The increasing demand for short wave infrared (SWIR) imaging technology for soldier-based and unmanned
platforms requires camera systems where size, weight and power consumption are minimized without loss of
performance. Goodrich, Sensors Unlimited Inc. reports on the development of a novel focal plane (FPA) array for
DARPA's MISI (Micro-Sensors for Imaging) Program. This large format (1280 x 1024) array is optimized for
day/night imaging in the wavelength region from 0.4 μm to 1.7 μm and consists of an InGaAs detector bump bonded to a
capacitance transimpedance amplifier (CTIA)-based readout integrated circuit (ROIC) on a compact 15 μm pixel pitch.
Two selectable integration capacitors provide for high dynamic range with low (< 50 electrons) noise, and expanded onchip
ROIC functionality includes analog-to-digital conversion and temperature sensing. The combination of high
quality, low dark current InGaAs with temperature-parameterized non-uniformity correction allows operation at ambient
temperatures while eliminating the need for thermoelectric cooling. The resulting lightweight, low power
implementation is suitable for man-portable and UAV-mounted applications.
Goodrich, SUI has developed a 15 μm pitch, 1280 x 1024 pixel InGaAs focal plane array (FPA) with low noise, and
visible to near infrared (0.4 μm to 1.7 μm) wavelength response for day and night vision applications. The readout
integrated circuit (ROIC), which uses a capacitive transimpedance amplifier (CTIA) pixel, is designed to achieve a noise
level of less than 50 electrons, due to its small integration capacitor. The ROIC can be read out at 120 frames per second,
and has a dynamic range of 3000:1 using rolling, non-snapshot integration. The ROIC was fabricated in a standard
CMOS foundry process, and was bump-bonded to Vis-InGaAsTM detector arrays. SUI has successfully hybridized 15 μm
pitch 1280 x 1024 pixel FPAs, and produced imagery.
The DARPA PCAR program is sponsoring the development of low noise, near infrared (1.5 &mgr;m wavelength) focal
plane arrays (FPAs) for night vision applications. The first phase of this work has produced a collection of 640 x 512
pixel, 20 &mgr;m pitch FPAs with low noise. The approach was to design four different read out integrated circuits
(ROICs), all compatible with the same bump-bonded InGaAs photodiode detector array. Two of the designs have
capacitive transimpedance amplifier (CTIA) pixels, each with a somewhat different amplifier design and with two
different sizes of small integration capacitors. The third design is a source follower per detector (SFD) pixel,
integrating on the detector capacitance. The fourth design also integrates on the detector capacitance, but uses a
moderate gain, in-pixel amplifier to boost the signal level, and also has a differential pixel output. All four designs
require off-chip correlated sampling to achieve the desired noise level. The correlated sampling is performed digitally
in the data acquisition software. Each design is capable of 30 frames per second read out rate, and has a dynamic range
of 1000:1 using a rolling, non-snapshot integration. The designs were fabricated in a standard CMOS foundry process,
and were bump-bonded to InGaAs detector arrays. All four designs are working without any significant design errors,
and are producing low noise imaging, with less than 50 electrons rms noise per pixel after correlated double sampling.
We report on a 320 x 256 pixel InGaAs focal plane array based camera with the ability to perform range gated imaging with sub-200 ns gates, while also allowing integration times longer than 16 ms for imaging in a staring mode at video rates. The combination of gated and video imaging is achieved through a high bandwidth pixel with a capacitive transimpedance amplifier (CTIA) design. The low dark current and high bandwidth of the InGaAs photodetectors enables both high sensitivity imaging at long exposure times and high bandwidth at short exposure times. The pixels are fabricated on a 25 μm pitch allowing for a compact device, and all pixels are gated simultaneously for "snapshot" exposure. The all solid-state gated camera improves reliability, while also allowing the system to be small and lightweight. The spectral sensitivity of InGaAs extends from 0.9 μm to 1.7 μm, allowing the use of eye-safe commercially available pulsed lasers with 1.5 μm wavelength, several millijoule pulse energies, and nanosecond scale pulse durations. In these experiments a 4 mJ and 2 ns pulse has allowed gated imaging to be achieved with a target at a range greater than 350 m away.
Range-gated imaging using indium gallium arsenide based focal plane arrays enables both depth and intensity imaging with eye-safe lasers while remaining covert to night vision goggles. We report on a focal plane array consisting of an indium gallium arsenide photodiode array hybrid-integrated with a CMOS readout circuit, resulting in an all solid state device. A 5 V supply avoids the complication of high voltage supplies and improves reliability, while also allowing the device to be small and lightweight. The spectral sensitivity of InGaAs extends from 0.9 microns to 1.7 microns, allowing the use of commercially available pulsed lasers with 1.5 micron wavelength, several millijoule pulse energies, and nanosecond scale pulse durations. SUI is developing a 320 x 256 pixel imager with the ability to conduct range gated imaging with sub-100 ns gates, while also allowing a 16 ms integration time for imaging in a staring mode. The pixels are fabricated on a 25 micron pitch for a compact device, and all pixels are gated simultaneously for “snapshot” exposure. High in-pixel gain with nearly noiseless amplification and low dark current enable high sensitivity imaging from ultra-short gates to video rate imaging.
We describe innovations in short wave infrared (SWIR) InGaAs focal plane arrays and cameras which now allow imaging under starlight only conditions at video rates. These lattice matched In.53Ga.47As imagers detect 0.9 μm to 1.7 μm SWIR band light, which is generally reflected from the imaged target. At night, the sources of light are the night glow, stars, the moon, or light pollution from nearby towns and cities. Detectivities, D*, greater than 6 x 1013 cm-√Hz/W and no image lag are necessary to image under starlight only conditions at RS-170 video rates. The InGaAs arrays are now commercially available in formats as large as 640 x 512 on a 25 μm pitch, and custom arrays are being manufactured on a 15 μm pitch with pixel counts as large as 1280 x 1024. The cameras are capable of adapting to the different light conditions that may occur in a scene over a 24-hour period, without the need for new corrections; this illumination variation can be over 5 orders of magnitude. The InGaAs material is stable, making new field corrections unnecessary for the life of the camera and eliminating the need for mechanical parts. The cameras have a dual output design to produce corrected analog output at video rates without the assistance of a computer, and corrected digital output through a 14 bit Camera Link interface.