Patent Application
20110102940
1. Field of Disclosure
The invention is generally related to hard disk drives and, in particular, to an improved system, method and apparatus for planarized surfaces on magnetic media disks for hard disk drives.
2. Description of Related Art
A magnetic media storage disk for a hard disk drive (HDD) requires a very flat surface to achieve optimal lift from the air bearing generated by flying the head slider over the disk surface. In particular, an ultra-flat disk surface helps maintain a constant flying height of the read and write elements of the slider relative to the disk. Planarity minimizes fluctuations in the magnetic spacing between the disk and the magnetic elements in the slider and thereby yields more consistent performance.
Both discrete track media (DTM) and bit patterned media (BPM) are future magnetic recording technologies for HDDs that involve non-planar disk surface topographies. These technologies will require enhanced surface planarization techniques to achieve constant flying heights. In DTM, the individual data tracks are physically patterned on the disk. With BPM, the individual bits are physically patterned resulting in nanometer-scale gaps, trenches and grooves between the data tracks or data bits. A suitable disk surface planarization technique is needed to fill in such topographic gaps. Improved planarization provides adequate support to the air bearing surface without compromising the magnetic spacing.
Conventional polymer-based planarization methods typically involve the techniques of dip coating or nano-imprint planarization. The dip coating technique relies on capillary action to fill in the gaps between the media elements. This process is generally limited by the formation of meniscus features of finite curvature, which may not comply with planarization specifications. Dip coating also faces challenges when attempting to fill gaps of various dimensions on the same disk.
The nano-imprint planarization process, on the other hand, faces film uniformity challenges. The nano-imprint process leaves a residual layer with a thickness that varies across the disk. This residual layer is etched away in a subsequent step, but a final planar surface can result only if the original residual layer is of uniform thickness. Nano-imprint planarization also faces economic limitations to be implemented in a manufacturing line because of the elevated cost of imprinting tools. Thus, an improved solution for planarizing the surfaces of magnetic media disks would be desirable.
Embodiments of a system, method and apparatus for planarized surfaces on magnetic media disks for hard disk drives are disclosed. Some embodiments use surface-grafted polymer chains that form a monolayer-thick film of uniform, self-limiting thickness to planarize the surface of the disk.
For example, the film may be formed by grafting the polymer to the surface, or growing the polymer from the surface. The film may be grafted to the disk with a functionalized polymer chain having a radical group that binds to the surface of the disk. This technique forms a monolayer film of uniform, self-limiting thickness. In an alternate embodiment, the technique involves surface-initiated polymerization that grows the polymer from the disk and also forms a monolayer film of uniform thickness.
The thickness of the polymer monolayer may be controlled by selection of the molecular weight of the polymer. If the gap or trench in the disk to be planarized is on the order of twice the thickness of the polymer monolayer, the conformal polymer layer fills in the gap to planarize the surface. This planarization process does not rely on capillary action (i.e., it has no meniscus profile). The film thickness is self-limiting to a single molecular layer, resulting in a uniform thickness over the disk. However, some trenches and gaps in disks have a variable width or non-uniform gaps. For these disks, the polymer film may be swollen by a solvent vapor to fill the variable width gaps. The polymer is then cross-linked in place by radiation or thermal processing.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
The use of the same reference symbols in different drawings indicates similar or identical items.
For surface planarization, embodiments of functionalized polymer chains contain a radical group for grafting the polymer to the surface of the disk. For example, some embodiments use polymers such as functionalized polystyrene (e.g., hydroxyl-terminated polystyrene chains), polymethyl methacrylate, polyethylene, polyethylene oxide, poly dimethylsiloxane, or poly dihydroxybenzyl alcohol may be used. In other embodiments, the functional group may comprise a hydroxyl group, carboxilic group, thiol or methyl ester. The polymer also may comprise a dendrimeric structure and at least one functional group, or a perfluoropolyether.
