Abstract:
A read element includes a magnetoresistive sensor having a side and an upper surface that defines an edge. An underlayer overlies the side of the magnetoresistive sensor, and a hard bias layer overlies at least part of the underlayer and defines a hard bias junction with the underlayer. A lead is formed atop the hard bias layer. The hard bias junction is recessed from the edge of the magnetoresistive sensor by a predetermined recess distance, to provide stability and sensitivity to the read element.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to data storage devices such as disk drives, and it particularly relates to a read/write head for use in such data storage devices. More specifically, the present invention provides a new head design with improved stability, increased sensitivity, and reduced side reading, by selectively recessing the hard bias and the current leads. 
   BACKGROUND OF THE INVENTION 
   An exemplary conventional high capacity magnetic storage system typically uses magnetoresistive read (MR) sensors to read data from a surface of the magnetic disk. An MR sensor comprises an MR sensing layer. Data stored in the form of a magnetic field emanating from the magnetic disk changes the resistance of the MR sensing layer. This change in resistance allows the MR sensor to detect the magnetic field on the magnetic disk. The resistance of the MR sensor changes as a function of the magnitude and direction of the magnetic flux from the magnetic disk. 
   A giant magnetoresistive (GMR) sensor is a type of MR sensor that comprises a GMR stack. The GMR stack includes a plurality of magnetic layers that are separated by a non-magnetic layer. The magnetization of one of the magnetic layers (the pinned layer) is pinned by exchange coupling with an antiferromagnetic layer. 
   Another magnetic layer (the free layer) is not pinned; the magnetic moments in this layer are free to rotate in response to the field from the magnetic disk. The electrical resistance of GMR sensor depends on the relative alignment of the magnetic moments in the free layer and the pinned layer. The magnetic field from the magnetic disk induces a change in the direction of magnetization in the free layer, thus changing the resistance of the GMR sensor. 
   The change in resistance of the GMR sensor can be measured by applying a current to the GMR sensor. The GMR sensor comprises conductive lead structures that connect to the GMR stack, providing means for applying current to the GMR stack. The change in resistance of a GMR sensor is typically determined by applying a constant current and measuring voltage variations caused by the change in resistance. Conventional GMR sensors are biased by a permanent magnetic known as a hard bias (HB). The hard bias provides a preferred direction or “off” resistance for the free layer in the GMR stack. 
   Although this technology has proven to be useful, it would be desirable to present additional improvements. A large hard bias layer is desired for better thermal and magnetic stability of the GMR sensor. However, as the hard bias layer increases in size, the “on” resistance of the free layer decreases, providing a lower amplitude voltage (or output signal) when reading the magnetic disk. 
   As the areal density of magnetic disks increases, magnetic read widths decrease. At very low magnetic read widths (below approximately 0.15 micron), the two sides of the permanent magnetic material in the hard bias are very close. Consequently, the hard bias field in the GMR sensor could cause the output signal to be below an acceptable level. 
   To maintain the amplitude of the output signal from the GMR sensor, the strength of the magnetic field applied by the permanent magnetic material in the hard bias is decreased. A hard bias at these small thicknesses is however susceptible to degradation. 
   At very low track widths, the hard bias becomes very thin and the junctions of the hard bias closest to the GMR stack become unstable. At high temperature, the junctions of the hard bias become demagnetized, allowing an increase in side reading. The read width of the MR sensor essentially becomes wider. In addition, magnetic instability of the device response is introduced by the weakening of the hard bias. 
   Furthermore, the top shield region that overlies the GMR stack should be as flat as possible to minimize side reading by the GMR sensor. At very low magnetic read widths (i.e., below approximately 0.15 micron), the conventional topography of the conductive leads does not allow this top shield region to be flat across substantially the entire width of the GMR stack, thus increasing undesirable side reading. 
   Therefore, what is needed is an MR read sensor with improved stability, increased amplitude of the output signal, and reduced side reading. The need for such an MR read sensor has heretofore remained unsatisfied. 
