Patent Publication Number: US-11651791-B2

Title: Heat-assisted magnetic recording (HAMR) head with tapered main pole and heat sink material adjacent the pole

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of co-pending U.S. patent application Ser. No. 16/943,995, filed Jul. 30, 2020, which application is a divisional of U.S. patent application Ser. No. 16/520,250, filed Jul. 23, 2019, each of which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     This invention relates generally to a heat-assisted magnetic recording (HAMR) disk drive, in which data are written while the magnetic recording layer on the disk is at an elevated temperature, and more specifically to an improved HAMR head. 
     Description of the Related Art 
     In conventional magnetic recording, thermal instabilities of the stored magnetization in the recording media can cause loss of recorded data. To avoid this, media with high magneto-crystalline anisotropy (K u ) are required. However, increasing K u  also increases the coercivity of the media, which can exceed the write field capability of the write head. Since it is known that the coercivity of the magnetic material of the recording layer is temperature dependent, one proposed solution to the thermal stability problem is heat-assisted magnetic recording (HAMR), wherein high-K u  magnetic recording material is heated locally during writing by the main magnetic pole to lower the coercivity enough for writing to occur, but where the coercivity/anisotropy is high enough for thermal stability of the recorded bits at the ambient temperature of the disk drive (i.e., the normal operating or “room” temperature of approximately 15-30° C.). In some proposed HAMR systems, the magnetic recording material is heated to near or above its Curie temperature. The recorded data is then read back at ambient temperature by a conventional magnetoresistive read head. HAMR disk drives have been proposed for both conventional continuous media, wherein the magnetic recording material is a continuous layer on the disk, and for bit-patterned media (BPM), wherein the magnetic recording material is patterned into discrete data islands or “bits”. 
     One type of proposed HAMR disk drive uses a laser source and an optical waveguide coupled to a near-field transducer (NFT) for heating the recording material on the disk. A “near-field” transducer refers to “near-field optics”, wherein the passage of light is through an element with sub-wavelength features and the light is coupled to a second element, such as a substrate like a magnetic recording medium, located a sub-wavelength distance from the first element. The NFT is typically located at the gas-bearing surface (GBS) of the gas-bearing slider that also supports the read/write head and rides or “files” above the disk surface. 
     A NFT with a generally triangular output end is described in US published applications 20110096639 and 20110170381, both assigned to the same assignee as this application. In this NFT an evanescent wave generated at a surface of the waveguide couples to surface plasmons excited on the surface of the NFT  74  and a strong optical near-field is generated at the apex of the triangular output end. 
     SUMMARY OF THE DISCLOSURE 
     In conventional HAMR heads the main magnetic pole for generating the magnetic field for writing has a relatively wide cross-track width to apply a high magnetic field at the optical spot generated by the NFT. However, the wide main pole increases the rise time of the magnetic field during writing and thus decreases the data rate. Thus it is desirable to reduce the width of the main pole but without substantially decreasing the magnetic field applied at the optical spot. Additionally, the main pole is easily oxidized at the GBS due to temperature rise and wear of the protective overcoat on the head. Thus it is desirable to minimize oxidation of the main pole. 
     In embodiments of this invention, the main pole is formed of two layers, with the first layer having a width that tapers down in the direction towards the NFT where the optical spot is formed, and the second layer located away from the NFT having a substantially wider width than the first layer so as to provide sufficient magnetic field. Layers of heat sink material are located on the sloped cross-track sides of the tapered main pole first layer to reduce the temperature and thus the likelihood of oxidation. 
     For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG.  1    is a top view of a heat-assisted magnetic recording (HAMR) disk drive according to an embodiment of the invention. 
         FIG.  2    depicts a sectional view, not drawn to scale because of the difficulty in showing the very small features, of a gas-bearing slider for use in HAMR disk drive and a portion of a HAMR disk according to the prior art. 
         FIG.  3 A  is a side sectional view of the layers of material making up the main pole and primary pole, the near-field transducer (NFT) and the waveguide according to the prior art and shown in relation to the recording layer on the disk. 
         FIG.  3 B  is a perspective view of the layers of material making up the main pole and primary pole, the NFT and the waveguide according to the prior art. 
         FIG.  3 C  is a view of a portion of the slider gas-bearing surface (GBS) showing the relative orientations of the waveguide, the NFT output tip and the main pole tip. 
         FIG.  4 A  is a side sectional view of the HAMR head according to an embodiment of the invention and shows the layers of material making up the primary pole, the first and second main poles (MP1 and MP2), the NFT and the waveguide. 
         FIG.  4 B  is a view of a portion of the GBS of the HAMR head according to an embodiment of the invention showing the relative orientations of the waveguide end, the NFT output tip, the MP1 end and the MP2 end. 
