Perpendicular magnetic recording writer having improved performance and wide area track erasure reliability

A magnetic writer includes a high magnetic moment write pole layer on a main write pole, the write pole layer including a proximal end recessed from the air bearing surface, and a Wide Area Track Erasure (WATER) reservoir recessed from the proximal end of the write pole layer and transverse to a longitudinal direction of the main write pole. The write pole layer may be conformal in shape to, but have smaller dimensions relative to, the main write pole, such that a distance between their outer surfaces is generally constant in a flare region. The WATER reservoir width, in a cross-track direction, may be greater than or equal to the maximum width of the main write pole.

BACKGROUND

A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read-write head that is positioned over a specific location of a disk by an actuator. A read-write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.

With perpendicular magnetic recording (PMR) based HDDs, a typical PMR head includes a trailing write pole, a trailing return pole or opposing pole magnetically coupled to the write pole, and an electrically conductive magnetizing coil surrounding the write pole. The bottom of the return/opposing pole has a surface area greatly exceeding the surface area of the tip of the write pole. Write current is passed through the write coil to create magnetic flux within the write pole. The magnetic flux passes from the write pole tip, through the hard magnetic recording track on the media, into the soft under-layer in the magnetic media, and across to the return/opposing pole to complete perpendicular writing process.

Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present goals of hard disk drive design evolution. As areal density increases, the recording data rate preferably increases accordingly. For example, the recording data rate for a 3.5″ 7200 RPM desktop product may achieve greater than 2.4 Gb/s. Such a high data rate requirement on the PMR writer demands a fast writer with much reduced write field rise time for recording at high frequencies. Meanwhile, the high data rate PMR writer design also needs to meet stringent reliability requirements, such as requirements associated with Wide Area Track Erasure (WATER). The WATER reliability issue is especially important for short yoke length PMR writer configurations, which intrinsically have worse WATER margins. Therefore, a dynamically fast writer with improved off track erasure or WATER capability may be desirable.

DETAILED DESCRIPTION

Approaches to a magnetic writer are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. It will be apparent, however, that the embodiments described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments described herein.

Physical Description of Illustrative Operating Environments

Embodiments may be used in the context of a magnetic recording head in a hard-disk drive (HDD) data storage device. Thus, in accordance with an embodiment, a plan view illustrating an HDD100is shown inFIG. 1to illustrate an operating environment example.

FIG. 1illustrates the functional arrangement of components of the HDD100including a slider110bthat includes a magnetic read-write head110a. Collectively, slider110band head110amay be referred to as a head slider. The HDD100includes at least one head gimbal assembly (HGA)110including the head slider, a lead suspension110cattached to the head slider typically via a flexure, and a load beam110dattached to the lead suspension110c. The HDD100also includes at least one recording medium120rotatably mounted on a spindle124and a drive motor (not visible) attached to the spindle124for rotating the medium120. The read-write head110a, which may also be referred to as a transducer, includes a write element and a read element for respectively writing and reading information stored on the medium120of the HDD100. The medium120or a plurality of disk media may be affixed to the spindle124with a disk clamp128.

The HDD100further includes an arm132attached to the HGA110, a carriage134, a voice-coil motor (VCM) that includes an armature136including a voice coil140attached to the carriage134and a stator144including a voice-coil magnet (not visible). The armature136of the VCM is attached to the carriage134and is configured to move the arm132and the HGA110to access portions of the medium120, all collectively mounted on a pivot shaft148with an interposed pivot bearing assembly152. In the case of an HDD having multiple disks, the carriage134may be referred to as an “E-block,” or actuator comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb.

An assembly comprising a head gimbal assembly (e.g., HGA110) including a flexure to which the head slider is coupled, an actuator arm (e.g., arm132) and/or load beam110dto which the flexure is coupled, and an actuator (e.g., the VCM) to which the actuator arm is coupled, may be collectively referred to as a head stack assembly (HSA). An HSA may, however, include more or fewer components than those described. For example, an HSA may refer to an assembly that further includes electrical interconnection components. Generally, an HSA is the assembly configured to move the head slider to access portions of the medium120for read and write operations.

With further reference toFIG. 1, electrical signals (e.g., current to the voice coil140of the VCM) comprising a write signal to and a read signal from the head110a, are transmitted by a flexible cable assembly (FCA)156(or “flex cable”). Interconnection between the flex cable156and the head110amay include an arm-electronics (AE) module160, which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The AE module160may be attached to the carriage134as shown. The flex cable156may be coupled to an electrical-connector block164, which provides electrical communication, in some configurations, through an electrical feed-through provided by an HDD housing168. The HDD housing168(or “enclosure base” or simply “base”), in conjunction with an HDD cover, provides a semi-sealed (or hermetically sealed, in some configurations) protective enclosure for the information storage components of the HDD100.

