Single-sided sputtered magnetic recording disks

An information-storage media is provided that includes:

FIELD OF THE INVENTION

The present invention is related generally to recording media and specifically to single-sided magnetic recording media.

BACKGROUND OF THE INVENTION

Hard disk drives are an efficient and cost effective solution for data storage. Depending upon the requirements of the particular application, a disk drive may include anywhere from one to twelve hard disks and data may be stored on one or both surfaces of each disk. While hard disk drives are traditionally thought of as a component of a personal computer or as a network server, usage has expanded to include other storage applications such as set top boxes for recording and time shifting of television programs, personal digital assistants, cameras, music players and other consumer electronic devices, each having differing information-storage capacity requirements.

As aerial bit densities of hard disks have dramatically increased in recent years, the large data storage capacities of dual-sided magnetic storage media far exceed demand in many applications. For example, dual-sided hard disks in personal computers have much greater storage capacity than most consumers require during the useful life of the computer. Consumers thus are forced to pay substantial amounts for excess data storage capacity. The intense price competition in the magnetic storage media industry has forced many disk drive manufacturers to offer single-sided magnetic storage media as an alternative. Single-sided storage media are of two types. In one type, a double-sided disk configured to store information on both sides of the disk is installed with a single read/write head serving only one side of the disk. In the other type, known as a single-sided processed disk, only one side of the disk is provided with an information-containing magnetic layer. The other side of the disk does not have an information-containing layer. Single-sided processed disks not only have sufficient storage capacities to satisfy most consumers but also can be manufactured at lower costs than dual-sided disks due to reduced material usage. Nonetheless, there is an ongoing need for less expensive storage media.

SUMMARY OF THE INVENTION

A single-sided processed disk has been developed to provide a low cost storage media. A recurring problem with the single-sided processed disks is the degree of planarity or flatness of the disk. Referring toFIGS. 1 and 2, a single-sided processed magnetic recording disk100is illustrated. The disk100includes a substrate disk200(which is typically aluminum or an aluminum alloy), upper and lower selected layers204and208(which are typically nickel phosphorus), an underlayer212(which is typically chromium or a chromium alloy), a magnetic layer216(which typically is a cobalt-platinum-based quaternary alloy having the formula CoPtXY or a five element alloy CoPtXYZ, where XY and Z can be tantalum, chromium, nickel or boron), an overcoat layer220(which is typically carbon), and a lubricant layer224(which is typically a perfluoropolyether organic polymer). The nickel phosphorus layers have the same thicknesses, “tu” (upper layer thickness) and tL(lower layer thickness), (each of which is typically from about 8 to about 15 micrometers) and are typically deposited by electroless plating techniques. The underlayer, magnetic layer, and overcoat layer have different thicknesses (their total thickness is typically from about 20 to about 100 nm) and are deposited by sputtering techniques. Although nickel phosphorus layers can be deposited in either compression or tension, they are typically deposited in compression and the sputtered layers are also typically deposited in compression. As can be seen fromFIG. 2, the compressive forces in the lower nickel phosphorus layer208are more than offset by the compressive forces in the upper nickel phosphorus layer204and the sputtered layers212,216and220, causing the disk100to be concave on the upper side228of the disk and convex on the lower side232.

The disk concavity on the information storing side of the disk can cause problems. Disk concavity can cause problems in read/write operations, such as due to head tracking errors and undesired contact of the head with the disk surface. Because of these issues, typical disk specifications require a flatness on the information-containing or active surface of the disk of no more than about 7 to about 15 microns. As will be appreciated, “flatness” refers to the distance between the highest and lowest points on a disk surface. With reference toFIG. 2, the flatness is the difference in the elevations of points1and2, where point1is the lowest point on upper disk surface228while point2is the highest point on the upper disk surface228.

These and other needs are addressed by the various embodiments and configurations of the present invention. The present invention is directed generally to controlling the stresses (either compressive and/or tensile) in the layers/films deposited on either side of information-storage media to produce a desired degree of flatness or shape in the media.