   SUMMARY OF THE INVENTION 
   The present invention can be regarded as a read/write head for use in a data storage device to provide improved stability, increased sensitivity, and reduced side reading, by selectively recessing the hard bias and the current leads. The read/write head comprises a read element that includes a magnetoresistive sensor having a side and an upper surface that defines an edge. An underlayer overlies the side of the magnetoresistive sensor, and a hard bias layer overlies at least part of the underlayer and defines a hard bias junction with the underlayer. A lead is formed atop the hard bias layer. The hard bias junction is recessed from the edge of the magnetoresistive sensor by a predetermined recess distance, to provide stability and sensitivity to the read element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary perspective view of a data storage device utilizing a read/write head of the present invention; 
       FIG. 2  is a perspective view of a head gimbal assembly comprised of a suspension, and a slider to which the read/write head of  FIG. 1  is secured, for use in a head stack assembly; 
       FIG. 3  is a cross-sectional view of a conventional MR sensor; 
       FIG. 4  is a cross-sectional view of an MR sensor with a recessed hard bias; 
       FIG. 5  is a graph illustrating the effect of increasing the width of a chromium layer on a magnetic field in the MR sensor of  FIG. 4 ; and 
       FIG. 6  is a cross-sectional view of an alternative MR sensor according to the present invention, having a recessed hard bias and recessed current leads. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a hard disk drive  100  in which an embodiment of the present invention may be used. An enclosure of the hard disk drive  100  comprises a cover  102  and a base  104 . The enclosure is suitably sealed to provide a relatively contaminant-free interior for a head disk assembly (HDA) portion of the hard disk drive  100 . The hard disk drive  100  also comprises a printed circuit board assembly (not shown) that is attached to base  104  and further comprises the circuitry for processing signals and controlling operations of the hard disk drive  100 . 
   Within its interior, the hard disk drive  100  comprises a magnetic disk  126  having a recording surface typically on each side of the disk, and comprises a magnetic head or slider that may suitably be a magneto-resistive (“MR”) head such as a GMR head. The GMR head has an MR element for reading stored data on a recording surface and an inductive element for writing data on the recording surface. The exemplary embodiment of the hard disk drive  100  illustrated in  FIG. 1  comprises three magnetic disks  126 ,  128 , and  130  providing six recording surfaces, and further comprises six magnetic heads. 
   Disk spacers such as spacers  134  and  136  are positioned between magnetic disks  126 ,  128 ,  130 . A disk clamp  132  is used to clamp disks  126 ,  128 ,  130  on a spindle motor  124 . In alternative embodiments, the hard disk drive  100  may comprise a different number of disks, such as one disk, two disks, and four disks and a corresponding number of magnetic heads for each embodiment. The hard disk drive  100  further comprises a magnetic latch  110  and a rotary actuator arrangement. The rotary actuator arrangement generally comprises a head stack assembly  112  and voice coil magnet (“VCM”) assemblies  106  and  108 . The spindle motor  124  causes each magnetic disk  126 ,  128 ,  130  positioned on the spindle motor  124  to spin, preferably at a constant angular velocity. 
   A rotary actuator arrangement provides for positioning a magnetic head over a selected area of a recording surface of a disk. Such a rotary actuator arrangement comprises a permanent-magnet arrangement generally including VCM assemblies  106 ,  108 , and head stack assembly  112  coupled to base  104 . A pivot bearing cartridge is installed in a bore of the head stack assembly  112  and comprises a stationary shaft secured to the enclosure to define an axis of rotation for the rotary actuator arrangement. 
   The head stack assembly  112  comprises a flex circuit assembly and a flex bracket  122 . The head stack assembly  112  further comprises an actuator body  114 , a plurality of actuator arms  116  cantilevered from the actuator body  114 , a plurality of head gimbal assemblies  118  each respectively attached to an actuator arm  116 , and a coil portion  120 . The number of actuator arms  116  and head gimbal assemblies  118  is generally a function of the number of magnetic disks in a given hard disk drive  100 . 
