Patent Application
20080043578
Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:
By way of background information, a practical high NA objective lens may consist of a single lens or the combination of two different lenses to enlarge the manufacturing tolerances of such a lens. Different lens manufacturing techniques can be applied to making small lenses such as, for example, glass-2P technology (see J. Braat, A. Smid, M. Wijnakker, Appl. Opt. 24 (1985)p1853-1855), glass moulding technology (see S. Hirota, “Progress of Aspheric Glass Lenses”, International Workshop on Optics Design and Fabrication ODF'98 (Tokyo, 1998)p29-32), plastic injection moulding (see G. Poetsch, W. Michaeli, “Injection Moulding” (C. Hanser, 1995)), and even direct diamond turning of a lens from bare plastic.
Furthermore, in view of the fact that a fast MFM coil is necessarily small, such a coil can be made using known thin film technology. Practical thin film magnetic coil designs are known, and are described in more detail in International Patent Application No. WO01/82299. In addition, various techniques for this are known, such as standard galvanic growing to a glass substrate, or using the Silicon on Anything (SoA) technique for making such small coils, as described in International Patent Application No. WO02/13188.
As stated above, it is an object of the present invention to combine the manufacturing techniques of thin film coils with the lens-making techniques such that a high performance, reliable and cost-effective lens-MFM coil combination can be realised.
The method of the following exemplary embodiment of the present invention comprises two principal steps: Step 1 is to make an MFM coil by means of a thin film technique, and Step 2 is to make the objective lens on top of the transparent (e.g. glass) plate in which the MFM coil is located.
In one exemplary embodiment of the present invention, it may be desired to employ a multi-layer MFM coil, such as that described in WO01/82299, then standard thin film technology may be used. Thus, starting with a transparent material, such as glass (BK7) or crystalline material such as quartz, two or more coil layers are deposited or galvanically grown onto the transparent substrate, the two or more coil layers extending substantially parallel to one another. The coils are separated from one another by respective layers of isolating material, such as SiO2 or AlO2, which can be deposited using sputtering techniques. After planarisation steps, the result of this manufacturing technique is typically a flat wafer of transparent material, in which a series of MFM coils is embedded.
In another exemplary embodiment of the present invention, an alternative manufacturing technology may be employed, such as that described in WO02/13188, which discloses the Silicon on Anything (SoA) technique. The method starts with a silicon substrate 1 on which an oxide, such as SiO2 or Al2O3, is deposited by, for example, thermal oxidation, sputtering or vapour deposition, to form a thin top layer 3. Next, a first conductive or metallic layer 7a having one or more coil turn sections is formed on one side of the substrate 1 by, for example, sputter deposition or electro deposition of copper or other suitably conductive material. Then a non-conductive layer 7b is formed on the first conductive layer 7a by, for example, deposition of SiO2 or Al2O3, or by spin-coating of a polymer. Thereafter, a second conductive layer 7c is formed on the insulating layer 7b and an interconnection is made, for example, by locally etching the non-conducting layer 7b before the second conductive layer 7c is formed. Thus, with this technique, a wafer with a series of embedded coils results: with the exception that the basic substrate is now standard silicon, rather than being a transparent (e.g. glass) plate, as shown in
Irrespective of the method of manufacturing an MFM coil embedded in a transparent plate, an objective lens can be made on top of the transparent plate by means of a number of different methods.
For example, a glass-photopolymer (glass-2P) process may be used to replicate an aspherical lens directly on top of the glass plate containing the coil. Replication is a technology in which a thin layer of lacquer is shaped on a substrate, for example, a glass plate, with the aid of a mold. In a preferred method, a UV-curing lacquer is used which, after UV curing, forms a stable polymer with good chemical and mechanical resistance. The mold may be treated with a release layer which allows replication of a large number of lenses without any re-treatment. The mold may be made of a UV-transparent material (e.g. fused silica) so that the lacquer can be irradiated through the mold.
Briefly, the method steps comprise filling the mold with lacquer and positioning the glass plate above the mold. The glass plate is placed against the mold and properly aligned. When the plate is well-aligned, the lacquer is hardened by illumination with UV light. Thus, it is possible to replicate an array of aspherical lenses on the plate and then cut the plate into separate lens/coil units. This is a very cost-effective process. Referring to
In another method, an array of injection molded lenses may be made and mounted on top of the glass plate. The wafer is then cut into separate lens/coil units.
In yet another method, separate objective lenses may be made by the glass/2P, glass moulding or plastic injection moulding process, and these separate lenses may then be mounted on respective separate glass plates (having MFM coil embedded therein). This requires a separate mounting step in the manufacturing process for each lens-MFM coil combination, but it eases the manufacturing tolerances of the lenses.
In yet another exemplary method, and referring to
Thus, the present invention provides a method of manufacturing a high-performance, reliable and cost-effective lens-MFM coil combination, which is suitable for use in all magneto-optical (MO) recording systems
Embodiments of the present invention have been described above by way of examples only, and it will be apparent to a person skilled in the art that modifications and variations can be made to the described embodiments without departing from the scope of the invention as defined by the appended claims. Further, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The term “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The terms “a” or “an” does not exclude a plurality. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that measures are recited in mutually different independent claims does not indicate that a combination of these measures cannot be used to advantage.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04101153.7 | Mar 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB05/50849 | 3/8/2005 | WO | 00 | 6/28/2007 |
