JPH01150246A - optical information recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical information recording medium capable of recording and reproducing information using a light beam, and particularly relates to an optical information recording medium capable of obtaining high recording sensitivity. It relates to information recording media.

[Conventional technology]

In recent years, there has been a demand for optical recording media with high recording sensitivity.

The recording sensitivity referred to here refers to how small the power of a light beam can be used to perform the recording. Therefore, if an optical information recording medium with high recording sensitivity is used, Compared to the case where an optical information recording medium with low recording sensitivity is used, the same recording can be performed using a smaller light beam power.

Such optical information recording media with high recording sensitivity are suitable for high-speed recording and high-density recording.

For example, when performing high-speed recording, if the recording speed is increased, the power of the light beam must be increased accordingly, but since the power of the light beam is finite, the power of the light beam must be as low as possible. Therefore, it is better to use a medium with high recording sensitivity that allows recording to be performed as an optical information recording medium.

In addition, when performing high-density recording, it is necessary to narrow the light beam to increase the recording density, but if the light beam is narrowed down in this way, the efficiency of using the light beam decreases; In order to utilize the light beam more effectively, it is better to use an optical information recording medium with high recording sensitivity.

Now, examples of conventional optical information recording media include IEE and Spectrum.

August (1979) pp. 26-33 (IE
EE Spectrum, August (1979
) As described in PP26-33), a thin metal film (recording film) with a low melting point such as Te is formed on a substrate with a guide groove, and the thin metal film is irradiated with a narrow laser beam. There was one in which recording pits were formed by melting and drilling holes.

FIG. 5(a) is an enlarged plan view of a part of the optical information recording medium using the above-mentioned melt hole punching method, and FIG. 5(b)
) is a sectional view showing a cross section in the BB direction of FIG. 5(a).

In FIG. 5, 20 is a substrate, 21 is an address header C and a spit, 22 is a guide groove for tracking,
23 is a recording film, and 24 is a recording pit formed by a laser beam. In addition, W is the width of the guide groove 22, d,
is the depth of the address pit 21 for the address header, d2
is the depth of the guide groove 22. However, λ represents the wavelength of the laser beam, and n represents the refractive index of the substrate 20.

In the optical information recording medium using the melt hole drilling method shown in FIG.
The film surface of the recording film 23 must be completely free (that is, no other film is formed on the film surface, etc.). Therefore, when constructing this optical information recording medium as an optical disk, it is necessary to adopt an air sand inch structure as described later.

In addition, as other conventional optical information recording media, as described in U.S. Pat. No. 3,530,441, a recording film is irradiated with a laser beam, and the heat is used to record data without changing the shape of the recording film. Some methods change the phase of the film and perform recording using the difference in reflectance between the amorphous phase and the crystalline phase.

In conventional optical information recording media as described above,
In order to obtain high recording sensitivity, Te is used as a recording film material.
, Bi, Se, In, Pb, and other low melting point materials have been used as its main components.

[Problem that the invention seeks to solve]

As mentioned above, in the prior art, Te is used as the material for the recording film in order to obtain high recording sensitivity.

Low melting point materials such as Bi, Se, In, and Pb are used as the main components, but such low melting point materials generally have low thermal and chemical stability, so conventional techniques However, if an attempt is made to increase the recording sensitivity, the thermal and chemical stability of the optical information recording medium itself will be lost, and as a result, the reliability of the information recording medium will also decrease. Ta.

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide an optical information recording medium that can improve recording sensitivity without reducing reliability as an information recording medium.

[Means for solving problems]

In order to achieve the above object, the present invention includes a thermoplastic resin substrate in which grooves for reducing reflectance are formed in advance in the data recording area, and a heat absorption film formed on the surface of the thermoplastic resin substrate. An optical information recording medium is configured.

[Effect]

When the optical information recording medium is locally irradiated with a light beam toward the grooves according to the information to be recorded, the heat absorption film absorbs the light beam and generates heat, causing heat to be generated in the vicinity. The portion of the thermoplastic resin substrate located, i.e.
The groove portion is thermally deformed. Then, due to the thermal deformation, the groove portion becomes flat and the reflectance of that portion increases, thereby recording the information.

That is, in the present invention, information is recorded by changing the reflectance due to deformation of the substrate surface.

Next, the relationship between deformation of the substrate surface and change in reflectance due to the deformation will be explained.

