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The feasibility of a 3-D-NAND-Flash-based heavy-ion detector is explored. The possibility of measuring the angle of incidence and the linear energy transfer (LET) of impinging particles by studying the pattern of the threshold voltage shifts along the track of the affected cells is discussed. The results of the experiments with different beams (both directly and indirectly ionizing) are illustrated. A set of Monte Carlo simulations is also presented, to study sensitive volumes on 3-D NAND floating gate cells and explore the possibility of distinguishing the effects generated by ionizing particles with different features, such as LET and angle of incidence.

The effects of total ionizing dose on 3-D flash memories irradiated with gamma rays are investigated. The evolution and shape of threshold voltage distributions are studied versus dose for floating gate cell NAND arrays with vertical-channel architecture. The dependence of total dose effects on the logic level stored in the cells, the underlying mechanisms, and the raw bit errors induced by gamma-rays are discussed. The results are then compared with planar NAND and NOR flash technologies, in terms of threshold voltage shifts and bit error rates, showing improvements over previous generations due to the new cell structure.

The effects of total ionizing dose on 3-D NAND floating gate cells with vertical architecture are analyzed as a function of the cell depth in the pillar. The focus of this work is on TID-induced threshold voltage shifts, but the implications on the raw bit error rates are also discussed. Underlying mechanisms are elucidated, concluding that due to the manufacturing process and the geometry of the pillars, the effects of total dose are larger at the bottom than at the top of the cell array.

A heavy-ion beam monitor based on 3-D NAND flash memories was designed and tested with heavy ions at high energy and low linear energy transfer (LET). The capability of measuring fluence, angle, uniformity, and LET of impinging particles is discussed, together with the advantages over SRAM-based implementations. We propose ad hoc algorithms for the extraction of the beam parameters, based only on user-mode commands. A validation of the system using low-LET ionizing particles impinging at different angles is presented. Experimental results show very good efficiency and accuracy.

The effects of heavy-ion irradiation on 3-D NAND flash memory cells are investigated. Threshold voltage distributions are studied before and after exposure, as a function of the linear energy transfer, fluence, and irradiation angle. Shifts are smaller in 3-D devices than those in planar ones, for the same equivalent bit density. The cell circular shape and the fact that the tunnel oxide and interpoly dielectric blocking layers are perpendicular to the semiconductor substrate make it possible to gain insight into the underlying upset mechanism, which cannot be obtained with planar devices. Evidence that energy deposition in the blocking oxide layer can contribute to charge loss from the floating gate is presented.

The sensitivity of vertical-channel 3-D NAND flash memories to wide-energy spectrum neutrons was investigated. The effects of neutron exposure on a 3-D floating gate (FG) cells were studied in terms of threshold voltage shifts and raw bit error rates. The neutron failure rates obtained in the accelerated tests were extrapolated to field conditions at sea level and aircraft altitudes. The results are compared with previous data on 3-D nand flash devices irradiated with heavy ions, as well as data on planar FG cell technologies.

Identifying novel biomarkers of resilience or vulnerability to stress could provide valuable information for the prevention and treatment of stress-related psychiatric disorders. To investigate the utility of blood microRNAs as biomarkers of resilience or vulnerability to stress, microRNAs were assessed before and after 7days of chronic social defeat in rats. Additionally, microRNA profiles of two important stress-regulatory brain regions, the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA), were assessed. Rats that displayed vulnerability to subsequent chronic stress exhibited reductions in circulating miR-24-2-5p, miR-27a-3p, miR-30e-5p, miR-3590-3p, miR-362-3p, and miR-532-5p levels. In contrast, rats that became resilient to stress displayed reduced levels of miR-139-5p, miR-28-3p, miR-326-3p, and miR-99b-5p compared to controls. In the mPFC, miR-126a-3p and miR-708-5p levels were higher in vulnerability compared to resilient rats. In the BLA, 77 microRNAs were significantly altered by stress but none were significantly different between resilient and vulnerable animals. These results provide proof-of-principle that assessment of circulating microRNAs is useful in identifying individuals who are vulnerable to the effects of future stress or individuals who have become resilient to the effects of stress. Furthermore, these data suggest that microRNAs in the mPFC but not in the BLA are regulators of resilience/vulnerability to stress.

