JPS632131A - Optical information recording member - Google Patents

Abstract

PURPOSE:To improve the stability of a heat resistant protective layer by providing the heat resistant protective layer which consists essentially of zinc sulfide and is mixed with zinc selenide or zinc telluride as an auxiliary component between an optically active layer and base material or right above the optically active layer. CONSTITUTION:ZnSe or ZnS added with ZnTe is used for the material of the heat resistant protective layer 4 to be provided between the optically active layer of an optical information recording member constituted by providing the optically active layer 3 on the transparent base material 1 and the base material or right above the optically active layer. The solid solubility limit increases larger than the solubility limit in an equil. state in the case of forming the thin film by quick cooling from the gaseous phase when the ZnTe is added to the ZnS; therefore, the force solutionization is possible up to about 15mo1%. The amt. of the ZnSe to be added is limited to max. 50mol% when the ZnSe is added to the ZnS. The stability of the heat resistant protective layer is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical information recording member that records, reproduces, and erases information at high speed and high density using optical means.

Conventional technology In erasable, non-destructive optical information recording members that can be repeatedly recorded and reproduced, such as optical disk memories, oxides and other materials are used to prevent the plastics used as the base material from being thermally damaged during laser heating. It has been proposed to provide a heat-resistant protective layer between the substrate and the optically active layer or directly above the optically active layer. Materials used as the heat-resistant protective layer include oxides (5i02, GeO2, 1120
5. BeO2), nitride (BN, 5isN417!N), carbide (SiC), chalcogenide (ZnS
, Zn5e), etc. have been proposed. -Generally,
The main characteristics required for a heat-resistant protective layer are (1)
(2) it has a melting point higher than the temperature at which it rises during operation; (3) it has high mechanical strength; and (4) it is chemically stable.

Problems to be Solved by the Invention Although the above-mentioned materials almost satisfy these conditions, they still do not completely satisfy the characteristics of an optical information recording member.

Particularly in the case of a rewritable optical memory, if the heat-resistant protective layer is altered by repeated laser irradiation heating and cooling, repeated recording and erasing reliability cannot be obtained. There remains room for improvement in the above-mentioned materials from the viewpoint of repeated recording/erasing life.

That is, the problem to be solved by the present invention is the deterioration of the heat-resistant protective layer, which is one of the causes that determines the repeated recording/erasing life of optical information recording members.

Means to Solve the Problems The present invention uses anine sulfide (ZnS), which has relatively good properties and fewer manufacturing problems among the materials for the heat-resistant protective layer.
Add selenium sulfide or tellurium sulfide to.

Function The function of the present invention is to add Zn5 to ZnS, which is the material of the heat-resistant protective layer.
By adding e or zn'ra, the stability and reliability of the heat-resistant protective layer can be improved.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a schematic cross-sectional view of the optical information recording member that is the basis of the present invention, where 1 is a base material, 2 and 4 are heat-resistant protective layers, 3 is an optically active layer, and 6 is a protective base material. It is attached with adhesive.

The properties of ZnS are shown in Table 1. Also Zn5
e, ZnTe is also shown in the same table. The refractive index tends to increase in the order of ZnS, znSe, and zn'ra. The refractive index of the heat-resistant protective layer is important. In the case of thin films, the transmittance is 1 depending on the film thickness due to optical interference effects.
This is because the reflectance changes. Ideally Table 1, ZnS
, Zn5a, ZnTe (7) Properties Table 2 Z
The mutual solid solubility of nS, Zn5e, and ZnTe is efficient when all of the incident light energy is absorbed by the optically active layer. In order to approach this condition, it is necessary to lower the reflectance. The non-reflection condition is approximately expressed as follows, where the thickness of the thin film located between the base material and the optically active layer is d1, the refractive index is n, and the wavelength is λ. The larger the refractive index n, the smaller d becomes.
Although it is convenient for manufacturing, if the difference in refractive index between the optically active layer and the heat-resistant protective layer becomes small, it becomes difficult to obtain a non-reflection condition.

In the case of an optically active layer containing Te as a main component, n) is 4, so the refractive index of the heat-resistant protective layer is preferably less than 3 and around 2.5. In the case of ZnS, n = 2.3, so this condition is met.

