Retention Degradation Research Articles

Insight into Effects of Oxygen Reservoir Layer and Operation Schemes on Data Retention of HfO2-Based RRAM

As a promising new generation of nonvolatile memory, HfO2-based resistive random-access memory (RRAM) has attracted extensive research. However, the problem of data retention has prevented its industrial production as embedded memory. In this paper, from the microscopic understanding, a Monte Carlo simulator is developed to investigate the effects of an oxygen reservoir layer (ORL) on the resistance instability of HfO2-based RRAM. The evolution of conductive filaments (CF) during the retention degradation is visualized by our simulation considering the physical mechanisms of oxygen ions absorbed and released by the ORL. The simulation results are further validated with experiments to provide the prediction of retention performance of RRAMs with different ORLs and operation schemes.

Design Principles of Dielectric Layers for High Density Flash Memories

High density flash memory is based on layered dielectric including charge trapping layers [1]. Device scaling can be facilitated by decreasing equivalent electrical thickness of the layered dielectric, which also induces degradation of charge retention. Moreover, the thickness combination of each dielectrics need to be optimized to give minimum charge loss at zero applied voltage (power-off condition). The optimal thickness combination can be experimentally found by characterizing bias dependent charge loss, at which combination, thickness scaling limitation for a given layered dielectric can be established. By applying higher dielectric constant materials, the equivalent electrical thickness of the layered dielectric can be reduced; where additional materials engineering is necessary. In this work, we have applied various compositional alloys of HfO2 and AlO2, and their spatial grading. As a result, it is shown that high post-deposition process temperature critically induces charge retention degradation, and the physical reasoning of compositional and spatial grading optimization is obtained for minimum charge losses. In addition, optimal thickness combination for minimum charge loss at zero bias is formulated supported by experimental evidence. Moreover, high energy edge of trap states are extracted from charge loss characteristics, which are compared for various dielectric materials and bias conditions. Keywords: dielectric; charge trap; flash memory. Acknowledgements This work was supported by NRF grant (NRF-2017R1D1A1B03029764) funded by Korean Government. Reference S. Choi, S. J. Baik, J.-T. Moon, Technical Digest of International Electron Device Meeting 2008, 2008, 925-928. Figure 1

Computational Exploration of the Catalytic Degradation of Sarin and Its Simulants by a Titanium Metal–Organic Framework

The catalytic degradation of chemical warfare agents (CWAs) into nontoxic products by metal organic frameworks (MOFs) has been exclusively focused on Zr-based materials so far, although Ti-MOFs might be also of interest owing to the well-known capacity of Ti compounds to efficiently hydrolyze CWAs. Here, we report for the first time a computational exploration of several possible hydrolysis mechanisms on the activated Ti site of a recently discovered highly stable Ti-MOF, MIP-177(Ti), in the presence/absence of water, considering sarin and its simulants dimethyl methylphosphonate and diisopropyl phosphorofluoridate. Density functional theory calculations were performed at the periodic level to accurately assess the main states of the degradation reaction (reactants, transition states, and products) and the associated activation energy barriers for each degradation reaction that are further compared to the corresponding data previously reported for Zr-MOFs. MIP-177(Ti) was demonstrated to be a promising candidate for an efficient degradation of sarin and retention of the resulting products with a level of performance as attractive as that of the best Zr-MOFs reported so far. Furthermore, the simulations performed on the two simulants emphasized that diisopropyl phosphorofluoridate better mimics sarin in terms of the transition states and products obtained during the reaction as well as of the activation energy required to achieve their degradation.

