Abstract:
A magnetoresistive (MR) sensor for use in a magnetic storage system including a magnetic storage media having multiple concentric microtracks with information stored thereon. The MR sensor includes a plurality of generally parallel layers that form an MR stack. The MR sensor also includes a top shield and a bottom shield that are spaced apart on opposite sides of the MR stack in a longitudinal direction. The Mr sensor further includes a first and a second side shield spaced apart on opposite sides of the MR stack in a transverse direction. The top shield, bottom shield, first side shield and second side shield substantially surround the MR stack.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the priority from provisional U.S. patent application 60/232,476, filed on Sep. 13, 2000 for “NEW MR STRUCTURES FOR HIGH AREAL DENSITY READER BY USING SIDE SHIELDS” for Lujun Chen, James Giusti, Juan Fernandez-de-Castro, Jian Chen and Sining Mao, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of electronic data storage and retrieval systems. In particular, the present invention relates to a novel configuration of a shielded magnetoresistive element of a transducing head. 
     In an electronic data storage and retrieval system, a transducing head typically includes a reader portion having a magnetoresistive (MR) sensor for retrieving magnetically-encoded information stored on a magnetic disc. MR sensors may be anisotropic magnetoresistive (AMR) sensors or giant magnetoresistive (GMR) sensors. AMR sensors generally have a single MR layer formed of a ferromagnetic material. GMR sensors generally have multiple layers of ferromagnetic material. 
     When an MR sensor is placed in close proximity to a rotating magnetized storage disc, the MR layer is exposed to magnetic bit fields previously written on the disc surface. Exposing the MR element to the magnetic bit fields in this way, affects the magnetization vector of the MR element. When a current is passed through the MR element, changes in resistance are detected as voltage changes. The change in resistance of the MR layer is due to the changing magnetization vector of the MR element. External circuitry then converts the voltage information into an appropriate format and manipulates that information into a series of binary ones and zeros that represent the recorded bits on the storage disc. 
     The information that is being read by the MR element is initially stored on the magnetic discs along concentric circular tracks or microtracks. A bit is the smallest unit of data that is stored on each microtrack. Obviously, only a finite amount of bits can be stored along a microtrack, and it is desirable to maximize that number. The number of bits written along a distance of one inch on one of those microtracks is called the linear bit density. It is also desirable to maximize the number of microtracks that are on a disc. The number of microtracks per inch along a radius of the disc is called the track density. The areal density is the product of the linear bit density and the track density. One way to accomplish the goal of increasing the total amount of information stored on a magnetic disc is to increase the areal density, that is, increase the bits stored in a microtrack, increase the amount of microtracks on a disc, or increase both. 
     As areal density increases, however, it becomes more and more difficult to read magnetically stored bits without also reading adjacent stored bits. As an ever-increasing amount of information is stored on a magnetized storage disc, it becomes more difficult for MR sensors to separately read the stored information without also reading noise from adjacent stored information. 
     This problem may be alleviated somewhat in MR sensors by placing soft magnetic material above and below the MR element to shield the element from the influence of bit fields of adjacent bits in a particular microtrack. During a read operation, these top and bottom shields typically insure that the MR sensor reads only the information stored directly beneath it on a specific microtrack of the magnetic medium or disc by absorbing any stray magnetic fields emanating from down track. 
     Top and bottom shields typically shield well as linear bit density increases, but they do not adequately shield stray magnetic fields from magnetically stored bits in adjacent microtracks to the microtrack being read at a particular time by the MR sensor when track density increases. As the track density increases, that is, as adjacent microtracks become closer and closer together, it becomes more imperative that a MR sensor is reading from only a single microtrack at any particular time and not from adjacent microtracks. As track pitch increases, that is, as spacing between adjacent microtracks become smaller, the reading error will increase. A MR sensor that accurately reads high track pitch media is a necessary improvement over the art of record. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention introduces a novel configuration of a shielded MR sensor for a read element of a magnetic head. The MR sensor includes an MR element that further has a top shield, a bottom shield, and first and second side shields. The first and second side shields decrease the response signal in the MR sensor to due to adjacent microtracks that are not intended to be read at a particular point in time. This allows accurate reading by MR sensor even where track density is relatively high. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of a disc drive. 
     FIG. 2 shows an MR sensor of the prior art positioned relative to a field source in a microtrack. 
