Abstract:
A disc drive microactuation system finely positions a transducing head carried by a slider adjacent a selected radial track of a rotatable disc. An electromagnetic microactuator having a stator and a rotor operatively connected to the slider is provided on a substrate. The rotor is movable with respect to the stator to effect fine movement of the slider. A magnetic shield layer is provided on the substrate for shielding the electromagnetic microatuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 09/071,790 filed May 1, 1998, now U.S. Pat. No. 6,067,215, entitled “Magnetic Shielding for Electromagnetic Microactuator” by L. Zhang, which in turn claims priority from U.S. Provisional Application No. 60/061,649 filed Oct. 9, 1997, entitled “Side Magnetic Shield Layer for Electromagnetic Micro Actuators” by L. Zhang. 
    
    
     Reference is hereby made to copending U.S. application Ser. No. 09/010,100, now U.S. Pat. No. 6,122,149, filed Jan. 21, 1998, for “Magnetic Microactuator and Inductive Sensor Having Shaped Pole Configuration” by L. Zhang, P. Ryan and P. Crane. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a disc drive microactuator system, and more particularly to a side shield layer for protecting a transducing head from fringe fields generated by the microactuator. 
     The density of concentric data tracks on magnetic discs continues to increase (that is, the radial spacing between data tracks is decreasing), requiring more precise radial positioning of the head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a head on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks. Various microactuator locations and designs have been considered to achieve high resolution head positioning. One promising design involves inserting a silicon-based thin-film structure between the suspension and the slider in the disc drive assembly. The microactuator includes, for example, an electromagnetic transducer having magnetic core materials having a stator and a rotor, with conductive coils wrapped around the stator core in a solenoid-type or planar-type configuration. One example of a high performance electromagnetic microactuator is disclosed in the aforementioned U.S. application Ser. No. 09/010,100, now U.S. Pat. No. 6,122,149, which is hereby incorporated by reference. 
     It is important when implementing an electromagnetic microactuator to ensure that fringe fields from the microactuator do not degrade the performance of the transducing head carried by the disc drive slider over the rotating disc media. Magnetoresistive (MR) heads are sensitive to magnetic fields, and giant magnetoresistive (GMR) heads even more so. Magnetic fields generated by the electromagnetic microactuator can potentially have significant effects on the off-track capability (OTC) performance of MR and GMR heads. The present invention is directed to microactuator systems, such as that described in the Zhang et al. U.S. Pat. No. 6,122,149 to prevent degradation of transducing head performance. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a disc drive microactuation system for finely positioning a transducing head carried by a slider adjacent a selected radial track of a rotatable disc. An electromagnetic microactuator has a stator and a rotor operatively connected to the slider. The rotor is movable with respect to the stator to effect fine movement of the slider. A magnetic shield layer is provided substantially around the periphery of the electromagnetic microactuator for shielding the transducing head from fields generated by the electromagnetic microactuator. In one aspect of the invention, the magnetic shield layer is embedded between the electromagnetic microactuator and the rotatable disc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a disc drive actuation system for positioning a slider over tracks of a disc. 
     FIG. 2 is an exploded perspective view of a portion of the disc drive actuation system shown in FIG. 1, illustrating the relationship between the flexure and the slider. 
     FIG. 3 is a perspective view of a microactuator con figured between the flexure and the slider of a disc drive microactuation system. 
     FIG. 4 is a plan view of a microactuator having a side magnetic shield according to a first embodiment of the present invention. 
     FIG. 5 is a plan view of a microactuator having a side magnetic shield according to a second embodiment of the present invention. 
     FIG. 6 is a plan view of a microactuator having a side magnetic shield according to a third embodiment of the present invention. 
     FIG. 7 is a plan view of a microactuator having a side magnetic shield according to a fourth embodiment of the present invention. 
     FIG. 8 is a plan view of a microactuator having a side magnetic shield according to a fifth embodiment of the present invention. 
