Patent Application
20060146445
The present invention relates to improved high areal recording density perpendicular magnetic recording media and systems including a soft magnetic underlayer (SUL) optimized for high -media signal-to-noise ratio (SNR), high erasure resistance, ease of manufacture, and method of manufacturing same. The invention is of particular utility in the manufacture and use of data/information storage and retrieval media, e.g., hard disks, and systems comprising same and having very high areal recording/storage densities.
Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. Conventional thin-film type magnetic recording media, wherein a fine-grained polycrystalline magnetic alloy serves as the active recording layer, are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation of the magnetic domains of magnetic material. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a “single-pole” magnetic transducer or “head” with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (i.e., as compared to the magnetic recording layer), magnetically “soft” underlayer (SUL) or “keeper” layer, i.e., a magnetic layer having a relatively low coercivity below about 1 kOe, between a non-magnetic substrate and a “hard” magnetic recording layer having perpendicular anisotropy K⊥ and a relatively high coercivity Hc of several kOe, typically about 3-6 kOe. The magnetically soft underlayer (SUL) e.g., of a NiFe alloy such as Permalloy serves to guide magnetic flux emanating from the head through the hard, perpendicular magnetic recording layer, typically comprised of a Co-based alloy material, such as CoCr. In addition, the magnetically soft underlayer (SUL) reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
Referring to
As illustrated in
Perpendicular magnetic recording systems such as system 10 comprising perpendicular recording medium 1 include SUL 4 in order to channel the magnetic field from the main pole 8 of the single-pole head 2 and thereby increase the effective magnetic field applied to the magnetically hard recording layer 6. The increased magnetic field enables an increase in the media coercivity Hc which can be utilized, ultimately resulting in improvements in the media signal-to-noise ratio (SNR), thermal stability, and areal recording density. Disadvantageously, however, the magnetic structure of the SUL 4 can contribute to media noise, and the DC noise contribution may increase rapidly if the thickness of the SUL is sufficient such that stripe domains are formed, as described below in more detail. In addition, it is desirable from manufacturing and cost perspectives that the thickness of the SUL 4 be minimized.
With continued reference to
Completing medium 1 is a protective overcoat layer 7, such as a layer of a diamond-like carbon (DLC) formed over magnetic recording layer 6, and a lubricant topcoat layer (not shown in the figure for illustrative simplicity), e.g., a layer of a perfloropolyether material, formed over the protective overcoat layer 7.
As indicated above, a conventionally-configured perpendicular magnetic recording medium such as illustrated in
Another way by which the perpendicular anisotropy component of the SUL may be suppressed is to form a laminated SUL structure, as by depositing a layer stack or laminate comprised of alternating layers of different materials (see F. Nakamura et al., 5th Perpendicular Magnetic Recording Conference (PMRC 2000), Sendai, Japan, Oct. 23-26, 2000, paper 23pA-13). Referring to
Adverting to
Pseudo-laminated SUL/adhesion layer/substrate structure 40L comprises a plurality n (illustratively 3) of vertically stacked magnetically soft sub-layers 4M formed over the surface of a suitable non-magnetic substrate 3 without intervening spacer layers 4S such as are present in the laminated SUL structure 4L of
The optimal thickness of the SUL 4 from the viewpoints of SNR and manufacturing cost may vary depending upon SUL parameters such as saturation magnetic moment (Ms), as well as upon the coercivity Hc of medium 1 and efficiency of the head 2. For a high Ms SUL 4, e.g., Ms˜1,500-2,000 emu/cm3, with a low intrinsic noise contribution and no detrimental effects on growth thereon of subsequent layers, a comparably high SNR is possible for saturation magnetization-thickness products (Mst) ranging from less than about 15 memu/cm2 to more than about 50 memu/cm2. Corresponding film thicknesses of SUL 4 are expected to range from less than about 100 nm to more than about 300 nm. From a manufacturing viewpoint, it is desirable to select the lowest satisfactory thickness within this range.
It is also desirable that perpendicular recording media be resistant to erasure of written bits by head 2 or by stray magnetic fields which are disadvantageously channeled to recording layer 6. It has been determined that such erasure frequently can be another limiting factor in the design of perpendicular magnetic recording systems such as system 10 and media 1. In particular, strong erasure is commonly observed in some media at distances as far from the written bit tracks as the width of the main pole 8 of single-pole head 2.
