Transducer head and method of making same

Abstract: In a magnetic recording system tape is transported bi-directionally across the interleaved head. The interleaved head includes two modules, each module having a plurality of alternate read and write transducer gaps spaced apart along a single gap line transverse to the movement of the magnetic tape. The two modules are placed together so that the write gaps of one module are aligned with the read gaps of the other module. Each module is formed on a nickel-zinc ferrite substrate by deposition of magneto-resistive material to form read transducer elements 69 and deposition of conductor material to form read conductors 74, 76 and 78 and write coils 80. A nickel zinc ferrite closure piece is secured to the substrate to complete the module. In order to provide leveling across the write and read transducers of the module, write back gap islands 90, 92 are provided in the back gap regions 68 of the write coils made of the same material with the same thickness as the magneto resistive element and the conductors interconnecting the magneto resistive element to the read/write network of the tape drive.

Description: This invention relates to transducer heads and methods of making same, and is of particular, though not exclusive, application to the field of magnetic recording. In the field of magnetic recording, magnetic tape is driven in a tape drive past a transducer head. Tape drives that operate bi-directionally are well-known. The tape is generally enclosed in a single reel cartridge and the tape is transported around the tape path onto a tape reel thereby placing the tape in contact with the transducer. The transducer in present day tape drives comprise a separate read and write element that cover each track of the data on the tape. It is known, for instance, that a one-half inch (12.7 mm) wide magnetic tape can include eighteen tracks. A higher number of tracks is desirable and it has been proposed that a one-half inch (12.7 mm) wide magnetic tape includes thirty six tracks. To be able to read thirty six tracks from the tape, an interleaved data transducing head has been proposed. Such an interleaved read/write head is disclosed in US-A 4,685,005, in which the read and write gaps of each of two modules of the magnetic head are alternately spaced across the width of the tape, so that the write gaps of one module are aligned with the read gaps of the other module. When one module is selected for writing, as a function of the direction of the tape movement, the other module is selected to read-after-write to check the data written by the write element of the first module. One module writes odd track data during one direction of the tape movement and reads even track data during the opposite direction of the tape movement. The problem arises in that both read and write elements are located within one module with the gaps of each element aligned along the same line. The read element of the modern day tape head is a magneto-resistive transducer and is formed of thin film layers deposited through a standard thin film deposition procedure. The write transducer, however, has its pole pieces formed from two blocks of magnetic ferrite magnetically connected together at the back gap and a transducing gap at the front face. A single block of magnetic ferrite operates as a closure structure after all of the elements of the read transducer and the write conductors are deposited onto the substrate magnetic ferrite block. Having different layers of material deposited at different locations into the side-by-side elements creates a leveling problem when the magnetic ferrite closure block is to be placed over the plurality of read and write elements. More layers form a greater thickness in the read element and therefore the write element generally lacks a supporting structure that can cause the magnetic ferrite closure piece to bend under stress when affixed to the completed transducer substrate. In any event, the write head gap must not be narrower than the read head gap to enable proper reading of the bits of information written onto the magnetic tape. Also, with the closure piece bent under stress at the time of manufacture, the stress may relieve in time, resulting in an unreliable gap. The present invention therefore seeks to provide an enhanced transducer head for multi-track operation. The present invention also seeks to provide an enhanced interleaved head to read and write magnetic transitions forming data from and onto a magnetic recording medium. The present invention further seeks to provide an enhanced magnetic head assembly and an enhanced method for making a magnetic head module. The present invention provides for a bi-directional tape drive, an interleaved transducing head that solves the mechanical and magnetic problems between the gap lengths of the read and write elements. A transducer head according to the preamble of claim 1 is known from EP-A-131 727. Accordingly, the present invention provides a transducer head including a module having a transducing gap line including a plurality of alternate write and read gaps, the module including a substrate and a closure of ceramic material which covers a plurality of thin film read transducer elements and write elements deposited on the substrate, and a plurality of gap islands of the same thickness as the