JP2000339765A - Phase transition type optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-reliability medium which has good recording and reproducing characteristics at the time of initial writing and at the time of repetitive overwriting at higher density, has excellent environment characteristics and allows long-term data preservation by using a phase transition recording material consisting of Ag, In, Sb and Te as essential elements. SOLUTION: This optical recording medium is constituted by successively laminating at least a lower protective layer, a recording layer, an upper protective layer and a reflection layer on a transparent substrate. The recording layer is the phase transition recording layer utilizing the reversible phase transition between an amorphous and a crystalline phase. In such a case, the material expressed by AlxTiyM(100-x-y) (where M is at least one element selected from the group consisting of Fe, Co, Ni and V and the weight% of the respective elements is 95<x<100, 0<<=0.5 and M>=Ti) and/or AgxTiyM(100-x-y) (where M is the same as above and the weight% of the respective elements is 90<x<100, 0<y<5) is used as the material constituting the reflection layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change optical disk.

[0002]

2. Description of the Related Art As a material used for a recording layer of a rewritable phase change recording medium utilizing a phase transition between an amorphous phase and a crystalline phase,
There are Ge-Sb-Te and Ag-In-Sb-Te, which are roughly classified into these two types. Ge-Sb-Te-based materials have already
It is applied to VD-RAM (single-sided capacity of 2.6 GB). On the other hand, Ag-In-Sb-Te system is already CD-RW
At present, the possibility of a larger-capacity recording medium has been studied, and it has been found that the medium is suitable for high-density recording materials.

[0003] In a phase change recording material in which the main elements are made of Ag, In, Sb, and Te, the boundary between the recording marks, that is, the phase boundary between the amorphous phase which is the mark and the crystal phase which is between the marks is clear. And good characteristics. Even in the case of overwriting, the boundary between the amorphous phase and the crystalline phase is sharp at the periphery of the recording mark, and the characteristics are good. Therefore, the recording / reproducing characteristics of the medium are good. The amorphous phase, which is a mark portion of the recording layer, is formed by rapid cooling by a metal reflection film mainly composed of a noble metal (Au, Ag, Cu) and Al having high thermal conductivity. However, it is necessary that the reflective film does not deteriorate in properties when exposed to high temperature and high humidity, and it is difficult to use expensive materials (Au, Pt, etc.) from the viewpoint of cost in mass production of media. Al alloys are mainly used. As the Al alloy, a system to which Ti is added is typical (JP-A-8-241537). There are other binary alloys mainly composed of Ag (JP-A-6-243).
509).

[0004]

SUMMARY OF THE INVENTION The present invention relates to Ag, I
Uses a phase change recording material containing n, Sb, and Te as main elements, and has higher density, good recording and reproduction characteristics during initial writing and repeated overwriting, excellent environmental resistance, and long-term data storage. The purpose is to provide highly reliable media.

[0005]

Means for Solving the Problems The present inventors have focused on a reflection layer of a phase change recording medium to solve the above-mentioned problem, and can solve the above-mentioned problem by improving the reflection layer. Was.

The characteristics required for the reflection layer of the phase change type optical recording medium are high thermal conductivity and excellent mechanical properties so as not to be thermally deformed in a high temperature state corresponding to the melting point of the recording layer material or at room temperature and high temperature. Being, crystallizing,
Crystal growth is difficult, and corrosion is difficult even in a high temperature and high humidity environment. In order to satisfy these requirements, it is effective to add another element to the main metal material. However, depending on the added element and the added amount, disadvantages such as a decrease in the originally required high thermal conductivity and segregation of the added element due to environment and heat occur. Therefore, there is a limit to the additive element and its amount.

The present inventors have proposed a third method which is more effective when a low-cost Al reflective film is combined with a Ti-added element.
Adding an element to improve the properties as a reflective film,
Focusing on an Ag reflective film having a higher thermal conductivity than Al to improve the corrosion resistance of Ag, and the case where the upper protective layer provided between the recording layer and the reflective layer is made of a material made of ZnS and SiO ₂ By examining the media configuration for suppressing the reaction under high temperature and high humidity, it was possible to provide a phase change type optical recording medium which maintained the recording / reproducing characteristics and ensured high reliability.