In one aspect of the present invention, an information-storage media is provided that includes:

(a) a substrate disk having first and second opposing surfaces;

(b) a first selected layer on the first surface;

(c) a second selected layer on the second surface; and

(d) an information-storage layer adjacent to one or both of the selected layers. The first selected layer has a first thickness, and the second selected layer a second thickness. The first and second selected layers have a different chemical composition than the substrate disk, which typically cause the selected layers to have a differing magnitude of internal compressive or tensile stress than is present in the substrate disk. In other words, the stress distribution across the thickness of the media is non-uniform. To provide a desired disk shape, the first and second thicknesses are different, causing a desired balance or imbalance between compressive/tensile stresses on either side of the substrate disk. As shown in the figures and discussed below, it is to understood that the “selected layer” may or may not be positioned between other layers. In one configuration, the selected layer is configured as a backing layer on a reverse side of the disk.

In one media configuration, the first thickness is no more than about 99.3% of the second thickness, and the difference in thickness between the first and second selected layers is at least about 0.075 microns. Although the selected layer adjacent to the information-storage layer is normally thinner than the nonadjacent selected layer, it may be desirable to have the thicker selected layer adjacent to the information-storage layer.

Preferably, the first and second selected layers comprise nickel phosphorus. Although the first and second selected layers typically have the same chemical composition, there may be applications where differing materials are used in the two layers.

The information-storage layer can store information by any suitable technique, such as by optical, magneto-optical, or magnetic techniques. The material in the layer can be a thin film, a thick film, or a bulk material. Preferably, the information-storage layer is a thin film ferromagnetic material.

The media can include other layers. For example, an underlayer may be positioned between the information-storage layer and the first selected layer, and an overcoat layer above the information-storage layer. The materials in the layers can be thin films, thick films, or bulk materials. In one media configuration, the information-storage layer, underlayer, and overcoat layer are each thin films and in compression. In other media configurations, one or more of the layers can be in tension.

In one media configuration, the first selected layer is positioned between the information-storage layer and the substrate disk while the second surface is free of an information-storage layer. So configured, the disk has one active side and one inactive side. The medium can be single- or dual-sided. In other words, one or both surfaces of the medium can be “active”. As used herein, “active” or “information-containing” means that the disk surface is configured to store data. As used herein, “inactive”, “non-active,” or “noninformation-containing” means that the medium surface is not configured to store data. For example, the active side of the medium has an information storage layer(s), such as a magnetic layer, while the inactive side of the medium has no information storage layer(s).

In another aspect, a method for manufacturing a single-sided information-storage media is provided that includes the steps of:

(a) providing first and second intermediate structures, each of the first and second intermediate structures comprising substrate disks and upper and lower selected layers on opposing upper and lower sides, respectively, of each substrate disk;

(b) placing the lower selected layer of the first intermediate structure adjacent to the lower selected layer of the second intermediate structure, such that the first and second intermediate structures are in a stacked relationship; and

(c) simultaneously removing at least a portion of each of the upper selected layers of the first and second intermediate structures while in the stacked relationship to provide, for each of the first and second intermediate structures, upper and lower selected layers having different thicknesses.

The present invention can have a number of advantages compared to conventional storage media configurations and fabrication processes. For example, disk concavity on the information storage side of a disk can be controlled, thereby avoiding problems in read/write operations, such as due to head tracking errors and undesired contact of the head with the disk surface. In particular, single-sided media can have reduced flatness values by eliminating the systematic stress imbalance across the disk cross-section. The final storage media can be consistently and repeatedly provided with a flatness in compliance with ever decreasing disk specifications, which currently require a maximum flatness on the information-containing surface of the disk in the range of about 7 to about 15 microns. The ability to control the flatnesses of the intermediate and final media permit manufacturers to produce media with desired shapes, e.g., flatnesses, for a wide variety of applications. For example, single-sided and dual-sided disks can both be provided with a desired degree of concavity or convexity. To provide a more curved shape, a stress imbalance can be introduced between the two sides of the media. The ability to remove simultaneously from two stacked media differing thicknesses of selected layer can provide substantial cost and throughput savings compared to conventional one-at-a-time disk processing. The use of a thicker carrier during rough and/or fine polishing can permit a manufacture to use existing media polishing machinery and materials to effect two-disk-at-a-time polishing.

