Abstract-Recently, the occurrence of multiple events in static tests has been investigated by checking the statistical distribution of the difference between the addresses of the words containing bitflips. That method has been successfully applied to Field Programmable Gate Arrays (FPGAs) and the original authors indicate that it is also valid for SRAMs. This paper presents a modified methodology that is based on checking the XORed addresses with bitflips, rather than on the difference. Irradiation tests on CMOS 130 & 90 nm SRAMs with 14-MeV neutrons have been performed to validate this methodology. Results in high-altitude environments are also presented and cross-checked with theoretical predictions. In addition, this methodology has also been used to detect modifications in the organization of said memories. Theoretical predictions have been validated with actual data provided by the manufacturer.

Abstract-Radiation tests with 15-MeV neutrons were performed in a COTS SRAM including a new memory cell design combining SRAM cells and DRAM capacitors to determine if, as claimed, it is soft-error free and to estimate upper bounds for the cross-section. These tests led to cross-section values two orders of magnitude below those of typical CMOS SRAMs in the same technology node. MUSCA SEP3 simulations complement these results predicting that only high-energy neutrons (> 30 MeV) can provoke bit flips in the studied SRAMs. MUSCA SEP3 is also used to investigate the sensitivity of the studied SRAM to radioactive contamination and to compare it with the one of standard CMOS SRAMs. Results are useful to make predictions about the operation of this memory in environments such as avionics.

After having carried out radiation experiments on memories, the detected bitflips must be classified into single bit upsets and multiple events to calculate the cross sections of different phenomena. There are some accepted procedures to determine if two bitflips are related. However, if there are enough bitflips, it is possible that unrelated pairs of errors appear in nearby cells and they are erroneously taken as a multiple event. In this paper, radiation experiments are studied as a special case of the urn-and-balls problem in probability theory to estimate how the measured multiple-event cross sections must be corrected to remove the overestimation due to the false events.

Abstract-This paper presents the characterization of the sensitivity to 14-MeV neutrons of a Commercial Off-The-Shelf (COTS) 90-nm Static Random Access Memories (SRAMs) manufactured by Cypress Semiconductor, when biased at ultra low voltage. Firstly, experiments exposing this memory at 14-MeV neutrons, when powering it up at bias voltages ranging from 0.5V to 3.3V, are presented and discussed. These results are in good concordance with theoretical predictions issued by the modeling tool MUSCA-SEP 3 (MUlti-SCAles Single Event Phenomena Predictive Platform). Then, this tool has been used to obtain Soft Error Rate (SER) predictions at different altitudes above the Earth's surface of this device vs. its bias voltage. Finally, the effect of contamination by α particles has also been estimated at said range of bias voltages.

Abstract-This paper presents a SEU sensitivity characterization at ultra-low bias voltage of three generations of COTS SRAMs manufactured in 130 nm, 90 nm and 65 nm CMOS processes. For this purpose, radiation tests with 14.2 MeV neutrons were performed for SRAM power supplies ranging from 0.5 V to 3.15 V. The experimental results yielded clear evidences of the SEU sensitivity increase at very low bias voltages. These results have been cross-checked with predictions issued from the modeling tool MUlti-SCAles Single Event Phenomena Predictive Platform (MUSCA-SEP 3 ). Large-scale SELs and SEFIs, observed in the 90-nm and 130-nm SRAMs respectively, are also presented and discussed.

Abstract-New generation electronic devices have become more and more sensitive to the effects of the natural radiation coming from the surrounding environment. These radiation sources are cosmic rays and radioactive impurities, able to corrupt the content of memory cells or to induce transient pulses in combinational logic. The growing sensitivity seems to be related to two main factors: the lower and lower charge needed to define the logic levels in advanced devices and the increasing number of basic components inside the modern integrated circuits. In this paper, are described state-of-art techniques to mitigate these effects as well as typical tests to verify the radiation-tolerance of the devices and/or systems.

International audienceThis paper addresses a well-known problem that occurs when memories are exposed to radiation: the determination if a bit flip is isolated or if it belongs to a multiple event. As it is unusual to know the physical layout of the memory, this paper proposes to evaluate the statistical properties of the sets of corrupted addresses and to compare the results with a mathematical prediction model where all of the events are single bit upsets. A set of rules easy to implement in common programming languages can be iteratively applied if anomalies are observed, thus yielding a classification of errors quite closer to reality (more than 80% accuracy in our experiments)

In radiation tests on SRAMs or FPGAs, two or more independent bitflips can be misled with a multiple event if they accidentally occur in neighbor cells. In the past, different tests such as the "birthday statistics" have been proposed to estimate the accuracy of the experimental results. In this paper, simple formulae are proposed to determine the expected number of false 2-bit and 3-bit MCUs from the number of bitflips, memory size and the method used to search multiple events. These expressions are validated using Monte Carlo simulations and experimental data. Also, a technique is proposed to refine experimental data and thus partially removing possible false events. Finally, it is demonstrated that there is a physical limit to determine the cross section of memories with arbitrary accuracy from a single experiment.