JPH064900A - Optical information recording medium and structure design method thereof - Google Patents

Abstract

(57) [Abstract] [Objective] The present invention relates to a phase change optical disc,
An object of the present invention is to provide an optical disc with high density and good erasing characteristics and cycle characteristics by limiting the phase difference between the recorded portion and the unrecorded portion and the magnitude relationship of the reflectance between the recorded portion and the unrecorded portion. To do. [Constitution] With respect to the wavelength λ of the reproduction light, the range of the phase difference between the reflected light at the recorded portion and the unrecorded portion is (0.5 to 1.5) π + 2.
The disc structure is limited so that nπ (n: integer) and the reflectance of the recorded portion is higher than the reflectance of the unrecorded portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium for recording / reproducing information with high density using a laser beam, and more particularly to a rewritable optical disc.

[0002]

2. Description of the Related Art As an optical disk capable of recording / reproducing and erasing signals, a phase change type optical disk using a chalcogenide as a recording thin film material is known. In general, when the recording thin film material is in a crystalline state, it is set as an unrecorded state, and the recording thin film is melted and rapidly cooled by laser light irradiation to be in an amorphous state to record a signal. On the other hand, in the case of erasing the signal, the recording thin film is heated to a crystalline state by irradiating a laser beam having lower power than that at the time of recording.

Recording thin film materials include, for example, Te, In,
It is common to use a material containing Sb, Se or the like as a main component and undergoing a phase change between an amorphous phase and a crystal, or a substance that causes a reversible phase change between two different crystal structures.

One of the merits of phase change recording is that an information signal can be overwritten by using only a single laser beam as a recording means. That is, when the laser output is modulated between the recording level and the erasing level according to the information signal and applied to the recorded information track, a new signal can be recorded while erasing the existing information signal. (JP-A-56-145530).

Further, for the purpose of improving the recording density, it has been proposed to determine the disc structure so that a phase difference occurs between the unrecorded portion and the recorded portion with respect to the wavelength λ of the reproducing laser light (special feature. JP-A-3-41638 and JP-A-3-15
7830). Recording area (record mark) due to reflectance changes
In the case of reading, a sufficient reproduction signal cannot be obtained unless there is a recording state area that is sufficiently larger than the size of the laser beam used for reproduction. Because the light intensity of the reproducing beam generally has a Gaussian distribution and spreads outside the phase-changed recording mark, the amount of reflected light depends on the reflectance of the recording mark and the surrounding unrecorded area. This is because the reflectance is proportional to the average value obtained by weighting each area and the light intensity distribution. On the other hand, in the case of the phase change reproduction structure,
The fact that the phases of the recorded portion and the unrecorded portion are different and they interfere with each other to change the reflected light amount is used. Therefore, the phase difference between the reflected light at the recorded portion and the unrecorded portion is (1 + 2
When n) π (n is an integer), the change in the reflected light amount is the largest, and it is desirable that the value be close to this value. Further, as the intensity distribution of the reproducing beam, the effect of interference is greatest when the intensity incident on the recording portion is equal to the intensity incident on the peripheral unrecorded portion, and thus the change in reflected light intensity is large. That is, when the recording mark is smaller than the size of the reproduction beam, the reproduction signal can be large. From the above, when reproducing with the same reproducing light beam, a larger amount of signal can be obtained with a recording mark having a smaller area in the phase change reproducing structure than in the reflectance changing reproducing structure.

[0006]

The recording / erasing characteristics and recording / erasing repetition characteristics of a phase-change type optical disk are as follows: material of recording thin film or dielectric protective layer, disk configuration, recording, power of recording / erasing beam, etc. However, further improvement of recording density, improvement of erasing characteristics-especially expansion of erasing power tolerance, and improvement of repetitive characteristics of recording / erasing are required.

[0007]

In order to solve the above-mentioned problems, the present invention provides a phase change type optical information recording medium, in which the recording thin film is formed as a recording mark having a different optical constant from that of an unrecorded area. The range of the phase difference between the reflected light in the unrecorded area and the recorded mark area of the optical information recording medium with respect to the wavelength λ of the laser light for reproducing information is (0.5 to 1.5) π + 2nπ n: an integer , And the wavelength λ of the laser light for reproducing the recorded information
On the other hand, the structure is limited so that the reflectance R1 of the recording mark area of the optical information recording medium is higher than the reflectance R2 of the unrecorded area.

