JPH06195753A - Optical data recording medium - Google Patents

Abstract

PURPOSE:To improve the C/N ratio by increasing the modulating degree of amplitudes. CONSTITUTION:An optical data recording medium 10 is a rewritable optical data recording medium, having a multi-layered lower protecting film 2 of four layers, a recording film 3, an upper protecting film 4 and a reflecting film 5 sequentially layered on a surface of a substrate 1 where a pregroove is formed. At the opposite surface is formed a multi-layered reflection preventing film 6 of a reflection preventing film (I) 6a and a reflection preventing film (II) 6b. Owing to the multi-layered reflection preventing film 6, the cast light is never reflected at the surface of the substrate in the optical data recording medium 10. Accordingly, the reflectance of a part of a lower reflectance of a recorded part or an erased part of the recording film can be decreased without lowering the reflectance of a higher reflectance of the recorded part or erased part of the recording film of the optical data recording medium. Eventually, the modulating degree of amplitudes of the optical data recording medium can be increased, thereby improving the C/N ratio and reducing reading errors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of recording information using light.

[0002]

2. Description of the Related Art Conventionally, compact discs (hereinafter referred to as CDs) have been widely spread and known as read-only optical information recording media. Further, as a rewritable optical information recording medium, the crystalline state is reversibly changed by light irradiation,
In other words, a phase change type is known in which a phase transition is made between amorphous and crystalline and the change in reflectance caused by the phase transition is utilized.

[0003]

By the way, as the performance required for the optical information recording medium, the reflectance in the erased state portion is 65% or more, and the C / N (carrier signal level / noise level) ratio is 47 dB. It is necessary to have the above signal strength. The larger the C / N ratio, the smaller the read error at the reproduction stage of the recorded information. C above
In order to increase the / N ratio, the difference in reflectance between the recorded state portion and the erased portion of the recording film of the optical information recording medium during reproduction may be increased. Where (amplitude modulation degree) =
It is represented by {(reflectance of erased portion)-(reflectance of recorded portion)} / (reflectance of erased portion). That is, if the noise level is the same, the amplitude modulation degree may be increased in order to improve the C / N ratio in the optical information recording medium. The inventors noticed that the reflectance of the recording state portion became unnecessarily high due to the light reflection on the substrate surface of the optical information recording medium, thereby increasing the amplitude modulation degree of the optical information recording medium to C It has been found that the / N ratio can be improved.

The present invention has been made to solve the above problems, and an object thereof is to increase the amplitude modulation degree in an optical information recording medium to improve the C / N ratio. is there.

[0005]

The structure of the invention for solving the above problems is an optical information recording medium in which a lower protective film, a recording film, and an upper protective film are sequentially formed on a substrate, and the recording film is formed. An antireflection film formed on the surface of the substrate on the opposite side to a transparent single-layer film having a refractive index different from that of the substrate or a transparent multilayer film having a refractive index different from that of the substrate and different from each other. Is characterized by.

[0006]

According to the above means, the optical information recording medium can eliminate the reflection of the light emitted by the antireflection film on the substrate surface. As a result, almost 100% of the light is incident on the substrate of the optical information recording medium. The reflectance differs between the recording state portion and the erasing state portion of the recording film, and the reflected light amount at each portion is the light amount including the increased amount of light incident from the substrate surface multiplied by each reflectance. Here, the reflectance of the substrate surface without the antireflection film is r _{1, the} reflectance of the substrate surface with the antireflection film is r _2, and the reflectance of the recording state portion or the erasing state portion of the recording film is R. To do. Then, in the portion of the reflectance R of the recording state portion or the erasing state portion of the recording film, the change of the reflectance when the reflectance of the substrate surface changes from r ₁ to r ₂ is approximately expressed by the following equation. It

[Number 1] _{{R (1-r 2)} + r 2} - {R (1-r 1) + r 1} = - (1-R) (r 1 -r 2) from the above equation, the recording state of the recording film It can be seen that the lower the reflectance R of the portion or the erased portion, the greater the change in reflectance to the negative side. Therefore, the optical information recording medium of the present invention can reflect the reflectance of the recording state portion or the erasing state portion of the recording film without lowering the reflectance of the recording state portion or the erasing state portion of the recording film. It is possible to reduce the reflectance of the low part. That is, the optical information recording medium of the present invention can increase the amplitude modulation degree as a result, and C /
The N ratio is improved and the reading error is reduced.

