Abstract:
A current perpendicular to plane (CPP) magnetoresistive sensor having a free layer that is magnetically coupled with a magnetic shield, thereby providing the free layer with a large effective flux guide. Sensor performance is improved by virtually eliminating demagnetization fields at the back edge of the sensor. The free layer can be magnetically connected with the shield by a magnetic coupling layer or shunt structure that is disposed between the free layer and the shield behind the capping layer.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to magnetoresistive sensors and more particularly to a current perpendicular to plane sensor (CPP GMR or tunnel valve) having a flux guide structure for improved sensor performance.  
       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 a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.  
         [0004]     In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment 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]     The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to 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]     When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to antiparallel couple the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer).  
         [0007]     The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head, a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.  
         [0008]     The ever increasing demand for increased data rate and data capacity has lead a relentless push to develop magnetoresistive sensors having improved signal amplitude. Sensors that show promise in achieving higher signal amplitude are current perpendicular to plane (CPP) sensors. Such sensors conduct sense current from top to bottom, perpendicular to the planes of the sensor layers. Examples of CPP sensors include current perpendicular to plane giant magnetoresistive sensors (CPP GMR sensors), and tunnel valves. A CPP GMR sensor operates based on the spin dependent scattering of electrons through the sensor, similar to a more traditional CIP GMR sensor except that, as mentioned above, the sense current flows perpendicular to the plane of the layers. A tunnel valve sensor operates based on the spin dependent tunneling of electrons through a thin, non-magnetic, electrically insulating barrier layer.  
         [0009]     Even with the use of CPP sensors, however, there remains an ever increasing need to increase the performance of the sensor. Therefore, there is a strong felt need for a manufacturable sensor design that can provide increased signal amplitude. Such a sensor design would preferably be implemented in a CPP sensor such as a CPP GMR or a tunnel valve.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention provides a current perpendicular to plane magnetoresistive sensor that increases free layer response by reducing demagnetization fields at the back edge of the free layer. The sensor includes a free layer having capping layer formed over a portion of the free layer. Another portion of the free layer near the back edge is magnetically connected with an electrically conductive, magnetic shield.  
         [0011]     Connection between the free layer and the magnetic shield can be achieved by a magnetic coupling layer formed behind the capping layer. The capping layer can be Ta, and can have a top and bottom surfaces that are coplanar with top and bottom surfaces of the magnetic coupling layer. The magnetic coupling layer can be NiFe, CoFe or some other magnetic material.  
         [0012]     A magnetoresistive sensor according to an embodiment of the invention can be constructed by depositing a plurality of sensor layers including a free layer and a non-magnetic capping layer deposited over the free layer. A mask can then be formed over the sensor layers, the mask having a back edge that determines a stripe height of the sensor. A reactive ion etch (RIE) can then be performed to remove portions of the capping layer that are not protected by the mask, and leaving the free layer substantially intact. A layer of magnetic material is then deposited. An ion mill can then be performed to remove sensor materials and horizontally disposed portions of the deposited magnetic layer. Then, a non-magnetic, electrically insulating fill layer can be deposited, a CMP performed, and a shield layer deposited. The remaining magnetic material layer, forms a magnetic coupling layer at the back edge of the free layer that magnetically connects the free layer with the shield.  
         [0013]     A CPP sensor according to the present invention advantageously couples the free layer with the shield to provide the shield with an effective flux guide, providing improved sensor performance. A CPP sensor according to the present invention can be easily manufactured using presently available manufacturing processes, with little additional cost or manufacturing complexity.  
         [0014]     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  
       [0015]     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.  
         [0016]      FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied;  
         [0017]      FIG. 2  is an ABS view of a slider illustrating the location of a magnetic head thereon;  
         [0018]      FIG. 3  is an enlarged cross sectional view taken from line  3 - 3  of  FIG. 2 ;  
         [0019]      FIG. 4  is an ABS view of the sensor of  FIG. 3  taken from line  4 - 4  of  FIG. 3 ;  
         [0020]      FIGS. 5-11  are cross sectional views of a magnetoresistive sensor in various intermediate stages of manufacture, illustrate a method of manufacturing a magnetoresistive sensor according to an embodiment of the invention; and  
         [0021]      FIG. 12  is a flow chart summarizing a method of manufacturing a magnetoresistive sensor according to an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     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.  
