Abstract:
In accordance with the present invention, an interleaved bi-directional magnetic tape head is provided in which the read element, write element, and servo element are formed on a common substrate. Each element has a contact pad area electrically associated withit, with each contact pad area located in a plane common to all contact pad areas. That is, the contact pad areas are planarized to each other. As a result of such planarization, two gold conduction layers, required in the prior art, are reduced to one layer. Further, the total number of mask layers is two less than the prior art, with a concomitant reduction in device fabrication time. Additionally, the unit cell size is reduced by about one-third.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a thin film magnetic head particularly for magnetic recording, and more specifically to a magnetic head having read and write elements in an improved side by side configuration. 
     BACKGROUND ART 
     In high speed data processing systems, magnetic recording has been employed for large memory capacity requirements. Data is read from and written onto the magnetic recordings using magnetic transducers commonly called magnetic heads which are positioned adjacent the magnetic recording medium. For a contact recording, wherein the magnetic recording medium comes in contact with the magnetic head, the pole pieces are generally made of a magnetic ferrite material because of its wearing characteristics. The magnetic ferrite pole pieces, while having good wearing characteristics for the contact recording particularly with magnetic tape, however, lack the efficiency to record on high coercivity recording medium in the higher data density requirements for present day data recording. Magnetic heads having thin film pole pieces were developed to increase the saturation moment of the pole pieces and to increase the operating efficiency of the transducers, especially in the write or data recording procedure. 
     Thin film pole pieces, however, while providing the required efficiency to write the higher data density requirements, could not withstand the abrasion of the magnetic recording medium, especially in the contact recording situation. A first order requirement for high density recording is the minimizing of spacing between the surface of the media and the functional recording gap between the pole pieces. With the soft magnetic material thin film poletips of nickel-iron, for instance, the functional recording gap and the poletips are susceptible to wear by the media. Increasing the spacing between the recording gap and the media deteriorates the recording performance. 
     The write saturation performance characteristics of an interleaved, bi-directional, magnetic head operating in ferrite-trailing mode are not as good as those during operation in poletip-trailing mode. The mode of operation depends on the direction of tape travel: during ferrite-trailing mode, the tape travels across the gap towards the deposited poletip; in poletip-trailing mode, the tape travels towards the ferrite poletip. Regardless of write mode, a head experiences amplitude loss at high write currents. However, because of the lower saturation moment of the ferrite poletip compared to that of the deposited poletip, the amplitude loss is significantly more severe in ferrite-trailing mode. The problem thus presented is how to better balance the saturation moments of the poletips. 
     U.S. Pat. No. 5,296,993 describes a magnetic head with magnetic substrate and an enhanced poletip thereon. Specifically, an interleaved bi-directional magnetic tape head for contact recording can have a poletip enhanced by providing a thin film of a soft magnetic material deposited onto a magnetic ferrite substrate. The second pole piece is a thin film of the soft magnetic material. A closure block of a non-magnetic ceramic encloses the layers together with leveling insulation layers and a deposited activating conductor turns. The stripe poletip deposited onto the magnetic ferrite extends for a distance just short of the first conductor turn and provides a balancing of the saturation moment of the pole pieces and provides for better recording capability, especially when operating in a trailing magnetic ferrite mode. 
     While this patent is fine for its intended uses, it, like many references dealing with interleaved magnetic heads, has reader, servo, and writer contact pad areas at different levels, which complicates contacting procedures. 
     What is needed is a simplified contacting process that retains most, if not all, of the advantages of the prior art devices. 
     DISCLOSURE OF INVENTION 
     In accordance with the present invention, an interleaved bi-directional magnetic tape head is provided in which the read element, write element, and servo element are formed on a common substrate. Each element has a contact pad area electrically associated therewith, with each contact pad area located in a plane common to all contact pad areas. That is, the contact pad areas are planarized to each other. 
