Patent ID: 12190922

DETAILED DESCRIPTION

The present disclosure is generally related to heat-assisted magnetic recording (HAMR), also referred to as energy-assisted magnetic recording (EAMR), thermally-assisted recording (TAR), thermally-assisted magnetic recording (TAMR), etc. In a HAMR device, a near-field transducer (NFT) concentrates optical energy into a tiny optical spot in a recording layer, which raises the media temperature locally, reducing the writing magnetic field required for high-density recording. A waveguide delivers light to the near-field transducer and excites the near-field transducer.

In some embodiments, an NFT includes an enlarged part which receives light energy from the waveguide and funnels this energy, which is in the form of surface plasmon polaritons (SPP), to an elongated part (e.g., a peg) that extends from the enlarged part towards the recording medium. The peg directs the SPP to the recording medium, which creates a hotspot that facilitates writing via the magnetic field.

In existing HAMR heads, the elongated part of the NFT terminates at the media-facing surface of the head, also referred to herein as the air-bearing surface (ABS). The ABS may be covered by a protective coating such as diamond-like carbon (DLC). The DLC protects various components (e.g., a write pole) from corrosion, burnish, and other effects that may result from exposure to the drive atmosphere and from contact with the disk surface.

In embodiments described below, an NFT of a HAMR head is manufactured to have an elongated part that extends from the ABS towards the recording medium. The material in an area surrounding the elongated part may also extend out from the ABS, forming a pedestal structure. While extending parts of the NFT beyond the ABS may seem counterintuitive, it has been found that having part of the NFT nearly in contact or in contact with the recording medium can improve performance of the HAMR head, such as reduction in required laser current (Ieff), reduction in track width that can increase areal density capacity (ADC). The fly height and clearance actuator settings of the HAMR head may be adjusted to account for some portions of the read/write transducer that may contact the recording medium before other parts of the ABS.

In reference now toFIG.1, a perspective view shows a recording head100according to an example embodiment. The recording head100may be used in a magnetic data storage device, e.g., HAMR hard disk drive. The recording head100may also be referred to herein interchangeably as a slider, head, write head, read head, read/write head, etc. The recording head100has a slider body102with read/write transducers108at a trailing edge104that are held proximate to a surface of a magnetic recording medium (not shown), e.g., a magnetic disk.

The illustrated recording head100is configured as a HAMR device, and so includes optical components that form a hot spot on the recording medium near the read/write transducers108. These HAMR components include an energy source106(e.g., laser diode) mounted to the slider body102and a waveguide110(e.g., a dielectric waveguide) integrated into the slider body102. The waveguide110delivers electromagnetic energy from the energy source106to a near-field transducer (NFT) that is part of the read/write transducers108. The NFT achieves surface plasmon resonance and directs the energy out of a media-facing surface112(also referred to herein as an air-bearing surface, or ABS) to create a small hot spot in the recording medium.

InFIG.2, a cross-sectional view shows details of a slider body102according to an example embodiment. The waveguide110includes a core200, top cladding layer202and bottom cladding206. Other cladding layers not shown in this figure may be used with this waveguide110, such as middle and side cladding. The core200delivers light to an NFT208that is located at the media-facing surface112. A write pole210(also referred to herein as a “magnetic pole”) is located near the NFT208. A heat sink212may be used to thermally couple the NFT208to the write pole210.

A magnetic coil (not shown) induces a magnetic field through the write pole210in response to an applied current. During recording, the waveguide110delivers light216from a light source to the NFT208. The NFT208directs surface plasmons out of the media-facing surface112to form a hotspot219within a recording layer of a moving recording medium220. The write pole210sets a magnetic orientation in the hotspot219, thereby writing data to the recording medium220.