[0008]

With the structure of the phase change type optical information recording medium, the optical information is recorded with respect to the wavelength λ of the laser beam for reproducing information formed on the recording thin film as a recording mark having an optical constant different from that of the unrecorded area. The range of the phase difference of the reflected light between the unrecorded area and the recorded mark area of the recording medium is (0.5 to 1.5) π + 2nπ n: an integer, and the wavelength λ of the laser light for reproducing the recorded information
On the other hand, by limiting the reflectance R1 of the recording mark area of the optical information recording medium to be higher than the reflectance R2 of the unrecorded area, a structure in which the reflectance R1 is the same as the reflectance R2 is compared, The same signal amplitude can be obtained by forming smaller recording marks. In this way, since the recording mark can be made small without degrading the signal quality, high density can be realized. At the same time, it is possible to improve the erasing characteristics, especially the erasing power tolerance. Also, because the recording mark can be made smaller,
When the erasing is repeated, the thermal load on the recording medium is reduced as compared with the case where the recording mark is large, and as a result, good recording / erasing repeating characteristics can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

A typical structure example of the recording medium of the present invention is shown in FIG.
Shown in. The laser light for recording, reproducing and erasing is the substrate 1
Incident from the side.

As the substrate 1, a resin having a smooth surface such as resin such as PMMA or polycarbonate, or glass is used. In the case of an optical disk, the substrate plane 8 is usually covered with spiral or concentric continuous grooves (tracks) for guiding laser light, or with irregularities such as pit rows.

It is desirable that the materials of the protective layers 2 and 4 are physically and chemically stable, that is, have a melting point and a softening temperature higher than the melting point of the recording material and do not form a solid solution with the recording material. For example, Al2O3, SiOx, Ta2O5, MoO3, WO
3, ZrO2, ZnS, AlNx, BN, SiNx, TiN, Zr
It is made of a dielectric material such as N, PbF2, MgF2 or a suitable combination thereof. The protective layer need not be dielectric or transparent. For example, it may be formed of ZnTe having a light absorbing property for visible light and infrared light. Further, when the protective layers 2 and 4 are made of different materials, there is an advantage that the degree of freedom of thermal and optical disk design is increased. Of course, the same material may be used.

The recording thin film 3 is a substance that reversibly changes its structure between a crystalline state and an amorphous state, such as Te or I.
It is made of a phase change material containing n, Se, etc. as main components. The well-known main components of phase change materials are Te-Sb-Ge and Te-
Ge, Te-Ge-Sn, Te-Ge-Sn-Au, Sb-Se, Sb-T
e, Sb-Se-Te, In-Te, In-Se, In-Se-Tl, In
-Sb, In-Sb-Se, In-Se-Te and the like can be mentioned. These thin films are usually formed in an amorphous state, but they absorb energy of laser light or the like to be crystallized and the optical constants (refractive index n, extinction coefficient k) change.

The reflection layer 5 is made of a metal element such as Au, Al, Ni, Fe, Cr or an alloy thereof, and has a function of enhancing the light absorption efficiency of the recording thin film. However, the reflection layer 6 may not be provided by increasing the thickness of the recording thin film 3 to improve the light absorption efficiency. Alternatively, by alternately stacking the recording thin film and the protective layer a plurality of times, it is possible to improve the light absorption efficiency as a whole even if the thickness of one recording thin film is small.

The protective substrate 7 is formed by spin-coating a resin or laminating a resin plate, a glass plate, a metal plate or the like similar to the substrate with an adhesive 6. Further, a structure capable of recording, reproducing and erasing from both sides may be realized by bonding two sets of recording media with the intermediate substrate or the reflection layer inside by using an adhesive.

The recording thin film, the protective layer, and the crystallization control layer are usually formed by an electron beam evaporation method, a sputtering method, an ion plating method, a CVD method, a laser sputtering method or the like.

The thickness of the recording thin film 3 is selected so that a part of the incident light can pass through the recording thin film 3 even when the recording thin film 3 is in a crystalline state. For example, considering the transmittance when the above-mentioned phase change material film (crystal phase) is sandwiched between protective layers (assuming infinite thickness) made of the same material as the dielectric thin film layers 2 and 4, the value is at least about 1%. As mentioned above, it is important to select the film thickness as much as possible, preferably about 2 to 3% or more. When the components reflected by the reflective layer 5 and re-incident in the recording thin film 3 are eliminated, the light interference effect is reduced, and even if the film thicknesses of the second dielectric thin film layer 4 and the reflective layer 5 are slightly changed, the entire medium is reduced. Optical path length of
It becomes difficult to control the reflectance and absorption in the recording thin film.

