Patent Description:
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.

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 (Ku) are required. However, increasing Ku 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-Ku 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 <NUM>-<NUM>). 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 bitpatterned 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 <CIT> and <CIT>, 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 <NUM> and a strong optical near-field is generated at the apex of the triangular output end. <CIT>, over which the independent claims are characterised, discloses a thermally-assisted magnetic recording head including a main pole and a plasmon generator, the main pole having a front end face including first to third face portions. <CIT> discloses a thermally-assisted magnetic recording head having a heat sink made up of separate metal layers.

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.

<FIG> is a top view of a heat-assisted recording (HAMR) disk drive <NUM> according to an embodiment of the invention. In <FIG>, the HAMR disk drive <NUM> is depicted with a disk <NUM> with magnetic recording layer <NUM> of conventional continuous magnetic recording material arranged in radially-spaced circular tracks <NUM>. Only a few representative tracks <NUM> near the inner and outer diameters of disk <NUM> are shown. However, instead of a conventional continuous magnetic recording layer, the recording layer may be a bitpatterned-media (BPM) layer with discrete data islands.

The drive <NUM> has a housing or base <NUM> that supports an actuator <NUM> and a drive motor for rotating the magnetic recording disk <NUM>. The actuator <NUM> may be a voice coil motor (VCM) rotary actuator that has a rigid arm <NUM> and rotates about pivot <NUM> as shown by arrow <NUM>. A head-suspension assembly includes a suspension <NUM> that has one end attached to the end of actuator arm <NUM> and a head carrier, such as an gas-bearing slider <NUM>, attached to the other end of suspension <NUM>. The suspension <NUM> permits the slider <NUM> to be maintained very close to the surface of disk <NUM> and enables it to "pitch" and "roll" on the bearing of gas (typically air or helium) generated by the disk <NUM> as it rotates in the direction of arrow <NUM>. The slider <NUM> 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 <NUM> with a wavelength of <NUM> to <NUM> may used as the HAMR light source and is depicted as being supported on the top of slider <NUM>. Alternatively the laser may be located on suspension <NUM> and coupled to slider <NUM> by an optical channel. As the disk <NUM> rotates in the direction of arrow <NUM>, the movement of actuator <NUM> allows the HAMR head on the slider <NUM> to access different data tracks <NUM> on disk <NUM>. The slider <NUM> is typically formed of a composite material, such as a composite of alumina/titanium-carbide (Al<NUM>O<NUM>/TiC). Only one disk surface with associated slider and read/write head is shown in <FIG>, 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> is a schematic cross-sectional view illustrating a configuration example of a HAMR head according to the prior art. In <FIG>, the disk <NUM> is depicted with the recording layer <NUM> being a conventional continuous magnetic recording layer of magnetizable material with magnetized regions or "bits" <NUM>. The gas-bearing slider <NUM> is supported by suspension <NUM> and has a GBS that faces the disk <NUM> and supports the magnetic write head <NUM>, read head <NUM>, and magnetically permeable read head shields S1 and S2. A recording magnetic field is generated by the write head <NUM> made up of a coil <NUM>, a primary magnetic pole <NUM> for transmitting flux generated by the coil <NUM>, a main pole <NUM> connected to the primary pole, and a return magnetic pole <NUM>. A magnetic field generated by the coil <NUM> is transmitted through the primary pole <NUM> to the main pole <NUM> arranged in a vicinity of an optical near-field transducer (NFT) <NUM>. <FIG> illustrates the write head <NUM> with a well-known "pancake" coil <NUM>, 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 <NUM>. At the moment of recording, the recording layer <NUM> of disk <NUM> is heated by an optical near-field generated by the NFT <NUM> and, at the same time, a region or "bit" <NUM> is magnetized and thus written onto the recording layer <NUM> by applying a recording magnetic field generated by the main pole <NUM>.

A semiconductor laser <NUM> is mounted to the top surface of slider <NUM>. An optical waveguide <NUM> for guiding light from laser <NUM> to the NFT <NUM> is formed inside the slider <NUM>. Materials that ensure a refractive index of the waveguide <NUM> core material to be greater than a refractive index of the cladding material may be used for the waveguide <NUM>. For example, Al<NUM>O<NUM> may be used as the cladding material and TiO<NUM>, T<NUM>O<NUM> and SiOxNy as the core material. Alternatively, SiO<NUM> may be used as the cladding material and Ta<NUM>O<NUM>, TiO<NUM>, SiOxNy, or Ge-doped SiO<NUM> as the core material. The waveguide <NUM> that delivers light to NFT <NUM> is preferably a single-mode waveguide.