     FIG. 9 is a section view of a microactuator having an embedded magnetic shield according to a sixth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a plan view of a disc drive actuation system  10  for positioning slider  24  over a selected track  34  of disc  30 . Actuation system  10  includes voice coil motor (VCM)  12  arranged to rotate actuator arm  16  around axis  14  on spindle  15 . Head suspension  18  is connected to actuator arm  16  at head mounting block  20 . Flexure  22  is connected to head suspension  18 , and carries slider  24 . Slider  24  carries a transducing head (not shown in FIG. 1) for reading and/or writing data on concentric tracks  34  of disc  30 . Disc  30  rotates around axis  32 , so that windage is encountered by slider  34  to keep it aloft a small distance above the surface of the disc  30 . 
     VCM  12  is selectively operated to move actuator arm  16  around axis  14 , thereby moving slider  24  between tracks  34  of disc  30 . However, for disc drive systems with high track density, VCM  12  lacks sufficient resolution and frequency response to position a transducing head on slider  24  precisely over a selected track  34  of disc  30 . Therefor, a higher resolution actuation device is necessary. 
     FIG. 2 is an exploded perspective view of a portion of the disc drive actuation system shown in FIG. 1, showing flexure  22  and slider  24  in more detail. Flexure  22  is mounted to the underside of a distal end of head suspension  18  (FIG.  1 ). Flexure  22  includes arms  22   a  and  22   b  forming aperture  44  therebetween to provide resilience and gimbaling spring to flexure  22 . The distal end of arms  22   a  and( 22   b  are connected by cross beam  45 . Central tongue  48  extends from cross beam  45  into aperture  44  in a plane generally parallel to a plane defined by flexure arms  22   a  and  22   b . The top surface of slider  24  is attached, such as by adhesive, to tongue spring  48 . Transducing head  40  is carried at a trailing edge of slider  24 . 
     FIG. 3 is a perspective view of microactuator  60  configured between flexure  22  and slider  24  in a disc drive microactuation system. Microactuator  60  includes first stator  62  and second stator  64  on substrate  61 , with bond pads  68  providing access to contact first and second stators  62  and  64 . Rotor  66  is formed on substrate  61  between first and second stators  62  and  64 , and is movable with respect to the stators. Flexible arms  72  and  74  extend from the body of the stator portion of microactuator  60  and connect on opposite sides to central tongue  76 , which is attached to a distal end of rotor  66  and is attached to slider  24  by an adhesive, for example. Pre-load force is applied through central tongue  76  to slider  74  at pre-load point  81 . Therefore, operation of microactuator  60  translationally moves rotor  66  with respect to first and second stators  62  and  64 , which in turn forces bending of arms  72  and  74  and alters the position of the central tongue  76 , moving transducing head  40  with respect to flexure  22  in the direction of arrows  78  to radially position head  40  over a radial data track of a rotating disc below slider  24 . A detailed description of the structure and operation of electromagnetic microactuator  60  is provided in the aforementioned Zhang et al. U.S. Pat. No. 6,122,149 incorporated by reference herein. 
     One problem with microactuator  60  is that it produces fringe fields that have potentially degrading effects on the performance of transducing head  40 . FIGS. 4-8 illustrate shielding configurations to reduce the fringe fields at transducing head  40 . FIG. 4 is a plan view of microactuator  60  having a side magnetic shield  100  according to a first embodiment of the present invention. Shield  100  is shaped to surround microactuator  60  except at aperture  102  where rotor  66  is connected to the slider (shown in FIG.  3 ), and has square corners  104  around its perimeter. Shield  100  is formed by conventional magnetic deposition methods such as electroplating and sputtering, preferably by electroplating during the same process in which microactuator  60  is formed. Shield  100  is preferably composed of a material with high magnetic permeability, such as permalloy, so that effective shielding is provided for the relatively low frequencies and field strengths associated with microactuator  60 . If a microactuator using high frequencies and field strengths is implemented, a conductive shield composed of a conductive material such as copper is preferred. 
     FIG. 5 is a plan view of microactuator  60  having a side magnetic shield  110  on substrate  61  according to a second embodiment of the present invention. Shield  110  is shaped to surround microactuator  60  except at aperture  112  where rotor  66  is connected to the slider (shown in FIG.  3 ), and has rounded corners  114  around its perimeter. Shield  110  is formed in substantially the same manner and of substantially the same materials as described above with respect to FIG.  4 . 