This paper presents a detailed investigation of the impact of cycling time and temperature on the threshold-voltage instability arising from damage recovery during data retention on nanoscale nand Flash. Statistical results from the programmed state show that instabilities result, on average, in a threshold-voltage loss, which increases logarithmically with the time elapsed since the end of cycling. The slope of the logarithmic behavior strongly depends on the electric field during data retention, the cycling dose, and the probability level at which the shift of the array cumulative distribution is monitored. Increasing the cycling time and temperature corresponds, instead, to an equivalent delay of the instant at which the first read operation on the array is performed. The delay is studied for a large variety of cycling and retention conditions, extracting the parameters required for a universal damage-recovery metric for nand.

Microparticles found in the air may be associated with organic matter that contains several compounds, such as Polycyclic Aromatic Hydrocarbons (PAHs) and nitro-PAHs, and may pose a significant risk to human health, possibly leading to DNA mutations and cancers. This study associated genotoxicity assays for evaluating human exposure with the atmospheric air of two urban areas in southern Brazil, that received different atmospheric contributions. Site 1 was under urban-industrial influence and the other was a non-industrial reference, Site 2. Organic extracts from the airborne particulate matter were tested for mutagenicity via the Salmonella /microsome assay and analyzed for PAH composition. Cells samples of people residing in these two cities were evaluated using the comet and micronucleus assay (MN).Concentrations of the individual PAHs ranged from 0.01 ng/m 3 (benzo[a]anthracene) to 5.08 ng/m 3 (benzo[ghi]perylene). As to mutagenicity analysis of airborne, Site 1 presented all the mutagenic responses, which varied from 3.2±1.22 rev/m 3 (TA98 no S9) to 32.6±2.05 rev/m 3 (TA98, S9), while Site 2 ranged from negative to minimal responses. Site 1 presented a high quantity of nitro and amino derivatives of PAHs, and peaked at 56.0±3.68 rev/μg (YG1024 strain). The two groups presented very low DNA damage levels without intergroup difference. Although Site 1 presented high mutagenic responses in the air samples, high PAH levels, healthy people exposed to this environment did not show significative damage in their genetic material. However, the evaluation of different environmental and genetic damage in such population is necessary to monitor possible damages.

In this work, we present clear experimental results pointing to a new microscopic picture for cycling-induced charge trapping/detrapping in Flash memories. In particular, the evidence gathered from experiments designed to investigate the dependence of charge detrapping on cell threshold-voltage reveals that the simple and widely used model based only on carrier exchange between oxide defects and substrate is not enough to explain the main features of the phenomenon. We then propose a new microscopic description of the detrapping phenomenology, including structural relaxation of oxide defects as a limiting step enabling carrier exchange. This new microscopic picture for the oxide defects is, finally, implemented in a statistical model able to reproduce the charge trapping/detrapping dynamics and the consequent threshold-voltage instabilities along the memory array lifetime.

We studied the angular dependence of heavy-ion induced errors and threshold voltage shifts in Flash memories. Combining experiments and Geant4-based simulations, we provide new insight about the sensitive volume in floating gate cells. At high LET, the sensitive volume for cells belonging to the heavy-ion induced secondary peak corresponds to a large part of the floating gate. The sensitive volume for upsets may be larger or smaller, depending on the relative position of the secondary peak with respect to the relevant reference voltage.

Heavy-ion irradiation of NAND flash memories under operating conditions leads to errors with complex, data-dependent signatures. We present upsets due to hits in the floating gate array and in the peripheral circuitry, discussing their peculiarities in terms of pattern dependence and annealing. We also illustrate single event functional interruptions, which lead to errors during erase and program operations. To account for all the phenomena we observe during and after irradiation, we propose an ldquoeffective cross section,rdquo which takes into account the array and peripheral circuitry contributions to the SEU sensitivity, as well as the operating conditions.

