The present invention relates to methods and devices for forming magnetic transition patterns in a layer or body of magnetic material. The invention has particular utility in the formation of servo patterns in the surfaces of magnetic recording layers of magnetic data/information storage and retrieval media, e.g., hard disks.
Magnetic recording media are widely used in various applications, e.g., in hard disk form, particularly in the computer industry for storage and retrieval of large amounts of data/information in magnetizable form. Such media are conventionally fabricated in thin film form and are generally classified as xe2x80x9clongitudinalxe2x80x9d or xe2x80x9cperpendicularxe2x80x9d, depending upon the orientation (i.e., parallel or perpendicular) of the magnetic domains of the grains of the magnetic material constituting the active magnetic recording layer, relative to the surface of the layer.
A portion of a conventional thin-film, longitudinal-type recording medium 1 utilized in disk form in computer-related applications is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically of metal, e.g., an aluminum-magnesium (Alxe2x80x94Mg) alloy, having sequentially deposited thereon a plating layer 11, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (xe2x80x9cDLCxe2x80x9d), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium 1, the magnetic layer 13 is locally magnetized by a write transducer or write head (not shown in FIG. 1 for simplicity) to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field applied by the write transducer is greater than the coercivity of the recording medium layer 13, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field applied by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
A typical recording system 20 utilizing a thin-film, vertically oriented, perpendicular-type magnetic medium 1xe2x80x2 is illustrated in FIG. 2, wherein reference numerals 10, 11, 12A, 12B and 13xe2x80x2, respectively, indicate the substrate, plating layer, soft magnetic underlayer, at least one non-magnetic interlayer, and vertically oriented, hard magnetic recording layer of perpendicular-type magnetic medium 1, and reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of single-pole magnetic transducer head 6. Relatively thin interlayer 12B (also referred to as an xe2x80x9cintermediatexe2x80x9d layer), comprised of one or more layers of non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 12A and the hard recording layer 13xe2x80x2 and (2) promote desired microstructural and magnetic properties of the hard recording layer. As shown by the arrows in the figure indicating the path of the magnetic flux xcfx86, flux xcfx86 is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through vertically oriented, hard magnetic recording layer 13xe2x80x2 (which, as is known, may comprise a Co-based alloy, an iron oxide, or a multilayer magnetic superlattice structure) in the region above single pole 7, entering and travelling along soft magnetic underlayer 12A for a distance, and then exiting therefrom and passing through vertically oriented, hard magnetic recording layer 13xe2x80x2 in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 2, vertical lines 9 indicate grain boundaries of each polycrystalline (i.e., granular) layer of the layer stack constituting medium 1. As apparent from the figure, the width of the grains (as measured in a horizontal direction) of each of the polycrystalline layers constituting the layer stack of the medium is substantially the same, i.e., each overlying layer replicates the grain width of the underlying layer. Not shown in the figure, for illustrative simplicity, are a protective overcoat layer 14, such as of a diamond-like carbon (DLC) formed over hard magnetic layer 13xe2x80x2, and a lubricant topcoat layer 15, such as of a perfluoropolyethylene material, formed over the protective overcoat layer. As with the longitudinal-type recording medium 1 shown in FIG. 1, substrate 10 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Alxe2x80x94Mg having an Nixe2x80x94P plating layer 11 on the deposition surface thereof, or substrate 10 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; soft underlayer 12A is typically comprised of an about 500 to about 4,000 xc3x85 thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc.; thin interlayer 12B typically comprises an up to about 100 xc3x85 thick layer of a non-magnetic material, such as TiCr; and hard magnetic layer 13xe2x80x2 is typically comprised of an about 100 to about 250 xc3x85 thick layer of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, iron oxides, such as Fe3O4 and xcex4-Fe2O3, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 xc3x85 thick, X is an clement selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 1 xc3x85 thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
A typical contact start/stop (CSS) method employed during use of disk-shaped media involves a floating transducer head gliding at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between mutually sliding surfaces of the transducer head and the disk. During reading and recording (writing) operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the transducer head is freely movable in both the circumferential and radial directions, thereby allowing data to be recorded and retrieved from the disk at a desired position in a data zone.
