JPH07220303A - Phase change type disk medium - Google Patents

Abstract

PURPOSE:To obtain good recording density, good recording and erasing characteristics and repetive characteristics for repetition of use even for fast line speed by forming a reflection layer of an alloy essentially comprising Ti and Al with specified compsn. and forming a recording layer of SbTeGe alloy with specified compsn. on a substrate. CONSTITUTION:A protective layer 2 comprising ZnS-SiO2, recording layer 1 comprising Sb21Te54Ge25 alloy, protective layer 3 comprising ZnS-SiO2, and reflection layer 5 comprising AlTi alloy are successively formed by sputtering on a polycarbonate substrate 4 having guide grooves. Further, the surface of the reflection layer 5 is coated with a UV-curing resin to obtain a phase ' type optical disk. The amt. of Al in the reflection layer 5 is 10-80 at.%. The compsn. ratio of elements in the recording layer is selected from a specified square region in the ternary diagram for Sb, Te and Ge. The region is defined by four points A(Sb32Te58Ge10), B(Sb34T56Ge10), C(Sb10Te50Ge40), and D(Sb8Te52Ge40).

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 capable of recording, erasing and reproducing information by a laser beam or the like, and particularly has high recording sensitivity and good even at a high linear velocity of 8 to 20 m / s. The present invention relates to a phase-change type optical disc having excellent recording and erasing characteristics and good repeating characteristics.

[0002]

2. Description of the Related Art Optical information recording media typified by optical discs have attracted attention because of their high density and large capacity, and have been used for various purposes up to now. For example, as a reproduction-only optical disc, there are a compact disc for reproducing music, a CD-ROM for reproducing data, and the like, which are widely used in the music field, computer field, game field, and the like. A write-once optical disc that can be recorded only once and cannot be erased is used in a document filing system, a data filing system, and the like.

Furthermore, a rewritable optical disk capable of erasing recorded information and re-recording it can be used for recovering and updating data, and can be repeatedly used by rewriting, which is expected to contribute to the expansion of applications of the optical disk. Has been done. As such a rewritable optical disk, a magneto-optical disk and a phase change disk have been put into practical use so far and used for data files and the like.

The magneto-optical disk records information by using the magneto-optical effect (Kerr rotation effect), whereas the phase-change disk records information by reversibly changing the two states of crystalline and amorphous. To be done. The crystalline state is changed to an amorphous state by heating the substance to a temperature equal to or higher than the melting point and melting the substance, and then cooling the substance all at once.
Further, in order to bring it into a crystalline state, it is crystallized by being kept at a temperature equal to or higher than the crystallization temperature for a time necessary for crystallization. In the phase change type optical disk, these two states can reversibly change the phase only by the irradiation intensity of the laser, so that there is an advantage that overwriting can be performed as it is without erasing once at the time of rewriting.

[0005]

However, in such a conventional phase change type optical disk, the laser power required for amorphization needs to be 15 mW or more on the plate surface, and the linear velocity is further increased (rotation speed). Raise)
Then, there is a problem that it is not possible to perform sufficient recording with a commercially available laser.

The demand for optical disc systems is ever increasing, and accordingly, there is an urgent need to develop a medium capable of achieving higher linear velocities, that is, higher rotational speeds. As the optical disk medium, a highly sensitive medium capable of recording / erasing at a laser irradiation intensity of 15 mW or less on the plate surface is preferable from the viewpoint of the semiconductor laser used in the drive.

In response to such a demand, it is generally known that the sensitivity can be increased by increasing the thickness of the protective layer on the reflection layer side or by decreasing the thickness of the reflection layer. If the sensitivity is increased by, the sensitivity is improved, but the phenomenon that the erasing ratio is decreased and the durability is repeatedly deteriorated is not preferable. The present invention is to solve the conventional problem by specifying and combining the physical properties of the material used for the reflective layer and the composition of the recording film, and the linear velocity is 8 to 20 m, which is higher than the conventional linear velocity. It is an object of the present invention to provide a phase change type optical disk medium which can be recorded / erased well even at / s and which is excellent in repeated durability.

