JPS63217542A - Optical information recording member - Google Patents

Abstract

PURPOSE:To improve recording and erasing characteristics and repetitive characteristic by providing a laminated structure of heat resistant protective layers having absorption in a service wavelength region and heat resistant protective layers having no absorption therein between a recording layer and a transparent heat resistant protective layer. CONSTITUTION:The recording layer 4 having the light absorptivity and the resistant protective layers 2, 6 having no light absorption in the wavelength region of laser light to be used for recording and erasure are provided on the substrate 1; further, the heat resistant protective layers 3, 5 which have the optical absorptivity in the service wavelength region and do not mix with the recording layer when irradiated by the laser are provided between the recording layer 4 and the protective layers 2, 6. The cooling rate of the recording layer 4 can be thereby varied to the cooling speed suitable for recording film and the temp. distribution in the track width direction of the track groove part of a disk is uniformized. The recording and erasing characteristics as well as the repetitive characteristic are, therefore, improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical information recording member capable of recording, erasing, and reproducing information by optical means at high speed and with high density using light, heat, or the like.

Conventional technology In non-destructive optical information recording members that can be repeatedly recorded and erased, such as optical disk memories, heat-resistant protective layers such as oxides are used to prevent the resin used as the base material from being damaged during laser heating. It has been proposed to provide it between the base material and the recording layer or on the recording layer. Materials used as the heat-resistant protective layer include oxides (SiO2, GeO2,
2, Al2O3゜B e O2), nitride (BN, 5t
3N4. AIN) J chemical compound 5ic), chalcogenide (Z
nS, Zn5e), etc. have been proposed.

The main characteristics required for a heat-resistant protective layer are (1)
Must be transparent in the wavelength range used (760nm to 840nm).

(The melting point must be higher than the operating temperature.)

斡) High mechanical strength; (4) Chemically stable.

(5) It must have appropriate thermal constants (thermal conductivity, specific heat).

It is.

It cannot be said that the above-mentioned substances completely satisfy these conditions.

The problem that the invention seeks to solve The intensity distribution of the laser beam has a glass distribution.

For this reason, the temperature and time characteristics of heating and cooling differ between the center and the end portions of the grooves of the disk, so that phase separation and segregation of the recording material occur within the grooves. For this reason, repeated recording and erasing increases phase separation and segregation, limiting the repeatable life. Further, there is a problem that recording/erasing characteristics cannot be improved unless the cooling rate is appropriate for the recording material.

The present invention solves the above-mentioned problems by changing the material and structure of the heat-resistant protective layer.

Means for Solving the Problems In the present invention, the heat-resistant protective layer is used in the wavelength range 760~
Heat-resistant protection by laminating at least two layers: a material with an optical extinction coefficient (k>o), at which the heat-resistant protective layer itself absorbs light and increases rMLw at 830 nm, and a transparent heat-resistant protective layer that does not absorb light. The structure uses layers.

Function The present invention uses a light-absorbing protective layer and a non-light-absorbing heat-resistant protective layer as the heat-resistant protective layer, so that the thickness of the light-absorbing layer (recording layer + protective layer) is thicker than before. Become. Since the heat capacity due to laser heating increases, the temperature distribution within the groove in the track width direction of the disk can be made uniform. Further, by changing the thickness of the light-absorbing heat-resistant protective layer, it is possible to change the cooling rate to suit recording and erasing of the recording material.Examples Hereinafter, examples of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of the optical information recording member that is the basis of the present invention. 1 and 7 are base materials, 2 and 6 are conventional heat-resistant protective layers, and 3 and 6 are light-absorbing heat-resistant The protective layer 4 is a recording layer, and is bonded to the protective base material 8 using an adhesive 7. The present invention is characterized in that the heat-resistant protective layers 3 and 6 are made of specific materials. Conventional materials such as germanium dioxide (GeO3), silicon dioxide (S
102).

When anine sulfide (ZnS) or the like is used, there are problems with thermal properties in particular.

