Abstract:
A scissor style magnetic sensor having a novel hard bias structure for improved magnetic biasing robustness. The sensor includes a sensor stack that includes first and second magnetic layers separated by a non-magnetic layer such as an electrically insulating barrier layer or an electrically conductive spacer layer. The first and second magnetic layers have magnetizations that are antiparallel coupled, but that are canted in a direction that is neither parallel with nor perpendicular to the air bearing surface by a magnetic bias stricture. The magnetic bias structure includes a neck portion extending from the back edge of the sensor stack and having first and second sides that are aligned with first and second sides of the sensor stack. The bias structure also includes a tapered or wedged portion extending backward from the neck portion.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to magnetic data recording and more particularly to an improved magnetic hard bias structure for use with a scissor type magnetoresistive sensor. 
       BACKGROUND OF THE INVENTION 
       [0002]    The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
         [0003]    The write head includes at least one coil, a write pole and one or more return poles. Whet a current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic disk, thereby recording a bit of data. The write field, then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head. 
         [0004]    A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor, or a Tunnel Junction Magnetoresisive (TMR) sensor can be employed to read a magnetic signal from the magnetic media. The sensor includes a nonmagnetic conductive layer (if the sensor is a GMR sensor) or a thin nonmagnetic, electrically insulating barrier layer (if the sensor is a TMR sensor) sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. Magnetic shields are positioned above and below the sensor stack and can also serve as first and second electrical leads so that the electrical current travels perpendicularly to the plane of the free layer, spacer layer and pinned layer (current perpendicular to the plane (CPP) mode of operation). The magnetization direction of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetization direction of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. 
         [0005]    When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering of the conduction electrons is minimized and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. In a read mode the resistance of the spin valve sensor changes about linearly with the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals. 
         [0006]    With the need to ever increase data density various novel sensor structures have been investigated. One way to increase data density is to reduce the sensor gap thickness which defines the bit length. Standard GMR or TMR sensors use an antiferromagnetic layer to pin the pinned layer structure of the sensor. In order to function as an antiferromagnetic layer, these layers must be very thick relative to the other sensor layers. This of course increases the gap thickness, which increases the bit length, which decreases data density. 
         [0007]    A sensor that has been investigated to overcome this challenge is a sensor that is known as a scissor sensor. Such a sensor has two free magnetic layers with magnetizations that move in a scissor fashion relative to each other. Such a sensor shows promise because it does not require a thick antiferromagnetic layer. However, such a sensor presents challenges with regard to magnetic biasing of the two free layers. Therefore, there remains a need for a sensor that can reduce gap thickness such as by eliminating an AFM layer, while providing robust, reliable and workable biasing of the magnetic layers. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a magnetic sensor comprising, a sensor stack including first and second magnetic layers and a non magnetic layer sandwiched between the first and second magnetic layers, the sensor stack having a front edge located at an air bearing surface a back edge located opposite the front edge and first and second laterally opposed sides each extending from the front edge to the back edge. The sensor also includes a magnetic bias structure located adjacent to the back edge of the sensor stack for providing a magnetic bias field to the sensor stack, the magnetic bias structure including a neck portion near the sensor stack that has first and second sides that are aligned with the first and second sides of the sensor stack and having a flared portion. 
         [0009]    The magnetic sensor can be constructed by a method that includes forming a magnetic shield and depositing a series of sensor layers over the magnetic shield. A first mask is formed over the series of sensor layers, the first mask being configured to define front and back edges of a sensor structure. A first ion milling is performed to remove portions of the series of sensor layers that are not protected by the first mask, thereby defining front and back edge of the sensor structure. A magnetic hard bias material is deposited, and the first mask is removed. A second mask is then formed, the second mask including a portion configured to define a sensor width and having another portion configured to define a shape of a magnetic hard bias structure extending from the back edge of the sensor. A second ion milling is performed to remove portions of the sensor material and magnetic hard bias material that are not protected by the second mask. 