     FIG. 3 shows a plot of the response of a MR sensor due to a field source versus the relative position of the MR sensor and the field source. 
     FIG. 4 shows an MR sensor in accordance with the present invention. 
     FIG. 5 show an MR sensor in accordance with the present invention positioned relative to a field source in a microtrack. 
     FIG. 6 shows a plot of the response of a MR sensor in accordance with the present invention due to a field source versus the relative position of the MR sensor and the field source. 
     FIG. 7 shows an alternative embodiment of an MR sensor in accordance with the present invention. 
     FIG. 8 shows another alternative embodiment of an MR sensor in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention is particularly contemplated for use in a disc drive  10  exemplified in FIG.  1 . Disc drive assembly  10  includes at least one disc  12  and actuator arm  14  with slider  16 . Disc  12  is mounted on drive spindle  18 , and during use of disc drive assembly  10 , disc drive spindle  18  rotates disc  12  about axis  20 . Actuator arm  14  is mounted on servo spindle  22  and is pivotable about axis  24  by an actuator such as a voice coil motor (not shown). Actuator arm  14  extends parallel to the plane of disc  12  and carries at least one flexure or suspension arm  26 . Suspension arm  26  supports air bearing slider  16  adjacent a surface of disc  12 . 
     As disc  12  rotates about drive spindle  18 , the aerodynamic properties of slider  16  cause it to “fly” above the surface of disc  12 . Slider  16  is supported on a thin cushion of air between the surface of disc  12  and the air bearing surface of slider  16 . 
     A magnetoresistive (MR) sensor may be fabricated on the trailing edge of slider  16 , and positioned as close as possible to rotating disc  12 . Pivoting of actuator arm  14  moves slider  16  through an arc, and allows the MR sensor fabricated on slider  16  to change track position on disc  12 . The MR sensor may then be employed for reading magnetically stored information from the surface of disc  12 . 
     FIG. 2 shows an MR sensor  30  of the prior art positioned relative to disc  12 . MR sensor  30  has a lower side that is parallel to an air bearing surface  32  of slider  16 . MR sensor  30  is positioned to be close enough to disc  12  so that magnetic fields extending from disc  12  will go through MR sensor  30 . In FIG. 2, microtrack  34  is shown on disc  12 . Microtrack  34  is one of a large multitude of microtracks on disc  12 . In FIG. 2, microtrack  34  represents a “sidetrack” relative to MR sensor  30 . In other words, at a particular point in time, MR sensor  30  is positioned to read a particular microtrack (not shown in FIG. 2) and microtrack  34  is an adjacent sidetrack or sidetrack, which MR sensor  30  is not intended to read at this particular point in time. Bit fields within microtrack  34  are magnetized in one direction or the other representing stored information on disc  12 . As disc  12  is rotated relative to MR sensor  30 , magnetic fields radiate radially in all directions from microtrack  34 . When MR sensor  30  is close enough to microtrack  34 , some of the magnetic field lines radiating from microtrack  34  penetrate into MR sensor  30 . Field lines  36 ,  38 ,  40  and  42  are shown going into MR sensor  30 . Field line  44  does not go through MR sensor  30 . As track density increases, MR sensor  30  will receive magnetic field signals from sidetracks like microtrack  34 . 
     The strength of the magnetic field from the stored bits in a microtrack like microtrack  34  is fairly strong in a sensor that is located directly proximate to the microtrack. The strength of this magnetic field fades rapidly, however, as the sensor moves away from the microtrack. The relationship between magnetic field strength and the position of the sensor relative to the microtrack is described by 1/r 2 , where r equals the radial distance between the sensor and the microtrack field source. Thus, as the sensor moves farther from the microtrack (i.e., as r increases), the strength of the magnetic field in the sensor due to the field source in that microtrack decreases. 
