Imaging Beyond the Visible in the Short Wave Infrared withIndium Gallium Arsenide

Martin H. Ettenberg, Ph. D., Director of Imaging Products

3490 US Rt. 1, Bldg. 12Princeton, NJ 08540Ph: 609-520-0610Fax: 609-520-0638mettenberg@sensorsinc.comwww.sensorsinc.com

Imaging Beyond VisibleTM

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Topics

•What is the Short Wave Infrared?•How the Devices Are

Manufactured•Applications the Technology

Serves•R&D Topics

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What is the Short Wave Infrared?

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One-Dimensional InGaAs FPA

ROIC InGaAs PDA

Current Standard Sizes Available:1024 elements on 25 m pitch512 and 256 elements on 25 m and 50 m pitch1.7 m and 2.2 m cutoff commercially available2.6 m has been demonstrated at room temperature

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2D Array Formats1.7 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

640x51225 m

320x24040 m

320x25630 m

128x12860 m

320x256, 25 µm

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SWIR MicroCamera

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What is InGaAs?An alloy of InAs and GaAs

5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.10.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

GaP

InP

InAs

GaAsCut

off W

avel

engt

h (µ

m)

Lattice Constant (Å)

In.53Ga.47As

0.9 m

-1.

7 m

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Epitaxy - A Core Capability, Especially for R&D

SUI’s Emcore LDM 180 Epitaxial Reactor6 -2”, 3 -3”, and 1 4” Wafer Capability

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4” Wafer with 320x240 Arrays

Sensors Unlimited is the first to 4” InP Wafer Processing for Optoelectronic Devices

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Nitride

Indium Phosphide

InGaAs

AR

Etch N-Channel

Light Light Light Light

Diffused - P-Type

Indium Bumps

Alloyed N-contact

P-ContactsOverlay (Step)

Back AR Coat

MULTIPLEXER

Process Cross-SectionBack Illuminated Devices

iP

N

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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

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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

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Quantum Efficiency of InxGa1-xAs

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

0.0

0.2

0.4

0.6

0.8

1.0

Si InGaAs1.7 InGaAs2.2 InGaAs2.5

Qua

ntum

Effi

cien

cy

Wavelength (µm)

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What is InGaAs?An alloy of InAs and GaAs

5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.10.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

GaP

InP

InAs

GaAsCut

off W

avel

engt

h (µ

m)

Lattice Constant (Å)

In.53Ga.47As

0.9 m

-1.

7 m

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Device cross section for a 2.5m p-i-n detector structure

Long Wavelength InGaAsp-i-n Structure

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Current Voltage Characteristics of Various InGaAs Alloys

1.00E -091.00E -081.00E -071.00E -061.00E -051.00E -041.00E -031.00E -02

0 0.5 1 1.5

R everse B ias (V)

Cu

rre

nt

De

ns

ity

(A/c

m )

2.2 m icron

2.0 m icron

1.7 m icron

2

RoA3000 -cm2

RoA150 -cm2

RoA80000 -cm2

RoA measurements use the electrical area not the optical area.

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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

MilitaryApplications

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Radiance of Night Sky

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00.00E+000

2.00E-011

4.00E-011

6.00E-011

8.00E-011

1.00E-010

1.20E-010

1.40E-010

1.60E-010

1.80E-010

night glow only night glow + .25 moon night glow + .50 moon night glow + .89 moon

Rad

ianc

e (W

/cm

2/sr

/.01µ

m)

Wavelength (µm)

Wavelength (µm)

Rad

ianc

e (W

/cm

2 /sr/

.01µ

m)

Vatsia, Mirshri, L. “Atmospheric Optical Environment”, Research and Development Technical Report ECOM-7023, September (1972)

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Night Vision Under a Moonless SkyRoom temperature commercial camera SU320MX

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Imaging Active Laser Sources

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Fog PenetrationGunston Cove

VISIBLE IMAGERY SWIR 320x240

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Multi-Sensor Image Fusion• Sophisticated Sensor Fusion

algorithms enable the user to identify the nature of objects in a scene in a sense through “coarse” hyperspectral imaging.

• Multisensor fusion enables imagers that are inherently more resistant to countermeasures.

SWIR

Visible

Thermal

Courtesy Dean Scribner, NRL

Commercial Applications

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Commercial Applications

Commercial applications break into two major catagories, imaging and spectroscopy.

Imaging- Observing a scene to fabricate and imageOnline Processing- Detecting moistureThermal analysis- Metal Smelting, Furnace monitoringInspection of Phenomenology-Agriculture, Pharmaceutical,

SemiconductorsSpectral- Looking at multiple wavelengths to conduct an analysis

Telecommunication- Wavelength Division MultiplexingSorting- Plastic, AgricultureGeneral Spectroscopy- Scientific Investigation

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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)

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Optical Performance MonitorsAre Needed All Over The Network

Laser, 2

Laser, n

R, 1

R, 2

R, n

Transmit terminal

Laser, 1

Laser, 2 AA OADM A DCM

Las

er,

i

R,

iD

CM

MUX

Receive terminalAdd/drop node

DEMUX

A A

Amplifier

A

OP

M

OP

M

OP

M

OP

M

OP

M

OP

M

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Industrial Process Monitors

•Plastic Sorting•Agricultural Sorting•Fruit and Vegetable

imperfections•Seed sorting

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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

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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

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Renoir’s Luncheon of the Boating Party; courtesy of the Phillips Collection, Washington, DC

Imaging Through Paint(Art Restoration)

R&D

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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)

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Who Do We Work With?

•Princeton University•University of Virginia•Penn State•Rutgers UniversitySBIR/STTR and NIST Programs allow for

collaboration on long term research

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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