Abstract:
A servo write head that provides fast servo pattern writing and improved tape manufacturing speed is provided. The write head may be fabricated using thin-film fabrication techniques. A coil is formed on a bottom pole of the write head. The coil has a plurality of turns that enable the write head to generate a magnetic field sufficient for writing data with reduced current. The inductance of the coil is reduced due to its small dimensions. Reduced inductance of the coil may enable increased switching frequency of the write head, allowing data to be written at a higher frequency. The write head includes a planar top pole coupled to the bottom pole. The top pole has more than one write gap is formed therein.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to magnetic tape heads, and more particularly, to a planar servo write head for flexible magnetic storage media. 
     2. Background Information 
     Linear recording media, such as magnetic tapes, store data on linear data tracks that run parallel to each other over the length of the media. The magnetic media, or tape, is moved across a magnetic tape head for reading data stored on the tape and writing data to the tape. For throughput, tape heads write eight or more tracks simultaneously. 
     As the tape runs transversely across the magnetic tape head, the tape may move laterally relative to the head. This lateral movement of the tape may result in the head reading or writing data off track or on the wrong track. Thus, accurate positioning of the tape head relative to the tape is critical. 
     To enable accurate positioning of the tape head, media manufacturers may write servo tracks on the magnetic tape parallel to the data tracks. Servo readers in the tape head read the servo information in the servo tracks. The servo information is then used for aligning transducers in the head with data tracks on the tape. The servo information is also used for deriving tape velocity and for data channel timing recovery. The servo information may also include the longitudinal position of the tape, manufacturers&#39; data, and servo-band or data-band identification. This additional data is typically encoded using phase modulation. 
     Servo tracks are typically written to the magnetic tape during manufacture of the tape by heads, known as servo write heads, that are dedicated to writing servo patterns. An exemplary prior art servo write head  100  is shown in  FIG. 1  of the drawings. The servo write head  100  may be constructed from two blocks  102 ,  104  that typically comprise magnetic ferrite. The blocks may be separated by a glass spacer  106  and are bonded to the spacer. The head  100  is then lapped to form a top surface  108  of a desired contour. 
     A magnetic seed layer  110  is then deposited on the top surface  108 . A photoresist layer may then be deposited on the seed layer  110  and patterned to form the desired write gaps  112 . The fabrication techniques and processes used to fabricate known servo write heads limits minimum achievable write gaps to approximately 0.5 to 1 micrometers. 
     As data track density on magnetic tape increases, data track width decreases. Track following errors must also decrease. Thus, increasing servo pattern linear density is required. Resultantly, write gap widths from about 0.5 to 1 micrometers are too large for future servo pattern writing requirements due to narrower data tracks. 
     After the write gaps are formed, a layer of magnetic material several microns thick  114  is plated on the seed layer  110 , with the write gaps extending though the magnetic layer. A wear-resistant overcoat may be deposited over the magnetic layer. 
     A coil  116  is wound around one of the blocks through a slot  118  that passes though the head. The coil typically has one to three coil turns that wind about the block. Electrical current is applied to the coil to create a magnetic field in the write gaps of the head. Several amperes of current are applied to the coil to generate enough magnetic field to write the servo patterns. The magnetic field sets the magnetization in the tape as it runs across the tape bearing surface, thus writing the servo patterns on the tape. 
     A disadvantage of the prior art head is that the large yoke structure has a very large inductance “L”. Since the response time of the head is L/r, where “r” is the series resistance, the larger inductance creates a longer rise time. Long rise time limits how fast the tape can be moved during servo pattern writing. This limits the speed that servo patterns can be written to the tape, limiting manufacturing speed of the tape. The inductance itself is proportional to N 2 , where N is the number of coil turns of the head. Thus, to keep inductance down, N is limited to one to three coil turns. However, this results in a requirement for larger currents flowing through the coil. 
     Accordingly, there is a clearly-felt need in the art for a servo write head that provides faster servo pattern writing and faster tape manufacturing speed, and has write gaps of a reduced width. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below. 
     SUMMARY OF THE INVENTION 
     An embodiment of the invention comprises a servo write head that enables faster servo pattern writing and thus faster tape manufacturing speed. The servo write head may be fabricated using thin-film fabrication techniques. 
