Abstract:
A read head is provided having having ultrathin read gap layers with improved insulative properties between a magnetoresistive sensor and ferromagnetic shield layers. The read head comprises a magnetoresistive sensor with first and second shield cap layers made of high resistivity permeable magnetic material formed between the first and second ferromagnetic shields and the first and second insulative read gap layers, respectively. The shield cap layers made of Fe—Hf—O x  material, or alternatively, the Mn—Zn ferrite material provide highly resistive or insulating soft ferromagnetic layers which add to the electrically insulative read gap layers to provide increased electrical insulation of the spin valve sensor from the metallic ferromagnetic shields while not adding to the magnetic read gap of the read head. The extra insulation provided by the highly resistive shield cap layers makes it possible to use ultrathin insulative first and second read gap layers without increased risk of electrical shorting between the spin valve sensor and the ferromagnetic first and second shields.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates in general to spin valve magnetoresistive sensors for reading information signals from a magnetic medium and, in particular, to a spin valve sensor with high resistance magnetic layers adjacent to the magnetic shields to improve insulation of the magnetoresistive sensor from the conductive shields.  
           [0003]    2. Description of the Related Art  
           [0004]    Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.  
           [0005]    In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR sensors, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.  
           [0006]    The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.  
           [0007]    Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.  
           [0008]    GMR sensors using only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect.  
           [0009]    [0009]FIG. 1 shows a prior art SV sensor  100  comprising end regions  104  and  106  separated by a central region  102 . A first ferromagnetic layer, referred to as a pinned layer  120 , has its magnetization typically fixed (pinned) by exchange coupling with an antiferromagnetic (AFM) layer  125 . The magnetization of a second ferromagnetic layer, referred to as a free layer  110 , is not fixed and is free to rotate in response to the magnetic field from the recorded magnetic medium (the signal field). The free layer  110  is separated from the pinned layer  120  by a non-magnetic, electrically conducting spacer layer  115 . Hard bias layers  130  and  135  formed in the end regions  104  and  106 , respectively, provide longitudinal bias for the free layer  110 . Leads  140  and  145  formed on hard bias layers  130  and  135 , respectively, provide electrical connections for sensing the resistance of SV sensor  100 . IBM&#39;s U.S. Pat. No. 5,206,590 granted to Dieny et al., incorporated herein by reference, discloses a GMR sensor operating on the basis of the SV effect.  
           [0010]    [0010]FIG. 2 shows a prior art read back head  200  incorporating an SV sensor. Referring to FIG. 2, the spin valve sensor  100  is sandwiched between nonmagnetic insulative first and second read gap layers  202  and  204 , and the read gap layers are sandwiched between ferromagnetic first and second shield layers  206  and  208 . The separation between the first and second shield layers  206  and  208  defines the read gap  210 . The ferromagnetic first and second shield layers  206  and  208  are needed to shield the sensor  100  from stray magnetic fields. The nonmagnetic insulative first and second read gap layers  202  and  204  provide electrical insulation of the sensor  100  from the metallic ferromagnetic shield layers  206  and  208 .  
           [0011]    A problem with the prior art sensors arises as the size of the read head is decreased in order to address the need for higher storage density disk files. As the read gap is made ultrathin, the insulative properties of the first and second read gap layers is reduced leading to possible shorting of the magnetoresistive sensor to the metallic shields. Therefore there is a need for improved insulation of the read sensor from the shields for read heads having ultrathin magnetic read gaps in order to read magnetic data at higher storage densities.  
         SUMMARY OF THE INVENTION  
         [0012]    Accordingly, it is an object of the present invention to disclose a magnetic read head having ultrathin read gap layers with improved insulative properties between a magnetoresistive sensor and ferromagnetic shield layers.  
           [0013]    It is another object of the present invention to disclose a magnetic read head having improved electrical insulation of the magnetoresistive sensor from the shields without increasing the magnetic read gap.  
