Patent Application
20190325906
The present invention relates to the field of magnetic recording technology, and more particularly to a magnetic recording device having a graphene overcoat and a method of fabricating the same.
A hard-disk drive (HDD) is a non-volatile storage device that magnetically records information on a computer. It usually consists of several high-speed rotating platters and a read/write head placed on the actuator arm. By using a magnetic head that is in extremely close proximity to the magnetic surface, the information can be written to the disc by changing the polarity of the electromagnetic current. In the opposite way, for example, when the magnetic head passes over the recorded data, the magnetic field causes a change in the electrical signal in the coil such that the data can be read.
It is known that to improve the read/write performance of the head/platter, in addition to the alloy design of the magnetic recording layer in the platter, the reduction of the head flying height is one of the key techniques to achieve ultra-high areal recording density of the hard disk drive. One of the key technologies for ultra-high magnetic recording density. The head flying height refers to the distance from the head to the upper surface of the magnetic recording layer, which usually includes the thickness of a diamond-like carbon (DLC) film. The DLC film is a high-hardness amorphous carbon (α-C) layer formed by plasma-assisted vapor deposition (PECVD) to protect the magnetic recording layer in the platter, which provides corrosion resistance and other features such as tribology.
Many studies have been focused on the improvements of the DLC film to thereby reducing the thickness of the DLC film so as to enhance read and write characteristics and recording density. However, when the thickness of the DLC film is reduced to less than or equal to 2 nanometers (nm), the abrasion and corrosion durability of such thin DLC film will become problematic. Therefore, there is still a need in the art for an improved magnetic recording component and method of fabrication to address the deficiencies and shortcomings of the prior art.
It is one object of the present invention to provide an improved magnetic recording device having a graphene overcoat of a single atom thickness, which can effectively protect the magnetic recording layer in the platter and reduce the head flying height in the hard disk drive.
Another object of the present invention is to provide a method for fabricating a magnetic recording device having a graphene overcoat, which only needs to add a laser process in the conventional fabrication process of the magnetic recording device, and which has the advantages of low cost, suitability of industrial grade mass production and applications.
According to an embodiment of the invention, a magnetic recording device includes a substrate; an intermediate layer disposed on the substrate; a magnetic recording layer disposed on the intermediate layer; and a graphene overcoat disposed on the magnetic recording layer. The graphene overcoat comprises at least one layer of a graphene monoatomic layer which is a sheet-like monoatomic layer of sp2 bonded carbon atoms. A transition layer is disposed between the graphene overcoat and the magnetic recording layer. The transition layer comprises carbon and at least one metal of the magnetic recording layer.
Another aspect of the invention discloses a method of fabricating a magnetic recording device, comprising: providing a laminated structure comprising a substrate, an intermediate layer, a magnetic recording layer, and a diamond-like carbon film; placing the laminated structure in a hermetic vacuum chamber and vacuumizing the vacuum chamber; irradiating and heating a predetermined area of the diamond-like carbon film by a laser beam; and moving the laser beam away from the predetermined area so that a graphene overcoat precipitates on the upper surface of the magnetic recording layer. Finally, the laminated structure is taken out from the chamber, and a lubricant layer is formed on the upper surface of the graphene overcoat. The laser beam provides a sufficient energy that exceeds an energy conversion barrier to temporarily dissolve carbon atoms of the diamond-like carbon film into the surface layer of the magnetic recording layer in the region irradiated by the laser beam.
According to an embodiment of the invention, a pressure in the vacuum chamber is less than 10−4 mbar. The laser beam is a continuous wave laser having a wavelength of 808 nm. The intensity of the laser beam is less than or equal to 0.1 W/mm2.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
In the following detailed description of the disclosure, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be considered as limiting, but the embodiments included herein are defined by the scope of the accompanying claims.
The present invention relates to an improved magnetic recording device having a graphene overcoat of a monoatomic thickness, which continuously and completely covers the entire upper surface of the magnetic recording layer in the platter. The graphene overcoat effectively protects the magnetic recording layer in the platter and reduces the head flying height of the head/platter in the hard disk drive. Another aspect of the present invention provides a method for fabricating a magnetic recording device having a graphene overcoat, which can form a graphene directly on the surface of the magnetic recording layer by only adding a laser irradiation process to the original fabrication process of the magnetic recording device. The disclosed method can be compatible with the current fabrication process of the magnetic recording device without affecting the characteristics of the magnetic recording layer thereof, which has the advantages of low cost and is easy to scale up to industrial scale mass production and application.
Currently, the magnetic recording technology used in hard disks is mainly divided into two types: Perpendicular Magnetic Recording (PMR) and Shingled Magnetic Recording (SMR). Heat Assisted Magnetic Recording (HAMR) is a promising next-generation technology when facing the challenge of physical limit when enhancing magnetic recording density. HARM technology uses laser heating to make the unit area where the platter can produce magnetism smaller, because increasing the temperature can reduce the critical size of the superparamagnetism of the magnetic particles, thereby improving the read/write density of the platter in unit area. HARM technology was first proposed by Fujitsu in 2006, and it usually uses a highly magnetically stable material such as platinum-iron alloy.