FIG. 2 shows Ge ₂ as a typical recording thin film composition.
Film thickness and transmittance (wavelength 780 nm) when Sb ₂ Te ₅ is sandwiched between ZnS—SiO ₂ mixture (SiO ₂ : 20 mol%) films
It shows the relationship of. From the figure, it can be seen that in the crystalline state, the transmittance is 1% or more when the film thickness is 60 nm or less, 2% or more when the film thickness is 50 nm or less, and 3% or more when the film thickness is 40 nm or less.

The film thicknesses of the first and second protective layers 2 and 4 are determined as follows. First, the complex index of refraction of the substances that make up each layer is calculated by the usual method (for example, a method of forming a thin film on a glass plate and calculating based on the measured values of the film thickness, reflectance, and transmittance, or using an ellipsometer). Method). Next, after fixing the thicknesses of the recording thin film 3 and the reflective layer 5, the first and second dielectrics are formed by a matrix method (see, for example, Hiro Wave Kubota, "Wave Optics", Iwanami Shoten, 1971, Chapter 3). The film thickness of is calculated. Specifically, assuming the film thickness of each layer, the balance of light energy is calculated for all interfaces including the surface based on the energy conservation law.
That is, by formulating this energy balance equation for each interface in the multilayer medium and solving the obtained simultaneous equations, the incident light of an arbitrary wavelength (actually, the wavelength λ used for reproducing information) can be obtained. The optical path length, the intensity of transmitted light, the intensity of reflected light, and the amount of absorption in each layer can be obtained.
By performing the above calculation both when the recording thin film is in the crystalline state and when it is in the amorphous state, the unrecorded area (usually in the crystalline state) and the recorded mark area for the reproduction light of the wavelength λ. It is possible to know the phase difference of the reflected light (which usually applies an amorphous state), the reflectance change ΔR between both regions, and the absorption difference between both regions in the recording layer. In the present invention, the range of the phase difference of the reflected light between the two states is (0.5 to 1.5) π + 2nπ n: an integer, and with respect to the wavelength λ of the laser light for reproducing the recorded information. Then, the reflectance R1 of the recording mark area is made higher than the reflectance R2 of the unrecorded area. If the phase difference between both regions is (0.5 to 1.5) π + 2nπn: an integer, sufficient phase difference reproduction can be realized. Further, since the reflectance R1 of the recording mark is larger than the reflectance R2 of the unrecorded area, the area of the recording mark where the optimum phase difference reproduction occurs is optimal when R1 <R2 or R1 = R2. The area is smaller than the area of the recording mark in which phase difference reproduction occurs. This is schematically shown in FIG.

Independent selection of the phase difference and the reflectance change of the reflected light between the two states satisfying the above conditions not only makes the reflectance difference reproducing structure different from the conventional structure design concept, It is important to accurately design the disc structure by the method already described and to accurately produce the resulting singularity disc structure.

Whether the recording medium is designed or not can be verified by measuring the reflectance and transmittance of the finished medium using a spectrum meter and comparing them with the values calculated in advance. In this case, the absorption in the recording thin film and the absorption in the reflective layer cannot be directly measured,
Accuracy can be increased by performing the same comparison at two or more wavelengths. The amount of phase change between the recorded area and the unrecorded area can be obtained by observing how the interference fringes of the light having the same wavelength as the reproduction light are deviated between the recorded area and the unrecorded area by using an interference film thickness meter or the like. be able to. Hereinafter, the present invention will be described in more detail with reference to specific examples.

(Example 1) Ge ₂ Sb ₂ Te ₅ was selected as a typical recording thin film composition. Ge ₂ Sb ₂ Te ₅ is known as a material that can obtain good recording / erasing characteristics and repetitive characteristics (Japanese Patent Laid-Open No. Sho 62-209742).

FIG. 1 shows a disk structure of one embodiment of the present invention. The material of the substrate was smooth polycarbonate having no guide groove. The recording thin film has a thickness of 15 nm, and a dielectric protective layer made of ZnS-20 mol% SiO ₂ is sandwiched on both sides thereof. Gold (Au) was used as the material of the reflective layer, and the film thickness was 50 nm. The formation of each layer was performed by the sputtering method. Table 1 shows the optical constants (measured values) of each layer. However,
Table 1 shows optical constants at a wavelength of 780 nm.

