Patent Publication Number: US-11661788-B2

Title: Heat-assisted recording head having sub wavelength mirror formed of first and second materials

Description:
RELATED PATENT APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/216,017, filed on Mar. 29, 2021, which is a continuation of U.S. patent application Ser. No. 16/855,047 filed on Apr. 22, 2020, issued as U.S. Pat. No. 10,964,340 on Mar. 30, 2021, which claims the benefit of Provisional Patent Application Ser. No. 62/839,863 filed on Apr. 29, 2019, all of which are hereby incorporated herein by reference in their entireties. 
    
    
     SUMMARY 
     The present disclosure is directed to a heat-assisted recording head having subwavelength mirror formed of first and second materials. In various embodiments, a recording head has a near-field transducer proximate a media-facing surface of the recording head. The near-field transducer extends a first distance away from the media-facing surface. A waveguide overlaps and delivers light to the near-field transducer. Two subwavelength focusing mirrors are at an end of the waveguide proximate the media-facing surface and extend a second distance away from the media-facing surface that is less than the first distance. The subwavelength mirrors are on opposite crosstrack sides of the near-field transducer and separated from each other by a crosstrack gap. The subwavelength focusing mirrors each include a first material at the media-facing surface and a liner covering the first material at an edge of the subwavelength focusing mirror that faces the near-field transducer. The first material is more mechanically robust than a plasmonic material that forms the liner. 
     These and other features and aspects of various embodiments may be understood in view of the following detailed discussion and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The discussion below makes reference to the following figures, wherein the same reference number may be used to identify the similar/same component in multiple figures. 
         FIG.  1    is a perspective view of a slider assembly according to an example embodiment; 
         FIG.  2    is a cross-sectional view of a slider along a down-track plane according to according to an example embodiment; 
         FIG.  3    is a wafer plane view of a slider according to an example embodiment; 
         FIGS.  4  and  5    are perspective and plan views of a subwavelength mirror according to an example embodiment; 
         FIGS.  6  and  7    are sets of graphs showing simulation results of the arrangement shown in  FIGS.  4  and  5   ; 
         FIGS.  8  and  9    are perspective and plan views of a subwavelength mirror according to another example embodiment; 
         FIGS.  10  and  11    are sets of graphs showing simulation results of the arrangement shown in  FIGS.  8  and  9   ; 
         FIG.  12    is a plan view of a subwavelength mirror according to another example embodiment; 
         FIGS.  13 - 17    are perspective cutaway views of protrusions of a subwavelength mirror according to various example embodiments; and 
         FIG.  18    is a set of graphs comparing performance of the subwavelength mirror embodiments shown in  FIGS.  13 - 17   . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is generally related to heat-assisted magnetic recording (HAMR), also referred to as energy-assisted magnetic recording (EAMR), thermally-assisted recording (TAR), thermally-assisted magnetic recording (TAMR), etc. In a HAMR device, a near-field transducer (NFT) concentrates optical energy into a tiny optical spot in a recording layer, which raises the media temperature locally, reducing the writing magnetic field required for high-density recording. A waveguide delivers light to the near-field transducer and excites the near-field transducer. 
     One challenge in developing in HAMR products involves wear of the optical components that can make impact life of the drives. One cause for this is separation of parts and voiding within regions surrounding the NFT. The optical components in this region are subject to high temperatures and may become oxidized, which can cause voiding or separation of some materials. A HAMR write transducer described below uses a subwavelength mirror that overlaps part of the NFT in an area near the air bearing surface (ABS), which may also be referred to herein as a media-facing surface. Generally, the subwavelength mirror has dimensions along its reflecting surface that are smaller than the wavelength of the incident light (e.g., 830 nm). 
     The subwavelength mirror focuses incident waveguide light onto the NFT to assist waveguide-NFT coupling. The subwavelength mirror also functions as an optical side shield to block background light. Therefore, the laser current used for writing can be reduced and thermal gradient improved. In order to obtain optimum optical performance, the mirror is made from a material such as Au that is a good optical and thermal characteristics. However, it has been found that Au and similar plasmonic materials are subject to degradation in the NFT region. Therefore, the present disclosure describes to additional features to increase robustness and durability of a subwavelength mirror. 
