Abstract:
A thin film servo head apparatus is described that provides verification of time-based servo marks on a magnetic tape. The thin film servo head apparatus includes a plurality of thin film servo heads formed in a substrate. The substrate is canted such that servo gaps included in each of the thin film servo heads are substantially parallel to the time-based servo marks. Thin film servo heads eliminate the high labor, low yield machining process associated with conventional ferrite composite servo heads. Thin film servo heads may be fabricated in bulk on substrate wafers to reduce manufacturing time and cost. The invention described herein enables thin film servo heads to be used with time-based servo markings by defining a servo gap spacing such that when the substrate is canted, the servo gaps of the thin film servo heads substantially align with the time-based servo markings.

Description:
TECHNICAL FIELD 
   The invention relates to servo heads for use with magnetic storage media and, more particularly, thin film servo heads. 
   BACKGROUND 
   Data storage media are commonly used for storage and retrieval of data, and come in many forms, such as magnetic tape, magnetic disks, optical tape, optical disks, holographic disks or cards, and the like. Magnetic tape media remains economical for storing large amounts of data. For example, magnetic tape cartridges, or large spools of magnetic tape, are often used to back up data in large computing centers. Magnetic tape cartridges also find application in the backup of data stored on smaller computers such as desktop or notebook computers. 
   In magnetic media, data is typically stored as magnetic signals that are magnetically recorded on the medium surface. The data stored on the medium is typically organized along “data tracks,” and transducer heads are positioned relative to the data tracks to write data to the tracks or read data from the tracks. A typical magnetic storage medium, such as magnetic tape, typically includes several data tracks in a data band. Optical media, holographic media, and other media formats can also make use of data tracks. 
   Servo patterns refer to signals or other recorded marks on the medium that are used for tracking purposes. In other words, servo patterns are recorded on the medium to provide reference points relative to the data tracks. A servo controller interprets detected servo patterns and generates position error signals. The position error signals are used to adjust the lateral distance of the transducer head relative to the data tracks so that the transducer head is properly positioned along the data tracks for effective reading and/or writing of the data to the data tracks. 
   With some data storage media, such as magnetic tape, the servo patterns are stored in specialized tracks on the medium, called “servo tracks.” Servo tracks serve as references for the servo controller. Servo tracks typically hold no data except for information that is useful to the servo controller to identify positioning of a transducer head relative to the surface of the medium. A plurality of servo tracks may be defined in a servo band. Some magnetic media include a plurality of servo bands, with data tracks being located between the servo bands. 
   The servo patterns recorded in the servo tracks may be sensed by one or more servo heads. For example, servo heads may be dedicated heads that read only servo patterns in the servo tracks. Alternatively, servo heads may be integrated with a read/write head. In any case, once a particular servo track is located by the servo head, one or more data tracks can be located on the medium according to the data track&#39;s known displacement from the servo track. The servo controller receives detected servo signals from the servo heads, and generates position error signals, which are used to adjust positioning of a read/write head relative to the data tracks. 
   Time-based servo techniques refer to servo techniques that make use of time variables. Time-based servo techniques are particularly effective for magnetic tape, which typically feeds past transducer heads at a constant velocity. For example, N-shaped servo markings, servo markings such as “&lt;&lt;&lt; &gt;&gt;&gt;” or “//// \\\\,” or the like, have been developed for time-based servo techniques. Such markings are typically formed in a servo band of the magnetic tape and may define a plurality of servo tracks in the servo band. 
   When time-based servo techniques are used, the time offset between detection of two or more servo marks can be translated into a position error signal, which defines a lateral distance of the transducer head relative to a data track. For example, given a constant velocity of magnetic tape formed with marking “/ \”, the time between detection of “/” and “\” becomes larger when the servo head is positioned towards the bottom of marking “/ \” and smaller if the servo head positioned towards the top of marking “/ \”. Given a constant velocity of magnetic tape, a defined time period between detected servo signals may correspond to a center of marking “/ \”. By locating the center of marking “/ \”, a known distance between the center of the servo track and the data tracks can be identified. Different servo tracks may be defined by different traverse locations along the marking “/ \”. 
