JPH0447538A - Information recording medium - Google Patents

Abstract

PURPOSE:To facilitate the execution of many valued recording with an inexpensive information recording medium driving device having one piece of laser light source by constituting the recording medium of at least two layers of recording layers and providing a transparent org. layer between the recording layers adjacently thereto. CONSTITUTION:An underlying layer 3 consisting of org. matter and a UV curing resin layer 2 are formed on the surface of a chemically tempered glass plate 1 to form a replica substrate. The 1st recording layer 4 of a hole forming type consisting of Pb5Te8oSe15 is formed on the replica substrate. This layer is spin coated thereon with a soln. of n-butyl acetate of nitrocellulose and is dried to form the transparent org. layer 5. Further, the 2nd recording layer 6 of the hole forming type consisting of Pb5Te8oSe15 is formed thereon. The many valued recording is executed in this way simply by modulating the lower of a laser beam for recording with one piece of the laser light source. The high- density recording is thus executed with the inexpensive information recording medium driving device.

Description

[Detailed description of the invention] [Industrial application field]

The present invention uses a recording optical energy beam such as a laser beam to record FM-modulated analog signals such as video and audio, and digital information such as computer data, facsimile signals, and digital audio signals in real time. The present invention relates to an information recording medium that can record information.

[Conventional technology]

BACKGROUND ART Conventionally, an information recording medium in which recording is performed by irradiating a light energy beam such as a laser beam to form a recess or a hole in a recording layer has only one recording layer. The information recording medium of the above-mentioned conventional structure consists of a substrate, an underlayer, and one recording layer. The substrate is coated with the photobolimerization method (
2P method) on which an ultraviolet curing resin layer with guide grooves for tracking is formed, or plastic disks made of acrylic resin, etc., and plastic disks made of polycarbonate, acrylic resin, polyolefin, etc. with guide grooves formed by injection molding. is used. For the base layer, solvent-soluble resins such as nitrocellulose, acetylcellulose, and copper phthalocyanine, and sputterable resins such as fluororesin are used. A thin film containing Te as a main component is used for the recording layer. Regarding the base layer, see JP-A No. 57-55544, and
The composition of the recording layer is explained in JP-A-57-66996. It is also known to perform multiplex recording and increase density by irradiating laser beams with different wavelengths or depths of focus onto information recording media that have multiple layers of recording films, instead of a single layer. . Regarding information recording media that use laser beams with different wavelengths, see "Chemistry and Industry, Vol. 42 (1989) 20.
26J, and information recording media using laser beams with different focal depths are described in Japanese Patent Application Laid-Open No. 59-21054.
It is explained in No. 3.

[Problem to be solved by the invention]

However, in the information recording medium shown in the above-mentioned prior art, binary recording of "0" and "1" is performed for laser light of one wavelength. Therefore, in order to perform multi-value recording of three or more values and multiplex recording of two or more layers as high-density recording,
Two or more laser beams with different wavelengths, such as 830 nm and 780 nm, and laser beams with different depths of focus were required. Therefore, when the information recording medium of the prior art described above is used, there is a drawback that the cost of the information recording medium driving device for performing multi-level recording is high. It is an object of the present invention to eliminate the drawbacks of the above-mentioned conventional techniques, to perform multilevel recording with an inexpensive information recording medium drive device having one laser light source, and to provide a system with good recording/reproducing characteristics and good stability. An object of the present invention is to provide an information recording medium suitable for high-density recording. [Means for Solving the Problems] In order to achieve the above object, the information recording medium of the present invention is composed of at least two recording layers on which information is recorded by being irradiated with a light energy beam. A transparent organic layer was provided adjacently between the recording layers. The recording layer was formed of a material that forms holes, depressions, or projections when irradiated with a light energy beam, or a material that changes optical constants. The recording layer forming the holes, recesses, or protrusions may be made of an inorganic material such as Te-based, Se-based, or Bi-based material, or may be made of a dye-based organic material. The recording layer whose optical constants change may be one that utilizes a phase change between crystalline and amorphous, or one that utilizes alloy formation. Of the two or more recording layers configured in the information recording medium of the present invention, it is preferable that the recording layer on the side opposite to the substrate forms holes when irradiated with a light energy beam. The composition of the hole-forming recording layer is preferably a Te-3e system containing Te, a Te-C system, or the like. The transparent organic layer is preferably made of a compound that undergoes thermal deformation such as melting, evaporation, decomposition, or sublimation at a temperature below the melting point of the pore-forming recording layer on the opposite side of the substrate, or a mixture of the compound and an organic resin. . The components of the compound that causes thermal deformation include nitrocellulose, polyvinyl alcohol, nitrated polyvinyl alcohol, a mixture of polyvinyl alcohol and barium azide, polymethylpentenesulfone (PMPS), polytetrafluoroethylene, guanine, and hydrocarbons. It is preferable to use at least one compound selected from plasma polymers. The information recording medium of the present invention can be used not only in the form of a disk but also in other forms such as a tape or a card.

