Patent Application
20090245078
Many modern information storage systems depend on ferroelectric recording due to its reliability, low cost, and high storage capacity. One such data storage system is known as a probe storage system which reads and writes information from and to ferroelectric media.
A read-write head in the form of a probe is used to make contact with the surface of the ferroelectric media. During the act of write-reading, the tip of the probe is extended over the medium and comes in contact across the surface of the medium in a controlled manner. The medium and the tip of the probe experience high speeds in search for data on the ferroelectric medium.
Intimate contact of the tip with the medium is necessary for reading of the data. The contact between the tip of the probe and the medium is generally considered a high contact pressure situation, resulting in high friction and large wear rates, on the storage medium. The high contact pressure also manifests in high interface temperatures, temperatures in the area between the tip and the storage medium.
Another problem that occurs during the write-read operation are current leaks that exist through the interface between the tip and the storage medium which increase the interface temperature through joule heating and which provides a source of electron flow through the interface. Because of the high contact pressure, high interface temperatures and electron flow, high wear rates especially in the storage medium have been observed.
There have been attempts to supply lubricants to the interface between the tip and the media surface. However, such attempts have had problems in that the lubricants used tend to polymerize due to the conditions found in the interface thereby leading to a large reduction in the lubricant thickness, an increase in the lubricant's average molecular weight and viscosity and in some cases an eventual gel being formed. The increase in average molecular weight, viscosity and in the cases in which a gel is formed result in a sticky product which adversely impacts the functioning of the tip in its write-read function of the storage medium.
A data sensing interface comprises a surface of a recording medium and a tip of a data sensor disposed to sense data stored on the recording medium and a layer of polyphenyl ether disposed between the tip and the surface for functioning as a lubricant.
A method of reducing wear within a data sensing interface provides a layer of polyphenyl ether between a tip of a data sensor and a surface of a recording medium such that the polyphenyl ether acts as a lubricant when the tip of the data sensor and the surface of the recording medium are positioned for the data sensor to sense data.
Other features and benefits will be apparent upon reading the following detailed description and review of the associated drawings.
A layer 100 of polyphenyl ether lubricant for lubricating a probe tip 102 designed for contact with a surface 104 of a recording medium 106, is illustrated in
One such structure is a ferroelectric data storage device 110 as illustrated in
Another structure is used is a disc drive 140, as illustrated in
In the example illustrated in
Other read-write structures that may be suitable include tape drives and optical discs.
The use of polyphenyl ether lubricant decreases the interfacial friction between the probe tip 102 and the surface 104 of the medium 106. Polyphenyl ether is represented by the general chemical formula illustrated in
The polyphenyl ethers should not substantially decompose due to the shear caused by the contact pressure between the probe tip 102 and the surface of the medium 104. The geometry of the probe/medium contacting surface results in large contact pressures such as p=60 MPa−4 Gpa wherein p=pressure. Such large contact pressures facilitate high wear rates which polyphenyl ether lessens.
Polyphenyl ethers do not decompose even when experiencing high shear rates such as 3×107 s−1 to 3×108 s−1 that result from the movement in the mechanical interface between the tip 102 and the surface 104 of the medium 106. Polyphenyl ether which meets this criteria enables the very close association of the probe tip with the surface of the recording medium.
The polyphenyl ether also has to withstand high intermittent interfacial temperatures due to the contact pressure described above and the possibility of current flow. Such high interfacial temperatures are expected to run approximately >200° C. The polyphenyl ether lubricant does not substantially decompose (oxidize) under such high intermittent interfacial temperatures.
The polyphenyl ether also withstands current flow in the range of up to approximately 10 μA between the tip and the surface of the medium. Current flows of this magnitude do not substantially decompose or do not cause substantial polymerization of the polyphenyl ether. By substantially decompose is meant that the polyphenyl ether does not degrade sufficiently to affect its viscosity or lubricating characteristics. By substantially polymerize, it is meant that the polyphenyl ether does not further react with itself to a point where the functioning of the read-write capability of the probe is affected by a change in viscosity or other characteristics.