[0024]

[Table 1]

Regarding some of the samples used in the experiment, the film thickness of the protective layer on the substrate side, the film thickness of the protective layer on the reflective layer side, the reflectance R1 in the amorphous state, the reflectance R2 in the crystalline state, Table 2 shows the phase difference between the two states. However, the optical characteristics are values for a wavelength of 780 nm.

The actual measured value of the reflectance was obtained using a spectrophotometer. The crystallization treatment was a heat treatment in nitrogen at 250 ° C. for 10 minutes. Further, a partial region of the sample piece was crystallized with a semiconductor laser to form an amorphous region and a crystalline region side by side, and this portion was observed with an interference film thickness meter. Wavelength 780
The phase difference was calculated from the amount of deviation of the nm interference fringes between the two regions. From Table 2, it can be seen that a sample having almost the same structure as the design was obtained.

[0027]

[Table 2]

These media were previously subjected to initialization (crystallization) treatment on the entire surface of the recording thin film by an initialization device using an Ar laser. Then, this medium was rotated at a linear velocity of 10 m / s, and a semiconductor laser beam having a wavelength of 780 nm was focused by a lens system having a numerical aperture of 0.5 and focused on the recording thin film for irradiation. The recording thin film is partially amorphized for recording by irradiating the recording thin film with light modulated at a single frequency of 10 MHz and a modulation factor of 50% with various powers, and a continuous output of 1 mW is irradiated. When the reflected light was detected by a photodetector to reproduce the reproduced signal, the reproduced signal amplitude was observed. Next, the recorded / reproduced disc was disassembled, and the shape of the recording mark was examined using a transmission electron microscope. The shape of the recording mark differs depending on the recording power. FIG. 4 shows the relationship between the recording mark area and the reproduction amplitude in each sample. The following can be seen from FIG. 1) As can be seen from the comparison of Samples 1 and 2, when the reflectance is the same, the maximum signal amplitude can be increased when the phase difference between the amorphous part and the crystal part is closer to π. However, the area where the maximum signal amplitude is obtained is the same for both samples. 2) As can be seen from the comparison of Samples 3 and 4, in the case where the equivalent phase difference is equivalent, in Sample 3, the reflectance of the amorphous part is larger than that of the crystalline part. Is larger than the reflectance of the amorphous portion), a large signal amplitude can be obtained with a small mark shape.

When the phase difference between the amorphous region and the crystalline region of the recording medium and the relationship between the reflectances of the two were examined in this way, the following facts were revealed. 1) Comparing samples with the same reflectance, the phase difference is (1
The maximum signal amplitude is obtained when + 2n) π (n is an integer). Also, the phase difference is (0.5 to 1.5) π + 2n
Within the range of π, a signal amplitude of about 60% or more of the maximum signal amplitude when the phase difference is (1 + 2n) π was obtained. This is a sufficiently practical value. However, (1.5-2.
5) With the phase difference of π + 2nπ, the signal amplitude was extremely small. 2) Comparing samples having a phase difference of (0.5 to 1.5) π + 2nπ, the same phase difference and the same reflectance in the crystalline state, the reflectance of the amorphous portion is crystalline. The higher the reflectance of the part, the smaller the area of the recording mark where the maximum amplitude was obtained. At this time, the maximum amplitude value itself does not change. This means that the recording density is increased by making the structure such that the reflectance of the amorphous portion is higher than that of the crystalline portion. The larger the difference in reflectance between crystalline and amorphous, the smaller the recording mark, and the larger the signal amplitude obtained. Of course, the maximum signal amplitude becomes maximum when the phase difference is (1 + 2n) π. The amorphous reflectance is 1.2 of the crystal reflectance.
In the case of doubling, the area of the recording mark showing the same maximum signal amplitude is about 9.5% compared with the case where both reflectances are the same,
The substantial contribution to densification was small. On the other hand, when the reflectance of the amorphous material is 1.3 times the reflectance of the crystalline material, the area of the recording mark showing the same maximum signal amplitude is about 80% of the area where the reflectances are the same, which is high. It came to show a sufficient contribution to the densification. 3) When the samples having the same retardation in the range of (0.5 to 1.5) π + 2nπ and the same phase difference and the same reflectance in the crystalline state are compared, the reflectance of the amorphous portion is crystalline. The higher the reflectance of the part, the greater the number of times recording / erasing was repeated. 4) After forming recording marks of the same area, various powers are continuously irradiated to crystallize the recording marks to erase the signal, and the erasing rate is measured. As a result, the phase difference is (0.5 to 1.5). Within the range of π + 2nπ and the phase difference is the same,
Further, comparing samples having the same reflectance in the crystalline state, the range of the erasing power at which the erasing rate is a certain level or more (for example, −20 dB) is widened in the sample in which the reflectance of the amorphous portion is higher than that of the crystalline portion. That is, it was found that the erase power range was widened.

