JPH08329521A - Optical recording medium - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a phase change type optical recording medium having a reflectance and a signal modulation degree conforming to the CD standard and capable of recording at the same linear velocity as the reproducing speed of the CD standard. A phase change in which recording is performed by providing a metal layer, a first protective layer, a recording layer, a second protective layer, and a reflective layer on a substrate and changing the crystalline state of the recording layer from an amorphous state. Optical recording medium. The recording layer is Ge-Te-Sb-
The recording layer is composed of a Se-based recording material, and the average composition in the film thickness direction of the recording layer, expressed in atomic%, satisfies Ge ≧ 40% and Sb + Se ≦ 25%. The reflectance is 70% with respect to the reproducing light when the recording layer is in either the crystalline state or the amorphous state.
It is above, and it is less than 40% in the other state. AuCo alloy is used as the metal layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a phase-change type optical recording medium in which recording is performed by a phase change between amorphous and crystalline, and particularly, a phase change type optical recording medium having a reflectance and a signal modulation degree conforming to the CD standard. The present invention relates to a variable recording medium.

[0002]

2. Description of the Related Art Currently, a reproduction-only optical disc is a C for music.
D, CD-ROM, CD-I, video C
It is widely used in the fields of music, video, and computers such as D. In general, an optical disc is produced by forming concave pits on a plastic substrate such as polycarbonate in advance and then coating a metal reflective layer such as aluminum, and irradiating it with a laser beam to determine the presence or absence of pits (signal). It is read as the difference in the amount of reflected light. This technology was first established as a standard for music, and was used in 1982.
The first product of the year was launched. This has been accepted in the market because of its excellent random accessibility, the size of the medium being 80 to 120 mm, which is easy to handle, and the low cost of the medium and the system. Came to. Next, a CD-ROM for data, a CD-I that can handle still images and moving images, a karaoke CD, which applies this technology,
A standard such as a video CD has been established, and various applications conforming to this standard have appeared. Also, 1
A write-once CD that allows data to be added only once in 1988.
(CD-R) was announced, small-volume CD publishing and CD-RO
A market is being formed for debugging during M development.

A rewritable medium has also been rapidly developed, and a rewritable medium utilizing a magneto-optical phenomenon of a magneto-optical recording material such as a transition metal-rare earth metal system or a reversible atomic arrangement change such as a phase change. Those used are known, and many are commercialized today. As the phase change recording medium, for example,
Ge-Sb-disclosed in JP-A-61-258787
Te-X recording material (X is Al, Si, Ti, etc.),
Ge-Te-disclosed in Japanese Patent Laid-Open No. 62-152786
ABC recording material (A is Sb, Sn, etc., B is Tl)
C, Co, Se, etc.) are known. Such a rewritable recording medium also has the above-mentioned CD or CD-R.
It is desirable to be able to reproduce information using a player or drive device compatible with OM.

Therefore, a rewritable medium (hereinafter referred to as a rewritable medium that can be reproduced by a CD player or a CD-ROM drive) is used.
Rewritable CDs) are being researched and developed centering on phase change recording media. For example, JP-A-4
No. 228126, Sb-Se based recording materials and Ge-
A technique relating to a rewritable CD using a Te-based recording material is disclosed.

Proceedings of the 5th Phase Change Recording Workshop Symposium Proceedings 5 to 8 and 9 to 14
The page discloses a technique relating to a rewritable CD using an In-Ag-Te-Sb-V recording material and a rewritable CD using a Ge-Sb-Te recording material.

[0006]

By the way, in order to reproduce information with a CD player or a CD-ROM drive, the characteristics such as reflectance and signal modulation of the optical recording medium are in accordance with the CD standard (Red Book). Need to meet. That is, the reflectance is 7 for light having a wavelength of 770 to 830 nm.
0% or more, EFM (Eight-Fourteen Modulation; 8-
14 modulation signal, the signal modulation degree when the 11T signal which is the longest mark is recorded at a mark interval of 11T is 60% or more, and the signal modulation degree when the 3T signal which is the shortest mark is recorded at a mark interval of 3T is 30%. It must satisfy the conditions such as ~ 70%.

However, the above-mentioned commercialized phase change type or magneto-optical type optical recording medium has a low reflectance, so that C
It did not meet the D standard and was not compatible with CD-related systems. Therefore, the phase change type or magneto-optical type optical recording medium is
Information cannot be reproduced by a CD player or a CD-ROM drive, and conversely, a music CD medium or a CD-ROM medium cannot be reproduced by a phase change medium drive or a magneto-optical medium drive. was there. Therefore,
As a playback system for recording media of phase change type or magneto-optical type,
I had no choice but to build a system completely different from the CD-related system.

On the other hand, as a rewritable CD, a possibility of being reproduced by a CD player or a CD-ROM drive using an overwritable phase change type optical recording medium has been shown, but in order to satisfy the CD standard. No one is known that simultaneously satisfies a high reflectance of 70% or more and a large signal modulation degree of 60% or more. In these phase-change optical recording media, the initial state and erased state correspond to the crystalline state with high reflectance, and the recording state corresponds to the amorphous state with low reflectance. In the case of recording, the film surface required a large laser power of 50 mW or more. In addition, when new information is directly overwritten on the old information by the mark edge method, if the amorphous portion where the old recording mark remains and the unrecorded crystal portion are irradiated with the laser light of the recording power. Since the amorphous part has a low thermal conductivity and a high endothermic effect, the former part is more likely to absorb and accumulate more heat than the latter part. As a result, there is a problem that the new recording mark is distorted and the jitter is increased.

Furthermore, since the linear velocity during reproduction is 1.2 to 1.4 m / sec according to the CD standard, even if a phase change recording medium that can be reproduced by a CD drive is developed,
It is desirable to be able to record at a linear velocity of 2 to 1.4 m / sec. However, at such a relatively low linear velocity, even if the recording layer is irradiated with light at the time of recording, the cooling rate of the recording layer becomes slow, so that the change from the crystalline state in the initial state to the amorphous state occurs. Less likely to happen. Therefore, even if the recording is performed at the linear velocity as described above in consideration of the crystal velocity and the thermal conductivity of the recording material, the recording is performed because the phase change from the crystalline state to the amorphous state surely occurs. It is necessary to select a phase change type recording material that

Japanese Unexamined Patent Publication (Kokai) No. 5-047036 discloses a recording layer having a G layer.
By using the e-Sb-Te system and using transparent interference layers above and below the recording layer and adjusting the film thickness and refractive index of each layer, the reflectance of the amorphized film in the recorded state is in the unrecorded state. A write-once type optical recording medium having a higher reflectance than that of a crystallized film is disclosed. However, it is not disclosed how much reflectance was actually obtained from the recording layer.

SPIE, Vol.2338, OPTICAL DATA STORA
GE, pp. 94-106 discloses a technique relating to a rewritable phase change type CD using a Ge-Sb-Te-Se based recording material. By using this recording material,
It is disclosed that a reflectance of 70% can be obtained for reproduction light. However, this phase change type C
The signal modulation degree of D was smaller than the value of the CD standard, and the number of rewritable times was about 10 times, which was not sufficient in terms of practicality. The Ge-Sb-Te-Se based recording material has a composition different from that of the Ge-Sb-Te-Se based recording material used in the present invention.

It is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to provide a phase change type optical recording medium having a reflectance and a signal modulation degree which conform to the CD standard.

Another object of the present invention is to provide a phase change recording medium which can prevent the recording mark from being deformed even when recording / reproducing by the mark edge method.

A further object of the present invention is to provide a phase change recording medium capable of recording with low laser power.

Still another object of the present invention is to provide a phase change type optical recording medium which has a reflectance and a signal modulation degree conforming to the CD standard and is recordable at the same linear velocity as the reproducing speed of the CD standard. It is in.

[0016]

To solve the above problems, according to one embodiment of the present invention, a metal layer, a first layer, and a metal layer are provided on a substrate.
Recording is performed by providing a protective layer, a recording layer, a second protective layer, and a reflective layer, and when the atomic arrangement of the recording layer changes from a stable state to a metastable state, recording is performed. In an optical recording medium subjected to erasing and erasing, the recording layer is composed of a material containing Ge, Te, Sb and Se as the main components, and the average composition in the film thickness direction of the recording layer is expressed in atomic%. ≧ 40% and Sb + Se ≦ 25% are satisfied, and when the atomic arrangement of the recording layer is in a stable state, the reflectance of the recording medium is 40% or less with respect to the reproducing light, and the atomic arrangement of the recording layer is There is provided an optical recording medium characterized in that the reflectance of the recording medium is 70% or more with respect to the reproducing light when is in a metastable state. In the above optical recording medium, the refractive index n ₁ and the film thickness d ₁ of the first protective layer, the refractive index n ₂ and the film thickness d _{2 of} the second protective layer, the refractive index n _c and the extinction of the recording layer in the stable state. Coefficient k _c , refractive index n _a and extinction coefficient k _{a of} the recording layer in the metastable state, film thickness d _{r of the} recording layer, and wavelength λ of the recording / reproducing light,

(Equation 3) It is preferable to satisfy the following relationship.