These and other advantages will be apparent from the disclosure of the invention(s) contained herein.

The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

DETAILED DESCRIPTION

Referring toFIG. 3, a first embodiment of a disk according to the present invention will be described. Although the invention is described with specific reference to a magnetic recording disk, it is to be understood that the principles of the present invention may be extended to other recording media types, such as optical recording media, and magneto-optical recording media, and can be used for floppy or hard disks.

FIG. 3depicts a plated disk (or intermediate (disk) structure)300having upper and lower selected layers304and308, respectively, on a substrate disk312. The substrate disk can be any suitable substrate disk, such as aluminum, aluminum alloys (e.g., AlMg), glass, ceramic materials, titanium, titanium alloys and graphite. The layers can be any suitable material for achieving acceptable magnetic recording properties in the overlying magnetic layer(s), such as iron oxide, nickel phosphorus, nickel molybdenum phosphorus, and nickel antimony phosphorus, with the latter three materials being preferred. The selected layers304and308are typically the same chemical composition and have different compositions from the substrate disk to provide an uneven internal stress distribution across the disk cross-section.

As can be seen fromFIG. 3, the thicknesses of the upper and lower-selected layers304and308, which are tuand tL, respectively, are different. When the selected layers are deposited so as to be in compression or have internal compressive stress, the thickness tuof the upper selected layer304which is to become the surface for sputtering of the underlayer, magnetic layer, and overcoat layer, is preferably less than the thickness tLof the lower selected layer308. This causes the disk300to be curved (e.g., have a spherical curvature) in cross-section or have a bowl-shape, with the concave side of the disk300being the surface on which the additional layers are to be sputtered. This is so because the compressive stress in the thicker lower selected layer308exceeds the compressive stress in the thinner upper selected layer304, thereby causing the disk to be warped towards the thinner selected layer.

The governing equations for this behavior are set forth below.

The stress ε in a selected layer is determined by the unique physical properties of a material and the technique and conditions of deposition:

The spherical curvature or radius of curvature R of the disk is provided by the following equation.
R=tsub2/(6×Δtlayer×ε)
where tsubis the thickness of the substrate disk312, Δtlayeris the difference in thicknesses between the upper and lower selected layers304and308, and ε is the stress in each of the layers.

While the relative thicknesses of the two layers depends on the magnitude of the internal compressive stress in each layer and the compressive stresses in the sputtered layers, the thickness of the upper selected layer304is typically no more than about 99.3%, more typically from about 98.3 to about 99.3% and even more typically from about 97.7 to about 98.3% of the thickness of the lower selected layer308. In absolute terms, the thickness of the upper selected layer304ranges from about 7.5 to about 14.5 microns and that of the lower selected layer308from about 8 to about 15 microns. In other words, the difference in thickness between the upper and lower selected layers is typically at least about 0.075 microns and more typically ranges from about 0.2 to about 2 microns.

The flatness (or first flatness) of the disk300is relatively high and the flatness distribution, 3σ, is relatively low. The flatness of each of the upper and lower surfaces316and320, respectively, of the disk300typically is at least about 5 microns and more typically ranges from about 2 to about 10 microns.