   A servo head that is able to read and/or write full band time-based servo marks includes servo gaps oriented parallel to the servo markings. A full band servo verify head is used to read back the entire width of the servo markings to detect flaws in the written servo signal. In time-based servo systems, part or all of the servo signal is recorded at an angle non-parallel to both the down tape and transverse directions of tape motion. The verification process for time-based servo markings requires servo read gaps to be oriented parallel to the directions of the servo markings. This is accomplished by orienting individual ferrite composite servo head cores using precision assembly and machining. The resultant servo head has high labor content and low yield, which makes this type of servo verify head expensive to manufacture. 
   SUMMARY 
   In general, the invention is directed to a thin film servo head apparatus that provides full band verification of time-based servo marks on a magnetic tape. The thin film servo head apparatus includes a plurality of thin film servo heads formed in a substrate. The substrate is canted such that servo gaps included in each of the plurality of thin film servo heads are substantially parallel to the time-based servo marks. Thin film servo verify heads eliminate the high labor, low yield machining process associated with conventional ferrite composite servo verify heads. Thin film servo heads may be fabricated in bulk on substrate wafers to reduce manufacturing time and cost. 
   It can be difficult or impossible to fabricate angled servo gaps for the thin film servo heads using conventional techniques. The invention described herein enables thin film servo heads to be used with time-based servo markings by defining a servo gap spacing such that when the substrate is canted, the servo gaps of the thin film servo heads substantially align with the time-based servo markings. For example, a servo gap spacing y may be defined according to the equation: 
             y   =     x     cos   ⁡     (   α   )           ,         
where x is a transverse distance between centers of adjacent servo bands on the magnetic tape and α is an angle at which the substrate is canted relative to a transverse direction of the magnetic tape.
 
   In one embodiment, the invention is directed to a thin film servo head apparatus positioned in a transverse direction of a magnetic tape moving over the thin film servo head apparatus. The apparatus comprises a first thin film servo head and a second thin film servo head formed on a substrate. The first thin film servo head includes a first servo gap. The second thin film servo head includes a second servo gap substantially parallel to the first servo gap. The substrate is canted relative to the transverse direction of the magnetic tape such that the first and second servo gaps are non-parallel to the transverse direction. 
   In another embodiment, the invention is directed to a system comprising a magnetic tape and a thin film servo head apparatus. The magnetic tape comprises servo bands with servo marks oriented non-parallel to both a down tape direction and a transverse direction. The thin film servo head apparatus, positioned in the transverse direction of the magnetic tape moving over the thin film servo head apparatus, comprises a first thin film servo head and a second thin film servo head formed on a substrate. The first thin film servo head includes a first servo gap corresponding to a first servo band on the magnetic tape. The second thin film servo head includes a second servo gap substantially parallel to the first servo gap that corresponds to a second servo band on the magnetic tape. The substrate is canted relative to the transverse direction of the magnetic tape such that the first and second servo gaps are substantially parallel to at least a portion of the servo marks in the first and second servo bands. 
   In another embodiment, the invention is directed to a method of fabricating a thin film servo head apparatus to be positioned in a transverse direction of a magnetic tape moving over the thin film servo head apparatus. The method comprises forming at least two thin film servo heads on a substrate. Each of the thin film servo heads comprises a servo gap. The method further comprises canting the substrate relative to the transverse direction of the magnetic tape such that the servo gaps are non-parallel to the transverse direction. 
   Various aspects of the invention can provide a number of advantages. For example, the thin film servo head apparatus reduces manufacturing time and cost relative to the conventional ferrite composite servo head. Furthermore, the thin film servo apparatus may be used as a servo verify head to read back the entire width of a time-based servo pattern to detect gross flaws in the recorded servo signal. 
   In some cases, the thin film servo head apparatus comprises a planar surface, as opposed to a conventional servo head apparatus that typically includes a cylindrically contoured surface with servo gaps positioned along an apex of the cylindrical contour in order to make full contact with a magnetic tape. The canted substrate of the invention causes the servo gaps to misalign with an apex of a cylindrical contour. Thus, if a contoured surface is used, the servo gaps not located at the apex may not maintain contact with the magnetic tape. In accordance with the invention, however, a planar surface allows each servo gap in the canted substrate to maintain full contact with the magnetic tape moving over the thin film servo head apparatus. Therefore, the planar surface increases the ability of the servo gaps to accurately read the time-based servo marks. The thin film servo head apparatus described herein may be used to read or write servo marks, or to verify that servo marks have been accurately recorded on a medium. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic diagram illustrating a servo head assembly including a first thin film servo head apparatus and a second thin film servo head apparatus. 
