Radially patterned media for circumferentially constrained grain growth

Abstract

The present application discloses a radially patterned medium for circumferentially constrained grain growth. A method of forming a patterned medium includes constraining the growth of magnetic grains in a circumferential direction without constraining growth in a radial direction such that the magnetic grains are aligned in rows extending in the radial direction. The patterned medium can allow the definition of the radial width of data tracks independent of grain size.

Description

Background Art

[0001] The areal recording density of magnetic storage devices is considered to be limited by the superparamagnetic limit, which is an areal density limit at which thermal fluctuations in the medium will spontaneously switch the polarization of the recorded bits in a relatively short time, resulting in data loss. The areal density of the superparamagnetic limit depends on the grain size and magnetic anisotropy of the medium. It is considered that the superparamagnetic limit can be postponed by increasing the medium anisotropy or by increasing the effective grain volume. Although an increase in anisotropy can be achieved using a relatively large switching field (e.g., via a technique such as thermal assisted magnetic recording), increasing the effective grain volume is considered to require a thicker medium or an increase in physical grain alignment via patterning of the medium (also known as "bit patterned media (BPM)").

[0002] In a BPM device, the magnetic material on the disk is patterned into small isolated islands or "grains" such that there is only a single magnetic domain in each island or "grain". The single magnetic domain can be a single grain or multiple strongly coupled grains that switch the magnetic state coherently as a single magnetic volume. This is in contrast to a continuous medium where a single "bit" may have multiple magnetic domains separated by domain walls. The medium can be fabricated such that there is no magnetic material in the regions between the blocks. Summary of the Invention

[0003] An example method for forming a patterned medium provides for constraining the growth of magnetic grains in the circumferential direction of the patterned medium without constraining the growth of the magnetic grains in the radial direction of the patterned medium, such that the magnetic grains are substantially aligned in rows extending in the radial direction. The patterned medium can allow the definition of the radial width of the data tracks independent of the grain size, while also providing information that allows for precise write transition timing without a separate write synchronization field in each data sector.

[0004] The Summary of the Invention is provided to introduce a selected group of concepts that are further described below in the Detailed Description. The Summary of the Invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Other features, details, utilities, and advantages of the claimed subject matter will become apparent from the more specific written Detailed Description of the various implementations as further illustrated in the Drawings and defined in the appended claims. Brief Description of the Drawings

[0005] Figure 1 An example data storage device including a patterned medium having magnetic grains aligned in a single direction (1D) is shown.

[0006] Figure 2AShows an example of magnetic grains that are substantially aligned in the cross-track (radial) direction of a patterned medium.

[0007] Figure 2B Shows an example of magnetic grains that are substantially aligned in the cross-track direction but staggered in the down-track direction.

[0008] Figure 2C Shows another example of magnetic grains that are substantially aligned in the cross-track direction.

[0009] Figure 2D Shows yet another example of magnetic grains that are substantially aligned in the cross-track direction.

[0010] Figure 3 Shows another example patterned medium having magnetic grains that are substantially aligned along rows extending in the radial (cross-track) direction of the disk due to grain growth confinement features present during the fabrication of the patterned medium.

[0011] Figure 4 Shows a cross-sectional view of a patterned medium formed via a first exemplary grain growth fabrication process.

[0012] Figure 5 Shows yet another cross-sectional view of a patterned medium formed via another exemplary grain growth fabrication process.

[0013] Figure 6 Shows another example patterned medium having magnetic grains that are substantially radially aligned due to grain growth confinement features that confine the position of the magnetic grains in the down-track direction of the patterned medium during the semiconductor fabrication process.

[0014] Figure 7 Shows yet another example patterned medium having magnetic grains that are substantially radially aligned due to grain growth confinement features that confine the position of the magnetic grains in the down-track direction of the patterned medium during the semiconductor fabrication process.

[0015] Figure 8 Shows a recording head for writing data to a series of bits in a patterned medium recording system.

[0016] Figure 9 Shows a dynamic head positioning correction that can be used in some patterned medium storage devices to compensate for skew angles that vary at different radial positions.

[0017] Figure 10An arcuate pattern of grain growth constraint features on a patterned medium is shown that can be used during fabrication to generate a pattern of magnetic grains that eliminates the need for head skew actuation based on the radial head position.

