semiconductor & semimetals, Vol. 30

AlGaAs/GaAs HEMT Surface depletion Interface depletion HEMT 관련: Semiconductor & semimetals, Vol. 30

2DEG properties Temperature dependence of ‘e’ mobility 2DEG properties are determined by Spacer layer thickness Background impurity concentration in the GaAs region -Si doping concetration in n-AlGaAs -Al mole fraction in AlxGa1-xAs (x) Temperature dependence of ‘e’ mobility and sheet concentration HEMT 관련: Semiconductor & semimetals, Vol. 30

2DEG vs. spacer layer thickness The most effective parameter for increasing 2DEG mobility at low temperature Under illumination, 2DEG concentration increases to ~ twice the original due to the PPC effect Two limiting factors of 2DEG mobility (1) Remote impurity scattering of 2DEG by Si impurities in n-AlGaAs is reduced with increasing the thickness,  increased ‘e’ mobility (2) 2DEG concentration decreases with increasing the thickness, resulting in enhanced ionized-impurity scattering and reduced ‘e’ mobility At the early stage, spacer thickness < 10nm due to the scattering center in AlGaAs All the Si impurities and not electrically active in AlGaAs for Nsi > 4x1018cm-3 due to PPC Under illumination In the dark HEMT 관련: Semiconductor & semimetals, Vol. 30

GaAs/n-AlGaAs HEMT (by Mimura et al., 1980 ) Advantages: 1) High mobility – due to spatial separation between mobile carriers in channel and parent ionized donor impurities. 2) High transconductance – due to high sheet concentration (2D gas in HEMT ~ inversion layer in MOSFET, but effective mass of GaAs is very small (0.06me), leading to significant quantum effect  Ef moves up to CB edge  high sheet concentration. - due to small separation between gate and channel (Cg increase fm, fT increase) 3) Higher turn-on voltage for the gate current, reducing the gate leakage Disadvantages: due to the DX center (or dopant induced traps) - Small voltage swing (Vg-Vt) Large Vt shift with temperature PPC, etc. HEMT 관련: Semiconductor & semimetals, Vol. 30

Limitations of GaAs/n-AlGaAs HEMT DX center causes I-V collapse at low temperature and thermal instability of the Vth of a HEMT (2) Small conduction-band edge discontinuity, leading to insufficient, low 2DEG concentration (3) Thermally unstable layer structures with respect to diffusion of Si from the n-AlGaAs layer into the GaAs channel region  difficult to anneal these materials.  flash-lamp annealing  using GaAs stopper layer (to prevent the penetration of 2DEG wavefunction into the GaAs (with a small diffusivity) stopper layer HEMT 관련: Semiconductor & semimetals, Vol. 30

Progress in HEMT (1) Pseudomorphic HEMT: AlGaAs/InGaAs, AlInAs/InGaAs structures: Advantages: by making a junction between two materials with a large discontinuity, - produced a large QW  increasing the electron density - Free of DX center  high doping becomes possible  high gm - High mobility of InGaAs. Disadvantages: high gate leakage current  Low VBD HEMT 관련: Semiconductor & semimetals, Vol. 30

Progress in HEMT (2) SL HEMT, proposed by Baba in 1983, using AlAs/GaAs SL instead of AlGaAs layer - dopants are incorporated in the GaAs QW. - DX center is eliminated HEMT 관련: Semiconductor & semimetals, Vol. 30

Progress in HEMT (3) Planar doped HEMT, proposed by Eastman in 1983, a few tens of A Si doping is made in a GaAs layer symmetric and asymmetric type HEMT 관련: Semiconductor & semimetals, Vol. 30

Enhancement/Depletion-Mode n-HEMTs E-mode D-mode HEMT 관련: Semiconductor & semimetals, Vol. 30