JP2003266938A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical recording medium capable of recording and reproducing a large volume of information in a high recording density by effectively lessening a beam diameter, in an optical recording medium which records and reproduces information. <P>SOLUTION: The optical recording medium comprises a substrate 1 which is transparent to a laser beam falling within the wavelength range of 350 to 480 nm and an organic thin film 2 having a non-linear light absorption to the laser wavelength range and is constituted so that the organic thin film 2 is composed of a molecular dispersion thin film obtained by mixing a porphyrin material and a phthalocyanine material. Thus the optical recording medium capable of recording and reproducing a large volume of information in a high recording density can be realized because a microspot beyond the diffraction threshold can be created and a effective beam diameter can be lessened, even when the laser beam wavelength for recording and reproducing information falls within the range of 350 to 480 nm. <P>COPYRIGHT: (C)2003,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 in particular, it is possible to record and reproduce high density information by reducing the beam diameter of laser light used in the wavelength range of 350 nm to 480 nm. The present invention relates to an optical recording medium.

[0002]

2. Description of the Related Art Optical recording media for reproducing information by laser light, which are called CDs and CD-ROMs, are now widely used for music reproduction and for computers. In these disk structures, a concave and convex information pit row is provided on one side of a transparent substrate having a thickness of 1.2 mm, a reflective film of aluminum, gold or the like is provided thereon by a sputtering method or a vapor deposition method, and a protective film is further coated. Has been made. Further, in these optical discs, a semiconductor laser beam of 780 nm is incident through a transparent substrate, a signal is read from a change in reflectance due to unevenness of pits, and information is reproduced.

CDs and CD-ROMs are read-only media and have no editing function. Therefore, as recordable optical disks, CD-R (recordable only once), PD
(Rewritable type) has been developed and put into practical use. C
In addition to the editing function, the D-R and PD are the CD-ROMs described above.
Compatible with (playback function). For such an optical disk, a recording layer made of a chalcogenite compound such as tellurium, a rare earth metal compound, a cyanine compound, a naphthalocyanine compound, or a phthalocyanine compound is used.

Recently, an optical recording medium having a larger recording capacity has been developed. A major feature of this high-density optical recording medium is that the wavelength of laser light is set to 600 to 680 nm and the track pitch interval and length are shortened to improve the recording density. ~
It is an optical recording medium that can handle 3 to 10 Gbytes of digital data, which is ten times as large, and is currently a DVD-ROM (reproduction only)
It has been put to practical use as a DVD-RAM (rewritable type), a DVD-RW (rewritable type), and a DVD-R (write-once type).

However, in the future, in order to record a high-quality digital moving image for more than 2 hours, a recording capacity of 25 GB or more will be required. For this reason, the current DVD-
Since a recording capacity about 5 times as large as that of ROM (recording capacity of 4.7 GB) is required, development of high density technology has been actively studied.

As means for increasing the density of the optical recording medium, miniaturization of tracks or pits formed on the optical recording medium can be mentioned. However, the spot diameter of the optical system is limited by the diffraction limit of light λ / 2NA (λ: wavelength of light, NA: numerical aperture of the objective lens of the optical system). Therefore, when the track or pit cycle becomes extremely small, there is a problem that a plurality of pits exist within the beam diameter of the reproduction light and the signal cannot be reproduced.

Therefore, in order to increase the density of the optical recording medium, it is necessary to reduce the laser beam diameter of the irradiation light. As a method of reducing the beam diameter, for example, a method of shortening the wavelength of laser light used for reproduction, a method of increasing the numerical aperture NA of the condenser lens, and the like have been studied.

As a method for shortening the laser wavelength, for example, a laser using a second harmonic wave generating element (SHG) or a semiconductor laser having a wavelength of about 400 nm is used.
Recently, it has been put to practical use. If an SHG laser is used, the current laser wavelength of about 800 nm can be halved, and the recording density can be quadrupled, but the required recording capacity must be satisfied. I can't.