       FIG. 2  is a schematic diagram illustrating another servo head assembly including the first thin film servo head apparatus and the second thin film servo head apparatus from  FIG. 1 . 
       FIG. 3  is a schematic diagram illustrating a portion of a magnetic tape passing over a servo head assembly. 
       FIG. 4  is a schematic diagram illustrating a portion of a magnetic tape passing over a thin film servo head apparatus. 
       FIGS. 5–13  are schematic diagrams illustrating a manufacturing process of thin film servo heads and thin film servo head apparatuses. 
       FIG. 14  illustrates an exemplary servo verify system for verifying servo patterns on a magnetic tape with thin film servo head apparatuses. 
       FIG. 15  is a schematic diagram illustrating an exemplary servo system for recording and verifying time-based servo patterns on a magnetic tape. 
       FIG. 16  is schematic diagram illustrating a servo head assembly according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic diagram illustrating a servo head assembly  5  including a first thin film servo head apparatus  10  and a second thin film servo head apparatus  20 . First apparatus  10  includes a first substrate  12  and five servo gaps  14 A– 14 E formed in first substrate  12 . First substrate  12  is mounted in a first mounting structure  16 . Second apparatus  20  includes a second substrate  22  and five servo gaps  24 A– 24 E formed in second substrate  22 . Second substrate  22  is mounted in a second mounting structure  26 . In other embodiments, first and second substrates  12  and  22  may respectively include any number of servo gaps. In other embodiments, first and second substrates  12  and  22  are not necessarily mounted in mounting structures. 
   First and second apparatuses  10  and  20  are positioned in a transverse direction  29  of a magnetic tape moving over the apparatuses in a down tape direction  28 . First substrate  12  is canted relative to transverse direction  29  such that servo gaps  14  are non-parallel to transverse direction  29 . Second substrate  22  is canted relative to transverse direction  29  such that servo gaps  24  are non-parallel to transverse direction  29 . Alternatively, the second substrate may be parallel to the traverse direction, and a third substrate could be used, e.g., for use with N-shaped servo patterns. In any case, second substrate  22  is positioned within mounting structure  26  to be non-parallel to first substrate  12 . The substrates  12  and  22  may be canted to define an angle α with transverse direction  29 . For N-shaped servo patterns, however, only one of the substrates would be canted, i.e., the substrate with the gaps corresponding to the hypotenuses of the N-shaped servo patterns. 
   First apparatus  10  and second apparatus  20  are substantially aligned to each other such that, for example, servo gaps  14 A and  24 A correspond to a first servo band on the magnetic tape passing over the apparatuses. Furthermore, servo gaps  14 B– 14 E and  24 B– 24 E respectively correspond a second, a third, a fourth, and a fifth servo band. The servo band may include time-based servo marks oriented non-parallel to both down tape direction  28  and transverse direction  29 . Canting the first and second substrates  12  and  22  allows servo gaps  14  and  24  to be substantially parallel to at least a portion of the time-based servo marks regardless of the servo marks&#39; orientation. Positioning the first and second substrates  12  and  22  to be non-parallel to each other enables reading of time-based servo patterns that include non-parallel servo marks. First and second apparatuses  10  and  20  may comprise servo verify apparatuses that read back the entire width of a servo pattern in each of the servo bands to detect flaws in the written servo signals. 
   Each of the five servo gaps  14 A– 14 E is included in a servo head (not visible in  FIG. 1 ). The servo heads are formed in first substrate  12  using a thin film fabrication process including photolithography and thin film deposition. Each of the servo heads comprises a core, such as a C-core, and a coil wound around the core. Each of the cores defines one of the servo gaps  14  corresponding to one of the servo heads. Each of the five servo gaps  24 A– 24 E is included in a servo head (not visible in  FIG. 1 ). The servo heads and corresponding servo gaps  24  are formed in a substantially similar thin film fabrication process as servo gaps  14 . In some embodiments, the servo heads may be formed in bulk on a substrate wafer. In that case, first and second substrates  12  and  22  may comprise slices from the same substrate wafer. 
   During the thin film fabrication process, a servo gap spacing is defined to ensure accurate alignment of servo gaps  14  and  24  to the servo marks on the magnetic tape passing over the first and second apparatuses  10  and  20 . The servo gap spacing is predefined such that when the substrate is canted by the angle α relative to transverse direction  29 , the servo gaps substantially align with servo marks recorded in adjacent servo bands on the magnetic tape. 
