Abstract:
A method of forming a servo track on a recording medium includes; forming a magnetic layer, defining a first servo track region having a plurality of first magnetic segments and a second servo track region having a second plurality of magnetic segments in the magnetic layer, applying a first magnetic field to induce a first magnetization direction in the first and second pluralities of magnetic segments, forming first magnetic patterns, each having a first width, and second magnetic patterns, each having a second width different from the first width, on a first side of a substrate, disposing the substrate on the recording medium, such that the first magnetic patterns are aligned in correspondence with the plurality of first magnetic segments and the second magnetic patterns are aligned in correspondence with the plurality of second magnetic segments, and applying a second magnetic field to the recording medium to selectively induce a second magnetization direction into first selected ones of the first plurality of magnetic segments and second selected ones of the second plurality of magnetic segments.

Description:
PRIORITY STATEMENT 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0076431 filed on Aug. 5, 2008, the subject matter of which is hereby incorporated by reference. 
     BACKGROUND 
     The present invention relates to a data storage apparatus. More particularly, the invention relates to methods of forming servo tracks on storage apparatus media, and a data storage apparatus having servo tracks formed using said method. 
     A hard disk drive (HDD) is an apparatus for writing data to or reading data from a rotating, disk-type magnetic recording medium using a read/write head located above the recording medium. In order to manufacture a HDD with a high recording density, the dense formation of the servo tracks on the recording medium is essential. Conventional servo writing technology was limited for some time to the formation of servo tracks on a HDD having a density of about 300 kTPI. 
     More recently, a method of forming servo tracks on a HDD using magnetic printing techniques has been introduced. Magnetic printing is a method of applying a magnetic material to the surface of a magnetic disk including servo tracks. The constituent data storage apparatus is thus enabled to store data according to a defined magnetization direction. While magnetic printing has allowed improved servo track densities, it nonetheless suffers from certain noise issues. For example, noise may occur in a non-signal field portion (e.g., a buffer field) of a servo track. This type of noise may lead to the generation of a direct current (DC) offset in a reproduced data signal. Undesired DC offsets deteriorate the quality of the reproduced data signal and may in certain circumstances cause malfunction of the data storage apparatus. 
     SUMMARY 
     Embodiments of the invention provide methods of forming servo tracks on recording media of a data storage apparatus that preclude or inhibit the generation of direct current (DC) noise. Embodiments of the invention also provide a data storage apparatus and system manufactured incorporating such servo tracks formed by said methods. 
     In one embodiment, the invention provides a method of forming a servo track on a recording medium of a data storage apparatus, the method comprising; forming a magnetic layer on a first side of the recording medium, defining a first servo track region having a plurality of first magnetic segments and a second servo track region having a second plurality of magnetic segments in the magnetic layer, applying a first magnetic field to the recording medium to induce a first magnetization direction in the first and second pluralities of magnetic segments, forming first magnetic patterns, each having a first width, and second magnetic patterns, each having a second width different from the first width, on a first side of a substrate, disposing the first side of the substrate on the first side of the recording medium, such that the first magnetic patterns are aligned in correspondence with the plurality of first magnetic segments and the second magnetic patterns are aligned in correspondence with the plurality of second magnetic segments, and applying a second magnetic field to the recording medium to selectively induce a second magnetization direction into first selected ones of the first plurality of magnetic segments and second selected ones of the second plurality of magnetic segments. 
     In another embodiment, the invention provides a method of reading servo data from a servo track formed on a recording medium of a data storage apparatus, the method comprising; detecting a first read signal having a first frequency from a first servo track region, and detecting a second read signal having a second frequency different from the first frequency from a second servo track region, and filtering the first read signal from the second read frequency in relation to the different first and second frequencies. The first and second frequencies of the first and second read signals are defined by forming an arrangement of first magnetic segments having a first width in the first servo track region and an arrangement of second magnetic segments having a second width different from the first width in the second servo track region, and inducing first and second magnetization directions in selected one of the first magnetic segments and the second magnetic segments. 
     In another embodiment, the invention provides a data storage apparatus comprising; a data storage unit comprising recording medium having a magnetic layer formed thereon, the magnetic layer comprising; a first servo track region having an arrangement of first magnetic segments, and a second servo track region having an arrangement of second magnetic segments, a read head configured to detect a first read signal from the first servo track region and a second read signal from the second servo track region, a filter configured to filter the first and second read signals, and a controller configured to control overall operation of the data storage unit, and the read head. The first and second frequencies of the first and second read signals are defined by forming the arrangement of first magnetic segments with a first width in the first servo track region and the arrangement of second magnetic segments with a second width different from the first width in the second servo track region, and inducing first and second magnetization directions in selected one of the first magnetic segments and the second magnetic segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a flowchart summarizing a method of forming a servo track according to an embodiment of the invention; 
         FIGS. 2 through 6  are conceptual diagrams further illustrating certain stages in the method summarized in  FIG. 1 ; 
         FIG. 7  is a general block diagram of a data storage apparatus manufactured according to the method of  FIGS. 1 through 6 ; and 
         FIG. 8  is a general block diagram of a data storage system including the data storage apparatus of  FIG. 7 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention now will be described in some additional detail with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as being limited to only the illustrated embodiments. Rather, these embodiments are presented as teaching examples. 
