Abstract:
A flying optical head assembly for a magneto-optical data storage device includes a slider body mounting an optical element having a narrowed optical aperture extending through a location of the slider body, a recessed region surrounding the location passing the optical aperture, a magnetic pole sheet layer for heat dissipation and reduced magnetic reluctance formed in the recessed region and having an insulation layer and an opening for the optical aperture, and a magnetic bias coil formed on the insulation layer and surrounding the narrowed optical aperture. When formed of electrically conductive material, the sheet layer includes at least one radial slot for preventing a single turn short circuit in direct proximity to the coil. Multiple slots are preferred for bonding and to reduce eddy currents.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to head design for an optical data storage system. More particularly, the present invention relates to a flying head assembly carrying e.g., a solid immersion lens having a light-beam mesa surrounded by a thin film electromagnetic coil and a field enhancing pole structure for concentrating the electromagnetic flux from the coil toward an underlying storage location of a magneto-optical storage medium over which the flying head assembly is passing for data storage and retrieval. The pole structure may also perform a thermal spreading function in order to remove heat from the mesa and coil, and medium adjacent thereto. 
     BACKGROUND OF THE INVENTION 
     New optical recording technologies, such as near field recording, require that an optical element, such as a solid immersion lens (“SIL”), present an optical aperture in very close proximity to an optical medium. Accordingly, placing the SIL onto a slider body which flies above a storage medium upon an air bearing achieves desired proximity. Examples of air bearing slider bodies are provided by U.S. Pat. No. 5,497,359 to Mamin et al., entitled: “Optical Disk Data Storage System with Radiation-Transparent Air-Bearing Slider”, and U.S. Pat. No. 5,729,393 to Lee et al., entitled: “Optical Flying Head with Solid Immersion Lens having Raised Central Surface Facing Medium”, the disclosures thereof being incorporated herein by reference. 
     Rewritable optical storage may be implemented with phase change media, and it may be implemented with magneto-optical (“MO”) media. In the case of MO media a recording layer presents very stable magnetic domain states at room temperature. However, when a storage site is heated (e.g. by laser light energy) to a temperature beyond a characteristic temperature, known as the Curie temperature, all memory of a prior magnetization polarity or state is lost. As this site cools to below the Curie temperature it assumes a magnetization state determined by a residual magnetic field, usually supplied by an external bias electromagnet. One example of an optical flying head having an external bias electromagnet is provided by commonly assigned U.S. Pat. No. 5,105,408 to Lee et al., entitled: “Optical Head with Flying Lens”, the disclosure thereof being incorporated herein by reference. In this prior approach the bias coil was formed as a printed microcircuit carried on a surface of the slider body facing the storage medium and having a central opening through which laser light energy passes from the lens While locating the coil in the manner described in U.S. Pat. No. 5,105,408 enables a field to be directed toward the storage site whose magnetic state is to be changed, the approach suffers from a number of drawbacks. 
     One drawback of this prior approach is that for a given driving current fully one half of the resultant magnetic field volume generated by the prior coil extended upwardly through the non-magnetic slider body and away from the storage medium. This condition uselessly added to the Amp*Turn requirement for a given magnetic field strength in the storage medium. Prior attempts at overcoming this drawback have been to provide multiple layers of thin-film coil windings, which adds further complexity and delicacy to an already complex and delicate manufacturing process. Another related drawback was that be cause the coil was inefficient in delivering flux at desired concentration to the storage medium, a higher driving current resulted in the generation of unwanted heat which results in undesirable thermal gradients within the head structure and may result in off-track operation of the optical drive mechanism. These drawbacks are overcome by the present invention. 
     SUMMARY OF THE INVENTION WITH OBJECTS 
     One object of the present invention is to provide a layer of nickel-iron alloy material directly between the coil and the slider body which reduces magnetic reluctance and increases flux density directed toward the storage medium in ways overcoming limitations and drawbacks of the prior art. 
     Another object of the present invention is to enable production and usage of a simpler-to-produce single layer thin f bias coil structure within a flying head assembly. 
     A further object of the present invention is to improve the thermal transfer characteristics of an optical flying head assembly having a thin film bias coil structure. 
