Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-09-28
2003-12-09
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S611000, C428S660000, C428S661000, C428S662000, C428S663000, C428S665000, C428S900000
Reexamination Certificate
active
06660413
ABSTRACT:
FIELD OF THE INVENTION
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.
BACKGROUND
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
,
21
′, such as chromium (Cr) or Cr-alloy, a magnetic layer
22
,
22
′, typically comprising a cobalt (Co)-base alloy, and a protective overcoat
23
,
23
′, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat
24
,
24
′ to the protective overcoat. Underlayer
21
,
21
′, magnetic layer
22
,
22
′, and protective overcoat
23
,
23
′, 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 20Å 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®, Z-DOL®, 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/inch
2
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, “Corrosion Resistant Overcoat For A Component Of A Recording Device,” 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 Å A overcoat media produced by the post-sputter process is shown in FIG.
1
. The t
Chour Kueir-Weei
Gui Jing
Ma Xiaoding
Tang Huan
Thangaraj Raj
Morrison & Foerster / LLP
Rickman Holly
Seagate Technology LLC
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