The present invention relates to a novel hard, highly abrasion and corrosion-resistant, hydrogenated carbon material useful as an ultra-thin protective overcoat layer for high areal recording density thin film magnetic and magneto-optical (xe2x80x9cMOxe2x80x9d) recording media, a method of depositing films or layers of the novel material, and to improved magnetic and MO media including a protective overcoat layer comprised of the novel material.
A magnetic recording medium, e.g., a hard disk, typically comprises a laminate of several layers, comprising a non-magnetic substrate, such as of Alxe2x80x94Mg alloy or a glass or glass-ceramic composite material, and formed sequentially on each side thereof, a polycrystalline underlayer, typically of chromium (Cr) or Cr-baed alloy, a polycrystalline magnetic recording medium layer, e.g., of a cobalt (Co)-based alloy, a hard, abrasion-resistant, protective overcoat layer, typically containing carbon (C), and a lubricant topcoat.
In operation of the magnetic recording medium, the polycrystalline magnetic recording medium layer is locally magnetized by a write transducer, or write head, to record and store information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer, then the grains of the polycrystalline recording medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the polycrystalline recording medium can subsequently produce an electrical response in a read transducer, allowing the stored information to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (CSS) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
As a consequence of the above-described cyclic CSS-type operation, the surface of the disk or medium surface wears off due to the sliding contact if it has insufficient abrasion resistance or lubrication quality, resulting in breakage or damage if the medium surface wears off to a great extent, whereby operation of the disk drive for performing reading and reproducing operations becomes impossible. The protective overcoat layer is formed on the surface of the polycrystalline magnetic recording medium layer so as to protect the latter from friction and like effects due to the above-described sliding action of the magnetic head. Abrasion-resistant, carbon (C)-containing protective coatings have been utilized for this purpose, and are typically formed by sputtering of a carbon target in an argon (Ar) atmosphere. Such amorphous carbon (a-C)-containing protective overcoat layers formed by sputtering have relatively strong graphitic-type bonding, and therefore exhibit a low coefficient of friction in atmospheres containing water (H2O) vapor, which characteristic is peculiar to graphite. However, the a-C layers produced in such manner have very low hardness as compared with many ceramic materials such as are employed as slider materials of thin film heads, and thus are likely to suffer from wear due to contact therewith.
In recent years, therefore, carbon-based protective overcoat layers having diamond-like hardness properties (i.e., HV of about 1,000-5,000 kg/mm2) have been developed, and films of diamond-like carbon (DLC) having a high percentage of diamond-type Cxe2x80x94C bonding have been utilized. Such DLC films exhibit a high degree of hardness due to their diamond-like sp3 bonding structure, and in addition, exhibit the excellent sliding properties characteristic of carbon, thus affording improved sliding resistance against sliders composed of high hardness materials. Such DLC films are generally obtained by DC or RF magnetron sputtering of a carbon target in a gas atmosphere comprising a mixture of Ar gas and a hydrocarbon gas, e.g., methane, or hydrogen gas. The thus-obtained films exhibit DLC properties when a fixed amount of hydrogen is incorporated therein. Incorporation of excessive amounts of hydrogen in the films leads to gradual softening, and thus the hydrogen content of the films must be carefully regulated.
Amorphous, hydrogenated carbon films (referred to herein as a-C:H films) obtained by sputtering of carbon targets in an Ar+H2 gas mixture exhibiting diamond-like properties have also been developed for improving the tribological performance of disk drives; however, the electrical insulating properties of such type films lead to undesirable electrical charge build-up or accumulation during hard disk operation which can result in contamination, glide noise, etc. In order to solve this problem without sacrifice or diminution of the advantageous mechanical properties of such a-C:H films, attempts have been made to dope or otherwise incorporate nitrogen (N) atoms into the a-C:H films, in view of a substantial decrease in electrical resistivity and optical band gap (EBG) exhibited by such nitrogen-doped a-C:H films relative to undoped films.
However, the continuous increase in areal recording density of magnetic recording media requires a commensurately lower flying height. Therefore, it would be advantageous to reduce the thickness of the carbon-based protective overcoat layer without adverse consequences. Conventional sputtered a-C:H materials are difficult to uniformly deposit and generally do not function satisfactorily at a thickness of about 30 xc3x85 or less. Specifically, conventional sputtered a-C:H films of about 30 xc3x85 thickness fail to provide adequate protection against corrosion of the underlying magnetic layer(s), particularly Co-containing ferromagnetic layers, when under environments of high temperature and humidity, and the resulting corrosion product(s) frequently are disadvantageously transferred to the transducer heads, often leading to failure of the disk drive.
