The present invention relates to a component of a recording device, such as a recording medium and slider, with a refractory metal or a refractory metal-containing alloy coating to protect the component from corrosion.
Most modem information storage systems depend on magnetic recording due to its reliability, low cost, and high storage capacity. The primary elements of a magnetic recording system are the recording medium, and the read/write head. Magnetic discs with magnetizable media are used for data storage in almost all computer systems.
FIG. 8 shows the schematic arrangement of a magnetic disk drive 10 using a rotary actuator. A disk or medium 11 is mounted on a spindle 12 and rotated at a predetermined speed. The rotary actuator comprises an arm 15 to which is coupled a suspension 14. A magnetic head 13 is mounted at the distal end of the suspension 14. The magnetic head 13 is brought into contact with the recording/reproduction surface of the disk 11. The rotary actuator could have several suspensions and multiple magnetic heads to allow for simultaneous recording and reproduction on and from both surfaces of each medium. A voice coil motor 19 as a kind of linear motor is provided to the other end of the arm 15. The arm 15 is swingably supported by ball bearings (not shown) provided at the upper and lower portions of a pivot portion 17.
A conventional longitudinal recording disk medium is depicted in FIG. 8 and typically comprises a non-magnetic substrate 20 having sequentially deposited on each side thereof an underlayer 21, 21xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 22, 22xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 23, 23xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat 24, 24xe2x80x2 to the protective overcoat. Underlayer 21, 21xe2x80x2, magnetic layer 22, 22xe2x80x2, and protective overcoat 23, 23xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer.
A conventional longitudinal recording disk medium is prepared by depositing multiple layers of metal films to make a composite film. In sequential order, the multiple layers typically comprise a non-magnetic substrate, a seedlayer, one or more underlayers, a magnetic layer, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) magnetic layer is deposited on a chromium or chromium-alloy underlayer.
The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20xc3x85 thick.
Lubricants conventionally employed in manufacturing magnetic recording media typically comprise mixtures of long chain polymers characterized by a wide distribution of molecular weights and include perfluoropolyethers, functionalized perfluoropolyethers, perfluoropolyalkylethers (PFPE), and functionalized PFPE. PFPE do not have a flashpoint and they can be vaporized and condensed without excessive thermal degradation and without forming solid breakdown products. The most widely used class of lubricants includes perfluoropolyethers such as AM 2001(copyright), Z-DOL(copyright), Ausimont""s Zdol or Krytox lubricants from DuPont.
There is a demand in computer hard drive industry to develop an areal storage density of 100 Gbits/inch2 and higher in the future. With this high areal density, the flying height between the read-write head and the media has to be minimized. Current magnetic hard disc drives operate with the read-write heads only a few nanometers above the disc surface and at rather high speeds, typically a few meters per second. Because the read-write heads can contact the disc surface during operation, a thin layer of lubricant overcoat is coated on the disc surface to reduce wear and friction. The overcoat thickness of the rigid disk on these future disk drives is estimated to be less than 3 nm.
In order for a disk drive to perform reliably in service, all the components in the drive need to perform reliably under severe mechanical and environmental conditions. Recording media is one of the components, which is subjected to cyclical head medium contact and, at times, exposed to severe environmental conditions. Wear and friction have been recognized as potential problems in a recording medium.
To protect the recording media from wear and friction, protective layers of carbon overcoat and liquid lubricant film are coated on the magnetic media. Diamond-like carbon (DLC) has been used as one of the protective layers for magnetic recording media. DLC films have primarily been deposited on to the magnetic media by DC or RF magnetron sputtering.
One solution for improving the wear resistance is proposed in U.S. Pat. No. 5,674,638 (Grill). Grill suggests using a thick fluorinated diamond-like carbon layer of thickness in the range between 3 nm and 30 nm. Column 3, lines 59-63 of Grill. Grill requires the use of a thick fluorinated carbon overcoat layer because the objective of Grill was to improve wear resistance, which generally increases with increased thickness.