   Due to canted first and second substrates  12  and  22 , servo gaps  14  and  16  may not be able to maintain full contact with the magnetic tape if first and second apparatuses  10  and  20  comprise cylindrically contoured surfaces. In some embodiments, first and second apparatuses  10  and  20  comprise planar surfaces to increase the accuracy and reliability of the servo signals read from the magnetic tape. 
     FIG. 2  is a schematic diagram illustrating a servo head assembly  8  including first thin film servo head apparatus  10  and second thin film servo head apparatus  20  from  FIG. 1 . First substrate  12  and second substrate  22  are mounted in a mounting structure  30 . First and second substrates  12  and  22  are canted and positioned as described in greater detail above. Mounting both substrates  12  and  22  in single mounting structure  30  allows servo gaps  14 A– 14 E and servo gaps  24 A– 24 E to accurately align to each other and to servo marks recorded in servo bands on the magnetic tape. 
     FIG. 3  is a schematic diagram illustrating a portion of a magnetic tape  40  passing over a servo head assembly  31 . In particular, servo head assembly  31  includes a first thin film servo head apparatus  32  and a second thin film servo head apparatus  34 . Apparatus  32  includes a first substrate  36  defining a first servo gap  37 A and a second servo gap  37 B. Apparatus  34  includes a second substrate  38  defining a third servo gap  39 A and a fourth servo gap  39 B. First and second substrates  36  and  38  are mounted in a single mounting structure  35 , substantially similar to  FIG. 2 . Magnetic tape  40  includes a first servo band  42  and a second servo band  44 . First servo band  42  includes servo marks  45 A and  46 A. Second servo band  44  includes servo marks  45 B and  46 B. First substrate  36  is canted to position first write gap  37 A and second write gap  37 B substantially parallel to the orientation of servo marks  45 A and  45 B respectively. Second substrate  38  is canted to position third write gap  39 A and fourth write gap  39 B substantially parallel to the orientation of servo marks  46 A and  46 B respectively. 
   Magnetic tape  40  moves over apparatuses  32  and  34  in a down tape direction  47 . Apparatuses  32  and  34  may be positioned in a transverse direction  48  of magnetic tape  40  to align the servo gaps to the servo bands. First servo gap  37 A and third servo gap  39 A align to servo band  42  in order to accurately read servo marks  45 A and  46 A respectively. Additionally, second servo gap  37 B and fourth servo gap  39 B align to servo band  44  in order to accurately read servo marks  45 B and  46 B. In some embodiments, apparatuses  32  and  34  comprise planar surfaces to ensure servo gaps  37 A,  37 B and  39 A,  39 B maintain full contact with magnetic tape  40  as it passes over apparatuses  32  and  34 . 
   Apparatuses  32 ,  34  may comprise servo verify apparatuses. For example, in the case of apparatus  32  comprising a servo verify apparatus, first servo gap  37 A generates a signal from servo mark  45 A in first servo band  42  on magnetic tape  40 . The generated signal may be used to detect flaws in the recorded servo signal. 
     FIG. 4  is a schematic diagram illustrating a portion of a magnetic tape  50  passing over a thin film servo head apparatus  56 . Magnetic tape  50  includes a first servo band  51 A, a second servo band  51 B, and a data band  52 . Any number of data tracks may define data band  52 . First servo band  51 A includes a first servo mark  54 A. Second servo band  51 B includes a second servo mark  54 B. Thin film servo head apparatus  56  is positioned in a transverse direction of magnetic tape  50 , which moves over apparatus  56  in a down-tape direction. Thin film servo head apparatus  56  comprises a first servo gap  58 A and a second servo gap  58 B formed in a first servo head and a second servo head, respectively, on a substrate  57 . In the illustrated embodiment, substrate  57  is not mounted in a mounting structure. In other embodiments, substrate  57  may be mounted in a mounting structure that defines edges substantially parallel to the transverse direction. 
