SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. The study of InGaAs FPA has begun few years ago with III-VLab, gathering expertise in InGaAs material growth and imaging technology respectively from Alcatel-Lucent and Thales, its two mother companies. This work has led to put quickly on the market a 320x256 InGaAs module. The recent transfer of imagery activities from III-VLab to Sofradir allows developing new high performances products, satisfying customers’ new requirements. Especially, a 640x512 InGaAs module with a pitch of 15µm is actually under development to fill the needs of low light level imaging.
CEA Leti has recently developed a new readout IC (ROIC) with pixel-level ADC for cooled infrared focal plane arrays
(FPAs). It operates at 50Hz frame rate in a snapshot Integrate-While-Read (IWR) mode. It targets applications that
provide a large amount of integrated charge thanks to a long integration time. The pixel-level analog-to-digital
conversion is based on charge packets counting. This technique offers a large well capacity that paves the way for a
breakthrough in NETD performances. The 15 bits ADC resolution preserves the excellent detector SNR at full well
(3Ge-). These characteristics are essential for LWIR FPAs as broad intra-scene dynamic range imaging requires high
sensitivity. The ROIC, featuring a 320x256 array with 25μm pixel pitch, has been designed in a standard 0.18μm CMOS
technology. The main design challenges for this digital pixel array (SNR, power consumption and layout density) are
discussed. The IC has been hybridized to a LWIR detector fabricated using our in-house HgCdTe process. The first
electro-optical test results of the detector dewar assembly are presented. They validate both the pixel-level ADC concept
and its circuit implementation. Finally, the benefit of this LWIR FPA in terms of NETD performance is demonstrated.
New applications require high sensitivity infrared (IR) sensors in order to detect very low incident fluxes. Laser
gated imaging has, in particular, additional specific needs. IR sensors for this type of application are synchronized
with eye-safe lasers, and have to detect a weak signal backscattered from the target on the order of 10 photons per
pulse. They also have to be able to operate with a very short integration time, typically one hundred nanoseconds,
to gate the backscattered signal around the target. In partnership with Sofradir, CEA/LETI (France) has developed
high quality HgCdTe avalanche photodiodes satisfying these requirements. In parallel, specific studies have been
carried out at the Read-Out Circuit level to develop optimized architectures. Thanks to these advances, a new
Integrated Dewar Detector Cooler Assembly has been developed. This new product is the first step in a road-map
to address low flux infrared sensors in the next few years.
The InfraRed staring arrays developed by SOFRADIR are more and more compact and offer system solutions
for wide range of IR wavebands. IR detectors have been taken to an even more advanced level of sophistication
to achieve staring arrays high performances. Latest developments have also been focused on the silicon readout
circuit. Digital conversion on chip is one of the recent progresses in this field of activity. In order to match each
system requirements, on chip high performance ultra low power ADCs have been developed. Beyond the
performance aspects, digital focal plane arrays can be considered as the first step towards low cost Dewar family,
since they allow for a more simple electrical interface on Dewar designs and on chip image processing. Recent
results concerning these new readout circuit architectures are presented in this paper.
The CMOS silicon focal plan array technologies hybridized with infrared detectors materials allow to cover a wide
range of applications in the field of space, airborne and
grounded-based imaging. Regarding other industries which are
also using embedded systems, the requirements of such sensor assembly can be seen as very similar; high reliability, low
weight, low power, radiation hardness for space applications and cost reduction. Comparing to CCDs technology,
excepted the fact that CMOS fabrication uses standard commercial semiconductor foundry, the interest of this
technology used in cooled IR sensors is its capability to operate in a wide range of temperature from 300K to cryogenic
with a high density of integration and keeping at the same time good performances in term of frequency, noise and power
The CMOS technology roadmap predict aggressive scaling down of device size, transistor threshold voltage, oxide and
metal thicknesses to meet the growing demands for higher levels of integration and performance.
At the same time infrared detectors manufacturing process is developing IR materials with a tunable cut-off wavelength
capable to cover bandwidths from visible to 20μm. The requirements of third generation IR detectors are driving to
scaling down the pixel pitch, to develop IR materials with high uniformity on larger formats, to develop Avalanche
Photo Diodes (APD) and dual band technologies.
These needs in IR detectors technologies developments associated to CMOS technology, used as a readout
element, are offering new capabilities and new opportunities for cooled infrared FPAs. The exponential increase of new
functionalities on chip, like the active 2D and 3D imaging, the on chip analog to digital conversion, the signal processing
on chip, the bicolor, the dual band and DTI (Double Time Integration) mode ...is aiming to enlarge the field of
application for cooled IR FPAs challenging by the way the design activity.