Europe’s next fleet of geostationary meteorological satellites, MeteoSat Third Generation, will introduce new functions in addition to continuity of high-resolution meteorological data. The atmosphere Infrared Sounder (IRS), as high –end instrument, is part of this challenging program.
IRS principle is a Fourier Transform Interferometer, which allows recomposing atmospheric spectrum after infrared photons detection. Transmission spectrums will be used to support numerical weather prediction. IRS instrument is able to offer full disk coverage in one hour, an on-ground resolution of 4 by 4 km, in two spectral bands (MWIR: 1600 to 2175cm-1 and LWIR: 700 to 1210cm-1) with a spectral resolution of 0.6cm-1.
Among critical technologies and processes, IRS detection chain shall offer outstanding characteristics in terms of radiometric performance like Signal to Noise Ratio (SNR), dynamic range and linearity. Selected detectors are HgCdTe two-dimensions arrays, cooled at 55 Kelvins, hybridized on snapshot silicon read-out circuit at 160x160 format. Video electronics present 16 bits resolution, and the whole detection chain (Detectors and electronics) permits to reach SNR between 2 000 and 10 000 as requested by the application. Radiometric onground test results performed on design representative detection chains are presented and are confirming the challenging phase A design choices.
More and more systems are requested to be more compact keeping constant system performances. One of the best
approach is to reduce the pixel pitch of the IR detector while new technology improvements are carried out to
improve the detector performance.
The last developments at SOFRADIR / France for cooled IR detectors are following these trends. As a matter of
fact, 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 15 μm pixel pitch detectors is offering a mid-TV format (384 x 288), a
TV format (640 x 512) and a HD-TV format (1280 x 1024). 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. This Focal Plane Arrays (FPA) is proposed in different
tactical dewars, corresponding to various systems solutions.
HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection do show constant
improvements regarding their compactness and performances.
Among the new detectors, the family of 15 μm pixel pitch detectors is offering a mid-TV format (384 x 288), a
TV format (640 x 512) and a HD-TV format (1280 x 1024). Each detector is available in a SWaP configuration
(meaning dedicated to applications requiring low Size, Weight and Power)
Thanks to recent improvements and new technological breakthrough, the MCT technology allows operating
detectors at higher temperature, 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.
We report our latest development of HgCdTe electron avalanche photodiode (e-APD) with Cd compositions between 0.3
to 0.41; exponentially increasing gain, synonym of exclusive electron multiplication, was observed in all the devices up
to M>600, associated with low noise factors F=1.2; 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 decreases with increasing band-gap and a record low value of 2 aA, was obtained 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. On the best devices, the
operability in gain and noise exceeds 99.6% and relative gain dispersion lower than 10 %, independently of the
wavelength at gains M=10-100. First characterizations of multi-mode 3D/2D FPA have shown on a range resolution
below 15 cm (1 ns).
KEYWORDS: Staring arrays, 3D image processing, Pulsed laser operation, LIDAR, Avalanche photodetectors, Ranging, 3D metrology, Readout integrated circuits, Mercury cadmium telluride, Signal to noise ratio
CEA-Leti has developed a 320x256 FPA for 3D flash LADAR active imaging. The readout IC (ROIC) performs time-of-flight
(TOF) measurement in addition to 2D intensity imaging with a single emitted laser pulse. The FPA consist of a
ROIC hybridized to a 30 μm pitch HgCdTe avalanche photodiode (APD) array. The illuminator used for testing this FPA
is a 1.57 μm 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 2D and 3D active
images obtained during the first field trial of our prototype LADAR system are presented.
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.
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 (3D) and the
returned intensity (2D) 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.
This paper presents an overview of the very recent developments of the MCT infrared detector technology developed by
CEA-LETI and Sofradir in France for next generation of applications. New applications require high sensitivity and dual
band detectors.
The Avalanche PhotoDiodes (APD) technology opens new interesting fields of investigation for low flux applications
and fast detectors for laser imaging. 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, in order to gate the backscattered
signal around the target. In partnership with Sofradir, CEA/LETI (France) has developed high quality MCT 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 presented in this paper is the first step in a road-map to address low flux infrared
sensors in the next few years.
In parallel, the development of dual-band infrared detectors has been the core of intense research and technological
improvements for the last ten years. New TV (640 x 512 pixels) format detectors of 24μm pixel pitch is available. It is
proposed with MWIR/MWIR or MWIR/LWIR dual band sensitivity integrated in dedicated tactical Dewars. At present,
focused on pixel pitch reduction, Sofradir is carrying out optimization of the materials quality, photodiode design as well
as flip-chip bonding process. 20 μm pixels have demonstrated dual color key performances (quantum efficiency, optical
fill factor, and pixel operability) in accordance with mono-spectral structures. Results are presented in this paper.