[0018] Figure 11 An additional pattern of grain growth constraint features on a patterned medium is shown that eliminates the need for head skew actuation based on the radial head position. DETAILED DESCRIPTION

[0019] Bit patterned media (BPM) technology presents many practical implementation challenges. Due to small grain size and magnetic grain isolation, BPM devices typically operate at a lower bit aspect ratio (BAR), or ratio of track pitch to bit length in the along-track direction, compared to conventional recording devices that utilize continuous media. Generally, when reading and writing data sequentially from the media, a low BAR is associated with a lower data throughput rate. In addition to producing lower data rates, the smaller track widths associated with a low BAR also require narrower recording head features. Since the readback signal output by a narrower read element has a lower amplitude compared to the readback signal output by a wider read element, low BAR devices (e.g., those employing BPM) drive the need for higher sensitivity read elements, thus increasing manufacturing cost and complexity. If BPM could actually be implemented in devices having a BAR similar to (e.g., not significantly lower than) that of conventional recording devices, such designs would thus yield fundamental performance and manufacturing benefits.

[0020] In addition to the above-mentioned obstacles to practical BPM implementations, the fact that BPM devices theoretically require a more advanced and dynamic servo tracking system than storage devices using conventional storage media presents a further challenge. In BPM, each bit of data is written by precisely aligning the recording head with both the along-track position and the cross-track position of a pre-designed magnetic island. In contrast, conventional recording systems utilize encoded servo information to align the recording head radially along the target data track, but there are no such tracking requirements in the along-track direction. Instead, the along-track position of a single data bit is selected based on the position of the head as it flies over the media – a model that is significantly lower in cost and complexity compared to current BPM designs. Thus, if the tracking requirements could be relaxed and / or the write synchronization in the along-track direction could be eliminated, the implementation complexity of BPM would be significantly reduced.

[0021] The techniques disclosed herein provide techniques for radially patterning a medium, which can be incorporated into a patterned media storage device in a way that has a higher bit aspect ratio (BAR) compared to existing BPM techniques (e.g., read / write throughput may be similar to conventional storage media), and thus has better performance. Additionally, the disclosed techniques can facilitate methods for relaxing head tracking requirements in a patterned media drive. According to one implementation, the patterned media disclosed herein includes magnetic grains that are aligned or substantially aligned in a radial direction and staggered (e.g., misaligned or substantially misaligned) in a circumferential direction. As used herein, grains are considered to be aligned in a row when one of the following conditions exists: (1) each magnetic grain in the row has a center that is substantially aligned along a common axis; or (2) each magnetic grain in the row has an edge that is substantially aligned along a common axis. "Substantially aligned" means an alignment within one quarter of the actual precise alignment pitch, where the "pitch" is the average center-to-center spacing between adjacent bits (data storage magnetic grains) on the medium. Further examples of radially aligned grains (e.g., center-to-center alignment and edge-to-edge alignment) are discussed below with respect to Figures 2A - 2C Discuss further examples of radially aligned grains (e.g., center-to-center alignment and edge-to-edge alignment).

[0022] When the medium is patterned with grains that are radially aligned in a single row, long-range order is observed at circumferential positions, which provides a clear boundary for predictable timing of write transitions. Due to this predictable transition timing, servo fields can be stored periodically at highly predictable locations (e.g., at the same set of rows as user data), and in this case, the servo sync field can double as a write sync field. In contrast, some earlier forms of BPM required the write sync field to be separated from the servo sync field in order to position the write element relative to the data portion of each sector. However, the predictable transition timing of the disclosed design allows write synchronization of data fields derived from the servo sync field.

[0023] At the same time, a pattern that allows the grains to be staggered (misaligned) in the circumferential direction can relax the head positioning requirements by allowing the recording head size to define the position and width of each data track. In other words, the disclosed patterning techniques can provide the beneficial effect of postponing the superparamagnetic limit without requiring a low BAR to achieve acceptable performance and without requiring head features that are narrower, more sensitive, or more advanced servo tracking capabilities than those commonly found in conventional magnetic recording devices.

[0024] Figure 1FIG. 0 shows an example data storage device 100 that includes a patterned medium 108 having magnetic grains aligned in a single direction (1D). The patterned medium 108 includes at least one magnetic storage disk on which data bits can be recorded using a magnetic write pole (not shown) on a transducer head assembly 120, and data bits can be read from the at least one magnetic storage disk using a magnetoresistive element on the transducer head assembly 120. As shown in view A, the patterned medium 108 rotates about a spindle center or disk rotation axis 112 and includes an inner diameter 104 and an outer diameter 102 between which are a plurality of concentric data tracks.

[0025] The transducer head assembly 120 is mounted on an actuator assembly 109 at one end distal to the actuator rotation axis 114. The transducer head assembly 120 flies closely above the surface of the patterned medium 108 during disk rotation. During a seek operation, the actuator assembly 109 rotates about the actuator rotation axis 114. The seek operation positions the transducer head assembly 120 on a target data track for read and write operations.

[0026] In one implementation employing thermal-assisted magnetic recording (HAMR), magnetic particles on the patterned medium 108 are temporarily heated during the recording process to selectively reduce the magnetic coercivity in a tightly packed region of the patterned medium 108 that substantially corresponds to a single data bit. The heated region is then encoded with the recorded data bit based on the polarity of the applied magnetic write field. After cooling, the magnetic coercivity substantially returns to its pre-heated level, thereby stabilizing the magnetization of the data bit. This write process is repeated for multiple data bits on the storage medium, and such data bits can be read using a magnetoresistive read head.