Heavy ions typical of the space environment have energies which exceed by orders of magnitude those available at particle accelerators. In this paper we are irradiating state of the art floating gate memories by using both a medium energy (SIRAD) and a high energy (RADEF) facilities. The corruption of stored information decreases when increasing ion energy. The proposed model deals with the broader track found for higher energy ions. Implications for testing procedures and for reliability considerations are discussed.

We irradiated floating gate (FG) memories with nor and nand architecture by using different TID sources, including 2 MeV, 98 MeV, and 105 MeV protons, X-rays, and Upsi-rays. Two classes of phenomena are responsible for charge loss from programmed FGs: the first is charge generation, recombination, and transport in the dielectrics, while the second is the emission of electrons above the oxide band. Charge loss from programmed FGs irradiated with protons of different energy closely tracks results from Upsi-rays, whereas the use of X-rays results in dose enhancement effects.

A 2D 16nm planar NAND cell technology is described with good cell to cell interference and reliability that can be used in a wide variety of applications. This second generation planar cell uses a high-K dielectric stack and a thin poly floating gate to maintain the needed gate coupling ratio and reduce adjacent cell interference. The technology includes select gates with the same planar structure as the cell. This select gate architecture simplifies the manufacturing of this NAND technology.

This paper highlights that cycling-induced threshold-voltage instabilities in nanoscale NAND Flash technologies display a non-negligible dependence on the background pattern of the memory array during idle/bake periods. Experimental results clearly reveal, in fact, that instabilities in a (victim) cell do not depend only on its memory state, but also on the memory state of its first neighboring (aggressor) cells. The magnitude of this new cell-to-cell interference effect, moreover, appears to depend on the memory state of the victim cell, decreasing with the increase of its threshold-voltage level. From all of the gathered experimental evidence a physical picture explaining the phenomenon is provided, which is, finally, confirmed with the help of numerical simulations.

We are showing for the first time the charge loss due to heavy ion irradiation on Flash memory arrays organized following the NAND architecture. Results complement those previously found for devices featuring a NOR architecture: large charge loss can be expected after the hit of a single ion on a single memory cell. The resulting threshold voltage shift DeltaVTH grows with ion LET and with applied electric field across the tunnel oxide (that is, with the programming conditions) and cannot be explained by simple generation-recombination-transport models. Further, in Floating Gates hit by a single ion a percolation path develops across the tunnel oxide, able to slowly discharge the Floating Gate

This work investigates cycling-induced threshold- voltage instabilities in nanoscale NAND Flash cells as a function of the array background pattern. Instabilities are mainly the result of charge detrapping from the cell tunnel oxide during post-cycling idle/bake periods and represent one of the major reliability issues for multi-level devices. Results reveal, first of all, that instabilities in a (victim) cell do not depend only on its memory state, but also on the memory state of its first neighboring (aggressor) cells. This new interference effect is shown to decrease in magnitude for higher threshold-voltage levels of the victim cell and to come mainly from an interaction with aggressor cells in the bit-line direction. From this evidence, a physical picture explaining the phenomenon and its main dependences is provided.

We analyzed the sensitivity of 45-nm phase change memory cells to neutrons and heavy ions. No errors have been recorded with neutrons with a terrestrial-like spectrum. With heavy ions, bit upsets have been observed at high incidence angle and high linear energy transfer, conditions possible only in space. Physical mechanisms have been investigated, concluding that the thermal spike model may explain the observed results.

We present the first evidence of single event upsets in 45-nm phase change memories caused by high linear energy transfer (LET) heavy ions at tilted angles along the word line. An- gular and LET dependences are presented, together with a discus- sion of the possible underlying mechanisms. The occurrence of a thermal spike, due to the ion passage, close to the heater/storage element interface is identified as the most plausible explanation. The upset cross section is compared with that of NOR Flash and finally the impact of scaling on the sensitivity of future memories is analyzed.

