fundamental aspects of deep uv light emitting diodes and ......accelerated testing results ::...

© 2016 Crystal IS, Inc. All Rights Reserved.

Rajul Randive Crystal IS, Green Island, NY

Fundamental aspects of Deep UV Light emitting diodes and failure reduction of LEDS grown on AlN Substrates


Outline

•  Introduction •  III-V Technology for UV LEDs •  UVC LED fabrication •  Device Reliability •  Summary

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WE ARE CRYSTAL IS

•  Location: Green Island, NY•  Employees: 50 employees •  Technology: From crystal growth to

packaged die •  Aluminum Nitride (AlN) crystal growth •  Die fabrication •  Packaged UVC LEDs •  34 Patents

•  Products: •  Optan: High spectral quality and long

lifetimes for measurement and monitoring. •  Klaran: High power and compact footprint

for disinfection of air, water and surfaces. •  ISO 9001:2008 Certified Company

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UVC LED Markets and Advantages

UVC LEDs are: •  Compact •  Safe and environmentally friendly •  Instantaneous •  Long-lasting •  Wavelength specific

The future of these devices is dependent on offering: •  High power •  Long lifetime

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INDUSTRIAL

ENVIRONMENTAL

CONSUMER

HEALTHCARE

LIFE SCIENCES


OUR PRODUCT OFFERINGS

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Optan KlaranApplication Instrumentation Disinfection

Package TO-39 and SMD SMD

Output power 1-5 mW > 20 mW

Lifetime 3000 hours @ 100 mA > 1000 @ 400 mA

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

Output angle 15°; 100°; 115° 105°

We are developing products to meet the performance requirements of our customers.


Radiation Spectrum

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We deliver long-life, high performing LEDs with a well-controlled supply chain and industry-leading production facility.

OUR MANUFACTURING PROCESS

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Crystal IS Green Island, NY, USA

Outsourced Contract

Manufacturing

AlN Crystal Growth

Substrate Processing

Epitaxial Growth

Device Fabrication

Packaging

Asahi Kasei Microdevices Fuji, Japan


Our Approach: Pseudomorphic UV LED (PUVLED) Structure

We have demonstrated smooth surface morphology throughout our device structure

Transition to p-GaN

MQW

AlN homoepitaxy

n-AlGaN

p-GaN

MQW

2×2µm

2×2µm

2×2µm

Starting AlN substrate surface finish is critical!

Cathodoluminescence confirms TDD density in MQW < 105 cm-2

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ADJUST THE BAND GAP TO GET THE SPECIFIC WAVELENGTH DESIRED

• 

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Crystal IS Advantage :: Bulk AlN for UVC LEDs

•  Low dislocation density enables 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 •  Easier to scale at larger diameters

Bulk AlN allows for more reliable devices with longer lifetimes and higher power than other substrates.

After n-AlGaN growth (smooth surfaces)

Typical GaN on sapphire

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RELIABILITY AND LIFETIME MEASUREMENTS

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Experimental Procedure

•  Lifetime testing was 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

•  Temperatures described are case temperatures unless otherwise specified •  Junction temperatures can be estimated from

measured package capability

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UVC LED Products Tested

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Optan TO-39 Optan SMDApplication Spectroscopy Biofilm Prevention

Package TO-39 SMD

Output power 1-5 mW > 2 mW

Lifetime 3000 hours @ 100 mA 3000 hours @ 100 mA

Wavelength 5 nm bins from 250 – 280 nm 260 - 275 nm

Output angle 15° 100°


The Lifetime of Crystal IS Optan LEDs

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2

4

10

0.0 0.2 0.3 0.4 0.7 0.8 0.9

Coun

t

Relative Output Power at 1,000 hr

0.1 0.5 0.6 1.0

6

8

20

40

60

80

100

0 500 1000 1500

Rati

o to

Init

ial P

ower

Time (hr)

Lifetime >> 1000 hours


Projected Optan Lifetime

•  Parts tested to a minimum of 1000 hours with data taken roughly every 150 hours. •  First 300 hours of data

eliminated before evaluating with the model

•  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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10,000

