Abstract:
A magnetoresistance effect magnetic head includes a magnetoresistance effect element having a first end and a second end. A biasing portion is provided at the first end and the second end of the magnetoresistance effect element for applying a longitudinal bias magnetic field to the magnetoresistance effect element at the first end or the second end. The biasing portion includes an intermediate layer disposed between an antiferromagnetic first layer and a second layer.

Description:
The present invention relates generally to a magnetoresistance effect magnetic head that uses a magnetoresistance effect element. More particularly, the invention relates to biasing layers of a magnetoresistance effect magnetic head disposed at ends of the magnetoresistance effect element for improving reproduction of the signal magnetic field from a magnetic recording medium. 
     BACKGROUND 
     Referring now to FIG. 1, a magnetoresistance effect magnetic head  100  (hereinafter called the magnetic head), for example, is well known. FIG. 1 shows a cross-section of the overall structure of the magnetic head  100  as it faces the magnetic recording medium (not shown). A magnetoresistance effect element  101  for sensing the signal magnetic field from the magnetic recording medium, such as a hard disk, is shown in the center portion of the magnetic head  100  in FIG. 1. A well-known magnetoresistance effect (MR) element  101  is a spin valve magnetoresistance effect (SVMR) element. This spin valve magnetoresistance effect element  101  is typically formed from multiple deposited thin-film layers including a first magnetic layer, a nonmagnetic layer, a second magnetic layer, and an antiferromagnetic layer (not shown). 
     The magnetoresistance effect element  101  also has ends  101 A,  101 B connected to electrically conductive lead terminals  102 A,  102 B. Hard films  103 A,  103 B are placed under the lead terminals  102 A,  102 B and in contact with the magnetoresistance effect element  101 . The magnetoresistance effect element  101 , the lead terminals  102 A,  102 B, and the hard films  103 A,  103 B are electrically insulated on both the upper and lower sides by an insulating upper gap material  104  and a lower gap material  105 . A top  104 A of the upper gap material  104  and a bottom  105 A of the lower gap material  105  are shielded by soft magnetic shields  106 ,  107 , respectively. 
     Recently, there has been considerable demand for higher density recording in magnetic recording/reproducing equipment. To detect information (signal magnetic field) magnetically recorded at high densities by using the magnetic head  100 , which is very sensitive, the width of the gap W 1  between the shields  106 ,  107  was narrowed and the film thickness of the entire magnetic head  100  was thinned. However, the gap materials  104 ,  105  must maintain a specific film thickness to maintain its insulating characteristics, and forming thinner gap materials  104 ,  105  is difficult and costly. 
     Thus, referring now to FIG. 2, a known magnetic head  200  further narrows a gap width W 2  without narrowing the gap material as disclosed in unexamined Patent Publication (Kokai) No. 9-28807. In the magnetic head  200 , a magnetoresistance effect element  201  is electrically connected to an upper shield  206  and a lower shield  207 , which also function as the lead terminals. This configuration eliminates the need for a gap material  204  between the shield  206  and insulating film  202 A, and between shield  206  and insulating film  202 B, and eliminates the need for gap material  205  between shield  207  and hard film  209 A, and between shield  207  and hard film  209 B to further narrow the gap width W 2 . This, in turn, enables a narrower gap to be fabricated. 
     The upper and the lower gap materials  204 ,  205  placed above and below the magnetoresistance effect element  201  are formed from electrically conductive materials. The insulating films  202 A,  202 B are provided on ends  201 A,  201 B of the magnetoresistance effect element  201 . 
     Referring again to FIGS. 1-2, the flow direction of the sense current for magnetic head  100  is different from the flow direction of the sense current for magnetic head  200 . In the magnetic head  100 , the sense current flows from the lead terminal  102 A through the magnetoresistance effect element  101  to the lead terminal  102 B (or in the reverse direction) in a direction parallel to a generally planar surface  108  of element  101  (only shown in cross section) hereinafter “planar direction”. In the magnetic head  200 , the sense current flows from the upper shield  206  through the magnetoresistance effect element  201  to the lower shield  207  (or in the reverse direction) in a direction perpendicular to a surface  208  of the element  201 , hereinafter “perpendicular direction”. The magnetic head  100 , in which the sense current flows in the planar direction, is called a CIP (Current In Plane) magnetic head. The magnetic head  200 , in which the sense current flows in the perpendicular direction, is called a CPP (Current Perpendicular) magnetic head. 
