JP2637982B2 - Optical information recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording member capable of recording and reproducing information signals at high density and at high speed using optical means such as a laser beam and rewritable.

2. Description of the Related Art Techniques for recording and reproducing high-density information using a laser beam are known, and currently applied to document file systems, still image file systems, and the like. Research and development has also been conducted on rewritable information recording systems, and examples have been reported. The active layer that controls the recording of the optical disc mainly contains chalcogen such as Te,
Or the compound (chalcogenide) is used as a main component. In these substances, an amorphous phase can be obtained relatively easily by heating and cooling, and the optical constant changes between the crystalline phase and the amorphous phase. By detecting this phenomenon, information is reproduced.

The amorphous phase is obtained by, for example, irradiating an intense and short pulse laser beam, raising the temperature of the irradiated portion to a liquid phase, and then rapidly cooling. On the other hand, the crystalline phase is obtained, for example, by irradiating a weak and long pulsed laser beam to heat and slowly cool the amorphous phase. Changes in optical constants are mainly observed as changes in reflectance.

In the case of a rewritable optical disk device, an amorphous phase is made to correspond to a recorded signal, and a crystalline phase is made to correspond to an erased state. That is, the state where the amorphous island is floating in the crystal sea is the pattern in which the information is recorded. This is more advantageous than the reverse case, because it is possible to cope with the rapid cooling condition at the time of recording that requires high-speed switching.

Elemental Te is stable as a crystal at room temperature and does not exist in an amorphous state. Therefore, addition of various elements to stably exist an amorphous phase at room temperature has been studied, and Ge is widely known as one of the typical additives.

Ge with strong covalent coordination number 4 has a certain concentration (about
Up to 30 atomic%), it penetrates into the chain of atoms (coordination number 2) by covalent bonds of Te and stabilizes the three-dimensional glass network structure. The structure becomes stable.

In other words, up to a Ge concentration of about 30 atomic%, the amorphous basic structure is a two-coordinate chain structure.
The scheme shows that the coordination structure is stabilized. Therefore, as Ge is added, the transformation temperature (Tx) between the amorphous state and the crystal shifts to a higher temperature side. However, although the addition of Ge increases Tx, the time required for crystallization (hereinafter, crystallization time) is still too long and insufficient for practical use in an actual optical disk device. Practically, the crystallization time (erasing time) needs to be set to several microseconds or less.

This is thought to be due in part to the large moment of inertia of the Te chain structure, which takes a long time to stop the movement (diffusion) of atoms during crystallization. From another viewpoint, this corresponds to the fact that the chain structure has a high viscosity and a high resistance to movement (a small damping coefficient). Second, the addition of Ge emphasizes the directionality of covalent bonds, reduces the degree of freedom of atomic bonding, and requires time for crystallization.

Therefore, in order to shorten the crystallization time, by changing from a structure mainly composed of covalent bonds with a strong bond direction to a structure mixed with more isotropic ionic and metal bonds,
It was anticipated that it would be necessary to partially break the chain and three-dimensional network structures so that atoms could freely diffuse and rearrange bonds.

Then, the present inventors added various elements for the purpose of destroying the chain structure, and examined the effects thereof. Before that, conventional optical recording materials based on Te—Ge (hereinafter referred to as recording films) include, for example, Ge ₁₅ Te ₈₁ Sb ₂ S ₂ (Japanese Patent Publication No. 47-26897). There is. However, the addition of small amounts of Sb and S stabilizes the amorphous state due to the nature of the element, but has little effect on promoting crystallization, so the crystallization time is about several tens of microseconds or more. Since the (erasing) time was long and the contrast ratio of the recording pattern was not sufficient, it was not practically satisfactory.

On the other hand, the present inventors have proposed a Te—Ge—Au alloy (Japanese Patent Application No.
-61137) or a Te-Ge-Sn-Au alloy (Japanese Patent Application No.
No. 0-112420) and the like, it has been found that the above-mentioned insufficient characteristics in a Te—Ge binary system are improved when specific amounts of Au and Sn are added. Au and Sn in these have a role of promoting crystallization by partially destroying a structure having strong covalent bonding, and the crystallization time is as short as several microseconds or less.

The present inventors have studied to obtain a recording material with higher performance, and found that the material system described below shows more excellent characteristics.

Problems to be Solved by the Invention However, in the above-mentioned rewritable optical disk medium, the erasing (crystallization) speed is sufficiently high to realize simultaneous erasing of writing while irradiating with a laser. Rather, improvements were required to be delivered in a practical time.