[0027] As shown in view B, the patterned medium 108 includes magnetic islands or grains (e.g., grain 128) formed at fixed positions on the patterned medium 108 that are separated from each other by non-magnetic material. In Figure 1 this case, the magnetic grains are aligned or substantially aligned in rows extending in the cross-track (radial) direction but not along the respective columns extending in the along-track direction (also referred to as the recording direction).

[0028] According to one implementation, the alignment of the radial direction within a single grain row is a result of the media manufacturing process that utilizes grain growth constraint features (e.g., grain growth constraint features 122, 124, 126) to limit the size and position of each of the magnetic grains in the along-track direction. For example, the grain growth constraint features 122, 124, 126 can be features patterned on a substrate that serve as boundaries physically limiting the growth of magnetic grains in the along-track direction. In different implementations, the grain growth constraint features 122, 124, 126 can assume various different forms, including, for example, positive features (e.g., lines of isolation material formed on the nucleation layer of the patterned media) or negative features (e.g., etched valleys).

[0029] When magnetic grains grow on the seed layer of the patterned media 108, the grain growth constraint features (e.g., 122, 124, or 126) constrain the position of each individual magnetic grain between the upper and lower boundaries in the along-track direction. For example, all magnetic grains formed in row 130 are prohibited from expanding beyond any of the adjacent grain growth constraint features 124 and 126 in the lower track position. At the same time, these magnetic grains are allowed to nucleate and grow at random positions in the radial (across-track) direction, which simplifies the manufacture of the patterned media 108 compared to a process that provides multi-dimensional constraints on the magnetic grain positions.

[0030] In the illustrated implementation, the controller 106 of the storage device 100 is configured to control the writer 132 to generate magnetic transitions in the magnetic particle material of the patterned media 108 to store data. Figure 1 The controller 106 can include software stored on a tangible computer-readable storage medium. As used herein, the term "tangible computer-readable storage medium" does not include transient propagated signals (e.g., carrier waves), but includes physically manufactured media (storage devices) that include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CDROM, digital versatile disks (DVD) or other optical disk storage, magnetic tape cartridges, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible medium that can be used to store the desired information and can be accessed by a mobile device or a computer.

[0031] In one implementation, the controller 106 controls the writer 132 to generate magnetic transitions such that each individual data bit is stored as a set (group) of adjacent grains on the patterned media 108 with the same polarity, and the patterned media 108 is converted to the same magnetic polarity as a single unit. In other words, multiple (e.g., two or three) magnetic grains on the patterned media 108 can be encoded with the same magnetic polarity and together represent one stored information data bit. In Figure 1Among them, the group of grains corresponding to each individual data bit is defined as those grains that are (1) between the same pair of identical grain growth constraint features (122, 124, 126, etc.) and (2) have a radial position corresponding to the magnetic coverage area of the writer (for example, as shown in the figure, when the writer passes over the grains, these bits are magnetized enough to switch the magnetic polarity). For example, the magnetic grains 134 and 136 are located between the grain growth constraint features 124 and 126 and have a center inside the "track width" coverage area of the writer 132. These grains together store the first data bit. Similarly, the three magnetic grains 138 are located between the grain growth constraint features 122 and 124 and have a center inside the "track width" coverage area of the writer 132. These three grains together are switched to store the second data bit.

[0032] When the writer 132 passes over the fixed data bits of the rotating patterned medium 108, the writer 132 emits a series of magnetic pulses, each magnetic pulse having an amplitude sufficient to perform a write transition that changes the magnetic state of the underlying data bit. To selectively write a single data bit to a group of grains, the magnetic pulses of the writer 132 are timed so that the magnetic pulses are aligned with the sequential passing of each of the grain growth constraint features (e.g., 122, 124, 126) under the writer 132. If the writer 132 is not aligned during the write transition, the corresponding misalignment of the magnetic pulses can cause the bit to be subjected to conflicting magnetization forces from the writer, resulting in incorrect data writing and damage to the stored data. In the example shown, the magnetic grains 134 and 136 are switched together to store the first data bit.

[0033] As described above, using multiple grains to store a single data bit can desirably increase the amplitude of the readback signal. In addition, since the inter-grain in-track spacing in this design is not staggered but ordered, the write transition can be precisely timed based on the position of the grain growth constraint features, resulting in a high signal-to-noise ratio (SNR) even when a relatively small number (e.g., two or three) of grains correspond to each recorded bit. Even with this relatively small grain size, the patterning on the patterned medium 108 can be scaled to support a higher areal density than conventional recording before reaching the paramagnetic limit.

