Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Utility Patent
1999-01-19
2001-01-02
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C204S192200, C427S128000, C427S130000, C427S131000, C427S132000, C427S250000, C427S255190, C427S255400, C427S259000, C427S267000, C427S269000, C427S282000, C427S331000, C427S398400, C427S399000, C427S404000, C427S405000, C427S407100, C427S409000, C427S419200, C427S539000, C427S552000, C427S576000, C427S595000, C428S065100, C428S065100, C428S065100, C428S450000, C428S457000, C428S690000, C428S690000, C428S697000, C428S701000, C428S702000, C428S704000, C428S900000
Utility Patent
active
06168845
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to patterning magnetic materials for use in magnetic storage media. In particular this invention relates to patterning magnetic materials by selective oxidation of a magnetic disk using an oxygen plasma.
BACKGROUND
Conventional magnetic recording disks are made with a continuous magnetic layer that is deposited on an aluminum alloy substrate coated with a nickel-phosphorus layer (referred to hereon as continuous magnetic disk media). The magnetic materials in magnetic disk fabrication are generally nickel, cobalt and iron alloys that are deposited on the nickel-phosphorus layer by evaporation or sputtering to form the continuous magnetic layer. A primary goal for developing improved magnetic storage media is to increase the bit densities.
In conventional magnetic recording media, each magnetic bit is composed of several hundred small grains. One approach to increasing the bit density of the magnetic media is to reduce the grain sizes along with the bit sizes while keeping the total number of grains per bit approximately constant. This approach is limited because grains that are too small (1 to 7 Nanometers) are thermally unstable and thus will spontaneously switch magnetization direction at normal operating temperatures. Additionally, if the number of grains is reduced, the noise arising from statistical fluctuations in grain positions or orientation will increase. Patterning magnetic disk media is a method to overcome the problems associated with increasing bit densities by reducing grains size.
Increasing bit densities of magnetic recording media can be achieved by patterning the magnetic material into small isolated islands such that there is a single magnetic domain in each island or bit. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. With only a single magnetic volume per island, noise fluctuations arising from grain positions or orientation are eliminated.
Methods of patterning magnetic disk media into small isolated magnetic domains has been demonstrated. For example, Fernandez et al. characterizes isolated Co magnetic domains in “Magnetic Force Microscopy of Single-Domain Cobalt Dots Patterned Using Interference Lithography”, IEEE Trans. Mag., Vol. 32, pp. 4472-4474, 1996, wherein Interference lithography is used to pattern a resist coated silicon wafer followed by thermal evaporation of Co to generate isolated arrays of magnetic domains. Krauss et al. in “Fabrication of Planar Quantum Magnetic Disk Structure Using Electron Beam Lithography, Reactive Ion Etching, and Chemical Mechanical polishing” J. Vac. Sci. Technol. B 13 (6), pp. 2850-2852, November/December 1995, describes an etching processes to define the magnetic domains followed by an electro-plating step to make isolated Ni magnetic domains. These methods of making isolated magnetic domains require that the magnetic material is deposited after the patterning step or steps and require polishing steps to make the surfaces of the magnetic media smooth.
Falcone et al., in U.S. Pat. No. 4,948,703 describes a method of embossing a photo-polymer to pattern the surface of an optical disk and Chou et al., in “Imprint Lithography with 25-Nanometer Resolution”, Science, Vol. 275, Apr. 5, 1996, and U.S. Pat. No. 5,772,905 describes a method for embossing PMMA at elevated temperatures and pressures with a template to achieve high resolution patterning. Chou in “Patterned Magnetic Nanostructures and Quantized Magnetic Disks”, Proc. IEEE, Vol. 85, No 4, pp. 652-671, April 1997, further describes a method for making magnetic domains with ferromagnetic materials such as cobalt or nickel by electroplating a PMMA embossed surface. The magnetic material fills the depressions in the embossed PMMA surface and creates small magnetic domains. The surface is polished to remove the magnetic material on the mask and leave the magnetic material in the patterned areas. Electro-plating magnetic material on a patterned surface limits compositions of magnetic materials that can be used for making a magnetic storage media, and therefore, common composite magnetic materials such as CoCrPt could not readily be used to make magnetic media by this method.
Patterning magnetic media has also been used for making magnetic disk media with alternating magnetic and non-magnetic radial tracks. Patterning a disk with magnetic and non-magnetic radial tracks allows the track widths to be reduced. Patterning magnetic disk media with alternating magnetic and non-magnetic radial tracks also reduces signal noise that results from track edge anomalies and cross-talk between magnetic information stored in adjacent bits.
A method for making magnetic media with alternating magnetic and non-magnetic tracks is described in the IBM Technical Disclosure Bulletin, Vol. 18 No. Oct. 15, 1975. The magnetic tracks are patterned by coating a photo-resist on an alpha-iron oxide layer and exposing the photo-resist through a patterned mask. The exposed photo-resist is then removed and cobalt or iron is deposited over the patterned alpha-iron oxide layer. The disk structure is then annealed and the cobalt or iron converts patterned alpha-iron oxide into ferro-magnetic material. The remaining photo-resist is removed resulting in a disk structure with magnetic tracks separated by non-magnetic tracks. Brady et al., in U.S. Pat. No. 5,571,591, describes a method for patterning magnetic material using standard lithographic techniques to leave protected and unprotected areas of the magnetic layer. Germanium or silicon is then deposited over the patterned magnetic layer and in a subsequent annealing the germanium or silicon diffuses into the patterned magnetic layer producing patterned areas that are non-magnetic. Both of these methods for patterning magnetic media require an annealing step and result in significant topographic variation between the magnetic and non-magnetic regions on the surface of the magnetic layer. U.S. Pat. No. 4,935,278, issued to Krounbi et al., describes making a magnetic disk structure with alternating magnetic and non-magnetic radial tracks by coating a photo-resist over a magnetic layer and patterning the photo-resist using standard lithographic techniques. The patterned areas of the magnetic material are then etched away and the created voids are refilled with non-magnetic material to generate a disk structure with separated magnetic and non-magnetic tracks.
What is needed is a method for producing magnetic disk media with magnetic and substantially non-magnetic zones where the magnetic zones are isolated and the magnetic domain sizes are made to optimize media storage densities. Substantially non-magnetic zones, herein is referred to as non-magnetic zones that have a local magnetic moment that is reduced by at least 25% by the method relative to the magnetic zones. The method needs to be applicable to pre-deposited composite films, such as smooth sputtered CoCrPt films on disk substrates. Furthermore, the method for producing such a magnetic storage disk needs to result in minimal surface topographic variations without requiring expensive polishing steps.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of the present invention to provide a new method of making magnetic material with patterned magnetic and substantially non-magnetic zones. The non-magnetic zones are created by selective oxidation of patterned magnetic layers. The patterned magnetic layers are exposed to an oxygen plasma through voids in a mask. The magnetic zones are protected by a mask during the oxidation process. Using oxygen plasma to selectively create non-magnetic zones has the advantages of being faster and less expensive than the annealing processes reported in prior art. Additionally, the method can be applied to patterning magnetic media, whereby the magnetic material is deposited before the patterning process allowing for a greater variety of magnetic media to be patterned by this method.
A second
Emilio Santini Hugo Alberto
Fontana, Jr. Robert Edward
Hsiao Richard
Marinero Ernesto Esteban
Terris Bruce David
International Business Machines - Corporation
Lumen Intellectual Property Services
Pianalto Bernard
LandOfFree
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