Patent Publication Number: US-6341416-B1

Title: Method for mass producing partial width linear tape recording head

Description:
This is a Divisional application of Ser. No. 08/896,356, filed Jul. 18, 1997 now U.S. Pat. No. 5,883,770, issued Mar. 16, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to magnetic tape recording heads, and, more particularly, to tape heads that span only a portion of the width of the tape. 
     BACKGROUND OF THE INVENTION 
     Conventional recording heads for linear tape drives have small transducers incorporated into a large head assembly to span the full width of the tape. For recording heads fabricated using thin film wafer technology, this requires that the head either be fabricated individually on a wafer which is at least as wide as the recording tape and lapped individually to the proper shape, or be fabricated as a small part and assembled with larger pieces and the full assembly lapped individually to the proper shape. 
     The conventional shape of a tape head comprises a cylindrical or complex contour which is critical in maintaining the moving tape at the desired head to transducer spacing (called “contact” or “near contact” recording). The contact, or near contact, spacing is maintained by controlling the contour shape to “bleed”, “skive” or “scrape” the boundary layer of air carried by the tape away before encountering the transducer to prevent the tape from “flying”, or losing contact with the transducer. 
     The spacing between the magnetic head and the magnetic tape is crucial so that the recording gap of the transducer, which is the source of the magnetic recording flux, is in intimate or near contact with the tape to effect efficient signal transfer for recording. The spacing is also crucial so that the playback element is in intimate or near contact with the tape to provide effective coupling of the magnetic field from the tape to the playback element. 
     The full width of the tape in the prior art is contacted by the head assembly to prevent steering the moving tape as the head assembly is moved to access different data tracks. In addition, when a short span head is near an edge of the tape, the tape, without support, tends to lift from the head as the result of upward flex curvature as it travels over the protruding head. Thus, a wide head is used to provide support for the tape when the recording element is positioned near an edge of the tape. Even with full width support, there is an antielastic bending effect that tends to lift the tape off the head near the edge of the tape. 
     FIG. 1 illustrates a conventional linear tape drive recording head  10 . A small transducer  11  is incorporated into a large unit  12  to span the full width of the tape  13 . FIG. 2 illustrates an example of one method of fabricating a conventional linear tape drive recording head of FIG. 1 using thin film wafer technology. In FIG. 2 a , an individual chip  14  is assembled with wings  15  and  16  and closure  17  and glued together to form a full assembly which is shown in an end view in FIG. 2 b . A portion of the top surface of the full assembly is then ground away to form the assembly shown in FIG. 2 c , leaving a rooftop  18 . The entire assembly is then individually lapped to the proper depth so as to attain the final stripe and throat heights for the magnetic transducer and to attain the desired contour  19  as shown in FIG. 2 d . The resultant assembly is illustrated in FIG. 2 e.    
     The conventional shape of FIG. 2 comprises a cylindrical or complex contour which is critical in maintaining the moving tape in contact with the transducer, as described above. The full width contour of FIGS. 1 and 2 serves three purposes. 1) It prevents tape steering as the recording element is moved to access different data tracks. 2) It provides support for the tape as the head is positioned near the edge of the tape  13 . and 3) It prevents the edges of the chip  14  from damaging the tape.  13 . 
     The contour of the head must also allow a low tension on the tape so as to not distort the tape. Typically, the contour is designed with a small radius  19  in FIG. 2 d  so the pressure on the head, which is proportional to the tape tension per unit width divided by the radius (T/wR), is high with tensions low enough not to excessively distort the tape. However, the contour of the head must be such that the pressure of the tape on the transducer is not so high that the surface of the transducer wears excessively. 
     Such full width heads are often provided with “outriggers” to maintain a small wrap angle over the recording elements of the head even though the wrap angle over the outriggers can change with different cartridges inserted into the tape drive. A change in wrap angle over the portion of the head containing the recording elements can lead to air entrainment and excessive flying height of the tape. 
     Like the head assembly, the outriggers must also be the full width of the tape in order to prevent distortion of the tape. Often, the outriggers must also be lapped to a contour which is coordinated with the contour of the head assembly. 
     Individual lapping of the tape head assembly and of the corresponding outriggers, especially to a contour, is very expensive and is a major contributor to the manufacturing cost of the tape head. 
