continued improvement of uv leds for curing applications · uvc leds vs. mercury lamps 22 mercury...

© 2015 Crystal IS, Inc. All Rights Reserved.

Continued Improvement of UV

LEDs for Curing Applications

Craig G. Moe

Crystal IS, Green Island, NY


Outline

Introduction

Crystal IS

Our UVC LED Products and Process

III-Nitride Technology for UV LEDs

Epitaxy and UVC LED fabrication

Device Reliability

Surface Applications

2


CRYSTAL IS TODAY

Location: Green Island, NY

Facility Size: ~1600 m2

Employees:

55 Crystal IS and growing

25 in Japan (Asahi Kasei)

3


UVC LEDS for a Range of Industries

Our UVC LEDS are used in monitoring, purification and

sterilization applications for water, food, air and

healthcare industries. UVC LEDs are also suitable for curing

applications. We are currently working with OEMs and

product integrators to incorporate our UVC LEDs into their

products.

4


UVC LED Products

5

Optan SMD PRODUCT

Application Instrumentation Disinfection

Package TO-39 SMD

Output power 1-5 mW 10 – 30 mW

Lifetime 3000 hours @ 100 mA > 1000 @ 300 mA

Wavelength 5 nm bins from 250 – 280 nm 250 - 280 nm

Appearance

Output angle 15° 100°


Our Manufacturing Process

6

Crystal IS (Green Island, NY) Subcontractors

AlN

Crystal

Growth

Substrate

Fab

Epitaxial

Growth

Device

Fabrication Packaging

AK

Microdevices Crystal IS

Test


MAKING LEDS WITH III-V

TECHNOLOGY

7


III-V Optoelectronics

Semiconductor material deposited on near defect-free substrates

Atom size determines emission wavelength (smaller -> shorter)

Single peak emission

Electrons added or removed (holes) from layers by substituting elements with more or less unpaired electrons (Si, Mg)

Electrons and holes recombine in the active region (multiple-quantum well) to produce light

Any defect creates a non-light generating recombination, reducing the efficiency of the device

8

I II III IV V VI VII VIII

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Fr Ra Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb

Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No


III-V Optoelectronics

Infrared

UV

9


Near and Mid-Ultraviolet

UVC UVB UVA

400 315 280 365

Bandgap

of GaN

InGaN

340 200 nm

Bandgap

of AlN

Shortest

MQW LED

227

Very dim,

inefficient

AlGaN Active Region, AlN or Al2O3 substrate

Mercury

lamp

253.7

250 285

10

Increasing likelihood of defects on AlN

Solid-state

lighting

technology

High power, high

efficiency


UV LED Efficiency

Kneissl et al., Semicond. Sci. Technol. 26 (2011) 014036

Crystal IS (2012)

Nitek (2012)

UCSB (2006)

11


Advantages of Bulk AlN for UVC LEDs

Low dislocation density transferred to light-

emitting layers, enabling high performance

Transparent to UV-C radiation

High thermal conductivity (~3 W/cm-K)

Using bulk AlN substrate for AlGaN

semiconductor devices mimics traditional

semiconductor processing

12


Comparison to Sapphire Technology

13

UVC LEDs Based on Alumium Nitride have fewer crystal defects

Sapphire Wafer

Dislocation

Density:

~108 cm-2

Heteroepitaxy-Current Commercial Technology

AlN Seed Crystal

Bulk AlN grown on a single crystal

seed. Minimum stress at interface

resulting from exact lattice match.

Low dislocation density in bulk

crystal.

Dislocation

Density:

~103 cm-2

Bulk Crystal Growth-CIS Technology

Sapphire wafer is inexpensive, but has wrong crystal structure

Dislocations needed to accommodate

Crystal lattice mismatch

Still many dislocations in device layer


266 nm Pseudomorphic UV-C LED

Output power measured at Army Research Lab.

266 nm LED, 66 mW at 300 mA CW, 125 mW pulsed at 500 mA

4.7% EQE, 2.7% WPE at 300 mA CW

5.4% EQE, 2.6% WPE at 500 mA pulsed

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0 100 200 300 400 5000

20

40

60

80

100

120

CW

Pulsed 0.4% Duty Cycle,

40 µs pulse width

Ou

tpu

t P

ow

er

(mW

)

Current (mA)

0 100 200 300 400 5000

1

2

3

4

5

6

CW EQE

Pulsed EQE (0.4% Duty Cycle, 40 µs width)

CW WPE

Pulsed WPE (0.4% Duty Cycle, 40 µs width)

Effic

ien

cy (

%)

Current (mA)

0 30 60 90 120

Current Density (A/cm2)


280 nm Pseudomorphic MUVLED

Output power measured at Army Research Lab.

