JPS63259855A - Optical type information recording member - Google Patents

Abstract

PURPOSE:To prevent deterioration of heat resistant protective layers and to improve recording and reproducing sensitivity by mixing plural compds. contg. compds. which do not solutionize each other and forming the grains to the smaller sizes thereby constituting the heat resistant protective layers. CONSTITUTION:This recording member is constituted of a substrate 1, the heat resistant protective layers 2, 4, an optically active layer 3, a metallic reflection layer 5, an adhesive agent layer 6 and a protective base material 7. The heat resistant protective layers 2, 4 are formed by mixing the plural compds. contg. the compds. which do not solutionize each other. These layers are constituted to the smaller grain sizes than the grain sizes in the case of forming the layers independently of the respective constituting compds. The compds. contain zinc sulfide as the chalcogenide of metal and silicon dioxide as the oxide. The particles are, therefore, uniformly pulverized and mixed to a solid soln. state by quick cooling from the vapor deposited matter. The improved reliability of the recording and reproduction is thus obtd. by the projection of laser light with the higher efficiency, the lower temp. rise and the decreased thermal damages of the protective layers.

Description

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

Conventional technology In nondestructive optical information recording members that can be erased and repeatedly recorded and reproduced, such as optical disk memories, heat-resistant materials such as oxides are used to prevent the plastics used as the base material from being damaged during laser heating. It has been proposed to provide a protective film 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 (SiO2, GeO2, Al2O3,
Be02), nitride (BN, 5i2N2.AIN),
Carbide (SiC), chalcogenide (ZnS, ZnSe
) have been proposed. The main characteristics required for a heat-resistant protective layer are (1) transparency in the wavelength range used, (2) melting point higher than the operating temperature, (3) high mechanical strength, (4) ) be chemically stable; (5) have appropriate thermal constants (thermal conductivity, specific heat), etc.

To explain these, it goes without saying that (1) is necessary for efficiently absorbing laser energy into the optically active layer, and (2) is necessary for the heat-resistant layer to change before the temperature at which the optically active layer thermally transforms. This is because it would be inconvenient if the material were to be exposed to water, (3) it would be a problem if it cracked especially during the heating and cooling process, and (4) it would be a problem if it hydrolyzed or deliquesced due to moisture. Finally, (5) is
Among optical information recording methods, in the case of the phase change type, recording and erasure are achieved by reversibly reciprocating between two phases by combining heating and rapid cooling or slow cooling. If the system is not properly controlled, the laser energy will not be used efficiently.

Therefore, the sensitivity to the irradiated laser power during recording and erasing is insufficient. In other words, a large amount of laser power is required to erase records.

Problems to be Solved by the Invention Although the above-mentioned materials almost satisfy these conditions, they still cannot be said to completely satisfy the requirements for optical information recording applications. Especially in the case of rewritable optical memory,
If the heat-resistant protective layer changes in quality due to repeated laser irradiation heating and cooling, sufficient reliability over repeated recording and erasing cannot be obtained.

The present invention aims to improve the deterioration of the heat-resistant protective layer, which is one of the factors that determine the repeated recording and erasing life of an optical information recording member, and the recording and erasing sensitivity.

Means for solving the problem The heat-resistant protective layer is composed of a mixture of a plurality of compounds, at least two of the constituent compounds of the mixture are compounds that do not dissolve in solid solution with each other, and the microstructural units in the protective layer are The structure is such that the size of the (grain) is smaller than the size of the microstructural unit (grain) when each constituent compound is formed alone.

Function: As a heat-resistant protective layer, a state is obtained in which very small structural units of at least two substances that do not dissolve into each other are forcibly dispersed into each other, changing the thermal properties of the heat-resistant layer. As a result, it is possible to improve the recording sensitivity of optical information recording and the reliability regarding repeated recording and erasing.

EXAMPLES Hereinafter, examples of the present invention will be described based on the accompanying drawings. FIG. 1 is a schematic cross-sectional view of an optical information recording member that is the basis of the present invention, in which 1 is a base material, 2 and 4 are heat-resistant protective layers, 3 is an optically active layer, and 5 is an optical reflective layer. This is a layer mainly made of metal, and the protective base material 7 is bonded with the adhesive 6. The present invention is characterized in that the heat-resistant protective layers 2 and 4 are made of specific materials. That is, when conventional materials such as germanium dioxide (Ge02), silicon dioxide (SiO2), and aene sulfide (ZnS) are used, their mechanical strength and thermal properties are insufficient.