Other electronic components, including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil140of the VCM and the head110aof the HGA110. The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle124which is in turn transmitted to the medium120that is affixed to the spindle124. As a result, the medium120spins in a direction172. The spinning medium120creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider110brides so that the slider110bflies above the surface of the medium120without making contact with a thin magnetic-recording layer in which information is recorded. Similarly in an HDD in which a lighter-than-air gas is utilized, such as helium for a non-limiting example, the spinning medium120creates a cushion of gas that acts as a gas or fluid bearing on which the slider110brides.

The electrical signal provided to the voice coil140of the VCM enables the head110aof the HGA110to access a track176on which information is recorded. Thus, the armature136of the VCM swings through an arc180, which enables the head110aof the HGA110to access various tracks on the medium120. Information is stored on the medium120in a plurality of radially nested tracks arranged in sectors on the medium120, such as sector184. Correspondingly, each track is composed of a plurality of sectored track portions (or “track sector”) such as sectored track portion188. Each sectored track portion188may include recorded information, and a header containing error correction code information and a servo-burst-signal pattern, such as an ABCD-servo-burst-signal pattern, which is information that identifies the track176. In accessing the track176, the read element of the head110aof the HGA110reads the servo-burst-signal pattern, which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil140of the VCM, thereby enabling the head110ato follow the track176. Upon finding the track176and identifying a particular sectored track portion188, the head110aeither reads information from the track176or writes information to the track176depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system.

An HDD's electronic architecture comprises numerous electronic components for performing their respective functions for operation of an HDD, such as a hard disk controller (“HDC”), an interface controller, an arm electronics module, a data channel, a motor driver, a servo processor, buffer memory, etc. Two or more of such components may be combined on a single integrated circuit board referred to as a “system on a chip” (“SOC”). Several, if not all, of such electronic components are typically arranged on a printed circuit board that is coupled to the bottom side of an HDD, such as to HDD housing168.

Introduction

The term “substantially” will be understood to describe a feature that is largely or nearly structured, configured, dimensioned, etc., but with which manufacturing tolerances and the like may in practice result in a situation in which the structure, configuration, dimension, etc. is not always or necessarily precisely as stated. For example, describing a structure as “substantially vertical” would assign that term its plain meaning, such that the sidewall is vertical for all practical purposes but may not be precisely at 90 degrees.

As discussed, a high data rate requirement on a PMR writer demands a fast writer with much reduced write field rise time for recording at high frequencies. Meanwhile, the high data rate PMR writer design also needs to meet stringent reliability requirements, such as requirements associated with Wide Area Track Erasure (WATER). The WATER reliability issue is especially important for short yoke length PMR writer configurations, which intrinsically have worse WATER margins. This is due, at least in part, to the presence of side shields, which are considered important in overcoming adjacent track interference (ATI). That is, the side shields are activated by write flux leaking out of the main pole during writing operations, which can result in WATER. One possible approach is to simply fabricate a PMR writer with a thicker main pole, which may improve on-track writability, but at the expense of further off-track WATER performance degradation. Therefore, a dynamically fast writer with improved off track erasure or WATER capability may be beneficial.

FIG. 2is a cross-sectional side view of a perpendicular magnetic recording (PMR) head, according to an embodiment of the invention.FIG. 2illustrates a PMR head200in recording relation with a perpendicular magnetic recording medium such as disk210. PMR head200comprises a reader220and a writer230.

PMR writer230comprises a main pole231, a first auxiliary pole232band a second auxiliary pole232a(on opposing sides of main pole231), a writer coil235, a magnetic wrap-around shield (WAS)234, and a return pole233. Main pole231is exposed at the air bearing surface (ABS), faces disk210, and forms recording bits by reversing the magnetization of magnetic particles in the disk210. The first and second auxiliary poles232b,232a, respectively, are magnetically connected to the main pole231but are not typically exposed at the ABS. Writer coil235is for exciting the main pole231and the auxiliary poles232a,232b, i.e., the electricity flowing through the coil235produces a magnetic field. The WAS234is positioned at the periphery of the main pole231tip for assisting with focusing the magnetic flux emitting from main pole231, and a return pole233is positioned for providing means for the magnetic flux to return to the writer230structure to complete the magnetic circuit.