     Since the sense current in the CIP magnetic head  100  described above flows in the planar direction, this head cannot use an MR element, for example, that requires the sense current to flow in the perpendicular direction as in a tunnel magnetoresistance effect (TMR) element. In contrast, magnetic heads using CPP are expected to become popular because of the ability of the magnetic head  200  described above to use the TMR element and to narrow the gap W 2  as described above. However, the magnetic head  200  leaks current at both ends  201 A,  201 B of the magnetoresistance effect element  201 , and therefore has difficulty in producing an efficient flow in the perpendicular direction. 
     To control the magnetic domain of the magnetoresistance effect element  201 , hard films  209 A,  209 B are formed on both ends  201 A,  201 B of the magnetoresistance effect element  201  for applying a longitudinal bias magnetic field (not shown). In this case, however, if the hard films  209 A,  209 B are electrically conductive materials, electrical shorts develop with the upper gap layer  204 , which in turn lowers the yield. 
     To prevent shorts and current leakage, the conventional material forming the hard films  209 A,  209 B is a magnetic material that is insulating and has a coercive force (Hc) above a specific value, for example, 500 Oe (oersteds). However, this kind of magnetic material is difficult to accurately form on ends  201 A,  201 B of the magnetoresistance effect element  201 . If a hard film does not have the required coercive force, the longitudinal bias magnetic field becomes unstable, and the signal magnetic field from the magnetic recording medium cannot be accurately reproduced. 
     Thus, a main object of the present invention is to provide an improved magnetoresistance effect magnetic head that does not have substantial leakage of current at the ends of the magnetoresistance effect element. 
     Another object of the present invention is to provide an improved magnetoresistance capable of applying a sufficiently stable longitudinal bias magnetic field to the magnetoresistance effect element. 
     Yet another of the present invention is to provide an improved magnetic recording/reproducing apparatus with the improved head. 
     These and other objects of the present invention are discussed or will be apparent from the detailed description of the invention. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, leakage currents in the ends of the magnetoresistance effect element can be suppressed by an insulating antiferromagnetic layer placed next to the ends of the element. When the magnetic layers are placed in contact with the antiferromagnetic layers, unidirectional anisotropic magnetic field is generated by the exchange coupling. The magnetic layers apply a stable longitudinal bias magnetic field to the magnetoresistance effect element. Thus, the bias application layer can apply the needed longitudinal bias magnetic field to the magnetoresistance effect element while maintaining an insulating property. 
     More specifically, a magnetoresistance effect magnetic head has a magnetoresistance effect element and a biasing portion for applying a longitudinal bias magnetic field to the magnetoresistance effect element on at least one end of the magnetoresistance effect element. The biasing portion includes an insulating antiferromagnetic layer and a magnetic layer in exchange coupling with the antiferromagnetic layer. 
     In another aspect of the present invention, a single antiferromagnetic layer can be provided above and below the magnetic layer to form a sandwich structure. Because the magnetic layer is sandwiched from the above and below by the insulating antiferromagnetic layers, a unidirectional anisotropic magnetic field stronger than the magnetic layer can be provided while also providing better insulation. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of the structure of a conventional magnetoresistance effect magnetic head as it faces a recording surface of a magnetic recording medium; 
     FIG. 2 is a cross-sectional view of the structure of another conventional magnetoresistance effect magnetic head; 
     FIG. 3 is a cross-sectional view of the overall structure of a magnetic head in accordance with one aspect of the present invention; 
     FIG. 4A is a cross-sectional view of layers used to form the magnetic head of FIG. 3 during a film fabrication process; 
     FIG. 4B is another cross-sectional view of the layers of the head of FIG. 3 during another portion of the film fabrication process for constructing the magnetic head of FIG. 3; 
     FIG. 4C is yet another cross-sectional view of the layers of the head of FIG. 3 during yet another part of the film fabrication process; 
     FIG. 5 is a cross-sectional view of the overall structure of another magnetic head of the present invention as it faces a magnetic recording medium; and 
     FIG. 6 is a plan view of an uncovered magnetic recording/reproducing apparatus that uses the magnetic head of either FIG. 3 or FIG. 5 of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 3, a CPP magnetic head  10  has an MR element  15 . The width of the MR element extends in the same general direction as the tracks of a magnetic recording medium (not shown) placed under the head  10 . A generally extending plane of the MR element  15  is defined by a surface  15 . 
