Abstract:
A magnetic head includes first and second magnetic yoke layers which contact each other at a back closure region at one end and delineate a transducer gap at another end. A toroidal coil encompasses one of the yoke layers. The coil axis of the toroidal coil passes through the encompassed yoke layer. During data writing, electrical current passes through the toroidal coil inducing magnetic flux along the coil axis, which flux is efficiently and directly delivered to the transducer gap for writing on a recording medium. During data reading, magnetic flux intercepted by the transducer gap flows along the encompassed yoke layer and efficiently induces electrical current in the toroidal coil for amplification. In alternative embodiments, separate read transducers are disposed adjacent to the toroidal coils to form merged heads.

Description:
FIELD OF THE INVENTION 
     This invention relates to magnetic heads and in particular to low profile magnetic heads incorporating toroidal coils capable of transducing high areal density signals at high data transfer rates. 
     BACKGROUND OF THE INVENTION 
     Magnetic recording media in the form of tapes or disks have widely been used for data storage. Magnetic heads are commonly employed to perform the tasks of interacting with these recording media. 
     FIG. 1 shows a conventional magnetic head  2  comprising a flat inductive coil  4  sandwiched between a first yoke layer  6  and a second yoke layer  8 . The two magnetic yoke layers  6  and  8  contact each other at a back closure region  10  at one end to form a magnetic path  9  and define a narrow transducing gap  12  at another end. During data writing, electrical current representing information passes through a pair of electrical leads  11  and  13  and through the inductive coil  4  to induce magnetic flux along the magnetic path  9 . The induced magnetic flux reaches the narrow gap  12  and magnetizes a moving recording medium (not shown) disposed close by. 
     During data reading, magnetic flux emanating from a recorded medium (not shown) is intercepted by the narrow gap  12 . The intercepted magnetic flux flows along the continuous magnetic path  9  defined by the two yoke layers  6  and  8  and induces electrical current in the inductive coil  4 . The induced current in the coil  4 , which is directed through the electrical leads  11  and  13 , corresponds to the data stored on the recording medium. 
     As shown in FIG. 1, the inductive coil  4  of the head  2  is geometrically flat in topology. As is known in the art, when current passes though a structure, such as the coil  4 , induced magnetic flux is mostly generated at the central region adjacent to the axis  14  of the coil  4 . It is the back closure region  10 , with its relatively wide physical area and high permeability, that captures the induced magnetic flux for transmission to the gap  12  during data writing. The magnetic flux has to pass through a long magnetic path  9  which is defined by the second yoke layer  8 . This arrangement is undesirable in several aspects. First, the long magnetic path  9  contributes substantially to the reluctance of the magnetic head  2  and renders the head  2  less effective in flux transmission. To compensate for the inefficiency, the coil  4  is normally wound with a large number of turns. As a consequence, the inductance of the coil is further increased. A magnetic head with high inductance is sluggish in response to writing current during the data writing mode and incapable of reading media at a high rate during the data reading mode. Furthermore, the long magnetic path with the irregular geometrical topology is the main source of magnetic domain instabilities, which is especially enhanced at the back closure region  10  where a highly unstable domain pattern, commonly called the “spider web” pattern, resides. The constant merging and splitting of the unstable magnetic domains in the yoke layers  6  and  8  during operation significantly produces Barkhausen noise (also called popcorn noise) to the head  2  and accordingly lowers the signal-to-noise ratio (SNR) of the head. To compound the situation further, the coil  4  with the large number of windings is also high in ohmic resistance which is a key contributor to Johnson noise. As a consequence, the SNR is further degraded. 
     To solve the aforementioned problems, different kinds of magnetic heads have been suggested. FIG. 2 illustrates a prior art magnetic head described in Cohen et al., “Toroidal Head Supports High Data Transfer Rates”, Data Storage, February 1997, pp 23-28. FIG. 2 shows a magnetic head  16  that includes a toroidal coil  18  formed of two coil segments  18 A and  18 B. The first coil segment  18 A is connected in series to the second coil segment  18 B. Electrical leads  20  and  22  are connected to the first and second coil segments  18 A and  18 B, respectively. The first coil segment  18 A wraps around a first yoke layer  24 . In a similar manner, the second coil segment  18 B surrounds a second yoke layer  26 . The two yoke layers  24  and  26  contact each other at a back closure region  28  at one end, and define a narrow transducing gap  30  at another end. With this arrangement, a continuous magnetic path  36  with the transducing gap  30  is defined by the two yoke layers  24  and  26 . 
