Patent Application
20130161181
The present invention relates to magnetic data recording and more particularly a method for manufacturing a magnetic media that decreases the time required to manufacture the magnetic disk and increases manufacturing yield.
A key component of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The magnetic disk has a high coercivity magnetic layer that can be locally magnetized to record a bit of data. The disk may also include a soft magnetic layer beneath the hard magnetic layer. This soft magnetic layer can be used to conduct magnetic flux through the media to the return pole of the magnetic head. In order to prevent corrosion or other damage to the magnetic media, the disk can include a hard non-magnetic protective overcoat. Above this overcoat layer is a lubrication layer that helps to allow the read and write heads to fly over the magnetic disk without damage to the disk or to the read or write heads.
In the highly competitive market for magnetic data storage, manufacturing cost and throughput have become ever more important. Minimizing the time required to produce a component such as a magnetic media greatly decreases the cost of the finished disk drive system. Certain processes have been relatively time consuming, reducing manufacturing rate and increasing cost. For example, the formation of the protective overcoat on the magnetic media has been very time consuming. After depositing the protective overcoat, the overcoat must be cured for a long time before the lubricant can be applied. Failure to allow the necessary curing time has resulted in insufficient protection to the magnetic media. Therefore, there remains a need for processes for reducing the time required to produce components of a magnetic recording system such as a magnetic media.
The present invention provides a method for manufacturing a magnetic media that includes constructing a magnetic disk having a magnetic media layer formed thereon, sputter depositing a protective overcoat layer on the magnetic disk, and exposing the protective overcoat to ozone. The method can be performed in a tool that includes a deposition chamber, an exit air lock connected with the deposition chamber such that a disk can be transported from the deposition chamber to the exit air lock, an air inlet connected with the exit air lock, and an ozone generator connected with the air inlet.
This process of exposing the protective coating to ozone greatly reduces the time required to treat the overcoat after deposition. Whereas prior art processes required the protective overcoat to be exposed to atmosphere for up to 24 hours prior to application of the lubricant layer, the present ozone treatment takes only 10 second to 30 minutes to perform. This, of course, greatly reduces the time necessary to manufacture the magnetic media.
These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout.
For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale.
The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein.
Referring now to
At least one slider 113 is positioned near the magnetic disk 112, each slider 113 supporting one or more magnetic head assemblies 121. As the magnetic disk rotates, slider 113 moves radially in and out over the disk surface 122 so that the magnetic head assembly 121 can access different tracks of the magnetic disk where desired data are written. Each slider 113 is attached to an actuator arm 119 by way of a suspension 115. The suspension 115 provides a slight spring force which biases slider 113 against the disk surface 122. Each actuator arm 119 is attached to an actuator means 127. The actuator means 127 as shown in
During operation of the disk storage system, the rotation of the magnetic disk 112 generates an air bearing between the slider 113 and the disk surface 122 which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension 115 and supports slider 113 off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk storage system are controlled in operation by control signals generated by control unit 129, such as access control signals and internal clock signals. Typically, the control unit 129 comprises logic control circuits, storage means and a microprocessor. The control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123 and head position and seek control signals on line 128. The control signals on line 128 provide the desired current profiles to optimally move and position slider 113 to the desired data track on disk 112. Write and read signals are communicated to and from write and read heads 121 by way of recording channel 125.
Magnetic recording density is continuously being increased by decreasing the head media spacing. The spacing reduction is achieved in part by decreasing the lubricant thickness, the protective overcoat thickness, and the surface roughness of the finished media. Throughout this evolution, the disk manufacturing yield must be improved or maintained in order to maintain the disk manufacturing profit margin.
However, with decreasing lubricant and overcoat thickness, and modified thinner overcoats to provide smoother surface topography with while providing adequate corrosion protection, the manufacturing process yield has become increasingly dependent on the time delay between application of the overcoat 206 and application of the lubricant layer 208. In order to achieve acceptable yield, disks have had to be stored for at least 6 hours after application of the protective coating 206 before the lubricant 208 can be applied. This has a negative impact on the manufacturing process flow and adds to the cost of manufacturing the disks 112.
The disc carbon overcoat was studied to determine how the time delay improves yield. The freshly sputtered overcoat is known to contain reactive (dangling) bonds, or carbon radicals. These active groups begin to react with oxygen and moisture when the sputter system exit air lock is vented to atmospheric pressure. Reflection Fourier transform infrared (FTIR) spectroscopy measurements of the disk carbon overcoat indicate the formation of a carbonyl (oxidation) peak with time in air after sputter.