According to a second aspect of the invention, on the substrate:
A metal layer, a first protective layer, a recording layer, a second protective layer, and a reflective layer are provided, and recording is performed by changing the atomic arrangement of the recording layer from a stable state to a metastable state. In an optical recording medium in which initialization and erasing are performed by changing the recording layer, the recording layer is composed of a material containing Ge, Te, Sb, and Se as main components, and the average composition in the film thickness direction of the recording layer is atomic%. , Ge ≧ 40% and Sb + Se ≦ 25% are satisfied, and when the atomic arrangement of the recording layer is in a stable state, the reflectance of the recording medium is 70% or more with respect to the reproducing light, There is provided an optical recording medium characterized in that the reflectance of the recording medium is 40% or less with respect to the reproducing light when the atomic arrangement of the recording layer is in a metastable state.

In the optical recording medium according to the second aspect of the present invention, the refractive index n ₁ and the film thickness d ₁ of the first protective layer, the refractive index n ₂ and the film thickness d _{2 of} the second protective layer are stable. Refractive index n _c and extinction coefficient k _{c of} a certain recording layer, refractive index n _a and extinction coefficient k _{a of} a recording layer in _a metastable state, film thickness d of the recording layer
_r and the wavelength λ of the recording / reproducing light,

[Equation 4] It is preferable to satisfy the following relationship.

In the optical recording medium of the present invention, in the average composition in the film thickness direction of the recording layer, the atomic% of Ge is Ge ≧ 40.
% And the atomic% of Sb and Se is Sb + Se ≦ 25
%, The recording layer is changed from a crystalline state to an amorphous state by light irradiation during recording even when recording is performed at a linear velocity of 1.2 to 1.4 m / s at the time of reproduction as defined by the CD standard. It can be changed to a state and reliable recording is performed. The average composition in the film thickness direction of the recording layer is preferably expressed in atomic%: 40% ≦ Ge ≦ 64% 45% ≦ Te ≦ 59% 1% ≦ Sb + Se ≦ 20% Sb <Se. By allowing Ge, Te, Sb and Se to coexist in the recording layer at the above ratio, the amorphous state can be stably maintained, and crystallization at the time of recording / erasing can be performed at high speed. More preferably, 40% ≤ Ge ≤ 55% 35% ≤ Te ≤ 50% 5% ≤ Sb + Se ≤ 20% Sb <Se, and particularly preferably 40% ≤ Ge ≤ 50% 35% ≤. Te ≦ 45% 10% ≦ Sb + Se ≦ 20% Sb <Se.

Ge, Te, Sb, Se are formed on the recording layer.
It is possible to include elements other than, and it is preferable to include them in a ratio of 10 atomic% or less. Ge that can be included in the recording layer,
Elements other than Te, Sb, and Se include Au, Ag, and C.
u, Pd, Ta, W, Ir, Sc, Y, Ti, Zr,
V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh
And a metal element having a high melting point such as Ni. These elements have the effect of facilitating the absorption of long-wavelength light such as semiconductor laser light and increasing the recording sensitivity, and because they are difficult to melt during recording and erasing, they tend to form crystal nuclei during crystallization, and high speed. Promotes crystallization. Further, an element having an effect of improving the crystallization rate and improving the stability of the amorphous state, such as Tl, a halogen element, or an alkali metal, can be included. When an element such as Tl and a refractory metal such as Co coexist, high-speed crystallization is possible, stability in an amorphous state is high, and recording sensitivity is high. When either one of the element such as Tl and the refractory metal such as Co is added, the addition of the element such as Tl is preferable from the viewpoint of easy film formation, but the oxidation resistance is lowered. Also, N, O,
Inactive elements such as H and Ar can also be included,
These have the effect of increasing the recording sensitivity by setting the thermal conductivity to an appropriate value, and the effect of improving the stability of the amorphous state. These also have the effect of suppressing the noise level by reducing the crystal grain size. Further, by adding a rare earth element or the like to the recording material in an amount of 1 to 5%, the reproduction signal intensity can be increased and the crystallization temperature can be increased. Above G
When at least two kinds of elements other than e, Te, Sb, and Se that can be contained in the recording layer are contained in the recording layer, these may be contained in the form of a compound.
For example, oxides such as SiO ₂ and Al ₂ O ₃ , ZnS
Such as sulfides, fluorides such as MgF ₂ , Si ₃ N ₄ , A
Examples thereof include nitride such as 1N and carbide such as SiC. These compounds have the effects of adjusting the optical constant of the recording layer to an appropriate value to increase the reflectance and increase the signal modulation degree. It also has the effect of increasing the recording sensitivity by adjusting the thermal conductivity to an appropriate value. When the above elements are added to the recording layer, they may form a compound with at least one element of Ge, Te, Sb and Se. For example, Z
nTe, Ag ₂ Te, SnTe, Cr ₄ Te ₅ etc. are
Since it has a high melting point and does not easily melt during recording and erasing, it easily forms crystal nuclei during crystallization, enabling high-speed crystallization.
It also has the effect of preventing physical deformation due to the flow of the recording layer and enables rewriting many times.

If the average composition in the film thickness direction is within the above range, the composition of the recording layer may be changed in the film thickness direction.
The change in the content of each element in the film thickness direction is usually small, but there may be any pattern change. However, it is preferable that the composition change is continuous. Sb, S
From the viewpoint of oxidation resistance, it is preferable that e and S have a higher content in the vicinity of one of the interfaces of the recording layer or in the interface with another layer than in the inside of the recording layer.

When the extremely small acicular magnetic material is uniformly dispersed or precipitated in the recording layer, the crystal is promoted with these as nuclei. Also, when recording is performed in an external magnetic field, the acicular magnetic material aligns with the direction of the external magnetic field when the recording layer melts, so when recording with an external magnetic field of zero, this magnetic material is oriented in a random direction. Compared with, it is possible to create a crystalline state or an amorphous state having a different structure.
This makes it possible to combine laser light modulation and magnetic field modulation
Three different states can occur.

When forming the recording layer, an intermediate layer may be provided in the recording layer so that the recording layer is divided into two layers. The intermediate layer can control the cooling time of the recording layer, the crystallization process, and the like. Further, by recording information in only one or both of the two recording layers divided by the intermediate layer, it is possible to give one recording bit a plurality of information. . The same material as that for the interface layer can be used for the intermediate layer, but the thickness thereof is preferably 10 nm or less. Further, the intermediate layer does not necessarily have to be formed uniformly and may be formed in an island shape.

In the present invention, the stable state and metastable state of the atomic arrangement of the recording layer typically mean that the atomic arrangement of the recording layer is in a crystalline state and an amorphous state, respectively. However, the present invention is not limited to this, and there may be two different states in which the optical properties are changed by various atomic arrangement changes that hardly accompany the shape change of the film. For example, it may be in a state in which the crystal grain size or the crystal form is different (α, β, π, γ, etc. different crystal states). In the change between the amorphous state and the crystalline state, the amorphous is not completely amorphous, and crystalline portions may be mixed. Also, some of the atoms constituting these layers move (due to diffusion, chemical reaction, etc.) between the recording layer and at least one of the protective layer and the intermediate layer.
This also applies to the case where one of the states can be stable and the other can be the metastable state due to the change of state due to the movement or both the movement and the phase change.

