JPH10222875A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly generate crosstalk and to obtain excellent reproducing characteristics even if pitches are narrowed. SOLUTION: At one main surface 1a side of a substrate 1, land parts 2 and pregroove parts 3 are formed so as to be alternately arranged in a radial direction and then recording layer 4 are formed thereon. When dsub is a depth of the pregroove part 3 and dg is a film thickness of the recording layer 4 in the pregroove part 3, a relation: dsub <dg is valid. Otherwise, when W is a groove width of the pregroove part 3 and Tp is a track pitch, a relation: 0.4<=W/Tp<=0.5 may be valid. Further, two conditions described above may be valid. The recording layers 4 preferably contain at least a cyanine series organic compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording layer in which, for example, a cavity is formed by irradiating light on a substrate on which a land portion and a pregroove portion are formed, and a reflective film is formed thereon. The present invention relates to an optical recording medium formed. More specifically, it relates to an optical recording medium capable of obtaining good reproduction characteristics by defining the relationship between the depth of the pre-groove portion and the thickness of the recording layer formed therein, the groove width of the pre-groove portion and the track pitch. It is.

[0002]

2. Description of the Related Art In recent years, in the field of information recording, researches on optical information recording systems have been advanced in various places. This optical information recording system is capable of non-contact recording and reproduction, achieving a recording density that is at least an order of magnitude higher than the magnetic recording system, and can be used in read-only, write-once, and rewritable memory formats. It has a number of advantages such as compatibility, and is expected to be used in a wide range of applications from industrial use to consumer use as a format that enables realization of inexpensive large-capacity files.

[0003] Of the above-mentioned memory types, the write-once type is a type that can be recorded and reproduced by an end user and cannot be erased. Therefore, it is mainly used as a long-term storage file of data, so-called CD-R (Compac).
t Disc-Recordable). This CD-R is a so-called CD-ROM (Compact Disc) which is a read-only optical recording medium.
It is a write-once optical recording medium that is only compatible with c-Read Only Memory in terms of reproduction signal standards, and is widely used because it is inexpensive and can be discarded. In recording on this CD-R, a local irreversible physical change of the recording layer caused by the absorption of light energy by the recording material and conversion into heat energy is used. Known irreversible physical changes include a change in the shape of the recording layer (formation of pits), a change in surface properties, a change in the crystal state, and the like.

Among the irreversible physical changes as described above, those utilizing a change in shape of a recording layer (formation of pits) include a pre-groove portion as a guide groove on one main surface of a light-transmitting substrate. The lands are formed alternately in the radial direction, and have a property of absorbing the recording light thereon, causing local sublimation, decomposition, etc. due to the heat of the recording light to form cavities or locally. A recording layer in which the complex refractive index is changed is formed, and a reflective film is further formed thereon. In addition, as a material for forming the recording layer as described above, a cyanine-based or phthalocyanine-based organic compound or the like can be given.

In order to record information on the CD-R, recording light is locally applied to the recording layer in the pre-groove portion from the substrate side, and sublimation and decomposition occur only in this portion to form a cavity. Alternatively, the pits corresponding to the information are formed by changing the complex refractive index only in this portion. That is, the adjacent pre-groove portions with the land portion interposed therebetween are used as recording tracks, and the land portions function to separate adjacent recording tracks.

[0006]

However, in a CD-R in which information is recorded by the above-described method, when information on a predetermined recording track is reproduced, information on an adjacent recording track leaks out. Talk is easy to occur. When such crosstalk occurs, reproduction characteristics such as jitter are deteriorated, which is not preferable.

This is because the influence of a change in the shape or refractive index of the land leaks into a signal obtained by reproducing the information recorded in the pre-groove portion, disturbing the reproduced signal and making it impossible to accurately extract the recorded information. It is.

Therefore, it is conceivable that the recording layer is not formed on the land portion. However, to realize this, a process and technology equivalent to a semiconductor process are required, and the cost becomes high. I will. In the case of a write-once optical recording medium such as the CD-R, compatibility with a CD-ROM type optical recording medium, low cost, and easy disposal are required.

Recently, as a next-generation high-density optical disk of a CD-ROM, an optical video disk (for example, a digital video disk, Hereinafter, referred to as DVD).