thickest of the transducer elements for supporting said closure to reduce the bending stresses exerted thereon. In a preferred embodiment of magnetic interleaved head according to the present invention, there are two data transducer head modules. Each of the head modules include one transducing gap line extending normal to the movement of the tape. Each gap line includes a plurality of alternating write and read gaps. Each of the head modules includes a substrate made of a magnetic ferrite material. An insulating layer is deposited onto the substrate to prepare for the deposition of the read element films and the write conductor. A patterned magneto resistive layer forming the read transducer is then deposited onto the insulating layer. The magneto resistive layers also form read, write and back gap write islands adjacent to the read elements and adjacent to the proposed write elements. A patterned conductor layer is deposited on each magneto resistive layer to connect the magneto resistive portion of the read transducer for interconnection to the rest of the tape drive. The patterned conductor layer is also deposited over the islands, namely, the read, write and back gap write islands. A patterned second insulating layer is deposited on each conductor layer such that the write track and the read leg regions are exposed. A read and a write conductor is deposited into each patterned write track region and read leg region. A read and a write interconnecting layer is deposited to connect each read and write conductor to the tape drive, namely the data transmitting means which writes the magnetic transitions onto the tape and senses or reads the written magnetic transitions from the tape for use by the drive and the connecting data processing system. A magnetic ferrite closure piece covering all of the plurality of alternating write and read gaps of the head is affixed over the preceding layers. The magnetic ferrite closure forms one write pole piece and a read gap shield for the magneto-resistive read element while the substrate provides the second write pole piece. The back gap write islands provide the mechanical support for the magnetic ferrite closure piece to produce a correct write gap length. The tape drive of the present invention, therefore, may comprise an interleaved transducer as just described and means for moving the tape past the interleaved transducer. The drive may include means for transmitting the data to and receiving the data from the interleaved transducer. By depositing an island of the read transducer material and the read conductor materials in the front and back gaps of the write track region and also in front of the read element in the read section, the film layers in both the read and write sections produce the same height in the various depositions. Therefore, when the closure is assembled to complete the head module, the gap length of the read and write transducers will be essentially the same, and no bending of the closure will occur. In the present invention, therefore, the supporting structure of one module of a magnetic head having alternating read and write elements includes supporting islands adjacent each of the shorter lengths of either the write or read gaps. In the case where the write gap lengths are shorter, the islands are placed adjacent each write element. In the case where the read gap lengths are shorter, the islands are placed adjacent each read element. The supporting structure is preferably magnetic ferrite but could be a non magnetic ceramic. The supporting islands could be made of magnetic materials to enable the independent variations of the magnetic properties of the read or write gaps containing the islands, or the supporting islands could be made of the same materials that comprise the layers of the longer gap length element. The invention seeks to minimize the bending stress in the closure of an interleaved head and hence provide a more stable and reliable gap length. The scope of the invention is defined by the appended claims; and how it can be carried into effect is hereinafter particularly described with reference to the accompanying drawings in which:- Fig. 1 is a schematic of a tape drive and controller including a head according to the present invention; Fig. 2 is a top plan view of a length of magnetic tape and its relationship to an interleaved head; Fig. 3 is a partial sectional view of a portion of an interleaved head; Figs. 4A to C are partial views of the mask drawings used to deposit different layers forming in the interleaved head; and Fig. 5 is a perspective partial view of a portion of the transducer head produced by the steps of Figs. 4A to C, during making according to showing the present invention. The present invention preferably involves the use of an interleaved magnetic head. The interleaved magnetic head has its use to read and write magnetic transitions from a multi-track recording medium. This in turn finds its major usage in tape drive systems. A typical tape drive system well known today is the IBM 3490 tape drive. In a tape drive system, the transducer generally remains fixed and the tape is moved across the transducer in both directions to read and write from various transducers in the magnetic head to record data information onto at least one of a plurality of tracks on the medium. The interleaved head is of