The protective layer used in the optical recording medium of the present invention is, for example, a fluororesin such as acrylic resin, polycarbonate, polyolefin, epoxy resin, polyimide, polyamide, polystyrene, polyethylene, polyethylene terephthalate, and polytetrafluoroethylene (Teflon). It may be formed of organic substances such as oxides, fluorides,
It may be formed of an inorganic material containing a nitride, a sulfide, a selenide, a carbide, a boride, boron, carbon, or a metal as a main component. Also, a composite material of these may be used. Inorganic substances are preferable to organic substances in terms of heat resistance. In the case of a protective layer made of an inorganic material, electron beam evaporation may be formed as it is, by sputtering or the like, but reactive sputtering, metal, metalloid, after forming a film made of at least one element of a semiconductor, The production is facilitated by reacting with at least one of oxygen, sulfur and nitrogen. Examples of the inorganic protective layer include Ce, La, S
i, In, Al, Ge, Pb, Sn, Bi, Te, T
an oxide of at least one element selected from the group consisting of a, Sc, Y, Ti, Zr, V, Nb, Cr and W, Cd,
Sulfide or selenide of at least one element selected from the group consisting of Zn, Ga, In, Sb, Ge, Sn, Pb and Bi, fluorides such as Mg, Ce and Ca, Si and A
l, Ta, B, etc. nitrides, B, Si, etc. carbides, T
i or other boride, boron, or carbon, whose main components are CeO ₂ , La ₂ O ₃ , SiO,
SiO ₂ , In ₂ O ₃ , Al ₂ O ₃ , GeO, Ge
O ₂ , PbO, SnO, SnO ₂ , Bi ₂ O ₃ , TeO
₂ , Ta ₂ O ₅ , Sc ₂ O ₃ , Y ₂ O ₃ , TiO ₂ , Z
rO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , Cr ₂ O ₃ , WO ₂ ,
WO ₃ , CdS, ZnS, CdSe, ZnSe, In ₂
S ₃ , In ₂ Se ₃ , Sb ₂ S ₃ , Sb ₂ Se ₃ , Ga
₂ S ₃ , Ga ₂ Se ₃ , GeS, GeSe, GeS
e ₂ , SnS, SnS ₂ , SnSe, SnSe ₂ , Pb
S, PbSe, Bi ₂ Se ₃ , Bi ₂ S ₃ , MgF ₂ ,
CeF ₃ , CaF ₂ , TaN, Si ₃ N ₄ , AlN, B
N, Si, TiB ₂ , B ₄ C, SiC, B, C and those having compositions similar thereto and mixtures thereof. Of these, sulfides are preferably ZnS or a compound having a composition similar to ZnS in that the refractive index is appropriate and the film is stable. As the nitride, TaN, Si ₃ N ₄ , AlN or AlSiN ₂ and compounds having a composition similar to TaN, Si ₃ N ₄ , AlN or AlN are preferable because the surface reflectance is not so high and the film is stable and strong. Preferred oxides are Y ₂ O ₃ , Sc ₂ O ₃ , CeO ₂ , and T.
iO ₂ , ZrO ₂ , SiO, Ta ₂ O ₅ , In ₂ O ₃ ,
It is a silicon oxide having a composition similar to that of Al ₂ O ₃ , SnO ₂ or SiO ₂ . Amorphous Si containing hydrogen is also suitable. A compound having a composition similar to that of SiAlON is also preferable. The first protective layer and the second protective layer are preferably formed of the same material because the film forming operation is facilitated, but different materials may be used. By appropriately selecting the thermal conductivity and thermal expansion coefficient of the materials used for each, it becomes possible to improve the recording sensitivity and prevent physical deformation of the recording layer.

An interface layer may be provided between the recording layer and the protective layer in contact with the recording layer. This may be provided only on one side of the recording layer or on both sides of the recording layer. By improving the wettability with the recording layer, this interface layer can prevent the recording layer from flowing and improve the number of times of rewriting. The interface layer can also control the crystallization process of the recording layer. The material forming the interface layer is Au, Ag, Cu, Pd, Ta, W, Ir, S.
c, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, F
A metal element or semiconductor element having a high melting point such as e, Ru, Co, Rh, Ni, Pt, Si, or Ge, or an alloy material thereof can be used. In addition, Ce, La, Si, In,
Al, Ge, Pb, Sn, Bi, Te, Ta, Sc,
Oxide of at least one element selected from the group consisting of Y, Ti, Zr, V, Nb, Cr and W, Cd, Zn, Ga, I
n, Sb, Ge, Sn, Pb, Bi, a sulfide or selenide of at least one element selected from the group consisting of M,
g, Ce, Ca, etc. fluorides, Si, Al, Ta, B, etc. nitrides, B, Si, etc. carbides, Ti, etc. boride,
A material different from the material used for the protective film can be used among boron and carbon. When a material having absorption of recording / reproducing light such as a metal or a semiconductor material is used, the film thickness is preferably 10 nm or less. This interface layer does not necessarily have to be formed uniformly and may be formed in an island shape.

The reflective layer used in the optical information recording medium of the present invention is preferably composed of Au, Ag, Cu, Al or at least one of these elements as a main component in terms of high reflectance. When these elements are used alone, the reflectance is extremely high, but the recording sensitivity is lowered due to the large thermal conductivity. A recording medium containing these elements as a main component and a small amount of other elements added thereto has a high reflectance and a small thermal conductivity as compared with the case where these elements are used alone, and thus has good recording sensitivity. For example, when Au is selected as the above element, Ti, Cr, Co, Ni are added as the additional elements.
Are preferred, and Co is most preferred. The content of the additional element is preferably 10 atomic% or less. Alloys of the above elements can also be used. For example, Au-Ag type alloy, Au-
The Cu-based alloy exhibits the same or higher characteristics as the Au alloy in terms of reflectance and recording sensitivity. In this case, the content of each is preferably 25 to 75%. In addition to the above, S
b, Bi, In, Te, Se, Si, Ge, Pb, G
a, As, Zn, Cd, Sc, Ti, V, Cr, Mn,
Fe, Co, Ni, Y, Zr, Nb, Mo, Tc, R
u, Rh, Pd, Hf, Ta, W, Re, Os, Ir,
A reflective layer containing at least one of Pt, a lanthanoid element, and an actinide element as a main component may be used, and these may be used as additional elements.

In the optical information recording medium of the present invention, the metal layer used between the substrate and the first protective layer may be made of the same material as the above reflective layer. As this metal layer, an AuCo alloy is preferable because it has a particularly high reflectance and a thermal conductivity smaller than that when each element is used alone, and improves the recording sensitivity of the optical recording medium of the present invention.

In the optical recording medium of the present invention, it is preferable to further form a protective layer on the side opposite to the recording layer side of the reflective layer. This is, for example, polystyrene, polytetrafluoroethylene (Teflon), polyimide, acrylic resin, polyolefin, polyethylene terephthalate, polycarbonate, epoxy resin, ethylene-vinyl acetate copolymer known as a hot melt adhesive, and the like, and Organic substances such as adhesives and UV curable resins are used. This organic layer may be the substrate. Of course, oxides, fluorides, nitrides, sulfides, selenides, carbides, borides,
Inorganic substances containing boron, carbon, or metal as a main component can also be used. Further, it may have a structure of two or more layers composed of an organic substance and an inorganic substance. By forming the protective film as described above, it is possible to prevent an increase in noise due to the deformation of the recording layer at the time of rewriting the recording.

The above-mentioned layers of the recording medium of the present invention can be formed by various methods, for example, vacuum vapor deposition, vapor deposition in gas,
It can be appropriately selected from sputtering, ion beam evaporation, ion plating, electron beam evaporation, injection molding, casting, spin coating, plasma polymerization and the like. The metal layer, the first and second protective layers, the recording layer, the reflective layer and the inorganic protective layer adjacent to the reflective layer are most preferably formed by sputtering because they have good reproducibility and excellent mass productivity.

In the optical recording medium of the present invention, it is necessary to initialize the entire surface of the recording layer by crystallizing it in advance. When an organic material is used for the substrate, the entire recording medium cannot be heated to a high temperature, so the recording layer is crystallized by another method. In that case, energization for a certain period of time, irradiation of laser light focused to a spot diameter of 2 μm or less, ultraviolet irradiation and heating of xenon lamp, mercury lamp, etc., irradiation of light from flash lamp, high power gas laser and high power semiconductor laser Irradiation with a large light spot of
Alternatively, it is preferable to perform a combination of heating and laser light irradiation. When irradiating light from a high-power gas laser or high-power semiconductor laser, the light spot diameter (half-value width) is 5 μm.
If it is 5 mm or less, the efficiency is good. Also in this case,
When the longitudinal direction of the light spot is perpendicular to the track, the time required for initial crystallization can be shortened. The crystallization may be performed only on the recording tracks, and the tracks may remain amorphous. On the other hand, for example, when a thin film containing Ge, Te, Sb and Se as a main component is formed by rotary evaporation from a plurality of evaporation sources, immediately after the evaporation, Ge, Te, Sb and Se are formed.
Are often not combined. Further, even when formed by sputtering, the atomic arrangement becomes extremely disordered. In such a case, it is preferable to first irradiate the recording track with laser light having a high power density to melt the film in some cases. Further, when the recording track is irradiated with laser light having a low power density to crystallize it, the reflectivity over the entire track tends to be uniform. To record data on the recording medium initialized in this way,
This is carried out by causing the atomic arrangement of the recording layer to change from a crystalline state to an amorphous state by light irradiation. At this time, the irradiation time and the optical power are set so as not to cause a large physical deformation of the recording layer.

The shape of the recording medium of the present invention is not limited to a disk shape, but may be various shapes such as a tape shape and a card shape.

The optical recording medium of the present invention is preferably a recording medium on which recording / reproduction is performed by the mark edge method. This is because recording / reproduction by the mark edge method requires precision of the position of the end portion of the recording mark, and the phase change material of the present invention has very little deformation of the recording mark during recording.

When the data on the recording film is rewritten, new data is recorded after the already recorded data is once erased or is directly recorded by overwriting, but in general, old data written on the same recording track is rewritten. The signal cannot be completely erased, and residual information may occur. The remaining unerased amount is small near the amorphous or near-state region and large near the crystalline or near-state region. Therefore, in order to erase these unerased residuals, the reproduced signal levels from the crystal or near the region close to it should be adjusted to a constant level, or at least the fluctuation should be reduced to reduce the effects of the unerased residuals. It can be reduced. Further, since such an unerased portion is likely to be unevenly distributed on the left and right sides instead of the center portion of the track, a difference occurs in the reflected light incident on each of the plurality of detectors arranged in the direction perpendicular to the track. On the other hand, the newly recorded signal has good symmetry on the left and right sides of the track. Therefore, take the difference between the signal on one side of the track and the detector on the other side,
If you take the appropriate multiple and subtract from the sum of these signals,
It is possible to reduce the signal based on the remaining portion. These methods for suppressing the remaining unerased are effective not only for the phase change type material between the crystal and the amorphous but also for other materials which record by the atomic arrangement change such as the phase change.