Electrical pulses are sent to the coil235of writer230with different patterns of positive and negative currents and the current in the coil235induces a magnetic field across the gap between the main pole231and the disk210, which in turn magnetizes a small area on the recording medium, disk210. A strong, highly concentrated magnetic field emits from the main pole231in a direction perpendicular to the disk210surface, magnetizing the magnetically hard recording layer211. The resulting magnetic flux then travels through the soft underlayer212, returning to the return pole233where it is sufficiently spread out and weak that it will not erase the signal recorded by the main pole231when it passes back through the magnetically hard recording layer211on its way back to the return pole233.

The writer main pole231switching characteristics directly determine the dynamic rise time property in PMR systems. Thus, PMR main pole231designs may address the following performance and reliability challenges: (a) dynamic fast response, i.e., small rise time and fast saturation; (b) steady state domain lock up (when write current is off); and (c) dynamic Wide Area Track Erasure (WATER). However, improvements in dynamic writer performance as seen in error margin (EM) or signal to noise ratio (SNR) often result in degradation of off track WATER reliability. Embodiments of PMR writer designs described herein may improve writer performance, such as write field rise time and/or saturation (thus error margin), while at least maintaining off track WATER reliability margin.

Recessed Main Pole Layer for Magnetic Writer

FIG. 3is a cross-sectional side view illustrating a PMR writer, according to an embodiment. Writer330comprises a main write pole331extending to an air bearing surface (ABS) in a longitudinal direction, a first auxiliary pole332bpositioned on one side of the main write pole331, and an additional high magnetic moment write pole layer340positioned on the main write pole331on the side opposing the auxiliary pole332b. The write pole layer340is composed of a “high magnetic moment” material. For example, and according to an embodiment, the write pole layer340may have a magnetic moment as high as (i.e., substantially equivalent to) the magnetic moment of the material of which the main write pole331is composed (for a non-limiting example, able to generate a magnetic flux density B≅2.4 T). The write pole layer340comprises a proximal end toward or near the ABS, which is recessed a particular distance (R1) from the ABS. Upon write current excitation in the coil (e.g., coil235ofFIG. 2), the main write pole331, the auxiliary pole332b(and an opposing auxiliary pole such as auxiliary pole232aofFIG. 2, if present), and write pole layer340function collectively to create magnetic flux for purposes of writing on corresponding media.

According to an embodiment, the distance R1between the proximal end of the write pole layer340and the ABS is in a range of 0.2-1.5 micrometers (μm). A distance R1near 0.55 μm has been found to produce suitably effective results in view of other component dimensions discussed elsewhere herein. For comparison, with an R1of around 0.55 μm, the distance R2between the proximal end of the auxiliary pole332band the ABS may be around 0.45 μm, for example. Hence, according to an embodiment, the write pole layer340is recessed farther from the ABS than is the opposing auxiliary pole332b. Further, according to an embodiment, a writer330comprising a second auxiliary pole (such as auxiliary pole232aofFIG. 2) is contemplated, where the second auxiliary pole is positioned on the same side of the main write pole331as the write pole layer340, and comprises a proximal end recessed from the ABS a greater distance than the write pole layer340is recessed from the ABS. For a non-limiting example, the second auxiliary pole may be recessed near 2.0 μm from the ABS, and may be around 0.6 μm thick in the down-track direction.

According to an embodiment, the write pole layer340is conformal to, but undersized from, the shape of main write pole331. This is best envisioned fromFIG. 4, whereFIG. 4is a top view illustrating a PMR writer including a recessed main pole layer on the main pole, according to an embodiment.FIG. 4depicts the writer330comprising the main write pole331with the write pole layer340deposited thereon (with the side gap and side shields not shown here, for purposes of clarity). According to an embodiment, the main write pole331comprises a first top profile shape with a first outer surface331ain a flare region A-A, similar to as depicted inFIG. 4. Similarly, write pole layer340comprises a second top profile shape encompassed by the first top profile shape, and with a second outer surface340ain at least a portion of the flare region A-A, similar to as depicted inFIG. 4. According to an embodiment, the distance L between the first outer surface331aof the main write pole331and the second outer surface340aof write pole layer340is substantially constant in at least a portion of the flare region A-A. Hence, as depicted, the shape of write pole layer340is considered substantially conformal to, but undersized from, the shape of the main write pole331. According to an embodiment, the distance L between the first outer surface331aof the main write pole331and the second outer surface340aof write pole layer340is in a range of 0.0-0.5 micrometers (μm). A distance L near 0.20 μm has been found to produce suitably effective results in view of other component dimensions discussed elsewhere herein. Another way of looking at this feature is that the respective flare angle (i.e., the angle, from the cross-track direction, of each respective outer surface331a,340ain the flare region) for each of the main write pole331and the write pole layer340are substantially equivalent, according to an embodiment.

