# Patent

## Title
Flat NFT for heat assisted magnetic recording

## Abstract

The present disclosure generally relates to an EAMR head having a plasmonic bulk metal plate adjacent thereto. The waveguide core has a trapezoidal shaped cross-section, when viewed from the ABS, and the plasmonic bulk metal plate is disposed adjacent the short side of the trapezoid. The plasmonic bulk metal plate reduces the temperature of the NFT.

## Background
BACKGROUND
1. Field of the Disclosure
Embodiments of the present disclosure generally relate to energy assisted magnetic recording (EAMR).
2. Description of the Related Art
In hard disk drives (HDDs), a magnetic head is disposed over a magnetic media. The magnetic head reads from, and writes data to, the magnetic media. The magnetic head has a surface, referred to as an air bearing surface (ABS), facing the magnetic media. As the magnetic media moves, air exerts a pressure on the ABS and pushes the magnetic head away from the magnetic media. The magnetic head is formed on a slider, which is coupled to a suspension. The suspension exerts a counter force that, when considered in concert with the moving media, ensures the magnetic head is disposed a predetermined distance from the magnetic media during operation.
In EAMR, the recording medium is locally heated to decrease the coercivity of the magnetic material during write operations. The local area is then rapidly cooled to retain the written information, which allows for conventional magnetic write heads to be used with high coercivity magnetic materials. The heating of a local area may be accomplished by, for example, a heat or thermal source such as a laser. One type of EAMR is heat assisted magnetic recording (HAMR). HAMR may also sometimes be referred to as thermally assisted magnetic recording (TAMR) or optically assisted magnetic recording (OAMR). EAMR is feasible to circumvent the limits of the magnetic recording areal density of perpendicular magnetic recording (PMR) technology, which is currently about 700-800 Gb/in2. EAMR is able to increase the areal density to beyond 1 TB/in2.
The energy in an EAMR head is directed from an energy source through the head by utilizing a waveguide and a near field transducer (NFT). The NFT coupled the diffraction limited light from a waveguide further focuses the light field energy beyond the diffraction limit of the waveguide down to a highly concentrated near field media heating spot. The NFT comprises plasmonic metals such as Au, Ag, Cu and their alloys. The plasmonic metals have a high density of free electrons and therefore are mechanically not very robust and thus susceptible to damage caused by thermal or mechanical stresses. Under those stresses, NFT failure is common.
Therefore, there is a need in the art for an improved EAMR head.



BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
FIG. 1 is a schematic illustration of a HDD according to one embodiment.
FIG. 2 is a schematic, cross-sectional illustration of an EAMR head according to one embodiment.
FIG. 3A is a schematic illustration of a waveguide core relative to a plasmonic bulk metal plate taken along line 3-3 of FIG. 2 according to one embodiment.
FIG. 3B is a schematic illustration of a waveguide core relative to a plasmonic bulk metal plate taken along line 3-3 of FIG. 2 according to another embodiment.
FIG. 4A is a schematic illustration a waveguide core relative to a plasmonic bulk metal plate taken along line 4-4 from FIG. 2, according to one embodiment.
FIG. 4B is a close-up illustration of FIG. 4A.
FIG. 5 is a flow chart illustrating a method of manufacturing an EAMR head according to one embodiment.



