Patent Application
20100321825
Magnetic transducers are combined read/write head structures having a writer portion for storing data and a reader portion for retrieving data, and are utilized by a wide variety of magnetic storage systems. The writer typically comprises a main pole (or write pole), a yoke, a back via, and one or more return poles. The main pole and return pole(s) are separated by nonmagnetic write gaps, located at or near an exterior media-facing surface. Magnetic flux is generated by switching the write current in a coil formed about the yoke and main pole. The coil is surrounded by insulating layers that typically extend from the write gap to the back via. Flux loops generated by the write current exit the tip of the main pole, cross into the magnetic medium through the external surface of the transducer, and close through the return pole and back via.
In disc-based magnetic storage systems, the external surface is typically an air-bearing surface (or ABS), and the transducer is typically formed on a slider attached to a suspension assembly and actuator. As the medium tracks past the transducer, it generates windage along the ABS that causes the slider to “fly” just above the surface of the medium. The suspension assembly and actuator position the slider over the medium, allowing the transducer to read and write data along side-by-side tracks that are spaced from one another in the transverse or crosstrack direction.
Data bits are stored by switching the write current as the magnetic transducer flies along the track. The write current determines the flux density and field direction at the main pole tip, and thus the magnetic domain orientation in the medium. In perpendicular writers, flux enters the medium in a substantially perpendicular sense, and the bits are formed perpendicularly along the track. In longitudinal writers, flux enters the medium along the tracking direction, and the bit orientation is along the track.
In general, perpendicular writers allow bits to be packed more closely, increasing areal density as compared to longitudinal designs. To facilitate this configuration, perpendicular media are formed with a top recording layer having high coercivity and unidirectional perpendicular anisotropy, and a soft underlayer (SUL) having high magnetic permeability, low reluctance and high in-plane anisotropy. The end of the main pole facing the recording layer is shaped into a narrow pole tip, which concentrates flux and reduces bit spacing. The return pole is relatively larger, so that the flux spreads out in the SUL before re-crossing the recording layer. This reduces the tendency for rewriting or erasure when the flux loops close back to the return pole.
Magnetic readers utilize read sensors such as magnetoresistive (MR) sensors and multilayer spin valve/giant magnetoresistive (GMR) elements, in which electrical resistance depends strongly upon field strength. The resistance is measured by a sense current, which varies as the reader element tracks across magnetic domain boundaries in the bit pattern, which is read out as a function of the sense current.
In magnetic transducer manufacture, the reader and writer structures are typically formed as a number of closely spaced layers. The reader (or read head) includes a reader element, a bottom shield and a top shield, with the reader element located in a read gap between the bottom and top shields. The writer (or write head) has a main pole (or write pole) formed into a tip at the external media-facing surface, with leading and trailing edges defined by the direction of media motion. Sometimes there are two return poles, one spaced from the leading edge and the other spaced from the trailing edge, with the main pole tip in between. The yoke, coils and back via are usually located away from the external surface and arranged adjacent to or around the main pole, between the first and second return poles.
In side-by-side configurations, the reader and writer are formed in a substantially coplanar sense, with the writer laterally spaced from the reader along the external media-facing surface. In stacked configurations, the writer is typically formed on top of the reader and spaced from the top read shield by a layer of nonmagnetic material. In merged/stacked configurations, which are less common, the reader and writer structures are merged such that the top shield of the reader also functions as a first or bottom return pole for the writer.
In order to increase areal storage density, it is necessary to address the write-plus-erase (WPE) width of the track. The WPE includes not only the useful bit width or write width (WW), where the bit pattern has a high signal-to-noise ratio, but also extends to erase bands located on either side. This creates a need for magnetic writer and transducer designs with reduced erase band width, as compared to total write-plus-erase width WPE.
This invention concerns a magnetic writer and a magnetic transducer using the writer. The writer has a main pole, a write gap and a write shield. The main pole is formed into a main pole tip for emitting magnetic flux perpendicular to a center axis of the writer. The write gap is formed in a nonmagnetic spacer material located adjacent the main pole tip, and which spaces the write shield from the main pole tip along the center axis.
