JP2804366B2 - 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 specifically, to optically record, reproduce, and erase information at high speed and high density using light, heat, and the like. The present invention relates to an optical information recording medium having excellent repetition characteristics.

2. Description of the Related Art A so-called phase-change optical information recording medium for recording and erasing information by utilizing a reversible phase change of an optical recording layer between crystalline and amorphous is called a laser light power. Has the advantage that new information can be recorded at the same time while erasing old information only by changing (overwrite).

As a recording material in such an overwritable phase-change optical information recording medium, an In-Se alloy having a low melting point and a high laser beam absorption efficiency [“Appl. Phys. Lett. Volume 50,
667 (1987)] and In-Sb-Te-based alloys [Appl. Phys.
t.) ", Vol. 50, p. 16 (1987)], and chalcogen alloys such as Ge-Te-Sb-based alloys (JP-A-62-53886) are mainly used.

When actually performing recording / erasing using these chalcogen alloys, the recording / erasing is usually performed to prevent deformation of the substrate due to heat during recording / erasing or to prevent oxidation or deformation of the optical recording layer. Metal or metalloid oxides, carbides, fluorides, sulfides, on both sides or one side of the optical recording layer
It is used by providing a protective layer made of a nitride, a mixture thereof, or the like.

The optical information recording medium comprising the optical recording layer and the protective layer is generally of a three-layer structure in which protective layers are provided on both sides of the optical recording layer in consideration of recording / erasing and repetition characteristics, A four-layer structure in which a reflective layer mainly made of metal is further provided on the opposite protective layer has been used.

However, in the optical information recording medium having the above-described three-layer structure or four-layer structure, when recording / erasing by overwriting is repeated, asymmetric thermal expansion and surface energy generated from the thermal history corresponding to the recording / erasing pattern are obtained. The difference causes a phenomenon in which the substance of the optical recording layer moves along the track direction, and as a result, the substance of the optical recording layer is locally dispersed around, so that recording / erasing becomes impossible.

Problems to be Solved by the Invention The present invention overcomes the drawbacks of the conventional phase-change type optical information recording medium, and optically uses high-speed and high-density information by using light, heat, and the like. It is an object of the present invention to provide a phase change type optical information recording medium having excellent repetition characteristics capable of recording, reproducing, and erasing without any troubles.

Means for Solving the Problems The present inventors have conducted intensive studies to develop an optical information recording medium having such excellent characteristics, and as a result, during overwriting, mass transfer occurred during recording / erasing. In order to avoid this, it is necessary to eliminate the asymmetry of the thermal history in the optical recording layer. This asymmetry of the thermal history can be controlled by the recording / erasing pattern, the recording / erasing power, and the layer configuration of the information recording medium. In the conventional layer configuration, the repetition characteristics are greatly affected by the selection of the recording / erasing pattern, recording / erasing, and power. On the other hand, in order to limit the repetition characteristics, the phase change of the optical recording layer is required. Since not the properties but the mass transfer of the optical recording layer are involved, if the optical recording layer is made extremely thin and its structure is made into a discontinuous island-like structure, the material of the optical recording layer can be obtained. It has been found that migration can be prevented, and that a better result can be obtained by providing a protective layer on both sides or one of the optical recording layer. Based on this finding, the present invention has been completed.

That is, the present invention provides an optical information recording medium for providing an optical recording layer on a transparent substrate, irradiating the recording layer with an energy beam, reversibly changing its optical constant, and recording and erasing information. The optical information recording medium, wherein the optical recording layer has a film thickness of 20 nm or less, and has a discontinuous island structure, and a protective layer is provided on both sides or one side of the optical recording layer in some cases. Is provided.

 Hereinafter, the present invention will be described in detail.

In the conventional optical information recording medium, in order to satisfy the optical characteristics, it is necessary that the thickness of the optical recording layer is 10 nm or more, therefore, the optical recording layer is a continuous film on the substrate. Is formed. Therefore, when the optical recording layer is melted by recording / erasing, it easily moves in a direction parallel to the substrate surface. FIG. 1 is a sectional view showing a configuration of an example of such a conventional optical information recording medium.
A configuration in which a lower protective layer 2, an optical recording layer 3 formed of a continuous film, an upper protective layer 4, a reflective layer 5, and an ultraviolet curable resin layer 6 are sequentially provided on a transparent substrate 1 is shown.

In contrast, the optical information recording medium of the present invention has a structure in which the optical recording layer has a thickness of 20 nm or less, and has a discontinuous island structure, whereby the optical recording layer is physically separated. ing. By physically separating the optical recording layer in this manner, the moving distance of the optical recording layer is greatly limited, and deterioration of the repetitive characteristics due to mass transfer of the optical recording layer is prevented.

FIG. 2 is a sectional view showing an example of the configuration of the optical information recording medium of the present invention, in which an optical recording layer 3 'having an island-like structure and a protective layer 4 are sequentially provided on a transparent substrate 1. Is shown.