     FIG. 6 is a plan view of microactuator  60  having side magnetic shields  120  and  122  on substrate  61  according to a third embodiment of the present invention. Shield  120  is shaped to substantially enclose stator  62 , and shield  122  is shaped to substantially enclose stator  64 , leaving aperture  124  where rotor  66  connects to the slider (shown in FIG. 3) and aperture  126  on the opposite side of rotor  66 . Shields  120  and  122  are formed in substantially the same manner and of substantially the same materials as described above with respect to FIG.  4 . 
     FIG. 7 is a plan view of microactuator  60  having side magnetic shields  130 ,  132 ,  134  and  136  on substrate  61  according, to a fourth embodiment of the present invention. Shields  130  and  132  are located on opposite sides of stator  62 , and shields  134  and  136  are located on opposite sides of stator  64 , leaving, aperture  138  between shields  130  and  134  where rotor  66  connects to the slider (shown in FIG. 3) and aperture  140  between shields  132  and  136  on the opposite side of rotor  66 . Shields  130 ,  132 ,  134  and  136  are formed in substantially the same manner and of substantially the same materials as described above with respect to FIG.  4 . 
     FIG. 8 is a plan view of microactuator  60  having side magnetic shields  150 ,  152  and  154  on substrate  61  according to a fifth embodiment of the present invention. Shields  150  and  152  are located on one side of stators  62  and  64 , respectively, leaving aperture  156  between them where rotor  66  connects to the slider (shown in FIG.  3 ). Shield  154  extends adjacent both stators  62  and  64  oil the side opposite shields  150  and  152 . Shields  150 ,  152  and  154  are formed in substantially the same manner and of substantially the same materials as described above with respect to FIG.  4 . 
     It will be apparent to one skilled in the art that numerous other variations and modifications of the shield configurations shown herein are possible, and are contemplated by the present invention. The arrangements shown in FIGS. 4-8 are exemplary to illustrate the concept introduced by the present invention. The shielding characteristics and processing steps involved vary with each embodiment shown in FIGS. 4-8, but all embodiments provide magnetic shielding of the microactuator in accordance with the principle of the present invention. 
     FIG. 9 is a section view of a microactuator  170  having embedded magnetic shields  180  and  181  according to a sixth embodiment of the present invention, to reduce the fringe field at the disc media below the microactuator. Before stator  62  and rotor  66  are formed on substrate portions  182  and  184 , respectively, shield layers  180  and  181  are formed on respective substrate portions  182  and  184 . Spacer layer  172  is formed between stator  62  and shield  180 , and spacer layer  174  is formed between rotor  66  and shield  181 . The layers of microactuator  170  are formed so that gap  178  between opposing faces of shields  180  and  181  is greater than gap  176  between opposing faces of stator  62  and rotor  66 . This design ensures that shield layers  180  and  181  act as magnetic shields in the vertical direction, rather than as a magnetic relay diverting flux flowing between stator  62  and rotor  66 . Shield layers  180  and  181  may be composed of permalloy, for example, and may be formed by electroplating or an alternative deposition method known in the art. 
     The present invention therefore provides a system to shield a transducing head and/or a disc media from fringe fields created by an electromagnetic microactuator. There are many possible configurations of the shielding layers, with each design limiting the magnetic field strength at the transducing head to an acceptable level. For example, with a microactuator having an air gap between the stator and the rotor of 8 microns, 62 coils wrapped around the stator, a current of 20 milliamps flowing through the coils, and a transducing head located 1650 microns from the center of the stator, the shield layer configuration shown in FIG. 4 reduced the magnetic field strength at the transducing head from 0.30 Oersted (without shielding) to 0.05 Oersted (with shielding), approximately an 83% reduction in fringe field strength at the head. This example illustrates the substantial reductions in fringe field strengths and effects that may be achieved through use of side shielding according to the present invention. 
     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.