JP2685754B2 - Information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is directed to irradiating a light beam, such as a laser beam, between a crystalline phase and an amorphous phase in a recording layer. The present invention relates to an information recording medium that records and erases information by causing a phase change. (Prior Art and Problems Thereof) A phase change type optical disc has been known as an optical disc from which information can be erased. In this phase change type optical disc, by irradiating the recording layer with a laser beam,
Information is recorded and erased by utilizing the reversible phase change of the recording layer between, for example, crystalline and amorphous. Examples of such phase change materials include Te, Ge,
There are semiconductors such as TeGe, InSe, SbSe, SbTe, semiconductor compounds or intermetallic compounds. These selectively take two states, a crystalline phase and an amorphous phase, depending on the temperature, and the complex refractive index expressed by N = n-ik is different in each state. Information is recorded and erased by reversibly changing these two states (SROvshinsky
Metallurgical Transactions 2 641 1971). In the case of this technique, the recording level is high because the reflectance is significantly different between the crystalline phase and the amorphous phase. However, all of these materials have a disadvantage that the erasing speed is low because the crystallization speed is slow. On the other hand, unlike the above-described method, there is also a technique of recording and erasing information by reversibly changing the phase between different crystalline materials by irradiation with a laser beam. An In-Sb alloy is known as a material that undergoes such a phase change. In the In-Sb alloy thin film, a fine crystal portion grows into a relatively large crystal in a short time by irradiation with a laser beam having a relatively large pulse width. These two crystal structures have different complex refractive indexes, and when reproducing by irradiating a laser beam, for example, the crystal states are distinguished as a difference in the amount of reflected light.
In this case, if the recording layer composition is an In ₅₀ Sb ₅₀ intermetallic compound, the intermetallic compound is extremely fast in ordering (ordering) at a short distance between atoms by laser beam irradiation.
Crystallization during initialization and erasure can be made extremely fast, and the above-mentioned defects of the recording layer for recording and erasing information due to the phase change between crystalline and amorphous can be eliminated. However, when forming a recording layer with In ₅₀ Sb ₅₀ , it is difficult to record information. That is, In-Sb
When a recording layer is formed of an alloy to change the phase between different crystal phases, In ₅₀ Sb ₅₀ crystal grains are generated by laser beam irradiation.
Information is recorded and erased by becoming a mixed phase with Sb crystal grains and changing the size of Sb crystal grains depending on the irradiation condition of the laser beam, so if Sb is not excessive in the In-Sb alloy, information is recorded. Not done. On the other hand, In-
When Sb alloy is used as the recording layer, Sb has a low crystallization speed, so the initialization and erasing speeds are low, resulting in poor initialization and unerased residue. Thus, using the In-Sb alloy as a recording layer, when recording and erasing information between different crystal phases, there are the disadvantages as described above, but In ₅₀ Sb ₅₀ has a high crystallization rate, It is thought that the above problems can be solved by forming a recording layer with In ₅₀ Sb ₅₀ and causing a phase change between a crystalline phase and an amorphous phase to record and erase information. To be However, when the recording layer is formed of In ₅₀ Sb ₅₀ , actually, even if the recording layer is irradiated with a laser beam having a high output of 20 mW, the phase change from the crystal chamber to the amorphous state does not occur.