Adverting to FIG. 3, shown therein, in simplified, schematic plan view, is a magnetic recording disk 30 (of either longitudinal or perpendicular type) having a data zone 34 including a plurality of servo tracks, and a contact start/stop (CSS) zone 32. A servo pattern 40 is formed within the data zone 34, and includes a number of data track zones 38 separated by servo tracking zones 36. The data storage function of disk 30 is confined to the data track zones 38, while servo tracking zones 36 provide information to the disk drive which allows a read/write head to maintain alignment on the individual, tightly-spaced data tracks.
Although only a relatively few of the servo tracking zones are shown in FIG. 3 for illustrative simplicity, it should be recognized that the track patterns of the media contemplated herein may include several hundreds of servo zones to improve head tracking during each rotation of the disk. In addition, the servo tracking zones need not be straight radial zones as shown in the figure, but may instead comprise arcs, intermittent zones, or irregularly-shaped zones separating individual data tracks.
In conventional hard disk drives, data is stored in terms of bits along the data tracks. In operation, the disk is rotated at a relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which radially positions the head on the disk surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disk, i.e., over a data track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above that track. By moving the actuator arm, the magnetic head assembly is moved radially on the disk surface between tracks. Many actuator arms are rotatable, wherein the magnetic head assembly is moved between tracks by activating a servomotor which pivots the actuator arm about an axis of rotation. Alternatively, a linear actuator may be used to move a magnetic head assembly radially inwardly or outwardly along a straight line.
As has been stated above, to record information on the disk, the transducer creates and applies a highly concentrated magnetic field in close proximity to the magnetic recording medium. During writing, the strength of the concentrated magnetic field directly under the write transducer is greater than the coercivity of the recording medium, and grains of the recording medium at that location are magnetized in a direction which matches the direction of the applied magnetic field. The grains of the recording medium retain their magnetization after the magnetic field is removed. As the disk rotates, the direction of the writing magnetic field is alternated, based on bits of the information being stored, thereby recording a magnetic pattern on the track directly under the write transducer.
On each track, eight xe2x80x9cbitsxe2x80x9d typically form one xe2x80x9cbytexe2x80x9d and bytes of data are grouped as sectors. Reading or writing a sector requires knowledge of the physical location of the data in the data zone so that the servo-controller of the disk drive can accurately position the read/write head in the correct location at the correct time. Most disk drives use disks with embedded xe2x80x9cservo patternsxe2x80x9d of magnetically readable information. The servo patterns are read by the magnetic head assembly to inform the disk drive of track location. In conventional disk drives, tracks typically include both data sectors and servo patterns and each servo pattern typically includes radial indexing information, as well as a xe2x80x9cservo burstxe2x80x9d. A servo burst is a centering pattern to precisely position the head over the center of the track. Because of the locational precision needed, writing of servo patterns requires expensive servo-pattern writing equipment and is a time consuming process.
An approach for overcoming, or at least alleviating, the above problems associated with writing of magnetic patterns in a magnetic layer, e.g., servo patterns, is disclosed in commonly assigned U.S. Pat. No. 5,991,104 to Bonyhard.
According to this approach, a method for forming a magnetic transition pattern, such as a servo pattern, in a layer of a magnetic material comprises steps of:
1) aligning a magnetic disk immediately adjacent a master servo writer medium, the latter constituted of a magnetic layer having a greater magnetic coercivity than the former, wherein the servo-writer medium has a master servo pattern magnetically stored thereon which defines a plurality of concentric tracks;
2) applying a magnetic assist field to the aligned master servo-writer medium and magnetic disk, the magnetic assist field having a substantially equal magnitude at all tracks on the aligned master servo-writer medium and magnetic disk; and
3) rotating the aligned master servo-writer medium and magnetic disk relative to the magnetic assist field.
However, the above-described method incurs several drawbacks associated with its implementation in an industrially viable manner. Specifically, a xe2x80x9cone-of-a-kindxe2x80x9d master writer with a very high write field gradient is necessary for writing the requisite high intensity, master magnetic servo pattern onto the master disk, and a complicated means for rotating the aligned master servo-writer disk and xe2x80x9cslavexe2x80x9d workpiece magnetic disk is required, as is a complex system for controlling/regulating/rotating the intensity (i.e., magnitude) and directions of the magnetic assist field.