     In reference now to  FIG.  1   , a perspective view shows a read/write head  100  according to an example embodiment. The read/write head  100  may be used in a magnetic data storage device, e.g., HAMR hard disk drive. The read/write head  100  may also be referred to herein interchangeably as a slider, head, write head, read head, recording head, etc. The read/write head  100  has a slider body  102  with read/write transducers  108  at a trailing edge  104  that are held proximate to a surface of a magnetic recording medium (not shown), e.g., a magnetic disk. 
     The illustrated read/write head  100  is configured as a HAMR device, and so includes additional components that form a hot spot on the recording medium near the read/write transducers  108 . These HAMR components include an energy source  106  (e.g., laser diode) and a waveguide  110 . The waveguide  110  delivers electromagnetic energy from the energy source  106  to a near-field transducer (NFT) that is part of the read/write transducers  108 . The NFT achieves surface plasmon resonance and directs the energy out of a media-facing surface  112  to create a small hot spot in the recording medium. 
     In  FIGS.  2  and  3   , respective cross-sectional and wafer plane views of the slider body  102  show a light delivery system according to an example embodiment. The slider body includes an NFT  208 , a magnetic writer  210  and a micro-sized focusing mirror  212 , referred to herein as a subwavelength mirror, subwavelength focusing mirror, subwavelength solid immersion mirror (SIM), mini-SIM, etc. Light, emitting from the laser diode  106 , is coupled into a three-dimensional, single mode channel waveguide  110  by a waveguide input coupler  206 , which directs the light to a waveguide core  200 . The input coupler  206  is replaced by a bottom cladding layer  207  towards the media-facing surface  112 . Note that other waveguide and input coupler arrangements may be used with the NFT  208  and mirror  212 . 
     The NFT  208  has an enlarged part with two curved ends  208   a - b  and a protruded peg  208   c . Other shapes may be possible for the enlarged part of the NFT  208 , e.g., rectangular, triangular. The NFT  208  is placed proximate a side cladding layer  204  and top cladding layer  202  of the waveguide  110  and near the waveguide core  200 . The NFT  208  could be also placed into the waveguide core  200 . The NFT  208  achieves plasmonic resonance in response to the light coupled via the waveguide  110 , and creates a small hotspot  220  on a recording medium  222  during recording. 
     A magnetic reader  224  is shown down-track from the NFT  208  and writer  210 . The magnetic reader  224  may include a magneto-resistive stack that changes resistance in response to changes in magnetic field detected from the recording medium  222 . These changes in magnetic field are converted to data by a read channel of the apparatus (e.g., hard disk drive assembly). 
     As best seen in  FIG.  3   , the subwavelength mirror  212  includes reflective metallic portions  212   a - b  on either crosstrack of the NFT  208 . The mirror portions  212   a - b  focus the incident waveguide light to the NFT  208  to assist in waveguide-NFT coupling. The mirror portions  212   a - b  can also function as optical side shields that block background light from exiting the media-facing surface  112 . The subwavelength mirrors described below utilize combinations of soft plasmonic materials and hard materials that help improve performance and life of the recording head  100 . 
     In  FIGS.  4  and  5   , diagrams illustrate details of a subwavelength mirror according to an example embodiment. The diagram in  FIG.  4    is a perspective view seen from the media-facing surface  112  and the diagram in  FIG.  5    is a plan view on a substrate-parallel plane. The subwavelength mirror includes a pair of subwavelength focusing mirrors  400  at an end of the waveguide  200  proximate the media-facing surface  112 . The subwavelength focusing mirrors  400  are on opposite crosstrack sides of the near-field transducer  208  and separated from each other by a crosstrack gap  404 . The width of crosstrack gap  404  may be less than a corresponding crosstrack width  406  of the NFT  208 . As seen in  FIG.  5   , the near-field transducer  208  extends a first distance  500  away from the media-facing surface  112  and the mirrors  400  extend a second distance  502  away from the media-facing surface that is less than the first distance  500 . For example, the second distance  502  may be less than half of the first distance  500 . 
     Each of the subwavelength focusing mirrors includes a first material  400   a  at the media-facing surface  112  and a second material  400   b  (e.g., a plasmonic material) facing away from the media facing surface  112  and in contact with the first material  400   a . In this example, an interface  400   d  between the first and second materials  400   a ,  400   b  is parallel with the media facing surface  112 . In other embodiments, the interface between the first and second materials  400   a ,  400   b  may be at an angle to the media-facing surface  112 . The first material  400   a  is more mechanically robust than the second material  400   b . A liner  400   c  coats an edge of the subwavelength focusing mirrors that faces the near-field transducer  208 . As seen here, the liner  400   c  covers both the first and second materials  400   a ,  400   b  and extends into the gap  404 . 
