JP2687358B2 - 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 medium 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 an optical disk mainly contains chalcogen such as Te or its compound (chalcogen compound). In these substances, an amorphous phase can be relatively easily obtained 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, for example, by irradiating an intense and short pulsed 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 irradiated with, for example, a weak and long pulsed laser beam to heat the amorphous phase.
It is obtained by cooling. 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. Compared to the case where this is the opposite, it is possible to deal with the rapid cooling condition at the time of recording that requires high-speed switching,
It is advantageous. Te alone is stable as a crystal at room temperature and does not exist in an amorphous state. Therefore, in order to make the amorphous phase stably exist at room temperature, addition of various elements has been studied, and Ge is widely known as one of the typical additives. Ge, which has a strong covalent bond with a coordination number of 4, penetrates into a chain of chain-like atoms (coordination number of 2) due to the covalent bond of Te up to a certain specific concentration (about 30 atom%), and is three-dimensional. Since it stabilizes the typical glass network structure, the addition of an appropriate amount stabilizes the amorphous structure even at room temperature. 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 between the amorphous state and the crystal (or crystallization temperature (Tx)) shifts to the high 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, it is necessary to set the crystallization time (erasing time) 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 predicted that it would be necessary to partially destroy the chain-like optical image and the three-dimensional network structure so that atoms could freely diffuse and recombine bonds. Then, the present inventors added various elements for the purpose of destroying the chain structure, and examined the effects thereof. Prior to that, as a conventional example, an optical recording material based on Te-Ge (hereinafter referred to as a recording film) includes, for example, Ge ₁₅ Te ₈₁ Sb ₂ S ₂ (Japanese Patent Publication No. 47-26897). is there. However, addition of a small amount of Sb and S stabilizes the amorphous state due to the nature of the element, but has little effect of promoting crystallization, so the crystallization time is approximately several tens of microseconds or more, and Since the (erasing) time is long and the contrast ratio of the recording pattern is 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.
No. 61137) or a Te-Ge-Sn-Au alloy (Japanese Patent Application No.
No. 0-112420), when the specific amount of Au and Sn is added, T
It has been found that the above-mentioned insufficient properties in the e-Ge binary system are improved. These Au and Sn play a role of promoting crystallization by partially destroying the structure having a strong covalent bond, and the crystallization time is shortened to 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. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In order to realize simultaneous erasure by writing while erasing by irradiating a laser, the purpose is to shorten the time required for erasing (crystallization) to a practical range. Means for Solving the Problem In an optical information recording / reproducing medium that records, reproduces, or erases information by causing a change in the optical constant by using a means such as light or heat, an activity showing a change in the optical constant. The materials are tellurium (Te), antimony (Sb), and silver (A
g) and the composition of the alloy is Te / Sb / Ag
B-F-G-H in FIG.
Within the range connecting -C, the range excluding point A of the stoichiometric composition. Action By using a Te-Sb-Ag alloy, it is possible to shorten the erasing time particularly in the recording and erasing characteristics. Example As described above, in a rewritable optical disc, crystallization, which requires more time than recording, that is, shortening the erasing time, is necessary for high-speed recording and erasing to bring out high performance. In order to shorten the crystallization time, the inventors of the present invention have considered that a substantial part of the material is isotropic rather than an amorphous structure composed of a network in which covalent bonds, which are anisotropic bonds, are mainly used. The study was added from the viewpoint that it is necessary to form an amorphous network in which various ionic bonds and metal bonds are mixed. As a result, it was proved that Te-Sb-Ag ternary alloy system as a recording material has the possibility. 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 a stoichiometric composition called AgSbTe ₂ (beta phase) is known. This compound is made by mixing the binary compounds at both ends of the phase diagram in a ratio of 1: 1 and has a bond 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 Marin et al., J. Mater. Sci. vol.20
(1983) 730.). A method such as vacuum deposition or sputtering can be applied to the recording layer, which is formed on the transparent substrate, and the recording layer after formation 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 material for protecting the substrate from heat, 3
Is a recording layer, 4 is a heat-resistant protective layer similar to 2, and the protective substrate of 6 is bonded with the adhesive of 5. Laser light for recording, reproducing, and erasing is made incident from one substrate side. The material of the substrate 1 is glass, quartz, polycarbonate,
Alternatively, polymethylmethacrylate (PMMA) was used. The film thickness of the recording film 3 is about 100 nm, and both sides thereof are protected by the heat resistant protective layers 2 and 4. Zinc sulfide (ZnS) was used as the material of the heat-resistant protective layers 2 and 4.