In this configuration, the NFT208includes an enlarged part208aand an elongated part208bextending from the enlarged part208atowards and normal to the media-facing surface112. The enlarged part208amay be configured, for example, as a circular disk and the elongated part208bmay be configured, for example, as a peg having a rectangular or triangular shape as seen normal to the media-facing surface112. The NFT208may be made from a combination of optically efficient materials such as Au or Ag, and mechanically robust materials such as Rh or Ir.

For example, the enlarged part208amay be made of Au. An Au disk/plate can maximize coupling light between the waveguide110and the enlarged part208a, and is large enough and recessed enough from the media-facing surface112such that there is a reduced chance for degradation (e.g., voiding, deformation) that may occur for smaller Au features that are closer to the media-facing surface112.

The elongated part208bmay be made from a mechanically robust material that is less susceptible to deformation, voiding, etc., that can occur with Au and similar soft metals. Such mechanically robust materials may also be resistant to oxidation and other types of corrosion. While robust materials such as Rh and Ir may be less optically efficient than Au, their mechanical durability generally outweighs losses in coupling efficiency. The NFT208may include additional structures shown here that are formed of the different types of materials. For example, the enlarged part208amay be formed of multiple layers of an optically efficient metal and a mechanically robust metal, or the elongated part208bmay have an expanded region where it is embedded within the enlarged part208a.

As indicated by dimension209, the elongated part208bextends beyond the media-facing surface112. This dimension209is as-manufactured, meaning that it is formed via a manufacturing process such as photolithography and layer deposition. This is in contrast to situations where a HAMR read/write head experiences local protrusion at or near the NFT due to local heating and thermal expansion. In those cases, when he head is at a uniform temperature (e.g., ambient temperature, with no local heating applied near the NFT), the NFT will not extend beyond the media-facing surface. In contrast, the illustrated NFT elongated part208bwill extend beyond the media-facing surface112when the slider body102is at a uniform temperature. The portion of the NFT elongated part208bthat extends beyond the media-facing surface112may be referred to herein as a pedestal204.

As shown in this example, regions207surrounding the elongated part208bmay also be manufactured to extend beyond the media-facing surface112. This surrounding material207may be considered as part of the pedestal204. The pedestal204allows the NFT208to be placed closer to the media surface220athan other components such as the tip of the write pole210.

InFIG.3, a diagram shows additional details of the pedestal204ofFIG.2. The media-facing surface112is offset from the moving media surface220aby a head-to-media separation (HMS)302. Unless stated otherwise, the term HMS in this disclosure is intended to describe a minimum clearance between a feature of the head and the media, which may be different at different regions of the head at a given passive fly height, e.g., distances300and302shown inFIG.3. The passive fly height is an average fixed clearance between the media-facing surface and the media induced by air-bearing features of the head. The passive fly height does not include clearance changes caused by fixed or adjustable regions that protrude from (or are recessed from) a plane of the media-facing surface. The HMS302is maintained by a combination of a passive fly height and a clearance actuator (not shown), e.g., a heater. The fly height is maintained by a thin layer of gas (e.g., air, helium) between air bearing features of the head's media-facing surface112and the media surface220a. The HMS302is a measure of the local separation between the read/write transducers and the media surface220a, which can be adjusted dynamically by regulating an amount of current applied to the clearance actuator. There may be multiple clearance actuators, e.g., used to separately control HMS of the read transducer(s) and HMS of the write transducer(s).

As seen inFIG.3, an HMS300of the pedestal204, which includes the elongated part208bof the NFT208, is less than the local HMS302, e.g., the average HMS of writer components such as write pole, return pole, shields, etc. Both HMS300,302may be affected similarly by a write transducer clearance actuator such that both HMS300,302are reduced or increased similarly by the clearance actuator. In some embodiments, the clearance control system may work on setting the writer HMS302, with the understanding that the HMS300of the pedestal204may be less than the HMS302. In some embodiments, the HMS300may be at or close to zero, such that the pedestal204comes into occasional or continuous contact with the media surface220a, even though the rest of the media-facing surface112has no contact or minimal contact.