     Partial span recording heads are used in helical scan tape recording and in floppy disks. They are individually assembled and then provided with a spherical or elliptical contour. Such heads have not been used in linear tape recorders due to the need for tape edge support and a requirement for substantial tape tension or contact pressure to maintain contact with the head. In addition, it is difficult to provide such a contour when a multiplicity of recording elements are required in the head. 
     U.S. Pat. No. 4,123,791, Rotter et al., describes a single element narrow tape head positioned between outrigger bars of 0.25 inch radius with radial centers 0.4 inch apart. An additional pair of stub outriggers aligned in the direction of tape travel, having the same shape as the head and spaced 25 to 30 mils on either side of the head, were required to support the edge of the tape. The narrow tape head and stub outriggers were required to allow the splitting and passage of the boundary layer of air. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a tape head that does not require or complex assembly with stub outriggers. 
     Another object of the present invention is to provide a tape head which attains optimum spacing with respect to the tape at all track positions across the width of tape. 
     Disclosed is a dimple magnetic recording head in a transducer assembly for linear tape drives. The dimple head has a flat transducing surface extending laterally a partial width of the magnetic recording tape. Two parallel tape support surfaces extend laterally the full width of the magnetic recording tape, positioned on either side of and spaced from the dimple head in the longitudinal direction of the magnetic recording tape. In addition, the anticlastic lift off of the tape near its edges is minimized with present tape thickness (approx. 9 microns) and tension for a dimple head length of 0.6 to 1 mm in the tape moving direction. Further miminization can be achieved by providing a slight contour on the edges of the dimple head. The tape support surfaces form a plane, and the dimple head flat transducing surface is parallel to the tape support surface plane and projects above the tape support surface plane to form tape wrap angles with respect to the tape support surfaces of approximately ½ degree to 2.5 degrees. The low wrap angle helps prevent tape steering as the head is moved to access different data tracks. The high end of the range (2.0 to 2.5 degrees) of wrap angle allows reading and writing nearer the edge of the tape at the expense of increased tape steering. 
     A method for forming a dimple magnetic tape head is disclosed. A plurality of transducers are formed on a common row of substrate elements, and the common row of substrate elements is lapped to achieve the proper throat height of the inductive write elements (approx ½ to 3 microns), appropriate magnetoresistive stripe height of the magnetoresistive read elements (approx ½ to 3 microns), and a flat transducing surface. This is the most critical and expensive lapping step in forming tape heads. With this disclosure a plurality of recording heads are lapped in a single rowbar in a single step thus reducing cost. The rowbar is subsequently diced into separate recording heads, each of which may contain a multiplicity of recording elements. The two parallel, spaced apart tape support surfaces are provided, and one of the diced substrate elements is mounted intermediate the tape support surfaces with the flat transducing surface exposed for forming a tape facing surface. 
     Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the figures by the accompanying drawings in which like references indicate similar elements and in which: 
     FIG. 1 is a perspective illustration of a linear tape head assembly of the prior art; 
     FIGS. 2 a  through  2   e  are illustrations of the method for producing the prior art linear tape head assembly of FIG. 1; 
     FIG. 3 is a perspective illustration of an embodiment of the linear tape head of the present invention; 
     FIG. 4 is a perspective illustration of an embodiment of the linear tape head assembly of the present invention; 
     FIG. 5 is an illustration of a cross section of the linear tape head assembly of FIG. 4; 
     FIG. 6 is a perspective illustration of a row of substrate elements with transducers; 
     FIG. 7 is a diagrammatic illustration of a lapping system for lapping the common row of substrate elements of FIG. 6; 
     FIG. 8 is a top view illustration of a substrate element diced from the common row of FIG. 6; 
     FIGS. 9 a ,  9   b  and  9   c  are top view illustrations of alternative embodiments of substrate elements of the present invention; 
     FIG. 10 is a perspective illustration of an alternative embodiment of a linear tape head assembly of the present invention; 
     FIG. 11 is an illustration of a cross section of another alternative embodiment of a linear tape head assembly of the present invention; 
     FIG. 12 is a perspective illustration of a movable head embodiment of the linear tape head assembly of the present invention; 
     FIG. 13 is an illustration of a cross section of the linear tape head assembly of FIG. 12; 
     FIG. 14 is an illustration of a cross section of an alternative embodiment of the linear tape head assembly of FIG. 12; and 
     FIG. 15 is a diagrammatic illustration of a tape drive which may incorporate the linear tape head assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 illustrates an embodiment of the partial span tape head  20  of the present invention. Tape head  20  is a partial span flat head, called a “dimple” head, because the recording elements are located about centered in a flat carrier. The head can be batch fabricated by stripe and throat height lapping then diced and assembled into carriers to provide completed heads. A row of heads is lapped to achieve the proper throat height of the inductive write elements (approx ½ to 3 microns), appropriate magnetoresistive stripe height of the magnetoresistive read elements (approx ½ to 3 microns), and a flat transducing surface. This is the most critical and expensive lapping step in forming tape heads. With this disclosure a plurality of recording heads are lapped in a single rowbar in a single step thus reducing cost. The rowbar is subsequently diced into separate recording heads, each of which may contain a multiplicity of recording elements. 