The write shield comprises a first component and a second component having different magnetic properties from the first component. The first component is formed above the main pole tip along the center axis. The second component extends perpendicularly to the center axis from opposing sides of the first component. The write shield reduces field curvature in the write gap, increasing the ratio of write width to write-plus-erase width for the write head.
Actuator 12 comprises actuator arm 18 and a suspension with baseplate/mounting block 20, load beam 22 and flexure 24. Load beam 22 is connected to actuator arm 18 at baseplate/mounting block 20, and supports slider 14 on flexure 24. Voice coil motor 26 rotates actuator arm 18 about spindle axis 28, positioning slider 14 with respect to magnetic medium 16.
In the embodiment of
The magnetic transducer on slider 14 writes magnetic data in the form of bits, which are defined by regions of a particular magnetic orientation in medium 16. The bit length is defined along the tracking direction, and determines the linear bit density (typically in bits per inch or BPI, or in metric units such as bits/cm). The crosstrack dimension is the write-plus-erase width (WPE), which includes write width WW and erase bands on either side, and which determines the linear track density (in tracks per inch or TPI, or in tracks/cm). The areal density goes as the product of linear densities TPI and BPI (that is, in bits per square inch or bits/cm2).
Slider 14 utilizes a magnetic transducer with a multi-component write shield, which increases the attainable areal density by reducing magnetic field curvature across the bit pattern. This reduces the relative size of the erase bands on either side of the write width (WW), increasing the maximum potential TPI. The multi-component write shield also produces a more regular write bubble, with less curvature and a more rectangular structure. This improves the packing ratio, increasing the maximum potential BPI and areal density.
Reader 42 comprises first (bottom) read shield 52, second (top) read shield 53 and reader element 54. Reader element 54 is located in read gap 58 between read shields 52 and 53, which shield reader element 54 from stray magnetic flux.
Reader element 54 reads magnetic data (bits) along tracking direction S by responding to the magnetic domain orientation in the recording layer of the medium, where the response is based on a magnetoresistive effect such as giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR). In the particular embodiment of
Writer 44 comprises first return pole 56 and a write pole (or main pole) shaped into main pole tip 60 with leading edge 61 and trailing edge 62. Main pole tip 60 is oriented toward the media-facing surface of magnetic transducer 40, and is shielded by multi-component write shield 46 located above trailing edge 62. In some embodiments, writer 44 also comprises second (or trailing) return pole 64, and in further embodiments writer 44 has side shields 65.
Typically, perpendicular writer 44 is spaced from reader 42 by nonmagnetic layer 59. In merged transducer configurations, nonmagnetic layer 59 is absent and top read shield 53 also functions as first (or leading) return pole 56 for write pole 60.
Leading edge 61 and trailing edge 62 of main pole tip 60 are defined in terms of tracking direction S, with magnetic media translation from the bottom to the top of magnetic transducer 40 and writer 44. Magnetic bits are laid down onto the media along main pole trailing edge 62, where the magnetic domains reflect the magnitude and polarity of the flux as the medium passes out of the footprint of main pole tip 60.
In the particular embodiment of
As shown in
Write gap layer 66 spaces trailing edge 62 of main pole tip 60 from multi-component shield 46, and is formed of a nonmagnetic spacer material to reduce flux couplings. Write gap layer 66 defines write gap G along tracking direction S, parallel to center axis A. Additional non-magnetic material 67 spaces main pole tip 60 from first return pole 56, and, depending on configuration, from one or more side shields 65.
First (center) component 48 of multi-component shield 46 is spaced directly above main pole tip 60 by write gap layer 66, along center axis A. The transverse width of first shield component 48 is the front shield notch width (FSNW), transverse to tracking direction S and perpendicular to center axis A. The axial length of first shield component 48 (NWT) is defined along tracking direction S, parallel to center axis A.
