COMPOSITE METAL AND FERRITE HEAD TRANSDUCER AND MANUFACTURING METHOD THEREFOR

Abstract: A magnetic transducer (10) formed as a composite of three different materials for reproducing and/or recording signals with a magnetic medium, the transducer including first and second generally identical sections (12, 12'), which, when bonded together in opposing relation, form a transducer having aligned recesses (13, 13') in the outer edges and a formed winding window opening (19, 19') adjacent the pole tips, the window being arranged for receiving coil turns therethrough for providing the coil (32) on a line generally parallel to the tape contact surface of the transducer (10), the core legs (18, 18') being formed of two strips of Alfesil material, or the like, deposited or sputtered on the substrate. Each core section (12, 12') is formed as a portion of an elongate ferrite block substrate (20) with a thin cap of non-magnetic material (16, 16'), initially shaped to provide opposing elongate bonding notches (26, 28) on opposite edges of a common surface (22), and an intermediate winding groove (19b) in proximate relation to one of the notches. The winding groove preferably protrudes into the non-magnetic material to about half its depth. Thereafter the workpiece is provided with an array or a plurality of equally spaced V-shaped track width defining grooves (40a-40j) oriented in a direction perpendicular to the winding groove (19b), with the grooves defining pole edges having tapered side surfaces. A chrome adhesion layer is deposited on the grooved surface and into the winding groove, followed by a core layer of suitable magnetic material, such as Alfesil material which provides a pole material covering the edges as well as the tapered side surfaces. A chrome adhesion layer is applied to the Alfesil layer, followed by a gap layer of insulating material. Two of such workpieces (20, 20') are then placed with the edges in facing opposing aligned abutting relation and glass bonding is effected by means of the two bonding notches (26, 28).

Description: COMPOSITE METAL AND FERRITE HEAD TRANSDUCER AND MANUFACTURING METHOD THEREFOR CROSS-REFERENCE TO RELATED APPLICATION The subject matter of this invention is related to the subject matter of U.S. Patent Application Serial Number 07/845,894, filed March 4, 1992, entitled ^"Laminated, High Frequency Magnetic Transducer and Manufacturing Method Therefor" by Beverlev R. Gooch and George R. Varian, and U.S. Patent Application Serial Number 07/846,454, entitled Small Core Metal Head Transducer and Manufacturing Method Therefor, filed March 4, 1992, by Beverlev R. Gooch, such applications being assigned to the assignee of the present invention. The latter application serial number 07/846,454 is hereby incorporated by reference as though fully set forth herein. BACKGROUND OF THE INVENTION This invention relates generally to magnetic head transducers and more particularly to a metal and ferrite composite magnetic video head transducer using sputtered strips for forming the core legs thereof. The performance of a magnetic tape data recorder depends heavily on the properties of the magnetic materials used to make the recording heads and tapes and on the structural configuration of these materials which influence their magnetic properties. Magnetically hard materials, characterized by their high remanence, high coercivity, and low permeability, are chiefly used in the manufacturing of the recording tape and other related recording media. On the other hand, magnetically soft materials, which exhibit low coercivity, low remanence, and relatively high permeability, are commonly utilized to make the magnetic cores for the heads which are the means by which electrical signals are recorded on and reproduced from the magnetic tape. The typical ring-type magnetic head is composed of two highly permeable magnetic cores, with a non-magnetic gap spacer and a coil to which signal information is connected. The record head is a transducer that changes the electrical energy from the signal system into a magnetic field that is emitted from a physical gap in the head which impresses a magnetic pattern on the magnetic tape proportional to the electrical signal. The reproduce head, conversely, is a transducer that collects the flux from the magnetic tape across a physical gap and changes it into an electrical signal that is proportional to the recorded flux. Ferrite materials have been conventionally used as the magnetic material in video heads. The advent of high-definition video tape recorders, digital video tape recorders, computer digital data storage devices and the like, with the resultant use of high coercivity recording media such as metal powder media, metal evaporated media etc., have accelerated the trend towards high density construction for recording even larger amounts of information. As part of this evolution, there is the resultant need to increase the density of the information signal recorded on the medium. Conventional ferrite cores have significant limitations in providing the desired characteristics to achieve the required performance for these applications. There are performance problems with ferrite heads, particularly when such heads are used with high coercivity magnetic tape, and particularly during the recording process. During recording, larger signals are required with high coercivity magnetic tapes than with conventional magnetic tapes. The problem is not severe with the use of a ferrite head during reproduce operations, since signal levels from the tape are much lower in magnitude. With higher recording signals, the signal tends to drive the ferrite heads into saturation. During reproducing or "playback", it has also been observed that there is a significant noise level resulting from contact of such high coercivity magnetic tapes with the ferrite heads, which, in turn, requires higher head efficiencies to achieve an acceptable signal to noise ratio. Bulk metal heads likewise have performance disadvantages, principally in that they have poor high frequency response. The above considerations have led to the use in recording heads of any number of other commercially available magnetic materials which have higher flux density saturation, such materials including cobalt- zirconium-niobium (CZN) alloys, iron-aluminum-silicon alloys including Alfesil, Sendust, Spinalloy, or Vacodur each having a nominal composition of 85% iron, 6%. aluminum, and 9% silicon, and also amorphous metals. Besides the magnetic properties of the head core materials used, the critical design considerations that dictate performance of the heads are track width, gap length, gap