Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2002-03-29
2004-07-27
Chen, Bret (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S523000, C427S569000
Reexamination Certificate
active
06767592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic discs for use in computer disc drives, and, more particularly, to application of the lubricant layer over the magnetic disc
2. Description of the Related Art
Computer disc drives commonly use components made out of thin films to store information. Both the read-write element and the magnetic storage media of disc drives are typically made from thin films.
FIG. 1A
is an illustration showing the layers of a conventional magnetic media structure including a substrate
105
, a seed layer
109
, a magnetic layer
113
, a diamond like carbon (DLC) protective layer
117
, and a lube layer
121
. The initial layer of the media structure is the substrate
105
, which is typically made of nickel-phosphorous plated aluminum or glass that has been textured. The seed layer
109
, typically made of chromium, is a thin film that is deposited onto the substrate
105
creating an interface of intermixed substrate
105
layer molecules and seed layer
109
molecules between the two. The magnetic layer
113
, typically made of a magnetic alloy containing cobalt (Co), platinum (Pt) and chromium (Cr), is a thin film deposited on top of the seed layer
109
creating a second interface of intermixed seed layer
109
molecules and magnetic layer
113
molecules between the two. The DLC protective layer
117
, typically made of carbon and hydrogen, is a thin film that is deposited on top of the magnetic layer
113
creating a third interface of intermixed magnetic layer
113
molecules and DLC protective layer
117
molecules between the two. Finally the lube layer
121
, typically made of a polymer containing carbon (C) and fluorine (F) and oxygen (O), is deposited on top of the DLC protective layer
117
creating a fourth interface of intermixed DLC protective layer
117
molecules and lube layer
121
molecules.
The durability and reliability of recording media is achieved primarily by the application of the DLC protective layer
117
and the lube layer
121
. The combination of the DLC protective layer
117
and lube layer
121
is referred to as a protective overcoat. The DLC protective layer
117
is typically an amorphous film called diamond like carbon (DLC), which contains carbon and hydrogen and exhibits properties between those of graphite and diamond. Thin layers of DLC are deposited on disks using conventional thin film deposition techniques such as ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering or chemical vapor deposition (CVD). During the deposition process, adjusting sputtering gas mixtures of argon and hydrogen varies the concentrations of hydrogen found in the DLC. Since typical thicknesses of DLC protective layer
117
, are less than 100 Angstroms, lube layer
121
is deposited on top of the DLC protective layer
117
, for added protection, lubrication and enhanced disk drive reliability. Lube layer
121
further reduces wear of the disc due to contact with the magnetic head assembly.
A typical lubricant used in lube layer
121
is Perfluoropolyethers (PFPEs), which are long chain polymers composed of repeat units of small perfluorinated aliphatic oxides such as perfluoroethylene oxide or perfluoropropylene oxide. The entire disclosure of U.S. Pat. No. 5,776,577 titled “Magnetic Recording Disk Having A Lubricant Reservoir On The Inner Circumferential Surface,” which discloses PFPE lubricant, is incorporated herein by reference. PFPEs are used as lubricants because they provide excellent lubricity, wide liquid-phase temperature range, low vapor pressure, small temperature dependency of viscosity, high thermal stability, and low chemical reactivity. PFPEs also exhibit low surface tension, resistance to oxidation at high temperature, low toxicity, and moderately high solubility for oxygen. Several different PFPE polymers are available commercially, such as Fomblin Z (random copolymer of CF
2
CF
2
O and CF
2
O units) and Y (random copolymer of CF(CF
3
)CF
2
O and CF
2
O) including Z-DOL and AM 2001 from Montedison, Demnum (a homopolymer of CF
2
CF
2
CF
2
O) from Daikin, and Krytox (homopolymer of CF(CF
3
)CF
2
O).
Lube layer
121
is typically applied evenly over the disc, as a thin film, by dipping the discs in a bath containing mixture of a few percent of PFPE in a solvent and gradually draining the mixture from the bath at a controlled rate. The solvent remaining on the disc evaporates and leaves behind a layer of lubricant less than 100 Angstroms. Recent advances have enabled the application of PFPE using an in-situ vapor deposition process that includes heating the PFPE with a heater in a vacuum lube process chamber. In this system, evaporation occurs in vacuum onto freshly deposited DLC protective layer
117
that has not been exposed to atmosphere, creating a thin uniform coating of PFPE lube layer
121
.
Since it is known in the art that recording media with higher lubricant bonded ratio has better corrosion protection and that an in-situ vapor lubrication process enhances the bonding between lubricants and amorphous carbon, in-situ vapor lubrication has been used to lubricate amorphous carbon layers. In-situ vapor lubrication of recording media is the lubrication of the recording media immediately after a DLC protective layer
117
has been deposited over the magnetic layer
113
without exposing it to atmosphere.
FIG. 1B
is a flow chart showing the typical steps used in an in-situ vapor lubrication process that deposits PFPE lubricant over a carbon layer. The process begins with step
150
by transferring a partially complete media with substrate
105
, seed layer
109
, and magnetic layer
1113
into a vacuum chamber. In step
155
an amorphous carbon layer is deposited over the partially complete media. Next in step
160
, the amorphous carbon is coated with a lube layer
121
of PFPE using an in-situ vapor lubrication process. Finally, in step
165
the lubed magnetic media is transferred to the next manufacturing operation.
The same technology, however, works less effectively with a DLC protective layer
117
. When a DLC protective layer
117
is applied over the magnetic layer
115
, unpaired carbon electrons pair with hydrogen electrons and dangling carbon bonds are tied up, as illustrated in FIG.
1
C. The termination of the carbon bonds on the surface by hydrogen effectively reduces the reactive sites. As a result, the bonding sites for lubricant molecules are reduced and therefore the lubricant bonded ratio decreases. This effect is particularly strong when lubricant is deposited in-situ after depositing the DLC protective layer
117
, as manifested by the poor adhesion of lube layer
121
to the DLC protective layer
117
. Because of this effect, IBD or PECVD processes, which produce DLC protective layer
117
, and in-situ vapor lubrication processes, which enhances bonding, have not been combined to achieve the maximum performance.
Therefore what is needed is a system and method which overcomes these problems and makes it possible to use IBD or PECVD processes to deposit DLC protective layer
117
and in-situ vapor lubrication processes to deposit lube layer
121
to make a reliable final overcoat.
SUMMARY OF THE INVENTION
In order to improve the adhesion between the diamond like carbon (DLC) protective layer
117
, and the lube layer
121
, deposited with an in-situ lubrication process, the DLC protective layer
117
is depleted of hydrogen prior to the application of lube layer
121
using in-situ vapor lubrication processes. Depletion of hydrogen activates the surface of the DLC protective layer
117
by creating unpaired electrons in the DLC that are ready to react. The unpaired electrons create a strong bond between the DLC protective layer
117
and the lube layer
121
.
The DLC protective layer
117
is depleted of hydrogen by bombarding it with argon ions. The hydrogen atoms are ejected from the surface of the DLC protective layer
117
when the accelerated argon ions collide with
Gui Jing
Ma Xiaoding
Stirniman Michael Joseph
Castillo Jesus Del
Chen Bret
Minisandram Raghunath S.
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