[0034] In addition to providing improved signal quality for patterned media technology, the storage device 100 can operate at a higher BAR (e.g., the ratio of track width to along-track bit length) because the track width and position are defined by the position and size of the write elements on the transducer head assembly 120 rather than the center of the radial direction of each magnetic grain. Defining the position and width of each data track on the patterned medium 108 using the physical properties of the transducer head assembly 120 also allows the storage device 100 to advantageously use the same servo methods and head actuation methods as conventional recording, which are more forgiving (less stringent and complex) than those common in patterned media devices.

[0035] Figures 2A - 2C An example of the magnetic grain arrangement in a bit patterned medium is shown. The magnetic grain arrangement includes magnetic islands or grains that can be arranged (grown) on the storage medium at fixed positions. In one implementation, the magnetic grains are separated from each other by non-magnetic material.

[0036] Figure 2A An example of magnetic grains 202 that are substantially aligned along the radial (cross-track) direction axis 210 is shown. These grains are considered to be substantially aligned with the radial direction axis 210 because each of the grains in a single cross-track column 208 intersects the radial direction axis 210 at a point corresponding to or near the center of the grain. In one implementation, each of the grains in the cross-track column 208 has a diameter of approximately 6 nm and a center within + / - 1 nm of the radial direction axis 210. In other implementations, the grains are assumed to have various different sizes, but each grain has a center that is offset from the radial direction axis 210 by no more than + / - 15% of the average grain size.

[0037] Figure 2B An example of magnetic grains 204 that are substantially aligned in the cross-track (radial) direction but staggered (e.g., not substantially aligned) in the along-track direction is shown. Although the radial direction axis can be drawn as intersecting substantially all of the grain centers along a common column (e.g., radial direction columns 212, 214), the along-track direction axis cannot be drawn as intersecting substantially all of the grain centers along a common row. For example, the grain centers are staggered with respect to the along-track direction axis 216. According to one implementation, this radial direction alignment within a single grain row is the result of a medium manufacturing process that uses grain growth constraint features to limit the size and position of each of the magnetic grains in the along-track direction, but allows the grains to grow unconstrained in the radial direction.

[0038] Figure 2C Another example of magnetic grains 206 that are substantially aligned in the cross-track (radial) direction is shown. As compared with Figure 2Acompared to the centers of the grains being substantially aligned along the radial axis of the patterned medium, Figure 2C is implemented such that the grain edges of column 218 are substantially aligned with the radial direction axis 220. In one implementation, each of the grains in column 218 has a diameter of approximately 6 nm and an edge within + / - 1 nm of the radial direction axis 210.

[0039] Figure 2D Another example of magnetic grains 222 that are substantially aligned in the cross-track direction is shown. Here, the left edges of the grains in column 224 are substantially aligned with the radial direction axis 226, and the right edges of the grains in column 228 are substantially aligned with the radial direction axis 230.

[0040] Figure 3 Another example patterned medium 300 having a plurality of magnetic grains is shown, the plurality of magnetic grains being substantially aligned along rows extending in the radial (cross-track) direction of the disk due to grain growth constraint features 302, 304, 306, 308, 310, 312, 314 in the grain growth during the manufacturing process of the patterned medium. The grain growth constraint features 302, 304, 306, 308, 310, 312, 314 are patterned features on the patterned medium 300 that effectively constrain the allowable in-track positions of each individual grain during the manufacturing process (e.g., by setting higher and lower in-track direction position limits for each grain). As with other examples provided herein, during formation, the grains on the patterned medium 300 (shown in detail in expanded view B) are only constrained in the in-track direction. Thus, the grains are aligned in rows extending in the radial direction of the disk. Here, grain growth is unconstrained in the radial direction, and the grains in adjacent rows in the radial direction (e.g., the grains in column 320) are not aligned in the in-track direction. In other words, the grain centers and edges are staggered with respect to any given in-track direction axis.

[0041] In Figure 3 the example, the grain growth constraint features 302, 304, 306, 308, 310, 312, 314 can be positive patterned features (e.g., features built by adding material to the surface) or negative patterned features (e.g., features formed by removing material from the surface). Figure 4 An example of a positive patterned grain growth constraint feature is shown and Figure 5 an example of a negative patterned grain growth constraint feature is shown.