[0010] In this DVD and the like, it is expected that a recording medium on which recording and reproduction can be performed by an end user will be required in the future. However, in these DVDs and the like, the track pitch is narrowed to, for example, 0.74 μm, which is less than half of the CD-R, and when a write-once recording medium such as the DVD described above is produced, the CD-R
It is more concerned than R that the reproduction characteristics are degraded due to the crosstalk as described above.

The present invention has been proposed in view of the conventional circumstances, and it is an object of the present invention to provide an optical recording medium in which crosstalk hardly occurs even if the pitch is narrowed, and which has good reproduction characteristics. I do.

[0012]

In order to achieve the above object, an optical recording medium according to the present invention is formed such that lands and pregrooves are alternately arranged in the radial direction on one principal surface of a substrate. A recording layer is formed over the land and the pre-groove portion on the main surface, and a reflective film is formed thereon. By irradiating light to a predetermined position of the recording layer in the pre-groove portion, recording is performed. Information is recorded by forming a cavity at a predetermined position of the layer or by changing a complex refractive index at a predetermined position of the recording layer, and the depth of the pre-groove portion is set to d.
_sub and the thickness of the recording layer in this pre-groove portion is d _g
, The relationship d _sub > d _g holds.

The optical recording medium of the present invention is formed such that lands and pre-groove portions are alternately arranged in the radial direction on one main surface of the substrate. A recording layer is formed over the recording layer, and a reflective film is formed thereon. By irradiating a predetermined position of the recording layer in the pre-groove portion with light, a cavity is formed at a predetermined position of the recording layer or Information is recorded by changing the complex refractive index at a predetermined position of the recording layer. When the groove width of the pre-groove portion is W and the track pitch is Tp, 0.4 ≦ W / Tp ≦ 0. 5 is established. At this time, W / Tp is 0.4
If it is smaller than this, the light for recording easily leaks to the land adjacent to the pre-groove part, and the effect of suppressing crosstalk is weak. If W / Tp is larger than 0.5, the groove width of the pre-groove part is wide. In other words, the width of the cavity portion and the complex refractive index change portion formed here becomes wider, and the crosstalk is rather increased.

Further, the optical recording medium of the present invention includes a medium characterized by satisfying both of the above two conditions.

Further, in the recording medium of the present invention, the recording layer preferably contains at least a cyanine-based organic compound.

In the optical recording medium of the present invention, lands and pregrooves are formed on one main surface of the substrate so as to be arranged alternately in the radial direction, and the lands and the pregrooves are formed on the main surface. When the depth of the pre-groove portion is d _sub and the thickness of the recording layer in the pre-groove portion is d _g , the relationship d _sub > d _g is established. Therefore, when recording is performed by irradiating a predetermined position of the recording layer in the pre-groove portion with light, a physical or chemical change occurring at a predetermined position of the recording layer in the pre-groove portion is caused on the adjacent land portion. Without reaching the recording layer, a cavity is formed only at a predetermined position of the recording layer, or the complex refractive index changes only at a predetermined position of the recording layer, and information is accurately recorded.

Further, in the optical recording medium of the present invention, lands and pre-groove portions are formed on one main surface of the substrate so as to be alternately arranged in the radial direction. A recording layer is formed over the groove portion,
The groove width of the pre-groove portion is W, and the track pitch is Tp
Since the relationship of 0.4 ≦ W / Tp ≦ 0.5 is established, when recording is performed by irradiating light to a predetermined position of the recording layer in the pre-groove portion, recording is performed. Most of the light to be emitted is radiated into the pre-groove portion, and light leaking to the adjacent land portion is greatly reduced. That is, physical and chemical changes of the recording layer in the land portion are suppressed, and a cavity is formed only at a predetermined position of the recording layer, or the complex refractive index changes only at a predetermined position of the recording layer, and information is accurately obtained. Is recorded.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

The optical recording medium of this embodiment has a configuration as shown in FIG. That is, one main surface 1a of the light transmitting substrate 1
On the side, a plurality of grooves are formed at predetermined intervals in the radial direction indicated by arrow D in the figure, the protrusions between the grooves are lands 2, and the grooves serving as the recesses are pregrooves 3. These are formed so as to be arranged alternately in the radial direction. On this main surface 1a, a recording layer 4 is formed over a land portion 2 and a pre-groove portion 3, and a reflection film 5 is formed thereon. Things. Further, a protective film 6 for protecting the recording layer 4 and the reflective film 5 is formed on the reflective film 5, and the surface thereof is a smooth surface.