Commonly assigned, co-pending U.S. patent application Ser. No. 10/082,178, filed Feb. 26, 2002, the entire disclosure of which is incorporated herein by reference, discloses an improvement over the invention disclosed in the aforementioned commonly assigned U.S. Pat. No. 5,991,104, and is based upon the discovery that very sharply defined magnetic transition patterns can be reliably, rapidly, and cost-effectively formed in a magnetic medium containing a longitudinal or perpendicular type magnetic recording layer without requiring expensive, complicated fabrication of a master disk.
Specifically, the invention disclosed in U.S. patent application Ser. No. 10/082,178 is based upon recognition that a stamper/imprinter (analogous to the aforementioned xe2x80x9cmasterxe2x80x9d) comprised of a magnetic material having a high saturation magnetization, Bsat, i.e., Bsatxe2x89xa7about 0.5 Tesla, and a high permeability, xcexc, i.e., xcexcxe2x89xa7about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, can be effectively utilized as a xe2x80x9cmasterxe2x80x9d contact mask (or xe2x80x9cstamper/imprinterxe2x80x9d) for contact xe2x80x9cimprintingxe2x80x9d of a magnetic transition pattern, e.g., a servo pattern, in the surface of a magnetic recording layer of a magnetic medium (xe2x80x9cslavexe2x80x9d), whether of longitudinal or perpendicular type. A key feature of this invention is the use of a stamper/imprinter having an imprinting surface including a topographical pattern, i.e., comprised of projections and depressions, corresponding to a desired magnetic transition pattern, e.g., a servo pattern, to be formed in the magnetic recording layer. An advantage afforded by the invention is the ability to fabricate the topographically patterned imprinting surface of the stamper/imprinter, as well as the substrate or body therefor, of a single material, as by use of well-known and economical electro-forming techniques.
According to this invention, the magnetic domains of the magnetic recording layer of the slave medium are first unidirectionally aligned (i.e., xe2x80x9cerasedxe2x80x9d or xe2x80x9cinitializedxe2x80x9d), as by application of a first external, unidirectional magnetic field Hinitial of first direction and high strength greater than the saturation field of the magnetic recording layer, typically xe2x89xa72,000 and up to about 20,000 Oe. The imprinting surface of the stamper/imprinter (master) is then brought into intimate (i.e., touching) contact with the surface of the magnetic recording layer (slave). With the assistance of a second externally applied magnetic field of second, opposite direction and lower but appropriate strength Hre-align, determined by Bsat/xcexc of the stamper material (typicallyxe2x89xa7100 Oe, e.g., from about 2,000 to about 4,500 Oe), the alignment of the magnetic domains at the areas of contact between the projections of the imprinting surface of the stamper/imprinter or at the areas facing the depressions of the imprinting surface of the stamper/imprinter and the magnetic recording layer of the medium to be patterned (slave) is selectively reversed, while the alignment of the magnetic domains at the non-contacting areas (defined by the depressions in the imprinting surface of the stamper/imprinter) or at the contacting areas, respectively, is unaffected, whereby a sharply defined magnetic transition pattern is created within the magnetic recording layer of the medium to be patterned (slave) which essentially mimics the topographical pattern of projections and depressions of the imprinting surface (master). According to the invention, high Bsat and high xcexc materials are preferred for use as the stamper/imprinter in order to: (1) avoid early magnetic saturation of the stamper/imprinter at the contact points between the projections of the imprinting surface and the magnetic recording layer, and (2) provide an easy path for the magnetic flux lines which enter and/or exit at the side edges of the projections.
