JP2811603B2 - Optical information recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a write-once and rewritable optical information recording medium.

(Prior art) Conventionally, as a typical write-once optical information recording medium using laser light, a Te-based recording thin film is formed on a transparent substrate such as glass or polycarbonate resin by vacuum evaporation or sputtering. The formed thin film was formed by irradiating a laser beam during recording to melt and sublime the recording thin film to form a bit. However, since Te is easily oxidized in a humid environment, a small amount of metal elements such as Se, In, Sn, Pb, and Bi are usually added.However, in thin film formation by a dry method such as vacuum evaporation or sputtering, It was difficult to keep the ratio of Te and the above-mentioned added metal element constant, and the productivity, yield, etc. were inferior.

In addition, there are optical information recording media using a recording thin film such as TeOx or a mixture of Te and TeOx, and the portion where the amorphous state changes to the crystalline state due to irradiation with laser light during writing has a laser light reflectance during reproduction. It is a method to go up. Also in this case, since the dry method is used for the film formation, the uniformity of the film composition, the yield, and the like are inferior.

In a rewritable optical information recording medium, an amorphous alloy made of a combination of a rare earth metal and a transition metal, such as GdTbFe or TbFeCo, is used as a recording thin film. Then, a magneto-optical recording method (MO) is used in which the rotation angle (Kerr rotation angle) of the polarization plane of the laser beam is read out as information during reproduction. In this method, the material cost is high, and the yield is low.
There are drawbacks such as a complicated writing / reproducing and erasing device.

There is also a method using an amorphous crystal phase change such as TeGeSnAu, but the same drawbacks such as a low yield are obtained because the dry method is used for film formation.

As a measure against these drawbacks, an optical recording system using an organic dye has been proposed. In this method, a film can be easily formed by a spin coating method using a solvent in which an organic dye that absorbs laser light is dissolved, so that cost reduction can be achieved. However, in this recording method, laser irradiation at the time of writing causes the organic dye to melt and sublimate, causing small holes in the recording thin film as bits, and reflection of laser light during reproduction due to decomposition and reaction of the organic dye. It is based on the principle of changing the rate, and it can be used for the write-once type but not for the rewritable type because the reaction of the organic dye lacks reversibility.

Furthermore, in addition to low cost, excellent film-forming properties, and a simple writing / reproducing device, a method that enables rewriting is proposed, in which a resin containing an organic dye is read as a bit from the change in shape due to laser irradiation during writing. (Japanese
63-136338).

In this method, a recording thin film, which is coated with a resin containing an organic dye that absorbs laser light, is irradiated with laser light during writing to absorb the organic dye at the time of writing, and the generated heat deforms (expands) the resin. Etc.), and used as a write-once optical information recording medium according to the principle of forming bits, or a two-layer resin layer containing two kinds of dyes each absorbing a laser beam having a different wavelength on a substrate. Forming
For example, the layer on the substrate side of the two-layer on the substrate, if contain a dye that absorbs a laser beam of lambda _1, is irradiated with laser light having a wavelength lambda ₁ at the time of writing, the layer is a laser beam The bit can be absorbed, deformed by heat generation, and the upper layer of the layer can be deformed.

Thereon, if contain a dye that absorbs a laser beam having a wavelength lambda _2, the upper layer of the resin is heated above the glass transition temperature by absorbing the laser beam of lambda ₂ at the time of erasing, based again And the bit disappears.

In this method, since a spin coating method or the like can be used, the composition and thickness of the recording thin film can be easily controlled, and the material cost is low, and an inexpensive and rewritable optical information recording medium can be obtained.

(Problems to be Solved by the Invention) However, in the above configuration, a resin layer having a thickness of several μm is required to form an identifiable bit by expanding the resin layer. When a bit is formed on the formed resin recording layer on the substrate on which the guide groove is formed, the distance between the bit and the guide groove is at least about the thickness of the resin. In an ordinary laser irradiation optical head, the depth of focus of the laser is 2 μm.
Therefore, there is a problem that when the focus servo is applied, a situation where the tracking servo is not applied may occur. As a countermeasure, the numerical aperture of the objective lens of the optical head may be reduced and the distance between the optical head and the recording medium may be increased. However, there is a problem that the device becomes large and expensive.

The present invention solves the above-mentioned problems, and provides an optical information recording medium having a film structure in which focus servo and tracking servo can be easily performed by using resin recording layers containing organic dyes having different absorption wavelengths. .

(Means for Solving the Problems) In an optical information recording medium according to the present invention, a light absorbing layer, a light reflecting layer, and a light transmitting substrate having guide grooves for receiving light for tracking servo formed on a surface thereof are provided. An optical information recording medium in which a layer and a protective layer are formed in that order directly or via another layer, and a distance between the surface of the guide groove and the light reflecting layer is equal to or less than a focal depth of condensed light. Wherein the surface of the guide groove located between the adjacent concave portion and the convex portion is formed so as to have an obtuse angle with respect to the upper surface of the convex portion and the bottom surface of the concave portion.

