Integrated heat assisted magnetic recording device

An integrated heat-assisted magnetic recording (HAMR) device comprises a slider that has a top surface, a bottom surface, and a trailing end. A waveguide is carried on the trailing end and a near field transducer is positioned to receive energy from the waveguide and produce plasmons for heating a region of a magnetic medium. A write pole is carried by the slider adjacent to the near field transducer. A laser is mounted on the top surface of the slider and produces a laser beam that passes through a beam shaper mounted on the top surface of the slider that collimates or focuses the laser beam. A mirror is mounted on the slider for directing the collimated or focused light beam into the waveguide.

BACKGROUND

In response to increased demand for higher magnetic storage capacity, areal bit densities approaching 1 TB/in2are being contemplated. The bit size of sub-50 nm required to fulfill this goal is within a range where superparamagnetic instabilities affect the life time of stored data. Superparamagnetic instabilities become an issue as the grain volume of the recording media is reduced in order to maintain the number of grains per bit. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality KuV/kBT>70 can no longer be maintained. Kuis the magnetocrystalline anisotropy energy density of the material, kBis Boltzmann's constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy can demagnetize the stored bits. As the grain size is decreased in order to increase the areal density, a threshold is reached for a given Kuand temperature T such that stable data storage is no longer feasible.

The thermal stability can be improved by employing a recording medium formed of a material with a very high Ku. However, with available materials, recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Accordingly, it has been proposed to overcome the recording head field limitations by employing thermal energy to heat a local area on the recording medium before or at about the time of applying the magnetic field to write to the medium in order to assist in the recording process.

Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity. This allows the applied magnetic writing fields to more easily direct the magnetization during the temporary magnetic softening caused by the heat source. HAMR allows for the use of small grain media, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability, which is desirable for recording at increased areal densities. HAMR can be applied to any type of magnetic storage media including tilted media, longitudinal media, perpendicular media, and patterned media. By heating the media, the Kuor coercivity is reduced such that the magnetic write field is sufficient to write to the media. Once the media cools to ambient temperature, the coercivity has a sufficiently high value to assure thermal stability of the recorded information.

For heat assisted magnetic recording, an electromagnetic wave of, for example, visible, infrared, or ultraviolet light can be directed onto a surface of a data storage medium to raise the temperature of a localized area to facilitate switching. Well known optical waveguides such as solid immersion lenses (SILs), solid immersion mirrors (SIMs), and mode index lenses have been proposed for use in reducing the size of a spot on the medium that is subjected to the electromagnetic radiation. SILs, SIMs, and mode index lenses alone are not sufficient to achieve focal spot sizes necessary for high areal density recording due to diffraction limited optical effects. Metal pins and other near field transducer (NFT) designs positioned at the focal point of the waveguide are used to further concentrate the energy and direct it to a small spot on the surface of the recording medium.

Because it has been known that a close proximity of the near field optical transducer and writing field is necessary, many techniques to deliver the electromagnetic wave from the energy source to the recording medium in an efficient way have been proposed. Some proposals have the energy source directed right at the waveguide, but the energy source is set some appreciable distance away. Another light delivery technique that has been proposed uses optical fibers as waveguides. But, optical fibers are very stiff and can affect the flyability of a slider in a disc drive system. The use of microelectromechanical systems (MEMS) mirrors has also been proposed for light delivery. The time and cost it takes to make and integrate those components into a HAMR system makes that proposed solution impractical.

There is a need for a compact, modular HAMR recording device that can provide localized heating without costly components or difficult interconnects.

SUMMARY

An integrated heat-assisted magnetic recording (HAMR) device comprises a slider which carries a laser, a beam shaper, a mirror, a write pole, a waveguide, and a near field transducer. The laser is mounted on a top surface of the slider and emits a light beam. The beam shaper is attached to the slider such that the light beam from the laser is collimated or focused. The mirror is attached to the slider such that the mirror directs the collimated or focused light beam into a waveguide mounted on the slider. A near field transducer is positioned adjacent to the write pole and receives energy from the waveguide and produces plasmons for heating a region of a magnetic medium.

Another aspect provides a method for creating integrated heat-assisted magnetic recording devices. A row of lasers are mounted to a slider bar, and a row of covers are bonded to the slider bar. The slider bar is lapped to a set of required dimensions. A plurality of ball pads and a plurality of electrical leads are patterned on a top surface of the row of covers. A plurality of electrical connections are made between the row of covers and the slider bar. The slider bar and row of covers are diced into a plurality of individual parts. A plurality of mirrors are aligned to the plurality of individual parts, and the plurality of individual parts are attached to a plurality of head gimbal assemblies.