Further, in order to increase the NA, it is very difficult to refine the manufacturing process such as the thickness of the transparent substrate and controllability of the optical system, so that the NA is about 0.6.

Therefore, it is not possible to satisfy the recording capacity of 25 GB or more even in the recording capacity due to the shortening of the wavelength of the laser light and the increase in the NA.

[0011]

As described above, in the prior art, it is possible to realize a recording medium satisfying the recording capacity of 25 Gbytes or more required for recording a high-quality digital moving image for more than 2 hours, for example. There wasn't.

An object of the present invention is to realize an optical recording medium capable of recording / reproducing a large amount of information at high density by reducing the effective beam diameter.

[0013]

In order to solve this problem, the present invention provides a substrate transparent to laser light having a wavelength in the range of 350 nm to 480 nm, and a non-linear optical absorption for the laser wavelength range. And an organic thin film having properties, wherein the organic thin film is a molecular dispersion thin film in which two kinds of a porphyrin-based material and a phthalocyanine-based material are mixed.

That is, by providing an organic non-linear light absorption layer which has been developed in recent years and is sensitive to a laser beam of around 400 nm, a minute beam system exceeding the diffraction limit of irradiation light is induced, whereby an effective beam diameter is obtained. It is possible to obtain an optical recording medium capable of high-density recording / reproduction with a small size.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is a substrate which is transparent to laser light having a wavelength in the range of 350 nm to 480 nm, and a non-linear optical absorption property to the laser wavelength range. An optical recording medium, comprising: an organic thin film having the following: wherein the organic thin film is a molecular dispersion thin film in which two kinds of a porphyrin-based material and a phthalocyanine-based material are mixed, and information is recorded / reproduced. Even if the wavelength of the laser light source is in the range of 350 nm to 480 nm, it has an effect of enabling a minute spot exceeding the diffraction limit.

The invention according to claim 2 of the present invention is the optical recording medium according to claim 1, characterized in that the organic thin film is formed by a vacuum vapor deposition method, whereby impurities in the atmosphere are contained. It has an effect that an optical non-linear thin film having excellent uniformity can be manufactured without being affected by.

The invention according to claim 3 of the present invention is the optical recording medium according to claim 1, wherein the porphyrin-based material is a tetraphenylporphyrin compound represented by the following general formula (Formula 2). This has the effect of enabling a minute spot exceeding the optical diffraction limit.

[0018]

[Chemical 2]

Here, in the chemical formula 2, M may have two hydrogens, or oxygen or halogens 2.
Is a trivalent, trivalent or tetravalent metal atom, and R1 to R4 are methoxy group, alkyl group, alkoxy group, dimethylamino group,
A substituent which is a halogen, hydrogen or a monovalent organic residue is shown.

Embodiments of the present invention will be described below.

(Embodiment) FIG. 1 is a sectional view of an optical recording medium according to the present embodiment. As shown in FIG. 1, a non-linear light absorption layer 2 is coated on a transparent substrate 1 by a spinner or the like. Alternatively, a film is formed by a vapor deposition method, and the reflective layer 3 is formed on the film.
The protective layer 4 is formed in order. A resin is used as the transparent substrate, and the optical characteristics have a wavelength of 350 to 8
In principle, any material may be used as long as it exhibits a high transmittance in the range of 00 nm. A transmittance of 80% or more is desirable, and 90
% Or more is more preferable. However, if the wavelength of the laser light used is only around 400 nm, at least 35
It may be transparent in the range of 0 to 480 nm.

Examples of effective substrate materials include substrates made of glass, acrylic resin, polycarbonate resin, polyamide resin, polystyrene resin, polyester resin and the like. Recently, polycarbonate is generally used.

The non-linear light absorbing layer is formed by a vacuum process such as a vacuum deposition method or an ion plating method in the dry process.
In the wet process, a thin film is usually formed by spin coating.