     FIG. 3 is an illustration of the response of MR sensor  30  due to a field source in microtrack  34  as the relative position of microtrack  34  and MR sensor  30  changes. This is also referred to as the microtrack transition decay. In FIG. 3, the Y-axis illustrates the relative strength of the magnetic field in MR sensor  30  due to a field source in microtrack  34 , while the X-axis represents the radial distance of MR sensor  30  to microtrack  34 . As is evident from FIG. 3, the strength of the magnetic field in sensor  30  is highest when MR sensor  30  and microtrack  34  are separated by only a minimal distance. As the separation between MR sensor  30  and the microtrack  34  increases, the strength of the signal in MR sensor  30  declines rapidly, that is, it decays. As indicated above, this relationship is described by the microtrack transition decay 1/r 2 , where r equals the distance between the corner edge of MR sensor  30  and the field source in microtrack  34 . The distance between two positions of microtrack  34  at which the signal strength decreases 50 percent from its maximum is known as MT50. The distance between two positions of microtrack  34  at which the signal decreases to 10 percent of its maximum is known as MT10. 
     Generally, when a sensor is reading from a particular microtrack at some point in time, adjacent microtracks, or “sidetracks” are far enough away from the sensor that the strength of the magnetic field in the sensor due to the field sources in the sidetracks is not high to affect the sensor&#39;s reading. As microtrack density increases, however, the strength of the signal in the sensor due to field sources in sidetracks will be high enough to affect the reading of the sensor and cause error. The field strength in a sensor at the position corresponding to MT10 is typically not high enough in a sidetrack to affect reading in the sensor. As the field strength increases for positions corresponding to MT10 through MT50, however, the field strength from sidetracks is strong enough to affect reading in the sensor. Thus, as microtrack density increase such that side tracks are in the MT10-MT50 positions relative to the sensor, the field sources in these sidetracks will introduce error in the sensor&#39;s reading. This “side reading effect” prevents accurate reading of information stored in the microtrack intended to be read. 
     FIG. 4 shows MR sensor  50  in accordance with the present invention. MR sensor  50  includes top shield  52 , bottom shield  54 , first side shield  56 , second side shield  58 , and MR stack  60 . Top and bottom and first and second side shields  52 ,  54 ,  56 , and  58  and MR stack  60  are insulated from each other by reader gaps  61  and  62 . Top and bottom and first and second side shields  52 ,  54 ,  56 , and  58  substantially surround MR stack  60 . First side shield  56  is bordered in certain locations by MR stack  60 , and by reader gaps  61  and  62  thereby defining first and second side shield corners  64  and  66 . Similarly, second side shield  58  is bordered in certain locations MR stack  60  and by reader gaps  61  and  62  thereby defining third and fourth side shield corners  68  and  70 . MR stack  60  in accordance with the present inventions can be any sensor stack, for example, any type of CIP or CPP stack. In FIG. 4 only a spin valve stack is shown for illustrative purposes, which includes pinning layer  72 , pinned layer  74 , ruthenium layer  76 , reference layers  78 , copper spacer  80 , MR element  82 , first sensor end  84  and second sensor end  86 . The unique configuration of MR sensor  50  allows an increase in microtrack density without causing reading errors in MR sensor  50  from sidetracks. 
     MR sensor  50  provides first and second side shields  56  and  58  to decrease the affect from adjacent microtracks as track density increases. MR sensor  50  as shown in FIG. 4 is a cross-sections taken parallel to air bearing surface  32 . When reading from disc  12 , MR sensor  50  and disc  12  move relative to each other such that MR stack  60  moves parallel or longitudinally to microtracks on disc  12 . Thus, top and bottom shields  52  and  54  move down a given microtrack that is to be read. Side shields  56  and  58  are therefore transverse to the microtracks on disc  12 . In this way, side shields  56  and  58  shield MR stack  60  from the affect of sidetracks to the track being read. 
     In MR sensor  50  first and second side shields  56  and  58  are a soft magnetic material and are in direct contact with first and second sensor ends  84  and  86 . First and second sensor ends  84  and  86  are connected by copper spacer  80 . Typically, first and second sensor ends  84  and  86  and copper spacer  80  are made of copper or other material with lower resistance but higher electron reflection ratio in order to enhance the GMR due to GMR side effect. Bias current is sent directly through first and second shields  56  and  58  and through MR element  82  such that changes in resistance in the MR element  82  are detected by sensing voltage changes, as with any AMR, GMR or similar device. 