[Effect]

When the information recording medium of the present invention is used, for example, when low-power recording light is irradiated, recording holes are formed only in the recording layer on the opposite side of the substrate, and when high-power recording light is irradiated, recording holes are formed from the recording layer on the substrate side. The recording points are formed by alloy formation in the recording layer on the substrate side, or the recording points are formed by phase change in the recording layer on the substrate side. For example, when low-power recording light is irradiated, recording points are formed in the recording layer on the substrate side due to alloy formation, or recording points are formed in the recording layer on the substrate side due to oxidation, and then irradiated with high-power recording light. Sometimes recording holes are formed in the recording layer on the opposite side of the substrate. Therefore, when the information recording medium of the present invention is used, when performing multilevel recording, it is sufficient to modulate the power of the recording laser beam using one laser light source. Therefore, compared to conventional information recording media that require two or more laser light sources with different wavelengths, the device cost can be kept low.

【Example】

The present invention will be explained in detail below. Embodiment 1 FIG. 1 shows a schematic structure of a recording medium according to an embodiment of the present invention. This example describes an information recording medium that has two recording layers and is capable of ternary recording. Both layers (referred to as layers) are of the pore-forming type. The information recording medium of this example was produced by the method shown below. A photopolymerization method (2P
An organic base layer 3 and an ultraviolet curable resin layer 2 having guide grooves for tracking at a pitch of 1.6 μm and prepits indicating addresses and an ultraviolet curable resin layer 2 were formed using a replica substrate. That is, at the beginning of the 2P method, a solution of nitrocellulose in n-butyl acetate is spin-coated in advance on a Ni stamper (not shown), dried to form an organic base layer, and an ultraviolet curing resin is dropped onto it. The replica substrate described above was formed. Next, the composition P J
T e,. S e,, the first hole-forming type with a thickness of 13 nm
A recording layer 4 was formed. On top of that, a solution of nitrocellulose in n-butyl acetate was spin-coated and dried to a film thickness of 27.
An organic transparent layer 5 with a thickness of 0 nm was formed. Furthermore, 1 composition PB was obtained using the current heating vapor deposition method. Tea. A hole-forming second recording layer 6 of Se5 and a thickness of 20 nm was formed to prepare a disc A. For comparison, the composition P b S T e IlOS
e 15, a disk B having the same structure as the conventional one and having only one hole-forming recording layer 4 with a thickness of 30 nm was produced. A schematic cross-sectional view of the disk B is shown in FIG. The complex refractive index (n-
) are 4.7-2.0i and 1.5-0.0i, respectively.
Met. Therefore, based on the above complex refractive index values, we calculated the changes in light absorption in each layer in the disks in the film thickness direction when disks A and B are irradiated with light with a wavelength of 830 nm. The results are shown in Figure 3. show. The recording and reproducing characteristics of the discs A and B were measured as follows. The disk is rotated at 90 rpm and a semiconductor laser beam with a wavelength of 830 nm is set to a numerical aperture (NA) of 0.
．． The light was focused by a No. 53 lens and recorded on a flat area between the tracking guide groove (group) and the group. The readout light was a continuous light of 1 mW so as not to cause deformation of the recording layer. Recording was performed at a position with a radius of 140 mm (outer periphery), and a 9.4 MHz signal was recorded at a high recording density so that the recording pit interval was 1.4 μm. Here, the recording pulse width was set to 42 ns. Disc A
FIG. 4 shows the dependence of the degree of modulation of the reproduced signal on the recording power when recording was performed while changing the recording power. Here, the reproduction signal modulation degree is defined by the following equation. Playback signal amplitude strength of playback signal modulation degree recording point Playback signal amplitude strength of pre-pit Here, the slice level for performing ternary recording is //
Modulation depth is 0.2 to 0.3 for 1 tp, II 2
The power margin (recording power range in which the reproduction signal modulation degree falls within the slice level) when the modulation degree is 0.4 or more with respect to +1 was investigated. For II 2 II, between 10.7 and 13.2 mW for disk A, 2.5 m
