Ultrahigh-density Storage Devices Research Articles

Performance analysis of DNA crossbar arrays for high-density memory storage applications

Deoxyribonucleic acid (DNA) has emerged as a promising building block for next-generation ultra-high density storage devices. Although DNA has high durability and extremely high density in nature, its potential as the basis of storage devices is currently hindered by limitations such as expensive and complex fabrication processes and time-consuming read–write operations. In this article, we propose the use of a DNA crossbar array architecture for an electrically readable read-only memory (DNA-ROM). While information can be ‘written’ error-free to a DNA-ROM array using appropriate sequence encodings its read accuracy can be affected by several factors such as array size, interconnect resistance, and Fermi energy deviations from HOMO levels of DNA strands employed in the crossbar. We study the impact of array size and interconnect resistance on the bit error rate of a DNA-ROM array through extensive Monte Carlo simulations. We have also analyzed the performance of our proposed DNA crossbar array for an image storage application, as a function of array size and interconnect resistance. While we expect that future advances in bioengineering and materials science will address some of the fabrication challenges associated with DNA crossbar arrays, we believe that the comprehensive body of results we present in this paper establishes the technical viability of DNA crossbar arrays as low power, high-density storage devices. Finally, our analysis of array performance vis-à-vis interconnect resistance should provide valuable insights into aspects of the fabrication process such as proper choice of interconnects necessary for ensuring high read accuracies.

Desolvation-Driven 100-Fold Slow-down of Tunneling Relaxation Rate in Co(II)-Dy(III) Single-Molecule Magnets through a Single-Crystal-to-Single-Crystal Process.

Single-molecule magnets (SMMs) are regarded as a class of promising materials for spintronic and ultrahigh-density storage devices. Tuning the magnetic dynamics of single-molecule magnets is a crucial challenge for chemists. Lanthanide ions are not only highly magnetically anisotropic but also highly sensitive to the changes in the coordination environments. We developed a feasible approach to understand parts of the magneto-structure correlations and propose to regulate the relaxation behaviors via rational design. A series of Co(II)-Dy(III)-Co(II) complexes were obtained using in situ synthesis; in this system of complexes, the relaxation dynamics can be greatly improved, accompanied with desolvation, via single-crystal to single-crystal transformation. The effective energy barrier can be increased from 293 cm−1 (422 K) to 416 cm−1 (600 K), and the tunneling relaxation time can be grown from 8.5 × 10−4 s to 7.4 × 10−2 s. These remarkable improvements are due to the change in the coordination environments of Dy(III) and Co(II). Ab initio calculations were performed to better understand the magnetic dynamics.

Aging mechanisms in amorphous phase-change materials.

Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.

A Reliability Enhanced Address Mapping Strategy for Three-Dimensional (3-D) NAND Flash Memory

The linear scaling down of NAND flash memory is approaching its physical, electrical, and reliability limitations. To maintain the current trend of increasing bit density and reducing bit per cost, 3-D flash memory is emerging as a viable solution to fulfill the ever-increasing demands of storage capacity. In 3-D NAND flash memory, multiple layers are stacked to provide ultrahigh density storage devices. However, the physical architecture of 3-D flash memory leads to a higher probability of disturbance to adjacent physical pages and greatly increases bit error rates. This paper presents a novel physical-location-aware address mapping strategy for 3-D NAND flash memory. It permutes the physical mapping of pages and maximizes the distance between the consecutively logical pages, which can significantly reduce the disturbance to adjacent physical pages and effectively enhance the reliability. The proposed mapping strategy is applied to a representative flash storage system. Experimental results show that the proposed scheme can reduce uncorrectable page errors by 70.16% with less than 10.01% space overhead in comparison with the baseline scheme.

The use of XAFS to determine the nature of interaction of iron and molybdenum metal salts within PS-b-P2VP micelles

The poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) micelle route is a well established method for the preparation of bimetallic nanoparticles used for the catalysis of carbon nanotubes and other applications like ultrahigh density storage devices, yet to date no information is available concerning the internal structure of the P2VP-metal salt complex. For the first time, XAFS measurements were performed on micelles loaded with either iron(III) chloride or molybdenum(V) chloride and a combination of both. Analysis of the data revealed that iron is tetrahedrally coordinated within the core, whereas molybdenum is octahedrally coordinated in the pure loaded micelles and trigonally coordinated in the mixed micelles. For the bimetallic samples, analysis of the Fe and Mo K-edge data revealed the existence of an interaction between iron and molybdenum. This approach to obtain detailed structural information during the preparation of these catalyst samples will allow for a deeper understanding of the effects of structure on the function of catalysts used for CNT growth i.e. to explain differences in yield as well as potentially providing a deeper understanding of the CNT growth mechanism itself.

Vertical 3D NAND Flash Memory Technology

We've developed Bit Cost Scalable (BiCS) flash technology as a three-dimensional memory for the future ultra high density storage devices, which extremely reduces the chip costs by vertically stacking memory arrays with punch and plug process. We've advanced it into Pipe-shaped BiCS flash memory introducing U-shaped NAND string structure, to improve operation window, speed and reliability. 32 G bit test chips with 16 stacked layers by 60nm P-BiCS flash process have been fabricated, and the functionality of Multi-Level-Cell (MLC) operation has been successfully demonstrated. P-BiCS is the most promising candidate of three-dimensional ultra high density data storage memories.