         [0010]    The novel hard bias structure having a neck portion that is aligned with the first and second sides of the sensor stack and having a tapered or wedged portion extending backwards from the neck portion provides a strong robust magnetic bias field for biasing the magnetic layers of the sensor stack. This bias field can be optimized by forming the tapered or wedged portion with side edges that define an angle of 25-50 degrees with respect to the air bearing surface. 
         [0011]    These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale. 
           [0013]      FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
           [0014]      FIG. 2  is an ABS view of a slider illustrating the location of a magnetic head thereon; 
           [0015]      FIG. 3  is an enlarged ABS view of a magnetoresistive sensor according to an embodiment of the invention; 
           [0016]      FIG. 4  is an exploded, top-down, schematic view of layers of the magnetoresistive sensor of  FIG. 3 ; 
           [0017]      FIG. 5  is a top down view of a magnetoresistive sensor and magnetic bias structure; 
           [0018]      FIG. 6  is a table illustrating bias fields for various hard bias structure configurations; 
           [0019]      FIGS. 7-17  are views of a magnetic sensor in various intermediate stages of manufacture, illustrating a method for manufacturing a magnetic sensor and hard bias structure according to an embodiment of the invention; and 
           [0020]      FIG. 18  is a top down view of a top down view of a magnetoresistive sensor and hard bias structure according to an alternate embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein. 
         [0022]    Referring now to  FIG. 1 , there is shown a disk drive  100  embodying this invention. As shown in  FIG. 1 , at least one rotatable magnetic disk  112  is supported on a spindle  114  and rotated by a disk drive motor  118 . The magnetic recording on each disk is in the form of annular patterns of concentric data tracks (not shown) on the magnetic disk  112 . 
         [0023]    At least one slider  113  is positioned near the magnetic disk  112 , each slider  113  supporting one or more magnetic head assemblies  121 . As the magnetic disk rotates, slider  113  moves radially in and out over the disk surface  122  so that the magnetic head assembly  121  can access different tracks of the magnetic disk where desired data are written. Each slider  113  is attached to an actuator arm  119  by way of a suspension  115 . The suspension  115  provides a slight spring force which biases slider  113  against the disk surface  122 . Each actuator arm  119  is attached to an actuator means  127 . The actuator means  127  as shown in  FIG. 1  may be a voice cod 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 controller  129 . 
         [0024]    During operation of the disk storage system, the rotation of the magnetic disk  112  generates an air bearing between the slider  113  and the disk surface  122  which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension  115  and supports slider  113  off and slightly above the disk surface by a small, substantially constant spacing during normal operation. 
         [0025]    The various components of the disk storage system are controlled in operation by control signals generated by control unit  129 , such as access control signals and internal dock signals. Typically, the control unit  129  comprises logic control circuits, storage means and a microprocessor. The control unit  129  generates control signals to control various system operations such as drive motor control signals on line  123  and head position and seek control signals on line  128 . The control signals on line  128  provide the desired current profiles to optimally move and position slider  113  to the desired data track on disk  112 . Write and read signals are communicated to and from write and read heads  121  by way of recording channel  125 . 
         [0026]    With reference to  FIG. 2 , the orientation of the magnetic head  121  in a slider  113  can be seen in more detail.  FIG. 2  is an ABS view of the slider  113 , and as can be seen the magnetic head including an inductive write head and a read sensor, is located at a trailing edge of the slider. The above description of a typical magnetic disk storage system and the accompanying illustration of  FIG. 1  are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders. 
         [0027]      FIG. 3  shows an air bearing surface (ABS) view of a magnetic sensor  300  according to an embodiment of the invention. The sensor  300  includes a sensor stack  302  that is sandwiched between first and second magnetic shields  304 ,  306  that cal be formed of an electrically conductive magnetic material so that they can function as electrical leads for supplying a sense current to the sensor stack  302  as well as functioning as magnetic shields. 