         FIG.  5 A  is a view of a portion of the slider GBS showing the heat-sink material (HSM) extending in the along-the-track direction beyond the region between the MP1 end and the NFT output tip. 
         FIG.  5 B  is a view of a portion of the slider GBS showing the HSM recessed in the along-the-track direction away from the region between the MP1 end and the NFT output tip. 
         FIG.  5 C  is a view of a portion of the GBS of the HAMR head according to an embodiment of the invention with three main pole layers. 
         FIG.  5 D  is a view of a portion of the GBS of the HAMR head according to an embodiment of the invention where both MP1 and MP2 are tapered. 
         FIG.  6 A  is a side sectional view of the HAMR head according to an embodiment of the invention and shows the MP2 end fully recessed from the GBS. 
         FIG.  6 B  is a side sectional view of the HAMR head according to an embodiment of the invention and shows the MP2 end with only a portion recessed from the GBS. 
         FIG.  7    is a view of a portion of the slider GBS showing an embodiment of the invention wherein the MP1 is formed with two tapered ends. 
         FIG.  8    is a view of a portion of the slider GBS showing an embodiment of the invention wherein the NFT is an E-shaped antenna. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a top view of a heat-assisted recording (HAMR) disk drive  100  according to an embodiment of the invention. In  FIG.  1   , the HAMR disk drive  100  is depicted with a disk  150  with magnetic recording layer  31  of conventional continuous magnetic recording material arranged in radially-spaced circular tracks  118 . Only a few representative tracks  118  near the inner and outer diameters of disk  150  are shown. However, instead of a conventional continuous magnetic recording layer, the recording layer may be a bit-patterned-media (BPM) layer with discrete data islands. 
     The drive  100  has a housing or base  112  that supports an actuator  130  and a drive motor for rotating the magnetic recording disk  150 . The actuator  130  may be a voice coil motor (VCM) rotary actuator that has a rigid arm  131  and rotates about pivot  132  as shown by arrow  133 . A head-suspension assembly includes a suspension  135  that has one end attached to the end of actuator arm  131  and a head carrier, such as an gas-bearing slider  120 , attached to the other end of suspension  135 . The suspension  135  permits the slider  120  to be maintained very close to the surface of disk  150  and enables it to “pitch” and “roll” on the bearing of gas (typically air or helium) generated by the disk  150  as it rotates in the direction of arrow  20 . The slider  120  supports the HAMR head (not shown), which includes a magnetoresistive read head, an inductive write head, the near-field transducer (NFT) and optical waveguide. A semiconductor laser  90  with a wavelength of 780 to 980 nm may used as the HAMR light source and is depicted as being supported on the top of slider  120 . Alternatively the laser may be located on suspension  135  and coupled to slider  120  by an optical channel. As the disk  150  rotates in the direction of arrow  20 , the movement of actuator  130  allows the HAMR head on the slider  120  to access different data tracks  118  on disk  150 . The slider  120  is typically formed of a composite material, such as a composite of alumina/titanium-carbide (Al 2 O 3 /TiC). Only one disk surface with associated slider and read/write head is shown in  FIG.  1   , but there are typically multiple disks stacked on a hub that is rotated by a spindle motor, with a separate slider and HAMR head associated with each surface of each disk. 
     In the following drawings, the X-axis denotes an axis perpendicular to the gas-bearing surface (GBS) of the slider, the Y-axis denotes a track width or cross-track axis, and the Z-axis denotes an along-the-track axis.  FIG.  2    is a schematic cross-sectional view illustrating a configuration example of a HAMR head according to the prior art. In  FIG.  2   , the disk  150  is depicted with the recording layer  31  being a conventional continuous magnetic recording layer of magnetizable material with magnetized regions or “bits”  34 . The gas-bearing slider  120  is supported by suspension  135  and has a GBS that faces the disk  150  and supports the magnetic write head  50 , read head  60 , and magnetically permeable read head shields S 1  and S 2 . A recording magnetic field is generated by the write head  50  made up of a coil  56 , a primary magnetic pole  53  for transmitting flux generated by the coil  56 , a main pole  52  connected to the primary pole, and a return magnetic pole  54 . A magnetic field generated by the coil  56  is transmitted through the primary pole  53  to the main pole  52  arranged in a vicinity of an optical near-field transducer (NFT)  74 .  FIG.  2    illustrates the write head  50  with a well-known “pancake” coil  56 , wherein the coil segments lie in substantially the same plane. However, alternatively the coil may be a well-known “helical” coil wherein the coil is wrapped around the primary magnetic pole  53 . At the moment of recording, the recording layer  31  of disk  150  is heated by an optical near-field generated by the NFT  74  and, at the same time, a region or “bit”  34  is magnetized and thus written onto the recording layer  31  by applying a recording magnetic field generated by the main pole  52 . 
