Recording Disks Research Articles

The Critical Conditions for Tribo-Demagnetization of Perpendicular Magnetic Recording Disk Under Sliding Contact

The critical conditions (critical stress and critical temperature) for the demagnetization of perpendicular magnetic recording disks were investigated. A tribo-demagnetization test of a perpendicular magnetic recording disk with a low load ball-on-disk system and the scan of the disk with the magnetic head were sequentially carried out to evaluate the critical force and sliding velocity for the occurrence of demagnetization, and the relationship between the two critical factors. Then, a finite element model using thermomechanical coupling was developed to calculate the critical stress and temperature of the magnetic disk based on the critical force and sliding velocity of the experiment result. Finally, a method based on the tribo-demagnetization test in combination with finite element analysis to calculate the critical conditions for the demagnetization of the perpendicular magnetic recording disk under sliding contact was proposed.

Use of Recordable Compact Discs to Fabricate Electrodes for Microchip-based Analysis Systems.

This work demonstrates that recordable compact discs (CDs) that contain gold as a reflective layer can be used as an electrode substrate for microchip-based analysis systems. A fabrication procedure that enables the reproducible patterning of multiple electrodes has been developed. It is shown that the microelectrodes can be integrated within a PDMS-based fluidic network and used for amperometric detection of electroactive analytes at both single and dual microelectrodes. A detailed comparison is made between the CD-based patterned electrodes and electrodes made by the traditional method of sputtering gold and titanium adhesion layers onto a glass substrate. It is also shown that mercury can be electrodeposited onto a CD-based microelectrode and the amalgam electrode used to selectively detect thiols. Finally, it is demonstrated that a decoupler for microchip-based electrophoresis can be made by electrodepositing palladium onto a gold electrode and a separate downstream gold working electrode can be used for amperometric detection. These CD-based patterned electrodes are attractive alternatives for situations where device cost is of a concern or sputtering facilities are unavailable.

A-14 表面張力の温度・膜厚依存性を考慮した液体超薄膜の変形特性 : 非定常線形長波方程式による3次元解析(口頭発表:ヘッド・ディスク・インターフェイス)

In the head-disk interface (HDI) of a hard disk drive (HDD), lubricant deformation affects flying characteristics of the head slider, as the flying height decreases. Therefore, it is very important to investigate the deformation and flow characteristics of lubricant on a recording disk. In particular, in heat-assisted magnetic recording (HAMR), laser heating of the lubricant induces surface tension distribution, which may cause deformation of the lubricant film. In this paper, we three-dimensionally analyzed the liquid film deformation caused by the temperature distribution by using the unsteady state and linearized long wave equation with consideration to temperature and film thickness dependence of the surface tension.

Multimode Surface Plasmon Excitations on Organic Thin Film/Metallic Diffraction Grating

In this work, we demonstrate multimode surface plasmon (SP) excitations by white light irradiation on metallic diffraction grating/plastic substrates. Recordable compact discs were used as the diffraction grating substrates on which silver films were deposited by vacuum evaporation. Since the grating pitch (1.6 µm) was larger than that of diffraction gratings commonly used for the excitation of SPs, multimode SP excitations due to several diffraction orders were observed simultaneously in the wavelength region from 400 to 800 nm. The obtained SP excitations were then compared with the calculated SP dispersion on the grating. The multimode SP excitations were further studied on spin-coated poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) thin film/silver grating substrates. An increased photoluminescence intensity due to SP excitations was observed on MEH-PPV/silver grating surfaces.

The synthesis and properties of highly organosoluble metal(II) complexes with hydrazone ligands derived from pivaloylacetonitrile

Using pivaloylacetonitrile as starting material and coupling component, a novel hydrazone ligand and four, highly organosoluble metal(II) complexes were synthesized via the procedure of oximation, cyclization, diazotization, coupling and metal chelation. In addition to elemental analysis, the structures of the novel compounds were postulated based on a series of spectroscopic methods. Smooth thin films of these metal(II) complexes on K9 glass substrates were prepared by spin-coating from 2,2,3,3-tetrafluoro-1-propanol solutions. The behaviour and relationships of the absorption bands both in solution and in spin-coated films are discussed; the thermal properties, photostability and the solubility of the metal(II) complexes were investigated. The synthesized Ni(II) complex exhibited a remarkable combination of excellent solubility and photostability, suitable absorption band and desirable thermal properties and, therefore, offers the potential of becoming a recording material for the recordable blu-ray disc system.

