JP2803315B2 - Optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention includes a recording layer made of a phase-change recording material, and irradiates the recording layer with focused light from a light source such as a gas laser or a semiconductor laser. Rewritable optical recording media for optically recording, reproducing, and erasing information, and especially C / N
The present invention relates to an improvement in an optical recording medium which is excellent in signal quality such as ratio and jitter and which can be rewritten at high speed.

[Conventional technology]

2. Description of the Related Art Conventionally, there is a magneto-optical recording medium as a rewritable optical recording medium for recording information using a laser beam or the like, and some of the rewritable optical recording media have been put to practical use.

That is, in this method, information is recorded by inverting the magnetization of the recording layer by applying light energy and a magnetic field, and a difference between the Faraday rotation angle or the Kerr rotation angle depending on the magnetization direction is detected to obtain a reproduction signal. .

However, in this method, there is no practical method for performing rewriting within at least one sector, so that it has been applied only to a limited field.

On the other hand, as another rewritable optical recording medium,
For example, a phase change type optical recording medium utilizing a phase change between “a crystalline phase and an amorphous phase” is under study.

That is, as shown in FIG. 5 (A), the writing of the information in this optical recording medium is usually performed by applying a high-power circular laser spot from a light source (not shown) to the recording layer of the high recording medium (f). (C), and the melting temperature T _{m of the} recording material
"High temperature heating and quenching" that heats and rapidly cools to the above high temperature
Is performed to change the irradiated portion from the crystalline state (cr) to the amorphous state (am), while the written information is erased as shown in FIG. 5 (B). irradiating the oval laser spot low output to cones (c), heated to a low temperature of below the melting temperature T _m at a crystallization temperature T _x above recording material and relatively slowly cooled "low temperature heating slow cooling By performing "processing", a method of changing a recording portion from an amorphous state (am) to a crystalline state (cr) is employed.

In this method, rewriting within one sector (that is, erasing recorded information with a preceding beam, and then recording with a next beam) can be performed using two light beams, and one Since overwriting (simultaneous rewriting) by a light beam is possible, there is an advantage that application in various fields is possible.

[Problems to be solved by the invention]

By the way, in order to improve the rewriting speed of this type of phase-change optical recording medium, recently, a search for a recording material having a short crystallization time has been actively conducted, and recently, Ge-Sb-
Excellent recording materials such as Te have been developed.

In an optical recording medium using this Ge-Sb-Te-based material, a high erasing rate can be obtained under a high-speed condition of 60 ns, and a sufficient value has been obtained in terms of the erasing speed. .

However, when such a crystallization time is shortened, on the other hand, a new problem of deterioration in signal quality due to recrystallization has become significant.

In other words, when recording information, it is necessary to melt the recording material as described above, and then perform a “high-temperature heating and quenching process” of rapid cooling to make the irradiated portion amorphous, but the laser spot is irradiated. There is a problem that it is difficult to secure a sufficient cooling rate in the peripheral portion of the spot as compared with the central portion, and the portion is recrystallized.

FIG. 6 shows the time and temperature of the central part (r = 0) of the irradiation spot on the recording layer irradiated with the laser spot and the part (r = 0.5r _{0 to} 2.5r ₀ ) sequentially separated from the center part. FIG. 4 is a graph showing the relationship between the changes. The gradient a of the cooling rate at the central part (r = 0) and the gradient a ′ of the cooling rate at the peripheral part (r = 0.5r ₀ ) at the glass transition temperature (Tg). From the comparison, it can be understood that the cooling rate of the peripheral part is extremely slow as compared with the central part of the irradiation spot.

FIG. 7 (A) shows the temperature distribution of the irradiation spot on the recording layer irradiated with the laser spot,
FIG. 7 is a graph showing that this distribution changes from time to time, as in FIG. 6, but shows that the cooling rate of the peripheral portion is much lower than that of the central portion of the irradiation spot.

For this reason, the peripheral portion of the irradiation spot is recrystallized and cannot be changed to an amorphous phase. Therefore, as shown in FIG. 7B, the recording mark (M) having the size indicated by α is indicated by β. As a result, the C / N ratio of the reproduced signal is reduced, and the jitter is increased.

Therefore, conventionally, to solve this problem, A
A cooling layer made of a material having a high thermal conductivity such as l, Au or the like is provided around the recording layer, and as shown in FIG. (M) is secured (see FIG. 8B).

However, when this method is adopted, a large heat loss is caused by heat radiation from the cooling layer, so that it is necessary to apply a large amount of heat energy to melt the recording material, and as a result, the recording sensitivity is reduced. There was a drawback.