     A semiconductor laser  90  is mounted to the top surface of slider  120 . An optical waveguide  73  for guiding light from laser  90  to the NFT  74  is formed inside the slider  120 . Materials that ensure a refractive index of the waveguide  73  core material to be greater than a refractive index of the cladding material may be used for the waveguide  73 . For example, Al 2 O 3  may be used as the cladding material and TiO 2 , Ta 2 O 5  and SiO x N y  as the core material. Alternatively, SiO 2  may be used as the cladding material and Ta 2 O 5 , TiO 2 , SiO x N y , or Ge-doped SiO 2  as the core material. The waveguide  73  that delivers light to NFT  74  is preferably a single-mode waveguide. 
       FIG.  3 A  is a side sectional view of a prior art HAMR head and shows the layers of material making up the main pole  52 , the NFT  74  and the waveguide  73  and shown in relation to disk  150  with recording layer  31 . The main pole  52  is typically a layer of high-moment material like FeCo and has a pole tip  52   a  at the GBS. The waveguide  73  is a layer of core material generally parallel to the main pole  52  layer with a length orthogonal to the GBS and may have a tapered region  73   a  extending from the GBS to a region  73   b  recessed from the GBS. The waveguide  73  has a generally planar surface  73   c  that faces and is parallel to NFT  74  layer and an end  73   d  at the GBS. The NFT  74  layer is a conductive low-loss metal (preferably Au, but also Ag, Al or Cu), is generally parallel to waveguide  73  layer and main pole  52  layer, and is located between and spaced from the waveguide  73  layer and the main pole  52  layer. The NFT  74  layer has a surface  74   a  that faces and is spaced from waveguide surface  73   c . The NFT  74  layer has an output tip  80  at the GBS. When light is introduced into the waveguide  73 , an evanescent wave is generated at the surface  73   c  and couples to a surface plasmon excited on the surface  74   a  of NFT  74 . Arrow  23  shows the direction of propagation of light in waveguide  73  and arrow  24  shows the direction of polarization of the light. The surface plasmon propagates to the output tip  80 . The output tip  80  has an apex  80   a  that faces the main pole tip  52   a  and a back edge  80   b  that faces the waveguide surface  73   c . At the apex  80   a  an optical near-field spot is generated in the space at the GBS between the output tip apex  80   a  and the main pole tip  52   a . The main pole tip  52   a  applies a magnetic field at the optical spot.  FIG.  3 B  is a perspective view of a prior art HAMR head and shows the primary pole  53 , the main pole  52 , the NFT  74  and the waveguide  73 .  FIG.  3 C  is a view of a portion of the GBS showing the relative orientations of the waveguide end  73   d , the NFT output tip  80  and the main pole tip  52   a . The output tip  80  has a generally triangular shape at the GBS with an apex  80   a  that faces the main pole tip  52   a  and a back edge  80   b  that faces the waveguide surface  73   c  and is wider than apex  80   a  in the cross-track direction. Thus the output tip  80  has a back edge  80   b  at the GBS perpendicular to a polarization direction of incident light transmitted through the waveguide (arrow  24  in  FIG.  3 A ) that gradually becomes smaller toward the apex  80   a  where an optical near-field is generated. The small lines  80   c  represent the optical spot generated at the output tip apex  80   a .  FIGS.  3 B- 3 C  show the tapered region  73   a  of waveguide  73  and how it tapers from a width at a region recessed from the GBS down to a smaller width that is generally at least the same cross-track width as the back edge  80   b  of NFT output tip  80 . 
     The main pole  52   a  ( FIG.  3 C ) has a relatively wide cross-track width to apply a high magnetic field at the optical spot  80 C. However, the wide main pole increases the rise time of the magnetic field during writing and thus decreases the data rate. Thus it is desirable to reduce the width of the main pole but without substantially decreasing the magnetic field applied at the optical spot. Additionally, the main pole is easily oxidized at the GBS due to temperature rise and wear of the protective overcoat on the head. Thus it is desirable to minimize oxidation of the main pole. 
     In embodiments of this invention, the main pole is formed of two layers, with the first layer having a width that tapers down in the direction towards the NFT where the optical spot is formed, and the second layer located away from the NFT having a substantially wider width than the first layer so as to provide sufficient magnetic field. Layers of heat sink material are located on the sloped cross-track sides of the tapered main pole first layer to reduce the temperature and thus the likelihood of oxidation. The heat sink material may extend slightly beyond the main pole at the GBS and thus help prevent the slider overcoat on the main pole from being worn away, which could also result in oxidation of the main pole. 