Stampers/imprinters for use in a typical application according to the disclosed invention, e.g., servo pattern formation in the recording layer of a disk-shaped, thin film, longitudinal or perpendicular magnetic recording medium, are formed according to conventional techniques, and typically comprise an imprinting surface having topographical features consisting of larger area data zones separated by smaller areas with well-defined patterns of projections and depressions corresponding to conventionally configured servo sectors, as for example, disclosed in the aforementioned U.S. Pat. No. 5,991,104, the entire disclosure of which is incorporated herein by reference. For example, a suitable topography for forming the servo sectors may comprise a plurality of projections having a height in the range from about 20 to about 500 nm, a width in the range from about 0.01 to about 1 xcexcm, and a spacing of at least about 0.01 xcexcm. Stampers/imprinters comprising imprinting surfaces with suitable surface topographies may be readily formed by a variety of techniques, such as electroforming onto a planar-surfaced substrate through an apertured, non-conductive mask, or by pattern formation in a planar-surfaced substrate by means photolithographic wet (i.e., chemical) or dry (e.g., plasma, sputter, or ion beam) etching techniques.
FIG. 4 illustrates a sequence of steps for performing magnetic transition patterning by contact printing of a perpendicular recording medium, e.g., medium 1xe2x80x2 depicted in FIG. 2 and comprised of a non-magnetic substrate 10 and an overlying thin layer 13xe2x80x2 of a perpendicular-type magnetic recording material (where plating layer 11, soft magnetic underlayer 12A, and non-magnetic interlayer 12B are omitted from FIG. 4 in order to not unnecessarily obscure the essential features/aspects of the present invention) is subjected to a DC erase or magnetic initialization process for unidirectionally aligning the perpendicularly oriented magnetic domains 13xe2x8axa5 of magnetic recording layer 13xe2x80x2. Magnetic initialization of perpendicular medium 1xe2x80x2 is accomplished by applying a first, high strength, unidirectional DC magnetic initialization field Hinitial normal to the opposed major surfaces thereof, i.e., normal to the lower surface of substrate 10 and upper surface of magnetic recording layer 13xe2x80x2, wherein Hinitialxe2x89xa7coercivity of layer 13xe2x80x2 and is typically in the range from above about 2,000 to about 20,000 Oe.
According to the next step of the process sequence, a stamper/imprinter 16 composed of composed of a body of magnetic material having a high saturation magnetization, Bsat, i.e., Bsatxe2x89xa7about 0.5 Tesla, and a high permeability, xcexc, i.e., xcexcxe2x89xa7about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, and having an imprinting surface 17 having a topography comprised of a plurality of projections 18 and depressions 19 arranged in a pattern corresponding to a magnetic transition pattern to be formed in the surface of magnetic recording layer 13xe2x80x2, e.g., a plurality of data zones separated by servo sectors, is placed in intimate (i.e., touching) contact with the surface of layer 13xe2x80x2. By way of illustration only, a suitable topography for the imprinting surface 17 of a contact mask-type stamper/imprinter 16 for use in forming a recording medium with data zones separated by servo sectors according to the invention may comprise a plurality of projections 18 having a height in the range from about 20 to about 500 nm, a width in the range from about 0.01 to about 1 xcexcm, and a spacing (defining the depressions 19) of at least about 0.01 xcexcm). A second, unidirectional DC magnetic re-alignment field Hre-align of direction reverse that of the DC magnetic initialization field Hinitial is then applied normal to the upper surface of stamper/imprinter 16 and the lower surface of substrate 10 of medium 1xe2x80x2, the strength of Hre-align being lower than that of Hinitial and optimized at a value determined by Bsat/xcexc of the stamper material (typicallyxe2x89xa7100 Oe, e.g., from about 2,000 to about 4,500 Oe for the above-listed high Bsat, high xcexc materials). According to the invention, due to the high permeability xcexc of the stamper material, the magnetic flux xcfx86 provided by the re-alignment field Hre-align tends to concentrate at the projections 18 of the stamper/imprinter 16, which projections are in touching contact with the surface of magnetic recording layer 13xe2x80x2. As a consequence, the surface areas of magnetic recording layer 13xe2x80x2 immediately beneath the projections 18 experience a significantly higher magnetic field than the surface areas at the non-contacting areas facing the depressions 19. If the re-alignment field strength Hre-align is optimized (e.g., as described supra), the direction of magnetization (i.e., alignment) of the perpendicularly oriented magnetic domains 13195  is selectively reversed (as indicated by the arrows in the figure) at the areas of the magnetic recording layer 13xe2x80x2 where the projections 18 of the imprinting surface 17 of the stamper/imprinter 16 contact the surface of the magnetic recording layer 13xe2x80x2, and the magnetic alignment of the perpendicularly oriented magnetic domains 13195  facing the depressions 19 in the imprinting surface 17 is retained. Consequently, upon removal of the stamper/imprinter 16 and the re-alignment field Hre-align in the next (i.e., final) step according to the inventive methodology, a perpendicular recording medium 1xe2x80x2 is formed with a magnetic transition pattern comprising a plurality of data zones separated by servo sectors each comprising a plurality of reversely oriented perpendicular magnetic domains 13xe2x8axa5R corresponding to the desired servo pattern.