     FIG. 5 shows MR sensor  50  in accordance with the present invention positioned relative to disc  12 . MR sensor  50  has a lower side that is parallel with the air bearing surface  32  of slider  16 . MR sensor  50  is positioned to be close enough to disc  12  so that magnetic fields extending from disc  12  will go through MR sensor  50 . In FIG. 5, microtrack  34  is shown on disc  12 . Microtrack  34  is one of a large multitude of microtracks on disc  12 . As in FIG. 2, microtrack  34  in FIG. 5 represents a sidetrack relative to MR sensor  50 . In other words, MR sensor  50  is positioned to read a particular microtrack (not shown in FIG. 5) at this point in time and microtrack  34  is an adjacent microtrack, which MR sensor  50  is not intended to read at this point in time. Bit fields within microtrack  34  are magnetized in one direction or the other representing stored information on disc  12 . As disc  12  is rotated relative to MR sensor  50 , magnetic fields radiate radially in all directions from microtrack  34 . MR sensor  50  is provided with first side shield  56  and second side shield  58 . Field lines  36 ,  38 ,  40 ,  42  and  44  are shown extending from microtrack  34 . Instead of field lines  36 ,  38 ,  40 , and  42  extending through MR stack  60 , however, field lines  38 ,  40  and  42  are diverted into first side shield  56 . Only field line  36 , for example, is able to penetrate MR stack  60 . In this way, first side shield  56  greatly decreases the affect that a sidetrack like microtrack  34  has on reading by sensor  50 . This avoids error in reading that would otherwise occur. 
     By adding first and second side shields  56  and  58 , the decay of the media field from sidetracks is enhanced. The solid line in FIG. 6 illustrates the response of MR sensor  50  due to a field source in a microtrack as the relative position of the microtrack and MR sensor  50  changes. Analogous to FIG. 3, the Y-axis in FIG. 6 illustrates the relative strength of the magnetic field in MR sensor  50  due to a field source in the microtrack, while the X-axis represents the radial distance of MR sensor  50  to the microtrack. While the relationship between magnetic field strength at the position of a prior art sensor relative to a microtrack as illustrated in FIG. 3 is described by 1/r 2  (this relationship shown in FIG. 3 is repeated in FIG. 6 as a dotted line above the solid line for ease of comparison), the relationship between magnetic field strength and the position of MR sensor  50  relative to a microtrack is approximated by a decay 1/r 3  (image dipole mixed with exponential decay), where r equals the radial distance between MR sensor  50  edge and the microtrack field source. Thus, MR sensor  50  greatly increases the microtrack transition decay compared to prior sensors. 
     As illustrated by the comparison of the dotted line curve (illustrating response of prior art MR sensor  30 ) and solid line curve (illustrating response of MR sensor  50 ) in FIG. 6, this change in the magnetic field strength to this new decay relationship corresponds to a much smaller MT10 and MT50. Thus, even when microtrack density increases, MT10-MT50 in MR sensor  50  will be decreased so that the affect of sidetracks on signal strength in MR sensor  50  will be greatly decreased. 
     FIG. 7 shows alternative MR sensor  90  in accordance with the present invention. MR sensor  90  includes top/side shield  92 , bottom/side shield  96 , and MR stack  100 . Top/side shield  92  includes top shield region  93  and side shield region  94 , while bottom/side shield  96  includes bottom region  97  and side shield region  98 . Thus, as is readily apparent, top/side shield  92  functions both as a top shield and as a side shield and bottom/side shield  96  functions both as a bottom shield and as a side shield. Top/side shield  92 , bottom/side shield  96 , and MR stack  100  are insulated from each other by reader gap  102 . Top/side shield  92  and bottom/side shield  96  substantially surround MR stack  100 . 
     Top/side shield  92  is bordered by reader gap  102  and by MR stack  100  thereby defining first, second, and third corners  104 ,  106  and  108 . Similarly, bottom/side shield  96  is bordered by reader gap  102  and by MR stack  100  thereby defining fourth, fifth, and sixth corners  110 ,  112  and  114 . MR stack  100  again can be any sensor stack, for example, any kind of CIP or CPP stack. In FIG. 7, only a spin valve stack is shown for illustrative purposes, which includes pinning layer  116 , pinned layer  118 , ruthenium layer  120 , reference layers  122 , copper spacer  124 , MR element  126 , first sensor end  128 , and second sensor end  130 . MR sensor  90  is uniquely configured to allow an increase in microtrack density without causing reading errors in MR sensor  90  from side tracks. 