This thermal property has appropriate thermal conductivity and specific heat in order to efficiently utilize the thermal energy of the laser.

It is necessary to have density. If the thermal conductivity is too high, heat easily escapes and a lot of energy is required, which is disadvantageous, and if the thermal conductivity is too low, it becomes impossible to obtain rapid cooling conditions.

Among optical information recording methods, in the case of the phase change type, the cooling conditions are achieved by reversibly reciprocating between the two layers by combining heating and rapid cooling or slow cooling. It is important because

A feature of the present invention is that by using a heat-resistant protective material with an optical extinction coefficient (k>O), the protective material itself can be heated, and the cooling conditions of the recording layer can be changed. Moreover, the temperature distribution in the disk track groove part of the laser irradiation part can be made uniform. This effect can improve the recording and erasing characteristics, and further improve the reliability of repeated recording and erasing.

As a result of examining the causes of deterioration of repeat characteristics using conventional heat-resistant protective materials, we found that there is a temperature distribution in the width direction of the track groove, as shown in 9 in Figure 2, and that the recording material undergoes phase separation or segregation. I understand. Therefore, we investigated a method to make the temperature distribution of the track groove uniform in the track width direction.

The present inventors thought that temperature distribution could be made uniform by increasing the heat capacity of the portion heated by laser irradiation. Therefore, Pb5(k
= o, s), sandwich the recording layer between PBS,
Furthermore, ZnS was sandwiched on top of that. By doing so, the temperature distribution within the track groove can be made smaller than before, and the repeatability characteristics can be improved.

The reason why we adopted a two-layer structure of a light-absorbing material and a non-light-absorbing material as a protective material is that the light-absorbing material has a thermal role, while the conventional protective layer has a chemical stability and a recording layer. This is to share the optical role with.

By using this light-absorbing protective material, the temperature distribution within the groove has become more uniform than in the past, as shown by 9 in FIG. However, a temperature distribution occurred in areas other than the groove. In this way, it was possible to change the portion where the temperature distribution occurs in the track width direction by using the light-absorbing protective material.

On the other hand, by providing this PbS layer, the heat capacity of the light-absorbing portion increases, so that the cooling rate of the recording film can be made slower than before, as shown at 11.12 in FIG. Therefore, by using this optically absorbing protective layer, it was possible to change the cooling rate to be suitable for recording and erasing the recording film.

Further experiments revealed that the optical extinction coefficient k (k>O
It has been found that by using a protective layer with ), it is possible to make the temperature of the laser irradiated part almost uniform, as with PBS, and it is also possible to change the cooling rate of the recording layer.

However, if this heat-resistant protective layer that absorbs light is made thinner, it will be difficult to improve its thermal properties, and if it is made thicker, the source will not reach the recording layer, making it impossible to detect recording or erasing. . Therefore, the thickness of this heat-resistant protective layer that absorbs light has an optimum thickness, as shown in Table 1.
00 people was appropriate.

Further, the appropriate value for the optical extinction coefficient was 0.2 to 3.0 according to optical calculation. If the value of k is small, it will be difficult to extract the temperature of the heat-resistant protective layer by laser irradiation, the range in which the cooling rate of the recording layer can be controlled by the thickness of the heat-resistant protective layer will be narrowed, and the temperature distribution in the disk groove will be reduced. There was a problem that it could not be made uniform. Furthermore, when the value of k is greater than 3.0, there are problems in that the transmittance of the sample is low and it becomes difficult to detect optical changes in the recording film.

It has been found that if the melting point of the heat-resistant protective layer is 800° C. or lower, the protective layer is damaged during recording and erasing, and elements constituting the recording film diffuse into the heat-resistant protective layer.

On the other hand, when two or more layers are used: a dielectric material with optical absorption, that is, a dielectric material with an optical extinction coefficient, and a transparent dielectric material with no optical absorption, for example, when the structure is as shown in Fig. 4. Also recorded in the same way as above.