And since the output of the laser which is the light source has a limit, the decrease in the recording sensitivity determines the recording speed,
As a result, there is a problem that the transfer speed (rewrite speed) is limited.

These problems are not limited to the above-mentioned optical recording medium utilizing the phase change between “crystal and amorphous”, but are referred to as “single-phase to two-phase (binodal or spinodal) accompanying binodal decomposition or spinodal decomposition. State), or an optical recording medium using a phase change between “binodal state and spinodal state”, and an optical recording medium using a phase change between “crystal and crystal”. Other phase-change type recording media in which information is rewritten according to the magnitude of the temperature and the cooling rate similarly exist.

[Means for solving the problem]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a high recording medium that is excellent in signal quality such as C / N ratio and jitter and that can be rewritten at high speed. It is in.

That is, the present invention comprises a substrate, and a recording layer formed on at least one surface of the substrate and made of a phase-change recording material. Assuming an optical recording medium on which information is optically recorded or erased by applying a high-temperature heating and quenching treatment, a semiconductor having a higher thermal conductivity than the above-mentioned recording material, and whose thermal conductivity decreases as the temperature increases A heat conduction control layer made of a material and acting also as a reflection layer is provided.

In such technical means, the substrate is made of a transparent single material such as glass, polycarbonate, polyacrylonitrile, polymethyl methacrylate, epoxy resin, and polypentene, or a laminated material of these materials, as in the related art. Alternatively, it may be made of a metal material such as aluminum. When a resin material such as polycarbonate is applied, in order to prevent thermal damage to the resin material, for example, between the substrate and the recording layer,
An inorganic dielectric layer composed of SiO ₂ , ZrO ₂ , ZnS or the like or a mixture thereof may be interposed.

Next, as a phase change type recording material formed on at least one surface of the substrate, a phase change between “crystal-amorphous” is used. For example, TeO _X (adding Ge and Sn), In-Se, In- Sb, In-Te, S
b-Te, Sb-Se, Sn-Te, Bi-Te, Bi-Se, Te-N, Ge-Te, Ag
-Zn, binary material such as _{As 2 S 3, Ge-Sn} -Te, In-Se-Te, In-Sb-Te, In-Sb-Se, In-
Se-Tl, Ge-Sb-Te, Ge-Te-Tl, Ge-Te-Au, Ge-Te-C
u, Ge-Te-Co, Ge-Te-Ni, Sb-Se-Bi, Sb-Se-Te, Sn-
Ternary materials such as Se-Te, Ge-Te-Sb-Se, Ge-Te-Sn-Au, Ge-Te-Sb-Au, Ge
Quaternary materials such as -Te-Sb-Cu, Ge-Te-Sn-Su, In-Se-Tl-Co, etc., or Ga, In, Tl, Ge, Sn, As, Sb, S, Se, the elements of Te, etc. can be used materials comprising at least one is below, (indicated by T _x) the crystallization temperature for a typical material
And the melting temperature (indicated by _Tm2 ) are displayed and listed as follows.

_{That, InTe (T x: 200 ℃} , T m2: 696 ℃) GeTe (T x: 170 ℃, T m2: 725 ℃) Ge 10 Te 90 (T x: 160 ℃, T m2: 380 ℃) such as two based _{material, SnSeTe (T x: 90 ℃} , T m2: 600 ℃) Ge 2 Tb 2 Te 5 (T x: 140 ℃, T m2: 630 ℃) Sb 40 Se 45 Ti 15 (T x: 80 ℃, _{T m2: 560 ℃) InSb 3} Te 2 (T x: 280 ℃, T m2: 450 ℃) ternary material such, _{and, Ge 20 Te 45 Sb 25 Se} 10 (T x: 190 ℃, T m2: Quaternary materials such as Ge ₃₀ Te ₅₀ Sb ₅ Se ₁₅ (T _x : 180 ° C., T _m2 : 604 ° C.).

In addition, "single phase-two phase (binodal or spinodal state)" accompanying binodal decomposition or spinodal decomposition
Utilize phase change between "Binodal state-spinodal state", TeO _X , Ge-O, Sn-O, Ti-O, etc., and phase change between "crystal-crystal" Do, for example
A material group such as InSb can also be applied.

