Recording Density Research Articles

Back heating effect of media hot spot at nanoscale head–disk interface

Heat-assisted magnetic recording (HAMR) is one of prospective high density recording technologies in current hard disk industry due to its theoretical potential. In this paper, we develop a new heat transfer model which enables us to predict near field thermal conduction and radiation across head–disk interface accurately. This new model, together with an Ansys finite element (FE) model for an integrated HAMR slider and an optical absorption model for temperature profile of media hot spot, is then used to solve for temperature rise and thermal protrusion on the slider body. Our simulation studies show that larger hot spot and smaller head–disk spacing will increase the temperature and thermal protrusion on the slider’s head components. When thermal radiation effect is further considered, this increment in temperature and protrusion becomes more significant; especially at very small gap below 1 nm. Therefore, the back heating effect from media hot spot should be addressed carefully for improving the reliability of HAMR head–disk interface.

Suppressing FePt order-disorder structural phase transition temperature by Ag doping: First principles investigation for enhancing magnetic recording density

ABSTRACTIn this work, we used density functional theory to study the structures, formation energy and order–disorder structural transition temperature (To) of L10 FePt with Ag additive. The results show that an Ag atom substituting for a Fe site is more energetically preferable than that of substituting for a Pt, thus Ag atom should replace Fe site. We found that To is significantly suppressed by Ag impurity because of the increasing in configurational entropy, whereas the magnetism tends to decrease due to the absence of some Fe atom in doping processes. The decrease in To could open the opportunity to prepare FePt with lower temperature and small grain size for the high density magnetic recording media application.

Lens-free laser nanopatterning of large-scale metal film areas with structured light for biosensing applications.

Pulsed laser nanotexturing of metal films represents an ultra-fast, high-performance and cost-effective processing technology for fabrication of various functional surfaces widely used in plasmonics, biosensing, and photovoltaics. However, this approach usually requires high-NA lenses to focus a laser beam onto a few-micron spot as well as a micropositioning platform to move this spot along the sample surface, which increases the cost of the produced functional surfaces and limits the performance of laser-assisted nanotexturing techniques. In this paper we report on a laser-assisted technology for the fabrication of large-scale nanotextured metal substrates. In our approach, speckle-modulated patterns obtained by passing nanosecond laser pulses through the simplest diffusive object were utilized to cover a thin gold film with closely packed micron-sized structures - nanojets, nanobumps and through holes - previously reported only for single-shot nanoablation with tightly focused laser beams. The presented easy-to-implement technology, being one of the simplest of ever reported, since it requires neither focusing lenses nor micropositioning platforms, was shown to provide a way to pattern millimeter-size areas with the nano-sized jets at an average recording density of 35∙103 nanostructures per square millimeter and an average recording speed of 4.5·103 nanostructures per pulse. The fabricated nanotextured Au substrates were shown to yield spatially uniform surface-enhanced fluorescence signals from the Rhodamine 6G organic dye with an averaged 5.3-fold enhancement factor as compared with non-treated Au surface.

Two high-density recording methods with run-length limited turbo code for holographic data storage system

Two methods for increasing the data capacity of a holographic data storage system (HDSS) were developed. The first method is called “run-length-limited (RLL) high-density recording”. An RLL modulation has the same effect as enlarging the pixel pitch; namely, it optically reduces the hologram size. Accordingly, the method doubles the raw-data recording density. The second method is called “RLL turbo signal processing”. The RLL turbo code consists of trellis modulation and an optimized convolutional code. The remarkable point of the developed turbo code is that it employs the RLL modulator and demodulator as parts of the error-correction process. The turbo code improves the capability of error correction more than a conventional LDPC code, even though interpixel interference is generated. These two methods will increase the data density 1.78-fold. Moreover, by simulation and experiment, a data density of 2.4 Tbit/in.2 is confirmed.