Next, by expanding the composition range of the recording thin film, both the crystallization / amorphization sensitivity and the repetition characteristics are good, and in the phase difference reproduction, the reflectivity of the amorphous part is better than that of the crystal part. We also investigated a disk structure that can improve the recording density, the erasing property, and the repetitive property of recording and erasing by increasing the value. As a result of the experiment, both the crystallization and the amorphization sensitivity are good (the heating time required for crystallization is 100 nsec or less in consideration of the overwriting by a single beam), and the good repetitive recording / erasing characteristics are obtained. The resulting configuration is G
The composition range of the main component of e-Sb-Te was (Ge) _x (Sb) _y (Te) _z 0.10 ≤ x ≤ 0.35 0.10 ≤ y 0.45 ≤ z ≤ 0.65 x + y + z = 1. The composition range of the Ge-Sb-Te main component is the range surrounded by A, B, C, D, and E in FIG.

As a result of further detailed examination of the Ge-Sb-Te composition range of the main component of the recording thin film, the range represented by (Ge ₂ Sb ₂ Te ₅ ) _x (GeSb ₂ Te ₄ ) _1-x 0 ≤ x ≤ 1 The recording thin film group has a particularly high crystallization speed, and at the same time, has good repeated recording / erasing characteristics. A recording medium having a recording thin film having such a composition has a great effect of combination with the present invention capable of achieving high density.

When the film thickness of the recording thin film is experimentally examined from the viewpoint of the repetitive characteristics of recording and erasing, in the case of a disk structure having a recording thin film containing Ge-Sb-Te as a main component, the recording thin film thickness is 40 nm or less. Otherwise, good repeatability could not be obtained. Further, in the disc structure, the film thickness tolerance of each layer for obtaining the effect of the present invention becomes extremely narrow when the recording thin film thickness is thicker than 40 nm, which makes it difficult to actually manufacture. In any recording thin film composition, when a grooveless substrate is used, (1 + 2n) π,
Moreover, the most effective phase difference reproduction can be performed when the reflectance of the recorded portion is higher than the reflectance of the unrecorded portion. However, if the phase difference is in the range of (0.5 to 1.5) π + 2nπ, the phase difference is A signal amplitude of about 60% or more of the maximum signal amplitude in the case of (1 + 2n) π was obtained. This is a sufficiently practical value. However, at the phase difference of (1.5 to 2.5) π + 2nπ, the signal amplitude was extremely small. On the other hand, in a grooved substrate, a phase is generated by the groove, so that the maximum phase difference reproduction amplitude is not necessarily obtained when the phase difference between the recorded portion and the unrecorded portion is (1 + 2n) π. At this time,
The optimum phase difference between the recorded portion and the unrecorded portion can be determined in consideration of the groove shape (groove interval, groove width, groove depth, etc.). In any case, the phase difference between the recorded part and the unrecorded part is (0.5
It has been found that the range is up to 1.5) π + 2nπ. Further, when the samples having the phase difference in the range of (0.5 to 1.5) π + 2nπ, the same phase difference and the same reflectance in the crystalline state are compared, the reflectance of the amorphous part is The higher the reflectance of the part, the smaller the area of the recording mark where the maximum amplitude was obtained. At this time, the maximum amplitude value itself does not change. This means that the recording density is increased by making the structure such that the reflectance of the amorphous portion is higher than that of the crystalline portion. The larger the difference in reflectance between crystalline and amorphous, the smaller the recording mark, and the larger the signal amplitude obtained. When the reflectance of the amorphous material is 1.2 times that of the crystal, the area of the recording mark showing the same maximum signal amplitude is about 9.5%, which is higher than that of the case where both reflectances are the same. The substantial contribution to densification was small. On the other hand, when the reflectance of the amorphous material is 1.3 times the reflectance of the crystalline material, the area of the recording mark showing the same maximum signal amplitude is about 80% of the area where the reflectances are the same, which is high. It came to show a sufficient contribution to the densification. Further, if the amorphous reflectance is twice as high as the crystal reflectance, the area of the recording mark showing the same maximum signal amplitude is about 60% compared to the case where both reflectances are the same. Has made a big contribution.
Further, comparing samples having a phase difference of (0.5 to 1.5) π + 2nπ, the same phase difference and the same reflectance in the crystalline state, the reflectance of the amorphous part is A sample having a higher reflectance than that of the portion had a wider erasing power tolerance and a good erasing property was obtained, and at the same time, a good number of times of repeated recording / erasing property was obtained. Further, it was found that the noise component of the medium during reproduction is reduced by reducing the reflectance in the crystalline state (unrecorded state) as much as possible. However, if the reflectance in the crystalline state (unrecorded state) is made too small, the signal amplitude will become small.
As a result of actually evaluating the C / N of the signal, by reducing the reflectance in the crystalline state, the
It was found that the effect of reducing the noise component is greater. As a result of studying various recording thin film materials and various disc configurations, it was found that good reproduction signal quality can be obtained when the reflectance during crystallization is suppressed to 15% or less.
Of course, at this time, the phase difference between the recorded portion and the unrecorded portion is (0.
5 to 1.5) π + 2nπ, and the reflectance of the recorded portion is set higher than the reflectance of the unrecorded portion.