   Substrate  57  is canted at an angle α with respect to the transverse direction of magnetic tape  50 . Canting substrate  57  allows first and second servo gaps  58 A and  58 B to be substantially parallel to first servo mark  54 A and second servo mark  54 B. As can be seen in  FIG. 4 , first servo gap  58 A corresponds to first servo band  51 A to read first servo mark  54 A. Second servo gap  58 B corresponds to second servo band  51 B to read second servo mark  54 B. In order to achieve alignment between servo gaps on substrate  57  and servo bands on magnetic tape  50 , a servo gap spacing is defined. Servo gap spacing, y, comprises a distance between first servo gap  58 A and second servo gap  58 B along a parallel axis of the canted substrate  57 . The servo gap spacing is defined such that when substrate  57  is canted, the transverse distance between first and second servo gaps  58 A and  58 B is substantially equal to the transverse distance, x, between the centers of first servo band  51 A and second servo band  51 B. Servo gap spacing, y, can be determined from the following equation. 
   
     
       
         
           
             
               
                 y 
                 = 
                 
                   x 
                   
                     cos 
                     ⁡ 
                     
                       ( 
                       α 
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 1 
                 ) 
               
             
           
         
       
     
   
   During fabrication of the thin film servo head apparatus  56 , the servo heads including servo gaps  58 A and  58 B are positioned on substrate  57  at a distance equal to the servo gap spacing, y. In that way, when substrate  57  is canted at angle α relative to the transverse direction, the first and second servo gaps  58 A and  58 B correspond to first and second servo bands  51 A and  51 B and are parallel to first and second servo marks  54 A and  54 B. The thin film servo head apparatus described herein may be used to read or write servo marks, or to verify that servo marks have been accurately recorded on a medium. 
     FIGS. 5–13  are schematic diagrams illustrating a manufacturing process of thin film servo heads and thin film servo head apparatuses, such as thin film servo head apparatuses  10  and  20  from  FIGS. 1 and 2 . It can be difficult or impossible to fabricate angled servo gaps for the thin film servo heads using conventional techniques. The invention described herein enables thin film servo heads to be used with time-based servo markings by defining a servo gap spacing such that when the substrate is canted, the servo gaps of the thin film servo heads substantially align with the time-based servo markings. 
     FIG. 5  is a cross-sectional side view of a thin film servo head  60 . Thin film servo head  60  is built on a substrate  62 , which may be a non-magnetic ceramic substrate, using thin film deposition and photolithography techniques. Thin film servo head  60  includes a first magnetic film layer  64 . The magnetic film may comprise a permalloy film, which is an easily magnetized and demagnetized 80/20 alloy of nickel and iron. A servo gap  70  is formed over first magnetic film layer  64  from, for example, a nonmagnetic amorphous alumina film. A coil  68  is then formed over servo gap  70  from a conductive metal, such as copper. A second magnetic film layer  66  is formed over coil  68 . Second magnetic film layer  66  may also comprise a permalloy film. Servo gap  70  is etched away at the center of coil  68  to provide contact between the first magnetic film layer  64  and the second magnetic film layer  66 . The first and second layers  64 ,  66  form a C-core. A hard-cured photoresist may be used to form insulation layers  65  between coil  68  and first and second magnetic film layers  64  and  66 . Thin film servo head  60  may comprise a magnetoresistive element. 
     FIG. 6  is a top view of the thin film servo head  60  from  FIG. 5 . Thin film servo head  60  includes first magnetic film layer  64 , and second magnetic film layer  66 , coil  68  wound between first and second layers  64 ,  66 , and servo gap  70 . Thin film servo head  60  may comprise a servo verify head. In that case, servo gap  70  generates a signal when servo marks recorded in a servo band on the magnetic tape are detected. The generated signal may be used to detect flaws in the recorded servo signal. 
     FIG. 7  is a top view of an example substrate wafer  72  including a plurality of thin film servo heads  60 . For purposes of illustration, thin film servo heads  60  are drawn very large relative to wafer  72 . In practice, a substrate wafer may include more than 100,000 thin film servo write heads. Each of the plurality of thin film servo heads  60  may comprise a magnetoresistive element and may be simultaneously fabricated as described in reference to  FIG. 5 . Forming the thin film servo heads  60  on wafer  72  includes separating servo heads  60  by a predefined servo gap spacing. After the batch fabrication is complete, substrate wafer  72  may be cut into substrates containing two or more thin film servo heads. The servo gap spacing is predefined such that when the substrates are canted relative to a transverse direction of a magnetic tape, servo gaps  70  will substantially align with time-based servo marks in servo bands on the magnetic tape. Thin film servo head apparatuses, similar to those described above, may include the substrates cut from wafer  72 . 