High-density channel model and detection method for signal readout from super-resolution near-field structure discs

Although a readout method using the super-resolution near-field structure (super-RENS) effect can overcome diffraction limits, readout characteristics for greatly surpassed high-density conditions do not become clear, because a high-density channel function having a differential response property is superimposed on a normal readout function. We propose a high-density channel model to indicate the properties of the super-RENS effect directly. This model can be expressed as a differential response function using the finite impulse response (FIR) filter model. It expresses the super-RENS readout process, which is divided on the basis of recording densities such as high and normal Blu-ray Disc™ densities. We estimated the properties of super-RENS readout signals by comparison between theoretical expressions and experiments. Results show that good signal quality require readout signals having sharp peaks and smaller offsets. We also evaluated the channel model by adding an adaptive FIR filter and a Viterbi decoder by simulations. Results show that the super-RENS disc can achieve a fourfold higher recording density if the signal-to-noise ratio (S/N) is improved to 6 dB in the case of partial response (PR) (1 + D + D2).

Towards low energy consumption data storage era using phase-change probe memory with TiN bottom electrode

Abstract Phase-change probe memory has been extensively regarded as one of the most prospective candidates to satisfy the recording density requirement from the incoming age of big data. However, in spite of recent advances, the energy consumption of phase-change probe memory still remains fairly high due to the use of the diamond-like carbon bottom electrode usually having a relatively high electric resistivity. In this case, the possibility of using titanium nitride to replace the diamond-like carbon as the electrode materials is investigated in this paper. The thickness and time-dependent resistivity of titanium nitride film is measured, allowing for a more conductive characteristic and a better stability than diamond-like carbon film at the same condition. Consequently, the writing of crystalline bit using the previously designed phase-change probe memory architecture but with titanium nitride bottom electrode is performed experimentally, and results show that using titanium nitride as bottom electrode would enable an achievement of ultra-high recording density with lower energy consumption than the phase-change stack with diamond-like carbon electrode.

Effect of Reader Sensitivity Rotation in TDMR With Head Skew

The 2-D magnetic recording (TDMR) by shingled magnetic recording (SMR) draws attention as a technology to increase the recording densities in a hard disk drive. The magnetization pattern is curved by the write field at the corner of the writer in SMR, and the information to read/write (R/W) channel performance is feared. Therefore, it is possible that the bit error rate performance is improved by fitting the reader sensitivity to the bit shape. In this paper, we evaluate the effect of reader sensitivity rotation in the TDMR R/W channel with head skew under a specification of 4 Tb/in2 by computer simulation, applying the low-density parity-check coding and the iterative decoding system with the 2-D finite impulse response filter. The results show that the rotated reader sensitivity fits the recorded bit magnetization shape, and the error-free skew range increases to $-3^{\circ }\sim 6^{\circ }$ . Therefore, the reader sensitivity rotation is considered to be an effective way to improve the skew margin in the TDMR system.

Synthesis of Co-Zr doped nanocrystalline strontium hexaferrites by sol-gel auto-combustion route using sucrose as fuel and study of their structural, magnetic and electrical properties

Sol-gel auto-combustion route using sucrose as fuel has been employed to synthesize nanocrystalline particles of SrZrxCoxFe(12−2x)O19 (0.0≤ x ≤1.0). The characterization of these materials has been done by TGA-DTA, FT-IR, XRD and EDS. SEM and TEM techniques have been used to study the structure and morphology. Magnetic properties have been investigated by VSM and Mössbauer spectroscopy (MS). The influence of calcination temperature on morphology and magnetic properties of samples is studied in a wide temperature range of 500–1100°C. XRD analysis indicates the formation of pure single phase hexagonal ferrites at 900°C. The crystallite size calculated using Scherrer equation lies in a narrow range of 21–33nm. The crystallite size is small enough to obtain a suitable signal to noise ratio in high density recording medium. Substitution of Zr and Co for Fe has been found to have a profound effect on the structural, magnetic and electrical properties. Upon substitution saturation magnetization (MS) first increases from 62.67emu/g to 64.84emu/g (up to x=0.4) followed by a decrease to 49.71emu/g at x=1.0. There is a slow fall in coercivity (HC) from 5785.74 (x=0.0) to 1796.51Oe (x=1.0). Dielectric constant, dielectric loss tangent and AC conductivity in the frequency range 20Hz to 120MHz have been studied for all the compositions (x=0–1.0). The composition and frequency dependence of these dielectric parameters has been qualitatively explained.

