In the present communication, the characterization results of an in-house developed four-quadrants detection module based on HgCdTe APDs and a Si-CMOS ROIC pre-amplifier is discussed. The module has been designed to be employed as high data rate ground-segment detector for 1.55 μm long-distance free-space optical communication links in the framework of a project funded by the European Space Agency. The detector is characterized by a multiplication gain in excess of M = 150, a ROIC input referred noise of Ne = 45 electrons rms and a measured bandwidth of BW = 450 MHz. These characteristics enable the linear-mode detection of meso-photonic states ranging from tens of photons per pulse down to the single-photon level at high count rates exceeding 500 MHz per quadrant (and 2 GHz if the signal is dispatched over all four-quadrants). For the present module, the performance for PPM and OOK modulation formats was estimated and its potentiality for long-distance free-space optical communications employing these modulation formats was validated. In particular, for the PPM format, a detection probability of 0.9 and a false alarm probability of 10-2 , a minimum PPM slot width of 500 ps and a temporal jitter with a FWHM ~ 160 ps were estimated, for an incident photonic state with 10 photons/pulse. The potentiality of the detector for 625 Mbps OOK modulation format was also evaluated and compared with a quantum limited situation. In this case, a -3.9 dB penalty from the quantum limited BER was obtained. A new generation of detectors is currently in development, which is expected to further improve the performance.
HgCdTe Avalanche Photo Diodes (APDs) are developed at CEA/Leti to enable applications that require the detection of information contained in a low number of photons in each spatial and/or temporal bin, such as LiDAR and free space optical communications. The requirements for such detectors are strongly application dependent, which is why both the HgCdTe APD technology and the proximity electronics, used to extract the detected photocurrent, needs to be optimized for each application. The present communication reports results obtained from the development of detectors for high dynamic range LiDAR applications, made within the scope of the H2020 project HOLDON, and high data rate FSO, made in collaboration with Mynaric Lasercom AG. For FSO applications, we have measured 10 GHz bandwidth at unity gain for APDs with 10 μm diameter. At higher APD gain and diameter, the BW is presently limited by carrier transit and by resistance-capacitance product in small and large area APDs, respectively. For LiDAR we have developed APDs with an made of an array of diodes in parallel with a diameter up to 200 μm and large avalanche gain, M<100, that will be hybridized with a dedicated CMOS amplifier. This circuit was designed to enable photon shot noise limited linear detection over a dynamic range of 6 order of magnitude of signal for observation times ranging from ns up to μs. First characterizations made at unity APD gain shows that the HOLDON detector will meet most of the required performance parameters in terms of sensitivity and linear dynamic range.
N-on-p extrinsically doped MWIR HgCdTe material and photodiodes have been developed to benefit from the expected reduction of the Auger generation in the p-type absorbing layer. Samples with two doping levels have been characterized using dark current, current noise, Hall effect and PhotoLuminescence Decay (PLD) measurements. The dark current and PLD measurements are consistent with a reduction of the Auger generation quantified by the ratio between the Auger 1 and 7 recombination coefficients 𝛾 around 10. The corresponding dark current in the sample with the lowest doping level was slightly higher than in typically p-on-n photodiodes. The low frequency noise, characterized by a Tobin coefficient below 10-5, is lower than the values reported for other MWIR HgCdTe photodiodes at the same dark current density. The low dark current and dark current noise show on the high potential of such photodiodes to form focal plane array that can be operated at high operating temperature without degradation of the image quality.
HgCdTe APD detector modules telecommunication are developed at CEA/Leti for atmospheric LIDAR and free space optical (FSO). The development is driven by the design and manufacture of generic sub-assemblies that can be adapted in each detector module to meet the specific detector requirements of each application. The optimization of such subassemblies is detailed in perspective of the challenges that are set by the specifications for detector modules currently developed for atmospheric LIDAR, in the scope of an R&T CNES project for Airbus and an H2020 project HOLDON, and FSO, in the scope of an ESA project and in collaboration with Mynaric Lasercom GmbH. Two detector modules have recently been delivered to Airbus DS for extensive LIDAR simulation tests. Initial characterization of these modules shows that the input noise, NEP=10-15fW/√Hz (5 photons rms) have been reduced by a factor three compared to previously developed large area detectors although the bandwidth have been increased to 180 MHz in order to respond to the requirements of high spatial depth resolution. The temporal remanence was 10-4 at 200 ns after the detection of short light impulse, which is compatible with demanding LIDAR applications such as bathymetric profiling.
HgCdTe avalanche photodiodes offers a new horizon for observing spatial or temporal signals containing only a few infrared (IR) photons, enabling new science, telecommunication and defence applications. The use of such detectors for free space optical communications is particularly interesting for both deep space and high data rate links as it enables wide field of view free space optical coupling to the detector at high sensitivity, down to single photon level and with a close to negligible loss of the information contained in the strongly attenuated photon flux. Measurement of the response time and dark current shows that such devices can be operated at room temperature with bandwidths up to 10 GHz in a back-side illuminated configuration. This configuration allows to use micro-lenses fabricated directly into the APD substrate and enables to use a large photosensitive area while maintaining a high bandwidth, low dark current and /or high operating temperature. We report on the expected performance 4-quadrant APD detector demonstrator with single photon sensitivity, which is currently developed to be used in deep space telecommunications by ESA and present the potential use for high data rates links of 10 Gbits/s.
KEYWORDS: X-rays, Tomography, Signal to noise ratio, Scanning electron microscopy, Electron beams, Nanowires, X-ray imaging, Sensors, X-ray detectors, Spatial resolution
We aim at resolving deca-nanometer features in microelectronic samples using a laboratory SEM-based X-ray tomography
microscope. Such a system produces X-rays through the interaction between a focused SEM electron beam and a metallic
target. The effective source size of the X-ray beam can be adjusted by varying the target material and geometry. For
instance, the use of tungsten nanowires (few hundred nanometers of length) combined with a high electron beam current
leads to an increased X-ray flux generated in a reduced volume, necessary for detecting interface details of the analyzed
object. It improves resolution and signal-to-noise ratio (SNR), but is also sensitive to electron beam-target instabilities
during the scan. To improve robustness, a FFT-based image correlation is integrated in the process through a closed-loop
control scheme. It allows stabilizing the electron beam on the target and to preserve the X-ray flux intensity and alignment.
Also, a state of the art high-resolution scientific-CMOS (sCMOS) X-ray detector was installed, allowing to reduce noise
and to increase quantum efficiency. Results show that such numerical and equipment improvements lead to significant
gains in spatial resolution, SNR and scanning time of the SEM-based tomography. It paves the way to routine, high
resolution, 3D X-ray imaging in the laboratory.
Synchrotron radiation is a good candidate for 3D imaging at high resolution. However, the difficult access to 3rd
generation synchrotron sources is prohibitive for daily analyses and we present hereafter a step towards x-ray
nanotomography using a laboratory system. To have a lens-free system, we use the electron beam of an SEM to produce
x-rays through the interaction between the SEM electron beam and a metallic anode. The inherent x-ray source size can
be properly shaped using different anode materials and geometries. This flexible system makes it possible to perform xray
imaging at energies of up to 10keV and resolution down to 100nm. Because of a low SNR, the exposure time is long
and forces to have a low angular sampling. This is counterbalanced by using algebraic reconstruction algorithms.
The technique has been applied to the study of plasma FIB-prepared macroporous silicon samples. Those samples come
from the controlled porosification of 200mm silicon wafer, with thicknesses from few nm to few hundreds of
micrometers. We quantified the 3D pore network, which is of interest for the optimization of the production of such
materials.
P. Bleuet, G. Audoit, J. Bertheau, J. Charbonnier, P. Cloetens, M. Djomeni Weleguela, D. Ferreira Sanchez, F. Hodaj, P. Gergaud, F. Lorut, J.-S. Micha, A. Thuaire, O. Ulrich
In microelectronics, more and more attention is paid to the physical characterization of interconnections, to get a better
understanding of reliability issues like voiding, cracking and performance degradation. Those interconnections have a 3D
architecture with features in the deep sub-micrometer range, requiring a probe with high spatial resolution and high
penetration depth. Third generation synchrotron sources are the ideal candidate for that, and we show hereafter the
potential of synchrotron-based hard x-ray nanotomography to investigate the morphology of through silicon vias (TSVs)
and copper pillars, using projection (holotomography) and scanning (fluorescence) 3D imaging, based on a series of
experiments performed at the ESRF. In particular, we highlight the benefits of the method to characterize voids, but also
the distribution of intermetallics in copper pillars, which play a critical role for the device reliability.