depth, and core geometry (e.g. path length). Each of these parameters must be selected in accordance with the design criteria of the magnetic tape recorder, while, at the same time, maintaining the head efficiency as high as possible. In miniaturized transducers, signal coupling is extremely important, and much of the efficiency is determined by the gap to core reluctance, that is, E = Rg/Rg + Re. If the reluctance of the core is negligible relative to the reluctance of the gap, the efficiency approaches unity. In many instances, in miniaturized transducers, matching transformers are required for impedance matching and amplification to the preamplifier circuitry. However, such matching transformers introduce an additional element of noise in the signal. If a winding window in the transducer is simply made larger to accommodate more windings, the larger window area increases the magnetic path length and, in turn, reduces the head efficiency. To counteract this reduction in efficiency, a gap depth reduction can be made; however, this, in turn, reduces the life of the head or transducer. Attempts have been made to provide transducers with better wear characteristics and longer life, for example, by plasma arc sputtering of an Alfesil layer on the tape contacting surface of a ferrite core transducer, such as shown and described in U.S. Patent No. 3,566,045, issued to Paine on February 23, 1971. In U.S. Patent No. 2,711,945, issued to Kornei on June 28, 1955, a core of magnetically soft material is provided with metallic high permeability pole shoes which are disposed for contact with the moving tape, the poles being intended to provide a sharp well-defined, narrow transducing gap and thus avoid the attendant wear disadvantages of the soft core material which, in one embodiment is a ferrite or iron powder. Composite video head transducers, such as the Kornei transducer have been around since the mid-fifties. Other such composite transducers utilized slabs or blanks of one material adhered to ferrite core material is side by side relationship. For example, one such transducer included a toroidally shaped ferrite core with first and second confronting Alfenol metal pole tips with a gap spacer between them and held in contact with a lateral surface of a slotted ferrite ring core, with the pole tips extending beyond the circumference of the ferrite ring core in a plane adjacent to the lateral surface. Another such composite head includes first and second generally planar Alfesil core blocks brazed together with a ferrite core member of shorter length abutted to one side of the brazed combination with the Alfesil core blocks protruding beyond the length of the ferrite core member. In both of these transducers the protruding portion contacted the tape during use. There exists, therefore, a significant need for an improved high frequency magnetic transducer having an optimum number of signal windings with a short magnetic path to reduce core reluctance and to make the head efficiencies less dependent on the permeability of the magnetic material used in the magnetic cores, and to eliminate the need for a transformer. In addition, losses should be minimized, leakage reluctance should be reduced, and the core material must not be driven into saturation when used at normal recording signal levels. The fabrication of such a transducer should be high volume, high accuracy, low cost and achieve a high degree of uniformity. The present invention fulfills these needs and provides further related advantages. SUMMARY OF THE INVENTION The foregoing and other objects of the invention are accomplished by providing an improved tri-composite magnetic transducer for reproducing and /or recording high frequency signals on a magnetic tape medium, the transducer including first and second generally identical sections, which, when bonded together in opposing relation, form a transducer having opposed winding receiving recesses in the side edges thereof in proximity to the head contact surface and a formed winding opening adjacent the pole tips, the winding opening and recesses being arranged for receiving coil turns therethrough for providing the coil about the recesses in a plane generally parallel to the head contact surface of the transducer, the core legs being formed of twc strips of Alfesil material, or the like, applied, such as by sputtering, on confronting edges of a composite ferrite and non-magnetic substrate. Each core section is formed as a portion of an elongate composite block substrate, initially shaped to provide opposing elongate bonding notches on opposite edges of a common surface, and a winding groove in the ferrite portion in proximate relation to the non-magnetic portion of the substrate. The block substrate is formed substantially of a ferrite block having a non-magnetic cap block or layer of shallow dimensions bonded thereto, the cap block being at a location for providing the head to tape contact surface. Thereafter the workpiece is provided with an array or a plurality of equally spaced V-shaped track width defining grooves oriented in a direction perpendicular to the winding groove. The track width grooves are of a depth sufficient to provide a plurality of adjacent, generally parallel isolated core sections. A chrome adhesion layer is deposited on the grooved surface and into the winding groove, followed by a core layer of suitable magnetic material, such as Alfesil material. The grooved surface then has deposited thereon, such as by sputtering, a chrome adhesion layer, followed by a suitable insulating, or gap layer of suitable material such as aluminum oxide or silicon dioxide. Two of such workpieces are then placed in opposing aligned abutting relation and glass bonding is effected by means of the two bonding notches, the temperature and time of flow of the glass being controlled to preclude flow of glass into the winding windows. The thus bonded workpiece is sliced into individual head workpieces, on which the cap block is radiused and narrowed in width to provide a narrow arc of non magnetic tape contact material disposed generally centrally relative to the width of the ferrite block, with a narrow track width. The front gap length is of a dimension generally equal to the thickness of the non magnetic material in the gap region, with the winding window commencing immediately thereafter and of an areal dimension to accommodate a large number of coil windings through the winding window and within the side edge recesses on a line generally parallel to the contact surface to enhance flux efficiencies without the need for matching transformers in the signal path. The size of the magnetic