JP2003303442A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium having a structure and the material characteristics of a recording layer suitable for a DRAW tape optical recording medium corresponding to the laser beams of the wavelength area of a shorter wavelength, 360 nm to 450 nm for instance, capable of increasing a recording density. <P>SOLUTION: For the optical recording medium 10, the recording layer 12 is formed on a supporting body 11, the recording layer 12 is irradiated with the laser beam L for recording/reproducing information to/from the opposite side of the supporting body 11 and the information is recorded/reproduced to/ from the recording layer 12 by a reflected light intensity modulation system. For the refractive index n0 and absorption coefficient k0 before recording of the recording layer 12, the refractive index n1 and the absorption coefficient k1 after recording, Δn=n1-n0, Δk=k1-k0 and the film thickness d of the recording layer 12, one of the conditions, which are (condition 1) n0≥2.25, k0≤0.35, Δn≤-0.25, -0.15≤Δk≤0 and 30≤d≤45 nm, (condition 2) n0≤1.2, k0≤0.35, |Δk|>0.15, -0.15≤Δk≤0 and d≥55 nm, and (condition 3) 1.3≤n0≤1.8, |Δk|>0.6, |Δn|<0.3, and 1.3<n1<1.8, is satisfied. <P>COPYRIGHT: (C)2004,JPO

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, and is particularly suitable for application to, for example, a write-once type optical recording medium.

[0002]

2. Description of the Related Art In recent years, an optical recording medium capable of recording and reproducing information by laser light has been developed and put into practical use. In particular, a so-called write-once type optical recording medium, which can store a huge amount of data such as a moving image and which is capable of writing information only once, is attracting attention as an inexpensive optical recording medium.

As a write-once type optical recording medium, a CD-R having reproduction compatibility with a reproduction-only CD (compact disc) is widely used. In addition, a so-called DVD-R having reproduction compatibility with a DVD (digital versatile disk) has been put into practical use. In these write-once type optical recording media, an organic dye is used as the material of the recording layer, and recording is performed by changing the optical characteristics of the recording layer due to the reaction of the organic dye.

In the conventional write-once type optical recording medium, as shown in the schematic sectional view of FIG. 23, a recording layer 52 made of an organic dye, a reflective layer 53 and a protective layer 54 are formed on a support 51. Further, a so-called groove recording method is adopted in which a guide groove 55 is provided on the surface of the support 51 below the recording layer 52, and recording is performed on the groove 56 side of the guide groove 55. The width GW of the groove 56, which is the recording portion, is
The width is set to be narrower than the width LW of the so-called land 57 (GW <LW) which is a non-recording portion. Further, the laser light L is made incident on the recording layer 52 from the side of the support 51, and the laser light is reflected at the interface between the recording layer 52 and the reflective layer 53.

Optically, the recording area (group)
The phase difference between the reflected light from 56 and the reflected light from the non-recording portion (land) 57 is changed by recording so that the combined wave of both reflected waves becomes smaller after recording than before recording. That is, as shown in FIG. 24A, the groove 56 is recorded before recording.
The reflected light LRg from the land 57 and the reflected light LRl from the land 57 have a small phase difference, and they are mutually strengthened to make a large synthetic wave L.
R (LR0) is formed. On the other hand, as shown in FIG. 24B, after recording, the phase difference between the reflected light LRg from the groove 56 and the reflected light LR1 from the land 57 is increased so that they cancel each other out to form a small combined wave LR (LR1). I am trying to do it. In FIGS. 24A and 24B, reference numeral 61 denotes a laser irradiation range. In other words, in the groove 56 having a narrow width with respect to the land 57, the reaction of the organic dye or the like is generated, and the optical recording is realized by the phase difference modulation.

These write-once type optical recording media, that is, the above-mentioned CD
-R and the above-mentioned DVD-R each have a wavelength of about 78.
Recording and reproduction are performed by laser light of 0 nm and about 650 nm.

Here, the recording density of the optical recording medium increases in principle in inverse proportion to the square of the wavelength, and in order to perform higher density recording, the wavelength of the laser light used is shortened. Will be required. In recent years, wavelengths of 360 nm to 450 using GaN, third harmonics (THG), etc.
Small lasers that emit light of nm have been developed, and large-capacity optical recording media using these have been actively developed.

[0008]

However, until now, in the write-once type optical recording medium having a recording layer made of an organic dye (hereinafter, simply referred to as a write-once type recording medium), the above-mentioned 3 is used.
There has not been sufficient development of a device that can handle laser light in the wavelength region of 60 to 450 nm.

