The present invention relates generally to a protective film that coats a metal substrate. More particularly, the present invention relates to a diamond-like carbon (DLC) layer having imperfections that are treatable with a self-assembled monolayer to improve corrosion resistance.
Disc drive storage systems are used for storage of digital information that can be recorded on concentric tracks of a magnetic disc medium. Several discs are rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs using a write transducer, is accessed using a read transducer. The read and/or write transducer is carried by a slider that is located on an actuator arm that moves radially over the surface of the disc. The slider and transducer can be collectively referred to as a magnetic head.
The discs are rotated at high speeds during operation. As the discs are spun, the slider and the read and/or write transducer glide above the surface of the disc on a small cushion of air. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disc where it is maintained during reading and recording operations. In order to maximize the high areal recording density, the flying height (i.e. the distance by which the head floats above the surface of the disc) must be minimized.
It is well known in the art to coat the air bearing surfaces of the head and the disc with a diamond-like carbon (DLC) protective overcoat and/or a lubricant layer. The function of the DLC overcoat is to protect underlying metals and alloys from wear and corrosion during the manufacturing process, and throughout the lifetime of the disc drive system. As applied to the head, the DLC overcoat includes a DLC layer and an adhesion layer. As applied to the disc, the DLC layer is applied directly to the disc and a lubricant layer is applied over the DLC layer. DLC overcoat thickness for the head can range from about 20 to 30 Angstroms while typical values of DLC overcoats for magnetic media are in excess of 30 Angstroms. The DLC overcoat thicknesses, along with the lubricant thickness, are one of the largest contributors of head media separation (HMS) distance. The HMS distance is measured from the magnetic surface of the head to the magnetic surface of the media. The HMS distance in turn affects the data reading and writing efficiency of the transducer. Thus, it is important to minimize the DLC overcoat thicknesses.
The DLC layer may be formed using any known thin film deposition technique, and it may be difficult to form a DLC layer that is both ultra-thin and uniform. As such, imperfections are commonly observed in the DLC layer. Such imperfections may inhibit the ability of the DLC layer to protect against corrosion, and thus result in premature failure of the storage systems.
Thus, there is a need for a thin DLC overcoat that decreases HMS distance, thereby increasing recording areal density, while still providing sufficient corrosion resistance.
The present invention relates to a protective coating for a substrate that includes a diamond-like carbon (DLC) layer overlying the substrate and having gaps where the substrate is not protected by the diamond-like carbon layer, and a self-assembled monolayer formed in the gaps of the DLC layer. The self-assembled monolayer is formed from at least one precursor molecule that preferentially reacts with an exposed portion of the substrate or an exposed portion of an adhesion layer disposed between the substrate and the diamond-like carbon layer.
Slider 10 is connected to a suspension (not shown) including an actuator arm and a load beam that operates to position slider 10 and transducer 18 over a pre-selected data track of the disc. Transducer 18 either reads data from or writes data to the pre-selected data track of disc 12, as disc 12 rotates below slider 10 and transducer 18. Slider 10 is configured such that DLC layer 24 on surface 22 is an air bearing surface that causes slider 10 to fly above the data tracks of disc 12 due to interaction between the air bearing surface of slider 10 and fluid currents that result from rotation of disc 12. As disc 12 reaches its operating rotational velocity, slider 10 pivots such that leading edge 14 of slider 10 rises to a higher level than trailing edge 16 of slider 10, as shown in
As shown in
Protective overcoat 20 is applied to surface 22 of slider 10. Primary functions of overcoat 20 are to protect against wear and corrosion. In particular, it is important to protect the exposed metal parts of transducer 18 which are susceptible to corrosion or oxidation. Layer 24, formed of diamond-like carbon (DLC) is configured to provide corrosion resistance to slider 10. Diamond-like carbon is a preferred material for protective overcoat 20 due to its high hardness, high wear resistance, low coefficient of friction and chemical inertness. DLC layer 24 may not sufficiently adhere to all surfaces, like surface 22 of slider 10. Therefore, adhesion layer 26 is used to attach DLC layer 24 to slider 10.