particular importance as the number of tracks can be increased while still providing the bi-directional operation of the medium and permitting an immediate read back check of the data just written onto the tape medium. A schematic view of the tape drive system preferred in the embodiment of the present invention is shown in Fig. 1, but US-A 4,125,881 provides a more complete description of a control circuit usable for a reel-to-reel tape drive. Only the apparatus and procedure for an understanding of the present invention is given herein. A controller 10 (Fig. 1) accepts information from a supply reel tachometer 12 which is connected to a supply reel motor 14. The supply reel motor 14 is driven by a motor drive circuit 23 reversibly to rotate a supply reel 16 located within a single reel cartridge 16A. The tachometer 12 directs count pulses to a counter 19 to indicate the number of rotations and the rotational position of the motor 14 and the supply reel 16. The output of the counter 19 is directed to a control unit 17. Another input to the control unit 17 is via the counter 19 that accepts count pulses from a take up reel tachometer 20. The tachometer 20 is connected to a take up reel motor 22 that is reversibly driven by the motor drive circuit 23 which is under the control of the control unit 17. The motor 22 drives a take up reel 24. A timer 26 is connected to the control unit 17 in the controller 10 to control the application of power from the motor drive circuit 23 to the motors 14 and 22. A magnetic tape 28 and its leader block 29 takes a path, shown by a dotted line 27, from the supply reel 16 to the take up reel 24 past an idler bearing 30, an air bearing tape guide 32, a magnetic head 36, an air bearing tape guide 34. The tape path 27 and a roller 38 on a tension arm transducer 18 to the take up reel 24. An example of a tape drive for threading the leader block 29 and the tape 28 through the complex tape path 27 is disclosed in US-A 4,335,858. The magnetic head transducer 36 is preferably an interleaved magnetic head such as is disclosed in the US-A 4,685,005. The output of the magnetic head 36 is connected to a read/write network 15. The read/write network 15, under control of the control unit 17, directs data to a data unit 13 in the read format, and accepts data from the data unit 13 when data is to be written onto the tape 28 by the magnetic head 36. The data unit 13 is generally connected to a central processing unit (CPU) which also controls the operation of the control unit 17. Whilst a head to be used in the practice of the present invention can take the form of any of a number of well known construction types and arrangements, a thin film construction is preferred. By the use of photolithography, it is possible to maximize use of the surface of the medium, as narrow, closely spaced tracks can be written. The present invention provides the advantage that transversely adjacent head elements are not operative at the same time, thus minimizing the possibility of cross-talk and the like. In the preferred embodiment of a thin film transducer used for the magnetic head 36, the write element is an inductive write element comprising two blocks of magnetic ferrite driven by a thin film coil formed by the standard photolithographic steps. The preferred read element is a magneto-resistive (MR) element. It is also preferred that such MR read gaps be of the soft film biased type, well-known to those skilled in the art. It is also preferred that the head construction implement the well known write-wide read-narrow format. In Fig. 2, the read elements for the magnetic head 36 are marked R 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, it is the preferred embodiment of the present invention to provide a format of thirty six tracks across the width of the medium, hereinafter called tape. One format provides that the odd numbered tracks, tracks 1, 3, 5, and so forth are operative during forward tape movement, while the even number tracks 2, 4, 6, 8 and so forth are operative during the opposite direction of the movement of the tape. Other formats useful in the practice of the present invention will of course be evident to those of skill in the art, and are considered to be within the teaching of the present invention. The same reference numerals indicate like structural features and operations in the various figures of the drawings. In general, referring to Fig. 2, the length of magnetic tape 28 moves in either a forward or a reverse direction, the arrow 40 designating the forward movement direction of the tape 28 and the arrow 42 designating the reverse direction. The magnetic tape 28 operates in transducing relationship with the magnetic head 36 in the standard well-known format. The magnetic head 36 includes two modules 44 and 46 of generally identical construction. These two modules are mounted 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 unit, but also, the module gaps are accurately aligned in the direction of tape movement. Each of modules 44 and 46 includes one gap line 48 and 50, respectively, to form the single physical unit of magnetic head 36. The individual gaps of each module are accurately located along the gap lines 48 and 50. As those skilled in the art will appreciate, it is essential that gap lines 48 and 50 be parallel, and that the head be mounted to the tape drive