A read/write head is an important component of a hard disk drive that moves over a disk platter and converts the magnetic field into a current (for reading), or vice versa, converting the current into a magnetic field (for writing). Hereinafter, the terms “head flying height”, “floating height” or “head/platter read/write gap” refers to the distance from the head on the hard disk to the surface of the magnetic recording layer in the platter. Hereinafter, the term “graphene” means a two-dimensional honeycomb crystal lattice structure consisting of sp2 bonded carbon atoms, which has a thickness of only one carbon atom. The term “multilayer graphene” is a layered structure in which sheets of graphene are stacked and bonded to each other through Van der Waals force.
Conventionally, graphene can be produced by mechanical exfoliation or chemical vapor deposition (CVD) methods. However, it is difficult to control the size and thickness of graphene when produced by mechanical exfoliation, and CVD methods require a high temperature exceeding 1000 degrees Celsius and have contamination problem when transferring graphene. Therefore, the conventional methods of producing graphene is not suitable for mass production of magnetic recording devices, and the cost is too high. The present invention can solve the deficiencies and shortcomings of the prior art.
Please refer to
According to an embodiment of the present invention, the intermediate layer 101 is provided for causing the magnetic recording layer 106 to have the columnar crystal structure with c-axis orientation, and the intermediate layer 101 may be composed of Ru or a Ru alloy. The aforesaid Ru alloy may be, for example, RuCo, RuAl, RuMn, RuMo, RuFe alloy, but is not limited thereto. For example, the Ru content in the Ru alloy may be between 50 at. % and 90 at. %. For example, the intermediate layer 101 may have a film thickness of about 30 nm or less. The magnetic recording layer 106 may be composed of a magnetic film having an axis of easy magnetization toward a direction perpendicular to the main surface of the substrate 100 (perpendicular magnetic recording layer). For example, the magnetic recording layer 106 may contain Co, Pt, or an alloy thereof, but is not limited thereto. Further, an oxide or elements such as Cr, B, Cu, Ta, Zr, Ru, or the like may be added to the magnetic recording layer 106. Example of the oxide may include, for example, SiO2, SiO, Cr2O3, CoO, Co3O4, Ta2O3, TiO2, B2O3, or the like.
According to another embodiment of the present invention, the intermediate layer 101 may comprise Cr, Ru or an alloy thereof. The magnetic recording layer 106 may comprise Fe, Pt, Ni, or an alloy thereof, but is not limited thereto. For example, the magnetic recording layer 106 may be a granular structure in which magnetic crystal grains are separated by grain boundaries of SiO2. Further, TiO2, Al2O3, Ta2O5, ZrO2, MnO, TiO, ZnO or a combination thereof may be used as a grain boundary phase.
According to an embodiment of the present invention, the graphene overcoat 108 may comprise at least one layer of a graphene monoatomic layer which is a sheet-like monoatomic layer of sp2 bonded carbon atoms. For example, the graphene overcoat 108 may comprise 1 to 10 layers of graphene monoatomic layers. For example, preferably, the graphene overcoat 108 may comprise 1 to 5 layers of graphene monoatomic layers, preferably 1 to 2 layers of graphene monoatomic layers. According to an embodiment of the invention, a single layer of graphene monoatomic layer is taken as an example, and its coefficient of friction may be less than about 0.2.
According to an embodiment of the invention, the single layer of graphene monoatomic layer has a thickness of about 0.345 nm. According to an embodiment of the invention, in a case that the graphene overcoat 108 is composed of two or more layers of graphene monoatomic layers, the spacing between the two adjacent graphene monoatomic layers may be about 0.345 nm, but is not limited thereto. this. According to an embodiment of the invention, the graphene overcoat 108 has a thickness of less than or equal to 2 nm. According to another embodiment of the invention, the thickness of the graphene overcoat 108 is less than or equal to 1.5 nm. According to still another embodiment of the present invention, the graphene overcoat 108 has a thickness of less than or equal to 1.0 nm.
According to an embodiment of the present invention, the graphene overcoat 108 continuously and completely covers the upper surface of the magnetic recording layer 106. According to an embodiment of the present invention, as shown in the enlarged view on the right side of
According to an embodiment of the invention, the lubricant layer 110 may be formed on the graphene overcoat 108. For example, the lubricant layer 110 may comprise perfluoropolyether or the like. According to an embodiment of the invention, the lubricant layer 110 has a thickness of about 1 nm. According to another embodiment of the invention, the thickness of the lubricant layer 110 is less than 1 nm.
According to an embodiment of the present invention, the intermediate layer 101 is provided for causing the magnetic recording layer 106 to have the columnar crystal structure with c-axis orientation, and the intermediate layer 101 may be composed of Ru or a Ru alloy. The aforesaid Ru alloy may be, for example, RuCo, RuAl, RuMn, RuMo, RuFe alloy, but is not limited thereto. For example, the Ru content in the Ru alloy may be between 50 at. % and 90 at. %. For example, the intermediate layer 101 may have a film thickness of about 30 nm or less. The magnetic recording layer 106 may be composed of a magnetic film having an axis of easy magnetization toward a direction perpendicular to the main surface of the substrate 100 (perpendicular magnetic recording layer). For example, the magnetic recording layer 106 may contain Co, Pt, or an alloy thereof, but is not limited thereto. Further, an oxide or elements such as Cr, B, Cu, Ta, Zr, Ru, or the like may be added to the magnetic recording layer 106. Example of the oxide may include, for example, SiO2, SiO, Cr2O3, CoO, Co3O4, Ta2O3, TiO2, B2O3, or the like.