In view of the foregoing, there exists a clear need for improved perpendicular magnetic recording media and systems, and methods of manufacture therefor, which media include a soft magnetic underlayer (SUL) optimized for high media signal-to-noise ratio (SNR) and high erasure resistance, do not adversely affect growth of subsequently deposited constituent layers, inhibit or prevent formation of low frequency or stripe domain noise, and utilize the thinnest SUL thickness for ease of manufacture.
The present invention, therefore, addresses and solves problems attendant upon the design and manufacture of high performance, high areal recording density perpendicular magnetic recording media and systems, while maintaining full compatibility with the economic requirements of cost-effective, large-scale automated manufacturing technology.
An advantage of the present invention is an improved perpendicular magnetic recording medium.
Another advantage of the present invention is an improved perpendicular magnetic recording medium adapted for use with a single-pole magnetic transducer head.
Still another advantage of the present invention is an improved perpendicular magnetic recording system.
Yet another advantage of the present invention is an improved perpendicular magnetic recording system including a single-pole magnetic transducer head.
A further advantage of the present invention is an improved method of manufacturing a perpendicular magnetic recording medium.
A still further advantage of the present invention is an improved method of manufacturing a perpendicular magnetic recording medium adapted for use with a single-pole magnetic transducer head.
These and additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a perpendicular magnetic recording medium, comprising:
(a) a non-magnetic substrate having a surface; and
(b) a layer stack formed over the substrate surface, the layer stack comprising, in overlying sequence from the substrate surface:
wherein the product (Ms(SUL)t) of the magnetic saturation (Ms(SUL)) and thickness (t) of the SUL has a minimum value which provides a desired amount of transducer head field channeling but is sufficiently large to provide a desired reduction of erasure of written bits.
In accordance with preferred embodiments of the present invention, the perpendicular recording medium is adapted for use in a magnetic recording system including a single pole magnetic transducer head comprising a main pole having a length λ, a magnetic saturation value Ms(head), a saturation current Isat, and a write current Iw; and wherein the thickness t of the SUL is determined based upon the design rule:
t>(λMs(head)Iw)/Ms(SUL)Isat
in order to eliminate written bit erasure due to a head field traversing laterally away from a written track and saturating a head pole comer.
According to certain preferred embodiments of the present invention, the write current Iw is equal to the saturation current Isat, whereby the thickness t of the SUL is determined based upon the design rule:
t>(λMs(head)/Ms(SUL).
Preferred embodiments of the invention include those wherein the thickness t of the SUL is one of the following:
(a) the calculated thickness tcalc according to the design rule;
(b) between about 0.7 and about 1.5 times tcalc; and
(c) between about 0.8 and about 1.2 times tcalc.
According to further preferred embodiments of the invention, the SUL comprises a layer of an amorphous magnetic material and includes a smooth surface facing the magnetically hard recording layer; the amorphous magnetic material of the SUL is free from low frequency grain noise and stripe domains and has a high Ms(SUL) value at least about 1,500 emu/cm3 for minimizing the thickness t of the SUL providing the Ms(SUL)t product.
According to certain preferred embodiments, Ms(SUL)t of the SUL is <˜15 memu/cm2; whereas, according to certain other preferred embodiments, Ms(SUL)t of the SUL is >˜15 memu/cm2, and the SUL is a laminated structure comprising a plurality of layers of the amorphous magnetic material separated by respective thin spacer layers of a non-magnetic material or a pseudo-laminated structure comprising a stacked plurality of contacting sub-layers of the amorphous magnetic material.
Further preferred embodiments of the invention include those wherein the non-magnetic substrate comprises glass or an Al-based alloy with an adhesion layer comprising a non-magnetic amorphous material on the surface thereof, and the layer stack includes a laminated SUL comprised of a plurality of amorphous Fe-based alloy layers separated by amorphous, non-magnetic spacer layers, an hcp interlayer with <0001> preferred growth orientation, a small-grain, low exchange coupled, hcp Co-based alloy magnetic recording layer, a hard carbon-containing protective overcoat, and a lubricant topcoat.