Further insight into the mechanism of the time delay is provided by the type of defects which are time-dependent. Studies have indicated that the first pass manufacturing glide yield increases as the zonal and hard defect types decrease with time after sputter. Zonal defects are moving defects and generally result from overcoat wear debris. Hard defects are stationary and can result from a disk asperity or a stationary patch of overcoat wear debris. Only the overcoat wear rate is expected to improve with time through partial oxidation of the overcoat surface layer.
The difference in glide yield between long and short time delay results from the lower wear rate of the lubricated carbon overcoat when the overcoat has been allowed time to oxidize before lubrication. This conclusion is deduced from the amount of lubricant removed during polishing (FTP), the polishing friction force, and the root-mean-square (RMS) acoustic emission in a low flying slider sweep test. Even though the ZMTD® lubricant (hydroxyl functionalized perfluoropolyether) will be 91.5 percent bonded on a short time delay disk (minimal oxidation), only 79.3 percent remained after the polishing process. In comparison, the lubricant on an overcoat that was stored in air for 25 hours after sputter deposition of the overcoat 206 was initially 98.2 percent bonded and 92.7 percent remained after the polishing pass.
Therefore, exposure to air after sputter deposition of the carbon overcoat 206 has been an important process in order to produce an overcoat that is robust enough to ensure high yield and long component life and reliability. However, atmospheric exposure for such a great length of time increases the time necessary to construct a disk and therefore greatly reduces throughput and increases manufacturing time. In addition, the necessity to remove the disks from the air lock chamber and store them before adding the lubricant adds additional steps to the process, thereby increasing manufacturing complexity.
The inventors found a way to achieve the same results as the above described long duration atmospheric exposure much more quickly and without the need to remove the disk from the exit air lock chamber of the sputter deposition tool. This method can be understood with reference to
After the sputter deposition of the protective overcoat layer 206, the disk is transferred to an exit air lock chamber 312 of the sputter deposition tool. The disk can be held along with many other disks in a cassette 314. It will be recalled that prior art processes required the disks 112 to be exposed to atmosphere for as long as 24 hours. The inventors have, however, found a way to greatly reduce this time requirement.
While the disks 112 are held within the exit air lock, a valve 316 is opened to allow air from the atmosphere to flow into the exit air lock chamber 312. This atmospheric air is passed through an ozone generator 318 so that the air passing into the chamber has a desired concentration of ozone (O3). Alternatively, pure oxygen O2 can be passed through the ozone generator 318 into the exit air lock chamber 312 to produce the ozone of desired concentration within the exit air lock chamber 312. The concentration of ozone entering the chamber can be controlled by controlling the flow rate of the air passing through the ozone generator 318. Passing air more slowly through the ozone generator 318 increases the relative amount of ozone in the air entering the chamber 312. Conversely, passing air more quickly through the chamber decreases the relative amount of ozone within the chamber. The chamber 312 can also include an exhaust vent for venting out residual ozone as indicated schematically by arrow 320.
The ozone generator 318 can be a commercially available ozone generator such as Ozone Solutions, Inc. Model OZV-4. The atmosphere within exit airlock chamber can have an ozone concentration of 5 to 50,000 ppm or can be 5% to 50%. The presence of the ozone greatly speeds the oxidation of the overcoat layer 206 (
After exposure to the ozone containing atmosphere, the disks 112 can be transferred to a bath 322 containing a desired lubricant such as ZTMD® (hydroxy functionalized perfluoropoyether) in order to apply the lubricant to the disks 112. It should be appreciated that while dip coating is described herein as a method for applying lubricant to the disks 112, other methods could be used as well, such as vapor deposition. After application of the lubricant, the disks can be polished (burnished) according to methods that will be familiar to those skilled in the art in order to remove any defects or asperities from the disk.
Tests were performed to verify the yield improvement by the ozone treatment. At least 100 disks were used for each data point in these examples tests. In the first example, disks were removed from the sputter tool and some were treated with ozone for 5 minutes at 5,000 ppm, and a control group of disks were left untreated. Both sets of disks were lubricated with 1 nm of ZTMD, polished as usual, and tested for yield. The yield for these two sets of disks are the left most points near time=0 in
In the second example, disks were collected immediately after sputter and exposed to ozone for various amounts of time between 2 and 5 minutes and ozone concentration from 450 to 5,000 ppm. This provided a set of disks with increasing levels of overcoat carbonyl (oxidation) peak area. These disks were lubricated with 1 nm of ZTMD, polished as usual, and tested for yield. The yield is shown plotted as a function of the carbonyl peak area in
While various embodiments have been described above, it should be understood that they have been presented by way of example only and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