Further, in the write-once type optical recording medium having a recording layer made of an organic dye, the reflected light phase modulation method has been conventionally used, but since it is necessary to form a deep groove on the support, the support 51 is formed. It has been difficult to further reduce the uneven pattern on the surface to increase the recording density.

In order to solve the above-mentioned problems, the present invention has a structure suitable for a write-once type optical recording medium and a material property of a recording layer which are compatible with a laser beam having a shorter wavelength, for example, a wavelength region of 360 nm to 450 nm. However, the present invention provides an optical recording medium capable of achieving high recording density.

[0011]

In the optical recording medium of the present invention, a recording layer is formed on a support, and a laser beam for recording / reproducing information is applied to the recording layer from the side opposite to the support. Information is recorded / reproduced on / from the recording layer by a reflected light intensity modulation method, the refractive index of the recording layer before recording is n0 and the absorption coefficient is k0, the refractive index of the recording layer after recording is n1, and the absorption coefficient is k1, Δn = n1-n0, Δk = k1-k
0, where d is the thickness of the recording layer, (condition 1) n0 ≧ 2.25, k0 ≦ 0.35, Δn ≦ −
0.25, −0.15 ≦ Δk ≦ 0, 30 ≦ d ≦ 45 nm (Condition 2) n0 ≦ 1.2, k0 ≦ 0.35, | Δn |>
0.15, −0.15 ≦ Δk ≦ 0, d ≧ 55 nm (Condition 3) 1.3 ≦ n0 ≦ 1.8, | Δk |> 0.6,
It satisfies one of the conditions of | Δn | <0.3 and 1.3 <n1 <1.8.

According to the above-mentioned structure of the optical recording medium of the present invention, since the laser beam is applied to the recording layer from the side opposite to the support, the laser beam before and after being reflected by the recording layer is attenuated in the intermediate layer. Less to do. In addition, since recording / reproducing of information to / from the recording layer is performed by the reflected light intensity modulation method, it is not necessary to form a narrow and deep guide groove for obtaining a sufficient phase difference as in the phase difference modulation method, and a wide width is achieved. A recording area can be secured. Further, it becomes easy to make the uneven pattern of the guide groove and the recording track fine. Furthermore, since the recording layer satisfies any of the above (condition 1) to (condition 3), the optical constants (refractive index n and absorption constant k) change before and after recording,
For example, a modulation degree of about 40% or more can be obtained. As a result, it is possible to sufficiently detect the signal based on the recording.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a recording layer is formed on a support, and a laser beam for recording / reproducing information is irradiated to the recording layer from the side opposite to the support, and the information on the recording layer is recorded. Recording / reproduction is performed by the reflected light intensity modulation method, the refractive index of the recording layer before recording is n0, the absorption coefficient is k0, the refractive index of the recording layer after recording is n1, the absorption coefficient is k1, and Δn =
When n1-n0, Δk = k1-k0, and the film thickness of the recording layer is d, (Condition 1) n0 ≧ 2.25, k0 ≦ 0.35, Δn ≦ −
0.25, −0.15 ≦ Δk ≦ 0, 30 ≦ d ≦ 45 nm (Condition 2) n0 ≦ 1.2, k0 ≦ 0.35, | Δn |>
0.15, −0.15 ≦ Δk ≦ 0, d ≧ 55 nm (Condition 3) 1.3 ≦ n0 ≦ 1.8, | Δk |> 0.6,
The optical recording medium satisfies the condition of | Δn | <0.3 and 1.3 <n1 <1.8.

According to the present invention, in the above optical recording medium, an uneven pattern is formed on at least one surface of the recording layer, and the height H of the step of the uneven pattern is the refractive index of the cover layer n _c and that for reproduction. H = λ / (6n _c ), where λ is the wavelength of the laser light.

Further, according to the present invention, in the above-mentioned optical recording medium, a concavo-convex pattern is formed on at least one surface of the recording layer, the concave and convex portions of the concavo-convex pattern have substantially the same width, and both concave and convex portions are formed. Recorded.

According to the present invention, in the above-mentioned optical recording medium, a concavo-convex pattern is formed on at least one surface of the recording layer, and the width of the concavity of the concavo-convex pattern is wider than or substantially equal to the width of the convex part of the concavo-convex pattern. In addition, the recording is performed only in the concave portion.