     The head  20  slightly penetrates the plane of the tape  21  to provide a small wrap angle for scraping the air off as it goes by the sharp edge. Cable  22  connects the dimple tape head  20  to the read/write channel of an associated tape drive. 
     Dimple tape head  20  works properly over only a small range of wrap angles. For one embodiment, the range of wrap angle is from about ½ degree to 2.5 degrees. 
     Because of the very small wrap angle, the head does very little tape steering as it moves from one side of the tape  21  to the other to access the recording tracks. In addition, the anticlastic liftoff of the tape near its edges is minimized with present tape thickness (approx. 9 microns) and tension for a dimple head length of 0.6 to 1 mm in the tape moving direction. Further minimization can be acheived by providing a slight contour on the edges of the dimple head. 
     FIG. 4 illustrates one embodiment of the tape head assembly which includes linear dimple tape head  20  with outriggers  24  and  25 . Outriggers  24  and  25  maintain the proper wrap angle and prevent tape steering by extending the full width of the tape  21 . 
     For one embodiment, a wrap angle between about ½ degree and 2.5 degrees is adequate to scrape the air off the tape and to provide the desired spacing between the tape and the transducer elements in the dimple head. Surfaces  26  of the outriggers  24  and  25  provide a convenient means of controlling the wrap angle. 
     FIG. 5 is a cross sectional view of the linear dimple tape head assembly of FIG.  4 . For one embodiment, the size of the wrap angle may be precisely controlled by lapping flat surfaces  26  of the outriggers  24  and  25  to a precise dimension in a common plane, and then mounting the dimple head  20  in a plane parallel to the plane formed by the surfaces  26  at a precise height with respect to the plane formed by the flat surfaces  26 . In a preferred embodiment, a penetration of the flat surface  27  of dimple head  20  above the plane of the flat outrigger surfaces  26  of the order of 0.001 inch (1 mil) is adequate to obtain the desired wrap angle and transducer to tape spacing. 
     FIG. 6 illustrates a row  30 , or rowbar, cut from a substrate or wafer along with a closure  31 . The transducers are mass produced using conventional etching and deposition techniques. The row  30  is typically formed on a ceramic substrate which is either magnetic, such as ferrite, or non-magnetic such as Alumina-Titanium-Carbide depending on the design. The write and read heads are formed on the substrate using convention thin film deposition, etching, and lithographic techniques. Both the inductive write elements and magnetoresistive read elements are provided with connection terminal  32 . Closure  31  is provided to protect the thin film read and write elements from being damaged by the tape and to form part of the flat transducing surface. As illustrated in FIG. 6, underside surface  33  of the row  30  and closure  31  is the transducing surface and is lapped to achieve the final throat and stripe heights of the transducers. 
     A typical lapping system for lapping flat transducing surface  33  of common row  30  is illustrated in FIG. 7. A lapping fixture  40  holds the common row  30  of substrate elements in position over a lapping plate  41 . Lapping plate  41  is a flat abrasive surface for accurately lapping surface  33  to a final dimension. 
     The force applied to lapping fixture  40  is derived from first and second pressure actuators  43  and  44 . Varying the force applied by the actuators  43  and  44  against substrate row  30  controls leveling of the lapped surface  33 . 
     The lapping device insures thereby insuring that the throat heights and stripe heights for all of the transducers are at the same length. 
     After completion of lapping of row transducer surface  33 , row  30  is diced or partitioned into separate dimple heads. The mass production of the dimple heads as described above substantially reduces the cost of providing lapped heads, as compared to the individual lapping required by the prior art. 
