Philips Lumiled 2001

High Power White LED Technology
for Solid State Lighting
Paul S. Martin
J. Bhat, C.-H. Chen, D. Collins, W. Goetz, R. Khare, A. Kim, M. Krames, C.
Bhat, C.- Khare, Krames,
Lowery, M. Ludowise, G. Mueller, R. Mueller-Mach, S. Rudaz, D. Steigerwald,
Ludowise, Mueller- Rudaz,
S. Stockman, S. Subramanya, S-C Tan, J. Thompson, T. Trottier
Subramanya, S-
1 Copyright (c) Lumileds Lighting LLC Company Confidential

High Power White LEDs

Who is Lumileds
• Fully integrated light source supplier that co-develops optimized system solutions!

• LED dice

• Luxeon™ Power Light Sources

• Arrays of High Flux LEDs on
a metal core PCB

• Automotive, Traffic Signals, Signage & Contour Solutions

2 Copyright (c) Lumileds Lighting LLC Company


Outline

• Competition in the market for Illumination, Incandescent & Fluorescent Bulbs.

• LED Metrics

• Options for making white light from LEDs

• Lumileds power white LED performance

• Some interesting demos


Illumination Markets

How Much Energy is Used for Lighting
• In 1999 the US used 3 Trillion kWhr of Electricity!

• 20% or 600 Billion kWhr of Electicity generated was used in Lighting!

• Incandescent/Hal. lamps burn 40% of electricity to produce 15% of light!

• Fluorescent/HID lamps use 60% to produce 85% of light!

• Illumination market is $60Billion/yr and growing slowly, ~2%/yr



Incandescent Bulbs
• Incandescent = hot light, emitted from a (tungsten) filament at around 2800oK
• Disadvantages:
• mostly infra-red
infra-
• glass vacuum envelope & filament both break easily
• <15 lm/W luminous (<5% power) efficiency
• fire hazard, burnt fingers, maintenance
• Advantages:
• Radiant cooling black body spectra
• Cheap 0.0005$/lumen 2
• klm per package! 1.8
power spectra, norm.@600 nm
3000K
1.6
1.4 4000
1.2
Basic disadvantage: 5500
1
no chance to come close 0.8
to DAYLIGHT = 6500oK 0.6 6500

0.4
7500
0.2
0
0.3 0.4 0.5 0.6 0.7 µm 0.8 0.9
Courtesy Gerd Mueller LL



Fluorescent Bulbs
• Fluorescent = cold light, emitted by phosphors excited by gas discharge.
• Advantages:
• High efficiency 80+lm/W & High Flux klm/lamp
klm/lamp
• Moderate cost for large lamps 0.002$/lm
• Disadvantages:
• Lifetime short <10,000 hrs resulting in high maintenance.
• Glass vacuum envelope leaks/breaks, ballast noisy.
• Mercury!! 0.025 1.2

1.0
0.02

0.8
black body 3600 K
rad. flux, a.u.

rad. flux, a.u.
0.015
Basic Advantage:
0.6
fluorescent, CCT=3600 K
any color temperature 0.01
Ra = 83
possible by tri-color mixing 0.4

0.005
0.2

0 0.0
400 450 500 550 600 650 700 750 800
Courtesy Gerd Mueller LL nm



Assumptions for using LEDs in lighting
• LED lamps will be far more expensive than incandescent, halogen or
fluorescent lamps for at least a decade.

• The expensive LED lamp must pay for itself through lifetime energy and
maintenance savings.

• The lighting industry has spoiled the users with superb color rendering and
color control.

• Near term LEDs must dominate monochrome and penetrate white niches!



Outline


• LED Technology & metrics





LED Metrics

Tower of Babble?
optical power out / electric power in = Wall-Plug-Efficiency, WPE, (%,W/W)
photons out / electrons in = External Quantum Efficiency, EQE, %
photons internally generated / electrons in = Internal Quantum Efficiency , IQE, %
photons out / photons generated = extraction efficiency, %, ηext
photon energy / applied voltage (times electron charge) = electrical efficiency, %, ηel
lumens out / electric power in = luminous efficiency [lm/W]
luminous efficacy, LE [lm/W] = luminous equivalent of the emission spectrum

luminous efficiency = IQE*ηext*ηel*LE
IQE*ηext = EQE
EQE*ηel = WPE
WPE*LE = lm/W


LED Metrics

LED Skulduggery

Paul’s Top 5 Sins What am I hiding?
1) Quoting EQE without Vf or WPE 1) Vf, power efficiency
2) Quoting low duty factor results 2) Thermal resistance, heating
3) Quoting WPE without current or 3) GaN in particular has strong
current density & total power out. dependence of WPE on current
not much light comes out of a
device at very low currents!
4) Quoting WPE without temperature 4) WPE is strongly dependent on
junction temperature for
AlInGaP, less so for AlInGaN.
5) Quoting Cd without Flux 5) Radiation pattern