         [0023]     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 .  
         [0024]     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  may 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 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 controller  129 .  
         [0025]     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.  
         [0026]     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 clock 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 .  
         [0027]     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.  
         [0028]     With reference now to  FIG. 3 , a cross sectional view of a CPP giant magnetorsistive sensor (CPP GMR)  300  according to an embodiment of the invention is described. The sensor  300  includes a sensor stack  302  sandwiched between first and second electrically conductive lead/shields  304 ,  306 . The lead/shields  304 ,  306  are constructed of an electrically conductive, magnetic material such as NiFe so that they can function as both leads (to provide a sense current to the sensor) and as magnetic shields. Although the layers  304 ,  306  function as both leads and shields, they will be referred to hereinafter as shields  304 ,  306 .  
         [0029]     The sensor stack has an air bearing surface ABS, and a back edge or stripe height  308 . A non-magnetic, electrically insulating fill material  310  such as alumina (Al 2 O 3 ) fills the space between the shields  304 ,  306  beyond the stripe height  308  of the sensor stack  302 .  
         [0030]     The sensor stack includes a magnetic free layer  312  and a pinned layer structure  314 . A non-magnetic layer  316  is sandwiched between the free layer  312  and pinned layer structure  314 . The non-magnetic layer  316  can be a non-magnetic, electrically conductive spacer layer constructed of, for example, Cu if the sensor  300  is embodied in a current perpendicular to plane giant magnetoresitive sensor (CPP GMR). If the sensor  300  is embodied in a tunnel valve sensor, the layer  316  can be a non-magnetic, electrically insulating barrier layer, such as MgO. Although the invention can be embodied in a CPP GMR sensor or a tunnel valve, for purposes of simplicity the invention will be described herein below as a tunnel valve having a barrier layer  316 .  
         [0031]     With continued reference to  FIG. 3 , the free layer  312  can be constructed of, for example Co, CoFe, NiFe, or a combination of these or other materials. The pinned layer can be of various types such as simple pinned, self pinned, etc., but is preferably embodied in an AFM pinned, AP coupled structure. Therefore, the pinned layer structure  314  may include a first magnetic layer AP  1   318 , a second magnetic layer  320  and a non-magnetic antiparallel coupling layer (AP coupling layer)  322  such as Ru sandwiched between the AP 1  and AP 2  layers  318 ,  320 . The AP 1  and AP 2  layers  318 ,  320  may be constructed of, for example, CoFe, or could be constructed of some other magnetic material. The AP 1  layer  318  is exchange coupled with a layer of antiferromagnetic material (AFM layer)  324 . This exchange coupling strongly pins the magnetization  325  of the AP 1  layer  318 . Antiparallel coupling between the AP 1  and AP 2  layers pins the magnetization  327  of the AP 2  layer  320  in a desired direction perpendicular to the ABS and anti-parallel with the magnetization  325  of the AP 2  layer  320 .  
         [0032]     A seed layer  326  may be provided at the bottom of the sensor stack  302  to promote a desired crystalline growth of the layers deposited over the seed layer  326 . A non-magnetic capping layer  328  is provided at the top of the sensor stack  302  and can be constructed of, for example Ta. The capping layer  328  is preferably constructed of a material having a low electrical resistance in order to minimize parasitic resistance through the sensor stack  302 .  
         [0033]     With reference to  FIG. 3 , it can be seen that the capping layer  328  has a back edge  330  that terminates short of the back edge or stripe height  308  of the rest of the sensor stack, and terminates short of the stripe height of the free layer  312 . A magnetic coupling layer  332 , is provided at the back end of the sensor opposite the ABS. The magnetic, coupling layer  332  magnetically connects the back of the free layer  312  with the shield  306 , thereby allowing the entire shield  306  to act as a flux guide to absorb magnetic flux from the free layer  312 . This greatly increases the responsiveness of the free layer by eliminating demagnetization fields at the back edge (stripe height edge) of the free layer  312 . The capping layer  328  preferably extends from the ABS toward the back edge of the free layer  312  a distance of at least  3 / 4  of the distance from the ABS to the back edge of the free layer. As can be seen, the capping layer  328  and the magnetic coupling layer  332  have coplanar top surfaces and coplanar bottom surfaces.  