Means for solving the problem The change of the optical constant is shown in the optical information recording / reproducing medium for recording, reproducing and erasing information by causing the change of the optical constant using light, heat or the like. The active materials are tellurium, antimony and silver, and copper is added to the stoichiometric compound composition and its near composition.

Action By using the Te-Sb-Ag-Cu alloy, the erasing time of the recording / erasing characteristics can be shortened and the recording power can be reduced. .

Embodiment As described above, in a rewritable optical disk, it is necessary to shorten the erasing time, that is, crystallization, which requires more time than recording, in order to perform high-speed recording and erasing, and to obtain high performance.

To shorten the crystallization time, the present inventors have found that a considerable part of the amorphous structure is more isotropic than an amorphous structure composed of a network in which a covalent bond, which is a material anisotropic bond, is mainly used. The study was conducted from the viewpoint that it is necessary to form an amorphous network having various ionic bonds and metal bonds. As a result, Te-Sb-Ag
The possibility has been demonstrated in a quaternary alloy system consisting of -Cu. AgSb, which is a ternary compound containing no Cu
The characteristics are excellent in the case where Ag is replaced with Cu in the vicinity of Te ₂ and its compound composition.

FIG. 2 shows a phase diagram of the Sb ₂ Te ₃ -Ag ₂ Te pseudo-binary system. As a ternary compound, a compound called AgSbTe ₂ (beta phase) is known. This compound has two binary compounds at both ends of the phase diagram.
It is a mixture of 1: 1 with a crystal structure of rock salt type and a melting point of about 570 ° C. Since it is a rock salt type in which atoms are randomly distributed, a solid solution is formed from Sb ₂ Te ₃ . (Reference: Rose-Marie Maine et al. (Rose-Marie Ma
rin et al. J. Mater. Sci. vol. 20 (1983) 730.).

On the other hand, in the Sb ₂ Te ₃ -Cu ₂ Te alloy, a compound having a 1: 1 composition is not known. However, Ag and Cu are homologous elements in the periodic table, and it is considered possible to replace Ag with copper.
Therefore, in the present invention, an attempt was made to replace Ag with Cu, and as a result, good recording and erasing characteristics could be obtained.

The recording layer is formed on a transparent substrate by a method such as vacuum evaporation or sputtering, and the formed recording film is amorphous. FIG. 3 shows the structure of the recording medium. 1 is a substrate, 2 is a heat-resistant protective layer made of an inorganic substance for protecting the substrate from heat, 3 is a recording layer, 4 is a heat-resistant protective layer similar to 2 and a protective substrate of 6 is adhered with an adhesive of 5 I'm matching. Laser light for recording, reproducing, and erasing is made incident from one substrate side.

As the material of the substrate, glass, polycarbonate, or polymethyl methacrylate (PMMA) was used.

The thickness of the recording film is about 100 nm, and both sides are protected by a heat-resistant protective layer. Zinc sulfide (Zns) was used as the material of the heat-resistant protective layer. The thickness of the heat-resistant protective layer is optical,
And it was determined to be optimal in terms of thermal design. Specifically, 100 nm was provided on the substrate side, and 200 nm was provided on the recording film.

The characteristics of the obtained recording layer were examined by various means. Among them, what is required in the present invention is a crystallization temperature (Tx) as an erasing characteristic and the power and pulse width of a laser beam for starting crystallization. First, with regard to the crystallization temperature, a sample prepared on a glass substrate is placed on a stage where the temperature is rising at a constant rate of temperature rise, and the transmittance or reflectance is measured while irradiating weak laser light. And by determining the temperature at which they begin to change.

Crystallization time was measured by static and dynamic methods. In the static measurement, a heat-resistant protective layer is provided on the PMMA, and a simulated sample having the same structure as the optical disk is measured in a state where the medium and the laser beam are stationary. The presence or absence of a change in reflectivity after irradiation with a laser pulse having a specific intensity is measured, and a pulse width at which the change starts is obtained, and the obtained pulse width is used as a threshold for crystallization. The threshold value of the amorphous state was also measured by irradiating the sample once crystallized with laser again. In the dynamic measurement, an optical disk was actually prepared, and recording, reproducing, and erasing characteristics were measured. The substrate of the optical disk was made of polycarbonate.