In practice, a broad range of contact pressures and sweep rates exist in the interface between the probe tip and the surface of the medium. Polyphenyl ether occurs in a broad range of viscosities. The viscosity of the polyphenyl ether will vary according to the degree or range of alkylation, the number of phenyl rings or ether linkages. Different viscosities may be needed to match the required viscosity for the appropriate functioning of the probe within the interface. The application of the polyphenyl ether to the media surface may be made via a multitude of methods.
The PPE is applied as a film to the media surface or the tip of the probe or both. Suitable methods of application include, for example, but are not limited to, solvent dilution, dipping, wiping or pressed to one or both of the contacting surfaces A suitable film thickness of the PPE ranges from 1 to 100 nanometers.
The PPE permits the tip of the probe to move through the PPE lubricant quickly enough to permit the tip to function properly in its write-read function in reading data from the surface of the recording medium. An effective time of descent through the PPE lubricant can be estimated by the following:
1/h2=1/h02+4Pt/3ηR2
where (h=the film thickness change, h0=the initial film thickness, P=the applied pressure, η=the viscosity, R=the contact radius and t=the time of descent. The effective time of descent is dependent on the write or read requirements for the selected probe to be in contact with surface of the medium to sense data.
The following example which is intended for illustrative purposes only since numerous modifications and variations may be made.
Polyphenyl ethers in alkylated form under the trade name OS-105, OS-124 and OS-137 were obtained from Arch Technology Holding LLC of St. Charles, Mo. The polyphenyl ethers were successfully applied at the head/media interface using several different methods. The media that the polyphenyl ethers were applied to was a ferroelectric surface of a probe storage system.
One method used to apply the polyphenyl ether was dip coating the media wafers using a dip coating system available from Nima Technology Ltd. of Coventry, England (Dipper Mechanism; type:D1L). Media wafers were immersed into a coating tank which contained 0.5% solution of OS-105 polyphenyl ether using hexane as a solvent to obtain a lubricant layer having a thickness of approximately 5 nanometers on the media surface. After immersion, the media wafers were withdrawn from the coating tank leaving the PPE lubricant on the media surface. During withdrawal from the tank, the hexane solvent was evaporated leaving the lubricant layer on the media surface.
Another method used to apply polyphenyl ether on a probe/media surface interface included applying droplets of polyphenyl ether which immersed the probe in the polyphenyl ether lubricant. Using this method, the polyphenyl ether lubricant was at a level that rose from the media surface up to the base of the probe at its point of attachment to the chip that controls the probe. Typically this distance may range from several micrometers to 100 micrometers. Two methods were used to apply the polyphenyl ether lubricant. One method was to apply the lubricant directly to the media surface and the other included applying a droplet of lubricant to the probe.
Another method used to apply the polyphenyl ether lubricant was by spraying a 0.5% polyphenyl ether in hexane solution using a nebulizer. The nebulizer used is described in the Jacobs U.S. Pat. No. 6,475,570, the entirety of which is hereby incorporated by reference. After the solution was sprayed and the solvent evaporated, the surface of the media was covered by a thin layer of pure polyphenyl ether lubricant.
All cases described in this example, after application of the polyphenyl ether lubricant, the probe tip and surface media were brought into contact and the probe storage device was tested for write-read performance in the presence of the polyphenyl ether lubricant at the interface. During the write-read function, the signal obtained was analyzed for failures. As shown in
It is to be understood that even though numerous characteristics and advantages of various aspects have been set forth in the foregoing description, together with details of the structure and function of various aspect, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for the polyphenyl ether system while maintaining substantially the same functionality. In addition, although the preferred aspects described herein are directed to a polyphenyl ester system for use as a lubricant in a probe interface, it will be appreciated by those skilled in the art that the teachings described herein can be applied to other mechanical sensing structures.
