Patent Publication Number: US-11393494-B2

Title: Reader with side shields decoupled from a top shield

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. application Ser. No. 16/813,989, filed on Mar. 10, 2020, which published as U.S. Publication No. 2020/0211586 A1, which is a divisional of U.S. application Ser. No. 16/110,701, filed on Aug. 23, 2018, which issued as U.S. Pat. No. 10,614,838 on Apr. 7, 2020, the contents of which are hereby incorporated by reference in their entireties. 
    
    
     SUMMARY 
     The present disclosure relates to read heads or readers having side shields that are decoupled from a top shield. 
     In one embodiment, a reader having a sensor stack and a top shield above the sensor stack is provided. The top shield has an upper surface and a lower surface. The reader also includes at least one side shield below the top shield and adjacent to the sensor stack. The reader further includes a decoupling layer between the upper surface of the top shield and the at least one side shield. The decoupling layer is configured to decouple a first portion of the at least one side shield, proximate to the sensor stack, from at least a portion of the top shield. 
     In another embodiment, a method of forming a reader is provided. The method includes forming a sensor stack, and forming a top shield above the sensor stack. The top shield has an upper surface and a lower surface. The method also includes forming at least one side shield below the top shield and adjacent to the sensor stack. A first portion of the at least one side shield, proximate to the sensor stack, is decoupled from at least a portion of the top shield. 
     In yet another embodiment, a reader is provided. The reader includes a sensor stack and a top shield above the sensor stack. The top shield has an upper surface and a lower surface. The reader also includes at least one side shield below the top shield and adjacent to the sensor stack. The at least one side shield has a first portion that is proximate to the sensor stack and a second portion that is away from the sensor stack. The second portion of the at least one side shield is coupled to the top shield. A decoupling layer is included between the upper surface of the top shield and the first portion of the at least one side shield. 
     Other features and benefits that characterize embodiments of the disclosure will be apparent upon reading the following detailed description and review of the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a data storage system including a data storage medium and a head for reading data from and/or writing data to the data storage medium. 
         FIG. 2  is a schematic diagram of a cross-section of one embodiment of a recording head that reads from and writes to a storage medium. 
         FIG. 3A  is a bearing surface view of a read head in accordance with one embodiment. 
         FIG. 3B  is a cross-sectional view of the read head of  FIG. 3A . 
         FIG. 4A  is a bearing surface view of a read head in accordance with another embodiment. 
         FIG. 4B  is a cross-sectional view of the read head of  FIG. 4A . 
         FIGS. 5A, 5B, 6A and 6B  are bearing surface views of still other read head embodiments. 
         FIG. 7  is a flow diagram of a method embodiment. 
         FIGS. 8A and 8B  are plots of results obtained using a reader of the type shown in any one of  FIGS. 3A-6B . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Cross track resolution of a reader is characterized by MT10, which is a distance between two positions on opposite sides of a narrow track or micro track (MT) on a data storage medium at which a sensed signal strength decreases to 10% of its maximum. MT10/MT50 (MT50 being a distance between two positions on opposite sides of a MT on a data storage medium at which a signal strength decreases to 50% of its maximum) directly impacts an areal density capability of a data storage device such as a disc drive. Cross track resolution of the reader depends on magnetic characteristics of side shields of the reader. In certain embodiments, the softer the side shields, the better the reader resolution. Embodiments of the disclosure improve the softness of the side shields and thus improve MT10 and MT10/MT50. However, prior to providing additional details regarding the different embodiments, a description of an illustrative operating environment is provided below. 