Peroxidase as indicator enzyme of blanching in bottle gourd ( Lagenaria siceraria ): Changes in enzyme activity, color, and morphological properties during blanching

This study investigated the effect of ohmic and conventional blanching on different characteristics of bottle gourd. The varying temperature–time combinations (60–90°C for 1–5 min) were used and optimum temperature–time of blanching was selected according to peroxidase activity and color retention. Residual peroxidase activity reached a level of no detection at 80°C for 4 min in ohmic blanching and 90°C for 5 min in conventional blanching. Ohmic blanching (80°C—4 min) was more effective than conventional blanching (90°C—5 min) at lesser temperature–time combinations. The temperature dependence of enzyme inactivation followed first-order reaction with R2 ranging from 0.955 to 0.997 in all temperature ranges. Increase in blanching temperature led to increase in rate constant, k from 0.26 to 2.6 at 60 to 90○C in conventional blanching and 0.30–1.6 at 60 to 80○C, respectively, in ohmic blanching. Color of blanched samples was well retained in both conventional and ohmic blanched samples as compared to control sample. Hue angle (h○) and (−a*) values of blanched samples increased with increasing temperature and time of blanching. Minimum browning index was observed in ohmically blanched (BO) samples. Microstructural and textural study of bottle gourd cubes blanched under optimized conditions (80°C—4 min; 90°C—5 min) were studied. Ohmic blanching was found more pronounced in faster degradation of residual enzyme activity and retention of color. Laser diffraction analysis of BO samples of bottle gourd showed highest decrease in particle size. Losses in functional properties were more pronounced in conventional blanched samples. Practical applications Consumer demand for bottle gourd juice (BGJ) owing to its high nutritional value and pharmacological benefits has led emphasis on improving its quality and market value. However, due to high enzymatic activity BGJ turn brown that appears to be unacceptable and leads to loss of market value. Peroxidases being high heat-resistant enzymes can act as potential trace markers for complete enzyme inactivation. Moreover, retention of color without much degradation to nutritional quality need to be assessed for increasing benefits and maximum returns.

Improvement of High-Rate Discharging Performance of LiFePO4 Cathodes By Forming Micrometer-Sized through-Holed Electrode Structures with a Pico-Second Pulsed Laser

Holing of lithium iron phosphate (LiFePO4, LFP) cathodes with a pico-second pulsed laser, whose the average diameter and opening rate were 20-30 mm and 1-2%, respectively, could retain the high-rate discharge performance even in the LFP cathodes having the thickness of LFP layer over 40 mm on an aluminum current collector. The conventional thick and flat LFP cathode electrodes exhibited the degradation of discharge retention at the high-rate discharge because of the low utilization of LFP materials in the case of the thick cathode layer. On the other hand, in through-holed and non-through-holed LFP cathodes, Li+ ions can do more efficient insertion/deinsertion to/from the LFP materials through the holes formed in the LFP layer, resulting in retaining the high-rate charge-discharge performance even in thick LFP cathodes. The electrochemical impedance spectroscopy analysis confirmed that the formation of through-holes in the thick LFP layer is significantly effective to improve the high-rate discharging performance as a result of the decreased charge-transfer resistance of the LFP discharge process. The decrease in the charge-transfer resistance was brought from the increase in the area for the LFP discharge process based on the fact that the sidewalls of the holes are also available for the process. Fig. １ Schematic description of the cell arrangement of the cells used. (A) Non-holed, (B) through-holed and (C) non-through-holed LFP/LFP cathodes.Two Li metal were used as anodes. Figure 1

Protein Quality Control in the Endoplasmic Reticulum.

The site of protein folding and maturation for the majority of proteins that are secreted, localized to the plasma membrane or targeted to endomembrane compartments is the endoplasmic reticulum (ER). It is essential that proteins targeted to the ER are properly folded in order to carry out their function, as well as maintain protein homeostasis, as accumulation of misfolded proteins could lead to the formation of cytotoxic aggregates. Because protein folding is an error-prone process, the ER contains protein quality control networks that act to optimize proper folding and trafficking of client proteins. If a protein is unable to reach its native state, it is targeted for ER retention and subsequent degradation. The protein quality control networks of the ER that oversee this evaluation or interrogation process that decides the fate of maturing nascent chains is comprised of three general types of families: the classical chaperones, the carbohydrate-dependent system, and the thiol-dependent system. The cooperative action of these families promotes protein quality control and protein homeostasis in the ER. This review will describe the families of the ER protein quality control network and discuss the functions of individual members.

