JPH07130000A - Rom type optical information medium - Google Patents

Abstract

PURPOSE:To shorten spacings between recording bits and to make high-density recording possible by forming a reproducing film on the optical information medium and detecting a change in the reflectivity of the reproducing film corre sponding to the central part of a laser spot. CONSTITUTION:A first dielectric film 2, the reproducing film 3, a second dielectric film 4, a recording layer 7 consisting of a low-thermal conductivity material and metallic material 6 and a protective film 8 are successively formed on a substrate 1. A low melting metal is used for the reproducing film 3 and its film thickness is specified to about 150 to 500Angstrom . The reproducing film 3 on the recording bit not overlapping on the central part of the spot of a laser beam 9 does not attain the m. p. and only the central part 3b turns to a liquid form if the reproducing film is irradiated with this laser beam 9. The reflectivity, film is changes in correspondence to information. Then, even if the plural recording pits exist within the spot diameter of the laser beam 9, only the information of the recording pit in the central part is obtd. The spacing of the recording pits is reduced to half the spot of the laser beam or below an the high-density recording is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ROM type optical information medium for irradiating a laser beam to reproduce recorded information.

[0002]

2. Description of the Related Art A ROM type optical information medium is a small-sized and large-capacity information recording medium, such as a compact disc or a CD-RO.
It is widely used as M, CD-I, laser disk, optical card and the like. In general, information is recorded in the recording layer on the medium substrate as uneven recording bits and is reproduced by the interference effect of the irradiated laser light.

[0003]

The ROM type optical information medium is required to be further downsized and have a large capacity. In order to realize this, it is necessary to increase the recording density of information by narrowing the interval between the irregularities of the recording bits.

However, in the conventional ROM type optical information medium,
The interval between recording bits cannot be less than half the spot diameter of laser light. This is because the interference of the laser light between the recording bits becomes large and the signals of two adjacent recording bits cannot be distinguished.

Incidentally, there is a magneto-optical disk as a medium for recording / reproducing information by utilizing the Kerr effect in the magnetic recording layer. Among these magneto-optical disks is a super-resolution magneto-optical disk in which the interval between recording bits is less than half the spot diameter of laser light. This type of magneto-optical disk is composed of a magnetic recording layer and a reproducing film. This reproducing film exchange-couples with the magnetic recording layer, and when the laser light is irradiated and the temperature rises above a certain temperature, the magnetic characteristics change corresponding to the recorded information, and the information of the magnetic recording layer is copied onto the reproducing film. .

That is, when the magnetic recording layer is irradiated with a laser beam having a distribution, the temperature of the central portion of the spot of the laser light becomes higher than that of its peripheral portion, and the information in the magnetic recording layer is transferred to the reproducing film. At the same time, the surrounding information in the reproduction film disappears. In this way, in the super-resolution magneto-optical disk, even if a laser beam spot contains a plurality of recording bits, it is possible to obtain signal information of only the central recording bit, and the information of the recording bits smaller than the spot diameter can be obtained. Playback is possible.

Therefore, the present invention provides a ROM type optical information medium which realizes high density recording by partially applying the above-mentioned reproducing method in a super-resolution magneto-optical disk and setting a recording bit interval to be half the spot diameter of laser light or less. The purpose is to do.

[0008]

In a ROM type optical information medium of the present invention, a reproducing film, a recording layer and a protective film are sequentially formed on a transparent substrate, and the recording layer has a recording bit portion of a low thermal conductive material.
The other part is made of a metal material, and is characterized in that the information recorded in the recording layer is reproduced by the laser beam applied to the transparent substrate surface. Further, in the ROM type optical information medium of the present invention, a first dielectric film, a reproducing film, a second dielectric film, a recording layer and a protective film are sequentially formed on a transparent substrate, and a recording bit portion of the recording layer. May be made of a material having low thermal conductivity, and the other part may be made of a metal material.

[0009]

FIG. 1 is a sectional view showing an example of the structure of the ROM type optical information medium of the present invention. A recording layer 7 made of a first dielectric film 2, a reproducing film 3, a second dielectric film 4, a low thermal conductivity material 5 and a metal material 6 and a protective film 8 are sequentially formed on a transparent substrate 1. is there.

