Size Scaling in Phase Change Memory Cells: From Traditional to Emerging Device Structures

This is the final version of the article. Available from E\PCOS via the URL in this record.1. INTRODUCTION AND METHODOLOGY Phase change memory (PCM) based on the reversible phase-transition of chalcogenides (such as Ge2Sb2Te5 (GST)) between a low-resistance crystalline state and high-resistance amorphous state is one of the leading candidates of emerging non-volatile solid-state memories [1]. Scaling is one of the most important aspects for PCM development as it leads to enhanced storage density, reduction in power consumption and improvement in switching speeds [2]. To demonstrate the excellent scalability of PCRAM, switching capability in the sub-10nm region [3-5], programming currents less than 10μA [4], switching speeds in picoseconds [6], and storage densities in Tb/in2 using scanning probe recording and thermal recording [7-8] have all been reported. In this manuscript we combine electro-thermal simulations with the Gillespie Cellular Automata (GCA) phase switching approach to simulate and predict the scaling behaviour (down to sub-10nm dimensions) of three GST-based device structures; (1) mushroom-type PCM cells, (2) trilayer patterned PCM cells, and (3) spherical phase change nanoclusters. The GCA approach is a sophisticated stochastic simulator capable of spatio-temporal modeling in PCM devices, and has previously been described in detail in [9]. This approach is potentially capable of spanning the length scales between atomistic modeling and bulk scale methods such as the JMAK or the classical nucleation and growth methods. Electrical switching is performed by applying trapezoidal Reset and Set pulses of various amplitudes and durations in a test bench consisting of an electrical pulse source, a series load resistance of 10kΩ, and the phase change memory cell itself. [...

A theoretical study of scaling behaviour of mushroom PCRAM devices using the Gillespie Cellular Automata Approach

This is the author accepted manuscript.We investigate the scaling characteristics of vertical “mushroom” phase change random access memory (PCRAM) cells down to sub-10nm dimensions using an electro-thermal model combined with the Gillespie cellular automata (GCA) phase-transition approach. The size of the amorphous dome formed during the Reset process decreases linearly with simultaneous reduction of the bottom TiN heater width and Ge2Sb2Te5 (GST) phase change layer volume with re-design of the cell geometry required for sub-15nm dimensions. Re-crystallisation of the amorphous dome is primarily nucleation-dominated, however a transition to growth-dominated crystallisation is observed for dimensions below 20nm. The scaling trend features a resistive window of a factor of 10 even for very small dimensions predicting the scalability and operability of mushroom PCRAM cells in the sub-10nm region

Can conventional phase-change memory devices be scaled down to single-nanometre dimensions?

ArticleThis is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.The scaling potential of “mushroom-type” phase-change memory devices is evaluated, down to singlenanometre dimensions, using physically realistic simulations that combine electro-thermal modelling with a Gillespie Cellular Automata phase-transformation approach. We found that cells with heater contact sizes as small as 6 nm could be successfully amorphized and re-crystallized (RESET and SET) using moderate excitation voltages. However, to enable the efficient formation of amorphous domes during RESET in small cells (heater contact diameters of 10 nm or less), it was necessary to improve the thermal confinement of the cell to reduce heat loss via the electrodes. The resistance window between the SET and RESET states decreased as the cell size reduced, but it was still more than an order of magnitude even for the smallest cells. As expected, the RESET current reduced as the cells got smaller; indeed, RESET current scaled with the inverse of the heater contact diameter and ultra-small RESET currents of only 19 μA were achieved for the smallest cells. Our results show that the conventional mushroom-type phase-change cell architecture is scalable and operable in the sub-10nm region.HH would like to thank the College of Engineering, Mathematics and Physical Sciences at the University of Exeter for PhD studentship funding while carrying out this work. CDW would like to thank the EPSRC for funding via grant EP/M015130/1. The authors would also like to thank Dr. Karthik Nagareddy (University of Exeter) for helpful discussions during this work

Domestication and inequality? Households, corporate groups and food processing tools at Neolithic Çatalhöyük