Folding Status Is Determinant over Traffic-Competence in Defining CFTR Interactors in the Endoplasmic Reticulum.

The most common cystic fibrosis-causing mutation (F508del, present in ~85% of CF patients) leads to CFTR misfolding, which is recognized by the endoplasmic reticulum (ER) quality control (ERQC), resulting in ER retention and early degradation. It is known that CFTR exit from the ER is mediated by specific retention/sorting signals that include four arginine-framed tripeptide (AFT) retention motifs and a diacidic (DAD) exit code that controls the interaction with the COPII machinery. Here, we aim at obtaining a global view of the protein interactors that regulate CFTR exit from the ER. We used mass spectrometry-based interaction proteomics and bioinformatics analyses to identify and characterize proteins interacting with selected CFTR peptide motifs or full-length CFTR variants retained or bypassing these ERQC checkpoints. We conclude that these ERQC trafficking checkpoints rely on fundamental players in the secretory pathway, detecting key components of the protein folding machinery associated with the AFT recognition and of the trafficking machinery recognizing the diacidic code. Furthermore, a greater similarity in terms of interacting proteins is observed for variants sharing the same folding defect over those reaching the same cellular location, evidencing that folding status is dominant over ER escape in shaping the CFTR interactome.

A Temperature-Aware Reliability Enhancement Strategy for 3-D Charge-Trap Flash Memory

Compared to the conventional planar flash memory, advanced 3-D flash memory adopts charge-trap technology that can significantly enhance cell density and storage capacity. Despite these advantages, 3-D charge-trap flash memory brings several new challenges. First, charge-trap flash is sensitive to temperature. Recent studies demonstrate that, the high temperature will incur both charge loss and retention degradation. This issue does not happen in 2-D flash memory which adopts floating gate technology. Second, current 3-D charge-trap flash integrates the extra large capacity physical block, and each block contains over 1024 physical pages. The large-capacity block infrastructure will cause extra garbage collection overhead, which makes the thermal issue more complicated. This paper presents TempCure , a temperature-aware reliability enhancement strategy for 3-D charge-trap flash memory. TempCure is a novel hardware and file system interface that can transparently allocate physical space based on the temperature status. TempCure adopts two reliability enhancement strategies, temperature mining and block allotment , to prevent the generation of hotspots and enhance the data integrity of 3-D flash memory. We conduct a set of experiments using standard benchmarks. Experimental results show that TempCure can effectively reduce the peak temperature and block erase counts with negligible timing overhead in comparison with representative schemes.

Improvement of High-Rate Discharging Performance of LiFePO4 Cathodes by Forming Micrometer-Sized through-Holed Electrode Structures with a Pico-Second Pulsed Laser

Holing of lithium iron phosphate (LiFePO4, LFP) cathodes with a pico-second pulsed laser, in which the average hole diameter and hole opening rate were 20-30 mm and 1-2%, respectively, enabled to retain the high-rate discharging performance even in the LFP cathodes composed of the having the LFP layer with the thickness of over 40 mm on an aluminum current collector. The conventional and flat LFP cathode exhibited the degradation of discharge retention at the high-rate discharge because of the low utilization of LFP materials in the case of the thick cathode layer. On the other hand, in the case of “through-holed” and “non-through-holed” LFP cathodes, there can be a more efficient insertion/de-insertion of Li+ ions to/from the LFP materials through the holes formed in the LFP layer, resulting in retaining the high-rate charging/discharging performance even in thick LFP cathodes. The electrochemical impedance spectroscopy analysis confirmed that the formation of through-holes in the thick LFP layer is significantly effective to improve the high-rate discharging performance as a result of the decreased charge-transfer resistance of the LFP discharge process. The decrease in the charge-transfer resistance results from the increase in the area available in the LFP discharge process because the sidewalls of the holes can also take part in the Li+ ion transfer during the discharge process. Figure 1

Mechanical and degradation properties of small-diameter vascular grafts in an in vitro biomimetic environment.