The use of alternative deposition techniques for developing thinner and harder a-C:H layers having the requisite mechanical and tribological properties has been studied, such as chemical vapor deposition (CVD), ion beam deposition (IBD), and cathodic arc deposition (CAD) techniques. For example, the IBD method can be utilized for forming hydrogenated ion-beam carbon films (referred to herein as i-C:H films) that exhibit superior tribological performance at thicknesses below about 100 xc3x85. However, such films are insulating and, thus, suffer from the above-described drawback of electrical charge build-up during hard disk operation associated with sputtered a-C:H films.
Accordingly, there exists a need for an improved hard, abrasion and corrosion-resistant material particularly suitable for use as an ultra-thin protective overcoat layer in high areal density magnetic recording media, and a method for manufacturing same, which method is simple, cost-effective, and fully compatible with the productivity and throughput requirements of automated manufacturing technology.
The present invention fully addresses and solves the above-described problems attendant upon the formation of ultra-thin, abrasion and corrosion-resistant protective overcoat layers suitable for use with high areal density magnetic recording media, such as are employed in hard drive applications, while maintaining full compatibility with all mechanical and electrical aspects of conventional disk drive technology. In addition, the present invention enjoys utility in the formation of ultra-thin, abrasion and corrosion-resistant protective overcoat layers required in the manufacture and use of thin film-based, ultra-high recording density magneto-optical (MO) data/information storage and retrieval media in disk form and utilizing conventional Winchester disk drive technology with laser/optical-based read/write transducers operating at flying heights on the order of a few micro-inches above the media surface.
An advantage of the present invention is an improved hard, abrasion and corrosion-resistant, hydrogenated carbon (xe2x80x9cC:Hxe2x80x9d) material formed by a simultaneous sputter+plasma enhanced chemical vapor deposition (xe2x80x9cPECVDxe2x80x9d) process.
Another advantage of the present invention is an improved protective overcoat material for magnetic and MO recording media and comprising an improved hard, abrasion and corrosion-resistant, sputter+PECVD-deposited C:H material.
Yet another advantage of the present invention is an improved magnetic or MO recording medium including an ultra-thin protective overcoat layer comprised of a sputter+PECVD-deposited C:H material.
Still another advantage of the present invention is an improved simultaneous sputter+PECVD method for forming C:H films or layers suitable for use as ultra-thin, abrasion and corrosion-resistant protective overcoat materials in magnetic and MO recording media applications.
A further advantage of the present invention is an improved method for regulating or controlling the amount of PECVD-derived carbon (C) atoms contained in sputter+PECVD deposited C:H materials, films or layers.
A still further advantage of the present invention is an improved apparatus for performing simultaneous sputtering+PECVD for forming films or layers of the improved C:H materials according to the present invention.
Still another advantage of the present invention is an improved magnetic recording medium comprising at least one ferromagnetic layer containing Co and means for protecting the at least one Co-containing ferromagnetic layer from corrosion under high temperature, high humidity conditions.
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 and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a novel hard, abrasion and corrosion-resistant material useful as an ultra-thin protective overcoat layer for a magnetic or magneto-optical (MO) recording medium, which novel material comprises hydrogenated carbon (C:H) formed by a process comprising simultaneous sputter and plasma-enhanced chemical vapor deposition (PECVD) of the hydrogenated carbon (C:H), wherein the amount of carbon atoms in the novel C:H material derived from the PECVD component of the process is less than about 50 at. %.
According to certain embodiments of the present invention, the amount of carbon atoms in the novel C:H material derived from the PECVD component of the process is at least about 30 at. %; the position of the Raman G-band of the C:H material is about 1553 cmxe2x88x921; and the film resistance of the C:H material is as high as about 85 k xcexa9.
Another aspect of the present invention is a magnetic or MO recording medium comprising a protective overcoat layer formed of the novel C:H material; and according particular embodiments of the present invention, the thickness of the protective overcoat layer is not greater than about 30 xc3x85.
Yet another aspect of the present invention is a method of forming a layer of a novel hard, abrasion, and corrosion-resistant hydrogenated carbon (C:H) material on a surface of a substrate, which method comprises the steps of:
(a) providing a vacuum chamber including a carbon sputtering target in the interior space thereof;
(b) providing a substrate in the interior space of the chamber, such that a surface of the substrate is in facing relation to the sputtering target;
(c) supplying the interior space of the vacuum chamber with at least one hydrocarbon gas and at least one inert gas at separately controllable flow rates and applying a sufficient negative potential to the carbon sputtering target to generate a plasma in the interior space to deposit a layer of a novel hard, abrasion and corrosion-resistant C:H material on the substrate surface by simultaneous sputtering of the carbon sputtering target and plasma enhanced chemical vapor deposition (PECVD) of carbon and hydrogen from the at least one hydrocarbon gas, wherein:
step (c) includes separately controlling the flow rates of each of the hydrocarbon and inert gases supplied to the vacuum chamber such that the amount of carbon atoms in the layer of C:H which are derived from PECVD of the hydrocarbon gas is less than about 50 at. %.