That is, the phase change between crystalline and amorphous may or may not occur depending on the alloy composition of the recording layer, and even if the alloy has a composition expected to have good characteristics as the recording layer. Even if the recording layer is formed, it is not always possible to record and erase the recording by causing a layer change between crystalline and amorphous. According to the experience of the inventor of the present application, a binary or ternary phase diagram is usually used when searching for a material and a composition that can change a phase between crystalline and amorphous and can be used as a recording layer. Based on, the melting point is 300-600 ℃, the crystallization temperature is about 15
Select an alloy whose composition is 0 ° C or higher. Because in order to form amorphous recording pits by laser beam irradiation, the material must be melted once and then rapidly cooled, so the melting point must be low to some extent,
In addition, the crystallization temperature must be high to some extent so that the amorphous recording pits once formed do not crystallize under a normal environment. However, even with a binary or ternary alloy prepared on the basis of such criteria, if the cooling rate after laser beam irradiation is low, it will be cooled as it is and crystallized without forming amorphous recording pits. In some cases, In addition, depending on the material, the crystalline material is more stable, so that the material may not be made amorphous, or even if it is once melted by the irradiation of a laser beam, it may naturally return to the crystalline material. Crystallization temperature is 150
C. or higher is a guideline only, and there is no compensation that the amorphous is stable at a temperature higher than that. According to a recent report, after making a sample of an information recording medium, the crystallization temperature is measured while changing the temperature rising rate, and a so-called Kinger plot is created to change from amorphous to crystalline. Methods for estimating the variability, that is, the lifetime of an amorphous material have been proposed, but these have the disadvantage that a sample must be prepared once and complicated measurement and calculation must be performed. As described above, conventionally, there is no means for easily and surely predicting the stability of an amorphous material before preparing a sample. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an information recording medium having a recording layer capable of reliably changing the phase between crystalline and amorphous. [Structure of the Invention] (Means for Solving the Problems) The information recording medium according to the present invention undergoes a phase change between a crystalline phase and an amorphous phase when irradiated with a light beam. An information recording medium having a recording layer on which information is recorded and erased, wherein the recording layer is composed of two or more elements,
It is characterized in that it is formed of an alloy whose mixing enthalpy in the liquid phase is lower than that in the solid phase at room temperature. (Operation) As a result of various investigations by the inventors of the present application, a recording layer is formed of an alloy composed of two or more elements, and a layer change between crystalline and amorphous is caused in the recording layer to obtain information. In order to cause this phase change in the information recording medium for recording and erasing, the alloy must be able to exist thermodynamically stably in an amorphous state at room temperature. It was found that the mixing enthalpy should be lower than that of solid phase. The present invention has been made on the basis of such knowledge, and by forming at least such a recording layer a phase change between crystalline and amorphous by irradiation of a light beam, It is possible to erase the record. (Example) Hereinafter, the Example of this invention is described concretely. The reason why the In ₅₀ Sb ₅₀ alloy layer does not become amorphous no matter how high the power of the laser beam is irradiated is that in the case of In ₅₀ Sb ₅₀ , the mixing enthalpy of the solid phase at room temperature is the liquid phase of the In-Sb alloy. This is because it exists below the mixed enthalpy curve of. That is, in order for the amorphous state to exist stably at room temperature, the mixing enthalpy of the liquid phase needs to be lower than the mixing enthalpy of the solid phase as described above.
In ₅₀ Sb ₅₀ is an intermetallic compound, and since the intermetallic compound is thermodynamically extremely stable in the crystalline state, the mixing enthalpy of the solid phase is extremely low. Has a lower mixing enthalpy. As described above, an In ₅₀ Sb ₅₀ is lower in enthalpy of mixing of the solid phase than enthalpy of mixing of the liquid phase, Eze and phase change between the crystalline and amorphous, such tendency, an In _x Sb
_Although it exists even when x is 35 to 80 in _100-x alloy, the composition region that can become amorphous is increased by adding a third element that can lower the mixing enthalpy of liquid phase to In-Sb alloy. Can be made. For example, when Te is used as the third element, the liquid phase mixing enthalpy can be reduced. Figure 2 shows In-Sb-
Is isenthalpic curve of Te alloy (G. Gather, B. Leque
ndre and R. Blacknik Journal of Less-Common
Metals 77 (1981) 71). As shown in the figure, in In _x Sb, when x is 35 to 80, the mixing enthalpy of the liquid phase is −2500 to −5000 J / mol. This value is higher than the mixing enthalpy of the solid phase, and even if the alloy layer of this composition is irradiated with a light beam, it does not become amorphous. However, in the figure, in the composition where the liquid phase mixing enthalpy is smaller than -5000 J / mol, this value is lower than the solid phase mixing enthalpy, and it can be sufficiently amorphous by irradiation with a light beam. Therefore, by forming the recording layer with such a composition, the layer can be reversibly changed between crystalline and amorphous. The details will be described below. The information recording medium according to this embodiment is configured, for example, as shown in FIG. The substrate 11 is made of a material that is transparent and does not easily change with time, such as a polycarbonate resin. The substrate 11 includes a protective layer 12 and a recording layer.
