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Studio sperimentale di celle T-RAM per memorie volatili di prossima generazione
No full textLAUREA MAGISTRAL
Characterization and modeling of innovative solid-state memory technologies
No full textNel corso dell’ultimo decennio, sia dispositivi di memoria volatile che di memoria non volatile hanno subito un’aggressiva riduzione delle rispettive dimensioni a causa del processo di scaling. Sebbene tale processo li abbia portati ad avere una straordinaria densità di integrazione, e di conseguenza, alla riduzione del costo per bit, li ha pure spinti ai propri limiti fisici. Da un lato, la memoria ad accesso casuale dinamica (DRAM), attualmente la memoria volatile a più alta densità di integrazione, è afflitta da correnti di leakage sempre più crescenti, mentre l’integrazione del condensatore di immagazzinamento rappresenta il maggior ostacolo per i dispositivi ultra-scalati. Dall’altro lato, le memorie flash, oggi la principale tecnologia di memoria non volatile a stato solido, si stanno avvicinando al punto in cui la granularità della materia e della carica severamente influenza le loro prestazioni.
Lo scopo di questa tesi è lo studio di due innovativi dispositivi di memoria, uno di tipo volatile e l’altro di tipo non volatile, che risultano ottimi candidati per sostituire le attuali DRAM e Flash, rispettivamente. Il primo tipo sfrutta la bistabilità dei gated-thyristors per immagazzinare in maniera semplice e affidabile il dato volatile e viene chiamato T-RAM (Thyristor-based RAM). Il secondo tipo, invece, codifica i due stati binari grazie all’inversione permanente della polarizzazione all’interno del gate-stack di un transistore a effetto di campo ferroelettrico (FeFET), basato sull’ossido di afnio. I due dispositivi risultano non solo interamente CMOS compatibili, ma esibiscono anche semplici principi di funzionamento e ottime prestazioni in vista di future applicazioni nel campo delle memorie.Over the past decade, both volatile and non-volatile solid-state memory devices have seen their physical size aggressively shrunk in order to meet the scaling process requirements. Although this led to a remarkable increase in device integration density, and consequently, to a reduction of the cost per bit, it pushed the respective technologies to their physical limits. On the one hand, Dynamic Random Access Memory (DRAM), as the most densely integrated volatile memory, is faced with ever increasing leakage currents, while the integration of the storage capacitor became the main issue for the ultra-scaled devices. On the other hand, Flash memory, today’s leading solid-state non-volatile memory technology, is approaching the point where the discreteness of the matter and of the charge flows is severely impacting its performance.
The goal of this thesis is to investigate two innovative memory devices, one of volatile and the other of non-volatile nature, which appear to be promising candidates for the future replacement of DRAM and Flash technologies, respectively. The former exploits the bistability of gated-thyristors to store the volatile data in a simple and reliable fashion and is called Thyristor-based RAM (T-RAM) cell. The latter one relies, instead, on the permanent polarization reversal within the gate stack of a Hafnium oxide-based Ferroelectric Field Effect Transistor (FeFET) to encode the two binary states. Not only are the two devices fully CMOS compatible, which would facilitate their path towards the semiconductor industry, but they also exhibit simple working principles and excellent performance features in view of their future memory applications.DIPARTIMENTO DI ELETTRONICA, INFORMAZIONE E BIOINGEGNERIAElectronics28FIORINI, CARLO ETTOREBONARINI, ANDRE
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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