in an accurate manner so that the gap lines 48 and 50 are perpendicular to the direction of tape movement as represented by the arrows 40 and 42. The magnetic head 36 includes the alternating read/write gaps along the length of each of the gap lines 48 and 50 for each of the modules 44 and 46. There are eighteen read transducers and eighteen write transducers in each of the modules 44 and 46. Magnetic tape 28, therefore, has thirty six tracks across its one half inch (12.7 mm) width. The tracks are written about 35 percent wider than the read gaps are able to read. The gaps of one module cooperate with the identically numbered gaps of the other module. Thus, the gaps identified as "1" to "36" of module 44 cooperate with the corresponding gaps identified as "1" to "36" of the module 46. The read gaps of one module are aligned with the write gaps of the other module. Thus a write gap 52 numbered 1 of module 44 is aligned with a read gap 54 numbered 1 of the module 46. The write gap 52 writes a 35 percent wider track onto the magnetic tape 28 and this track is then read by the narrower read gap 54 of the module 46. Each of the modules 44 and 46 include a ferrite substrate 56 and a ferrite closure piece 58. A portion of the thin film structure of the head is shown in Fig. 3. Thin film is deposited onto the substrate 56 of the module 46 and two magneto-resistive (MR) read elements 60 and 62 are shown deposited onto the substrate 56, as is one thin film write coil 64 positioned adjacent to and between the MR elements 60 and 62. The transducing gap of the write coil 64 on the ferrite substrate 56 is shown at reference numeral 66 and those of the read elements 60 and 62 at 69. A back gap region 68 completes the magnetic circuit to be energized by the write coil 64. The ferrite closure 58 (not shown) is then affixed to the ferrite substrate 56 to complete the module 46 and thereby form the adjacent read and write elements shown in Fig. 2. The module 44 is essentially of similar construction to that of module 46. The steps in forming the structure of the module 46 according to the present invention are shown in Figs. 4A, 4B and 4C. In producing the different thin film layers for the MR read elements 60 and 62 and in producing the write coil 64, different thicknesses of layer are required. For instance, the MR read elements 60 and 62 require more thin film layers and, therefore, are thicker than the write coil 64 which operates to write the magnetic transitions onto the tape 28. Thus, when the closure block 58 is placed over the thin film layers, the ferrite closure will be supported by the layers of the MR read elements 60 and 62 but will not be supported by the write coil 64. This could lead to the ferrite closure 58 bending under stress after the module 46 is closed. The total film layers in the read gap are thicker then the total film layers in the write gap. To read the written bits of information on the tape media 28 properly, the write head gap 66 must not be narrower than the MR read elements 60 and 62. The problem is solved according to this embodiment of the present invention by depositing islands of material of similar thickness to the MR read elements 60 and 62 at the back gap 68 region. Thus, the magnetic head 36 and especially each module 46 and 44 include a back gap write island in the back gap 68. In forming the thin film structure (Fig. 4A), an insulation layer of silicon dioxide and/or alumina is deposited over the entire substrate layer. The insulation layer can be a combination of silicon dioxide and aluminium deposited to a total thickness of approximately 60.6 micrometres (6,000 angstroms). In the next step, the layers of the MR elements 60 and 62 are deposited. All the MR elements are deposited at the same time covering the entire ferrite substrate 56 for the module 46. For the preferred embodiment of the magneto-resistive element, a NiFeRh layer of approximately 36 nanometres (360 angstroms) is deposited followed by a 20 nanometre (200 angstrom) layer of Ta and a 54 nanometre (540 angstrom) thickness layer of NiFe. The tri-layer for the MR element includes the NiFe MR layer itself together with the Ta isolation layer and the NiFeRh soft film bias layer. The operation of such an MR element is well known in the art and will not be further described here. At the same time that the MR elements are deposited onto the substrate 56, the same layers are deposited onto read islands 70, write islands 72, and back gap write islands deposited into the write back gap regions 68. This is the first portion of the leveling for the magnetic closure block to be placed over the entire thin film deposition as will be described later. A mask is used to define the read tracks and to define the different islands. The next step (Fig. 4B) is the deposition of the conductor layers onto the read legs up to the MR element itself. A mask is used to define the deposition of an adhesion layer of Ti of approximately 10 nanometres (100 angstroms) followed by the gold conductor layer of approximately 100 nanometres (1000 angstroms) followed again by an adhesion layer of 5 nanometres (50 angstroms). These conductor layers are deposited over the read islands 70, the write islands 72, and the back gap write islands formed in the back gaps 68. The MR elements according to the preferred design are centre tapped