JP2733341B2 - Optical information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a novel optical information recording medium, in particular, optically records information at high speed and high density using light, heat, etc.
The present invention relates to an optical information recording medium having excellent repetition characteristics that can be reproduced and erased.

2. Description of the Related Art A so-called phase-change type optical disc that records and erases information by utilizing a reversible phase change between a crystalline phase and an amorphous phase in an optical recording layer changes the power of laser light. This has the advantage that new information can be simultaneously recorded while erasing old information (hereinafter referred to as "overwriting"). As a recording material for the overwritable phase-change optical disk, an In-Se alloy (Appl. Phys. Lett., Vol. 50, p. 667, 1987) or In-Se alloy
Sb-Te (Appl. Phys. Lett. Vol. 50, p. 16, 1987)
), Chalcogen alloys such as Ge-Te-Sb alloys are mainly used. On the other hand, when recording / erasing is actually performed using these chalcogen alloys, the optical recording layer is usually used 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,
A protective layer comprising sulfides, nitrides and mixtures thereof is provided. In particular, when a chalcogen alloy is used for the optical recording layer, zinc sulfide (ZnS) has a strong adhesion to the optical recording layer and is preferred in terms of repetition characteristics.

(Problems to be Solved by the Invention) However, as long as ZnS alone is used as a protective layer, repeated recording / erasing by overwriting causes coarsening of ZnS crystal grains, resulting in insufficient heat resistance. Therefore, conventionally, a glass-forming material such as SiO ₂ has been added to ZnS to improve the heat resistance of ZnS. However, the addition of SiO ₂ or the like causes the optical recording layer material to undergo mass transfer when it is melted when repeated recording / erasing by overwriting in order to weaken the adhesive force with the optical recording layer, and finally the optical recording layer material However, there is a problem in that the recording and erasing become impossible due to the dispersion around the periphery.

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-change type optical disc which eliminates the above problems and has excellent repetition characteristics in overwriting.

(Means for Solving the Problems) As a result of intensive studies to achieve the above object, the present inventors have found that by using a protective layer composed of a mixture of ZnS and a sulfide having a melting point of 1000 ° C. or more, an optical recording layer can be formed. It has been found that mass transfer can be prevented, and the present invention has been accomplished. That is, the present invention is an optical information recording medium characterized in that a protective layer is provided on both sides or one of the optical recording layers, and the protective layer is made of a mixture of ZnS and a sulfide having a melting point of 1000 ° C. or more.

In order to prevent mass transfer during recording / erasing in repeated overwriting, it is necessary that the adhesion between the protective layer and the optical recording layer be strong. Further, many optical recording layers using a phase change have a melting point of 500 ° C. or higher, and in actual recording / erasing, the temperature of the optical recording layer is
It is thought to be up to 700-800 ° C. Therefore, the protective layer material must be able to withstand the above-mentioned temperatures, and the melting point is desirably at least 1000 ° C. or higher. However, at temperatures approaching 1000 ° C., ZnS crystal grains become coarse and cannot be present stably. Therefore,
When a rare earth sulfide having a melting point of 1000 ° C. or more is mixed with ZnS, the thermal stability can be increased without impairing the adhesion of ZnS to the chalcogen material. Among the sulfides, rare-earth metal sulfides are (1) most of the sulfides have a high melting point, (2) the rare-earth metal itself has a high adhesion to the chalcogen material, and (3) thermodynamically stable ones. Abundant, (4) Rare earth metals easily bond with sulfur in ZnS decomposed by heat,
This is considered to be preferable as a mixture for reasons such as enhancing the thermal stability of ZnS.