     During data writing, writing current I passes through the coil  18  via the electrical leads  20  and  22 . Magnetic flux is accordingly induced in the coil  18 . In a similar fashion as with the coil  4  shown in FIG. 1, the coil segments  18 A and  18 B, being spiral structures, generate magnetic flux around the areas adjacent to the coil axes  32  and  34 , respectively. The induced flux flows directly through the two yoke layers  24  and  26  without relying on the back closure region  28  for flux collecting. The head  16  is more efficient in controlling flux flow, and consequently has better performance. 
     Advantageous as it appears, the head  16  still requires the coil  18  to be wound with a large number of coil turns. Therefore, the head  16  has undesirable high inductance. 
     In Cohen et al., the authors are fully aware of the detrimental effects of the high coil inductance on head performance. In fact, Cohen et al. specifically state that the head inductance L is proportional to the square of the number of coil windings N, while the output signal generated by the head  16  only increases linearly with the number of coil windings N. The prior art head  16  is fabricated with a large number of coil turns N, required to effectively drive the two long yoke layers  24  and  26  which are high in magnetic reluctance. There are two coil segments  18 A and  18 B sandwiched between the two yoke layers  24  and  26  which exacerbate the curvature of the second yoke layer  26 . Consequently a longer second yoke layer  26  is required to define the magnetic path  36 . With a longer and more curved magnetic path  36 , more coil windings are needed to drive the yoke layers  24  and  26  in order to supply sufficient field strength from the narrow gap layer  30 . The overall effect is that the head  16  is burdened with a high inductance. 
     Data storage products are now built with smaller geometrical sizes and with higher storage capacities. To interact with these storage products having narrow track widths and high areal densities, a magnetic head needs to have low head inductance, thereby providing sufficient agility and responsiveness to the head during normal operation. Also, the head must provide a high SNR such that valid signals are not overshadowed by background noise. Furthermore, the head must be small in physical geometry and thus be compatible with miniaturized air bearing sliders which are designed to accommodate the rapid movements of the actuator arms of the disk drives. All of these features impose stringent requirements in the design and manufacturing of a magnetic head. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a magnetic head with a magnetic path which is efficient in flux flow enabling the head to perform with agility and sensitivity. 
     It is another object of the invention to provide a magnetic head with low inductance allowing the head to operate with high frequency signals. 
     It is yet another object of the invention to provide a magnetic head characterized by a high signal-to-noise ratio. 
     It is still another object of the invention to provide a magnetic head that is easy to fabricate and with low manufacturing cost. 
     In an embodiment of the invention, a magnetic head includes first and second magnetic yoke layers having a toroidal coil encompassing one of the yoke layers. The yoke layers contact each other at a back closure region at one end, and define a transducing gap at the other end. The axis of the toroidal coil is positioned to pass within the encompassed yoke layer. During the data writing mode, electrical current passing through the toroidal coil induces magnetic flux along the coil axis, which flux is efficiently delivered to the transducing gap for writing data. During the data reading mode, magnetic flux intercepted by the transducing gap flows along the encompassed yoke layer and efficiently induces electrical current in the toroidal coil for amplification. 
     In alternative embodiments, the magnetic heads are built as merged heads that include read sensors, such as anisotropic magnetoresistive (AMR) transducers or giant magnetoresistive (GMR) transducers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art magnetic head; 
     FIG. 2 is a perspective view of another prior art magnetic head; 
     FIG. 3 is a perspective view, partially broken away, illustrating an exemplary use of the magnetic head of the invention; 
     FIG. 4 is a perspective view of an embodiment of the magnetic head of the invention; 
     FIG. 5 is a top plan view taken along the line  5 — 5  of FIG. 4; 
     FIG. 6 is a front elevational view taken along the line  6 — 6  of FIG. 4; 
     FIG. 7 is cross-sectional side view taken along the line  7 — 7  of FIG. 4; 
     FIG. 8 is a cross-sectional side view of a variation of the magnetic head shown in FIGS. 4-7 implemented with laminated yoke layers; 
     FIG. 9 is a cross-sectional side view of a second embodiment of the invention, fabricated as a merged head with the read transducer disposed below the write transducer; and 
     FIG. 10 is a cross-sectional side view of a third embodiment of the invention, fabricated as a merged head with the read transducer disposed above the write transducer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 3, a magnetic transducer  50  is supported by an air bearing slider  52 , which is mounted on a flexure  56 , which in turn is attached to a load beam  54 . The slider  52 , the flexure  56 , and the load beam  54  are collectively called a head gimbal assembly (HGA)  58  that is joined to an actuator arm  60 A of an arm assembly  62  rotatable about an arm axis  64 . A stack of spaced apart rotary magnetic disks  66  is mounted to a common spindle  68 . The actuator arm assembly  62  includes a plurality of actuator arm branches  60 A- 60 C which extend into the spacings between the disks  66 A and  66 B. 
