JPH05325264A - Optical recording medium - Google Patents

Abstract

PURPOSE:To increase allowable recording frequencies more than conventional ones by reducing the extrusion of a recording material due to heat expansion of upper and lower protective layers at the time of information recording or the like, and to prevent the shift of the recording material. CONSTITUTION:The optical recording material has the layer structure formed by successively laminating on a substrate 1 at least a lower protective layer 2, a recording layer 3, and an upper protective layer 4. Information is recorded and reproduced by utilizing the change of the conditions of the recording material. A mark-forming part 7a on the track 7 in which the information is recorded is bent so as to protrude it at least in one direction of the lamination directions of each layer upward or downward or alternately in both directions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium for recording and reproducing information by utilizing changes in optical properties associated with changes in the recording layer material. The above-mentioned state change includes phase change between a crystal phase and an amorphous phase, between a crystal phase and a crystal phase, or between an amorphous phase and an amorphous phase, and phase separation between a binodal decomposition phase and a spinodal decomposition phase.

[0002]

2. Description of the Related Art Conventionally, as an optical recording medium for recording and reproducing information by irradiating a laser beam or the like to cause a state change of a recording layer material and utilizing the accompanying change in optical properties, For example, a phase change optical recording medium utilizing a phase change between a crystal phase and an amorphous phase is known.
As shown in FIG. 4, this phase change optical recording medium comprises a lower protective layer 22 and a recording layer 2 made of a phase change type material on a substrate 21.
3, upper protective layer 24, reflective layer 25 and surface protective layer 26
Are sequentially laminated, and the upper surface of the raised track 27 is generally used as an information recording section for irradiating a laser beam to record information. Also,
In this medium, the area between adjacent tracks can also be used as an information recording section. In this phase change optical recording medium, a high-power laser beam (laser light) with a diameter of about 1 micron is irradiated onto the recording layer in a crystalline state, and the irradiated portion is melted and then rapidly cooled to make it amorphous. Information is recorded by changing the state to form marks and irradiating the recording layer with a low-power laser beam to determine the difference in optical properties between the crystalline state and the amorphous state. The information is reproduced by detecting as. Further, in this optical recording medium, the recording layer is irradiated with an intermediate output laser beam and the irradiated portion is kept at a crystallization temperature or higher for a predetermined time to change it to a crystalline state to erase the mark. Moreover, in this medium, new information can be overwritten on the previous information by irradiating the recording layer with a laser beam whose intensity is modulated with a high output and an intermediate output corresponding to the information. A recording layer material used in such a phase change optical recording medium is disclosed in JP-A-63-2259.
Ge-Sb-Te and the like described in Japanese Patent No. 34 are known.

[0003]

However, in such an optical recording medium, the document “T. Ohta et.
al. , SPIE, 1078 Optical Dat
a Storage Topical Meeting,
p27,1989 ”, etc., in order to irradiate a high-power laser beam at the time of recording information,
The phenomenon that the recording layer material melted by the irradiation is extruded toward the recording direction side due to the deformation due to the thermal expansion of the protective layer material occurs. Then, particularly after recording a large number of times, a part of the recording layer material is largely moved and displaced from the initial position due to the pushing action, and as a result, normal recording becomes difficult and the number of recording times is limited. There was a problem that

In Japanese Patent Laid-Open No. 3-256239, there is disclosed a substrate in which a surface of a track in an optical recording medium substrate is curved so that a cross-sectional shape crossing the reading direction is a concave or convex curved surface. An optical information recording medium configured by using it has been proposed. That is, this optical information recording medium improves resistance to compressive stress due to thermal expansion applied to the recording layer by curving the track surface in a concave shape or a convex shape, thereby preventing separation of the substrate and the recording layer. It is intended to prevent the temperature rise of the recording layer induced by the delamination, thereby preventing the deterioration (reading deterioration) of the recording layer. However, in the optical information recording medium, as in the present invention, it is possible to suppress the extrusion phenomenon of the recording material that occurs in the recording layer having the layer structure in which the protective layers are laminated on the upper and lower sides thereof and improve the recording frequency. Not intended.

The present invention has been made to solve the above problems, and an object thereof is to reduce the extrusion phenomenon of the recording material due to the thermal expansion of the upper and lower protective layer materials at the time of recording information, etc. An object of the present invention is to provide an optical recording medium capable of increasing the allowable number of recording times as compared with a conventional product by preventing the recording material from moving due to extrusion.

[0006]

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, the above-mentioned extrusion phenomenon occurring in a conventional product is located above and below the molten recording layer. We found that both protective layers are caused by displacement deformation by pressing so that the recording layer part in a fluid state is pressed by melting, and further research based on this finding revealed that both upper and lower protective layers were heated and expanded. It has been found that the above object can be achieved by sometimes displacing and deforming the recording layer in the same direction as much as possible so that the recording layer portion sandwiched between the two protective layers is not strongly pressed, and thus the present invention has been completed.

