Quantum Well Infrared Photodetectors: From Laboratory ...€¦ · Quantum Well Infrared Detectors:...
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Research & Technology
Quantum Well Infrared Photodetectors: From Laboratory Objects to Products
P. Bois6th Rencontres du Vietnam: Hanoi 2006
Nanophysics: from fundamental to applications
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois2
QWIP history: from laboratory objects to products
late 80's : first QWIP Bell Labs (B. Levine)90's : Focal Plane Arrays Demonstrators00's : equipment, systems and programs
FPAs: ACREO, AIM/IAF, BAE-US, QWIPTech, QmagiQ, Thales, ...Imagers: AIM, FLIR Systems, Indigo Systems, Thales, ...
QWIPs : attractive physics and devices ...
but Thales is an industrial group (⇒ products : yield, costs, ...)
How introduce an emergent technology (QWIP) in an unfavourable context due to other IR technologies (MCT, InSb, µbolometers, ...)?
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INTRODUCTION: Imagery
Reflected Luminance
Ultra-violet Visible "Solar" IR Thermal IR
0.5 µm 3 µm 10 µm
Wavelength
EmittedLuminance
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Nature is perfect ...LWIRMWIR
Infrared imaging : passive detection, night, all weather
10-3
10-2
10-1
100
101
102
103
104
Spec
tral
Emitt
ance
(W.m2 µ-1
)2 3 4 5 6 7 8 9
102
Wavelength (µm)
0.8
0.6
0.4
0.2
0.0
Atm
ospheric Transmission
TBB =600 K
TBB =300 K
λλ
dTdRBB ),(
⇒ Defence & Security⇒ Aerospace (Enhanced Vision System) ⇒ Industry (non destructive testing)⇒ Medical (breast cancer, cardiovascular diseases, ...)
With and without IR EVS
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IR technologies for LWIR and MWIR
Thermal detectorsMicrobolometers (→ 640x512)Advantage = uncooled (low cost)Drawback = low performance
Quantum DetectorsAdvantage = high sensitivityDrawback = cryogenics (cost and reliability)Eligibles semiconductors for 8-12 µm range (LWIR) :
HgCdTe (MCT) : linear arrays, small staring arrays 128x128 (→ 10000 pixels)QWIP (GaAs): large staring arrays 640x512 (330000 pixels) → 1 Mpixel
Eligibles semiconductors for 3-5 µm range (MWIR) :HgCdTe (MCT) : staring arrays 320x240 → 640x512InSb: large staring arraysQWIP (GaAs): large staring arrays 640x512 → 1 Mpixel
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EVOLUTION OF IR IMAGERS
3rd gen thermal imagers: high sensitivity & high resolution
General trend : from mono-detector to 2D array
easier opto-mechanics better sensitivity / resolution / reliabilityA mastered processing technology is required for large formats :small pitch, uniformity, production yield ⇒⇒ availability and cost
Catherine FC
Catherine QW
Catherine GP
Castor
300 mK 60 mK 180 mK 60 mK
1rst gen | 2ndgen | 3rst gen
ΝΕ∆Τ :
Medium range IR cameras
(1-3 km)Thales Optronics
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THALES OBJECTIVES
Build an alternative technology for moderate costLWIR Thermal Imagers
• cost reduction of IR imagers :
- active layer for staring arrays → QWIPs- cryogenics- optics- read-out circuits
• performance improvement
• integration of advanced functions
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Quantum Well Infrared Detectors: Basics
Ga As1-xxAl Ga As1-xxAl Ga As
d
∆Ec
+++
hν
MBE growth•GaAs substrate •GaAs well•AlXGa1-XAs barrier
Silicon doped⇒ carriers = electrons
TEM picture Modulated conduction band
⇓
Quantum levels in wells
•Thermal stability
•Uniformity
•3", 4", … 6" substrates
hν
SC heterostructureSC heterostructuren type dopantn type dopant
Unipolar devicesSilicon
Intraband transitions
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QWIP: customized spectral detection range
200
50
100
150
400
10060 80 120
20 %
X = 5 %
10 %
E LIE2
40 %
E ETENDU2
Al Ga Asx 1-x GaAs
E
E 2
1
15
20
10
5
E
- E
(
meV
)2
1
d ( Å )
( m)
λp
µd
30
Example for detection around 8.5 µm: d = 5.2 nm ; x = 26 %
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QWIP Advantages and Drawback: 1990'sADVANTAGES :
III-V TECHNOLOGY (DUALITY)⇓
Large FPAs→ 640 x 512 → …
BAND GAP ENGINEERING
DRAWBACK :OPERATING TEMPERATURE
SPECIFICITY :
- Large substrates (3", 4", …)- Process and metallurgy mature- Uniformity ⇒ Performances- Production yield ⇒ Cost- Resistance to CMO
- Versatility (3 µm → 20 µm)- Advanced functions
Tunability, Multispectrality- LWIR : ∆T ≈ - 15 K vs MCT PV
(MCT FPAs<128x128)
- Optical coupling (gratings)
SO WHAT ? ⇒ APPLICATIONS, MARKET !