W, and for disk B it was 2.4 mW, between 8.2 and 10.6 mW. On the other hand, between tz 1 n and 8.0-10゜2 mW for disk A,
2.2mW, whereas for disk B it is 7.4~7mW.
．． It was 0.3W between 7mW and 7mW. Therefore, in disk B with the conventional structure, the power margin for "1" is 0.
．． 3 mW, which is extremely small and makes ternary recording difficult, whereas in the disc A of the present invention, the power margin for 1'' is 2.2 mW, and the power margin for II 2 II is 2.5 mW, which is sufficiently large. , three-value recording was possible.Similar results were obtained by using a plastic substrate such as polycarbonate, PMMA, or polyolefin instead of the above-mentioned glass substrate as the substrate material.Organic base layer and organic transparent layer Similar results were obtained using acetyl cellulose, guanine, fluororesin, polyamide, polyimide, etc. in addition to the above nitrocellulose.As the first and second recording layers, the above Pb-Te-5e
Instead of the pore-forming recording layer, Te-C, Te-3b
Similar results were obtained using other chalcogenide-based pore-forming recording layers such as Te-C type and Te-C type. Example 2 A disk in which a cyanine dye was formed to a thickness of 26 nm by spin coating as the hole-forming first recording layer 4 in the disk hole in Example 1 instead of the Pb-Te-3e recording layer. C was produced. Wavelength 83 of cyanine dye in the first recording layer in disc C
The complex refractive index (n-) at 0 nm was 2.7-1.7i. FIG. 5 shows the results of calculating the change in light absorption in each layer of the disk in the film thickness direction when the disk C is irradiated with light at a wavelength of 830 nm based on the value of the complex refractive index. The recording and reproducing characteristics of the disc C were measured in the same manner as in Example 1. FIG. 6 shows the dependence of the degree of modulation of the reproduced signal on the recording power when recording was performed while changing the recording power. For disc C, the slice level for ternary recording is set to "1" with a modulation degree of 0.2 to 0.3.62.
The power margin (recording power region where the reproduction signal modulation degree falls within the slice level) when the modulation degree is 0.4 or more was investigated for ``. For II 211, it was 2.1 mW between 10.1 and 12.2 mW. Therefore, in disk C of the present invention, Lr Both the power margin for I++ and the power margin for 62'' were sufficiently large, at 2 mW or more, and three-value recording was possible. Similar results were obtained when a plastic substrate such as polycarbonate, PMMA, or polyolefin was used as the substrate material instead of the glass substrate. Similar results were obtained by using acetyl cellulose, guanine, fluororesin, polyamide, polyimide, etc. in addition to the above-mentioned nitrocellulose as the organic base layer and organic transparent layer. Similar results were obtained by using other dye-based recording layers such as naphthalocyanine-based dyes instead of the cyanine-based dyes as the first recording layer. As the second recording layer, instead of the Pb-Te-Se thread-forming type recording layer, a Te-C system, Te-5
Similar results were obtained using other chalcogenide-based pore-forming recording layers such as b-based and Te-C-based. Example-3 Also, the first recording layer 4 in the disk hole in Example-1
, a disk in which an alloy-forming type recording layer is formed instead of a Pb-Te-8e-based pore-forming type recording layer, that is, the first
An information recording medium of the present invention in which the recording layer 4 was of an alloy-forming type and the second recording layer 6 was of a hole-forming type was produced by the method shown below. By injection molding method, diameter 300mm, thickness 1°2mm
A replica substrate was fabricated on the surface of a disc-shaped polycarbonate plate having guide grooves for tracking at a pitch of 1.6 μm and pre-pits for indicating addresses. Next, 5b2Se, B1.5b2Se, and B1.5b2Se were successively deposited on the replica substrate by heating and energizing to a thickness of 15 nm, 14 nm, and 50 nm, respectively, to form an alloy-forming first recording layer 4. A solution of nitrocellulose in n-butyl acetate was spin-coated thereon and dried to form an organic transparent layer 5 with a thickness of 270 nm. Furthermore, 1 composition P b s was obtained using the 2-current heating lid bonding method.
Tes. Then, a hole-forming second recording layer 6 with a thickness of 20 nm was formed, and a disk D was manufactured. Also, in the structure of the disc D, the first recording layer is 5b2S.
The film thicknesses of e1, Bi, Sb, and Se are each 60 nm.
, 10 nm, and 90 nm were sequentially formed by electrical heating vapor deposition to produce disks E. Wavelength 83 of the Sb2Se 3 layer and Bi layer of the first recording layer