To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. It is to be understood that all drawings are not to scale.
DETAILED DESCRIPTION
The present disclosure generally relates to an EAMR head having a plasmonic bulk metal plate adjacent thereto. The waveguide core has a trapezoidal shaped cross-section, when viewed from the ABS, and the plasmonic bulk metal plate is disposed adjacent the short side of the trapezoid. The plasmonic bulk metal plate reduces the temperature of the NFT.
FIG. 1 is a schematic illustration of a magnetic recording device, such as a hard disk drive (HDD) 100 according to one embodiment. The HDD 100 includes at least one magnetic recording medium, such as a disk 102 that is supported on a spindle 104. A motor causes the spindle 104, and hence the disk 102, to rotate. A magnetic head that is mounted on a slider 108 moves over the disk 102 to read and write information from/to the disk 102. The head rides on an air bearing above the disk 102 during read/write operations. The slider 108 is coupled to an actuator 110 by a suspension 112 and arm 114. The suspension 112, which may comprise stainless steel, provides a slight spring force, which biases the slider 108 towards the disk surface. Each actuator 110 is attached to an actuator means that controls the movement of the head 106 relative to the disk 102.
FIG. 2 is a schematic, cross-sectional illustration of an EAMR head 200 according to one embodiment. The head 200 is positioned across from a magnetic media 202, such as a disk. The head 200 includes a slider 204 having a read head with a sensor 206 for reading information from the media 202. The head 200 also includes a write portion. The write portion includes a write pole 208 and return pole 210. The head 200 has an ABS 212 facing the disk 202. The EAMR head 200 includes an energy source 214, such as a laser, that directs energy through a waveguide core 216. The waveguide core 216 is at least partially surrounded by cladding material 218. As will be discussed below, a plasmonic bulk metal plate 220 is disposed adjacent the waveguide core 216 and the cladding 218. In one embodiment, the plasmonic bulk metal plate 220 is disposed directly on both the cladding 218 and the waveguide core 216. In another embodiment, the plasmonic bulk metal plate 220 is spaced from the waveguide core 216 by the cladding 218. An NFT 222 is also present. The NFT 222 has an end exposed at the ABS 212 while both the waveguide core 216 and plasmonic bulk metal plate 220 are recessed from the ABS. Suitable materials for the waveguide core include Ge, Si, amorphous Si, GaAs, GZO (Gallium Zinc Oxide), GaP, ITO, TiO2, TeO2, GaN, ZrO2, AlN, Ta2O5, Al2O3 and AlSb. Suitable materials for the cladding 218 include AlAs, Al2O3, borosilicate glass, fluoride glass and SiO2. Suitable materials for the plasmonic bulk metal plate 220 include Au, Ag, Cu and alloys thereof.
FIG. 3A is a schematic illustration of a waveguide core 304 relative to a plasmonic bulk metal plate 220 taken along line 3-3 of FIG. 2 according to one embodiment. The view in FIG. 3A is taken from the leading edge side of the head 200. In other words, the view is rotated 90 degrees from the view shown in FIG. 2. The cladding material 218 has been removed for clarity. As shown in FIG. 3A, the waveguide core 302 is a linear core. The core 302 may extend from the surface opposite the ABS 212 to a point near, but recessed from, the ABS 212. As shown in FIG. 3A, the plasmonic bulk metal plate 220 is significantly wider than the waveguide core 302. As will be discussed below, the plasmonic bulk metal plate 220 is at least 1.5 times wider than the width of the waveguide core 302. FIG. 3A shows the entire distance that the plasmonic bulk metal plate 220 extends relative to the waveguide core 302. The distance is shown by arrows “A”. In one embodiment, the distance is between about 500 nm and about 2.0 microns. In another embodiment, the distance is about 1.2 microns.
FIG. 3B is a schematic illustration of a waveguide core relative to a plasmonic bulk metal plate taken along line 3-3 of FIG. 2 according to another embodiment. The view in FIG. 3B is taken from the leading edge side of the head 200. In other the view is rotated 90 degrees from the view shown in FIG. 2. The cladding material 218 has been removed for clarity. As shown in FIG. 3B, the waveguide core 304 comprises two cores 304A, 304B that converge at a point 306. In one embodiment, the plasmonic bulk metal plate 220 extends for a distance “B” that is between about 500 nm and about 2.0 microns. In one embodiment, the distance “B” is the length of the convergence point 306.
The core 304 may extend from the surface opposite the ABS 212 to a point near, but recessed from, the ABS 212. As shown in FIG. 3B, the plasmonic bulk metal plate 220 is significantly wider than the waveguide core 302. As will be discussed below, the plasmonic bulk metal plate 220 is greater in width than the waveguide core 304. In one embodiment, the plasmonic bulk metal plate 220 is at least 1.5 times wider than the width of the waveguide core 304. It is to be understood that while a single waveguide core 304 has been shown, the embodiments disclosed herein are applicable to EAMR heads having multiple waveguide cores. Additionally, while a straight waveguide core 304 is shown, it is to be understood that a tapered waveguide core is also contemplated. Furthermore, while the waveguide core 304 and plasmonic bulk metal plate 220 are shown recessed from the ABS 2112, it is contemplated that both the waveguide core 304 and plasmonic bulk metal plate 220 may extend to the ABS 212.
