Self-anneal process for a near field transducer and chimney in a hard disk drive assembly

[0001] This application claims the benefit of U.S. Provisional Application Ser. No. 61/917,799, filed on Dec. 18, 2013, which is expressly incorporated by reference herein in its entirety.

[0002] The disclosure relates to energy assisted magnetic recording transducers or hard disk drives.

[0003] A conventional heat assisted magnetic recording (HAMR) transducer is used in writing data to a recording media. The conventional HAMR receives light, or energy, from a conventional laser, which may be a diode laser, for example. The current areal data density using HAMR is about 1 Tb/in⁻². The HAMR is conventionally bonded to a slider that rides on an air bearing surface of the recording media. The slider is attached to an arm that rotates to provide the slider and HAMR access to write tracks on the media at different radii.

[0004] The surface plasmon effect may be applied in a near-field transducer (NFT) to write data bits of smaller dimension than with conventional HAMR, on the order of 70 nm or less, but with higher heat energy density, increasing the possible areal data density that may be written to a magnetic disk. It is estimated that areal densities approaching 3 Tb/in⁻² are possible.

[0005] The NFT is effective in heating high magnetic anisotropy materials for about 1 nsec above the phase transition temperature to briefly lower the high coercivity, enabling the write head to record data that becomes stable once the heated bit region cools to ambient. The small size of the data bit translates into a large increase of storage density as compared to current areal densities of about 1 Tbm⁻².

[0006] However, because of the intensity of the resonant electromagnetic field that builds up in the NFT, the accumulated heat concentration may cause migration of the NFT material, thereby degrading the effectiveness of a HAMR. In-process anneals and better alloys have been proposed to mitigate this problem but studies indicate the need for anneals at greater than 200° C. However the disk reader and hard baked photoresist structures of the hard disk drive may degrade for >200° C. Local heating with a laser spot has been proposed but may not be economic and readily reduced to practice. Therefore a local annealing technique is needed.

[0015] The detailed description set forth below in connection with the appended drawings is intended as a description of various exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the present invention. Acronyms and other descriptive terminology may be used merely for convenience and clarity and are not intended to limit the scope of the invention.

[0016] The word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiment” of an apparatus, method or article of manufacture does not require that all embodiments of the invention include the described components, structure, features, functionality, processes, advantages, benefits, or modes of operation.

[0017] Any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations are used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element.

[0018] As used herein, the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0019] In the following detailed description, various aspects of the present invention will be presented in the context of a process for locally annealing a heat sinking chimney and near field transducer (NFT) in a HAMR transducer for hard disk drive read/write assemblies. However, those skilled in the art will realize that these aspects may be extended to other materials or components in other apparatus or articles of manufacture. Accordingly, any reference to a process for annealing a heat sinking chimney and NFT in a HAMR transducer is intended only to illustrate the various aspects of the present invention, with the understanding that such aspects may have a wide range of applications.

[0020] Various aspects of articles of manufacture and methods of manufacturing such articles of manufacture are disclosed. The articles of manufacture may include a HAMR transducer having an NFT and a chimney thermally coupled to the NFT. The articles of manufacture may also include an electrical conductor having section with a reduced width that is thermally coupled to the chimney. The methods include applying an electrical current to the electrical conductor to generate heat in the section and annealing the chimney and the NFT from the heat generated.

[0021] Various aspects of articles of manufacture and methods of manufacturing such articles of manufacture in batch are also disclosed. The articles of manufacture may include an array of HAMR transducers each having a near field transducer (NFT) and a chimney thermally coupled to the NFT. The articles of manufacture may further include an array of electrical conductors arranged with the array of HAMR transducers with each of the electrical conductors having section with a reduced width that is thermally coupled to a respective one of the chimneys. The methods include applying an electrical current to the electrical conductors to generate heat in their respective sections, and annealing the chimneys and the NFTs from the heat generated.