[0008]

The present inventors have found that by specifying the material of the reflective layer, recording and erasing can be satisfactorily performed even at a high linear velocity of 8 to 20 m / s. Completed That is, the present invention relates to a phase-change type optical disk medium capable of excellent recording, erasing and reproducing, and is suitable for recording, erasing and reproducing particularly at a high linear velocity of 8 to 20 m / s, and further repeats. The present invention relates to a medium having excellent durability.

The phase-change optical disk of the present invention has a structure having at least a recording layer and a reflective layer on a substrate, the reflective layer containing Ti and Al as main components, and the content of Al being 10 to 80 at% in atomic weight ratio. It is characterized by being. As a material forming the recording layer of the present invention, a chalcogen compound is preferable, and in particular, a SbTeGe-based material is an optimum material because it can be erased at high speed and has excellent stability in an amorphous state. In the SbTeGe-based material, particularly in the triangular diagram with Sb, Te, and Ge as the vertices, A (Sb ₃₂ Te ₅₈ Ge ₁₀ ), B (S
b ₃₄ Te ₅₆ Ge ₁₀ ), C (Sb ₁₀ Te ₅₀ Ge ₄₀ ), D
The composition inside the quadrangle surrounded by (Sb ₈ Te ₅₂ Ge ₄₀ ) is easy to crystallize because of its high crystallization speed, and is particularly excellent in erasing characteristics at a high linear velocity of 8 to 20 m / s. (Fig. 1).

In the phase change type optical disk of the present invention,
It is desirable to provide protective layers above and below the recording layer in order to prevent aging of the recording layer, such as oxidation. A material for the protective layer, typically _{Si0 X, Al 2 O 3,} ZnO 2, Ta 2
_{O 3, Si 3 N 4,} AlN, ZnS or a metal or semi-metal oxides such as SiC, fluorides, nitrides, sulfides,
Inorganic or organic substances such as carbides and borides and metals, as well as mixtures and mixed materials of these.

In the disc structure of the present invention, as shown in FIG. 2, the layer structure is such that the protective layer 2 is provided on both sides of the recording layer 1,
It is preferable to have a four-layer structure in which a reflective layer 5 also serving as a heat diffusion layer is provided on the side opposite to the light incident side (transparent substrate 4 side). The thickness of the protective layer 2 on the substrate 4 side is preferably 50 to 300 nm from the viewpoints of reflectance and contrast for the purpose of protecting the recording film and preventing thermal deformation of the substrate. The recording layer 1 has a film thickness of 15 to 15 from the viewpoint of contrast.
35 nm is good. The protective layer 3 on the reflective layer side preferably has a thickness of 15 nm or less from the viewpoint of erasing properties, and has a recording sensitivity and a film thickness of 3 n because the thin film formed is not in an island shape but in a stable layer shape.
m or more is good. The reflective layer 5 has a recording sensitivity of 250 nm.
The following is preferable, and 100 nm from the viewpoint of repeated durability.
The above is preferable.

The present invention will be described in detail below. In a rewritable phase change type optical disc, information is recorded / reproduced by utilizing the difference in optical constant between crystal and amorphous. To change the amorphous state to the crystalline state, hold it at a certain temperature (crystallization temperature) or more for a certain period of time (crystallization time). To make the amorphous state, heat the substance to the melting point or higher. After melting, it is performed by cooling at once.

