Quantum Well Infrared Photodetectors: From Laboratory Objects to Products

Transcription

1 Quantum Well Infrared Photodetectors: From Laboratory Objects to Products 6th Rencontres du Vietnam: Hanoi 2006 Nanophysics: from fundamental to applications P. Bois

2 QWIP history: from laboratory objects to products late 80's : first QWIP Bell Labs (B. Levine) 90's : Focal Plane Arrays Demonstrators 00'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,...)? 2

3 INTRODUCTION: Imagery Wavelength Ultraviolet Reflected Luminance Emitted Luminance 0.5 µm 3 µm 10 µm Visible "Solar" IR Thermal IR 3

4 Nature is perfect... Infrared imaging : passive detection, night, all weather Spectral Emittance (W.m 2 µ -1 ) MWIR LWIR T BB =600 K T BB =300 K dr BB ( λ, T ) dλ Atmospheric Transmission Wavelength (µm) With and without IR EVS Defence & Security Aerospace (Enhanced Vision System) Industry (non destructive testing) Medical (breast cancer, cardiovascular diseases,...) 4

5 IR technologies for LWIR and MWIR Thermal detectors Microbolometers ( 640x512) Advantage = uncooled (low cost) Drawback = low performance Quantum Detectors Advantage = high sensitivity Drawback = cryogenics (cost and reliability) Eligibles semiconductors for 8-12 µm range (LWIR) : HgCdTe (MCT) : linear arrays, small staring arrays 128x128 ( pixels) QWIP (GaAs): large staring arrays 640x512 ( pixels) 1 Mpixel Eligibles semiconductors for 3-5 µm range (MWIR) : HgCdTe (MCT) : staring arrays 320x x512 InSb: large staring arrays QWIP (GaAs): large staring arrays 640x512 1 Mpixel 5

6 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 / reliability A mastered processing technology is required for large formats : small pitch, uniformity, production yield availability and cost 1 rst gen 2 nd gen 3 rst gen Medium range IR cameras Catherine GP Catherine FC (1-3 km) Thales Optronics ΝΕ Τ : Castor Catherine QW 300 mk 60 mk 180 mk 60 mk 6

7 THALES OBJECTIVES Build an alternative technology for moderate cost LWIR Thermal Imagers cost reduction of IR imagers : - active layer for staring arrays QWIPs - cryogenics -optics - read-out circuits performance improvement integration of advanced functions 7

8 Quantum Well Infrared Detectors: Basics SC heterostructure n type dopant MBE growth GaAs substrate GaAs well Al X Ga 1-X As barrier TEM picture Modulated conduction band Al Ga As x 1-x Ga As Al Ga As x 1-x Quantum levels in wells Thermal stability Uniformity 3", 4", 6" substrates hν d +++ Silicon E c Intraband transitions Silicon doped carriers = electrons Unipolar devices 8

9 QWIP: customized spectral detection range 40 % Al Ga As x 1-x GaAs E 2 E - E (mev) % d E E LIE λ p µ ( m) E ETENDU 2 10 % X = 5 % d ( Å ) Example for detection around 8.5 µm: d = 5.2 nm ; x = 26 %

10 QWIP Advantages and Drawback: 1990's ADVANTAGES : 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! 10

11 TRT APPROACH Analyze, understand : ADVANTAGES DRAWBACKS Modelize, optimize : OPERATING TEMPERATURE Realize : LABORATORY DEVICES Develop : FPA DEMONSTRATORS Produce : FPAs 11

12 hν η ( R = qαg hν τ g = t exc tr QWIP: Principle of operation QWIPs are "extrinsic" photoconductors steady state operation current is conserved F 0 F i-1 F i Injected current at emitter contact p c J J th + J op Capture probability A Optical current Thermionic current 12

13 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" E y 2 grating a ) b) 2 µm LWIR xˆ E i e i k r λ 2n Incident field 13

14 These are not diffraction gratings: near field optics! QWIP pixel scheme At resonance Near field E E y i h< λ E E x i IR Flux xˆ E i e i k r Incident field 14

