171,027 research outputs found
ELECTRICAL CHARACTERIZATION, PHYSICS, MODELING AND RELIABILITY OF INNOVATIVE NON-VOLATILE MEMORIES
No full textEnclosed in this thesis work it can be found the results of a three years long research
activity performed during the XXIV-th cycle of the Ph.D. school in Engineering Science of
the Università degli Studi di Ferrara. The topic of this work is concerned about the
electrical characterization, physics, modeling and reliability of innovative non-volatile
memories, addressing most of the proposed alternative to the floating-gate based
memories which currently are facing a technology dead end. Throughout the chapters of
this thesis it will be provided a detailed characterization of the envisioned replacements for
the common NOR and NAND Flash technologies into the near future embedded and
MPSoCs (Multi Processing System on Chip) systems. In Chapter 1 it will be introduced the
non-volatile memory technology with direct reference on nowadays Flash mainstream,
providing indications and comments on why the system designers should be forced to
change the approach to new memory concepts. In Chapter 2 it will be presented one of the
most studied post-floating gate memory technology for MPSoCs: the Phase Change
Memory. The results of an extensive electrical characterization performed on these
devices led to important discoveries such as the kinematics of the erase operation and
potential reliability threats in memory operations. A modeling framework has been
developed to support the experimental results and to validate them on projected scaled
technology. In Chapter 3 an embedded memory for automotive environment will be shown:
the SimpleEE p-channel memory. The characterization of this memory proven the
technology robustness providing at the same time new insights on the erratic bits
phenomenon largely studied on NOR and NAND counterparts. Chapter 4 will show the
research studies performed on a memory device based on the Nano-MEMS concept. This
particular memory generation proves to be integrated in very harsh environment such as
military applications, geothermal and space avionics. A detailed study on the physical
principles underlying this memory will be presented. In Chapter 5 a successor of the
standard NAND Flash will be analyzed: the Charge Trapping NAND. This kind of memory
shares the same principles of the traditional floating gate technology except for the storage
medium which now has been substituted by a discrete nature storage (i.e. silicon nitride
traps). The conclusions and the results summary for each memory technology will be
provided in Chapter 6. Finally, on Appendix A it will be shown the results of a recently
started research activity on the high level reliability memory management exploiting the
results of the studies for Phase Change Memories
Improving 3D NAND Flash Memories Reliability: a Cross-Layer Perspective
No full textThe 3D NAND Flash memory technology is the main building block of storage architectures such as multimedia cards and Solid-State Drives. Applications ranging from mobile to high-performance computing are continuously calling for an increased storage density, requiring massive scaling efforts at the device and array level. This leads to a natural degradation of the functional metrics of the technology while exposing new reliability issues that jeopardize the inherent memory trade-off with performance. A simple device optimization would be insufficient to tackle the problem. In this work, we show through some case studies how a cross-layer approach spanning from devices and circuits to system-level optimizations is mandatory for future storage systems development
Editorial for the special issue on flash memory devices
No full textFlash memory devices represented a breakthrough in the storage industry since their inception in the mid-1980s, and innovation is still ongoing after more than 35 years. This Special Issue provides insight on and advancements in Flash memory devices
Machine Learning and Non-volatile Memories
No full textThis book presents the basics of both NAND flash storage and machine learning, detailing the storage problems the latter can help to solve. At a first sight, machine learning and non-volatile memories seem very far away from each other. Machine learning implies mathematics, algorithms and a lot of computation; non-volatile memories are solid-state devices used to store information, having the amazing capability of retaining the information even without power supply. This book will help the reader understand how these two worlds can work together, bringing a lot of value to each other. In particular, the book covers two main fields of application: analog neural networks (NNs) and solid-state drives (SSDs).
After reviewing the basics of machine learning in Chapter 1, Chapter 2 shows how neural networks can mimic the human brain; to accomplish this result, neural networks have to perform a specific computation called vector-by-matrix (VbM) multiplication, which is particularly power hungry. In the digital domain, VbM is implemented by means of logic gates which dictate both the area occupation and the power consumption; the combination of the two poses serious challenges to the hardware scalability, thus limiting the size of the neural network itself, especially in terms of the number of processable inputs and outputs. Non-volatile memories (phase change memories in Chapter 3, resistive memories in Chapter 4, and 3D flash memories in Chapter 5 and Chapter 6) enable the analog implementation of the VbM (also called “neuromorphic architecture”), which can easily beat the equivalent digital implementation in terms of both speed and energy consumption.
SSDs and flash memories are strictly coupled together; as 3D flash scales, there is a significant amount of work that has to be done in order to optimize the overall performances of SSDs. Machine learning has emerged as a viable solution in many stages of this process. After introducing the main flash reliability issues, Chapter 7 shows both supervised and un-supervised machine learning techniques that can be applied to NAND. In addition, Chapter 7 deals with algorithms and techniques for a pro-active reliability management of SSDs. Last but not least, the last section of Chapter 7 discusses the next challenge for machine learning in the context of the so-called computational storage.