FIG. 4A is a schematic illustration a waveguide core relative to a plasmonic element taken along line 4-4 from FIG. 2, according to one embodiment. FIG. 4B is a close-up illustration of FIG. 4A. As shown in FIGS. 4A and 4B, the waveguide core 402 has a trapezoidal shaped cross section when viewed from the ABS. The trapezoid shape has two parallel sides of different length. The long, or first, side 404 has a width represented by arrow “E” that may be between about 90 nm and up to about 1 micron. The short, or second, side 406 has a width represented by arrow “D” that may be greater than zero, but up to about 200 nm. In one embodiment, the short side 406 may approximate a point such that the waveguide core 402 appears to have a triangle shaped cross-section when viewed from the ABS 212. The plasmonic bulk metal plate 220, on the other hand, has a width shown by arrow “C” that is at least 1.5 times greater than the width of the second side 406. In fact, the width of the plasmonic bulk metal plate 220 may extend to the edge of the slider 204. As shown in both FIGS. 4A and 4B, cladding material 218 is disposed between the plasmonic bulk metal plate 220 and the waveguide core 402, but it is to be understood that the plasmonic bulk metal plate 220 may be disposed directly on both the waveguide core 402 and the cladding 218 that at least partially surrounds the waveguide core 402. If the waveguide core 402 is spaced from the plasmonic bulk metal plate 220, the distance may be greater than 0 nm and up to about 40 nm, for example, between about 8 nm and about 15 nm, as shown by arrow “G”. The area between the waveguide core 402 and the plasmonic bulk metal plate 220 is not limited to cladding material. An adhesion layer may be present on the cladding 218. In such a situation, the adhesion layer has a thickness of about 1 nm to about 4 nm. In one embodiment, the adhesion layer, if present, may comprise the same material as the waveguide core 402, such as Ta2O5. It is contemplated that the adhesion layer may comprise dielectric material that is different from the waveguide core 402. The waveguide core 402 may have a thickness of between about 350 nm and about 500 nm, such as 400 nm as shown by arrow “F”.
During operation, the trapezoidal shaped waveguide core 402 results in a high efficiency coupling into the plasmonic bulk metal plate 220. The coupling occurs along the length of the plasmonic bulk metal plate 220. In one embodiment, the plasmonic bulk metal plate 220 has a length between about 500 nm and about 2.0 microns, such as 1.2 microns. At the coupling length (i.e., the length of the plasmonic bulk metal plate 220 represented by arrow “A” in FIG. 3A), the electromagnetic field energy results in a highly confined distribution. Most of the energy is coupled out from the waveguide core 402 and into the plasmonic bulk metal plate 220. To further confine the distribution, the second side 406 of the waveguide core 402 may be reduced.
FIG. 5 is a flow chart 500 illustrating a method of manufacturing an EAMR head according to one embodiment. The manufacturing involves depositing cladding material on a slider substrate at item 502. Waveguide core material is deposited on the cladding material in item 504. The waveguide core material is etched to form the final structure of the waveguide core in item 506. In one embodiment, the etching is a dry etch process that produces the trapezoidal cross-section when viewed from the ABS. Optionally, additional cladding material and an adhesion layer may be deposited on the waveguide core and previously deposited cladding material in item 508. Finally, the plasmonic bulk metal layer may be deposited adjacent the cladding material and the waveguide core. In one embodiment, the plasmonic bulk metal layer is formed directly on the waveguide core and cladding material. In another embodiment, the plasmonic bulk metal layer is formed on the additional cladding material. In yet another embodiment, the plasmonic bulk metal layer is formed on an adhesion layer.
The benefit of using a plasmonic bulk metal plate and a trapezoidal waveguide core is the lifetime of the head is increased because the NFT is less likely to fail. With the design discussed herein, the NFT does not need any 2D or 3D nanometer features in the plasmonic metals, yet the nano-focusing is still achieved. The device can be easily fabricated using a dry etching process for the waveguide core. In the fabrication process, the profile of the sidewalls of the trapezoid is not critical. Additionally, the distance between the write pole edge and the HFT heating spot in the down track direction can be reduced by about 40 nm in absence of the plasmonic features beyond bulk metal plate. The temperature at which the device can operate is also higher than may be obtained in absence of the plasmonic fine features beyond bulk metal plate.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