We present a semi-analytical model for the description of charge trapping and detrapping phenomena occurring during cycling and idle periods in NAND Flash memories. The model is based on a statistical distribution of detrapping time constants that is affected by the composition of cycles and idle periods and accounts for charge discreteness, statistical charge capture and emission and statistical distribution of the threshold-voltage shift due to single detrapping events. The model can reproduce the experimental data under different conditions and allows to develop and monitor accelerated schemes able to mimic realistic on-field usage of the memory device.

The impact of program/erase (P/E) cycling on the random telegraph noise (RTN) threshold voltage instability of NOR and NAND flash memories is studied in detail. RTN is shown to introduce exponential tails in the distribution of the threshold voltage variation between two subsequent read operations on the cells. Tail height is shown to increase as a function of the stress levels, with a larger relative increase for the NAND case. The slope of the distribution instead remains nearly independent of the number of applied P/E cycles. This reveals that trap generation takes place according to the native trap distribution over the active area and means that the tail slope is a basic RTN parameter, depending on the cell process details for a fixed technology. These results are important for the design of the threshold voltage levels in multilevel nor and NAND technologies.

This work is focused on the accelerated testing of Flash memory reliability, taking our 45 nm NOR technology as a case study to highlight some major issues that may affect the investigation of modern nanoscale devices. In particular, results will be shown on cycling-induced threshold-voltage instabilities coming from charge trapping/detrapping in the cell tunnel oxide during post-cycling data retention or bake experiments, whose characterization relies on the possibility to reduce the experimental time by an increase of the test temperature according to an Arrhenius law via an activation energy EA. These accelerated characterization schemes come from a detailed physical understanding and modeling of the damage creation/recovery dynamics and rely on the careful evaluation of EA. As shown in the case of the investigated NOR technology, this often does not represent a trivial task, due to the large number of spurious effects affecting the threshold voltage of nanoscale memory cells.

This paper shows that the reliability characterization of nanoscale Flash memories requires an accurate control of the adopted experimental tests, preventing spurious issues to emerge and alter the basic conclusions on the investigated reliability constraints. To this aim, the paper reports a case study on a 45-nm NOR technology, where the experimental investigation of the activation energy for damage recovery during post-cycling bakes and of distributed-cycling effects is substantially affected by parasitic threshold-voltage (VT) drifts, activated by the repeated acquisition of the whole array VT map during the experiment. Only when this spurious effect is taken into account, the typical 1.1-eV activation energy for damage recovery and the effectiveness of the conventional distributed-cycling schemes are correctly demonstrated on the investigated technology.

This paper investigates the validity of distributed-cycling schemes on scaled Flash memory technologies. These schemes rely on the possibility to emulate on-field device operation by increasing the cycling temperature according to an Arrhenius law, but the assessment of the activation energy that has to be used on scaled technologies requires a careful control of the experimental tests, preventing spurious second-order effects to emerge. In particular, long gate-stresses required to gather the array threshold voltage (V T ) map are shown to give rise to parasitic V T -drifts, which add to the V T -loss coming from damage recovery during post-cycling bake. When the superposition of the two phenomena is taken into account, the effectiveness of the conventional qualification schemes relying on a 1.1 eV activation energy is fully confirmed at the 45 nm NOR node.

We investigate atmospheric neutron effects on floating-gate cells in NAND Flash memory devices. Charge loss is shown to occur, particularly at the highest program levels, causing raw bit errors in multilevel cell NAND, but to an extent that does not challenge current mandatory error correction specifications. We discuss the physical mechanisms and analyze scaling trends, which show a rapid increase in sensitivity for decreasing feature size.

We investigate the effects of X-ray exposure in 41-nm single level NAND Flash memories at small doses, comparable to those used in printed circuit board inspections. We analyze both short-term effects, such as cell threshold voltage shifts during irradiation, and retention and endurance performance of devices exposed to x rays. For doses smaller than 1krad(Si), no effect is observed. At higher doses, charge loss is observed after the exposure and a modest read margin degradation is seen during hightemperature retention tests.