No doubt that machine learning and non-volatile memories can help each other, but we are just at the beginning of the journey; this book helps researchers understand the basics of each field by providing real application examples, hopefully, providing a good starting point for the next level of development
A cross-layer approach for new reliability-performance trade-offs in MLC NAND flash memories
No full textIn spite of the mature cell structure, the memory controller architecture of Multi-level cell (MLC) NAND Flash memories is evolving fast in an attempt to improve the uncorrected/miscorrected bit error rate (UBER) and to provide a more flexible usage model where the performance-reliability trade-off point can be adjusted at runtime. However, optimization techniques in the memory controller architecture cannot avoid a strict trade-off between UBER and read throughput. In this paper, we show that co-optimizing ECC architecture configuration in the memory controller with program algorithm selection at the technology layer, a more flexible memory sub-system arises, which is capable of unprecedented trade-offs points between performance and reliabilit
La relazione di cura nel rispetto della dignità individuale. Interruzione dei trattamenti, cure palliative e formazione del personale
No full textCosa rimarrà dall’esperienza della pandemia? È questa la domanda che ha condotto una saggia riflessione di tre professori dell’Università di Bologna che mette in luce un importante aspetto, imprescindibile per la buona pratica medica, ma posto in secondo piano e oscurato durante l’emergenza sanitaria: l’etica. Il volume contiene uno sguardo d’insieme, ragionato, imparziale, esente da influenze politiche, intorno al quale gravitano considerazioni, insegnamenti e amarezze per ciò che non si è potuto, ma che si sarebbe dovuto fare durante l’emergenza pandemica e che deve necessariamente essere recuperato, ossia “prendersi cura” del malato e superare l’approccio basato sulla semplice “cura”. Gli autori del volume intervengono sul tema dell’etica congiuntamente a quello della solidarietà, puntando l’attenzione sulla partecipazione emotiva del malato in termini di qualità della relazione e della comunicazione tra medico e paziente, soprattutto nel contesto di progressiva virtualizzazione della medicina. Gli studi e le riflessioni proposti nel testo rappresentano il punto di partenza di un percorso etico da intraprendere con una prospettiva giuridico-sanitaria, attraverso il quale sarà possibile acquisire la consapevolezza che la figura professionale del medico deve essere restaurata e preparata ad affrontare il cambiamento in atto nel sistema della tutela sanitaria
SSD Reliability Assessment and Improvement
No full textSolid State Drives (SSDs) are one of the electronic systems with the highest development rate in the last decade [1]. Their adoption as a hard disk drive (HDD) replacement in hyper scale environments like cloud computing and big data servers, as well as in consumer electronics, is relentless
C-13-enriched end groups of poly(3-methyl-1-pentene) prepared in the presence of metallocene catalysts
No full textPolymerization of both (S)-3-methyl-1-pentene and (R,S)-3-methyl-1-pentene in the presence of two metallocene catalysts prepared from metallocene precursors of different symmetry (C-2 and C-s) and C-13-enriched MAO shows that the insertion of the monomer in the initiation step is diastereoselective to an extent similar to that previously observed in the presence of the heterogeneous isotactic specific catalyst delta-TiCl3-Al((CH3)-C-13)(3). Surprisingly, the catalyst prepared with the metallocene precursor of C-s symmetry promotes coisotactic polymerization of the two enantiomers of 3-methyl-1-pentene but only dimerization of (S)-3-methyl-1-pentene
Formazione degli insegnanti e ricerca didattica universitaria
No full textL’obiettivo di questo articolo e’ quello delineare una struttura universitaria che funga da punto di riferimento per la formazione degli insegnanti a tutti i livelli di istruzione e per l’organizzazione della ricerca didattica ad essa connessa, cercando, al contempo, di stimolare una riflessione su un tema che nel nostro paese e’ stato finora trascurato, quello della formazione didattica dei docenti universitari e del complessivo miglioramento della didattica. A tal fine, viene considerata inizialmente la questione della formazione degli insegnati alla luce delle attuali politiche europee guidate dalla strategia di Lisbona, distinguendo tra scuola e universita' ed esaminando alcuni tra i principali documenti elaborati da organismi europei che forniscono condivisi orientamenti su tale questione. Successivamente, poiche’ per l’istruzione superiore la produzione di documenti e’ più limitata, sono prese in considerazione alcune strutture accademiche largamente diffuse, Centre for Teaching and Learning e Subject Centre, preposte tanto alla formazione degli insegnanti quanto all’organizzazione della ricerca didattica, che esemplificano possibili implementazioni dei recenti orientamenti di politica educativa europea. Entrambe le linee di analisi forniscono molteplici suggerimenti per mettere a punto e realizzare un Centro di ateneo per l’insegnamento e l’apprendimento o un Centro per la didattica disciplinare, che, affrontando anche le problematiche ad essi connesse, si occupi della formazione dei nuovi docenti, del sostegno alla didattica e della ricerca didattica
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