When irradiated with a laser, if the mechanical strength at high temperatures is weak, the heat-resistant protective layer will be thermally deformed and cracked, or if there are many structural defects, the protective layer itself will shrink due to heating and become permanently deformed. In addition, in order to efficiently utilize the thermal energy of the laser, it is necessary to have appropriate thermal conductivity and specific heat. If the thermal conductivity is too large, extra energy is required, which is disadvantageous, and if it is too small, quenching conditions cannot be obtained.Quick cooling conditions are one of the most important optical information recording methods. In the case of a phase change type, recording and erasing are realized by reversibly moving back and forth between two layers by combining heating and rapid cooling or slow cooling, which is important.

The features of the present invention are to improve the recording and erasing characteristics by controlling the thermal constants while minimizing the mechanical properties and the noticeable thermal deformation at high temperatures, and to improve the recording and erasing characteristics. This improves reliability.In terms of actual design conditions for the protective layer, optically it is desirable that the absorption efficiency of the laser energy is high.To achieve this, the incident laser light must satisfy the non-reflection condition. The refractive index of an optically active layer containing Te as a main component is approximately 4, so in order to obtain a non-reflection condition, the refractive index of the heat-resistant protective layer should be 4 or less, and according to calculations, the refractive index should be 2 or more and 3 or less. The non-reflection condition is approximately expressed as follows, where N is the refractive index of the protective layer, d is the wavelength of the laser, and d is the thickness of the protective layer.

d=L/4N A typical material that satisfies this condition is aene sulfide (ZnS: N=2.3). However, as mentioned above, although ZnS has excellent initial characteristics, it was found through experiments that the repeated recording and erasing characteristics were not necessarily satisfactory, so the present inventors attempted to improve it. . The resulting material was a mixture of aene sulfide and silicon dioxide. Further experiments revealed that the particles that make up the thin film were uniformly atomized by rapid cooling from the gas phase, such as in vapor deposition, and were mixed together to force the two materials to form a solid solution. We have discovered a group of materials that exhibit novel properties as if they were formed as a solid solution. The characteristics of the components of this material group are that they do not form a solid solution with each other, but the combination of materials is a combination of crystalline materials and glassy materials. Examples of crystalline materials include the above-mentioned ZnS and ZnSe.
Examples of glassy materials or materials that promote vitrification include oxide glasses such as silicon dioxide and germanium dioxide.

It is not known why the properties improve when glass and chalcogenide are mixed. (By mixing glassy materials, the growth of microstructural units (grains or crystal grains) in the thin film structure of crystalline materials may be suppressed and become finer, or they may become amorphous and become less heat conductive.) It is thought that this is because the input laser energy efficiently contributes to increasing the temperature of the optically active layer by decreasing the size of the microstructure.The smaller the average size of the microstructural units, the better, but The microstructural units described in this invention are so small that no peak can be observed using a transmission electron microscope.
This is the measured value and means the final observed size, that is, the size (diameter) of the grains observed in the diffraction image of the crystal. Hereinafter, in the present invention, all particle sizes were determined by this method. It has been found that the particle size that is specifically effective is 10 nanometers or less, preferably 5 nanometers or less.

When the laser power is efficiently absorbed by the optically active layer,
Since less irradiation power is required and the temperature around the optically active layer does not rise during recording and erasing, thermal damage to the active layer and the heat-resistant protective layer is reduced accordingly. As a result, the number of times of recording and erasing increases, improving reliability.

Therefore, it is essential that the laser power required for recording and erasing is small in order to increase the number of repetitions of recording and erasing.Although not specified in each of the following examples, recording and erasing sensitivity was improved. When using a heat-resistant protective layer, the number of times static recording/erasing is repeated is at least 1.
It has been confirmed that the number is 0 to the 6th power or more. Chalcogen compounds generally have a large refractive index and can satisfy the condition of (N > 2), but oxide glasses often have a refractive index of 2 at most, so chalcogen compounds are blindly combined with glass. Although it is clear that forced mixing of quality materials is not good in terms of properties, the properties can be dramatically improved by mixing an appropriate amount. Specific examples by the present inventors are shown below.

Example 1 A heat-resistant protective layer made of a mixture of aene sulfide and silicon dioxide was created on a base material made of polymethyl methacrylate (PMMA) by a binary vapor deposition method. Aene sulfide (ZnS)
The mixing ratio of silicon dioxide and silicon dioxide was determined by controlling the amount of evaporation of each material, and quantitative chemical analysis was also performed. The deposition rate of the thin film is lnm7 seconds. The components of the optically active layer are TeGe5nO, which is a type of phase change material that can erase records by reversibly reciprocating between a crystalline state and an amorphous state, and the film thickness is 40r+m. . The heat-resistant protective layer has a thickness of approximately 100 nm and 200 nm on the substrate side and the upper side of the optically active layer, respectively.
m created. This film thickness structure was determined from the viewpoint of laser absorption efficiency and from the viewpoint of ensuring a large change in optical constants. Figure 3 shows the refractive index of the heat-resistant protective film itself obtained. The dependence of S i O2 on the mixed amount X is shown.

