Universal Memory Research Articles

Integration of lead zirconium titanate thin films for high density ferroelectric random access memory

Interests are being focused on types of nonvolatile memories such as ferroelectric random access memory (FRAM), phase change random access memory, or magnetoresistance random access memory due to their distinct memory properties such as excellent write performance which conventional nonvolatile memories do not possess. Among these types of nonvolatile memories, FRAM whose cell structure and operation are almost identical to dynamic random access memory (DRAM) can ideally realize cell size and speed of DRAM. Thus FRAM is the most appropriate candidate for future universal memory where all memory functions are performed with a single chip solution. Due to the poor ferroelectric properties of downscaled ultrathin lead zirconium titanate (PZT) capacitors as well as technical issues such as hydrogen and plasma related degradation arising from embedding ferroelectric metal-insulator-metal capacitors into conventional complementary metal oxide semiconductor processes, current FRAM still falls far below its ideally attainable cell size and performance. In this paper, based upon PZT capacitor, current mass-productive one pass transistor and one storage capacitor (1T1C), capacitor over bit line (COB) cell technologies are introduced upon which cell size of 0.937μm2 at 250nm minimum feature size technology node has been realized. And then, most recent 1T1C, COB cell technologies are discussed from which cell size of 0.27μm2 at 150nm minimum feature size technology node has been realized, and finally future three dimensional capacitor technologies for the FRAM with cell size of less than 0.08μm2 beyond 100nm minimum feature size technology node are suggested.

A 6-F/sup 2/ bit cell design based on one transistor and two uneven magnetic tunnel junctions structure and low power design for MRAM

Novel cell structures based on one transistor and two uneven magnetic tunnel junction cell and pillar write word line architecture are proposed to shrink the bit size with a potential down to 6 F2 by a so-called extended via process, and to reduce the writing current by a factor of 2, combined with the nature of nonvolatility and high speed, making the magnetoresistive random access memory suitable for universal memory applications

Magnetic memories: Memory hierarchy and processing perspectives (invited)

A variety of magnetic memory devices, including MRAM, spin-torque RAM, plated wire, and bubbles, either are or have been under investigation as candidate “universal memory” devices. Such devices would combine the performance attributes of DRAM with the nonvolatility of a disk drive. This paper examines the past and present magnetic memories from two perspectives: (1) processing and extendability to smaller dimensions, and (2) the memory hierarchy of the applications to which they are directed. From a processing requirement, magnetic memories must converge to the cell sizes of competitive memory technologies, which range from 8F2 for DRAM to 0.5F2 for disk drives, where F is the minimum processing feature. From a memory hierarchy perspective, magnetic memories must balance the advantages of nonvolatility with the market demands for performance and low cost, and must address the application shifts away from classical enterprise storage hierarchy to the now rapidly developing mobile storage needs. The success of magnetic memories will depend on their ability to fulfill the evolving memory hierarchy requirements of a large set of new and nontraditional applications and on their ability to approach the device sizes of competing DRAM and flash devices.

Switching and reliability issues of magnetic tunnel junctions for high-density memory device

Abstract Magnetoresistive random access memory (MRAM) is one of the promising universal memories, which combines the high speed of static RAM, high-density of dynamic RAM, and non-volatility of FLASH memory. However, MRAM faces several challenges prior to the appearance at the commercial market on a large scale. The most important challenge among them will be an issue, related to the magnetic switching. The conventional MRAM structures and writing methods cause several issues to be overcome for high packing density without cross-talk. Furthermore, small ferromagnetic elements will require high magnetic field, which will increase the power consumption of the devices. This article will review new writing schemes, such as thermal-assisted switching and spin-transfer switching methods. In addition, reliability characteristics and thermal stability of magnetic tunnel junctions will be presented, because ensuring the reliability of magnetic tunnel junctions emerges as an another challenging problem for the successful application of the new writing schemes to the high-density MRAM devices in the next generation.

From shoebox to performative agent: the computer as personal memory machine

Digital technologies offer new opportunities in the everyday lives of people: with still expanding memory capacities, the computer is rapidly becoming a giant storage and processing facility for recording and retrieving ‘bits of life’. Software engineers and companies promise not only to expand the capacity of personal memory infinitely, but even revolutionize its nature. Both in the past and recent years, the idea of a universal memory machine has been conceptualized in fantasies and actual projects (e.g. Vannevar Bush’s ‘Memex’, 1945). Discussing the intentions of contemporary technical projects (Shoebox, Experience on Demand) as well as visionary projects (Lifestreams, Memories for Life, MyLifeBits), this article critically analyses how digital personal memory machines use the computer as a model for the way in which memory works. Rather than looking at computers as jukeboxes of memory, it proposes to pay attention to the performative nature of machines in the acts of remembering.

Effective boson-spin model for nuclei-ensemble-based universal quantum memory

We study the collective excitation of a macroscopic ensemble of polarized nuclei fixed in a quantum dot. Under the approximately homogeneous condition that we explicitly present in this paper, this many-particle system behaves as a single-mode boson interacting with the spin of a single conduction-band electron confined in this quantum dot. Within this effective spin-boson system, the quantum information carried by the electronic spin can be coherently transferred into the collective bosonic mode of excitation in the ensemble of nuclei. In this sense, the collective bosonic excitation can serve as a stable quantum memory to store the quantum spin information of the electron.