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TRT APPROACH
Analyze, understand : 1988 - 1994ADVANTAGES
DRAWBACKS
Modelize, optimize : 1993 - 1998OPERATING TEMPERATURE
Realize : 1997 - 2000LABORATORY DEVICES
Develop : 2000 - 2002FPA DEMONSTRATORS
Produce : 2002 -FPAs
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QWIP: Principle of operation
• steady state operation ⇒ current is conserved
F0 Fi-1
Fi
Injected current at emitter contact
Capture probability
Optical current
Thermioniccurrent
pcJ Jth + Jop
A
+ + +
+ + +
+ + + + + +
hν
Rq gh
=αν
η(
g exc
trt= τ
QWIPs are "extrinsic" photoconductors
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Optical coupling
Polarization selection rule forbids normal incidence⇓
artificial way is required for realizing FPAs:prisms, antennas, slope edges, diffraction gratings, ...
Standard QWIPs : diffraction gratings : reference• are now modeled, optimized, mastered with "standard III-V recipes"
rkii eEx̂ ⋅−
Incident field
grating
n2λ
a)
b)
2
yE
2 µm
LWIR
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These are not diffraction gratings: near field optics!
iy
EE
ix
EE
Near field
rkii eEx̂ ⋅− Incident field
At resonance
QWIP pixel scheme
h λ⎫⎪⎪⎬⎪⎪⎭
<
IR Flux
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois15
QWIP PARAMETERS
Gratings : Period, Aspect ratio, depth
Contact layers : Thickness, doping
Active layer : Number of wells,
Barrier thicknessAl contentWell doping and width.
A.R. coating : Thickness
Substrate : Residual Thickness
IR
• QWIP optimization implies a global modeling of the structure
• including operating conditions (temperature, optical flux)
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TBB = 300K
F/1.6
D*(70K, peak)cm.Hz1/2/W
D*(77K, peak)cm.Hz1/2/W
D*(81K, peak)cm.Hz1/2/W
D*(110 K, peak) cm.Hz1/2/W
λp = 10.6 µm, ∆λ = 0.9 µm 3.5 1010 1.2 1010 9 109 λp = 8.8 µm, ∆λ = 1 µm 1011 8 1010 5 1010 109
λp = 4.6 µm, ∆λ = 0.5 µm 2 1012 2 1012 8 1011 2 1011 0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Spe
ctra
l res
pons
e (A
/W)
1816141210864Wavelength (µm)
D*(100 K) = 2.5 1011 cm.Hz1/2/W
D*(77 K) = 8 1010 cm.Hz1/2/W
D*(50 K) = 1.4 1010 cm.Hz1/2/W
D*(77 K) = 1.6 1010 cm.Hz1/2/W
Spectral Response and D* for QWIP
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois17
QWIP TECHNOLOGY
⇒ Avoid degradation of intrinsic performancesWarning: uniformity has to be preserved for each new QWIP quantum design or processing step
⇒ Prefer ascendant compatibility technologiesStandard III-V processing
Cheap fabrication processing : •Contact photolithography (5 to 9 steps)
•Dry etch
•Sputtering metal deposition
⇒ Large format FPAs (640x512 and above)
⇒ Bispectral FPAsPitch= 25 µm
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois18
Thinning: required for thermal cycling reliabilityOnly 1 chemical step (100% yield)
Detail of a 384 x 288 QWIP array after thinning
Si ROIC Si ROIC
QWIP FPA
After substrate removalAfter hybridization
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Maturity of QWIP technology: 2000
Physics understanding OKOptical coupling OKProcessing steps OKGood performances achieved at 77K (60-65K in 1995 !) OK
All the building blocks are mastered ⇒ products
US TV format: 640x512 (25 µm)European 1/2 TV format: 288x384 (25 µm)
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LWIR QWIP PRODUCTS