First, an example of the spin coating method will be shown. It is sufficient to dissolve the porphyrin-based material and the phthalocyanine-based material in a solvent and drop the dye solution while rotating the transparent substrate to form the nonlinear light absorbing layer. The dye solution is adjusted to a dye concentration of 0.5 to 5% by weight. It is desirable that

The solvent for preparing this dye solution can be used as long as it dissolves the dye and is harmless to the transparent substrate, but as the solvent, methyl alcohol, ethanol, propanol,
Butanol, tetrafluoroalcohol, acetone, methyl ethyl ketone, diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, dioxane, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, benzene, toluene, xylene, hexane, cyclohexane, chloroform, methylene chloride. , Dichloroethane, carbon tetrachloride, methoxyethanol, ethoxyethanol, acetonitrile, triethylamine, dipropylamine, dimethylformamide and the like, which are determined in consideration of dye solubility, workability, influence on the substrate, and economical efficiency.

Further, a resin may be added to the dye solution as a binder, and nitrocellulose, cellulose phosphate, cellulose sulfate, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose palmitate, acetic acid.
Cellulose esters such as cellulose propionate and cellulose acetate / butyrate, cellulose ethers such as methyl cellulose, ethyl cellulose, propyl cellulose and butyl cellulose, polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyvinyl pyrrolidone. Copolymer resins such as vinyl resins such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, polymethyl acrylate, polyacrylic acid, poly Acrylic resins such as methacrylic acid, polyacrylamide, polyacrylonitrile, polyethylene terephthalate Polyesters such as, polyethylene, polypropylene, or the like can be used polyolefins such as chlorinated polyethylene, these resins may be added over a range of 1 to 1000 parts per dye weight 100 parts.

In order to form the non-linear light absorbing layer by the spin coating method, the desired film thickness may be adjusted by the rotation speed and the rotation time, and the coating conditions should take into consideration the viscosity of the dye solution and the dye concentration. decide.

The non-linear light absorption layer is 10 to 400 n.
Since it is desirable to set in the range of m, the rotation speed is 10
It is necessary to adjust the concentration and viscosity of the dye solution so that the desired film thickness of the non-linear light absorbing layer is obtained at about 00 to 5000 rpm.

On the other hand, when the non-linear light absorption layer is formed by the vapor deposition method, it is desirable that the vapor deposition is performed at a vacuum degree of 10 ^-2 Pa or less. The porphyrin-based material and the phthalocyanine-based material are vapor-deposited at the same time, and The deposition rate is controlled to control the composition ratio of the thin film.

The reflective layer is made of a material having a high reflectance with respect to the light source used. As a material to be used, metals such as silver, copper, platinum, aluminum, cobalt, tin and nickel are preferable, and these can be used alone or as an alloy. The film thickness of these reflective layers is preferably 20 to 200 nm, and the forming method is a sputtering method or a vacuum evaporation method. Further, the reflective layer is not limited to these metals, and it is possible to use an organic high reflective film.

The protective layer is provided for the purpose of protecting scratches and stains on the nonlinear light absorbing layer or the reflective layer and for storage stability, and SiO, SiO ₂ or the like can be used as the inorganic material. Organic materials such as polymethyl acrylate, polycarbonate,
Epoxy resin, polystyrene, polyester resin, vinyl resin, cellulose, aliphatic hydrocarbon resin, natural rubber, wax, alkyd resin, drying oil, heat-softening resin such as rosin, and heat-melting resin can also be used. If necessary, a flame retardant, a stabilizer, an antistatic agent, etc. can be added to the protective layer. As the protective film, a thermosetting or photocurable resin and a polycarbonate substrate may be bonded.

The shape of the guide groove is not particularly limited, but the average groove width is preferably 0.1 to 0.8 μm, and the groove depth is preferably 50 to 200 nm.

In such an optical recording medium, the nonlinear light absorption layer 2 is irradiated with laser light through the transparent substrate, and the transmittance changes depending on the intensity of the light at this time, so that the minute amount exceeding the diffraction limit is exceeded. Spotting is possible. This allows
It is possible to obtain an optical recording medium capable of high-density recording / reproducing with a small effective beam diameter.

Examples of the present invention will be described below, but the present invention is not limited thereto.