(Operation) According to the configuration of the present invention, the guide groove for obtaining light used for tracking servo and the light reflection layer are located at different positions, and the difference in the distance between the guide groove and the light reflection layer is collected. Since the recording depth is less than the focal depth of the light, both the tracking servo and the focus servo can be performed satisfactorily, the error rate at the time of recording / reproduction is reduced, and a highly reliable optical information recording medium is formed. By forming the surface located between the adjacent concave portion and the convex portion in the above so as to have an obtuse angle with respect to the upper surface of the convex portion and the bottom surface of the concave portion, it is easy to form the concave and convex portion, and the guide groove is formed. An optical information recording medium having a low defect rate and high productivity is obtained.

(Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. 1 and FIG.

FIG. 1 and FIG. 2 are enlarged cross-sectional views of main parts schematically showing a typical structure of an optical information recording medium (hereinafter referred to as an optical disk) using a substrate having a guide groove and a planar substrate, respectively. It is.

In FIG. 1, an optical disc is formed such that a light absorbing layer 2, a light reflecting layer 3 and a protective layer 4 are sequentially laminated on a light transmitting substrate 1 having a guide groove 1a for tracking servo formed on the surface. Have been. In FIG. 2, the optical disk is formed by forming an ultraviolet-curable resin layer 6 having a guide groove 6a formed thereon and a solvent-resistant layer 7 on the surface of a planar light-transmitting substrate 5 as in FIG. The light absorbing layer 2, the light reflecting layer 3, and the protective layer 4 are formed so as to be sequentially laminated. In both structures, as is apparent from the drawings, the guide groove 1a or 6a is formed on the surface located between the adjacent concave portion and the convex portion, so that the concave and convex portions are easily formed during molding. The light-absorbing layer 2 sandwiched between the surface of the light-transmitting substrate 1 or the ultraviolet curable resin layer 6 formed so as to have an acute angle with respect to Has a thickness of 2μ
m or less. The light absorbing layer 2 absorbs the irradiated laser beam and generates heat, and melts, evaporates, sublimates,
The bit is deformed or denatured to form a bit on the surface of the translucent substrate 1 or the ultraviolet curable resin layer 6.

Next, embodiments of the optical information recording medium according to the present invention will be specifically described.

In the first embodiment, the transparent substrate 1 has a diameter of 46 mm or less.
0.8μm width, 0.08μm depth, 1.6 pitch in the range of 117mm
A polycarbonate (PC) disk with a thickness of 1.2 mm, an outer diameter of 120 mm, and an inner diameter of 15 mm having a spiral guide groove 1 a of μm is formed by injection molding. The solvent layer 7 was formed.

The light absorption layer 2 is formed by dissolving a cyanine dye as an organic dye and bisphenol A and a polyamino resin as binder components in a mixed solvent of methyl ethyl ketone and dichloroethane, and spinning the mixture on the surface of the solvent resistant layer 7. Coating was performed by a coating method to obtain a light absorbing layer 2 having a thickness of 1.8 μm.

Next, the light reflection layer 3 is formed by depositing an Au film by a sputtering method on the entire surface in a region having a diameter of 45 mm to 118 mm to a thickness of 100 nm.
Was obtained.

Further, a protective layer 4 having a thickness of 4 μm was formed on the light reflecting layer 3 by using an ultraviolet curable resin. The total thickness of the solvent-resistant layer 7 and the light-absorbing layer 2 formed between the surface of the light-transmitting substrate 1 and the light-reflecting layer 3 is 1.83 μm.

The thus obtained optical disk was irradiated with a semiconductor laser having a wavelength of 780 nm at a linear velocity of 1.2 m / sec and a recording power of 7.5 mW, and the EFM was applied.
A signal is recorded on a commercially available CD player (wavelength of reproduction light 780n
m), the laser beam reflectance is 72%, I ₁₁ / I _top obtained from the eye pattern of the reproduced signal is 0.63, I ₃ / I
_{The top} was 0.36.

According to the CD standard, the reflectance of laser light is more than 70%, I ₁₁ / I _top
Is set to 0.6 or more, and I ₃ / I _top is set to 0.3 to 0.7. The optical disc according to this embodiment satisfies this standard.

The difference between the second embodiment and the first embodiment is that
The point that a polyolefin disk was used as the light-transmitting substrate 1, the point that only an acrylic resin layer having a thickness of 50 nm was formed between the light absorbing layer 2 and the light reflecting layer 3 by spin coating, The first embodiment is different from the first embodiment in that a Pt film is formed, and only an acrylic resin layer having a thickness of 2 μm is formed between the light reflecting layer 3 and the protective layer 4 by a spin coating method. An optical disk was manufactured in the same manner as in the above. In addition,
The total thickness of the solvent-resistant layer 7, the light-absorbing layer 2, and the acrylic resin layer formed between the surface of the light-transmitting substrate 1 of the optical disk and the light reflecting layer 3 is 1.88 μm.