When the reflectance in the metastable state such as the amorphous state is set low and the reflectance in the stable state such as the crystalline state is set high as in the present invention, the distortion of the newly recorded mark is caused by the direct overwrite. Although it has an advantage that it is unlikely to occur, the effect can be further enhanced by devising the recording waveform. For example, in a multi-pulse recording method in which a rectangular recording waveform is divided into a plurality of pulses, it is necessary to prevent heat from accumulating at the trailing end of the recording mark and form a mark with good symmetry at the leading and trailing ends of the recording mark. You can N
When recording an EFM signal of T (N = 3 to 11), 1T
A method of generating N pulses of 1 for each, or (N-1)
The method of individually generating can form a multi-pulse waveform with a simple circuit and can form a recording mark having good symmetry and small jitter. If the pulse width is made constant for all the pulses by this method, it is possible to generate a multi-pulse with an extremely simple circuit, which has an advantage that an inexpensive drive can be supplied. On the other hand, when it is desired to change the pulse width, it is possible to form a recording mark with higher symmetry. As a method of changing the pulse width, there are a method of lengthening only the first pulse to quickly raise the temperature of the mark front end portion where it is difficult to raise the temperature, and a method of lengthening the pulse width for the subsequent pulses. The subsequent pulse lengthening method is particularly effective when recording is performed by rotating a medium using a recording film having a high crystallization rate at a low linear velocity (standard linear velocity to double speed of CD-ROM). When the medium is rotated at a low linear velocity, heat easily accumulates in the recording layer, and the cooling time of the recording layer becomes long. Then, even if the recording layer is melted to form an amorphous recording mark, crystallization occurs during cooling and the recording mark cannot be formed. At this time, in the vicinity of the last pulse corresponding to the trailing edge of the mark, it is difficult to store heat and the cooling time is shortest. Therefore, only this portion is amorphized, and a normal mark with good symmetry cannot be formed. Therefore, if the pulse width of the first part is shortened to prevent heat accumulation and the cooling time of the recording layer is shortened, the amorphization is normally performed, and it is possible to form a recording mark with good symmetry. When the pulse width is changed in this way, the change may be continuous or discontinuous. Furthermore, the power of each pulse may be changed. When changing the power, it is preferable that the head pulse has a higher power and the energy of each pulse is substantially constant. When changing only the pulse width or both the pulse width and the power, the recording mark is optimized as a function of the mark length of the mark to be recorded, the distance between the recording mark immediately before and immediately after, the recording mark length immediately before and immediately after, etc. Alternatively, a test writing area may be provided in a part of the medium, and test writing may be appropriately performed in the area, and the recording mark may be adjusted each time to be optimum.

Before forming a new recording mark,
When erasing with continuous light is performed, a recording mark with higher symmetry can be formed. The continuous light erasing may be performed by an optical head for recording, or may be performed by an erasing head other than that. Further, the wavelength of light for continuous light erasing can be changed to that for recording. In this case, the semiconductor laser for recording and the semiconductor laser for continuous erasing having different wavelengths may be condensed by one objective lens, and of course, two heads may be used.

The optical recording medium of the present invention has a linear velocity of 1.2 m / s.
It is preferable that solid phase erasing can be performed as described above. If solid phase erasing is performed, the recording film will not melt during erasing, so the recording layer will flow,
Segregation is less likely to occur and the number of rewrites is improved. Further, when recording and erasing at a linear velocity of 1.2 m / s or more, it is preferable to use a recording layer capable of solid-phase erasing at a linear velocity or more used.
Further, since the phase-change optical recording medium of the present invention is a medium that can be reproduced by a CD player or the like, it can be recorded at the same linear velocity as 1.2 to 1.4 m / s which is the linear velocity when reproducing a CD. Is advantageous in reading data.

[0038]

According to the optical recording medium of the present invention, the reflectance of the recording medium is as low as 40% when the atomic arrangement of the recording layer is in a stable state, that is, when the recording medium is in the initialized state. In addition, the light absorption rate of the recording layer becomes large, and when recording, high sensitivity recording can be performed with a small laser power. Further, when performing direct overwrite in which new information is directly recorded on old information, the reflectance of the recording mark (amorphous state) is set higher than the reflectance of the erased state (crystalline state). The light applied to the portion of the recording mark is difficult to be absorbed, and the light applied to the portion without the recording mark is easily absorbed. FIG. 8 shows a reflectance distribution 35 when a new mark is recorded on an old recording mark in a conventional phase change recording medium. Until now, since the reflectance of the old mark 31 was low, the light of high laser power during recording was more absorbed by the portion 33 where the new mark 32 overlaps. Furthermore, since the thermal conductivity of the amorphous portion where the recording mark exists is low, heat is more likely to accumulate at the tip portion 33 of the new recording mark. Since the accumulated heat gradually diffuses from the portion 33, the tip portion 33 of the recording mark 32 is easily deformed. On the other hand, in the present invention, since the reflectance distribution is inverted between the recording mark and the initialization portion, heat is less likely to be accumulated in the new recording mark portion 33 overlapping the old recording mark. On the other hand, since the thermal conductivity of the recording mark is smaller than that of the initialized portion, the heat is likely to stay in the portion 33 where the heat is less accumulated, and conversely, the portion where the heat is accumulated (other than the portion 33 of the mark 32). Heat easily escapes from the area. As a result, even if a new recording mark is formed by irradiating the portion where the old recording mark remains and the portion where the old recording mark does not exist, the influence of the heat absorption rate and the conductivity on the recording mark is offset, and the mark The distortion becomes smaller than that of the mark in the conventional phase change recording medium.

In the present invention, the condition of the reflectance as described above can be achieved by adjusting the film thickness and the refractive index of the first and second protective films and the recording layer as follows. . That is, the refractive index n ₁ and the film thickness d ₁ of the first protective layer, the refractive index n ₂ and the film thickness d _{2 of} the second protective layer, the refractive index n _c and the extinction coefficient k _{c of} the recording layer in the stable state, For the refractive index n _a and the extinction coefficient k _{a of} the recording layer in the metastable state, the film thickness d _{r of the} recording layer, and the wavelength λ of the recording / reproducing light,

[0040]

(Equation 5) The recording medium is configured to simultaneously satisfy the following relationship.

Equation (1) absorbs light of wavelength λ when the recording layer is in a metastable state such as an amorphous state, rather than in a stable state such as a crystalline state. The conditions for difficult materials are shown below. The left-hand side of equation (2) and (3), when the light passes through the recording layer having a thickness of d _r, represents the amplitude ratio of the light transmitted through the recording layer to the amplitude of the incident on the recording layer light. In the formula (2), when the recording layer is in a metastable state, the desired range of light transmission through the recording layer is shown. FIG. 4 shows how light is reflected from the optical recording medium in this case. Since a relatively large amount of light passes through the recording layer 17, the contribution of the reflected light from the interface between the second protective layer 18 and the reflective layer 19 is large in the entire reflected light from the recording medium. Therefore, reflected light 21 at the interface between the substrate 14 and the metal layer 15 (hereinafter referred to as reflected light 1) and reflected light 22 at the interface between the second protective layer 18 and the reflective layer 19 (hereinafter referred to as reflected light 4). It is possible to improve the reflectance of the entire recording medium by causing an interference action between the recording medium and the recording medium. When the influence of this interference action is investigated by examining the relationship between the film thicknesses of the first protective film 16 and the second protective film 18, the sum of the film thicknesses of the first protective layer 16 and the second protective layer 18 is summed up. It has been found that the reflectance from the entire recording medium is substantially constant when is constant. That is, the isoreflectance line 23 as shown in FIG. 5 can be written for the film thicknesses of the first and second protective layers. Here, for the sake of simplicity, the first protective layer 16 and the second protective layer 18 are made of the same material, considering that the film thickness, the refractive index, etc. of the recording layer are constant.

On the other hand, the expression (3) shows that when the recording layer is in a stable state, the amount of light transmitted through the recording layer should be below a predetermined value. That is, of the reflected light from the entire recording medium, the amount of light that passes through the recording layer is limited to reduce the influence of reflected light from the interface between the second protective layer 18 and the reflective layer 19. In the material satisfying this condition, as shown in FIG. 6, reflected light 21 (reflected light 1) at the interface between the substrate 14 and the metal layer 15 and reflection at the interface between the first protective layer 16 and the recording layer 17 are obtained. The interference with the light 26 (reflected light 2) has a great influence on the overall reflectance. When the relationship between the total reflectance and the film thickness of the first protective layer 16 and the second protective layer 18 is examined, it is possible to draw an equireflectance line as shown in FIG.
The reflectance from the entire recording medium almost depends only on the film thickness of the first protective layer 16.