Further, according to the present invention, in the above-mentioned optical recording medium, a concavo-convex pattern is formed on at least one surface of the recording layer, and the width of the convex part of the concavo-convex pattern is wider than or substantially equal to the width of the concave part of the concavo-convex pattern. In addition, recording is performed only on the convex portion.

As an embodiment of the present invention, a schematic configuration diagram (cross-sectional view) of an optical recording medium 10 is shown in FIG. In this optical recording medium 10, a recording layer 12 is formed on a support 11, and a surface of the recording layer 12 is covered with a cover layer 13. Further, the guide groove 14 is formed on the upper surface of the support 11 by the unevenness, and the upper surface of the recording layer 12 is also formed by the unevenness according to the guide groove 14. That is, the cover layer 13 is provided in place of the protective layer 54 of the conventional optical recording medium 50 of FIG.
Moreover, the structure is such that there is no reflective layer.

The optical recording medium 10 has a structure in which the laser beam L is incident from the upper side in the figure, that is, the cover layer 13 side opposite to the support 11. This is because the laser light L having a shorter wavelength causes the loss due to absorption and attenuation in the support 11 to increase when the laser light L is incident from the side of the thick support 11 serving as a substrate. Therefore, the laser light L is made incident from the surface side of the cover layer 13 which is closer to the recording layer 12.

The material of the support 11 is polycarbonate, for the purpose of forming the guide groove 14 having a fine concavo-convex structure.
It is preferable to use a thermoplastic resin such as polymethacrylate or polyolefin. When a thermoplastic resin is used as the material of the support 11 in this manner, the support 11 is mass-produced at low cost by, for example, injection molding using a stamper on which unevenness for transferring the guide groove 14 is formed. It is possible. Further, as the material of the support 11, it is also possible to use a photocurable resin (for example, an ultraviolet curable resin). In this case, it is suitable for the production of a large number of small quantities of the supports 11 by the glass 2P (photopolymer) method.

The recording layer 12 on the support 11 is composed of a layer containing an organic dye or a layer containing an organic dye. Such a recording layer 12 is formed by dissolving an organic dye in a predetermined solvent, applying the solution by spin coating, and then performing a drying treatment, or by a spin coating method, or by forming the support 11 and the organic dye in a vacuum chamber. And the organic dye is heated and sublimated to be deposited on the support 11 to form a vacuum vapor deposition method. The film thickness d of the recording layer 12 is preferably in the range of 25 to 90 nm.

The cover layer 13 is provided in order to keep the recording density high and to avoid the influence of dust, oils and the like adhering to the surface of the optical recording medium 10, and is formed to have a thickness of, for example, about 0.1 mm. Further, as the material of the cover layer 13, a plastic which is transparent at the wavelength of the laser light L for recording / reproducing is suitable. Then, for example, when a photo-curable resin or the like is used as the material of the cover layer 13, it can be formed by coating on the surface by spin coating. Also,
When a thermoplastic resin such as a polyolefin resin, a methacrylate resin, or a polycarbonate resin is used as the material of the cover layer 13, it can be formed by adhering the thermoplastic resin to the surface with an adhesive. This cover layer 13
Is formed to have a thickness of, for example, about 0.1 mm.

Also in the present embodiment, the recording layer 1
In order to protect 2, the cover layer 13-the recording layer 12
It is possible to provide a protective layer (not shown) on either or both of the space and the space between the recording layer 12 and the support 11.
When a protective layer is provided between the cover layer 13 and the recording layer 12, it is preferable to use a material transparent to the wavelength of the recording / reproducing laser beam L, such as silicon nitride, silicon oxide, magnesium fluoride, It is desirable that an inorganic dielectric material such as zinc sulfide be formed by a sputtering method.

Then, the optical recording medium 10 of the present embodiment.
Can record and reproduce by irradiating the laser beam L in the wavelength range of 360 to 460 nm, which has a shorter wavelength than before.

Further, in the optical recording medium 10 of the present embodiment, a system different from the phase modulation system adopted in the conventional write-once type recording medium, that is, a reflected light intensity modulation system is adopted. The reflected light intensity modulation method detects that the intensity of reflected light reflected by the recording layer 12 is modulated before and after recording. As described above, in order to modulate the intensity of the reflected light before and after recording, the reflectance of the recording layer 12 should be changed by a sufficient change amount before and after recording. do it.