     During normal operation, the disks  66 A and  66 B spin at high speed in the direction  70  about the spindle  68 . The aerodynamics of the moving air between the slider  52  and the disk surface  72  suspends the slider  52  above the disk surface  72  of the disk  66 A, for example. On the other hand, the spring forces of the load beam  54  and the resilient flexure  56  urge the slider toward the disk surface  72 . An equilibrium point is reached where the slider  16  flies over the disk surface  72  at a substantially constant flying height. 
     FIGS. 4-7 show one embodiment of a magnetic head  74  which may be an inductive head. For the sake of clarity, the protective and insulating layers are removed in FIGS. 4-6 exposing the relevant components of the magnetic head  74 . The protective and insulating layers are shown in FIG.  7 . 
     The magnetic head  74  is formed on a substrate  76  preferably made of a material that is nonmagnetic and nonconducting, such as ceramic, for example. Above the substrate  76  is a first yoke layer  84 . An inductive coil  78  is disposed above the first yoke layer  84 . The coil  78  is toroidal in shape and encompasses the second yoke layer  86 . The toroidal coil  78  has a coil axis  104  which passes through the second yoke layer  86 . A portion of the coil  78  is sandwiched between the first yoke layer  84  and a second yoke layer  86 . 
     The first and second yoke layers  84  and  86  of the magnetic head  74  form a closed magnetic path  100  through a back closure region  88  and a tip region  90 . The back closure region  88  includes a feedthrough  83  joining the first yoke layer  84  and the second yoke layer  86 . The tip region  90  comprises first and second pole tip layers  92  and  94  separated by gap layer  96 . The head  74  comprises vertically aligned sidewalls for the first and second pole tips  92  and  94  as shown in FIG.  6 . Specifically, the left sidewall  92 L of the first pole tip  92  is in vertical alignment with the left sidewall  94 L of the second pole tip  94 . Similarly, the right sidewall  92 R of the first pole tip  92  is flush with the right sidewall  94 R of the second pole tip  94 . The aligned sidewalls  92 L,  94 L, and  92 R,  94 R substantially reduce fringing flux from one pole tip to another, thereby enabling the magnetic head  74  to write data with well-defined data tracks on the medium surface  72  (FIG.  5 ). 
     As illustrated in FIG.4, the second yoke layer  86  has a “nose” section  87  that is formed between the air bearing surface of the magnetic head and the rectangular second yoke layer. The length of the nose section  87  from the air bearing surface to its inflection point is greater than the throat height which is defined as the length of the pole tips  92  and  94 . The inflection point is that point at which the second yoke layer diverges from the nose section  87 . The nose section  87  is disposed above the pole tip layer  94 . The length of the nose section  87  is measured from the air bearing surface, which is defined by the ends of the pole tips  92 ,  94  and the transducing gap  96  therebetween, to the inflection point  89  where the nose section meets the diverging portion of the second yoke layer  86 . A distinct advantage of having a longer nose section is that the gap field is effectively reduced, thereby significantly improving high density data recording. 
     During data writing, current passing through the coil  78  induces magnetic flux in the yoke layers  84  and  86 . The induced magnetic flux passes through the closed magnetic path  100 , reaching the gap layer  96  and magnetizes the recording medium  72  (FIG.  5 ). 
     During data reading, magnetic flux emanating from the recording medium  72  (FIG. 5) is intercepted by the insulating gap  96 . The intercepted magnetic flux flows along the continuous magnetic path  100  defined by the two yoke layers  84  and  86  and induces electrical current in the inductive coil  78 . The induced current in the coil corresponds to the data content stored on the recording medium  72 . 
