Dynamic magnetic information storage or retrieval – Fluid bearing head support – Disk record
Reexamination Certificate
2002-02-15
2004-06-08
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Fluid bearing head support
Disk record
C360S125330
Reexamination Certificate
active
06747846
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head used in a recording and reproducing magnetic element, and more particularly to a thin film magnetic head and a thin film magnetic head slider, and a method of producing the same.
2. Description of the Prior Art
In recent years, magnetic recording/reproducing technology has improved remarkably, and accordingly magnetic recording densities are increasing rapidly year after year. To achieve high density and small size, magnetic disk drive, which is typically a recording and reproducing magnetic element, generally writes data onto a magnetic recording medium by magnetic induction and reads data stored on the medium by a magneto-resistive effect. Two recent trends are for magnetic recording/reproducing systems to use giant magneto-resistive effect type devices to improve magnetic reproduction efficiency, and for recording magnetic elements to use magnetic materials that produce higher magnetic flux densities to offset the decrease in recording magnetic field intensity due to increasingly dense and narrow tracks. In general, however, many of the types of materials used to achieve high density and small size in such devices are highly susceptible to corrosion.
The structure of a typical thin film magnetic head will now be described. The thin film magnetic head has a multilayer cross-sectional structure comprising thin magnetic films and insulating films laminated on a substrate. The magnetic thin films are usually formed by sputtering. The laminated thin films form part of an air bearing surface facing the magnetic recording medium. The air bearing surface section is completed through a lapping step for achieving a higher accuracy in the device height and a washing step for removing residues after lapping. A practical thin-film magnetic head manufacturing process uses an aqueous suspension of diamond abrasive grains and a surfactant agent for lapping, a washing fluid that is a mixture of pure water and a surfactant agent for washing, and pure water for rinsing the washing fluid out. After that, the air bearing surface that will face the magnetic recording medium is coated with an over coat consisting of carbon or other suitable material for higher sliding quality and corrosion resistance. In the subsequent processes, including the completion of the thin film magnetic head sliders and in a thin-film magnetic head assembly process involving bonding of spring suspensions and wiring, the air bearing surface also undergoes washing with a washing fluid that is a mixture of pure water and a surfactant agent and rinsing thereof with pure water, and is then installed in the magnetic disk drive.
During these conventional lapping and washing processes, the metal section including the magnetic thin films on the air bearing surface is exposed to the aqueous solutions. Even after the over coat of air bearing surface is formed, the metal section including the magnetic thin films may be exposed to the aqueous solutions through local defects in the over coat. Protective strength against corrosion has depended on the corrosion resistance of the metal. Since all metals do not have sufficient anticorrosion properties, corrosion may unavoidably occur, depending on the type of a metal selected for use. Such corrosion causes bumps and depressions on the air bearing surface, resulting in degraded magnetic characteristics.
One approach to this problem from the manufacturing side employs a nonpolar hydrocarbon solvent in the lapping and washing fluids instead of using an aqueous solution, but the washing power in particular of such hydrocarbon solvent solutions is known to be considerably lower than that of an aqueous solution. Therefore, water washing is much more effective in achieving a high level of cleanliness of the air bearing surfaces.
A method of suppressing corrosion of the metal thin films that occurs due to the use of such aqueous solutions has been disclosed by JP-A-102710/1989. The method brings another thin film, consisting of a substance having an ionization tendency greater than that of the magnetic thin film, into contact with the recording magnetic thin film section of the magnetic head, and exposes part of this other thin film to the air bearing surface. As a result, the magnetic thin film and the other thin film form a local battery, which causes corrosion to develop from the other thin film, thereby retarding corrosion of the magnetic thin film.
The thin film of the substance having an ionization tendency greater than that of the magnetic thin film, however, must be so formed on the air bearing surface as not to affect the magnetic recording/reproducing qualities; more specifically, it should be formed in such a way that its area is the same as or smaller than that of the exposed area of the recording magnetic thin film on the air bearing surface. It is difficult to provide a thin film consisting of a substance having an ionization tendency greater than that of the magnetic thin film with this small an area on the air bearing surface where the magnetic thin film requiring protection against corrosion is exposed. Therefore, this method cannot provide a sufficient corrosion retarding effect.
In addition, a thin film consisting of a substance having a comparatively great ionization tendency is susceptible to corrosion, so if it is exposed on the air bearing surface, the ensuing corrosion products may become projecting faults, which adversely affects anti-sliding properties with respect to the magnetic recording medium, resulting in poor reliability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thin film magnetic head and a thin film magnetic head slider and methods of producing the same that can effectively retard corrosion of the magnetic thin film immersed in aqueous solutions during the lapping and washing stages of the manufacturing process.
The problem addressed by the present invention can be effectively solved by providing a recording magnetic element and an external conductor electrically coupled to the recording magnetic element by a lead wire, the conductor having an equilibrium electrode potential in an aqueous solution higher than that of the recording magnetic element alone, and having a surface area larger than the cross-sectional area of the recording magnetic element on an air bearing surface facing a magnetic recording medium. The conductor is exposed on an outer surface of the thin film magnetic head that will be immersed in the aqueous solution.
Use of this method can provide the conductor area necessary for suppressing metal dissolution from the recording magnetic element on the air bearing surface in the aqueous solution. This is because corrosion of the magnetic thin film can be retarded.
As described above, the conductor should consist of a material with an equilibrium electrode potential in an aqueous solution higher than the equilibrium electrode potential of the magnetic thin film alone. More specifically, the conductor is preferably an elemental metal conductor, an alloy conductor, or a chemical compound conductor including a material selected from a group of metals such as Au, Ag, Pt, Ru, Rh, Pd, Os, and Ir, or a group of conductive ceramics such as Al
2
O
3
.TiC, SiC, TiC, WC, and B
4
C.
Corrosion retarding mechanisms will now be described. One mechanism in which a conductor consisting of a material such as those described above retards corrosion of a magnetic thin film placing the magnetic thin film in electrically conductive contact with a conductor having an equilibrium electrode potential higher than that of the magnetic thin film, thereby shifting, that is, raising, the equilibrium electrode potential in an aqueous solution (more specifically, a lapping or washing fluid) into passive region, thereby retarding corrosion of the magnetic thin film. It is known that, generally, a stable passive film is formed on the surface of a metal in the passive region and the metal is immune to corrosion at this potential. Accordingly, it i
Isono Yukihiro
Kato Takahiro
Kikuchi Hiroshi
Saiki Noriyuki
Evans Jefferson
Hitachi Global Storage Technologies Japan Ltd.
Mattingly Stanger & Malur, P.C.
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