In the present embodiment, since the reflected light intensity modulation method is adopted, it is not necessary to detect it by utilizing the unevenness as in the phase modulation method. Therefore, the narrow groove portion does not have to be a recording area. Since it is also possible to perform recording on both the land portion and the groove portion, a wide area can be used as the recording area. Further, since it is not necessary to form the guide groove deeply, it is possible to form the guide groove in a fine concavo-convex pattern, and it is easy to miniaturize the recording track. Therefore, it is possible to increase the recording density of the optical recording medium. It will be possible.

Here, in the configuration of the optical recording medium 10 of FIG. 1, it will be described that the portion where the recording area can be set changes depending on the size of the width LW of the land portion and the width GW of the groove portion.

First, as shown in FIG. 2, the width L of the land portion is
When W and the width GW of the groove portion are substantially equal to each other, recording can be performed on both the land portion and the groove portion, and so-called land / groove recording can be performed. Note that the recording may be performed on any one of the land portion or the groove portion.

Next, as shown in FIG. 3, the width L of the land portion is
W is wider than the width GW of the groove (LW> GW)
In some cases, recording can be done on the land. That is, the land portion 15 becomes a recording portion and the groove portion 16 becomes a non-recording portion.

Further, as shown in FIG. 4, the width G of the groove is
When W is wider than the land width LW (GW> LW), recording can be performed in the groove portion. That is, the groove portion 17 becomes the recording portion and the land portion 18 becomes the non-recording portion.

Next, the optical effect due to the uneven shape of the guide groove in the case of recording on the land portion and the case of recording on the groove portion will be described respectively. First, in the case of recording on a land portion (FIGS. 2 and 3), schematic diagrams of optical effects before and after recording are shown in FIGS. 5A and 5B. The recording layer 12 is irradiated with the condensed laser light from the cover layer 13 side and is reflected by the recording layer 12. The laser irradiation range 21 in the recording layer 12 is a range shown by hatching in FIG. Since the intensity of the laser light has a Gaussian distribution, the land portion 15 of the recording layer 12 is strongly irradiated, while the groove portion 16 is hardly irradiated in terms of intensity. Further, looking at the area ratio of the laser irradiation range 21, it can be seen that most of the land 15 is irradiated. In such a case, the reflectance from the recording layer 12 is determined by the relationship of the complex refractive index of each layer of the cover layer 13-recording layer 12-support 11 in the land portion 15, and the reflected wave from the groove portion 16 is the recording layer. It hardly affects the reflectance from 12. In addition, the cover layer 13 and the recording layer 1
Even if there is an additional layer such as a protective layer between the recording layer 12 and the recording layer 12, the reflectance from the recording layer 12 is such that the cover layer 13 of the land portion 15-added layer-recording layer 12-support 11 The reflected wave from the groove portion 16 has almost no influence on the reflectance from the recording layer, which is determined by the relationship of the complex refractive index.

Further, the step H between the land portion 15 and the groove portion 16 is set to H = λ / (6n _c ) where the refractive index of the cover layer 13 is n _c and the reproduction wavelength is λ, so that the land portion 15 is separated from the land portion 15. It is possible to reduce the influence of the phase difference generated between the reflected wave of 1 and the reflected wave from the groove portion 16.
Therefore, in the optical recording medium having such a configuration, recording (writing of information) causes a change in the complex refractive index, which will be described later, in the land portion 15 of the recording layer 12, so that the reflected light LRl1 from the land portion 15 is changed. It is possible to make the intensity weaker than that of the reflected light LR10 before recording to cause a change in reflectance as recording. That is, the reflected light intensity can be modulated.

Similarly, in the case of recording in the groove portion (FIGS. 2 and 4), schematic diagrams of optical effects before and after recording are shown in FIGS. 6A and 6B. The recording layer 12 is irradiated with the condensed laser light from the cover layer 13 side and is reflected by the recording layer 12. Laser irradiation range 21 in recording layer 12
Indicates a range shown by hatching in FIG. Since the intensity of the laser light has a Gaussian distribution, the groove portion 17 of the recording layer 12 is strongly irradiated, while the land portion 1
Intensity 8 was hardly irradiated. Further, looking at the area ratio of the laser irradiation range 21, it can be seen that most of the laser irradiation range 21 is irradiated to the groove portion 17. In such a case, the reflectance from the recording layer 12 is determined by the relationship of the complex refractive index of each layer of the cover layer 13-recording layer 12-support 11 in the groove portion 17, and the reflected wave from the land portion 18 is the reflected wave. It hardly affects the reflectance from 12. In addition, even if there is an additional layer such as a protective layer between the cover layer 13 and the recording layer 12, the reflectance from the recording layer 12 can be determined by the cover layer 13 of the groove portion 17-the added layer- It is determined by the relationship of the recording layer 12 and the complex refractive index of the support 11, and the reflected wave from the land portion 18 hardly affects the reflectance from the recording layer.