Advanced Dual-Free-Layer CPP GMR Sensors for High-Density Magnetic Recording

All-metal current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) read sensors with a shield-to-shield spacing (S2S) of 16–21 nm and a narrow track width of down to 25 nm were fabricated using ferromagnetic CoFeMnSi Heusler-alloy-based spin valves. Room temperature GMR ratios from these read sensors are obtained of up to 6% and 14–24% ( $\Delta \textrm {RA}= 7.1$ –12.0 $\text{m}\Omega \mu \text{m}^{2}$ ) at $\mathrm {S2S} = 16$ and 21 nm, respectively. Studies and results of electron transport and CPP GMR support the sustainability and scalability of the CPP GMR process for Tb/in2 the areal density of magnetic recording. A universal parameter defined as magnetic resistivity for a sensor device, $\Delta \textrm {RA}/\mathrm {S2S}$ in ohm micrometers, is proposed to gauge the practically and rationally applicable CPP GMR for the read sensor process. The investigation of the CPP GMR operation range and micromagnetic simulation demonstrates the feasibility of the CPP GMR read sensors at $\mathrm {S2S} = 21$ nm for sustaining 1.0 Tb/in2 and of those at $\mathrm {S2S}= 16$ nm for marginally supporting 2.0 Tb/in2 the areal density of magnetic recording, The future path to and potential of the technology for ever increasing areal density beyond 2.0 Tb/in2 are addressed with emphasis on the importance of further enhancing the CPP GMR for process margin improvement.

High-density ferroelectric recording using a hard disk drive-type data storage system

Ferroelectric probe data storage has been proposed as a novel data storage method in which bits are recorded based on the polarization directions of individual domains. These bits are subsequently read by scanning nonlinear dielectric microscopy. The domain walls of typical ferroelectric materials are quite thin: often only several times the lattice constant, which is advantageous for high-density data storage. In this work, high-density read/write (R/W) demonstrations were conducted using a hard disk drive-type test system, and the writing of bit arrays with a recording density of 3.4 Tbit/in.2 was achieved. Additionally, a series of writing and reading operations was successfully demonstrated at a density of 1 Tbit/in.2. Favorable characteristics of ferroelectric recording media for use with the proposed method are discussed in the latter part of this paper.

A flow cytometric method to measure prokaryotic records in ice cores: an example from the West Antarctic Ice Sheet Divide drilling site

ABSTRACTMicroorganisms were the earliest inhabitants on our planet that occupy nearly every environment, and play a major role in biogeochemical cycles. Despite their global importance, there remains a paucity of data on microbial responses to long-term environmental and climatic changes. Microorganisms are known to be immured in glacial ice, but no high-resolution temporal records of their density exist, owing in large part to the lack of appropriate clean methodology that allows for rapid analysis of samples over depth. We describe a clean and time efficient method that can produce a high-temporal resolution record of prokaryotic density archived in ice cores. The method combines acquisition of discrete samples using a continuous ice-core melting system coupled with flow cytometry (FCM) of DNA-stained samples. Specifically, we evaluate the performance of the FCM measurement technique in terms of specificity, precision, accuracy and minimum detection limits. Examples from the West Antarctic Ice Sheet Divide ice core are included to show the efficacy of the method.

Comparison of climate datasets for lumped hydrological modeling over the continental United States

Summary Climate data measured by weather stations are crucially important and regularly used in hydrologic modeling. However, they are not always available due to the low spatial density and short record history of many station networks. To overcome these limitations, gridded datasets have become increasingly available. They have excellent continuous spatial coverage and no missing data. However, these datasets are usually interpolated using station data, with little new information besides elevation. Furthermore, minimal validation has been done on most of these datasets. This study compares three such datasets covering the continental United States to evaluate their differences and their impact on lumped hydrological modeling. Three daily time step gridded datasets with resolutions varying between 0.25° and 1 km were used in this study – Santa-Clara, Daymet and CPC. The hydrological modeling evaluation of these datasets was performed over 424 basins from the MOPEX database. Results show that there are significant differences between the datasets, even though they were essentially all interpolated from almost the same climate databases. Despite those differences, the hydrological model used in this study was able to perform equally well after a specific calibration to each dataset. While there were a few exceptions, by and large, Nash–Sutcliffe efficiency metrics obtained in validation were not statistically different from one database to the other for most basins. It appears that there are no reasons to favor one dataset versus another for lumped hydrological modeling, and that these datasets perform just as well as using the original station data.