           [0014]    It is a further object of the present invention to disclose a magnetic read head having reduced smearing and telegraph noise by keeping metallic parts of the shields at an increased distance from the magnetoresistive sensor.  
           [0015]    In accordance with the principles of the present invention, there is disclosed a preferred embodiment of the present invention wherein first and second shield cap layers made of high resistivity permeable magnetic material are formed between the first and second ferromagnetic shields and the first and second insulative read gap layers, respectively, of a magnetoresistive read head. In the preferred embodiment, the read head comprises a first shield cap layer of iron hafnium oxide (Fe—Hf—O x ), or alternatively, manganese zirconium ferrite (Mn—Zn ferrite) disposed between the first ferromagnetic shield and the first insulative read gap layer, a spin valve sensor sandwiched between the read gap layer and a second insulative read gap layer, and a second shield cap layer of Fe—Hf—O x , or alternatively, Mn—Zn ferrite disposed between the second read gap layer and a second ferromagnetic shield.  
           [0016]    The Fe—Hf—O x  material, or alternatively, the Mn—Zn ferrite material provide highly resistive or insulating soft ferromagnetic layers which add to the electrically insulative read gap layers to provide increased electrical insulation of the spin valve sensor from the metallic ferromagnetic shields while not adding to the magnetic read gap of the read head. The extra insulation provided by the highly resistive shield cap layers makes it possible to use ultrathin insulative first and second gap layers without increased risk of electrical shorting between the spin valve sensor and the ferromagnetic first and second shields.  
           [0017]    The above, as well as additional objects, features and advantages of the present invention will become apparent in the following detailed written description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    For a fuller understanding of the nature and advantages of the present invention, as well as of the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.  
         [0019]    [0019]FIG. 1 is an air bearing surface view, not to scale, of a prior art SV sensor;  
         [0020]    [0020]FIG. 2 is a vertical cross-section view, not to scale, of a read head portion of a read/write magnetic head using a prior art spin valve sensor;  
         [0021]    [0021]FIG. 3 is a simplified drawing of a magnetic recording disk drive system using the improved read head of the present invention;  
         [0022]    [0022]FIG. 4 is a vertical cross-section view, not to scale, of a “piggyback” read/write magnetic head;  
         [0023]    [0023]FIG. 5 is a vertical cross-section view, not to scale, of a “merged” read/write magnetic head;  
         [0024]    [0024]FIG. 6 is an air bearing surface view, not to scale, of the read head portion of a read/write head using the present invention; and  
         [0025]    [0025]FIG. 7 is a vertical cross-section view, not to scale, of the read head portion of a read/write head using the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    The following description is the best embodiment presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein.  
         [0027]    Referring now to FIG. 3, there is shown a disk drive  300  embodying the present invention. As shown in FIG. 3, at least one rotatable magnetic disk  312  is supported on a spindle  314  and rotated by a disk drive motor  318 . The magnetic recording media on each disk is in the form of an annular pattern of concentric data tracks (not shown) on the disk  312 .  
         [0028]    At least one slider  313  is positioned on the disk  312 , each slider  313  supporting one or more magnetic read/write heads  321  where the head  321  incorporates the SV sensor of the present invention. As the disks rotate, the slider  313  is moved radially in and out over the disk surface  322  so that the heads  321  may access different portions of the disk where desired data is recorded. Each slider  313  is attached to an actuator arm  319  by means of a suspension  315 . The suspension  315  provides a slight spring force which biases the slider  313  against the disk surface  322 . Each actuator arm  319  is attached to an actuator  327 . The actuator as shown in FIG. 3 may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by a controller  329 .  
         [0029]    During operation of the disk storage system, the rotation of the disk  312  generates an air bearing between the slider  313  (the surface of the slider  313  which includes the head  321  and faces the surface of the disk  312  is referred to as an air bearing surface (ABS)) and the disk surface  322  which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of the suspension  315  and supports the slider  313  off and slightly above the disk surface by a small, substantially constant spacing during normal operation.  