Example 2 Sb ₂ Se ₃ is known as a recording thin film composition having good recording / erasing characteristics. Sb ₂ S
optical constants of e ₃ thin film is disclosed, for example, in JP-A-2-266978. Here, Sb ₂ disclosed herein is used.
A phase change recording medium was optically designed with reference to the optical constants of the Se ₃ thin film to prepare a sample disk.

FIG. 1 shows the structure of the sample disk prepared. The material of the substrate was smooth polycarbonate having no guide groove. Both sides of the recording thin film were sandwiched by a dielectric protective layer made of ZnS-20 mol% SiO ₂ . Gold (Au) was used for the reflective layer material. The formation of each layer was performed by the sputtering method. Table 3 shows the optical constants (measured values) of each layer.
However, Table 3 shows optical constants for a wavelength of 780 nm.

[0035]

[Table 3]

When the Sb ₂ Se ₃ thin film is used as the recording thin film, it is possible to find a disk structure in which the reflectance of the recorded portion is three times or more the reflectance of the unrecorded portion while keeping the phase difference large. For example, the film thickness of the ZnS-20 mol% SiO ₂ protective layer on the substrate side is 104 nm, the film thickness of the recording thin film is 160 nm, the film thickness of the ZnS-20 mol% SiO ₂ protective layer on the reflective layer side is 35 nm,
When the film thickness of the Au reflective layer is 50 nm, the phase difference between the recorded portion and the unrecorded portion is 0.9π, the reflectance of the recorded portion is 30%, and the reflectance of the unrecorded portion is 10%. With such a disc, a large signal amplitude was obtained even with a very small recording mark. Thus, when Sb ₂ Se ₃ is used for the recording thin film,
A phase difference reproducing structure recording medium having a high degree of freedom can be manufactured.

A disc was formed by changing the recording layer thickness, the protective layer thickness, and the reflection layer thickness to record signals, and the phase difference between the amorphous region and the crystalline region of the recording medium, and the reflectance of both. When we investigated the relationship between the two, the following facts became clear. 1) Comparing samples with the same reflectance, the phase difference is (1
The maximum signal amplitude is obtained when + 2n) π (n is an integer). Also, the phase difference is (0.5 to 1.5) π + 2n
Within the range of π, a signal amplitude of about 60% or more of the maximum signal amplitude when the phase difference is (1 + 2n) π was obtained. This is a sufficiently practical value. However, (1.5-2.
5) With the phase difference of π + 2nπ, the signal amplitude was extremely small. 2) Comparing samples having a phase difference of (0.5 to 1.5) π + 2nπ, the same phase difference and the same reflectance in the crystalline state, the reflectance of the amorphous portion is crystalline. The higher the reflectance of the part, the smaller the area of the recording mark where the maximum amplitude was obtained. At this time, the maximum amplitude value itself does not change. This means that the recording density is increased by making the structure such that the reflectance of the amorphous portion is higher than that of the crystalline portion. The larger the difference in reflectance between crystalline and amorphous, the smaller the recording mark, and the larger the signal amplitude obtained. Of course, the maximum signal amplitude becomes maximum when the phase difference is (1 + 2n) π. The amorphous reflectance is 1.2 of the crystal reflectance.
In the case of doubling, the area of the recording mark showing the same maximum signal amplitude is about 9.5% compared with the case where both reflectances are the same,
The substantial contribution to densification was small. On the other hand, when the reflectance of the amorphous material is 1.3 times the reflectance of the crystalline material, the area of the recording mark showing the same maximum signal amplitude is about 80% of the area where the reflectances are the same, which is high. It came to show a sufficient contribution to the densification. 3) When the samples having the same retardation in the range of (0.5 to 1.5) π + 2nπ and the same phase difference and the same reflectance in the crystalline state are compared, the reflectance of the amorphous portion is crystalline. The higher the reflectance of the part, the greater the number of times recording / erasing was repeated. 4) After forming recording marks of the same area, various powers are continuously irradiated to crystallize the recording marks to erase the signal, and the erasing rate is measured. As a result, the phase difference is (0.5 to 1.5). Within the range of π + 2nπ and the phase difference is the same,
Further, comparing samples having the same reflectance in the crystalline state, the range of the erasing power at which the erasing rate is a certain level or more (for example, −20 dB) is widened in the sample in which the reflectance of the amorphous portion is higher than that of the crystalline portion. That is, it was found that the erase power range was widened.