When the recording / reproducing linear velocity is increased with the increase in the speed of the optical disc system, the laser beam immediately passes through the disc, and the residence time of the laser is shortened. The phenomenon that it becomes difficult to record (difficult to record) occurs.
Considering the semiconductor laser used in the drive, it is preferable to use a medium that can record and erase with a low laser irradiation intensity even at a high linear velocity. If a general laser of about 30 mW is used, the margin is taken into account at 12 mW on the board surface. Sufficient recording is required. Here, the carrier-to-noise ratio (C /
If the minimum recording power required for the (N ratio) to be 40 dB or more is defined as the recording sensitivity, the recording sensitivity needs to be 8 mW or less in order to sufficiently record at 12 mW.

This recording sensitivity changes depending on the material, film thickness, film quality, etc. of each layer constituting the optical disk medium.
In the four-layer structure as shown in FIG. 2, it is easy to change the film thickness of the protective layer 3 and the film thickness of the reflective layer 5. When a material having a high thermal conductivity such as Al or Au which is commonly used as a reflective layer material is used for the reflective layer and characteristics are evaluated at a high linear velocity, the residence time of the laser is short and Since it is easy to escape, high sensitivity is difficult, and measures such as increasing the film thickness of the protective layer 3 or reducing the film thickness of the reflective layer 5 to make it difficult for heat to escape to the reflective layer are taken. However, if the thickness of the protective layer 3 is increased, heat is more likely to remain in the direction perpendicular to the laser traveling direction, so that the amorphous region is likely to spread laterally during recording,
Since the amorphous region becomes thicker than the width that can be erased at the time of erasing, there is a problem that amorphous residue occurs and the erase residue becomes large (FIG. 3). In order to increase the sensitivity while suppressing the unerased residue, an attempt was made to reduce the thickness of the protective layer 3 and the reflection layer 5, but a material having a high thermal conductivity such as Al. When is used for the reflective layer 5, there is no characteristic range where the erasing ratio is 20 dB or more and the recording sensitivity is 8 mW or less even with a film thickness of about 20 nm, and it is difficult to achieve both recording and erasing.

The inventors of the present invention have conducted heat transfer as a material for the reflective layer 5.
By using a material with low conductivity, the thickness of the protective layer 3 is thin.
Even if the thickness of the reflective layer 5 is large, the recording sensitivity can be improved,
It is thought that both recording and erasing can be achieved at the same time.
I arrived. That is, is the material of the reflective layer an alloy of Al and Ti?
And the atomic weight ratio of Al is 10-80 at%
The thermal conductivity is 3 × 10^-2calcm^-1s^-1K
^-1Could be: As a result, the thickness of the protective layer 3
The recording sensitivity can be improved while the thickness is thin, and good recording is possible.
・ Achieved compatibility of erasing characteristics. Furthermore, the thickness of the reflective layer
Of 100 nm or more
We can provide media with long lastingness.

On the other hand, the thermal conductivity of the reflective layer material is 8 × 10 ^-3.
When calcm ^-1 s ^-1 K ^-1 or less, the erasing rate is lowered and the repeated durability is deteriorated, which is not preferable. These phenomena are particularly remarkable on the low linear velocity side of 10 m / s or less. As a result, the range of 8 × 10 ^{−3 to} 3 × 10 ⁻² calcm ⁻¹ s ⁻¹ K ⁻¹ is preferable as the thermal conductivity range of the reflective layer material, especially under a high linear velocity condition of 8 to 20 m / s. Can be said.

Next, the composition range of the recording layer will be described. When the linear velocity of recording / reproducing is increased, the crystallization temperature cannot be maintained for the crystallization time, which causes a phenomenon that crystallization becomes difficult (hard to erase). SbTeG as a recording material that tends to crystallize at high linear velocity
Although e is well known, it is necessary to use a composition that is particularly easily crystallized among the SbTeGe.