     The second material  400   b  and liner  400   c  may include the same or different material. The second material  400   b  (and optionally the liner  400   c ) may be a plasmonic material with good optical characteristics such as Au, Ag, Cu, Al or their alloys. In some embodiments, the liner  400   c  can be made of hard material, such as Rh, Ir, Pt, Pd, Ru, or their alloys. The hard, first material  400   a  is presented at the media-facing surface  112  for ABS protection and design robustness, and may include such materials as Rh, Ir, Pt, Pd, Ru, or their alloys. The soft plasmonic materials  400   b ,  400   c  are inside the media-facing surface  112  for better optical coupling and thermal conduction. The liner thickness  402  may be from 1 nm to 25 nm. 
     In  FIGS.  6  and  7   , a set of graphs show results of an analysis performed on the mirror arrangement shown in  FIGS.  4  and  5    with a liner  400   c  formed of a soft plasmonic material, Au, Ag, Cu, Al or their alloys. There is a slight drop in thermal gradient (TG) with thicker soft plasmonic liner. The NFT temperature (NFT ΔT) and mirror temperatures (mSIM ΔT) drop with a thicker soft plasmonic liner  400   c . The liner thickness  402  has little impact on laser current (Ieff). In  FIG.  7   , a set of graphs show an analysis performed on the mirror arrangement shown in  FIGS.  4  and  5    with a liner  400   c  formed of a hard material, such as Rh, Ir, Pt, Pd, Ru, or their alloys. The NFT and mirror temperatures go up with thicker hard material liner  400   c , as does the required laser current. Though the temperature is higher in this case, this design may have better robustness than one with a softer plasmonic material liner  400   c.    
     In  FIGS.  8  and  9   , diagrams illustrate details of a subwavelength mirror according to another example embodiment. The diagram in  FIG.  8    is a perspective view seen from the media-facing surface  112  and the diagram in  FIG.  9    is a plan view on a substrate-parallel plane. The subwavelength mirror includes a pair of subwavelength focusing mirrors  800  at an end of the waveguide  200  proximate the media-facing surface  112 . Each of the subwavelength focusing mirrors includes a first material  800   a  at the media-facing surface  112  and a second material  800   b  facing away from the media facing surface and in contact with the first material  800   a . The first material  800   a  is more mechanically robust than the second material  800   b . This embodiment has no liner comparable to what is shown in  FIGS.  4  and  5   . 
     The second material  800   b  may include a plasmonic material with good optical characteristics such as Au, Ag, Cu, Al or their alloys. The hard, first material  800   a  is presented at the media-facing surface  112  for ABS protection and design robustness, and may include such materials as Rh, Ir, Pt, Pd, Ru, or their alloys. In other embodiments, the first material  800   a  may be ceramic materials as ZrN, TiN, etc., or a magnetic material such as Fe, Ni, NiFe, FeCo, or alloys thereof. The soft plasmonic material  800   b  is inside the media-facing surface  112  for better optical coupling and thermal conduction. 
     One parameter that can affect performance of this and other embodiments is the crosstrack gap  802  opening between the mirrors  800 . In  FIG.  10   , a set of graphs show results of a simulation using various values of the gap  802  (labeled “SIM opening” in the graphs). These graphs generally show a higher downtrack thermal gradient (DTTG) with a narrower opening. The NFT and mirror temperature will increase if that gap  802  is too small, and laser current will also increase for a smaller gap  802 . These gap dimensions may also be used for embodiments with a liner as shown in  FIGS.  4  and  5   , as well as embodiments described below. 
     Another parameter that can affect performance of this and other embodiments is the height  900  of the second material  800   b  as it extends away from the media-facing surface as shown in  FIG.  9   . In  FIGS.  10  and  11   , a set of graphs show results of a simulation using various values of the height  900 . Higher NFT and mirror temperatures are seen with larger height  900 , and laser current will also increase with larger height  900 . Thermal gradient is not particularly sensitive to the height  900 . These height dimensions may also be used for embodiments with a liner as shown in  FIGS.  4  and  5   , as well as embodiments described below. 