   As stated above, performing a batch fabrication may result in more than 100,000 servo write heads  60  formed on wafer  72 . A single substrate wafer  72  may create a large number of thin film servo head apparatuses. Therefore, batch processing thin film servo heads  60  increases thin film servo head apparatus fabrication speed as well as decreases the cost of manufacturing. 
     FIG. 8  is a top view of a substrate  74  including five thin film servo heads  60 . Substrate  74  may be cut from substrate wafer  72  from  FIG. 7 . In the illustrated embodiment, substrate  74  comprises five thin film servo heads  60 . In other embodiments, substrate  74  may comprise any number of thin film servo heads  60 . Substrate  74  is cut such that servo gaps  70  of thin film servo heads  60  are adjacent an edge of substrate  74 . In that way, servo gaps  70  are able to make contact with a magnetic tape. Therefore, substrate  74  may be used to create thin film servo head apparatuses, such as thin film servo apparatuses  10  and  20  from  FIGS. 1 and 2 . 
     FIG. 9  is a side view of substrate  74  from  FIG. 8 . The five servo gaps  70  of the five thin film servo heads  60  are positioned adjacent an edge of substrate  74  and, protrude from substrate  74 . Again, this allows servo gaps  70  access to a magnetic tape passing over the side of substrate  74 . 
   FIG  10  is a side view of a superstrate  76  being placed over substrate  74 . Superstrate  76  may comprise a nonmagnetic ceramic superstrate substantially similar to substrate  74 . Superstrate  76  protects thin film servo heads  60  (not visible in  FIG. 10 ) from damage due to exposure to dust, debris, and magnetic fields while allowing servo gaps  70  to make contact with a passing magnetic tape. 
     FIG. 11  is a side view of a thin film servo head apparatus  80 . Apparatus  80  comprises substrate  74  including five servo gaps  70 , superstrate  76  placed over substrate  74 , and an insulator  78  (such as aluminum oxide) between the five servo gaps  70 . Oxide  78  is included between the servo gaps  70  to smooth over a surface of thin film servo head apparatus  80 . Servo gaps  70  remain exposed such that thin film servo heads  60  (not visible in  FIG. 11 ) may read servo patterns on a magnetic tape passing over apparatus  80 . 
     FIG. 12  is a schematic diagram illustrating thin film servo head apparatus  80  mounted in a pre-mounting structure  82 .  FIG. 13  is a schematic diagram illustrating thin film servo head apparatus  80  canted relative to a transverse direction. Apparatus  80  and pre-mounting structure  82  are canted until apparatus  80  defines a specific angle relative to a transverse direction of a magnetic tape. The angle is determined such that servo gaps  70  substantially align with time-based servo marks in servo bands on a magnetic tape. Pre-mounting structure  82  is then cut to define a mounting structure  84  with edges parallel to the transverse direction. In the illustrated embodiment, apparatus  80  is first mounted parallel to the transverse direction in a pre-mounting structure  82 . In other embodiments, apparatus  80  is canted prior to being mounted in a mounting structure. Mounting structures may comprise ceramic mounting structures. 
     FIG. 14  illustrates an exemplary servo verify system  90  for verifying servo patterns on a magnetic tape  98  with thin film servo head apparatuses as described herein. Servo system  90  includes a first thin film servo head apparatus  92 , a second thin film servo head apparatus  94 , a pattern verifier  96 , and magnetic tape  98  spooled on spools  104  and  106 . Magnetic tape  98  feeds from spool  104  to spool  106  along guides  100  and  102 , passing in close proximity to first and second apparatuses  92 ,  94 . For example, magnetic tape  98  may contact apparatuses  92 ,  94  during recording. 
   Each of thin film servo head apparatuses  92 ,  94  comprise a substrate including five thin film servo heads defining five servo gaps. In other embodiments, apparatuses  92  and  94  may comprise two or more servo gaps, i.e., any plurality of servo gaps. The substrates in each of apparatuses  92  and  94  may be canted in differing direction, substantially similar to thin film servo head apparatuses  10  and  20 , respectively, from  FIGS. 1 and 2 . In that way, time-based servo patterns that include oppositely oriented servo marks may be read by servo system  90 . First and second apparatuses  92 ,  94  may comprise planar surfaces to ensure each of the five servo gaps maintains full contact with magnetic tape  98 . 