It has been shown that as SiO2 is added to ZnS, the refractive index decreases almost linearly. This is ZnS and S
This indirectly indicates that i O2 is not combined and mixed, but simply mixed. The same can be said of changes in the refractive index of other material combinations shown in the following examples. Table 1 shows S i
The minimum laser energy required for crystallization (erasing) and amorphization (recording) with respect to the amount of O2 added is shown. Table 1 shows Zn observed with a transmission electron microscope.
The average size of S grains is also shown.

This measurement was performed dynamically while rotating a disk-shaped disk, and the circumferential speed of the disk was approximately 5 l.
I/s. The wavelength of the laser is 830 nm, and the beam is focused to the diffraction limit on the disk. The power of the laser should be as small as possible (preferably, it can be dispensed with).

Table 1 Effect of adding 5i02 to ZnS It can be seen that when the amount of S i O2 added is lθ~30, there is an effect when the grain diameter is 10 nm.

By adding SiO2 to ZnS, the minimum energy required for crystallization and amorphization decreases, and as the amount of addition increases further, it begins to increase again. As is clear from this result, there is an optimum value for the amount of SiO2 added.

In this example, when the amount of SiO2 is 10 mol% or more and 30 mol% or less, the laser power required for crystallization is 6+nW to 7.5 mW, which is lower than 9 mW when there is no SiO2. I can see that Further, at this mixing ratio, the refractive index is approximately 2 or more, and optically the above-mentioned conditions are satisfied.

As shown above, when SiO2 is added to ZnS, there is an effect shown by a decrease in the laser power required for crystallization. Addition amount of S i 02 is 10~
It can be seen that it is effective at a concentration of 30 moles and a grain diameter of 10 nm.

FIG. 3 shows the change in reflectance when recording and erasing is repeatedly performed statically using a laser. Among the respective curves in FIG. 3, the upper side corresponds to the reflectance in the crystalline state, that is, the erased state, and the lower side corresponds to the amorphous state, that is, the recorded state. The difference in reflectance is proportional to the intensity of the recorded signal. It can be seen that the number of repetitions changes depending on the amount of 5i02 added. Furthermore, the laser power was determined to simulate the thermal load on the disk.

The projection of the power distribution of the laser used for recording onto the disk is adjusted so that it is approximately circularly symmetrical, and the distribution for erasing is adjusted so that it is elliptical. In this case as well, S i
The best results were obtained when 20 mol % of O2 was added, and it was possible to repeat the process more than 10 times.

Example 2 In Example 2, characteristics were obtained by forcibly dispersing and mixing SiO2 and ZnS using a means of rapidly cooling from a gas phase such as vapor deposition. The deposition rate at this time was 1 nm/sec. Under conditions where slow cooling occurs even from the same gas phase, such as when the deposition rate is extremely slow, the average grain diameter of ZnS increases, hindering dispersion and promoting phase separation, which not only improves sensitivity but also The number of repetitions of record deletion did not increase. In order to confirm the cause of this, the dependence of the laser power sensitivity for recording and erasing on the deposition rate was measured when the amount of 5in2 added was 25 mol %. Table 2 shows the results.

Table 2: Deposition rate vs. grain diameter As is clear from Table 2, when the grain diameter is large, extra laser power is required and the performance becomes worse. It can also be seen that the grain diameter also needs to be 10 nm.

The same can be said for any combination of materials in any of the embodiments described.

Example 3 A heat-resistant protective layer made of a mixture of aene selenide and silicon dioxide was prepared on a base material made of polymethyl methacrylate by a binary vapor deposition method. The ultimate vacuum degree is on the order of 10-6. The mixing ratio of ZnSe and silicon dioxide was determined by controlling the amount of evaporation of each material as in Example 1, and quantitative chemical analysis was also performed.

The same TeGe5nO components as in Example 1 were used for the optically active layer, and the film thickness was 100 nm. The heat-resistant protective layer is provided on the substrate side and on the top side of the optically active layer, each having a thickness of about 10
0 nm and 200 nm.

Next, Table 3 shows the minimum laser energy required for crystallization and amorphization with respect to the amount of SiO2 added. The measurement method is the same as in Example 1.

Table 3 Table 3 shows the effect of adding 5i02 to ZnSe.
The average size of ZnS grains observed with a transmission electron microscope is also shown.

As in Example 1, the laser energy required for crystallization and amorphization decreases by adding SiO2 to ZnSe, and begins to increase again when the amount added is further increased. As is clear from this result, S i O
It can be seen that there is an optimum value for the addition amount of 2.

In this example, when the amount of Si O2 is 15 mol % or more and 35 mol % or less, the grain diameter becomes 10 nm or less, and the laser power required for crystallization is 6 iW to 7.5 mW. 9mW without O2
It can be seen that it has decreased further.