core is extremely small with a short magnetic path length. By lowering the core reluctance by decreasing its path length, the head efficiency is more dependent on the gap reluctance and, hence, less frequency dependent. With the magnetic path extremely short with a large volume of ferrite material in the core, the core reluctance is lowered, resulting in significant gains in flux efficiency particularly in the megahertz frequency range. The non-magnetic cap block, the composition of which is selected for its wear characteristics, is very shallow in dimension and thus the reluctance from the tape contact surface to the ferrite core can be minimized. The entire transducer is fabricated by high volume production, extremely high accuracy, and low cost techniques such as material deposition processes. With batch fabrication, all of the magnetic core material for a large number of transducers is deposited during the same process step and all of the transducing gaps are formed at the same time. This results in a high degree of uniformity for all of the transducers. Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings in which like reference numerals refer to like elements in the several views. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of the completed composite metal and ferrite transducer according to the invention; FIGURE 2 is a top plan view of the composite metal and ferrite transducer of FIGURE 1; FIGURE 3 is a front plan view of the composite metal and ferrite transducer of FIGURE 1; FIGURE 4 is a perspective view of a transducer head section used with a like section to form the body of the transducer of FIGURE 1; FIGURES 5 through 8 are perspective views showing the sequential method steps utilized in the fabrication and assembly of the sections of the transducer of FIGURE 1; FIGURE 9 is a perspective view of the composite metal and ferrite transducer of Figure 1 with further processing for use on a rotary head assembly; and FIGURE 10 is a diagrammatic partial top view of the processed transducer of FIGURE 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and particularly to FIGURES 1 through 4, there is shown a head or transducer, generally designated 10, the transducer 10 being formed of first and second composite core halves, generally designated 12, 12', which as will become apparent during the discussion of the fabrication thereof, are identically configured halves, both of which may be formed at the same time, if desired. The transducer 10, as assembled, is a formed as a generally plate-shaped member of thin cross- section, which is formed, such as by slicing of two block arrays of transducer halves after the two blocks are aligned and bonded together. The transducer 10 is formed as a composite ferrite block portion 15, 15' and a thin non-magnetic cap layer or block portion 16, 16' structure and includes first and second generally identical sections or core halves 12, 12', which, when bonded together in opposing relation, form a transducer having aligned edge winding recesses 13, 13 " , and a centrally disposed formed winding opening 19b, 19b' aligned with the gap 31 adjacent the pole tips. The winding opening and recesses are arranged for receiving turns of a signal coil 32 therethrough for providing the coil 32 on a line generally perpendicular to, and in proximity to, the gap 31 of the transducer 10, the core legs 18, 18' being formed of two strips of high permeability magnetic alloy material, such as Alfesil material, or the like, deposited or sputtered on confronting edges of a face of the composite substrate. In the instant embodiment, sputtering of the Alfesil material is preferred. Each core section or half 12, 12' is formed as a portion of an elongate composite ferrite and non-magnetic material block substrate 20 (See FIGURES 5 through 8), formed of a first ferrite block 15 and a cap block of non-magnetic material 16 bonded thereto, with the ferrite block 15 being of substantially greater dimension and volume than the non-magnetic cap block 16. As best depicted in FIGURE 4, the core section 12 is formed as a thin plate-shaped or block like structure of ferrite material 15 overlaid with and bonded to an upper shallow or thin block of non-magnetic material 16 of the same width and length, the composite structure having a first generally planar outer edge 17, with a recess 13 optionally formed therein in proximate relation to and displaced slightly below the junction of the two materials. The opposite edge, generally designated 19, includes a narrow strip-like land or pole face 19a and a V-shaped groove 19b extending in a direction transverse to the face 19a and between the outer planar side surfaces 21, 21a. On either side of the pole face 19a, there are rearwardly tapered sections 22a, 22b, of like dimension and angle with the pole face 19a protruding slightly outwards from the sections 22a, 22b, the width of the pole face 19a defining the track width, designated TW in the various figures. The apex of the V-shaped groove 19b is formed within the ferrite material 15 and is in general alignment with the center of the recess 13, with the upper terminal edge of the groove 19b extending into the non¬ magnetic cap layer or block 16. The core leg 18 is formed by depositing, such as by sputtering, a high permeability magnetic alloy material on the surfaces of land or pole face 19a, the tapered sections 22a, 22b and the V- shaped winding groove 19b. Referring now to FIGURES 2 through 5, the substrate 20 is initially formed by starting with a block 15 of ferrite material to which is bonded a cap layer or block 16 of non-magnetic material, the block 15 being substantially greater in dimension and volume than the cap block 16. The cap block 16 has the same length and width as the areal surface of the upper surface of block 15 The composite substrate 20 is then initially shaped to provide opposing elongate glass bonding notches 26 (at the lower edge of ferrite block 15), 28 (at the upper edge of non-magnetic cap block 16) on opposite long corners or edges of a front or common surface 22, and an elongate winding groove 19b in proximate relation and generally parallel to the upper surface of the non-magnetic cap block 16. Thereafter the workpiece is provided with an array or a plurality of equally spaced V- shaped track width defining grooves 40a-40j oriented in a direction perpendicular to the winding groove 19b. The track width grooves 40a-40j are of a depth sufficient to provide a plurality of adjacent, generally parallel core sections, with the width of the land 19a defining the track width TW. A thin chrome adhesion layer (not shown) is deposited cm the grooved