Design and Implementation of a Hybrid Shingled Write Disk System

Disk data density improvement will eventually be limited by the super-paramagnetic effect for perpendicular recording. While various approaches to this problem have been proposed, Shingled Magnetic Recording (SMR) holds great promise to mitigate the problem of density scaling cost-effectively by overlapping data tracks. However, the inherent properties of SMR limit Shingled Write Disk (SWD) applicability since writing data to one track destroys the data previously-stored on the overlapping tracks. As a result, various data layout management designs have been proposed. In this paper, we present a hybrid wave-like shingled recording (HWSR) disk system, which can improve both the performance and the capacity of a shingled write disk. We propose a novel segment-based data layout management and a new wave-like shingled recording that overlaps adjacent tracks from two opposite radial directions. This new scheme can not only efficiently reduce the write amplification, but also double the areal density of conventional circular log-based shingled recording. A new replacement policy based on least write amplification is also devised to manage the hybrid system to effectively eliminate the performance degradation. Our measurements on HWSR implemented in Linux kernel 2.6.35.6 show that it provides superb performance. For example, HWSR reduces the average I/O response time by an order of magnitude compared to S-block for Financial1 trace, and provides up to 3.7 speedup over standard hard disks without using shingled magnetic recording technology.

Simulation of HGA Vibration Characteristics Inside the Helium-Filled Hard Disk Drive

The reliability and stability of hard disk drives (HDDs) are especially important as the areal recording density is rapidly increasing and target to 10 Tb/in2 in the future. The vibrations of the head gimbals assembly (HGA) are inevitable by internal fluid flow and external shock impulses. In this paper, a 3-D finite-element model of an HDD is developed. The internal flow-induced HGA vibrations are investigated by a fluid–structure interaction approach. The external shock-induced vibrations of HGA are also analyzed. The investigated filling gases in the HDD include air and helium.

Finite element analysis simulations of thermomechanical head-disk interface contact in thermal flying-height control slider design

In order to achieve higher recording density in hard disk drive (HDD), thermal flying-height control (TFC) slider design has been used to reduce the physical spacing between the read/write elements in the slider and the rotating disk surface. During the read/write operation in hard disk drives, the intermittent contact at the head-disk interface (HDI) directly affects its performance and reliability. In this study, the thermomechanical micro-contact between a TFC slider and a disk defect was systematically investigated through finite element analysis (FEA) modeling and simulations. The thermal actuation technology in a TFC slider was incorporated into the FEA model to enable the thermal protrusion of read/write sensors outward the air bearing surface (ABS). In order to obtain the scientific relationship between the thermal protrusion and the resulting HDI contact behavior, parametric FEA simulations were carried out based on the 23-factorial design of experiment (DOE), where the surface temperature rise and the residual deformation on the TFC slider surface were used as the output parameters. From the statistical data analysis, it could be found that the larger thermal protrusion resulted in higher temperature rise and more residual deformation.

Nanostructured Metal Substrates Fabrication for Surface Enhanced Fluorescence Using the Nanosecond Speckle-Modulated Laser Pulses

Nanosecond speckle-modulated laser pulses were applied to fabricate nanotextured metal substrates for surface enhanced fluorescence (SEF) applications. The speckle-modulated patterns obtained by passing the laser nanosecond pulse through the simplest diffusive object were found suitable for fast large-scale texturing of metal films with micron-sized structures - nanojets, nanobumps and submicron through holes, previous reported only for single-shot nanoablation with tightly focused beams. The optimal regime for pattering the mm-scale areas of Au films with nanojets with an averaged recording density of 105 nanojets per square millimeter were determined and realized. The fabricated nanotextured Au substrates demonstrate spatially uniform SEF signal from the Rhodamine 6G organic dye with averaged 5-fold enhancement factor being compared with unmodified Au surface.

