High Track Density Research Articles

Narrow track recording in TbFeCo by laser-assisted magnetic recording using a blue laser

Laser-assisted magnetic recording technology enables narrower track recording and reproducing than the track width of a magnetic head. The size of the assisting beam is a critical issue for high track density in this technology. In this study, the possibility of the 100 kTPI recording was demonstrated with laser-assisted magnetic recording using a blue laser.

Analysis of radial runout for symmetric and asymmetric HDD spindle motors with rotor eccentricity

Radial runout of disk drive spindle is one of the major limiting factors in achieving higher track densities in hard disk drives. Mechanical, magnetic and their coupled origins, such as unbalanced mass, reaction forces and magnetic forces, introduce radial runout of spindle motors. In this paper, radial magnetic forces are calculated with respect to the various rotor eccentricities using analytic method. Based on the results of the radial magnetic forces, the radial runout of the spindle motor is analyzed using finite element and transfer matrices. Results show that an asymmetric motor has a worse performance on unbalanced magnetic forces and radial runout when mechanical and magnetic coupling exists.

Improvement of RRO using hybrid-type STW for hard disk drives

Accurate servo track writers (STWs) are indispensable for hard disk drives (HDDs) with high track density. We have developed a prototype hybrid-type STW which has two writing stages. In the first stage, master patterns are written on one surface of the master disk prior to drive assembly. In the second stage, the master disk is assembled with several raw disks in a HDD, and the servo patterns are written on the all disks, including the master, based on the master patterns. In this paper, a new servo compensator and a new algorithm to compensate for position signal nonlinearity are proposed. These are necessary items for the hybrid-type STW. Finally, experimental results are described showing that the hybrid-type STW reduces the maximum value of repeatable runout (RRO) and write-to-write track mis-registration.

Development of the pushpin free STW [servo track writer

In order to avoid thermal degradation in magnetic recording, it can be predicted that development will he made in the future toward higher track density (TPI) compared with that of bit density (BPI). For practical use of a super-high density TPI drive, it is essential to develop a servo track writer (STW). This paper introduces that we have successfully developed a high precision, highly efficient, and low-priced STW using a new sheet scale developed recently.

Piezo-based milliactuator on a partially etched suspension

This paper describes a piezo-based moving-suspension secondary actuator (called milliactuator) which provides increased servo bandwidth and reduced track-misregistration in a hard disk drive. The milliactuator comprises a pair of piezo-elements driving a relatively thick loadbeam that is partially etched in selected areas to form a honeycomb like structure. Partial etching allows more freedom in optimizing mass and stiffness to enhance the milliactuator dynamics. For a 18 mm (swage to dimple) milliactuator head gimbal assembly (HGA) with load/unload tab, we were able to achieve a first torsion frequency (T1) of 6 kHz. In a prototype drive populated with milliactuators, a new dual stage servo algorithm resulted in 60% higher bandwidth (0 dB open-loop crossover) compared to without the milliactuator. Further modifications to the milliactuator along with improvements in sampling rate and computational time could allow up to 100% higher servo bandwidth. The benefits and limitations of milliactuators are also discussed. The milliactuator provides a low cost, enhanced performance solution for high track densities.

Identification of contributors to HDD servo errors by measuring PES only

In this paper, disturbances, the source of TMR being the barrier to high track density of HDD are analyzed quantitatively using PES only without extra sensors. Disturbances are separated into RRO and NRRO, then, NRRO is separated into input torque disturbance, output disturbance, and noise. The effect of each disturbance on PES is compared. It is shown that PES NRRO measured in open-loop and in closed-loop can be used to calculate sensitivity transfer function. Using separated disturbances, PSD of PES RRO and NRRO are predicted for various gain levels in track following servo, and they are compared with PSD of PES measured in experiments. We propose that this can be used to predict servo performance accurately. Also addressed are some discussions on the differences between this work and the former contributing work.

TrueTrack/sup TM/ servo technology for high TPI disk drives

The performance of a high track density disk drive is critically limited by positioning errors induced by disk shift, spindle vibration and disk warp-based servomechanics. The spectrally rich error components can be compensated for by high-gain digital filters. The filters augment the basic function of a conventional controller. Using a novel method for initializing filters, precision tracking is achieved without compromising the settle out performance of a disk drive. An autonomous filter state propagation method during seek is shown to simplify the implementation process. A silicon servo chip has been designed to incorporate the key functions of the algorithm.

Crosstalk Evaluation in Laser-Assisted Magnetic Recording Using a Blue Laser.