     As a result of such planarization, two gold conduction layers, required in the prior art, are reduced to one layer. Further, the total number of mask layers is reduced by two. Concomitantly, there is a reduction in the amount of process time. Additionally, the unit cell size is reduced by one-third of its original size. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic perspective view of a section of an interleaved magnetic head that uses the elements of the present invention; 
     FIG. 2 a  is a top plan view of the prior art interleaved bi-directional magnetic head; 
     FIG. 2 b  is a top plan view of the magnetic head of the present invention, illustrating the reduced unit cell size; 
     FIG. 3 a  is a cross-sectional view of a prior art interleaved bi-directional magnetic head, taken along the line  3   a — 3   a  of FIG. 2 a,  showing a reader and a writer side-by-side; 
     FIG. 3 b  is a view similar to that of FIG. 3 a,  but taken along the line  3   b — 3   b  of FIG. 2 b;    
     FIG. 4 a  is a cross-sectional view of the prior art interleaved bi-directional magnetic head, taken along the line  4   a — 4   a  of FIG. 2 a,  showing the details of the read element; 
     FIG. 4 b  is a view similar to that of FIG. 4 a,  but taken along the line  3   b — 3   b  of FIG. 2 b;    
     FIG. 5 a  is a cross-sectional view of the prior art interleaved bi-directional magnetic head, taken along the line  5   a — 5   a  of FIG. 2 a,  showing the details of the write element; 
     FIG. 5 b  is a view similar to that of FIG. 5 a,  but taken along the line  5   b — 5   b  of FIG. 2 b.   
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the drawings in which like reference numerals refer to like elements throughout, an interleaved, thin film magnetic recording head  10  is shown in FIG.  1 . The read elements are marked R for the magnetic head  10 , while the write elements are marked W. The read and write gaps are used in immediately alternating, odd/even fashion. The term “alternating” is intended to include other formats. For example, one embodiment of the present invention provides a format of 72 tracks across the width of the media, hereinafter called tape media. One format provides that the odd numbered tracks, tracks  1 ,  3 ,  5 , and so-forth, are operated during forward tape movement, while the even numbered tracks  2 ,  4 ,  6 , and so-forth, are operative during the opposite direction of the movement of the tape media. 
     In general, the length of the magnetic tape  12  moves in both a forward and reverse direction as indicated by arrows  14  and  16 . The arrow  14  designates the forward movement direction of the tape  12  and the arrow  16  designates the reverse direction. The magnetic tape  12  operates in transducing contact relationship with the magnetic head  10  in the conventional well-known format. The magnetic head  10  includes two modules  18  and  20  of generally identical construction. These two modules are bonded together to form a single physical unit. In this manner, the transducing gaps of one module are not only closely spaced to the transducing gaps of the other modules, but also the module gaps are accurately aligned in the direction of tape movement. There are  36  read transducers and  36  write transducers in each of the modules  18  and  20 . The magnetic tape  12 , therefore, has  72  tracks across its one-half inch width. Each module includes one gap line  22  for module  18  and one gap line  24  for module  20  to form the single physical unit of the magnetic head  10 . 
     FIG. 2 a  is a plan view of a prior art unit cell  26  comprising a write element  28 , a read element  30 , and a servo element  32 . The elements are formed on a substrate, not shown in this Figure, but visible in FIG. 3 a,  for example. 
     FIG. 2 b  is a plan view of the unit cell  26 ′ of the present invention, also comprising the write element  28 ′, the read element  30 ′, and the servo element  32 ′. The unit cell  26 ′ is seen to be considerably shorter than the prior art unit cell  26 , for reasons which will become apparent. As an example, in one embodiment, the unit cell size is reduced by one-third from the device shown in FIG. 2 a  to the device shown in FIG. 2 b.    
     While one write element  28 ,  28 ′ and one read element  30 ,  30 ′ are shown in FIGS. 2 a,    2   b,  respectively, it will be appreciated that in fact a plurality of such elements, together with servo elements  32 ,  32 ′ and ancillary elements are formed in a side-by-side arrangement, as shown in FIG.  1 . 