Small-diameter vascular grafts may fail after implantation due to various reasons from mechanical and biological aspects. In order to evaluate the mechanical durability of small-diameter vascular grafts after implantation, an artificial vascular biomimetic environment that can simulate body temperature, the liquid environment outside the vessel, and continuous blood flow and pulsatile pressure was constructed. This device can be used as a "pre-test" prior to animal experiments to explore the changes of mechanical and degradation properties in the long-term in vivo environment. At the same time, braided tube-reinforced silk fibroin/poly (l-lactic acid-co-ε-caprolactone) small-diameter vascular grafts were fabricated and tested under the biomimetic environment. Mechanical changes, including tensile properties, suture retention strength, compliance, and degradation behavior of the braided tube-reinforced poly (l-lactic acid-co-ε-caprolactone)/silk fibroin small-diameter vascular grafts were explored over various periods of time in the biomimetic environment. The results shown that under a period of testing in the in vitro biomimetic environment, the comprehensive mechanical properties (including tensile properties, suture retention strength, estimated-bursting pressure, and compliance) of small-diameter vascular grafts exhibited varying degrees of changes but that there was no obvious degradation behavior in the short term.

Endurance and Retention Degradation of Intermediate Levels in Filamentary Analog RRAM

The understanding of the retention and endurance degradation behavior of different levels of filamentary analog RRAM is critical for the development of the neuromorphic computing. This paper investigates the conductance distribution of different levels during retention and endurance tests. The low conductance states and high conductance states change from the normal distribution at the beginning to asymmetric skewed distribution with baking time increasing. But intermediate states remain the normal distribution. A model is proposed to predict the conductance evolution of different levels. It is also found that endurance lifetime depends on the ratio and position of endurance window. The longer endurance lifetime is attributed to switching in a smaller high-C window. Physical mechanism of endurance degradation is discussed.

Creep effects on crack initiation and propagation in reinforced concrete walls

The present paper presents an analysis of creep cracking on base-constrained reinforced concrete walls. Crack initiation and propagation in reinforced concrete walls due to creep are simulated using an in-house finite element method developed by the authors. The original model was extended and modified to account for creep strain in the numerical modelling. Crack widths and pattern, and degree of restraint are analysed and compared without creep. Concrete is modelled as nonlinear material, and smeared crack approach, tension stiffening, shear retention and stress degradation of concrete are included in the model. It was found that creep influences the time of first cracking in reinforced concrete walls restrained at the base; creep causes to delay crack initiation and propagation. It was also found that the cracks in the base-restrained wall were found to be the most numerous in the base level and they decrease with distance above the base.

Effects of compost characteristics on nutrient retention and simultaneous pollutant immobilization and degradation during co-composting process

This study was conducted to examine the effects of controlled addition of liquid (LM) to solid (SM) manure compost using a volume-model technique on the co-composting of SM and LM, and further to investigate the major effects of bulking material sizes and LM types on the co-composting process and final compost characteristics. Results indicated that this volume-model technique played a critical role in reducing leachate generation and improving the overall efficiency of the co-composting process. Specifically, the developed model enhanced the evaporation rates of windrows during the co-composting process. For improved final compost properties, small bulking materials and swine-effluent-based LM were found to be more efficient for organic matter degradation, LM consumption, hazardous metals immobilization, and essential nutrients retention than large bulking materials and biogas-based LM. Thus, process parameter optimizations represent major research options for successful co-composting applications for the future.