     It should be noted that like reference numerals are used in different figures for same or similar elements. It should also be understood that the terminology used herein is for the purpose of describing embodiments, and the terminology is not intended to be limiting. Unless indicated otherwise, ordinal numbers (e.g., first, second, third, etc.) are used to distinguish or identify different elements or steps in a group of elements or steps, and do not supply a serial or numerical limitation on the elements or steps of the embodiments thereof. For example, “first,” “second,” and “third” elements or steps need not necessarily appear in that order, and the embodiments thereof need not necessarily be limited to three elements or steps. It should also be understood that, unless indicated otherwise, any labels such as “left,” “right,” “front,” “back,” “top,” “bottom,” “forward,” “reverse,” “clockwise,” “counter clockwise,” “up,” “down,” or other similar terms such as “upper,” “lower,” “aft,” “fore,” “vertical,” “horizontal,” “proximal,” “distal,” “intermediate” and the like are used for convenience and are not intended to imply, for example, any particular fixed location, orientation, or direction. Instead, such labels are used to reflect, for example, relative location, orientation, or directions. It should also be understood that the singular forms of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. 
       FIG. 1  shows an illustrative operating environment in which certain specific embodiments disclosed herein may be incorporated. The operating environment shown in  FIG. 1  is for illustration purposes only. Embodiments of the present disclosure are not limited to any particular operating environment such as the operating environment shown in  FIG. 1 . Embodiments of the present disclosure are illustratively practiced within any number of different types of operating environments. It should be noted that the same reference numerals are used in different figures for same or similar elements. 
       FIG. 1  is a schematic illustration of a data storage device  100  including a data storage medium and a head for reading data from and/or writing data to the data storage medium. In data storage device  100 , head  102  is positioned above storage medium  104  to read data from and/or write data to the data storage medium  104 . In the embodiment shown, the data storage medium  104  is a rotatable disc or other magnetic storage medium that includes a magnetic storage layer or layers. For read and write operations, a spindle motor  106  (illustrated schematically) rotates the medium  104  as illustrated by arrow  107  and an actuator mechanism  110  positions the head  102  relative to data tracks  114  on the rotating medium  104  between an inner diameter  108  and an outer diameter  109 . Both the spindle motor  106  and actuator mechanism  110  are connected to and operated through drive circuitry  112  (schematically shown). The head  102  is coupled to the actuator mechanism  110  through a suspension assembly which includes a load beam  120  connected to an actuator arm  122  of the mechanism  110  for example through a swage connection. Although  FIG. 1  illustrates a single load beam coupled to the actuator mechanism  110 , additional load beams  120  and heads  102  can be coupled to the actuator mechanism  110  to read data from or write data to multiple discs of a disc stack. The actuator mechanism  110  is rotationally coupled to a frame or deck (not shown) through a bearing  124  to rotate about axis  126 . Rotation of the actuator mechanism  110  moves the head  102  in a cross track direction as illustrated by arrow  130 . 
     The head  102  includes one or more transducer elements (not shown in  FIG. 1 ) coupled to head circuitry  132  through flex circuit  134 . Details regarding elements of a head such as  102  are provided below in connection with  FIG. 2 . 
       FIG. 2  is a schematic diagram showing a cross-sectional view of portions of a recording head  200  and a data storage medium  250  taken along a plane substantially normal to a plane of a bearing surface (for example, an air bearing surface (ABS))  202  of recording head  200 . The recording head elements shown in  FIG. 2  are illustratively included in a recording head such as recording head  102  in  FIG. 1 . Medium  250  is illustratively a data storage medium such as medium  104  in  FIG. 1 . Those skilled in the art will recognize that recording heads and recording media commonly include other components. Embodiments of the present disclosure are not limited to any particular recording heads or media. Embodiments of the present disclosure may be practiced in different types of recording heads and media. 
     Recording head  200  includes a write pole  205 , a magnetization coil  210 , a return pole  215 , a top shield  218 , a read transducer  220 , a bottom shield  222  and a wafer overcoat  224 . Storage medium  250  includes a recording layer  255  and an underlayer  260 . Storage medium  250  rotates in the direction shown by arrow  265 . Arrow  265  is illustratively a direction of rotation such as arrow  107  in  FIG. 1 . 
     In an embodiment, electric current is passed through coil  210  to generate a magnetic field. The magnetic field passes from write pole  205 , through recording layer  255 , into underlayer  260 , and across to return pole  215 . The magnetic field illustratively records a magnetization pattern  270  in recording layer  255 . Read transducer  220  senses or detects magnetization patterns in recording layer  255 , and is used in retrieving information previously recorded to layer  255 . 
