continued improvement of uv leds for curing …uvc leds for a range of industries our uvc leds are...
TRANSCRIPT
© 2015 Crystal IS, Inc. All Rights Reserved.
Continued Improvement of UV
LEDs for Curing Applications
Craig G. Moe
Crystal IS, Green Island, NY
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
CRYSTAL IS TODAY
Location: Green Island, NY
Facility Size: ~1600 m2
Employees:
55 Crystal IS and growing
25 in Japan (Asahi Kasei)
3
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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°
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
MAKING LEDS WITH III-V
TECHNOLOGY
7
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
III-V Optoelectronics
Infrared
UV
9
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
UV LED Efficiency
Kneissl et al., Semicond. Sci. Technol. 26 (2011) 014036
Crystal IS (2012)
Nitek (2012)
UCSB (2006)
11
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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
14
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)
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
RELIABILITY AND LIFETIME
MEASUREMENTS
16
© 2015 Crystal IS, Inc. All Rights Reserved.
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
17
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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
19
© 2015 Crystal IS, Inc. All Rights Reserved.
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.
20
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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
© 2015 Crystal IS, Inc. All Rights Reserved.
APPLICATIONS
23
© 2015 Crystal IS, Inc. All Rights Reserved.
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
24
© 2015 Crystal IS, Inc. All Rights Reserved.
Sterilizing Strip
25
Used only that area for coverage
© 2015 Crystal IS, Inc. All Rights Reserved.
Pictures during operation
26
© 2015 Crystal IS, Inc. All Rights Reserved.
Vial Disinfection
27
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
© 2015 Crystal IS, Inc. All Rights Reserved.
Vial Disinfection – Alternative Design
28
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
© 2015 Crystal IS, Inc. All Rights Reserved.
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
29