As shown above, when SiO2 is added to ZnSe, there is an effect shown by a decrease in the laser power required for crystallization and amorphization. Further, when the composition is the same, static repetition of recording and erasing can be repeated 106 times or more as in Example 1.

Example 4 Chalcogenated aene, that is, aene sulfide (ZnS) was deposited on a base material made of polymethyl methacrylate by a binary vapor deposition method.
Alternatively, a combination of aene selenide (ZnSe) or aene telluride (ZnTe) and vitrified germanium dioxide (
GeO2), tin oxide (SnO2), indium oxide (
A heat-resistant protective layer made of a mixture of In202) and tellurium dioxide (TeO2) was prepared. The mixing ratio of chalcogenated enene (ZnX: The same TeGe5nO components as in Example 1 were used for the optically active layer, and the film thickness was 100 nm.
It is m. Heat-resistant protective layers were formed to a thickness of approximately 100 nm and 200 nm on the base material side and above the optically active layer, respectively.

Next, Table 4 shows the minimum laser energy required for crystallization and amorphization with respect to the amount of oxide added. The measurement method is the same as in Example 1. By adding a glassy oxide to the chalcogenated aene, the minimum energy required for crystallization decreases, and begins to increase again as the amount added is further increased. As is clear from this result, there is an optimum value for the amount of vitrification oxide added.

In this example, when the addition amount of S n O2 is 15 mol % or more and 35 mol % or less, the grain diameter becomes lonm or less, and the laser power required for crystallization is 6IIIW to 7iW, and the oxide glass It can be seen that this is lower than 91 when there is no. It can also be seen that the laser power required for amorphization is also reduced.

Almost similar results were obtained with the other two chalcogenated enenes and oxides.

Table 4 also shows the average size of ZnS grains observed with a transmission electron microscope.

-21= As shown in the above examples, it can be said that the present invention is effective in improving the characteristics of optical information recording members. In particular, it has great effects in efficiently utilizing incident laser power, increasing the number of recording and erasing operations, and improving reliability in protecting the optically active layer from acids and the like. In the above example, a crystalline material such as aene sulfide and a glassy material such as silicon dioxide were rapidly cooled from a gas phase, so that the particles constituting the thin film were made fine and forced into a solid solution. Although we have shown an example of a similar structure, this idea is unprecedented.

Effects of the Invention According to the present invention, in an optical information recording member comprising an optically active layer provided on a base material, between the optically active layer and the base material,
Alternatively, a heat-resistant protective layer made of a plurality of compounds is provided on the optically active layer, and at least two of the constituent compounds of the mixture are selected from those that do not dissolve in solid solution with each other. It is possible to increase the sensitivity to power or increase the number of repetitions of recording and erasing.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an optical information recording medium according to an embodiment of the present invention, FIG. 2 is a graph showing the refractive index of the ZnS+S i02 system, and FIG. 3 is a graph showing the repetition characteristics of the ZnS+S i02 system. It is. DESCRIPTION OF SYMBOLS 1... Base material, 2.4... Heat-resistant protective layer, 3... Optical active layer, 5... Adhesive layer, 6... Protective base material.

Claims (7)

[Claims] (1) A base material, an optically active layer provided on the base material, and a heat-resistant protective layer provided between the optically active layer and the base material or on the optically active layer, the heat-resistant protective layer consists of a mixture of a plurality of compounds, at least two of the constituent compounds of the mixture are compounds that do not dissolve in solid solution with each other, and microstructural units (grains) in the protective layer
1. An optical information recording member characterized in that the size of the grain is smaller than the size of a microstructural unit (grain) when formed from each constituent compound alone. (2) At least one of the compounds constituting the heat-resistant protective layer is glass or one that promotes vitrification;
2. The optical information recording member according to claim 1, wherein at least one of the members is crystalline. (3) The optical information recording member according to claim 1, wherein at least one of the compounds constituting the heat-resistant protective layer is a metal chalcogenide, and at least one of the compounds is an oxide. (4) Optical information recording according to claim 3, characterized in that at least one of the metal chalcogenides is a chalcogenated aene, and at least one of the oxides is a vitrified oxide. Element. (5) Chalcogenated enenes are ZnS, ZnSe and Z
At least one kind selected from nTe, and the vitrified oxide is SiO_2, GeO_2, SnO_2, I
The optical information recording member according to claim 4, characterized in that it is at least one selected from n_2O_2 and TeO_2. (6) The optical information recording member according to claim 1, wherein the average size of the microstructural units of the crystalline portion of the thin film constituents is 10 nanometers (nm) or less. . (7) ZnS and Z, which form the crystalline part of the thin film components
Claim 5 or 6, characterized in that the average size of microstructural units in the thin film of at least one selected from nSe and ZnTe is 10 nanometers (nm) or less optical information recording member.