Further, the step H between the groove portion 17 and the land portion 18 is set to H = λ / (6n _c ) where n _{C is} the refractive index of the cover layer 13 and λ is the reproduction wavelength. It is possible to reduce the influence of the phase difference generated between the reflected wave of 1 and the reflected wave from the land portion 18.
Therefore, in the optical recording medium having such a configuration, the groove portion 17 of the recording layer 12 is recorded (recording information) by recording.
By causing a change in complex refractive index, which will be described later,
By making the intensity of the reflected light LRg1 from the groove portion 17 weaker than that of the reflected light LRg0 before recording, it becomes possible to cause a change in reflectance as recording. That is, the reflected light intensity can be modulated.

As described above, the land portion and the groove portion
The step H, that is, the guide groove 14 formed on the surface of the support 11.
Is the depth of the cover layer 13 and the refractive index of the cover layer 13 is n._c, Playback laser light
Is set to λ, and H = λ / (6n_c) By
On the surface of the recording layer 12 where the laser light L is reflected
Also, a step H = λ / (6n
_c) Is formed. And, as mentioned above, the groove part
Between the reflected wave from the land and the reflected wave from the land
By reducing the influence of the phase difference, the reflected light intensity modulation method
The detection can be performed well.

Here, the optical recording medium of the above-mentioned embodiment
Like the body 10, the optical recording medium according to the present invention reflects light
Since the intensity modulation method is adopted, the degree of modulation is
It can be calculated by matrix theory. This total
The calculation method will be described below. As shown in FIG.
An optical multilayer film consisting of L layers is formed on the light emitting medium s.
And the incident medium of light is m. Also, optical multilayer film
Each layer constituting the
.., j, ... L is numbered. Each layer of optical multilayer film
The number attached to each layer is used as a subscript for the physical quantity in.
In addition, light is incident on the incident medium m at an angle of θ0.
And Also, after that, enter a complex number in italics or
Attach and show. The film thickness of each layer is d (d₁, D₂,,, d
_j・ ・ ・ D _L). Then, the refractive index of each layer is And

The reflection intensity coefficient of the optical multilayer film is expressed as follows. Then, the following equation holds for the light incident angle θ _j in the j-th layer.

The modulation degree I before and after recording is the reflectance Rinit before recording and the reflectance Rafter after recording.
On the other hand, I = (Rinit-Rafter) / Rinit.

Optical recording medium 10 of the above-described embodiment
Since the recording layer 12 is composed of only one layer, the case where L = 1 is considered in the above description. At this time, the complex refractive index of the recording layer 12 And n indicates the refractive index of the recording layer 12, and k indicates the recording layer 1.
2 shows an absorption coefficient of 2. And the wavelength of the light source is 405 nm
As a result, the reflectance R was calculated from the film thickness d of the recording layer 12, the refractive index n, and the absorption coefficient k. The cover layer 1
3 and the support 11 had a refractive index of 1.6. The result of this calculation is used for each film thickness d (25 nm, 30 nm, 35 nm, 4
0 nm, 45 nm, 50 nm, 55 nm, 60 nm, 6
5nm, 70nm, 75nm, 80nm, 85nm, 9
0 nm) is shown in each of FIGS. 7 to 20.
7 to 20, the vertical axis represents the absorption coefficient k, the horizontal axis represents the refractive index n, and the reflectance R is shown by contour lines.

From these figures, the desired characteristics of the recording layer 12, for example, the characteristics of the material of the recording layer 12 required for the medium having the initial reflectance of 10% (= 0.1) to obtain the modulation degree of 60% or more are shown. can get. For example, in order to obtain an initial reflectance of 10% (0.1) and a modulation of 60% or more, the reflectance after modulation, that is, after recording is 4% (0.04) or less. Before recording, the refractive index n0 and the absorption coefficient k0 are such that R = 0.1,
After recording, parameters n0, k0, n1, such that the refractive index n1 and the absorption coefficient k1 satisfying R ≦ 0.04 are satisfied.
A material capable of obtaining k1 may be used for the recording layer 12.

Here, the initial reflectance is 10% and the modulation degree is 6
Assuming that it is 0% or more, in order to satisfy this, the change in the optical constant of the material of the recording layer 12 Δc = √
The required minimum value of (Δn ² + Δk ² ) was examined for each film thickness d of the recording layer 12 from FIGS. 7 to 20. Note that Δn and Δk
Is the change in the refractive index and the change in the extinction coefficient due to recording, respectively. The results are shown in Fig. 22.