This SbTeGe-based material is Sb ₂ Te ₃
And GeTe have the property of mixing each property, and the line (compound line) connecting Sb ₂ Te ₃ and GeTe is one reference line in the triangular diagram with Sb, Te and Ge as vertices in FIG. Has become. For example, it is known that a compound having a composition on this compound line has a high crystallization rate, and the crystallization rate becomes slower as the distance from the compound line increases. In order to achieve erasure at a high linear velocity, it is preferable to have a compound line around which the crystallization rate is high. In addition, since Ge has a high melting point and crystallization temperature in the SbTeGe system, the melting point and crystallization temperature increase as the proportion of Ge in the compound increases, and conversely, the melting point and crystallization temperature decrease when the proportion of Ge decreases. I know. If the melting point of the compound is high, the Ge ratio will deteriorate the recording sensitivity, so it must be 40 at% or less. Further, when the crystallization temperature is 160 ° C. or less, crystallization of amorphous pits proceeds in an environmental test under high temperature and high humidity,
The reliability of recorded data becomes poor. Ge ratio is 10a
If it is less than t%, the crystallization temperature becomes 160 ° C. or less, and the reliability of the data is poor, so the Ge ratio is preferably 10 to 40 at%. More preferably, when the Ge ratio is 20 at% or more, the crystallization temperature is 180 ° C. or more, and higher reliability can be secured, so the Ge amount is preferably 20 to 40 at%.

Therefore, A (Sb ₃₂ Te ₅₈ Ge ₁₀ ), B in terms of atomic weight ratio in a triangular diagram with Sb, Te and Ge as vertices.
(Sb ₃₄ Te ₅₆ Ge ₁₀ ), C (Sb ₁₀ Te ₅₀ Ge ₄₀ ),
It is preferable to select the composition inside the quadrangle surrounded by D (Sb ₈ Te ₅₂ Ge ₄₀ ), and more preferably A (Sb ₂₄
Te ₅₆ Ge ₂₀ ), B (Sb ₂₆ Te ₅₄ Ge ₂₀ ), C (Sb
From the viewpoint of reliability, it is preferable to use a composition inside the quadrangle surrounded by ₁₀ Te ₅₀ Ge ₄₀ ), D (Sb ₈ Te ₅₂ Ge ₄₀ ).

In the present invention, the method for forming the recording layer, the protective layer and the reflective layer is a known method such as vacuum deposition, sputtering, ion beam sputtering, ion beam deposition, ion plating, electron beam deposition, plasma polymerization and the like. Can be appropriately adopted depending on the purpose, material and the like. In the optical disc medium of the present invention, as the substrate on which the optical information recording film is provided, for example, a glass plate or a glass plate provided with a photocurable resin, or a plastic substrate such as polycarbonate, acrylic resin, epoxy resin, or polystyrene, A metal plate such as an aluminum alloy is used.

[0021]

【Example】

[0022]

Examples 1 to 4 Comparative Examples 1 to 4 Next, the present invention will be described in more detail with reference to Examples. 1.0μ as shown in Figure 4
On a clean 0.6 mm thick polycarbonate substrate 4 provided with m guide grooves, a protective layer 2 made of ZnS-SiO ₂ having a thickness of 180 nm, a recording layer 1 made of a Sb ₂₁ Te ₅₄ Ge ₂₅ alloy having a thickness of 25 nm, A protective layer 3 made of ZnS-SiO ₂ having a thickness of 12 nm, and a reflective layer 5 made of an AlTi alloy having a thickness of 100 nm and having an arbitrarily changed composition ratio were sequentially formed by a sputtering method to be laminated, and then the reflective layer. A phase change type optical disk was prepared by coating the surface of No. 5 with an ultraviolet curable resin. Two single-sided discs thus produced, with the substrates on both sides, were adhered with a hot melt adhesive to obtain a phase-change type optical disc having a full-face contact structure.

Each phase-change optical disk thus obtained was applied to a driving device (laser light wavelength λ = 680 nm, objective lens numerical aperture NA = 0.6), and power-modulated as shown in FIG. The characteristics were evaluated by irradiating laser light. In FIG. 5, Pp indicates a peak power corresponding to recording (amorphization), Pb indicates a bias power corresponding to erasing (crystallization), and Pr indicates a read level read power.