It is preferable that the recording layer 4 contains at least an organic compound such as cyanine or phthalocyanine. The substrate 1 may be formed by injection molding using a thermoplastic resin such as polycarbonate, the reflective film 5 may be formed of a thin metal film such as aluminum or gold, and the protective film 6 may be formed of ultraviolet light. What is necessary is just to form with a hardening type resin etc.

In the optical recording medium of the present embodiment, as shown in FIG.
_When the thickness of the recording layer 4a in the pre-groove portion 3 is d _g , the relationship d _sub > d _g is satisfied.

At this time, the refractive index of the substrate 1 is set to n _sub
Where the complex refractive index of the recording layer 4 is n _d -ik _d ,
Is assumed to be n _r −ik _r . Here, i represents an imaginary number.

In order to record information on the optical recording medium of this embodiment, the following may be performed. That is, as schematically shown in FIG. 3, the land 2 and the pre-groove 3
From the main surface 1b side opposite to the one main surface 1a where
Light to be recorded by being condensed by a condenser lens 7 of a predetermined optical system is applied to the recording layer 4a in the predetermined pre-groove portion 3 as shown by an arrow L in the figure. Then, the recording layer 4a absorbs light and generates heat. When the amount of generated heat exceeds a certain threshold,
In this portion of the recording layer 4a, there is formed a changing portion 8 where physical and chemical changes such as melting, decomposition, sublimation, etc. occur as shown by dots in the figure, and are schematically shown in FIG. 4 in the recording layer 4a. The cavity 9 is formed as described above, and information is recorded.

At this time, in the optical recording medium of this embodiment,
When the depth of the pre-groove portion 3 is d _sub and the thickness of the recording layer 4a in the pre-groove portion 3 is d _g , d
_{Since the} relationship of _sub > d _g is established, a physical or chemical change occurring at a predetermined position of the recording layer 4a in the pre-groove portion 3 reaches the recording layer 4 on the adjacent land portion 2. Therefore, the cavity 9 is formed only at a predetermined position of the recording layer 4, and information is accurately recorded.

The reproduction of information from the optical recording medium according to the present embodiment is performed as follows.
The reproduction may be performed with the same optical system as during recording, and reproduction is performed with a lower light quantity than during recording so that the recording layer 4 is not changed by the light to be reproduced.

That is, in the optical recording medium of this embodiment,
As described above, when information is recorded, the physical and chemical change of the recording layer in the pre-groove portion 3 does not reach the recording layer 4 on the adjacent land portion 2, so that the recording layer is adjacent to the land portion 2. It is possible to partition between the pre-groove portions 3, and even if the pitch is narrowed, crosstalk hardly occurs, and good reproduction characteristics can be obtained.

In the above-described example, the depth of the pre-groove portion 3 is d _sub, and the recording layer 4 in the pre-groove portion 3
Although the example of the optical recording medium in which the relationship of d _sub > d _g holds when the thickness of a is d _g has been described, in the optical recording medium having the same configuration as the above-described optical recording medium, FIG. As shown, when the groove width of the pre-groove portion 3 is W and the track pitch, which is the interval between adjacent pre-groove portions 3, is Tp, the relationship of 0.4 ≦ W / Tp ≦ 0.5 is established. Then, when recording is performed by irradiating light to a predetermined position of the recording layer 4a in the pre-groove portion 3, most of the light to be recorded is radiated into the pre-groove portion 3 and is applied to the adjacent land portion 2. Light leakage is greatly reduced. That is, physical and chemical changes of the recording layer 4 in the land portion 2 are suppressed, and a cavity is formed only at a predetermined position of the recording layer 4 so that information is accurately recorded.

Also in this optical recording medium, when information is recorded as described above, physical and chemical changes of the recording layer in the pregroove 3 reach the recording layer 4 on the adjacent land 2. Therefore, the adjacent pre-groove portions 3 can be separated by the land portions 2, and crosstalk hardly occurs even if the pitch is reduced, so that good reproduction characteristics can be obtained.

