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Recent developments in the Integral Data Assimilation (IDA) methods within Bayesian framework have been achieved at CEA to tackle the problem of correlated experiments (through technological uncertainties) and neutron transport model numerical effects. Hence, reference Monte-Carlo and deterministic calculations (TRIPOLI4® and APOLLO3®) are used together to solve neutron transport equations and get the sensitivity profiles. Furthermore, the analysis of the mock-up experiments technological parameters is performed to get accurate uncertainties and correlations between the experiments (finally the covariance experimental matrix required for IDA). We apply here the IDA approach with a new, extend set of statistical indicators (Cook’s distance, Bayesian and Aikike Information criteria (BIC, AIC)) implemented in the nuclear physics CEA CONRAD code, to the integral experiments UH1.2 in reference and voided configurations (standard PWR fuel assembly in the EOLE mock-up reactor). The adjusted multigroup cross-sections and posterior covariances are compared by choosing different ingredients in the assimilation process. Finally, the investigated key neutron parameters; reactivity, reactivity worth (void effects) and fissions rates are transposed (with the same CONRAD code) to a standard PWR core. This in-depth analysis enables us to predict the residual uncertainties and biases due to the multigroup cross-section adjustments assessing at the same time the similarity of these integral experiments for the main PWR neutronic safety parameters. In addition, technological parameters uncertainties and their impact on Bayesian adjustment process are taken into account through a global experimental covariance matrix. We point out that the UH1.2 experiments bring relevant additional information to PWR keff calculations reducing significantly the posterior results but are less relevant for fission rate distribution in reference and voided configurations.

In order to improve passive safety of Sodium-cooled Fast Reactors The French Alternative Energies and Atomic Energy Commission (CEA) has proposed a new core design called CADOR - an SFR core with enhanced Doppler reactivity feedback. One of its most important design features is the introduction of solid moderating materials inside each fuel assemblies to slightly decrease the average neutron energy. The article focuses on development and validation of a neutronics calculation scheme able to produce accurate results in case of CADOR and other fast cores with moderating materials. The study uses two different fuel assembly models moderated by metallic beryllium and zirconium hydride (ZrH2) respectively The study includes discussion of neutron scattering treatment and different ways of spatial homogenization and energy condensations. The results indicate that the accurate scattering treatment leads to much better estimation of Doppler constant, especially in case of ZrH2 moderated core. By using combined deterministic-Monte Carlo calculation scheme we are able to quantify the biases on global reactivity, reactivity feedbacks and control rod worth. We demonstrate that spatial homogenization plays a more important role in case of moderated CADOR assemblies and thus preserving certain level of heterogeneity within fuel assemblies can lower the calculation bias significantly.

This paper presents a new 3D methodology to simulate Multiple Bit Upsets in commercial SRAMs. Experiments are performed at the Los Alamos neutron facility on 90, 130, and 250 nm SRAMs and compared to Monte-Carlo simulations. A discussion on ions inducing MBUs is also proposed. Index Terms--Bulk, diffusion, Monte-Carlo, multiple bit upsets (MBU), neutron, SEU, SRAM.

A reliable criterion for SEU occurrence simulation is presented. It expresses the relationship existing at threshold between the magnitude and duration of the ion-induced parasitic pulse. This criterion can be obtained by both three-dimensional device and SPICE simulations. Using this criterion, the simulated and experimental SER on 130 and 250 nm technologies are shown to be in good agreement.

A methodology to quantify the single event upset (SEU) cross section in a simplified random access memory (RAM) device for neutron energy ranging from 10 MeV up to 150 MeV has been proposed and accounts for both heavy and light ions. Usual Monte Carlo method is shown to be suitable for the contribution of short range ions but not for long range ones such as alphas. An analytical approach to investigate the contribution of these long ranges particles on SEU cross section is given. It uses the efficient ions distribution which is the probability that a neutron produces an ion able to deposit a given energy over a given distance after a given range. Results show, for accurate calculations in sensitive RAMs, alphas might be considered up to 100 [micro]m from the sensitive volume. Index Terms--Efficient ion distribution, long range ions, monte carlo, neutron.

The off-NMOS and off-PMOS transistor single-event upset (SEU) sensitivities are studied in a 0.6-[micro]m SRAM. In some cases, the off-PMOS sensitivity is shown to be similar to the off-NMOS one. This could affect SEU rate calculations. Index Terms--Electric field, NMOS, PMOS, SEU, SRAM, transistor sensitivity.

The aim of this work is to show the contribution of nuclear events occurring with oxygen nuclei in SRAM-oxide such as Si[O.sub.2] and emphasize that they are likely to increase the soft error rate by about several tens of percent. Recoil energies are calculated with a dedicated subroutine, which accounts for elastic and nonelastic reactions in the 5-150-MeV energy range. SEU cross sections are evaluated using the criterion of critical energy deposited in a cubic sensitive volume. Index Terms--Monte Carlo, neutron, nuclear cross sections, oxygen, passivation layer, recoil, sensitive volume, SEU, silicon oxide, SRAM, silicon.