DLC layer 24 and adhesion layer 26 may be formed using any known thin film deposition technique, including, but not limited to, chemical vapor deposition, ion beam deposition, evaporation or sputtering. Commonly, adhesion layer 26 is deposited onto surface 22 of slider 10 by physical vapor deposition, and DLC layer 24 is deposited onto adhesion layer 26 by physical sputtering.
A suitable range for total thickness TT of overcoat 20 is between about 10 and 30 Angstroms. Exemplary ranges for total thickness TT include, but are not limited to, about 10 to 21 Angstroms, and about 15 to 25 Angstroms. It may be desirable to decrease or minimize total thickness TT of overcoat 20 in order to decrease HMS distance. However, when total thickness TT is less than about 30 Angstroms, non-acceptable imperfections in DLC layer 24 and adhesion layer 26 may be present. Such imperfections result in surface 22 being exposed to wear and corrosion.
In the embodiment of
If there is an imperfection in adhesion layer 126, DLC layer 124 may likely have an imperfection immediately above the gap in adhesion layer 126, as illustrated by defect 136, because DLC layer 124 does not adhere well to surface 122.
As shown in
The present invention focuses on repairing the imperfections in DLC layer 124 and adhesion layer 126, thereby improving corrosion resistance without contributing to HMS distance.
Substrate 100 may commonly be any type of magnetic material, for example, nickel, iron, cobalt or combinations thereof. In other embodiments, substrate 100 may be any other type of element. As stated above, adhesion layer 126 may commonly be made of silicon. Exposed portions of surface 122 of substrate 100 and adhesion layer 126 are active molecular sites that create reactive substrates.
Imperfections in DLC layer 124 and adhesion layer 126 may be repaired by treating the exposed surfaces with reactive molecules that will preferentially react with exposed surface 122 and adhesion layer 126, but not react with DLC layer 124. An example of such a reactive molecule is a chemical precursor to a self-assembled mono-layer (SAMs), which may be used to pacify the exposed reactive surfaces resulting from imperfections 134, 136, 138 and 140 of
The precursor to the self-assembled organic monolayer may commonly include a tri-chloro, tri-methoxy, or tri-ethoxy silane that is bonded to a chain of about four to twenty carbons. The carbon chain may include hydrocarbons, fluorocarbons, and combinations thereof. The silane portion forms a head group of the molecule and the carbon chain forms a tail group of the molecule.
The chemical precursors are reactive molecules with high energy such that they are able to find the exposed surfaces of substrate 100 and adhesion layer 126 caused by imperfections 134, 136, 138, and 140. The head groups of the molecules will form strong bonds with surface 122 and adhesion layer 126, but will not bond to DLC layer 124. Thus, as explained in more detail below, the chemical precursors will form a self-assembled organic monolayer (SAMs) inside imperfections 134-140, but they will not adhere at all to DLC layer 124. Thus, the SAMs will not increase HMS.
As explained more below in reference to
A portion of tail group 154 of each molecule 150 may be slightly longer or significantly longer than a depth of the imperfection where each molecule 150 resides, depending, for example, on whether there is a gap in both adhesion layer 126 and DLC layer 124 or only DLC layer 124, and the number of carbons in that particular chain. In preferred embodiments, tail group 154 is equal to or slightly larger than a depth of the imperfection. Tail group 154 is soft and bendable such that tail groups 154 of molecules may be folded down flush with DLC layer 124. Alternatively, excess portions of tail groups 154 may be burnished off.
As mentioned above, a significant benefit of the present invention is that forming a self-assembled monolayer in gaps of DLC layer 124 to negate imperfections in protective overcoat 120 does not negatively impact HMS. Moreover, as detailed below, the formation of a self-assembled monolayer on protective overcoat 120, like the embodiment shown in
In preferred embodiments, head group 152 is made from tridecafluoro-tetrahydrooctyl-trichlorosilane, heptadecafluoro-tetra-hydrodecyl-trichlorosilane, trichloro-silane, trimethoxy-silane, triethoxy-silane, dimethylaminosilane, octadecyltrichlorosilane, dodecyltricholorosilane, and combinations thereof. In other embodiments, head group 152 may be made from any silane or thiol based molecule.