That is, the optical recording medium of the present invention has a layer structure in which at least a lower protective layer, a recording layer and an upper protective layer are sequentially laminated on a substrate, and the recording material forming the recording layer changes in state. In an optical recording medium that records / reproduces information by utilizing changes in optical properties, at least a mark forming portion on a track on which information is recorded is alternated in one of upper and lower directions of a stacking direction of each layer or both directions. It is characterized in that it is curved so as to project to the.

The present invention will be described below with reference to the drawings. The optical recording medium of the present invention generally comprises a substrate 1 and a lower protective layer 2, a recording layer 3, an upper protective layer 4, a reflective layer 5 and a surface protective layer which are sequentially laminated on the substrate 1 as shown in FIG. 6 and has a layer structure in which the protective layers 2 and 4 are laminated on the upper and lower sides of the recording layer 3 in particular.

The track referred to in the present invention is a continuous or discontinuous defined area used as an information recording portion for irradiating a laser beam to record information. In the present invention, as shown in FIG. 2, at least a portion of the track 7 where the laser beam 8 is irradiated to actually record information, that is, the mark forming portion 7a is provided in the stacking direction of each of the above layers (usually, on the substrate). It is curved so as to alternately project in an upward direction, a downward direction, or both upper and lower directions thereof (a direction perpendicular to the horizontal plane). That is, the mark forming portion 7a has a track direction (a laser beam scanning direction).
Curved only in the cross section orthogonal to, or
It may be curved only in the cross section along the track direction, and further, may be curved in both cross sections in the track direction and the direction orthogonal to the track direction. It is necessary that at least the lower protective layer 2, the recording layer 3, and the upper protective layer 4 located in the mark forming portion 7a are all curved in the same manner.

As a specific form of the mark forming portion 7a, it is assumed that the mark forming portion 7a has a curved surface that is curved only in a cross section orthogonal to the track direction. For example, when viewed as a whole, the shape of a chamfer (tunnel) is the track direction. Some of them have a surface morphology (see FIG. 3) that is formed along the track, and have a curved surface that is curved only in the cross section in the track direction, for example, Kamaboko (tunnel).
Some of them have a surface morphology in which the shapes are set sideways and are sequentially arranged for each mark forming portion along a plurality of track directions, and it has a curved curved surface in both cross sections orthogonal to the track direction and the track direction. , For example,
There is a surface morphology in which hemispherical curved shapes are sequentially arranged along the track direction for each of a plurality of mark forming portions.

The curving protrusion of the mark forming portion is not limited to the one projecting upward in the stacking direction as in the above-described specific example, but may be the one projecting downward. Therefore, for example, between adjacent tracks, with respect to a track in which a mark forming portion that is curved so as to project upward is formed,
In a track adjacent to the track, the mark forming portion may be formed so as to project and curve downward, and the projecting direction of the curve may be alternately different between the adjacent tracks. Further, in the same track, the mark forming portions protruding upward and the mark forming portions protruding downward may be alternately arranged under regular or irregular arbitrary conditions.

Further, in the present invention, when the protruding direction of the curve of the mark forming portion is either one of the upper and lower directions of the stacking direction of each layer, the protective layer of the upper protective layer or the lower protective layer located outside the curving direction. It can be set so that the material has a higher coefficient of thermal expansion than the protective layer material of the lower protective layer or the upper protective layer located on the inner side in the bending direction. That is, the coefficient of thermal expansion of the protective layer material of the protective layer located on the outer side in the curving protrusion direction of the mark forming portion is set to be higher than that of the protective layer material of the protective layer located on the inner side in the curving direction. More specifically, as shown in FIG. 1, when the mark forming portion 7a is projectingly curved upward in the stacking direction, the upper protective layer 5 is formed.
When the protective layer material has a higher thermal expansion coefficient than the protective layer material of the lower protective layer 2, and conversely the mark forming portion is protruding and curved downward, the protective layer material of the lower protective layer 2 is The coefficient of thermal expansion is larger than that of the upper protective layer 5.

The degree of curvature of the mark forming portion in the present invention is w (μ) when the width of the curved mark forming portion 7a shown in FIG.
m), the degree of curvature C = h / w when the height of the curve is h (μm) is set so as to satisfy the following condition. That is, the curvature C in the present invention depends on mechanical material constants such as thermal expansion coefficient and Young's modulus of the material used, but is usually 0.05 ≦ C ≦ 1, and preferably 0.
1 ≦ C ≦ 0.5. If the curvature C is less than 0.05, the pushing action of the recording material due to the thermal expansion deformation of 2 and 4 for protecting the upper and lower sides cannot be sufficiently reduced. There is a problem that it is difficult to manufacture a curved mark forming portion that satisfies the conditions by a normal manufacturing method.