As rare earth sulfides, for example, LaS, CeS, PrS, NdS, Sm
S, EuS, GdS, YbS, YS, La ₃ S ₄ , Ce ₃ S ₄ , Pr ₃ S ₄ , Nd ₃ S ₄ , Sm ₃ S ₄ , Eu ₃
S ₄ , La ₂ S ₃ , Ce ₂ S ₃ , Pr ₂ S ₃ , Nd ₂ S ₃ , Sm ₂ S ₃ , Gd ₂ S ₃ , Tb ₂ S ₃ , Dy
₂ S ₃ , Y ₂ S ₃ , Ho ₂ S ₃ , Er ₂ S ₃ , Tm ₂ S ₃ , Yb ₂ S ₃ , Lu ₂ S ₃ , LaS ₂ , CeS ₂ , P
rS ₂ , NdS ₂ , SmS _{2 and the} like are used. These are all 1000
It has a melting point of at least ℃ and is suitable as a mixture.

The mixed amount of sulfide to ZnS needs to be such that the adhesion of ZnS to the optical recording layer is not impaired, and in view of improving the repetition characteristics, the mixed amount is 5 to 40.
mol% is good, and the range of 10 to 30 mol% is particularly preferable. The thickness of the protective layer may be determined in the range of 50 to 5000 ° based on the balance between contrast and sensitivity.

FIG. 1 shows an example of the layer structure according to the present invention. On a transparent substrate 1, a lower protective layer 2, an optical recording layer 3, an upper protective layer 4, and a UV curable resin layer 5 are sequentially laminated.

Further, in some cases, a reflective layer made of metal or the like may be provided between the upper protective layer 4 and the UV curable resin layer 5. Also,
As a method for forming the protective layer, a sputtering method using a mixed target, a multi-source simultaneous sputtering method using a plurality of targets, or a vacuum evaporation method (resistance heating, electron beam)
Or a method such as a CVD method.

Further, as the optical recording layer, Sb-Te-Ge, In-Sb-Te,
An alloy such as In-Se-Tl is preferable, and a known method such as a sputtering method or a vacuum evaporation method may be used as a method for forming these.

As the transparent substrate in the optical information recording medium, a substrate conventionally used as a substrate for an optical disk can be used, but the optical characteristics are good and the mechanical strength is large.
Polycarbonate, glass, and the like having excellent dimensional stability are preferable. Also, irregularities such as address information may be formed on these transparent substrates.

According to the present invention, on both sides or one side of the optical recording layer,
By providing a protective layer consisting of a mixture of ZnS and a sulfide with a melting point of 1000 ° C or higher, it is possible to prevent the deterioration of the characteristics due to mass transfer of the optical recording layer during repeated overwriting, greatly improving the repetition characteristics. Can be done.

 Hereinafter, the present invention will be described in detail with reference to examples.

(Example) Example 1 An optical recording layer and a protective layer were formed on a 1.2 mm-thick polycarbonate substrate by the following procedure. FIG. 2 shows an outline of the sputtering apparatus used. First, ZnS and Sm ₂ S ₃ were sputtered simultaneously from separate targets to form a 100 nm mixed layer. The mixing ratio between ZnS and Sm ₂ S ₃ was determined by controlling the sputtering power applied to each target. Next, on the protective layer of this mixture, as an optical recording layer
An Sb-Te-Ge alloy was formed to a thickness of 80 nm. In addition,
A protective layer of a mixture of ZnS and Sm ₂ S ₃ was formed to a thickness of 150 nm. A 5 μm UV-curable resin was applied thereon and UV-cured. The substrate thus prepared was irradiated with laser light in a stationary state to evaluate repetitive characteristics. The wavelength of the laser light is 830 nm. For the evaluation, the laser light emission time was from 20 nsec to 60 μsec, and the power of the laser light was 1
The measurement was performed by arbitrarily changing the range from mW to 20 mW. The results of the above evaluation are shown in FIG. The mixing amount is Sm ₂ S ₃
Are 0 mol%, 5 mol%, 10 mol% and 15 mol%. Here, “0 mol%” is a layer structure in which Sm ₂ S ₃ in the protective layer is 0 mol%, that is, both sides of the optical recording layer are sandwiched by ZnS, and has been conventionally used. 3, the upper curve corresponds to the reflectance in the crystalline state, ie, the erased state, and the lower curve corresponds to the reflectance in the amorphous state, ie, the recorded state. That is, the difference between the reflectances is proportional to the signal-to-noise ratio (C / N ratio) of the reproduced signal. Sm ₂
An optical information recording medium using a protective layer in which S ₃ is mixed is 10
The reflectance in the recorded state and the reflectance in the erased state did not change up to ^six times, and the number of repeatable times was increased by 100 times or more by mixing ZnS with Sm ₂ S ₃ .