DETAILED DESCRIPTION

FIG. 1is a perspective view of disc drive10including an actuation system for positioning slider12over track14of magnetic medium16. The particular configuration of disc drive10is shown for ease of describing the present invention and is not intended to limit the scope of the present invention in any way. Disc drive10includes voice coil motor (VCM)18arranged to rotate actuator arm20on a spindle around axis22. Load beam24is connected to actuator arm20at head mounting block26. Suspension28is connected to an end of load beam24and slider12is attached to suspension28. Magnetic medium16rotates around an axis30, so that the windage is encountered by slider12to keep it aloft a small distance above the surface of magnetic medium16. Each track14of magnetic medium16is formatted with an array of data storage cells for storing data. Slider12carries a magnetic transducer (not shown inFIG. 1) for reading and/or writing data on tracks14of magnetic medium16. The magnetic transducer utilizes additional electromagnetic energy to heat the surface of medium16to facilitate recording by a process termed heat assisted magnetic recording (HAMR).

Heat assisted magnetic recording (HAMR) relies on an energy source such as a laser to locally heat the surface of storage medium16. The present invention utilizes a special recording head assembly on the end of suspension28and in conjunction with slider12to provide the localized heating. Specifically, the invention integrates many of the necessary HAMR components into and around slider12.

Before a more detailed description of the invention is given, a brief overview of how HAMR functions will be given.FIG. 2shows a cross sectional schematic view of a portion of magnetic writer32and a portion of associated perpendicular magnetic storage medium16. Magnetic writer32includes write pole36and return pole38coupled by yoke40. Coil42comprising conductors44and46, encircles yoke40and is supported by insulator48. Perpendicular magnetic storage medium16comprises magnetically hard storage layer50and soft magnetic underlayer52. A current in write coil42induces a magnetic field in yoke40and write pole36. The polarity of the magnetic field will depend on the direction of current flow through write coil42. Magnetic flux exits the write pole tip of write pole36at air bearing surface (ABS)56, passes through magnetically hard layer50into soft magnetic underlayer52of storage medium16. The magnetic flux returns from storage medium16to return pole38. Near field transducer58is coupled to waveguide60that receives an electromagnetic wave from an external source such as a laser. Near field radiation at the end of near field transducer58is used to heat a portion62of magnetically hard layer50to lower the coercivity so that the magnetic field from write pole36can affect the magnetization of the storage medium.

HAMR devices can incorporate various waveguides such as mode index lenses or planar solid immersion mirrors or lenses to generate focused beams. In the example shown inFIG. 3, edge66of waveguide60is substantially parabolic in shape. If edge66is reflective, waveguide60acts as a solid immersion mirror. Electromagnetic waves68and70traveling along the longitudinal axis of waveguide60will be reflected at boundary66toward focal point72as shown. Diffraction gratings74or other means known in the art can be used to couple external energy into waveguide60.

The dimensions of the spot concentrated at focal point72of waveguide60are diffraction limited and are not sufficient for the sub-100 nm dimensions required for high areal density HAMR recording media. Near field transducers (NFTs) such as metallic pins, sphere/pin, or disc/pin combinations are required to focus the energy to acceptable sub-100 nm spot sizes. Near field transducer58positioned at focal point72of waveguide60can couple with incident waves68and70to generate surface plasmons that propagate axially down NFT58until they exit as evanescent energy schematically shown as arrows78that heat a small region62of recording media16.

The waveguide60can be made of, for example, a high index dielectric core material like TiO2, Ta2O5, Si, SiN, or ZnS depending on the wavelength and refractive index desired. For example, Si has a very large index of 3.5 at a wavelength of 1550 nm in the near infrared, but it is not transparent to visible light. Ta2O5has a lower index of about 2.1, and is transparent throughout the near infrared and visible portions of the spectrum. Waveguide60also contains dielectric cladding layers on either side of the core.

One type of NFT comprises two and three dimensional metallic shapes in the form of pins, disc/pin, sphere/pin, as well as “C” shape, “L” shape, and “bowtie” shape apertures in metallic films. These structures resonate when irradiated with properly designed incident electromagnetic radiation, whereby the resulting surface plasmons generated can illuminate minute areas of proximate surfaces with intense radiation. Generally, the structures are metallic shapes in an insulating environment. Planar NFTs are shaped metallic films with or without apertures depending on the orientation of the transducer with respect to the incident radiation.