That is, the present invention is constituted by sequentially laminating at least a lower protective layer, a recording layer, an upper protective layer and a reflective layer on a transparent substrate, and the recording layer has an amorphous phase and a crystalline phase. In a phase-change optical recording medium that is a phase-change recording layer using a reversible phase change, a material represented by the following formulas (1) and / or (2) is used as a material forming a reflective layer. I do.

Embedded image AlxTiyM _(100-xy) (1) (wherein, M is at least one element selected from the group consisting of Fe, Co, Ni and V. , 95% <x <100, 0 <y ≦ 0.5, and M ≧ Ti)

Embedded image AgxTiyM _(100-xy) (2) (in the formula, M is the same as described above. In addition, the weight% of each of the above elements is used.)
Is 90 <x <100, 0 <y <5)

Hereinafter, the configuration and function of the optical recording medium of the present invention will be described in the case where the above-mentioned layers are laminated to a predetermined thickness on a substrate in the order of a lower protective layer, a recording layer, an upper protective layer, and a reflective layer. This will be specifically described as an example. However, the configuration of the optical recording medium is the basic configuration of the optical recording medium of the present invention, and is not limited to these configurations.

The substrate is, for example, a polycarbonate substrate. In the case of the substrate, the thickness of the substrate is 0.6 mm, and the substrate is laminated with a UV curable resin, an adhesive sheet, or the like to have a thickness of 1.2 mm.

As the lower and upper protective layers, ZnSSiO
_And a dielectric material consisting of
_{iOx, ZnO, SnO 2, Al} 2 O 3, TiO 2, I
_{n 2 O 3, In-Sn} -O, MgO, ZrO 2, Ta 2
Metal oxides such as O ₅ , Si ₃ N ₄ , AlN, TiN, B
Nitrides such as N, ZnS, ZnSe, TaS ₄ or, Si
Carbides such as C, TaC, B ₄ C, WC, TiC, ZrC and the like can be mentioned. These materials may be used alone or as a mixture thereof. The thickness of the lower protective layer is 50 to 25
If the thickness is less than 50 nm at 0 nm, the environmental resistance protection function decreases, the heat resistance decreases, and the heat radiation effect decreases, which is not preferable.
However, if the lower protective layer is made up of multiple layers of different materials to improve these disadvantages, it is better to make one layer thinner than 50 nm. If the thickness is more than 250 nm, there are problems such as film peeling and crack generation due to an increase in film temperature in the film forming process by a sputtering method or the like, and warpage of the substrate increases. The thickness of the upper protective layer is in the range of 10 to 100 nm, preferably 15 to 50 nm. In the case of the upper protective layer, if the thickness is less than 10 nm, the heat resistance is basically lowered and the recording sensitivity is lowered, and if it is more than 100 nm, the overwrite characteristics are repeatedly deteriorated due to deformation and heat radiation.

The thickness of the recording layer is preferably from 10 nm to 30 nm. Further, as a material constituting the recording layer,
A quaternary material composed of g, In, Sb, and Te is preferable.
The quaternary material has a composition represented by a chemical formula of Agα, Inβ, S
In the case of bγ and Teδ, the optimum composition satisfies the following requirements. 1 ≦ α <10 1 <β ≦ 20 35 <γ ≦ 70 20 ≦ δ ≦ 35 α + β + γ + δ = 100 where the material constituting the recording layer of the present invention is Ag,
It is not limited to a quaternary material composed of In, Sb, and Te.

The reflection layer of the optical recording medium of the present invention will be described. The reflective layer is made of the above formula (1) or (2) having a specific effect by a combination of certain additional elements in an alloy system mainly containing Ag or Al, which has been mainly used in optical recording media so far. Ag or A represented by
This is a reflective film made of an alloy. Ag, the main element
Alternatively, the Al material is lower in cost than Au and Pt.
Ag is a reflective layer material that has high thermal conductivity and high reflectivity and is suitable for a phase-change recording medium. On the other hand, Al also has relatively high thermal conductivity and reflectance. These reflective layer materials alone have poor corrosion resistance even though they are excellent in physical properties. Further, in the phase change recording method, heat is applied to near the melting point of the recording layer material, and high temperature and room temperature are repeated. Therefore, the mechanical strength (hardness), deformation and concomitant unevenness, or the portion near the interface on the protective layer side. There is a characteristic change due to crystal growth. On the other hand, the same applies to Ag alone. However, Ag has another problem. ZnSSiO ₂ used for the protective layer, especially when placed under high temperature and high humidity
The reaction between the S component and Ag is promoted to form a sulfide, and the recording / reproducing characteristics deteriorate.