The thickness of the heat-resistant protective layer was determined to be optimal in terms of optical and thermal design. Specifically, the heat-resistant protective layer 2 on the substrate 1 side was provided with 100 nm, and the heat-resistant protective layer 4 on the recording film 3 was provided with 200 nm. 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, regarding the crystallization temperature, place the sample prepared on the glass substrate on the stage that is heating at a constant temperature rise rate, and measure the transmittance or reflectance while irradiating weak laser light. And by measuring the temperature at which they start 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 disc is used, and the measurement is performed with the medium and the laser light stationary. The presence or absence of a change in reflectance after irradiation with a laser having a specific intensity while changing the pulse width is measured, and the pulse width at which the change starts is determined and used as the threshold for crystallization. The threshold for amorphization was similarly measured by irradiating the once crystallized sample with laser again. In the dynamic measurement, an optical disk was actually prepared, and recording, reproducing, and erasing characteristics were measured. Polycarbonate was used for the substrate of the optical disc. Reference Example 1 As a recording film, a stoichiometric compound of Te ₅₀ Sb ₂₅ Ag was used.
₂₅ (composition at point A in FIG. 1) was formed into a film by the vacuum evaporation method, and the recording and erasing characteristics were measured. The thickness of the recording film is 100n
m, and zinc sulfide was used for the heat-resistant protective layer. The Tx of the obtained recording film was 110 ° C. FIG. 4 shows crystallization characteristics obtained by static measurement. As shown in the figure, as the irradiation power is increased from 2 mW to 10 mW, the crystallization start pulse width shifts to the short pulse side. Also, from the figure, 30n with 10mW power
It can be seen that the crystallization threshold of seconds is obtained. Amorphization characteristics are as follows.
The measurement was performed by irradiating the same position as the position of the recording film irradiated with a single pulse of μ second with a laser beam stronger than the power. As shown in FIG. 5, the change in reflectance occurs at a power of 14 mW or more, which indicates that the amorphous state is realized. Reference Example 2 As a recording film, a stoichiometric compound Te ₅₀ Sb ₂₅ Ag ₂₅ (composition at point A in FIG. 1) was formed by a vacuum vapor deposition method with the same configuration as in Reference Example 1, and was used as an optical disk. Various characteristics were measured.
The thickness of the recording film was 100 nm, and zinc sulfide was used for the heat resistant protective layer. The Tx of the obtained recording film was 110 ° C. A 5.25 inch substrate is used as the disk, and the relative speed of the laser beam and the disk is 10 m / sec. FIG. 7 shows the relationship between the CN ratio (carrier-to-noise ratio) of recording and the writing power when the frequency is 5 MHz. As can be seen from the figure, as the recording power increases from 14 mW to 20 mW, the CN ratio increases. FIG. 8 shows the erase characteristic of the recorded signal. The horizontal axis is the power of the erasing laser beam, and the vertical axis is the erasing rate. The erasing laser beam has a circular shape and the power has a Gaussian distribution. The power of the recording signal is 18mW and it erases (crystallizes)
Was performed by irradiating the laser beam in a direct current. It can be seen that crystallization (erasing) is sufficiently performed even under this condition. Reference Example 3 As a recording film, a stoichiometric compound of Te ₅₀ Sb ₂₅ Ag was used.
₂₅ (composition at point A in FIG. 1) was directly deposited on a quartz substrate by a vacuum evaporation method, and the crystallization process was traced by an X-ray diffraction method. The recording film had a thickness of 100 nm, and was coated with 50 nm of silicon dioxide in order to prevent the sublimable element from scattering. Since the Tx of the obtained recording film was 110 ° C., X-ray diffraction measurement was performed after heat treatment at 100 ° C., 200 ° C. and 350 ° C. in an argon atmosphere. Table 1 shows the results. Since the composition at point A is a stoichiometric composition, after crystallization is completely completed, AgSbTe ₂
Diffraction line was observed and no other phase was observed. That is, it can be seen that this recording film is composed of a single-phase compound. Example 1 A recording film having a composition slightly deviated from the stoichiometric compound was used.