The recording layer composed of the phase change type recording material is formed on the recording layer for the purpose of preventing deformation until the recording layer is solidified after melting, or for the purpose of preventing mechanical damage, oxidation and the like of the recording layer. May be provided with a protective layer. In this case, as the material forming the protective layer, in addition to the same material as the material forming the inorganic dielectric layer, an ultraviolet curable resin, acrylic,
Resin materials such as polycarbonate and epoxy, glass and the like can be used. In addition, the protective layer may be constituted by a single layer of these materials, or may be constituted by laminating a plurality of the above materials. Further, when the portion in contact with the recording layer is made of a resin material, an inorganic dielectric layer may be interposed between them as in the case of the substrate.

On the other hand, the material constituting the heat conduction control layer is Si, Ge, Ga
Semiconductor materials such as As, InP, GaP, and AlSb. This semiconductor material has a thermal conductivity that is at least 10 times greater than the thermal conductivity of the recording material, and the "heat carrier" of this semiconductor material
Is mainly lattice vibration. Therefore, the higher the temperature, the greater the scattering due to impurities and the like, and the lower the thermal conductivity is (see Table 1).

On the other hand, Al, A
The "heat carrier" in metal materials such as u and Ag is mainly free electrons, and its thermal conductivity hardly changes even when the temperature rises (see Table 1 above). The reduction of "" is caused.

There is no particular limitation on the formation site of the heat conduction control layer, and the heat conduction control layer can be formed at an arbitrary site around the recording layer. Here, the meaning around the recording layer means a position where the heating and cooling of the recording material constituting the recording layer can be thermally affected, even in contact with the recording layer, or via another layer. Good. Further, since the heat conduction control layer is made of a semiconductor material such as Si which does not show light transmissivity, it is provided on the side opposite to the light irradiation side of the recording layer and functions as a reflection layer.

In addition, when the material constituting the heat conduction control layer has a property that can be used as a material layer for another purpose in addition to the property showing the above-described thermal conductivity, it is needless to say that the materials can be used together. For example, if its heat resistance is high, it can function as a protective layer, and if its light absorptance is high, it can function as a light absorbing layer. Further, the number of the heat conduction control layers is usually one, but two heat conduction control layers may be provided with the recording layer interposed therebetween, and the number of the heat conduction control layers is of course arbitrary.

As a method of forming the heat conduction control layer, for example, a sputtering method, a vacuum evaporation method, an ion plating method, or the like can be used, similarly to the method of forming other layers such as a recording layer.

Next, in this technical means, the "high-temperature heating and quenching treatment" means that the recording layer is heated to a certain temperature higher than the melting point of the recording material.
It refers to a process of changing the one phase state by heating and rapidly cooled to T _1, for example, "crystalline - amorphous"
In the case of an optical recording medium utilizing a phase change between, means a process for changing a recording layer in an amorphous state or a crystalline state to an amorphous state which is one phase state,
Similarly, in an optical recording medium utilizing a phase change between “single-phase and two-phase (binodal or spinodal state)”, a recording layer in a single-phase state or a two-phase state is changed to a single-phase state in one phase state. In the optical recording medium utilizing the phase change between "binodal state-spinodal state", the recording layer in the binodal state or spinodal state is in one phase state. Means a process for changing to a spinodal state. In an optical recording medium utilizing a phase change between “crystal and crystal”, crystal 1 (fine crystal grain state) or crystal 2 (coarse crystal grain state) Means a process for changing the recording layer in the state of (1) to the state of the crystal 1 as one of the phase states.

On the other hand, the above-mentioned "low-temperature heating / gradual cooling treatment"
A process of heating to T ₂ (T ₂ <T ₁ ) and cooling it relatively slowly to change to the other phase state. For example, an optical recording medium utilizing a phase change between “crystal and amorphous” This means a process for changing a recording layer in an amorphous state or a crystalline state to a crystalline state, which is the other phase state, and similarly, between "single-phase and two-phase (binodal or spinodal state)". In the case of an optical recording medium utilizing the phase change of the above, it means a process for changing the recording layer in a single relative state or a two-phase state to a two-phase state which is the other phase state. In the case of an optical recording medium utilizing the phase change between the `` spinodal state '', it means a process for changing the recording layer in the binodal state or the spinodal state to the other phase state, the binodal state. In an optical recording medium utilizing a phase change between "crystal-crystal", a recording layer in a crystal 1 (fine crystal grain state) or crystal 2 (coarse crystal grain state) is in the other phase state. This means a process for changing the state of the crystal 2.

Further, in the optical recording medium according to this technical means, for example, in the case of an optical recording medium utilizing a phase change between “crystal and amorphous”, the amorphous phase of the recording material forming the recording layer is made to correspond to the recording state, and The crystalline phase may correspond to the erased state, and conversely, the amorphous phase may correspond to the erased state and the crystalline phase may correspond to the recorded state, and the selection is arbitrary.