It can be seen from FIG. 22 that the required minimum value of Δc becomes smaller as the film thickness d of the recording layer 12 becomes larger, although there is some increase or decrease. Then, in order to obtain the initial reflectance of 10% and the modulation degree of 60% or more, at least Δc needs to be larger than the plotted value of this graph. That is, the value of Δc in the film thickness of the corresponding recording layer 12 is (d, Δc) = (25 nm, 0.294) (30 n
m, 0.278) (35 nm, 0.254) (40n
m, 0.249) (45 nm, 0.254) (50n
m, 0.239) (55 nm, 0.216) (60n
m, 0.197) (65 nm, 0.183) (70n
m, 0.173) (75 nm, 0.155) (80n
m, 0.157) (85 nm, 0.151) (90 n
m, 0.148) above the line connecting them, it is necessary to select the material of the recording layer 12.

Since the plotted values in FIG. 22 are the minimum necessary values, they are merely reference values, and the values shown in FIGS.
In FIG. 20, depending on the actual values of the refractive index n and the absorption coefficient k of the material, it may be necessary to make Δc much larger in order to obtain the initial reflectance of 10% and the modulation degree of 60% or more.

As described above, when the initial reflectance is 10% and the degree of modulation is 60% or more, sufficient detection can be performed. Depending on the configuration of the detector (photodiode, etc.) that detects the reflected light and the signal detection circuit, the modulation factor may be 6
Even if it is less than 0%, it is possible to detect the presence or absence of recording, but it is desirable to obtain a modulation degree of at least about 40% or more.

Therefore, the refractive index of the recording layer 12 before recording is set to n.
Where n is 0, the absorption coefficient is k0, the refractive index of the recording layer 12 after recording is n1, and the absorption coefficient is k1.
0, n1, k1, and Δn = n1-n0 and Δk = k
Regarding 1-k0 and the film thickness d of the recording layer 12, any one of the following (condition 1), (condition 2), and (condition 3) may be satisfied. (Condition 1): n0 ≧ 2.25, k0 ≦ 0.35, Δn ≦
−0.25, −0.15 ≦ Δk ≦ 0, 30 ≦ d ≦ 45n
m (condition 2): n0 ≦ 1.2, k0 ≦ 0.35, | Δn |
> 0.15, −0.15 ≦ Δk ≦ 0, d ≧ 55 nm (Condition 3): 1.3 ≦ n0 ≦ 1.8, | Δk |> 0.
6, | Δn | <0.3, 1.3 <n1 <1.8

Next, an optical recording medium was actually manufactured and its characteristics were examined.

Example 1 On the surface of a support 11 made of a disc-shaped polycarbonate resin having a thickness of 1.1 mm,
0.32 μm wide guide groove 14 with a depth of 40 nm
It was formed in a spiral shape with an interval of μm. A thin film of the triphenylamine compound represented by Chemical formula 1 was formed as the recording layer 12 on the support 11 by a vapor deposition method to a thickness of 40 nm.

[0048]

[Chemical 1]

On this recording layer 12, a light-transmitting polycarbonate sheet having a thickness of 0.1 mm is attached via a transparent adhesive layer to form a cover layer 13, and the same structure as that shown in FIG. Thus, the (recordable type) optical recording medium 10 was obtained. This was used as the optical recording medium of Example 1. Next, with respect to the optical recording medium 10 of Example 1, laser light having a wavelength of 405 nm and a peak power of 4.5 mW was condensed by an objective lens having a numerical aperture NA of 0.85 by a blue semiconductor laser, and a linear velocity of 5. Recording was performed at 7 m / s and a shortest mark length of 0.173 μm.

Recording and reproduction were performed on the optical recording medium 10 to examine the characteristics. As a result, a modulation degree of 63% and a signal noise ratio CNR of 54 dB were obtained for each of the land portion and the groove portion. The crosstalk from the land portion to the groove portion was 15.5 dB, and the crosstalk from the groove portion to the land portion was 5.2 dB. That is, good results were obtained in all cases.