Yield on 3” wafer: > 70% (6/8) Yield on 3” wafer: > 80% (25/30)
20022004
ROIC : Indigo ISC 0208 (pitch = 25 µm)½ TV format 384x288
Specifications
ROIC : Indigo ISC 9803 (pitch = 25 µm)TV format 640x512
Specifications for f/2.5 & >70 K: •NETD< 30mK (Tint < 5ms)•Pixel operability : >99.95%•Uniformity > 99.97 % after NUC•no cluster > 6 pixels (central zone)
for f/2.7 & >75 K: •NETD< 40mK (Tint < 5ms)•Dynamic range +/- 50K•Responsivity > 15 mV/K•Operability : >99.5% (all criteria)•no cluster > 5 pixels (central zone)
640x512
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CATHERINE XP: LW 384x288 QWIP product•Pupil : 50 mm•FOV : 10°x7,5° and 4°x3° •Electronic zoom : x 2•288x384 LWIR QWIP FPA•Pitch : 25 µm ; f/2.7•Sensitivity : NETD < 60 mK •Dynamics : 100 K (Tbb=300K)•175 mm x 215 mm x 72 mm•2.5 kg•TFPA = 75 K
cooler
Power supplyProximity electronics
Optics
detectorIntegration time < 4ms:
format 768 x 576 using µscan (2x2)
Uniformity and stability:- 2 pts correction in factory……. even for very high performance- 1 pt correction during initialization
4° NFov Version 3° NFov Version10° Wfov 9° WFov
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois22
SIRIUS-LW
TRT QWIP Product
640x512 ; pitch 20 µm
16 arrays on 3" wafer
Catherine MP MegaPixelµscanned SXGA format
(1280 x 1024)Thales Optronics (UK)
THALES LW QWIP Camera: CATHERINE-MP
E&O test cell
2005
Largest cluster (5 pixels)Yield on 3” wafer: > 70% (12/16)
Catherine MP
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois23
QWIP performance evolutions
Increase operating temperature: lower the cost⇒ more compact systems (cost, volume, consomption)
⇒ more reliable systems
Increase detector format: enhance resolution> 300 000 pixels, pitch reduction⇒ survey applications
Multispectrality, polarimetry: get more informationmultiband or multi-subband spectral detectorspolarimetric detectors ⇒ better identification, multi-weather adaptability
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois24
2 color (LW/LW or MW/LW) QWIP arrays
Building blocks validated on+ V1 + V2Signal 256x256 FPA
pitch 25µmIWR mode, 100Hz
Spatial correlation
25 µm
MWIR / LWIR4.6µm / 8.6 µm
NETD: 40mK / 39 mKOperability: 99.5% / 99.9%
LWIR / LWIR8.6µm / 10.8 µm
NETD: 50mK / 59 mKOperability: 99.5% / 99.4%
(details of a 2 color QWIP array)
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois25
Polarimetric QWIP FPA : 2006-2007100
90
80
70
60
50
40
30
20
10
0
-10
Pola
rizat
ion
ratio
(%)
10090807060504030
Pixel size (µm)
no diffraction pattern 2D pattern, period 2.6 µm
1D pattern, period 2.6 µm 1D pattern, period 2.7 µm
I0 / I90 = 10
1D pattern1D pattern2D pattern2D pattern 1D pattern1D pattern2D pattern2D pattern
unpolarized "natural" light
polarized light
Polarimetric demonstrator under development- 640 x 512, 20 µm pitch, including microscan
⇒320x256 (x4) polarimetric FPA
Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois26
CONCLUSIONAfter 15 years of R&D at THALES:
• Physics of QWIP is relatively well understood• Complete modeling is available• Processing is mature (high yield in production)
• still R&D (→FPA level) to increase operating temperature, extend spectral range (4µm-18µm) and implement new functions (multispectrality, polarimetry)
Transition from physics to business is almost achieved, but end-users and equipment manufacturers were hard to convince !