     As will be described in detail further below, read transducer  220  has multiple layers including a sensing layer or free layer. The layers of the read transducer  220  may be stacked along a track direction (e.g., a z-direction in  FIG. 2 ) or a track width direction that is perpendicular to the track direction (e.g., a cross-track direction, which is an x-direction in  FIG. 2 ). A y-direction in  FIG. 2  is then defined as a direction that is perpendicular to x and z simultaneously, which is a stripe-height direction. As indicated earlier, side shields (not shown in  FIG. 2 ) are also included on either side of read transducer  220 . Also, as noted above, embodiments of the disclosure improve the softness of the side shields and thus improve MT10 and MT10/MT50. In different embodiments, which are described further below in connection with  FIGS. 3A-6B , the side shields are completely or partially decoupled form the top shield  218  or from an upper part of the top shield  218 . Element  230  (shown with dashed lines in  FIG. 2 ) represents a decoupling layer that is positioned to decouple the side shields (not shown in  FIG. 2 ) from the top shield  218 . Complete or partial decoupling the side shields from the top shield  218  makes the side shields softer, which improves their shielding characteristics and thus improves cross track resolution of the reader. 
       FIG. 3A  is a schematic block diagram showing a bearing surface view of a read head  300  including side shields that are at least partially decoupled in accordance with one embodiment. Read head  300  includes a magnetoresistive sensor  302  that is positioned between top shield  218  and bottom shield  222 . Top and bottom shields  218  and  222 , which may include a material having high magnetic permeability, reduce or substantially block extraneous magnetic fields, such as, for example, those from adjacent bits on data discs from impacting the magnetoresistive sensor  302 , thus improving the performance of the magnetoresistive sensor  302 . In one implementation, the top and bottom shields  218  and  222  permit magnetic fields from the bit directly under magnetoresistive sensor  302  to affect the magnetoresistive sensor  302 , and thus be read. 
     The magnetoresistive sensor  302  includes a plurality of layers including a sensor stack synthetic antiferromagnetic (SAF) structure  306 , a spacer layer  308  and a free layer or sensing layer  310 . In certain embodiments (not shown), free layer  310  may be a multi-layered structure. A stack cap layer (not shown) may also be included above the free layer. A sensor antiferromagnetic (AFM) layer  304  may optionally be included in some embodiments. Also, an SAF shielding structure  314  may optionally be included above the free layer  310  (or above the stack cap layer (not shown)). Thus, top shield  218  may include a single pinned layer  218 A or may include multi-layered SAF structure  314 . Dashed lines are used to represent elements within structure  314  to indicate that structure  314  is optional. Also, dashed lines are used to indicate that AFM layer  304  is optional. 
     In the embodiment shown in  FIG. 3A , the sensor SAF structure  306  includes a pinned layer  316  a thin separation layer  318 , which may comprise a metal such as ruthenium (Ru) in some embodiments, and a reference layer  320 . The magnetic moments of each of the pinned layer  316  and the reference layer  320  are not allowed to rotate under magnetic fields in the range of interest (for example, magnetic fields generated by the bits of data stored on the data discs). The magnetic moments of the reference layer  320  and the pinned layer  316  are generally oriented normal to the plane (e.g., the y direction) of  FIG. 3A  and anti-parallel to each other. 
     The magnetic moment of the free layer  310  is free to rotate under the influence of an applied magnetic field in a range of interest. The read head  300  further includes side shields  322 , which reduce or substantially block extraneous magnetic fields, such as, for example, those from bits on adjacent tracks from impacting the magnetoresistive sensor  302 . Further, side shields  322  may produce a magnetic field that biases the free layer  310  with a magnetic moment parallel to the plane of the figure and generally oriented horizontally. The bias is sufficiently small, however, that the magnetic moment of the free layer  310  can change in response to an applied magnetic field, such as a magnetic field of a data bit stored on the data discs. In some embodiments, the side shields  322  are formed of soft magnetic material (e.g., material that can be easily magnetized and demagnetized at relatively low magnetic fields). The soft magnetic material may be an alloy comprising Ni and Fe. The magnetoresistive sensor  302  is separated and electrically isolated from the side shields  322  by an isolation layer  324  including, for example, insulating materials. Isolation layer  324  may also be present in other regions of head  300  as shown in  FIG. 3A . 