The recording characteristics are as follows: rotating at a linear velocity of 8 m / s,
A signal having a recording frequency of 7.6 MHz and a pulse width of 40 ns was recorded, and the peak power required for the C / N ratio to exceed 40 dB was evaluated as the recording sensitivity. In addition, the erase characteristic is that the recording speed is 18.9 MHz when rotated at a linear velocity of 20 m / s.
The signal was recorded at the peak power that maximizes the C / N ratio, and then the erase ratio when the signal at the recording frequency of 7.1 MHz was overwritten by changing the bias power was evaluated.
Further, the repeated durability is as follows: A signal having a recording frequency of 7.6 MHz is repeatedly overwritten on the same track at a linear velocity of 8 m / s, which causes a large thermal damage, and C
The number of overwrites at which the / N ratio was decreased by 3 dB from the initial stage was evaluated as the number of repeatable times.

Table 1 shows the thermal conductivity, recording characteristics and erasing characteristics with respect to the composition of the AlTi alloy used as the reflecting layer 5. In measuring the thermal conductivity, each AlTi alloy was deposited as a single layer on silica glass with a thickness of about 10 μm by a sputtering method, and the thermal diffusivity and volume specific heat were measured by the optical alternating current method to measure the thermal conductivity. Was calculated. From the results shown in Table 1, changes in recording sensitivity with respect to the thermal conductivity of the reflective layer 5 are shown in FIG. As seen in Comparative Examples 1 and 2, when the thermal conductivity of the reflective layer 5 is larger than 0.03 cal / cm · s · k, the heat dissipation effect is large and the repeated durability is strong.
At a linear velocity of 8 m / s, the recording sensitivity is unfavorably low at 8 mW or more. Further, as shown in Comparative Example 4, AlTi having a thermal conductivity of 0.007 cal / cm · s · k.
When O _X is used for the reflective layer 5, the heat flow is insufficient, so that the thermal deterioration of the recording layer is large during repeated overwriting, and the repeated durability is significantly weakened. Also, A
In the case of 1TiOx, the maximum erasing ratio is reduced to 20 dB or less. This is because, when the thermal conductivity of the reflective layer 5 is low, the heat storage effect is large and amorphous pits protruding from the groove are formed in a direction perpendicular to the laser scanning direction, and even after erasing, there remains amorphous residue or low thermal conductivity. It is considered that in the case of conductivity, the holding time above the crystallization temperature is shortened.

Next, Examples 1 to 4 show disk characteristics in which the thermal conductivity of the reflective layer 5 is in the range of 0.008 to 0.03 cal / cm · s · k. The recording sensitivity is as good as 8 mW or less, and the erasing ratio is 20 dB or more. Also, 20
It can be seen that it has a durability that can be repeated 10,000 times, and that it has favorable characteristics and that it has well-balanced properties such as good durability and repeatability.

From these results, the range of thermal conductivity used for the reflective layer 5 is 0.008 to 0.03 cal / cm · s · k.
It has been found that it is preferable to set it during the period. AlTi
The change in thermal conductivity with respect to the Al content of the alloy is shown in FIG. A preferable thermal conductivity range of the material used for the reflective layer 5 is 0.
The Al content in the AlTi alloy corresponding to 008 to 0.03 cal / cm · s · k is 10 to 80 at%.

[0028]

Comparative Example 5 As Comparative Example 5, the material of the reflective layer 5 is Al.₉₈T
i₂The thickness of the protective layer 3 and the reflective layer 5 is changed.
The recording characteristics and the erasing characteristics at the time of application were examined. In addition, Al₉₈
Ti ₂Has a thermal conductivity of 0.134 cal / cm · s · K.
FIG. 8 shows the recording sensitivity for each film thickness of the protective layer 3 and the reflective layer 5.
In addition, FIG. 9 shows the maximum erasure for each film thickness as the erasure characteristic.
The ratio is shown. From these results, recording sensitivity is 8mW or less
And there is a compatible range where the maximum erase ratio is 20 dB or more.
I found it wasn't there. This is the thickness of the protective layer 3
In the thick range (> 15 nm), the heat storage effect of the recording layer is large
Although the recording sensitivity can be improved, the
The phenomenon that the erase ratio cannot be obtained due to the existence of gas residue
It is thought to have occurred.