Another aspect of the present invention is an improved perpendicular magnetic recording system, comprising:
(a) a single-pole magnetic transducer head comprising a main pole having a length λ, a magnetic saturation value Ms(head), a saturation current Isat, and a write current Iw; and
(b) a perpendicular magnetic recording medium adapted for use with the single-pole magnetic transducer head, comprising:
wherein the product (Ms(SUL)t) of the magnetic saturation (Ms(SUL)) and thickness (t) of the SUL has a minimum value which provides a desired amount of head field channeling but is sufficiently large to provide a desired reduction of erasure of written bits.
According to preferred embodiments of the invention, the thickness t of the SUL is determined based upon the design rule:
t>(λMs(head)Iw)/Ms(SUL)Isat
in order to eliminate written bit erasure due to a head field traversing laterally away from a written track and saturating a head pole corner.
In accordance with certain preferred embodiments of the invention, the write current Iw is equal to the saturation current Isat, whereby the thickness t of the SUL is determined based upon the design rule:
t>(λMs(head)/Ms(SUL).
In accordance with further preferred embodiments of the present invention, the thickness t of the SUL is selected from the following:
(a) the calculated thickness tcalc according to the design rule;
(b) between about 0.7 and about 1.5 times tcalc; and
(c) between about 0.8 and about 1.2 times tcalc
According to preferred embodiments of the present invention, the SUL comprises a layer of an amorphous magnetic material and includes a smooth surface facing the magnetically hard recording layer; and the amorphous magnetic material of the SUL is free from low frequency grain noise and stripe domains and has a high Ms(SUL) value at least about 1,500 emu/cm3 for minimizing the thickness t of the SUL providing the Ms(SUL)t product.
In accordance with certain preferred embodiments of the invention, Ms(SUL)t of the SUL is <˜15 memu/cm2; whereas, according to certain other preferred embodiments of the invention, Ms(SUL)t of the SUL is >˜15 memu/cm2, and the SUL comprises a laminated structure, wherein the laminated structure comprises a plurality of layers of the amorphous magnetic material separated by respective thin spacer layers of a non-magnetic material or a pseudo-laminated structure comprising a stacked plurality of contacting sub-layers of the amorphous magnetic material.
Preferred embodiments of the present invention include those wherein the non-magnetic substrate comprises glass or an Al-based alloy with an adhesion layer comprising a non-magnetic amorphous material on the surface thereof, and the layer stack includes a laminated SUL comprised of a plurality of amorphous Fe-based alloy layers separated by amorphous, non-magnetic spacer layers, an hcp interlayer with <0001> preferred growth orientation, a small-grain, low exchange coupled, hcp Co-based alloy magnetic recording layer, a hard carbon-containing protective overcoat, and a lubricant topcoat.
Yet another aspect of the present invention is a method of manufacturing a perpendicular magnetic recording medium, comprising:
providing a non-magnetic substrate having a surface; and
forming a layer stack over the substrate surface, the layer stack comprising, in overlying sequence from the substrate surface:
the product Ms(SUL)t) of the magnetic saturation (Ms(SUL)) and thickness (t) of the SUL has a minimum value which provides a desired amount of head field channeling but is sufficiently large to provide a desired reduction of erasure of written bits.
According to preferred embodiments of the invention, the method comprises forming a perpendicular magnetic recording medium adapted for use with a single-pole magnetic transducer head comprising a main pole with a length λ, and having a magnetic saturation value Ms(head), a saturation current Isat, and a write current Iw, wherein the thickness t of the SUL is determined based upon the design rule:
t>(λMs(head)Iw)/Ms(SUL)Isat
in order to eliminate written bit erasure due to a head field traversing laterally away from a written track and saturating a head pole corner.
In accordance with a preferred embodiment of the invention, the method comprises forming a perpendicular magnetic recording medium wherein the write current Iw is equal to the saturation current Isat, and the thickness t of the SUL is determined based upon the design rule:
t>(λMs(head)/Ms(SUL).