Example 2 On a polycarbonate substrate having a thickness of 1.2 mm, an optical information recording medium having the same layer configuration as in Example 1 was produced. However, a mixture of ZnS and Ce ₂ S ₃ was used as a material for the protective layer. The mixing amount is 0 mol%, 5 mol%, 10 mol% and 15 mol% Ce ₂ S ₃
It is. The evaluation was performed with the substrate stationary as in Example 1. The results of the above evaluation are shown in FIG. ZnS and Ce ₂
Similarly to the case where Sm ₂ S ₃ was mixed, the reflectance in the recording state and the reflectance in the erased state were not changed, and the same effect was obtained when the protective layer made of the mixture of S ₃ was used.

Example 3 A film having a layer configuration similar to that of Example 1 was formed on a polycarbonate substrate having a diameter of 130 mm, a thickness of 1.2 mm, and a pitch of 1.6 μm in advance. However, two types of protective layers were prepared, one in which ZnS was mixed with 10 mol% of Sm ₂ S ₃ and the one in which Sm ₂ S ₃ was not mixed. The measurement was performed dynamically while rotating the substrate thus prepared. The linear velocity is approximately
Overwriting with a recording frequency of 3.7 MHz and a recording pulse width of 90 nsec was repeated at 7.5 m / s. The recording power and the erasing power were 16 mW and 7 mW, respectively. FIG. 5 and FIG.
Figure shows respectively ZnS only (Sm ₂ S ₃ 0mol%) and the results of those mixed 10 mol% of Sm ₂ S _3. The sm ₂ S ₃ a mixture 10 mol% is no change in the C / N ratio (signal-to-noise ratio) to 10 ⁵ times, Zn
The repetition characteristics were improved about 10 times compared to the case of S.

Effects of the Invention ZnS and melting point of 1000 ° C. on both sides or one side of the optical recording layer
By providing the protective layer made of a mixture of the above sulfides, the repetition characteristics are improved, and the reliability of the recorded data can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a layer configuration of an optical information recording medium according to the present invention, wherein reference numeral 1 denotes a transparent substrate, 2 denotes a protective layer, 3 denotes an optical recording layer, 4 denotes a protective layer, 5 denotes a protective layer. Is a UV curable resin layer. FIG. 2 is a schematic view of a sputtering apparatus used in the present invention, in which reference numeral 6 denotes a substrate holder, 7 denotes a substrate, 8 denotes a bell jar, and 9 denotes a target. FIG. 3 shows Embodiment 1.
FIG. 9 is a characteristic diagram showing an example in which the repetition characteristics are statically evaluated. FIG. 4 is a characteristic diagram showing an example of statically evaluating repetition characteristics in the second embodiment. FIG. 5 is a diagram showing the repetition characteristics when the protective layer in Example 3 is made only of ZnS, and FIG. 6 is a graph showing the case where the protective layer obtained by mixing Sm ₂ S ₃ with 10 mol% of ZnS in Example 3 is used. FIG. 9 is a diagram showing a repetition characteristic.

Claims (2)

(57) [Claims] 1. An optical information recording medium, comprising: an optical recording layer provided on a transparent substrate; and irradiating the optical recording layer with an energy beam to change its optical constant to record and erase information. An optical information recording medium, wherein a protective layer is provided in contact with an optical recording layer on both sides or one side, and the protective layer is made of a mixture of zinc sulfide and a sulfide having a melting point of 1000 ° C. or higher. 2. A protective layer provided on both sides or one side of an optical recording layer, wherein a sulfide having a melting point of 1000 ° C. or more is a sulfide of a rare earth metal among materials constituting the protective layer. The optical information recording medium according to claim 1, wherein