FIG. 5 illustrates a similar sequence of steps for performing magnetic transition patterning by contact printing of a longitudinal recording medium, e.g., medium 1 depicted in FIG. 1 and comprised of a non-magnetic substrate 10 and an overlying thin layer 13 of a longitudinal-type magnetic layer (where plating layer 11, polycrystalline underlayer 12, protective overcoat layer 14, and lubricant topcoat layer 15 are omitted from FIG. 5 in order not to unnecessarily obscure the essential features/aspects of the present invention) is initially subjected to a magnetic erase (or xe2x80x9cinitializationxe2x80x9d) process for unidirectionally aligning the longitudinally oriented magnetic domains 13= of magnetic recording layer 13. Magnetic initialization of longitudinal medium 1 is accomplished by applying a first, high strength, unidirectional magnetic field Hinitial parallel to the surface of the magnetic recording layer, such that Hinitialxe2x89xa7coercivity of layer 13xe2x80x2 and is typically in the range from about 2,000 to about 20,000 Oe. In this instance, Hinitial is applied perpendicularly (i.e., normal) to the side edges of medium 1, whereas, by contrast, Hinitial for a perpendicular medium would be applied normal to the upper and lower major surfaces of the medium.
According to the next step of the process sequence, a stamper/imprinter 16 comprised of a body of magnetic material having a high saturation magnetization, Bsat, i.e., Bsatxe2x89xa7about 0.5 Tesla, and a high permeability, xcexc, i.e., xcexcxe2x89xa7about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, and having an imprinting surface 17 having a topography comprised of a plurality of projections 18 and depressions 19 arranged in a pattern corresponding to a magnetic transition pattern to be formed in the surface of magnetic recording layer 13, e.g., a plurality of data zones separated by servo sectors, is placed in intimate (i.e., touching) contact with the surface of layer 13. By way of illustration only, a suitable topography for the imprinting surface 17 of a contact mask-type stamper/imprinter 16 for use in forming a recording medium with data zones separated by servo sectors in longitudinal recording layer 13 according to the invention may comprise a plurality of projections 18 having a height in the range from about 20 to about 500 nm, a width of at least about 0.01 xcexcm, and a spacing (defining the depressions 19) in the range from about 0.01 to about 1 xcexcm. A second, unidirectional magnetic re-alignment field Hre-align parallel to the major surface of magnetic recording layer 13 but of lower strength and direction reverse that of the magnetic initialization field Hinitial is then applied normal to the side edge surfaces of stamper/imprinter 16, the strength of Hre-align being optimized at a value determined by Bsat/xcexc of the stamper material (typicallyxe2x89xa7100 Oe, e.g., from about 2,000 to about 4,500 Oe for the above-listed high Bsat, high xcexc materials).
According to the invention, due to the high permeability xcexc of the stamper material, the magnetic flux xcfx86 provided by the re-alignment field Hre-align enters and exits the side edges of the projections and tends to concentrate at the depressions 19 of the stamper/imprinter 16 (rather than at the projections 18). As a consequence, the non-contacted surface areas of magnetic recording layer 13 immediately beneath the depressions 19 experience a significantly higher magnetic field than the surface areas of the magnetic recording layer 13 in contact with the projections 18. If the re-alignment field strength Hre-align is optimized, the direction of magnetization (i.e., alignment) of the longitudinally oriented magnetic domains 13= of the magnetic recording layer 13 will be selectively reversed (as indicated by the arrows in the figure) at the areas facing the depressions 19 of the imprinting surface 17 of the stamper/imprinter 16, whereas the alignment of the longitudinally oriented magnetic domains 13=of the magnetic recording layer 13 in contact with the projections 18 of the imprinting surface 17 of the stamper/imprinter 16 will be retained. Consequently, upon removal of the stamper/imprinter 16 and the re-alignment field Hre-align in the next (i.e., final) step according to the inventive methodology, a longitudinal recording medium 1 is formed with a magnetic transition pattern comprising a plurality of data zones separated by servo sectors each comprising of a plurality of reversely longitudinally oriented magnetic domains 13=R corresponding to the desired servo pattern.