     MR sensor  90  provides the improve performance characteristics as discussed with respect to MR sensor  50  in FIG.  4 . In MR sensor  90 , top/side shield  92  is an integrated top shield and side shield. Thus, top/side shield  92  provides the known benefits of a top shield, while also providing the inventive benefits of a side shield. Similarly, in MR sensor  90 , bottom/side shield  96  is an integrated bottom shield and side shield. Thus, bottom/side shield  96  provides the known benefits of a bottom shield, while also providing the inventive benefits of a side shield. Top/side shield  92  and bottom/side shield  96  enhance the decay of the media field from sidetracks as did first and second side shields  56  and  58  in MR sensor  50 . Consequently, the response of MR sensor  90  due to a field source in a microtrack as the relative position of the microtrack in MR sensor  90  changes can also be illustrated by the solid line curve in FIG.  6 . 
     MR sensor  90  also provides the advantage of less corner domain formation than MR sensor  50 . In MR sensor  50 , first, second, third, and fourth corners  64 ,  66 ,  68 , and  70  of first and second side shields  56  and  58  are somewhat sharp. In other words, corners  64 ,  66 ,  68 , and  70  are only slightly more than 90 degrees. With such sharp corner regions, first and second side shield  56  and  58  may have domain problems in these areas of the shields. The configuration of MR sensor  90  improves these regions to decrease the domain problems in corner regions of the shields. Specifically, first, second, third, fourth, fifth, and sixth corner regions  104 ,  106 ,  108 ,  110 ,  112 , and  114  are more obtuse, that is, they are significantly larger that 90 degrees. In this way, the domain problems with the sharper corner regions of the first and second side shields  56  and  58  in MR sensor  50  are reduced in MR sensor  90 . 
     FIG. 8 shows another alternative MR sensor  140 , which is based on MR sensor  90 , in accordance with the present invention. MR sensor  140  includes top/side shield  142 , bottom/side shield  146 , and MR stack  150 . Top/side shield  142  includes top shield region  143  and side shield region  144 , while bottom/side shield  146  includes bottom region  147  and side shield region  148 . Thus, as in MR sensor  90 , top/side shield  142  functions both as a top shield and as a side shield and bottom/side shield  146  functions both as a bottom shield and as a side shield. Top/side shield  142 , bottom/side shield  146 , and MR stack  150  are insulated from each other by reader gap  152 . Top/side shield  142  and bottom/side shield  146  substantially surround MR stack  150 . 
     Top/side shield  142  is bordered by reader gap  152  and by MR stack  150  thereby defining first, second, third, fourth, fifth and sixth corners  154 ,  156 ,  158 ,  160 ,  162  and  164 . Similarly, bottom/side shield  146  is bordered by reader gap  152  and by MR stack  150  thereby defining seventh, eighth, ninth, tenth, eleventh, and twelfth corners  166 ,  168 ,  170 ,  172 ,  174  and  176 . MR stack  150  is as described with respect to MR stack  100  in FIG.  7 . 
     MR sensor  140  provides the improve performance characteristics as discussed with respect to MR sensors  50  and  90 . Furthermore, the shield corners that were improved from MR sensor  50  to MR sensor  90  are further improved in Mr sensor  140 . In MR sensor  140 , first through twelfth corners  154 - 176  are all made even more obtuse, that is, they are all closer to 180 degrees than they are to 90 degrees. In this way, the domain problems with the sharper corner regions of the first and second side shields  56  and  58  in MR sensor  50  are reduced in MR sensor  140 . 
     Side shields  56  and  58  in MR sensor  50 , top/side shield  92  and bottom/side shield  96  in MR sensor  90 , and top/side shield  142  and bottom/side shield  146  in MR sensor  140  are typically made of soft magnetic material such as nickel-iron alloy. Consequently, these side shields have low anisotropy and high permeability. These material properties allow the side shields to enhance the microtrack transition decay for each of the MR sensors. 
     MR sensors  50  and  90  as shown in FIGS. 4 and 7 are cross-sections taken parallel to air bearing surface  32 . The dimension of MR sensors  50  and  90  extending perpendicular from air bearing surface  32  is commonly referred to as sensor height. The dimension of MR sensors  50  and  90  extending from one edge of the sensor to the opposite edge is the sensor width. When the sensor height and sensor width are comparable with the MR stack thickness, side shields become particularly important. Side shields can tolerate a higher sensor width to sensor height ratio, and reduce sensor height lapping. This is especially useful for perpendicular or pattern media recording. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.