LED Metrics

Tower of Babble take 2 for white LEDs
How well can a source reproduce “natural” colors = Color-Rendering-Index, Ra, %
(100 = sunlight, 85 = office, 60 = cabinet/lantern light)
Color Correlated Temperature = CCT, Kelvin
(x,y coordinates normal to black body curve)

0.9
CIE1931
Phosphor Converted LED = PCLED 0.8 Planckian locus
tungsten, 2850K
LED photons pump phosphor which emits secondary, 0.7 halogen, 3100K
and longer, wavelength of light. daylight, 6500K
0.6

Stoke’s shift = Difference in wavelength between 0.5
absorbed and emitted photons. Emitted photons
always have longer wavelength, i.e. lower 0.4
10,000K
energy! 0.3
2500K
3300K
5000K
0.2

0.1

0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8



Outline







White Light from LEDs

Three methods of Generating LED White Light
• Each method has potential strengths!

Red + Green + Blue LEDs UV LED + RGB Phosphor Binary Complimentary

UV LED
Spectrum Combined
Red Peak Spectrum
Blue Peak Combined
Phosphor Phosphor Spectrum
Green Peak Emission Emission Blue LED
Spectrum

410 470 525 590 630 (nm)
470 525 590 630 (nm)
470 525 590 630 (nm)

RGB LEDs UV LED + RGB phosphor Blue LED
+
Yellow phosphor


Combining Red, Green and Blue LEDs
• Advantages:
• Long term likely the most efficient!
• Dynamic tuning of color temperature possible!
• Excellent color rendering!
• Very large color Gamut available!
• Challenges
• Color Feedback required today to account for LED degradation with T & t!
• Color mixing tricky!
• Yellow-Green Gap!

LED
CCFL
NTSC
EBU


Combining Red, Green and Blue LEDs

Lumileds LCD Backlight!
• 20 Green, 10 Red, 10 Blue Luxeon’s, ~ 1000 lumens!
• Today LED Solution has 140% Color Gamut and 120% CCFL power!

Both displays showing
the same slide
(red only background)
via a splitter

LED solution

CCFL solution

White from RGB LEDs

The Yellow-Green Gap!
• Eye Sensitivity Peaks right in the middle of the Yellow-Green GaP!

60
Tj = 25ºC VCSEL
LEDs
50

40
C o n v e r s i o n

Best Laboratory
30
Result

20 Production
Average

10

0
450 470 490 510 530 550 570 590 610 630 650 850

Wavelength (nm)


UV LED pumped RGB Phosphors
• Advantages:
• White point determined by phosphors ONLY! (i.e. tolerant to LED variation)
• Excellent color rendering possible!
• Theoretically “Simple to manufacture!” (Looks like TV or Fluorescent lamp except
for pump is now UV LED rather than electrons.)
• Temperature stability of phosphors. (Can be great!)
• Disadvantages
• Potential for damaging UV light leakage.
• Fundamental limits on efficiency due to phosphor conversion efficiency, Stokes
shift, self absorption,…
• Challenges
• None available yet!?
• Efficient Blue LED pumped phosphor not available yet?!
• Color uniformity with angle!
• Packaging must be robust to UV exposure.
• Temperature stability of phosphors. (Great phosphors not available in all colors!)


UV LED pumped RGB Phosphors

UV LED must be >2x Green LED WPE for same lm/W!
• Downshift in color causes fundamental energy loss.
• Scattering in phosphor + absorption in package (inc. phosphor) reduces extraction
efficiency! Today’s best package efficiency is ~50% for Blue + Yellow phosphor,
UV + RGB phosphor likely to be even worse!