<FIG> is a side sectional view of a prior art HAMR head and shows the layers of material making up the main pole <NUM>, the NFT <NUM> and the waveguide <NUM> and shown in relation to disk <NUM> with recording layer <NUM>. The main pole <NUM> is typically a layer of highmoment material like FeCo and has a pole tip 52a at the GBS. The waveguide <NUM> is a layer of core material generally parallel to the main pole <NUM> layer with a length orthogonal to the GBS and may have a tapered region 73a extending from the GBS to a region 73b recessed from the GBS. The waveguide <NUM> has a generally planar surface 73c that faces and is parallel to NFT <NUM> layer and an end 73d at the GBS. The NFT <NUM> layer is a conductive low-loss metal (preferably Au, but also Ag, Al or Cu), is generally parallel to waveguide <NUM> layer and main pole <NUM> layer, and is located between and spaced from the waveguide <NUM> layer and the main pole <NUM> layer. The NFT <NUM> layer has a surface 74a that faces and is spaced from waveguide surface 73c. The NFT <NUM> layer has an output tip <NUM> at the GBS. When light is introduced into the waveguide <NUM>, an evanescent wave is generated at the surface 73c and couples to a surface plasmon excited on the surface 74a of NFT <NUM>. Arrow <NUM> shows the direction of propagation of light in waveguide <NUM> and arrow <NUM> shows the direction of polarization of the light. The surface plasmon propagates to the output tip <NUM>. The output tip <NUM> has an apex 80a that faces the main pole tip 52a and a back edge 80b that faces the waveguide surface 73c. At the apex 80a an optical near-field spot is generated in the space at the GBS between the output tip apex 80a and the main pole tip 52a. The main pole tip 52a applies a magnetic field at the optical spot. <FIG> is a perspective view of a prior art HAMR head and shows the primary pole <NUM>, the main pole <NUM>, the NFT <NUM> and the waveguide <NUM>. <FIG> is a view of a portion of the GBS showing the relative orientations of the waveguide end 73d, the NFT output tip <NUM> and the main pole tip 52a. The output tip <NUM> has a generally triangular shape at the GBS with an apex 80a that faces the main pole tip 52a and a back edge 80b that faces the waveguide surface 73c and is wider than apex 80a in the cross-track direction. Thus the output tip <NUM> has a back edge 80b at the GBS perpendicular to a polarization direction of incident light transmitted through the waveguide (arrow <NUM> in <FIG>) that gradually becomes smaller toward the apex 80a where an optical near-field is generated. The small lines 80c represent the optical spot generated at the output tip apex 80a. <FIG> show the tapered region 73a of waveguide <NUM> 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 80b of NFT output tip <NUM>.

The main pole 52a (<FIG>) has a relatively wide cross-track width to apply a high magnetic field at the optical spot 80C. 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> 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 <NUM>, the first and second main magnetic poles <NUM>, <NUM> (MP1 and MP2), the NFT <NUM> and the waveguide <NUM>. <FIG> 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 273d, the NFT output tip <NUM>, the MP1 end 251a and the MP2 end 252a.

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 <NUM> degrees. As shown in <FIG>, the MP1 end 251a has a tapered or generally trapezoidal shape with its narrow portion facing and aligned in the along-the-track direction with the NFT tip <NUM>. The MP2 end 252a is wider in the cross-track direction than the wider portion of the MP1 end 251a. For example, MP2 may have a cross-track width of about <NUM> and the wider portion of MP1 may have a cross-track width of about <NUM>. The width of MP1 can be smaller than <NUM> to reduce the rise time of the write current. Alternatively, it can be wider than <NUM>, 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 <NUM>-<NUM>. MP1 and MP2 may be formed of the same or different ferromagnetic materials like NiFe, CiFe and CoFeNi. For example, MP2 may be formed of NiFe and MP1 of a higher magnetic moment material like CoFeNi.

Heat sink material (HSM) <NUM> is located on the sloped sides on the MP1 end 251a. 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 <NUM> is located between MP1 and the HSM. The material of diffusion layer <NUM> may be Rh, Ru, In, Co, W, Rh oxide, Ru oxide, Indium oxide, or TiN, with a thickness preferably in the range of <NUM>-<NUM>. 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>. 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 <NUM> 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 251a, as shown in <FIG>. Alternatively, if less temperature reduction is required the HSM may be recessed in the along-the-track direction away from the MP1 end 251a, as shown in <FIG>. Computer modeling has shown that the use of HSM on both sloped sides of the tapered MP1 end 251a can result in a <NUM>-<NUM>% reduction in the temperature of the NFT and a <NUM>-<NUM>% reduction in the temperature of MP1.

<FIG> also shows an optional electrically conductive thermal shunt layer <NUM> between and in contact with MP1 and the NFT <NUM>. The thermal shunt layer <NUM> is described in <CIT>, which is assigned to the same assignee as this application, and allows heat flow from NFT <NUM> to HSM <NUM>.

The main pole may be formed of more than two layers. <FIG> 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> 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 has its end 252a at least partially recessed from the GBS to avoid oxidation of MP2. As shown in <FIG>, MP2 end 252a is fully recessed from the GBS. Alternatively, as shown in <FIG>, only a portion of MP2 end 252a 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>. 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 nonmagnetic 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>.

Claim 1:
A heat-assisted magnetic recording (HAMR) head for writing to a magnetic recording layer comprising:
a head carrier (<NUM>) having a recording-layer-facing surface with an along-the-track axis and a cross-track axis substantially orthogonal to the along-the-track axis;
a main pole on a surface substantially orthogonal to the recording-layer-facing surface, the main pole comprising a first layer (MP1, <NUM>) and a second layer (MP2, <NUM>) in contact with the first layer, the first layer tapering in the along-the-track direction from the second layer, the first layer having a tapered end at the recording-layer-facing surface;
a near-field transducer (NFT) layer (<NUM>) on the head carrier oriented substantially parallel to the main pole first layer, the NFT layer having an output tip at the recording-layer-facing surface aligned with the main pole first layer tapered end in the along-the-track direction; and
heat sink material (<NUM>) adjacent the cross-track sides of the tapered main pole first layer; and characterised in that:
the main pole second layer (MP2, <NUM>) has an end (252a) with a sloped surface at least partially recessed from the recording-layer-facing surface.