In the range in which the thickness of the protective layer 3 is thin, the erasing property is good, but heat radiates to the reflecting layer 5 which also functions as a heat transfer layer at once, so the recording sensitivity is poor and the peak power is 8 mW. Has not been able to record enough. From these results, when a material having a high thermal conductivity is used as the material of the reflective layer 5, it is possible to obtain both the recording sensitivity and the erasing property by only adjusting the heat flow with the film thicknesses of the protective layer 3 and the reflective layer 5. It is found that it is more effective to set the thermal conductivity of the material within a predetermined range, because the region in which is excellent is not obtained.

[0030]

EXAMPLES 5-7 Comparative Examples 6 and 7] on the 1.0μm guide clean 0.6mm thick polycarbonate substrate 4 provided with grooves, the protective layer 2 made of ZnS-SiO ₂ having a thickness of 180 nm, a thickness Recording layer 1 made of a 25 nm SbTeGe alloy thin film, the composition ratio of which was changed to a predetermined value, and the thickness was 12 n.
m ZnS-SiO ₂ protective layer 3 and thickness 1
A reflective layer 5 made of Al ₆₀ Ti ₄₀ alloy having a thickness of 00 nm is sequentially formed by a sputtering method to be laminated, and further coated with an ultraviolet curable resin and laminated as in Example 1, and a phase change of the entire adhesion structure is performed. Type optical disc.

Each phase-change optical disk thus obtained was subjected to the same method as the evaluation conditions of Example 1 (recording characteristic was linear velocity 8 m / s, erasing characteristic was linear velocity 20 m / s) and recording power was 12 mW. The C / N ratio and the maximum erasing ratio after recording 100 times were evaluated. The results are shown in Table 2. In the composition ratio of the recording layer used in the experiment, as the Te ratio increases, the compound line connecting Sb ₂ Te ₃ —GeTe is closer, and the crystallization speed is correspondingly increased.

The compositions shown in Comparative Examples 6 and 7 had a linear velocity of 20.
The erasing ratio at m / s is 20 dB or less, which is not sufficient. When the laser light is emitted by DC and irradiated several times, the erasing ratio is gradually improved, which is considered to be caused by the lack of crystallization speed. On the other hand, when the compositions shown in Examples 5 to 7 were used, a good erasing ratio of 20 dB or more was obtained even under a very high linear velocity of 20 m / s, and a sufficient crystallization speed was obtained. You can see that
In addition, the C / N ratio at 8 m / s was 50 dB or more, and it can be said that the characteristics are sufficient for amorphization.

[0033]

Example 8: Clean 0.6 m with 1.0 μm guide groove
180 nm thick on m polycarbonate substrate 4
ZnS- SiO₂Protective layer 2 consisting of 25 nm thick
Sb _{twenty one}Te₅₄Ge_{twenty five}Providing an alloy recording layer 1
ZnS-SiO with different thickness₂Protective layer consisting of
3, and Al₆₀Ti₄₀The reflective layer 5 made of an alloy is sequentially formed.
A film was formed by a sputtering method and laminated, and the same as in Example 1.
Protective coating with UV curable resin, then paste
Combined to form a phase-change optical disk with a full-face contact structure
It was Phase change type consisting of each film thickness thus obtained
The optical disc was subjected to the same method as the evaluation conditions of Example 1 (recording characteristics).
(The linearity is 8 m / s and the erasing property is a linear speed of 20 m / s.)
Then, the recording sensitivity and the erasing property were evaluated.