In some embodiments (see, e.g.,
After rinsing, only the first monolayer 33 bound to the surface remains, leaving a film of uniform thickness. For example, the length of the polymer chain may be chosen such that the thickness of the first monolayer is on the order of about half the gap width “w” in the trenches 19 being planarized. When a monolayer forms on both sides of the trench 19, the film closes the gap to planarize the surface as shown in
In alternate embodiments (see, e.g.,
As shown in
In still other embodiments (see, e.g.,
These embodiments are generally fabricated by one of two processes for BPM and DTM. In the first type of process (hereinafter referred to as “post-etched media”), the layers that form the magnetic recording media are deposited first on a flat substrate and subsequently milled or etched to form the grooves and trenches that define tracks for DTM or bits for BPM. In this first process, the overcoat or top layer may be chosen as the first material 51, to which the functional groups of the planarizing polymer do not react.
In a second type of process (hereinafter referred to as “pre-patterned substrate”), the substrate is textured first with the lands and grooves that form the DTM or BPM structures, followed by a subsequent deposition of the materials that form the magnetic recording media. In the “pre-patterned” substrate, both lands and grooves are covered by the same materials. A different top layer 51 is then deposited by a grazing angle deposition (e.g., evaporation, e-beam evaporation, ion beam deposition, sputtering, etc.) where the deposited species arrive at a shallow angle with respect to the substrate. In this technique the material is deposited only on the top of the “lands” but not in the “grooves.”
In some applications, the disk surface has gaps that are not all identical in width. In other applications (see, e.g.,
The polymer film is subsequently swollen (
In solvent swelling or annealing in accordance with these embodiments, the solvent is chosen according to the polymer used and the desired degree of swelling. For example, for polystyrene polymer, the solvent may comprise toluene, propylene glycol monomethyl ether acetate (PGMEA) or other types of solvents.
The molecules utilized by the invention to form the polymer monolayers are much larger in size than those used in conventional planarizing materials. A portion of the polymer molecules reacts with the disk materials to form a permanent bond. It is only the functionalized portion of the polymer that reacts with and remains adhered to the disk.
Referring now to
A read/write head 110 may be moved across the disk surface by an actuator assembly 106, allowing the head 110 to read or write magnetic data to a particular track 13. The actuator assembly 106 may pivot on a pivot 114. The actuator assembly 106 may form part of a closed loop feedback system, known as servo control, which dynamically positions the read/write head 110 to compensate for thermal expansion of the magnetic recording media 11 as well as vibrations and other disturbances. Also involved in the servo control system is a complex computational algorithm executed by a microprocessor, digital signal processor, or analog signal processor 116 that receives data address information from an associated computer, converts it to a location on the magnetic recording media 11, and moves the read/write head 110 accordingly.
Specifically, read/write heads 110 periodically reference servo patterns recorded on the disk to ensure accurate head 110 positioning. Servo patterns may be used to ensure a read/write head 110 follows a particular track accurately, and to control and monitor transition of the head 110 from one track 13 to another. Upon referencing a servo pattern, the read/write head 110 obtains head position information that enables the control circuitry 116 to subsequently realign the head 110 to correct any detected error.
Servo patterns may be contained in engineered servo sectors 112 embedded within a plurality of data tracks 13 to allow frequent sampling of the servo patterns for optimum disk drive performance. In a typical magnetic recording media 11, embedded servo sectors 112 extend substantially radially from the center of the magnetic recording media 11, like spokes from the center of a wheel. Unlike spokes however, servo sectors 112 form a subtle, arc-shaped path calibrated to substantially match the range of motion of the read/write head 110.
Accordingly, some embodiments may comprise a hard disk drive having a planarized magnetic media disk having an axis and concentric data tracks of magnetic elements. The concentric data tracks are separated from each other by gaps. The magnetic elements have top surfaces and the gaps have a gap surface that is axially spaced apart from the top surfaces of the magnetic elements. The gaps are filled and planarization is achieved by a functionalized polymer such that the gaps are substantially flush with the top surfaces and the top surfaces are exposed. An actuator has a magnetic transducer for reading data from the magnetic media disk, and the actuator is movable relative to the magnetic media disk.