Flash memories operating in space are subject at the same time to the progressive accumulation of total ionizing dose and to intrinsic aging phenomena. In this work we investigate latent Total Ionizing Dose (TID) effects in 41-nm NAND single level cells that do not display neither floating gate errors nor any apparent kind of degradation after exposure. Retention of irradiated cells is analyzed at room and high temperature as a function of total dose previously received. We found that FG cell retention at room temperature is practically unchanged after a total dose up to 30 krad(Si). On the contrary, TID exposure slightly worsens the cell retention time during high-temperature tests. We attribute this behavior to the removal of compensating electrons from the tunnel oxide at high temperature.

Urban areas are both major sources and major targets of air pollution. The atmospheric environment receives diverse chemical substances, including genotoxic agents that may affect human health. The purpose of this study was to evaluate and compare the atmospheric quality in two urban areas in Rio Grande do Sul State (Brazil), under the influence of greater (Site 1) or lesser (Site 2) anthropogenic sources. Polycyclic aromatic hydrocarbons (PAHs) of environmental interest were quantified and the Salmonella /microsome assay was used for the measurement of mutagenicity. Organic compounds extracted from the airborne particulate matter were analyzed by high-performance liquid chromatography (HPLC) to detect PAHs of interest (known or possible carcinogens). The organic extracts were also tested for mutagenic and cytotoxic activity in the Salmonella /microsome assay with strains TA98, TA100, YG1021 and YG1024, with or without S9 activation. At Site 1, benzo[ ghi ]perylene (BghiP) and indeno[1,2,3- cd ]pyrene (IP) were found at higher concentrations and mutagenicity (revertants per μg extract) varied from 1.0 ± 0.25 (TA98, no S9) to 5.2 ± 0.45 (TA98, S9). At Site 2, BghiP and IP were present in larger amounts and the mutagenic responses ranged from 0.6 to 3.7 revertants per μg (both in TA98, S9). The occurrence of BghiP and IP may be related to vehicular emissions. These and the other PAHs studied, as well as the nitro compounds, may contribute to the mutagenicity found in these airborne particles.

This paper presents a detailed experimental investigation of the cycling-induced threshold voltage instability of deca-nanometer NAND Flash arrays, focusing on its dependence on cycling time and temperature. When the array is brought to a programmed state after cycling, instability mainly shows up as a negative shift of its threshold voltage cumulative distribution, increasing with time and resulting from partial recovery of cell damage created in the previous cycling period. The threshold voltage loss displays a strong dependence not only on the tunnel oxide electric field during retention, but also on the cycling conditions. In particular, performing cycling over a longer time interval or at higher temperatures delays the threshold voltage transients on the logarithmic time axis. The delay factor is studied as a function of the cycling duration and temperature on 60 and 41 nm technologies, extracting the parameter values required for a universal damage-recovery metric for NAND.

We investigate atmospheric neutron effects on floating gate cells in MLC NAND Flash memories. Loss of information is shown to occur especially at the highest program levels, but to an extent that does not challenge current error correction capabilities. We discuss the physical mechanisms and analyze scaling trends, which show a rapid increase in sensitivity for decreasing feature size. A large spread in the cross section is visible from vendor to vendor for comparable feature size. © 2010 IEEE.

We discuss the room temperature annealing of Floating Gate errors in Flash memories with NAND and NOR architecture after heavy-ion irradiation. We present the evolution of rough bit errors as a function of time after the exposure, examining the annealing dependence on the particle LET, cell feature size, and for Multi Level Cells, on the program level. The results are explained based on the statistical properties of the cell threshold voltage distributions before and after heavy-ion strikes.

We discuss new experimental results on the post-radiation annealing of Floating Gate errors in Flash memories with both NAND and NOR architecture. We investigate the dependence of annealing on the program level, linking the reduction in the number of Floating Gate errors to the evolution of the threshold voltage of each single cell. To understand the underlying physics we also discuss how temperature affects the number of Floating Gate errors.

Atmospheric neutrons can interact with the matter inside a microelectronic chip and generate ionizing particles, which in turn can change the state of one or more memory bits [soft error (SE)]. In this letter, we show that SEs are possible in Flash memories, although with extremely low probabilities. While this problem will increase for future technologies, we do not expect SEs to be the reliability limiting factor for further floating gate scaling.