     In accordance with one aspect of the principles of the present invention, a flying optical head assembly is provided for an optical data storage system including a magneto-optical data storage medium. The assembly has a slider body flexibly suspended above said medium on an air bearing, and an optical element mounted to the slider body and having a narrowed optical aperture extending through a location of the slider body. The slider body defines a recessed region surrounding the location passing the optical aperture. A magnetic pole sheet layer is formed in the recessed region and has an insulation layer and an opening for the optical aperture; and, a generally spiral magnetic bias coil is formed on the insulation layer and surrounding the narrowed optical aperture. The magnetic pole sheet layer desirably reduces magnetic reluctance and results in greater flux concentration reaching the magneto-optical data storage medium. Also, the magnetic pole sheet layer may include a thermally conductive material and thereby serve as a heat sink and spreader which spreads heat otherwise generated at the optical aperture/bias coil location (either in the coil or due to media or lens heating by the laser beam) more effectively than heretofore. 
     In accordance with a second aspect of the principles of the present invention, a flying optical head assembly is provided for an optical data storage system including a magneto-optical data storage medium. The assembly includes a slider body flexibly suspended above said medium on an air bearing, and an optical element mounted to the slider body and having a narrowed optical aperture extending through a location of the slider body. The slider body defines a region of ferromagnetic pole material surrounding the location passing the optical aperture. A thermally conducting heat spreading structure is attached to the slider body at the region and has an insulation layer and an opening for the narrowed optical aperture. A generally spiral magnetic bias coil is fixed on the insulation layer and surrounds the narrowed optical aperture. 
     In accordance with a third aspect of the principles of the present invention, an optical disk drive data storage system includes a flying optical head assembly for flying over a data storage surface of a rotating magneto-optical data storage disk upon an air bearing, and also includes a voice coil actuator and suspension assembly for positioning the flying optical head radially relative to the data storage surface. The flying optical head assembly has a slider body flexibly suspended above the disk on an air bearing and supports an objective lens and a light-direction-changing mirror assembly. A solid immersion lens optical element is mounted to the slider body and has a narrowed optical mesa extending through a location of the slider body in general alignment with a light path formed by the mirror assembly and the objective lens and further has a surface generally coplanar with air bearing surfaces of the slider body. The slider body defines a recessed region surrounding the location passing the optical mesa. A multi-layer magnetic pole-providing and heat-spreading structure is formed in the recessed region and has an outer insulation layer surrounding an opening for the narrowed optical aperture. A generally spiral magnetic bias coil is patterned and deposited onto the insulation layer and surrounds the narrowed optical aperture. In this aspect of the invention the multi-layer magnetic pole-providing and heat-spreading structure preferably comprises a first layer of nickel-iron alloy, a second layer of copper alloy, and a third layer of nickel-iron alloy, and further comprises a series of circumferentiauly spaced apart radial slots defined in the structure, and further comprises a bonding agent present in each slot for bonding the magnetic pole-providing and heat-spreading structure to the slider body and for reducing eddy currents and a single-turn short in close proximity to the magnetic bias coil. 
    
    
     These and other objects, advantages, aspects, and features of the present invention will be more fully appreciated and understood upon consideration of the following detailed description of preferred embodiments presented in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Drawings: 
     FIG. 1 is a highly diagrammatic view in elevation of an optical data storage device including a flying optical head assembly including a magnetic pole sheet layer in accordance with principles of the present invention. 
     FIG. 2 is an enlarged air bearing surface plan view of the FIG. 1 flying optical head assembly showing a series of radially extending slots in the magnetic pole sheet layer of the FIG. 1 structure in order to promote attachment of the layer to the slider and to reduce eddy current losses in the magnetic pole structure. 
     FIG. 3 is a greatly enlarged, diagrammatic view in end elevation and section (taken along line  3 — 3  in FIG. 2) of the FIG. 1 flying optical head assembly showing the magnetic pole sheet layer in relation to the slider body, lens, and bias coil structure. 
     FIG. 4 is a greatly enlarged portion of the FIG. 3 view showing a laminar structure forming the magnetic pole sheet layer. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-4, where like characters designate like or corresponding parts throughout the views, an optical storage device  10  includes a base or frame  12 , a spindle  14  which rotates at an angular velocity relative to the base  12 , an optical data storage disk  16  mounted to the spindle  14 , a flying optical head  18  including an air bearing slider body  20 , a solid immersion lens (SIL)  22 , an objective lens  24 , and a mirror unit  26 . A voice coil controlled actuator  28  shown diagrammatically as a linear actuator, but in practice either a rotary actuator or a linear actuator, controllably positions the flying optical head  18  relative to circular track locations defined on a confronting surface of the data storage disk  16 . A solid state laser light source  30  generates coherent light energy and directs that light toward the mirror unit  26  of the flying optical head  18 . Other elements including the optical data detection path and optical head position servo control path, are not shown because they are not particularly pertinent to an understanding of the present invention; however, these other elements, well understood by those skilled in the art, are present in the optical drive  10 . In the presently preferred example, the optical drive  10  employs magneto-optical principles. 