Further, in order to specify the characteristics of the material of the recording layer 12, the following sample was prepared separately from the optical recording medium 10 and the change in the optical constant due to the irradiation of the laser beam having the wavelength of 405 nm was measured. Five triphenylamine compound thin films, which are materials for the recording layer 12, were vapor-deposited on a flat quartz substrate having a thickness of 1.1 mm to a thickness of 40 to 200 nm, and five sheets were prepared. A sample was prepared by depositing silicon by a sputtering method. Then, this sample was irradiated with laser light under the same irradiation conditions as the optical recording medium 10. However, here, the laser light is 5 m
The area was squarely scanned so that no unirradiated area was formed, and an area having the same optical constant as the recorded area was formed. Before and after this laser irradiation, the surface shape was measured by AFM. As a result, it was confirmed that the five samples were not deformed before and after laser irradiation.

Further, with respect to these samples, changes in transmittance and reflectance before and after laser irradiation were measured by using a spectroscope. The optical constants before and after laser irradiation were determined by the RT method comparing the calculated values of transmittance and reflectance with the measured values. Before laser irradiation, n = 2.30, k = 0.
20 and R = 0.11, after irradiation n = 1.95, k
= 0.20 and R = 0.04. That is, the case classification corresponds to case 1. As a result, Δc = 0.3
5, and the above-mentioned modulation degree of 63% is obtained. And in the case of this Example 1, the above-mentioned (condition 1) is satisfied.

(Comparative Example) The procedure of Example 1 was repeated except that the compound shown in Chemical formula 2 was used as the material of the recording layer 12.
A (write-once type) optical recording medium 10 was produced. This was used as the optical recording medium of Comparative Example 1.

[0054]

[Chemical 2]

Recording layer 12 of the optical recording medium of Comparative Example 1
The optical constant of was measured to be n = 2.3, k before recording.
= 0.10, R = 0.107, and after recording n = 2.
15, k = 0.15, R = 0.07, and Δc = 0.
It was 16. The modulation due to recording was 35%, and the signal noise ratio CNR was 50 dB. Therefore, since the optical recording medium of Comparative Example 1 has a small change Δc in optical constant, the modulation degree is as small as 35% and the signal noise ratio is as large as 50 dB, so that the optical recording medium has sufficient characteristics as a write-once type optical recording medium. It turns out that it has not been obtained.

In the above-described embodiment, the write-once type optical recording medium provided with the recording layer 12 made of an organic dye is used.
The present invention can be similarly applied to optical recording media having other configurations. For example, the present invention can be applied to a structure in which a plurality of similar recording layers are formed between a support and a cover layer, or when the recording layer is a phase change recording layer.

Further, in the above embodiment, the recording layer 12
Although the concavo-convex pattern is formed on both sides of the above, in the present invention, the concavo-convex pattern may be formed on at least one surface of the recording layer. For example, a structure in which unevenness is formed on the surface of a substrate (support or intermediate layer) on which a recording layer is formed when producing an optical recording medium, and an uneven pattern is formed on the surface of the recording layer on the substrate side, or For example, a configuration in which a concavo-convex pattern is formed on the surface of the recording layer on the side of the cover layer or the like formed after the recording layer can be considered. Then, even when the uneven pattern is formed on either side of the recording layer,
The height H of the step of the uneven pattern is H = λ / (6n
It is possible to adopt a configuration of _c ) or a configuration that defines the relationship between the widths of the groove portions (recesses) and the land portions (projections) and the recording portion.

The present invention is not limited to the above-mentioned embodiments, and various other configurations can be adopted without departing from the gist of the present invention.

[0059]

According to the present invention, since it is easy to increase the recording density of the optical recording medium, it is possible to realize an optical recording medium corresponding to a laser beam having a shorter wavelength, for example, a wavelength range of 360 nm to 450 nm. It will be possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram (cross-sectional view) of an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration in which the lands and grooves have substantially the same width in the optical recording medium having the configuration of FIG.

3 is a diagram showing a configuration in which the width of a groove is made narrower than the width of a land in the optical recording medium having the configuration of FIG.

FIG. 4 is a diagram showing a configuration in which the width of a groove is wider than the width of a land in the optical recording medium having the configuration of FIG.

5A and 5B are views of the optical recording medium having the configuration of FIG.
FIG. 6 is a diagram illustrating a change in reflected light before and after recording when recording is performed on a land portion.

6A and 6B are optical recording media having the configuration shown in FIG.
It is a figure explaining the change of the reflected light before and after recording when recording on a groove part.

7 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 25 nm in the optical recording medium having the configuration of FIG.

8 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 30 nm in the optical recording medium having the configuration of FIG.

9 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 35 nm in the optical recording medium having the configuration of FIG.