     FIGS. 3 a  and  3   b,  which are cross-sectional views of the faces of the heads, depict the write element  28  and  28 ′ and the read element  30  and  30 ′, respectively, in adjacent proximity. The servo unit  32  and  32 ′ is not shown in these Figures, but could be on either side of the read or write elements, depending on the particular layout designed. 
     FIGS. 4 a  and  4   b,  which are cross-sectional views of the read element  30  and  30 ′, orthogonal to FIGS. 3 a  and  3   b,  respectively, depict the details of the various layers comprising the read element. 
     FIGS. 5 a  and  5   b,  which are cross-sectional views of the write element  28  and  28 ′, orthogonal to FIGS. 3 a  and  3   b,  respectively, depict the details of the various layers comprising the write element. 
     In FIGS. 2-5, the “a” figures depict the prior art interleaved bi-directional magnetic head, while the “b” figures depict the interleaved bi-directional magnetic head of the present invention. The discussion below requires consideration of FIGS. 2-5 for a fall understanding of the present invention. The prior art structure is described, which includes the structure of the present invention, but where changes are made in accordance with the invention, these are separately described, in order to point up the differences. More specific details of the prior art device may be found in U.S. Pat. Nos. 3,908,194; 4,685,005; and 5,208,714, which are assigned to the same assignee as the present invention. 
     The magnetic tape head of FIGS. 2-5 is formed on a substrate  34 , which typically comprises a ferrite material, such as a magnetic nickel-zinc ferrite or a magnetic manganese-zinc ferrite or any of the magnetic ferrite materials known for use in magnetic heads. A first pole piece P 1   36  is formed on a portion of the substrate  34 . The first pole piece  36  typically comprises a Ni—Fe alloy, such as Permalloy. After ion milling and etching P 1 , a first insulating layer I 1   38 , typically Al 2 O 3 , is formed on the substrate  34  and over the first pole piece  36 . 
     A magneto-resistive (MR) element  40 , preferably comprising a soft bias material, is formed, along with a hard bias (HB) layer  42 , both on a portion of the first insulating layer  38 . Specifically, the soft bias material is deposited first, followed by deposition of the hard bias material. Then, the MR element and associated HB layer are defined at the same time. The MR element  40  typically comprises a permalloy layer, an insulating layer, and a soft bias adjacent layer, with the magnetic layers adjusted in composition to provide a near-zero magnetostriction, while the HB layer  42  typically comprises CoPt. The MR element  40  is formed behind the HB layer  42 ; together, these elements form the read unit  30 ,  30 ′, seen in FIGS. 4 a,    4   b,  respectively. 
     In the prior art device, a first metal layer  44 , such as gold, is next deposited over the MR element  40  and contacting the HB layer  42 . The gold layer  44 , which actually comprises a three-layer structure of Ti/Au/Ti, is typically about 0.5 to 0.6 μm thick. A second insulating layer I 2   46  is formed on the first insulating layer  38  as well as on the HB layer  42  and the first gold layer  44 . A third insulating layer I 2 ′  48  is formed on the second insulating layer  46 . Although the two insulating layers  46 ,  48  may comprise any of the common insulating materials, since alumina is used elsewhere in the fabrication of the device, it is advantageously employed here as well. The third insulating layer  48  is patterned and portions thereof removed. In association with the read element  30  (FIGS. 4 a  and  4   b ), the third insulating layer  48  is removed over the HB layer  42 , but left over the MR element  40  and extending to the back (contact) end of the device. A via  50  is next etched through a portion of the third insulating layer  48 , the second insulating layer  46 , and the first insulating layer  38  to expose an underlying portion of the first pole piece  36 . A layer  52  of SiO 2 , which acts as an etch stop layer, is next deposited. A second metal layer  54 , again, gold, is then deposited and patterned to form coils  56  and contacts  58 . The second gold layer  54  is also a three-layer structure of Ti/Au/Ti, having a thickness of about 3.5 μm. 
