JP2810092B2 - Optical information recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical information recording medium, and more particularly, to high-speed, high-density recording, reproduction, and erasing of optical information using light or heat. The present invention relates to an optical information recording medium having excellent repetition characteristics.

2. Description of the Related Art In recent years, there has been an increasing demand for an optical disk capable of repeatedly recording and erasing information using a semiconductor laser beam. Heretofore, as a so-called rewritable optical disk capable of recording and erasing this information, a method of recording information by utilizing a difference in optical constant due to a phase change of an optical recording layer, for example, modulation of laser beam power. There is known a method of recording and erasing information by utilizing the fact that an optical recording layer reversibly changes phase between crystalline and amorphous.

As such a phase-change type optical recording layer, it is desired that a material having absorption in a wavelength region of a semiconductor laser and having a relatively low melting point is used, and therefore, a chalcogen material is mainly used. Things have a melting point of about
Since the substrate is easily deformed at a temperature of 500 ° C. or higher, in order to prevent the deformation of the substrate or to prevent the optical recording layer from being oxidized or changed, an oxide, a nitride, a carbide, It has been practiced to provide a heat-resistant protective layer made of fluoride, sulfide, or a mixture thereof.

When such a protective layer is provided, the refractive index of the protective layer is set to n, and the protective layer on the substrate side is set in order to increase the change in reflectance before and after recording or to efficiently absorb the semiconductor laser light into the optical recording layer. Assuming that the thickness of the (lower) layer is d ₁ , the thickness of the protective layer (upper layer) on the opposite side is d ₃ , and the wavelength of the semiconductor laser light is λ, It is optically advantageous to satisfy the relationship

However, if you try to meet these conditions,
There is a problem that the reflectance of the recording medium itself is low, the focus servo and the tracking servo tend to be unstable, and the drive design becomes difficult. In addition, in the phase change method, the optical recording layer is made amorphous or crystalline due to a difference in cooling rate of the optical recording layer during recording / erasing. There is also a problem that the film thickness becomes different from the optically designed film thickness.

The present invention is directed to a phase-change optical information recording medium having an optical recording layer on a substrate and heat-resistant protective layers on both sides of the optical recording layer. It is an object of the present invention to provide an optical information recording medium capable of recording, reproducing, and erasing at high density and having excellent repetition characteristics.

Means for Solving the Problems The present inventors have conducted intensive studies to overcome the above-mentioned drawbacks in the optical information recording medium using phase change, and as a result, the optical recording layer is a Sd-Te-Ge alloy, In an optical information recording medium in which the heat-resistant protective layer is mainly composed of zinc sulfide, the thickness of the heat-resistant protective layer provided on the substrate side is in the range of 100 to 150 nm, and the thickness of the heat-resistant protective layer provided on the opposite side. The 120-1
In the range of 80 nm, by setting the thickness of the optical recording layer in the range of 60 to 100 nm, it has been found that the object can be achieved,
Based on this finding, the present invention has been completed.

That is, the present invention has an optical recording layer for recording and erasing information by utilizing a phase change between amorphous and crystalline on a transparent substrate, and a heat-resistant protective layer on both sides of the optical recording layer. In the provided optical information recording medium, the optical recording layer is made of an Sd-Te-Ge alloy, the heat-resistant protective layer is mainly composed of zinc sulfide, and the heat-resistant protective layer provided on the substrate has a thickness of 100 to 150nm,
The thickness of the heat-resistant protective layer provided on the opposite side is 120 to 180 nm
And an optical information recording medium characterized in that the thickness of the optical recording layer is 60 to 100 nm.

FIG. 1 is a cross-sectional view showing an example of the structure of the optical information recording medium of the present invention, in which a lower heat-resistant protective layer 2, an optical recording layer 3, an upper heat-resistant protective layer 4, and an ultraviolet curable resin are provided on a transparent substrate 1. The layers 5 are sequentially stacked. d ₁ , d ₂ and d ₃ are the thicknesses of the lower heat-resistant protective layer, the optical recording layer and the upper heat-resistant protective layer, respectively.