Table 2 shows the mutual solubility of ZnS, Zn5a, and ZnTe. The ZnS-Zn5a system is entirely solid solution, and Z
The nS-ZnTa system forms a solid solution only on the side of each base component, and Zn5
The a-ZnTe system is also entirely solid solution. Therefore, ZnS
When mixing 5e or ZnTe, it is necessary to consider solid solubility.

When adding ZnTe to ZnS, the solid solubility limit of ZnTe is a problem. As shown in Table 2, the solid solubility limit is 8 mol%, but when forming a thin film by rapid cooling from the gas phase, the solid solubility limit is higher than the equilibrium solid solubility limit, so it is forced to solidify up to about 15 mol%. Possible to melt.

When adding znse to ZnS, there is no problem like that of ZnTe because the whole is in solid solution, but as the fraction of znSe becomes larger, the refractive index n also becomes larger, making it difficult to obtain the above-mentioned non-reflection condition. The maximum amount of Zn5e added is 5
It is 0 mol%. In the case of adding ZnTe, the amount added is small, so even if the refractive index of ZnTe is 3.6, the change is small.

Example 1 ZnS added with Zn5e was created as a heat-resistant protective film on a polymethmethylacrylate (PMMA) substrate, then a TeGe5nO-based thin film was created as an optically active layer, and then the heat-resistant protective layer with the same composition was created. A sample was prepared by adhering it to a protective substrate.

The film thickness d of the heat-resistant protective layer on the base material side is set so as to provide a non-reflection condition. For example, in the case of ZnS, n = 2.3, so d = 90 nm assuming the wavelength of light λ = 8301 m.

Since n changes in the field where Zn5e is added, d was also changed accordingly. The thickness of the optically active layer is uniformly 1100n.
It is.

The upper heat-resistant protective layer directly above the optically active layer is λ/2n as a result of study.
It was found that the characteristics were best when In the case of ZnS, it is 1800 nm.

In order to investigate the effect of the amount of Zn5e added, the dependence on the Zn5e ratio was investigated. A mixed crystal of ZnS and Zn5e was produced using a binary thin film deposition apparatus shown in FIG. The substrate 7 is attached to the support jig 8, and the rotating shaft 9 is rotated.

ZnS and Zn5a were evaporated from evaporation source (1) 1o and evaporation source mark 11, respectively, and the composition was changed by controlling the evaporation rate. Although the heating method for the evaporation source is electron beam heating in this embodiment, it may be replaced by other conventional heating methods.

Compositional analysis was determined by determining the S/Ss ratio using xaI microanalysis.

The lifetime of the obtained sample was measured by repeatedly performing a static characteristic evaluation in which recording and erasing was performed by irradiating the same point with a laser beam. An example of static evaluation is shown in Figure 3.

The vertical axis is the reflectance, and the horizontal axis is the number of repetitions of recording and erasing. The upper diagram shows the case of ZnS alone, and the life is 105 times, but the lower diagram shows no change even after 10' cycles of ZnS added with 20 mol% of Zn5ei. Table 3 shows the composition dependence of the repeat life.

Table 3 Relationship between Zn5e addition amount and lifespan As can be seen from the above results, Zn5e is suitable for ZnS! If you add it, it will be recorded.
The number of times erasing can be repeated can be increased.

Example 2 As in Example 1, Zn was produced using the apparatus shown in FIG.
A heat-resistant protective layer made of a mixed crystal of S and ZnTe was created. The thickness of each layer was determined in the same manner as in Example 1.

The substrate is PMMA. In this case, since there is a solid solubility limit, the composition range studied is up to 25 mol % of ZnTe. Table 4 shows the repeated life based on static property evaluation.

4th Coordination: Relationship between amount of Zn5e added and lifespan As can be seen from the above results, when ZnTef is added to ZnS, the number of times recording and erasing can be repeated can be extended. The upper limit of the effective addition amount is 16 mol%.