## Claims

1. A magnetic recording head, comprising:
a head body;
an energy source coupled to the head body;
a waveguide core disposed within the head body, wherein the waveguide core has a trapezoidal cross section when viewed from the air bearing surface, wherein the trapezoid has a first side having a first width and a second side having a second width that is less than the first width;
cladding material disposed at least partially around the waveguide core; and
a plasmonic metal element disposed adjacent the cladding material and the second side of the waveguide core.

2. The magnetic recording head of claim 1, wherein the waveguide core comprises Ge, Si, amorphous Si, GaAs, GZO (Gallium Zinc Oxide), GaP, ITO, TiO2, TeO2, GaN, ZrO2, AlN, Ta2O5, Al2O3 and AlSb.

3. The magnetic recording head of claim 1, wherein the plasmonic metal element comprises Au, Ag, Cu or alloys thereof.

4. The magnetic recording head of claim 1, wherein the first side has a width of between about 90 nm and about 1 micron.

5. The magnetic recording head of claim 1, wherein the second side has a width of greater than 0 nm and up to about 200 nm.

6. The magnetic recording head of claim 1, wherein the plasmonic metal element has a width that is greater than the width of the second side.

7. The magnetic recording head of claim 1, wherein the cladding material comprises AlAs, Al2O3, borosilicate glass, fluoride glass and SiO2.

8. A hard disk drive, comprising:
a magnetic media; and
a magnetic recording head disposed opposite the magnetic media, wherein the magnetic recording head comprises:
a head body;
an energy source coupled to the head body;
a waveguide core disposed within the head body, wherein the waveguide core has a trapezoidal cross section when viewed from the air bearing surface, wherein the trapezoid has a first side having a first width and a second side having a second width that is less than the first width;
cladding material disposed at least partially around the waveguide core; and
a plasmonic metal element disposed adjacent the cladding material and the second side of the waveguide core.

9. The hard disk drive of claim 8, wherein the waveguide core comprises Ge, Si, amorphous Si, GaAs, GZO (Gallium Zinc Oxide), GaP, ITO, TiO2, TeO2, GaN, ZrO2, AlN, Ta2O5, Al2O3 and AlSb.

10. The hard disk drive of claim 8, wherein the plasmonic metal element comprises Au, Ag, Cu or alloys thereof.

11. The hard disk drive of claim 8, wherein the first side has a width of between about 90 nm and about 1 micron.

12. The hard disk drive of claim 8, wherein the second side has a width of greater than 0 nm and up to about 200 nm.

13. The hard disk drive of claim 8, wherein the plasmonic metal element has a width that is greater than the width of the second side.

14. The hard disk drive of claim 8, wherein the cladding material comprises AlAs, Al2O3, borosilicate glass, fluoride glass and SiO2.

15. A method of making a magnetic recording head, comprising:
depositing cladding material on a substrate;
depositing waveguide core material on the cladding material;
etching the waveguide core material to form a waveguide core, wherein the waveguide core has a trapezoidal cross section when viewed from an air bearing surface, wherein the trapezoid has a first side having a first width and a second side having a second width that is less than the first width; and
depositing a plasmonic metal element adjacent the cladding material and the second side of the waveguide core.

16. The method of claim 15, wherein the waveguide core comprises Ge, Si, amorphous Si, GaAs, GZO (Gallium Zinc Oxide), GaP, ITO, TiO2, TeO2, GaN, ZrO2, AlN, Ta2O5, Al2O3 and AlSb.

17. The method of claim 15, wherein the plasmonic metal element comprises Au, Ag, Cu or alloys thereof.

18. The method of claim 15, wherein the first side has a width of between about 90 nm and about 1 micron.

19. The method of claim 15, wherein the second side has a width of greater than 0 nm and up to about 520 nm.

20. The method of claim 15, wherein the plasmonic metal element has a width that is greater than the width of the second side.