Failure of Brittle and Ductile Hard Disks Due to High Shock Levels

The failure due to accidental drop of magnetic recording disks made of brittle or ductile materials is of great interest in the design of small form factor hard disk drives. In this study, fracture of glass disks (brittle material) and plastic deformation of aluminum disks (ductile material) at very high shock levels caused by accidental drop are investigated using finite element analysis. It is found that failure inception for both disk types occurs at the inside perimeter of the disk. For glass disks, cracks are found to propagate toward the outer perimeter of the disk along distinct radial lines associated with the largest bending moment of the disk. The critical shock level at which failure originates increases with an increase in the clamp diameter, a reduction in the disk diameter, and an increase in the thickness of the disk. Some experimental results are presented to validate the numerical model.

Numerical Simulation of a “Spherical Pad” Slider Flying Over Bit Patterned Media

Bit patterned media are being studied as a promising approach for achieving storage densities beyond 1 Tb/in2 in magnetic recording disk drives. In this investigation we study the flying characteristics of a so-called ldquospherical pad sliderrdquo where a spherical pad is implemented on the top of the trailing pad of a traditional slider. We numerically simulate the flying characteristics and slider attitude of the spherical pad slider and compare this design with a traditional slider flying over the same bit patterned media. The effect of the design parameters of the bit pattern and the spherical pad on the flying characteristics is investigated.

Numerical Simulation of a Thermal Flying Height Control Slider With Dual Heater and Insulator Elements

Thermal flying height control (TFC) has recently been implemented in magnetic recording disk drives to reduce the flying height at the read/write element of magnetic recording sliders. This paper investigates the flying characteristics of a new TFC slider design with two heater and insulator elements. The flying height reduction of the slider is determined as a function of the placement and thermal characteristics of the heater and insulator elements. Simulation results show that for a constant heater power, the dual TFC heater with thermal insulators achieves a larger flying height reduction at the read/write element than the single TFC heater design.

Wear corrosion properties of DLC films with different C2H2 gas flows and CN layer of magnetic recording disks

The wear corrosion properties of magnetic recording disks which correlate to hardness, lubricant bonded ratio and friction coefficient of ultra thin diamond like carbon films deposited with ion beam hydrogenated carbon and sputtering nitrogenated carbon respectively when, deposited on NiP/Al substrates were investigated. Results show that the ion beam deposition hydrogenated carbon (IBD–CH) films prepared at lower C2H2 gas flowrates or 1 nm sputter nitrogenated carbon (CN) deposited on 2 nm IBD–CH layers, exhibit a higher Raman intensity ratio Id/Ig and G peak frequency. The hardness of diamond like carbon films increases with decreasing G peak frequency and intensity ratio IdI/g. The lubricant bonded ratio is dramatically increased from 12 to 38% when a 1·0 nm CN is deposited on a 2·0 nm IBD–CH layer. IBD–CH with 35 sccm C2H2 gas flowrate which shows the lowest weight loss, the lowest friction coefficient and the best wear corrosion resistance because of the optimised lubricant bonded ratio and the highest hardness.

Direct near-field optical investigation of phase-change medium in blue-ray recordable and erasable disk

The authors report a direct examination of recorded marks in blue-ray recordable and erasable disks with scattering-type scanning near-field optical microscopy. The optical contrasts of the crystalline and amorphous regions of the phase-change layer match with the prediction based on their optical constants. The determined spatial optical variation in the recorded marks reflects the intensity profile of the recording laser beam. The identified nanometer-sized optical features are shown to correspond to 10 nm-sized crystalline domains within the amorphous recorded marks. The revealed near-field signatures show a potential influence on the carrier-to-noise ratio of this optical storage medium.