The optical disk thus obtained was recorded with an EFM signal in the same manner as in the first embodiment, and was reproduced by a commercially available CD player. As a result, the reflectance of the laser beam was 71%, and I ₁₁ obtained from the eye pattern of the reproduced signal was ₁₁ %. / I _top was 0.64 and I ₃ / I _top was 0.33.

The third embodiment is different from the first embodiment in that the surface of the light-transmitting substrate 1 is a 2P method (PHOTO POLYMARIZATION MET).
HOD). The first embodiment is different from the first embodiment in that a polymethyl methacrylate disk having a guide groove 1a is formed and a light absorbing layer 2 is formed directly on the translucent substrate 1. An optical disk was manufactured in the same manner as in the example. It is to be noted that only the light absorbing layer 2 is formed between the surface of the light transmitting substrate 1 of the optical disc and the light reflecting layer 3, and therefore the thickness thereof is 1.8 μm.

The optical disk thus obtained was recorded with an EFM signal in the same manner as in the first embodiment, and was reproduced by a commercially available CD player. As a result, the reflectance of the laser beam was 74%, and I ₁₁ obtained from the eye pattern of the reproduced signal was ₁₁ %. / I _top was 0.63 and I ₃ / I _top was 0.34.

The difference between the fourth embodiment and the first embodiment is that
As a translucent substrate 1, a glass disk having a guide groove 1a formed on the surface by a 2P method was used, and a solution obtained by directly dissolving a cyanine dye and nitrocellulose in dimethylformamide by spin coating was used. Apply, film thickness 1.3
The point where the light absorbing layer 2 of μm was formed and the light reflecting layer 3
The first embodiment is different from the first embodiment in that an Ag film is formed, and only a 3 μm epoxy resin layer is formed by spin coating between the light reflection layer 3 and the protective layer 4 made of an ultraviolet curable resin. An optical disk was manufactured in the same manner as in the above. The layer formed between the surface of the light-transmitting substrate 1 of the optical disc and the light reflecting layer 3 is only the light absorbing layer 2, and its thickness is therefore 1.3 μm.

The optical disk thus obtained was recorded with an EFM signal in the same manner as in the first embodiment, and was reproduced by a commercially available CD player. The reflectance of the laser beam was 72%, and the I ₁₁ obtained from the eye pattern of the reproduced signal was ₁₁ %. / I _top was 0.61 and I ₃ / I _top was 0.31.

As a first comparative example, an optical disc was manufactured by setting the thickness of the light absorbing layer 2 of the first embodiment to 2 μm, and was formed between the surface of the light transmitting substrate 1 and the light reflecting layer 3. Solvent resistant layer 7
When the total thickness of the light-absorbing layer 2 and the light-absorbing layer 2 was 2.03 μm, tracking servo did not work well, and signal recording was impossible.

As a second comparative example, the thickness of the solvent-resistant layer 7 of the first embodiment was set to 0.5 μm, and the thickness of the light absorbing layer 3 was set to 1 μm.
m, and a 0.5 μm thick acrylic resin layer formed by a spin coating method between the light absorbing layer 2 and the light reflecting layer 3 as in the second embodiment was added to manufacture an optical disk. When the total thickness of the solvent-resistant layer 7, the light-absorbing layer 2, and the acrylic resin layer formed between the surface of the light-transmitting substrate 1 and the light-reflecting layer 3 was 2.0 μm, tracking servo was successfully performed. Nevertheless, signal recording was not possible.

(Effects of the Invention) As described above, according to the present invention, both tracking servo and focus servo can be performed satisfactorily, the error rate at the time of recording and reproduction is reduced, and highly reliable optical information recording is performed. A medium can be realized, and an optical information recording medium with high productivity can be obtained in which the concave and convex portions of the guide groove are easily formed and the occurrence rate of the guide groove is low.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are enlarged cross-sectional views of a principal part schematically showing an optical recording medium according to the present invention. Reference numeral 1 denotes a translucent substrate having a guide groove formed therein, 1a, 6a denotes a guide groove, 2 denotes a light absorbing layer, 3 denotes a light reflecting layer, 4 denotes a protective layer,
5: a flat translucent substrate; 6: an ultraviolet curable resin layer having a guide groove formed therein; 7: a solvent-resistant layer.

Claims (3)

(57) [Claims] 1. A light-absorbing layer, a light-reflecting layer, and a protective layer are formed on a light-transmitting substrate having a guide groove for receiving light for tracking servo formed on a surface thereof, in that order. An optical information recording medium formed through a gap, wherein a distance between the surface of the guide groove and the light reflecting layer is equal to or less than a focal depth of light to be collected, wherein an adjacent concave portion and a convex portion in the guide groove are provided. An optical information recording medium characterized in that a surface located between the optical information recording medium and the upper surface of the convex portion and the bottom surface of the concave portion have an obtuse angle. 2. The optical information recording medium according to claim 1, wherein the guide groove is formed directly on the substrate. 3. The optical information recording medium according to claim 1, wherein said guide groove is formed by a photopolymer method.