InFIG.3, an overcoat304is shown covering the media-facing surface112. The overcoat304may be made from an impact-resistant and corrosion resistant material such as DLC. The overcoat304is shown conformably covering at least part of the pedestal204. The overcoat304may fully cover the pedestal204as manufactured, and after some time in operation, the overcoat304may be burnished from the tip204aof the pedestal due to contact with the media surface220a.

Another overcoat306is shown inFIG.3, this one covering the recording media surface220a. The media overcoat306may be formed of a carbon material similar to the head overcoat304. Note that for purposes of this discussion, the HMS302is shown being measured from the top of the media overcoat306to the bottom of the head overcoat304. For other purposes, a distance308between a component at the media-facing surface112of the head and the magnetic media material at surface220amay be described as the HMS. For example, the HMS-dependent performance of the write pole would be determined based on the HMS308and not HMS302, as this is the distance that is spanned by the magnetic field emitted by the write pole.

InFIG.4, the pedestal204is seen in a plan view looking at the media-facing surface112. The outline of the pedestal204appears as an oval in this view, however may have any shape. Generally, the pedestal may be formed so that it does not extend to the write pole210, but may affect other components near the elongated part208bof the NFT208, such as side shields400, write pole210, and waveguide core402. The write pole210is made of an iron alloy, which could corrode if exposed to the drive's atmosphere, so the pedestal204may have a size and shape that prevents burnishing near the write pole210or other structures made of material that might corrode. Generally, the current process capability can for a pedestal204as small as 1-2 μm in the downtrack direction and can be positioned on the media-facing surface112to within 1-2 μm.

InFIG.5, a plan view at a larger scale thanFIG.4shows additional components surrounding the pedestal204, including return poles500and501, contact sensor502, and read transducer504(e.g., magnetoresistive stack). The contact sensor502may be a temperature sensor, sometimes referred to as a dual-ended, temperature coefficient of resistance (DETCR) sensor. The contact sensor502is sensitive to sudden temperature changes that occur when the head approaches and contacts the media surface. The signal of the contact sensor502is used by the clearance control system to adjust and control the HMS near the writer and reader.

The highlighted region506inFIG.5generally indicates a region that contacts the media during contact detect. In one embodiment, the pedestal204is sized and located to be outside this region506(e.g., >0.5 μm separation from the sensor502), therefore allowing the existing contact algorithms to maintain the HMS for the regions of the media-facing surface112except for the pedestal204. The estimated HMS using these algorithms can also be used to estimate the clearance between the tip of the pedestal204and the media surface. For example, if the HMS is estimated to be 6 nm and the pedestal204extends 4 nm from the media-facing surface112, then the pedestal204will be about 2 nm from the media surface.

In other embodiments, the contact sensor502and pedestal204can be located close enough to each other that the contact sensor502detects contact between the pedestal204and the recording medium before the rest of the media-facing surface112contacts. This is indicated by circle508inFIG.5, which is an alternate extent of the pedestal204. The contact detect algorithms can be adapted to account for this configuration as well. Using the example above, where the desired HMS for the head is 6 nm and the pedestal extends 4 nm, the contact detection controller cause the clearance actuator to back off 2 nm from the operating point where contact is detected.

WhileFIG.5shows pedestal dimensions204,508that are roughly equal in downtrack and crosstrack directions, these dimensions may be significantly different from each other. For example, if the pedestal dimensions affect the contact detect and clearance setting (e.g., if pedestal is too close to DETCR clearance detector) then this may prescribe tight control of the downtrack dimension of the pedestal, however significant variation in the crosstrack direction may be acceptable. If the pedestal dimension is such that clearance modulation can be affected (e.g., pedestal area hitting disc is too large) then both downtrack and cross-track dimensions may be more tightly controlled. In one embodiment, the downtrack dimension of the pedestal may be around 2 μm or less, whereas the crosstrack dimension may be much larger, e.g., two times larger. For a smaller downtrack dimension, e.g., 1 μm or less, an even larger aspect ratio may be possible, e.g., three or more times larger in the crosstrack direction.

