Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-04-19
2002-12-31
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S013550, C428S064400
Reexamination Certificate
active
06501728
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Applications Nos. P2000-121336 filed Apr. 21, 2000, P2000-260765 filed May 30, 2000, P2000-160766 filed May 30, 2000, P2000-206988 filed Jul. 7, 2000 and P2000-229605 filed Jul. 28, 2000, which applications are incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
The present invention relates to a magneto-optical recording medium.
An optical recording medium is a recording medium in which a laser beam is applied to a signal-recording layer by a recording/reproducing apparatus to record and/or reproducing a record signal.
The following are known as optical recording media: a reproducing-dedicated digital audio disk (so called compact disk), an optical video disk (so called laser disk), a magneto-optical disk, and a phase-change-type optical disk.
As an example of the above optical recording media, a magneto-optical recording medium is used, having a multilayer structure in which a first dielectric layer a signal-recording layer, a second dielectric layer, and a metallic reflective layer are formed in order on a transparent substrate made of, for example, polycarbonate.
In the case of the above optical recording medium, a signal is recorded on or reproduced from a signal-recording layer along a recording track, and a groove is formed on a transparent substrate along the recording track, and it is requested to realize a recording medium having a larger capacity by improving the recording density.
For example, an MD (minidisk) which is one of standards of magneto-optical recording media has a configuration which has an easily-magnetized axis in the vertical direction to a substrate surface and in which a magnetic recording layer made of a magnetic film having a large magneto-optical effect is formed, the recording layer, a metallic reflective layer and a dielectric layer are laminated so that a recording section having a laminated structure on a transparent substrate is formed, and a protective layer made of, for example, an ultraviolet-curing resin is laminated on the recording section.
This minidisk is marketed as a re-writable magneto-optical recording medium and a magnetic-field-modulating magneto-optical recording medium in which a user can repeatedly record and erase information.
The following types are realized as the above minidisk (MD): a minidisk in which the pitch between recording tracks is set to 1.6 (&mgr;m) to allow music signals to be recorded for 60 or 74 (min) and a minidisk in which the pitch between recording tracks is narrower to set to 1.5 (&mgr;m) and thereby, the recording density is improved to allow music signals to be recorded for 80 (min).
Moreover, because a magneto-optical recording medium such as a (MD) minidisk can be used for various cases from home use to use by mounting the recording medium on a car because it is possible to easily record music in the recording medium serving as a household recording unit.
As described above, to accelerate general use of the above minidisk, it is indispensable to downsize an apparatus for recording or reproducing information in or from a magneto-optical recording medium and reduce the power consumption of the apparatus.
Particularly, in the case of a magneto-optical recording medium using a magnetic-field modulating system, it is necessary to modulate an applied magnetic field at a high speed. Therefore, it is necessary to make a magnetic head greatly approach a magneto-optical recording medium by decreasing the distance between the magnetic head and the corresponding face of the recording medium.
As recording systems for the above magnetic-field-modulating magneto-optical recording medium, it is proposed to use various types of fixed heads such as a sliding system and a flying head system.
However, as described above, when narrowing the pitch between recording tracks in order to increase a storage capacity, a problem occurs that a tolerance to a shift of the focus of a laser beam (hereafter referred to as defocus tolerance) to be irradiated for recording or reproducing data is decreased.
Thus, the decrease of the defocus tolerance causes the crosstalk for recording or reproducing data. Moreover, a difference occurs between optical characteristics of optical pickups due to the intrinsic performance of respective various types of recording and reproducing apparatuses. Thus, a problem occurs that a stable C/N characteristic cannot be obtained because a preferable reproduced signal is obtained from a recording/reproducing apparatus but a jitter value (time-axis fluctuation value) increases and an error rate deteriorates in another reproducing apparatus.
SUMMARY OF THE INVENTION
To solve the above problems, in the case of a magneto-optical recording medium such as a minidisk for repeatedly recording and reproducing information, a signal characteristic is improved by the so-called enhanced effect capable of enhancing an apparent Kerr rotational angle by adjusting the thickness of a dielectric film having a refractive index higher than that of a transparent substrate and obtaining effects of multiple reflection and interference so that a laser beam accurately traces a recording layer forming a magneto-optical medium.
However, also in the above description, it is difficult to obtain a signal characteristic enough for practical use in accordance with various types of reproducing apparatuses.
Therefore, as a result of earnestly repeating studies, the present inventor et al. provide an over-writable magneto-optical recording medium from which a superior signal characteristic and a high durability are obtained by sufficiently securing the defocus tolerance of a laser beam to be irradiated, improving the jitter characteristic, magnifying a power margin and thereby improving the C/N characteristic, and holding the surface strength of a disk even if a track pitch is narrowed.
An optical recording medium of the present invention has a configuration in which a recording section constituted of at least a first dielectric layer, a first recording layer, a second recording layer, and a second dielectric layer is sequentially formed, and a reflective layer and a protective layer are formed on the recording section.
In the case of an optical recording medium in which a groove is formed on the transparent substrate along a recording track and both sidewalls of the groove are respectively formed into an independent wobbling shape, the relation of 0.470≦W/Ø≦0.610 is effectuated when assuming the width of the groove as W and the relation of 0.120≦D/(&lgr;
)≦0.142 is effectuated when assuming the depth of the groove as D, and the angle &thgr; between the wall faces of the groove is kept at 150° ±10°.
In this case, Ø denotes the spot diameter of a laser beam, &lgr; denotes the wavelength of a laser beam in a vacuum state, and n denotes the refractive index of a transparent substrate.
Then, a refractive index in the in-plane direction is made to range between 140 and 25 (nm) and a double-refractive index in the vertical direction is made to range between 200 and 300 (nm).
Then, the first recording layer is made of Gd, Fe, and Co and contains 28 to 30 (at %) of Gd and the thickness of the layer is selected in a range of 50 to 100 Å, and the second recording layer is made of at least Tb, Fe, and Co, contains 22 to 24 (at %) of Tb and has a thickness of 180 to 250 Å.
Moreover, the relation of 0.55≦(d
2
/d
1
)≦0.9 is effectuated when assuming the thickness of a first dielectric layer as d
1
and that of a reflective layer as d
2
, and the reflective layer is made of Al, Au, and Ti and contains 20 to 40 (wt %) of Au and 0.5 to 2.0 (wt %) of Ti.
According to the present invention, also when narrowing the track pitch of a magnetic-field-modulating over-writable magneto-optical recording medium, a superior signal characteristic and a high durability can be obtained by sufficiently securing the defocus tolerance of a laser beam for recording or reproducing a signal, improving the jitter character
Adachi Norio
Koizumi Takeshi
Sakai Hiroyuki
Dinh Tan
Sonnenschein Nath & Rosenthal
Sony Corporation
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