FIG. 4depicts the same disk400after deposition of the overlying layers. Specifically, the upper surface404of the disk400has the underlayer408, the magnetic layer412, and the overcoat layer416deposited, preferably by sputtering. The underlayer408can be any material capable of providing the desired crystallography in the magnetic layer412. Preferably, the underlayer408is chromium or a chromium alloy and has a thickness ranging from about 5 to about 20 nm. The magnetic layer412can be any ferromagnetic material, with the cobalt-platinum-based quaternary alloy having the formula CoPtXY or the five element alloy CoPtXYZ, wherein XY and Z can be tantalum, chromium, boron, or nickel. The thickness of the magnetic layer typically ranges from about 7 to about 20 nm. The overcoat layer416can be any suitable overcoat material, with carbon being preferred, and the thickness of the layer typically ranges from about 1 to about 6 nm.

The layers are typically in compression or have internal compressive stresses. The stress in each layer can be calculated using the equation above. The cumulative magnitude of the compressive stresses in the upper selected layer304, the underlayer408, the magnetic layer412, and the overcoat layer416counteract the compressive stress in the lower selected layer308to cause the disk to flatten out or become more planar. For a given thickness of the lower selected layer308, the resulting radius of curvature of the disk is inversely proportional to the cumulative thicknesses of the layers304,408,412, and416. Typically, the flatness of the disk400(or second flatness) is no more than about 17 microns and more typically is no more than about 12 microns.

The relative magnitudes of the cumulative compressive stress in the upper layers304,408,412, and416versus that in the lower selected layer308may be controlled to provide a desired degree of flatness in the final disk. For example, when the cumulative compressive stress in the upper layers exceeds that in the lower selected layer, the upper surface404of the disk will be convex with the opening of the bowl-shape facing downward. When the cumulative compressive stress in the upper layers is less than that in the lower selected layer, the upper surface404of the disk will be concave with the opening of the bowl-shape facing upward. When the cumulative compressive stress in the upper layers is approximately equal to that in the lower selected layer, the upper surface404of the disk will be substantially or completely flat or planar as shown inFIG. 4. By these techniques, disks of varying radii of curvature and flatnesses can be produced. Typically, the flatness values can be made to range from about 1 to about 50 microns.

The control of the radius of curvature or flatness of the disk can be important. Not only is it important for the disk to comply with pertinent flatness specifications but also as the disk temperature fluctuates during read/write operations due to disk rotation the disk curvature changes. For example, the disk may become more concave or convex depending on the rate of change of the compressive stress of each layer due to thermal fluctuations. In one configuration, it is desirable for the disk to be more convex at higher operating temperatures and more concave at lower operating temperatures.

As seen inFIG. 8, for example, the thickness of the upper selected layer804can be selected to be thicker than that of the lower selected layer808to provide a convex upper disk surface800. This surface will become even more convex when the underlayer, magnetic layer, and overcoat layer are deposited on the upper disk surface. In one configuration, the underlayer, magnetic layer, and overcoat layer are deposited so as to have a net internal tensile stress. This can be effected by selecting suitable materials for each layer and/or by using a suitable deposition technique other than sputtering. In that configuration, the use of an upper selected layer having a greater thickness than that of the lower selected layer may be used to counteract the tensile stress to provide the desired degree of disk surface flatness.

When nickel phosphorus is the selected layer on both sides of the disk, it is possible to deposit the layers with a desired degree of internal compressive or tensile stress by varying the composition of the electroless plating bath. When the layers are in tensile as opposed to compressive stress, the use of an upper selected layer904that is thinner than the lower selected layer908will, as shown inFIG. 9, cause the upper disk surface912to be convex. To offset this effect, the underlayer, magnetic layer, and overcoat layer, which are in compressive stress, are preferably deposited on the side having the thicker selected layer, which in the configuration ofFIG. 9is the lower selected layer908. The tensile force exerted by the sputtered layers and the compressive force exerted by the upper selected layer offsets the tensile force exerted by the lower selected layer to provide a relatively planar disk1000as shown inFIG. 10.

An embodiment of the process to produce the disk ofFIGS. 3 and 4will now be discussed with reference toFIGS. 5 and 6.

