Patent Application
20070196673
The present invention relates to coatings that protect and lubricate surfaces of microelectrical mechanical systems.
Layers within some micro electromechanical systems (for example disc drives) include a substrate, an adhesion layer, a magnetic layer, a diamond like carbon (DLC) protective layer, and a lubricant layer. The DLC protective layer, typically made of carbon and hydrogen, is a coating that is deposited on top of the magnetic layer creating an interface of intermixed magnetic layer molecules and DLC protective layer molecules between the two. The lubricant layer, typically polar bonded molecules, is deposited on top of the DLC layer creating another interface of intermixed DLC layer molecules and lubricant layer molecules.
The durability and reliability of magnetic media located within microelectrical mechanical systems is achieved primarily by the application of the DLC protective layer and the lubricant layer. The combination of the DLC protective layer and lubricant layer is referred to as a protective overcoat. The DLC protective layer is typically an amorphous film, which contains carbon and hydrogen and exhibits properties between those of graphite and diamond. Thin layers of DLC are deposited on discs 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. Typical thicknesses of the DLC protective layer are around 20 to 80 Angstroms. The lubricant layer is typically deposited on top of the DLC protective layer, for added protection, lubrication, and enhanced disc drive reliability.
Typical lubricants used are perfluoropolyethers (PFPEs), which are long chain polymers composed of repeat units of small perfluorinated aliphatic oxides such as perfluoroethylene oxide or perfluoropropylene oxide. 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.
Depending on the ratio of bonded and non-bonded groups, the lubricant layer thickness can vary from about 10 Angstroms to about 50 Angstroms. The non-bonded portion of the lubricant facilitates lubrication while the bonded portion prevents DLC wear since it adsorbs onto the DLC film. The transducing head and media (i.e. a disc) DLC thickness, along with the lubricant thickness, are the biggest contributors of head media separation distance (HMSD). The HMSD in turn affects the data reading and writing efficiency of the head onto the media.
As a result of the demand for reduced HMSD, the thicknesses of the DLC and the lubricant layers has to be reduced to the smallest proportions possible. At these molecular thicknesses, the DLC and/or the lubricant can cease to perform its intended important function.
Therefore what is needed is a way to decrease the HMSD with a thinner film that can act as both a lubricant and a protector to the underlying substrate.
A lubricative and protective thin film often used within micro electromechanical systems. The film comprising an adhesion layer and a self-assembled monolayer, wherein the self-assembled monolayer comprises a head group bonded to the adhesion layer and a tail group attached to the head group.
Film 10 has a thickness in a range of about 8 to about 25 Angstroms and tightly conforms to whatever surface it bonds to. Film 10 is shown bonded to adhesion layer 12. Adhesion layer 12 has a thickness in a range of about 5 to about 10 Angstroms. Adhesion layer 12 is shown deposited onto the surface of substrate 14. In other embodiments, film 10 can be deposited directly onto substrate 14. In one embodiment, substrate 14 can be any type of magnetic alloy, for example, nickel, iron, or cobalt. In other embodiments, substrate 14 may be any other type of element.
Film 10 can be sub-divided into a head group 16 and a tail group 18. Head group 16 is shown bonded to adhesion layer 12 and tail group 18 is shown interacting with lubricant layer 20 (illustrated as circles). As mentioned above, film 10 acts both as a protective film and a lubricating film. Therefore, lubricant layer 20 may be used in some embodiments to provide added lubrication, and in other embodiments lubricant layer 20 may be omitted altogether.
Traditionally, polar bonded lubricants had to be used because non-polar non-bonded lubricants would preferentially interact with the DLC layer and cause lubricant build-up on the slider. These polar bonded lubricants do not increase the disc lifetime and reliability as well as the non-polar non-bonded lubricants do. With the use of the present invention, however, these previously thought unusable non-polar non-bonded lubricants can be used because the DLC layer has been replaced with film 10, which has tail group 18 that does not preferentially react with non-polar non-bonded lubricants. In other embodiments, tail group 18 could be designed to preferentially react with lubricant layer 20, if so desired.
Lubricant layer 20, therefore, may be any type of substance (i.e. non-bonded, bonded, non-polar, or polar). In one embodiment, lubricant layer 20 is perfluoropolyether, hydrocarbon oil, helium gas, and combinations thereof. In other embodiments, lubricant layer 20 maybe other substances that are chosen to optimize performance and reliability of the micro electromechanical system.
Within tail group 18 is site 28, where the about 4 to about 20 carbon tail resides. Tail group 18 further comprises hydrocarbons, fluorocarbons, and combinations thereof In other embodiments, tail group 18 can comprise any halide or any carbon based molecule.
In one embodiment, adhesion layer 12 is selected from one of silicon, alumina, silicon nitride, silica, titanium carbide, metal oxide, and combinations thereof and has a thickness in a range of about 5 to about 10 Angstroms. In other embodiments, adhesion layer 12 can be any type of substance that will preferentially bind to head group 16 of film 10.
First, the portions of adhesion layer 12 that are to be coated with film 10, and the film composition itself, are hydroxylated (represented as arrow 30). Next, adhesion layer 12 with the attached OH groups are exposed to the hydroxylated film composition through at least one of molecular layer deposition, chemical vapor deposition, solution immersion, and combinations thereof(all of which are represented by arrow 32). At this point, a monolayer of film 10 is bound to adhesion layer 12.
Whichever type of film deposition is used, film 10 will be self-assembling and cross-linking, meaning that a single functional silane molecule will automatically bind to an exposed OH group on adhesion layer 12 and then subsequently cross-link to two adjacent molecules that are bonded to two adjacent OH groups on adhesion layer 12. This allows film 10 to be self-assembled (thereby allowing for faster film deposition) and cross-linking (providing a stronger film).
In one embodiment, the transducing head of slider 42 and the magnetic storage medium on disc 44 are fully or partially covered by film 10. In other embodiments, film 10 can be used to lubricate and protect any substrate having an adhesion layer.
Film 10 is shown with head group 16 bonded to adhesion layer 12 and tail group 18 projected towards lubricant layer 20. Slider 42 is shown with transducing head 47. Adhesion layer 48 is located on the under surface of slider 42 and transducing head 47. Adhesion layer 48 has film 50 with its head group 52 and tail group 54. Film 50 has its tail group 54 projected towards lubricant layer 20. In one embodiment, films 10 and 50 are identical and in other embodiments, films 10 and 50 have different compositions.
Films 10 and 50 provide a lubricative and protective thin coating for slider 42, transducing head 47, and substrate 14, protecting them from corrosion and wear. The HMSD in
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scope of the invention. For example, although described as being used in a disc drive, the lubricative and protective thin film can be used to advantage in other types of micro electromechanical systems.