     In FIG. 3, the magnetic head  10  has an upper shield  11  and a lower shield  12 . These two magnetic shields  11 ,  12  are fabricated from a soft magnetic material, such as FeZrN, with a film thicknesses around 1 to 2 mm. These shields  11 ,  12  are electrically conductive and also function as lead terminals. 
     A gap  9  is formed between the shields  11 ,  12 . The MR element  15  is located in the gap  9 , and it is electrically connected to the upper shield  11  and the lower shield  12  through electrically conductive upper gap material  13  and lower gap material  14 , respectively. Thus, the sense current (not shown) flows from the upper shield  11  (or the lower shield  12 ) through the upper gap material  13  (or lower gap material  14 ) into the MR element  15 , and then flows perpendicular to plane or surface  15 A through the lower gap material  14  (or upper gap material  13 ) to the lower shield  12  (or upper shield  11 ). 
     The MR element  15  described above can be a TMR element or an SVMR element. The TMR element can be a laminated film composed of Al 2 O 3  as the insulating layer on the bottom, followed by the deposited layers of PdPtMn (20)/Co (2)/Al2O3 (5)/Co (1)/NiFe (2) (The numbers enclosed by parentheses indicate the thickness of each layer in nanometers (nm).). A laminated film composed of Cu can be used as the nonmagnetic layer on the bottom of the SVMR element, followed by the deposited layers of NiFe (2)/CoFeB (4)/Cu (3)/CoFeB (2.2)/PdPtMn (25). The TMR element and SVMR element can also be laminated films with the layers deposited in the reverse order than previously described. 
     Electrically conductive copper, gold, silver, platinum, or an alloy composed of these elements can be used for the upper gap material  13 . Preferably, the upper gap material  13  is formed from copper with a film thickness about 20 nm. This also applies to the lower gap material  14 . A 20 nm thick copper film can be used for the lower gap material. To form the preferred film formation, however, about 5 nm of tantalum (Ta) film  16  is formed as an underlayer of the lower gap material  14 . Each layer described above can be formed as sequentially deposited layers using conventional thin film fabrication techniques. 
     Referring again to FIG. 3, bias portions or bias application layers  21 A,  21 B are provided on ends  15 B,  15 C of the MR element  15 . In FIG. 3, the insulating antiferromagnetic layers  17 A,  17 B are respectively, and preferably, placed above the magnetic layers  18 A,  18 B. Insulating layers  19 A,  19 B are placed below the magnetic layers  18 A,  18 B. The biasing portions  21 A,  21 B are provided with left-right symmetry on both ends of the MR element  15 . The antiferromagnetic layers  17 A,  17 B are preferably a single 30-nm thick layer of NiO, and can also be iron oxide (α-Fe 2 O 3 ) if it is a single layer. 
     In the alternative, the antiferromagnetic layer  17 A or  17 B can be a laminated body with multiple layers with, for example, insulating cobalt oxide-nickel oxide (CoO—NiO) or iron oxide-nickel oxide (α-Fe 2 O 3 —NiO). In this case, the cobalt oxide or the iron oxide should be placed in contact with the magnetic layer  18 A or  18 B. 
     The magnetic layers  18 A,  18 B are preferably 20nm thick and can be either insulating or electrically conductive, depending on the goal of the design. Since layers  17 A,  17 B already insulate, magnetic layers  18 A,  18 B can be electrically conductive permalloys such as (NiFe), cobalt or cobalt ferrite (CoFe). 
