JPH07201076A - Optical information medium - Google Patents

Abstract

PURPOSE:To obtain an optical information medium having a high reflectance and a satisfactory jitter value. CONSTITUTION:This optical information medium has a recording layer 2 disposed on the transparent substrate 1, reflecting layers 3 and 6 disposed on the recording layer 2 and reflecting light made incident from the substrate side and a protective layer 4 disposed on the reflecting layers 3 and 6. The reflecting layer has a two-layered structure, at least one of the layers is formed from a material having a Brinell hardness HB of >25 and the real number part (n) of the refractive index of the 1st layer of the reflecting layers on the recording layer side is <=1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information medium having a recording layer in which so-called additional recording is possible by irradiation with light.

[0002]

2. Description of the Related Art In recent years, a recording layer using a dye layer or the like has been provided.
A so-called write-once type optical information medium capable of recording data by irradiating the recording layer with a laser beam, and a write-once type CD satisfying the compact disc (hereinafter referred to as "CD") standard was developed. Has been done.

In this type of optical information medium, a recording layer made of a dye or the like is formed on a transparent substrate made of polycarbonate or the like having a groove for tracking formed on its surface,
It is a general structure that a metal layer is formed as a reflective layer on the metal layer, and the metal layer is further covered with a protective layer made of an ultraviolet curable resin or the like.

According to the standard stipulated for CDs, that is, the so-called Red Book, Orange Book, etc., the reflectance of reproduced light at a wavelength of 780 nm is 70%.
It is said that the above is required. In a general CD having no recording layer as described above, an Al film was formed as the reflective layer, and thereby a reflectance of 70% or more satisfying the CD standard was obtained.

However, in the optical information medium having the recording layer composed of the dye film or the like as described above, when the reflective layer composed of the Al film is used, sufficient reflectance cannot be obtained.
Therefore, in the write-once type CD, an Au film that can obtain higher reflectance has been used as the reflective layer.

[0006]

Jitter is an important characteristic in evaluating a write-once CD. What is Jitter?
It means the fluctuation of the digital signal in the time axis direction, and the lower the jitter value, the better the recording state. However, in the conventional write-once type CD using the Au film as described above as the reflective layer, there is a problem that this jitter value is bad especially in low linear velocity recording. Therefore, in view of the problems in the conventional optical information medium, an object of the present invention is to provide an optical information medium having a high reflectance and obtaining a good jitter value.

[0007]

That is, in order to achieve the above-mentioned object, the present invention provides a recording layer provided directly or through another layer on a translucent substrate, and a recording layer on the recording layer. And a protective layer provided directly on the transparent layer and reflecting the light incident from the transparent substrate side, and a protective layer provided on the reflective layer directly or via another layer. In the optical information medium, the reflective layer has a multilayer structure, at least one of which is made of a material having a Brinell hardness H _{B of more} than 25, and the refractive index of the first layer on the recording layer side of the reflective layer. The real part n of is less than or equal to 1.

In this case, the film thickness of the first layer whose real part n of the refractive index on the recording layer side of the reflective layer is 1 or more is 50 nm.
The above is preferable. Further, it is preferable that the interface of the reflective layer with the other layer on the protective layer side has unevenness caused by the groove provided on the surface of the transparent substrate, and the unevenness has a depth of 30 nm or more. .

[0009]

In the optical information medium according to the present invention, since at least a part of the reflective layer is made of a material having a Brinell hardness H _{B of more} than 25, thermal distortion of the reflective layer during recording occurs. It is difficult and the jitter value becomes good. Specifically, as in Comparative Example 3 described later, in an optical information medium having a reflective film formed of Au, a semiconductor laser having a wavelength of 780 nm was irradiated at a linear velocity of 1.2 m / sec (CLV).
The average value of the pit land of T jitter (α) is about 28 ns. On the other hand, in the optical information medium according to the present invention, 2
An average value of pit lands of 3T jitter (α) of about 1 to 23 ns can be obtained.

Further, since the real part n of the refractive index of the first layer of the reflective layer which reflects the light incident from the transparent substrate side is 1 or less, a high reflectance can be obtained. In this case, when the film thickness of the first layer having a real part n of the refractive index of 1 or less on the recording layer side of the reflective layer is 50 nm or more, a higher reflectance can be obtained more reliably.