NAND Flash memories are the leader among high capacity non-volatile memory technologies and are becoming attractive also for radiation harsh environments, such as space. For these applications, a careful assessment of their sensitivity to radiation is needed. In this contribution, we analyze TID effects on the many different building blocks of NAND Flash memories, including the charge pumps, row-decoder, and floating gate array. Since each of these elements have dedicated circuital and technological characteristics, we identify and study the characteristic failure mode for each part.

We present a thorough investigation of the random telegraph noise scaling trend for both NAND and NOR floating-gate flash memories, including experimental and physics-based modeling results. The statistical distribution of the random telegraph noise amplitude is computed using conventional 3D TCAD simulations, establishing a direct connection with cell parameters. The analysis results in a simple formula for the random telegraph noise amplitude standard deviation as a function of cell width, length, substrate doping, tunnel oxide thickness and drain bias. All the simulation results are in good agreement with experimental data and are of utmost importance to understand the random telegraph noise instability and to control it in the development of next generation flash technologies.

Atmospheric neutrons are a known source of Soft Errors (SE), in static and dynamic CMOS memories. This paper shows for the first time that atmospheric neutrons are able to induce SE in Flash memories as well. Detailed experimental results provide an explanation linking the Floating Gate (FG) cell SE rate to the physics of the neutron-matter interaction. The neutron sensitivity is expected to increase with the number of bits per cell and the reduction of the feature size, but the SE issue is within the limit of current ECC capabilities and will remain so in the foreseeable future.

This paper investigates the ultimate accuracy of the NAND flash program algorithm that is determined by the statistical injection of electrons from the substrate to the floating gate. The granular nature of the electron flow during a constant-current Fowler-Nordheim program operation is shown to spread the programmed threshold-voltage distribution of the array cells. The electron injection statistics displays a Poissonian behavior for low amounts of transferred charge, but a sub-Poissonian character becomes clearly evident when large charge packets are stored. This effect is expected from the reduction of the tunnel oxide field that follows each electron storage event into the floating gate, establishing a correlation among such events. Finally, the impact of the electron injection statistical spread on the accuracy of the NAND flash program algorithm is investigated as a function of the technology node feature size, drawing projections on future NAND technologies.

We present for the first time the direct evidence of an injection statistical spread in the number of electrons placed into the floating-gate of deeply-scaled NAND Flash memories during constant-current Fowler-Nordheim programming. The spread directly affects the precision of the programmed levels and sets the ultimate accuracy of the NAND programming algorithm. Experimental results on technology nodes ranging from 90 nm to 60 nm reveal that the injection statistical spread increases as cell dimensions are reduced and this introduces a new constraint for future NAND memories design.

We tested a commercial 1 Gbit 90 nm NAND memory under exposure to a constant flux of heavy ions, aiming to study its behaviour in the space environment. We identified and classified different types of errors under various operating conditions. We observed single bit upsets both in the floating gate array and in the page buffer, alongside with functional interruptions during program and, to a lesser extent, erase operations. Our results provide some insight on possible issues which may arise also at sea-level with future (and more sensitive) flash generations.

Complement was proposed to play an important role in the onset of Multiple Sclerosis (MS) lesions by inducing physical damage to myelin-producing cells. Every somatic cell is however endowed with a repertoire of membrane-bound molecules which normally down-regulate the complement activation cascade (Regulators of Complement Activation, RCA) and therefore protect cells from complement-dependent lysis. We show here that antibodies against two complement regulatory molecules expressed in the membrane of human cells (CD46 and CD59) are present in sera from relapsing-remitting MS patients in the acute phase, that they are directed against the active site of the RCA molecules and that they inactivate their regulatory function, thus providing a mechanism by which cells of the nervous system might be damaged in a complement-dependent fashion during the acute MS phase. Moreover, we found that most of these sera also contain antibodies reacting with an epitope of the transmembrane glycoprotein of HIV which is conserved in most retroviruses; this may support the hypothesis that self-reacting antibodies might have arisen in these patients as an immune response after retroviral infection or expression of endogenous retroviral proteins.