     Turning to FIG. 2, the slider body  20 , preferably formed of a suitable hard ceramic material, such as aluminum oxide ceramic (Al 2 O 3 ), includes e.g. two longitudinal rails  32  defining highly polished air bearing surfaces  34  and having slightly beveled regions  36  along a leading edge. The air bearing surfaces  34  may have known geometries and features such that the slider body  20  will have a controlled small flying height above a data storage surface of the disk  16  as the disk is rotated by the spindle  14  at a controlled angular velocity. (The surfaces  34  may be controlled to create a negative pressure, or a positive pressure, air bearing, as is well understood in the air bearing slider art). 
     A central region  38  of the slider body  20  between the rails  32  includes a recess  40  which may be suitably etched or otherwise formed to present a flat major surface generally parallel to the air bearing surfaces presented by the rails  32 . A light portal or mesa  50  of a flying optical lens element, such as the SEL  22 , extends through an appropriately sized and shaped opening of the slider body in a central part of the recess  40 . The recess  40  may be rectangular or square, or it may be circular or have any other desired shape. The mesa  50  is an integral part of the SIL  22 , and in one example is rectangular and has a longitudinal dimension (relative to slider body  20 ) of 42 μm (1.7 mils) and a transverse dimension of 75 μm (3 mils). 
     A magnetic bias coil  52  comprises at least one layer of thin film conductive metal deposition which has been suitably patterned and formed to surround the mesa  50  as a generally spiral continuous trace. The bias coil  52  connects to two widened terminal pads  54  which enable the coil  52  to be connected to external driver circuitry by connections made at a trailing edge of the slider body  20 . A beveled region  56  may be formed adjacent the trailing edge to facilitate these electrical connections to an external electrical circuit. 
     A via and buried path structure  58  connect one of the pads to an inner end of the coil winding in conventional fashion. So far, the flying optical head assembly is conventional. It is conventionally suspended by a load beam, suspension assembly from the linear or rotary actuator  28 , such that it may be precisely positioned at a storage track or location being followed for data writing or read back, and it may be displaced from a departure location to a destination location by a head positioning actuator assembly, also conventional, and not further described herein. 
     Returning to the slider body  20 , in accordance with principles of the present invention a magnetic pole-forming sheet layer  60  is deposited directly to the slider body  20 , or otherwise suitably attached to the slider body  20 , within the recess  40 , and occupies most of the space defined by the recess  40 . As shown in FIGS. 3 and 4, the sheet layer  60  is preferably formed as a composite laminar deposition of a first layer  62  of nickel-iron alloy (NiFe), a second layer  64  of copper (Cu), and a third layer  66  of NiFe. An insulative and encapsulation layer  68 , for example of aluminum oxide (Al 2 O 3 ), is formed over the third layer  66  and exposed edges of layers  62  and  64 . The turns of the coil  52  are deposited onto the encapsulation layer  68 . Following formation of the turns of coil  52  a second encapsulation layer  70  may be deposited over the coil windings to protect them mechanically and from any oxidizing influences present in the operational ambient environment. 
     As shown in FIG. 2 the magnetic pole sheet layer  60  may be separated into radial sectors or segments by a pattern of radially extending narrow slots  72 . While eight slots are shown in the FIG. 2 example, a greater number of slots is generally preferred, such as 16 or 24 slots, or more, depending upon the particular design, manufacturing capability and space available. These slots  72 , if extended to the optical mesa  50 , effectively reduce eddy currents otherwise generated within the magnetic pole sheet layer  60 , and they also provide access points enabling the aluminum oxide encapsulation layer  68  to make a positive mechanical bond to the slider body  20  within the recess  40 , thereby positively securing the magnetic pole sheet layer  60  to the slider body  20 . 
     The SIL  22  having the light aperture or mesa  50  is secured in a suitably contoured recess defined in the slider body  20 , as best shown in FIG. 3. A suitable bonding medium, such as low temperature glass, is emplaced and cured as a narrow layer  74  between the SIL  22  and the slider body  20 . This layer  74  secures the SIL  22  to the slider body  20 , and it also provides a heat conduction path for conducting heat generated within the SIL  22  by passage therethrough of a laser light beam having a suitable energy to erase/write a thin film MO storage medium formed in the rotating optical disk  16  shown in FIGS. 1 and 3 in close proximity to the ABS  34  of slider body  20  including optical mesa  50  of SIL  22 . 
