Kohki Noda

Novel Nrro Minimization Algorithm For An Ultra-high-density Servo Track Writer

Since the introduction of magnetoresistive (MR) heads, the areal density of hard disk drives (HDDs) has been increasing at a rate around 60% a year, and the track density is increasing at roughly half that rate. The servo track writer (STW), which is used to write accurate servo patterns for head positioning on the surfaces of disks in the HDD, is a key instrument in this regard. A novel algorithm for the STW of the sector-servo architecture, using an accurate air-bearing motor and rotary-positioner, and a repeatable runout (RRO) compensation method, is proposed in order to minimize the effects of nonrepeatable runout (NRRO) components, which are generated by a spindle motor and other mechanical components of the HDD, and have a dominant influence in retarding track density growth.

Increasing electronic display information content: an introduction

This paper is an introduction to a group of eighteen papers on electronic display research and development within IBM. Displays in the computer industry and some of the directions display research is taking are discussed. A motivation for the IBM work on increasing the spatial resolution and image content of various liquid crystal displays is offered. Finally, the significant progress in IBMs display technology over the last decade is discussed.

Recording characteristics of rigid disks with Co-based alloy films using durable silicon substrates

Co-based alloy films using silicon substrates were investigated for high-density magnetic recording disks. Silicon-disk substrates have several advantages, such as microscopically ultraflat surface roughness in the range of 1 nm or less, which results in a lower than ever flying height, lithographic fabrication of grooves for servo patterns, minimal outgassing from the substrates, higher substrate temperatures than for aluminum or glass substrates, and higher mechanical strength than for glass substrates. Recent Si substrates are mechanically durable because they have fewer microcracks than previous ones as a result of large improvements in machining processes such as chamfering and holing. In this study, Co85Cr13Ta2/Cr films were deposited by facing targets sputtering on 2.5 in. Si substrates at a substrate temperature of 100 °C and an argon gas pressure of 0.2 mTorr. A carbon protective layer and Z-DOL lubricant were applied on top of the magnetic layers. Their magnetic properties and recording characte...

Microstructure and noise characteristics of Co-Cr-Ta films on ultraflat glass substrates for longitudinal recording disks

Co–Cr–Ta/Cr bilayered films for longitudinal recording disks were deposited by facing targets sputtering (FTS) on 2.5 in. and ultraflat disk substrates of durable single-crystal silicon at temperature Ts of 100 °C and Ar pressure PAr of 0.2 mTorr. TEM observation of the films revealed ultrafine microstructures, and grain boundaries were unclear. The noise and recording characteristics of those disks were comparable with those of very high-performance disks with Co–Cr–Pt films, with coercivity Hc of 2.4 kOe, employed as a reference, even though the Co–Cr–Ta films exhibited macroscopic Hc of only 800 Oe. In this study, Co85Cr13Ta2/Cr bilayered films with the same composition as the above-mentioned disks were deposited by plasma-enhanced (PEFTS) on 2.5 in. and glass–ceramic substrates with ultraflat surface and tough durability at Ts of 100 °C to obtain better microstructure, signal-to-noise ratio (SNR), and surface flatness, with consequent lower flying height, than those on Si substrates, thus making it po...

Protective carbon films deposited by dc-bias facing targets sputtering with microscopic ultraflatness and strong sp3 coordination

Carbon thin films were deposited on hard disks as protective layers by facing targets sputtering (FTS), and their characteristics were evaluated to determine whether they would be suitable protective layers for thin-film magnetic recording media. The performance and lifetime of a hard disk drive (HDD) are intimately related to the head-disk interface. Increase in performance due to reduction of the flying height and magnetic spacing, and longer product lifetime are related to the properties of protective layers covering the surfaces of hard disks. Currently, such layers are generally sputtered amorphous carbon films, whose characteristics are strongly dependent on various sputtering conditions such as the argon gas pressure, substrate temperature, and dc and rf bias voltages. In this study, the dependence of the characteristics of carbon films on the dc bias voltage of the FTS was investigated, and the characteristics were also compared with those obtained without a dc bias voltage supply. The carbon film...

Deposition of high-durability protective layers with a composite structure of DLC and GLC by facing-targets sputtering

An amorphous carbon film is currently used for the protective layer for overcoating the surface of the recording layer of a hard disk. In this study, the film was deposited by faring-targets sputtering (FTS), which can discharge at a lower argon gas pressure than other sputtering, such as dc magnetron sputtering, because the plasma is sufficiently confined by a magnetic field applied perpendicular to both of the target planes. As a result, the layers can be deposited without plasma damage. Thus, very smooth and uniform thin films can be obtained. The dependence of the structure and properties of carbon layers on various sputtering conditions such as the argon gas pressure, dc and rf bias voltages, and substrate temperature at room temperature, compared with the previous report, was investigated when layers with a thickness of 500 /spl Aring/ were deposited by FTS on glass and Al/Ni-P substrates. The surface appearances of the layers were observed by FE-SEM, and their structures were characterized by Raman spectroscopy. All the carbon films in this study revealed both diamondlike carbon (DLC: D) and graphitelike carbon (GLC: G) structures. The ratio of the integral intensity of the D peak to that of the G peak, I(D)/I(G), was measured by Raman spectroscopy. As a result, it was found that the ratio I(D)/I(G) was significantly dependent on the sputtering conditions and was well correlated with the surface appearance. The films with very low surface roughness had I(D)/I(G) ratios in the range of 196-1.99. This seems to indicate that the fine DLC grains are isolated and distributed with almost equal spacing in the homogeneous GLC matrix, occupying twice the area of the GLC structure. The films appear to have a composite structure of strong DLC and GLC.

Micromagnetic properties of CoCrPtTa/CrV thin films for high density recording media

The magnetization reversal, the magnetostatic interactions and the thermal stability of CoCrPtTa thin films for high density recording media are investigated. The reversal is found to be remarkably incoherent, particularly in the thicker films. The magnetic stability is better in the thinnest film (10 nm), and the switching volume results larger than the grain size. The behavior is influenced by the grain segregation state of the films.

Composition monitoring for one year of lube cross-contamination of hard disks using aluminum substrates

The possibility of chemical reactions between different lubes for hard disks is a concern that should be investigated to ensure a high level of quality for hard disk drives when the same assembly process is used for different drives. To investigate cross-contamination by different disk lubes, a novel characterization method was developed, using an aluminum disk substrate with an Ni-P underlayer as a witness disk, instead of the silicon wafers currently used. One-year monitoring of organic and ionic materials in a clean room for manufacturing lines showed that the method had good detection ability and operability. It was also confirmed that lube cross-contamination was below the level at which it could cause chemical reactions between lubes.