surface 22 (including the lands 19a and the tapered sections 22a, 22b) and into the winding groove 19b, followed by a core layer, generally designated 18, of suitable high permeability magnetic material, such as Alfesil material. Alternatively, a cobalt-zirconium-niobium alloy may be employed, but in the preferred embodiment, Alfesil is used. The Alfesil layer of the grooved surface 22 then has deposited thereon a second thin chrome adhesion layer (not shown), followed by an insulating, or gap layer (not shown) of suitable material such as aluminum oxide or silicon dioxide. The chrome adhesion layers and the thin insulating gap layer are not shown in the drawings due to the relative thinness of the layers and addition to the drawings of such layers would unduly complicate the figures. Two of such workpieces 20, 20' are then placed in opposing aligned abutting relation and glass bonding is effected by means of the two grooves formed by the two pairs of opposing bonding notches 26, 28, the temperature and time of flow of the glass 57 being controlled to preclude flow of glass into the winding windows. For assembly and fabrication, there will now be described the sequential method steps utilized in the fabrication of each core section or half 12, 12' of the magnetic transducer 10 of the present invention. Referring specifically to FIGURE 5, the starting point in the method is the use of a generally elongate thin block substrate, or workpiece 20, formed of a first block 15 of ferrite material capped with a thinner block 16 of a suitable non magnetic, non-conducting material such as calcium titanate, other ceramic material or other comparable dielectric materials. The substrate or workpiece 20, at the outset, has at least first and second mutually perpendicular surfaces, generally designated 22 and 24, the surface 22 hereinafter being referred to as the bonding surface, and the surface 24 hereinafter being referred to as the head edge surface. The substrate or workpiece 20 is then shaped by conventional machining methods or by a reactive ion beam etching (RIBE) to form first and second longitudinally extending right-angularly configured bonding notches, generally designated 28 and 26, respectively, in the upper and lower (as viewed in the drawings) longitudinal edges of substrate 20. The notches 28, 26 are of generally equal depth (in a direction perpendicular to the bonding surface 22) and formed so that one surface thereof is generally perpendicular to the bonding surface 22. A coil winding furrow or groove 19b is formed in the bonding surface 22 of the substrate 20 adjacent the • upper edge thereof just below the junction of the blocks 15 and 16, in proximate relation to, but displaced from, the upper bonding notch 28. The winding groove 19b may take any convenient configuration, such as V- shaped, U-shaped or semicircularly shaped, the primary function dictating the configuration and depth of the groove 19b being that it be of sufficient dimension to receive the coil winding 32 when bonded to another section as will be described, and further that the groove be placed such that the upper apex preferably protrude into the cap layer 16 or as close thereto as possible. The partially fabricated workpiece 20 is then provided with a plurality of equally spaced track width notches 40a-40j, the notches 40a-40j extending in a direction perpendicular to the edge surface 24, and being of a depth which approximates half the depth of the bonding notches 26, 28. The track width notches may be formed by any convenient method, that is, by conventional machining techniques or by reactive ion beam etching, but, in any event, the forming leaves the lands 19a in a bar-shaped configuration, that is, opposite edges of the lands 19a are parallel to one another. The track width notches 40a-40j are symmetrical in the horizontal plane, that is, they are preferably V-shaped in cross-section, as a consequence of which, after slicing as will be hereinafter described, the pole tips 19a, are generally trapezoidally configured in cross-section (See FIGURES 2 and 4), with the width of the forward bar-shaped edge of the trapezoid defining the track width, designated TW, and which is about 0.002 inch. To complete the workpiece 20, the surface 25 opposite surface 22 is grooved or notched along its length at a position just below the junction of the two blocks 15 and 16 to form the winding receiving recess 13. The recess 13 is not necessary to the invention but does provide a convenience for winding of the coil 32. After formation and shaping of the substrate or workpiece 20, an adhesion layer (not shown) of a suitable substance, such as chrome, is deposited on the surface 22, followed by a core layer 18 of a suitable high permeability magnetic alloy material, such as Alfesil, which is an iron- aluminum-silicon alloy having a nominal composition of 85% iron, 6% aluminum, and 97o silicon. The Alfesil core layer 18 sputters into the track notches, that is, it coats the tapered sections 22a, 22b as well as the land 19a to form a composite metal and ferrite core half as shown in FIGURE 4 with intimate magnetic coupling between the layer 18 and the ferrite block 15. The choice of composition for the adhesion layer is dictated by compatibility with the composition of the two materials of the substrate 20 or workpiece as well as compatibility with the composition of the core layer 18. The chrome layer and Alfesil core layer 18 may be deposited by any suitable means such as sputtering, with the chrome layer thickness being extremely nominal and of the order of 1 to 2 micro inches. The core layer 18 is of a thickness of about 0.0005 to 0.001 inch and, essentially forms the core of the head 10. In depositing the chrome adhesion layer and the core layer 18, the bonding notches 28, 26 are protected in any suitable manner to preclude depositing of material thereon, such as by using masking techniques or the like. Thereafter additional layers are deposited, first there is deposited a second thin adhesion layer (not shown) of about 1 to 2 micro inches of chrome followed by an insulation or gap layer (not shown), this thickness of the gap layer being one half the desired track gap spacing. In this embodiment, the gap layer is approximately 4 micro inches, resulting in a gap spacing of 12 micro inches. The chrome adhesion layer is optional and may be omitted provided that there is proper adhesion between the insulation or gap layer and the core layer 18 in the fabrication process employed. As shown in FIGURES 7 and 8, the two core halves 12, 12' (See FIGURE 1) are portions of the two like blocks 20, 20' which are placed in opposing facing