JPH03201228A - Optical recording medium - Google Patents

Abstract

PURPOSE:To enlarge the allowance of an attenuation coefft. of an optical layer and to enable use of various kinds of materials by forming each specified optical recording layer, light-reflecting layer and interferential layer to constitute the medium. CONSTITUTION:An optical recording layer 2 is formed on a substrate 1, on which an interference layer 3 is formed. The attenuation coefft. of the optical recording layer 2 is made <0.5 for the wavelength of reproducing light, and the attenuation coefft. of the interference layer 3 is made <=0.05 for the wavelength of reproducing light. Further a light-reflecting layer 4 is formed on the interference layer 3 so that the reflectance of the reflecting layer 4 is >=90 % for the wavelength of reproducing light. A protective layer 5 is formed on the light-reflecting layer 4. Therefore, the interference layer 3 increases the reflectance of the medium itself. Thereby, the allowance for the attenuation coefft. of the optical recording layer 2 is widened, which enables use of various kinds of materials.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium, and particularly to a writable optical recording medium that is compatible with a CD (compact disc).

(Prior Art) In recent years, there has been active development of writable optical recording media that are compatible with CDs. FIG. 2 is a structural diagram showing a conventional optical recording medium. In the figure, 11 is a base made of polycarbonate on which a pre-group (tracking guide groove) is molded, and a dye recording layer 121, a reflective layer (for example, silver) 13, and a protective layer 14 are formed on this base 11. There is.

In order to be compatible with CDs, the reflectance of the medium itself must be 70% or more during playback (according to Red Book published by Philips). However, materials with high reflectance have low light absorption, making writing difficult. For this reason, there are very few recording materials that are compatible with CDs and suitable as the recording layer of writable optical recording media.

For example, optical data storage
1989 Techni, cal Digest 5e
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According to CD-RJ, in the conventional structure shown in Fig. 2,
It has been reported that recording materials within the shaded area shown in FIG. 3 are required to have a reflectance of 70% or more in the CD reproduction wavelength band (770 to 70 nm). In the figure, the horizontal axis represents the extinction coefficient of the recording material, and the vertical axis represents the refractive index n of the recording material.

Furthermore, in order to write reliably, the extinction coefficient K must be approximately 0.
It is said that the refractive index n needs to be 1 or more, and as shown in Figure 3 above, in order to achieve a reflectance of 70% or more, the refractive index n must be approximately 2.5.
The above requirements are limited to the materials within the cross hatched area in FIG.

(Problems to be Solved by the Invention) As described above, in order to make an optical recording medium with a conventional structure compatible with a CD and writable, it is necessary to have a limited extinction coefficient and a refractive index. It was necessary to form the recording layer with a recording material having n.

Further, the recording material having the above-mentioned extinction coefficient and refractive index n is
The absorption characteristic (transmittance) with respect to the wavelength of the reproduction light is not flat, and the wavelength band of the CD reproduction light (770 to 790 n1
In the case of n), there is a problem that the absorption characteristics change significantly and the permissible wavelength range of reproduction light becomes narrow.

(Means for Solving the Problems) In order to solve the above problems, the present invention, as shown in FIG. 4, the optical interference layer 3 has an extinction coefficient of 0.05 or less with respect to the wavelength of the reproduction light, and the extinction coefficient of the optical interference layer 3 with respect to the wavelength of the reproduction light is 0.05 or less; The present invention provides an optical recording medium in which the extinction coefficient of the recording layer 2 is 0.5 or less, and the reflectance of the light reflective layer 4 with respect to the wavelength of reproduction light is 90% or more.

(Function) In the optical recording medium, writing is reliably performed on the recording layer having a relatively large extinction coefficient, and the interference layer increases the reflectance of the medium itself to the reproduction light.

(Example) An example of the optical recording medium according to the present invention will be described below with reference to the drawings.

FIG. 1 is a structural diagram of an optical recording medium according to the present invention. An optical recording layer 2 (2a, 2b) is formed on the substrate 1, and an optical interference layer 3 (3a, 3b) is formed on the optical recording layer 2. The extinction coefficient of the optical recording layer 2 with respect to the wavelength of the reproduction light is 0.5 or less, and the optical interference layer 3 with respect to the wavelength of the reproduction light
The extinction coefficient of is 0.05 or less. 4 is a light reflection layer formed on the light interference layer 3, and the reflectance of the light reflection layer 4 with respect to the wavelength of reproduction light is 90% or more. A protective film 5 is formed on this light reflecting layer. In addition, below, the extinction coefficient, n is the refractive index, and the wavelength of the reproduction light of the CD is 770 ns to 79
0 r++s.

Specific Example 1 A phthalocyanine vapor-deposited film of 80 nm was formed on a polycarbonate substrate 1 on which a pre-group (guide*) was formed to form an optical recording layer (approximately -0.1 to 0.2) 2a. do.