In order to solve these problems, the original characteristics of Al and Ag are kept as much as possible to improve corrosion resistance under high temperature and high humidity, to improve mechanical characteristics, and to maintain flatness. The additive element focuses on the currently used Ti, and when combined with other additional elements, has a more specific effect even with a small amount of Ti, Fe,
That is, a ternary alloy represented by the above formula (1) or (2), which is combined with at least one of Co, Ni, and V elements. In the case of the alloy represented by the formula (1), T
i amount is 0 to 0.5 wt%, and Fe, Co, Ni, V
Is less than 5 wt%. These unique effects include not only corrosion resistance but also high mechanical properties, particularly high hardness, and crystallization is suppressed. Among Fe, Co, Ni, and V, the order of good characteristics is Fe>V>Co> Ni. Further, it is more effective that the amounts of these additional elements are in relation to Ti such that M ≧ Ti.

On the other hand, in the case of Ag, the smaller the amount of the added element, the better, but the total content of Ti and the third added element M is preferably less than 5 wt%. Also in this case, the preferred order of the elements is Fe> V
>Co> Ni. However, even if the reflective layer is formed using an Ag alloy, the problem remains. The protective layer constituting the medium, particularly the upper protective layer in contact with the reflective layer, is ZnS,
This is deterioration of the medium due to sulfide formation that occurs under high temperature and high humidity in the case of SiO ₂ . In order to suppress or prevent this, a layer made of the Al alloy is formed between the upper protective layer and the Ag alloy reflective layer, and the Al alloy layer is formed from the first reflective layer and the Ag alloy layer is formed from the second reflective layer. In a two-layer configuration. However, the thickness of the first reflective layer is preferably smaller than the thickness of the second reflective layer.
Preferably, the first reflection layer (Al alloy layer) / the second reflection layer (A
g alloy layer) = 0.1 to 0.5 is preferable, but in order to make use of the characteristics of Ag, it is more preferable that the first reflective layer has a minimum thickness in a range that can prevent the reaction. In spite of such a problem, the Ag alloy is used not only for the heat dissipation described above, but also when the film is formed by the sputtering method, the film forming speed is about three times faster than that of Al. In addition, since it can be formed at a high speed, there is an advantage that the temperature rise of the medium is suppressed, and the warpage and deformation of the substrate, which is likely to occur with a thin substrate having a thickness of 0.6 mm, can be reduced.

It is important for the thickness of the reflection layer to efficiently release heat, and the thickness is preferably 30 nm to 250 nm. Preferably it is 50 nm to 200 nm. If the film thickness is too large, the heat radiation efficiency is too good to lower the sensitivity, and the substrate tends to be warped due to a rise in the film temperature. If it is too thin, the sensitivity is good, but the overwrite characteristics repeatedly deteriorate.

[0017]

Examples of the present invention will be described below. Examples 1-12, Comparative Examples 1-3 Thickness 0.6 mm, T.I. On the polycarbonate substrate P0.74Myuemu, it was deposited ZnSSiO ₂ lower protective film on a substrate by sputtering. Ag5, In3, Sb6
3. A phase change recording layer made of Te28 (atomic%) was laminated. Next, a ZnSSiO ₂ upper protective layer is laminated, and Al
-Ti-M of the Ti-M reflective layer was added at a predetermined ratio, and an organic protective film was formed thereon with a thickness of several μm. After that, the used substrate and the same substrate were used as a bonding medium with an ultraviolet curable resin. Thereafter, initialization was performed to crystallize the entire surface. Linear velocity 3.5 m / s to 6.5 m / s, recording frequency 26 MHz
５０50 MHz, 8-16 modulation, recorded by PWM method.
After recording, after measuring the reflectance and Block error number,
After a continuous 500 hour test under high temperature and high humidity of 80 ° C. and 85% RH, the reflectance and the Block error number were measured again. The test was further performed for 500 hours, and was performed for a total of 1000 hours. Table 1 shows examples. As a comparative example, T
The same test results are shown when only i is added at less than 0.5 wt%.