   Each of the head gimbal assemblies (HGA)  118  is secured to one of the actuator arms  116 . As illustrated in  FIG. 2 , HGA  118  is comprised of a suspension  205  and a read/write head  210 . The suspension  205  comprises a resilient load beam  215  and a flexure  220  to which the read/write head  210  is secured. 
   The read/write head  210  comprises a slider  225  secured to the free end of the resilient load beam  215  by means of flexure  220  and a read/write element  230  supported by slider  225 . In the example illustrated in  FIG. 2 , the read/write element  230  is secured to the trailing edge  235  of slider  225 . Slider  225  can be any conventional or available slider. In another embodiment, more than one read/write element  230  can be secured to the trailing edge  235  or other side(s) of slider  225 . The read/write element  230  comprises a write element and a read element. 
   A cross-sectional view of a conventional magnetoresistive read (MR) read element  300  is illustrated  FIG. 3 . The exemplary conventional read element  300  comprises a giant magnetoresistive (GMR) stack  305 ; a chromium (Cr) underlayer  310 ,  315 ; a hard bias  320 ,  325 ; a current lead  330 ,  335 ; and a shield layer  340 . The GMR stack  305  comprises a first gap and a first shield layer that are collectively referenced by the numeral  305 ; a stack of layers, such as a first pinned layer, an Ru spacer, a second pinned layer, and a copper spacer that are collectively referred to herein as the pinned layer, and referenced by the numeral  345 ; a free layer  350 ; and a cap that is not shown for the purpose of simplifying the illustration. A second gap and a second shield that are collectively referred to herein as the second shield layer, and referenced by the numeral  340 , overlie the lead  330 ,  335 , the free layer  350 , and the cap. 
   The free layer  350  comprises an active region  355  and two dead zones  360 ,  365 . The hard bias  320 ,  325  is sized to provide adequate magnetic field to pin the free layer  350  in the GMR stack  305 . Consequently, the magnetic field from the hard bias  320 ,  325  in the dead zones  360 ,  365  causes the dead zones  360 ,  365  not to respond to the magnetic field of a magnetic disk such as magnetic disk  126 . 
   In addition, the hard bias  320 ,  325  tapers in proximity to the GMR stack  305 . The taper regions of the hard bias  320 ,  325  are susceptible to thermal instabilities, allowing side reading by the GMR stack  305 . 
   Furthermore, the relatively flat region  380  of second shield layer  340  is less than the width W of the GMR stack  305 . Consequently, additional side reading is induced in the GMR stack  305 . 
     FIG. 4  illustrates a cross-section of a read element  400  according to the present invention. The read element  400  comprises a magnetoresistive (MR) sensor  405 , for example, a spin valve, a giant a magnetoresistive sensor (GMR), an anisotropy magnetoresistive sensor (AMR), a colossal magnetoresistive sensor (CMR). In order to facilitate the illustration and description of the present invention, the MR sensor  405  will be described as a GMR sensor. 
   The read element  400  further includes a first gap and a first shield layer that are collectively referenced by the numeral  405 ; a chromium underlayer  410 ,  415 ; a hard bias  420 ,  425 ; current leads  430 ,  435 ; and a second gap second and a second shield layer that are collectively referenced by the numeral  440 . Similarly to the GMR stack  405 , and as described earlier, the GMR stack  405  comprises a pinned layer  445  and a free layer  450 . The free layer  450  comprises an active region  455  and two dead zones  460 ,  465 . 
   The hard bias  420 ,  425  is recessed from the edges  466 ,  467  of the GMR stack  405 , so that a recess distance  470  of, for example, approximately 0.5 to 20 nm, is formed between each of the edges  466 ,  467  and the corresponding hard bias junctions  486 ,  487 , respectively. The thickness  475  of the hard bias  420 ,  425  is selected to provide the desired magnetic field in the GMR stack  405 , so as to pin the free layer  450 . Since the hard bias  420 ,  425  is recessed from the GMR stack  405 , the thickness  475  of the hard bias  420 ,  425  can be larger than in conventional read element  330  of  FIG. 3 . 