The transparent substrate 1 has a conventional RO made of glass, polycarbonate, epoxy resin, polyolefin resin or the like.
The materials used for the M-type optical information medium can be used. A continuous groove or pit for guiding the laser head to the recording track may be provided on the transparent substrate 1.

A material having a melting point of 150 to 600 ° C. can be used for the reproducing film 3 in consideration of the power of laser light and the like. Further, when an organic resin is used as the transparent substrate material, it is preferable that the melting point is 500 ° C. or less so that the organic resin does not deteriorate at high temperature. Therefore, the reproduction film 3 contains In, which is a low melting point metal,
Metals such as Pb, Sn, or Se, alloys containing these, GaTe, GeTe, SbTe, InSe, AgZ
Binary alloys such as n, GeSbTe, InSbSe, Cu
Materials such as ternary alloys such as AlNi can be used.

Further, since it is desirable that the reproduction film 3 has a small light transmission and a small heat capacity, its thickness is 1
About 50 to 500 A is preferable.

As the low thermal conductivity material 5 of the recording bit portion of the recording layer 7, a material having a thermal conductivity of 0.1 W / cm · K or less can be used, and particularly a thermal conductivity of 0.05 W / cm · K or less can be used. Materials are preferred. Therefore, an acrylic or polyester organic resin, CaCO ₃ , KBr, PbTe, or the like can be used.

The metal material 6 other than the recording bit portion of the recording layer 7 is preferably a material having high thermal conductivity, such as Au or A.
Metals such as g, Al, Cu, Cr and Ti, and alloys thereof can be used.

Although the thickness of the recording layer 7 varies depending on the melting point of the reproducing film 3, it is preferably 300 A or more in order to increase the temperature difference between the recording layer and the recording bit portion.
A value of 3000 A or less is sufficient. Further, in the recording layer 7, the metal material 6 may be thicker than the low thermal conductivity material 5.

The protective film 8 is made of acrylic, epoxy,
Alternatively, an unsaturated polyester-based UV curable resin can be used.

First and second dielectric films 2 sandwiching the reproducing film 3 between
The materials of No. ₄ are oxides such as SiO ₂ and TaO ₅ and SiN.
A nitride such as CrN or CrN can be used. Since the first dielectric film 2 transmits laser light, it is desirable to use a transparent dielectric material. The film thickness of each of the dielectric films 2 and 4 is 200 to 20 from the optical and thermal viewpoints.
00A is preferred.

When the reproduction film 3 is sandwiched between these dielectric films 2 and 4, the reproduction film 3 does not come into contact with the recording layer 7. Therefore, even if the low melting point material melts during laser light irradiation, the reproduction film 3 is formed at the boundary surface. Does not react, and the reliability of information reproduction and the durability of the medium are improved.

To reproduce information, a phenomenon in which the reflectance of the reproducing film 3 is different between a solid state and a liquid state is used. That is, FIG.
As shown in, in the portion where the reproduction film 3 is in contact with the metal material 6 or where the reproduction film 3 is in contact with the second dielectric film 4,
The heat generated by the irradiation of the laser light diffuses through the metal film 6 having high thermal conductivity, and the reproduction film 3 remains below the melting point.
The part remains solid.

On the other hand, in the portion where the reproducing film 3 is in contact with the low thermal conductivity material 5 or the second dielectric film 4 is in contact, the heat generated by the irradiation of the laser beam is difficult to diffuse. The temperature of the central portion of the spot of the laser light rises, the reproduction film 3 is melted at the melting point or higher, and partially becomes liquid. The reflectance of the reproducing film 3 is relatively low for liquid and relatively high for solid. Information is obtained by this difference in reflectance.

Further, as shown in FIG. 2, even if a plurality of recording bits are present within the spot diameter of the laser beam 9, the reproducing film 3 on the recording bit which does not overlap the central portion of the spot of the laser beam 9 is formed. The temperature does not reach the melting point, the reproduction film 3 remains in the solid state, and the reflectance does not decrease. It is only the recorded bits at the center of the spot of the laser beam 9 that the reflectance changes in accordance with the information. Here, by measuring the change in the reflected light amount of the laser light, the state of the recording bit at the center of the spot can be determined. Therefore, even if there are a plurality of recording bits within the spot diameter of the laser beam 9, it is possible to obtain information of only one recording bit in the central portion, and the recording bit interval is half or less than the spot diameter of the laser beam. Therefore, high density recording can be realized.