According to another embodiment of the present invention, the intermediate layer 101 may comprise Cr, Ru or an alloy thereof. The magnetic recording layer 106 may comprise Fe, Pt, Ni, or an alloy thereof, but is not limited thereto. For example, the magnetic recording layer 106 may be a granular structure in which magnetic crystal grains are separated by grain boundaries of SiO2. Further, TiO2, Al2O3, Ta2O5, ZrO2, MnO, TiO, ZnO or a combination thereof may be used as a grain boundary phase.
According to an embodiment of the present invention, the diamond-like carbon film 202 may be formed by plasma assisted vapor deposition (PECVD), but is not limited thereto. In other embodiments, the diamond-like carbon film 202 can be formed using different methods, such as sputtering. According to an embodiment of the invention, the diamond-like carbon film 202 has a thickness d1, wherein the thickness d1 may be between 0.5 nm and 5.0 nm. According to another embodiment of the invention, the thickness d1 may be between 1.0 nm and 3.0 nm. According to an embodiment of the invention, the diamond-like carbon film 202 directly contacts the upper surface of the magnetic recording layer 106.
As shown in
According to an embodiment of the invention, the intensity of the laser beam 310 may be less than or equal to 0.1 W/mm2. Under this condition, the laser beam 310 can provide sufficient energy to exceed the energy conversion barrier, temporarily dissolving the carbon atoms of the diamond-like carbon film 202 into the surface layer of the magnetic recording layer 106 within the region irradiated by the laser beam 310. When the laser beam 310 is subsequently moved to other areas, the originally irradiated area is cooled, so that carbon atoms dissolved in the surface layer of the magnetic recording layer 106 are precipitated on the upper surface of the magnetic recording layer 106, forming a partial graphene overcoat 108a comprising one or more layers of graphene monoatomic layers.
According to an embodiment of the invention, the partial graphene overcoat 108a has a thickness d2, wherein the thickness d2 is smaller than the thickness d1 of the diamond-like carbon film 202. According to an embodiment of the invention, the thickness d2 is less than or equal to 2 nm.
As shown in
Since the metals such as Co or Fe in the surface layer of the magnetic recording layer 106 act as a catalyst to lower the energy conversion barrier, the present invention can employ a low-intensity (less than or equal to 0.1 W/mm2) laser beam. The carbon atoms of the diamond-like carbon film 202 in the region irradiated by the low-intensity laser beam 310 are dissolved in the surface layer of the magnetic recording layer 106 at relatively low temperatures, wherein the local temperature in the region irradiated by the laser beam 310 can be controlled below 500° C. or even below 200° C., so the magnetic characteristics of the magnetic recording layer 106 are not affected. In addition, the vacuum environment also plays a key role because it has been found through experiments that no graphene overcoat 108 is formed on the upper surface of the magnetic recording layer 106 unless vacuum is applied.
From the experimental results, even though the same procedure as described above was carried out under a nitrogen atmosphere of 10−2 mbar, the signal of graphene was not found by Raman spectroscopy, and therefore the applicant believes that the pressure should be an important factor.
As shown in
The graphene overcoat 108 may comprise at least one layer of a graphene monoatomic layer which is a sheet-like monoatomic layer of sp2 bonded carbon atoms. For example, the graphene overcoat 108 may contain 1 to 10 layers of graphene monoatomic layers. For example, preferably, the graphene overcoat 108 may comprise 1 to 5 layers of graphene monoatomic layers, preferably 1 to 2 layers of graphene monoatomic layers. According to an embodiment of the invention, a single layer of graphene monoatomic layer is taken as an example, and the coefficient of friction thereof may be less than about 0.2.
According to an embodiment of the invention, the single layer of graphene monoatomic layer has a thickness of about 0.345 nm. According to an embodiment of the invention, in a case that the graphene overcoat 108 is composed of two or more layers of graphene monoatoms, the spacing between the adjacent graphene monoatomic layers may be about 0.345 nm, but is not limited thereto. According to an embodiment of the invention, the graphene overcoat 108 has a thickness of less than or equal to 2 nm. According to another embodiment of the invention, the thickness of the graphene overcoat 108 is less than or equal to 1.5 nm. According to still another embodiment of the present invention, the graphene overcoat 108 has a thickness of less than or equal to 1.0 nm.
Subsequently, the laminated structure 10 is taken out from the vacuum chamber 20, and a lubricant layer 110 composed of, for example, perfluoropolyether or the like, is formed on the upper surface of the graphene overcoat 108, and the magnetic recording device 1 is completed.
Structurally, as shown in
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 108100954 | Jan 2019 | TW | national |