100%
90%
Power Conversion (%)

80%
70%
60%
50%
40% Red 630nm
30% Blue 460nm
20% Green 540nm
10% White
Assuming 50% pkg. Efficiency! White + Pkg
0%
370 380 390 400 410 420 430
UV Pump Wavelength (nm)



White from Blue LED + Phosphor(s)
• Advantages:
• Simple and single Yellow phosphor versions available today!
• Decent color rendering (Ra = 75 for Blue LED + Yellow Phosphor)
• Temperature stability of phosphors. (Can be great!)
• Disadvantages
• Limits on efficiency due to phosphor conversion efficiency, Stokes shift, self
absorption,…
• Better color rendering (i.e. multi phosphor comes at cost of efficiency)
• Challenges
• Temperature stability of phosphors. (Great phosphors not available in all colors)
• Color uniformity vs. angle
• Multi phosphor versions to improve color rendering



Today, PC LEDs are in the 20-30lm/W range!
• Todays white LEDs are in the ~20-30lm/W range!
0.9

LED, T = 25C Ce3+ doped garnet family,
LED,T = 105C
0.8
e.g.(Y,Gd)3Al5O12
YAG:Ce
Planckian locus
0.7
530 CIE1931 Combined with the same LED, Ce3+
520
540
phosphors hit the Planckian at different
0.6

510 color temperatures:
0.5

500
590 70
0.4
600
60 CCT=4000K, Ra=75
10,000K
50
620
2500K 630 40
0.3
490 3300K 30
640
5000K 20
0.2 10
480 0
400 500 600 700 nm 800
0.1
470

460
450 nm
Ra = 75 is not great (good FL has 83)
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
but it is OK for some applications.



Color Uniformity can be good for PC White!
• CCT uniformity of 50-100K is sufficient for high quality illumination.

5400
5200
5000
4800
4600
CCT (K)

4400
800K
4200
4000
3800
3600
80K
3400
3200
3000
-85 -75 -65 -55 -45 -35 -25 -15 -5 5 15 25 35 45 55 65 75 85

Theta (degrees)


Progress on Temperature stability of Phosphors
(Y,Gd)AG:Ce
measured on powders
1200000 25 C

radiance under 460 nm excitation
50
(Y,Gd)AG, 4 mol% Ce
1000000 100
120
100 [Gd]
800000
150
0% 200
600000
80
400000
I(T)/I(25C), %

60 25
200000
40
50 0
75 400 450 500 550 600 650 700 750 800
20
nm

0
25 50 75 100 125 150 1200000

Temperature, C 25
1000000
50
100
800000
120

novel phosphors with improved 600000 150
200
color specs emerge; in this case 400000
using a Ce3+ - Pr3+ transfer of
200000
excitation energy and yielding
more temperature stable behavior 0
400 500 600 700 800



The 2-phosphor-converted LED – 2pcLED
0.9
combospec
1 LED + 2 phosphors 2.00

1.50
Ra = 92 Adding green and red to the
0.8
1.00
blue of the LED opens a huge
0.50

0.7
0.00 color gamut and allows for
400 500 600 700 800
530
TG:Eu de-luxe white of any color
520 HP LED, T = 25C
0.6
540
HP LED,T = 105C temperature – our best choice
Planckian locus
510
8206 Phosphors • SrGa2S4:Eu2+ - green
7193 CIE1931
0.5 7118 Series15 • SrS:Eu2+ - red
500 590
0.4
600
10,000K 610
SrS:Eu
620
0.3
2500K 630 The dipole-allowed 5d-4f
490 3300K
5000K
640 transitions of Ce3+ and Eu2+
0.2 1.60
combospec are uniquely suited for color
1.40
480 1.20
1.00
Ra = 92 converters:
0.1
0.80
0.60
high absorption, small
470 0.40

460
0.20
0.00
Stoke’s shift
400 500 600 700 800
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8



All three white LED technologies share Three
challenges!

90 lm/bulb
1 Maximize efficiency in lm/W
6 lm/W
0.005 $/lm
2 Maximize flux density in lm/package

3 And of coarse reduce cost $/lm

475 lm/bulb 145 lm/bulb
10 lm/W 50 lm/W
0.01 $/lm 0.02 $/lm



Outline








Gold Wire Bond

Epoxy Dome Lens
LED Chip

p pad
Reflector Cup
semitransparent
contact
Cathode Lead Anode Lead
n pad

Junction area ~ 0.06mm2

Limitations of conventional 5mm Indicator LED lamps
• Very high thermal resistance, >200°C/W,
• Epoxy limited to <<120°C due to thermal yellowing,
• Light utilization efficiency is low.



Luxeon™ approach
Die design
• Large area die for high power capability,
• Electrode design for low spreading resistance,
• Flip-chip configuration;
Flip-
• high extraction efficiency,
• low thermal resistance,
• ability to integrate electronics.