Referring toFIG. 5, the substrate disk process will first be discussed. In step500, the disk substrate disk312is stamped out of a sheet of material. The stamped disk in step504is ground to provide flat or planar upper and lower substrate disk surfaces. In step508, the disk is baked, and in step516chamfers are formed on the upper and lower substrate disk surfaces. In step520, the upper and lower selected layers, which are nickel phosphorus, are formed on the upper and lower substrate disk surfaces by electroless plating techniques. In this step, the thicknesses of the upper and lower selected layers are the same or substantially the same. Typically, the thickness of the upper selected layer is at least about 95% of the thickness of the lower selected layer and vice versa. Steps500through520are performed using techniques known to those of skill in the art.

In steps524and528, the selected layers are rough (step524) and fine (step528) polished to provide the plated disk configuration ofFIG. 3. As shown inFIG. 6A, in each of steps524and528a disk holder600contains compartments (or holes) for receiving two disks simultaneously (referred to as “two-at-a-time disk polishing”). Upper and lower polishing pads604and608polish the outwardly facing surfaces612and616of the adjacent stacked disks620a,b. The contacting disk surfaces624and628are not polished. The polished surfaces612and616are the upper disk surface316inFIG. 3. In this manner, two adjacent or stacked disks are polished simultaneously to provide a significant cost savings relative to the costs to produce dual-sided disks.

Preferably, the reduction in thickness of the upper selected is at least about 0.70% and more preferably ranges from about 1.0 to about 4.0%.

There are several ways to effect the reduction in layer thickness reduction in the polishing steps. In one approach, all of the thickness difference between the upper and lower selected layers is effected in the rough polishing step524. In a second approach, all of the thickness difference between the upper and lower selected layers is effected in the fine polishing step528. These two approaches require both sides of the disk to be polished in one of the polishing steps, which can be costly. The polishing in this step is performed using one-disk-at-a-time polishing as shown inFIG. 6B. Referring toFIG. 6B, upper and lower polishing pads604and608engage simultaneously the upper and lower sides704and708of each disk700. The carrier712transports the disks through the polishing operation. In a third approach, a portion of the thickness difference between the upper and lower selected layers is effected in each of the rough and fine polishing steps. In this approach, the disks remain in the carrier600(FIG. 6A) through each of the polishing steps, which can represent a significant cost savings relative to the other two approaches.

In one process configuration, the thickness of the upper and lower selected layers304and308is the same after step520and range from about 8 to about 15 microns. In the rough polishing step524, from about 70 to about 95% of the desired thickness reduction in the upper selected layer304is realized. The remaining desired thickness reduction in the upper selected layer304is realized in the fine polishing step528.

After the fine polishing step528, the plated disk is sent to the media process.

The media process will be discussed with reference toFIG. 7.

In step700, the plated disks are merged for processing. “Merging” refers to placing the disks back-to-back such that the upper disk surfaces316face outwardly. In other words, the lower disk surfaces320are adjacent to one another. The disks can be contact merged (as shown inFIG. 6A) in which case the lower disk surfaces320of each disk300physically contact one another or gap merged in which case the lower disk surfaces320of each disk300are separated by a gap.

In step704, the upper disk surfaces316are data zone textured by known techniques.

In step708, the upper disk surfaces316are washed to remove any debris or contaminants from the data zone texturing step.

In step712, the upper disk surfaces316are layer zone textured by known techniques followed by washing of the upper disk surfaces in step716.

In step720, the underlayer408, magnetic layer412, and overcoat layer416are sputtered onto the upper disk surface by known techniques to produce the disk configuration ofFIG. 4. As noted previously, the sputtered layers cause the disk curvature to flatten out. Other techniques can be used to deposit these layers, such as evaporation techniques, ion beam techniques, plating techniques, and the like.

The disk is then subjected to the application of a lubrication layer (such as an organic polymer, e.g., a perfluoropolyether) in step724and tape burnishing in step728. Steps724and728are performed by techniques known to one of skill in the art.