         [0028]    The sensor stack  302  includes first and second magnetic layers  308 ,  310  with a thin non-magnetic layer  312  sandwiched between the magnetic layers  308 ,  310 . The sensor  300  is preferably a tunnel junction sensor, wherein the layer  312  is a non-magnetic, electrically insulating layer such as MgO. However, the sensor  300  could also be a giant magnetoresistive sensor (GMR sensor), in which case the layer  312  would be a non-magnetic, electrically conductive layer such as Cu, Ag, AgSn. The sensor stack  302  can also include a seed layer  314 , provided at the bottom of the sensor stack  300  to initiate a desired grain formation in the above formed layers. The sensor stack  300  can also include a capping lay  316  such as Ru/Ta/Ru or Ru to protect the under-lying sensor layers during manufacture. The space to either side of the sensor stack  302 , between the magnetic shields  306 ,  304  is filled with a non-magnetic, electrically insulating material  318 ,  320  such as alumina as well as other non-magnetic, electrically insulating materials, as will be seen. 
         [0029]    The magnetic layers  308 ,  310  have a magnetic anisotropy that tends to align magnetizations  322 ,  324  of the magnetic layers in anti-parallel directions parallel with the air bearing surface (ABS) as shown. However, the magnetizations  322 ,  324  are canted away from being perfectly parallel with the ABS by a magnetic bias structure that will be described in greater detail herein below. 
         [0030]      FIG. 4  shows a top down, exploded, schematic view of the magnetic layers  308 ,  310  and magnetizations  322 ,  324 , The magnetization  322  is shown in dashed line to indicate that it is the magnetization of the layer  308 , which is hidden behind the magnetic layer  310 . A magnetic bias structure  402  located behind the air bearing surface (ABS), which applies a magnetic bias field that pulls the magnetizations  322 ,  324  away from being parallel with the ABS and away from being perfectly anti-parallel with one another. In the presence of an external magnetic field, such as from a magnetic medium, the magnetizations  322 ,  324  will deflect so that they are either more or less anti-parallel or parallel with one another. This change in the relative orientations  322 ,  324  of the magnetic layers  308 ,  310  changes the electrical resistance through the sensor stack  302  ( FIG. 3 ) based on the spin dependent tunneling effect of electrons passing through the thin barrier layer  312 . 
         [0031]    Because the relative movement of the magnetizations  322 ,  324  resembles the motion of a scissor during operation, such a sensor can be referred to as a scissor sensor or scissor TMR sensor. In order for such as scissor sensor to operate effectively and reliably, the magnetic bias field provided by the bias layer  402  must be sufficiently strong to overcome the magnetic anisotropy of the magnetic layers  308 ,  310  to keep the magnetizations  322 ,  324  generally perpendicular to one another in the absence of an external magnetic field. Keeping the magnetizations  322 ,  324  oriented in this manner, so that the pivot about a perpendicular orientation, ensures that a signal processed from such as sensor is within the linear region of the signal curve. Therefore, in order to provide excellent sensor performance it is necessary to provide a hard bias structure  402  that provides robust biasing. 
         [0032]      FIG. 5  shows an expanded view of a sensor stack  302  and hard bias structure  402  according to an embodiment of the invention. Areas outside of the sensor stack  302  and hard bias structure can be filled with a non-magnetic, electrically insulating material such as alumina and may include the fill layers  318 ,  320  described above with reference to  FIG. 3 . Also, the sensor  302  is separated from the hard bias structure  402  by a thin, non-magnetic, electrically insulating layer  505 , which can be a material such as alumina and which preferably also covers the bottom shield  304  in order to prevent shunting of sense current through the hard bias layer  402 . 
         [0033]    As can be seen, the hard bias structure includes a neck portion  504  that has sides  506 ,  508  that are generally parallel with and aligned width first and second sides  510 ,  512  of the sensor stack  302 . The hard bias structure  402  also includes a flared portion having flared sides  510 ,  512 . These flared sides  510 ,  512 , preferably define an angle □ of 25-50 degrees relative to a plane that is parallel with the air bearing surface (ABS). The inventors have found that this range of angles, along with the neck portion  504 , provide and an optimal magnetic bias field for use with a scissor type sensor. 