     In accordance with the present invention, the foregoing steps are revised to deposit only one gold layer  54 ′, which is also patterned to form coils  56 ′ and contacts  58 ′. Specifically, following formation of the MR element  40  and HB bias layer  42 , a layer  52 ′ of SiO 2 , which also acts as an etch stop layer, is deposited. The gold layer  54 ′ is then deposited and patterned as described above. As above, the gold layer  54 ′ comprises the three-layer structure of Ti/Au/Ti, but is about 2.5 μm thick. The second insulating layer I 2   46 ′ is now deposited, followed by deposition of the third insulating layer I 2 ′  48 ′. The via  50 ′ is now etched, also down to the P 1  layer  36 . 
     Returning to the basic process, a cross-link layer  60  is next formed and patterned so as to cover (1) the MR element  40  back to the contact area and (2) the coils  56 ,  56 ′ as well as provide a region for a subsequent P 2  cross-over  61  behind the coils. The cross-link layer  60  typically comprises a layer of photoresist that has been crosslinked by light. The second pole piece P 2   62  is next deposited, ion-milled, and etched. The second pole piece  62  comprises the same material, e.g., Ni—Fe, as the first pole piece  36 . In the write device  28 ,  28 ′ (FIGS. 5 a,    5   b ), the second pole piece  62  is formed on the third insulating layer  48  at the front of the device, is spaced above the coils  56 ,  56 ′ by the cross-linked layer  60 , and contacts the first pole piece  36  through the via  50 ,  50 ′. A protective overcoat layer  64 , typically a mechanically hard dielectric, such as silica, alumina, silicon nitride, etc., is blanket deposited and, in the prior art device, is etched twice, once to open a via to the write element contact level  66 , and one to open a via to the read element contact level  68 . However, in the device of the present invention, the over-coat layer  64  is etched only once, to form vias to both read element and write element contacts  58 ′, which are on the same level  70 . 
     FIG. 3 a  depicts the two different contact levels  66 ,  68 , required in the prior art device. The device of the present invention shown in FIG. 3 b,  however, has only one contact level  70 . 
     As seen in FIGS. 4 and 5, the gold layer  54 ,  54 ′ extends to a back contact area  72 , which permits contact to be made, for example, to the MR device  40 , 
     From the foregoing process, two direct advantages provided by the device of the present invention are evident. First, the prior art process requires two additional process steps over that of the present invention. Second, the two gold conduction layers  44 ,  54  of the prior art, both at different contact levels  66 ,  68 , are reduced to one gold layer  54 ′, on one contact level  70 . 
     One advantage of using only one gold layer  54 ′ for contacting the MR element  40 , is that the prior art design requires two separate gold layers  44  and  54 , thereby increasing the possibility of poorer electrical contact. 
     In addition, shrinking the unit cell, as shown in FIGS. 2 a  and  2   b,  results in an increase in bandwidth, which is defined, in a thin film environment, as an increase in chip count per wafer. The reduction in unit cell size by the process of the present invention permits forming more chips on a wafer. 
     Further, the gold coils  56  of the prior art device are covered only by the cross-linked material  60 , while the gold coils  56 ′ of the device of the present invention are protected by two additional layers: insulating layer  46 ′ and insulating layer  48 ′. The additional insulating layers  46 ′,  48 ′ serve to provide further protection to the coils  56 ′. 
     Finally, only one gold layer  54 ′ is necessary for contacting the MR element  40 , in contrast to the prior art design, which requires two separate gold layers  44  and  54 , thereby increasing the possibility of poorer electrical contact. 
     INDUSTRIAL APPLICABILITY 
     The interleaved bi-directional magnetic tape head comprising a read element, a write element, and a servo element is expected to fund use in magnetic recording and playback applications. 
     Thus, there has been disclosed an interleaved bi-directional magnetic tape head comprising a read element, a write element, and a servo element formed on a substrate, wherein a single conducting layer is used for providing contacts to each element and for forming coils associated with the write element. It will be appreciated by those skilled in the art that various changes and modifications of an obvious nature may be made, and all such changes and modifications are considered to fall within the scope of the appended claims.