Sofradir detectors for hyperspectral applications from visible up to VLWIR
Authors: Bruno Fièque, Philippe Chorier, Bertrand Terrier Published 13 October 2010
Sofradir has extended its Visible-Near infrared technology, called VISIR, largely as a result of its participation in the PRISMA mission. This technology has been specially developed for hyperspectral applications and enables detection in both visible range and SWIR detection range (0.4μm up to 2.5μm). Sofradir has developed MCT detectors that cover MWIR and LWIR infrared ranges, ideal for space applications. For example, 1000x256 (Saturn) and 500x256 arrays (Neptune) 30μm pitch detectors have already been validated in terms of irradiation behavior, thermal cycling, and ageing. In addition, Sofradir now offers a large MWIR or LWIR 1016x440 array with a 25μm pixel pitch for hyperspectral imaging.

Operating temperature: A challenge for cooled IR technologies
Authors: Michel Vuillermet, Philippe Tribolet. Published 3 May 2010
Cooled IR technologies are challenged for answering new system needs like the reduction of power. This reduction is requested in new IR system designa in particular for cooled IR detection. The goal is to reduce system sizes, to increase system autonomies and reliabilities and globally to reduce system costs. One of the key drivers for cooled systems is the cooler and the operating temperature of the detector. As far as operating temperature is concerned, Sofradir put a lot of efforts for years for adapting its technologies to increase the operating temperatures of IR detectors. Main examples are dealing with long wave staring arrays based on QWIP technology and on MCT technology as well as medium wave staring arrays using MCT technologies.

HgCdTe-based APD focal plane array for 2-D and 3-D active imaging: first results on a 320x256 with 30µm pitch demonstrator
Authors: Eric de Borniol, Fabrice Guellec, Johan Rothman, et al. Published 3 May 2010
CEA-Leti has developed a new 320x256 hybrid focal plane array (FPA) for flash LADAR imaging. The detector array consists of 30μm pixel pitch MWIR HgCdTe avalanche photodiodes operating at 80K and the readout integrated circuit (ROIC) is fabricated on a standard 0.18μm CMOS process. The custom ROIC can operate as a passive thermal imager or a flash LADAR imager. In this second mode, each pixel will provide the time of flight measurement (3-D) and the returned intensity (2-D) of one laser pulse. For the first laboratory trials the e-APD photodiode array performances were measured in passive mode and the same FPA was then tested in one shot LADAR mode. This paper describes the readout IC pixel architecture and reports the first electro-optical test results in both passive and active modes. This new prototype takes advantage of the latest developments of the partnership between Sofradir and CEA-Leti.

New IR detectors with small pixel pitch and high operating temperature
Authors: David Billon-Lanfrey, Philippe Trinolet, Frédéric Pistone, et al. Published 15 December 2010
More and more systems are requested to be more compact keeping constant system performance. One of the best strategies is to reduce the pixel pitch of the IR detector while new technology improvements are carried out to improve the detector performance. The latest developments at SOFRADIR / France for cooled IR detectors are following these trends. HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection do show constant improvements regarding their compactness by reducing the pixel pitch, and regarding performances. Among the new detectors, the family of 15μm pixel pitch detectors is offering a mid-TV format (384x288), a TV format (640x512) and a HD-TV format (1280x1024). The latest development concerning the mid-TV format is performed according to very challenging specifications regarding compactness and low power consumption. Thanks to recent improvements, the MCT technology allows to operate detectors at higher temperature (HOT detectors), in order to save power consumption at system level. In parallel, the 15μm pitch permits to reach challenging density and spatial resolution. These Focal Plane Arrays (FPA) are proposed in different tactical dewars, corresponding to various systems solutions.

A 25μm pitch LWIR focal plane array with pixel-level 15-bit ADC providing high well capacity and targeting 2mK NETD
Authors: Fabrice Guellec, Arnaud Peizerat, Michael Tchagaspanian, et al. Published 3 May 2010
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-bit 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.

Low IR input flux condition operations thanks to MCT e-APD
Authors: Frédéric Pistone, Philippe Tribolet, Gilbert Decaens, et al. Published 3 May 2010
Low IR input flux conditions are answering different system applications as gas detection needs, active imagery, very long ranges detection and identification and some scientific applications. Then for other applications like ground applications, some system design trade-off could be made between thermal performance and identification and equipment size and cost.

HgCdTe APD-focal plane array development at DEFIR
Authors: Johan Rothman, Eric De Borniol, Olivier Gravrand, et al. Published 28 October 2010
Reports of the latest development of HgCdTe electron avalanche photodiode (e-APD) with Cd compositions between 0.3 to 0.41. Exponential increases in gain are described with observations of M>600 associated with low noise factors F=1.2. Also, a record high gain of M=7000 was measured in e-APDs with λc=4.6μm at 80K, which shows on the stability of the junction. The equivalent input dark current is shown to decrease with increasing band-gap. Measurements in a λc=2.9 μm e-APD at M=24 and spectral response measurements have shown that the gain and quantum efficiency is conserved down to the UV. Dedicated ROICs have been designed for passive and active laser assisted imaging. A passive imaging ROIC for low flux application have been designed for a full frame readout speed of 1.5 kfps and an equivalent input noise lower than 2 electrons. Two active imaging ROICs have already been validated with e-APD arrays. Dual-mode passive and active 2D (range gated) e-APDs FPAs have been made using with cut-off wavelengths ranging from 2.9μm to 5.3μm at T=80 K.

Experimental characterization of an infrared focal plane array for flash laser radar imaging
Authors: Eric de Borniol, Fabrice Guellec, Johan Rothman, et al. Published 27 October 2010
CEA-Leti has developed a 320x256 FPA for 3-D flash LADAR active imaging. The readout IC (ROIC) performs time-of-flight (TOF) measurement in addition to 2-D intensity imaging with a single emitted laser pulse. The FPA consists of a ROIC hybridized to a 30μm pitch HgCdTe avalanche photodiode (APD) array. The illuminator used for testing this FPA is a 1.57μm laser producing 8 ns pulses with a maximum energy of 8 mJ per pulse. This paper describes the readout IC pixel architecture and presents ranging performances obtained in laboratory conditions. The first 2-D and 3-D active images obtained during the first field trial of our prototype LADAR system are presented.