     The coil  78  is dielectrically insulated from the first and second yoke layers  84  and  86  through intervening dielectric layers  98  (FIG.  7 ). An insulating overcoat layer  102  deposited on the second yoke layer  86  physically protects the magnetic head  74 . In this embodiment, the material selected for the dielectric and insulating layers  98  and  102  is alumina (Al 2 O 3 ). Alternatively, other insulating materials such as silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum nitride (AlN 4 ) or diamond-like-carbon (DLC) can also be used. The material for the first and second yoke layers  84  and  86 , and the first and second pole tip layers  92  and  94 , is preferably made of a material having a high magnetic moment. Exemplary materials are cobalt zirconium tantalum alloy (CoZrTa), cobalt zirconium niobium alloy (CoZrNb), iron nickel alloy (NiFe), and iron tantalum niobium alloy (FeTaNb). The choice of high magnetic moment material for the layers  84 ,  86 ,  92  and  94  is to prevent premature magnetic saturation of the magnetic head  74  during data writing. Writing on media with high coercivity necessitates the use of higher writing current. However, higher writing current generates higher magnetic flux which in turn can drive the yoke layers  84  and  86  and the pole tip layers  92  and  94  into a deeper state of magnetization. At still higher driving current through the coil  78 , a point may be reached in which the yoke layers  84  and  86  and the tip layers  92  and  94  can no longer be responsive to the corresponding increase in driving flux. The layers are then said to be in magnetic saturation. Premature magnetic saturation in these layers would render the head  74  incapable of accepting high writing current necessary to write media with high coercivity. Using high magnetic moment material for the layers  84 ,  86 ,  92  and  94  prevents these layers from running into premature saturation when the head  74  is operating at a high current mode. 
     It should be noted that the second yoke layer  86  of the invention has a substantially level cross-sectional profile as can be shown in FIGS. 4-7. Making the second yoke layer  86  topographically flat provides various advantages. 
     To begin with, the problem of step coverage commonly encountered in thin film product processing is less of a concern. In microelectronic thin film product fabrication, the overlying layers are very often more difficult to be deposited than the underlying layers and thus less reliable. The reason is that the overlying layers normally encounter more topological unevenness during deposition, and thus are confronted with more step coverage problems than the underlying layers. Providing a flat second yoke layer  86  in accordance with this invention is especially advantageous in the formation of a merged head where the read transducer is formed over the flat second yoke layer  86 . 
     It is a feature of this invention that the flat second yoke layer  86  reduces the length and curvature of the magnetic path  100 . The consequential benefit of a short and more direct magnetic path  100  is multi-fold. First, the reluctance R of the magnetic path  100  is reduced. The reluctance R is defined by the following mathematical formula:              R   =     E   φ             (   1   )                                
     where E is the electromotive force driving the coil  78 , measured in A-turns; and p is the magnetic flux induced in the magnetic path  100  in Webers. The definition of the reluctance R is somewhat analogous to that of the resistance in Ohm&#39;s law and is determined by the following algebraic equation:              R   =     ν                   l   A               (   2   )                                
     where l is the length of the magnetic path  100  in μ; A is the cross-sectional area of the path  100  in μ 2 ; and v is the reluctancy of the material which defines the magnetic path  100 . Here, the flat second yoke layer  86  virtually has no profile curvature. Thus, the magnetic path  100  can be implemented with a short path length l, which in turn lowers the overall reluctance R of the magnetic path  100 . Second, the flat second yoke layer  86  and the shortened path length l impose less mutual inductance upon the coil  78 . The coil  78  operates with less inductance and is a more agile coil. Furthermore, the second yoke layer  87  with its flat topology is less prone to trigger magnetic domain instability in the layer  86 , and consequently allows the head  74  to operate with less susceptibility to Barkhausen noise. Also, the shorter path length l can be driven by the coil  78  with less number of turns, which in turn reduces the overall resistance of the current path through the coil  78 . Lower resistance of the current path through the coil  78  cuts down Johnson noise of the head  74  and thus improves the signal-to-noise ratio. 