When FIG. 5 and FIG. 7 are overlapped, the isoreflectance line 24 that maximizes the overall reflectance Ra when the recording layer is in an amorphous state and the recording layer in the crystalline state are shown. There is a point where the iso-reflectance line 25 that minimizes the overall reflectance Rc at a certain point intersects, and the reflectance difference between the crystal and the amorphous is measured in a relatively wide region around this point. You can see that it can be taken big. Therefore, by satisfying the expressions (2) and (3), the first
Also, a large difference in reflectance can be obtained between crystalline and amorphous while maintaining a wide margin with respect to the film thickness of the second protective layer.

[0044] Equation (4) to (7) indicate conditions for R _a is not less than 70% and R _c of 40% or less.
Formula (4) represents the reflected light (reflected light 1) at the interface between the substrate and the metal layer and the interface between the second protective layer and the reflective layer when the recording layer is in a metastable state such as an amorphous state. Conditions that interfere with the reflected light (reflected light 4) at and strengthen each other:

[0045]

(Equation 6) It is shown that the deviation from is λ / 4 or less, and it is found that the reflectance from the recording medium becomes 70% or more when this condition is satisfied. It should be noted that Δ1 in the equation represents a phase shift of the reflected light 4 with respect to the reflected light 1 when the optical path difference is not taken into consideration. Δ1 can take various values depending on the material and film thickness of each layer, and can take a value up to λ / 2 as an absolute value. For example, a material containing Au as a main component in the metal layer and the reflective layer, In the case where a material having a refractive index of about 2 is used for the first and second protective layers and a material having a refractive index of about 4 and an extinction coefficient of about 1 is used for the recording layer, Δ1 is calculated to be λ / 20. It will be about. Therefore, equation (4) becomes

[0046]

(Equation 7) At this time, N = 1 is most preferable.

Equation (5) is the reflected light (reflected light 1) at the interface between the substrate and the metal layer and the interface between the first protective layer and the recording layer when the recording layer is in a stable state such as a crystalline state. Conditions that interfere with and interfere with the reflected light (reflected light 2) at:

[0048]

(Equation 8) It shows that the deviation from λ / 4 is λ / 4 or less, and that the reflectance is 40% or more when this condition is satisfied. It should be noted that Δ2 in the equation represents a phase shift of the reflected light 2 with respect to the reflected light 1 when the optical path difference is not taken into consideration. Δ2 can take various values depending on the material and film thickness of each layer, and can take a value up to λ / 2 as an absolute value. For example, a material mainly containing Au for the metal layer and the reflection layer, When using a material having a refractive index of about 2 for the first and second protective layers, and a material having a refractive index of about 5.5 and an extinction coefficient of about 4 for the recording layer, Δ2 is calculated to be about λ / 3. Becomes Therefore, equation (5) becomes

[0049]

[Equation 9] At this time, N = 0 is most preferable.

As the optical recording medium of the present invention, the following materials, that is, a metal layer and a reflective layer: a material containing Au as a main component First and second protective layers: a material having a refractive index of 2 Recording layer: amorphous When a material such as a recording material having a refractive index of 4 in the quality state and an extinction coefficient of 1 and having a refractive index of 5.5 in the crystalline state and an extinction coefficient of 4 is used and a laser beam having a wavelength of 780 nm is used for recording and reproduction. The most preferable range of the film thickness of each layer to satisfy the above conditional expression is as follows. First protective layer: 114 to 211 nm Recording layer: 4 to 27 nm Sum of first protective layer and second protective layer: 129 to 250 nm

Next, the optical recording medium according to the second aspect of the present invention, that is, the reflectance of the recording medium is 70% or more when the atomic arrangement of the recording layer is in a stable state, and the atomic arrangement of the recording layer is When in the metastable state, the reflectance of the recording medium is 40
An optical recording medium having a content of not more than% can be achieved by adjusting the film thickness and the refractive index of the first and second protective films and the recording layer as follows. Refractive index n ₁ and film thickness d ₁ of the first protective layer, refractive index n ₂ and film thickness d ₂ of the second protective layer
_2. Refractive index n _c and extinction coefficient k of the recording layer in the stable state
_c , the refractive index n _a and the extinction coefficient k _{a of} the recording layer in the metastable state, the film thickness d _{r of the} recording layer, and the wavelength λ of the recording / reproducing light,

[0052]

[Equation 10] The recording medium is configured to simultaneously satisfy the following relationship.

Equation (8) absorbs light with a wavelength λ when the recording layer is in a metastable state such as an amorphous state, rather than in a stable state such as a crystalline state. The conditions for difficult materials are shown below. The left side of equations (9) and (10) is
Similar to (3), when the light passes through the recording layer having a thickness of d _r, represents the amplitude ratio of the light transmitted through the recording layer to the amplitude of the incident on the recording layer the light, in the formula (9) , Shows a desirable range of light transmission through the recording layer when the recording layer is in a metastable state. FIG. 4 shows how light is reflected from the optical recording medium in this case. As in the previous case, the substrate 1
4 and the reflected light 1 at the interface between the metal layer 15 and the second protective layer 18
The reflectance of the entire recording medium can be improved by causing an interference action between the reflected light 4 and the reflected light 4 at the interface between the reflective layer 19 and the reflective layer 19. Further, if the sum of the film thicknesses of the first protective layer 16 and the second protective layer 18 is constant, the reflectance from the entire recording medium becomes substantially constant, and the film thicknesses of the first and second protective layers are On the other hand, the isoreflectance line 23 as shown in FIG. 5 can be written. Here again, for simplicity, the first protective layer 16 and the second protective layer 18 are made of the same material, considering that the film thickness, refractive index, etc. of the recording layer are constant.

On the other hand, the expression (10), like the expression (3), indicates that when the recording layer is in a stable state, the amount of light transmitted through the recording layer should be below a predetermined value. That is, of the reflected light from the entire recording medium, the amount of light that passes through the recording layer is limited to reduce the influence of reflected light from the interface between the second protective layer 18 and the reflective layer 19. In materials that meet this condition,
As shown in FIG. 6, the reflected light 21 (reflected light 1) at the interface between the substrate 14 and the metal layer 15, the first protective layer 16, and the recording layer 1
The interference with the reflected light 26 (reflected light 2) at the interface with 7 significantly affects the overall reflectance. The relationship between the total reflectance and the film thickness of the first protective layer 16 and the second protective layer 18 is represented by the equi-reflectance line as shown in FIG. The reflectance almost depends only on the film thickness of the first protective layer 16.

From the superposition of FIG. 5 and FIG. 7, the isoreflectance line 24 that maximizes the overall reflectance Ra when the recording layer is in the amorphous state, and the recording layer is in the crystalline state. And the isoreflectance line 25 such that the overall reflectance Rc is minimized.
It can be seen that there is a point where and intersect, and a large difference in reflectance between the crystal and the amorphous can be obtained in a relatively wide region around this point. Therefore, by satisfying the equations (9) and (10), the reflectance difference between the crystalline and the amorphous is increased while maintaining a wide margin with respect to the film thickness of the first and second protective layers. Can be taken.

[0056] Equation (11) - (14) shows the condition for R _a is at most 40% and R _c is 70% or more.
Formula (11) represents the reflected light (reflected light 1) at the interface between the substrate and the metal layer and the interface between the second protective layer and the reflective layer when the recording layer is in a metastable state such as an amorphous state. Conditions that interfere with and interfere with the reflected light (reflected light 4) at:

[0057]

[Equation 11] It is shown that the deviation from is λ / 4 or less, and it is found that the reflectance from the recording medium becomes 40% or less when this condition is satisfied. It should be noted that Δ1 in the equation represents a phase shift of the reflected light 4 with respect to the reflected light 1 when the optical path difference is not taken into consideration. Δ1 can take various values depending on the material and film thickness of each layer, and can take a value up to λ / 2 as an absolute value. For example, a material containing Au as a main component in the metal layer and the reflective layer, In the case where a material having a refractive index of about 2 is used for the first and second protective layers and a material having a refractive index of about 4 and an extinction coefficient of about 1 is used for the recording layer, Δ1 is calculated to be λ / 20. It will be about. Therefore, equation (11) becomes:

[0058]

(Equation 12) At this time, N = 0 is most preferable.

Equation (12) is the reflected light (reflected light 1) at the interface between the substrate and the metal layer and the interface between the first protective layer and the recording layer when the recording layer is in a stable state such as a crystalline state. Conditions that interfere with the reflected light (reflected light 2) and strengthen each other:

[0060]

(Equation 13) The deviation is from λ / 4 or less, and it is found that the reflectance is 70% or more by satisfying this condition. It should be noted that Δ2 in the equation represents a phase shift of the reflected light 2 with respect to the reflected light 1 when the optical path difference is not taken into consideration. Δ2 can take various values depending on the material and film thickness of each layer, and can take a value up to λ / 2 as an absolute value. For example, a material mainly containing Au for the metal layer and the reflection layer, When using a material having a refractive index of about 2 for the first and second protective layers, and a material having a refractive index of about 5.5 and an extinction coefficient of about 4 for the recording layer, Δ2 is calculated to be about λ / 3. Becomes Therefore, equation (12) becomes:

[0061]

[Equation 14] At this time, N = 0 is most preferable.