relationship, with the pole faces of the individual blocks in aligned facing or face confronting relationship. The pole faces of the individual blocks 20, 20' are essentially those remaining abutting portions of the surface 22 on which the aforedescribed layers have been sequentially deposited. The block, designated 20' is identical to the block 20 and, for ease of description, corresponding elements thereof are identified with the same reference numerals followed by a prime (')• With the blocks 20, 20' in facing abutting relationship, as can be seen, there is formed a box-shaped or generally diamond-shaped winding window 30 formed from the facing juxtaposition of the two window grooves 19b, 19b'. Upper and lower bonding grooves or channels are formed by the upper pair of bonding notches 28, 28' and the lower pair of bonding notches 26, 26'. The two blocks 20, 20' are then suitably clamped together for bonding. In bonding the blocks 20, 20' together with a glass bonding technique, care must be exercised to preclude the entry of glass bonding material into the winding window. For this purpose, a two step bonding method is employed as described in the aforementioned U.S. Patent Application Serial No. 07/846,454, which has been incorporated by reference. After glass bonding, the upper adjoined surfaces 24, 24' are then lapped along line L-L (shown in Figure 8). Individual transducers 10, as illustrated in FIGURES 1 through 3, are then obtained by slicing or dicing the substrate block 20, 20' along the cut lines 60 shown in FIGURE 8. These cut lines 60 would normally be at an angle 0 relative to the side of the substrate block 20, 20' to create the desired angle for azimuth recording. While the individual transducers 10 can be sliced off one at a time, it would normally be the practice to gang slice all of the transducers 10 at the same time in a single pass. The thus bonded and sliced transducers would have the appearance of the transducer shown in FIGURE 1 (minus the coil winding 32). FIGURE 9 shows the transducer 10 after further processing for use in a rotary head assembly. As shown, the transducer 10 has the head surface thereof rounded or contoured, with the head geometry further modified by the removal of portions to form lateral notches or shoulder portions 24a, 24b, which coincide with the junction between block 15 and cap layer or block 16, thereby providing a narrow ridge portion 24c on which the tape moves. In dimension, the radius is such that at its highest point, which coincides with the gap 31 position, the dimension is between 0.0035 and 0.040 inch, while the width of the narrow ridge portion 24 is about 0.004 inch. This tape contact surface is formed in the non-magnetic block 16 material which may have exceptional wear characteristics as an attribute. In practice, during assembly, this contouring and notching will be performed prior to slicing the substrate blocks 20, 20'. First the head surface 24 will be contoured; then, grooves of appropriate width will be formed at the cut lines 60 (See FIGURE 7); then the block will be sliced at the midpoint of these grooves to provide the configuration as shown in FIGURES 9 and 10, with the track width TW, being about 0.002 inch, fne thickness W of the transducer being about 0.008 inch, and the thickness X of the resultant ridge 24c being about 0.004 inch, with the ridge centrally positioned relative to the thickness of the transducer. The transducer 10 of the present invention is a tri-composite construction, that is, three different materials are utilized for different purposes in an assembled arrangement. The greater portion of the mass of the transducer 10 is the ferrite material 15 which is low reluctance and efficiently couples magnetic paths; the second material employed is the non-magnetic material 16 which forms the cap layer and provides a durability or resistance to wear under high head to tape speed contact with high coercivity magnetic tape; and the third material is the material which provides the metal in gap, which is the sputtered core legs 18, 18' of high permeability magnetic material. By reference to FIGURE 10, the upper surface or tape contact surface, which is predominantly layer 16, is depicted with two sets of vertical lines designated 'TC" and "MM", these being respectively the tape contact dimension TC which is about 0.050 to 0.060 inch, and the magnetic material dimension MM, which is, at the center, about 0.001. The ratio of the tape contact dimension TC to the magnetic material dimension MM is about 50 or 60 to 1, this being referred to as the aspect ratio. For wear purposes, this is an important consideration in that it indicates the ratio of the tape contact between the harder non-magnetic material 16 and the metal material 18 of the gap, that is, for the most part, the tape is substantially in contact with the non-magnetic material 16. Furthermore, by reference to this figure, another important advantage of the present invention, in addition to the tri-composite material construction, resides in the fact that not only are the pole faces 19a sputtered with the high permeability magnetic material to form core legs 18, but the adjacent tapered sections 22a, 22b (See also FIGURE 4) are also coated with the high permeability magnetic material. This effectively increases the cross-sectional area of the magnetic material of the core legs 18, thereby effectively decreasing the reluctance of the magnetic path between the magnetic tape and the ferrite material 16 and windings 32. Since the reluctance of a magnetic structure is R = 1/Aμ, the reluctance is directly proportional to the path length ("1") and inversely proportional to the effective cross-sectional area of the magf.e-.cr material (A), and by increasing this area, reluctance is correspondingly reduced. On an overall basis, and by way of example, the length and width of an individual transducer 10 would be in the order of 0.100 to 0.125 inches while the thickness would be in the order of 0.008 inches. By reference to FIGURE 2, the gap dimension, designated "A", is on the order of about 12 micro inch, and by reference to FIGURE 3, the dimension "B" from the bottom of the winding window to the upper surface of cap block 16 is about 0.0098 inch, the dimension of "C" being about 0.002 inch, that is the intrusion of the upper apex of the winding window into the cap or block layer 16, with the distance E between this upper apex and the upper tape contact surface 24 being about 0.001 inch. The signal coil window size in the vertical direction is about 0.0088 inch, which is about 2 1/2 times greater than the corresponding window of the transducer of the