Patent Application
20070291629
A best mode (exemplary embodiment) for carrying out the present invention is described below based on the drawings. The present invention is not limited to the exemplary embodiment below, but may be modified in various forms within the gist of the invention. Further, the drawings used are used for description of the present exemplary embodiment, but not intended to represent an actual size.
First, a structure of the optical recording medium, to which the present exemplary embodiment is applied, is described.
Next,
A surface of the substrate 5 has a guide groove constituting groove 2 with a given groove width (groove width, Wp) and a groove depth (Dp), and land 1 placed between two adjacent grooves of the groove 2. The groove 2 forms a wobble groove to meander a surface of the substrate 5.
Groove depth (Dp) of the guide groove formed on the surface of the substrate 5 is preferably from 25 nm to 35 nm. Track pitch (Tp) of wobble groove (Gv) is preferably from 200 nm to 250 nm.
In the present exemplary embodiment, the substrate 5 is prepared by injection molding, in which the groove 2 with groove width (Wp) of 240 nm and groove depth (Dp) of 30 nm is formed at a track pitch (Tp) interval of 400 nm on a surface of the polycarbonate resin (Panlite AD-5503 manufactured by Teijin Chemicals Ltd.) disc with a center hole inner diameter of 15 mm, an outer diameter of 120 mm and a thickness of 0.6 mm. Information for disc recognition, address information and the like are pre-recorded by above wobble groove (Gv,
In such a disc to record the signal within wobble groove (Gv), tracking is generally performed using the push-pull signal. The push-pull signal herein is a signal generated by an arithmetic operation of each output signal from a four-division photo-detector used in a pickup of the recording and reading device.
The amount of push-pull signal is known to vary with the influence of a pattern transfer in molding of the substrate 5, a making process for the phase-change recording layer 4, the amount of birefringence in the substrate 5, and the like.
Materials constituting each layer are described next.
A material for the substrate 5 is not particularly limited to, but include, in addition of the above polycarbonate resin, for example, resins such as acrylic resins, methacrylic resins, amorphous polyolefin resins, polyester resins, polystyrene resins, epoxy resins and the like, glass, and others.
The phase-change recording layer 4 is composed of a phase-change recording material. A thickness of the phase-change recording layer 4 is generally from 10 nm to 15 nm. Specific examples of the phase-change recording material include, for example, materials such as Sb—Te, Ge—Te, Ge—Sb—Te, In—Sb—Te, Ag—In—Sb—Te, MA-Ge—Sb—Te (MA is at least one of the elements from Au, Cu, Pd, Ta, W, Ir, Sc, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Ag, Tl, S, Se and Pt), Sn—Sb—Te, In—Se—Tl, In—Se—Tl-MB (MB is at least one of the elements from Au, Cu, Pd, Ta, W, Ir, Sc, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Ag, Ti, S, Se and Pt), Sn—Sb—Se, Bi—Ge—Te and the like.
The reflective layer 6 is composed of a reflective material such as a metal, an alloy or the like. A thickness of the reflective layer 6 is generally around 100 nm. As the reflective material, a metal, for example, Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Cr and Pd can be used singly or as an alloy. Moreover, in addition to these metals as a major component, it may contain a metal and a metalloid such as Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Cu, Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi and the like.
The dummy substrate 3 is not required to have optical transparency like the substrate 5 and may use, for example, plastics, metal, glass and the like with appropriate processability and rigidity. The dummy substrate 3 is formed in a disc shape with an inner diameter of 15 mm, an outer diameter of 120 mm and a thickness of 0.6 mm similarly to the substrate 5.
The optical recording medium 10, to which the present exemplary embodiment is applied, may have other layers as needed. For example, between the substrate 5 and the phase-change recording layer 4 or between the phase-change recording layer 4 and the reflective layer 6 may be formed, for example, a protective layer composed of a ZnS—SiO2 mixture, SiNx and the like, respectively. A UV protective layer composed of a UV curable resin may be also placed between the reflective layer 6 and the dummy substrate 3. Moreover, an interface layer, a heat diffusion layer and the like may be placed.
The substrate 5 for the optical recording medium 10, to which the present exemplary embodiment is applied is next detailed further.
In the present exemplary embodiment, the disc-shaped substrate 5 is characterized with a distribution of the amount of birefringence in the radial direction of the substrate 5 to cancel out the birefringence derived from the stress (principal stress in the radial direction (σr) and the principal stress in the circumferential direction (σt)) generated in rotating and with reduction of an increase of retardation as an optical distortion, for example, even in high speed rotating with the number of revolutions at 6,000 rpm or more.
In case of the hollow centered disc which rotates at a high speed, for instance, at a linear velocity of 26.44 m/s (CLV) (number of revolutions, 6,000 rpm or more) as shown in
When an absolute value of the amount of birefringence (Ri) is excessively large or excessively small, a sufficient push-pull signal is difficult to obtain, when a drive uses the optics system equipped with the light source of wavelength λ at 405 nm and the condenser objective lens with the numerical aperture NA of 0.65 and the optical recording medium 10 rotates at a constant linear velocity and the number of revolutions at 6000 rpm or more.