[0007]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a schematic diagram showing a cross-sectional structure of an optical information recording medium according to the present invention. The optical information recording medium 10 is a rewritable optical information recording medium, and is formed, for example, by sequentially laminating the following films on a substrate 1 made of disk-shaped transparent glass or plastic. A multi-layer lower protective film 2 was formed as a lower protective film on a surface of a substrate 1 made of polycarbonate (refractive index 1.58), on which a pre-groove (a portion having a low reflectance for tracking by an optical pickup) was formed. . This multilayer lower protective film 2 has a wavelength (
Four layers, which are transparent to two lights having different reproducing wavelengths of 780 nm and recording and erasing wavelength of 830 nm) and different in refractive index, are laminated next to each other.
The multilayer lower protective film 2 is a lower protective film (I) 2a made of TiO ₂ (refractive index 2.5) having a thickness of 80 nm and SiO ₂ (refractive index 1.46).
The lower protective film (II) 2b of 110 nm thick and the lower protective film (III) 2c of TiO ₂ having a thickness of 260 nm were formed. These films were formed by a sputtering method or a vacuum evaporation method (a resistance heating method, an electron beam method, an ion plating method). TiO ₂ and SiO ₂ were used for the targets that are the source of these materials, respectively. In addition, TiO ₂
May be formed by vapor deposition of Ti in an oxygen atmosphere and reaction. Further, a lower protective film (IV) 2d made of ZnS—SiO ₂ (refractive index 2.0) was formed to a thickness of 250 nm. This film is also formed by the sputtering method or the vacuum evaporation method, but the target which is the material source is a mixture of ZnS and SiO ₂ and sintered.

Next, the thickness of the recording film 3 made of GeSbTe is set.
The film was formed at 50 nm. This film is also formed by a sputtering method or a vacuum evaporation method, and a target which is a material source is a mixture of Ge, Sb, and Te which is appropriately mixed and sintered (GeSb ₂
Te _4, Ge ₂ Sb ₂ Te _5, etc.) was used. On the recording film 3,
An upper protective film 4 made of ZnS—SiO _{2 was formed} to a thickness of 200 nm. The method for forming this film was the same as that for the lower protective film (IV) 2d. Further, a reflective film 5 made of Au was formed to a thickness of 100 nm. This film was formed by a sputtering method or a vacuum evaporation method.

On the other hand, a multilayer antireflection film 6 was formed as an antireflection film on the surface of the surface of the substrate 1 where there was no pre-groove. This multilayer antireflection coating 6 has a wavelength (reproduction wavelength 780 nm, recording / erasing wavelength
Two layers having different refractive indices, which are transparent to two lights of 830 nm) are laminated. The multilayer antireflection film 6 is an antireflection film (I) 6a made of TiO ₂ (refractive index 2.5) having a thickness of 20 nm and Mg.
Thickness of antireflection film (II) 6b made of F ₂ (refractive index 1.38)
Each film was formed at 180 nm. These films were formed by a sputtering method or a vacuum evaporation method (a resistance heating method, an electron beam method, an ion plating method), and TiO ₂ and MgF ₂ were used as targets which were material sources.
Incidentally, TiO ₂ may be formed into a film by vapor-depositing and reacting Ti in an oxygen atmosphere.