[0035]

EXAMPLE An example of the present invention will be described below with reference to FIG. FIG. 1 shows a cross-sectional view of the optical recording medium used for the description in (Embodiment 1).

Reference numeral 1 is a substrate, 2 is a non-linear light absorption layer provided on the substrate, 3 is a reflective layer provided on the non-linear light absorption layer,
And 4 are protective layers provided on the reflective layer.

As this substrate 1, a disc-shaped transparent substrate made of polycarbonate having a thickness of 0.6 mm, a track pitch of 0.53 μm and a 3T pit length of 0.25 μm is used, and a nonlinear light absorbing layer 2 is formed on the substrate. Further, aluminum was formed as a reflection film 3 on the non-linear light absorption layer by a sputtering method, and finally a protective film 4 was formed of a UV curing resin.

As materials for the non-linear light absorbing layer, two kinds of tetraphenylporphyrin zinc and copper phthalocyanine as shown in (Chemical Formula 3) were simultaneously vapor-deposited by a vacuum vapor deposition method to form a film.

[0039]

[Chemical 3]

At this time, the vapor deposition conditions are as follows: substrate temperature is room temperature, vacuum degree is 4 × 10 ⁻⁴ Pa, vapor deposition rate is 0.1 nm / s.
Met. The film thickness of the obtained organic thin film was measured using DEKTAK3 ST, manufactured by SLOAN, and the absorption spectrum of the thin film organic was measured by Hitachi spectrophotometer (U-
4000) was used for the measurement. The mixing ratio of tetraphenylzinc and copper phthalocyanine is 1: 1.

The light absorption peak of this nonlinear light absorption layer is 40.
It is in the range of 0 to 430 nm and has absorption in the wavelength region of the blue semiconductor laser of 407 nm.

With respect to the optical recording medium constructed as described above, a blue semiconductor laser having an NA of 0.65 and a wavelength of 407 nm was used to obtain a speed of 4.0 m / s and a laser power of 0.2 to 4 m.
When reproduction was performed at W, an increase in reproduction signal amplitude was observed.

In order to clearly show the optical non-linearity of the non-linear light absorption layer of the present invention, a non-linear light absorption layer is formed on a polycarbonate substrate by co-evaporation, and 407n is formed on the non-linear light absorption layer.
When the laser power of m was changed and evaluated, it was revealed that a nonlinearity of the transmittance appeared at a laser power of 4 mW.

[0044]

As described above, according to the present invention, a non-linear light absorption layer in which a porphyrin-based material and a phthalocyanine-based material are mixed is provided on a transparent substrate to form a minute beam diameter exceeding the diffraction limit of irradiation light. However, since the beam diameter is effectively reduced and it is possible to reproduce minute information pits having an optical resolution or less, it is possible to dramatically improve the recording capacity of the optical recording medium.

[Brief description of drawings]

FIG. 1 is a sectional view showing an optical recording medium according to an embodiment of the present invention.

[Explanation of symbols]

1 Polycarbonate substrate 2 Non-linear light absorption layer 3 reflective film 4 protective film

Claims (3)

[Claims] 1. A substrate having a wavelength of 350 nm to 480 nm, which is transparent to a laser beam, and an organic thin film having a non-linear absorption property for the laser wavelength region, wherein the organic thin film is a porphyrin. An optical recording medium comprising a molecular dispersion type thin film in which two kinds of a base material and a phthalocyanine base material are mixed. 2. The optical recording medium according to claim 1, wherein the organic thin film is formed by a vacuum evaporation method. 3. The optical recording medium according to claim 1, wherein the porphyrin-based material is a tetraphenylporphyrin compound represented by the following general formula (Formula 1). [Chemical 1] Here, in (Chemical Formula 1), M is two hydrogen, or a divalent, trivalent, or tetravalent metal atom optionally having oxygen or halogen, and R1 to R4 are methoxy groups or alkyl groups. , An alkoxy group, a dimethylamino group, halogen, hydrogen or a substituent which is a monovalent organic residue.