As the optical recording medium of the present invention, the following materials, that is, a metal layer and a reflective layer: a material containing Au as a main component First and second protective layers: a material having a refractive index of 2 Recording layer: amorphous When a material such as a recording material having a refractive index of 4 in the quality state and an extinction coefficient of 1 and having a refractive index of 5.5 in the crystalline state and an extinction coefficient of 4 is used and a laser beam having a wavelength of 780 nm is used for recording and reproduction. The most preferable range of the film thickness of each layer to satisfy the above conditional expression is as follows. First protective layer: 16 to 114 nm Recording layer: 11 to 43 nm Sum of first protective layer and second protective layer: 134 nm or less

[0063]

【Example】

Example 1 According to the present invention, the reflectance of the recording medium is 40% or less when the atomic arrangement of the recording layer is in the stable state, and the reflectance of the recording medium when the atomic arrangement of the recording layer is in the metastable state is 70
An optical recording medium having a content of at least 100% was manufactured as follows. On the surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 1.2 mm, a U having a width of 0.8 μm and a depth of 20 nm is used.
A substrate in which V-shaped guide grooves were formed in advance at a pitch of 1.6 μm was prepared. This substrate was arranged in a first sputtering chamber in a magnetron sputtering apparatus having a plurality of sputtering chambers and excellent in film thickness uniformity and reproducibility. Used AuCo alloy as a target, Au ₉₇ with a thickness of 18nm on the substrate using an argon gas as a sputtering gas
A Co ₃ metal layer was formed. Next, after moving this substrate to the second sputtering chamber, the targets were ZnS and SiO ₂
As a mixture thereof, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first protective layer having a thickness of 135 nm was formed in argon gas. Similarly, in a third sputtering chamber, a GeTeSbSe sintered body was used as a target, and a Ge ₄₃ Te ₄₁ Sb ₇ Se ₉ recording layer having a thickness of 10 nm was formed in argon gas. Then, the target is Zn in the fourth sputtering chamber.
A 30 nm-thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ second protective layer was formed as a mixture of S and SiO ₂ in argon gas. Finally, in the fifth sputtering chamber, the target was AuCo alloy, and the thickness was 35 nm in argon gas.
Au ₉₇ Co ₃ reflective layer was formed. The laminated substrates were taken out from the sputtering device, and an ultraviolet curable resin protective layer was spin-coated on the uppermost layer. A sectional view of the optical recording medium thus obtained is shown in FIG. The optical recording medium of the present embodiment has a Au—Co based metal layer 2, a ZnS—SiO ₂ based first protective layer 3, and a Ge—Te—S layer on a polycarbonate substrate 1.
The b-Se based recording layer 4, the ZnS-SiO ₂ based second protective layer 5, the Au-Co based reflective layer 6, and the ultraviolet curable resin protective layer 7 are sequentially laminated.

The refractive index and extinction coefficient of the material forming each layer for light having a wavelength of 780 nm were measured. The results are shown below: Au ₉₇ Co ₃ metal layer and Au ₉₇ Co ₃ reflective layer: 0.34
5-5.069i (ZnS) ₈₀ (SiO ₂ ) ₂₀ First and second protective layers: 2.
0-0.0i Ge ₄₃ Te ₄₁ Sb ₇ Se ₉ recording layer: 4.14-0.89
i (amorphous) 5.52-3.80i (crystal) Here, the refractive index and the extinction coefficient were measured by a spectroscopic ellipsometer. Further, the recording layer was also calculated by the Male method from the values of the transmittance and the reflectance.

The disk manufactured as described above was rotated at a linear velocity of 1.2 m / s by a drive device while
Automatic focusing was performed using a semiconductor laser beam of 80 nm. At this time, the laser light intensity is kept at a level at which recording is not performed, the light is focused by the lens in the recording head, and then the recording layer is irradiated through the substrate and the reflected light is detected to bring the focus on the recording layer. Was adjusted. In this way, while performing automatic focusing, the head was driven so that the center of the light spot was always aligned with the center of the guide groove for tracking. At this time, the reflectance of the specially prepared portion having no guide groove was 74%, and the reflectance of the guide groove portion was 70%.

Next, while tracking,
The recording layer on the recording track was heated by continuously irradiating the laser beam of W, and each element was reacted and crystallized to initialize the recording layer. The reflectance after initialization was 25% in the portion without the guide groove and 21% in the portion with the guide groove. At this time, no large physical deformation was observed in the recording layer.

Then, when the linear velocity of the disk was kept at 1.2 m / s and a repetitive signal of 11T was recorded with a laser light power of 15 mW, the reflectance of the recorded portion increased to 70%. Reflectance of the recorded area (signal strength)
Is defined as the difference in reflectance (difference in signal intensity) between the recorded portion and the unrecorded portion, the signal modulation degree obtained at this time is 70
It became%. 3 on the track once recorded in this way
Overwrite recording of the repeated signal of T was performed. At this time, recording, erasing and reproducing were performed with an overwrite waveform as shown in FIG. Recording power is 15m, same as the first recording
W, erase power and reproduction power are 9 mW each
And 1 mW. 45% signal modulation when recording 3T signals
was gotten. At this time, the erase ratio of the 11T signal was 30 dB.

The disc manufactured as described above was
After the initialization with the continuous light of mW, the 3T signal was first recorded and then the 11T signal was overwritten, the same signal modulation degree and the same erasing ratio of the 3T signal were obtained. Further, this overwrite operation was repeated 1000 times, but thereafter these values hardly changed. Erase power is 12
When the melting erase is performed by raising the power to mW, the erase ratio decreases to 25 dB or less after 10 times of overwrite,
The degree of modulation of the signal was also 50%.

Then, the laser power is changed to 15 mW and 9 mW.
Modulate between and record the EFM signal,
It was mounted on a CD-ROM tester having an optical head of 80 nm and the block error rate (BLER) was measured. At this time, the C1 error rate was 0.3%, which was a good value.

The same experiment as above was performed by dividing the recording pulse into a plurality of pulses. First, when an 11T signal is recorded, 11 pulses having a pulse width of 77 ns are generated in a 231 ns cycle, and when a 3T signal is recorded, three pulses having the same pulse are generated in the same cycle. It was Recording with this method increased the symmetry of the recording marks and reduced the jitter. Further, in this method, as in the recording pulse waveform shown in FIG. 9, the number of pulses is decreased by one and the laser power between one pulse and the next pulse is reduced to 0 mW or near the power of the reproduction light. This has the effect of further reducing the jitter and the C1 error rate. Moreover, it was confirmed that the effect of preventing recrystallization was confirmed by changing the pulse width of each pulse and shortening the pulse width as it approaches the leading pulse. At this time, it was more effective to increase the power as the distance from the pulse was closer. After erasing with continuous light of 9 mW and writing new information by direct overwrite, the jitter was reduced as compared to the case where continuous light erasing was not performed.

Various discs were produced by changing the film thickness of the second protective layer as shown in Table 1 while keeping the film thickness of the recording layer and the film thickness of the first protective layer in the above disc. The reflectance of each disk and the laser light power required for recording changed as shown in Table 1.

[0072]

[Table 1]

In the above disc, the thickness of the recording layer and the thickness of the second protective layer are 10 nm and 3 respectively.
While maintaining 0 nm, the thickness of the first protective layer was changed as shown in Table 2, and various discs were manufactured according to the operation of the above-mentioned example. Table 2 shows the reflectance of each of the obtained disks.

[0074]

[Table 2]

In the above disc, the film thicknesses of the first and second protective layers are 135 nm and 30 n, respectively.
Various discs were produced according to the operation of the above-mentioned example while changing the film thickness of the recording layer as shown in Table 3 while maintaining m. The reflectance of each of the obtained disks is shown in Table 3.

[0076]

[Table 3]

From the above, when the film thickness is set within the range satisfying the above equations (2) and (5), the reflectance in the amorphous state is 7
It can be seen that 0% or more and 40% or less of the crystalline state can be realized and recording can be performed with high sensitivity. In terms of recording sensitivity,
The thickness of the second protective layer is preferably 5 nm or more, more preferably 10 nm or more, and most preferably 20 nm or more.

In the recording layer used in the above experiment, the Ge content is 40% to 60%, and the Te content is 45% to 59%.
%, The results similar to the above were obtained when the sum of the contents of Sb and Se was changed in various ranges from 1 to 20%.

Further, by keeping the contents of Ge and Te constant and changing the sum of the contents of Sb and Se within the following range, the maximum linear velocity at which solid phase erasing can be performed with one laser irradiation is performed. Examined.