The solution adopted to overcome wear and friction in the newer generation of recording media is to use new air bearing design that minimize wear due to the contact of the disk and the slider. By using the advanced air bearing designs, it would be possible to reduce the overcoat layer thickness to less than 3 nm to decrease the gap between the head and the recording medium and, thereby, increase the areal density of the recording medium.
However, when the thickness of the overcoat is reduced to less than 5 nm, applicants recognized that the magnetic layer is more prone to corrosion. The problems associated with the poor corrosion resistance of a thin overcoat layer having a thickness of less than 3 nm was not recognized and solved prior to this invention and the invention of co-pending application Ser. No. 09/870,685, entitled, xe2x80x9cCorrosion Resistant Overcoat For A Component Of A Recording Device,xe2x80x9d filed Jun. 1, 2001, which includes inventors from those listed on this application. Applicants of Ser. No. 09/870,658 found that amorphous fluorinated carbon (a-C:F,H) has a great potential to replace the conventional overcoat materials for hard disk and sliders because it shows significant superiority in corrosion resistance over the traditional hydrogenated carbon produced by sputtering and ion beam deposition.
More recently a variety of techniques such as plasma enhanced chemical vapor deposition (PECVD), ion beam deposition (IBD), and filtered cathodic arc deposition (FCA) are being evaluated for making durable corrosion resistant overcoat films. In a typical manufacturing method using DC or RF magnetron sputtering or any coating technique which uses plasma process, microconatmination of the magnetic surface may occur as a result of flakes or debris sticking to virgin magnetic surface prior to carbon deposition. The amount of contamination will depend upon the chamber cleanliness and target conditions. After carbon overcoat deposition, the disks undergo post process steps, which includes a buffing process to remove asperities, for flying a read/write head at close proximity to the disk surface. In the process of removing asperities, flakes or debris introduced during the carbon overcoat process may be removed, which leaves behind voids. The size of the voids depends upon the flake/debris size. If the size of the voids equals the thickness of the overcoat, then it leaves open metal sites, which are prone to corrosion. A typical void in a 60 xc3x85 A overcoat media produced by the post-sputter process is shown in FIG. 1. The typical size as measured by AFM of these voids in a batch of disks range from 3-15xcexcm, and the depth varies from 20-50 xc3x85. As can be seen, these voids may not create any corrosion issues in a 60 xc3x85 thick overcoat media. However, when the size of the voids equals or exceeds the thickness of the overcoat, these voids promote corrosion of the magnetic layer, which in turn generates magnetic defects as shown in FIG. 2. The AFM phase image on the right-hand side shows the magnetic defect at the location of the carbon void shown on the left-hand side image. Unless an extremely clean environment free of nanometer-sized or larger debris can be maintained inside the deposition chamber the issue of carbon voids and subsequent corrosion causing magnetic defects becomes a serious problem for media with decreasing overcoat thickness. Hence a media design, which includes methods to eliminate flakes/debris or to protect the magnetic layer with an intermediate protective coating, should be beneficial for the corrosion protection.
Also, most disk drives produced currently operate in the Contact Start/Stop (CSS) mode. Since the recording head contacts with recording media during takeoff and landing, corrosion of the magnetic layer due to a large number of CSS cycles could be a major cause of drive failure. To ensure good corrosion resistance, applicants have found that a sealing layer having the ability to prevent corrosion of the magnetic layer is required and a layer of a traditional overcoat material, such as hydrogenated (a-C:H), nitrogenated (a-C:N) carbon, hybrid (a-CHN), dual layer (a-CH/a-CHN) or graded (a-CH/a-CHN), having a thickness of 50 xc3x85 or less, could be insufficient in protecting the hard disk media from corrosion, and at the thickness level of less than 3 nm, corrosion will be a serious problem.
Therefore, there exists a need for a system that provides a good corrosion resistance of the magnetic layer.