Fig. 6 is a characteristic diagram showing the relationship between the groove depth of a conventionally used guide groove and the ratio of reflected light quantity, and Fig. 7 is a characteristic diagram showing the relationship between the groove width of the guide groove and the reflected light quantity ratio. It is.

That is, in FIGS. 6 and 7, the pitch P=1.6 on the substrate
The wavelength λ=830 nm is applied to the guide groove formed in μm.
The relationship between the groove depth d of the guide groove and the reflected light amount ratio and the groove width of the guide groove when the laser beam is irradiated through an objective lens with a numerical aperture of NA-0.5 and the reflected light is observed. It shows the relationship between W and the reflected light amount ratio.

In these figures, n is the refractive index of the substrate. As shown in Figure 6, the reflected light quantity ratio changes greatly depending on the groove depth d. The length is 130nm (nd=λ/4) to 75nm (nd=λ/4)
/8), the reflected light amount ratio changes from 0.05 to 0.55.
, and sufficient reproduction signal strength can be obtained. .

Therefore, as is clear from FIGS. 6 and 7, the dimensions of the groove before recording in the present invention, that is, before thermal deformation, are as follows: When using an objective lens with a numerical aperture of NA=0.5, the groove width is W=0.2~0.8μm, groove depth d=3λ/32n~
It can be seen that λ/4n is optimal.

Further, in the present invention, the power of the light beam during recording is used to cause thermal deformation of the substrate. For example, as a thermoplastic resin substrate, PMMA (polymethyl methacrylate), PC When an injection molded substrate such as (polycarbonate) is used, the thermal deformation temperature is about 140°C at the highest, and in optical information recording media using the conventional melt hole punching method, the recording film such as Te is melted. Since the temperature is considerably lower than the 450° C. or higher required for recording, recording can be performed with a smaller optical beam power.

Furthermore, in the present invention, since the heat absorbing film only generates heat by absorbing the light beam as described above, the material for the heat absorbing film is limited to materials with a particularly low melting point, like conventional recording films. Since it is possible to use a wide variety of materials such as materials with high melting points, it is also possible to select materials with high thermal and chemical stability.

As described above, according to the present invention, recording sensitivity can be improved without reducing reliability as an information recording medium.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, let us consider the case where the present invention is applied to an optical disk of the guide groove tracking method (ie, continuous servo method).

As shown in FIG. 5, the continuous servo method means that a guide groove 22 for tracking is provided on a substrate 20, and
Tracking control is performed using

As mentioned above, in the present invention, a groove for reducing the reflectance is formed on the substrate, so the above-mentioned guide groove in the continuous servo system may be used as this groove. The dimensions of this groove are shown in Figures 6 and 7.
As mentioned in the figure, the dimensions that provide the maximum reflectance change, i.e., the groove depth is λ/4n (λ is the wavelength of the light beam, n is the refractive index of the substrate), and the groove width is 0.4 to 0.5 μm. Suppose that
The size of this groove becomes a problem because it becomes such a size that normal tracking control cannot be performed as a guide groove for tracking.

Now, in recent years, in addition to the continuous servo system as described above, an optical disk using a sampling servo system has been proposed in which a wobble bit dedicated to tracking is provided outside the data recording area. Next, we will consider the case where the present invention is applied to this sampling servo type optical disc.

FIG. 1(a) is a plan view showing an enlarged part of an optical information recording medium as an embodiment of the present invention, and FIG. 1(b) is a direction taken along the line AA in FIG. 1(a). Cross-sectional view showing the cross section, Figure 1 (
c) is a waveform diagram showing the signal waveform of the reproduced output obtained when the portion shown in FIG. 1(a) is irradiated with a laser beam.

In FIGS. 1(a) and (b), 1 is an address pit for an address header, 2 is a wobble bit for tracking, 3 is a groove for reducing reflectance, 4 is a recording pit formed by a laser beam, and 5 is a recording pit formed by a laser beam. is a heat absorption film, 7 is a laser beam, 8 is an objective lens, 10 is PC (polycarbonate)
Base) anti, is.

The PC board 10 shown in FIG. 1(b) is a disc-shaped injection molded board made of PC and having a diameter of 130 mm.

In addition, the data recording area on the surface has a depth d=λ/4
n=130 nm (λ is the wavelength of the laser beam 7, which is 830 nm in this case. Also, n is the refractive index of the PC board 10, which is 1°69 in this case.) 2 Width W=0
．． A groove 3 having a thickness of 5 μm and a rectangular cross section (cross section perpendicular to the track direction) is formed in the address header portion, with a depth d=λ/4n=130 nm and a width W=
An address pit 1 of 0.5 μm is formed, and the wobble bit part has a depth of d=λ/4 n = 130 nm.
, a wobble bit 2 having a width W=0.5 μm is formed. Furthermore, on such a PC board 10, 5
A BiTe-based thin film of 6.0% is formed as the heat absorbing film 5.