A method to form a distribution of the amount of birefringence (Ri) in the radial direction of the substrate 5 to cancel out the birefringence derived from a stress generated in rotating the substrate 5 is not particularly limited. Specifically, for example, when the substrate 5 is formed by injection molding of an appropriate optically transparent resin, a distribution of the amount of birefringence (Ri) in the substrate 5 can be obtained by a proper combination of factors such as molecular orientation by resin flow, hydrostatic distortion by fill compression, heat stress by solidification cooling, relaxation phenomenon thereof and the like.
The optical recording medium 10, to which the present exemplary embodiment is applied has a distribution of the amount of birefringence (Ri) in the radial direction of disc-shaped substrate 5 to cancel out the birefringence derived from a stress (σr and σt) generated in rotating. When the substrate 5 rotates at the constant linear velocity and the number of revolutions at 6,000 rpm and an optical spot formed by the optical pickup with the light source of a wavelength (λ) of 405 nm and a condenser objective lens with the numerical aperture (NA) of 0.65 is used to read the information, a value of the push-pull signal (Pp) across the substrate 5 is 0.2 or more and a ratio (Ppmax/Ppmin) of the maximum value (Ppmax) to the minimum value (Ppmin) in the above push-pull signal is 2.0 or less. As a result, tracking does not deviate in high-speed rotating, and the recording and reading are performed stably.
The present exemplary embodiment is further detailed below according to examples. However, the present exemplary embodiment is not limited by examples.
Using a given injection compression molding machine (SD40E manufactured by Sumitomo Heavy Industries, Ltd.), a 0.6 mm thick polycarbonate resin substrate (inner radius r1=15 mm and outer radius r2=120 mm) having a guide groove of a groove depth of 30 nm and a groove width of 240 nm is molded. The molding condition involves an initial mold opening of 0.6 mm, a maximum injection fill speed of 150 mm/s, a resin temperature of 380° C. and a mold temperature of 115° C. for a fixed die and 110° C. for movable die, respectively. Clamping is controlled in multistage and its initial clamping force is 300 MPa.
A phase-change recording layer composed of a Bi—Ge—Te alloy and a reflective layer composed of a Ag—Nd—Cu alloy each are next deposited in turn by sputtering on the surface of this substrate, to which a dummy substrate (inner radius r1=15 mm and outer radius r2=120 mm) with a thickness of 0.6 mm is laminated to prepare the optical recording medium.
In
An evaluation device equipped with an optical pickup with a laser beam of wavelength (λ) at 405 nm and the condenser objective lens with the numerical aperture (NA) of 0.65 is used.
The amount of the push-pull signal (hereinafter, amount of PP signal (Pp)) at a given radial location (ri) in the radial direction of the substrate is measured using the above information recording and reading device, when the optical recording medium prepared by the above method rotates at a high speed of a 1× speed (linear velocity, 6.61 m/s) (CLV) and a 4× speed (linear velocity, 26.44 m/s) (CLV) (number of revolutions, 6,000 rpm or more). The results are shown in Table 1.
The results given in Table 1 indicate that the amount of the PP signal (Pp) in the optical recording medium has a distribution of the amount of birefringence as shown in
Further, the minimum value (Ppmin) of the amount of the PP signal (Pp) within a radial area r from 25.0 mm to 58.0 mm becomes 0.240.
Moreover, Ppmax/Ppmin is 0.276/0.240, thus giving 1.15, indicating that a relation of Ppmax/Ppmin≦2.0 is satisfied.
Such a disc has a sufficient margin in a value of an acceptable inner circumference variation for the amount of the push-pull signal with roughly a +100/−50% tolerance.
The optical recording medium used in the present example allows stable tracking by the above evaluation device as well as stable recording and reading from the inner circumference to the outer circumference.
Furthermore, at a 1× speed, the maximum value (Ppmax) of the amount of the PP signal (Pp) is 0.378 in an area of a radius r from 25.0 mm to 58.0 mm.
Further, the minimum value (Ppmin) of the amount of the PP signal (Pp) is 0.283 in an area of a radius r from 25.0 mm to 58.0 mm.
Moreover, Ppmax/Ppmin is 0.378/0.283, thus giving 1.34, indicating that a relation of Ppmax/Ppmin≦2.0 is satisfied. Such a disc has a sufficient margin in a value of an acceptable inner circumference variation for the amount of the push-pull signal (Pp) with roughly a +100/−50% tolerance even in a low speed rotating.
As described above, the optical recording medium according to the present exemplary embodiment allows stable recording and reading at high speed rotating even if a blue semiconductor laser is used as the optics system.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodies are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the forgoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
The entire disclosure of Japanese Patent application No. 2006-165848 filed on Jun. 15, 2006 including the specification, claim, drawings and summary is incorporated herein by reference in its entity.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-165848 | Jun 2006 | JP | national |