         [0034]    The benefit of the above described hard bias structure  402  can be better understood with reference to  FIG. 6  which shows the hard bias field for various hard bias layer shapes. For purposes of the table of  FIG. 6 , the hard bias field (HBF) is the field as measured at the center of the sensor  302  ( FIG. 5 ). In the table of  FIG. 6 , a basic hard bias structure that extends straight back from the sensor is shown in column I and is used as a reference for the other hard bias shapes. Because this is the reference shape, the HBF for this structure in column I is denoted as being zero for purposes of comparison with the other shapes. Column II shows that a bias structure that is significantly wider than the sensor, but extends straight outward from the sensor has a  50 % increase in bias field compared with the structure of column I. Column III shows that the bias field for a bias structure having a wedge shape (i.e. shallow tapered front edge) with the taper initiating right at the back edge of the sensor (e.g. no neck portion) provides an 84% increase in bias field. Column IV shows a structure similar to that of column III, but with a sharper taper, and shows that this structure provides a 99% increase in bias field. In column III, the taper angle is 25-50 degrees relative to a plane that is parallel with the air bearing surface. Column V shows a bias structure having a shallow taper and also having a neck portion at the back edge of the sensor. As can be seen, this structure provides a 109% increase in bias field. Finally, column VI shows the bias field from a bias structure that has both a neck and a steep tapered wedge (forming an angle of 25-50 degrees relative to the air bearing surface). This structure provides a bias field that has a 117% increase compared with the structure of column I. As can be seen, this structure of column VI provides the highest bias field of all of the structures shown in  FIG. 6 . 
         [0035]      FIG. 18  shows a top down view of a magnetoresistive sensor  302  having a hard bias structure  1800  according Lo an alternate embodiment of the invention. Like the embodiment described above with regard to  FIG. 5 , the hard bias structure  1800  extends from the back edge of the sensor  302  and is separated from the sensor by a thin insulation layer  505 . The hard bias structure includes a neck portion  504 . The bias structure also includes a flared portion having a front edge portion  1702  (nearest to the neck  504 ) that defines an angle θ of 25-50 degrees with respect to the ABS. The hard bias structure  1800  also includes a second tapered edge portion  1704  that is further from the neck portion  504  than the first edge portion  1702 , the edge  1704  defining an angle with respect to the ABS that is greater than θ, but which is less than 90 degrees. 
         [0036]      FIGS. 7 through 17 , illustrate a method for manufacturing a scissor style magnetic sensor having a magnetic bias structure according to an embodiment of the invention. With particular reference to  FIG. 7 , a substrate  702  is provided, which can be a layer of a non-magnetic, electrically insulating material such as alumina. An electrically conductive, magnetic shield  704 , constructed of a material such as NiFe is formed on or into the substrate  702 . The shield  704  is preferably constructed such that the shield is embedded into the substrate  702  and has an upper surface that is coplanar with the surface of the substrate.  702 . A series of sensor layers  706  is deposited over the magnetic shield  704  and the substrate  702 . The series of sensor layers can include layers of the sensor stack  302  described above with reference to  FIG. 3 , but also includes layers of sensors having various other structures as well. The series of sensor layers  706  preferably includes a layer of material that is resistant to chemical mechanical polishing (CMP resistant material) such as diamond like carbon (DLC) or amorphous carbon a its top. 
         [0037]    Then, with reference to  FIG. 8 , a mask structure  802  is formed. This mask structure can include various layers. These various mask layers can include, for example, a bottom hard mask layer  804  preferably constructed of a material that is resistant to chemical mechanical polishing, an image transfer layer, such as DURIMIDE®  806 , an optional top hard mask/bottom antireflective coating layer  808 , and a photoresist layer  810 . The photoresist layer  810  can be patterned as desired by a photolithographic patterning and developing process, and the pattern of this image transfer layer can be transferred onto the underlying layers  804 ,  806 ,  808  by one or more reactive ion etching processes and/or ion milling. The patterned mask  802  has a central covered portion  804  (which will define a sensor area and first and second openings at either end of the central portion. The dashed line denoted (ABS) indicates the location of the air bearing surface plane. Therefore, the openings in the mask are in front of and behind the sensor area. The pattern of the mask  802  can be better understood with reference to  FIG. 9  which shows a top down view of the mask  802  and openings through which the sensor layers  706  are exposed. 