Example 1 A stoichiometric compound Te ₅₀ Sb ₂₅ Ag as a recording film
(Ag ₈₅ Cu ₁₅ ) ₂₅ Sb ₂₅ Te ₂₅ , which is a composition obtained by substituting 15% Cu for _{25 in} FIG. 1 (A composition in FIG. 1), was prepared by a vacuum evaporation method, and the recording and erasing characteristics were measured. Recording film thickness is 10
For the heat-resistant protective layer at 0 nm, zinc sulfide was used. Tx of the obtained recording film was 130 ° C. FIG. 4 shows crystallization characteristics obtained by static measurement. As shown in the figure, the irradiation power is 2 mW
It can be seen that the crystallization start pulse width shifts to the short pulse side as it increases from 10 mW to 10 mW. In this embodiment, a crystallization start threshold value of 30 ns is obtained with a power of 10 mW.

Amorphization characteristics are as follows.
The same position irradiated with a single-second pulse of μ seconds was irradiated with a laser beam stronger than the power to measure. As shown in FIG. 5, a change in reflectance occurs at a power of 14 W or more, indicating that amorphousization has been achieved.

Example 2 As a recording film, Ag ₃₀ slightly shifted from the stoichiometric compound was used.
A ₃₀ Sb ₂₂ Te ₄₈ recording film in which a part of Ag of the Sb ₂₂ Te ₄₈ composition (FIG. 1: E composition) was replaced with Cu (Ag ₈₀ Cu ₂₀ ) was prepared by a vacuum deposition method, and the characteristics were measured. The thickness of the recording film was 100 nm, and the heat-resistant protective layer was made of zinc sulfide. Tx of the obtained recording film was 14
It was 0 ° C. FIG. 6 shows crystallization characteristics obtained by static measurement. As in Example 1, it can be seen that as the irradiation power is increased from 2 mW to 10 mW, the crystallization start pulse width shifts to the shorter pulse side. In this embodiment, a crystallization start threshold of 10 mW and a power of 100 ns is obtained.
The properties were almost the same as those of the composition.

Amorphization was also observed at a power of 14 mW or more, as in Example 1.

Example 3 As a recording film, Ag whose composition was slightly deviated from AgSbTe ₂ which is a stoichiometric compound in a Te-Sb-Ag ternary system was used.
A part of is replaced with Cu, and a composition in which the substitution is made by a vacuum evaporation method,
The properties were measured. The ratio of Ag and Cu is 80:20. The thickness of the recording film was 100 nm, and the heat-resistant protective layer was made of zinc sulfide.
The composition of the recording film obtained in Table 1, the crystallization temperature Tx, and
3 shows a threshold of crystallization onset by static measurement. The irradiation power at that time was set to 10 mW. The composition exhibited substantially the same properties as the composition of Example 1. The table also shows the threshold value of the start of amorphization when the laser power is 18 mW. As is clear from Table 1, it can be seen that there is a region where the crystallization rate is large, centering on the composition near A in FIG. In particular, the first
In the area surrounded by points F, G, H, J, K, and L, the crystallization threshold is 2
00n seconds or less. The reason why this region is wide especially in the direction rich in SbTe ₃ around the point A is considered to be due to the existence of the solid solution phase (beta phase) shown in FIG.

Example 4 In the same manner as in Example 3, a composition in which a part of Ag was substituted with Cu but slightly shifted from AgSbTe ₂ was prepared by a vacuum deposition method, and the characteristics were measured.

The ratio of Ag and Cu is 50:50. Example 3
Is the same as Table 2 shows the composition of the obtained recording film, the crystallization temperature Tx, and the threshold value of the crystallization start by static measurement. The irradiation power at that time was set to 10 mW. The table also shows the threshold value of the start of amorphization when the laser power is 18 mW. As is evident from Table 2, also in this example, there is a region where the crystallization rate is large, centered on the composition near A in FIG. In particular, FIG.
The crystallization temperature is 200 ns or less in the region surrounded by the H, J, K, and L points.

Example 5 A stoichiometric compound (Ag ₆₀ Cu ₄₀ ) ₂₅ Sb ₂₅ Te 50 was prepared by a vacuum deposition method as a recording film in the same manner as in Example 1.
The dynamic characteristics of the optical disk were measured. The thickness of the recording film was 100 nm, and the heat-resistant protective layer was made of zinc sulfide. The disk used was 5.25 inches, and the relative speed between the laser beam and the disk was 11 m / s. FIG. 7 shows the relationship between the writing power and the CN ratio (carrier-to-noise ratio) for recording at a frequency of 5 MHz. As can be seen from the figure, the recording power is 8 mW
It can be seen that the CN ratio increases as the power is increased to 20 mW.