         [0034]     With reference now to  FIG. 4 , the sensor  300  may include hard bias layers  402 ,  404  extending from either lateral side of the sensor stack  302  to bias the magnetization  406  of the free layer in a desired direction parallel with the ABS. Thin insulation layers  408 ,  410  are formed at either side of the senor stack and extend over the first shield layer  304  to prevent sense current from being shunted across the hard bias layers  402 ,  404 . The hard bias layers  402 ,  404  can be constructed of, for example CoPt, CoPtCr or some other magnetically hard material. The insulation layers  408 ,  410  can be constructed of, for example, alumina.  
         [0035]     With reference now to  FIGS. 5-11 , a method for constructing a CPP magnetoresistive sensor according to an embodiment of the invention is described. With particular reference to  FIG. 5 , a series of sensor layers  502  are deposited over a substrate  504 , such a first shield layer. The sensor layers can include: a seed layer  506 , an AFM layer  508 , AP 1  layer  510 , coupling layer  512 , AP 2  layer  514 , spacer or barrier layer  516 , a magnetic free layer  518 , and a capping layer  520 . The capping layer  520  can be constructed of, for example Ta, or some other electrically conductive, non-magnetic material.  
         [0036]     With continued reference to  FIG. 5 , a mask structure  522  is constructed over the sensor layers  502 . The mask may be of various types, and may include a hard mask  524  such as alumina, silicon dioxide, diamond like carbon (DLC), etc. The mask  522  may also include an image transfer layer  526  formed over the hard mask and a photosensitive layer  528  formed over the image transfer layer  526 . The image transfer layer  526  can be a soluble polyimide material such as DURIMIDE® or some similar material. The photosensitive material  528  can be a material such as photoresist.  
         [0037]     With reference now to  FIG. 6 , a reactive ion etch (RIE) is performed just sufficiently to remove the capping layer  520 , but not long enough to remove the free layer  518 . Then, with reference to  FIG. 7 , a layer of magnetic material  702  such as NiFe CoFe or any suitable magnetic material is deposited. The magnetic material  702  can be deposited by sputter deposition in a sputtering chamber.  
         [0038]     With reference to  FIG. 8 , an ion mill  802  is performed to remove portions of the sensor layers  502  that are not protected by the mask  522  and magnetic layer  702 . As can be seen in  FIG. 8 , the ion mill  802  removes the horizontally disposed portions of the magnetic layer leaving a vertical wall of the magnetic layer  702 .  
         [0039]     With reference to  FIG. 9 , a layer of non-magnetic, electrically insulating fill material  902  is deposited. The insulating fill material  902  could be of various materials, but is preferably constructed of alumina. The fill layer  902  can be deposited by sputter deposition, and is preferably deposited to a level at least as high as the top of the capping layer  520 .  
         [0040]     With reference to  FIG. 10 , a chemical mechanical polish (CMP) can be performed to form smooth, coplanar surfaces across the fill layer  902 , magnetic layer  702  and capping layer  520 . Then, with reference to  FIG. 11  an electrically conductive, magnetic shield layer  1102  is deposited to form the second shield  306  described with reference to  FIG. 3 .  
         [0041]     With reference to  FIG. 12 , a method  1200  for constructing a CPP magnetoresistive sensor according to an embodiment of the invention is summarized. In a step  1202 , plurality of sensor layers are deposited over a substrate such as a magnetic, electrically conductive first shield layer. The sensor layers include a non-magnetic, electrically conductive capping layer at the top. The capping layer can be, for example Ta. Then, in a step  1204  a mask structure is formed over the deposited sensor layers. In a step  1206  reactive ion etch is performed sufficiently to remove portions of the cap layer that are not covered by the mask structure. Then, in a step  1208  a magnetic material is deposited. The magnetic material, which can be NiFe, CoFe or some other material, is preferably deposited by a sputter deposition in a sputter deposition chamber. Then, in a step  1210  an ion mill is performed to define the sensor stripe height by removing portions of the sensor layers that are not covered by the mask structure or the remaining magnetic layer. In a step  1212  a fill layer is deposited. Then, in a step  1214  a chemical mechanical polishing process (CMP) is performed to planarize the fill layer, magnetic layer and top of the sensor layers. Finally, in a step  1216  a magnetic electrically conductive material such as NiFe is deposited to form the second shield.  
         [0042]     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.