Questions about the early Near Eastern Neolithic include whether domestic groups were autonomous and self-sufficient; whether they had access to similar goods; whether households were competitive; whether specialization existed; and how domestic units articulated with corporate groups. Feasting models emphasize household competition and inequality, but ethnographies show that hoe-farming societies in areas of land abundance are usually egalitarian, with little material wealth, little inequality, and little wealth transmission (inheritance). This paper explores the origins of social inequality, via a case study of Neolithic Çatalhöyük East (Turkey), in particular its ground stone artefacts, which were central to food preparation and craft production. Analysis of 2429 artefacts from 20 buildings and 9 yards reveals a mix of egalitarian features and emerging inequality. Households had private property and relatively equal access to cooking features and some ground stone tools; but toolkits do not indicate self-sufficiency. In particular, large millstones (querns) were expensive to procure and possibly shared between households. Most were deliberately destroyed, suggesting taboos on inheritance. Lorenz curves for features and ground stone artefacts suggest that storage units, unbroken querns and unfinished querns were the most unequally distributed food preparation tools/facilities. There are indications of intensification, craft specialization, and emerging factional competition

Response to "comment on 'Threshold switching via electric field induced crystallization in phase change memory devices'" [Appl. Phys. Lett. 102, 236101 (2012)]

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4th Treasures of Jazz: Jazz Divas of Cleveland and the Jazz Heritage Orchestra (2012)

Cleveland jazz artists Evelyn Wright and Ki Allen perform with the CSU Jazz Heritage Orchestra.https://engagedscholarship.csuohio.edu/clbsjz_pr/1004/thumbnail.jp

Systematic review of the role of social inclusion within sustainable urban developments

Rapid urbanisation presents multiple opportunities, but also poses challenges for equitable distribution of gains from socio-economic developments. This systematic review explored the role of social inclusion within the urban sustainability agenda. Sustainable urban developments were conceptualised as comprising environmental, spatial, social and economic perspectives; and social inclusion as entailing access to core services (healthcare) and resources (food). A search of five databases and grey literature returned 1,015 articles; 26 papers were included following screening using pre-determined criteria. Data was analysed thematically. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations were followed. Most included studies were from North America and few were from Africa and Asia. More empirical than conceptual studies were found, and more focused on food than healthcare. Social inclusion was generally included within the urban sustainability but was often an autonomous component, rather than mainstreamed, within urban sustainability. Social inclusion was mostly related to multiple elements of sustainability, with the greatest focus on combinations of environmental, social and economic opportunities for under privileged groups. However, less consideration was given to gender, ethnicity and other aspects of intersectionality. Multiple theories contributed to transferability of lessons. Key policy implications include prioritising the most vulnerable socially excluded populations, ensuring equal representation in urban planning, designing people-centred systems, building partnerships with communities, considering socio-cultural-political-economic contexts, and recognising both intended and unintended effects. More research is needed in low and middle-income countries (LMICs) on the role of social inclusion in achieving sustainable development, using cross-disciplinary approaches

Pulmonary Nodular Lymphoid Hyperplasia Associated with Sjögren's Syndrome

Pulmonary nodular lymphoid hyperplasia (NLH) is a term first suggested by Kradin and Mark to describe one or more pulmonary nodules or localized lung infiltrates consisting of reactive lymphoid proliferation. To date, there have been only a few cases of pulmonary NLH reported associated with autoimmune disorders. There is no case of NLH associated with Sjögren's syndrome from Korea in the medical literature. A 56-year-old woman was referred to our hospital with cough productive of sputum and chest tightness. The Computed tomography scans of the chest revealed multiple and well-defined peribronchiolar nodular opacities. A video assisted thoracoscopic surgery (VATS) biopsy was performed and the nodular opacity in the lung parenchyma was pathologically confirmed as NLH. Through meticulous review of patient's record, we found that she had been suffering from dry eye and dry mouth. The symptoms suggested Sjögren's syndrome, which was confirmed by specific laboratory tests including the Schirmer test, anti-nuclear antibody and anti-Ro/La antibody. The patient is followed regularly and has no further progression of symptoms