Second (left and right) shield components 50, 51 of multi-component write shield 46 are located adjacent first (center) shield component 48. First shield component 48 spaces second shield components 50, 51 in a transverse (crosstrack) direction from center axis A, at least along axial length NWT. Second components 50, 51 extend from opposing side 68, 69 of first component 48, transverse to tracking direction S and perpendicular to center axis A. Typically, first (center) and second (left and right) shield components 48, 50 and 51 are symmetrically arranged about center axis A, but in some embodiments the arrangement is asymmetric.
As shown in
Second shield components 50, 51 have different magnetic properties from first shield component 48. In some embodiments, for example, first component 48 is formed of a nonmagnetic material and second components 50, 51 are formed of magnetic materials, such that first component 48 forms a nonmagnetic notch or gap in multi-component write shield 46.
In some of these embodiments, first (center) shield component 48 and write gap layer 66 are comprised of the same materials, but the notch or gap formed by first shield component 48 is nonetheless structurally and functionally distinct from write gap layer 66. In particular, write gap layer 66 spaces multi-component write pole shield 46 from trailing edge 62 of main pole tip 60 in a trackwise direction, while first shield component 48 spaces second shield components 50, 51 (or portions thereof) from center axis A in a crosstrack direction.
From a functional perspective, write gap layer 66 reduces magnetic flux connections to main pole tip 60, while first shield component 48 shapes the field within write gap layer 66, in order to reduce field curvature along trailing edge 62 of main pole tip 60. Field shaping is determined by the geometry and composition of first shield component 48 and second shield components 50, 51, relative to the other elements of writer 44. In particular, the different magnetic properties of first shield component 48 and second shield component 50, 51 are selected to reduce field curvature and increase the attainable storage density, while retaining sufficient effective field strength and gradient to define a readable bit pattern.
Reader 42 comprises bottom read shield 52, top read shield 53 and reader element 54, as described above. In merged configurations, top read shield 53 also serves as first return pole 56 for writer 44.
Perpendicular writer 44 comprises first return pole 56, main pole 74, multi-component write shield 46 and, in some embodiments, side shields (not shown) and second (trailing) return pole 64, as described above. Main pole (write pole) 74 has a proximal (media-facing) end defined at main pole tip 60. Typical embodiments of writer 44 also comprise back vias 76 and 78, yoke 80 and one or more sets of coils 82 with insulating layers 83.
Medium 70 translates in tracking direction S with respect to magnetic transducer 40 and writer 44. In the particular embodiment of
Coils 82 are formed of a low resistivity material such as Cu, and generate time-varying magnetic flux when energized by a switching write current. Insulating layers 83 are formed of a high resistivity material such as a dielectric, in order to electrically insulate coils 82. In some embodiments, insulating layers 83 are formed of the same or similar materials as write gap layer 66 and nonmagnetic spacers 58, 59 and 67, as shown in
Yoke 80 is formed of a magnetically soft material such as NiFe, in order to improve flux delivery to main pole 74. Main pole 74 is formed of a magnetically soft material with high magnetic moment, such as CoFe, in order to direct the magnetic flux through main pole tip 60 for perpendicular write operations onto magnetic medium 70.
Return poles 56, 64 and back vias 76, 78 are formed of magnetically soft materials such as NiFe, in order to close flux loops from main pole tip 60 through yoke 80 and main pole 74. First back via 76, for example, forms a flux connection between the distal (non media-facing) ends of first return pole 56 and main pole 78. Second back via 78 forms a flux connection between the distal ends of second return pole 64 and yoke 80.
In some embodiments, reader element 54, main pole tip 60 and other elements of magnetic transducer 40 are provided with protective coating 87 at external surface 72. Typical protective coatings include encapsulants, diamond-like coatings (DLCs) and combinations thereof, which protect magnetic transducer 40 and reduce hard particle contamination of magnetic medium 70. In coated embodiments, main pole tip 60 and the proximal (media-facing) end of reader element 54 are spaced from external surface 72 by the coating width. In uncoated embodiments, main pole tip 60 and the media-facing end of reader element 54 are defined along external surface 72.