13, the protective layer 14 and the outer protective layer 15 are formed in this order. The protective layers 12 and 14 are formed of SiO ₂ and prevent the recording layer 13 from evaporating and forming holes during recording and erasing. The outer protective layer 15 is formed of an ultraviolet curable resin and has a function of preventing scratches and the like from being generated on the surface in handling the disc. The recording layer 13 is made of In _X Sb _Y Te _Z.
It is formed of an alloy having a composition of, so that the mixing enthalpy of the liquid phase shows a value smaller than -5000 J / mol,
The X, Y, Z values are adjusted. When the recording layer 13 has such a composition, it is possible to change the phase between crystalline and amorphous by irradiation with a light beam such as a laser beam. Within the range satisfying such conditions, the recording layer 13 is X,
Samples formed by using alloys having various values of Y and Z were prepared. As an example where the mixing enthalpy of the liquid phase is smaller than −5000 J / mol and is −10,000 J / mol or more, In ₅₀ Sb ₄₀ Te ₁₀ , In ₄₅ Sb ₄₅ Te ₁₀ , In _31.5 Sb _58.5 Te ₁₀ shown by crosses in FIG. , In ₁₆ Sb ₆₄ Te ₂₀ were prepared and designated as group A. In addition, as an example where the mixing enthalpy of the liquid phase is about −10,000 J / mol, In ₄₂ Sb ₄₃ Te ₁₅ , In ₇₃ Sb ₁₂ Te ₁₅ , In ₆₂ Sb ₂₅ Te ₁₃ shown by circles in FIG. It was set as sample B group.
Hereinafter, as an example in which the mixing enthalpy of the liquid phase is about 15000 J / mol, In ₇₆ Sb ₁₁ Te ₂₃ , In ₃₆ Sb ₃₇ Te ₂₇ , In ₅₄ Sb ₂₃ Te ₂₃ shown by triangle marks in FIG. As an example of 20000 J / mol, In ₅₉ Sb indicated by a square mark in Fig. 2
₁₀ Te ₃₁ , In ₄₆ Sb ₀₀ Te ₃₄ , and In ₃₁ Sb ₂₈ Te ₄₁ were used as the sample D group. Such an optical disc is manufactured as follows.
First, the substrate 11 is placed in a sputtering apparatus, and a SiO ₂ target is used to perform sputtering in an argon atmosphere,
A protective layer 12 made of O ₂ is formed. Then, while maintaining the same atmosphere, the recording layer 13 having a predetermined composition is formed by simultaneous ternary sputtering with a target made of each constituent element of the recording layer or sputtering with a target adjusted to a recording layer composition to be obtained in advance. To form. After that, the protective layer 14 made of SiO ₂ is formed again by sputtering the SiO ₂ target, then the substrate is removed from the sputtering apparatus, and the ultraviolet curable resin is applied on the protective layer 14 by the spin coating method. To form the outer protective layer 15. Next, the results of evaluating the characteristics of the above-described sample groups A to D by a dynamic evaluation device are shown. In this case, all the samples were amorphous immediately after the film formation. Moreover, the rotation speed of the disk was set to 900 rpm. The evaluation process will be described below. Initialization The recording layer 13 is amorphous immediately after it is formed.
The recording layer 13 is crystallized by irradiating 13 with a laser beam having an output of 5 mW continuously. Recording On the initialized recording layer 13, the output is 10 mW and the pulse width is
Amorphous recording pits 17 are formed by irradiating a pulsed laser beam 16 with 100 ns and a duty ratio of 50%. Information is read by irradiating the recording layer with a relatively weak laser beam and detecting the intensity of the reflected light. Erasing The recording pit 17 is irradiated with a laser beam under the same conditions as in the case of initialization, and this portion is recrystallized to erase information. Table 1 shows the results of the characteristic evaluation performed in this manner. As shown in this table, although the reproduction signal levels of the samples A to D are almost the same, the erase characteristics of the A and B groups were the same.