         [0030]    The various components of the disk storage system are controlled in operation by control signals generated by the control unit  329 , such as access control signals and internal clock signals. Typically, the control unit  329  comprises logic control circuits, storage chips and a microprocessor. The control unit  329  generates control signals to control various system operations such as drive motor control signals on line  323  and head position and seek control signals on line  328 . The control signals on line  328  provide the desired current profiles to optimally move and position the slider  313  to the desired data track on the disk  312 . Read and write signals are communicated to and from the read/write heads  321  by means of the recording channel  325 . Recording channel  325  may be a partial response maximum likelihood (PMRL) channel or a peak detect channel. The design and implementation of both channels are well known in the art and to persons skilled in the art. In the preferred embodiment, recording channel  325  is a PMRL channel.  
         [0031]    The above description of a typical magnetic disk storage system, and the accompanying illustration of FIG. 3 are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuator arms, and each actuator arm may support a number of sliders.  
         [0032]    [0032]FIG. 4 is a side cross-sectional elevation view of a “piggyback” magnetic read/write head  400 , which includes a write head portion  402  and a read head portion  404 , the read head portion employing a SV sensor  406  according to the present invention. The SV sensor  406  is sandwiched between nonmagnetic insulative first and second read gap layers  408  and  410 , and the read gap layers are sandwiched between ferromagnetic first and second shield layers  412  and  414 . In response to external magnetic fields, the resistance of the SV sensor  406  changes. A sense current I S  conducted through the sensor causes these resistance changes to be manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry of the data recording channel  346  shown in FIG. 3.  
         [0033]    The write head portion  402  of the magnetic read/write head  400  includes a coil layer  416  sandwiched between first and second insulation layers  418  and  420 . A third insulation layer  422  may be employed for planarizing the head to eliminate ripples in the second insulation layer  420  caused by the coil layer  416 . The first, second and third insulation layers are referred to in the art as an insulation stack. The coil layer  416  and the first, second and third insulation layers  418 ,  420  and  422  are sandwiched between first and second pole piece layers  424  and  426 . The first and second pole piece layers  424  and  426  are magnetically coupled at a back gap  428  and have first and second pole tips  430  and  432  which are separated by a write gap layer  434  at the ABS  440 . An insulation layer  436  is located between the second shield layer  414  and the first pole piece layer  424 . Since the second shield layer  414  and the first pole piece layer  424  are separate layers this read/write head is known as a “piggyback” head.  
         [0034]    [0034]FIG. 5 is the same as FIG. 4 except the second shield layer  514  and the first pole piece layer  524  are a common layer. This type of read/write head is known as a “merged” head  500 . The insulation layer  436  of the piggyback head in FIG. 4 is omitted in the merged head  500  of FIG. 5.  
         [0035]    [0035]FIG. 6 shows an airbearing surface (ABS) view of a read head  600  incorporating an SV sensor  601  having improved insulation according to a preferred embodiment of the present invention. The read head  600  comprises end regions  604  and  606  separated from each other by a central region  602 . The active magnetoresistive layers of the SV sensor  601  are located in the central region  602 . Longitudinal bias layers  611  and  614  and leads  613  and  615  for the SV sensor  601  are located in the end regions  604  and  606 . The SV sensor  601  in the central region  602  and the bias layers  611  and  614  and leads  613  and  615  in the end regions  604  and  606  are sandwiched between nonmagnetic electrically insulative read gap layers  612  and  616 , and the read gap layers are sandwiched between first and second shield cap layers  610  and  618  which, in turn, are sandwiched between ferromagnetic first and second shields  608  and  620 .  