[0022] It is understood that other aspects of apparatus, articles of manufacture and methods will become readily apparent to those skilled in the art from the following detailed description, wherein various aspects of articles of manufacture and methods are shown and described by way of illustration. As will be realized, these aspects may be implemented in other and different forms and its several details are capable of modification in various other respects. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

[0023] FIG. 1 is a conceptual view of an exemplary embodiment of a HAMR disk drive. The HAMR disk drive 100 is shown with a rotatable magnetic disk 102. The magnetic disk 102 may be rotated on a spindle 104 by a disk drive motor (not shown) located under the magnetic disk 102. A head 106 may include read and write poles (not shown) that detect and modify the magnetic polarization of the recording layer on the disk's surface. The head 106 is generally integrally formed with a slider 108. The function of the slider 108 is to support the head 106 and any electrical connections between the head 106 and the rest of the HAMR disk drive 100. The slider 108 is mounted to a positioner arm 110 which may be used to move the head 106 on an arc across the rotating magnetic disk 102, thereby allowing the head 106 to access the entire surface of the magnetic disk 102. The arm 110 may be moved using a voice coil actuator 112 or by some other suitable means.

[0024] The slider 108 is aerodynamically designed to fly above the magnetic disk 102 by virtue of an air bearing created between the surface of the slider 106 and the rotating magnetic disk 102. This surface of the slider 108 is referred to as an air bearing surface (ABS). The ABS is the portion of the slider 108 surface which is closest to the rotating magnetic disk 102, which is typically the head 104. A HAMR transducer 114 may be coupled to the distal end of the slider 108 to assist writing data to the magnetic disk 102. The HAMR transducer 114 includes an NFT (not shown) aligned with the ABS of the slider 108. Light from a laser is coupled to the HAMR transducer 114 and guided by waveguide (not shown) to the NFT. The NFT focuses (or concentrates) the light to the magnetic disk 102, and heats a small region of the media. The head 106 magnetically writes data to the heated region of the media by energizing the write pole. When the laser, as the heat source, is turned off, the localized magnetic media cools and the written bit becomes thermally stable at ambient temperature.

[0025] FIG. 2 is a conceptual view of an exemplary embodiment of a HAMR transducer arranged with a slider for a HAMR disk drive. The HAMR disk drive 100 includes the magnetic disk 102, a subassembly 202 and a slider 108 on which a HAMR transducer 114 is formed. The subassembly 202 includes a light source, such as a laser diode 204 having an emission exit 206, attached to a submount 208. The slider 108 has a back side 210 to which the submount 208 may be bonded, and an ABS. In the embodiment shown, the back side 210 is opposite to the ABS. However, in other embodiments, the back side 210 (i.e, the side to which the submount is bonded) may not be opposite to the ABS.

[0026] A surface plasmon effect may be applied in the NFT (not shown) to potentially increase areal data density that may be written to a magnetic disk 102. Surface plasmons (SPs) are collective oscillations of surface charge that are confined to an interface between a dielectric and a metal. When SPs are resonantly excited by an external optical field, the field amplitude in the vicinity of the surface may be orders of magnitude greater than that of the incident field. Moreover, the region of enhanced field may be tightly confined to a spot much smaller than the incident wavelength, e.g., on the order of 70 nm or less. Gold is a suitable plasmonic material for wavelengths longer than ˜700 nm as it is chemically inert with a relatively high melting point.

[0027] A gold NFT that is excited at a SP resonance can couple light even more efficiently into a nearby medium by including a sharp tip in its design to take advantage of a “lightning rod” effect. A “lollipop” NFT may include a disk and a peg, where the peg acts as the sharp tip. At resonance the surface charge oscillates along the length of the lollipop peg to generate an electric field at the tip of the peg that couples energy into the magnetic disk 102. The peg provides the lightning rod effect for field confinement. A plasmonic metal beneath the recording layer of the magnetic disk 102 acts as both a heat sink and an image plane for the electric field. The recording layer is effectively within the gap of two nanoparticles, i.e., where the two nanoparticles constitute the NFT and its (virtual charge) image, resulting in good coupling efficiency and further confinement of the electric field.