Towards a universal memory?

Materials that undergo a structural transformation between amorphous and crystalline phases under the influence of an electrical current have been known for decades. But with the discovery of new phase-change materials and new device configurations to make them switch, interest in them is being rejuvenated.

Nanotubes in the Clean Room

The article profiles the nanotube research and development of Nantero, formed by former Harvard graduate students, whose projects may soon make their way into electronic memories. Charles M. Lieber, a major figure in nanotechnology, asked one of his graduate students in 1998 to undertake the design of a radically new type of computer memory. It would read and write digital bits with memory elements that measured less than 10 billionths of a meter (10 nanometers). Until then, the student, a German native named Thomas Rueckes, had been spending his time in Lieber's laboratory at Harvard University measuring the electrical and material properties of carbon nanotubes. Many researchers were trying to use nanotubes as wires or components in new transistor designs. Rueckes chose to focus instead on their extraordinary tensile strength and resilience. Until his graduation in 2001, Rueckes continued to develop the concept. As he worked, he realized that nanotubes had more and more to offer. They could, in theory, provide the makings of a universal memory, one that combined the speed of static random-access memory, the low cost of dynamic random-access memory (DRAM), and the nonvolatility (instant on operation) of flash memory. Its status as uber-material would also make it a low consumer of electrical power as well as resistant to potentially damaging heat, cold and magnetism. In 2001, Schmergel and Rueckes, along with Brent M. Segal, another former Harvard chemistry doctoral student, formed Nantero. When Nantero had gained confidence with the technology, it began a new round of visits to semiconductor manufacturers. In 2003 LSI Logic, a leading maker of customized chips for the telecommunications, storage and consumer electronics industries, agreed to bring the process for making what Nantero calls nanotube random-access memory (NRAM) into its factory in Gresham, Ore.

A signal boost is in order

Magnetic random-access memory (MRAM) has been touted as a universal memory with a wide range of potential applications in portable computers, consumer electronics and wireless devices. The use of certain combinations of materials that can now be deposited as thin-film layers with excellent crystalline order provides a significantly larger signal in the devices, and is expected to help advance the commercialization of MRAM.

Current aspects and future perspectives of high-density MRAM

Magnetoresistive random access memory (MRAM) is regarded as one of the leading candidates for universal memory [1] that will be commercialized in the foreseeable future. The figure of merits for MRAM technology includes non-volatility, high speed, high density, radiation hardness, and unlimited endurance. Very promising R & D results have been announced wordlwide. For a high density MRAM as a stand-alone memory, uniform resistance and switching control for sub-micron and deep sub-micron devices must be guaranteed. To achieve this goal, several material and device issues related with MRAM core cell should be resolved. Resistance (R) as well as magnetoresistance (MR) are limited by the uniformity of barrier thickness induced by bottom electrode. Switching issues appear controllable with a choice of appropriate shape and fine patterning process.

News briefs - Nanotech ram holds promise for universal memory

News briefs - Nanotech ram holds promise for universal memory

Real-time computing without stable states: a new framework for neural computation based on perturbations.

A key challenge for neural modeling is to explain how a continuous stream of multimodal input from a rapidly changing environment can be processed by stereotypical recurrent circuits of integrate-and-fire neurons in real time. We propose a new computational model for real-time computing on time-varying input that provides an alternative to paradigms based on Turing machines or attractor neural networks. It does not require a task-dependent construction of neural circuits. Instead, it is based on principles of high-dimensional dynamical systems in combination with statistical learning theory and can be implemented on generic evolved or found recurrent circuitry. It is shown that the inherent transient dynamics of the high-dimensional dynamical system formed by a sufficiently large and heterogeneous neural circuit may serve as universal analog fading memory. Readout neurons can learn to extract in real time from the current state of such recurrent neural circuit information about current and past inputs that may be needed for diverse tasks. Stable internal states are not required for giving a stable output, since transient internal states can be transformed by readout neurons into stable target outputs due to the high dimensionality of the dynamical system. Our approach is based on a rigorous computational model, the liquid state machine, that, unlike Turing machines, does not require sequential transitions between well-defined discrete internal states. It is supported, as the Turing machine is, by rigorous mathematical results that predict universal computational power under idealized conditions, but for the biologically more realistic scenario of real-time processing of time-varying inputs. Our approach provides new perspectives for the interpretation of neural coding, the design of experiments and data analysis in neurophysiology, and the solution of problems in robotics and neurotechnology.