Further, in the optical recording medium having the same configuration as the optical recording medium described above, the depth of the pre-groove portion 3 is d _sub, and the thickness of the recording layer 4a in the pre-groove portion 3 is When d _g , the relationship of d _sub > d _g holds, and the groove width of the pre-groove portion 3 is W,
Assuming that the track pitch, which is the interval between adjacent pre-groove portions 3, is Tp, even if the relationship of 0.4 ≦ W / Tp ≦ 0.5 is satisfied, the same effect as that of the optical recording medium described above is obtained. Is obtained.

In the examples described so far, an example of the optical recording medium in which information is recorded by forming a cavity in the recording layer has been described, but the information is recorded by changing the complex refractive index at a predetermined position of the recording layer. It is needless to say that the same effect can be obtained also in an optical recording medium on which is recorded the same configuration as that of the above-mentioned optical recording medium.

[0031]

EXAMPLES Next, in order to confirm the effects of the present invention, an optical recording medium having the above-described structure was actually manufactured, and its reproduction characteristics were examined. The specifications of the optical recording medium were as shown below.

That is, the track width Tp is 0.74 μm
The width W of the pre-groove portion is 0.35 μm, the depth d _sub of the pre-groove portion is 145 nm, the thickness d _g of the recording layer in this pre-groove portion is 137 nm, and the thickness of the recording layer in the land portion is d _l is 37 nm, the refractive index of the substrate n _sub is 1.58, and the complex refractive index of the recording layer is n _d -ik
_{d is set} to 2.1−i0.15, and the complex refractive index n _{r of the} reflection film is set.
The -ik _r was 0.0-i3.8. The reflectance is for a wavelength of 640 nm.

In this optical recording medium, d _sub -d _g
= 12 nm, W / Tp = 0.47, and d _sub > d
_g and 0.4 ≦ W / Tp ≦ 0.5.

Next, EFM + known as a DVD signal modulation method was recorded on such an optical recording medium at a recording density of 0.28 μm / bit as a recording signal. This recording was performed by a recording device having the following specifications. That is, the recording wavelength was 640 nm, the numerical aperture of the condenser lens was 0.6, the linear velocity was 3.5 m / s, and the recording power was 12 mW at the maximum.

Subsequently, the recorded signal was reproduced to examine reproduction characteristics. Specifically, set the focus servo to O
N and RF when tracking servo is OFF
The signal, the so-called traverse signal, was investigated. Fig. 5 shows the results.
Is shown schematically in FIG. In FIG. 5, the horizontal axis indicates time, the vertical axis indicates signal strength, and the figure indicates the outline of the entire changing waveform. In FIG. 5, the portion where the contour of the waveform indicating the signal strength is narrow indicates the reproduced signal when the light to be reproduced moves on the land.

Next, for comparison, the specifications are substantially the same as those of the above-mentioned optical recording medium, and have no recording layer, pits are formed directly in the pregroove portion, and a reflective film is formed directly thereon. A read-only optical recording medium was prepared, and the reproduction characteristics were similarly investigated. At this time, it is needless to say that the recorded signal is the same as that recorded on the optical recording medium described above. The results are shown schematically in FIG. Also in FIG. 6, the horizontal axis indicates time, the vertical axis indicates signal intensity, and the figure indicates the outline of the entire changing waveform. In FIG.
A portion where the contour of the waveform indicating the signal strength is narrow indicates a reproduced signal when the light to be reproduced moves on the land.

Comparing the results of FIG. 5 and FIG. 6, the width of the constriction is smaller in the write-once optical recording medium to which the present invention is applied than in the read-only optical recording medium, and the land area is better. It can be seen that it is detected. That is, in the optical recording medium to which the present invention is applied, a cavity is formed only at a predetermined position of the recording layer, information is accurately recorded, and even if the pitch is narrowed, crosstalk hardly occurs, and good reproduction is achieved. It was confirmed that characteristics were obtained.