In step732, the adjacent disks are separated or demerged to provide the finished disk736. The lower side420of the disk is the “inactive” or non-information storing side while the upper side404of the disk is the “active” or information storing side.

EXPERIMENTAL

A number of experiments were performed to illustrate the principles of the present invention. In a first series of experiments, various magnetic disks were made using both one-at-a-time and two-at-a-time disk polishing to evaluate the varying degrees of flatness of the disks and the use of such polishing techniques in the fine and rough polishing steps.

Type1disks were formed by electroless plating of nickel phosphorous (NiP) on both sides of aluminum magnesium (AlMg) disks. The NiP layers on both sides of the disks were equal and about 500μ. The concavity of the disks was approximately 5μ. The disk thickness was about 50 mil with a 95 mm outer diameter (OD) and 25 mm inner diameter (ID). The Type1disks were rough-polished using one-at-a-time polishing (as shown inFIG. 6B) maintaining equal removal of nickel material or both sides. The rough-polished substrate disks were then washed thoroughly and ensured to be virtually free of particulates. Washing of the disks minimizes formation of deep scratches during the final step polishing on the non-information-storing side (or inactive side). Such scratches usually penetrate on the information-storing side (or active side). The washed substrate disks are kept fully immersed in distilled water until ready for the final polishing step.

The final polishing step is performed by loading 2-disks at a time in the carrier hole, as shown inFIG. 6A. The carrier600is designed to accommodate the thickness of the two disks. The removal of the nickel material takes place only on one side of each disk during this final polishing step. By adjusting polishing time, the NiP thickness delta between the active and inactive sides and the resulting degree of concavity of the substrate disk can both be controlled.

The process variables in the rough and fine polishing steps are as follows:

The intended thickness differential in the NiP layers on the active and inactive sides was about 10 to about 20μ″, with the active side having the thinner NiP layer. The carrier had six carrier holes, each accommodating a single disk, in the rough polishing step and six holes, each accommodating two disks, in the fine polishing step. The thickness of the carrier was about 40 mil for the rough polishing step and about 90 mil for the fine polishing step. For each run, nine carriers were used.

Type2disks were formed by electroless plating of nickel phosphorous (NiP) on both sides of aluminum magnesium (AlMg) disks. The NiP layers on both sides of the disks were equal and about 500μ. The concavity of the disks were approximately 35μ. The disk thickness was about 50 mil with a 95 mm outer diameter (OD) and 25 mm inner diameter (ID).

The plated substrate disks were rough-polished by two-disk-at-a-time polishing techniques, such that two disks at a time were loaded in the same or a common carrier hole. The rough polishing step was thus different than the rough polishing step for Type1disks, in which one-disk-at-a-time polishing techniques were employed. The removal of the nickel material occurred on only one side of each disk during the rough polishing step. The washing and fine polishing steps were the same as the steps used for the Type1disks.

The process variables were the same as those shown above for Type1disk fabrication except for the thickness differential between the NiP layers on the active and inactive sides of the disks and the carrier thickness in the rough polishing step. The thickness of the carrier for both the rough and fine polishing steps was the same at about 90 mil.

The intended NiP thickness differential for the active and inactive sides of the disks was about 70 to about 90μ″, with the NiP layer on the active side being thinner than the NiP layer on the inactive side.