     An embodiment of the servo write head includes a magnetic bottom pole with a conductive coil and a magnetic top pole coupled to the bottom pole. The coil has a plurality of turns that wind around the bottom pole. The top pole is formed with a planar tape bearing surface that has at least one write gap formed therein. Alternatively, the write gaps may be formed by disposing pole islands between segments of the top pole. The pole islands may be formed of materials having a relatively high magnetic moment. 
     The write gaps are defined using thin-film fabrication techniques to provide gaps having a reduced width as compared to known write heads. In an embodiment of the write head, write gaps having a width of less than about 0.5 micrometers are formed. In another embodiment the width of the write gaps may be about 0.2 to 0.3 micrometers. The narrower write gaps enable writing sharp transitions to a magnetic data storage media, such as a magnetic data storage tape. This allows for improved reading of the information written to the tape by the invented head, such as servo information. The write gaps may be formed in any suitable pattern, such as a chevron pattern, for writing servo data. 
     The multi-turn coil enables generating a magnetic field sufficient for writing data with reduced current. Current in the range of 10 milliamps to 50 milliamps is sufficient for writing data. Performing write data operations with reduced current applied to the coil may increase the switching frequency of the write head, allowing data, such as servo data, to be written at a higher frequency. Further the invented write head has an inherently lower inductance magnetic core, which enhances the frequency response of the head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary prior art servo write head; 
         FIG. 2  is a side elevation view of an exemplary embodiment of a servo write head of the present invention; 
         FIG. 3  is a top plan view showing a fabrication step of the exemplary embodiment of the servo write head of the invention; 
         FIG. 4  is a top plan view of an exemplary embodiment of the servo write head of the invention; 
         FIG. 5  is side elevation view of the alternative embodiment of the servo write head of the invention; 
         FIG. 6  is a top plan view of the alternative embodiment of the servo write head of the invention; 
         FIG. 7  is a top plan view of another alternative embodiment of the servo write head of the invention; 
         FIG. 8  is a perspective view of the other alternative embodiment of the servo write head of the invention; 
         FIG. 9  is a partial plan view showing the servo write head of the invention in communication with a magnetic data storage tape; and 
         FIG. 10  is a functional block diagram showing a data writing apparatus adapted for use with the servo write head of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 2  through  FIG. 4  of the drawings, there is shown an exemplary embodiment of a servo write head. The servo write head  10  enables fast servo pattern writing and improved tape manufacturing speed. 
     The servo write head  10  may be fabricated using known processes. The write head  10  is fabricated using techniques common to both hard disk drive head and semiconductor industries, such as thin-film fabrication techniques. Building the servo write head  10  using thin-film fabrication techniques may provide several advantages over other known methods for fabricating servo write heads. Building servo write heads using thin-film techniques enables these write heads to be built on AlTiC (Aluminum-Titanium-Carbon) wafers or on silicon wafers, which may reduce the costs associated with manufacturing the heads. Also, servo write heads built on a silicon wafer may be integrated with other active devices on the wafer. Additionally, fabricating servo write heads using thin-film techniques may enable these write heads to be built at a single processing location, which can reduce the costs associated with manufacturing these heads. Further, a servo write head having reduced dimensions is achievable using thin-film fabrication techniques. 
     The servo write head  10  may be fabricated in layers as is common to thin-film fabrication. A substrate  12 , that the head  10  is fabricated on may comprise any suitable material, such as silicon. A first layer L 1  of the head  10  includes a layer of insulation  11  that is disposed on the substrate  12 . The layer of insulation  11  may comprise SO 2  or AL 2 O 3 , for example. 