     In the drawings, the size and relative sizes of certain layers and regions may be exaggerated for clarity. Throughout the written description and drawings, like reference numbers refer to like or similar elements. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first signal could be termed a second signal, and, similarly, a second signal could be termed a first signal without departing from the teachings of the disclosure. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present application, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1  is a flowchart summarizing a method of forming a servo track according to embodiments of the present invention.  FIGS. 2 through 6  are conceptual diagrams further illustrating certain stages in the method of  FIG. 1 . 
     In one embodiment, a data storage apparatus according to the present invention is assumed to include a single magnetic disk having defined thereon at least one data area and a servo track area. Other embodiments of the invention may include multiple disks written to and read from by one or more read/write heads. 
     Each data area on the disk is able to receive and store externally provided “write data” and thereafter return identified “read data.” Write data and read data may be termed “payload data” as they contain information relevant to a host device data request or application running on an associated host device. In contrast, the servo track area stores “servo data” or information characterizing one or more data area, (e.g., preamble information, address information, sector information, track information, and/or burst information). In certain embodiments, a servo track area may include one or more first servo track region(s) serving as buffer region(s), and a second servo track region storing the servo data. The one or more first servo track region(s) may be formed before and/or after a corresponding second servo track region. 
     Referring to  FIGS. 1 and 2 , in the illustrated method of forming the servo track, a magnetic layer  12  may be formed on a disk  11  of a data storage apparatus  10  (S 10 ). A servo track area within the data storage apparatus  10  includes dual (left/right) first servo track regions  15  and bracketing a corresponding second servo track region  16 . Each first servo track region  15  is assumed to be a no-signal field serving as a buffer region in relation to the second servo track region  16 . In contrast, the second servo track region  16  is used to store servo data and/or certain payload data. 
     The magnetic layer  12  is formed to a predetermined thickness on one side of the disk  11 . That is, the servo track area including the first servo track region(s)  15  and the second servo track region  16  are disposed on a single side of the disk  11 . The magnetic layer  12  may be formed on this one side of the disk  11  by selectively applying to a magnetic material a magnetization direction induced by an externally applied magnetic field. 
     This magnetic material may have been applied using a printing method, but embodiments of the invention are not limited to only magnetic material layers formed using a printing method. The magnetic layer  12  is divided into a plurality of magnetic segments  13  and a predetermined “first” magnetization direction may be formed in each portion of the magnetic layer  12  containing each one of the plurality of magnetic segments  13 . In the illustrated example, three magnetic segments  13  are formed in each first servo track region  15 . However, those skilled in the art will recognize that the specific number of magnetic segments used is a matter of design choice. Because each one of the magnetic segments  13  is magnetized in the first magnetization direction  14 , a uniform magnetic field may be applied to the disk  11 . 
     The magnetization direction assigned to each magnetic segment  13  of magnetic layer  12  is determined by the direction (or polarity) of the applied magnetic field. For instance, a magnetic field may be applied to a bottom side of the disk  11 , (i.e., a side opposite the side having the magnetic layer  12  formed thereon), in a direction perpendicular to the principal planar surface of the magnetic layer  12 . Alternately, a magnetic field may be applied to the front side of the disk  11  in a direction perpendicular to principal planar surface of the magnetic layer  12 . This alternate application of the magnetic field would, in the nomenclature of the illustrated embodiment, result in a magnetization of the plurality of magnetic segments  13  in a second magnetization direction opposite to that of the first magnetization direction  14 . 
     Referring to  FIGS. 1 and 3 , according to another method of forming a servo track on a magnetic disk, first and second magnetic patterns  23  and  24  are formed on a substrate  21  (S 20 ). In this stage, a writing apparatus  20  is used to write predetermined information to the magnetic layer  12  on the disk  11  of the data storage apparatus  10 , as described above. The first and second magnetic patterns  23  and  24  correspond to the first and second arrangements of the magnetic segments  13  on the disk  11  in the respective first and second servo track regions. The first and second magnetic patterns  23  and  24  may be separately formed on the substrate  21  which may be implemented using a semiconductor substrate. 