[0042] Figure 4 A cross-sectional view of a patterned medium 400 formed via a first exemplary grain growth manufacturing process is shown. According to one implementation, the patterned medium 400 has relative toFigure 3 The features described for the patterned medium 300 are the same or similar features. In the process exemplified by Figure 4 In the process exemplified, a seed layer 416 is deposited onto a substrate 418 using a thin film deposition process. For example, the seed layer 416 can be deposited by sputtering, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), or any other suitable thin film deposition process. Although there are various suitable seed layer materials, example materials include but are not limited to Ru, NiFe, Ta50\Au199, Ta50\NiFe1000, Ta50\Ru1000, Ta50\Cu1000, indium tin oxide, combinations thereof, or other seed materials. Then, an isolation material is patterned on the seed layer 416 to form positive (e.g., surface protruding) grain growth confinement features 402, 404, 406, 408, 410, 412, 414. Although various isolation materials can be suitable for such purposes, example materials include but are not limited to nitrides, carbides, borides, such as BN, AlN, B2O3, TiO2, SiO2, SiB3, BC, SiC, AlOx, etc.

[0043] The patterning of the grain growth confinement features 402, 404, 406, 408, 410, 412, 414 can be achieved using a variety of different techniques, which include but are not limited to lithography, nanoimprinting, block copolymers, and other methods. In one implementation, the grain growth confinement features 402, 404, 406, 408, 410, 412, 414 are elongated (e.g., linear) features that extend parallel to the radial direction of the patterned medium, as shown in the figure.

[0044] After patterning the grain growth confinement features, a hard magnetic material can be deposited such that magnetic grains (e.g., grains 420, 422) nucleate at the growth points between the various grain growth confinement features 402, 404, 406, 408, 410, 412, 414. In various implementations, the hard magnetic material can have one or more elements selected from the group consisting of Fe, Ta, Ni, Mo, Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, Cu, Ag, and Pd and / or can be an alloy including Fe, Pt, and / or Cr.

[0045] According to yet another implementation, the seed layer 416 is deposited on the stack after the grain growth confinement features 402, 404, 406, 408, 410, 412, 414 have been patterned (e.g., rather than before such patterning), such as according to a method the same as or similar to the method described in U.S. Patent No. 9,245,566, the content of which is incorporated herein by reference in its entirety for its disclosure and teachings. In one such process, the nucleation of the seed layer 416 at the growth points between the grain growth confinement features 402, 404, 406, 408, 410, 412, 414 is thicker than the nucleation in the regions on top of the grain growth confinement features 402, 404, 406, 408, 410, 412, 414, and this difference in the relative thickness of the seed layer causes the subsequently deposited magnetic material to nucleate and grow between the grain growth confinement features 402, 404, 406, 408, 410, 412, 414, forming rows of magnetically aligned grains that are radially aligned relative to Figure 3 the radially aligned rows of magnetic grains shown.

[0046] Figure 5 Another cross-sectional view of a patterned medium 500 formed via another exemplary grain growth manufacturing process is shown. According to one implementation, the patterned medium 500 has features the same as or similar to those described for the patterned medium 300 relative to Figure 3 . In the process exemplified in Figure 5 , a seed layer is deposited on a substrate 518, and an etching process is employed to remove portions of the seed layer, leaving raised seed layer portions 520, 522, etc. As a result of this etching, hollow, elongated channels (e.g., one of channels 502, 504, 506, etc.) are formed in the y-direction across the substrate. The hollow, elongated channels (e.g., channels 502, 504, 506) are an example of a negatively formed patterned feature that can be used to confine magnetic grain growth in a single direction. When magnetic material is subsequently deposited on top of the substrate 518 and the raised seed layer portions 520, 522, etc., the magnetic material nucleates in the regions on top of the raised seed layer portions 520, 522. Thus, one or more rows of radially aligned magnetic grains (e.g., magnetic grains 526, 528) are formed on top of each raised seed layer portion such that the row extends in the Figure 5 radial direction (y-direction, into the page) of

[0047] Figure 6Shows another example of a patterned medium 600 having magnetic grains that are substantially radially aligned due to grain growth confinement features 602, 604, 606, 608, which confine the positions of the magnetic grains in the along-track direction of the patterned medium during the semiconductor manufacturing process.

[0048] Figure 6 The implementation of Figure 1 and Figures 3 - 5 differs from that shown with respect to Figure 6 in that a greater spacing is employed between adjacent grain growth confinement features to allow multiple rows of grains in multiple radial directions to nucleate and grow in a substantially aligned manner between each individual pair of lines of grain growth confinement features 602, 604, 606, 608. In the example of Figure 6 , the along-track spacing (labeled "line spacing") between adjacent pairs of confinement features is set to be approximately equal to twice the average natural magnetic grain diameter, such that two rows of grains can be formed in the space between two adjacent confinement features. For example, two rows of substantially radially aligned magnetic grains 610, 612 are formed in the space between the first pair of confinement features 602, 604; two additional rows of substantially radially aligned magnetic grains 614, 616 are formed in the space between the second pair of confinement features 604, 606, and so on.

