Patterned magnetic media via thermally induced phase transition

Details Patterned magnetic media via thermally induced phase transition Patterned magnetic media via thermally induced phase transition

2002-05-06

2004-06-15

Pianalto, Bernard (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Pretreatment of substrate or post-treatment of coated substrate

C427S282000, C427S283000, C427S287000, C427S372200, C427S516000, C427S376300, C427S376600, C427S383300, C427S383500, C427S555000, C427S557000, C427S595000, C427S596000, C427S597000, C427S599000

Reexamination Certificate

active

06749904

ABSTRACT:

CROSS-REFERENCE TO PROVISIONAL APPLICATION
This application claims priority from U.S. provisional patent application Serial No. 60/151,029 filed Aug. 27, 1999, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to improved magnetic data/information recording, storage and retrieval media and to a method for manufacturing same. More specifically, the present invention relates to improved, high areal recording and storage density, patterned magnetic media and to a method for manufacturing same which can be readily practiced at a low cost comparable to that of conventional multi-grain magnetic media.
BACKGROUND OF THE INVENTION
Magnetic media are widely utilized in various applications, particularly in the computer industry, and efforts are continually made with the aim or increasing the areal recording density, i.e., the bit density, or bits/unit area, of the magnetic media. Conventional magnetic thin-film media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are typically formed as “perpendicular” or “longitudinal” media, depending upon the direction of magnetization of the grains. In this regard, the “perpendicular” recording media have been found superior to the more common “longitudinal” media in achieving very high bit densities. However, as grain sizes decrease in order to achieve increased recording bit densities, e.g., to somewhere around 20 Gb/in
2
, effects ansing from thermal instability, such as “super-paramagnetism” are encountered. One proposed solution to the problem of thermal instability with ultra-high recording density magnetic recording media is to increase the crystalline anisotropy, and thus the squareness of the bits, in order to compensate for the smaller grain sizes.
An alternative approach, however, to the formation of very high bit density magnetic recording media, is one which delays the onset of thermal instability problems by storing the data/information in isolated magnetic particles. In contrast with conventional polycrystalline-based magnetic media where thousands of very small-sized grains are required for storing a single data bit, so-called “patterned” magnetic media utilize only a single, relatively large-sized particle for storage of a single data bit. For example, in “patterned” media, the single particles (i.e., the basic storage unit) are more than about ten times larger than the thermally unstable grains of conventional very high recording density magnetic media, in principle permitting storage densities of about 100 Gb/in
2
and above.
Analogous to the situation with conventional polycrystalline thin film magnetic media, both “longitudinal” and “perpendicular” types of patterned magnetic media have been developed, depending upon whether the magnetization direction of the particles is parallel or perpendicular to the media surface. When fabricated in disk form, such “patterned” media are readily adapted for use in conventional hard drives, with most of the drive design features remaining the same. Thus, hard-drive based “patterned” media technology would comprise a spinning disk with a slider head flying above it in closely-spaced relation thereto, with read sensors or a read/write head that magnetizes and/or detects the magnetic fields emanating from the magnetic particles.
To date, several approaches have been utilized for the formation of “patterned” magnetic media, which approaches can be classified into two major categories, i.e., (1) mechanical or mechanical replication; and (2) lithographic patterning.
According to the first approach, as exemplified by the Atomic Force Microscopy (“AFM”) approach of IBM (B. Terris et al.,
Data Storage
, August 1998, pp. 21-26), a sharp tip is utilized for scanning extremely close to the surface of a storage medium. The tip is located at the end of a flexible cantilever, which deflects in response to changes in the force imposed on the tip during scanning. The force may arise from a variety of effects, including, inter alia, magnetic force. To date, two types of AFM drives have been demonstrated, i.e., write-once/read-only and read-only. The former type of AFM drive, which provides write-once/read-only capability, utilizes a heated AFM tip for writing once by forming small indentations or pits in the surface of a substrate. e.g., of polycarbonate. Data is read by using the AFM tip to scan the thus-indented surface and sensing the changes in the force imposed on the AFM tip due to the presence of the indentations.
The latter type of AFM drive functions in a read-only mode, and data is initially written in the form of indentations (pits) which are created in the surface of a SiO
2
master by means of an electron beam. The data, in the form of the indentations, is then transferred, by replication, to a photopolymer-coated glass substrate, which photopolymer is cured by exposure to ultra-violet (UV) radiation to thereby form a surface topography representing the data. The data is then read from the cured photopolymer surface by scanning with the AFM tip to sense the changes in force thereat due to the indentations.
According to the second, lithographic approach, thin film processes such as are utilized in the fabrication of semiconductor integrated circuits including micro-sized features are adapted for making high aspect ratio, single column/bit, perpendicularly patterned media. According to one particular approach (M. Todorovic et al.,
Data Storage
, May 1999, pp. 17-20), designed to increase coercivity, hence stability, of the individual magnetic columns, electroplated nickel (Ni) is utilized for forming the columns, and gallium arsenide (GaAs) and alumina (Al
2
O
3
) are employed as embedding media for the columns. The fabrication process starts with an electrically conductive GaAs substrate, on which thin layers of aluminum arsenide (AlAs) and GaAs are successively deposited. Scanning electron-beam lithography is then utilized to define the magnet patterns on a resin-coated sample. The patterns in the e-beam exposed resin are developed utilizing an appropriate solvent system and then transferred, as by chemically-assisted ion beam etching (“CAIBE”), into the AlAs/GaAs layers. After pattern definition, the AlAs layer is converted into Al
2
O
3
by wet thermal oxidation. The thus-produced patterned layer acts as a mask for additional etching for extending the pattern of depressions perpendicularly into the GaAs substrate. The etched depressions in the Al
2
O
3
substrate are then filled with electroplated Ni. Overplated Ni “mushrooms” are then removed, as by polishing, to create a smooth surface for accommodating slider contact therewith.
Thus, the overall process sequence for forming such media requires successive, diverse technology steps for (1) MBE growth and mask deposition; (2) electron beam lithography; (3) chemically assisted ion beam etching; (4) wet thermal oxidation; (5) chemically assisted ion beam etching; and (6) electroplating and polishing. The result is a complex and time-consuming fabrication process. Moreover, each of the above-described approaches for patterned media manufacture typically involves substantial capital investment for the process equipment, which together with the inherent process complexity, render them too costly for use in high product throughput, magnetic disk media manufacture.
Accordingly, there exists a need for improved, high bit density, patterned magnetic data/information recording, storage, and retrieval media, e.g., in hard disk form, and a method for manufacturing same, which can be implemented at a cost compatible with that of conventional, multi-grain disk media by primarily utilizing current media manufacturing methodologies, technologies, and instrumentalities.
The present invention, therefore, addresses and solves problems attendant upon patterned magnetic media manufacture, and affords rapid, cost-effective fabrication of high bit density, patterned magnetic media, e.g., in the form of hard disks, while providing substa

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