InFIGS.6-9, graphs illustrate how pedestal height can affect performance of a HAMR recording head according to example embodiments. In these graphs, the HAMR head is modeled as having an HMS302(seeFIG.3) away from the pedestal of around 6.5 nm, with the x-axes of the graphs (pHMS) corresponding to the clearance300shown inFIG.3. The dashed lines indicate a baseline performance value with pedestal dimension209equal to zero, which corresponds to no pedestal being used.

As shown inFIG.6, the thermal gradient increases with decreasing pHMS, and this can increase the linear bit density that can be written to the tracks. As shown inFIG.7, the write-plus-erase width decreases with decreasing pHMS, and this can increase the track density that can be written to the disk. The results inFIGS.6and7indicate an increase in ADC in response to a decrease in pHMS. As shown inFIGS.8and9, both laser current and peg temperature decrease with decreasing pHMS. These latter figures indicate an extension of the life of the HAMR head in response to a decrease in pHMS.

In order to validate these simulations, a set of prototype HAMR heads were fabricated with three pedestal heights of 2, 4, and 6 nm. The trends in performance of these heads generally matched those shown in the simulations, with the following seen for the 6 nm pedestal heads: 3.2% ADC gain, 1.6K/nm downtrack thermal gradient (DTTG) gain, 1.5K/nm crosstrack thermal gradient (CTTG) gain, 2.5 mA decrease in laser current (Ieff). No bit error rate (BER) degradation was detected in the heads or media. Note that the prototype heads used in this testing had an Rh peg.

In reference again toFIG.3, assuming the pedestal dimension209is large enough (e.g., >1 nm), the passive fly height can be increased by a similar height. For example, if an existing NFT design without a pedestal is known to work with a passive fly height of X, and the design is changed to include a pedestal dimension209of Y, the passive fly height with the pedestal may be set in a range from X to X+Y, assuming other components such as the write pole and return poles can operate effectively at the higher clearance, which can help lower reader temperature for better reliability and reduce the variance of the passive fly height. Note that in this scenario, if X=Y, then the pedestal would be in contact with the media at the lower end of this range.

InFIG.10A, a process diagram shows pedestal formation on a HAMR slider1000according to an example embodiment. The recording head1000is shown after completing a lapping operation. Generally, sliders are formed on a wafer using layer deposition and photolithography processes, and the wafer separated into slider structures, e.g., bars of sliders. A mechanical lapping process removes materials from the media-facing side of the slider1000, resulting in lapped surface1002that exposes some components of the slider1000, such as an extended part1004of an NFT1005, write pole1006, and read transducer1008.

In this example, the lapping has stopped at surface1002, which is short of the final dimension, represented by dashed line1003. As seen in the top ofFIG.10A, the NFT extended part1004is covered by a feature1010, which may be a resist or hardmask that is shaped through photolithography. A second feature1012is also shown protecting the read transducer1008.

As seen in the middle ofFIG.10A, an operation has etched the media-facing surface1014to the final dimension1003, except for the areas covered by features1010,1012. At the bottom ofFIG.10, the resist/hardmask has been removed, and the read transducer1008brought to final dimension, e.g., through a mechanical process. The overcoat1015is then deposited over the surface1014. The resulting pedestal1016is shown with the overcoat1015covering end1017. The material at the end1017may later be removed (burnished) during operation of the drive through contact with the disk, or may be removed during another manufacturing operation.

InFIG.10B, a process diagram shows pedestal formation on a HAMR slider1000according to another example embodiment. The recording head1000is shown after completing a lapping operation. Generally, sliders are formed on a wafer using layer deposition and photolithography processes, and the wafer separated into slider structures, e.g., bars of sliders. A mechanical lapping process removes materials from the media-facing side of the slider1000, resulting in lapped surface1002that may expose some components of the slider1000, such as an extended part1004of an NFT1005, write pole1006, and read transducer1008.