Another type of NFT includes reverse near field transducers which comprise dielectric shapes in a metal matrix. When a reverse NFT is irradiated with the proper electromagnetic energy, surface plasmons are generated at the metal/dielectric interface at the boundaries of the structure.

FIGS. 4A and 4Bshow integrated HAMR device80.FIG. 4Ais an exploded view of integrated HAMR device80that shows four main parts or components: slider12, cover82, mirror84, and laser86. Slider12has trailing edge88and leading edge90. Leading edge90faces toward head mounting block26, and trailing edge88faces away from head mounting block26. Slider12flies above storage medium16on an air bearing surface. Slider12includes top surface92upon which laser86is mounted. Laser86(or other source of electromagnetic radiation) projects unshaped light beam94in a direction towards trailing edge88. This unshaped light beam94needs to be either collimated or focused before it can couple into a transducer and heat storage medium16. Cover82acts as a beam shaper and accomplishes the collimation or focusing when it is placed on slider12; cover82also protects laser86when it is placed on slider12. Cover82is made up of cap piece96and lens piece98. Cap piece96is preferably made of glass or another suitable substance such as silicon, while lens piece98is typically made of glass, and includes collimating or focusing lenses100A (shown inFIGS. 7 and 9) and100B. Cap piece96and lens piece98are bonded together to make cover82. Many types of bonding are suitable such as anodic and fusion bonding. Cover82is also bonded to slider12with suitable methods such as solder bonding or an adhesive bond. When cover82is bonded to slider12, a hermetic seal may be created around laser86and collimating or focusing lenses100A and100B line up with unshaped light beam94and collimate or focus it. Mirror84is typically made out of silicon, and it is affixed to trailing edge of slider12and cover82. The purpose of mirror84is to help direct the shaped light beam into waveguide60. Its structure and function are explained in more detail below as well as seen more clearly inFIG. 9.

InFIG. 4B, integrated HAMR device80is shown in an assembled state. Cover82has plurality of ball pads102connected to plurality of electrical leads104which connect to plurality of contact terminals106on slider12through plurality of interconnects108. Interconnects108provide electrical communication between electrical leads104and contact terminals106, and therefore provide electrical communication between cover82and slider12. Two preferred embodiments of interconnects108are soldered connections and wire-bonded connections, but any other suitable electrical interconnects may be used, including inter-wafer bond connections. Soldered connections are shown inFIG. 4Bas well as all other FIGS., except forFIG. 4Cwhich shows wire-bonded connections110. A flex circuit (not shown) is typically used to connect to plurality of ball pads102in order to control the various components of integrated HAMR device80. Electrical power leads connected to electrical leads104and/or contact terminals106are laid out on slider12leading to laser86in order to power and control it. A more detailed explanation is given below in the discussion ofFIG. 6.

FIG. 5shows integrated HAMR device80with mirror84removed. Laser86is mounted on slider12and is completely enclosed within cover82. Laser86projects a light beam in a direction towards trailing edge88, and when cover82is placed on slider12the light beam passes through collimating or focusing lenses100A and100B contained within lens piece98to become shaped light beam112. Waveguide60is mounted on trailing edge88of slider12. Waveguide60may be a planar solid immersion mirror waveguide with coupling grating74, and is usually parabolic in shape. Other types of waveguides such as three-dimensional solid immersion mirrors or three-dimensional solid immersion lenses may also be used. A light beam must be collimated or focused before it can hit coupling grating74and couple into waveguide60effectively. When collimated or focused light hits coupling grating74, it propagates through waveguide60and condenses towards the focal point where near field transducer58is located. A view of the complete path that a light beam takes can be seen more clearly inFIG. 9.