     In  FIG.  12   , a diagram illustrates details of a subwavelength mirror according to another example embodiment. In this example, subwavelength focusing mirrors  1200  are at an end of the waveguide  200  proximate the media-facing surface  112  and separated from each other by a crosstrack gap  1202 . Each of the subwavelength focusing mirrors  1200  includes a first material  1200   a  at the media-facing surface  112  and a second material  1200   b  facing away from the media facing surface and in contact with the first material  1200   a . The first material  1200   a  is more mechanically robust than the second material  1200   b , and may include any of the mechanically robust materials described above. Similarly, the second material  1200   b  may include any of the plasmonic materials described above. 
     In this embodiment, the first material  1200   a  protrudes into the gap  1202  further than the second material  1200   b . This results in a discontinuity  1200   c  (e.g., a non-smooth transition) in edges of the mirrors that face the NFT  208 . In this way, the protrusion of the first material  1200   a  acts as an optical side shield. By extending the first material  1200   a  this way, the gap  1202  can be decreased to less than 100 nm, or even less than 50 nm. As indicated by dashed lines  1204 , a liner as shown in  FIGS.  4  and  5    may optionally be used with this embodiment. 
     In  FIGS.  13 - 17   , perspective cutaway views show various optical side shield embodiments according to various embodiments. In each of these figures, side shields are extensions from first material parts  1300 ,  1400 ,  1500 ,  1600 ,  1700  of a mirror that is joined to a second material part  1300 , the second material part being formed of any plasmonic materials as described above. For all of these embodiments, a recording head would include a mirror-image first and second material parts on an opposing crosstrack side of the NFT  208  separated by a gap  1304 . The first material parts  1300 ,  1400 ,  1500 ,  1600 ,  1700  may be made from any robust, hard material as described above. All of these embodiments may be used with a liner as shown in  FIGS.  4  and  5   . 
     In  FIG.  13   , a first material part  1302  has a protrusion  1302   a  that extends into an inter-mirror gap  1304  in the crosstrack direction. The downtrack dimension of the protrusion  1302   a  matches that of the NFT peg  208   c  and is aligned with the peg  208   c  in the downtrack direction. In  FIG.  14   , a first material part  1400  has a protrusion  1400   a  that extends into the inter-mirror gap  1304 . The downtrack dimension of the protrusion  1400   a  nearly matches that of the entire NFT  208  and is roughly aligned with the NFT  208  in the downtrack direction. The protrusion  1400   a  does not quite extend to the waveguide core  200  in the downtrack direction, as indicated by gap  1402 . 
     In  FIG.  15   , a first material part  1500  has a protrusion  1500   a  that extends into the inter-mirror gap  1304 . The downtrack dimension of the protrusion  1500   a  matches that of both the NFT  208  and waveguide core  200 , such that the protrusion extends into the waveguide core  200 . In  FIG.  16   , a first material part  1600  has a protrusion  1600   a  that extends into the inter-mirror gap  1304 . The downtrack dimension of the protrusion  1600   a  extends into and matches that the waveguide core  200  only, with which it is aligned in the downtrack direction. In  FIG.  17   , a first material part  1700  has a protrusion  1700   a  that extends into the inter-mirror gap  1704 . The protrusion  1700   a  extends the full length of the mirror portion in the downtrack direction, matching a downtrack dimension of the first material part  1300 . 
     In  FIG.  18   , graphs  1800 - 1802  show analyses of the different protrusion designs in  FIGS.  13 - 17   , as well as a non-protruding design as shown in  FIG.  8   . For these analyses, the NFT temperature, downtrack TG, and laser current were determined for different ABS opening sizes, which here refer to the minimum crosstrack distances between opposing protrusions on either side of the gap  1304 . Note that in graph  1802 , only the minimum and maximum current curves are labeled for purposes of maintaining clarity in the drawing. With design having a protrusion that matches the NFT sides and waveguide as shown in  FIG.  15   , TG is same as full protrusion shown in  FIG.  17   . The NFT Temperature can be 20-30 K lower with a protrusion that matches the NFT sides and waveguide as shown in  FIG.  15   . 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. 
     The foregoing description of the example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Any or all features of the disclosed embodiments can be applied individually or in any combination are not meant to be limiting, but purely illustrative. It is intended that the scope of the invention be limited not with this detailed description, but rather determined by the claims appended hereto.