While InGaAs-based SWIR imaging technology has been improved dramatically over the past 10 years, the motivation
remains to reduce Size Weight and Power (SWaP) for applications in Intelligence Surveillance and Reconnaissance
(ISR). Goodrich ISR Systems, Princeton (Sensors Unlimited, Inc.) has continued to improve detector sensitivity.
Additionally, SUI is working jointly with DRS-RSTA to develop innovative techniques for manufacturing dual-band
focal planes to provide next generation technology for not only reducing SWaP for SWIR imagers, but also to combine
imaging solutions for providing a single imager for Visible Near-SWIR (VNS) + LW imaging solutions. Such
developments are targeted at reducing system SWaP, cost and complexity for imaging payloads on board UASs as well
as soldier deployed systems like weapon sights. Our motivation is to demonstrate capability in providing superior image
quality in fused LWIR and SWIR imaging systems, while reducing the total system SWaP and cost by enabling Short
Wave and Thermal imaging in a single uncooled imager.
Under DARPA MTO awarded programs, a LW bolometer (DRS-RSTA) is fabricated on a Short Wave (SW) InGaAs
Vis-SWIR (SUI-Goodrich) Imager. The combined imager is a dual-band Sensor-Chip Assembly which is capable of
imaging in VIS-SWIR + LW. Both DRS and Goodrich have developed materials and process enhancements to support
these dual-band platform investigations. The two imagers are confocal and coaxial with respect to the incident image
plane. Initial work has completed a single Read Out Integrated Circuit (ROIC) capable of running both imagers. The
team has hybridized InGaAs Focal planes to 6" full ROIC wafers to support bolometer fabrication onto the SW array.
There are few choices when identifying detector materials for use in the SWIR wavelength band. We have exploited the
direct-bandgap InGaAs material system to achieve superior room temperature (293°K) dark current. We have
demonstrated sensitivity from 400nm through 2.6um with this material system and thus provide the opportunity to sense
not only the visible, but also the J-band (1.25um), H-band (1.65um) and K-band (2.2um) windows. This paper discusses
the advantages of our hybridized CMOS-InGaAs material system versus other potential SWIR material systems.
The monolithic planar InGaAs detector array enables 100% fill factor and thus, high external quantum efficiency. We
have achieved room-temperature pixel dark current of 2.8fA and shot noise of 110 electrons per pixel per second. Low
dark current at +300K allows uncooled packaging options, affording the system designer dramatic reductions in size,
weight (cameras <28grams), and power (<2.5W). Commercially available InGaAs pin arrays have shown diode lifetime
mean time between failures (MTBF) of 1011hours for planar InGaAs detectors1, far exceeding telecom-grade reliability
requirements. The use of a hybrid CMOS-InGaAs system allows best of breed materials to be used and permits efficient, cost-effective,
volume integration. Moreover, we will discuss how the InGaAsP material system is compatible with CMOS monolithic
integration. Taken together, these advantages, we believe, make InGaAs the obvious choice for all future SWIR
Historically, the natural structure of Indium Gallium Arsenide backside illuminated FPAs has allowed them to detect
light with wavelengths between 0.9 and 1.7 μm. However, new wafer growth and processing methods have allowed
extended response InGaAs imagers to be used in high sensitivity cameras to detect light down to 0.7 μm. These
extended response imagers hold many advantages over standard cut-on InGaAs.
One of these advantages is being able to detect beacons, lasers, and illuminators in the 800-900 nm range, light sources
that have historically only been detectable with I2CCD cameras or night vision tubes, while simultaneously being able to
detect the longer wavelength convert illuminators and lasers. Another advantage is capturing any additional available
photons with wavelengths between 0.7 μm and 0.9 μm. This improves overall imaging capability in most low light level
This paper will address the methods used to achieve stable, high sensitivity extended response imagers, as well expand
on the applications of this breakthrough.
Extended wavelength InGaAs material is ideal for laser beam profiling applications from 1 micron to 2 microns wavelength. We report on a focal plane array and camera designed specifically for this application. The format of the camera is 320 x 256 pixels on a 25 micron pitch, and the operation is snapshot exposure with a 16 ms exposure time. The camera may be triggered for synchronization with laser pulses and has a 60 Hz maximum readout rate. Two challenges are encountered with extended wavelength InGaAs material compared to lattice matched material. The first is lower quantum efficiency at the shorter wavelengths due to transitional buffer layers that absorb at the shorter wavelengths. The second is the larger dark current caused by lattice mismatch between the InP substrate and the absorption layers. Neither challenge is a problem for laser beam profiling, since a large energy or power is available from the source. To accommodate the dark current, a gate modulated (GMOD) readout circuit is used, where the continuously variable capacity is increased to several million electrons. Both CW and pulsed illumination linearity are good, allowing accurate profiling. The temperature of the focal plane array is held near room temperature with a thermoelectric cooler for stability. To provide a corrected image, nonuniformity corrections for offset and gain are stored in the camera.
We report on our 640x512 pixel InGaAs/InP focal plane array camera for visible and short-wavelength infrared imaging. For this camera, we have fabricated a 640x512 element substrate-removed backside-illuminated InGaAs/InP photodiode array (PDA) with a 25 mm pixel pitch. The PDA is indium bump bonded to a silicon read out integrated circuit. Removing the InP substrate from the focal plane array allows visible wavelengths, which would otherwise be absorbed by the InP substrate due to its 920 nm wavelength cut-off, to reach the pixels' active region. The quantum efficiency is approximately 15% at 500 nm, 70% at 850 nm, 85% at 1310 nm, and 80% at 1550 nm.
Features incorporated into this video-rate, 14-bit output camera include external triggering, windowing, individual pixel correction, 8 operational settings of gain and exposure time, and gamma correction. The readout circuit uses a gate-modulated pixel for high sensitivity imaging over a wide illumination range. This camera is useable for visible imaging as well as imaging eye-safe lasers and is of particular interest seeing laser designators and night vision as well as hyperspectral imaging.
We report on the recent production release of our 320x240 pixel InGaAs/InP focal plane array and camera for visible and short-wavelength infrared light imaging. For this camera, we have fabricated a substrate-removed backside-illuminated InGaAs/InP photodiode array hybridized to a silicon read out integrated circuit (ROIC). Removing the InP substrate from the focal plane array allows visible wavelengths, which would otherwise be absorbed by the InP substrate due to its 920 nm wavelength cut-off, to reach the pixels’ active region. Quantum efficiency is approximately 15% at 500 nm, 70% at 850 nm, 85% at 1310 nm and 80% at 1550 nm. This focal plane array is useable for visible imaging as well as imaging eye-safe lasers and is of particular interest for day and low light level imaging as well as hyperspectral imaging.