Measurement of edge verticality of optical recording bits on blu‐ray discs using scanning probe microscopy

This work investigates recording bits on recordable and rewritable blu-ray discs using atomic force microscopy and conducting atomic force microscopy with high contrast, respectively. The geometric structure of the recording bits is clearly observed in images, which, when coupled with cross-section analysis, yields precise bit dimensions, and edge horizontal extended length values. The microscopic results are a valuable reference for increasing the recognition rate of digital signals in optical storage media. Furthermore, such a rapid and convenient measuring mode is an indispensable research tool for developing new recording materials and improving formation mechanisms.

Optimal Design of Slider Air-Bearing for Discrete Track Recording Technology

This paper suggests a design methodology for slider air bearings over a discrete track recording (DTR) disk using a simplified static analysis including the flying-height (FH) loss equation instead of a computationally expensive, time consuming transient dynamic analysis. Because a slider over a DTR disk has different flying characteristics than a slider over a continuous track recording (CTR) disk, the design of the slider requires modification. However, it is challenging to dynamically simulate slider air bearings over a DTR disk. Furthermore, it is nearly impossible to design the slider using an expensive dynamic analysis as a solver. Therefore, we define the flying characteristics of the DTR slider as a function of that of the CTR slider by using the FH loss equation based on averaged flow effect. A design optimization problem is formulated to meet the design requirements of the DTR slider, which include target FH, FH flatness, altitude FH drop, pitch and roll angle ranges, and altitude pitch drop. The design problem is changed to an inverse problem using a conventional static analysis for a CTR disk instead of an expensive dynamic analysis for a DTR disk. Simulation results showed that the optimally designed DTR slider can meet the target FH while satisfying all design requirements over the entire recording band.

Mechanism study of scratch-induced demagnetization for perpendicular magnetic disks

The mechanism for scratch-induced demagnetization was studied in perpendicular magnetic recording (PMR) disks. Scratches, which may occur on a disk’s surface during head/disk contact, cause demagnetization, which results in read/write errors. Scratch-induced demagnetization is thus a serious issue. Scratch depths and demagnetization were compared using prototype PMR disks. We confirmed that demagnetization due to scratch depths were different because of the disk structures such as the cap and granular layers through observation using atomic force and magnetic force microscopy. We found that crystal planes in the grains of the granular layer slipped under the scratches, where demagnetization was observed from transmission electronic microscopy cross-sectional analyses of those disks. Scratch-induced demagnetization was mainly caused by plastic deformation of the grain due to crystal plane slippage in the granular layer. Therefore, a grain structure that is dense and cannot easily slip is needed to produce reliable hard disk drives.

Reduced-State Sequence Estimation with Level Adaptation for High-Density Disc

We report a new data-reproducing scheme for a high density of over 40 Gbytes with a commercial Blu-ray recordable disc. Bit error rates (bERs) of 3×10-5 and 3.3×10-3 with 45 and 50 Gbytes, respectively, were experimentally obtained using this new data-reproducing scheme, which indicates the possibility of achieving 50 Gbytes data storage with a commercial single-layer Blu-ray disc.

Strain imaging of a magnetic layer formed on an air bearing surface of a hard disk drive head for perpendicular recording

The detection and imaging of magnetic-field-induced strains using scanning probe microscopy enable us to observe magnetic domain structures. A perpendicular recording head in a hard disk drive has been observed in this method in order to investigate distribution of magnetic fields applied to a recording disk. In perpendicular recording, the magnetic field circuit consists of a main pole, a main pole tip, a soft magnetic underlayer (SUL) in the disk and a return pole. The authors formed a magnetic layer on the air bearing surface of the head, and observed the layer subjected to magnetic fields by the write head. The layer plays a role in the SUL and constitutes a part of the magnetic field circuit. The authors imaged the magnetic-field-induced strains in the layer and discussed field distribution in recording media.