Further, in the optical information medium, if the interface of the reflective layer with the other layer on the protective layer side has irregularities caused by the groove provided on the surface of the transparent substrate,
Compared with a mere flat reflective layer, the second moment of area of the reflective layer is large, its rigidity is high, and distortion is less likely to occur. Therefore, it is more effective by reducing the jitter value. Here, on a translucent substrate having a groove having a general depth of 80 nm, a recording layer having a thickness of about 130 nm,
When a reflective layer having a total film thickness of about 110 nm is formed and the depth of the irregularities at the interface between the reflective layer and the other layer on the protective layer side is 30 nm or more, distortion of the reflective layer can be effectively suppressed. on the other hand,
If the depth of the irregularities is less than this, the effect of increasing the rigidity of the reflective layer is poor.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. An example of a schematic structure of the optical information medium according to the present invention is shown in FIGS. In FIG. 1, reference numeral 1 denotes a light-transmissive substrate made of, for example, polycarbonate. On the light-transmissive substrate 1, as shown in FIG. Groove 5 is provided. Reference numeral 2 is a recording layer formed of a pigment film or the like formed on the transparent substrate 1. Further, 3 and 6 are reflective layers formed thereon, which are composed of a composite layer of the first layer 3 and the second layer 6. These composite layers may be three or more layers. Reference numeral 4 denotes a protective layer provided on the second layer of the reflective layer. Other layers not shown may be interposed between these layers.

The first layer 3 of the reflective layer is made of a metal film having a real part n of the refractive index of 1 or less, and specifically, Au, Ag.
Alternatively, it is made of Cu or an alloy film thereof. When only the first layer 3 reflects light with a wavelength of about 780 nm,
When the film thickness is 50 nm or less, the reflectance increases as the film thickness increases. When the film thickness exceeds 50 nm, the increase in reflectance is saturated, and even if the film thickness is further increased, the reflectance hardly increases. For this reason, the thickness of the first layer 3 needs to be at least 50 nm.

Further, any one of the composite layers constituting the reflection layer, for example, the second layer 6 in the illustrated example, is made of a metal having a Brinell hardness H _{B of more} than 25, and is, for example, C.
r, Ni, Al alloy, Au alloy, Ag alloy, Cu alloy,
It can be formed of Pt, Mo, W, Zn, Zr, or the like. The thickness of the second layer is preferably 60 nm or more so that the original hardness of the material in the bulk state can be exhibited.

The reflective layers 3 and 6 can be formed by a thin film forming means such as a sputtering method or a vacuum evaporation method. further,
As shown in FIG. 2, the interface between the reflective layer 6 and the protective layer 4 has unevenness caused by the pre-groove 5 provided on the surface of the transparent substrate 1. The depth of the pre-groove 5 is usually 80 nm, but the depth d of the irregularities on the interface side of the reflective layer 6 with the protective layer 4 is preferably 30 nm or more. As a result, the elastic moment of inertia of the reflective layers 3 and 6 becomes larger and the rigidity thereof becomes higher than that of a simple flat reflective layer.

Next, specific examples of the optical information medium according to the present invention will be described together with comparative examples. (Embodiment 1) A width of 0.
A polycarbonate substrate having a thickness of 1.2 mm, an outer diameter of 120 mmφ and an inner diameter of 15 mmφ in which spiral pregrooves having a thickness of 8 μm, a depth of 0.08 μm and a pitch of 1.6 μm were formed was molded by an injection molding method.

As the organic dye for forming the recording layer,
0.65 g of 1,1 'dibutyl 3,3,3', 3 'tetramethyl 4,5,4', 5 'dibenzoindodicarbocyanine perchlorate (manufactured by Nippon Senshoku Co., Ltd., product number NK3
219) was dissolved in diacetone alcohol solvent 10 cc, and this was coated on the surface of the substrate 1 by spin coating to form a recording layer having an average film thickness of 130 nm.

Next, an Au film having a film thickness of 50 nm is formed on the entire surface of the area of the polycarbonate substrate having a diameter of 45 to 118 mmφ from the recording layer by a sputtering method, and further, an Au film having a film thickness of 60 nm of 95: 5 Al-M
A g-alloy film was formed to form a reflective layer having a two-layer structure. Using an electron beam cross-sectional shape measuring device manufactured by Orionix, the depth d of the unevenness caused by the pregroove was measured from above the reflective layer, and was d = 30 nm. Further, an ultraviolet curable resin (SD-17 manufactured by DIC Co., Ltd.) was spin-coated on this reflective layer, and this was irradiated with ultraviolet rays to be cured to form a protective layer 4 having a film thickness of 5 μm.

The wavelength 780 of the optical disk thus obtained
The reflectance of the semiconductor laser light of nm was 72%. After recording the EFM signal on this optical information medium,
An 80 nm semiconductor laser with a linear velocity of 1.2 m / sec (CL
It was 22 ns when the average value of 3T jitter (α) pit land was measured by irradiation with V).

(Example 2) On a polycarbonate substrate having the same shape and pregroove as in Example 1,
After forming the recording layer 2 in the same manner as described above, an Ag film having a film thickness of 60 nm is formed thereon by a vacuum vapor deposition method, and further, a 98: 0.8: 1.2 Al film having a film thickness of 60 nm is formed thereon. -S
An i-Mg alloy film was formed and a reflective layer was formed. When the depth d of the unevenness caused by the pregroove was measured from above the reflective layer in the same manner as in Example 1, d = 42.
was nm. Further, a protective layer similar to that in Example 1 was formed on the reflective layer.

