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ABSTRACT: 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.
IEEE Transactions on Electron Devices 09/2011; · 2.32 Impact Factor
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ABSTRACT: 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 raw 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.
IEEE Transactions on Nuclear Science 09/2010; · 1.45 Impact Factor
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ABSTRACT: 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.
Reliability Physics Symposium (IRPS), 2010 IEEE International; 06/2010
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ABSTRACT: 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.
Reliability Physics Symposium (IRPS), 2010 IEEE International; 06/2010
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ABSTRACT: 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.
IEEE Transactions on Nuclear Science 01/2010; · 1.45 Impact Factor
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ABSTRACT: 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.
IEEE Transactions on Nuclear Science 09/2009; · 1.45 Impact Factor
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ABSTRACT: 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.
IEEE Electron Device Letters 03/2009; · 2.85 Impact Factor
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ABSTRACT: 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.
Electron Devices Meeting, 2008. IEDM 2008. IEEE International; 01/2009
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G. Cellere,
S. Gerardin,
M. Bagatin,
A. Paccagnella,
A. Visconti,
M. Bonanomi, S. Beltrami,
P. Roche,
G. Gasiot,
R. Harboe Sorensen,
A. Virtanen,
C. Frost,
P. Fuochi,
C. Andreani,
G. Gorini,
A. Pietropaolo,
S. Platt
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ABSTRACT: 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.
Electron Devices Meeting, 2008. IEDM 2008. IEEE International; 01/2009
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ABSTRACT: 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.
IEEE Transactions on Nuclear Science 01/2009; · 1.45 Impact Factor
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G. Cellere,
A. Paccagnella,
A. Visconti, S. Beltrami,
J. Schwank,
M. Shaneyfelt,
D. Lambert,
P. Paillet,
V. Ferlet-Cavrois,
J. Baggio,
R. Harboe-Sorensen,
E. Blackmore,
A. Virtanen,
P. Fuochi
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ABSTRACT: The production of secondary recoiled particles from interactions between high energy protons and microelectronics devices was investigated. By using NAND Flash memories, we were able to directly obtain analog information on recoil characteristics. While our results qualitatively confirm the role of nuclear reactions, in particular of those with tungsten, a quantitative model based on Monte Carlo and device-level simulations cannot describe the observed results in terms of recoils from proton-W reactions.
IEEE Transactions on Nuclear Science 01/2009; · 1.45 Impact Factor
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ABSTRACT: 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.
IEEE Transactions on Electron Devices 11/2008; · 2.32 Impact Factor
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ABSTRACT: 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.
IEEE Transactions on Nuclear Science 09/2008; · 1.45 Impact Factor
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ABSTRACT: 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.
IEEE Electron Device Letters 09/2008; · 2.85 Impact Factor
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ABSTRACT: 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.
Electron Devices Meeting, 2007. IEDM 2007. IEEE International; 01/2008
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ABSTRACT: Radiation effects have been traditionally studied for niche applications such as the high energy physics or the satellite industry, but modern semiconductor technologies are becoming more and more sensitive to ground-level events such as those generated by atmospheric neutrons. Floating Gate memories are not exception: a single ion crossing a Floating Gate array can severely degrade the information stored in several contiguous memory cells. Further, the ion leaves a permanent damage to the oxide, resulting in degraded retention performances.
Non-Volatile Memory Technology Symposium, 2007. NVMTS '07; 12/2007
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[show abstract]
[hide abstract]
ABSTRACT: 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 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.
Radiation and Its Effects on Components and Systems, 2007. RADECS 2007. 9th European Conference on; 10/2007
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[hide abstract]
ABSTRACT: 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.
IEEE Transactions on Nuclear Science 09/2007; · 1.45 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: 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.
On-Line Testing Symposium, 2007. IOLTS 07. 13th IEEE International; 08/2007
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13th IEEE International On-Line Testing Symposium (IOLTS 2007), 8-11 July 2007, Heraklion, Crete, Greece; 01/2007