[0049] In the implementation shown, the patterned medium 600 can be implemented in a storage device having a controller that controls a writer 618 on a recording head 620 to generate magnetic pulses to simultaneously switch the magnetic polarities of multiple grains. Here, a single data bit of information can be represented by the polarities of all the grains, and region 622 encompasses grains that: (1) are between the same pair of grain growth confinement features (e.g., between 602 and 604); (2) are substantially radially aligned along column 610; and (3) have a radial position corresponding to the size of the writer 618 (e.g., as generally shown, those grains that are close enough to the writer 618 when the writer passes over the grains are switched in polarity jointly). In another implementation, a single data bit of information can be represented by grains in more than one row in the radial direction (e.g., by the polarities of grains in a region spanning two or three rows of grains between the same pair of grain growth confinement features). It is noted that in this implementation, the effective track width (e.g., the radial direction width of region 622) is determined independently of the grain size and independently of the patterned medium as a whole. Instead, the center and width of each data track can be based on the size and position of the recording head 620, rather than considering the size and / or radial position of each individual magnetic grain.

[0050] As shown, widening the spacing between the grain growth constraint features 602, 604, 606, 608 can simplify manufacturing (e.g., by reducing the density of the grain growth constraint features to be patterned), thereby effectively reducing the total manufacturing cost. Provided that the spatial interval between each pair of constraint features is set to be equal to or substantially equal to (e.g., + / - 5%) an integer multiple of the average grain diameter, and this integer is relatively small (e.g., 2 grains, 3 grains, 4 grains), a substantially aligned number of rows of grains can be formed within each such interval. In these cases, the resulting grain pattern can provide performance and cost benefits that are the same as or similar to those Figure 1 discussed in terms of performance and cost effectiveness.

[0051] In one implementation, the servo system of a storage device uses grain growth constraint features to provide write synchronization timing for a single write transition, instead of the "write synchronization field" used in a conventional BPM device. Generally, a BPM device requires such precise timing between a write pulse and the passage of the center of the magnetic grains under the write head, so each data sector typically includes a write synchronization field to notify the storage controller of the start of the data portion of the sector. In this system, the lines of the grain growth constraint features force a regular spacing between the magnetic grains in the along-track position, such that the start of each row 610, 612 in the radial direction is predictable. If the servo pattern is written at bits within a predictable sequence of the same patterned bits as the user data, the servo field synchronization markers can be deterministically synchronized with the start of each user data region. For example, during the write of a given data track sector, the storage controller can detect the servo pattern information at the start of the sector and be able to accurately predict from the pattern the timing and position information of the passage of the first data bit (e.g., the bit assigned to store user data) of the sector. In this sense, the patterning of the magnetic grains on the magnetic medium makes the conventional write synchronization field unnecessary, thus allowing more total space on the medium to be allocated to store user data.

[0052] It should be noted that if the spacing between the grain growth constraint features becomes too large, the resulting pattern may lose its order in the radial direction, thereby reducing the transition time relative to the reliability of the grain growth constraint features.

[0053] Figure 7 Another example patterned medium 700 with magnetic grains is shown, where the magnetic grains are substantially radially aligned due to the grain growth constraint features 702, 704, 706, which constrain the positions of the magnetic grains in the along-track direction of the patterned medium during the semiconductor manufacturing process. In Figure 7In the example, the along-track spacing (labeled "line spacing") between adjacent pairs of confinement features is set to be approximately equal to three times the average natural magnetic grain diameter, such that three rows of grains can be formed in the space between two adjacent grain growth confinement features. Just as Figure 6 , the radial width of each data track is determined by the size of a writer (not shown) on the recording head 712 and can be completely independent of the size of the individual grains on the patterned medium. In this case, region 708 can store a first data bit, region 710 can store a second data bit, and so on.

[0054] Figure 8 Shown is a recording head 802 for writing data to a series of bits in a patterned medium recording system 800. In Figure 8 , the recording head 802 is writing data in the along-track direction, and two magnetic grains are used to represent each individual data bit. When the patterned medium has a linear pattern of bits on the disk surface similar to that shown in Figure 8 , the recording head 802 has a skew angle α (e.g., the angle between the axis of the recording head 802 and the tangent to the underlying row of magnetic grains on the patterned medium), and this skew angle α varies as the actuator arm 806 moves the recording head 802 between the inner diameter and the outer diameter of the medium.

[0055] Since writing to the patterned medium typically depends on the exact alignment between one or more target magnetic grains and the write element (e.g., as shown, located at the end of the recording head), some patterned medium systems can include a servo system with complex, dynamic microactuation controls that vary the fine positioning of the recording head to ensure the desired alignment with the underlying grains is achieved even as the skew angle changes within the position range. Figure 9 Further shown is the reason for this dynamic correction for varying skew angles.