Laser-assisted magnetic recording is an interesting method for narrowing a track pitch; in particular, crosstalk canceling in laser-assisted magnetic readout has a unique feature that it enables us to reproduce a narrower track than an assisting laser spot size. Shorter wavelength of the assisting laser promises the higher track density, accordingly. In this paper, we have demonstrated the crosstalk evaluation by using a blue laser for the assisting beam and obtained as high track density as 85ktpi.

４０Ｇｂ／ｉｎ｀２´を超える面内磁気記録再生特性に関する検討

We studied the read/write characteristics of a high-density longitudinal recording system at more than 40 Gb/in2. For accurate design of a recording system with high track density, we introduced noise/signal ratio by unit read track width as a parameter. This method was employed in the design of a 40 Gb/in2 recording system.Based on the design parameters, we fabricated CoCrPtX media with a layer structure optimized for low noise and thermal stability. A narrow shield Spin-Valve (SV) GMR head was also fabricated to achieve high linear recording density. System tests registered a density of 39.8 Gb/in2.After, we improved the media and the head, 53 Gb/in2 was demonstrated.

A multilayer inplane bending piezoelectric actuator for dual-stage head-positioning control system

A novel multilayer in-plane bending piezoelectric actuator, called a multilayer split-morph, was designed and fabricated by thick-film screen-printing technology for a dual-stage head-positioning actuator system in a hard disk drive. The design, operation and theoretical principles have been described. The electromechanical performance of the fabricated actuators has been evaluated. The actuation stroke of the actuator is in inverse proportion to the thickness of the piezoelectric layer. The highest displacement/voltage sensitivity of 0.154µmV-1 is achieved in a trapezoidal multilayer split-morph with a thickness of 35 μm in each piezoelectric layer. The corresponding fundamental resonance frequency of the sway mode is high at 47 kHz in the trapezoid actuator with dimensions of 10.14 mm length, 3.08 mm and 1.54 mm widths of the two parallel sides of the trapezoid. The multilayer split-morph was designed to integrate directly onto a modified suspension load beam. With the combined attractive performances indicated above, the batch fabricated multilayer split-morph can provide a low-cost but promising solution for achieving very high track densities in a hard disk drive by implementing a high performance dual-stage head-positioning actuator system.

An application of nuclear emulsions with automatic scanning

It will be shown that emulsions can be mass produced and automatically scanned in large quantities. CHORUS demonstrated the first large-scale application. Emulsions can be used to search for rare events in a high track density environment like DONUT. Heavy target masses as in OPERA are possible. The use of emulsions is getting more and more easier.

Quantitative image analysis of laminin immunoreactivity in skin basement membrane irradiated with 1 GeV/nucleon iron particles.

We previously reported that laminin immunoreactivity in mouse mammary epithelium is altered shortly after whole-body irradiation with 0.8 Gy from 600 MeV/nucleon iron ions but is unaffected after exposure to sparsely ionizing radiation. This observation led us to propose that the effect could be due to protein damage from the high ionization density of the ion tracks. If so, we predicted that it would be evident soon after radiation exposure in basement membranes of other tissues and would depend on ion fluence. To test this hypothesis, we used immunofluorescence, confocal laser scanning microscopy, and image segmentation techniques to quantify changes in the basement membrane of mouse skin epidermis. At 1 h after exposure to 1 GeV/nucleon iron ions with doses from 0.03 to 1.6 Gy, neither the visual appearance nor the mean pixel intensity of laminin in the basement membrane of mouse dorsal skin epidermis was altered compared to sham-irradiated tissue. This result does not support the hypothesis that particle traversal directly affects laminin protein integrity. However, the mean pixel intensity of laminin immunoreactivity was significantly decreased in epidermal basement membrane at 48 and 96 h after exposure to 0.8 Gy 1 GeV/nucleon iron ions. We confirmed this effect with two additional antibodies raised against affinity-purified laminin 1 and the E3 fragment of the long-arm of laminin 1. In contrast, collagen type IV, another component of the basement membrane, was unaffected. Our studies demonstrate quantitatively that densely ionizing radiation elicits changes in skin microenvironments distinct from those induced by sparsely ionizing radiation. Such effects may might contribute to the carcinogenic potential of densely ionizing radiation by altering cellular signaling cascades mediated by cell-extracellular matrix interactions.

Cross-recording reduction by trial recording on a magneto-optical disk

A technique for reducing cross-recording on data storage media with high track density is described. In order to detect cross-recording sensitively, an inverted mark pattern was first recorded on adjacent tracks and then synchronized with a normal recorded mark pattern on the central track. These patterns were repeatedly recorded as the recording power was increased. Readout signals of the recorded mark pattern were evaluated on the central track in each condition, and an optimum recording power was precisely determined from the maximum amplitude of the signals. When this new technique was applied to a magneto-optical disk, the bit error rate was reduced to less than 10/sup -4/. This is the first technique to reduce cross-recording by laser power only.