Remaining erasure was confirmed in groups C and D. In addition, as a result of conducting an environmental test on these samples in an environment of a temperature of 65 ° C. and a humidity of 85% and grasping a change in reflectance, in the samples C group and D group containing a relatively large amount of Te,
Although a decrease in reflectance due to the oxidation of Te was confirmed, the samples A and B had almost no deterioration. From the above results, it was confirmed that among these samples, the erasing characteristics and the environmental resistance characteristics were good even in the samples A and B having a small Te content at a high rotation speed of 900 rpm. Was done. That is, it was found that even an InSb alloy film that could not be made amorphous conventionally can be easily made amorphous by adding a small amount of Te. On the other hand, the sample C group and the D group can easily form the amorphous recording pits, but since they contain a relatively large amount of Te, erasure residue occurs and the environmental resistance is also high. It was poor. As a result of morphological observation of the recording pit portion and the erased portion of the above sample with a transmission electron microscope (TEM), the erased portion is a crystal in each of sample groups A to D,
The recording pits were microcrystals in which sample group A was amorphous and fine crystals were scattered, and sample groups B to D were completely amorphous. As described above, in this example, when the recording layer was formed of an alloy, the possibility of phase change between crystalline and amorphous was judged by focusing on the mixing enthalpy of the liquid phase. Thus, the melting point and crystallization temperature of the alloy are more reliable than judging the possibility of phase change between crystalline and amorphous. In this embodiment, the case where the In—Sb—Te ternary alloy is used as the recording layer has been described, but the present invention is not limited to this, and other binary ternary alloys or alloys of more elements are used. The present invention can also be applied to the case where the recording layer has a recording layer, and the point is that the mixing enthalpy of the liquid phase is lower than that of the solid phase. EFFECTS OF THE INVENTION According to the present invention, since the recording layer is made of an alloy having a mixed enthalpy of liquid phase smaller than that of solid phase, the light beam irradiation portion of the recording layer is made of crystalline and amorphous. It is possible to surely change the phase between. That is, in the information recording medium of the type that records and erases information by utilizing the phase change between crystalline and amorphous, by selecting the composition as described above when selecting the alloy composition of the recording layer. ,
The proper composition can be reliably selected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the present invention, and FIG. 2 is a view showing an isenthalpy curve of an In—Sb—Te ternary alloy system. 11; substrate, 12, 14, 15; protective layer, 13; recording layer, 16; laser beam, 17; recording pit

Claims (1)

(57) [Claims] Of a substrate and an alloy provided on the substrate and composed of two or more elements having a mixed enthalpy of liquid phase lower than the mixed enthalpy of solid phase at room temperature, an alloy excluding the following composition ranges (a) to (c) And a recording layer that changes in phase between a crystalline phase and an amorphous phase when irradiated with a light beam, the information recording medium. (A) in atomic%, a range represented by _{(R x -Sb 1-x)} y Q 1-y wherein, R in the formula is Ga or an In, Q is Se or Te, x
= 0.46 to 0.54, y = 0.94 to 1.00. (B) in atomic%, the _{In x Sb y Te z, 5} ≦ x ≦ 25,25
Ranges of ≦ y ≦ 45, 30 ≦ z ≦ 70, and x + y + z = 100. (C) Te, In as main components, Se, Ge, As, Ga, Sb, S, A
u, Cu, Pb, consisting of an alloy containing at least one element selected from the element group of Pd, the atomic content ratio of Te and In is 1: 1 ~ 1: 9
And a range in which at least one element selected from the group of elements Se, Ge, As, Ga, Sb, S, Au, Cu, Pb, and Pd is contained at 3 to 30 atomic%. 2. The recorded signal was erased by changing the phase to the crystalline phase after the information was recorded, with respect to the reproduction signal level obtained when the information was recorded by changing the phase to the amorphous phase. If the ratio of the reproduced signal level obtained in
The information recording medium according to claim 1, wherein the content is 30% or less. 3. Mixing enthalpy of liquid phase at room temperature is 5000 J / mol
The information recording medium according to claim 1, wherein the information recording medium is smaller than the above and has an enthalpy range of -20,000 J / mol or more. 4. The recorded signal was erased by changing the phase to the crystalline phase after the information was recorded, with respect to the reproduction signal level obtained when the information was recorded by changing the phase to the amorphous phase. If the ratio of the reproduced signal level obtained in
The information recording medium according to claim 3, wherein the content is 30% or less. The alloy composition is adjusted so that the mixing enthalpy of the liquid phase at room temperature is lower than the mixing enthalpy of the solid phase by adding other elements to the elements of 5.2 or more. A method for manufacturing an information recording medium, which comprises forming a recording layer that undergoes a phase change between a crystalline phase and an amorphous phase when irradiated with a light beam.