In accordance with embodiments of the present invention, step (c) includes separately controlling the flow rates of each of the hydrocarbon and inert gases to the vacuum chamber such that the amount of carbon atoms in the layer of C:H which are derived from PECVD of the at least one hydrocarbon gas is at least about 30 at. %; step (c) further includes supplying the interior space of the vacuum chamber with at least one hydrocarbon gas of formula CxHy, where x=an integer from 1 to 5 and y=an integer from 2 to 10 and at least one inert gas selected from the group consisting of He, Ne, Ar, Kr, and Xe.
According to particular embodiments of the present invention, step (c) includes supplying the interior space of the vacuum chamber with at least one of acetylene (C2H2) and ethylene (C2H4) as the at least one hydrocarbon gas and Ar as the at least one inert gas; step (a) comprises providing an elongated, cylindrical carbon sputtering target rotatable about its axis of elongation; step (c) further comprises rotating the cylindrical carbon sputtering target about the axis of elongation; and step (b) further comprises applying a bias voltage within the voltage range from 0 to about xe2x88x92150 V to the substrate during step (c).
Embodiments of the present invention include comprises providing a magnetic or magneto-optical (MO) recording medium as the substrate in step (b), the surface thereof comprising the exposed surface of an uppermost layer of a stack of layers comprising the medium; and step (c) comprises forming a protective overcoat layer of the hard, abrasion and corrosion-resistant C:H on the exposed surface of the uppermost layer of the medium.
According to particular embodiments of the present invention, step (b) comprises providing a disk-shaped substrate; and step (c) comprises forming the protective overcoat layer to a thickness not greater than about 30 xc3x85.
Still another aspect of the present invention is a recording medium, comprising:
(a) a substrate;
(b) a stack of thin film layers on the substrate; and
(c) a protective overcoat layer on an uppermost layer of the stack of thin film layers, the protective overcoat layer comprising a novel hard, abrasion and corrosion-resistant material comprised of hydrogenated carbon (C:H) formed by a process comprising simultaneous sputter and plasma-enhanced chemical vapor (PECVD) deposition of the novel hydrogenated carbon (C:H) material, wherein the amount of carbon atoms in the C:H material derived from the PECVD component of the process is less than about 50 at. %.
According to embodiments of the present invention, the amount of carbon atoms in the C:H material derived from the PECVD component of the process is at least about 30 at. %; the position of the Raman G-band of the C:H material of the protective overcoat layer is about 1553 cmxe2x88x921; and the film resistance is as high as about 85 k xcexa9.
In accordance with particular embodiments of the present invention, the stack (b) of thin film layers comprises a stack of layers for a magnetic or magneto-optical (MO) recording medium; and the substrate (a) is disk-shaped.
According to specific embodiments of the invention, the stack (b) of thin film layers comprises a stack of layers for a magnetic recording medium; the protective overcoat layer (c) is not greater than about 30 xc3x85 thick; and the stack (b) of thin film layers includes at least one ferromagnetic layer comprising Co.
A further aspect of the present invention is an apparatus for performing simultaneous sputter and plasma-enhanced chemical vapor (PECVD) deposition of a layer of a novel hard, abrasion and corrosion-resistant, hydrogenated carbon (C:H) material on a surface of a substrate, comprising:
(a) a vacuum chamber defining an interior space;
(b) a carbon sputtering target in the interior space of the vacuum chamber, the carbon target being in the form of an elongated cylinder rotatable about its axis of elongation;
(c) substrate mounting means for mounting a substrate in the interior space of the vacuum chamber, such that a major surface of the substrate is in parallel, facing relation to the elongated cylinder sputtering target; and
(d) gas supply means for supplying the interior space of the vacuum chamber with at least one hydrocarbon gas and at least one inert sputtering gas at separately controllable flow rates.
According to embodiments of the present invention, substrate mounting means (c) comprises means for mounting a disk-shaped substrate such that a major surface thereof is in parallel, facing relation to the cylindrical sputtering target; and the apparatus further comprises a bias voltage applying means (e) for applying to the substrate a bias voltage within the range from 0 to about xe2x88x92150 V.
A still further aspect of the present invention is a magnetic recording medium, comprising:
(a) at least one ferromagnetic thin film layer containing Co; and
(b) means for protecting the at least one Co-containing ferromagnetic thin film layer from corrosion under high temperature, high humidity environments.
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. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.