[0028] FIG. 3 is a cross-section view of an exemplary embodiment of an NFT 302402. The NFT 302 is arranged as a disk in thermal and electrical contact with the peg 304. In operation, the NFT 302 is excited by light directed at it, typically by a laser, such as a laser diode, through an optical waveguide (not shown). The excitation is a resonant surface plasmon, in which the intensity of the evanescent field at the surface of the disk is enhanced relative to the field intensity of the illuminating light. The relatively intensified evanescent field is coupled down the length of the peg 304, where the tip of the peg 304 faces toward the ABS of the HAMR transducer 114 (see FIG. 2). This results in a lightning rod effect, which may produce a large electromagnetic field at the surface of the magnetic recording media, which absorbs and dissipates enough energy to raise the media temperature locally and reduce the magnetic coercivity in a high localized area corresponding to the dimensions of the peg 304.

[0029] The NFT 302 may be arranged with a heat removal, or heat sinking “chimney” 306. The chimney 306 may be made of gold because of the thermal conductivity properties of the metal. The NET 302 and chimney 306 may be partially or completely encapsulated in ceramics (SiO₂ and Al₂O₃), oxides or other materials commonly used for optical waveguides and electrical insulation. To mitigate the effects of atomic migration of gold due to localized heating of the NFT 302 and chimney 306, an electrical conductor may be deposited over the HAMR transducer during the manufacturing process. In a manner to be described later, the electrical conductor may act as a heater by passing an electrical current through it. In accordance with the present embodiment, the heat generated by the electrical conductor anneals the NFT 302 and the chimney 306.

[0030] FIG. 4 is a plan view of an exemplary embodiment of an electrical conductor 402, which passes over the chimney heat sink and NFT for annealing when an electrical current passes through. The electrical conductor 402 has a section 404 with a reduced width that is electrically coupled to the chimney during the annealing process. The reduced width increases the resistance of the portion of the electrical conductor 402 localized at the chimney, and therefore causes localized joule heating when an electrical current is applied.

[0031] FIG. 5A is a plan view illustrating an exemplary embodiment of the narrow section of the electrical conductor on a surface of the HAMR transducer directly over the chimney 306 and NFT 302, where both are shown with dotted lines to indicate that they are beneath the electrical conductor, and therefore embedded beneath the surface of the HAMR transducer. The NFT 302 and chimney 306 are shown in this view merely for clarity but, in fact, are not visible. As mentioned above, the electrical conductor 402 may be gold, and serves for thermal conduction of heat over the region including the chimney 306, NFT 302 and peg 304, and it provides heat from resistive losses in the narrow section of the electrical conductor 402. The chimney 306 is substantially in line with the center of the NFT 302, and provides thermal connection to the electrical conductor 402.

[0032] FIG. 5B is a cross-section view of the exemplary embodiment shown in FIG. 5A. The electrical conductor 402.404 is at the surface of the encapsulating substrate of the HAMR transducer that includes the NFT 302 and peg 304, which have been fabricated and where the encapsulant may be ceramic, oxide or other insulating materials. The chimney 306, which may be a gold filled via in the insulating encapsulant, provides thermal contact to the electrical conductor 402 so that heat generated in the section 404 of the electrical conductor 402 is effectively transferred to the NFT 302 and peg 304, which may also be gold. The encapsulant may have a lower thermal conductivity, and thus serve to thermally insulate other components of a magnetic read/write assembly from thermal damage due to the annealing.