and, therefore, each MR element has three conductors, two outer conductors 74 and 76 and a centre conductor 78. The same conductor layers are deposited over all the read elements. Next an insulation layer is deposited over the entire substrate to prepare for the deposition of the write conductors and the extensions of the read conductors onto the read legs. The insulation layers (Fig. 4C) are chemically etched to expose the write conductor region 80 of each of the write transducers and also to expose a portion of the read legs 74, 76 and 78 of the MR read elements. The write conductors are then deposited together with a thicker conductor deposition onto the read legs, by depositing an adhesion layer of Ti to an approximate 50 nanometres (500 angstrom) thickness followed by approximately 900 nanometres (9000 angstrom) thickness of gold. Material is not deposited into the write back gap regions 68 nor onto the read islands 70 or write islands 72. The closure block 58 (see Fig. 2) when affixed to the substrate 56 extends in width approximately to the thick leg portions of the read conductions so that these thicker layers do not affect the gap lengths between the substrate 56 and the closure block 58. Further deposition steps (not shown) form an insulation layer for the crossover from a pad 82 of the write conductor 80 to an external pad 84. The crossovers are then deposited to interconnect the pads 82 and 84 together with any other conductors necessary in order to connect the write conductors and the read conductors to the read/write network 15. The crossovers are encapsulated into an insulation material to insulate the conductors from the housing and other structures of the module 46. An active MR section 69 (Fig. 5) of the MR read element 60 is connected to the conductors 74, 76 and 78. The read island 70 is deposited adjacent the active MR section 69. The write conductors 80 surround the back gap section 68. The write island 72 is shown at the end of the conductors 80 adjacent to what will be the active write gap area 66 (Fig. 3) after abrading is performed to the completed module 46 which includes the ferrite closure 58. The abrading determines the contour of the face of the module that interfaces with the tape 28 as well as the height of the active MR section 69 of the MR read element 60. The write islands 72 as well as the read islands 70 are removed by the abrading step. The write back gap island in the write back gap area 68, the read island 70, and the write island 72 include a layer 90 of the same material as the layers of the active MR read element 69, and a layer of conductor material 92 which is deposited over the conductors 74, 76, and 78 for the read element and on the write back gap island area 68. These islands support the ferrite closure 58, when the ferrite closure block is placed over all the deposited elements. The ferrite closure 58 becomes the second pole piece for the writing procedure as energized by the write conductors 80. The ferrite closure 58 also operates as a shield to the read elements of the MR read head 60 in a manner well known to those skilled in the art. Thus, as is disclosed herein, an improved interleaved head is shown for use in tape recording. It is, of course, understood that a single module could be used with the tape recording drive of the present invention. In the embodiment disclosed, the layers of the read element are thicker than the thin film layers of the write element and therefore a supporting structure, the write back gap island in write back gap area 68, is provided to support the close 58 on the substrate 56 of the module 46. The supporting structure need not be magnetic ferrite if thin film read and write elements are provided. It should also be understood that supporting islands could be provided in the read element area if the write element materials provide a larger write gap. The purpose of this invention being that supporting islands can be included to provide a constant distance between the supporting structure of a multi-gap head. Preferably, the material for the islands is the same as that of the thicker gap element. It should be further understood that the supporting islands could be only magnetic material in order independently to vary the magnetic properties of the read or write gaps containing the islands. The principles of the present invention have now been made clear in an illustrated embodiment. There will be immediately obvious to those skilled in the art many modifications of the structure, arrangement, proportion, the elements, materials and components used in the practice of the invention. For instance, a nickel-zinc ferrite material is shown for use in the ferrite substrate 56 and the ferrite closure 58 for the present invention. It should be understood that other magnetic ferrite material could be used such as a manganese-zinc ferrite, or non magnetic ceramics if the read and write thin film elements are self operational. Further, specific materials are used in the creation of the different layers for the thin film elements and conductors. It is well within the knowledge of a person skilled in the art that other materials could be used as well as other thicknesses, all well within the total lithographic teachings of the prior art. The different masks and photo-lithographic treatments to form the different layers are also well known.