The film coated as the antireflection film is
In the optical information recording medium 10 as described above, a transparent multilayer film having a different refractive index on the substrate side and a different refractive index from each other or a transparent single layer film having a different refractive index from the substrate may be used.
As a material for the antireflection film, M which has high transparency and high melting point
g, Ca, Sr, Y, La, Ce, Ho, Er, Yb, Ti, Zr, Hf, V,
Oxides, sulfides such as Nb, Ta, Zn, Al, Si, Ge, Pb,
A nitride or a fluoride such as Ca, Mg or Li can be used. It should be noted that the reflective film 5 of the optical information recording medium 10 described above may be overcoated with a resin or the like, or a protective plate or another similar optical information recording medium may be attached thereto by an adhesive or the like.

FIG. 2 shows the reflection of the substrate surface with respect to the wavelength (nm) of the irradiated light when the same multilayer antireflection film is applied to the substrate surface made of the same polycarbonate (refractive index 1.58) as in the above embodiment. It is a characteristic view showing a simulation result of the dependency of the rate (%). Here, the reflectance of the surface of the substrate made of polycarbonate without the antireflection film is about 5%.
Is. From the figure, it is 0.03 when the light wavelength is 780 nm (reproduction wavelength).
%, The reflectance is low at 0.1% at 830 nm (recording / erasing wavelength). That is, it can be said that the reflectance at these wavelengths can be regarded as 0%.

FIG. 3 is a recording state portion (amorphous portion) and an erasing state portion (crystalline) in an optical information recording medium (inventive product: shown by a solid line) provided with an antireflection film having the structure of FIG. FIG. 7 is a characteristic diagram showing a simulation result of the dependency of reflectance (%) on the wavelength (nm) of light with (part). The wavelength of light for reproduction on the optical information recording medium 10 is 780
The wavelength of light for recording / erasing is 830 nm. For comparison, the characteristics of the optical information recording medium having a structure in which an antireflection film is not provided on the substrate surface are shown by broken lines.
In the optical information recording medium (product of the present invention) provided with an antireflection film, the reflectance of the erased portion is 70% at the reproduction wavelength of 780 nm.
There is almost no change from that without the antireflection film. On the other hand, the reflectance of the recorded state portion is reduced from 35% to 31%. That is, it can be seen that the above-mentioned amplitude modulation degree can be increased from 50% to 56%. Furthermore, recording / erasing wavelength 830
In nm, the reflectances of the erased state portion and the recorded state portion are both 34
% To 30% and the light absorption rate can be increased by 4%. That is, in the optical information recording medium 10 having the structure shown in FIG. 1, the antireflection film is applied to improve the C / N ratio which is the original purpose at the reproducing wavelength and to improve the optical absorptance at the recording / erasing wavelength. Since it will be large, recording /
A further advantage is that the optical power for erasing can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross-sectional structure of an optical information recording medium according to a specific example of the present invention.

FIG. 2 is a characteristic diagram showing a simulation result of dependence of reflectance (%) on a substrate surface with respect to a wavelength (nm) of irradiated light when a multilayer antireflection film similar to that in Example is applied to the substrate surface. Is.

FIG. 3 is a simulation of the dependence of reflectance (%) on the wavelength (nm) of light in the recorded state portion (amorphous portion) and the erased state portion (crystalline portion) in the optical information recording medium of the same example. It is a characteristic view showing a result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Multilayer lower protective film 3 ... Recording film 4 ... Upper protective film 5 ... Reflective film 6 ... Multilayer antireflection film 6a ... Antireflection film (I) 6b ... Antireflection film (II) 10 ... Optical information recording medium

Claims (1)

[Claims] 1. An optical information recording medium in which a lower protective film, a recording film, and an upper protective film are sequentially formed on a substrate, and the refractive index of the substrate is on the surface of the substrate opposite to the side on which the recording film is formed. An optical information recording medium comprising an antireflection film formed of a transparent single-layer film different from the above or a transparent multilayer film having a refractive index different from each other and different from each other.