As the transparent substrate in the optical information recording medium of the present invention, those conventionally used as substrates for optical discs, for example, polyethylene, polypropylene, polystyrene, polycarbonate, resins and glass such as polymethyl methacrylate and the like can be used. Among them, polycarbonate, polymethyl methacrylate, glass, and the like, which have good optical properties, high mechanical strength, and excellent dimensional stability, are preferable. Further, irregularities such as address information may be formed on these transparent substrates.

In the optical information recording medium of the present invention, as the optical recording layer provided on the transparent substrate, the phase of which changes reversibly between amorphous and crystalline by modulating the power of laser light, Sd-Te- A ternary alloy of Ge is used. The method for forming the optical recording layer is not particularly limited, and a known method, for example, a method such as evaporation, co-evaporation, flash evaporation, sputtering, reactive sputtering, or ion plating can be used.

Further, in the optical information recording medium of the present invention, on both sides of the optical recording layer, in order to prevent deformation of the substrate or to prevent oxidation or deformation of the optical recording layer, heat protection mainly comprising zinc sulfide is adopted. A layer is provided. The method for forming the heat-resistant protective layer is not particularly limited, and any method conventionally used, for example, a vapor deposition method, a sputter rig method, an ion plating method, or the like can be arbitrarily used.

In the optical information recording medium of the present invention, it is necessary to control the thickness of each of the layers within a predetermined range. That is, the thickness of the heat-resistant protective layer provided on the substrate side is 100 to 150 nm.
The thickness of the heat-resistant protective layer provided on the opposite side
It is necessary that the thickness of the optical recording layer be in the range of 60 to 100 nm in the range of 120 to 180 nm.

That is, the refractive index of the Sd-Te-Ge alloy used for the optical recording layer and the refractive index of zinc sulfide used for the heat-resistant protective layer are about 4 and 2.3, respectively, the wavelength of the semiconductor laser light is 830 nm, and the film thickness of the optical recording layer is 80 nm. Then, if the optical recording layer is amorphous, the thickness d _{1 of} the heat-resistant protective layer (lower layer) provided on the substrate side
And the thickness of the heat-resistant protective layer (upper layer) provided on the opposite side
and d _3, the relationship between the reflectance of the optical information recording medium is as shown in the graph of Figure 2.

As described above, where the reflectivity is low, the focus servo and tracking servo become unstable. Therefore, it is desirable that the reflectivity of the optical information recording medium is 10% or more. lower protective layer thickness d ₁ from the second figure 50nm or less, or it is found that is necessary is 100nm or more. However, when recording, the optical recording layer is 500
In the region where d ₁ is 50 nm or less, the heat-resistant protective layer itself is deformed, so that the previously recorded data cannot be erased. Become.

FIG. 3 shows the lower protective layer thickness d ₁ and the upper protective layer thickness d ₃ and the semiconductor laser absorption efficiency of the optical recording layer when the optical recording layer becomes crystalline (refractive index: about 6). η
3C is a graph showing the relationship with c), and shows the lower protective layer thickness d _1.
When the film thickness is larger than 100 nm, as the film thickness increases, the absorption efficiency decreases and the recording sensitivity decreases. To prevent the absorption efficiency from falling below 50%, the thickness of the lower protective layer is required.
It is necessary to set d ₁ to 150 nm or less. From the above results, the lower protective layer thickness d ₁ may be necessary to choose a range of 100 to 150 nm.

On the other hand, the upper layer of the heat-resistant protective layer, a thickness d ₃ is 100nm or less is undesirable cause thermal deformation. FIG. 4 shows the lower protective layer thickness d ₁ and the upper protective layer thickness d ₃ and the absorption efficiency (ηa) of the semiconductor laser in the optical recording layer when the optical recording layer is amorphous (refractive index: about 4). As can be seen from FIG. 4, in the region where the upper protective layer thickness d ₃ is 100 nm or more, the absorption efficiency increases as the thickness increases, Erasure sensitivity is reduced. Therefore, in order absorption efficiency does not fall below 70%, the upper protective layer thickness d ₃ is required to be 120nm or more. Further, as the upper protective layer thickness d ₃ becomes thicker, the cooling rate becomes higher half of the recording time of the optical recording layer, since the heating requires a large energy, the upper protective layer thickness is too thick,
Rather, the recording sensitivity decreases. Thus, the upper protective layer thickness d ₃ is required to be 180nm or less.