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.
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 optimization of HgCdTe avalanche-photo-diodes (e-APD) and focal plane arrays (FPA) are reported. The gain
performances was measured in planar homo-junction APDs with Cd compositions between xCd=0.3 to 0.41.
Exponentially increasing gain, synonym of exclusive electron multiplication, was observed in all the devices up to
M>100. The high gain at high xCd opens the path to thermo-electric cooled active imaging at T=200K. This perspective is
corroborated by the demonstration of high gains and low excess noise factor F=1.2 in extrinsically doped MW-APDs,
which enables reduced dark-current at high temperatures. The equivalent input dark current (Ieq_in) decreased from 200
fA to 1 fA, when the cut-off wavelength was reduced from λ
c=5.2 μm to 4.1 μm at M=100 and T=80 K. This shows that
sensitivity can be optimized by increasing xCd, at the cost of increased reverse bias. A new horizontal-gain-well (HGW)
hetero-structure was processed to optimize the sensitivity at high gain and low bias. The first HGW-APDs had gains
comparables with MW e-APDs and 50 times lower dark-current at T=200 K. They did also display surprisingly high
quantum efficiency in the MWIR range, ηpeak=30%, which enables thermal imaging at high operating temperature. The
high performance of MW-APDs was confirmed by the characterizations of a first 320x256 30μm pitch APD-FPA,
yielding a 99.8 % operability, low gain dispersion (<10%) and low noise equivalent photons (NEPh=3 at tint=1 μs) for
gains up to M=70. The maturity of the DEFIR HgCdTe e-APD-FPA technology was highlighted by the first
demonstration of passive amplified imaging.
HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection demonstrate constant improvements regarding their compactness and performances.
Among the new detectors, the family of 15 µm pixel pitch detectors is offering a mid-TV format (384 × 288), a TV format (640 × 512) and a HD-TV format (1280 × 1024). The latest development dealing with 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, in order to save power consumption at system level. In parallel, the 15μm pitch enables to reach challenging density and spatial resolution. This Focal Plane Arrays (FPA) is proposed in different tactical dewars, corresponding to various systems solutions.
HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection do show constant improvements
regarding their compactness and performances. New detectors are now proposed offering system solutions in the
different IR wavebands and profiting of the latest technology improvements as well as MCT performance advantages
and cost reduction.
Among these new detectors, one can find the family of 15 µm pixel pitch detectors including a mid-TV format (384 x
288), a TV format (640 x 512) and a twice-TV format (1280 x 1024). The latest development concerning the mid-TV
format is performed according to very challenging specifications regarding small cost and low power consumption.
These Focal Plane Arrays (FPA) are integrated in dedicated tactical Dewars, taking advantages on last development in
coolers manufacturing and Dewar assembly.
Another development axis at CEA\LETI-LIR and Sofradir concerns the avalanche photodiodes for FPA sensitivity
improvement. This very promising technology is dedicated for low flux applications as active imagery, hyperspectral
applications or small aperture systems.
New development results are presented and future trends are discussed.
KEYWORDS: Modulators, Digital filtering, Analog electronics, Readout integrated circuits, Amplifiers, Staring arrays, Signal to noise ratio, Indium nitride, Digital electronics, Sensors
Designing a digital IR focal plane array (IRFPA) requires fulfilling very stringent requirements in terms of power consumption, silicon area and speed. Among the various ADC architectures like successive approximation, ramp or over-sampled converters, the best choice strongly depends on the application. We believe that sigma-delta converters, in spite of their quite high power consumption, are a promising solution for high-performance and medium size FPA, e.g. 320x240.
This paper presents the design of a second-order incremental sigma-delta ADC dedicated to cooled (77K) IRFPA applications. System-level simulations used to define the modulator parameters and specify its analog building blocks are presented. Circuit design of the switched-capacitor modulator and the digital decimation filter is described. The column ADC including the filter has been implemented in a standard 0.35μm CMOS process on the basis of a 25μm pitch and lead to a total length of 3200μm.
Test chips including a single ADC have been manufactured end of 2006. The first measurement results, at 77K, are presented along with perspectives and future developments. They demonstrate the following performance: 81dB Signal-to-Noise Ratio (SNR), 13 bits Effective Number Of Bits (ENOB) and 270μW power consumption at 17kSamples/s rate.
HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection do show constant improvements regarding their compactness and performances. New detectors are now proposed offering system solutions in the different IR wavebands and profiting of the latest technology improvements as well as MCT performance advantages and cost reduction. As a matter of fact, the size of MCT wafer has grown to 4", the pixel pitch was lowered to 15μm while maintaining outstanding results on the Focal Plane Arrays (FPA) uniformity. New functions as the Analog to Digital Conversion (ADC) are added to read-out circuits.
Results are presented concerning Non Uniformity Corrections (NUC) stabilities for two Sofradir products. Then results from developments of integrated ADC are addressed and finally, the Jupiter 1280x1024 mid-wave (MWIR) MCT detector performance results are presented.
KEYWORDS: Staring arrays, Sensors, Modulation transfer functions, Mercury cadmium telluride, Diodes, Optical transfer functions, Signal to noise ratio, Semiconducting wafers, Analog electronics, Infrared detectors
The InfraRed staring arrays are more and more compact and offer system solutions in the different IR wavebands. The HgCdTe (Mercury Cadmium Telluride / MCT) material and process, as well as the hybridization technology, have been taken to an even more advanced level of sophistication to achieve these new staring arrays high performances. Latest developments allow progress at different stages of products offered by SOFRADIR. Uniformity of Focal Plan Arrays (FPA) is improved, read-out circuits propose new functions as the analogic to digital conversion, and the reliability of the whole dewar detector and cooler assembly is increased. New products take advantages on these progresses. In mid-wave (MWIR), 1280x1024 MCT detector available in a tactical dewar is presented.
The InfraRed staring arrays offered by SOFRADIR are more and more compact and offer system solutions in the
different IR wavebands. The HgCdTe (Mercury Cadmium Telluride / MCT) material and process, as well as the
hybridization technology, have been taken to an even more advanced level of sophistication to achieve these new
staring arrays high performances. Latest developments have also been focused on the readout silicon circuit. A frame
rate increase, new types of customized functions and digital converter are an important progress in this field. In order
to match each system requirements, different flexible architectures of Analog To Digital Converter (ADC) have been
developed. These developments implement specific requests in terms of frame rate, power consumption and
resolution. Beyond the performance aspects, digital focal plan arrays can be considered as the first step towards a new
low cost dewar family, since they allow for a more simple electrical interface on dewar designs. New results
concerning these new readout circuit architectures are presented in this paper.
As a general tendency in the microelectronics field, the miniaturization of the products is more and more important and provides cost and system advantages. Following this general tendency, new InfraRed (IR) staring arrays are more and more compact and offer system solutions in the different IR wavebands. In France, the HgCdTe (Mercury Cadmium Telluride / MCT) material and process, as well as the hybridization technology, have been taken to the next even more advanced level of sophistication to offer these new staring arrays. Thus, for Mid Wave (MW) applications, a 15 μm pitch TV format (640×512) HgCdTe detector, called SCORPIO, is offered with a 1/4W micro cooler with miniaturized cryogenics. This optimized dewar has been extended to TV/4 format, using the successful focal plan array which is in mass production since 2000. Concerning Long Wave array, SOFRADIR has been offering for several years 320×256 LW detectors with a cut-off wavelength tuned between 9μm and 12μm depending on the required application. Based on that experience, two new LW HgCdTe products have been developed in 2004 and are offered since beginning of 2005. Relying on the standard HgCdTe production process with the latest improvements and on the optimized dewar family, VENUS-LW detector is now offered. This is a higher resolution 25μm pitch 384×288 LW IDDCA with a 0.5W micro cooler and with a cutoff between 9μm and 10μm for an operational temperature between 77K and 85K and for a spectral band pass fully satisfying the imagery requirements of compact LW FLIRs. This paper overviews the electro-optical and thermal performances of these three detectors and points out some reliability advantages of this new dewar design. Finally, the development trends for even higher resolution IR detector are discussed.
As far as high performance IR detectors are concerned, cooled 2D arrays are more and more used in both IR medium and long wavebands for many different applications. Although it is easy to get an image with 2D staring arrays in comparison with TDI linear arrays, it is more difficult to answer the full system needs in terms of high performances in very tough environmental conditions. As a matter of fact, performances of large cooled staring arrays are mainly limited by the ability of the system to correct the non-uniformities of the arrays and this ability depends on some keys parameters like linearity, uniformity, and stability of operating temperature. These parameters have to remain constant in function of the change of environmental conditions. In this paper, the main key parameters for staring arrays are reviewed and performances of large new SOFRADIR cooled staring arrays are discussed in MW. Finally third generation key drivers are discussed.
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