[0056] Figure 9 Shown is a dynamic head positioning correction that can be used in some patterned medium storage devices to compensate for varying skew angles at different radial positions. At a first head position 902 near the outer diameter of the disk, the recording head assumes a first skew angle α relative to the underlying data track. At a second head position 904 near the inner diameter of the disk, the skew angle is naturally different (e.g., the skew angle is naturally +β). To maintain the same angle of the recording head relative to the magnetic grains on the underlying data track, the magnetic head can be dynamically adjusted by the correction angle β. Figures 10 - 11 A pattern feature design is proposed that can eliminate the need to dynamically adjust the head in this manner.

[0057] Figure 10Shows an arcuate pattern of grain growth constraint features 1002 on a patterned medium 1000 that can be used during fabrication to generate a pattern of magnetic grains that eliminates the need for head skew actuation based on the radial head position (e.g., to eliminate the need for the dynamic position correction with respect to Figures 8 - 9 as described above). When the positions of the magnetic grains are constrained by the grain growth constraint features 1002 shaped as shown, the resulting magnetic grains adopt a pattern that ensures that the writer on the head is at the same angle relative to the underlying radially aligned bit tracks regardless of whether the head is at the inner diameter position 1004, the outer diameter position 1006, or any position in between. Here, the magnetic grains are radially aligned at the track local level (e.g., when locally examining a small portion of the data track being written, the alignment is substantially in the radial direction), but are curved at the global level between the inner and outer diameters of the disk. Thus, there is a consistent angle between the recording head and the underlying row of magnetic grains at all radial positions. Here, the arcuate radial pattern is shaped to ensure that as the recording element moves from the inner diameter to the outer diameter of the disk, the write element remains parallel to the line of the grain growth constraint features and thus parallel to the grain columns at the recording point. This arcuate patterning eliminates the need for head skew actuation based on the head position from the inner diameter to the outer diameter.

[0058] Figure 11 Shows an additional pattern of grain growth constraint features 1102 on a patterned medium 1100 that can allow for varying bit pitch in different radial zones. In Figure 11 , the grain growth constraint features (hereinafter referred to as "lines") are patterned differently within different radial bands (e.g., radial band 1104) on the disk. In one implementation, the spacing between the lines is varied to maintain a constant line pitch as a function of the disk radius. For example, the pitch of the patterned lines may be lower in the radial zone closest to the inner diameter, where the data rate is lower and the signal-to-noise ratio (SNR) is naturally higher. Due to this higher SNR, the medium can support a higher linear density of bits in the inner diameter radial zone than in the outer radial zones. Thus, the patterned lines can generally increase in pitch (e.g., spacing) as the radial zone gets closer to the outer diameter, where the data rate is higher, the SNR is lower, and the linear density is lower, to ensure high system performance.

[0059] The foregoing specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the disclosed technology. Since many embodiments of the disclosed technology can be made without departing from the spirit and scope of the disclosed technology, the disclosed technology resides in the claims appended hereto. Additionally, the structural features of different embodiments may be combined in another embodiment without departing from the claims.

[0060] Further examples

[0061] Example 1. A method of forming a patterned medium, comprising:

[0062] Constraining the growth of magnetic grains in the circumferential direction of the patterned medium, without constraining the growth of the magnetic grains in the radial direction of the patterned medium, such that the magnetic grains are substantially aligned in rows extending in the radial direction.

[0063] Example 2. The method according to Example 1, wherein the magnetic grains in the rows have grain centers that are substantially aligned with each other or grain edges that are substantially aligned with each other.

[0064] Example 3. The method according to Example 1, wherein constraining the growth of the magnetic grains further comprises patterning a line of a grain growth constraining feature, the line of the grain growth constraining feature separating the rows of magnetic grains from each other.

[0065] Example 4. The method according to Example 3, wherein the grain growth constraining feature is patterned only in the radial direction of the patterned medium.

[0066] Example 5. The method according to Example 3, wherein the grain growth constraining feature is a positive feature formed by adding a material to a layer of the patterned medium.

[0067] Example 6. The method according to Example 3, wherein the grain growth constraining feature is a negative feature formed by removing a material from a layer of the patterned medium.

[0068] Example 7. The method according to Example 3, wherein the grain growth constraining feature forms an arcuate pattern.

[0069] Example 8. The method according to Example 7, wherein the spacing between the grain growth constraining features increases with the radial distance from the inner diameter of the patterned medium.

[0070] Example 9. A system, comprising:

[0071] A patterned medium comprising magnetic grains that are substantially aligned in rows extending in the radial direction, the magnetic grains lacking substantial alignment in the recording direction.

[0072] Example 10. The system according to Example 9, further comprising:

[0073] A read / write controller configured to control a write head to write a single data bit onto the patterned medium by converting a set of magnetic grains to the same magnetic polarity, the set of magnetic grains having a radial width defined based on the size of the write head and independent of the patterned medium.

[0074] Example 11. The system according to Example 10, wherein the set of magnetic grains storing the data of the single data bit are substantially aligned along the same radial direction row on the patterned medium.