10 is a diagram showing the relationship between the refractive index, the absorption coefficient, and the reflectance when the thickness of the recording layer is 40 nm in the optical recording medium having the configuration of FIG.

11 is a diagram showing the relationship between the refractive index, the absorption coefficient, and the reflectance when the thickness of the recording layer is 45 nm in the optical recording medium having the configuration of FIG.

12 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 50 nm in the optical recording medium having the configuration of FIG.

13 is a diagram showing the relationship between the refractive index, the absorption coefficient, and the reflectance when the thickness of the recording layer is 55 nm in the optical recording medium having the configuration of FIG.

14 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 60 nm in the optical recording medium having the configuration of FIG.

15 is a diagram showing the relationship between the refractive index, the absorption coefficient, and the reflectance when the thickness of the recording layer is 65 nm in the optical recording medium having the configuration of FIG.

16 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 70 nm in the optical recording medium having the configuration of FIG.

17 is a diagram showing the relationship between the refractive index, the absorption coefficient, and the reflectance when the thickness of the recording layer is 75 nm in the optical recording medium having the configuration of FIG.

18 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the film thickness of the recording layer is 80 nm in the optical recording medium having the configuration of FIG.

19 is a diagram showing the relationship between the refractive index, the absorption coefficient, and the reflectance when the thickness of the recording layer is 85 nm in the optical recording medium having the configuration of FIG.

20 is a diagram showing the relationship between the refractive index and the absorption coefficient and the reflectance when the thickness of the recording layer is 90 nm in the optical recording medium having the configuration of FIG.

FIG. 21 is a diagram for explaining a method of calculating a modulation factor in a multilayer film.

FIG. 22 is a diagram showing a relationship between a film thickness of a recording layer and a required minimum value of Δc.

FIG. 23 is a schematic cross-sectional view of a conventional write-once type optical recording medium.

24A and 24B are views for explaining changes in reflected light before and after recording on the recording medium of FIG. 23.

[Explanation of symbols]

10 optical recording medium, 11 support, 12 recording layer, 1
3 cover layers, 14 guide grooves, 15 and 18 lands,
16, 17 Groove part, L laser light

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuaki Oyamada             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Shinichiro Tamura             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Sakuya Tamada             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F term (reference) 5D029 JC05 WB11 WB17 WC05 WC08

Claims (5)

[Claims] 1. A recording layer is formed on a support, and a laser beam for recording / reproducing information is applied to the recording layer from the side opposite to the support to record / record information on the recording layer. Reproduction is performed by a reflected light intensity modulation method, where the refractive index of the recording layer before recording is n0 and the absorption coefficient is k0, the refractive index of the recording layer after recording is n1, and the absorption coefficient is k.
1 and Δn = n1-n0, Δk = k1-k0, and the film thickness of the recording layer is d, it is necessary to satisfy one of the following (condition 1), (condition 2), and (condition 3). Characteristic optical recording medium. (Condition 1) n0 ≧ 2.25, k0 ≦ 0.35, Δn ≦ −
0.25, −0.15 ≦ Δk ≦ 0, 30 ≦ d ≦ 45 nm (Condition 2) n0 ≦ 1.2, k0 ≦ 0.35, | Δn |>
0.15, −0.15 ≦ Δk ≦ 0, d ≧ 55 nm (Condition 3) 1.3 ≦ n0 ≦ 1.8, | Δk |> 0.6,
| Δn | <0.3, 1.3 <n1 <1.8 2. An uneven pattern is formed on at least one surface of the recording layer, and a step height H of the uneven pattern is formed.
Is H = λ / (6n _c ), where n _{c is} the refractive index of the cover layer and λ is the wavelength of the laser light for reproduction. recoding media. 3. A concave-convex pattern is formed on at least one surface of the recording layer, the concave and convex portions of the concave-convex pattern have substantially the same width, and recording is performed in both the concave and convex portions. The optical recording medium according to claim 1, wherein the optical recording medium is a recording medium. 4. A concave-convex pattern is formed on at least one surface of the recording layer, and the width of the concave portion of the concave-convex pattern is wider than or substantially equal to the width of the convex portion of the concave-convex pattern, and recording is performed only in the concave portion. The optical recording medium according to claim 1, wherein: 5. A concave-convex pattern is formed on at least one surface of the recording layer, and a width of a convex portion of the concave-convex pattern is wider than or substantially equal to a width of a concave portion of the concave-convex pattern, and only in the convex portion. The optical recording medium according to claim 1, wherein recording is performed.