Study of slider-defect interaction at ultralow flying height by dynamic flying height control

In this study, the interaction of the magnetic head slider and magnetic disk defects were studied as the function of the head flying height controlled by the dynamic flying height (DFH) control method. In the conventional glide test, the flying height is set as a function of the rotational velocity. However, in the glide test using the DFH control method, the flying height could be set as a function of DFH power on a constant rotational velocity. A magnetic disk with two types of defects—a crater and a 5nm bump—was prepared. The acoustic emission (AE) signal at the slider-defect contacts from the conventional glide test and the DFH glide test were then compared. The results of the experiment indicated that the DFH glide test could detect these defects at a few nanometers flying height, but the conventional glide test could not detect them. This was because the AE signal burst below a flying height of 3nm. The AE signal output of the DFH glide test was higher than that of the conventional glide test, and the AE signal of the defect contact increased at a greater rotational velocity. It was concluded that the DFH control glide testing was one of the most important techniques for the future high-density recording disks.

Controlling multidomain states to enable sub-10-nm magnetic force microscopy

The letter reports experimental data to demonstrate magnetic force microscopy (MFM) with sub-10-nm resolution under ambient conditions. To achieve this record high resolution, multidomain states in a nanomagnetic probe were controlled. Two demagnetized (multidomain) FePt (45/55) films sputtered on a silicon probe and separated by an 8 nm thick MgO layer were further annealed at temperature of 650 °C to trigger the high-anisotropy L10 phase. A field of above 2 T was applied to drive the probes into a saturated “single-domain” state. The multidomain probes were equivalently compared with state-of-the-art conventional MFM probes via comparative imaging of benchmark magnetic recording disks.

Scratch-Induced Demagnetization of Perpendicular Magnetic Disk

The mechanism of scratch-induced demagnetization was studied in perpendicular magnetic recording (PMR) disks. These scratches, which may occur on the disk's surface during head/disk contact, cause demagnetization that results in read/write errors. The scratch-induced demagnetization is thus investigated by the scratch test, observation of atomic force microscopy and magnetic force microscopy, and analysis of transmission electronic microscopy. It was found that the angle of the grain in the recording layer, which is vertically orientated on a PMR disk, was tilted under the scratch. These analyses revealed that scratch-induced demagnetization is caused mainly by plastic deformation which results in grain tilt in the recording layer, rather than by stress. Therefore, a dense and not-easily titled grain structure in the recording layer is needed to produce a reliable hard disk drive (HDD).

Analytical prospect of compact disk technology in immunosensing

A sensitive and versatile methodology involving recordable compact disks as molecular screening surfaces and a standard optical CD/DVD drive as detector, is reported. Quantitative immunoanalysis, in microarray format, of a cancer marker (alpha-fetoprotein, AFP) and a selective herbicide (atrazine) on four types of audio-video disc was conducted. Enzyme or gold nanoparticle-labeled antibodies were used as tracers, forming a precipitate on the sensing disk surface. The principle of disk reading is based on capture of analog signals with the disk drive that were proportional to the darkness of the immunoreaction product. Detection limits for AFP (8.0 microg L(-1)) and for atrazine (0.04 microg L(-1)) were under the threshold needed to detect nonseminomatous testicular cancer, and below the maximum E.U. residue limit for drinking water, respectively. The described methodology improves the previous developments using CDs and highlights the enormous potential of immunoassay methods using standard audio-video disk surfaces in combination with the CD/DVD drive for clinical analysis, drug discovery, or high-throughput multiresidue screening applications.

Optical Head Using Single Objective Lens for Four Types of Optical Disks

An optical head using a single objective lens for Blu-ray disc (BD), high-density digital versatile disc (HD DVD), digital versatile disc (DVD), and compact disc (CD) has been developed, which is suitable for high-speed recording and reading. A relay lens unit, which consists of two convex lenses and one concave lens, corrects the spherical aberration and realizes high light power efficiency for each disk. A numerical aperture (NA) control element, which contains a liquid crystal aperture and a wavelength selective aperture, controls the NA of the objective lens for each disk. A coma aberration caused by the objective lens shift is detected based on differential phase detection signals for read-only disks and push–pull signals for recordable or rewritable disks, and is corrected by moving one of the lenses in the relay lens unit by an actuator. A diffraction-limited focused spot and good readout signal characteristics were obtained for each disk, and the validity of this optical design has been demonstrated.