On this optical recording layer 2a, a 2 wt % solution of acid red methyl cellosolve is applied and dried to form an optical interference layer (abbreviated to -0) 3a having a thickness of 200 nm. Further, on this optical interference layer 3a, an Au (gold) reflective layer is formed to a thickness of 70 to 80 nm by sputtering method to form a light reflective layer (approximately reflectance of 97 to 80 nm).
98%) 4.

Said substrate 1. A light reflection recording layer 2a and a light interference layer 3a.

When the optical recording medium comprising the light reflective layer 4 was irradiated with a laser beam having a wavelength of 780 nm as reproduction light, the reflectance was 75 to 80%. In addition, the linear speed is 1.4 m/s,
Recording power 10 mv with laser light of 780 ns wavelength
When I recorded and played back an 11T (CD format) signal, the C/N was 45 to 50 dB.

A characteristic with a modulation depth of 70% was obtained.

Specific Example 2 On a polycarbonate substrate 1 on which pre-groups (guide grooves) have been molded, guanine and Au are co-evaporated to form a film with a thickness of 80 mm (equivalent film thickness ratio 3:2) to form an optical recording layer 2b. do. A 200 nm thick guanine film is formed on this optical recording layer 2b to form an optical interference layer (abbreviated to -0) 3b. Further, on this interference layer 3b, a 70-80 nm Au reflective film is formed by sputtering to form a light reflective layer (approximately reflectance 97-98).
%) 4.

The substrate 1, the optical recording layer 2b, the optical interference layer 3b, the optical reflective layer 4
780n as reproduction light for an optical recording medium consisting of
When irradiated with m-wavelength laser light, the reflectance was approximately 75%.
Met. Also, the linear velocity was 1.4+n/s.

Recording power 10+a with 780 nm wavelength laser light
When an 11T (CD format) signal was recorded and played back using the CD-ROM, C/N was approximately 47 dB and the modulation depth was 68%.

Simulation example> Specific example 1 above. Based on Specific Example 2, the substrate 1 shown in FIG. Optical recording layer 2. Optical interference layer 3. Light reflective layer 4. The reflectance of an optical recording medium made of the protective film 5 was simulated. The simulation flow is based on a general multilayer film reflectance formula.

Base 1. The protective films 5 are all n-L, 5. to ~0,
The optical recording layer 2 has n −1,6~, 1.8, K −0,
05-0.5. Film thickness: 80nm (this is the reproduction destination 780nm)
), the optical interference layer 3 has a thickness corresponding to n-1,6~
2.0°K -0.01~0.05. Film thickness O~300n
I111 light reflection layer 4 has n −0,01~(1,05,K
-4,993, film thickness 5O-10Q■ (this has a reflectance of 9
0% to 97.98%).

The simulation results are substantially consistent with the specific example and specific example 2, and the reflectance of the optical recording medium shown in FIG. 1 hardly depends on the refractive index n, and the extinction coefficient K of the optical recording layer 2 is 0. 5
If the extinction coefficient K of the optical interference layer 3 is 0.05 or less and the reflectance of the light reflective layer 4 is 90% or more, the reflectance of the optical recording medium is 70% or more. , it was found that the reflectance of CD was satisfied.

In this optical recording medium, the extinction coefficient of the optical recording layer 2 is 0.5.
Writing (recording) can be performed reliably since a relatively large value such as the following is sufficient.

Furthermore, the optical recording layer 2 has an extinction coefficient K of 0 regardless of the refractive index n.
．． 5 or less, the tolerance range for wavelength is wide, and the optical interference layer 3 has an extinction coefficient K of 0.05 or less.
In other words, by using a material that has almost no absorption toward the tip of 770 to 790 cm, C with a reflectance of 70% or more can be used.
An optical recording medium compatible with D is obtained.

(Effects of the Invention) As described in detail above, according to the present invention, the optical interference layer increases the reflectance of the medium itself, so the permissible range of the extinction coefficient of the optical recording layer becomes wide and large.

Therefore, a wide variety of materials can be used as the optical recording layer.

[Brief explanation of drawings]

Figure 1 is a structural diagram of an optical recording medium according to the present invention, Figure 2 is a structural diagram of a conventional optical recording medium, and Figure 3 is an extinction coefficient and refractive index of a conventional optical recording medium compatible with CDs. FIG. DESCRIPTION OF SYMBOLS 1...Substrate, 2 (2a, 2b)...Optical recording layer, 3
(3a, 3b)...Light interference layer, 4...Light reflection layer, 5...Protective film, K...Extinction coefficient, n...Refractive index. ￥1 Figure 2nd item

Claims (2)

[Claims] (1) An optical recording medium comprising an optical recording layer, a light reflective layer, and an optical interference layer provided between the optical recording layer and the light reflective layer, the optical recording medium comprising the optical interference with respect to the wavelength of reproduction light. Extinction coefficient of layer is 0.0
5 or less, and the extinction coefficient of the optical recording layer with respect to the wavelength of the reproduction light is 0.5.
An optical recording medium characterized in that the reflectance of the light reflective layer with respect to the wavelength of reproduction light is 90% or more. (2) In claim 1, the wavelength of the reproduction light is 770n.
An optical recording medium characterized in that the wavelength is m to 790 nm.