A recording film of Te ₄₈ Sb ₂₂ Ag ₃₀ (composition at point E in FIG. 1) was formed by the vacuum evaporation method and the characteristics were measured. The thickness of the recording film is 10
At 0 nm, zinc sulfide was used for the heat-resistant protective layer. The Tx of the obtained recording film was 120 ° C. Figure 6 shows the crystallization characteristics based on static characteristics. As in Reference Example 1, it can be seen that the crystallization start pulse width shifts to the short pulse side as the irradiation power is increased from 2 mW to 10 mW. In this embodiment, 70n with a power of 10mW
A threshold value for crystallization initiation of seconds was obtained, and the properties were almost the same as the stoichiometric composition of Reference Example 1. Amorphization was also observed at a power of 14 mW or higher, as in Reference Example 1. Example 2 As a recording film, a composition slightly deviated from the stoichiometric compound was formed by a vacuum evaporation method, and the characteristics were measured. The film thickness of each recording film was 100 nm, and zinc sulfide was used for each heat-resistant protective layer. Table 2 shows the composition of the obtained recording film, the crystallization temperature Tx, and the threshold value of the crystallization start by the static measurement. The irradiation power at that time was set to 10 mW. Further, Table 2 also shows the threshold value for starting the amorphization when the laser power is 18 mW. As is clear from Table 2, it can be seen that a compound having a high crystallization rate exists on the composition line connecting Sb ₂ Te ₃ and Ag ₂ Te of the binary composition stoichiometric compound. In particular, B, F, G,
In the region surrounded by the points H and C, the crystallization threshold is 100 nsec or less, the amorphization threshold is 70 nsec or less, and the crystallization temperature (Tx) is 115 ° C. or more, and the stoichiometric ternary composition is used. It can be seen that the characteristic as a recording film is superior to point A. It is considered that the above preferable composition range tends to be biased toward the Sb ₂ Te ₃ side of the stoichiometric compound having a binary composition because the solid solution phase (beta phase) shown in FIG. 2 exists. . Example 3 As a recording film, a stoichiometric compound of Te ₅₀ Sb ₂₅ Ag was used.
Compounds of ₂₅ (composition point A in FIG. 1) and peripheral compositions (B, C, D, G, J, K in FIGS. 1 and 2) were directly formed on a quartz substrate by a vacuum deposition method. The film-forming compound was identified by the X-ray diffraction method. The film thickness of each was 100 nm, and 50 nm of silicon dioxide was coated on each to prevent the sublimable element from scattering. Identification by X-ray diffraction was performed in an argon atmosphere.
It was performed after heat treatment at 0 ° C. The results are shown in Table 3. The composition after crystallization was the same as the stoichiometric ternary compound AgSbTe ₂ and a small amount of Sb ₂ Te ₃
It can also be seen that it consists of a mixture of each stoichiometric binary compound of Ag ₂ Te. According to the present invention, among alloys of tellurium, antimony and silver, the composition point B (Te ₅₆ Sb ₃₄ Ag ₁₀ )-shown in FIG.
F (Te ₅₆ Sb ₃₅ Ag ₁₀ ) -G (Te ₄₀ Sb ₂₅ Ag ₃₅ ) -H (Te ₄₀ Sb
Elimination by using an active material within the range connecting ₃₅ Ag ₂₅ ) -C (Te ₄₆ Sb ₁₉ Ag ₃₅ ) excluding the stoichiometric ternary compound A (Te ₅₀ Sb ₂₅ Ag ₂₅ ). There is an effect that the crystallization speed can be increased to a practical use level and an optical information recording medium capable of stable recording and erasing can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a composition diagram showing a composition range of a Te—Sb—Ag type recording medium material of the present invention, and FIG. 2 is a phase of an Sb ₂ Te ₃ —Ag ₂ Te binary alloy. FIG. 3 is a sectional view showing the structure of the recording medium, FIG. 4 is a graph showing static crystallization characteristics, FIG. 5 is a graph showing static amorphization characteristics, and FIG. 6 is a static crystallization characteristics. FIG. 7 is a graph showing dynamic crystallization characteristics, and FIG. 8 is a graph showing erase power dependence of erase ratio.

Claims (1)

(57) [Claims] Tellurium (Te) is an active material that exhibits a change in optical constant in an optical information recording / reproducing medium that records, reproduces, or erases information by causing a change in optical constant using a means such as light or heat. An alloy of nickel, antimony (Sb), and silver (Ag), the composition of which is Te.
BF of FIG. 1 showing a triangular composition diagram with Sb and Ag as vertices
An optical information recording medium, characterized in that it is within the range connecting GHC and excluding point A of the stoichiometric composition.