     In the embodiment shown in  FIG. 3A , optional SAF shielding structure  314  includes a SAF shield reference layer  326 , a thin SAF shield separation layer  328 , which may comprise a metal such as Ru in some embodiments, a SAF shield pinned layer  330  and a SAF shield AFM layer  332 . In some embodiments, SAF shield reference layer  326  may have a relatively fixed magnetization to assist in stabilizing the magnetizations of side shields  322 . Thus, AFM layer  332  pins the magnetization of layer SAF shield pinned layer  330  substantially parallel to the bearing surface, which results in the relatively fixed magnetization of SAF shield reference layer  326  due to antiferromagnetic coupling across SAF shield separation layer  328  and thus in stabilizing the magnetizations of the side shields  322  substantially parallel to the bearing surface as well. SAF shield reference layer  326  and SAF shield pinned layer  330  may be formed of a soft magnetic material (for example, an alloy comprising Ni and Fe). 
     As noted above, side shields  322  are at least partially decoupled from top shield  218 . Accordingly, a decoupling layer  334  is included between the top shield  218  and the side shield  322 . The dashed portions in decoupling layer  334  indicate that the layer  334  may or may not be present in those portions between side shields  322  and top shield  218 . 
       FIG. 3B  illustrates a sectional side view of read head  300  taken along section AA′, which shows decupling layer  334  behind the bearing surface. As can be seen in  FIG. 3B , a stripe height of the decoupling layer  334  may be different in different embodiments as shown by the rear dashed portion of layer  334 . Thus, in different embodiments, the top shield  218  may be either partially of completely decoupled from the side shield  322  in the stripe height direction. 
     Decoupling layer  334  may be formed of, for example, ruthenium or tantalum and may be about 2 nm thick in order to achieve decoupling in some embodiments. It should be noted that, in certain embodiments, layer  334  may be greater than 2 nm to achieve proper decoupling. Further, in some embodiments, layer  334  may be less than 2 nm. In such embodiments, a level of decoupling may be reduced, but stability of the side shield  322  magnetization may be improved. 
     Referring back to  FIG. 3A , in some embodiments, sensor  302  may utilize tunnel magnetoresistance (TMR) or giant magnetoresistance (GMR) effects. In embodiments that utilize TMR effects, spacer layer  308  is a tunneling barrier layer that separates the SAF structure  306  from the free layer  310 . The tunneling barrier layer  308  is sufficiently thin that quantum mechanical electron tunneling occurs between a reference layer  320  in the SAF structure  306  and the free layer  310 . The electron tunneling is electron-spin dependent, making the magnetic response of the magnetoresistive sensor  302  a function of the relative orientations and spin polarizations of the SAF structure  306  and the free layer  310 . The highest probability of electron tunneling occurs when the magnetic moments of the SAF structure  306  and the free layer  310  are parallel, and the lowest probability of electron tunneling occurs when the magnetic moments of the SAF structure  306  and the free layer  310  are antiparallel. Accordingly, the electrical resistance of the magnetoresistive sensor  302  changes in response to an applied magnetic field. The data bits on the data discs in the disc drive may be magnetized in a direction normal to the plane of  FIG. 3A , either into the plane of the figure, or out of the plane of the figure. Thus, when the magnetoresistive sensor  302  passes over a data bit, the magnetic moment of the free layer  310  is rotated either into the plane of  FIG. 3A  or out of the plane of  FIG. 3A , changing the electrical resistance of the magnetoresistive sensor  302 . The value of the bit being sensed by the magnetoresistive sensor  302  (for example, either 1 or 0) may therefore be determined based on the current flowing from a first electrode (not shown) to a second electrode (not shown) connected to the magnetoresistive sensor  302 . 