aforementioned patent application serial no. 07/846,454. The distance "D" which is the vertical distance from the upper apex of winding window 30 to the bottom of the transducer is about 0.107 inch. As a consequence, the coil 32 can incorporate a larger number of windings, the magnetic path of which is primarily in the ferrite material 15, yet closely adjacent the tape contact surface due to the minimal spacing between the upper apex of the winding window 30 protruding into the non-magnetic cap layer or block 16, with the winding window 30 (formed by grooves 19b, 19b') being substantially filled with the turns of the coil 32, with the coil 32 lying along a line generally parallel to the surface 24 at a distance of about 0.00175 to 0.002 inch from the path of the surface of the magnetic media or tape. As best shown in FIGURE 3, the window formed by the grooves 19b, 19b' is approximately square, with the angle β of the grove 19b, 19b' being about 45 degrees. In such a metal-in-gap transducer 10, the magnetic path encounters two gaps, the front gap and the back gap. The front gap is that portion of the facing abutting core legs 18, 18' lying between the upper apex of the winding window 30 (formed from the confronting pair of notches 19b, 19b') and the upper surface 24, with the back gap being that portion of the facing abutting core legs 18, 18' between the lower apex of the winding window 30 and the lower surface of the transducer adjacent notch 26. With the large surface area of the gap confronting surfaces in the back gap relative to the area of the gap confronting surface of the front gap, coupled with the back gap being totally included within the region of the ferrite material of block 15, the back gap provides an extremely low reluctance path compared to the front gap (which is totally included within the region of the non-magnetic material of block 16), as a result of which the flux concentration is at the front gap in very close proximity to the coil 32. With the small size of the transducer 10 constructed in accordance with the instant invention, the inductance per turn of the windings of the coil 32 is also reduced, thus allowing more turns for a given resonant frequency which will result in more head output voltage without the need for a matching transformer. The small physical size of the magnetic core results in a short magnetic path length. By having the magnetic path extremely short, the core reluctance becomes less dependent on the core permeability, resulting in significant gains in flux efficiency in the high frequency range, for example in the 100 to 150 MHz frequency range. The entire transducer 10 is fabricated by high volume production, extremely high accuracy, and low cost techniques such as material deposition and sputtering processes. With batch fabrication, all of the magnetic core material for a large number of transducers 10 is deposited during the same process step and all of the transducing gaps are formed at the same time. This results in a high degree of uniformity for all of the transducers 10. In contrast to totally ferrite heads of similar dimensions, the metal in gap transducer 10 of the present invention exhibits significant improvement in signal levels in the frequency range of interest, and a significant reduction in the noise level associated with tape contact with the transducer. In addition with the composite head structure, the non-magnetic material may be selected according to wear characteristics for the unit. The construction of the transducer 10 is economical, straightforward and uncomplicated, and the ultimate in simplicity. The transducer 10 of the present invention is essentially two sputtered core legs on the formed facing edges of a composite substrate. The fabrication techniques are simple and uncomplicated resulting in a low cost, highly flux efficient unit utilizing conventional readily available fabrication equipment. A wide variety of modifications and improvements to the composite metal and ferrite high frequency, magnetic transducer and manufacturing method therefor described herein are believed to be apparent to those skilled in the art. Accordingly, no limitation on the present invention is intended by way of the description herein, except as set forth in the appended claims.

Claims: What is claimed is: CLAIMS 1. A magnetic transducer for reproducing and/or recording high frequency signals with a magnetic medium, comprising: a pair of generally identical magnetic core sections each of said sections being formed of a ferrite substrate bonded to a non-magnetic substrate cap and having facing edges thereof formed of said ferrite material and said non-magnetic material, said edges being separated by a gap and bonded together to define a surface in said non-magnetic substrate generally transverse to said edges, each magnetic core section having a thin layer of high permeability magnetic material deposited on said facing edges, said edges being configured such that when opposed together said pair of magnetic core sections form a winding window adjacent said surface; and coil means through said window and into engagement with the side edges of said ferrite substrate and substantially filling said winding window. 2. The magnetic transducer of claim 1 wherein the ferrite substrate of said magnetic core sections is substantially greater in dimension and volume than that of said non-magnetic substrate cap. 3. The magnetic transducer of claim 2 wherein the width of the facing edge defines the track width and wherein said thin layer of high permeability material is a sputtered magnetic material. 4. The magnetic transducer of claim 3 wherein the thickness of said non-magnetic substrate is about one-half the thickness of said ferrite substrate. 5. The magnetic transducer of claim 3 wherein said magnetic material is selected from the group consisting of cobalt-zirconium-niobium alloys, and iron-aluminum-silicon alloys. 6. The magnetic transducer of claim 5 wherein said non¬ magnetic substrate material is selected from the group consisting of alumina, silicon dioxide, and ceramics. 7. The magnetic transducer of claim 1 wherein said winding window is positioned such that said coil means substantially surround said ferrite substrate. 8. The magnetic transducer of claim 1 wherein the spacing between said winding window and another surface opposite said surface is substantially greater than the spacing between said surface and said winding window. 9. The magnetic transducer of claim 8 wherein the spacing between said winding window and said another surface is at least ten times greater than the spacing between said surface and said winding window. 