A splice variant of human Bmal1 acts as a negative regulator of the molecular circadian clock

Bmal1 is one of the key molecules that controls the mammalian molecular clock. In humans, two isoforms of Bmal1 are generated by alternative RNA splicing. Unlike the extensively studied hBmal1b, the canonical form of Bmal1 in most species, the expression and/or function of another human-specific isoform, hBmal1a, are poorly understood. Due to the lack of the N-terminal nuclear localization signal (NLS), hBMAL1a does not enter the nucleus as hBMAL1b does. However, despite the lack of the NLS, hBMAL1a still dimerizes with either hCLOCK or hBMAL1b and thereby promotes cytoplasmic retention or protein degradation, respectively. Consequently, hBMAL1a interferes with hCLOCK:hBMAL1b-induced transcriptional activation and the circadian oscillation of Period2. Moreover, when the expression of endogenous hBmal1a is aborted by CRISPR/Cas9-mediated knockout, the rhythmic expression of hPer2 and hBmal1b is restored in cultured HeLa cells. Together, these results suggest a role for hBMAL1a as a negative regulator of the mammalian molecular clock.

Improvement of high-rate discharging performance of LiFePO4 cathodes by forming micrometer-sized through-holed electrode structures with a pico-second pulsed laser

Holing of lithium iron phosphate (LiFePO4, LFP) cathodes with a pico-second pulsed laser, in which the average hole diameter and hole opening rate were 20–30 μm and 1–2%, respectively, enabled to retain the high-rate discharging performance even in the LFP cathodes composed of the having the LFP layer with the thickness of over 40 μm on an aluminum current collector. The conventional and flat LFP cathode exhibited the degradation of discharge retention at the high-rate discharge because of the low utilization of LFP materials in the case of the thick cathode layer. On the other hand, in the case of “through-holed” and “non-through-holed” LFP cathodes, there can be a more efficient insertion/de-insertion of Li+ ions to/from the LFP materials through the holes formed in the LFP layer, resulting in retaining the high-rate charging/discharging performance even in thick LFP cathodes. The electrochemical impedance spectroscopy analysis confirmed that the formation of through-holes in the thick LFP layer is significantly effective to improve the high-rate discharging performance as a result of the decreased charge-transfer resistance of the LFP discharge process. The decrease in the charge-transfer resistance results from the increase in the area available in the LFP discharge process because the sidewalls of the holes can also take part in the Li+ ion transfer during the discharge process.

Prolonged co-treatment with HGF sustains epithelial integrity and improves pharmacological rescue of Phe508del-CFTR

Cystic fibrosis (CF), the most common inherited disease in Caucasians, is caused by mutations in the CFTR chloride channel, the most frequent of which is Phe508del. Phe508del causes not only intracellular retention and premature degradation of the mutant CFTR protein, but also defective channel gating and decreased half-life when experimentally rescued to the plasma membrane (PM). Despite recent successes in the functional rescue of several CFTR mutations with small-molecule drugs, the folding-corrector/gating-potentiator drug combinations approved for Phe508del-CFTR homozygous patients have shown only modest benefit. Several factors have been shown to contribute to this outcome, including an unexpected intensification of corrector-rescued Phe508del-CFTR PM instability after persistent co-treatment with potentiator drugs. We have previously shown that acute co-treatment with hepatocyte growth factor (HGF) can significantly enhance the chemical correction of Phe508del-CFTR. HGF coaxes the anchoring of rescued channels to the actin cytoskeleton via induction of RAC1 GTPase signalling. Here, we demonstrate that a prolonged, 15-day HGF treatment also significantly improves the functional rescue of Phe508del-CFTR by the VX-809 corrector/VX-770 potentiator combination, in polarized bronchial epithelial monolayers. Importantly, we found that HGF treatment also prevented VX-770-mediated destabilization of rescued Phe508del-CFTR and enabled further potentiation of the rescued channels. Most strikingly, prolonged HGF treatment prevented previously unrecognized epithelial dedifferentiation effects of sustained exposure to VX-809. This was observed in epithelium-like monolayers from both lung and intestinal origin, representing the two systems most affected by adverse symptoms in patients treated with VX-809 or the VX-809/VX-770 combination. Taken together, our findings strongly suggest that co-administration of HGF with corrector/potentiator drugs could be beneficial for CF patients.