The shape and flatness of resulting disks are shown inFIGS. 11A through 15B(Type1disks) andFIGS. 16A through 20B(Type2disks). It is important to note that the Type2disk flatness plots appear to be truncated in some areas because the measurement tool limits were locally exceeded. The Root Mean Square or RMS, Peak-to-Peak (P-V) and average flatness (Ra) values along with the scanned area are as follows for each figure:

inFIGS. 11A and 11B, the RMS is 1.270 microns, the P-V is 5.167 microns, the Ra is 1.093 microns, and the area scanned is the product of 93.77 and 92.76 square mm;

inFIGS. 12A and 12B, the RMS is 1.221 microns, the P-V is 4.773 microns, the Ra is 1.054 microns, and the scanned area is the product of 93.77 and 92.76 square mm;

inFIGS. 13A and 13B, the RMS is 0.666 mm, the P-V is 2.673 mm, the Ra is 0.575 mm, and the scanned area is the product of 93.77 and 92.76 square mm;

inFIGS. 14A and 14B, the RMS is 1.078 microns, the P-V is 4.417 microns, the Ra is 0.922 mm, and the scanned area 93.77 and 92.76 square mm;

inFIGS. 15A and 15B, the RMS is 1.378 microns, the P-V is 5.381 microns, the Ra is 1.191 microns, and the scanned area is the product of 93.77 and 92.76 square mm;

inFIGS. 16A and 16B, the RMS is 361.58 microns, the P-V is 1485.83 microns, the Ra is 318.23 microns, and the scanned area is the product of 91 and 86.33 square mm;

inFIGS. 17A and 17B, the RMS is 315.92 microns, the P-V is 1193.22 microns, the Ra is 273.25 microns, and the scanned area is the product of 71.61 and 92.30 square mm;

inFIGS. 18A and 18B, the RMS is 363.17 microns, the P-V is 1524.48 microns, the Ra is 300.23 microns, and the scanned area is the product of 48.27 and 89.54 square mm;

inFIGS. 19A and 19B, the RMS is 376.56 microns, the P-V is 1424.40 microns, the Ra is 324.26 microns, and the scanned area is the product of 63.70 and 86.79 square mm;

inFIGS. 20A and 20B, the RMS is 365.63 microns, the P-V is 1432.22 microns, the Ra is 315.11 microns, and the scanned area is the product of 64.89 and 94.14 square mm;

inFIGS. 21A and 21B, the RMS is 1.437 microns, the P-V is 5.645 microns, the Ra is 1.235 microns, and the scanned area is the product of 91.00 and 90.00 square mm;

inFIGS. 22A and 22B, the RMS is 0.728 microns, the P-V is 2.870 microns, the Ra is 0.626 microns, and the scanned area is the product of 92.58 and 92.76 square mm;

inFIGS. 23A and 23B, the RMS is 1.265 microns, the P-V is 4.808 microns, the Ra is 1.088 microns, and the scanned area is the product of 91.39 and 90.46 square mm;

inFIGS. 24A and 24B, the RMS is 1.203 microns, the P-V is 4.822 microns, the Ra is 1.031 microns, and the scanned area is the product of 91.79 and 90.92 square mm;

inFIGS. 25A and 25B, the RMS is 1.339 microns, the P-V is 5.317 microns, the Ra is 1.145 microns, and the scanned area is the product of 90.60 and 91.38 square mm;

inFIGS. 26A and 26B, the RMS is 1.107 microns, the P-V is 4.192 microns, the Ra is 0.956 microns, and the scanned area is the product of 91.39 and 91.38 square mm;

inFIGS. 27A and 27B, the RMS is 0.128 microns, the P-V is 0.617 microns, the Ra is 0.107 microns, and the scanned area is the product of 93.77 and 94.14 square mm;

inFIGS. 28A and 28B, the RMS is 0.442 microns, the P-V is 2.254 microns, the Ra is 0.354 microns, and the scanned area is the product of 93.77 and 94.14 square mm;

inFIGS. 29A and 29B, the RMS is 0.234 microns, the P-V is 0.982 microns, the Ra is 0.202 microns, and the scanned area is the product of 93.77 and 94.14 square mm;

inFIGS. 30A and 30B, the RMS is 0.246 microns, the P-V is 1.358 microns, the Ra is 0.190 microns, and the scanned area is the product of 93.77 and 94.14 square mm;

inFIGS. 31A and 31B, the RMS is 0.592 microns, the P-V is 2.926 microns, the Ra is 0.475 microns, and the scanned area is the product of 93.77 and 94.14 square mm; and

inFIGS. 32A and 32B, the RMS is 0.454 microns, the P-V is 2.234 microns, the Ra is 0.371 microns, and the scanned area is the product of 93.77 and 94.14 square mm;

The peak-to-valley flatness values and selected layer thicknesses are summarized in the table below.