       FIG. 4A  is a schematic block diagram showing a bearing surface view of a read head  400  including side shields that are at least partially decoupled from an upper portion of the top shield in accordance with one embodiment. The elements of read head  400  are substantially similar to the elements of read head  300  of  FIGS. 3A and 3B  and therefore same or like reference numerals are used in  FIG. 4A  for the same or similar elements. Read head  400  differs for read head  300  (of  FIGS. 3A and 3B ) in that decoupling layer  334  is positioned within top shield  218  (e.g., within SAF shield reference layer  326 ) such that side shields  322  and a relatively thin lower part of the top shield  218  are partially or completely decoupled from the remainder of the top shield  218 .  FIG. 4B  illustrates a sectional side view of read head  400  taken along section BB′, which shows decupling layer  334  behind the bearing surface. As can be seen in  FIG. 4B , a stripe height of the decoupling layer  334  may be different in different embodiments as shown by the rear dashed portion of layer  334 . Thus, in different embodiments, side shields  322  and the relatively thin lower part of the top shield  218  are partially or completely decoupled from the remainder of the top shield  218  in the stripe height direction. 
       FIGS. 5A, 5B, 6A and 6B  illustrate read head embodiments in which no SAF structure is included in the top shield.  FIG. 5A  illustrates a read head  500  embodiment in which side shields  322  are completely decoupled from top shield  218 . Thus, decoupling layer  534  completely separates the top shield  218  from the side shields  322 .  FIG. 5B  illustrates a read head  550  embodiment in which side shields  322  are partially decoupled from top shield  218 . In read head  550 , decoupling layer  534  is included only in a vicinity of a junction of the side shield  322  and the sensor stack including free layer  310 . Thus, a first portion  322 A of the side shield  322  is decoupled from the top shield  218  and a second portion  322 B of the side shield  322  is coupled to the top shield  218 . 
       FIG. 6A  illustrates a read head  600  embodiment in which side shields  322  and a substantially thin lower part of the top shield  218  are completely decoupled from the remaining part of the top shield  218  by decoupling layer  634 . Accordingly, in read head  600 , decoupling layer  634  is between an upper surface  603  of the top shield  218  and a lower surface  605  of the top shield  218 .  FIG. 6B  illustrates a read head  650  embodiment in which side shields  322  and a substantially thin lower part of the top shield  218  are partially decoupled from the remaining part of the top shield  218  by decoupling layer  634 . Thus, in read head  650 , decoupling layer  634  is included only in a vicinity of a junction of the side shield  322  and the sensor stack  302 . 
       FIG. 7  is a flow diagram of a method  700  embodiment. The method includes, at block  702 , forming a sensor stack. At block  704 , a top shield is formed above the sensor stack. The top shield has an upper surface and a lower surface. The method also include, at block  706 , forming at least one side shield below the top shield and adjacent to the sensor stack. The method further includes, at block  708 , decoupling a first portion of the at least one side shield, proximate to the sensor stack, from at least a portion of the top shield. 
     In some of embodiments described above, width and/or stripe height dimensions of the decoupling layer may be different from the width and/or stripe height dimensions of the top shield and/or the side shields. In such embodiments, masks may be employed to implement the desired structures. 
       FIG. 8A  is a MT10 versus side shield-top shield decoupling length plot  800  for a read head having a reader width of 24 nm. In  FIG. 8A , a vertical axis  802  represents MT10 in nm and a horizontal axis  804  represents decoupling length in nm.  FIG. 8B  is a MT10/MT50 versus side shield-top shield decoupling length plot  806  for a read head having a reader width of 24 nm. In  FIG. 8A , a vertical axis  808  represents MT10/MT50 the horizontal axis  804  is the same as in  FIG. 8A . As can be seen in the example of  FIGS. 8A and 8B , for side shields decoupled at the junction of the side shields and the sensor stack, a full gain is achieved at 20 nm decoupling length. Thus, the embodiments described above provide an improvement in cross track resolution of the reader, which improves the areal density capability of the data storage device (e.g., disc drive). 
     The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be reduced. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive. 
     One or more embodiments of the disclosure may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description. 
     The Abstract of the Disclosure is provided to comply with 37 C.F.R. § 1.72(b) and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments employ more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. 
     The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.