[Action]

According to the technical means as described above, the recording material has a higher thermal conductivity, and comprises a semiconductor material whose thermal conductivity decreases as the temperature increases.
Because a heat conduction control layer that also acts as a reflection layer is provided, during “high-temperature heating and quenching treatment”, the heat conduction control layer that exhibits high heat conductivity at low temperatures in the area around the low-temperature irradiation spot The action promotes heat radiation from the recording layer and can secure a sufficient cooling rate. Therefore, recrystallization at the peripheral portion of the irradiation spot can be prevented.
Under the high-temperature condition, the heat conductivity of the heat-conduction control layer is reduced, so that the heat radiation function is weakened, so that the heat loss at the spot central portion is reduced and the sensitivity can be prevented from lowering. In the case of "heating slow cooling treatment", the recording layer is not exposed to such a high temperature and the cooling rate of the entire irradiation spot is slow as compared with the above-mentioned high temperature heating and rapid cooling treatment. Low-temperature heating and slow-cooling treatment can be performed.

〔Example〕

Hereinafter, an embodiment in which the present invention is applied to an optical recording medium utilizing a phase change between “crystal and amorphous” will be described in detail with reference to the drawings.

The optical recording medium according to this embodiment has a 1.2 mm-thick PMMA on which a pre-groove (not shown) is formed as shown in FIG.
A substrate (1) made of (polymethyl methacrylate), and a 100 nm thick ZnS underlayer (2) deposited on the substrate (1) by RF sputtering to prevent thermal damage to the substrate (1). A recording layer (3) made of Ge ₂ Sb ₂ Te _{5 and} having a thickness of 30 nm, which is formed on the underlayer (2) by RF sputtering.
And a 30 nm-thick ZnS protective layer (which is deposited on the recording layer (3) by an RF sputtering method to prevent a change until the recording layer (3) is solidified after fusion, mechanical damage, oxidation, etc. 40) a thickness which is deposited on the protective layer (40) by RF sputtering to control the heat conduction of the recording layer (3);
A 0 nm Si heat conduction control layer (4), an ultraviolet curing resin layer (5) formed on the heat conduction control layer (4) for lamination, and formed on the ultraviolet curing resin layer (5). The main part thereof is constituted by a PMMA protective plate (6) having a thickness of 1.2 mm for preventing thermal damage and mechanical damage of the recording layer (3) and the like. The light absorption of this optical recording medium extends from visible light to near-infrared light, and it can be used as an optical recording medium at least in the range of 400 to 860 nm.

The recording layer (3) is irradiated with a laser beam having an output of 15 mW while rotating the optical recording medium at 1800 rpm to heat the recording layer (3) to a temperature higher than the melting point (T _m2 ) of the recording material, and rapidly cooled to form an amorphous state. Alternatively, while the recording layer (3) in a crystalline state is in an amorphous state and information is written, the recording layer (3) is irradiated with a laser beam having an output of 8 mW under the same rotation speed and the recording material is irradiated. By heating to a temperature lower than the crystallization temperature (T _x ) and slowly cooling the recording layer (3) in a crystalline state or an amorphous state to a crystalline state, the written information is erased. It has become.

Thus, in the optical recording medium according to this embodiment, at the time of the `` high-temperature heating and quenching treatment '' during recording, in the vicinity of the irradiation spot with a low temperature, a portion made of Si exhibiting high thermal conductivity at a low temperature. By the action of the heat conduction control layer (4), heat radiation from the recording layer (3) is promoted, and a sufficient cooling rate can be secured. Therefore, recrystallization at the periphery of the irradiation spot can be prevented, and high-temperature irradiation can be performed. At the spot central portion, the heat conductivity of the heat conduction control layer (4) becomes lower under the high temperature condition, so that the heat radiation effect is weakened, so that the heat loss at the spot central portion is reduced and the recording sensitivity is prevented from lowering. On the other hand, at the time of "low temperature heating slow cooling process" at the time of erasing, the output of the laser beam is as low as 8 mW and the recording layer (3) is much higher than the high temperature heating rapid cooling process. Since the cooling rate of the entire irradiation spot is low without being exposed to the temperature, the low-temperature heating / low-cooling treatment of the recording layer (3) does not interfere with the heat conduction control layer (4).

