Imaging Beyond the Visible in the Short Wave Infrared with Indium Gallium Arsenide Martin H. Ettenberg, Ph. D., Director of Imaging Products 3490 US Rt. 1, Bldg. 12 Princeton, NJ 08540 Ph: 609-520-0610 Fax: 609-520-0638 mettenberg@sensorsinc.com
Topics What is the Short Wave Infrared? How the Devices Are Manufactured Applications the Technology Serves R&D Topics
What is the Short Wave Infrared?
One-Dimensional InGaAs FPA ROIC InGaAs PDA Current Standard Sizes Available: 1024 elements on 25 m pitch 512 and 256 elements on 25 m and 50 m pitch 1.7 m and 2.2 m cutoff commercially available 2.6 m has been demonstrated at room temperature
2D Array Formats 1.7 m cutoff commercially available 128x128x60 m (First array >12 years old) 320x240x40 m (Old Industry standard) 320x256x25 m (Industry standard) 640x512x25 m (Industry standard) Custom Sizes available through foundry services 1024x1024x17 m photodiode array- demonstrated 320x256 30 m 640x512 25 m 320x256, 25 µm 128x128 60 m 320x240 40 m
SWIR MicroCamera
What is InGaAs? An alloy of InAs and GaAs 4.0 3.5 InAs 3.0 Cutoff Wavelength (µm) 2.5 2.0 1.5 1.0 0.5 GaP GaAs In.53 Ga.47 As InP 0.9 m - 1.7 m 0.0 5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.1 Lattice Constant (Å)
Epitaxy - A Core Capability, Especially for R&D SUI s Emcore LDM 180 Epitaxial Reactor 6-2, 3-3, and 1 4 Wafer Capability
4 Wafer with 320x240 Arrays S e ns or sunl i mi t e di st hef i r s tt o4 InP Wafer Processing for Optoelectronic Devices Imaging Beyond VisibleTM
Process Cross-Section Back Illuminated Devices Indium Bumps Overlay (Step) P-Contacts AR Nitride Diffused - P-Type Alloyed Etch N-Channel N-contact InGaAs Indium Phosphide MULTIPLEXER P i N Back AR Coat Light Light Light Light
The Difficulty of Fabricating Staring Detectors High signal-to-noise requires low dark current from the photodiode array The multiplexer limits the amount of signal gathering by the full-well capacity The user is limited by the number of scans that can be taken by the readout noise of the multiplexer
Full-well capacity of the multiplexer demands low dark current Linear Arrays <130 million electrons Area Arrays <10 million electrons 1 na is ~ 6 billion electrons/sec Dark signal collected at video rates (16ms) would fill a FPA array ~10x Lattice Matched InGaAs has dark current around 50 fa
Quantum Efficiency of In x Ga 1-x As 1.0 0.8 Si InGaAs1.7 InGaAs2.2 InGaAs2.5 Quantum Efficiency 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 Wavelength (µm)
What is InGaAs? An alloy of InAs and GaAs 4.0 3.5 InAs 3.0 Cutoff Wavelength (µm) 2.5 2.0 1.5 1.0 0.5 GaP GaAs In.53 Ga.47 As InP 0.9 m - 1.7 m 0.0 5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.1 Lattice Constant (Å)
Long Wavelength InGaAs p-i-n Structure Device cross section for a 2.5 m p-i-n detector structure
Current Voltage Characteristics of Various InGaAs Alloys Current Density (A/cm ) 2 1.00E -02 1.00E -03 1.00E -04 1.00E -05 1.00E -06 1.00E -07 1.00E -08 1.00E -09 RoA 80000 -cm 2 RoA 150 -cm 2 RoA 3000 -cm 2 2.2 micron 2.0 micron 1.7 micron 0 0.5 1 1.5 R everse B ias (V) RoA measurements use the electrical area not the optical area.