The average NiP thickness differential for Type1disk samples is about 14μ″ while that for Type2disk samples about 85μ″. Each value corresponds to the amount of NiP material removed (stock removal) during final polishing (Type1disks) and during rough and final polishing (Type2disks). Type1disks exhibited about 5μ concavity, with simultaneous two-disks-at-a-time polishing being implemented only in the final polishing step. Type2disks exhibited about 35μ concavity, with simultaneous two-disks-at-a-time polishing being implemented in both the rough and fine polishing steps.

The degree of concavity induced as a result of uneven material removal on the active/inactive sides appears to be proportional to the NiP layer thickness differential between the two sides. Typical counterpart substrate disks polished utilizing conventional methods (as depicted inFIG. 6B) exhibited average flatness values of about 2μ″ (˜50% of the flatnesses being concave and ˜50% of the flatnesses being convex) and the NiP layer thickness differential being less than about 3μ″. Strictly speaking, the thickness differential is the average of the absolute values of NiP layer thickness differentials among the various disks. Further experiments were performed to determine the degree to which sputtered thin films can flatten pre-bent disks, such as the Type1and2disks above. Two different types of magnetic recording disks were fabricated. The two different types of disks had the following structures:

The shapes and flatnesses of resulting disks are shown inFIGS. 21A and 26B(Type A disks) andFIGS. 27A through 32B(Type B disks). The flatnesses of the disks are set forth below:

As can be seen from the above test results, Type-A disks exhibited all “cone”-shapes with higher flatness values whereas Type-B disks exhibited some “cone” shapes and some “bowl” shapes but with reduced flatness values. Type-B disks were flatter than Type-A disks because Type-B disks had a NiP layer thickness differential of around ˜20μ″ whereas Type-A disks had a NiP layer thickness differential of around 0μ″. This NiP layer thickness differential can be tailored to achieve specific flatnesses for specific applications, as noted previously.

The experimental results provided above show that pre-bent disks can be utilized in the magnetic media industry when one-side sputtering causes disks to bend and form a convex shape due to compressive stress imbalance within the various layers/films. By depositing sputtered films onto the side of the substrate disk which is already bent to form a concave shape (“bowl”-shape, looking to the side in question), the two bending tendencies in opposite directions (from the thicker NiP layer on one side of the disk and the thinner NiP layer and sputtered films on the other side of the disk) are cancelled. The cancellation (or equalization) of the compressive stresses on both sides of the disks cause the resulting disks (after sputter) to be flatter.

In another alternative embodiment, the use of differential thicknesses of selected layers can be employed in dual-sided disks in which differing cumulative intra-layer stresses are present on both sides of the disk. This situation can occur, for example, when differing types or numbers of layers are located on both sides of the disk. By way of illustration, one side of the disk can have one magnetic layer and the other side two magnetic layers or one side of the disk can have a magnetic layer having a different chemical composition than a magnetic layer on the other side of the disk. The stress imbalance can cause warping of the disk as previously noted. Differential thicknesses of selected layers on the two sides of the disk can be used to reduce or eliminate the stress imbalance and therefore provide a more planar disk.

In yet another alternative embodiment, the thicknesses in the upper and lower selected layers304and308is effected during selected layer deposition rather than or in addition to that effected during rough and/or fine polishing. In other words, differing thicknesses of selected layers are applied to the different sides of the disk.

In yet another alternative embodiment, pre-bending or pre-shaping of the substrate disk and selected layers can be accomplished using mechanical techniques (which cause the plated disk to deform plastically), thermal techniques, and combinations thereof.