If the coefficient of thermal expansion α ₁ of the protective layer material of the protective layer located outside the curved protruding direction of the mark forming portion is larger than the coefficient of thermal expansion α ₂ of the protective layer located inside thereof, α ₁ is preferably twice or more of α ₂ .

As the mark forming portion curved as described above, usually, as shown in FIG. 3, the substrate 1 provided with the bending portion 9 which can obtain the curved surface of the target mark forming portion is used, and on the substrate. It is formed by laminating each protective layer and recording layer in a thin film shape with a uniform film thickness.

The substrate 1 and each layer in the present invention are made of the same materials as those conventionally known, but among them, the recording material for forming the recording layer 3 is Ge-Sb-Te, I.
n-Ge-Sb-Te, Ge-Sb-Te-Co, Ge
In addition to a material containing a Ge-Sb-Te-based material such as -Sb-Te-Pd as a main component, a material containing In-Sb-Te or Ge-Te as a main component is preferably used.
Materials that cause phase separation such as e-O and Sb-O can be used. The protective layer material forming the lower protective layer 2 and the upper protective layer 4 is SiO ₂ , ZnS, ZnS-Si.
O ₂ , AlN, Si ₃ N ₄ , Al ₂ O ₃ , Ta ₂ O ₅ , CaF ₂
Etc. are preferably used. When the coefficient of thermal expansion of the protective layer material is made different between the two protective layers 2 and 4 as described above, for example, a material having a small coefficient of thermal expansion and containing SiO ₂ as a main component is used. Zn as a large material
A material containing S, AlN, Al ₂ O ₃ , CaF ₂ or the like as a main component may be appropriately combined and used.

The thickness of each layer is 10 to 2 for the recording layer 3.
00 nm, the lower protective layer 2 is about 50 to 300 nm,
The upper protective layer 4 has a thickness of about 10 to 300 nm.

[0018]

According to the present invention, as shown in FIG. 2, the laser beam 8 is formed at least on the track 7 on which information is recorded.
Since the mark forming portion 7a which is irradiated with is curved in a predetermined direction, the lower protective layer 2 and the upper protective layer 4 located in the area of the mark forming portion 7a (that is, the most heated portion).
At the same time, due to the thermal expansion, the curved shape tends to displace in the same direction (outward of the curved surface) in a well-balanced manner. As a result, both of the protective layers 2 and 4 are displaced in the same manner as the portion of the recording layer 3 between the layers (hatched portion in the figure), so that the recording layer 3 as in the conventional product is displaced.
The action of pinching the portion of is suppressed. Therefore,
Since the force for pushing out the molten recording material in the portion of the recording layer 3 becomes small, the moving amount of the recording material can be reduced.

In the present invention, the coefficient of thermal expansion of the protective layer material located outside the mark forming portion in the direction of curvature is made larger than the material coefficient of thermal expansion of the protective layer located inside the mark forming portion, so that FIG. As shown in the figure, the ratio of the thermal expansion M proceeding along the curved surface direction is always relatively larger in the protective layer located outside in the bending direction, so that the protective layer located outside in the bending direction is inside. Attempts to deform more toward the outside in the bending direction than the protective layer located at. As a result, the force of pushing out the material of the recording layer portion sandwiched between these protective layers becomes further smaller, so that the amount of movement of the recording material can be further reduced.

As described above, the upper and lower protective layers 2, 4
The phenomenon that both of them try to displace in the same direction is, for example, a thermal expansion phenomenon in which, when a circular ring is heated, both the inner part and the outer part of the ring deform and move toward the curved outer direction due to thermal expansion. Considered to be substantially the same. Further, in such an annular thermal expansion phenomenon, the force of displacing in the outward curved direction is such that the greater the curvature of the curvature (in other words, the smaller the radius of curvature), the more the coefficient of thermal expansion of the material. The larger is, the larger.