Why Image in the SWIR? Military Surveillance/Passive Imaging Covert Illumination Range Gated Imaging Free Space Communication Hyperspectral Imaging Camouflage detection Friend/Foe ID Commercial Inspection/Sorting Agricultural products Plastic Sorting Semiconductors Telecommunications Thermal Measurements Spectroscopy
Military Applications
Radiance of Night Sky 1.80E-010 Radiance (W/cm 2 /sr/.01µm) Radiance (W/cm2/sr/.01µm) 1.60E-010 1.40E-010 1.20E-010 1.00E-010 8.00E-011 6.00E-011 4.00E-011 2.00E-011 night glow only night glow +.25 moon night glow +.50 moon night glow +.89 moon 0.00E+000 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Wavelength (µm) Vatsia, Mirshri, L. Atmospheric Optical Environment, Research and Development Technical Report ECOM-7023, September (1972)
Night Vision Under a Moonless Sky Room temperature commercial camera SU320MX
Imaging Active Laser Sources
Fog Penetration Gunston Cove VISIBLE IMAGERY SWIR 320x240
Multi-Sensor Image Fusion SWIR Sophisticated Sensor Fusion algorithms enable the user to identify the nature of objects in a scene in a sense through coarse hyperspectral imaging. Visible Thermal Courtesy Dean Scribner, NRL Multisensor fusion enables imagers that are inherently more resistant to countermeasures.
Commercial Applications
Commercial Applications Commercial applications break into two major catagories, imaging and spectroscopy. Imaging- Observing a scene to fabricate and image Online Processing- Detecting moisture Thermal analysis- Metal Smelting, Furnace monitoring Inspection of Phenomenology-Agriculture, Pharmaceutical, Semiconductors Spectral- Looking at multiple wavelengths to conduct an analysis Telecommunication- Wavelength Division Multiplexing Sorting- Plastic, Agriculture General Spectroscopy- Scientific Investigation
Telecommunications Monitor and control WDM lasers Alignment of components AWGs Diode Lasers General Inspection Light loss from waveguides From High Resolution Fiber Grating Optical Network Monitor, Koeppen, Wagener, Strasser, and DeMarco, Proceedings of NFOEC, Orlando (1998)
Optical Performance Monitors Are Needed All Over The Network Transmit terminal Add/drop node Receive terminal R, 1 Laser, 1 Amplifier Laser, 2 M U X A A A OADM A A A DCM D E M U X R, 2 Laser, n OPM OPM OPM R, i DCM Laser, i OPM OPM OPM R, n
Industrial Process Monitors Plastic Sorting Agricultural Sorting Fruit and Vegetable imperfections Seed sorting
Thermal Imaging Lattice matched InGaAs is useful for imaging thermal processes above 80ºC Too cold for silicon Glass is transparent Glass manufacturing Smelting of metals Furnace monitoring
Inspection Applications Many features can be seen in the SWIR that are not apparent in the visible Si is transparent to light >1.1 m Allows defects in Si to be detected before processing In process defects can be identified Emission microscopy used in failure analysis Some plastics are transparent to SWIR light and not visible light making measurement of fill levels difficult
Imaging Through Paint (Art Restoration) Re noi r slunc he onoft hebo at i ngpar t y;c o ur t e s yo f the Phillips Collection, Washington, DC Imaging Beyond VisibleTM
R&D
What needs Development? Longer wavelength cameras operating at room temperature Long wavelength materials because of the defects have very high dark current New read out integrated circuits Handle large amounts of dark current Large gain for high sensitivity applications Advanced features High speed readouts Wide Bandwidth detectors (communication and imaging)
Who Do We Work With? Princeton University University of Virginia Penn State Rutgers University SBIR/STTR and NIST Programs allow for collaboration on long term research
Conclusions InGaAs imaging technology has seen major advances in the last 10 years Imaging arrays capable of imaging at night Avalanche Photodiode Arrays (APDs) InGaAs has many more opportunities for research to improve the technology Longer wavelength materials Lowering the dark current in all InGaAs alloys Improving the ROIC circuits Imaging technologies will become critical in commercial and military applications