   As magnetic tape  98  passes over thin film servo head apparatuses  92  and  94 , the servo gaps within apparatuses  92  and  94  detect time-based servo marks recorded on magnetic tape  98 . The thin film servo heads generate signals as functions of the detected time-based servo marks. The signals generated by the thin film servo heads may be in the form of a current or a voltage. Pattern verifier  96  analyzes the generated signals to determine if each of the servo marks has the proper qualities, such as pattern, position, amplitude, dropout rate and consistency with other marks. If pattern verifier  96  detects an unacceptable servo mark, pattern verifier  96  may note the error, and/or may initiate action to mark the unacceptable portions of magnetic tape  98 . 
   Conventional servo head apparatuses typically include a cylindrical contour along which servo gaps are positioned. In that case, each servo gap is located at the apex of the cylindrical contour in order to make full contact with a magnetic tape. The invention described herein includes thin film servo gaps positioned along a canted substrate. The canted substrate causes the servo gaps to misalign with the apex of the cylindrical contour. Servo gaps not located at the apex are not able to maintain contact with the magnetic tape. 
   As an alternative, the substrate may be co-linear with the cylindrical contour and the axis of the cylinder can be canted such that the servo gaps are substantially parallel to servo marks on the magnetic tape. In that way, each of the servo gaps is located at the apex of the cylindrical contour. However, the canted cylindrical contour causes the tape path to distort, which creates non-uniform tension and stress across the magnetic tape. 
     FIG. 15  is a schematic diagram illustrating an exemplary servo system  110  for recording and verifying time-based servo patterns on a magnetic tape  114 . Time-based servo marks are used by a servo read head to determine the position of the servo read head and associated write/read transducer heads. Time-based servo marks usually comprise two or more servo lines angularly offset from one another. When the servo read head reads a time-based servo mark, the servo read head generates a pulse. Because the servo lines are angularly offset from one another, the timing between pulses is indicative of the location of the servo read head relative to the servo mark. The timing of the position signal pulses varies continuously as the servo read head is moved across the width of the servo mark. 
   Magnetic tape  114  dispenses from a spool  112  and passes by a recording head  126 , which records the servo marks. Tape  114  then passes by a thin film servo verify head  128 , which reads the servo marks for purposes of verification. In this manner, servo marks can be recorded and verified in a single pass of magnetic tape  114 . Tape  114  is taken up by a spool  124 . If an error in the servo marks is detected, the error may be noted so that portions of the medium having poor quality marks can be easily identified at a later time. 
   Guides  116 ,  118  and  120  steer magnetic tape  114  past heads  126  and  128 . Guides  116 ,  118  and  120  and capstans and vacuum columns (not shown in  FIG. 1 ) may also measure and regulate the speed and tension of tape  114  as tape  114  passes heads  126  and  128 . 
   Recording head  126  may include a ferromagnetic C-shaped core wrapped with a wire coil. When current flows through the coil, magnetic flux flows through the core and a magnetic field forms. The field penetrates tape  114  as tape  114  passes the head, resulting in residual magnetization of tape  114 . Tape  114  magnetically records the effect of the flux and the magnetic field. In other embodiments, recording head  126  may comprise a thin film servo head. 
   A driver  132  causes current to flow in the coil, thereby energizing recording head  126  and generating the magnetic field. Driver may, for example, send pulses of current to recording head  126 , energizing recording head  126  with each pulse. A controller  136  regulates driver  132  by, for example, regulating the timing and intensity of the current pulses. 
   After recording head  126  writes a time-based servo mark to tape  114 , tape  114  advances past thin film servo verify head  128 . Verify head  128  detects the servo mark and generates a signal as a function of the detection. The signal generated by verify head  128  may be in the form of a current or a voltage. An amplifier  134  amplifies the signal and passes the amplified signal to a pattern verifier  138 . Amplifier  134  may also change a current signal to an amplified voltage signal or a voltage signal to an amplified current signal. 
   Pattern verifier  138  analyzes the amplified signal to determine if the servo mark has the proper qualities, such as pattern, position, amplitude, dropout rate and consistency with other marks. If pattern verifier  138  detects an unacceptable servo mark, pattern verifier  138  may note the error, and/or may initiate action to mark the unacceptable portions of tape  114 . 