280 nm LED, 76 mW at 300 mA CW, 145 mW pulsed at 500 mA

5.7% EQE, 2.7% WPE at 300 mA CW

6.6% EQE, 2.6% WPE at 500 mA pulsed

15

0 100 200 300 400 5000

30

60

90

120

150Pulsed 0.4% Duty Cycle, 40 s pulse width

CW

Outp

ut

Pow

er

(mW

)

Current (mA)

0 50 100 150 200 250 300 350 400 450 5000

1

2

3

4

5

6

7

8

9

10 CW WPE

CW EQE

Pulsed EQE (0.4% Duty Cycle, 40 s width)

Pulsed WPE (0.4% Duty Cycle, 40 s width)

Effic

iency (

%)

Current (mA)

250 300 350 400

Inte

nsity (

arb

. u

nits)

Wavelength (nm)

10 mA

4 mA

2 mA


RELIABILITY AND LIFETIME

MEASUREMENTS

16


Reliability Testing

Lifetime testing is performed on fabrication lots of 10 to 20 Optan™ devices per test

Each fabrication lot consists of LEDs from multiple substrates and multiple epitaxial runs

Parts tested to a minimum of 1,000 hours with data taken roughly every 150 hours.

First 300 hours of data eliminated from before evaluating with model

7/10 lots can predict L50 point from 1,000 hours of testing, others require further testing

Degradation is modeled as with the visible TM-21 standard, an exponential least squares fit of relative output power versus time

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LED Reliability

Ten groups of 10 LEDs (100 LEDs total) were evaluated

No group showed L50B50 failure through 2,500 hours

Half of the groups showed L50B50 of longer than 4,500

hours

18


Lifetime Decrease with Cycling (Hg)

Philips Mercury Lamp on/off cycle

0 100 200 300 400 5000

30

60

90

120

150

0.4% Duty Cycle, 40 µs pulse width

CW

Ou

tpu

t P

ow

er

(mW

)

Current (mA)

1,000,000

switches per

3 hours

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Accelerated Testing Results - Failure

Failure rate in 1000 hours (fraction of devices <50% of initial power at 1000 hours.

Activation energy of 0.54 eV calculated from 300 mA data.

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Case

Temp. (C)

Current

(mA)

# of

devices

25 100 40

25 200 20

25 300 30

55 300 30

85 100 30

85 300 30


Failure Analysis of Accelerated Testing

21

Leakage paths identified through emission response imaging at reverse bias.

Defect in substrate -> locally large defect density in epi layers.

-2V bias, 95 µA

No bias

AlN epi/

substrate

interface

Defect

in substrate


UVC LEDs vs. Mercury Lamps

22

Mercury Lamp UVC LED

Heavy Metals Mercury (20-200mg) None

Warm Up Time 1-15 Minutes Instantaneous

Robustness Fragile quartz lamp Shock-resistant

Design Flexibility Typically straight and long Small footprint with versatile

design options

Voltage 110 - 240V AC 6 - 12V DC

Current 0.5 - 2.0 A 0.02 – 0.3 A

Heat Management Radiated heat Back side heat extraction


APPLICATIONS

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Surface Sterilization

Applications:

Decontaminating equipment

and packaging in food and

beverage industry

Sterilization of medical

devices and instruments

UV LED Advantage:

Wavelength specific

Mercury-free

Compact and lightweight

Instantaneous

Environmentally-friendly

Energy efficient

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Sterilizing Strip

25

Used only that area for coverage


Pictures during operation

26


Vial Disinfection

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81m

m

LEDs

28mm

0.0000

0.0500

0.1000

0.1500

0.2000

0.2500

0.3000

0.3500

0.4000

0.4500

0.5000

Detector Image: Incoherent Irradiance

3/5/2015Detector 13, NSCG Surface 1: DetectorSize 30.000 W X 30.000 H Millimeters, Pixels 500 W X 500 H, Total Hits = 139840Peak Irradiance : 1.9713E+000 Milliwatts/cm^2Total Power : 2.0976E+000 Milliwatts


Vial Disinfection – Alternative Design

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66m

m

28mm

Detector

14m

m

0.0000

0.0400

0.0800

0.1200

0.1600

0.2000

Detector Image: Incoherent Irradiance

3/17/2015Detector 24, NSCG Surface 1: DetectorSize 66.000 W X 30.000 H Millimeters, Pixels 500 W X 500 H, Total Hits = 4006661Peak Irradiance : 7.4041E+000 Milliwatts/cm^2Total Power : 2.0033E+001 Milliwatts


Summary

First commercial product based on single crystal AlN substrate

Improved performance possible because of low defect density

Higher internal efficiency

Superior reliability

Higher current density

Accelerated lifetime testing carried out to study effect of increased current and temperature on lifetime.

Typical lifetime much greater than 3,000 h.

Primary failure mechanism is leakage current increase and associated power degradation.

Modeling shows LEDs to be suitable for many surface treatments unachievable through conventional mercury lamps

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continued improvement of uv leds for curing applications · uvc leds vs. mercury lamps 22 mercury...

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