     A portion of a coil  14  is then formed on the insulation  11 . The coil  14  may comprise a known configuration, such as a helical coil or a pancake coil configuration (not shown). In the embodiment shown in the Figures, the coil  14  is helical. A conducting bar  16  of each of a plurality of coil turns  18  of the coil  14  are then formed on the insulation  11 . The conducting bars  16  may comprise a conductive material, such as copper. The bars  16  are formed by the known process of electroplating and patterning. The conducting bars  16  are aligned generally diagonally to a longitudinal axis A of the head  10 , to form the helical coil  14 . In the exemplary embodiment shown in the drawings, ten coil turns  18  are shown. However, it is to be understood that the plurality of turns  18  may range from about three to more than twelve turns  18 . The coil  14  turns pitch may be about 3.0 μm or less, while the width of the coil turns  18  is typically not less than about 1 μm. There may be a gap  15  of about 0.5 μm to 1.0 μm between adjacent coil turns  18 . A second layer of insulation  13  is then disposed over the conducting bars  16  and etched. The second layer of insulation  13  may comprise SO 2  or AL 2 O 3  as discussed. 
     A next layer L 2  of the head  10  comprises a bottom pole  20  that is formed over the conducting bars  16  of the turns  18  and second insulation layer  13 , by disposing the material comprising the bottom pole  20 . The bottom pole  20  may comprise a magnetic alloy having a high magnetic permeability. In one embodiment, the bottom pole  20  comprises a magnetically permeable material of the type conventionally used to fabricate inductive write heads for information storage, such as Permalloy, that comprises 19% iron and 81% nickel. The Permalloy may be plated and patterned using well known processes and techniques. 
     In an exemplary embodiment, the bottom pole  20  may range in thickness from about 3 μm to about 5 μm. In one embodiment, the width of the pole  20  may substantially equal the width of a track of a tape where servo information (servo track width), is written (more thoroughly discussed hereinafter). Alternately, the width of the pole  20  may be greater than the servo track width to help ensure that it does not saturate at the current needed to write servo information to the media. 
     A vertical segment  22  of each turn  18  may be formed on an insulation layer  28  that is formed on an upper surface  30  of the bottom pole  20 . The insulation layer  28  may comprise a suitable non-electrically conductive material, such as alumina, aluminum oxide, or photoresist. A conductive metal is plated on an exposed end  24  (shown in  FIG. 3 ) of each conductive bar  16  through a via  23  to form each vertical segment  22 . The metal may be plated on each bar portion  16  to a depth approximately equal to a height of the bottom pole  20  plus the thickness of the insulation layer  28 . 
     On a next layer L 3  of the head  10 , a top portion  26  of each coil turn  18  is formed. The top portion  26  of each coil turn  18  may be formed on the insulation layer  28 . The top portion  26  of the coil turns  18  may be formed in a manner similar to forming the conducting bars  16 . The top portion  26  of each coil turn  18  may extend across the insulation layer  28  and between opposing vertical segments  22 , for coupling the top portion  26  to the segments  22 , to complete the helical coil  14 . The conductive metal comprising the coil  14  is plated to form the top portion  26  of the coil turns  18  to complete the coil  14 . 
     A pole magnetic yoke segment  32  may be formed on each end  34  of the bottom pole  20  adjacent to the coil  14 . The pole magnetic yoke segments  32  are formed by etching the insulating layer  28  at each end  34  of the bottom pole  20 , to expose the ends  34 . The material comprising the segments  32  may then be plated or otherwise formed on the exposed ends  34 . The height of pole segments  32  is determined, in part, by the thickness of the top bars  26  of the coil  14 . In an exemplary embodiment, the height of the pole segments  32  is about 3 μm to 5 μm. However, the height of the segments  32  may be more or less, depending upon the thickness of the bars  26 . The width of the segments  32  may be substantially similar to the width of the bottom pole  20 . The configuration of the pole segments  32  prevents magnetic saturation in this region of the head  10 . The pole segments  32  comprise a magnetically permeable material, such as Permalloy. In one embodiment, the segments  32  comprise the same magnetic alloy that the bottom pole  20  comprises. 
     Referring to  FIG. 2  and  FIG. 4 , a next layer L 4  of the servo write head  10  comprises a top pole  36  that is formed on the pole segments  32  to provide a complete magnetic circuit. The top pole  36  preferably comprises a material having a high magnetic moment. For example, the top pole  36  may comprise a nickel-iron alloy that contains approximately 45% nickel and 55% iron. 