The complex refractive index (n fist) at 0 nm is 2.7-0, respectively.
．． 06i and 2.3-4.9i. Therefore, based on the value of the above complex refractive index, the wavelength 83 is applied to disks D and E.
FIG. 7 shows the results of calculating the change in light absorption in each layer in the disk in the thickness direction when irradiated with 0 nm light. The recording and reproducing characteristics of the discs D and E were measured in the same manner as in Example 1. FIG. 8 shows the dependence of the degree of modulation of the reproduced signal on the recording power when recording was performed while changing the recording power. Regarding disks D and E, the slice level for performing ternary recording is set to a modulation depth of 0.2 for it 1 +1.
We investigated the power margin (recording power range where the modulation degree of the reproduced signal falls within the slice level) when the modulation degree is 0.4 or more for ~0.3, 2''. For 71'',
For disk D, between 9°0 and 11.1mW, 2.1m
W, disk E between 11.7 and 14.0 mW, 2
．． It was 3mW. Further, for u 2 u, the disc D was 2.2 mW between 6.0 and 8.2 mW, and the disc E was 2° IW between 8.8 and 10.9 mW. Therefore, in both disks D and E of the present invention, the power margin for 1'' and the power margin for '2'' were both sufficiently large, 2 mW or more, and three-value recording was possible. For the substrate material, instead of the above polycarbonate substrate,
Similar results were obtained using other plastic substrates such as PMMA and polyolefin. Further, similar results were obtained even when a glass substrate was used as in Example 1. Similar results were obtained by using acetyl cellulose, guanine, fluororesin, polyamide, polyimide, etc. in addition to the above-mentioned nitrocellulose as the organic base layer and organic transparent layer. As the first recording layer 4, instead of the above-mentioned alloy forming type recording layer, Ge-Te-8b system, In-5b-Te system, In-8
Similar results were obtained using phase change type recording layers such as b-based and In-3e-based. As the second recording layer 6, instead of the above-mentioned Pb-Te-8e-based pore-forming recording layer, Te-C-based, Te-5b-based, Te-
Similar results were obtained using other chalcogenide-based pore-forming recording layers such as 0-based recording layers. Effects of the Invention As explained above, if the information recording medium according to the present invention is used, three-value recording is possible with an information recording medium driving device having one laser beam. This enables high-density recording.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of an information recording medium of the present invention, FIG. 2 is a schematic cross-sectional view showing the structure of an information recording medium with a conventional structure, and FIG. FIG. 4 is a diagram showing the calculation results of the change in the amount of optical energy in the film thickness direction. FIG. 4 is a diagram showing the recording power dependence of the degree of modulation of the reproduced signal on disk A according to the embodiment of the present invention. FIG. FIG. 6 is a diagram showing the calculation results of the change in the amount of optical energy in the film thickness direction in the disc C of the embodiment; FIG. FIG. 7 shows a disk D according to an embodiment of the present invention.
FIG. 8 is a diagram showing the dependence of the degree of modulation of the reproduced signal on the recording power in discs D and E according to the embodiment of the present invention. . Explanation of symbols 1...Chemically strengthened glass disk 2...Ultraviolet curing resin layer

Claims (1)

[Claims] 1. An information recording medium in which information is recorded by being irradiated with a light energy beam, which has at least two recording layers, and a transparent organic layer adjacent to the recording layers. An information recording medium characterized by: 2. The information set forth in claim 1, wherein the recording layer is one that forms holes, depressions, or projections when irradiated with a light energy beam, or one that changes optical constants. recoding media. 3. Information according to claims 1 and 2, characterized in that, among the recording layers, the recording layer on the side opposite to the substrate forms holes when irradiated with a light energy beam. recoding media. 4. The transparent organic layer is made of a compound that undergoes thermal deformation such as melting, evaporation, decomposition, or sublimation at a temperature below the melting point of the pore-forming recording layer on the opposite side of the substrate, or a mixture of the above compound and an organic resin. An information recording medium according to claims 1, 2, and 3, characterized in that: