Single Event Effects in CMOS Image Sensors

In this work, 3T Active Pixel Sensors (APS) are exposed to heavy ions (N, Ar, Kr, Xe), and Single Event Effects (SEE) are studied. Devices were fully functional during exposure, no Single Event Latch-up (SEL) or Single Event Functional Interrupt (SEFI) happened. However Single Event Transient (SET) effects happened on frames: line disturbances, and half or full circular clusters of white pixels. The collection of charges in cluster was investigated with arrays of two pixel width (7 and 10 \textmu{}m), with bulk and epitaxial substrates. This paper shows technological and design parameters involved in the transient events. It also shows that STARDUST simulation software can predict cluster obtained for bulk substrate devices. However, the discrepancies in epitaxial layer devices are large - which shows the need for an improved model

Theoretical evaluation of MTF and charge collection efficiency in CCD and CMOS image sensor

Classical models used to calculate the Modulation Transfer function (MTF) of a solid-state image sensor generally use a sinusoidal type of illumination. The approach, described in this paper, consists in considering a point-source illumination to built a theoretical three dimensional model of the diffusion and the collection of photo-carriers created within the image sensor array. Fourier transform formalism is used for this type of illumination. Solutions allow to evaluate the spatial repartition of the charge density collected in the space charge region, i.e. to get the Pixel Response Function (PRF) formulation. PRF enables to calculate analytically both MTF and crosstalk at every needed wavelengths. The model can take into account a uniformly doped substrate and an epitaxial layer grown on a highly doped substrate. The built-in electric field induced by the EPI/Substrate doping gradient is also taken into account. For these configurations, MTF, charge collection efficiency and crosstalk proportion are calculated. The study is established in the case of photodiode pixel but it can be easily extended to pinned photodiode pixels and photogate pixels

La conséquence de l’expression de hnRNP A1B sur la réponse cellulaire au stress

L’un des mécanismes de protection de première ligne par lequel les cellules répondent à une agression ou à un facteur de stress environnemental défavorable est la formation de granules de stress (GS). Les GS sont des structures cytoplasmiques, de la taille d’un micron, hautement dynamiques, contenant des ARNm, transcrits, mais non traduits, ainsi qu’une large gamme de protéines. Plusieurs éléments suggèrent que la réponse au stress via les GS est perturbée dans la sclérose latérale amyotrophique (SLA). Cependant, on en sait très peu sur les mécanismes de régulation de l'assemblage et du désassemblage de ces granules ribonucléoprotéiques. HnRNP A1 est une protéine de liaison à l’ARN qui pourrait affecter la récupération des cellules. HnRNP A1 est très abondante dans les motoneurones. L’épissage alternatif produit une seconde isoforme, hnRNP A1B, qui est physiologiquement exprimée à un plus faible niveau. HnRNP A1B provient de l'inclusion de l'exon 7B dans le transcrit de hnRNPA1. Cela conduit à la rétention de 52 acides aminés dans le domaine apparenté aux prions de la protéine. Nous avons récemment démontré que hnRNP A1B est augmentée dans les tissus de patients affectés par la SLA et que la protéine possède une plus forte propension à s'agréger comparé à la forme sauvage, hnRNPA1 et par conséquent, cela augmente la toxicité pour la cellule. La fonction de hnRNP A1B dans la dynamique des granules de stress n'a pas encore été élucidée. Nous avons émis l'hypothèse que l'épissage alternatif augmenté de hnRNP A1B contribue à la toxicité cellulaire par: i) la perturbation de la dynamique des granules de stress, et ii) la formation d'inclusions cytoplasmiques déclenchée par hnRNP A1B. À l’aide de méthodes in vitro, nous avons démontré comment hnRNP A1B affecte la réponse au stress cellulaire en altérant la dynamique des granules de stress.A first-line protective mechanism by which cells respond to an adverse environmental insult or stressor is the formation of stress granules (SGs). SGs are micron-sized, cytoplasmic structures that are highly dynamic and contain translationally arrested mRNAs and a broad range of proteins. Several lines of evidence suggest that the SG response is perturbed in amyotrophic lateral sclerosis (ALS). However, very little is known regarding the regulatory mechanisms of SG assembly and disassembly. One protein that could affect the recovery of cells from stress is the RNA binding protein hnRNP A1. This protein is highly abundant in motor neurons. The protein product of its alternatively spliced isoform, hnRNP A1B, is physiologically expressed at low levels. HnRNP A1B arises from the inclusion of exon 7B in the hnRNP A1 transcript. This leads to the retention of 52 amino acids in the protein’s prion-like domain. We have recently shown that hnRNP A1B is increased in ALS-affected tissues and that it has a higher propensity to aggregate compared to hnRNP A1 and this correlates with increased toxicity. The function of hnRNP A1B in SG dynamics has yet to be elucidated. We hypothesize that increased splicing of hnRNP A1 to hnRNP A1B contributes to cellular toxicity by: a) disrupting SG dynamics, and b) hnRNP A1B triggers formation of cytoplasmic inclusions. Our work indicates how hnRNP A1B affects the cellular stress response by altering SG dynamics