FIG. 10 shows the film thickness dependence of the recording sensitivity of the protective layer 3 and the reflective layer 5. The recording sensitivity is improved as the protective layer 3 is thicker and the reflective layer 5 is thinner, which is largely related to heat flow of heat. Further, FIG. 11 shows the film thickness dependence of the maximum erasing ratio of the protective layer 3 and the reflective layer 5. The erasing characteristics are largely dependent on the film thickness of the protective layer 3, and the protective layer 3 having a film thickness of 15 nm or less shows good characteristics. This is because when the thickness of the protective layer 3 becomes thin, the time for which the protective layer 3 is kept above the crystallization temperature becomes long, and in the region where the thickness of the protective layer 3 is large, amorphous residue is likely to exist during erasing. Conceivable.

The repeated durability of each disk was also measured. Repetitive durability: Overwriting the signal of recording frequency 7.6MHz repeatedly at linear velocity 8m / s,
The number of times until the C / N ratio fell 3 dB from the initial value was evaluated. Results are shown in FIG.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

According to the present invention, good recording and erasing characteristics can be obtained even in a linear velocity region faster than before.
Further, it is possible to provide a well-balanced phase change type optical disc medium which is excellent in repeated durability.

[Brief description of drawings]

FIG. 1 is a triangular graph showing a composition ratio of each element constituting a material of a recording layer in the present invention.

FIG. 2 is a cross-sectional view showing an example of a phase change optical disc of the present invention.

FIG. 3 is an explanatory diagram showing the influence of the film thickness of a protective layer upon erasing.

FIG. 4 is a schematic view of a substrate of a phase change optical disc used in an example of the present invention.

FIG. 5 is a graph showing a power modulation waveform of laser light.

FIG. 6 is a graph showing an example of the relationship between the thermal conductivity of the reflective layer and the recording sensitivity.

FIG. 7 is a graph showing an example of the relationship between the thermal conductivity and the Al content of an AlTi alloy.

FIG. 8 is a graph showing an example of a relationship of recording sensitivity with respect to film thicknesses of a reflective layer and a protective layer.

FIG. 9 is a graph showing an example of the relationship between the maximum erasing ratio and the film thickness of the reflective layer and the protective layer.

FIG. 10 is a graph showing an example of a relationship of recording sensitivity with respect to film thicknesses of a reflective layer and a protective layer.

FIG. 11 is a graph showing an example of the relationship between the maximum erasing ratio and the film thickness of the reflective layer and the protective layer.

FIG. 12 is a graph showing an example of the relationship of the repeatable number of times with respect to the film thicknesses of the reflective layer and the protective layer.

Claims (2)

[Claims] 1. An optical recording medium, which has at least a recording layer and a reflective layer on a substrate and records information by utilizing a change of an optical constant due to a phase change, wherein the reflective layer is Ti and Al.
Of Al as the main component has an atomic ratio of 10 to 80 at%
And the recording layer is an SbTeGe alloy, and the elemental composition ratio thereof is A (Sb ₃₂ Te ₅₈ Ge ₁₀ ), B in terms of atomic weight ratio in a triangular diagram with Sb, Te, and Ge as vertices.
(Sb ₃₄ Te ₅₆ Ge ₁₀ ), C (Sb ₁₀ Te ₅₀ Ge ₄₀ ),
A phase-change type optical disk medium characterized by being in a range selected from the inside of a quadrangle surrounded by D (Sb ₈ Te ₅₂ Ge ₄₀ ). 2. An optical recording medium having protective layers on both sides of a recording layer, wherein the thickness of the protective layer on the substrate side is 50 to 300 n.
m, the thickness of the recording layer is 15 to 35 nm, the thickness of the protective layer on the reflective layer side is 3 to 15 nm, and the thickness of the reflective layer is 100 to 250 nm.
The phase change type optical disk medium according to claim 1, which is