     The substrate  21  includes a first magnetic pattern region  25  and a second magnetic pattern region  26 . The first magnetic pattern region  25  corresponds to the first servo track region(s)  15 , and the second magnetic pattern region  26  corresponds to the second servo track region  16 . 
     A magnetic material  22  is applied to a predetermined thickness on one side of the substrate  21  including the first magnetic pattern region  25  and the second magnetic pattern region  26 . The magnetic material  22  may be formed from a material capable of effectively communicating an externally applied magnetic field, and may be applied using conventionally understood spin coating or print coating techniques. 
     The magnetic material  22  formed on the substrate  21  is selectively patterned. In the illustrated embodiment, the magnetic material  22  is patterned such that the first magnetic pattern  25  is formed by alternating pattern regions  23  having a first width d 1 , and the second magnetic pattern  26  is formed by alternating pattern regions  24  having a second width d 2 . The first width dl of the first magnetic pattern  25  is smaller than the second width d 2  of the second magnetic pattern  26 . In one embodiment of the invention, the first width d 1  is 1/N, where N is an integer greater than 0, of the second width d 2 . The first and second patterns regions  23  and  24  may be defined using photolithography or wet/dry etching using a mask on the magnetic material  22 , for example. 
     Referring to  FIGS. 1 and 4 , the substrate  21  containing the first and second magnetic patterns  25  and  26  is disposed over the disk  11  (S 30 ). In the illustrated embodiment of  FIG. 4 , the first surface of the disk  11  including the plurality of magnetic segments  13  faces the working surface of the substrate  21  including the first and second magnetic patterns  25  and  26 , such that each one of the magnetic segments  13  is vertically under a corresponding first pattern  23  in the first servo track regions  15 , or a corresponding second pattern  24  in the second servo track region  16 . 
     Referring to  FIGS. 1 ,  4  and  5 , a second magnetic field is now vertically applied to the upward facing bottom surface of the substrate  21  (S 41 ) in order to change the magnetization direction of certain magnetic segments  13  (in the second servo track region  16 ) or magnetic segment portions (in the first servo track regions(s)  15 ) within the magnetic layer  12  (S 43 ). Operations S 41  and S 43  actually happen in a single operation (S 40 ). Thus, assuming that the working (first) surfaces of the disk  11  and substrate  21  are disposed facing one another, the second magnetic field is applied “through” the upward facing bottom surface (i.e., in a direction from the bottom surface to top surface) of the substrate  21 . 
     Since the applied second magnetic field is effectively conducted (i.e., communicated) to the magnetic layer  12  of the disk  11  via the first and second patterns  23  and  24  and is not effectively conducted by the intervening gaps (i.e., the regions of the substrate working surface between adjacent patterns), only selected ones (or selected portions) of the plurality of magnetic segments  13  have their magnetization direction changed. In the illustrated embodiment, the applied second magnetic field is vertically applied through the substrate  21  in a direction substantially opposite to that of the first magnetization direction  14 , or in effect yielding a second magnetization direction  17 . However, other relative magnetization directions (non-vertical with respect to a substantially horizontal magnetic layer  12 ) may be defined by the applied first and second magnetic fields. 
     Thus, in the illustrated embodiment of  FIG. 5 , each one of the magnetic segments  13  disposed in a first servo track region  15  includes a first segment region  13   b  having the first magnetization direction  14  and a second segment region  13   a  having the second magnetization direction  17 . Here, each one of the first and second segment regions has the first width d 1  approximately equal to about half of the original magnetic segment region width d 2 , but other geometries may be used by other embodiments of the invention. In contrast, the magnetic segments  13  disposed in the second servo track region  16  are alternately polarized between the first and second magnetization directions  14  and  17 . 
     Referring to  FIGS. 1 ,  5 , and  6 , read signals may be detected from the magnetic layer  12  of the disk  11  using a read head  150  (S 50 ). The resulting read signals may be filtered (S 60 ) prior to use by external circuitry. 
     That is, a first read signal  40  may be detected using the read head  150  placed near magnetic segments  13  of the first servo track region  15 . A second read signal  50  may be detected using the read head  150  placed near magnetic segments  13  of the second servo track region  16 . The first and second read signals  40  and  50  will exhibit different cycles or read frequencies in relation to the different spacing between the alternately polarized magnetic segments  13  in each region. For instance, the first read signal  40  detected in the first servo track region  15  will have a first cycle period T 1  defined by high/low signal transitions associated with the first magnetization direction  14  and the second magnetization direction  17 . The second read signal  50  detected in the second servo track region  16  will have a second cycle period T 2  similarly defined by high/low signal transitions. 