   Relative to the conventional sensor  300  of  FIG. 3 , the hard bias  420 ,  425  of the present sensor  400  is thicker than the sensor  300 , at a distance from the GMR stack  405 , and tapers, that is gets progressively becomes narrower, toward the GMR stack  405  where it terminates. The present design of the hard bias  420 ,  425  provides added thermal and magnetic stability to the sensor  400 , since the hard bias could be made thicker than in conventional designs. 
   In addition, recessing the hard bias  420 ,  425  from the edges  466  and  467  of the GMR stack  405 , reduces the magnetic field applied to the edge of the GMR stack  405 . Consequently, the dead zones  460 ,  465  that do not respond to the magnetic field of the magnetic disk  126  are small compared to the conventional read element  300 . Because active region  455  is wider than the corresponding active region  355  of the conventional read element  300 , the read element  400  is more sensitive to the magnetic field of the magnetic disk  126  and provides an output signal with higher amplitude. 
   In one embodiment, recessing the hard bias  420 ,  425  can be implemented by extending the chromium layers  410 ,  415 , so that the underlayers  410 ,  415  overlie the sides  496  and  497  of the GMR stack  405 , respectively, and extend to the edges  466 ,  467 , respectively. The effect of extending the chromium layers  410 ,  415  on the magnetic field applied to the GMR stack  405  by the hard bias  420 ,  425  is illustrated in the graph  500  of  FIG. 5 . The exemplary magnetic disk used for analysis in  FIG. 5  has a data storage capacity of 80 GB or higher. 
   Referring to graph  500 , the magnetic field of the hard bias  420 ,  425  is plotted as a function of distance across the GMR stack  405 , where the origin corresponds to one side of the GMR stack  405 . The magnetic field of the hard bias  420 ,  425  is plotted for three thicknesses of the chromium layer  410 ,  415 : 165 Å, 185 Å, and 210 Å. Line  505  corresponds to the chromium layer  410 ,  415  with thickness 165 Å. Line  510  corresponds to the chromium layer  410 ,  415  with thickness 185 Å. Line  515  corresponds to the chromium layer  410 ,  415  with thickness 210 Å. 
   As the thickness of the chromium layer  410 ,  415  increases, the recess distance  470  increases. Consequently, the magnetic field at the edges of the GMR stack  405  decreases while the magnetic field at the center of the GMR stack  405  maintains the desired magnitude for pinning the free layer  450 . The edges of the GMR stack  405  correspond to approximately 1 Å and approximately 21 Å in graph  500 . At these points, the amplitude of the magnetic field from the hard bias  420 ,  425  is approximately 980 Oe for a chromium layer  410 ,  415  of thickness of 165 Å and approximately 840 Oe for a chromium layer  410 ,  415  of thickness 210 Å, a reduction of approximately 15%. 
     FIG. 6  illustrates another embodiment of the present invention wherein a read element  600 , in which current leads  605 ,  610  are recessed from the edges  466 ,  467  of the GMR stack  405 . Recess distance  620 , between the edges  466 ,  467  and the corresponding lead junctions  652 ,  653 , respectively, may range from approximately 0.5 to 20 nm. Recess distance  470  between the edges  466 ,  467  and the corresponding hard bias junctions  486 ,  487 , may range from approximately 0.5 to 20 nm. It should be clear that while the lead junctions  652 ,  653  are shown as a being distinct and a distance from the corresponding hard bias junctions  486 ,  487 , these junctions could coincide and co-located. Recessing current leads  605 ,  610  allows the shield layer  615  to form a flat region  625  over the substantially the entire width of the GMR stack  405 , reducing side reading induced by the shape of the shield layer  615  at the edges  466 ,  467  of the GMR stack  405 .