Displacement damage effects due to neutron and proton irradiations on CMOS image sensors manufactured in deep submicron technology

Displacement damage effects due to proton and neutron irradiations of CMOS image sensors dedicated to imaging are presented through the analysis of the dark current behavior in pixel arrays and isolated photodiodes. The mean dark current increase and the dark current nonuniformity are investigated. Dark current histogram observations are compared to damage energy distributions based on GEANT 4 calculations. We also discuss, through annealing analysis, which defects could be responsible for the dark current in CMOS image sensors

Similarities Between Proton and Neutron Induced Dark Current Distribution in CMOS Image Sensors

Several CMOS image sensors were exposed to neutron or proton beams (displacement damage dose range from 4 TeV/g to 1825 TeV/g) and their radiation-induced dark current distributions are compared. It appears that for a given displacement damage dose, the hot pixel tail distributions are very similar, if normalized properly. This behavior is observed on all the tested CIS designs (4 designs, 2 technologies) and all the tested particles (protons from 50 MeV to 500 MeV and neutrons from 14 MeV to 22 MeV). Thanks to this result, all the dark current distribution presented in this paper can be fitted by a simple model with a unique set of two factors (not varying from one experimental condition to another). The proposed normalization method of the dark current histogram can be used to compare any dark current distribution to the distributions observed in this work. This paper suggests that this model could be applied to other devices and/or irradiation conditions

L’écosystème buccal chez le patient âgé

La bouche est une cavité naturelle complexe qui forme le segment initial du tube digestif. Elle est un acteur essentiel des fonctions vitales que sont la nutrition, le langage et la communication. L’ensemble de la bouche (dents, parodonte, muqueuses, langue) est constamment hydraté et lubrifié par la salive. À tout âge, un équilibre s’établit entre la prolifération bactérienne, le flux salivaire et la réponse tissulaire : c’est l’écosystème buccal. La régulation de cet écosystème participe à la protection du complexe buccal contre les pathologies inflammatoires et infectieuses courantes (caries, gingivites, parodontopathies,candidoses). Chez les patients âgés, la modification du flux salivaire, l’apparition de pathologies spécifiques (caries radiculaires, absence de dents, parodontopathies. . .), les conditions locales (présence de prothèses amovibles), le développement de pathologies générales telles que le diabète, l’hypertension, la baisse des défenses immunitaires, la négligence de l’hygiène quotidienne sont autant d’éléments qui vont déséquilibrer l’écosystème buccal, favoriser la formation du biofilm (plaque bactérienne) et fragiliser les tissus bucco-dentaires. Le maintien de cet écosystème est essentiel pour le patient âgé : il lui permet de s’alimenter dans de bonnes conditions et ainsi prévenir les risques de dénutrition. Les auteurs décrivent la physiopathologie buccale (flore buccale, sécrétion salivaire) et les stratégies à adopter pour préserver l’équilibre buccal chez le patient âgé

Influence of displacement damage dose on dark current distributions of irradiated CMOS image sensors

Dark current increase distributions due to displacement damages are modeled using displacement damage dose concept. Several CMOS image sensors have been exposed to neutrons or protons and we have characterized their degradation in terms of dark current increase. We have been able to extract a set of two factors from the experimental dark current increase distributions. These factors are used to predict and build dark current increase distribution and leads to a better understanding of displacement damage effects on CMOS image sensors

Single Event Effects in 4T Pinned Photodiode Image Sensors

This paper describes how Single Event Effects (SEEs) produced by heavy ions disturb the operation of Pinned Photodiode (PPD) CMOS Image Sensors (CISs) in the frame of space and nuclear applications. Several CISs with 4T and 5T pinned photodiode pixels were exposed to ions with a broad Linear Energy Transfer range (3.3 to 67.7 MeV.cm²/mg). One sensor exhibited Single Event Latchups (SELs). Physical failure mechanism and latchup properties were investigated. SELs are caused by the level shifters of the addressing circuits, which create frame perturbations - following which, in some cases, parts of the addressing circuits need to be hardened. In the second part of the paper, the effects of anti-blooming capabilities on the Single Event Transient effects (SETs) are analyzed. SETs in pixels can be partially mitigated by anti-blooming through the transfer gate and/or a dedicated transistor. This work also shows that the number of pixels disturbed by SETs can be reduced by using appropriate anti-blooming techniques