     In other words, the first read signal  40  detected in the first servo track region  15  will have a higher frequency (or a shorter cycle period) than the second signal  50  detected in the second servo track region  16 . For example, the first cycle period T 1  for the first signal  40  may be 1/M, where M is an integer greater than 0, of the second cycle period T 2  for the second signal  50 . 
     As noted above, the first servo track region  15  may be used as a no-signal field of a buffer field and the second servo track region  16  may be used to store servo data. Like all magnetic recording media, it is possible that noise may affect the first read signal  40  detected in the first servo track region  15 . However, since such noise will be associated with the first read signal  40 , and the first read signal has a different frequency than the second read signal containing the desired servo data, the noisy first read signal associated with a first servo track region  15  may be readily filtered out. A conventional high/low filter, band pass filter, or band reject filter may be used to effectively separate the second read signal containing servo data from the first read signal. 
       FIG. 7  is a general block diagram of a data storage apparatus  200  manufactured in accordance with a method of forming a servo track as described above.  FIGS. 1 through 6  will be referred to as well as  FIG. 7  in describing the data storage apparatus  200 . The data storage apparatus  200  may be implemented using a hard disk drive (HDD) capable of electronically or magnetically storing data. Such drives are usually cheaper on a per-stored-data-bit basis than non-volatile memory devices, such as solid state drives (SSD) having similar storage capacity. 
     Referring to  FIG. 7 , the data storage apparatus  200  includes a storage unit  100 , the read head  150 , a controller  170 , and a filter  160 . The storage unit  100  includes recording media having at least one servo track as described with reference to  FIGS. 1 through 6 . For instance, the storage unit  100  may be implemented with at least one disk  11 . The disk  11  includes a data storage area and a servo track area. As described above, in the servo track area of the disk  11  is formed with magnetic layer  12  including the plurality of magnetic segments  13  each having either the first magnetization direction  14  and/or the second magnetization direction  17 . 
     As described with reference to  FIG. 5 , the head  150  detects a read signal when proximate to the magnetic layer  12 . The controller  170  controls the overall operation of the read head  150  and storage unit  100 , as is conventionally understood. For instance, the controller  170  will control the rotation of the disk  11  at a predetermined velocity and the movement of the read head  150  across the disk  11  in order to detect data signals from the disk  11 . 
     The filter  160  is used to filter the signals detected by the read head  150  and may thereafter provide filtered signals to the controller  170 . As described above with reference to  FIGS. 1 and 6 , the filter  160  may be used to eliminate a noisy first read signal  40  from a desired second read signal  50 . 
       FIG. 8  is a general block diagram of a data storage system  300  including the data storage apparatus  200  illustrated in  FIG. 7 . The data storage system  300  may be a computer system, a terminal system, or an input/output system. In addition, the data storage system  300  may be any type of consumer equipment (CE) including the data storage apparatus  200  according to some embodiments of the present invention. The CE may be an HDD recorder, a personal terminal (e.g., a cellular phone or a personal digital assistant (PDA)), a computer (e.g., a personal computer (PC), a laptop computer, or a notebook computer), a navigator device, a home automation system, a music player (e.g., an MP3 player), a camcorder, a video player (e.g., a DivX player), a storage server, or a portable multimedia player (PMP). For clarity of the description, it is assumed that the data storage system  300  is a computer system. 
     Referring to  FIG. 8 , the data storage system  300  includes a bus  270 , a central processing unit (CPU)  250 , the data storage apparatus  200 , and an interface (I/F)  260 . Although not shown, the data storage system  300  may also include a battery so that the data storage system  300  is portable. 
     The CPU  250  generates control signal(s) controlling the overall operation of the data storage apparatus  200  and provides the control signal to the data storage apparatus  200  via the bus  270 . As described with reference to  FIG. 7  above, the data storage apparatus  200  may include the storage unit  100 , read head  150 , filter  160 , and controller  170  and may store externally input data therein or transmit stored data outside according to the control signal provided from the CPU  250 . The I/F  260  may be an input/output (I/O) I/F or a wireless I/F and functions as a passage through which the CPU  250  or the data storage apparatus  200  can access the outside. 
     According to certain embodiments of the invention, a noisy read signal arising from a first servo track region (i.e., a buffer region) may be effectively removed by causing the first read signal to have a different frequency than a desired second read signal arising from a second servo track region. This difference in respective read signal frequency may be induced by differently sized alternating magnetic segment regions for the first and second servo track regions. More effective removal of the noisy first read signal arising from a servo track buffer region will reduce the likelihood of malfunction in a data storage apparatus, and systems incorporating the data storage apparatus. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in forms and details may be made therein without departing from the scope of the invention as defined by the following claims.