     The inventive arrangement of encompassing the flat second yoke layer  86  with the toroidal coil  78  is especially advantageous for high data rate transfer applications. By virtue of coinciding the coil axis  104  with the second yoke layer  86 , induced magnetic flux need not traverse through a long, inductive magnetic path. Instead, the generated flux is efficiently delivered to the pole tip layers  92  and  94  for use during data writing. Likewise, during data reading, the same advantages are available. The combined effect is that the head  74  can be fabricated with a less number of coil turns and yet with no compromise in performance. 
     It also needs to be pointed out that magnetic heads are now fabricated on microscopically confined areas with limited heat dissipation capacity. In most prior heads, in order to effectively drive the yoke layers with high reluctance and inductance on the one hand, and to ease the heat dissipation problem by avoiding injecting excessive current into the coil on the other hand, the number of windings of the coils are accordingly increased by stacking the coil windings to more than one level. However, an increase in coil winding levels requires additional profile curvature for the yoke layers harnessing the coils, resulting in a further increase in both the self inductance of the coils and the mutual inductance of the yoke layers. Balancing the need for performance and and the need for reliability, a compromise point needs to be struck. Accordingly, most prior art heads are not optimally designed. The aforementioned problems are less of a concern in the magnetic heads disclosed herein, because the inventive heads need no excessive coil windings. 
     FIG. 8 shows a variation of the magnetic head  74  implemented with laminated first and second yoke layers  84  and  86 . Each yoke layer  84  or  86  is laminated by means of an insulating layer. For example, in the first yoke layer  84 , an insulating layer  108  is sandwiched between two sublayers  84 A and  84 B. Likewise, in the second yoke layer  86 , another insulating layer  106  is interposed between two sublayers  86 A and  86 B. Laminating the yoke layers  84  and  86  prevents the formation of eddy current during high frequency operations. An exemplary eddy current path is shown as path  110  in FIG.  8 . Eddy current can flow along the path  110  if the insulating layer  106  is absent. Eddy current arises mainly in response to oppose any magnetic flux changes in accordance with Lenz&#39;s law. Formation of eddy current is undesirable because it deleteriously affects the intercepted flux during data reading and the driving flux during data writing, and thereafter converts and dissipates the flux as wasteful heat. The eddy current effect, especially occurring in high frequency applications, can be prevented by laminating the yoke layers  84  and  86  as shown in FIG.  8 . 
     FIG. 9 illustrates a second embodiment of the invention, wherein a magnetic head  112  includes a read transducer  114 , which is a magnetoresistive transducer that can be an anisotropic magnetoresistive (AMR) transducer, a giant magnetoresistive (GMR) transducer, or a spin valve sensor. The magnetoresistive transducer  114  is sandwiched between and dielectrically separated from a pair of magnetic shields  116  and  84 . In this embodiment, the layer  84  performs the dual function acting as a first yoke layer for the coil  78  and as a shield layer for the read transducer  114 . 
     FIG. 10 shows a third embodiment of a magnetic head  118 , made in accordance with the invention. In this embodiment, the read transducer  114  is disposed above the write transducer and the substrate  76 . Again, the read transducer  114  can be an anisotropic magnetoresistive (AMR) transducer, a giant magnetoresistive (GMR) transducer, or a spin valve sensor. As with the second embodiment, the magnetoresistive transducer  114  is sandwiched between and dielectrically separated from a pair of magnetic shields  86  and  120 . In this embodiment, the layer  86  performs the dual role as a second yoke layer for the coil  78  and as a shield layer for the read transducer  114 . Conventionally, the read transducer  114  is fabricated prior to the write transducer. The rationale behind this arrangement is that the formation of the magnetoresistive transducer involves laying a number of delicate and ultra-thin layers which need level supporting layers. Depositing the delicate layers associated with the read transducer close to the substrate poses less of a step coverage problem. However, the disadvantage with this approach is that forming the inductive head including the coil with the associated layers subsequently involves several high heat annealing cycles, which may be detrimental to the already built read transducer with the delicate layers. The magnetic head  118  of the third embodiment eases this problem because the flat topographical feature of the second yoke layer  86  substantially alleviates the problem of step coverage. 
     Other variations are possible within the scope of the invention. Materials used for the magnetic heads of the invention need not be restricted to those described. For example, in addition to the insulating materials recited, hard-baked photoresist can be used as a substitute.