       FIG.  4 A  is a side sectional view of the HAMR head according to an embodiment of the invention and shows the layers of material making up the primary magnetic pole  253 , the first and second main magnetic poles  251 ,  252  (MP1 and MP2), the NFT  274  and the waveguide  273 .  FIG.  4 B  is a view of a portion of the GBS of the HAMR head according to an embodiment of the invention showing the relative orientations of the waveguide end  273   d , the NFT output tip  280 , the MP1 end  251   a  and the MP2 end  252   a.    
     The MP1 layer is in in contact with the MP2 layer and has a generally trapezoidal shape that tapers in the along-the-track direction from the MP2 layer toward the NFT. The taper angle may be up to about 60 degrees. As shown in  FIG.  4 B , the MP1 end  251   a  has a tapered or generally trapezoidal shape with its narrow portion facing and aligned in the along-the-track direction with the NFT tip  280 . The MP2 end  252   a  is wider in the cross-track direction than the wider portion of the MP1 end  251   a . For example, MP2 may have a cross-track width of about 200 nm and the wider portion of MP1 may have a cross-track width of about 50 nm. The width of MP1 can be smaller than 50 nm to reduce the rise time of the write current. Alternatively, it can be wider than 50 nm, as long as it is narrower than the width of MP2, to increase the alignment tolerance between the NFT and MP1. MP1 may have an along-the-track length between about 50-500 nm. MP1 and MP2 may be formed of the same or different ferromagnetic materials like NiFe, CoFe and CoFeNi. For example, MP2 may be formed of NiFe and MP1 of a higher magnetic moment material like CoFeNi. 
     Heat sink material (HSM)  260  is located on the sloped sides on the MP1 end  251   a . The HSM is a material with a thermal conductivity greater than that of the MP1 material. These materials include Au, Cu, Ag, Al, Mg, In, Ir, Rh, Ru, Cr, Be, Mo, Co, W, Ti, Ni and Pt, or alloys including two or more of these elements, such as AuAg, AuCu, AuRh, AuNi, AuPt, WCu, MoCu and CuMoW. 
     If the HSM includes an element that may diffuse into the magnetic material of MP1, like Au or Cu, then a diffusion layer  262  is located between MP1 and the HSM. The material of diffusion layer  262  may be Rh, Ru, In, Co, W, Rh oxide, Ru oxide, Indium oxide, or TiN, with a thickness preferably in the range of 5-10 nm. The cross-track width of the HSM is at least as wide as the cross-track width of MP2 and preferably wider, as shown in  FIG.  4 B . If the HSM is selected from a material that is not likely to diffuse into the MP1, like Ru or Rh, then the diffusion layer  262  is not required. The temperature of MP1 may be reduced further by extending the HSM in the along-the-track direction beyond the MP1 end  251   a , as shown in  FIG.  5 A . Alternatively, if less temperature reduction is required the HSM may be recessed in the along-the-track direction away from the MP1 end  251   a , as shown in  FIG.  5 B . Computer modeling has shown that the use of HSM on both sloped sides of the tapered MP1 end  251   a  can result in a 4-8% reduction in the temperature of the NFT and a 9-15% reduction in the temperature of MP1. 
       FIG.  4 A  also shows an optional electrically conductive thermal shunt layer  275  between and in contact with MP1 and the NFT  274 . The thermal shunt layer  275  is described in U.S. Pat. No. 8,619,516 B1, which is assigned to the same assignee as this application, and allows heat flow from NFT  274  to HSM  260 . 
     The main pole may be formed of more than two layers.  FIG.  5 C  is a view of a portion of the GBS of the HAMR head according to an embodiment with three main pole layers, wherein MP3 has a wider cross-track width than MP2. MP2 may also be tapered.  FIG.  5 D  is a view of a portion of the GBS of the HAMR head according to an embodiment of the invention where both MP1 and MP2 are tapered, with the tapered end of MP2 in contact with MP1. 
     MP2 may have its end  252   a  at least partially recessed from the GBS to avoid oxidation of MP2. As shown in  FIG.  6 A , MP2 end  252   a  is fully recessed from the GBS. Alternatively, as shown in  FIG.  6 B , only a portion of MP2 end  252   a  may recessed from the GBS, and with a sloped surface at its recessed portion, to increase the magnetic field applied at the GBS. 
     MP1 may also be formed to have two tapered ends, MP1a and MP1b, with the NFT being aligned in the along-the-track direction with a portion of each tapered end, as shown in  FIG.  7   . The center of MP1, the region between the two tapered ends, will have the highest temperature because it is closest to the NFT. Because that region is formed of non-magnetic HSM, there is less likelihood of oxidation of either of the two tapered ends. 
     Embodiments of the invention have been shown and described with an NFT having a generally triangular or generally trapezoidal end at the GBS. However, the invention is fully applicable with other types of well-known NFTs, like an E-shaped antenna as shown in  FIG.  8   . 
     While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.