   A system similar to system  110  may be used for recording and verifying servo marks on magnetic disks. In particular, a system adapted to magnetic disks may include a recording head, a verify head, a driver, a controller, an amplifier and a pattern verifier. The apparatus used to hold the disk and to move the medium relative to the heads, however, may be different. 
   Various embodiments of the invention have been described. For example, a thin film servo head apparatus has been described that enables thin film servo heads to read time-based servo marks on a magnetic tape. As described above, the thin film servo head apparatus may be a servo verify head apparatus used to verify time-based servo patterns recorded on the magnetic tape. The thin film servo heads are formed on a substrate separated by a predetermined servo gap spacing. The substrate is canted relative to a transverse direction of the magnetic tape such that servo gaps of the thin film servo heads align with servo bands on the magnetic tape and are substantially parallel to the time-based servo marks in the servo bands. In addition, the thin film servo head apparatus may include a planar surface so that servo gaps along the canted substrate can maintain full contact with the magnetic tape. The thin film servo head apparatus described herein may be used to read or write servo marks, or to verify that servo marks have been accurately recorded on a medium. 
   Nevertheless, various modifications may be made without departing from the scope of the invention. For example, the time-based servo patterns described above have generally included two differently angled lines, but any servo pattern may be used as long as the servo gaps are substantially parallel to at least a portion of the servo marks. Furthermore, although the thin film servo head apparatuses are generally described above as including five thin film servo heads, the thin film servo head apparatuses may include two or more thin film servo heads. 
   In addition, the thin film servo head apparatus may be a servo write head apparatus. A magnetic field may be generated across the servo gaps by a magnetic flux flowing through first and second magnetic film layers that comprise the core of each of the thin film servo heads. The magnetic flux is generated by currents flowing through coils wound around each of the cores. The magnetic field may be pulsed as a magnetic tape passes over the thin film servo head apparatus to record time-based servo marks in servo bands on the magnetic tape. 
   In the case of the thin film servo head apparatus comprising a servo write head apparatus, each of the thin film servo heads within the apparatus may be pulsed simultaneously or individually. In any case, the servo head apparatus described herein may find use in writing servo patterns, in addition to verifying recorded signals as outlined above. In some cases, one or more of the thin film servo heads may comprise a magnetoresistive element. 
   Although the thin film servo head apparatus described above has primarily been described in the context of servo patterns in which each set of gaps defines “/ \,” or the like, similar structures could be defined for N-shaped servo patterns. For N-shaped servo patterns, however, three substrates may be used, and only one of the substrates would be canted, i.e., the substrate with the gaps corresponding to the hypotenuses of the N-shaped servo patterns. In other words a first substrate could include gaps parallel to the traverse direction, the second substrate could include canted gaps as described herein, and an optional third substrate could include gaps parallel to the traverse direction. 
   For example, as shown in  FIG. 16 , for N-shaped servo patterns, the invention may comprise a thin film servo head apparatus  200  positioned in a transverse direction of a magnetic tape moving over the thin film servo head apparatus  200 , the apparatus  200  comprising a first thin film servo head  210  formed on a first substrate  201 , the first thin film servo head  210  including a first servo gap, and a second thin film servo head  211  formed on the first substrate  201 , the second thin film servo head  211  including a second servo gap substantially parallel to the first servo gap, and wherein the first substrate  201  is canted relative to the transverse direction of the magnetic tape such that the first and second servo gaps are non-parallel to the transverse direction. Moreover, for N-shaped servo patterns, or the like, the apparatus  200  may further comprise a third thin film servo head  220  or  230  formed on a second substrate  205  or  206  and comprising a third servo gap corresponding to the first servo band on the magnetic tape, and a fourth thin film servo head  221  or  231  formed on the second substrate  205  or  206  and comprising a fourth servo gap substantially parallel to the third servo gap and corresponding to the second servo band on the magnetic tape, and wherein the second substrate  205  or  206  is non-canted relative to the transverse direction of the magnetic tape and positioned parallel to the traverse direction. In that case, the first substrate  201  would define the gaps which correspond to the hypotenuses (“\”) of the N-shaped patterns and the second substrate  205  or  206  would define the gaps which correspond to either the leading or trailing parallel gaps (“|”) of the N-shaped patterns. These and other embodiments are within the scope of the following claims.