In perpendicular embodiments of writer 44, magnetic flux loops from main pole tip 60 cross external surface 72 to enter top recording layer 84 of magnetic medium 70 in a substantially perpendicular sense. The flux loops cross interlayer 85 and spread out along bottom layer (SUL) 86, reducing field intensity in order to reduce the tendency for rewriting and erasure when the loops close back across recording layer 84 to return poles 56 and 64. Alternatively, flux enters recording layer 84 in a substantially parallel sense, and interlayer 85 and SUL 86 are sometimes absent.
Multi-component write shield 46 is configured to reduce field curvature proximate main pole tip 60 when writer 44 writes data to magnetic medium 70. Reduced field curvature is reflected in a modified write bubble structure, and in particular by an increased ratio of write width WW to write-plus-erase width WPE. Multi-component write shield 46 thus increases the attainable storage density of writer 44 and magnetic transducer 40, as described below.
The write bubble structure or “footprint” is illustrated by effective field strength (flux) contours 88, which shown field curvature in the region proximate main pole trailing edge 62, where data are recorded onto magnetic medium 70. The flux contours at main pole leading edge 61 are not shown.
Multi-component write shield 46 is spaced above main pole tip 60 along tracking direction S, with leading edge 89 of multi-component write shield 46 separated from trailing edge 62 of main pole tip 60 by write gap G. First (center) shield component 48 is located directly above main pole tip 60 along center axis A, extending across leading edge 89 of multi-component shield 46 with transverse width FSNW, and extending along center axis A with axial length NWT.
Center component 48 of multi-component shield 46 spaces side components 50 and 51 from center axis A at leading edge 89, with side components 50, 51 extending transversely from opposing sides 68, 69 of center component 48. In this particular embodiment, side components 50 and 51 also extend behind center component 48, such that nonmagnetic component 48 forms a notch in magnetic components 50 and 51. The notch has axial length NWT along center axis A, and extends transversely along leading edge 89 of multi-component shield 46 as shown in
Multi-component write pole shield 46 reduces field curvature in the write bubble of perpendicular writer 44, particularly along trailing edge 62 of main pole tip 60. Curvature reduction decreases the transverse width of the erase bands relative to write width WW (the useful bit width), reducing ratio R of write width WW to full write-plus-erase width WPE:
Typically, ratio R is measured in percent and defined at a particular flux contour, for example at an effective field strength of about 10-12 kOe (for instance, at H≈10 kOe). Increasing R decreases the minimum track spacing transverse to tracking direction S, and increases the maximum attainable TPI.
Curvature reduction also increases the flatness of flux contours 88 across write width WW, including the write gap region between trailing edge 62 of main pole tip 60 and leading edge 89 of multi-component write shield 46. This produces a more regular and rectangular bit structure across write width WW, decreasing the minimum bit spacing along tracking direction S, and increasing the maximum attainable BPI.
Each of these effects increases the maximum bit packing fraction and data storage density. Magnetic field effects are often unpredictable, however, and the benefits depend upon a detailed relationship between multi-component shield 46 and the associated elements of perpendicular writer 44. In particular, the benefits of multi-component shield 46 depend upon the particular geometry of shield components 48, 50 and 51 with respect to main pole tip 60.
In previous baseline designs, main pole tip 60 was formed with trailing edge width TPWT of about 80 nm and axial length TPL of about 200 nm. The trailing edge shield was formed of a single-component material, with write gap G of about 45 nm. Write currents varied between relatively low and relatively high values on the order of 10-100 mA, depending upon writer configuration. With relatively low write currents, for example, write width WW varied from about 54 to about 64 nm and write-plus erase width WPE varied from about 75-100 nm, with ratio R in the range of about 62-72%.