In this example, the lapping has stopped at surface1002, which is short of the final dimension, represented by dashed line1003. As seen in the top ofFIG.10B, the NFT extended part1004is covered by a feature1010, which may be a resist or hardmask that is shaped through photolithography. A second feature1020is also shown that was previously formed to protect the read transducer1008. The lapping operation exposes one face of this second feature.

As seen in the middle ofFIG.10B, an operation has etched the media-facing surface1014to the final dimension1003, except for the areas covered by feature1010. At the bottom ofFIG.10B, the resist/hardmask has been removed. In this example, a small amount of the second feature1020remains over the read transducer1008, resulting in a small recession from the media-facing surface1014. The overcoat1015is then deposited over the surface1014. The resulting pedestal1016is shown with the overcoat1015covering end1017. The material at the end1017may later be removed (burnished) during operation of the drive through contact with the disk, or may be removed during another manufacturing operations.

Other variations of the processes shown above may be possible. In one embodiment, the process may further involve lifting off part of the overcoat1015, so it doesn't cover the pedestal1016, or other parts of the slider surface1014. In such a case, a different overcoat may be deposited over the pedestal1016, read transducer1008, and/or recessed write pole1006. In other embodiments, instead of etching the media-facing surface to form the pedestal, the pedestal and part of the NFT can be deposited on the completed head. In such a case a cap or extension of the NFT can be added to the existing peg/elongated part, and may be made of the same or different materials than the peg/elongated part.

InFIG.11A, a flowchart shows a method of manufacturing a HAMR head according to an example embodiment. The method involves forming1100a HAMR recording head that has a waveguide, a write pole, and a near-field transducer proximate the write pole. The near-field transducer has an elongated part operable to direct plasmons to a recording medium. The surface of recording head is lapped1101to form a lapped surface. A resist or hardmask is patterned1102in a region over the elongated part. The lapped surface with the resist or hardmask pattern is etched1103to form a media-facing surface. The location of the resist or hardmask is such that the extended portion protrudes beyond the media-facing surface by a first distance after the etch. The resist or hardmask is removed1104and a carbon overcoat is deposited1105over the media-facing surface.

InFIG.11B, a flowchart shows a method of manufacturing a HAMR head according to another example embodiment. The method involves forming1100a HAMR recording head that has a waveguide, a write pole, and a near-field transducer proximate the write pole. The near-field transducer has an elongated part operable to direct plasmons to a recording medium. The surface of recording head is lapped1101to form a lapped surface. Then a carbon overcoat is deposited1112, and a resist or hardmask is patterned1113in a region that encompasses the elongated part. The surface is etched1114to some depth beyond the depth of the overcoat such that the extended portion protrudes beyond the media-facing surface by a first distance after the etch. A second overcoat layer is applied1115over the resist or hardmask and the region that encompasses the extended portion. The resist or hardmask is then removed1116to leave one layer of overcoat everywhere.

A HAMR head implementing the extended NFT part/pedestal as described herein may take the height of the pedestal into account when performing active clearance control. As noted in the description ofFIG.5, a contact sensor can be located relative to the pedestal such that wherein the contact detection sensor detects contact between the pedestal and a recording medium. In other embodiments, the pedestal is separated from the contact detection sensor such that the contact detection sensor detects contact between the recording medium and a region of the media-facing surface located away from the pedestal. In the latter case, it may be assumed that when contact is not detected on the region of the media-facing surface, there still may be contact between the pedestal and the media-facing surface.

InFIG.12, a flowchart illustrates a method of use of a HAMR drive according to an example embodiment. The method involves measuring1200a signal from a contact detection sensor that is at a media-facing surface of a recording head. The recording head has a near-field transducer that creates a hotspot on a recoding medium while a magnetic field is applied to the hotspot. The near-field transducer has an extended portion that, as-manufactured, protrudes beyond the media-facing surface by a first distance. Based on a transition in the signal, contact is determined1201between the recording head the recording medium.