FIG. 8 shows the erase characteristics of the recorded signal. The horizontal axis is the power of the erasing laser beam, and the vertical axis is the erasing rate. The shape of the laser beam to be erased is circular, and the power has a Gaussian distribution. The power of the recording signal was 16 mW. Erasure (crystallization) was performed by irradiating a laser beam in a DC manner. It can be seen that crystallization (erasing) is sufficiently performed even under this condition.

Example 6 As a recording film, a stoichiometric compound of Te ₅₀ -Sb ₂₅ -Ag
(Ag ₆₀ Cu ₄₀ ) ₂₅ Sb in which 40% of Ag in ₂₅ was replaced by Cu
₂₅ Te ₅₀ (FIG. 1: composition A) was directly formed on a quartz substrate by vacuum evaporation, and the crystallization process was followed by X-ray diffraction. The film thickness is
Silicon dioxide was coated at 50 nm to prevent scattering of sublimable elements at 100 nm. Tx of the obtained recording film is 130 ° C
100 ° C., 200 ° C. in an argon atmosphere and
After heat treatment at 350 ° C., X-ray diffraction measurement was performed. The results are shown in Table 3. A composition is stoichiometric Ag
Since a part of Ag of SbTe ₂ is replaced by Cu, after complete crystallization, diffraction lines of AgSbTe ₂ are mainly observed, and other weak intensity Cu ₂ Te or CuTe The diffraction line corresponding to was observed.

As can be seen from this fact, it is understood that this recording film is almost composed of a single-phase compound.

Example 7 As a recording film, a stoichiometric compound of Te ₅₀ -Sb ₂₅ -Ag
₂₅ (Point A in Fig. 1) Peripheral composition (B, C, D, G,
A recording film in which 10% of Ag in (J, K points) is replaced with Cu is directly formed on a quartz substrate by vacuum evaporation, and then heat-treated for crystallization. The resulting compound is then subjected to X-ray diffraction. Identified. The film thickness was 100 nm, and silicon dioxide was coated to a thickness of 50 nm to prevent scattering of sublimable elements. 350 ° C in an argon atmosphere
After the heat treatment, X-ray diffraction measurement was performed. The results are shown in Table 4.

The composition after crystallization is a compound having the same structure as the stoichiometric compound AgSbTe ₂ and a small amount of Sb ₂ Te ₃ , Ag ₂ Te, a small amount of CuTe,
Or it turned out to be composed of a mixture of Cu ₂ Te. In addition, although the table did not show the Te compound of Cu, a small amount was contained in each case.

Effects of the Invention According to the present invention, an alloy composed of tellurium, antimony, and silver, particularly, a stoichiometric ternary compound having a composition of Te ₅₀
To increase the erasing (crystallization) speed of a rewritable optical disk to a practical speed by using a material in which Ag in an alloy centered on Sb ₂₅ Ag ₂₅ is partially replaced with Cu for the active layer And the sensitivity to laser light during recording can be improved.

[Brief description of the drawings]

FIG. 1 is a composition diagram showing the composition range of the material for a Te—Sb—Ag—Cu recording medium of the present invention, FIG. 2 is a binary alloy phase diagram of Sb ₂ Te ₃ —Ag ₂ Te, and FIG. FIG. 4 is a static crystallization characteristic diagram, FIG. 5 is a static amorphous characteristic, FIG. 6 is a static crystallization characteristic diagram, and FIG. 7 is a recording power of a CN ratio. FIG. 8 is a graph showing the erasing power dependency of the erasing rate.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-219692 (JP, A) JP-A-61-270190 (JP, A) JP-B-47-26897 (JP, B1)

Claims (3)

(57) [Claims] 1. An active material exhibiting a change in an optical constant in an optical information recording / reproducing medium for recording, reproducing, and erasing information by causing a change in an optical constant using means such as light or heat. But tellurium (Te), antimony (S
b) An optical information recording medium characterized by being an alloy comprising silver (Ag) and copper (Cu). 2. A composition stoichiometric ternary compound of the active material _{(Te 50 Sb 25 Ag 25)} Te 50 a part of Ag was replaced by Cu and Sb
_2. The optical information recording medium according to claim 1, wherein ₂₅ (Ag _100-x Cu _x ) ₂₅ (0 <x ≦ 50). 3. The composition of the active material in the range surrounded by F, G, H, J, K, L in FIG. 1 showing a triangular composition diagram having Te, Sb, and Ag as vertices. 2. The optical information recording medium according to claim 1, wherein the composition is a composition in which part of Ag is replaced with Cu, and the amount y of the Ag replaced by Cu is 0% <y ≦ 50%. .