Crossover analysis of geophysical data in Bay of Bengal

Geophysical data (magnetic, gravity, and bathymetric) collected by international and national agencies along intersecting track lines in the Bay of Bengal show discrepancies that are analyzed and adjusted by crossover techniques. The original magnetic anomaly map over this region exhibits high gradients over the entire region, which do not fit with the known geological framework. The corrected map is devoid of artifacts, and the contours became smooth, which can be utilized for meaningful geological interpretation. The corrected free-air gravity map indicates improvements from the original in resolution with clear isolated anomalies in high track density areas. Corrected bathymetry does not show much improvement.

203 ハイブリッド型 STW による RRO の低減

Accurate servo track writer (STW) is indispensable for hard disk drives (HDDs) with high track density. We have developed a prototype of the Hybrid-type STW, which consists of two writing stages. In the first stage, master patterns are written on one surface of the master disk prior to drive assembly. In the second stage, the master disk is assembled with several raw disks in a HDD, and the servo patterns are written on the disks on the basis of the master patterns. This paper describes the design of servo system for the Hybrid-type STW and experimental results using a 2.5 type HDD. One of our results is that in comparison with the conventional STW, the Hybrid-type STW can suppress low frequency vibrations of ball bearings and reduce the maximum value of repeatable runout (RRO).

Recording performance and tribological evaluation of FIB defined tape recording heads

Aggressive growth in cartridge capacity in future generation tape drives requires amongst others, high linear recording and track densities. In order to improve the track misregistration (TMR) budget at smaller track pitches, the erase band and tolerances on the recorded track width need to be minimized. This can be achieved by "trimming" the write element to the desired track width by forming a longitudinal channel on either side of the clement on the tape bearing surface (TBS) using focused ion beam (FIB) milling. Cross-track measurements depict desired track widths with reduced forward-reverse track width asymmetry in the read-write-read head configuration. Investigation of the head/tape interface does not predict any undesirable effects. These channels capture debris and hence will reduce the recording loss, especially at higher linear recording densities, due to tape tenting over loose debris transported through the interface and near the recording elements. A conceptual channel design is presented that will further reduce debris near the recording elements during the life of the head.

Servo bandwidth and positioning accuracy design for high track density disk drives

Possibility of achieving positioning accuracy to meet the areal density of 40 Gb/in/sup 2/ has been studied. Stationary and nonstationary position errors are shown, and the servo design approaches have been proposed. A precise model of head-positioning system has been developed, and the required open loop servo bandwidth is estimated using the model. The experimental results using 2.5-inch HDD show that 750 Hz to 1 kHz servo bandwidth (open loop crossover frequency) is effective to achieve 40 nm positioning accuracy during track-following to meet 60 kTPI for 40 Gb/in/sup 2/.

Suppression of Disk Flutter by Squeeze Air Bearing.

Due to the need for an increase in rotational speed of hard disk spindles, disk flutter has become one of the largest disturbance for the head positioning servomechanism in high track density recording. As means of suppressing disk flutter, we propose a squeeze air bearing plate, which is positioned close to the rotating disk, and investigate the flutter-suppressing effect of the bearing both experimentally and theoretically. It was found that the squeeze air bearing plate with a radial width of 15 mm, angular length of 90 degrees, and bearing gap of 170 microns can decrease the disk flutter near the leading edge of the bearing to less than one third of the original disk flutter.

Fourier series-based repetitive learning variable structure control of hard disk drive servos

The demand for larger capacity and higher track density of hard disk drives requires significant improvement of actuator track following control. We developed a new repetitive learning system which synthesizes variable structure control (VSC) and repetitive learning during track following to improve tracking accuracy. Proof shows it completely nullifies the tracking error caused by bias force and repeatable runout. The proposed learning scheme uses the past VSC signal for updating instead of the past tracking error, and hence achieves a fast convergence. The Fourier series-based implementation selectively attenuates disturbance at given frequencies, hence avoids the influence from noise and other nonrepeatable factors.

A high track-density servo-access system for magnetic recording disk storage

This paper is concerned with an investigation of the feasible track-density potential of random-access magnetic-disk storage where magnetic-head positioning is essential. Primary emphasis is given to a novel, servo-access concept (closed-looped head-positioning control which includes the record member) for track location and registration. This servo concept has been investigated as a means of making possible automatic tracking as well as precision positioning. Inherent in such an access control technique is an enhanced suitability for interchangeable record members. Included in the discussion are design and performance results of an access model operated at 154 tracks per inch.