FIG. 2 is a sectional view showing a specific example of the optical information recording medium shown in FIG. 1 configured as an optical disk.

An optical information recording medium configured as shown in FIG.
To construct an optical disk, as shown in FIG. 2, first prepare two PC boards 10 with heat absorbing films 5 formed on their surfaces as shown in FIG. They are bonded together with a spacer 33 in between so that the absorbing film 5 is on the inside.

By doing this, a double-sided disk with an air sandwich structure can be created.

When recording data using the optical disk configured as described above, the optical disk is rotated at 180 rpm, and as shown in FIG. Wavelength λ=830nm, power 5
A laser beam 7 of mW is focused to a beam diameter of about 1.5 μm and irradiated onto this optical disk, thereby thermally deforming the groove 3 and forming a recording pit 4.

In addition, when reproducing recorded data, if the power of the laser beam 7 is lowered to 1 mW and irradiated in the same manner as during recording, a reproduction output as shown in Figure 1 (C) can be obtained, and the recorded data can be reproduced. The recorded data is played back from the output of the section.

Note that during both recording and reproduction, tracking control is performed based on the output of the tracking section of the reproduction output.

As described above, when the optical information recording medium shown in FIG. 1 is constructed as a double-sided disk with an air sandwich structure as shown in FIG.
The power is only 5mW.

When an optical information recording medium based on the above-mentioned melt perforation method shown in FIG. 5 is configured as a double-sided disk with an air sand inch structure as shown in FIG. Since the power of the beam 7 is about 10 mW, taking this into account, it is easy to understand how high the recording sensitivity of the optical disk shown in FIG. 2 is.

FIG. 3 is a sectional view showing another specific example of the optical information recording medium of FIG. 1 configured as an optical disk.

In FIG. 2, the optical information recording medium of FIG. 1 is configured as a double-sided disk with an air sandwich structure, but in the present invention, as shown in FIG. 3, it is configured as a double-sided disk with a closely bonded structure. Also good.

This is because, when thermal deformation is used as in the present invention, the film surface of the heat absorbing film is completely destroyed, as is the case with the recording film of an optical information recording medium using the melt-opening method described in FIG. This is because being free is not necessarily necessary.

However, when the optical information recording medium shown in FIG. 1 is configured as a double-sided disc with a tightly bonded structure,
In order to freely thermally deform the substrate, it is important to use a material with a low elastic modulus for bonding, and in the example shown in FIG. 3, urethane acrylate ultraviolet curing resin was used.

Therefore, first, prepare two PC boards 10 having heat absorbing films 5 formed on their surfaces as shown in FIG. A protective film 35 of urethane acrylate ultraviolet curable resin is formed in the same manner, and then they are bonded to each other using a hot melt adhesive 36 so that the protective film 35 is on the inside. By doing this, a double-sided disc with a closely bonded structure can be created.

When data is recorded using the optical disc configured as described above under the same conditions as described in the example of FIG. 2, a laser beam power of 10 mW is required. As mentioned above, this value is equivalent to the case where the optical information recording medium using the fused perforation method shown in FIG. 5 is configured as a double-sided disk with an air sandwich structure as shown in FIG. The optical disk shown in FIG. 3 has a great advantage in improving reliability as an information recording medium by adopting a closely bonded structure.

FIGS. 4(a) to 4(c) are perspective views showing other specific examples of the reflectance reducing grooves 3 shown in FIG. 1, respectively.

In the explanation in FIG. 1, the cross-sectional shape of the groove 3 for reducing reflectance is described as being rectangular, but it is not limited to this, and may be trapezoidal, for example, as shown in FIG. 4(a). However, it may be v-shaped as shown in FIG. 4(b), or semi-circular as shown in FIG. 4(C), that is, the reflection in the groove 3 before being substantially thermally deformed. Any shape is acceptable as long as the ratio is reduced to a desired value.

As described above, in this example, a case was explained in which a BiTe-based thin film was used as the material for the heat absorption film 5°, but the present invention is not limited to this, and the invention is not limited to this. Any material can be used if possible. For example, Bi.