The optical recording layer having the island structure can be formed from an interface energy difference between a substrate and a metal by forming the film into an extremely thin film [“Journal of Applied Physics (J. Appl. Phys.). 37, p. 3405 (19
66)). In the present invention, the thickness of the optical recording layer is 20
It is necessary to be not more than 10 nm, preferably not more than 10 nm. When this film thickness is more than 20 nm, it is difficult to form an optical recording layer having an island structure.

The layer configuration of the optical information recording medium of the present invention differs depending on the intended use and the like, and is not particularly limited. For example, as shown in the cross-sectional view of FIG. A structure having only the layer 3 'may be used, but when actually used as an optical information recording medium, it is necessary to increase the optical characteristics, particularly the degree of light modulation (contrast). As shown in the cross-sectional view, a structure in which a protective layer 2, an optical recording layer 3 'having an island-shaped structure and a protective layer 4 are sequentially provided on a transparent substrate 1 is preferable, and as shown in the cross-sectional view of FIG. In addition, a protective layer 2 is provided on a transparent substrate 1, an optical recording layer 3 'having an island-like structure and a protective layer 4' are sequentially and repeatedly laminated thereon, and a protective layer 4 having a film thickness is further provided thereon. Structures are preferred.

In an optical information recording medium having such a laminated structure,
The thicknesses of the optical recording layer and the protective layer may be determined in consideration of an interference effect, optical characteristics, and thermal characteristics. Further, a reflective layer made of metal or the like may be provided on the uppermost part for the purpose of improving optical characteristics.

FIG. 6 is a sectional view showing the structure of one example of the optical information recording medium of the present invention, in which a thick protective layer 2 is provided on a transparent substrate 1, and an optical recording layer having an island structure is provided thereon. 3A shows a configuration in which a 3 ′ and a protective layer 4 ′ are sequentially and repeatedly laminated, and further a reflective layer 5 and an ultraviolet (UV) curable resin layer 6 are sequentially provided.

As the material of the optical recording layer in the optical information recording medium of the present invention, for example, Sb-Te-Ge, In-Sb-Te, In-Se-Tl, Ge-T
Alloys based on Te or Se, such as e-Sn-Au and Sb-Te-Ge-Pd, are preferably used. Examples of the material for the protective layer include oxides such as SiO ₂ , SiO, Ta ₂ O ₅ and ZrO ₂ , and Si ₃ N
_4, nitrides such as AlN, sulfides such as ZnS, fluorides and mixtures thereof, such as MgF _2, further polyvinyl chloride,
Polyimide, organic compounds such as polyethylene and the like are used, as a material of the reflective layer, for example, Al, Cr, Ni, Au,
Metals such as Ti and alloys thereof are used.

There is no particular limitation on the method for forming the optical recording layer,
Conventionally used methods for forming a thin film, for example, a sputtering method, a vacuum evaporation method, a CVD method, and a spin coating method can be used.

Further, a layer made of an organic material may be provided on the reflective layer, if necessary, for protection and reinforcement of the film. As this material, for example, a UV curable resin such as a urethane-based, acrylic-based, silicone-based, or polyester-based resin, or a hot-melt-based adhesive is used.

The transparent substrate in the optical information recording medium of the present invention is not particularly limited, and those conventionally used as substrates for optical information recording media can be used, but the optical characteristics are good, the mechanical strength is high, and A polycarbonate substrate, a glass substrate, or the like is preferable from the viewpoint of excellent dimensional stability. Further, irregularities such as address information may be formed on these transparent substrates.

Effect of the Invention The optical information recording medium of the present invention uses an ultra-thin film having a discontinuous island structure as the optical recording layer, so that mass transfer of the optical recording layer due to repetition of recording / erasing is greatly reduced. Since the deterioration of the characteristics due to the mass transfer is suppressed, the reliability of the recorded data in the repetition characteristics is greatly improved.

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.

In the embodiment, as shown in the schematic diagram of FIG. 7, the sputtering apparatus includes a substrate holder 8 for holding the substrate 1 in the bell jar 7 and a support table 10 for placing the target 9 in the system. The one having a structure connected to a vacuum pump to evacuate the inside was used.

Example 1 An optical information recording medium shown in FIG. 8 having an optical recording layer, a protective layer, a reflective layer, and a UV curable resin layer on a 1.2 mm thick polycarbonate disk substrate was prepared by the following procedure.

First, using a target made of ZnS, a thickness of 100 nm was formed on the polycarbonate substrate 1 by RF sputtering.
Is formed on the protective layer 2, a Sb-Te-Ge alloy film is formed as an optical recording layer 3 'having an island structure, a ZnS film is formed as a protective layer 4', and a 2 nm and 5 nm This was repeated 10 times to form a film, and then a ZnS protective layer 4 was formed thereon to a thickness of 150 nm in the same manner as described above. Further, a reflective layer 5 of an Al alloy is formed thereon to a thickness of 100 nm, and then a UV curable resin is applied thereon by a spin coating method to a thickness of 5 μm and UV cured to form a UV curable resin layer 6. Was provided to produce an optical information recording medium (layer structure A).