[0018]

[Table 1]

Examples 13 to 27, Comparative Examples 4 to 6 On the polycarbonate substrate P0.74Myuemu, it was deposited ZnSSiO ₂ lower protective film on a substrate by sputtering. Ag5, In3, Sb6
3. A phase change recording layer made of Te28 (atomic%) was laminated. Next, a ZnSSiO ₂ upper protective layer is laminated, and Ag
-Ti-M of the Ti-M reflective layer was added at a predetermined ratio, and an organic protective film was formed thereon with a thickness of several μm. Further ZnSS
the iO ₂ upper protective layer, Ag98.5, Ti0.5, F
e, a medium (ratio of atomic%) was prepared, Ti and M of the Ag-Ti-M reflective layer were added at a predetermined ratio, and another organic protective film having a thickness of several μm was formed thereon. Was prepared. afterwards,
A substrate using each medium and the same substrate were used as a bonding medium with an ultraviolet curable resin. Thereafter, initialization was performed to crystallize the entire surface. Recording was performed by a linear velocity of 3.5 m / s to 6.5 m / s, a recording frequency of 26 MHz to 50 MHz, 8-16 modulation, and a PWM method. After recording, reflectivity and Block ero
After measuring the r-number, a test was conducted continuously at a high temperature and high humidity of 80 ° C. and 85% RH for 500 hours, and then the reflectance and the Block were again measured.
The error number was measured. Table 2 shows examples. As a comparative example, a similar test result when only Ti is added to Ag at less than 0.5 wt% is shown. However, ZnSS is used for the upper protective layer.
Since iO ₂ is used, Al 99.5, Ti 0.5 w
The layer which is t% is sandwiched. The total thickness of the reflective layer is 140 n
m. From the above results, in terms of reflectance change and Error number, Al-Ti-M of the above formula (1) or Ag-Ti-M of the above formula (2) (M is at least one selected from Fe, V, Co, and Ni). Addition) The reflective layer using the alloy is A
Compared to 1-Ti and Ag-Ti, both the rate of change and the number of errors are smaller, indicating that the reflective layer material is more excellent in corrosion resistance.

[0020]

[Table 2]

[0021]

[Effect] 1. Claim 1 It is possible to provide a phase change type optical recording medium having a reflective layer having excellent corrosion resistance, mechanical properties and flatness. 2. Claim 2 It is possible to provide a highly reliable optical recording medium which maintains corrosion resistance, mechanical properties, and flatness and does not form sulfide even when a ZnSSiO ₂ protective layer is used. 3. [Claim 3] The recording / reproducing characteristics are maintained by maintaining the corrosion resistance, the mechanical properties, and the flatness, by using the ZnSSiO ₂ protective layer, by forming no sulfide, and by using the Ag property even with two reflective layers. An excellent optical recording medium can be provided. 4. (4) In addition to the effects of the above (1) to (3), an optical recording medium having excellent recording / reproducing characteristics can be provided.

Continued on the front page (72) Inventor Katsunari Hanaoka 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. 5D029 JA01 MA13 MA15 MA16

Claims (4)

[Claims] 1. A reversible phase change between an amorphous phase and a crystalline phase, wherein at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer are sequentially laminated on a transparent substrate. In a phase-change optical recording medium which is a phase-change recording layer using a material, a material represented by the following formulas (1) and / or (2) is used as a material forming a reflection layer. Optical recording medium. Embedded image AlxTiyM _(100-xy) (1) (wherein M is at least one element selected from the group consisting of Fe, Co, Ni and V. And the weight% of each element is 95 <x <100, 0 <y ≦ 0.5, and M ≧ Ti). AgxTiyM _(100−xy) (2) Wherein M is the same as above.
Is 90 <x <100, 0 <y <5) 2. When the upper protective layer is a dielectric protective layer composed of ZnS and SiO ₂ , the first reflective layer is made of a reflective layer material of the formula (1) in contact with the reflective layer. 2. The phase-change optical recording medium according to claim 1, wherein the medium has a two-layer structure including a layer and a second reflective layer formed of the reflective layer material of the formula (2) on the first reflective layer. 3. The phase-change optical recording medium according to claim 2, wherein the thickness ratio of the first reflective layer to the second reflective layer is 0.1 to 0.5. 4. As a constituent material of the phase change recording layer, Ag,
A quaternary material comprising In, Sb, and Te is used.
3. The phase-change optical recording medium according to any one of 3.