Site 162 is tail group 154, where the about 4 to about 20 carbon tail resides. Tail group 154 further comprises hydrocarbons, fluorocarbons, and combinations thereof. In other embodiments, tail group 154 may comprise any halide or any carbon based molecule.
In the exemplary embodiment shown in
To form the self-assembled monolayer, an exposed surface of adhesion layer 126 is reacted with molecules 150 through at least one of molecular layer deposition, chemical vapor deposition, solution immersion, and combinations thereof. Molecular layer deposition and chemical vapor deposition occur through an atomization process to form a self-assembled monolayer on adhesion layer 126. Liquid or solvent immersion allows adhesion layer 126 to be fully or partially immersed into a solution to form the self-assembled monolayer. In an exemplary embodiment using solvent immersion, the solution may be a non-polar hydrocarbon based solvent.
For each molecule 150, a single functional silane molecule (head group 152) will automatically bind to an exposed hydroxyl group on adhesion layer 126 at site 156 to form a strong bond between molecule 150 and adhesion layer 126. The silane molecule will also subsequently cross-link to two adjacent molecules 150 that are also bonded to adhesion layer 126, as shown in
Regardless of the type of film deposition used, once molecules 150 are deposited onto a surface of adhesion layer 126, they will be self-assembling and cross-linking. A single functional silane molecule will automatically bind to an exposed hydroxyl group on adhesion layer 126 and then subsequently cross-link to two adjacent molecules that are bonded to two adjacent hydroxyl groups on adhesion layer 126. A self-assembled monolayer may be similarly formed on exposed portions of substrate 100 of
Because molecules 150 are self-assembling, they allow for faster film deposition. Because molecules 150 are cross-linking, they provide strength to the self-assembled monolayer. As mentioned above, because the self-assembled monolayer is made up of tightly packed molecules within each gap in the layers of the overcoat, the monolayer functions to repel other molecules from entering the gaps. In this way, the self-assembled monolayer helps the DLC layer to provide corrosion resistance.
A diamond-like carbon layer may also be applied as a protective coating to a magnetic storage medium. In the embodiment shown in
A film exhibits better corrosion resistance if it is able to endure a higher current without exhibiting film failure, which includes pitting and other mechanisms indicating a breakdown in the film's ability to resist corrosion. Film failure is indicated when there is an abrupt increase in current at a relatively constant potential. The ability to withstand higher potentials before failure, thus resisting corrosion, is preferred.
In
The untreated protective overcoat exhibited failure at a potential of approximately 0.85 volts. (The broken-line arrow in
The results from
The present invention relates to forming a self-assembled monolayer in the gaps of layers of a protective overcoat in order to occupy the exposed reactive sites. Although the present invention has been described above in reference to a protective overcoat for a magnetic read and/or write head, and/or a magnetic storage medium, it is recognized that the present invention could be used in other applications in which a thin, protective overcoat may be preferred or required. For example, the present invention could be used for other parts of a disc drive system or any other type of metal substrate.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
This application is a continuation-in-part of U.S. patent application Ser. No. 10/700,031, entitled ENCAPSULANT FOR A DISC DRIVE COMPONENT, and filed on Nov. 3, 2003, the disclosure of which is incorporated by reference in its entirety. U.S. patent application Ser. No. 10/700,031 is a continuation-in-part of U.S. patent application Ser. No. 10/409,385, entitled ENCAPSULANT FOR MICROACTUATOR SUSPENSION, and filed on Apr. 8, 2003, the disclosure of which is incorporated by reference in its entirety, and issued on Aug. 16, 2005 as U.S. Pat. No. 6,930,861.
Number | Date | Country | |
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Parent | 10700031 | Nov 2003 | US |
Child | 11586922 | Oct 2006 | US |
Parent | 10409385 | Apr 2003 | US |
Child | 10700031 | Nov 2003 | US |