Micro-Mineral Retention and Anti-Nutritional Compounds Degradation During Bean Cooking Process

The objective of this study was to determine the effect of soaking, boiling and frying on retention of micro-minerals as well as degradation of polyphenols and phytic acids. Soaking of the beans did not significantly (p > 0.05) decrease mineral, total polyphenol and phytic acid content of beans. While boiling of beans significantly (p < 0.05) decreased the concentration of total polyphenols and phytic acid but not the mineral content of the beans. Frying of boiled beans decreased the total polyphenol content but increased the concentration of phytic acids in beans. Data obtained in this study indicates that cooking of beans without discarding of soaking water and broth results into greater retention of minerals but frying may be detrimental to mineral bioavailability because it leads to increase in phytic acid content.

Proteomic interaction profiling reveals KIFC1 as a factor involved in early targeting of F508del-CFTR to degradation.

Misfolded F508del-CFTR, the main molecular cause of the recessive disorder cystic fibrosis, is recognized by the endoplasmic reticulum (ER) quality control (ERQC) resulting in its retention and early degradation. The ERQC mechanisms rely mainly on molecular chaperones and on sorting motifs, whose presence and exposure determine CFTR retention or exit through the secretory pathway. Arginine-framed tripeptides (AFTs) are ER retention motifs shown to modulate CFTR retention. However, the interactions and regulatory pathways involved in this process are still largely unknown. Here, we used proteomic interaction profiling and global bioinformatic analysis to identify factors that interact differentially with F508del-CFTR and F508del-CFTR without AFTs (F508del-4RK-CFTR) as putative regulators of this specific ERQC checkpoint. Using LC-MS/MS, we identified kinesin family member C1 (KIFC1) as a stronger interactor with F508del-CFTR versus F508del-4RK-CFTR. We further validated this interaction showing that decreasing KIFC1 levels or activity stabilizes the immature form of F508del-CFTR by reducing its degradation. We conclude that the current approach is able to identify novel putative therapeutic targets that can be ultimately used to the benefit of CF patients.

Improved switching reliability achieved in HfOx based RRAM with mountain-like surface-graphited carbon layer

In this work, we demonstrated an effective method to improve the switching reliability of HfOx based RRAM device by inserting mountain-like surface-graphited carbon (MSGC) layer. The MSGC layer was fabricated through thermal annealing of amorphous carbon (a-C) film with high sp2 proportion (49.7%) under 500 °C on Pt substrate, whose characteristics were validated by XPS and Raman spectrums. The local electric-field (LEF) was enhanced around the nanoscale tips of MSGC layer due to large surface curvature, which leads to simplified CFs and localization of resistive switching region. It takes responsibility to the reduction of high/low resistance states (HRS/LRS) fluctuation from 173.8%/64.9% to 23.6%/6.5%, respectively. In addition, the resulting RRAM devices exhibited fast switching speed (<65 ns), good retention (>104 s at 85 °C) and low cycling degradation. This method could be promising to develop reliable and repeatable high-performance RRAM for practical applications.

A Link Between CBRAM Performances and Material Microscopic Properties Based on Electrical Characterization and Atomistic Simulations

In this paper, we investigate the link between various resistive memory (RRAM) electrical characteristics: endurance, window margin (WM), and retention. For this purpose, several RRAMs are characterized using various resistive layers and bottom electrodes. By focusing on one technology and optimizing programming conditions (current, voltage, and time), we establish a tradeoff between endurance and WM. Then, by changing memory stack, we demonstrate the correlation between endurance plus window marging improvement and retention degradation. Studying this last feature from a material point of view, we analyze different oxides by density functional theory. We realize a systematic review for possible exchanges of species between resistive layer and Cu-based top electrode and study their diffusion. This provides insights on conductive filament composition in different stacks. Combining previous experiments and simulations, we propose a link between memory characteristics and material microscopic parameters, through the ion energy migration barrier. Finally, we extract how endurance, WM, and retention are correlated to material properties and electrical parameters in order to choose the suitable material for a defined application using the RRAM technology.