Example 3 A ZnS thin film doped with ZnTe was formed on a base material such as polycarbonate (PC) using a sputtering thin film forming apparatus shown in FIG. The film thickness conditions for each layer are the same as in Example 1. The amount of ZnTe added was determined by using a composite structure of the polar target during sputtering.

The amount of ZnTe added was controlled by adjusting the area of several ZnTe pellets placed on a large ZnS target. The characteristics of the obtained sample were almost the same as in Example 2.

From the above three examples, the effect of adding ZnS K Zn5e and ZnTe is clear. The reason for this effect is not yet well understood, but it is probably because the growth conditions when forming the thin film are different from those for ZnS alone. That is, since ZnS has a high melting point (sublimes at 1800'C at 150 atmospheres and 1180'C at normal pressure), the bonding energy between atoms is also large, and surface microresonance of atoms is difficult to occur when forming a thin film. As a result, it is difficult to form a thin film with a uniform structure, and the film structure is full of gaps. If there are many gaps, sintering will occur during heating.
It easily shrinks and the heat-resistant protective layer deteriorates. Therefore, the following are possible reasons why the addition of Zn5e and ZnTe was effective.

Zn5a and ZnTe have lower melting points than ZnS and have lower interatomic bonding energy, so if the energy at the time of evaporation is the same, surface migration is more likely to occur. The structure of the resulting thin film is more uniform than that of ZnS and has fewer gaps. In this case, since the rate at which the gap is reduced by heating is small, the deterioration of the heat-resistant protective layer is also reduced. Furthermore, reducing the gap also has the effect of improving the weather resistance of the optically active layer. The main deterioration of the optically active layer under storage conditions is oxidation of the optically active layer.

If there are many gaps in the heat-resistant protective layer, oxygen and moisture will permeate to the optically active layer, resulting in faster deterioration.

The sample used in Example 1.2.3 was heated to 40'C.

When a storage test was conducted in an environment with 90% humidity, Zn5
Those to which E and ZnTe were added had a clear moisture-proofing effect.

For example, while a change was observed in the optically active layer after 30 days in the case of ZnS alone, no change was observed in the sample to which 10 mol % of ZnTe was added.

From the viewpoint of improving oxidation resistance, the present invention is also effective for optical recording members that use a magneto-optical effect and have a metal as an optically active layer. In particular, it is effective in improving the oxidation resistance of magneto-optical memories that use amorphous alloys of rare earths and transition metals.

Effects of the Invention The effects of the present invention are such that the heat-resistant protection material provided between the optically active layer and the substrate or directly above the optically active layer of an optical information recording member in which an optically active layer is provided on a transparent substrate is made of Zn5e or , by using ZnS to which zn'ra is added,
Deterioration of the heat-resistant protective layer can be prevented, and since the protective layer itself becomes dense, deterioration of the optically active layer can also be prevented.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an optical information recording member according to an embodiment of the present invention, Fig. 2 is a cross-sectional view of a binary evaporation apparatus for producing a heat-resistant protective film, and Fig. 3 is a cross-sectional view of an optical information recording member using a ZnS film doped with ZnS and Zn5e. FIG. 4 is a plan view of the target when the heat-resistant protective film of the present invention is created by sputtering. 1...Base material, 2...Heat-resistant protective layer, 3.
...Optically active layer, 4...Heat-resistant protective layer, 5
...Adhesive, 6...Protective base material, 7...
...Base material, 8...Base material support jig, 9...
... Rotating shaft, 10... Evaporation source (T), 11.
... Evaporation source (II), 12 ... Vacuum container, 13 ... Exhaust system, 14 ... Base material, 1
5... Base material support jig, 16... Cathode target, 17... High frequency power supply. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 7 10' is 103 10'105
ノ0'107 碌 Sending L @ number (times)

Claims (3)

[Claims] (1) A heat-resistant protective layer containing zinc sulfide as a main component and zinc selenide or aene telluride as a secondary component is used between the optically active layer and the base material or directly above the optically active layer. Optical information recording member. (2) The optical information recording member according to claim 1, wherein the fraction of zinc selenide is less than 50 mol percent. (3) The optical information recording member according to claim 1, wherein the fraction of aene telluride is less than 15 mol percent.