     A single dimple head is illustrated in FIG.  8 . Substrate  50 , closure  51  and gap  52  form flat transducing surface  27  of the dimple head. In a preferred embodiment, a plurality of read and write elements are contained in gap  52 . 
     FIGS. 9 a-c  illustrate alternative embodiments of the dimple head. FIG. 9 a  shows a square head embodiment with sharp corners  55 . Although the sharp corners  55  may be effective in scraping the boundary layer of air from the tape, the tape exerts its greatest pressure on the corners. FIG. 9 b  shows a dimple head with rounded corners, called “edge blend”, to minimize edge pressure when used with a carrier like that of FIG.  4 . The corners are rounded after the head has been diced from the common row. 
     FIG. 9 c  shows a round configuration which reduces the edge pressure when used with the carrier of FIG.  10 . Other shapes, such as those of FIGS. 9 a  and  9   b  may also be used. The dimple head  60  is still flat, but is circular in the other dimension. The dimple head is rounded after the head has been diced from the row. Outriggers  61  and  62  are joined by flat surfaces  63 , and the head is placed in a circular cutout so as to protrude slightly so that tape  65  forms a wrap angle of between approximately ½ degree and 2.5 degrees with respect to the edges formed by outriggers  61  and  62  with flat surface  63 . Outrigger flat surface  63  may be lapped or ground to a common plane. 
     FIG. 11 illustrates an alternative embodiment of the present invention having a dimple head  66  and outrigger dowels  67  mounted in a carrier  68 . The dimple head  66  is mounted so as to protrude slightly above the outrigger dowels  67  and  68  and penetrate into tape  69  sufficiently to form a wrap angle of between approximately ½ degree and 2.5 degrees. 
     FIG. 12 illustrates an alternative embodiment of a linear tape head assembly of the present invention having a fixed set of outriggers  70  and a moveable head  71 . The outriggers  70  extend the full width of tape  72 , while head  71  moves in the lateral direction between tracks. 
     FIG. 13 is a cross section view of the linear tape head assembly of FIG. 12, illustrating the slight penetration of the head  71  into the tape  72  above outriggers  70 . The slight penetration by head  71  provides a wrap angle of tape  72  of between about ½ degree and 2.5 degrees. The outriggers  70  maintain the proper wrap angle and prevent tape steering by the movement of the head  71 . Single recording gap  73  is provided in head  71 , which may include a multiplicity of transducers. 
     FIG. 14 illustrates a moveable read after write head  76  having dual recording gaps. Head  76  comprises two heads  71  whose flat transducing surfaces  77  slope down from the center ½ to 1 degree each. The wrap angle of tape  72  is provided by outriggers  70  in the range between about ½ degree and 2.5 degrees with respect to each side of the head  76 . Read after write head  76  may also be employed in any of the embodiments of the invention. 
     FIG. 15 illustrates an embodiment of a tape drive  80  incorporating dimple head assembly  81 . A tape drive control unit  82  provides a motor control signal to rotate tape reels  83  and move tape  84  across the dimple head assembly  81 . Read/write channel  86  amplifies, decodes or encodes, and transmits read signals from the dimple head and/or write signals to the dimple head with respect to control unit  82 . The data is communicated through I/O channel  87  with host  88 . Lateral repositioning of the dimple head assembly  81  with respect to the tape  84  is accomplished by positioning actuator  90 . The lateral repositioning is required to access the various tracks of the tape  84  with the dimple head  81 . A servo system may be employed for accurate lateral repositioning of the head assembly  81 . An exemplary servo system includes a servo detector  91  to detect both the track that the head is currently on and whether the head is off center. Control unit  82  indicates the track address of a desired new track to position error detection controller  93  for repositioning the head. Servo detector  91  indicates the current track to position error detection controller  93 , and the controller provides a servo position error signal to positioning actuator  90  which repositions the dimple head assembly  81  to the new track. The servo system also provides track following signals to positioning actuator  90  so that the tracks on tape  84  may be closely spaced. 
     Alternatively, positioning actuator  90  may comprise a stepping motor which repositions the dimple head assembly  81  between fixed positions. These and other repositioning means are within the skill of those skilled in the art. 
     Outriggers of the dimple head assembly  81  support the tape  84  in all lateral positions of the dimple head transducer across the tape and maintain the wrap angle of the tape with respect to the dimple head. 
     While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.