Preferred embodiments of the invention include those wherein the method comprises selecting the thickness t of the SUL from the following:
(a) the calculated thickness tcalc according to the design rule;
(b) between about 0.7 and about 1.5 times tcalc; and
(c) between about 0.8 and about 1.2 times tcalc
Further preferred embodiments of the invention include those wherein the method comprises forming a perpendicular magnetic recording medium wherein the SUL comprises a layer of an amorphous magnetic material which includes a smooth surface facing the magnetically hard recording layer; and the amorphous magnetic material is free from low frequency noise and stripe domains and has a high Ms(SUL) value at least about 1,500 emu/cm3 for minimizing the thickness t of the SUL.
According to certain preferred embodiments of the invention, the method comprises forming a perpendicular magnetic recording medium wherein Ms(SUL)t of the SUL is <˜15 memu/cm2; whereas, according to certain other preferred embodiments of the invention, the method comprises forming a perpendicular magnetic recording medium wherein Ms(SUL)t of the SUL is >˜15 memu/cm2, and the SUL comprises a laminated structure including a plurality of layers of the amorphous magnetic material separated by respective thin spacer layers of a non-magnetic material or a pseudo-laminated structure including a stacked plurality of contacting sub-layers of the amorphous magnetic material.
Further preferred embodiments of the invention include those wherein the method comprises forming at least the SUL by sputter deposition, and where the method comprises providing a non-magnetic glass or Al-based alloy substrate with an adhesion layer comprising a non-magnetic amorphous material on the surface thereof, and forming thereon a layer stack including a laminated SUL comprised of a plurality of amorphous Fe-based alloy layers separated by amorphous, non-magnetic spacer layers, an hcp interlayer with <0001> preferred growth orientation, a small-grain, low exchange coupled, hcp Co-based alloy magnetic recording layer, a hard carbon-containing protective overcoat, and a lubricant topcoat.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.
The following detailed description of the embodiments of the present invention can best be understood when read in conjunction with the following drawings, in which the various features are not necessarily drawn to scale but rather are drawn as to best illustrate the pertinent features, and in which like reference numerals are employed throughout to designate similar features, wherein:
The present invention is based upon recognition by the inventors that improved, very high areal recording density perpendicular magnetic recording media, and recording systems comprising same, can be reliably and controllably fabricated with increased erasure resistance, improved SNR, elimination of stripe domains, and ease of manufacturability, by appropriate design and optimization of the soft magnetic underlayer (SUL) of the perpendicular media.
According to the several features of the present invention:
1. the SUL comprises a high (i.e., at least about 1,500 emu/cm3) magnetic saturation (Ms) material of amorphous microstructure and reduced surface roughness. The high value of Ms(SUL) allows for a reduced SUL thickness t for a desired Ms(SUL)t product; and the reduced surface roughness decreases detrimental effects of the thickness of the SUL upon the microstructure of layers subsequently deposited thereon. In addition, the reduced surface roughness decreases detrimental effects of the SUL upon the crystallographic preferred orientation of layers subsequently deposited thereon, e.g., as measured by X-ray rocking curves;
2. the amorphous, high Ms(SUL) material is found to be substantially free from low frequency grain noise and formation of stripe domains when Ms(SUL)t<15 memu/cm2. When Ms(SUL)t<15 memu/cm2, it is necessary to separate portions, segments, or regions (e.g., sub-layers) of the SUL by insertion of thin, non-magnetic spacer layers, as in the laminated SUL structure shown in
3. erasure of recorded bits due to traversal of the head-field laterally away from a written track and saturating a corner of the transducer head pole is substantially eliminated by observing the following design rule for the thickness t of the SUL, wherein the single-pole magnetic transducer head comprises a main pole with a length λ, has a magnetic saturation value Ms(head), a saturation current Isat, and a write current Iw:
t>(λMs(head)Iw)/Ms(SUL)Isat. (1)
For example, for a transducer head with a main pole length of 9 μin. (2.3×10−5 cm), saturating at Isat=30 mA, writing at Iw=20 mA, and with a magnetic saturation value Ms(head)=2,400 emu/cm3, the thickness t of the SUL of a perpendicular recording medium according to the above design rule, when the SUL material has a magnetic saturation value Ms(SUL), is >203 nm.