Beyond morphological imaging, an original acquisition scheme based on scanning Laue tomography is introduced. It
consists in performing a raster scan (z,θ) of a sample illuminated by a synchrotron polychromatic beam while recording
diffraction data. After processing and image reconstruction, it allows for 3D reconstruction of grain orientation, strain
and stress in copper TSV and also in the surrounding Si matrix.
KEYWORDS: Luminescence, Tomography, Silicates, Absorption, Chemical elements, Synchrotrons, X-ray microscopy, Chemical analysis, Signal attenuation, Iron
To settle an optimal analytical strategy of the search for life traces, it is decisive to start their study in the preliminary
examination stages of the extraterrestrial Returned Samples, once they are still stored in their original container. The
relevance of the application of on-going synchrotron micro-X-ray fluorescence (XRF) methodological developments
performed at the ID21/ID22 beamlines of the ESRF is critically examined in this paper. XRF computed tomography
(CT) at ID22 is in general a precious tool allowing a non-invasive and non-destructive determination of the three-dimensional
mineralogy with micrometer resolution of sub-millimeter silicate grains. A combination of absorption and
Compton tomographies is a more promising method to image bulk views of the organic matter distribution. XRF-scanning
X-ray microscopy (SXM) at ID21 is in general not adapted for studying samples across a container. However, it
appears to be a unique tool to draw up a list of the sub-surface sites where tiny amounts of organic matter are present.
Adaptation of the SXM chamber to the quarantine criteria stipulated by the spatial agencies is a way to permit such
analyses in the preliminary examination stages.
At the ESRF Micro-Fluorescence, Imaging and Diffraction beamline ID22, X-Ray micro-tomography is a routine technique proposed to users for 3D microanalysis of various samples. The purpose of this work is to extend 3D micro-tomography in order to obtain in-situ 3D information about samples at increasing pure axial loads. We developed a new device that allows one to combine mechanical testing and micro-tomography. The device is optimised for low Gpa Young moduli like plastics or bone but can easily be adapted to higher values. In this paper we present first results obtained with animal and human bone samples to gain insight into the bone microcrack problem.
In high-resolution microtomography, the alignment of the axis of
rotation with respect to the optical axis and to the rows of the
detector pixel array is an important issue, misalignment being a
critical source of reconstruction artifacts. A common calibration
method is based on the use of small fiducial markers on a
sample. However, the automatic detection and identification of such
markers is difficult. Moreover, the exact determination of their
positions in the radiographs is prone to errors in the presence of
noise, beam-profile fluctuations or nonuniform detector response. This is largely due to the fact that the markers cover only a small number of pixels in the image, which results in poor signal statistics. We have developed a new method that overcomes this limitation. It is based on the use of a purpose-built reference sample with periodic grid structures that cover large regions of the
radiographs. Straightforward Fourier analysis techniques are used to
determine from the images not only the tilt angles of the rotation
axis, but also the lateral position of the axis and the exact pixel
size.
Linear digital tomosynthesis consists in acquiring on a digital detector a few projections, at different view angles and for a linear X-ray source path. A simple shift and add process reconstructs planes parallel to the detector plane but with a low vertical resolution. To improve it, we propose to use Algebraic Reconstruction Technique (ART) and Half Quadratic Regularization (HQR) methods, which are based on an iterative process. In such a linear digital tomosynthesis context, we propose to reconstruct independent 2D tilted planes passing through the linear source trajectory. Thus, computation time is reduced and it becomes possible to regularize in an anisotropic way to adapt the regularization process to the reconstructed volume sampling. We validate our approach with experimental data acquired on a digital detector. ART significantly improves the vertical resolution in comparison with usual process. However, ART is sensitive to noisy projections and may produce poor quality reconstructions. The HQR piecewise smoothness constraint stabilizes the reconstruction process. With a total angular range of 40 degrees, we can reach a vertical resolution lower than 1 cm, while it is superior to 3 cm with the usual process. Furthermore, HQR method significantly reduces truncation artifacts due to high projection angles.
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