10. The magnetic transducer of claim 3 wherein said thin layer is a sputtered layer of about one thousandths of an inch. 11. The magnetic transducer of claim 10 wherein the spacing between said surface and said window is about two thousandths of an inch. 12. The magnetic transducer of claim 1 wherein the facing edges between said surface and said window are formed entirely in said non¬ magnetic substrate. 13. The magnetic transducer of claim 1 wherein the width of the facing edge defines the track width and wherein each such facing edge includes first and second tapered surfaces contiguous therewith and wherein said thin layer of high permeability material is a magnetic material sputtered on each such facing edge and said first and second tapered surfaces. 14. The magnetic transducer of claim 1 wherein said window extends at least partially into said non-magnetic substrate. 15. A magnetic transducer for reproducing and/or recording high frequency signals with a magnetic tape medium, comprising: a pair of generally identical magnetic core sections having facing edges thereof separated by a gap and bonded together to define a surface generally perpendicular to said edges, said surface being configured for placement adjacent a magnetic tape medium, each magnetic core section including a composite substrate formed substantially of a ferrite material bonded to a thin cap of a non-magnetic material forming said surface, said substrate having one of said facing edges; a thin layer of high permeability magnetic material deposited on said facing edges, said edge being configured such that when opposed together with another like edge, said edges form a winding window closely adjacent said surface and in general alignment with said recesses, said winding window having a portion thereof projecting into said non-magnetic material; and a signal coil threaded through said window and into engagement with said recesses in generally parallel relation with said surface, said signal coil substantially filling the winding window. 16. The magnetic transducer of claim 15 wherein said thin layer of high permeability material is a sputtered magnetic material. 17. The magnetic transducer of claim 15 wherein said magnetic material is selected from the group consisting of cobalt-zirconium-niobium alloys, and iron-aluminum-silicon alloys. 18. The magnetic transducer of claim 16 wherein said non¬ magnetic material is selected from the group consisting of alumina, silicon dioxide, and ceramics. 19. The magnetic transducer of claim 15 wherein the dimensions of said ferrite material are such that said signal coil substantially encircles said ferrite material portion of said composite substrate. 20. The magnetic transducer of claim 15 wherein said ferrite material is generally block shaped and said non-magnetic material is a generally bar-shaped portion capping said ferrite material. 21. The magnetic transducer of claim 15 wherein said thin layer is a sputtered layer of about one thousandths of an inch. 22. The magnetic transducer of claim 20 wherein the spacing between said surface and the winding window is about two thousandths of an inch. 23. The magnetic transducer of claim 15 wherein said thin layer of magnetic material is deposited on the facing edge of said winding window adjacent said surface. 24. A workpiece for forming a plurality of magnetic transducers for reproducing and/or recording high frequency signals with a magnetic tape medium, said workpiece comprising: a first generally block-shaped substrate of ferrite material; a second generally block-shaped substrate of non-magnetic material bonded to said first substrate to form a block-shaped composite substrate wherein said ferrite material is substantially greater in volume and dimension than said second substrate, said composite substrate having a first surface formed substantially of said non-magnetic material and a second mutually perpendicular surface; a winding groove in said second surface on a line generally parallel to and proximate said first surface, said winding groove having a portion thereof formed within said non-magnetic material with the majority of said groove formed in said ferrite material; a plurality of equally spaced generally identically configured grooves in said second surface in a direction generally perpendicular to said winding groove for providing a plurality of lands intermediate said spaced grooves; and a thin layer of high permeability magnetic material fleposfteα υn -ar least said plurality of lands, said workpiece being configured, dimensioned and arranged so that when positioned in edge facing relation with another like workpiece and bonded thereto with a gap therebetween a matrix of transducer blanks is formed, which when separated by cutting, the so bonded workpieces form transducers, each having signal coil receiving means formed by said recess means and said winding window. 25. The workpiece of claim 24 wherein said workpiece further includes winding recess means formed in the surface of said composite substrate opposite said second surface on a line generally parallel to said first surface. 26. The workpiece of claim 24 wherein said thin layer of high permeability magnetic material is a sputtered magnetic material. 27. The workpiece of claim 24 wherein said magnetic material is selected from the group consisting of cobalt-zirconium-niobium alloys, and iron-aluminum-silicon allovs. 28. The workpiece of claim 24 wherein said non-magnetic material is selected from the group consisting of alumina, silicon dioxide, and ceramics. 29. The workpiece of claim 26 wherein said thin layer of magnetic material is a sputtered layer of about one thousandths of an inch. 30. The workpiece of claim 26 wherein the spacing between said surface and the winding window is about one thousandths of an inch. 31. The workpiece of claim 26 wherein the width of said lands is about two thousandths of an inch. 32. A method of fabricating a magnetic transducer for reproducing and /or recording high frequency signals with a magnetic medium, comprising the steps of: forming a composite substrate of a first generally block-shaped piece of ferrite material bonded to a second generally block-shaped piece of non- magnetic material bonded wherein said ferrite material is substantially greater in volume and dimension than said second substrate, said composite substrate having a first surface formed substantially of said non¬ magnetic material and a second mutually perpendicular surface; shaping said second surface to form a groove in proximate relation to, and generally parallel to, said first surface with said groove at least partially formed in said non-magnetic material; forming a plurality of equally spaced generally identical notches in said second surface with said notches in a direction generally perpendicular to said groove and of a depth sufficient to form lands between said notches; depositing a thin layer of high permeability magnetic material on the thus notched and grooved second surface; depositing a gap insulation layer on at least said lands; bonding together two such processed substrates with the lands thereof in abutting facing relationship; slicing individual magnetic transducers from said bonded substrates; and providing signal coils for at least some of said individual transducers by passing windings through the window and about the recesses with the windings of said signal coils substantially filling the window formed by the first grooves. 