For comparison, an optical information recording medium shown in FIG. 9 was prepared as a conventionally used optical information recording medium having a continuous structure using the same film forming apparatus and method as described above. That is, from the polycarbonate substrate 1 side, a ZnS protective layer 2 having a thickness of 150 nm, an optical recording layer 3 made of a continuous Sb-Te-Ge film having a thickness of 20 nm, a ZnS protective layer 4 having a thickness of 20 nm, and a thickness 1
00 nm Al alloy reflective layer 5 and 5 μm thick UV curable resin layer 6
Were laminated to form an optical information recording medium (layer structure B).

Each of the optical information recording media thus produced was irradiated with a laser beam having a wavelength of 830 nm in a stationary state to evaluate the repetition characteristics. The evaluation was performed by arbitrarily changing the emission time of the laser light within a range from 20 nsec to 60 μsec and the power of the laser light within a range from 1 mW to 20 mW. The result is shown in FIG.

FIG. 10 is a graph showing the relationship between the number of repetitions and the reflection level, and in each curve in the figure, the upper curve corresponds to the crystal state, that is, the reflectance in the erased state,
The lower curve corresponds to the reflectance in the amorphous state, ie, the recorded state. Therefore, the difference between the respective reflectances is proportional to the signal-to-noise ratio (C / N ratio) of the reproduced signal.

As can be seen from FIG. 10, the conventional layer configuration (layer configuration B)
The optical information recording medium comprising an optical having from 10 ₆ or more times, while the decrease in the reflectance of the recording state by a change in thickness due to mass transfer begins, the optical recording layer is an island-like structure of the present invention information recording medium, both the reflectivity of reflectivity and erased state of the recording condition, no change even by ₁₀₇ or more times, extends repeatable number 10 times or more.

Example 2 A polycarbonate disk substrate having a diameter of 130 mm, a thickness of 1.2 mm and a pitch of 1.6 μm was previously provided on a polycarbonate disk substrate.
Optical information recording media having two types of layer structures, A and B, were prepared in the same manner as in Example 1, and dynamic measurements were performed while rotating them to evaluate repetition characteristics. Linear velocity is about 7.5m / s
Overwriting with a recording frequency of 3.7 MHz and a recording pulse width of 90 nsec was repeated. The recording power and erasing power were 19 mW and 7 mW, respectively.

FIGS. 11 and 12 are graphs showing the relationship between the number of repetitions and C / N in the optical information recording medium having the conventional structure (layer structure B) and the optical information recording medium of the present invention (layer structure A), respectively.

From these figures, in the optical information recording medium of the conventional structure,
Number of repetitions 10 ₅ times in response to a change in thickness due to the mass transfer of the optical recording layer from, while the decrease in the C / N ratio by reduction and noise increase in the reproduction signal amplitude (signal to noise ratio) begins, In the optical information recording medium of the present invention, the number of repetitions
10 ₆ no change in C / N ratio to times, can be seen the repetition characteristics of about 10 times or more than that of the conventional structure is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a layer configuration of one example of a conventional optical information recording medium. FIGS. 2 to 6 are cross-sectional views showing layer configurations of different examples of the optical information recording medium of the present invention. FIG. 7 is a schematic view of a sputtering apparatus used in the embodiment of the present invention, and FIG.
FIG. 9 and FIG. 9 are cross-sectional views showing the layer configurations of the optical information recording medium of the present invention and the conventional optical information recording medium used in the examples of the present invention, respectively, and FIG. 10 is used in the examples of the present invention. FIGS. 11 and 12 are graphs showing the static repetition characteristics of the optical information recording medium of the present invention and the conventional optical information recording medium, respectively. 5 is a graph showing dynamic repetition characteristics of the optical information recording medium of FIG. In the figure, reference numeral 1 denotes a transparent substrate, 2, 4 and 4 'are protective layers, 3 is an optical recording layer composed of a continuous film, 3' is an optical recording layer having an island structure, 5 is a reflective layer, and 6 is a UV curable resin. The layer, 7 is a bell jar, 8 is a substrate holder, 9 is a target, and 10 is a support.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-152035 (JP, A) JP-A-2-18971 (JP, A) JP-A-3-259437 (JP, A) 62451 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/24 522

Claims (3)

(57) [Claims] An optical information recording medium for recording and erasing information by providing an optical recording layer on a transparent substrate and irradiating the recording layer with an energy beam to reversibly change its optical constant to record and erase information. An optical information recording medium, wherein the optical recording layer has a thickness of 20 nm or less and has a discontinuous island structure. 2. The optical information recording medium according to claim 1, wherein a protective layer is provided on both sides or one side of the optical recording layer. 3. The optical information recording medium according to claim 2, wherein the optical information recording medium has a structure in which an optical recording layer having an island structure and a protective layer are sequentially and repeatedly laminated on a transparent substrate directly or via a protective layer.