[0080]

[Table 4]

Next, the total content of Sb and Se was changed within the following range, and 3T signal and 11T signal were alternately recorded at a linear velocity of 1.2 m / s with a recording power of 15 mW and an erasing power of 9 mW.
The erase ratio was examined by rewriting 0 times.

[0082]

[Table 5]

If the total content of Sb and Se is 30 atomic%, the melt erasure must be performed, and the number of rewrites is 1
The erase ratio decreased by 5 dB or more at 0 times. Further, when the erasing power is increased in the above range to perform the melt erasing, the number of rewritings is 10 regardless of the total content of Sb and Se.
The erasing ratio decreased by 5 dB or more after repeated times.

Between the recording layer and the protective layer, Au, Ti, W, CO, C was formed as an interface layer on at least one of the recording layer and the protective layer.
Refractory metal elements such as r, Mo, Si and Ge, semiconductor elements and alloy materials thereof, oxides such as Si, Al, Y and Zr, selenium compounds and sulfides such as Zn and Pb, Si and A
When a layer made of a nitride such as l, Ta, etc., a fluoride such as Mg, a carbide such as B, Si, etc. was provided, there was an effect of improving the number of times of rewriting. The same effect was confirmed by forming this interface layer in an island shape.

Further, in the above embodiment, when a layer made of the same material as the above-mentioned interface layer was provided as an intermediate layer in the recording layer so as to divide the recording layer into two layers, the cooling time of the recording layer was reduced. The effect of controlling and controlling the crystallization process was observed. In addition, one recording bit has a plurality of information by recording information in only one of the two recording layers divided by the intermediate layer or both in accordance with the magnitude of the recording power. I was able to make it.

In the above embodiment, the recording layer is a very small needle-shaped magnetic substance α-Fe, ferrite, barium ferrite, manganese zinc ferrite, α-FeOO.
H, α-FeO (OH), α-Fe ₂ O ₃ , γ-Fe _{2
O 3, Fe 3 O 4,} Co-Ni, Co-Cr, was uniformly dispersed or precipitate CoO or Co-Pt or the like, crystallisation is promoted these as nuclei, also recorded in the external magnetic field When performed, it was possible to create a crystalline state or an amorphous state having a structure different from that in the case of recording with no external magnetic field.

The recording layer of the recording medium of the present invention can be overwritten by a single circular light spot, but these recording layers are once erased and then recorded, or rewritten by overwriting. When doing so, the previously written signal may be left unerased on the same recording track. The remaining portion could be reduced by adjusting the reproduction signal level from near the crystal region to a constant level as described above. Also, reduce the remaining component by subtracting the difference between the signals of the detector that detects the reflected light from one side of the track and the detector on the opposite side, and multiplying by a suitable multiple and subtracting from the sum of these signals. I was able to.

Only the recording layer portion was taken out from the recording medium obtained in this example, and it was subjected to 1 at 60 ° C. and 95% relative humidity.
After standing for 000 hours, an oxidation resistance test was performed. The recording layer portion after 1000 hours was hardly oxidized.

Example 2 According to the present invention, the reflectance of the recording medium is 70% or more when the atomic arrangement of the recording layer is in a stable state, and the reflectance of the recording medium is not stable when the atomic arrangement of the recording layer is in a metastable state. 40 reflectance
An optical recording medium having a content of not more than 100% was manufactured as follows. On the surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 1.2 mm, a U having a width of 0.8 μm and a depth of 20 nm is used.
A substrate in which V-shaped guide grooves were formed in advance at a pitch of 1.6 μm was prepared. This substrate was placed in the first sputtering chamber in the magnetron sputtering apparatus used in Example 1. Using AuCo alloy as a target and argon gas as a sputtering gas, a thickness of 14
nm Au ₉₇ Co ₃ metal layer was formed. Then, after moving this substrate to the second sputtering chamber, the target was changed to Zn.
As a mixture of S and SiO ₂ , thickness 2 in argon gas
A 5 nm (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first protective layer was formed. Similarly, in the third sputtering chamber,
Using a GeTeSbSe sintered body as a target, a Ge ₄₃ Te ₄₁ Sb ₇ Se ₉ recording layer having a thickness of 20 nm was formed in an argon gas. Then, a 30 nm-thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ second protective layer was formed in argon gas using a mixture of ZnS and SiO _{2 as} a target in the fourth sputtering chamber. Finally, in the fifth sputtering chamber, an AuCo alloy was used as a target, and an Au ₉₇ Co ₃ reflective layer having a thickness of 35 nm was formed in argon gas. The laminated substrates were taken out from the sputtering device, and an ultraviolet curable resin protective layer was spin-coated on the uppermost layer.

The optical recording medium thus obtained has the sectional structure shown in FIG.
u-Co based metal layer _2, ZnS-SiO 2 based first protective layer 3, Ge-Te-Sb- Se -based recording layer 4, ZnS-Si
The O ₂ -based second protective layer 5, the Au—Co-based reflective layer 6, and the ultraviolet curable resin protective layer 7 are sequentially laminated. The refractive index and the extinction coefficient of the material forming each layer with respect to light having a wavelength of 780 nm were measured by the same method as in Example 1, and the same results as in Example 1 were obtained.

The disk produced as described above was subjected to automatic focusing and tracking in the same manner as in Example 1. At this time, the reflectance of the specially prepared portion without the guide groove was 20%, and the reflectance of the guide groove portion was 18%.

Then, while tracking,
The recording layer on the recording track was heated by continuously irradiating the laser beam of mW, and each element was reacted and crystallized to initialize the recording layer. The reflectance after the initialization was 72% in the portion without the guide groove and 70% in the portion with the guide groove. At this time, no large physical deformation was observed in the recording layer.

Then, when the linear velocity of the disk was kept at 1.2 m / s and a repetitive signal of 11T was recorded with a laser light power of 34 mW, the reflectance of the recorded portion decreased to 27%. When the signal modulation degree is defined as the difference between the reflectance (signal intensity) of the unrecorded portion and the reflectance of the recorded portion and the unrecorded portion (signal intensity difference), the signal modulation degree obtained at this time was 61%. . Thus, a 3T repetitive signal was overwritten on the track once recorded. At this time, recording, erasing and reproducing were performed with an overwrite waveform as shown in FIG. However, in this example, the recording power was 34 mW as in the first recording, and the erasing power and the reproducing power were 15.5 mW and 1 mW, respectively. Three
A signal modulation factor of 40% during T signal recording was obtained. On this occasion,
The erase ratio of the 11T signal was 30 dB.

The disk produced as described above was
After the initialization with the continuous light of 7 mW, the 3T signal was first recorded and then the 11T signal was overwritten, the same signal modulation degree and the erasing ratio of the 3T signal were obtained. Further, this overwrite operation was repeated 1000 times, but thereafter these values hardly changed. Erase power is 2
When the melting and erasing was performed by increasing the power to 0 mW, the erasing ratio decreased to 25 dB or less after 10 times of overwriting, and
The modulation degree of the T signal was also 50%.

Then, the laser power was set to 34 mW and 15.
The EFM signal was recorded by modulating between 5 mW and mounted on a CD-ROM tester having an optical head with a wavelength of 780 nm, and the block error rate (BLER) was measured.
At this time, the C1 error rate was 0.3%, which was a good value.

The same experiment as above was carried out by dividing the recording pulse into a plurality of pulses in the same manner as in Example 1. As a result, it was found that the symmetry of the recording mark was increased and the jitter was decreased. Also, the number of pulses in this method is 1
By reducing the number of lasers or reducing the laser power from one pulse to the next pulse to 0 mW or near the power of the reproduction light, the jitter is further reduced and the C1 error rate is reduced. Moreover, it was confirmed that the effect of preventing recrystallization was confirmed by changing the pulse width of each pulse and shortening the pulse width as it approaches the leading pulse. At this time, it was more effective to increase the power as the distance from the pulse was closer. When new information was written by direct overwriting after erasing with continuous light of 17 mW, the jitter was reduced as compared with the case where continuous light erasing was not performed.

In the recording layer used in the above experiment, the Ge content is 40% to 60%, and the Te content is 45% to 59.
%, The results similar to the above were obtained when the sum of the contents of Sb and Se was changed in various ranges from 1 to 20%.

Further, by keeping the Ge and Te contents constant and changing the sum of the Sb and Se contents within the following range, the maximum linear velocity at which solid phase erasing is possible by one irradiation of laser light was investigated. It was

[0099]

[Table 6]

Next, the total content of Sb and Se was changed within the following range, and the 3T signal and 11T signal were alternately rewritten 1000 times with a recording power of 34 mW and an erasing power of 15.5 mW at a linear velocity of 1.2 m / s. , The erase ratio was investigated.

[0101]

[Table 7]

If the total content of Sb and Se is 30 atomic%, it must be melt-erased.
The erase ratio decreased by 5 dB or more at 0 times. Further, when the erasing power is increased in the above range to perform the melt erasing, the number of rewritings is 10 regardless of the total content of Sb and Se.
The erasing ratio decreased by 5 dB or more after repeated times.