A Monte Carlo approach is used to obtain statistical information on the effect of the spatial distribution of the numerous secondary ions involved in neutron induced soft error rates (SER). The sorting criteria for the occurrence of upset are derived from a simplification of previous work on full-cell three-dimensional (3-D) SRAM device simulation. The time thus saved allows the treatment of a wide variety of track conditions. The shape and extension of the sensitive region is explored and correlated to the secondary ion properties. Details on the variations of the sensitivity with depth into the sensitive region as well as on the geometrical conditions associated with those tracks that cause upsets are given. Index Terms--Atmospheric neutrons, device simulation, ion tracks, recoils, sensitive volume, single event upset (SEU), soft error rate (SER), SRAM.

A new method of neutron soft error rate calculation derived from device simulations and nuclear physics results is presented. The main inputs are only a critical linear energy transfer, a critical charge, and layout dimensions. No classical sensitive volume size is needed because the extension of the sensitive region is described in terms of the variation of the ion efficacy versus its position with respect to the sensitive drain. Index Terms--Detailed analysis of secondary ions, neutron, sensitive volume, single-event upset (SEU), soft error rate, SRAM.

Various single-event upset (SEU) conditions are studied by three-dimensional device simulation with the purpose of going deeply into the understanding of the mechanisms governing the SEU sensitivity for a large variety of tracks. The results give a better view of what regions are sensitive. They clearly point out that some generally accepted notions must be revised as considering the normal incidence case to be the most sensitive or neglecting PMOS contribution. Index Terms--Critical charge, device simulation, sensitive regions, single-event upset (SEU), SEU mechanisms, SRAM sensitivity.

Academic 128 x 128 bit structures are simulated to study soft error cross sections induced by high-energy nucleons (n/p) in SRAM memories. The distributions of secondary ions are obtained by the nuclear high energy transport code and analyzed in terms of energy deposited in the sensitive volume of each memory cell. Multiple-bit upset cross sections are compared to single-event upset cross sections, and trends associated to scaling effects are presented. Index Terms--Critical energy, downscaling, HETC, Monte Carlo, multiple-bits upset, nucleon, sensitive volume, single-event upset (SEU), SRAM.

This paper presents an up-to-date overview of the single-event latchup (SEL) hard failure mode encountered in electronic device applications involving heavy ion environment. This phenomenon is specific to CMOS technology. Single-event latchup is discussed after a short description of the effects induced by the interaction of a heavy ion with silicon. Understanding these effects is necessary to understand the different failures. This paper includes a description of the latchup phenomenon and the different triggering modes, reviews of models and hardening solutions, and finally presents new developments in simulation approaches.

The aim of this work is to validate the results of the Monte Carlo recoil energy determination nuclear physics code used to determine the deposited energy in a silicon volume taking into account the probabilistic approach of the physical phenomenon. A silicon sensor has been used to measure the deposited energy spectrum after an irradiation with a neutron source. The experimental results were then compared with the one obtained by Monte Carlo simulations in the same silicon volume. Experiments and simulations are shown to be in good agreement in the field of interest for soft error rate evaluation that means for deposited energy range leading to memory point upsets in static random access memory. [ABSTRACT FROM AUTHOR]

Examines the modifications of the electronic properties of cleaved GaAs (110) surfaces induced by oxygen adsorption, using contact potential difference measurement. Factors that affect the initial work function and surface photovoltage topographies; Indicators of the density and energy of induced states; Analysis of noticeable surface modification that appears at low exposures.

Single-event upsets (SEUs) in static random access memories (SRAMs) are investigated using three-dimensional (3-D) full cell device simulations for tracks that do not cross the OFF n-channel MOSFET drain. These tracks are representative of the most probable geometrical cases when the ions are generated inside the device by nuclear reactions, and then address one important part of neutron- or protons-induced soft errors. It is found that the duration and magnitude of the ion-induced current pulse strongly depends on the track location. As a result, the flipping of the memory cell is delayed, and the critical charge involved during the upset is no longer constant. A linear relationship between the critical charge and the delay is found and is explained by the contribution of the ON p-channel MOSFET. The increase of the ion current pulse delay and broadening when the track is moved away from the drain is explained on the basis of the diffusion-collection mechanism. Indications on the size of the sensitive regions are derived. Index Terms--Charge collection, device simulation, ion track, neutron induced single-event upset, proton induced SEU, single-event upset (SEU), soft error rate (SER).

Neutron reactions with silicon nuclei can be responsible for much of the soft errors rate (SER) observed, for instance, in high density memories. The nuclear reactions create ionizing particles that then can induce charge collection at sensitive nodes. In many cases, the nuclear reaction produces a shower of ions. Models for the prediction of SER are much more complicated if all the simultaneously created ions must be considered. In this paper, we examine the proportion of events in which a shower of particles is actually involved. Spallation reaction effects for incident neutrons in the 50-2000 MeV energy range are analyzed using a simple spherical structure. Calculations are performed using BRIC (Bruyeres le Chatel Intra-nuclear Cascade), an improved version of HETC (High Energy Transport Code). The results show that the proportion of events actually due to showers is less than 2% of the total number of SER's.

A 3-D entire SRAM cell, based on a 0.35-[micro]m current CMOS technology, is simulated in this work with a DEVICE simulator. The transient current, resulting from an heavy ion strike in the most sensitive region of the cell, is studied as a function of the LET value, the cell layout and the ion penetration depth. A definition of the critical charge is proposed and two new methods are presented to compute this basic amount of charge only using SPICE simulations. Numerical applications are performed with two different generations of submicron CMOS technologies, including the determination of the sensitive thicknesses.