Luo Y.,Carnegie Mellon University |
Ghose S.,Carnegie Mellon University |
Cai Y.,Carnegie Mellon University |
Haratsch E.F.,Seagate Technology |
Mutlu O.,ETH Zurich
IEEE Journal on Selected Areas in Communications | Year: 2016
NAND flash memory is a widely used storage medium that can be treated as a noisy channel. Each flash memory cell stores data as the threshold voltage of a floating gate transistor. The threshold voltage can shift as a result of various types of circuit-level noise, introducing errors when data are read from the channel and ultimately reducing flash lifetime. An accurate model of the threshold voltage distribution across flash cells can enable mechanisms within the flash controller that improve channel reliability and device lifetime. Unfortunately, existing threshold voltage distribution models are either not accurate enough or have high computational complexity, which makes them unsuitable for online implementation within the controller. We propose a new low-complexity flash memory model, built upon a modified version of the Student's t-distribution and the power law, which captures the threshold voltage distribution and predicts future distribution shifts as wear increases. Using our experimental characterization of the state-of-the-art 1X-nm (i.e., 15-19 nm) multi-level cell NAND flash chips, we show that our model is highly accurate (with an average modeling error of 0.68%), and also simple to compute within the flash controller (requiring 4.41 times less computation time than the most accurate prior model, with negligible decrease in accuracy). Our model also predicts future threshold voltage distribution shifts with a 2.72% modeling error. We demonstrate several example applications of our model in the flash controller, which improve flash channel reliability significantly, including a new mechanism to predict the remaining lifetime of a flash device. Our evaluations for two of these applications show that our model: 1) helps improve flash memory lifetime by 48.9% and/or (2) enables the flash device to safely sustain 69.9% more write operations than manufacturer specifications. We hope and believe that the analyses and models developed in this paper can inspire other novel approaches to flash memory reliability and modeling. © 2016 IEEE.
Peng C.,Seagate Technology |
Ko K.D.,Seagate Technology
Optics Express | Year: 2017
We demonstrate the lightning-rod resonance of a lollipop near-field transducer integrated in magnetic writer for heat-assisted magnetic recording by collecting the twophoton excited photoluminescence (TPL) signal when excited by a pulsed femto-second fiber laser tuned to the desired mode resonance. The lollipop transducer consists of a round disk and a protruding peg to take advantage of the lightning-rod effect. It is found that the TPL signal is extremely sensitive to the peg length where even a 3-5 nm deviation from the optimal peg length halves the TPL signal. This method conveniently quantifies the optical performance of an NFT device in situ as a function of geometry with a resolution of better than the light wavelength (λ) divided by 200. © 2017 Optical Society of America.
Agency: GTR | Branch: EPSRC | Program: | Phase: Training Grant | Award Amount: 3.94M | Year: 2014
The achievements of modern research and their rapid progress from theory to application are increasingly underpinned by computation. Computational approaches are often hailed as a new third pillar of science - in addition to empirical and theoretical work. While its breadth makes computation almost as ubiquitous as mathematics as a key tool in science and engineering, it is a much younger discipline and stands to benefit enormously from building increased capacity and increased efforts towards integration, standardization, and professionalism. The development of new ideas and techniques in computing is extremely rapid, the progress enabled by these breakthroughs is enormous, and their impact on society is substantial: modern technologies ranging from the Airbus 380, MRI scans and smartphone CPUs could not have been developed without computer simulation; progress on major scientific questions from climate change to astronomy are driven by the results from computational models; major investment decisions are underwritten by computational modelling. Furthermore, simulation modelling is emerging as a key tool within domains experiencing a data revolution such as biomedicine and finance. This progress has been enabled through the rapid increase of computational power, and was based in the past on an increased rate at which computing instructions in the processor can be carried out. However, this clock rate cannot be increased much further and in recent computational architectures (such as GPU, Intel Phi) additional computational power is now provided through having (of the order of) hundreds of computational cores in the same unit. This opens up potential for new order of magnitude performance improvements but requires additional specialist training in parallel programming and computational methods to be able to tap into and exploit this opportunity. Computational advances are enabled by new hardware, and innovations in algorithms, numerical methods and simulation techniques, and application of best practice in scientific computational modelling. The most effective progress and highest impact can be obtained by combining, linking and simultaneously exploiting step changes in hardware, software, methods and skills. However, good computational science training is scarce, especially at post-graduate level. The Centre for Doctoral Training in Next Generation Computational Modelling will develop 55+ graduate students to address this skills gap. Trained as future leaders in Computational Modelling, they will form the core of a community of computational modellers crossing disciplinary boundaries, constantly working to transfer the latest computational advances to related fields. By tackling cutting-edge research from fields such as Computational Engineering, Advanced Materials, Autonomous Systems and Health, whilst communicating their advances and working together with a world-leading group of academic and industrial computational modellers, the students will be perfectly equipped to drive advanced computing over the coming decades.
Justice J.,Tyndall National Institute |
Bower C.,Semprius |
Meitl M.,Semprius |
Mooney M.B.,Seagate Technology |
And 2 more authors.