     If on the other hand, more insulation to suppress current leaks is desired, the magnetic layers  18 A,  18 B can be soft or hard magnetic material. The hard magnetic materials can be cobalt ferrite (CoFe 2 O 4 ), barium ferrite (BaO.6Fe 2 O 3 ) cobalt-platinum-silicon oxide (CoPt—SiO 2 ), or ferrite metals (MO.Fe 2 O 3 , MO indicates a metal oxide where M is any metal, for example, Cu or Mg). The soft magnetic materials mentioned above can be manganese-zinc-ferrite (MnZnFe 2 O 4 ) or nickel-zinc-ferrite (NiZnFe 2 O 4 ). 
     The magnetic layers  18 A,  18 B are preferably placed in contact with the antiferromagnetic layers  17 A,  17 B and with both ends  15 B,  15 C of the MR element  15 . By shifting a B-H loop by exchange coupling with antiferromagnetic layers  17 A,  17 B, the magnetic layers  18 A,  18 B have their directions of magnetization fixed. As a result, because unidirectional anisotropic magnetic fields are generated in the magnetic layers  18 A,  18 B, a stable longitudinal bias magnetic field can be applied from the magnetic layers  18 A,  18 B to the MR element  15 . 
     The insulating layers  19 A,  19 B can be formed from material such as alumina (Al 2 O 3 ) to a 30-nm thicknesses. The insulating layers  19 A,  19 B can also be an insulating antiferromagnetic material, for example, 30-nm thick NiO. The bias application layers  21 A,  21 B form a sandwich including a magnetic layer between two antiferromagnetic layers (NiO/nickel-zinc-ferrite/NiO) so that the magnetic layer  18 A,  18 B is exchange coupled to both antiferromagnetic layers  17 A and  19 A or  17 B and  19 B, respectively, on both ends  15 B,  15 C of the MR element  15 . With this structure, the biasing portions become powerful insulators, and the longitudinal bias magnetic field from the magnetic layers  18 A,  18 B is very stable. 
     Referring now to FIG. 4A, the film fabrication process in the method for manufacturing the magnetic head  10  includes forming a FeZrN layer about 2-μm thick as the lower shield  12  by sputtering on an alumina-tantalum carbide substrate (Al 2 O 3 —TiC). On top of this, a tantalum film about 5-nm thick is formed as the lower gap substrate  16 , and a copper film about 20-nm thick is formed as the lower gap material  14 . 
     Materials for the head  10  are successively deposited by sputtering one layer on top of another layer starting with the lower gap material  14  on the bottom. Each layer of the SVMR element and the TMR element is formed as described above. Then a copper layer about 20-nm thick is formed on the MR element  15  as the upper gap material  13 . The film fabricating process described above can be implemented as a continuous or a discontinuous process. 
     Referring now to FIG. 4B, about 1 μm wide by about 3 μm high resist  5  is patterned on the upper gap material  13  and then etched by ion milling until the copper of the lower gap material  14  or the tantalum of the lower gap substrate  16  is detected. 
     Referring now to FIG. 4C, after ion milling, the longitudinal bias application layers  17 A to  19 B are formed on both ends of the MR element  15 . The films are successively formed from the bottom up by sputtering. Alumina (Al 2 O 3 ) or NiO is used for the insulating layers  19 A,  19 B; nickel-zinc-ferrite is used for the magnetic layers  18 A,  18 B; and NiO is used for the antiferromagnetic layers  17 A,  17 B. The thicknesses of the layers are about 30 nm, 20 nm, and 30 nm, respectively. Then the resist  5  is lifted off. Finally, the FeZrN film is formed as the upper shield  11  (shown in FIG. 3) on the MR element  15  to complete the magnetic head  10  of FIG.  3 . 
     Referring now to FIG. 5, another aspect of the present invention includes a magnetic head  20 . The same reference numbers used for parts in FIG. 3 are assigned to the same parts for FIG.  5 . Longitudinal bias application layers or biasing portions  22 A,  22 B of the magnetic head  20  each has two layers, an insulating antiferromagnetic layer  27 A or  27 B and an electrically conductive magnetic layer  28 A or  28 B in contact with the antiferromagnetic layer  27 A or  27 B respectively. The antiferromagnetic layers  27 A,  27 B can be insulating NiO. The magnetic layers  28 A,  28 B can be a magnetic material such as electrically conductive NiFe or CoFe. 