     The top pole  36  is formed by first disposing and patterning a mask layer over a top surface  38  of the pole segments  32  and insulating layer  28 . The mask layer is patterned and etched to form at least one write gap  40  in the top pole  36 . The top pole  36  is dimensioned so that its width is about equal to the servo track width, where the head  10  will be writing servo data. The bottom pole  20  may be wider than the top pole to help insure that the bottom pole  20  does not saturate before the top pole  36 . The width of the top pole  36  may range from about 10 μm to more than 185 μm, depending upon the selected application and servo track width. The top pole  36  may range in thickness from approximately 1 μm to 5 μm. 
     In the exemplary embodiment, two write gaps  40  are shown to be formed on the top pole  36  of the servo write head  10 . Although two write gaps  40  are shown in the write head  10  in  FIG. 2 , the head  10  may include two or more write gaps  40 . The write gaps  40  may be formed in any suitable pattern. For example, the write gap  40  may be positioned at an angle relative to a transverse axis T of the head  10 , for writing time-based servo patterns. The write gaps  40  may be patterned to form an angle with the transverse axis T from approximately 6° to approximately 25°, depending upon the selected application of the head  10 . 
     Preferably, the write gaps  40  are formed in a pattern desirable for writing servo data, such as a chevron pattern shown generally at  42 . Since the write gaps  40  are formed using thin-film techniques, the gaps  40  of the exemplary embodiment have reduced width compared to the write gaps of known servo write heads. 
     In one embodiment, each write gap  40  is patterned with a narrow region  41  located adjacent to a tape bearing surface  46  of the head  10  and a widened portion  43 . The widened portion  43  of the write gap  40  focuses magnetic flux flowing across the gap  40  through the narrow region  41  of the gap  40 , to efficiently write data. 
     The reduced width of the narrow region  41  of the write gaps  40  may enable sharp transitions when writing data, such as servo pattern data, which provides improved signals for reading the servo data written by the head  10 . In the exemplary embodiment, the height of the narrow region  41  of the write gaps  40  is less than about 0.5 micrometers. In a preferred embodiment, the width of the narrow region  41  of the write gaps  40  may be about 0.3 micrometers. 
     A top surface  44  of the top pole  36  may be formed generally planar to provide the planar tape bearing surface  46 . The top surface  44  may be planarized using known methods, such as by lapping or Chem-mechanical polishing (CMP), for example. In one embodiment, CMP, or other planarization technique used in semiconductor fabrication, is used for planarizing the top surface  44  of the top pole  36 . Planarizing the top surface  44  using a planarization technique common to semiconductor fabrication may reduce the costs associated with fabricating the head  10 . 
     Optionally, a layer of a wear resistant material  48  may be disposed over the top surface  44  of the top pole  36 . The layer wear resistant material  48  would be provided to increase the life of the invented head  10 . The wear resistant material may comprise any suitable material known in the art, such as diamond-like carbon, for example. 
     Referring to  FIG. 5  and  FIG. 6 , there is shown an alternative embodiment  50  of the servo write head, where the top pole  36  is formed with opposing end portions  52 . In this embodiment, the top pole  36  comprises a magnetically permeable material, comprising about 20% iron and 80% nickel. The end portions  52  are formed such that there is a substantial gap  54  between the end portions  52 . The top surface  44  of the top pole  36  is planarized, as discussed previously. 
     On a next layer L 5 , pole islands  56  are formed on the top surface  44  of the top pole  36  to provide the write gaps  40 . The pole islands  56  preferably comprise a ferromagnetic material having a high magnetic moment, optimal for writing data. In an exemplary embodiment, the pole islands  56  comprise an alloy of about 45% Nickel and 55% Iron. The pole islands  56  may comprise materials having a magnetic moment of about 2.0 Tesla or greater. 
     The islands  56  may be formed by disposing a mask layer  58  on the top surface  44 , then patterning and etching the mask layer  58 . The high magnetic moment pole material is then disposed on the top surface  44  forming the islands  56 , with write gaps  40  being defined between adjacent islands  56 . A number of islands  56  may be formed, to achieve a desired number of write gaps  40 . Typically two or more write gaps  40  are formed in a chevron pattern  42 , as previously discussed. In this embodiment the write gaps  40  are formed with a uniform width. Since the islands  56  are formed using thin-film techniques, the narrow region  41  of the write gaps  40  of this embodiment may be less than approximately 0.5 micrometers. 