InFIG. 6, cover82has been removed from integrated HAMR device80for a clearer view of slider12and laser86. The slider12includes top surface92upon which laser86is mounted. Laser86projects unshaped light beam94in a direction towards trailing edge88. Laser86may be, for example, a GaAs-type diode laser with P-type region120and N-type region122. P-type region120is typically much thinner relative to N-type region122even to the point where P-type region120constitutes a thin layer on an N-type substrate. Therefore, although unshaped light beam94is emitted from the junction of P-type region120and N-type region122, beam94will effectively be emitted from whichever side of laser86P-type region120is on. Accordingly, laser86can either be mounted with P-type region120adjacent to top surface92(P-side down) or P-type region120away from top surface92(P-side up). If laser86is mounted with P-side up, then unshaped light beam94will be lined up with collimating or focusing lenses100A and100B when cover82is bonded to slider12. If, however, laser86is mounted with P-side down, then laser86needs to be elevated above top surface92to line up unshaped light beam94with collimating or focusing lenses100A and100B. The elevation is attained with pedestal124. Mounting laser86with P-side down and using pedestal124allows for better heat transfer from laser86to the ultimate destination, data storage medium16. In this embodiment, pedestal124is made of three parts, but it can be monolithic or otherwise comprise any number of parts. Pedestal124is preferably made from a material that matches or is very similar to the thermal expansion coefficient of the laser material (one example of the laser material is GaAs). Some examples of suitable materials for pedestal124are BeO, copper, or diamond chips. Mounted on trailing edge88of slider12are contact terminals106and waveguide60(with grating74). A number of contact terminals106are connected to electrical power leads126that are laid out on top surface92of slider12. Electrical power leads126are connected to laser power contacts128by power connections130. Power connections130can be wire-bonded connections or any other suitable types of connections.

InFIGS. 7 and 8, cover82for integrated HAMR device80is shown in different perspectives. Cover82includes cap piece96and lens piece98, each of which is preferably formed from a wafer. Cap piece96and lens piece98are bonded together. Many types of bonding are suitable, such as anodic and fusion bonding. Cavity132is created by the bonding of cap piece96and lens piece98. Cavity132is spacious enough to fit around laser86. Lens piece98includes inner lens surface134and outer lens surface136. Either one or both of these surfaces may have individual lenses on them to either collimate or focus a light beam. In other words, cover82may include two surface cross-cylindrical collimating lenses100A and100B as shown, or may be a single surface collimating lens. Cover82can also include two surface focusing lenses or a single surface focusing lens.FIGS. 5 and 6show that cylindrical lens100A (FIG. 5), located on inner lens surface134, has its axis oriented 90° to the axis of cylindrical lens100B (FIG. 6), which is located on outer lens surface136. Therefore, this embodiment employs a cross-cylindrical arrangement. As a result, when cover82is placed on slider12and over laser86, the unshaped light beam emitted from laser86is collimated and ready to be coupled into a grating74and waveguide60.

Lens piece98is ground and polished to a thickness of about 150 μm to 200 μm in between the inner lens surface134and the outer lens surface136. For example, a thickness of about 174 μm may be used. Outer lens surface136is located at the trailing end of cover82and front surface137is located at the leading end. Cover82also includes top surface138, bottom surface140, and two side surfaces142. Cover82is fashioned to fit on slider12, and the length of cover82from its trailing end to its leading end may be, for example, about 1170 μm to about 1250 μm. The height of the cover82from top surface138to bottom surface140may be, for example, about 225 μm to about 275 μm. The width of the cover82in between side surfaces142may be, for example, about 790 μm to about 850 μm.

Slider12may have similar length and width dimensions to cover82. This will be the case, for example, when a fabrication process such as the one described inFIGS. 10A-10Iis used.

Generally, laser86is about one-third the size of both cover82and slider12. However, laser86can be any size that can be mounted on top surface92of slider12and fits inside cavity132of cover82.

FIG. 9illustrates the internal path that unshaped light beam94and shaped light beam112take within integrated HAMR device80. In this view, a portion of mirror84is broken away. Mirror84, which may be made of silicon, has angled surface144created by silicon etching. Angled surface144has a mirror finish typically produced by etching and is able to reflect collimated light beam112at a given angle. Alternatively, mirror84may be made of a transparent material such as glass, with reflective surface144produced by polishing. Surface144may have a reflective coating such as a metal deposited on it. In this embodiment, unshaped light beam94is emitted from laser86and goes through a cross-cylindrical collimating lens which is made up of first collimating lens100A and a second collimating lens100B. Unshaped light beam94is thus transformed into shaped light beam112as it enters mirror84. Angled surface144reflects or directs shaped light beam112onto coupling grating74and into waveguide60. Mirror84can be aligned such that the angle at which shaped light beam112hits coupling grating74and enters into waveguide60creates the optimal energy heat transfer to near field transducer58to heat a localized spot on magnetic storage medium16. If this alignment is done while the output of the electromagnetic radiation is monitored, it is called an “active” alignment.