33. The method of claim 32 further including the step of forming a recess in a surface opposite said second surface of said composite substrate; 34. The method of fabricating a magnetic transducer of claim 32 wherein said magnetic material is sputtered and selected from the group consisting of cobalt-zirconium-niobium alloys and iron-aluminum-silicon alloys. 35. The method of fabricating a magnetic transducer of claim 32 wherein said insulation material is selected from the group consisting of alumina, silicon dioxide, and ceramics. 36. The method of fabricating a magnetic transducer of claim 32 wherein the thickness of said thin layers of magnetic material is on the order of one thousandths of an inch. 37. The method of fabricating a magnetic transducer of claim 36 wherein the window formed by said first groove is about square and having a dimension of about ten thousandths of an inch. 38. The method of fabricating a magnetic transducer of claim 32 wherein said recesses are formed in said ferrite material and said groove is substantially formed in said ferrite material. 39. A method of fabricating a magnetic transducer for reproducing and /or recording high frequency signals with a magnetic medium, comprising the steps of: shaping one flat first surface of a composite block substrate having a second surface generally perpendicular to the first surface to form a first groove in said first surface in proximate relation to, and generally parallel to, said second surface, said composite block substrate being comprised essentially of ferrite material with a non-magnetic portion forming said second surface, said groove having at least a portion thereof within said non-magnetic portion; forming a plurality of equally spaced generally identical notches in said one surface with said notches in a direction generally perpendicular to said groove and of a depth sufficient to form lands between said notches; forming a recess within said ferrite material generally parallel to said first surface in a surface of said composite block substrate opposite said first surface; depositing a thin layer of high permeability magnetic material on said one surface at least in said groove and on said lands; depositing a gap insulation layer on at least said lands; bonding together two thus processed substrates with the lands thereof in abutting facing relationship; slicing individual magnetic transducers from said bonded substrates; and providing signal coils for at least some of said individual transducers by passing windings through the recesses and the window formed by said first and second grooves. 40. The method of fabricating a magnetic transducer of claim 39 wherein said window is generally diamond-shaped and the apex thereof protrudes into said non-magnetic material to approximately one half the thickness thereof. 41. The method of fabricating a magnetic transducer of claim 39 wherein the windings of said signal coil substantially fill the window formed by the first grooves and said signal coil substantially encircles the ferrite material of said composite block substrate. 42. The method of fabricating a magnetic transducer of claim 39 wherein said magnetic material is sputtered and selected from the group consisting of cobalt-zirconium-niobium alloys and iron-aluminum-silicon alloys. 43. The method of fabricating a magnetic transducer of claim 39 wherein said insulation material is selected from the group consisting of alumina, silicon dioxide, and ceramics. 44. A magnetic transducer for reproducing and/or recording high frequency signals with a magnetic medium, comprising a pair of generally identical magnetic core sections each of said sections being formed of a ferrite substrate bonded to a non-magnetic substrate cap and having facing edges thereof formed of said ferrite material and said non-magnetic material, said edges being separated by a gap and bonded together to define a surface in said non-magnetic substrate generally transverse to said edges, each magnetic core section having a thin layer of high permeability magnetic material deposited on said facing edges, said edges being configured such that when opposed together said pair of magnetic core ' sections form a winding window adjacent said surface. 45. The magnetic transducer of claim 44 wherein the ferrite substrate of each said magnetic core section is substantially greater in dimension and volume than that of said non-magnetic substrate cap. 46. The magnetic transducer of claim 44 wherein the width of the facing edge defines the track width and wherein each such facing edge includes first and second tapered surfaces contiguous therewith and wherein said thin layer of high permeability material is a magnetic material sputtered on each such facing edge and said first and second tapered surfaces. 47. The magnetic transducer of claim 44 wherein said window is configured, dimensioned and arranged so that at least a portion thereof protrudes into said non-magnetic substrate. 48. The magnetic transducer of claim 44 further including first and second generally aligned recesses formed in the edges of the ferrite portion of said transducer opposite said facing edges in general alignment with said window for receiving signal coils. 49. The magnetic transducer of claim 44 wherein said surface in said non-magnetic substrate cap is a tape contact surface and has a thickness of about half of the thickness of the ferrite substrate adjacent thereto with the reduced thickness cap being centrally disposed relative to the thickness of the transducer. 50. The magnetic transducer of claim 49 wherein said tape contact surface is arcuately contoured.

Inventors: GOOCH BEVERLEY R, NIEDERMEYER REX, GOOCH, BEVERLEY, R., NIEDERMEYER, REX
Applicants: AMPEX SYSTEMS CORP, AMPEX SYSTEMS CORPORATION
Application year: 1993
Main classification: G11B5
IPC codes: G11B5