In other embodiments, each of the gaps has a width in a range of 1 to 100 nm. The functionalized polymer may form a monolayer film having a single molecular thickness in a range of 10% to 200% of the width of the gaps. The functionalized polymer may be a functionalized polystyrene, polymethyl methacrylate, polyethylene, polyethylene oxide, poly dimethylsiloxane, or poly dihydroxybenzyl alcohol, and the functional group may be a hydroxyl group, carboxilic group, or thiol and methyl ester. The functionalized polymer may have a dendrimeric structure and at least one functional group. At least a portion of the functionalized polymer may comprise a perfluoropolyether. The magnetic elements may comprise DTM and the gaps comprise grooves that isolate the DTM from each other. The magnetic elements also may be BPM having individual bits formed in rows of nanometer-scale pillars that are separated from one another by the gaps, and the pillars in each row also are separated from each other in a transverse direction.
In other embodiments, a method of planarizing the surface of a magnetic media disk comprises providing a patterned substrate having an axis and concentric data tracks of magnetic elements, the concentric data tracks being separated from each other by gaps, and the magnetic elements having top surfaces and the gaps having a gap surface that is axially spaced apart from the top surfaces of the magnetic elements; depositing a solution containing a functionalized polymer on the patterned substrate to form a film on the patterned substrate; removing any solution from the patterned substrate exceeding a first monolayer of the solution comprising a single molecular layer that is not bound to the patterned substrate, such that the film comprises a uniform thickness; and then removing (e.g., etching) a top portion of the film such that the gaps are filled by the functionalized polymer, the gaps are substantially flush with the top surfaces, and the top surfaces are exposed to planarize a surface of the patterned media.
In still other embodiments, the depositing step comprises spin coating or dip casting, and the removing step comprises rinsing with a solvent. A length of the polymer chain may be selected such that a thickness of the first monolayer is approximately half of a width of the gaps. The first monolayer may form on side walls of the magnetic elements to close the gaps between adjacent ones of the magnetic elements to planarize the surface of the patterned media. The method may further comprise, after the depositing step, subjecting the film to thermal annealing to bind the functional group to the patterned substrate. The etching may comprise reactive ion etching, and the functionalized polymer may be grown directly on the patterned substrate to form a planarized polymer layer.
In some embodiments, the gaps are not necessarily identical in width, and after the removing step the method may further comprise swelling the film to extend into and close the gaps; and cross-linking the film to fix the polymer in a swollen structure. The width of the gaps may be about twice as large as the monolayer thickness of the polymer, the film swollen by solvent annealing and exposing the patterned substrate to a controlled atmosphere containing a solvent vapor to form swollen polymer chains, and cross-linking by radiation or thermal cross-linking. The method also may further comprise removing the patterned substrate from a controlled atmosphere and performing the removal step. The swelling and cross-liking steps may planarize the surface of the patterned media such that no additional removal step is required.
In additional embodiments, the functionalized polymer is grown from a functionalized surface by atom transfer radical polymerization or nitroxide-mediated radical polymerization. The method may further comprise providing the surface of the patterned media with an initiator, exposing the patterned media to a precursor for a selected period of time to grow the functionalized polymer directly on the surface based on a chemical reaction between the initiator and the precursor, removing the precursor to form the film on the surface, and removing a portion of the film until the surface is planarized.
The initiator may be an inherent material of the patterned media, or deposited on the surface. The top surfaces of the magnetic elements may be formed from a first material, and side walls of the magnetic elements and the gaps formed from a second material, such that the functional group of the polymer grafts only to the side walls and gaps but not to the top surfaces to form the planarized surface without the removal step. In some embodiments, the planarized surface of the patterned media has a maximum variation of no more than 5 nm.
Applications for these embodiments may include the use of surface modification layers among various disciplines, ranging from organic or inorganic interfaces for electrical and optical devices, nanofabrication, MEMS, liquid crystals, templating of bio-structures and bio-inspired polymers, self-assembly, etc. As all these and other new disciplines require more complex structures at the nanometer scale, a planarization scheme combined with a surface modification layer may find applications beyond the scope of hard disk drives into these types of technologies.
This written description uses examples to disclose the invention, including the best mode, and also to enable those of ordinary skill in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