8,000

6,000

4,000

2,000

0 0 100 200 300

Life

tim

e (h

r)

Current Density (A/cm2)


Temperature Dependence at 100 mA

•  Degradation increases with increasing temperature (0.25 % per °C above room temperature)

•  Greater than expected degradation at -40 °C (corresponding to higher reverse leakage at -5 V)

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1.00

0.80

0.60

0.40

0.20

0.00 -40 -20 0 20 40 60 80 100

Error bars constructed using 95% confidence interval of the mean

160 total samples

Rela

tive

Out

put

Pow

er

at 1

,000

hou

rs

Temperature °C


Accelerated Testing

•  Devices operated at various case temperatures and current to accelerate the degradation and failure of the LEDs. •  Three case temperatures and three currents with

devices from three different lots

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Case Temperature (°C ) Current (mA) # of Devices

25 100 40

25 200 20

25 300 30

55 300 30

85 100 30

85 300 30


Accelerated Testing Results :: Degradation

Junction temperature (Tj) estimated from thermal resistance, input power and case temperature.

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Accelerated degradation only seen at high junction temperatures.

1.2

1.0

0.8

0.6

0.4

0

0.2

40 60 80 100 120 140 160

Rela

tive

Out

put

Pow

er

at 1

,000

hou

rs

Estimated Tj °C

! Current 100 mA

✚ Current 200 mA

Current 300 mA


Accelerated Testing Results :: Failure

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

•  Activation energy calculated from 300 mA data

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1.0

0.8

0.6

0.4

0

0.2

40 60 80 100 120 140 160

Estimated Tj °C

Failu

re R

ate

! Current 100 mA

✚ Current 200 mA

Current 300 mA

0.0

-0.5

-1.0

-1.5

-2.5

-2.0

-3.0 28 29 30 31 32

1/kT

In (

Failu

re R

ate)

Ea=0.54 eV


Effect of Current and Temperature on Leakage

•  Devices stressed at 100 mA for 48 hrs, then at 300 mA for 1000+ hrs

•  Established leakage current failure spec at >1 mA at -5 V •  >35% of leakage failures occur at first test after 300 mA stress

(all temperature conditions) •  Leakage failures likely to have a significant current component

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0.6

0.5

0.4

0.3

0.2

0.1

0.0 0 200 400 600 800 1000

Perc

ent

Leak

y

Time (hours)

300 mA, 25°C

Tj = 85°C

0.6

0.5

0.4

0.3

0.2

0.1

0.0

0.7

0.8

0 400 800 1200 1600 2000 2400 Fr

acti

on L

eaky

Time (hours)

300 mA, 55°C

Tj = 115°C

0.0

0.2

0.4

0.6

0.8

0 200 400 600 800 1000

Leak

age

Time (hours)

300 mA, 85°C

Tj =145°C


Failure Analysis of Accelerated Testing

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•  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


APPLICATIONS

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UVC LEDs vs. Mercury Lamps

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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


Lifetime Decrease with Cycling (Hg)

Mercury Lamp on/off cycle

Instant on/off capability of UVC LEDs offers up to 1,000,000

switches per 3 hours

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NARROW VERSUS WIDE VIEWING ANGLE

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Simulation Result (2.5mW, 10mm away from detector)

Unit: mW/cm2

Optan SMD

Simulation Result (1mW, 10mm away from detector)

Optan Ball Lens


Summary

•  First commercial product based on single crystal AlN substrate

•  Accelerated lifetime testing studied the effect of increased current and temperature on lifetime. •  Typical lifetime much greater than 3000 hours •  Identified junction temperature as the primary

acceleration factor over the ranges tested. •  Further work continues to verify acceleration mechanisms.

•  Low defect density of AlN substrates provides improved performance for customers •  Higher internal efficiency •  Superior reliability •  Higher current density

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Questions?

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fundamental aspects of deep uv light emitting diodes and ......accelerated testing results ::...

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