Super-Resolution Readout for Magneto-Optical Disk by Optimizing the Deposition Condition of Non-Magnetic Mask Layer
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Super-Resolution Readout for Magneto-Optical Disk by Optimizing the Deposition Condition of Non-Magnetic Mask Layer Takayuki Shima, Johoo Kim, Hiroshi Fuji1, Nobufumi Atoda and Junji Tominaga Laboratory for Advanced Optical Technology (LAOTEC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan 1 Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho, Tenri, Nara 632-8567, Japan ABSTRACT Super-resolution near-field structure (Super-RENS) was prepared by a heliconwave-plasma sputtering method to improve the disk property that is combined with a magneto-optical (MO) recording disk. Antimony and silver-oxide mask layers were prepared by the method and refractive indices were measured. Recording and retrieving of signals beyond the resolution limit (0.2 Pa) was used [9]. In Raman scattering spectra, two crystalline peaks were observed and there were no evidences of the film being amorphous. Similar decrease of k value can also be recognized when Sb film was prepared by RF magnetron sputtering method, but at much higher sputtering pressure (>1.0 Pa). We believe that the effect of sputtering pressure is more evident in HWP sputtering since the distances between the substrate and targets are long (200 mm) compared to a conventional sputtering method. Furthermore, index of refraction n decreased monotonically from about 4.1 to 2.8 as the thickness is increased and was less dependent on the sputtering pressure. For TA-type Super-RENS, it is necessary to prepare an opaque crystalline Sb film in as-deposited condition [1]. Therefore, the film-thickness
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Figure 1. Refractive index of Sb films prepared by the HWP sputtering method as a function of film thickness. Closed circles: index of refraction (n) and open circles: extinction coefficient (k). should be 15-nm or thick. Also it is preferred to use lower sputtering pressure to avoid any deterioration of the film quality, especially for thick Sb film [9]. Figure 2 shows the indices change of AgOx film as a function of oxygen-gas flow ratio. The target RF-power and sputtering pressure were 100 W and 0.4-0.5 Pa, respectively. As oxygenratio is increased, k-value rapidly decreased and became nearly transparent at the ratio higher than 0.25. The result is almost similar to the one made by RF magnetron sputtering [2] and this confirms that AgOx film is successfully made by the HWP sputtering method. Refractive indices
Figure 2. Refractive index of AgOx films prepared by the HWP sputtering method as a function of oxygen gas flow ratio. Closed circles: index of refraction (n) and open circles: extinction coefficient (k).
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Reflective layer (Ag, 50 nm) Dielectric layer (SiN, 25 nm) MO recording layer (TbFeCo, 25 nm) Dielectric layer (SiN, 40 nm) Mask layer (Sb or AgOx, 15 nm) Dielectric layer (SiN, 130 nm) Polycarbonate substrate
Figure 3. The disk structure with Super-RENS and MO recording layer. for AgOx were less dependent on the film thickness, as
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