[0075] Example 12. The system according to Example 10, wherein the read / write controller is configured to determine the time to initiate writing the single data bit by deriving write synchronization information from a servo synchronization field.

[0076] Example 13. The system according to Example 9, wherein the aligned magnetic grains in the row have grain centers that are substantially aligned with each other or grain edges that are substantially aligned with each other.

[0077] Example 14. The system according to Example 9, wherein the patterned medium further includes grain growth constraint features that separate rows of magnetic grains from each other.

[0078] Example 15. The system according to Example 14, wherein the grain growth constraint features extend only in the radial direction of the patterned medium.

[0079] Example 16. The system according to Example 9, wherein the rows of magnetic grains extending in the radial direction form an arc pattern.

[0080] Example 17. A system comprising:

[0081] A patterned medium including substantially aligned magnetic grains in rows extending in a radial direction;

[0082] A read / write controller configured to control a write head to write a single data bit onto the patterned medium by converting a set of magnetic grains, the set of magnetic grains having a radial width defined based on the size of the write head and independent of the grain size of the patterned medium.

[0083] Example 18. The system according to Example 17, wherein the magnetic grains lack substantial alignment in the recording direction.

[0084] Example 19. The system according to Example 17, wherein the set of magnetic grains storing the data of the single data bit are substantially aligned along the same radial direction row on the patterned medium.

[0085] Example 20. The system as described in Example 17, wherein the read / write controller is configured to determine the time to initiate writing the single data bit by deriving write synchronization information from a servo synchronization field.

Claims

1. A method of forming a patterned medium, comprising: Constraining the growth of magnetic grains in a circumferential direction of the patterned medium, without constraining the growth of the magnetic grains in a radial direction of the patterned medium, such that the magnetic grains extend in the radial direction to be substantially aligned in rows of an arcuate pattern, each of the magnetic grains being magnetically separated from each other by non-magnetic material within each individual row in the rows in the radial direction.

2. The method according to claim 1, wherein The magnetic grains in the rows have grain centers that are substantially aligned with each other or grain edges that are substantially aligned with each other.

3. The method according to claim 1, wherein Constraining the growth of the magnetic grains further comprises patterning lines of grain growth constraint features that separate the rows of the magnetic grains from each other.

4. The method according to claim 3, wherein The grain growth constraint features are patterned only in the radial direction of the patterned medium.

5. The method according to claim 3, characterized in that, The grain growth constraint features are positive features formed by adding material to a layer of the patterned medium.

6. The method according to claim 3, wherein The grain growth constraint features are negative features formed by removing material from a layer of the patterned medium.

7. The method according to claim 1, wherein The spacing between the grain growth constraint features increases with the radial distance from the inner diameter of the patterned medium.

8. A system, comprising: A patterned medium including magnetic grains that are substantially aligned in rows extending in a radial direction, each of the magnetic grains being magnetically separated from each other by non-magnetic material within each individual row in the rows in the radial direction, the magnetic grains lacking substantial alignment in a recording direction; And A read / write controller configured to control a write head to write a single data bit to the patterned medium by converting a group of magnetic grains to the same magnetic polarity, the group of magnetic grains having a radial width defined based on the size of the write head and independent of the patterned medium.

9. The system according to claim 8, wherein The group of magnetic grains storing the data of the single data bit are substantially aligned along the same radial direction row on the patterned medium.

10. The system according to claim 8, characterized in that, The read / write controller is configured to determine a time to initiate writing the single data bit by deriving write synchronization information from a servo synchronization field.

11. The system according to claim 8, wherein The magnetic grains aligned in the rows have grain centers that are substantially aligned with each other or grain edges that are substantially aligned with each other.

12. The system according to claim 8, wherein The patterned medium further includes grain growth constraint features that separate the rows of magnetic grains from each other.

13. The system according to claim 12, wherein, The grain growth constraint features extend only in the radial direction of the patterned medium.

14. A system, comprising: A patterned medium including magnetic grains that are substantially aligned in rows extending in a radial direction, the magnetic grains within each row in the rows in the radial direction being magnetically separated from each other by non-magnetic material; A read / write controller configured to control a write head to write a single data bit to the patterned medium by converting a group of magnetic grains, the group of magnetic grains having a radial width defined based on the size of the write head, the radial width of the group of magnetic grains being independent of the grain size on the patterned medium.

15. The system according to claim 14, wherein The magnetic grains lack substantial alignment in a recording direction.

16. The system according to claim 14, wherein The group of magnetic grains storing the data of the single data bit are substantially aligned along the same radial direction row on the patterned medium.

17. The system according to claim 14, wherein The read / write controller is configured to determine the time to initiate writing the single data bit by deriving write synchronization information from a servo synchronization field.

Images