The conventional method of manufacturing sliders uses wafers that comprise a laminate disposed on a substrate and includes a thin-film magnetic head integrated into the wafers. The substrate is typically made from such materials as aluminum oxide and titanium carbide. Generally, a disc shaped wafer is formed from the slider materials and long rows or bars are cut out of the wafer for further processing.FIGS. 10A through 10Cshow a typical process by which these rows of sliders are made.FIGS. 10D through 10Fshow a similar type of process by which rows of covers can be made, andFIGS. 10G through 10Ishow the process by which multiple integrated HAMR devices can be made with the rows of sliders, the rows of covers, lasers, and mirrors.

InFIG. 10A, slider wafer200is shown, comprising substrate204with laminate206and coating layer208stacked on substrate204by a known technique. As shown, laminate206is formed such that a number of thin-film magnetic recording heads202are arranged in a matrix on laminate206.

Next, inFIG. 10B, slider wafer200is cut into predetermined sizes and forms, usually into slider bars210comprising a plurality of magnetic recording heads202arranged in a row and exposed at side face212. Side faces212can then be subjected to a lapping or grinding step so as to form an air bearing surface. Alternatively, this lapping step can be saved until after a few more steps are performed, as discussed below. Moreover, opposite faces214running parallel to side faces212(not visible from the perspective inFIG. 10B) become the top surfaces of the slider where the lasers are placed pursuant to this invention.

InFIG. 10C, cap wafer216is similarly made of a suitable substance such as glass or silicon and includes grid of cavities218.

As seen inFIG. 10D, lens wafer220is also fashioned, usually out of glass. The lens wafer includes a similar grid of inner lenses100A that match up with cavities218of cap wafer216.

InFIG. 10E, lens wafer220is flipped completely over from its orientation shown inFIG. 10D, so that inner lenses100A are faced toward cap wafer216and its grid of cavities218, and the two wafers216and220are bonded together, creating lens/cap wafer222shown inFIG. 10E. Anodic and fusion bonding, among others, are considered suitable types of bonding for this step. Lens wafer220(as part of lens/cap wafer222) may then be ground and polished to a thickness of about 150 μm to 200 μm (as indicated by line A inFIG. 10F). After lens wafer220is ground and polished, outer lenses100B may be formed on lens wafer220.

Next, lens/cap wafer222is cut into rows.FIG. 10Fshows row232of covers that include cavities132because they are cut as such along the dotted lines shown inFIG. 10C. Row232of covers is ready to be cut into plurality of individual covers234. The total length of individual covers234(i.e. the thickness of lens wafer220and cap wafer216together and as indicated by line B inFIG. 10F) may be about 1170 μm to about 1250 μm. The height of individual covers234(as indicated by line C inFIG. 10F) may be about 225 μm to about 275 μm. The width of individual covers234(as indicated by line D inFIG. 10F) may be about 790 μm to about 850 μm.

InFIG. 10G, slider bar210has electrical connections126deposited on it for the lasers86. Then, lasers86are mounted to slider bar210, and cover row232is aligned to fit over slider bar210, ready for bonding by suitable methods such as solder bonding or an adhesive bond. When cover row232is bonded to slider bar210, hermetic seals may be created around lasers86. This alignment may be a passive alignment, or it may be an active alignment for lasers86located at the opposite ends of slider bar210. Again, if this alignment is done while the output of the electromagnetic radiation from lasers86is monitored, it is called an “active” alignment. Otherwise, it is a passive alignment.

InFIG. 10H, cover row232is bonded to slider bar210, and electrical leads104are formed on the trailing end of cover row232. Next, electrical leads104and ball pads102are patterned on plurality of cover top surfaces138, and interconnects110are made between slider bar210and cover row232. Interconnects110may be, for example, soldered connections or wire-bonded connections, but any suitable electrical interconnect can be used, including inter-wafer bond connections. Finally, the combined slider bar210and cover row232can be diced into individual parts along dashed lines250shown inFIG. 10H.

At this point, the individual parts are slider12and cover82bonded together. Integrated HAMR device80is complete except for the mounting of mirror84. The individual devices are then attached to head gimbal assemblies. Mirror84can be actively or passively aligned as shown inFIG. 10Ito create individual integrated HAMR device80. Again, an active alignment entails monitoring the output of the electromagnetic radiation from waveguide end118while mirror84is being adjusted. A passive alignment relies on the geometry of the structure and the tolerances of the parts to affix mirror84in a correct spot.