Currently, contact printing for servo patterning of magnetic media is performed on one surface of one disk at-a-time, which practice disadvantageously imposes severe limitations on product throughput rates. Another disadvantage associated with the one surface at-a-time approach is the difficulty in performing contact printing of magnetic media such that the magnetic transition pattern on one media surface is a mirror image of the magnetic transition pattern on another surface. Formation of mirror image magnetic transition patterns on different media surfaces is considered desirable in order to minimize xe2x80x9cWIRROxe2x80x9d (Written In Repeatable Run Out) problems in multi-disk hard drive devices.
A further problem associated with the need for dual-side contact printing means for obtaining increased product throughput rates necessary for economic competitiveness of servo-patterned disk manufacture is that conventional techniques for forming stampers/imprinters with topographically patterned imprinting surfaces, e.g., electroforming techniques, are limited to formation of single-sided stampers/imprinters.
Accordingly, there exists a need for means and methodology for performing dual-sided servo patterning by contact printing which are free of the above-described drawbacks and disadvantages associated with the use of conventional single-sided stampers/imprinters, and facilitate high quality, high throughput replication of servo patterns in single and dual-sided magnetic recording media via contact printing. Moreover, there exists a need for methodology and instrumentalities, e.g., improved stampers/imprinters for performing rapid, cost-effective servo patterning of dual-sided, thin film, high areal recording density magnetic recording media which do not engender the above-stated concerns and disadvantages associated with existing methodologies/instrumentalities for patterning magnetic recording media by contact printing.
The present invention addresses and solves the above-described problems, disadvantages, and drawbacks associated with prior methodologies for servo pattern formation in single and dual-sided thin film magnetic recording media, while maintaining full compatibility with the requirements of automated hard disk manufacturing technology.
An advantage of the present invention is an improved method of manufacturing a dual-sided stamper/imprinter for use in simultaneously forming magnetic transition patterns in spaced-apart first and second layers of magnetic material by means of contact printing.
Another advantage of the present invention is an improved method of manufacturing a dual-sided stamper/imprinter for use in simultaneously forming servo patterns in spaced-apart first and second layers of magnetic recording material by means of contact printing.
A further advantage of the present invention is an improved dual-sided stamper/imprinter for use in simultaneously forming magnetic transition patterns in spaced-apart first and second layers of magnetic material by means of contact printing.
A still further advantage of the present invention is an improved dual-sided stamper/imprinter for use in simultaneously forming servo patterns in spaced-apart first and second layers of magnetic recording material by means of contact printing.
Yet another advantage of the present invention is an improved method of simultaneously forming magnetic transition patterns in a plurality of spaced-apart layers of magnetic material by means of contact printing.
Still another advantage of the present invention is an improved method of simultaneously forming servo patterns in a plurality of spaced-apart layers of magnetic recording material by means of contact printing.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a method of manufacturing a dual-sided stamper/imprinter for use in simultaneously forming magnetic transition patterns in spaced-apart first and second layers of magnetic material by means of contact printing, comprising sequential steps of:
(a) providing a master having a surface with a first topographical pattern formed therein and comprising a patterned plurality of spaced-apart recesses with a plurality of non-recessed areas therebetween, the first topographical pattern corresponding to a first magnetic transition pattern to be formed in the first layer of magnetic material;
(b) forming a thin layer of an electrically conductive material on the surface with the first topographical pattern;
(c) forming a blanket layer of a magnetic material having high saturation magnetization Bsatxe2x89xa7about 0.5 Tesla, and high permeability xcexcxe2x89xa7about 5, on the thin layer of electrically conductive material, the blanket layer over-filling each of the plurality of recesses and including an overburden portion extending over each of the non-recessed areas, the blanket layer having an exposed surface opposite the thin layer of electrically conductive material;
(d) forming a second topographical pattern in the exposed surface of the blanket layer, the second topographical pattern comprising a patterned plurality of spaced-apart recesses with a plurality of non-recessed areas therebetween and corresponding to a second magnetic transition pattern to be formed in the second layer of magnetic material; and
(e) separating the blanket layer together with the underlying thin layer of electrically conductive material from the surface of the master with the first topographical pattern formed therein to provide a dual-sided stamper/imprinter having first and second oppositely facing topographically patterned imprinting surfaces.