FIG. 2 (A) shows this, and it can be understood from the comparison with the graph of FIG. 7 (A) that the cooling rate around the irradiation spot is increased. As shown in FIG. 2 (B), a recording mark (M) of the original size is obtained, and therefore, the recording level is saturated and stable recording is performed.

For this reason, as in the related art, it has an advantage that high-speed rewriting is possible, and also has an advantage that signal quality such as C / N ratio and jitter is excellent.

<< Comparative Example >> Next, the following comparative example was performed for the purpose of confirming the effect of the optical recording medium according to the above-described example.

○ First comparative example The optical recording medium according to this comparative example
Instead of a 30 nm ZnS protective film (40) and a 200 nm Si thermal conduction control layer (4), a 200 nm thick ZnS protective film (40) was incorporated as shown in FIG. And the structure of the optical recording medium according to the embodiment.

In this optical recording medium, the recording level is not saturated even when a laser beam having an output of 20 mW is irradiated.
The C / N ratio, jitter, and the like of the reproduced signal were extremely inferior to those of the optical recording medium according to the example.

As for the cause, since the optical recording medium does not include the heat conduction control layer (4) made of Si, the cooling rate around the irradiation spot during writing is low, and
This is presumed to be due to recrystallization at this site.

○ Second comparative example The optical recording medium according to this comparative example
The optical recording medium according to the embodiment except that a 200 nm thick Au cooling layer (41) is incorporated as shown in FIG. 4 instead of the 200 nm Si heat conduction control layer (4). The structure is almost the same.

In the optical recording medium, the cooling layer (41)
A large amount of heat energy escapes from the recording medium, resulting in a decrease in recording sensitivity. As a result, the recording level does not saturate even when a laser beam with an output of 20 mW or more is irradiated.
The ratio, jitter, and the like were extremely inferior to those of the optical recording medium according to the example.

〔The invention's effect〕

According to the present invention, the recording material has a higher thermal conductivity, and, the higher the temperature, the lower the thermal conductivity is composed of a semiconductor material,
Because a heat conduction control layer that also acts as a reflection layer is provided, during “high-temperature heating and quenching treatment”, the heat conduction control layer that exhibits high heat conductivity at low temperatures in the area around the low-temperature irradiation spot By the action, heat radiation from the recording layer is promoted, and a sufficient cooling rate can be secured. Therefore, recrystallization at the periphery of the irradiation spot can be prevented.
Under the high temperature conditions, the heat conductivity of the heat conduction control layer is reduced, so that the heat radiation function is weakened, so that the heat loss at the spot central portion is reduced and the sensitivity can be prevented from lowering. In the case of "heating slow cooling treatment", the recording layer is not exposed to such a high temperature and the cooling rate of the entire irradiation spot is slower than the high temperature heating rapid cooling treatment. Low-temperature heating and slow-cooling treatment can be performed.

Therefore, there is an effect that high-speed rewriting with excellent signal quality such as C / N ratio and jitter can be performed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical recording medium according to an embodiment of the present invention, FIG. 2 (A) is a graph showing a change in temperature distribution of an irradiation spot on a recording layer irradiated with a laser spot with time, FIG. 2 (B) is a schematic view of a recorded recording mark, FIGS. 3 and 4 are cross-sectional views of an optical recording medium according to a comparative example, and FIGS. 5 (A) and 5 (B). Is a diagram for explaining the principle of recording and erasing on a “phase-change type” optical recording medium. FIG. FIG. 7 (A) is a graph showing the change of the temperature distribution over time of the irradiated spot on the recording layer irradiated with the laser spot in the conventional optical recording medium, and FIG. ) Is a schematic diagram of the recorded marks, FIG. FIG. 8A is a graph showing the change in the temperature distribution with time of the irradiated spot on the recording layer irradiated with the laser spot in the conventional optical recording medium having the cooling layer, and FIG. The schematic diagram of each mark is shown. [Description of Symbols] (1) ...... Substrate (3)… Recording layer (4)… Heat conduction control layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-258242 (JP, A) JP-A-63-187435 (JP, A) JP-A-63-214938 (JP, A) JP-A-62-1987 24451 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/24

Claims (1)

(57) [Claims] 1. A recording medium comprising: a substrate; and a recording layer formed on at least one surface of the substrate and formed of a phase-change recording material. In an optical recording medium on which information is optically recorded or erased by performing a high-temperature heating and quenching treatment, a semiconductor material having a higher thermal conductivity than the recording material, and having a lower thermal conductivity as the temperature becomes higher. An optical recording medium comprising a heat conduction control layer which also functions as a reflection layer.