This was effective in improving erasing characteristics and repeatability.

In this figure, the same parts as in FIG. 1 are given the same numbers and their explanations will be omitted.

As a result of various experiments on heat-resistant protective materials with optical extinction coefficients, we found chalcogenides and nitrides.

Carbides, oxides, or heptadides had similar effects to those described above.

In particular, sulfides (PbS, Mn5) as chalcogenides,
When tellurides (PbTe, ZnTe) are used, when TaN, TiN, ZrN are used as nitrides, transition metal oxides (Tio2.Fe3O4, Ni) are used as oxides.
p.

Cr2o3. When using WO2), Ta is used as a carbide.
C.

When TIC, W2G is used, C as a fluoride
It has been found that when rF3-FeF2-NzF2 is used, the repetition characteristics and recording/erasing characteristics are improved compared to the conventional ones.

Specific examples are shown below.

Example 1 A heat-resistant protective layer such as ZnS was deposited on a PMMA substrate by a vapor deposition method. Furthermore, on top of this, PbS'1100°200.
400,500,600,800 people were deposited. Recording is performed by reversibly reversing the components of the recording layer between a crystalline state and an amorphous state.

TeGe5 is one of the phase change materials that can be erased.
Use an nO-based material, and the film thickness is 100% fco C.
PbS'i100.200.400゜500 on O
．． 600 and 800 people were steamed. Furthermore, on top of this, ZnO
2000 people vaporized.

This ZnS film thickness structure was determined from the viewpoint of laser absorption efficiency and from the viewpoint of increasing the change in optical constants.

Table 1 shows the number of repetitions with respect to the film thickness of PBS. This measurement was performed dynamically while rotating a disc-shaped disc. The wavelength of the laser is 830n
At m, the beam is focused to the diffraction limit on the disk. P
By providing the bS layer, the number of repetitions is increased.

Further, as the PbS layer becomes thicker, the number of repetitions begins to decrease. As is clear from this result, PbS is 200~
The repeatability increased when SOO was turned on.

Table 1 Example 2 Example 10 The temperature in the track width direction was thermally analyzed by computer simulation. The results are shown in FIG. 9 in Figure 2 is the temperature distribution when conventional ZnS is used, 1 in Figure 2
0 is the temperature distribution when the pbs layer+ZnS layer of the present invention is used. As is clear from the figure, in the PBS layer+ZnS layer, the peak temperature value was suppressed compared to the conventional case, and the value was almost the same within the track groove. As a result, the recording film deteriorates! IIIK<<became. The repeatability with the disk increased from 105 times to 107 times.

Example 3 The cooling process of recording pits after laser irradiation was analyzed by thermal simulation. FIG. 3 shows the relationship between the temperature and time of the optically active layer. 11 in Figure 3 is the cooling curve when conventional ZnS is used, and 12 in Figure 3 is the cooling curve when PbS layer and ZnS layer are used.By providing the PBS layer, the cooling rate is faster than before. I knew it was going to be late.

Next, a disk using a conventional ZnR layer and a disk using a PbS layer + Z
A comparison was made of the characteristics of disks using the nS layer.

As a result of recording power of 8 mW and erasing power of 16 mW, the ZnS system had a C/N of 52 dB and an erasure rate of 5 sdB.The PBS layer + ZnS layer system had a C/N of 50 dB and an erasure rate of 6.
It was 0dB. In this way, the busy recording and erasing characteristics have been improved.

Further, as a result of observing the recorded bits using a microscope, it was found that in the conventional ZnS system, the central part of the bit was amorphous and white after erasing, whereas in the PbS layer + ZnS layer system, no amorphous part remained after erasing.

Example 4 A sample having the structure shown in FIG. 4 was prepared on a PMMA substrate by vapor deposition. PMMA is used for the base material 1, and Zn is used for the heat-resistant protective layer 2.
S, optical extinction coefficient k) The heat-resistant protective layer 3 with O is pb.
s, the recording layer 4 was made of TeGe5nO. P
The thickness of the bS layer was 4 layers for 100 people, and the thickness of the recording layer was 1.
It was set as 0008. In addition, the thickness of Zn8 layer 2 is 500,6
The thickness was 1000A. The thickness of this ZnS layer was determined from the viewpoint of laser absorption efficiency.