     By placing the sheet  60  of magnetic pole material above the bias coil  52 , the reluctance at this part of the magnetic path is greatly reduced. The required number of amp-turns is nearly cut in half. (The gain would be precisely twice were there no opening for optical mesa  50 ). The required power with the same coil  52  with the magnetic pole sheet layer  60  is reduced by almost four times over a similar coil structure without the magnetic pole sheet layer  60 . However, the inductance would be nearly doubled, so the inductive voltage spike is reduced by nearly times two (V=L(di/dt)=2 * 0.25=0.5). 
     A conventional two-layer coil structure can therefore be reduced to a single layer spiral coil, such as coil  52 , which is simpler and more reliable to manufacture. In this event the net inductance is reduced by more than times two and the required driving current is slightly higher. The net power requirement (and consequent thermal load effect) is reduced by nearly one half over the prior two-layer design. 
     In addition to these performance advantages, the new head design can also be produced by following a more simplified process. It is easier to deposit a magnetic sheet layer  60  than it is to deposit and pattern a coil layer plus insulating layers above and below the coil. A simplified manufacturing process for forming the improved optical flying head includes the following steps: 
     A. Form the air bearing surface of the slider  20  including ABS surfaces  34  and the central portion  38 . 
     B. Photo pattern and etch the recessed cavity region  40 , and beveled region  56  for bonding pads  54  into the defined air bearing surface side of the slider  20 . 
     C. Sputter deposit NiFe plating seed, photo pattern and plate the magnetic pole NiFe sheet layer  62  (two units thickness), the copper layer  64  (a single unit thickness) and the lower pole NiFe sheet layer  66  (two units thickness). 
     D. Sputter deposit the aluminum oxide insulating gap layer  68  (a single unit thickness). 
     E. Photo pattern and etch two electrical vias through the aluminum oxide layer  68  for interconnect bridge  58 . 
     F. Deposit copper seed, photo pattern and plate the coil  52 , electrical interconnection bridge  58 , a coil centertap connection to the magnetic pole sheet layer, and the connection pads  54 , and then sputter etch away the seed layer outside of the patterned coil, interconnect and pad areas. 
     G.Encapsulate the coil structure with the aluminum oxide layer  70  and then lap the structure flat and parallel with the ABS rails  32 . 
     This approach includes a copper heat sink layer  64  in the center of the nickel-iron pole structure. This copper layer  64  will conduct heat out of the coil caused by the driving current, and heat out of the center region at the optical aperture  50  caused by laser heating of the media (and any heating of the SIL itself). Under certain circumstances it may be found desirable or necessary to “live” plate the nickel-iron and copper layers  62 ,  64  and  66 . This means that the plating voltage is present while the slider wafer is inserted into a plating bath, so that the corrosive plating bath does not corrode away the previous layer before it becomes covered by the next layer. It should also be observed that the pole/heat sink structure  60  may be more readily deposited by sputtering through a metal mask or by sputtering layers followed by subsequent ion etching through a mask. These latter approaches produce sloped edges of the layers  62 ,  64  and  66  and turns of coil  52  which are more readily covered by the aluminum oxide encapsulation layer. 
     Other arrangements may be used which are within the spirit and scope of the present invention. For example, the slider body may be formed of a suitable ferromagnetic ceramic material such that the slider body provides the magnetic pole. In this case, the thermal spreading sheet structure  60  could be fabricated out of a suitable, thermally conductive, non-magnetic material, such as copper or aluminum. However, if an electrically conductive thermal spreading sheet layer is used, it is important to include at least one of the slots  72  to prevent a single shorting turn to be present in directly proximity to the coil  52 , particularly in the case of high frequency bias currents needed for high speed writing. 
     Alternative magnetic materials may be used to form the sheet pole  60 . One example is METGLAS™ amorphous magnetic alloy offered by Allied Signal Corporation. This particular material has excellent magnetic pole properties while presenting a high electrical resistance, thereby reducing the need for the eddy current, single turn eliminating slots  72 . Also, those skilled in the art will appreciate that the sheet structure  60  may be formed as a discrete unit structure carrying the coil  52  and pads  54  with suitable insulating layers, such that the resultant unitary structure is bonded or otherwise suitably attached to the slider body  20  in the recess  40  by e.g. low temperature glass bonding techniques known in the art. 
     It is to be understood that the particular implementations described are intended as illustrations of, and not as limiting the scope of, the claims. It will of course be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints and that these goals will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill having the benefit of this disclosure. 
     Although the present invention has been described in terms of the presently preferred embodiment, i.e., a flying optical head assembly having a magnetic pole sheet layer, it should be clear to those skilled in the art that the present invention may also be utilized in conjunction with, for example, a flying optical head assembly carrying forms of light paths and lenses other than a SIL. Thus, it should be understood that the instant disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.