On the other hand, the optical recording layer has a maximum reflectance difference in the vicinity of about 80 nm, and the recording sensitivity is improved as the optical recording layer becomes thinner, but the erasure sensitivity and the reflectance difference are reduced as the thickness becomes thinner. However, the recording sensitivity sharply decreases. Accordingly, the optical recording layer thickness d ₃ is 60~100nm
It is necessary to choose within the range.

Effects of the Invention According to the present invention, in a phase-change rewritable optical information recording medium, by specifying the film thicknesses of an optical recording layer and a heat-resistant protective layer, recording / erasing sensitivity is increased, and repetition characteristics are significantly improved. be able to.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example: Diameter provided with 1.6 μm pitch grooves in advance
On a 3.5-inch polycarbonate substrate, zinc sulfide was deposited as a lower heat-resistant protective layer by RF sputtering, and then DC sputtering was used.
A -Te-Ge alloy was formed, and then a zinc sulfide film was formed thereon as an upper heat-resistant protective layer by an RF sputtering method. In addition, in order to suppress the deformation of the upper protective layer thereon,
An ultraviolet curable resin layer having a thickness of about 3 to 10 μm was provided.

The thickness of each layer was 80 nm for the optical recording layer, 120 nm for the lower protective layer, and 160 nm for the upper protective layer.
A disc having the structure shown in FIG. 1 was produced.

Using the disk obtained in this way, a linear velocity of 7.5 m
Recording / erasing characteristics were examined under the conditions of / s, a recording frequency of 3.1 MHz, and a pit length of 1.2 μm. Recording laser power and C /
FIG. 5 is a graph showing the relationship between the N ratio and the erase ratio. Here, the erasing ratio is a difference between the C / N ratio at the time of recording and the C / N ratio at the time of erasing. As can be seen from FIG. 5, the C /
N ratio and erase ratio of 30 dB or more were obtained in a wide power range, and good recording and erasure identification was shown.

Next, using the same disk, the repetition characteristics were examined. FIG. 6 is a graph showing the relationship between the number of repetitions and the C / N ratio and the erase ratio. This up to the sixth number of repetitions As can be seen from FIG. 10 ^five times, without changing both C / N ratio and erase ratio, stable initial properties are maintained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a layer structure of an example of an optical information recording medium of the present invention, and FIG. FIG. 3 is a graph showing the relationship between the upper protective layer thickness and the lower protective layer thickness and the absorptivity of the optical recording layer of the optical information recording medium in a crystalline state, and FIG. 4 is a graph showing the upper protective layer thickness and the lower protective layer. FIGS. 5 and 6 are graphs showing the relationship between the layer thickness and the absorptance of the optical recording layer of the optical information recording medium when the optical recording layer is in an amorphous state. 5 is a graph showing erasing characteristics and repetition characteristics. In FIG. 1, reference numeral 1 denotes a substrate, 2 denotes a lower heat-resistant protective layer,
Reference numeral 3 denotes an optical recording layer, 4 denotes an upper heat-resistant protective layer, and 5 denotes an ultraviolet curable resin layer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-20449 (JP, A) JP-A-61-137784 (JP, A) JP-A-62-204449 (JP, A) JP-A-63-204 317939 (JP, A) JP-A-63-100632 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/24

Claims (1)

(57) [Claims] 1. An optical recording layer for recording and erasing information on a transparent substrate by utilizing a phase change between amorphous and crystalline,
In an optical information recording medium provided with a heat-resistant protective layer on both sides of the optical recording layer, the optical recording layer is made of an Sb-Te-Ge alloy, the heat-resistant protective layer is mainly composed of zinc sulfide, and is provided on the substrate side. The optical information, wherein the thickness of the heat-resistant protective layer provided is 100 to 150 nm, the thickness of the heat-resistant protective layer provided on the opposite side is 120 to 180 nm, and the thickness of the optical recording layer is 60 to 100 nm. recoding media.