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. These recording media are conventionally fabricated in thin film form and are generally classified as “longitudinal” or “perpendicular”, 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. FIG. 1 shows a disk recording medium and a cross section of a disk demonstrating the difference between longitudinal and perpendicular recording.
In the operation of magnetic media, the magnetic layer is locally magnetized by a write transducer or write head 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, then the grains of the polycrystalline magnetic layer 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.
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. By moving the actuator arm, the magnetic head assembly is moved radially on the disk surface between tracks. Typically, recording media require pattern formation in the surface of the disk to facilitate operation. For example, servo patterns of magnetically readable information are embedded in the disk to inform the magnetic head assembly of track location. The patterns include both radial indexing information and centering patterns to precisely position the head over the center of the track.
On each track, eight “bits” typically form one “byte” 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 “servo patterns” 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 “servo burst”. 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.
A stamper/imprinter comprised of a magnetic material having a high saturation magnetization, Bsat, i.e., Bsat=about 0.5 Tesla, and a high permeability, μ, i.e., μ=about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, can be effectively utilized as a contact “stamper/imprinter” for contact “imprinting” of a magnetic transition pattern, e.g., a servo pattern, in the surface of a magnetic recording layer of a magnetic medium (“workpiece”), whether of longitudinal or perpendicular type. FIG. 2 illustrates contact imprinting in the case of perpendicular media.
An advantage of this process 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.
Stampers/imprinters for use in a typical application, e.g., servo pattern formation in the recording layer of a disk-shaped, thin film, longitudinal or perpendicular magnetic recording medium 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.
Stampers/imprinters suitable for use in performing the foregoing patterning processes are typically manufactured by a sequence of steps which include providing a “master” comprised of a substantially rigid substrate, e.g., Si, with a patterned layer of a resist material thereon, the pattern comprising a plurality of projections and depressions corresponding (in positive or negative image form, as necessary) to the desired pattern to be formed in the surface of the stamper/imprinter. Stampers/imprinters are made from the master by initially forming a thin, conformal layer of an electrically conductive, magnetic material (e.g., Ni) over the patterned resist layer and then electro-forming a substantially thicker (“blanket”) magnetic layer (of the aforementioned magnetic metals and/or alloys) on the thin layer of electrically conductive material, which electro-formed blanket layer replicates the surface topography of the resist layer. Upon completion of the electro-forming process, the stamper/imprinter, termed a “father” is separated from the master, and is then in turn used for making a “family” of stampers/imprinters, including one or more “mother” and “son” stampers/imprinters.
The critical process step in manufacturing the stamper/imprinter is separation from the master. The bond between a Ni stamper and a Si master is so strong that the Si wafer may be torn apart during separation and fragments of Si may adhere to the surface of the Ni father stamper. This result in a stamper that is not well-formed and a master that cannot be used to make additional stampers because its features are damaged or distorted.