With reference toFIG. 3, the write pole layer340is configured with a tapering angle α from the longitudinal direction (e.g., in an up-track direction) at its proximal end, as depicted. While the write pole layer340is depicted with a proximal angled (α) surface340bmeeting or intersecting with the top surface of the main write pole331, according to an embodiment, the proximal end of the write pole layer340may have a substantially vertical surface that meets with or intersects with the top surface of the main write pole331, from which the angled surface340bextends at angle α. According to an embodiment, the tapering angle α from the longitudinal direction is in a range of 15-60 degrees. A tapering angle α near 35 degrees has been found to produce suitably effective results in view of other component dimensions discussed elsewhere herein. According to an embodiment, the tapering angle α of the proximal end of the write pole layer340is substantially equivalent to the tapering angle of the proximal end of the write main pole331.

With reference toFIG. 3, the write pole layer340has a thickness t1(in the down-track direction). According to an embodiment, the thickness t1of the write pole layer340is in a range of 20-150 nanometers (nm). A thickness t1near 80 nm has been found to produce suitably effective results in view of other component dimensions discussed elsewhere herein.

Writer330further comprises a Wide Area Track Erasure (WATER) reservoir element342(“WATER reservoir342”) recessed from the proximal end of the write pole layer340in the longitudinal (flying height) direction, and configured substantially transverse to the longitudinal direction (e.g., “into the paper” ofFIG. 3). According to an embodiment, and as depicted inFIG. 3, the WATER reservoir342may extend in the down-track direction a distance substantially equivalent to the thickness of the main write pole331. However, the precise size of the WATER reservoir342in each direction may vary from implementation to implementation and, therefore, a WATER reservoir342that is different from the thickness of the main write pole331is contemplated.

FIG. 5is a top view illustrating a PMR writer main pole and a WATER reservoir, according to an embodiment. As depicted inFIGS. 3 and 5, the WATER reservoir342is recessed from the ABS a distance R3. According to an embodiment, the WATER reservoir342is recessed from the ABS a distance R3in a range of 0.5-1.7 micrometers (μm). A distance R3near 1.0 μm has been found to produce suitably effective results in view of other component dimensions discussed elsewhere herein.

According to an embodiment, and as depicted inFIG. 5, the WATER reservoir342has a width, in the cross-track direction which is transverse to the longitudinal (or flying height) direction, that is greater than or equal to a maximum width, in the cross-track direction, of the main write pole331. Such a configuration for the WATER reservoir342facilitates, for example, its ability to affect the flux that may otherwise undesirably leak from the main write pole331into the side shields and thereby activating the side shields, and thus negatively affecting WATER, as previously described.

With reference toFIG. 5, the WATER reservoir342has a thickness t2in the longitudinal (or flying height) direction. According to an embodiment, the thickness t2of the WATER reservoir342is in a range of 0.1-0.7 micrometers (μm). A thickness t2near 0.3 μm has been found to produce suitably effective results in view of other component dimensions discussed elsewhere herein.

According to an embodiment, the WATER reservoir342is structurally connected to, and composed of a same material as, the main write pole331, as depicted inFIG. 5. According to an alternative embodiment, the WATER reservoir342is structurally disconnected from the main write pole331. As such, there may be a gap502between surfaces of the WATER reservoir342and the main write pole331(depicted as gap502between the dashed lines ofFIG. 5), filled with a different material than that of the WATER reservoir342and/or the main write pole331. According to an embodiment, the WATER reservoir342is structurally disconnected from, and composed of a different material than, the main write pole331.

The foregoing PMR writer embodiments with an additional piece of high magnetic moment main pole layer340in combination with an aggressive WATER reservoir342may enable a high data rate, short yoke length (e.g., 2×2 or fewer coil turns) writer platform with improved saturation speed/reduced field rise time (e.g., at least in part by way of the high moment main pole layer340) without mitigating off track WATER reliability (e.g., at least in part by way of the aggressive WATER reservoir342). Note that a combination of the foregoing features, i.e., a stack comprising the auxiliary pole332b, the main write pole331with a WATER reservoir342, and the write pole layer340is likely to have demonstrably better performance collectively than each feature otherwise would separately, especially in view of the foregoing component dimensions.

Extensions and Alternatives

In the foregoing description, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Therefore, various modifications and changes may be made thereto without departing from the broader spirit and scope of the embodiments. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

In addition, in this description certain process steps may be set forth in a particular order, and alphabetic and alphanumeric labels may be used to identify certain steps. Unless specifically stated in the description, embodiments are not necessarily limited to any particular order of carrying out such steps. In particular, the labels are used merely for convenient identification of steps, and are not intended to specify or require a particular order of carrying out such steps.