According to embodiments of the present invention, step (a) comprises providing a master including a substrate and a layer of a resist material formed on a surface of the substrate, the first topographical pattern corresponding to the first magnetic transition pattern being formed in the layer of resist material; step (b) comprises forming the thin layer of an electrically conductive material on the surface with the first topographical pattern by means of a thin film deposition process selected from the group consisting of: electroless plating, physical vapor deposition (PVD), and chemical vapor deposition (CVD); step (c) comprises forming the blanket layer of a magnetic material selected from the group consisting of Ni, NiV, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV by means of an electrochemical process, e.g., electroforming; and step (d) comprises forming the second topographical pattern in the exposed surface of the blanket layer by means of a process comprising sequential steps of:
(d1) forming a layer of a resist material on the exposed surface of the blanket layer;
(d2) patterning the layer of resist material to expose portions of the surface of the blanket layer corresponding to the second magnetic transition pattern to be formed in the second layer of magnetic material;
(d3) forming recesses in the blanket layer at the exposed surface portions thereof, utilizing the patterned layer of resist material as an etch mask, the recesses forming a pattern corresponding to the second magnetic transition pattern to be formed in the surface of the blanket layer; and
(d4) removing the layer of resist material from the surface of the blanket layer.
Particular embodiments of the invention are those wherein:
step (a) comprises providing a master having a surface with a first topographical pattern corresponding to a servo pattern to be formed in the first magnetic layer (on a first substrate);
step (b) comprises sputtering a thin layer of a material selected from the group consisting of Ni, NiV, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV on the first topographical pattern;
step (c) comprises electroforming on the thin layer a blanket layer comprised of at least one magnetic material selected from the group consisting of Ni, NiV, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV; and
step (d) comprises forming a second topographical pattern in the exposed surface of the blanket layer corresponding to a servo pattern to be formed in the second magnetic layer (on a second substrate).
Another aspect of the present invention is a dual-sided stamper/imprinter for use in simultaneously forming magnetic transition patterns in spaced-apart first and second layers of magnetic material by means of contact printing, comprising a magnetic material having high saturation magnetization Bsatxe2x89xa7about 0.5 Tesla, and high permeability xcexcxe2x89xa7about 5, and including first and second oppositely facing imprinting surfaces, wherein:
the first imprinting surface has a first topographical pattern formed therein comprising a patterned plurality of spaced-apart recesses with a plurality of non-recessed areas therebetween, the first topographical pattern corresponding to a first magnetic transition pattern to be formed in the first layer of magnetic material; and
the second imprinting surface has a second topographical pattern formed therein comprising a patterned plurality of spaced-apart recesses with a plurality of non-recessed areas therebetween, the second topographical pattern corresponding to a second magnetic transition pattern to be formed in the second layer of magnetic material.
According to certain embodiments of the present invention, the first and second topographical patterns are identical and may be aligned in mirror-image relation; whereas according to other embodiments of the invention, the first and second topographical patterns are different.
Preferred embodiments of the present invention are those wherein each of the first and second topographical patterns are servo patterns for disk-shaped recording media.
According to embodiments of the present invention, at least the first and second imprinting surfaces of the stamper/imprinter are comprised of at least one magnetic material selected from the group consisting of Ni, NiV, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV.