Package design
• Low thermal resistance package,
• Stable, soft gel inner encapsulant,
encapsulant,
• Controlled radiation pattern and efficient optics.

System design
• Low thermal resistance board design,
• Efficient secondary optical elements.



Lumileds LuxeonTM Power LED Efficiency
• Leading the charge into Solid State Illumination

Production Typical R&D Demonstrations
350mA If lm/W lm/LED lm/W lm/LED
Red 44 43 50 50
Red-Orange 55 54 65 65
Amber 36 36 44 44
Green 25 30 50 55
Blue 11 14 15 20
White 18 22 30 36


LED Technology

Haitz’s Law for LED Flux
• LED Flux per package has doubled every 18-24 months for 30+ Years!!
• 1965 Moore’s Law “# of Transistors/chip will double every 18-24 months!”

1000
Flux/Package (lumens)

100
TM
Luxeon
10

1
Indicator LEDs
0.1

0.01

0.001
1960 1970 1980 1990 2000 2010
Year


Lumileds LuxeonTM Series A & B LEDs
• First ever White LED > 100lm!! (100.2lm and 15lm/W to boot!!)
1000

Luxeon Series B White LED
100
Flux output (lm)

Luxeon Series A White LED
10

Indicator White LED
1

0.1

All data AC 1%DF & 25C case
0.01
0.1 1 10 100 1000 10000

30
Power input (mW)
Copyright (c) Lumileds Lighting LLC Company


Lumileds 100 lumen Club!
• These are the only LEDs that approach “Illumination” flux!

Red 1000 105 February-01
Amber 700 110 December-99
Green 700 108 March-01
White 1870 100.2 July-01
White 1400 >110 1-Sep



What about Radiometric Power?!
• State of the art 400nm indicator LEDs provide 15mW of power.
• How much power can a Luxeon part generate? :-)

If (mA) W/LED Date
Deep Blue 430nm Dan Steigerwald July-01
1400 >1.0

Talk 4445-19 08:30 8/1/2001



Lumileds LuxeonTM Series B Cyan LED
• Single Series B Cyan LED can replace an 80W bulb in an 8” traffic ball!

130 lm/bulb
30 lm/W
0.20? $/lm



Lumileds LuxeonTM Ring
• Fixture design by Philips Lighting and Lumileds.
• 12 Luxeon’s, ~240 lumens. Ring available Now!



Outline


• LED Technology and metrics

• Comparison of options for making white LEDs





Evolution of LED Package Technology
• Power LEDs can handle ~50x power of an Indicator LED!

Pmax~0.6-4.0W
Pmax~0.2-0.4W 9-14 K/W
50 K/W 1998
LumiLeds LuxeonTM
1994
LumiLeds SnapLEDTM Today’s Power LED
Pmax~0.1W
150-200 K/W First Power LED
1970
Standard 5mm Lamp
1962
First Packaged LED Indicator LED

Indicator LED


Lumileds LuxeonTM Power LED
• Packages designed to handle 1-5W!

High-Power Package:
Improved thermal properties
Heat sink body with good thermal interface
Soft gel inner encapsulant
Including power AlInGaN or AlInGaP or
Phosphor Converted AlInGaN Chip:
qjc~ 12°C/W

High optical efficiency > 95%



Potential Power Savings vs. Traditional Lighting
• Todays white LEDs are in the ~20-30lm/W range, but still low flux!

100
Incandescent
80
Power Saved (%)

Halogen
60
CFL
40
Fluorescent
20

0
0 25 50 75 100 125 150 175 200 225 250
LED Efficiency (lm/W)


LED Technology

Indicator LEDs vs. Power LEDs
• Indicator LEDs have output powers < ~50mW and Thermal resistances > 50K/W

0
10

InGaN LEDs Operating Point

-1
λ ~450 nm
10
Output Power (W)

Power LED
-2
10
Operating Point

-3
10

"5 mm" LED

-4
10 -3 -2 -1 0 1
10 10 10 10 10

Input Power (W)


Indicator LEDs vs. Power LuxeonTM LEDs!
• Luxeon’s are designed for low thermal resistance & high current density!

20 InGaN LEDs 120 InGaN LEDs
λd ~530 nm λd ~530 nm
100
Wall Plug Efficiency (%)

16
Power LED

Luminous Flux (lm)
80
12
60
Power LED
8
40
"5 mm" LED
4
20
"5 mm" LED
0 0

0 50 100 150 200 0 50 100 150 200
2 2
Current Density (A/cm ) Current Density (A/cm )

Philips Lumiled 2001

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