The number of repetitions was measured using the above disk. The wavelength of the laser is 830 nm. The repeatability was improved to 106 times compared to 104 times without the PbS layer.

Example 5 The optical constants n and k of the heat-resistant protective layer were set to n=2.0. k is 0.
As a result of a simulation study of the transmittance (r) to the heat-resistant protective layer 200 when changing it from 1 to 3.6, k=
T: 96% when o, 1, 37% when ni = 3.0.

When k=3.5, it was 25%. Therefore, when k was made larger than 3.0, the transmittance of the heat-resistant protective layer was reduced and the optical change of the recording film was reduced.

Effect of the Invention The effect of the present invention is that the recording layer and the transparent heat-resistant protective layer that does not absorb in the wavelength range used are provided on the base material. By creating a heat-resistant protective layer that absorbs in the wavelength region, or a laminated structure of at least two layers: a heat-resistant protective layer that absorbs and a heat-resistant protective layer that does not absorb, the cooling rate of the recording layer can be adjusted to a cooling rate that is suitable for the recording film. It is possible to make the temperature distribution variable and to make the temperature distribution in the track width direction of the track groove portion of the disk uniform, so that the recording and erasing characteristics and the repetition characteristics can be improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a Motago Mushroom information recording member in an embodiment of the present invention, Fig. 2 is a graph showing the temperature distribution in the track width direction of the disk, and Fig. 3 is a graph showing the temperature distribution of the recording film after laser irradiation. FIG. 4, a graph showing the relationship with time, is a sectional view of an optical information recording member in another embodiment of the present invention. 1...Base material, 2...Heat-resistant protective layer (k=
o), 3... Heat-resistant protective layer (k>O), 4...
...Recording layer, 6...Heat-resistant protective layer (k>O),
6...Heat-resistant N layer (k=oλ7...Adhesive, 8...Base material. Name of agent: Patent attorney Toshio Nakao and 1 other person18)
-Base material Figure 2 Paragraph,) Width Figure 3 Figure 1-11 Base interpretation

Claims (8)

[Claims] (1) A light-absorbing recording layer on the base material and a transparent first layer that does not absorb light in the wavelength range of the laser light used for recording and erasing.
and a second heat-resistant protective layer that is optically absorbed in the used wavelength range and that does not mix with the recording layer by laser irradiation, between the recording layer and the transparent heat-resistant protective layer.
An optical information recording member characterized by being provided with a heat-resistant protective layer. (2) The optical information recording member according to claim 1, wherein the compound constituting the second heat-resistant protective layer is a chalcogenide, nitride, carbide, oxide, or fluoride. (3) The chalcogenide constituting the second heat-resistant protective layer is
Sulfides (e.g. PbS, MnS) or tellurides (
The optical information recording member according to claim 2, wherein the optical information recording member is made of, for example, PbTe or ZnTe. (4) The nitride constituting the second heat-resistant protective layer is TaN,
The optical information recording member according to claim 2, characterized in that it is TiN or ZrN. (5) The oxide constituting the second heat-resistant protective layer is a transition metal oxide (for example, Fe_3O_4, NiO, Cr_2
The optical information recording member according to claim 2, wherein the optical information recording member is O_3). (6) The carbides constituting the second heat-resistant protective layer are TaC and T.
The optical information recording member according to claim 2, which is iC or W_2C. (7) The fluoride constituting the second heat-resistant protective layer is CrF_
3. The optical information recording member according to claim 2, which is FeF_2 or NiF_2. (8) The optical extinction coefficient k of the second heat-resistant protective layer is 0.2≦
Claim 1 characterized in that k≦3.0.
Optical information recording member described in Section 2.