Yet another aspect of the present invention is an improved method of simultaneously forming magnetic transition patterns in a plurality of spaced-apart layers of magnetic material by means of contact printing, comprising steps of:
(a) providing a dual-sided stamper/imprinter having a first topographically patterned imprinting surface comprising a plurality of projections and depressions arranged in a pattern corresponding to a first magnetic transition pattern to be formed in a first one of the plurality of spaced-apart layers of magnetic material and an oppositely facing second topographically patterned imprinting surface comprising a plurality of projections and depressions arranged in a pattern corresponding to a second magnetic transition pattern to be formed in a second one of the plurality of spaced-apart layers of magnetic material, at least the first and second imprinting surfaces of the stamper/imprinter comprised of at least one magnetic material having high saturation magnetization Bsatxe2x89xa7about 0.5 Tesla, and high permeability xcexcxe2x89xa7about 5, selected from the group consisting of Ni, NiV, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV;
(b) providing a first workpiece including a first surface comprised of the first layer of magnetic material, the first layer of magnetic material including a plurality of unidirectionally magnetically aligned magnetic domains extending to the first surface with an initial direction of alignment;
(c) providing a second workpiece including a second surface comprised of the second layer of magnetic material, the second layer of magnetic material including a plurality of unidirectionally magnetically aligned magnetic domains extending to the second surface with an initial direction of alignment;
(d) contacting the first surface of the first workpiece with the first topographically patterned imprinting surface of the dual-sided stamper/imprinter;
(e) contacting said second surface of the second workpiece with the second topographically patterned imprinting surface of the dual-sided stamper/imprinter;
(f) simultaneously selectively re-aligning the direction of alignment of the magnetic domains of those portions of the first and second layers of magnetic material in contact with the projections or facing the depressions of the first and second topographically patterned imprinting surfaces, respectively, such that the magnetic domains of the contacted portions or the facing portions are aligned in a direction reverse that of the initial direction, wherein the combination of aligned+re-aligned magnetic domains of each of the first and second layers of magnetic material form first and second magnetic transition patterns replicating the patterns of projections and depressions of the first and second topographically patterned imprinting surfaces, respectively; and
(g) removing the first and second workpieces from contact with the dual-sided stamper/imprinter.
According to preferred embodiments of the present invention, step (f) comprises applying a unidirectional DC magnetic field having a direction opposite that of the initial direction of alignment of the plurality of unidirectionally magnetically aligned magnetic domains of the first and second layers of magnetic material, the DC magnetic field having sufficient strength to selectively reverse the initial alignment of the magnetic domains of the first and second layers of magnetic material contacting the projections or facing the depressions of the first and second imprinting surfaces of the dual-sided stamper/imprinter, while retaining the initial direction of alignment of the magnetic domains of the first and second layers of magnetic material facing the depressions or contacting the projections, respectively, of the first and second imprinting surfaces of the dual-sided stamper/imprinter.
Preferred embodiments of the present invention include those wherein steps (b) and (c) each comprise providing a disk-shaped workpiece for a magnetic recording medium, each including at least one layer of a magnetic recording material on at least one surface of a substrate comprised of a non-magnetic material selected from the group consisting of Al, NiP-plated Al, Alxe2x80x94Mg alloys, other Al-based alloys, other non-magnetic metals, other non-magnetic metal-based alloys, glass, ceramics, polymers, glass-ceramics, and composites or laminates of the aforementioned materials; and step (a) comprises providing a dual-sided stamper/imprinter having first and second topographically patterned imprinting surfaces each comprising a plurality of projections and depressions arranged in a pattern corresponding to a servo pattern to be formed in the first and second layers of magnetic material.
According to further embodiments of the present invention, at least one of steps (b) and (c) further comprises providing a plurality of spaced-apart disk-shaped workpieces arranged in a stack, each workpiece including a substrate with a layer of a magnetic recording material on both major surfaces thereof; and step (a) further comprises providing a dual-sided stamper/imprinter between each adjacent pair of workpieces of said stack.
Particular embodiments of the present invention are those wherein steps (b) and (c) each comprise providing a workpiece with a longitudinal magnetic recording layer; and step (f) comprises applying the unidirectional magnetic field in a direction parallel to said at least one surface of each of said substrates.
Further particular embodiments of the present invention are those wherein steps (b) and (c) each comprise providing a workpiece with a perpendicular magnetic recording layer; and step (f) comprises applying the unidirectional magnetic field in a direction perpendicular to the at least one surface of each of the substrates.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not limitative.