Low melting point metals such as Te, In, Pb, Sn, Sb, Zn, and their compounds and mixtures, Pt, Au.

Affi, Ti, Cr, Ni, Cu, Co, Rh, Nb
.

High melting point metals such as Ta and Zr and their compounds.

Can be applied freely to mixtures. In particular, Pt, Au.

A1. Materials containing Cu, Ti, Zn, etc. as main components are highly safe for the human body and are preferable as materials for use in optical information recording media.

Further, when a high reflectance metal is used as a material for the heat absorption film 5, the high reflectance metal may include St, Al.

The effects of the present invention can be further improved by laminating thin films of oxides or nitrides such as Ta to reduce the reflectance.

In addition, in the above explanation, the groove dimensions that provide the maximum reflectance change were mainly explained, but the groove dimensions are not limited to this, and groove depths of 3λ
/32n to λ/4n and a groove width of 0.2 to 0.8 μm, a reflectance change ratio of 20% or more required for signal recording can be obtained.

Furthermore, if a groove depth of 3λ/32n to 3λ/16n is used,
Sufficient tracking signal strength can be obtained using the diffraction method, and in addition to the sampling servo method mentioned above,
It is easy to understand that the present invention can also be applied to continuous servo systems.

〔Effect of the invention〕

As described above, in the present invention, recording is performed by thermal deformation of a thermoplastic resin substrate, and the thermal deformation temperature of the thermoplastic resin substrate at this time is about 140°C at most, so compared to conventional , recording can be performed with a smaller optical beam power.

In addition, as for the material of the heat absorption film, like the conventional recording film,
It is not limited to materials with a particularly low melting point, and a wide variety of materials can be used, including materials with a high melting point, so it is also possible to select a material with high thermal and chemical stability.

Therefore, according to the present invention, the recording sensitivity can be improved without reducing the reliability as an information recording medium, and it is possible to sufficiently cope with high-speed recording and high-density recording.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view showing an enlarged part of an optical information recording medium as an embodiment of the present invention, and FIG. 1(b) is a direction taken along the line AA in FIG. 1(a). Cross-sectional view showing the cross section, Figure 1 (
C) is a waveform diagram showing the signal waveform of the reproduced output obtained when the part shown in FIG. 1(a) is irradiated with a laser beam;
The figure is a cross-sectional view showing an example of an optical information recording medium when the optical information recording medium shown in FIG. 1 is configured as an optical disk, and FIG. 3 shows another specific example when the optical information recording medium shown in FIG. 4(a) to 4(C) are respectively perspective views showing other specific examples of the groove 3 for reducing reflectance shown in FIG. 1, and FIG. 5(b) is a cross-sectional view taken along the line B-B in FIG. 5(a), and FIG. 6 is a plan view showing a part of the optical information recording medium according to the conventional method. A characteristic diagram showing the relationship between the groove depth of the guide groove used and the reflected light amount ratio, FIG. 7 is a characteristic diagram showing the relationship between the groove width of the guide groove and the reflected light amount ratio,
It is. Explanation of codes■...Address bit, 2...Wobble bit, 3
... Groove, 4... Recording bit, 5... Heat absorption film, I
O... PC board, 33... Spacer, 35... Protective film, 36... Adhesive. Agent Patent Attorney Akio Namiki Figure 2 Figure 4 Figure 5 Figure □ Track direction z6: A d 5 sub'22 d (ram) 薯 7 Ko! Iris width & W (μm)

Claims (1)

[Claims] 1. In an optical information recording medium capable of optically recording and reproducing information, a heat absorbing film is formed on the surface of a thermoplastic resin substrate on which grooves for reducing reflectance are formed. A light beam is locally irradiated toward the groove according to the information to be recorded, and the irradiated portion of the groove is thermally deformed and the reflectance of that portion increases, thereby recording the information. An optical information recording medium characterized by recording. 2. In the optical information recording medium according to claim 1, the groove has a generally rectangular cross-sectional shape and a depth of 3λ/32n to λ/4n (where λ is An optical information recording medium characterized in that the wavelength of the light beam (n is the refractive index of the thermoplastic resin substrate) and the width thereof is 0.2 to 0.8 μm. 3. The optical information recording medium according to claim 1, wherein the thermoplastic resin substrate is made of polymethyl methacrylate resin or polycarbonate resin. 4. In the optical information recording medium according to claim 1, the groove is formed in an area sandwiched between wobble bit parts dedicated to tracking provided on the surface of the thermoplastic resin substrate. Characteristic optical information recording media.