Based on the determination of the contact, a control signal is applied1202to a clearance actuator of the recording head. The control signal causes the media-facing surface to maintain a first head-to-media spacing from the recording medium. The control signal also causes the extended portion of the near-field transducer to maintain a second head-to-media spacing from the recording medium that is less than the first head-to-media spacing.

In one embodiment, the contact determined1201is between the recording head and a region of the media-facing surface located away from the extended portion of the near-field transducer. In such a case, a response of the control signal applied at1202is based on maintaining the first clearance. In another embodiment, the contact is between the recording head and the extended portion of the near-field transducer (also referred to as the pedestal). In such a case, a response of the control signal applied at1202response of the control signal is based on maintaining the second clearance.

InFIG.13, a block diagram illustrates components of a HAMR drive1300according to an example embodiment. The drive1300includes circuitry1302that may include a system on a chip (SoC), power supply, host interface circuitry, etc. The circuitry1302may include one or more processors1304coupled to memory1306. The memory1306may include volatile and non-volatile memory, and is used to at least store and execute firmware of the drive1300. A read/write channel1308is used to communicate with one or more heads1310that read from and write to a magnetic disk1312.

The head1310includes a laser1316(or other energy source), a waveguide1317(or other energy delivery path) and an NFT1318. Part of the NFT1318extends beyond a media-facing surface1322of the head to form a pedestal1320. A contact detection sensor1324is located at the media-facing surface1322, and sends a signal1336via the channel1308back to a clearance control module1330. As indicated by block1334, the signal1336may be a time varying signal that measures temperature at the media-facing surface1322. Typically, the temperature rises as the head1310approaches the surface of the disk1312, with a sharp transition when contact is made. This transition, indicated by line1338, is due to heat transfer from the head1310to the disk1312during the contact.

The clearance control module1330uses the signal1336to send a control signal to a clearance actuator1326located near the media-facing surface1322. This actuator1326may include a heater that causes local deformation of the media-facing surface1322due to thermal expansion of the head material. More than one contact detection sensor1324may be used as well as more than one clearance actuator1326. For example, different head-to-media spacings may be maintained for a read transducer1328during reading and a write transducer (which includes NFT1318and write pole1329) during writing. Different heaters and/or contact detection sensors may be used in the different modes.

Note that the due to the extension of the pedestal1320, it may be subject to additional wear due to more frequent contact with the disk than what is seen by the other regions of the media-facing surface1322. This can be mitigated by performing a ‘dummy’ write operation at a high clearance (e.g., a clearance high enough that no data is written) and/or at a region of the disk1312where no important data is stored. This writing with subsequent idling of the write transducer has been found to build up a layer of oxide (e.g., SiO2) at the write transducer. Generally, a servo control subsystem1332schedules operations of the heads, include times when the write transducer of the heads will be idled, e.g., when heads are parked or otherwise minimally powered, during long reads, etc. Thus, if the system determines that the writer will be idled, the head could perform the dummy writing for a sufficient period of time (e.g., 1-2 seconds) to put a build-up of SiO2on the heads thereby protecting the pedestal1320against corrosion. The dummy write could be performed use any signal, e.g., a 2T tone, random data, etc.

The various embodiments described above may be implemented using circuitry, firmware, and/or software modules that interact to provide particular results. One of skill in the arts can readily implement such described functionality, either at a modular level or as a whole, using knowledge generally known in the art. For example, the flowcharts and control diagrams illustrated herein may be used to create computer-readable instructions/code for execution by a processor. Such instructions may be stored on a non-transitory computer-readable medium and transferred to the processor for execution as is known in the art. The structures and procedures shown above are only a representative example of embodiments that can be used to provide the functions described hereinabove

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

The foregoing description of the example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Any or all features of the disclosed embodiments can be applied individually or in any combination are not meant to be limiting, but purely illustrative.