[0038]

As is clear from the above description, the present invention
In optical recording media, the land portion is located on one main surface of the substrate.
And pre-groove parts are arranged alternately in the radial direction
And the land and pre-groove on this main surface.
The recording layer is formed by adjusting the depth of the pre-groove part.
d_sub And the thickness of the recording layer in this pre-groove portion is d
_g Then, d_sub > D_g So that the relationship
Specified for the recording layer in the pre-groove section.
When recording by irradiating light to the position
Physical and chemical changes that occur at specified locations on the recording layer within the unit
Does not reach the recording layer on the adjacent land,
A cavity is formed only at a predetermined position on the recording layer or
The complex refractive index changes only at the specified position
Is recorded.

In the optical recording medium of the present invention, lands and pre-groove portions are formed on one main surface of the substrate so as to be alternately arranged in the radial direction. A recording layer is formed over the groove portion,
The groove width of the pre-groove portion is W, and the track pitch is Tp
Since the relationship of 0.4 ≦ W / Tp ≦ 0.5 is established, when recording is performed by irradiating light to a predetermined position of the recording layer in the pre-groove portion, recording is performed. Most of the light to be emitted is radiated into the pre-groove portion, and light leaking to the adjacent land portion is greatly reduced. That is, physical and chemical changes of the recording layer in the land portion are suppressed, and a cavity is formed only at a predetermined position of the recording layer, or the complex refractive index changes only at a predetermined position of the recording layer, and information is accurately obtained. Is recorded.

That is, in the optical recording medium of the present invention, when information is recorded as described above, the physical and chemical changes of the recording layer in the pre-groove reach the recording layer on the adjacent land. Therefore, it is possible to distinguish between adjacent pre-groove portions by lands,
Even if the pitch is narrowed, crosstalk hardly occurs and good reproduction characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing an optical recording medium to which the present invention is applied.

FIG. 2 is an enlarged sectional view of a main part showing a vicinity of a pre-groove part of an optical recording medium to which the present invention is applied.

FIG. 3 is a schematic cross-sectional view of a main part showing how information is recorded on an optical recording medium to which the present invention is applied.

FIG. 4 is a schematic cross-sectional view of a main part showing how information is recorded on an optical recording medium to which the present invention is applied.

FIG. 5 is a characteristic diagram showing a traverse signal of an optical recording medium to which the present invention has been applied.

FIG. 6 is a characteristic diagram showing a traverse signal of a read-only optical recording medium.

[Explanation of symbols]

Reference Signs List 1 substrate, 1a one main surface, 2 lands, 3 pregrooves, 4 recording layers, 5 reflective films, 9 cavities

Claims (5)

[Claims] 1. A recording layer is formed on one main surface of a substrate so that lands and pre-groove portions are alternately arranged in a radial direction, and a recording layer is formed on the main surface over the land and the pre-groove portion. A reflective film is formed thereon, and by irradiating light to a predetermined position of the recording layer in the pre-groove portion, a cavity is formed at a predetermined position of the recording layer or a complex portion at a predetermined position of the recording layer is formed. In an optical recording medium for recording information by changing the refractive index, when the depth of the pre-groove portion is d _sub and the thickness of the recording layer in the pre-groove portion is d _g , d _sub > d _g
An optical recording medium characterized by the following relationship: 2. When the groove width of the pregroove portion is W and the track pitch is Tp, 0.4 ≦ W / Tp ≦ 0.5.
The optical recording medium according to claim 1, wherein the following relationship is established. 3. The optical recording medium according to claim 1, wherein the recording layer contains at least a cyanine-based organic compound. 4. A land portion and a pre-groove portion are formed on one main surface side of the substrate so as to be alternately arranged in a radial direction, and a recording layer is formed on the main surface over the land portion and the pre-groove portion. A reflective film is formed thereon, and by irradiating light to a predetermined position of the recording layer in the pre-groove portion, a cavity is formed at a predetermined position of the recording layer or a complex portion at a predetermined position of the recording layer is formed. In an optical recording medium for recording information by changing the refractive index, the groove width of the pre-groove portion is W, and the track pitch is Tp.
An optical recording medium characterized by satisfying the following relationship: 0.4 ≦ W / Tp ≦ 0.5. 5. The optical recording medium according to claim 4, wherein the recording layer contains at least a cyanine-based organic compound.