JP2926955B2 - Phase change type optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium using a phase change of a thin film in an optical disk used as a rewritable large-capacity file.

[Prior Art] A phase-change optical recording medium is used as a large-capacity rewritable optical disk. The characteristics required as a recording medium are that a phase change occurs at a high speed, that the recording / erasing state is stable, and that the recording / erasing characteristics do not change even after repeated rewriting.

As a material that causes a high-speed phase change, a Ge—Sb—Te-based alloy is known as a typical material, and an optical disc having excellent overwrite characteristics has already been manufactured. These disks are excellent recording and erasing characteristics when repeatedly rewritten 10 ⁶ times.

However, since the protective film of these disks has a weak adhesive force with the recording layer, there is a disadvantage that the recording layer and the protective layer are easily peeled off. For this reason, the long-term storability of the optical disc was inferior.

[Problems to be Solved by the Invention] From the above viewpoint, when developing a phase-change optical recording medium,
A protective film having a high number of repetitions and strong adhesion to the recording film has been sought. However, since a protective film capable of increasing the number of repetitions generally takes a strong covalent bond, its adhesion to the recording film is weak.

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-change type optical recording medium having excellent repetitive recording / erasing characteristics and excellent long-term storage characteristics.

Means for Solving the Problems The present invention relates to a phase change type optical recording medium for recording, reproducing, and erasing information by utilizing a phase change between an amorphous state and a crystal state. Adhesion enhancement layer, recording layer, adhesion enhancement layer,
A phase-change type optical recording medium characterized by comprising a protective layer and a reflective layer, and wherein the adhesion reinforcing layer is made of a transparent derivative.

FIG. 1 is a sectional view showing a basic structure of a phase change type optical recording medium of the present invention, in which an underlayer 2, a first adhesion strengthening layer 3, a recording layer 4, and a second adhesion enhancing layer are formed on a substrate 1. 5, a protective layer 6, and a reflective layer 7 are sequentially laminated. The material of the substrate 1 includes polycarbonate, PMMA, polyolefin, grooved glass and the like. The underlayer 2 and the protective layer 6 are made of various transparent dielectrics or dielectric mixtures, for example, Si ₃ N ₄ , SiO, AlN, Ta ₂ O ₅ , Ti
It is formed from O ₂ , ZrO _{2 and the} like. These layers are the recording layer 4
In addition to amplifying the difference in reflectivity caused by the above, it has a role of preventing thermal deformation of the substrate 1 and the recording layer 4 due to repetition of recording / erasing. The adhesion enhancing layers 3, 5 are various transparent dielectrics, for example, Z
It is composed of nS, ZnSe, SiO ₂ , CdS, In ₂ O _{3 and the} like. These layers, like the underlayer 2 and the protective layer 6, also play a role in amplifying the difference in reflectance generated in the recording layer 4. The recording layer 4 is formed between the adhesion enhancing layers 3 and 5. Reference numeral 7 denotes a reflection layer made of Al, Au, Si, Ni—Cr, or the like.

The materials of the underlayer 2, the adhesion reinforcing layers 3, 5 and the protective layer 6 need to be transparent to the wavelength of the laser beam. Underlayer 2
The protective layer 6 is selected under the condition that the recording layer 4 satisfies sufficient heat resistance against a temperature rise and sufficient mechanical strength against deformation. On the other hand, if the adhesion enhancing layers 3 and 5 are made of a material having good wettability with the underlayer 2, the protective layer 6 and the recording layer 4, the heat resistance and the mechanical strength do not need to be as strong as those of the protective layer. All of the compounds exemplified above have an intermediate bonding mode between the chalcogenide-based amorphous material and the ceramic material such as an oxide or a nitride. At the interface, the bond is bonded to both the chalcogenide-based amorphous material and the ceramic material. Is a material that can produce The recording layer 4 is a material that exhibits a reversible phase change. The thickness of each layer is set so that the optical absorption is large at the wavelength of the laser beam irradiated at the time of recording / erasing, and the amplitude of the reproduced signal is increased.

The underlayer 2, the adhesion enhancing layers 3, 5 and the protective layer 6 are formed by sputtering.
It is formed by a vacuum deposition method, a CVD method, or the like. The recording layer 4 and the reflection layer 7 are formed by a sputtering method or an evaporation method.