The optical constant of the Sb ₂ Se ₃ thin film is characterized by a small extinction coefficient. Therefore, light is transmitted even with a much thicker film than the recording thin film containing Ge-Sb-Te as a main component. Even when designing a phase recording medium, a maximum of 50
At a thickness of 0 nm, there is a configuration in which a large phase change is exhibited and the reflectance of the amorphous portion is higher than that of the crystalline portion. Further, in any of the recording thin film compositions, the use of the grooveless substrate is most effective when (1 + 2n) π and the reflectance of the recorded portion is larger than the reflectance of the unrecorded portion. Phase difference reproduction is possible, but the phase difference is (0.
5 to 1.5) π + 2nπ, the phase difference is (1
A signal amplitude of about 60% or more of the maximum signal amplitude in the case of + 2n) π was obtained. This is a sufficiently practical value. However, at the phase difference of (1.5 to 2.5) π + 2nπ, the signal amplitude was extremely small. On the other hand, in a grooved substrate, a phase is generated by the groove, so that the maximum phase difference reproduction amplitude is not necessarily obtained when the phase difference between the recorded portion and the unrecorded portion is (1 + 2n) π. At this time, the optimum phase difference between the recorded portion and the unrecorded portion can be determined in consideration of the groove shape (groove interval, groove width, groove depth, etc.). In any case, the phase difference between the recorded portion and the unrecorded portion is (0.5-1.
5) It has been found that the range is π + 2nπ.
Further, when the samples having the phase difference in the range of (0.5 to 1.5) π + 2nπ, the same phase difference and the same reflectance in the crystalline state are compared, the reflectance of the amorphous part is The higher the reflectance of the part, the smaller the area of the recording mark where the maximum amplitude was obtained. At this time, the maximum amplitude value itself does not change. This means that the recording density is increased by making the structure such that the reflectance of the amorphous portion is higher than that of the crystalline portion. The larger the difference in reflectance between crystalline and amorphous, the smaller the recording mark, and the larger the signal amplitude obtained. When the reflectance of the amorphous material is 1.2 times that of the crystal, the area of the recording mark showing the same maximum signal amplitude is about 9.5%, which is higher than that of the case where both reflectances are the same. The substantial contribution to densification was small. On the other hand, when the reflectance of the amorphous material is 1.3 times that of the crystal, the area of the recording mark showing the same maximum signal amplitude is larger than that of the case where the reflectances are the same.
It was about 80%, and it came to show a sufficient contribution to high density. Further, if the amorphous reflectance is twice as high as the crystal reflectance, the area of the recording mark showing the same maximum signal amplitude is about 60% compared to the case where both reflectances are the same. Has made a big contribution.

Further, the phase difference is (0.5 to 1.5) π + 2n
Comparing samples in the range of π with the same phase difference and the same reflectance in the crystalline state, the erase power tolerance is higher in the sample in which the reflectance of the amorphous portion is higher than that of the crystalline portion. A wide range of good erasing characteristics was obtained, and at the same time, a good number of times of repeated recording / erasing characteristics was obtained. Further, it was found that the noise component of the medium during reproduction is reduced by reducing the reflectance in the crystalline state (unrecorded state) as much as possible. However, if the reflectance in the crystalline state (unrecorded state) is made too small, the signal amplitude will become small. As a result of actually evaluating the C / N of the signal, it was found that the effect of reducing the noise component is larger by reducing the reflectance in the crystalline state than the rate of decreasing the signal amplitude. As a result of studying various recording thin film materials and various disc configurations, the reflectivity during crystallization is 15
It was found that good reproduction signal quality can be obtained when the content is controlled to be less than or equal to%. Of course, at this time, the phase difference between the recorded portion and the unrecorded portion is set in the range of (0.5 to 1.5) π + 2nπ, and the reflectance of the recorded portion is set larger than the reflectance of the unrecorded portion. .