Claims: A transducer head including a module (44, 46) having a transducing gap line (48, 50) including a plurality of alternate write and read gaps (52, 54), the module including a substrate (56) and a closure (58) of ceramic material which covers a plurality of thin film read transducer elements (60, 62) and write elements (64) deposited on the substrate, characterised by a plurality of gap islands (68, 90, 92) of the same thickness as the thickest of the transducer elements for supporting said closure (58) to reduce the bending stresses exerted thereon. A head according to claim 1, wherein the thicker transducer elements are the read transducer elements (60, 62) and conductor material (74, 76, 78). A head according to claim 1, wherein the islands are made of the same material and thickness as the read transducer elements and conductor material. A head according to claim 1, 2 or 3, wherein the read transducer elements are magneto-resistive elements. A head according to any preceding claim, wherein the write transducer elements include write coils of electrically conductive material, each coil having a write back gap region (68) in which is located the respective island (90, 92). A head according to any preceding claim, wherein the substrate and closure are made from blocks of nickel-zinc ferrite. A head according to any preceding claim, which, in the course of manufacture, has further gap islands (70, 72) of the same thickness as the gap islands (68, 90, 92), adjacent each gap (69, 66) in a region of the head, which is to be removed. A head according to any preceding claim, wherein said gap islands comprise only magnetic material in order to independently vary the magnetic properties of the read and write gaps (52, 54) containing the islands. A data transducing magnetic head assembly including a head according to any preceding claim. A data transducing magnetic head assembly including two magnetic heads according to any preceding claim, wherein the gap lines (48, 50) of the two heads are parallel and each read gap (54) in one head is aligned with a write gap (52) in the other head. A magnetic medium drive, including a data transducing magnetic head assembly according to claim 9 or 10 including means for moving the medium past the assembly in a direction normal to the gap line in head. A method of making a magnetic head module having a transducing gap line including a plurality of alternate write and read gaps, comprising the steps of depositing material upon a substrate of magnetic ferrite material to form a plurality of alternate thin film transducer read elements and gaps islands, depositing electrically conductive material upon the deposited read elements and gaps islands and to form a plurality of write coils between the read elements and around the gap islands, and securing a closure of magnetic ferrite covering said plurality of read and write elements to the substrate wherein the islands provide mechanical support for the closure to reduce the bending stresses exerted thereon. A method according to claim 12, wherein the steps of depositing to form the gap islands also form read and write gap islands adjacent to the read and write gaps, and the secured substrate and closure are abraded adjacent to the gap line to remove the material including the read and write gap islands.

Inventors: DENISON EDWARD VIRGIL, KAHWATY VINCENT NOEL, STERN GUSTAVE CHRISTIAN, STEVIN GERALD, ZAMMIT ROBERT PAUL, DENISON, EDWARD VIRGIL, KAHWATY, VINCENT NOEL, STERN, GUSTAVE CHRISTIAN, STEVIN, GERALD, ZAMMIT, ROBERT PAUL
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1991
Main classification: G11B5
IPC codes: G11B5