     To increase the strength of the magnetic field across the write gaps  40 , for improved servo track writing, the coil turns  18  may be positioned as close as possible to the bottom surface of the top poles  36 . 
     In another embodiment, shown in  FIG. 7  and  FIG. 8 , a top pole  36 A is formed at an angle to the longitudinal axis A of the head  70 . The top pole  36 A of the head  70  extends at an angle relative to the longitudinal axis A for reducing the reluctance between the bottom pole  20  and top pole  36 A. to provide a more uniform gap fringing field. 
     In the embodiment of  FIGS. 7 and 8 , pole segments  30 A are formed on the bottom pole  20  and comprise Permalloy, as previously discussed. However, the pole segments  30 A are etched such that each pole segment  30 A offset relative to the longitudinal axis A, so that the top pole  36 A is positioned at an angle to the longitudinal axis A when formed. 
     The top pole  36 A is then formed on the pole segments  30 A and nonconductive layer  28  (shown in  FIG. 2 ) as discussed and preferably comprises a material having a high magnetic permeability. For example, the top pole  36 A may comprise an alloy of approximately 45% nickel and 55% iron. 
     In the embodiment of  FIGS. 7 and 8 , the top pole  36 A may be formed with more than one write gap  40  therein. The top pole  36 A is positioned at an angle to the longitudinal axis A, so that the write gaps  40  form a reduced angle with the longitudinal axis A of the head  70 . Reducing the angle that the write gaps  40  form with the longitudinal axis A of the head  70  may provide more uniform magnetic reluctance across the width of the write gaps  40 , which may provide a more uniform gap fringing field. 
     To provide a symmetrical gap field at the ends of the write gaps  40 , the top pole  36 A of the embodiment of the head  70  is configured with protuberances  74  along each side  76  of the pole  36 A to form an angle θ with the write gaps  40 . In one embodiment, angle θ is twice the write gap angle. 
     Referring to  FIG. 9  and  FIG. 10 , the inventive concepts described herein may be embodied in an apparatus  200  for writing data, such as servo control data  202  to a tape  204 . The apparatus  200  is preferably configured for writing servo data  202  to a magnetic tape  204  during manufacture thereof. The servo data writing apparatus  200  may be coupled to a host computer  206  for receiving instructions therefrom. 
     The apparatus  200  includes plural components that provide control of writing servo control data  202  to the magnetic tape  204 , during manufacture. By way of example only, those components may conventionally include a microprocessor controller  208 , a data buffer  210 , a servo write data flow circuit  212 , a motion control system  214 , and a tape interface system  216  that includes a motor driver circuit  218  and one or more of the invented servo write heads  10 . 
     The microprocessor controller  208  provides overhead control functionality for the operations of the apparatus  200 . When writing servo data  202  to the tape  204 , the controller  208  communicates with the host  206  for sending servo data to the data buffer  210  that stores the data for subsequent writing. The data buffer  210  in turn communicates the data block received from the host  206  to the data flow circuit  212 , which formats the data  202  into physically formatted data that may be written to the magnetic tape  204 . The formatted physical data is then communicated to the tape interface system  216  from the data flow circuit  212 . 
     The tape interface system  216  includes one or more servo write heads  10  described herein. The interface system  216  also includes drive motor components (not shown) for performing forward and reverse movement of the tape  204  which is mounted on a supply reel  220  and a take-up reel  222 . The drive components of the tape interface system  216  are controlled by the motion control system  214  and the motor driver circuit  218 , for moving the tape  204  transversely across a tape bearing surface  224  when writing servo data  202  to the tape  204 . 
     The servo data  202  written to the tape  204  produces peaks in a read-back signal when the servo data  202  is read by another device (not shown). However, noise from the media, or tape  204 , may cause the apparent position of servo marks  206 , comprising the servo data  202  to shift slightly in time, referred to in the art as “peak jitter”. Peak jitter is random, but the mean time difference between peaks can be improved by writing more servo marks  206  to the tape  204  within a given length of tape  204 . 
     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.