The wavelength 780 of the optical disk thus obtained
The reflectance of the semiconductor laser light of nm was 73%. After recording an EFM signal on this optical information medium, the average value of pit lands of 3T jitter (α) was measured in the same manner, and it was 21 ns.

Example 3 On a polycarbonate substrate having the same shape and pregroove as in Example 1,
After forming the recording layer 2 in the same manner as described above, an Au film having a film thickness of 50 nm was formed thereon by a sputtering method, and a Cr film having a film thickness of 60 nm was further formed thereon to form a reflective layer. . When the depth d of the unevenness caused by the pregrooves was measured from above the reflective layer in the same manner as in Example 1, d = 38 nm. Further, a protective layer similar to that in Example 1 was formed on the reflective layer.

The wavelength 780 of the optical disk thus obtained
The reflectance of the semiconductor laser light of nm was 72%. After recording an EFM signal on this optical information medium, the average value of the pit lands of 3T jitter (α) was measured in the same manner, and it was 20.5 ns.

Example 4 On a polycarbonate substrate having the same shape and pregroove as in Example 1,
After forming the recording layer 2 in the same manner as described above, an Au film having a film thickness of 50 nm is formed thereon by a sputtering method, and a 95: 5 Al-Si alloy film having a film thickness of 60 nm is further formed thereon. Then, a reflective layer was formed. When the depth d of the unevenness caused by the pregroove was measured from above the reflective layer in the same manner as in Example 1, d = 32 nm was obtained. Further, a protective layer similar to that in Example 1 was formed on the reflective layer.

The wavelength 780 of the optical disk thus obtained
The reflectance of the semiconductor laser light of nm was 72%. After recording an EFM signal on this optical information medium, the average value of the pit lands of 3T jitter (α) was measured in the same manner, and it was 23 ns.

(Comparative Example 1) In Comparative Example 1, except that the reflective layer was formed of only a 70 nm thick Au film.
An optical disk was manufactured in the same manner as in the same example. In addition,
In the same manner as in Example 1, the depth d of the unevenness caused by the pregroove was measured from above the reflective layer.
It was 20 nm. The optical disk thus obtained had a reflectance of 73% for semiconductor laser light having a wavelength of 780 nm. However, after the EFM signal was recorded on this optical information medium, the average value of the pit lands of 3T jitter (α) was measured in the same manner, and it was 28 ns.

(Comparative Example 2) On a polycarbonate substrate having the same shape and pre-groove as in Example 1,
After forming the recording layer 2 in the same manner as described above, an Au film having a film thickness of 50 nm is formed thereon by a sputtering method, and a 95: 5 Al—Mg alloy film having a film thickness of 60 nm is further formed thereon. Then, a reflective layer was formed. When the depth d of the irregularities caused by the pregrooves was measured from above the reflective layer in the same manner as in Example 1, d = 20 nm was obtained. Further, a protective layer similar to that in Example 1 was formed on the reflective layer.

The wavelength 780 of the optical disk thus obtained
The reflectance of the semiconductor laser light of nm was 72%. Also, after recording an EFM signal on this optical information medium, the average value of the pit lands of 3T jitter (α) was measured in the same manner, and it was 26 ns.

[0029]

As described above, according to the present invention, since the reflective layer has a special multilayer structure, it is possible to provide an optical information medium having a high reflectance and a good jitter value.

[Brief description of drawings]

FIG. 1 is a schematic half cross-sectional perspective view showing an example of the structure of an optical recording medium.

FIG. 2 is an enlarged cross-sectional view taken along the tracking direction before optical recording in FIG. 1 translucent substrate 2 recording layer 3 first layer of reflective layer 4 protective layer 6 second layer of reflective layer

Claims (3)

[Reference number] 0050592-01 [Claims] 1. A recording layer provided directly on a translucent substrate or via another layer, and from the translucent substrate side provided directly on this recording layer or via another layer. In an optical information medium having a reflective layer for reflecting incident light and a protective layer provided directly on the reflective layer or via another layer, the reflective layer has a multilayer structure, at least one of which is An optical information medium which is formed of a material having a Brinell hardness H _{B of more} than 25, and in which the real part n of the refractive index of the first layer on the recording layer side of the reflective layer is 1 or less. 2. The optical information medium according to claim 1, wherein the thickness of the first layer on the recording layer side of the reflective layer is 50 nm or more. 3. The surface of the light-transmissive substrate according to claim 1 or 2, wherein an interface between the reflective layer and another layer of the reflective layer has irregularities generated by a groove provided on the surface of the translucent substrate. An optical information medium having a depth of 30 nm or more.