     In the magnetic head  20 , the MR element  25  has extensions  23 A,  23 B on both ends  25 A,  25 B of MR element  25  that are part of the biasing portions  22 A,  22 B. On the biasing portions  22 A,  22 B, magnetic layers  28 A,  28 B are disposed between insulating antiferromagnetic layers  27 A,  27 B and the extensions  23 A,  23 B, respectively. Thus, at least a portion of the same layer used to form the MR element  25  is present at the lead terminal sides or biasing portions  22 A,  22 B in the laminated structure, but only the region  26  of the MR element  25  interposed between the biasing portions  22 A,  22 B functions as the actual MR element  25 . 
     The magnetic head  20  can be manufactured in the same manner as shown in FIGS. 4A-4C to manufacture the magnetic head  10 . However, the magnetic head  20  reduces the amount of etching of the MR element  25  required and eliminates the need to etch the lower gap material  14 , since the magnetic head  20  preferably only requires etching through a portion of the MR element  25  (as best seen in FIG.  5 ). 
     Specifically, MR element  25  can be an SVMR element with films successively deposited in layers from bottom to top of NiFe (2 nm)/CoFeB (1 nm)/Cu (3 nm)/CoFeB (2 nm)/PdPtMn (20 nm)/NiFe (2 nm), or a TMR element with films successively deposited in layers from bottom to top as NiFe (2 nm)/PdPtMn (20 nm)/Co ( 2  nm)/Al 2 O 3  (5 nm)/Co (1 nm)/NiFe (2 nm). For the longitudinal bias application layers or biasing portions  22 A,  22 B in magnetic head  20 , the SVMR element is preferred for suppressing the effect of leakage current. 
     Both ends  25 A,  25 B are etched by ion milling until the top layer of NiFe of the MR element  25  is detected. Then the remainder of the biasing portions are formed from a NiFe magnetic layer  28  about 10 nm thick and an insulating NiO antiferromagnetic layer  27  about 40 nm thick. 
     Referring now to FIG. 6, a magnetic recording/reproducing apparatus  50  equipped with a composite magnetic head  30  has a magnetic recording medium such as a hard disk  51  rotatably mounted in the magnetic recording/reproducing apparatus  50 . At a specific flying height above the surface of the hard disk  51 , magnetic reproduction is performed by a composite magnetic head  30 , which has the MR element  15  on the reproduction part of the head. The composite magnetic head  30  is fixed to the front end of a slider  71  at the front end of an arm  70 . Positioning the composite magnetic head  30  can be accomplished by a two-stage actuator that combines an ordinary actuator and an electromagnetic fine motion actuator. 
     From the description above, it will be appreciated that the free magnetic layers (not shown) in the MR elements  15  or  25  have magnetic domains controlled in preferred states by the longitudinal bias magnetic fields originating from the biasing portions  21 A,  21 B or  22 A,  22 B, and specifically from the magnetic layers  18 A,  18 B or  28 A,  28 B due to coupling with the antiferromagnetic layers  17 A,  17 B or  27 A,  27 B respectively. The magnetoresistance effect can then effectively eliminate or reduce problems like Barkhausen noise. The antiferromagnetic layers  18 A,  18 B or  27 A,  27 B also suppress the generation of leakage current. Consequently, the sense current efficiently flows in the direction perpendicular to the MR elements  15  or  25 , and the magnetic head  10  or  20  can accurately detect the signal magnetic field from the magnetic recording medium. Thus, the biasing portions  21 A,  21 B or  22 A,  22 B replace the known hard films that had strong insulating properties and provided the desired coercive force but were difficult to manufacture. In addition, the yield is improved. 
     It will be appreciated that although magnetic heads  10 ,  20  are designed to reproduce the signal magnetic field from the magnetic recording medium with high sensitivity, either magnetic head  10  or  20  of the present invention can be combined with an inductive thin-film head to form a recording/reproducing head or composite head. 
     Although preferred embodiments of the present invention were described above, the present invention is not limited to these specific embodiments. Various modifications are possible within the scope of the present invention as described in the appended claims.