15 QWIP PARAMETERS Gratings : Period, Aspect ratio, depth Contact layers : Thickness, doping IR Substrate : Residual Thickness Active layer : Number of wells, Barrier thickness Al content Well doping and width. A.R. coating : Thickness QWIP optimization implies a global modeling of the structure including operating conditions (temperature, optical flux) 15

16 Spectral Response and D* for QWIP D*(70K, peak) cm.hz 1/2 /W D*(77K, peak) cm.hz 1/2 /W D*(81K, peak) cm.hz 1/2 /W D*(110 K, peak) cm.hz 1/2 /W λp = 10.6 µm, λ = 0.9 µm λp = 8.8 µm, λ = 1 µm λp = 4.6 µm, λ = 0.5 µm Spectral response (A/W) D*(100 K) = cm.hz 1/2 /W D*(77 K) = cm.hz 1/2 /W D*(77 K) = cm.hz 1/2 /W D*(50 K) = cm.hz 1/2 /W T BB = 300K F/ Wavelength (µm) 18

17 QWIP TECHNOLOGY Avoid degradation of intrinsic performances Warning: uniformity has to be preserved for each new QWIP quantum design or processing step Prefer ascendant compatibility technologies Standard III-V processing Cheap fabrication processing : Contact photolithography (5 to 9 steps) Dry etch Sputtering metal deposition Large format FPAs (640x512 and above) Bispectral FPAs Pitch= 25 µm 17

18 Thinning: required for thermal cycling reliability Only 1 chemical step (100% yield) Si ROIC Si ROIC QWIP FPA After hybridization After substrate removal Detail of a 384 x 288 QWIP array after thinning 18

19 Maturity of QWIP technology: 2000 Physics understanding OK Optical coupling OK Processing steps OK Good 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) 19

20 LWIR QWIP PRODUCTS Yield on 3 wafer: > 70% (6/8) Yield on 3 wafer: > 80% (25/30) ROIC : Indigo ISC 9803 (pitch = 25 µm) ROIC : Indigo ISC 0208 (pitch = 25 µm) TV format 640x512 ½ TV format 384x Specifications for f/2.5 & >70 K: NETD< 30mK (Tint < 5ms) Pixel operability : >99.95% Uniformity > % after NUC no cluster > 6 pixels (central zone) 640x512 Specifications 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)

21 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 T FPA = 75 K Proximity electronics cooler Integration time < 4ms: format 768 x 576 using µscan (2x2) Power supply Optics detector 4 NFov Version 3 NFov Version 10 Wfov 9 WFov Uniformity and stability: - 2 pts correction in factory. even for very high performance - 1 pt correction during initialization 21

22 2005 THALES LW QWIP Camera: CATHERINE-MP TRT QWIP Product 640x512 ; pitch 20 µm SIRIUS-LW 16 arrays on 3" wafer E&O test cell Catherine MP MegaPixel µscanned SXGA format (1280 x 1024) Thales Optronics (UK) 22 Largest cluster (5 pixels) Yield on 3 wafer: > 70% (12/16) Catherine MP

23 QWIP performance evolutions Increase operating temperature: lower the cost more compact systems (cost, volume, consomption) more reliable systems Increase detector format: enhance resolution > pixels, pitch reduction survey applications Multispectrality, polarimetry: get more information multiband or multi-subband spectral detectors polarimetric detectors better identification, multi-weather adaptability 23

24 2 color (LW/LW or MW/LW) QWIP arrays + V 1 Signal + V 2 Building blocks validated on 256x256 FPA pitch 25µm IWR mode, 100Hz MWIR / LWIR 4.6µm / 8.6 µm NETD: 40mK / 39 mk Operability: 99.5% / 99.9% 25 µm Spatial correlation LWIR / LWIR 8.6µm / 10.8 µm NETD: 50mK / 59 mk Operability: 99.5% / 99.4% (details of a 2 color QWIP array) 24

25 Polarimetric QWIP FPA : D pattern 1D pattern unpolarized "natural" light polarized light Polarization ratio (%) no diffraction pattern 2D pattern, period 2.6 µm 1D pattern, period 2.6 µm 1D pattern, period 2.7 µm I 0 / I 90 = Pixel size (µm) Polarimetric demonstrator under development x 512, 20 µm pitch, including microscan 320x256 (x4) polarimetric FPA 25

26 CONCLUSION After 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! 26