Flat NFT for heat assisted magnetic recording

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

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.

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. 1is a schematic illustration of a magnetic recording device, such as a hard disk drive (HDD)100according to one embodiment. The HDD100includes at least one magnetic recording medium, such as a disk102that is supported on a spindle104. A motor causes the spindle104, and hence the disk102, to rotate. A magnetic head that is mounted on a slider108moves over the disk102to read and write information from/to the disk102. The head rides on an air bearing above the disk102during read/write operations. The slider108is coupled to an actuator110by a suspension112and arm114. The suspension112, which may comprise stainless steel, provides a slight spring force, which biases the slider108towards the disk surface. Each actuator110is attached to an actuator means that controls the movement of the head106relative to the disk102.

FIG. 2is a schematic, cross-sectional illustration of an EAMR head200according to one embodiment. The head200is positioned across from a magnetic media202, such as a disk. The head200includes a slider204having a read head with a sensor206for reading information from the media202. The head200also includes a write portion. The write portion includes a write pole208and return pole210. The head200has an ABS212facing the disk202. The EAMR head200includes an energy source214, such as a laser, that directs energy through a waveguide core216. The waveguide core216is at least partially surrounded by cladding material218. As will be discussed below, a plasmonic bulk metal plate220is disposed adjacent the waveguide core216and the cladding218. In one embodiment, the plasmonic bulk metal plate220is disposed directly on both the cladding218and the waveguide core216. In another embodiment, the plasmonic bulk metal plate220is spaced from the waveguide core216by the cladding218. An NFT222is also present. The NFT222has an end exposed at the ABS212while both the waveguide core216and plasmonic bulk metal plate220are 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, Al2O3and AlSb. Suitable materials for the cladding218include AlAs, Al2O3, borosilicate glass, fluoride glass and SiO2. Suitable materials for the plasmonic bulk metal plate220include Au, Ag, Cu and alloys thereof.

FIG. 3Ais a schematic illustration of a waveguide core304relative to a plasmonic bulk metal plate220taken along line3-3ofFIG. 2according to one embodiment. The view inFIG. 3Ais taken from the leading edge side of the head200. In other words, the view is rotated 90 degrees from the view shown inFIG. 2. The cladding material218has been removed for clarity. As shown inFIG. 3A, the waveguide core302is a linear core. The core302may extend from the surface opposite the ABS212to a point near, but recessed from, the ABS212. As shown inFIG. 3A, the plasmonic bulk metal plate220is significantly wider than the waveguide core302. As will be discussed below, the plasmonic bulk metal plate220is at least 1.5 times wider than the width of the waveguide core302.FIG. 3Ashows the entire distance that the plasmonic bulk metal plate220extends relative to the waveguide core302. 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. 3Bis a schematic illustration of a waveguide core relative to a plasmonic bulk metal plate taken along line3-3ofFIG. 2according to another embodiment. The view inFIG. 3Bis taken from the leading edge side of the head200. In other the view is rotated 90 degrees from the view shown inFIG. 2. The cladding material218has been removed for clarity. As shown inFIG. 3B, the waveguide core304comprises two cores304A,304B that converge at a point306. In one embodiment, the plasmonic bulk metal plate220extends 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 point306.

The core304may extend from the surface opposite the ABS212to a point near, but recessed from, the ABS212. As shown inFIG. 3B, the plasmonic bulk metal plate220is significantly wider than the waveguide core302. As will be discussed below, the plasmonic bulk metal plate220is greater in width than the waveguide core304. In one embodiment, the plasmonic bulk metal plate220is at least 1.5 times wider than the width of the waveguide core304. It is to be understood that while a single waveguide core304has been shown, the embodiments disclosed herein are applicable to EAMR heads having multiple waveguide cores. Additionally, while a straight waveguide core304is shown, it is to be understood that a tapered waveguide core is also contemplated. Furthermore, while the waveguide core304and plasmonic bulk metal plate220are shown recessed from the ABS2112, it is contemplated that both the waveguide core304and plasmonic bulk metal plate220may extend to the ABS212.

FIG. 4Ais a schematic illustration a waveguide core relative to a plasmonic element taken along line4-4fromFIG. 2, according to one embodiment.FIG. 4Bis a close-up illustration ofFIG. 4A. As shown inFIGS. 4A and 4B, the waveguide core402has a trapezoidal shaped cross section when viewed from the ABS. The trapezoid shape has two parallel sides of different length. The long, or first, side404has a width represented by arrow “E” that may be between about 90 nm and up to about 1 micron. The short, or second, side406has a width represented by arrow “D” that may be greater than zero, but up to about 200 nm. In one embodiment, the short side406may approximate a point such that the waveguide core402appears to have a triangle shaped cross-section when viewed from the ABS212. The plasmonic bulk metal plate220, 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 side406. In fact, the width of the plasmonic bulk metal plate220may extend to the edge of the slider204. As shown in bothFIGS. 4A and 4B, cladding material218is disposed between the plasmonic bulk metal plate220and the waveguide core402, but it is to be understood that the plasmonic bulk metal plate220may be disposed directly on both the waveguide core402and the cladding218that at least partially surrounds the waveguide core402. If the waveguide core402is spaced from the plasmonic bulk metal plate220, 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 core402and the plasmonic bulk metal plate220is not limited to cladding material. An adhesion layer may be present on the cladding218. 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 core402, such as Ta2O5. It is contemplated that the adhesion layer may comprise dielectric material that is different from the waveguide core402. The waveguide core402may 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 core402results in a high efficiency coupling into the plasmonic bulk metal plate220. The coupling occurs along the length of the plasmonic bulk metal plate220. In one embodiment, the plasmonic bulk metal plate220has 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 plate220represented by arrow “A” inFIG. 3A), the electromagnetic field energy results in a highly confined distribution. Most of the energy is coupled out from the waveguide core402and into the plasmonic bulk metal plate220. To further confine the distribution, the second side406of the waveguide core402may be reduced.

FIG. 5is a flow chart500illustrating a method of manufacturing an EAMR head according to one embodiment. The manufacturing involves depositing cladding material on a slider substrate at item502. Waveguide core material is deposited on the cladding material in item504. The waveguide core material is etched to form the final structure of the waveguide core in item506. 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 item508. 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.