[Operation] In a phase change optical recording medium, recording, that is, amorphization utilizes a rapid cooling process from a liquid state. At this time, if the recording material in a liquid state and the protective layer for protecting the recording material have good wettability, the two will keep close contact during the recording operation, and if the wettability is poor, they will separate. In addition, the shape of the substance changes depending on the balance between the magnitude of the surface tension and the wettability with the base. If such a relationship between the wettability of the recording layer and the protective layer is used, it is possible to improve the adhesion during the recording operation and suppress the shape change.

The present invention provides a phase-change optical recording medium that can be stored for a long time by optimizing the degree of wettability between the recording layer and the protective layer. Here, by providing an adhesion-enhancing layer having good wettability to both layers between the protective layer and the recording layer,
Increases the adhesion between the recording layer and the protective layer, suppresses peeling of the film, and enhances long-term storage.

In order to increase the number of repetitions of recording / erasing, it is advantageous to use a protective film having high hardness. For example, a ceramic material such as silicon nitride corresponds to this. on the other hand,
It is known that a chalcogenide amorphous alloy is suitable for a phase change type optical recording material. However, the wettability between the ceramic and the chalcogenide amorphous is poor. this is,
This is because ceramics have a strong covalent bond and an alkogenide alloy has a weak covalent bond and a mixed ionic bond. Therefore, the bonding force at the interface between the two is weak.

Therefore, if a layer that has good wettability to both the recording layer and the protective layer, that is, a substance that can bond to both the ceramics and chalcogenide, is sandwiched, the properties with repeated recording / erasing characteristics are excellent. It is possible to obtain a phase-change type optical recording medium which is hard to peel off between the recording layer and the protective layer from the viewpoint of long-term storage while utilizing the above.

[Example] Next, an example of the present invention will be described.

Example 1 An underlayer having a thickness of 100 nm was formed on a polycarbonate substrate using silicon nitride. A first adhesion enhancement layer ZnS having a thickness of 50 nm, a recording layer Ge ₂ Sb ₂ Te _{5 having} a thickness of 30 nm, and a Second adhesion strengthening layer Z
A phase-change optical disk was manufactured by depositing nS, a protective layer silicon nitride having a thickness of 40 nm, and a reflective film Si having a thickness of 50 nm.

The recording / erasing characteristics of this disk and the number of times of repeated recording / erasing were measured. Linear velocity 11.3m / s, recording frequency 7.4MHz, 3.7M
When overwriting by irradiating the pulse light shown in Fig. 2 under the condition of Hz and duty 50%, the maximum of CNR is the recording power of 19m.
55 dB in W, maximum erasure rate 19 mW recording power, 8 mW erasing power
Was 35 dB in the combination of. The recording power is 1 at a linear velocity of 11.3 m / s, recording frequencies of 7.4 MHz and 3.7 MHz, and a duty of 50%.
9 mW, when the overwriting is irradiated repeatedly pulsed light of FIG. 2 as a combination of the erasing power 8 mW, CNR at repeated up to 10 ⁶ times the erasure rate did not change together.
In FIG. 2, 8 is a reading light, 9 is an erasing pulse, 10
Is a recording pulse.

Next, put this disc in an environment with a temperature of 80 ° C and a humidity of 90% RH.
After 1000 hours, the environment resistance was examined, and no peeling was observed between the recording film and the protective film. When a disk with the same recording and erasing characteristics and the same number of repetitions as the one in which the adhesion enhancement layer was not formed was placed in the same environment, the film was peeled off in about 50 hours in the shortest case. It can be seen that the long-term storability of the phase change optical disk can be improved.

[Effects of the Invention] As described above, according to the present invention, by providing the adhesion strengthening layer, a phase change type optical recording medium having excellent long-term storage characteristics while maintaining the recording / erasing characteristics and the number of repetitions is maintained. Can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a basic configuration of a phase change type optical recording medium according to the present invention, and FIG. 2 is a view showing a recording / erasing characteristic and a pulse shape of a laser beam used in measurement of the number of repetitions. DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Underlayer 3 ... 1st adhesion reinforcement layer 4 ... Recording layer 5 ... 2nd adhesion reinforcement layer 6 ... Protective layer 7 ... Reflective layer 8 ... Readout light 9 …… Erase pulse, 10 …… Record pulse

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Claims (1)

(57) [Claims] 1. A phase change type optical recording medium for recording, reproducing and erasing information by utilizing a phase change between an amorphous phase and a crystal phase. Reinforcement layer,
A phase-change optical recording medium, comprising a protective layer and a reflective layer, and wherein the adhesion reinforcing layer is made of a transparent derivative.