[0021]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 As the substrate 1, a substrate 1 made of synthetic resin, glass, or the like, in which a curved portion having a chamfered shape curved only in the track direction is formed as shown in FIG. 3, is used. This bending portion was formed so that the bending degree was about 0.3. Next, a lower protective layer (material: Zn
S-SiO ₂ , layer thickness 160 nm), recording layer (material: Ge)
-Sb-Te, layer thickness 20 nm), upper protective layer (material: Z
nS-SiO ₂ , layer thickness 30 nm, reflective layer (material: Al
Ti and a layer thickness of 100 nm) are formed in this order by a sputtering method, and then an acrylate-based UV curable resin is applied thereon so that the layer thickness is 10 μm, and then dried to form a surface protective layer. An optical recording medium having a cross sectional structure as shown in 1 was prepared. The recording layer located on the curved portion of the substrate and the upper and lower protective layers are both curved and laminated so as to follow the curved shape of the curved portion.
In the present embodiment, the portion composed of the curved recording layer and the upper and lower protective layers was used as a track for recording information. The thermal expansion coefficients of the lower protective layer material and the upper protective layer material are the same. Using the obtained optical recording medium, while irradiating a laser beam at a linear velocity of 10 m / s to record information, the track portion on which the information was recorded was judged from the degree of distortion of the reproduced waveform.
No movement of the recording material was observed even after the recording was carried out 0,000 times.

Example 2 The coefficient of thermal expansion α ₁ of the upper protective layer material was made larger than the coefficient of thermal expansion α ₂ of the lower protective layer material (α ₁ −α ₂ = 5 × 10 ⁻⁶ /
An optical recording medium was prepared in the same manner as in Example 1 except for the difference of ° C). When information recording was performed using this optical recording medium in the same manner as in Example 1, the movement of the recording layer material was not recognized even at the stage of recording 2 million times.

Here, the number of recordings in the second embodiment is the same as that in the first embodiment.
It is thought that the reason for the above is more than the following. That is, as shown in FIG. 2, the force P that tends to deform toward the outside of the curved surface is generally generated by the thermal expansion action of the material, and therefore increases as the thermal expansion coefficient of the material increases. Therefore, in Example 2, the upper protective layer 4 located outside the curved direction of the spot irradiation portion.
Since the coefficient of thermal expansion of the material is larger than the coefficient of thermal expansion of the lower protective layer 2 located inside thereof, when the laser beam is irradiated and heated, the lower protective layer 2 is stronger than the upward force in the figure. The upward force of the upper protective layer 4 becomes larger, and the upper protective layer 4 is displaced more outward in the bending direction than the lower protective layer 2. Therefore, it is considered that the force for pushing out the recording layer portion sandwiched between both protective layers is further suppressed as compared with the first embodiment.

Comparative Example An optical recording medium was prepared in the same manner as in Example 1 except that a conventional substrate having a smooth track surface was used as a substrate, and information was recorded under the same conditions. When the number of recordings reached 100,000, the movement of the recording layer material was confirmed, and normal recording became difficult. From this result, the following is estimated. That is, when the surface of the portion where information is recorded by irradiating the laser beam is flat as in the comparative example, when heated, the protective layer is located on either side in the vertical direction due to thermal expansion along the surface direction of the protective layer. Although it receives a displacing force or becomes indeterminate in shape, in the end, it will be deformed to the side of the recording layer that melted and became mechanically weak, and due to such deformation of the protective layer. The action of extruding the recording layer material occurs. Therefore, as the above results show, the number of times recording is possible is smaller in the medium of the comparative example than in the first and second embodiments.

[0025]

As described above, the optical recording medium of the present invention has at least the mark forming portion in the track on which information is recorded, which is curved in a predetermined direction. Compared with the above, since the extruding phenomenon of the recording layer material due to the thermal expansion of the protective layer material is reduced and the moving amount of the recording material is reduced, the allowable number of times of recording can be increased. When the coefficient of thermal expansion of the protective layer material located outside the curved direction of the mark forming portion is made larger than the material coefficient of thermal expansion of the protective layer located inside thereof, the number of recordings is dramatically increased compared to the conventional product. Can be increased to
Incidentally, according to the present invention, it is possible to stably perform recording up to about 1 million times (more times depending on the configuration content).

[Brief description of drawings]

FIG. 1 is a sectional view of an optical recording medium showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view for explaining the operation principle of the present invention.

FIG. 3 is a perspective view showing an example of a substrate.

FIG. 4 is a cross-sectional view showing a conventional optical recording medium.

[Explanation of symbols]

1 ... Substrate, 2 ... Lower protective layer, 3 ... Recording layer, 4 ... Upper protective layer, 7 ... Track, 7a ... Mark forming part, 8 ... Laser beam.

Claims (1)

[Claims] 1. A substrate having a layer structure in which at least a lower protective layer, a recording layer and an upper protective layer are sequentially laminated on a substrate, and the change in the optical property due to the change in the state of the recording material forming the recording layer is utilized. In an optical recording medium for recording / reproducing information by means of information recording, at least the mark forming portion in the track on which information is recorded is curved so as to protrude in either one of the upper and lower directions of the stacking direction of the respective layers or alternately in both directions. An optical recording medium characterized by the above.