TMR Sensitive Equalization for Electronic Servoing in Array-Reader-Based Hard Disk Drives

To achieve enhanced recording density, hard disk drive industry is transitioning into array-reader-based magnetic recording (ARMR) technology, which provides an enhanced signal-to-noise ratio for data detection by exploiting the diversity in signal, interference, and noise provided by the multiple read-elements. A 2-D equalizer, which is the heart of ARMR signal processing, acts to electronically steer the array-reader to provide optimum signal pickup from the track to result in better error-rate performance. To realize this enhanced performance, the 2-D equalizer should be matched to the reader location on the track, which cannot be guaranteed in practice due to track misregistration (TMR) arising from the servo control system. To mitigate this, we present an electronic servoing scheme that estimates the location of the dual-reader on a per-fragment basis and uses this to transform the reference equalizer to a new equalizer that is matched to the estimated location, hence, the name TMR sensitive equalization. Performance evaluation done ~1 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> shows that the proposed approach significantly improves read performance in the presence of large read-/write-TMR even without requiring additional adaptation cycles for the 2-D equalizer.

Patterned Magnetic Recording Media – Issues and Challenges

ABSTRACTThe conventional magnetic recording approached the physical frontiers of the recording density. The magnetic recording must face the famous trilemma: In order to increase the recording density, smaller grain volumes are needed, but in order to ensure the thermal stability of recorded information, the anisotropy constant should be increased accordingly; what results is an increased anisotropy field, which requires higher writing fields. Such fields are unavailable with the maximum saturation magnetization obtainable with the magnetic materials of the current heads. In order to overcome these problems, new media structures have been proposed. The most promising is the bit-patterned magnetic media (BPM), intensively studied over the last years with the aim of obtaining obtain an ultra-high recording density of hard-disk drives. A BPM comprises monodisperse high-anisotropy nano-particles in a self-organized patterning. They have a higher thermal stability, a lower noise and a higher signal resolution, which leads to a higher recording density and a better SNR. They eliminate the transition noise and, due to the large fraction of the bit volume occupied by the magnetic dots, improve thermal stability. Nevertheless, some important issues such as long-range patterning, control of the surface roughness, signal readout, etc., remain critical problems to solve. Another challenge is the fact that recording on BPM is sensitive to the material and geometry parameter fluctuations that may lead to additional constraints and require tight synchronization of the write-field misregistration time and bit positions. A possible route to higher recording densities is to use a multilevel recording, where more than two states are stored per dot.

High density holographic versatile disc (HVD) system using collinear technologies

Collinear Holography was proposed by OPTWARE Corporation, in which the information and reference beams were aligned co-axially and modulated by the same SLM. With this unique configuration the optical pickup can be designed as small as the DVD's, and can be placed on one side of the recording disc. A 2-dimensional digital page data format was used and the shift-multiplexing method was employed to increased recording density of HVD. As the servo technology is being introduced to control the objective lens to be maintained precisely to the disc in the recording and the reconstructing process, a vibration isolator is no longer necessary. In HVD, the pre-formatted meta-data reflective layer was used for the focus/tracking servo and reading address information, and the dichroic mirror layer was used for detecting holographic recording information without interfering with the preformatted information. Experimental and theoretical studies suggest that the holographic material is very effective to increased recording density of the system. HVD will be compatible with existing disc storage systems, like CD and DVD, and enable us to expand its applications into other optical information storage systems.

インナーロータ型スピンドルにおける空気軸受の特性解析

Recently, amount of information is increasing every year all over the world. Therefore, the data centers which can manage information are increasing too. Hard disk drives are used in the data centers because of their reasonability and high recording density. On the other hand, electric consumption has been increased with increasing data center amount. Therefore, the new structure of a spindle motor applied air bearing is proposed in this study. As new structure of the spindle motor, inner rotor is applied instead of outer rotor. The new structure is expected improve the characteristics of the air bearing. In this paper, the characteristic of the air bearing which is mounted new structural spindle motor was analyzed. In addition, this paper studied theoretically about effectivity of the air bearing. As a result, air bearing friction torque is lower than oil bearing one. In addition, angular stiffness of air bearing is larger than oil bearing.