A refractory metal or a refractory metal-containing alloy material has a great potential for corrosion prevention of a magnetic material when the refractory metal-containing material is used as a sealing layer material for a component of a recording medium. A component of a magnetic recording medium of this invention includes a recording disk medium, a recording tape medium or a recording head.
An embodiment of this invention is a component of a magnetic recording medium, comprising a magnetic layer and a sealing layer on the magnetic layer, wherein the sealing layer comprises a refractory metal or a refractory metal-containing alloy and has a thickness of less than 10 xc3x85. The refractory metal is selected from the group consisting of Ti, Zr, Nb, Mo, Ta, and W. The sealing layer could further comprise oxygen and/or nitrogen. The sealing layer is selected from the group consisting of Ti, Zr, Nb, Mo, Ta, W, CrTi, CrZr, CrNb, CrMo, CrTa, CrW, TiW, ZrW, NbW, TaW, an oxide of Ti, an oxide of Zr, an oxide of Nb, an oxide of Mo, an oxide of Ta, an oxide of W, an oxide of CrTi, an oxide of CrZr, an oxide of CrNb, an oxide of CrMo, an oxide of CrTa, an oxide of CrW, an oxide of TiW, and oxide of ZrW, an oxide of NbW, an oxide of TaW, a nitride of Ti, a nitride of Zr, a nitride of Nb, a nitride of Mo, a nitride of Ta, a nitride of W, a nitride of CrTi, a nitride of CrZr, a nitride of CrNb, a nitride of CrMo, a nitride of CrTa, a nitride of CrW, a nitride of TiW, and oxide of ZrW, a nitride of NbW, and a nitride of TaW. The component could further comprise a carbon overcoat on the sealing layer. The carbon overcoat could have a thickness in a range from about 10 to 50 xc3x85. The component could further comprise another sealing layer. The another sealing layer could comprise a material selected from the group consisting of a refractory metal, a refractory metal-containing alloy, an oxide of a refractory metal, an oxide of a refractory metal-containing alloy, a nitride of a refractory metal, a nitride of a refractory metal-containing alloy, and combinations thereof. The component could further comprise a carbon overcoat on the another sealing layer, the carbon overcoat having a thickness in a range from about 10 to 50 xc3x85.
Another embodiment of this invention is a method for preventing corrosion of a magnetic layer due to contact start-stop of a recording medium, comprising exposing the magnetic layer to a refractory metal or a refractory metal-containing alloy and depositing a sealing layer comprising the refractory metal or the refractory metal-containing alloy on the magnetic layer, wherein the sealing layer prevents corrosion of the magnetic layer due to contact start-stop of the recording medium. The method could further comprise depositing a carbon overcoat of a thickness in a range from about 10 to 50 xc3x85 on the refractory metal-containing sealing layer.
Another embodiment of this invention is a method of manufacturing a component of a recording medium comprising depositing a first sealing layer on a magnetic layer and depositing a second sealing layer on the first sealing layer, wherein the first sealing layer comprises a refractory metal or a refractory metal-containing alloy. The first sealing layer and/or the second sealing layer could further comprise oxygen and/or nitrogen. In a method of this invention, the carbon overcoat could be deposited by a technique selected from the group consisting of plasma enhanced chemical vapor deposition, ion beam deposition and filtered cathodic arc deposition.
Another embodiment of this invention is a component of a recording medium, comprising a first sealing layer on a magnetic layer and a second sealing layer on the first sealing layer, wherein the first sealing layer comprises a refractory metal or a refractory metal-containing alloy.
Yet another embodiment of this invention is a component of a magnetic recording medium comprising a magnetic material and means for preventing corrosion of the magnetic material due to contact start-stop of the recording medium.
The phrase xe2x80x9cmeans for preventing corrosion of the magnetic material due to contact start-stop of the recording mediumxe2x80x9d refers to a refractory metal or a refractory metal-containing alloy layer of thickness less than 10 xc3x85.