[0033] The electrical conductor 402 may be formed by depositing a conductive layer (preferably gold, due to its thermal conductivity) and patterning the electrical conductor 402 in a photolithographic process. The electrical conductor 402 is shown wider at the ends 406, so that the resistance is higher in the narrow section 404 of the electrical conductor 402. Therefore, an electrical current passing through the section 404 of the electrical conductor 402 will dissipate an amount of thermal power in proportion to its resistance, and the surrounding region of NFT 302, chimney 306, and encapsulating material will heat up. The low thermal impedance of the path from the electrical conductor 402 through the chimney 306 to the NFT 302 and peg 304 enables the NET 302, peg 304 and chimney 306 to get nearly as hot as the electrical conductor 402. At a sufficient temperature, the gold will anneal, which may reduce or prevent degradation of the structures in operational use. The low thermal conductivity of the encapsulating ceramics (e.g., SiO₂ and/or Al₂O₃) may contribute to confining the heat to the NFT 302, peg 304 and chimney 306, thus preventing damage to surrounding structures, such as the read and/or write poles, which may include, for example, hard baked photoresist that cannot withstand temperature required to anneal gold. The narrow section 404 of electrical conductor 402 may be on the order of 1 micron wide, and is narrower than the wider current carrying ends 406 of the electrical conductor 402, which is wide enough to dissipate less heat due to a lower path resistance that is proportional to the width. In practice, the actual dimension of the narrow section 404 of the electrical conductor 402 may vary, depending on the thickness of the metallization and the electrical current delivered to generate heat.

[0034] Passing an electrical current through a network of electrical conductors 402 may cause sufficient heating in the localized region beneath it to generate an annealing temperature only sufficient to affect the immediate chimney 304, NFT 302 and peg 306. Because of localization of the heating in the HAMR transducer localized near the NFT 302, the temperature of the hot region below the electrical conductor 402 will decrease with depth, shielding other components in the HAMR transducer from suffering heat damage. Furthermore, a bottom pole layer of the write pole in a read/write assembly may tend to heat sink its surroundings and prevent the read pole from experiencing damaging high temperatures.

[0035] After the anneal process, the electrical conductor 402, may be removed, for example, by chemical mechanical polishing (CMP), ion milling, or other suitable means, down to the encapsulant substrate surface, leaving the chimney 306 intact for heat sinking to other structural features during operational use of the HAMR transducer.

[0036] It may be appreciated that the embodiment described may achieve anneal temperatures for gold localized at the NFT 302, peg 304 and chimney 306 above 200° C. for greater structural stability without damaging the reader and hard baked photoresist in adjacent structures in a magnetic read/write pole.

[0037] During the manufacturing process, an array of HAMR transducers may be manufactured in bulk in a single wafer by means well known in the art. As shown in FIG. 6, an array 600 of individual electrical conductors 402 may be connected in series and parallel so that a broken or shorted conductor will not lead to a failure of annealing capability in an entire wafer containing a plurality of chimneys 306, NFTs 302 and pegs 304. As part of the process, after annealing, the array 600 may be removed by a chemical-mechanical-polish (CMP) step, ion milling step, or by some other suitable means. As described above, the array 600 may be formed by depositing and patterning a metal layer, such as gold to form the plurality of electrical conductors 402, A group of serially interconnected electrical conductors 402 may be arranged to form a group 602. A plurality of groups 602 may be arranged in parallel to form the array 600, wherein the groups are connected by summing traces 604 that connect to contacts 606. Current is applied to the array 600 at contacts 606. The current divides among the plurality of parallel groups 602. The divided current i flows through each of the serial electrical conductors 402 in a respective group 602. The power dissipation in each of the electrical conductors 402 is given by i²R, with R being higher in the narrow sections 404 of the serially connected electrical conductors 402.

[0038] The various aspects of this disclosure are provided to enable one of ordinary skill in the art to practice the present invention. Various modifications to exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art, and the concepts disclosed herein may be extended to other devices. Thus, the claims are not intended to be limited to the various aspects of this disclosure, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the various components of the exemplary embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”