In this instance, the head field primarily travels directly from the main (i.e., write) pole of the transducer to the auxiliary (i.e., return) pole through a high permeability path, and bit erasure is low. Higher flux saturates the SUL in the path along the x-z plane (see
Therefore, according to the invention, the thickness t and the number of laminations of the SUL are selected as to minimize the Ms(SUL)t product while providing a sufficient amount of head field channeling, but have a sufficient Ms(SUL)t product according to the design rule to reduce recorded bit erasure. For low recorded bit erasure operation at any write current Iw, the latter should be set equal to the saturation current Isat, whereby the design rule (1) simplifies to:
t>(λMs(head)/Ms(SUL). (2)
According to a preferred embodiment of the invention, the amorphous SUL is deposited by sputter deposition at sputter gas pressures below about 3 mTorr in order to minimize surface roughness of the deposited film resulting from ion bombardment and re-sputtering during deposition, the magnetic saturation value Ms(SUL) of the SUL material is at least about 1,500 emu/cm3, and the value of the Ms(SUL)t product is selected to be greater than that required to maximize the SNR in order to reduce recorded bit erasure.
According to a preferred embodiment, the thickness t of the SUL is the calculated design rule thickness tcalc; whereas, according to a more preferred embodiment, the thickness t is selected to be between about 0.7 and about 1.5 times tcalc. According to an even more preferred embodiment, the thickness t is selected to be between about 0.8 and about 1.2 times tcalc.
Referring to
Except as described below, each of the constituent layers of medium 1′ is essentially similar in composition and thickness to the respective constituent layers of conventional medium 1 as shown in
According to embodiments of the invention, substrate 3 comprises glass or an Al-based alloy and is provided with an adhesion layer 3A on the surface thereof, comprised of an amorphous, non-magnetic material as is known in the art; SUL 4′ comprises a laminated structure such as 4L shown in
As indicated supra, the laminated SUL structure 4L consists of a stacked plurality of alternating relatively thicker soft magnetic layers 4M and relatively thinner spacer layers 4S formed over the surface of a suitable substrate 3. An adhesion layer 3A may be provided on the upper surface of the substrate 3, at the interface with the lowermost soft magnetic layer 4M, which adhesion layer 3A may be formed of the same material as that of the spacer layers 4S. According to the invention, the materials of the soft magnetic and spacer layers, their thicknesses, and number of lamination cycles are selected in accordance with the principles and design rule as set forth supra in order to provide desired t and Ms(SUL) values. Stated differently, according to the invention, the thickness t of SUL 4′ and number of lamination cycles n are selected so as to minimize Ms(suL)t while providing sufficient head channeling, and having sufficient Ms(SUL)t to reduce erasure according to the design rule.
By contrast, pseudo-laminated SUL/adhesion layer/substrate structure 40L comprises a plurality n of vertically stacked magnetically soft sub-layers 4M formed over the surface of a suitable non-magnetic substrate 3 without intervening spacer layers 4S such as are present in the laminated SUL structure 4L of
According to a preferred embodiment of the invention, the thickest SUL laminate or pseudo-laminate 4L or 40L has Ms(SUL)t<15 memu/cm2. Another preferred embodiment of the invention has the number of lamination cycles n set equal to the ratio (total SUL Ms(SUL)t/15 memu/cm2)+1.
Referring to
Thus, the present invention advantageously provides improved performance, high areal density, magnetic alloy-based perpendicular magnetic data/information and storage retrieval media and systems, and methods therefor, which media include an improved soft magnetic underlayer (SUL) which afford improved performance characteristics, such as SNR, erasure resistance, elimination of stripe domains, and facilitate manufacture thereof. The media of the present invention are especially useful when employed in conjunction with single-pole recording/retrieval transducer heads and enjoy particular utility in high recording density systems for computer-related applications. In addition, the inventive media can be fabricated by means of conventional media manufacturing technologies, e.g., sputtering.
In the previous description, numerous specific details are set forth, such as specific materials, structures, processes, etc., in order to provide a better understanding of the present invention. However, the present invention can be practiced without resorting to the details specifically set forth. In other instances, well-known processing materials and techniques have not been described in detail in order not to unnecessarily obscure the present invention.
Only the preferred embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is susceptible of changes and/or modifications within the scope of the inventive concept as expressed herein.