Merry Christmas! Celebrating America's Greatest Holiday

Merry Christmas! is an exuberant romp through the stuff of Christmas—wrapping paper, Christmas trees, candy and cookies, greeting cards, charity, Santa Claus, and television specials. Karal Ann Marling, a professor of art history at the University of Minnesota, examines the material culture of Christmas and much more. As she unpacks (and unwraps) the various rituals that mark the holiday season, she speculates about why Americans love Christmas. The book's intended audience is nonaca-demic, and so there is some latitude for asides and digressions; for example, the chapter on Christmas charity begins with an analysis of Charles Dickens's A Christmas Carol (1843). Other parts of the book assess almost every prop associated with celebrating Christmas. Marling opens with the claim that “Christmas is the universal memory, one of the few rituals on the calendar of life that virtually everybody has played a part in.” The book, however, is not about the wide range of Christ-mases Americans may have celebrated; instead it is about the Christmas of white middle-class America in the middle decades of the twentieth century. The title of the chapter that addresses depictions of African American Christ-mases is tellingly titled “Somebody Else's Christmas.” The book's America, then, is Betty Crocker's and the young Elvis Presley's, both subjects of earlier and better books by Marling. To be sure, each chapter looks backward to the nineteenth-century origins of a variety of practices. The chapter about wrapping paper is especially thorough; it addresses the origins of gift boxes, tissue paper, ribbons, holly boxes, and Christmas seals.

Fundamentals of MRAM Technology

Developments in portable communication and computing systems are creating a growing demand for nonvolatile random access memory that is dense and fast. None of the existing solid-state memories can provide all the needed attributes in a single memory solution. Therefore, to achieve the required multiple functionality requirements, a number of different memories are being used while compromising performance and adding cost to the system. Magnetoresistive Random Access Memory (MRAM) has the potential to replace these memories in various systems with a single, universal memory solution. Key attributes of MRAM technology are nonvolatility and unlimited read and write endurance. In addition, MRAM can operate at high-speed and is expected to have competitive densities. In this paper we describe several fundamental technical and scientific aspects of MRAM with emphasis on recent accomplishments that enabled our successful demonstration of a 256 kbit memory chip.

Joyce's book of memory: the mnemotechnic of Ulysses

For James Joyce, perhaps the most crucial of all human faculties was memory. It represented both the central thread of identity and a looking glass into the past. It served as an avenue into other minds, an essential part of the process of literary composition and narration, and the connective tissue of cultural tradition. In Joyce’s Book of Memory John S. Rickard demonstrates how Joyce’s body of work— Ulysses in particular—operates as a “mnemotechnic,” a technique for preserving and remembering personal, social, and cultural pasts. Offering a detailed reading of Joyce and his methods of writing, Rickard investigates the uses of memory in Ulysses and analyzes its role in the formation of personal identity. The importance of forgetting and repression, and the deadliness of nostalgia and habit in Joyce’s paralyzed Dublin are also revealed. Noting the power of spontaneous, involuntary recollection, Rickard locates Joyce’s mnemotechnic within its historical and philosophical contexts. As he examines how Joyce responded to competing intellectual paradigms, Rickard explores Ulysses ’ connection to medieval, modern, and (what would become) postmodern worldviews, as well as its display of tensions between notions of subjective and universal memory. Finally, Joyce’s Book of Memory illustrates how Joyce distilled subjectivity, history, and cultural identity into a text that offers a panoramic view of the modern period. This book will interest students and scholars of Joyce, as well as others engaged in the study of modern and postmodern literature.

Reciprocal age-related patterns of allergen-specific T-cell immunity in normal vs. atopic infants.

By adulthood there is almost universal immunological memory to aeroallergens, and the presence of allergic disease appears to be related to the nature of the underlying T-helper (Th) cell cytokine responses. The hypothesis of this study is that adult patterns of allergen specific Th-cell memory (Th-2 polarized in atopics vs. Th1 in non-atopics) can be determined in early infancy. Mononuclear cell cytokine responses to house-dust mite were measured at 6-monthly intervals from birth to 2 years of age, using ELISA (IL-10, IL-13, IFN-gamma) and sqRT/PCR (IL-4, IL-5, IL-9, IFN-gamma) in normal infants (n = 14) with no family history or allergic symptoms, and infants with a family history and definite atopy by 2 years (n = 16). Both normals and atopics showed low-level Th2 skewed allergen-specific responses at birth with little accompanying IFN-gamma. The Th2 responses to house-dust mite were higher in normal newborns, who then show a rapid downregulation of these responses in the first year of life. Atopic infants instead show a consolidation of their neonatal patterns of Th2 polarized allergen specific immunity. Earlier studies indicate that neonates at high risk of atopy display diminished capacity for production of the Th1 cytokine IFN-gamma. The present study suggests for the first time that neonates who subsequently develop atopy also initially have reduced capacity to mount Th2 responses. However, in contrast to non-atopics who selectively downregulate their fetal Th2 polarized allergen-specific responses, atopic children display age-associated upregulation of Th2 immunity.

CMOS J-K triflop

ABSTRACT An all-CMOS ternary J-K triflop (ternary flip-flop) is presented. It has three ternary logic outputs with levels 0, 1 and 2, representing present, future and past output states, and has preset facilities to obtain any one of these three logic levels as is required at the output. This ensures great flexibility for ternary sequential circuit design (ternary shift registers, counters, latches, etc.) and can as such be considered as a universal memory element for ternary logic design.