Nature Photonics | Year: 2012
The hard-drive and electronic industries can benefit by using the properties of light for power transfer and signalling. However, the integration of silicon electronics with lasers remains a challenge, because practical monolithic silicon lasers are not currently available. Here, we demonstrate a strategy for this integration, using an elastomeric stamp to selectively release and transfer epitaxial coupons of GaAs to realize III-V lasers on a silicon substrate by means of a wafer-scale printing process. Low-threshold continuous-wave lasing at a wavelength of 824 nm is achieved from Fabry-érot ridge waveguide lasers operating at temperatures up to 100°C. Single and multi-transverse mode devices emit total optical powers of >60 mW and support modulation bandwidths of >3 GHz. This fabrication strategy opens a route to the low-cost integration of III-V photonic devices and circuits on silicon and other substrates. © 2012 Macmillan Publishers Limited. All rights reserved.
Fan Y.,College of William and Mary |
Smith K.J.,College of William and Mary |
Lupke G.,College of William and Mary |
Hanbicki A.T.,Washington Technology |
And 4 more authors.
Nature Nanotechnology | Year: 2013
The ferromagnet/oxide interface is key to developing emerging multiferroic and spintronic technologies with new functionality. Here we probe the Fe/MgO interface magnetization, and identify a new exchange bias phenomenon manifested only in the interface spin system, and not in the bulk. The interface magnetization exhibits a pronounced exchange bias, and the hysteresis loop is shifted entirely to one side of the zero field axis. However, the bulk magnetization does not, in marked contrast to typical systems where exchange bias is manifested in the net magnetization. This reveals the existence of an antiferromagnetic exchange pinning layer at the interface, identified here as FeO patches that exist even for a nominally 'clean' interface. These results demonstrate that atomic moments at the interface are non-collinear with the bulk magnetization, and therefore may affect the net anisotropy or serve as spin scattering sites. We control the exchange bias magnitude by varying the interface oxygen concentration and Fe-O bonding. © 2013 Macmillan Publishers Limited. All rights reserved.
Zhang Y.,University of Pittsburgh |
Wang X.,Seagate Technology |
Chen Y.,University of Pittsburgh
IEEE/ACM International Conference on Computer-Aided Design, Digest of Technical Papers, ICCAD | Year: 2011
The rapidly increased demands for memory in electronic industry and the significant technical scaling challenges of all conventional memory technologies motivated the researches on the next generation memory technology. As one promising candidate, spin-transfer torque random access memory (STT-RAM) features fast access time, high density, non-volatility, and good CMOS process compatibility. However, like all other nano-scale devices, the performance and reliability of STT-RAM cells are severely affected by process variations, intrinsic device operating uncertainties and environmental fluctuations. In this work, we systematically analyze the impacts of CMOS and MTJ process variations, MTJ switching uncertainties induced by thermal fluctuations and working temperature on the performance and reliability of STT-RAM cells. A combined circuit and magnetic simulation platform is also established to quantitatively analyze the persistent and non-persistent error rates during the STT-RAM cell operations. Finally, an optimization flow and its effectiveness are depicted by using some STT-RAM cell designs as case study. © 2011 IEEE.
Peng C.,Seagate Technology
Journal of Applied Physics | Year: 2012
An optical near-field transducer composed of a rectangular patch and a protruded peg has been numerically studied for heat-assisted magnetic recording. This transducer strongly interacts with a planar solid immersion focusing field and efficiently couples optical energy into a recording medium in a region determined by the peg cross-section. The transducer is excited through the electric field predominantly normal to its edges. The optimal size of the rectangular patch is found to be a half-wave optical antenna in height and between half-wave and full-wave in width. © 2012 American Institute of Physics.
Peng C.,Seagate Technology
Optics Express | Year: 2015
Focal point shift in a solid immersion mirror of a high numericalaperture is experimentally demonstrated with a scanning near-field optical microscope. The solid immersion mirror focuses light by a two-dimensional parabolic reflective surface integrated in a planar waveguide. The focal point shifts inward along the optical axis for metallized surface. The amount of shift from its geometrical node depends on the wavelength of the incident light and is determined to be roughly one-fifth of the wavelength. © 2015 Optical Society of America.
Peng C.,Seagate Technology
Applied Physics Letters | Year: 2014
Surface-plasmon resonance of a lollipop near-field transducer integrated in a planar solid immersion mirror for heat-assisted magnetic recording has been characterized by measuring the amount of transmitted light in the polarization state orthogonal to the illumination in the far field. This resonance is compared to that probed with a photothermal measurement in near-field. The difference in peak wavelength between the two measures is only about 20nm. © 2014 AIP Publishing LLC.
Seagate Technology | Date: 2012-10-05
The embodiments disclose a block copolymer assembly structure, including a first pattern and second pattern with a first density of patterned features integrated in data and servo zones, a silicon substrate with thin film layers deposited thereon and patterned using the first density of first pattern and second pattern features and a template fabrication pattern with a second density greater than the first density created using ordered block copolymer periodic structures across a portion of the substrate.