[0040]

The structure of the phase change type optical information recording medium has the above-mentioned structure with respect to the wavelength λ of the laser beam for reproducing the information formed on the recording thin film as the recording mark having the optical constant different from that of the unrecorded area. The range of the phase difference of the reflected light between the unrecorded area and the recorded mark area of the optical information recording medium is (0.5 to 1.5) π + 2nπ n: an integer, and the wavelength of the laser light for reproducing the recorded information. λ
On the other hand, by limiting the reflectance R1 of the recording mark area of the optical information recording medium to be higher than the reflectance R2 of the unrecorded area, a structure in which the reflectance R1 is the same as the reflectance R2 is compared, The same signal amplitude was obtained with the formation of smaller recording marks. In this way, the recording mark can be made small without degrading the signal quality, so that high density can be realized. At the same time, the erasing characteristics-especially the erasing power tolerance could be improved. Also, because the recording mark can be made smaller,
When the erasing was repeated, the thermal load on the recording medium was reduced as compared with the case where the recording mark was large, and as a result, good recording / erasing repeating characteristics were obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the thickness and the transmittance of a recording thin film that constitutes a recording medium in an example of the present invention.

FIG. 3 is a diagram for explaining the relationship between the size of the reproducing light focused on the recording thin film and the shape of the recording mark for the purpose of causing optimum phase difference reproduction.

FIG. 4 is a diagram showing a relationship between a recording mark area and a reproduction amplitude.

FIG. 5 is a diagram showing a range of main components of a recording thin film containing Ge-Sb-Te as a main component.

[Explanation of symbols]

 1 Substrate 2 Protective Layer 3 Recording Thin Film 4 Protective Layer 5 Reflective Layer 6 Adhesive Layer 7 Protective Substrate 8 Substrate Plane

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenichi Nishiuchi, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Noboru Yamada, 1006, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. An optical information recording medium used in an apparatus for recording / reproducing information by irradiating a laser beam of a predetermined wavelength, wherein the optical information recording medium comprises a substrate, at least a protective layer on the substrate, and a laser. A recording thin film capable of causing a phase change by irradiation of light and shifting to a state having different optical constants (refractive index n, extinction coefficient k), and a laser beam for reproducing information formed on the recording thin film. The range of the phase difference between the reflected light in the unrecorded area and the recorded mark area of the optical information recording medium with respect to the wavelength λ is (0.5 to 1.5) π + 2nπ n: an integer, and the recorded information is recorded. An optical information recording medium, wherein a reflectance R1 of a recording mark area of the optical information recording medium is larger than a reflectance R2 of an unrecorded area with respect to a wavelength λ of a laser beam for reproducing information. 2. The optical information recording medium according to claim 1, wherein the range of the phase difference of the reflected light between the unrecorded area and the recording mark area is (2n + 1) π n: an integer. 3. The optical information recording medium according to claim 1, wherein R1 is 1.3 times or more than R2. 4. The optical information recording medium according to claim 1, wherein R2 ≦ 15%. 5. The recording thin film is made of a material that reversibly changes its phase into a state having different optical constants by irradiation of laser light, and the recording thin film material is made of a material containing Ge—Sb—Te as a main component. The optical information recording medium according to claim 1, wherein the thickness of the recording thin film is 40 nm or less. 6. A recording thin film whose main components are Ge, Sb, and Te, and the composition ratio of the main components is (Ge) _x (Sb) _y (Te) _z 0.10≤x≤0.35 0.10≤y 0.45≤z≤0.65 The optical information recording medium according to claim 5, wherein the optical information recording medium is in a range represented by x + y + z = 1. 7. The composition ratio of Ge, Sb, Te is within the range represented by (Ge ₂ Sb ₂ Te ₅ ) _x (GeSb ₂ Te ₄ ) _1-x 0 ≤x≤1. The optical information recording medium according to claim 5. 8. The recording thin film is made of a material that reversibly changes its phase into a state where optical constants are different by irradiation of laser light, and the recording thin film material is made of a material containing Sb-Se as a main component. The optical information recording medium according to claim 1, wherein the thickness is 500 nm or less.