         [0038]    With the mask thus formed, an ion milling process is performed to remove portions of the sensor layers  706  that are not protected by the mask (e.g. parts that are exposed through the openings in the mask  802 ), leaving a structure as shown in  FIG. 10 . Then, as show in  FIG. 11 , a thin insulation layer  1102  is deposited followed by a layer of magnetic material having a high coercivity, (hard magnetic material)  1104 . The insulation layer can be SiN and is preferably deposited by a conformal deposition process such as ion beam deposition to a thickness of about 30 Angstroms. The hard magnetic material  1104  can be constructed of a material such as CoPt or CoPtCr and is preferably deposited to at thickness that is about as high as the height of the sensor layers  706 . The hard bias layer  1104  is preferably deposited to a thickness that is about 4 times the thickness of the insulation layer or about 120 Angstroms. 
         [0039]    Then, another layer of material that is resistant to chemical mechanical polishing (CMP resistant material) such as diamond like carbon (not shown) is deposited. A wrinkle bake process is then performed, followed by a chemical liftoff process to remove the mask  802 . This is followed by a chemical mechanical polishing process, which is then followed by a reactive ion etching to remove the CMP resistant material. These processes leave a planarized structure as shown in  FIG. 12 , having a smooth planar surface  1202  across the hard bias layers  1104  and the sensor material  706 . 
         [0040]    With reference now to  FIG. 13 , another mask structure  1302  is formed. Like the previously formed mask  802 , the mask  1302  can include a CMP resistant hard mask  1304  such as DLC, an image transfer layer  1306  such as DURIMIDE®, an optional top hard mask/bottom antireflective coating layer  1308  and a photoresist mask  1310 . The photoresist mask  1310  is photolithographically patterned to the desired mask shape, and the shape of the photoresist mask  1310  can be transferred onto the underlying layers  1304 ,  1306 ,  1308  by one or more reactive ion etching processes. 
         [0041]    The pattern of the mask  1302  can be better seen with reference to  FIG. 14  which shows a top down view. As can be seen, the mask  1302  has a narrow, constant width, throat portion  1402  that extends over the portion of the sensor material layer  506  that is between the two portions of hard bias material  1104 . Preferably, however, the throat portion  1402  also extends slightly over the hard bias material  1104  as well. This throat portion  1402  has a width that defines the width of the sensor  302  and that also defines the neck portion  504  of the hard bias structure  402  (as described above with reference to  FIG. 5 ). The mask  1302  also has a flared portion  1404  that is formed over the hard bias material  1104 . This flared portion will define the wedged or tapered portion of the hard bias layer structure as will be seen. 
         [0042]    With the second mask  1302  in place, a second ion milling can be performed to remove sensor material  706  and hard bias material  1302  that is not protected by the mask  1302 . Then, with reference to  FIG. 15 , a fill layer is deposited. Most preferably, this includes depositing an anti-diffusion layer such as 30 Angstroms of SiN  1502 , followed by a non-magnetic, dielectric fill layer such as alumina  1504  followed by a CMP resistant layer such as about 2 Angstroms of diamond like carbon (DLC). 
         [0043]    This can then be followed by a wrinkle bake process and a chemical liftoff process to remove all or a portion of the mask  1302 , followed by a chemical mechanical polishing process to remove any remaining mask materials and to polarize the structure. A reactive ion etching RIE can then be performed to remove any of the remaining CMP resistant material  1506 ,  1304 . This leaves a structure as show in  FIG. 16 , with all of the mask  1302  and CMP resistant material removed and with a smooth planar surface across the sensor material  706  hard bias  1104  and fill layer  1504 . 
         [0044]    A magnetic material can then be electroplated over this structure to form an upper shield (not shown in  FIG. 16 , but shown as shield  306  in  FIG. 3 .  FIG. 17  shows a top down view of the structure of  FIG. 16 . After the sensor and any other necessary structures have been formed (such as a write head, not shown), a dicing and lapping operation can be performed to define the air bearing surface. The lapping operation removes material from the direction indicated by arrows  1702  and is terminated when the air bearing surface plan (dashed line ABS) has been reached. 
         [0045]    While various embodiments have been described above, it should be understood that they have been presented by way of example only and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.