         [0036]    The SV sensor  601  may be any one of the many SV sensors known to the art for use in high density magnetic recording applications including those known to the art as simple top and bottom SV sensors, anti-parallel (AP) pinned sensors and dual sensors. Alternatively, magnetic tunnel junction (MTJ) sensors may be used in place of the SV sensor  601  in applications where the shield layers are not used as the electrical leads for providing a sense current. In the present embodiment, the SV sensor  601  is preferably an ultrathin SV sensor suitable for use with the very small read gaps needed for high density recording applications.  
         [0037]    The read head  600  may be fabricated in a magnetron sputtering or an ion beam sputtering system to sequentially deposit the multilayer structure shown in FIG. 6. The first shield  608  of Ni—Fe (permalloy) having a thickness in the range of 5000-10000 Å is deposited on a substrate  607 . The first shield cap layer  610  of Fe—Hf—O x  having a thickness in the range 10-1000 Å is deposited over the first shield, and first read gap layer  612  of Al 2 O 3  having a thickness in the range of 5-300 Å is deposited over the first shield cap layer. Alternatively, the first read gap layer may be omitted. The multilayers comprising the SV sensor  601  are sequentially deposited over the first read gap layer  612  and are defined in the central region  602  by depositing a photoresist and using photolithography and ion milling processes well known in the art. The longitudinal bias layers  611  and  614  and the leads  613  and  615  are deposited over the first read gap layer  612  in the end regions  604  and  606 . The second read gap layer  616  of Al 2 O 3  having a thickness in the range 5-300 Å is deposited over the SV sensor  601  in the central region  602  and over the leads  613  and  615  in the end regions  604  and  606 . Alternatively, the second read gap layer may be omitted. The second shield cap layer  618  of Fe—Hf—O x  having a thickness in the range 10-1000 Å is deposited over the second read gap layer  616  and the second shield  620  of Ni—Fe having a thickness in the range 5000-10000 Å is deposited over the second shield cap layer  618 .  
         [0038]    The first and second shield cap layers  610  and  618  are made of soft ferromagnetic material having electrically insulative properties. The Fe—Hf—O x  used to form shield cap layers  610  and  618  is a granular high resistivity material having a permeability μ in the range of 100-1000 and resistivity ρ in the range of 10 4 -10 7  ohm-cm. Alternatively, shield cap layers  610  and  618  may be made of ferromagnetic Mn—Zn ferrite, an insulator having a permeability μ in the range 20-100 and resistivity ρ in the range of 10 7 -10 10  ohm-cm.  
         [0039]    The use of shield cap layers  610  and  618  having soft magnetic properties and high electrical resistivity improves the read head  600  by increasing the electrical insulation of the SV sensor  601  from the metallic shields  608  and  620  without increasing the small magnetic read gap needed for high density recording applications. FIG. 7 shows a vertical cross-section of the read head  600  of the present invention. Because the first and second shield cap layers  610  and  618  are ferromagnetic, first and second magnetic read gaps  704  and  706  are defined by the thin first and second read gap layers  612  and  616 , respectively, while the electrical insulation of the SV sensor  601  from the shields  608  and  620  is determined by adding the resistance of the first and second shield cap layers  610  and  618  to the resistance of the first and second read gap layers  612  and  616 , respectively. The read gap  702  of the read head  600  can be significantly reduced by using very thin first and second read gap layers  612  and  616  while maintaining the required level of electrical isolation of the SV sensor  601  from the shields  608  and  620 . Insulation layer  722  of Al 2 O 3 , sandwiched between first and second read gap layers  612  and  616 , is deposited at a back edge  724  of the SV sensor  601  to provide insulation of the back edge.  
         [0040]    Another advantage of the first and second shield cap layers  610  and  618  of the present invention is reduced smearing of the metallic shields  608  and  620  at the ABS resulting in electrical shorting to the SV sensor  601  due to keeping the shields at a greater distance from the SV sensor. The greater distance of the metallic shields from the SV sensor also results in decreased telegraph noise on the magnetoresistive read signal provided by the SV sensor.  
         [0041]    While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.