[0022]

EXAMPLE A ROM type recording medium of the present invention having the structure shown in FIG. 1 was manufactured. As the transparent substrate 1, a disc-shaped substrate made of polynate with grooves at 1.6 μm intervals was used, and SiN _x having a thickness of 1200 A was used as the first dielectric film and Ga ₁₂ was used as the reproducing film 3 by the sequential sputtering method. Te ₈₈ thickness 30
0A, SiN _x as the second dielectric film 4 has a thickness of 500A
Then, a negative type polyimide film having a thickness of 1000 A was formed on the second dielectric film 4 by spin coating.

Next, the groove is tracked on the transparent substrate 1 by using a laser cutting device, the polyimide film is exposed by irradiating light according to a recording signal, and the polyimide film is developed by dry etching to form a recording layer 7. A cylindrical recording bit of polyimide was formed. The recording condition at this time was a constant linear velocity (CLV), and the pit position recording method was used.
The recording bit length was 0.4 μm, the shortest recording bit interval was 0.4 μm, and a single pattern was used so that 1-7 modulated random data could be recorded.

Next, Al ₉₉ Ti as the metal material 6 is formed on the second dielectric 4 on which the recording bits of polyimide are formed.
₁ was formed to a thickness of 1000 A by the sputtering method. Finally, an ultraviolet curable resin was spin-coated on the metal material 6 and irradiated with ultraviolet rays to form an organic resin protective film 8 to obtain a disk-shaped ROM type optical information medium.

Next, the performance of this ROM type optical information medium was confirmed. The numerical aperture NA of the objective lens is 0.53, the laser wavelength is 0.83 μm, and the laser beam spot diameter is 1.25 μ.
The recorded information was reproduced with a laser beam having a linear velocity of 5.65 m / sec and an output of 3 mW using an optical head of m.

As a result, the CNR in a single pattern is 46.
The eye opening ratio of the eye pattern in dB and the random pattern was 45%, and the asymmetry of the eye pattern was 17%.
Normally CNR is 45 dB or more, eye numerical aperture is 40% or more,
Since the asymmetry should be 20% or less, the RO of the present invention
It has been found that the M-type optical information medium allows actual reproduction.

Further, in the conventional ROM type optical information medium, half of the spot diameter of the laser beam is the shortest recording bit interval. Under the above conditions, the shortest recording bit interval is 0.63 μm.
However, the shortest distance between the recording bits of the ROM type optical information medium of the present invention is 0.4 μm, which is about 1.6 by simple calculation.
Realizes double the recording density.

[0028]

According to the ROM type optical information medium of the present invention, the recording bit interval can be reduced to less than half the laser spot diameter, and recording can be performed at a higher density than before.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a structure of a ROM type optical information medium of the present invention.

FIG. 2 is a conceptual diagram showing a reproducing principle of the ROM type optical information medium of the present invention.

[Explanation of symbols]

 1 Transparent Substrate 2 First Dielectric Film 3 Reproduction Film 3a Solid State Reproduction Film 3b Liquid State Reproduction Film 4 Second Dielectric Film 5 Low Thermal Conductivity Material 6 Metal Material 7 Recording Layer 8 Protective Film 9 Laser Light

Claims (2)

[Claims] 1. A reproducing film, a recording layer, and a protective film are sequentially formed on a transparent substrate, and the recording bit portion is made of a low thermal conductive material and the other portion is made of a metal material, and the transparent substrate surface is irradiated. A ROM type optical information medium in which the information recorded in the recording layer is reproduced by the laser light. 2. A first dielectric film, a reproduction film, and a transparent film on a transparent substrate.
A second dielectric film, a recording layer, and a protective film are sequentially formed. The recording layer has a recording bit portion made of a low thermal conductive material and the other portion made of a metal material. R for reproducing information recorded on the recording layer
OM type optical information medium.