In embodiments of the present design, multi-component shield 46 is formed with nonmagnetic spacer 66 having a transverse width between about half the trailing pole width and the full trailing pole width (½ TPWT<FSNW<TPWT), and an axial length about equal to the write gap or larger (TNW>G, where G<50 nm). This increases ratio R, allowing write-plus-erase width WPE to be decreased without a commensurate increase in write width WW; or, conversely, allowing write width (WW) to be increased without a commensurate increase in write-plus-erase width WPE (see Eq. 1).
Multi-component write shield 46 also allows the main pole trailing edge width (TPWT) to be reduced without substantially decreasing effective field strength and gradient across write width WW, providing additional benefits for storage density. In particular, multi-component write pole 46 allows narrower writer structures to function with lower write currents and smaller write gaps (e.g., about 30 to about 45 nm), providing higher R with narrower WPE, a more uniform bit profile across write width WW, and closer track and bit spacing.
In particular embodiments with main pole trailing edge width TPWT of about 60 nm, for example, write gap G varies from about 30 to about 45 nm and transverse width FSNW of first shield component 48 varies from about 30 to about 60 nm. Depending on write current, this yields write width WW between about 58 and about 61 nm, with write-plus erase width WPE between about 75 and about 83 nm. Ratio R varies from about 73% to about 78%, an improvement of up to 8% over the previous single-component write shield designs.
Additional embodiments of multi-component write shield 46 improve attainable TPI by about 5-10% or about 15-20%, depending upon write gap size and write shield configuration. For first component width FSNW and write gap G of about 30 nm, for instance, the improvement in TPI is about 8% as compared to a single-component write shield design with write gap G≈30 nm, and about 16% as compared to a single-component write shield design with write gap G≈45 nm.
In additional embodiments, with FSNW≈G, ratio R improves by about 3% to about 5% for write gap G≈30 nm, about 5% to about 10% for write gap G≈45 nm, and about 13% to about 16% when write gap G is reduced from 45 nm in the single-component write shield design to 30 nm in the multi-component write shield design. In further embodiments, with FSNW≦2G, ratio R improves by up to 7% for write gap G≈30 nm, up to 10% for write gap G≈45 nm, and up to 15% when write gap G is reduced from 45 nm in the single-component write shield design to 40 nm in the multi-component write shield design.
As shown in
First (center) shield component 48 is located directly above main pole 60 along center axis A, forming a center shield piece that is spaced from main pole trailing edge 62 by write gap G in write gap layer 66. Second shield components 50, 51 are spaced from center axis A by first shield component 48, forming left and right shield pieces that extend transversely from opposing sides 68, 69 of first (center) component 48. Third shield components 90, 91 are spaced from first component 48 by second (left and right) components 50, 51, forming outriggers that extend transversely from opposing sides 92, 93 of second shield components 50, 51. In further embodiments, fourth, fifth or additional shield components are similarly arranged about third (outrigger) shield components 90, 91.
Third shield components 90, 91 have different magnetic properties from second shield components 50, 51, in order to further reduce field curvature and further increase ratio R. This improves the maximum potential TPI and BPI, increasing the attainable packing fraction and areal density over a range of write currents and field strengths. In some embodiments, for example, third shield components 90, 91 are formed the same material as center component 48, or of the same or similar (i.e., non-magnetic) materials as write gap 66. Alternatively, third shield components 90, 91 are formed of a material with magnetic properties that are different from those of both first component 48 and second components 50, 51.
In typical embodiments, third shield components 90, 91 are also formed of the same material, such that the left and right outrigger pieces have a symmetric effect. In these embodiments, multi-component shield 46 is sometimes symmetrically arranged about center axis A, as shown in
While this invention has been described with reference to particular embodiments, the terminology used is for the purposes of description, not limitation. Workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention, including the substitution of various equivalents for particular invention elements and adaptations of the invention's teachings to different materials, situations and circumstances. Thus the invention is not limited to the particular embodiments disclosed herein, but encompasses all embodiments falling within the scope of the appended claims.