Similar to Example 1, between the recording layer and the protective layer, A was used as an interface layer on at least one side in contact with the recording layer.
refractory metal elements and semiconductor elements such as u, Ti, W, CO, Cr, Mo, Si, and Ge, and alloy materials thereof, Si,
A layer made of oxides such as Al, Y and Zr, selenium compounds and sulfides such as Zn and Pb, nitrides such as Si, Al and Ta, fluorides such as Mg and carbides such as B and Si is provided. However, there was an effect of improving the number of times of rewriting. The same effect was confirmed by forming this interface layer in an island shape.

Further, in this embodiment, when a layer made of the same material as the above-mentioned interface layer was provided as an intermediate layer in the recording layer so as to divide the recording layer into two layers, the cooling time of the recording layer was reduced. The effect of controlling and controlling the crystallization process was observed. In addition, one recording bit has a plurality of information by recording information in only one of the two recording layers divided by the intermediate layer or both in accordance with the magnitude of the recording power. I was able to make it.

In this embodiment, the recording layer is a very small acicular magnetic substance, α-Fe, ferrite, barium ferrite, manganese zinc ferrite, α-FeOO.
H, α-FeO (OH), α-Fe ₂ O ₃ , γ-Fe _{2
O 3, Fe 3 O 4,} Co-Ni, Co-Cr, was uniformly dispersed or precipitate CoO or Co-Pt or the like, crystallisation is promoted these as nuclei, also recorded in the external magnetic field When performed, it was possible to create a crystalline state or an amorphous state having a structure different from that in the case of recording with no external magnetic field.

Also in the optical recording medium of the present embodiment, the unerased component of the signal generated at the time of overwriting by a single circular light spot could be reduced by the method described in the first embodiment.

Only the recording layer portion was taken out from the recording medium obtained in Example 2 and subjected to 1 under the conditions of 60 ° C. and 95% relative humidity.
After standing for 000 hours, an oxidation resistance test was performed. The recording layer portion after 1000 hours was hardly oxidized.

[0108]

As described above, according to the present invention,
It has been possible to obtain an optical recording medium capable of recording with high sensitivity even at low laser power and capable of rewriting recording extremely many times. Since the recording medium of the present invention satisfies the CD standard in terms of reflectance and signal modulation, it is a CD player or a CD-ROM.
Playback on the drive is possible. Since the phase change recording medium of the present invention has very little deformation of the recording mark during recording,
It is suitable for mark edge recording / reproduction. In addition, the phase-change recording medium of the present invention has a recording layer having a specific composition of Ge.
Since a Te-Sb-Se-based material is selected, it is possible to record at the same linear velocity as the reproducing linear velocity of the CD standard.
Data can be easily read by a D player or a CD-ROM drive. The optical recording medium of the present invention is also excellent in durability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an optical recording medium obtained in Example 1 of the present invention.

FIG. 2 is a diagram showing an overwriting recording laser waveform in an example of the present invention.

FIG. 3 is a cross-sectional view showing the structure of the optical recording medium obtained in Example 2 of the present invention.

FIG. 4 is a conceptual diagram showing a reflection state when a recording layer is in an amorphous state.

FIG. 5 is a graph showing the reflectance with respect to the film thickness of the first protective film and the second protective film when the reflection of FIG. 4 is dominant.

FIG. 6 is a conceptual diagram showing a state of reflection when the recording layer is in a crystalline state.

FIG. 7 is a graph showing the reflectance with respect to the film thickness of the first protective film and the second protective film when the reflection of FIG. 6 is dominant.

FIG. 8 shows reflectance and laser power of recording laser light when a new recording mark is overwritten on an old recording mark.

FIG. 9 is a diagram showing pulse signal waveforms used in overwrite recording of 11T and 3T signals on an optical recording medium in an example of the present invention.

[Explanation of symbols]

1 polycarbonate substrate 2 Au-Co based metal layer 3 ZnS-SiO ₂ based first protective layer 4 Ge-Te-Sb-Se-based recording layer 5 ZnS-SiO ₂ based second protective layer 6 Au-Co-based reflective layer 7 UV Cured resin protective layer 8 Polycarbonate substrate 9 First protective layer consisting of ZnS-SiO ₂ based transparent layer and SiO ₂ based transparent layer 10 Ge-Te-Sb-Se based recording layer 11 ZnS-SiO ₂ based second protective layer 12 Au -Co-based reflective layer 13 UV-curable resin protective layer 21 Reflected light 1 22 Reflected light 4 23 Iso-reflectance line 24 Iso-reflectance line showing maximum reflectance 25 Iso-reflectance line showing minimum reflectance 26 Reflected light 2 31 Old Record mark 32 New record mark

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location // G11B 7/00 7416-2H B41M 5/26 X (72) Inventor Norio Ohta Ibaraki City, Osaka Prefecture 1-88, Tora-Tora Hitachi Maxell Co., Ltd.

Claims (14)

[Claims] 1. Recording is performed by providing a metal layer, a first protective layer, a recording layer, a second protective layer and a reflective layer on a substrate and changing the atomic arrangement of the recording layer from a stable state to a metastable state. In an optical recording medium that is initialized and erased by changing from a metastable state to a stable state, the recording layer is made of a material containing Ge, Te, Sb, and Se as the main components, and the film thickness of the recording layer is Direction average composition is atomic%
Is expressed as follows: Ge ≧ 40% and Sb + Se ≦ 25% are satisfied, and when the atomic arrangement of the recording layer is in a stable state, the reflectance of the recording medium is 40% or less with respect to the reproducing light, An optical recording medium, wherein the reflectance of the recording medium is 70% or more with respect to the reproducing light when the atomic arrangement of the recording layer is in a metastable state. 2. The refractive index n ₁ and the film thickness d _{1 of} the first protective layer,
Refractive index n ₂ and film thickness d _{2 of} the second protective layer, refractive index n _c and extinction coefficient k _c of the recording layer in the stable state, refractive index n _a and extinction coefficient k of the recording layer in the metastable state _a , the film thickness d _{r of the} recording layer and the wavelength λ of the recording / reproducing light, The optical recording medium according to claim 1, which satisfies the following relationship. 3. Recording is performed by providing a metal layer, a first protective layer, a recording layer, a second protective layer and a reflective layer on a substrate and changing the atomic arrangement of the recording layer from a stable state to a metastable state. In an optical recording medium that is initialized and erased by changing from a metastable state to a stable state, the recording layer is made of a material containing Ge, Te, Sb, and Se as the main components, and the film thickness of the recording layer is Direction average composition is atomic%
Is expressed as follows: Ge ≧ 40% and Sb + Se ≦ 25% are satisfied, and when the atomic arrangement of the recording layer is in a stable state, the reflectance of the recording medium is 70% or more with respect to the reproducing light, An optical recording medium, wherein the reflectance of the recording medium is 40% or less with respect to reproducing light when the atomic arrangement of the recording layer is in a metastable state. 4. The refractive index n ₁ and the film thickness d _{1 of} the first protective layer,
Refractive index n ₂ and film thickness d _{2 of} the second protective layer, refractive index n _c and extinction coefficient k _c of the recording layer in the stable state, refractive index n _a and extinction coefficient k of the recording layer in the metastable state _{For a} , the film thickness d _{r of the} recording layer and the wavelength λ of the recording / reproducing light, The optical recording medium according to claim 3, which satisfies the following relationship. 5. The relationship in which the average composition in the film thickness direction of the recording layer is expressed in atomic%: 40% ≦ Ge ≦ 64% 45% ≦ Te ≦ 59% 1% ≦ Sb + Se ≦ 20% Sb <Se The optical recording medium according to any one of claims 1 to 4, which is satisfied. 6. The recording layer includes Ge, Te, Sb, Se
The optical recording medium according to any one of claims 1 to 5, characterized in that it contains elements other than 10 atomic% or less. 7. The relationship that the average composition in the film thickness direction of the recording layer is represented by atomic%: 40% ≦ Ge ≦ 55% 35% ≦ Te ≦ 50% 5% ≦ Sb + Se ≦ 20% Sb <Se The optical recording medium according to any one of claims 1 to 6, which is satisfied. 8. The average composition in the film thickness direction of the recording layer is expressed in atomic%: 40% ≦ Ge ≦ 50% 35% ≦ Te ≦ 45% 10% ≦ Sb + Se ≦ 20% Sb <Se The optical recording medium according to any one of claims 1 to 7, which is satisfied. 9. The optical recording medium according to claim 1, wherein the metal layer is made of an AuCo alloy. 10. The optical recording medium according to claim 1, wherein the reflective layer is made of an AuCo alloy. 11. The optical recording medium according to claim 1, which is recorded at a linear velocity of 2.8 m / sec or less during recording. 12. The optical recording medium according to claim 1, which is recorded at a linear velocity of 1.4 m / sec or less during recording. 13. The optical recording medium according to claim 1, wherein recording / reproducing is performed by a mark edge method. 14. The optical recording medium according to claim 1, which is a phase change type optical recording medium in which the stable state is a crystalline state and the metastable state is an amorphous state.