JP2000132863A - Optical disk and its recording/reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the information recording operation with further higher density by reading out the difference of reflectivity between the irradiated part and non-irradiated part of a stimulating light and reproducing it in such a manner that the change of reflectivity is generated by the irradiation of the excited light on an assembly and the reflected light of the reproduced light made incident on this assembly after the recording the information is detected. SOLUTION: The material such as a film consisting of the assembly of light emitting particulates is formed on a disk-like solid substrate is used for the recording thin film of the optical disk, and when this substrate is irradiated by the specified excited light (the light at the short wavelength side than the absorbing end of the film consisting of the assembly of light emitting particulates), the reflectivity in the certain specific wavelength range of the excited light irradiation area is decreased or lowered by the TDRM function. The area where the reflectivity is decreased or lowered, is treated as the recording pit. The information recorded on the recorded thin film is reproduced in such a manner that the difference in the reflectivity is detected by using the light of suitable wavelength different from the excited light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk having a novel recording medium and a recording / reproducing method for the optical disk. More specifically, the phenomenon that the reflectance decreases when irradiated with excitation light and the function of indicating the reflectance before storage even after long-term storage in a dark place without light irradiation, that is, the function of storing (referred to as "TDRM" (Time Dependent Reflectance and Memor
y)) and a recording / reproducing method for the same, and information recorded by generating a change in reflectivity by irradiating excitation light is supplied to the optical disc by applying a reproducing light to the reflected light. The present invention relates to a recording / reproducing method for an optical disk capable of reproducing data by detecting a difference in reflectance between a recording pit and a non-recorded pit.

[0002]

2. Description of the Related Art In a conventional optical disk, the surface geometry is controlled using a photoresist (pits are formed).
Melting or phase change (crystal-
It has been the basic principle of recording / reproducing to cause a change in the reflectance of a signal recording portion by making it amorphous.

[0005] CDs and read-only MDs are typical optical disks of a system in which a signal is recorded by controlling the surface geometry (forming pits) and a signal is reproduced by reading a change in the reflectance of the recorded portion. . These are formed by sputtering a metal thin film on a photoresist on which pits corresponding to signals have been formed by laser light in advance.
It is manufactured with the signals already recorded.

[0004] A CD-R (CD recordable) is an example of an optical disk of a type in which an irradiated portion is melted by locally heating by laser beam irradiation, and a signal is reproduced by reading a change in reflectance of a recorded portion.
This is because when the organic dye film coated on the resin substrate is irradiated with laser light, the organic dye is heated and melted, and the interface between the partially decomposed organic dye and the heated and softened resin substrate in contact with it is deformed Thus, a recording pit is formed.

[0005] By locally heating by laser beam irradiation, the irradiated portion undergoes a phase change (crystal-amorphous).
A phase change optical disk is an example of an optical disk that reproduces a signal by reading a change in the reflectance of a recording portion. This is a recording thin film on a substrate (eg, Ge-
A thin film of an Sb-Te-based material) is heated and heated by a laser beam to cause a crystallographic phase change in its structure to form and erase information recording pits.

[0006]

However, the conventional recording / reproducing optical disk as described above still has insufficient recording density and high equipment cost in order to cope with the information society in the future. . Accordingly, it is an object of the present invention to provide an optical disk which has a high recording density, can be repeatedly erased (erasable), and can be reduced in cost as a next-generation optical medium.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has applied the above-mentioned aggregate of specific luminescent fine particles having the TDRM function as a recording medium of an optical disk, The present inventors have found that the object can be achieved by utilizing the reflectance changed by the irradiation of the excitation light, and reached the present invention.

That is, the gist of the present invention is characterized in that the recording medium has an aggregate of luminescent fine particles having a function of reducing or decreasing and storing the reflectance as a function of the irradiation time or irradiation intensity of the excitation light. Optical disk. Another aspect of the present invention is to reproduce a recorded signal by recording a signal by reducing the reflectance by irradiating the excitation light and detecting a change in the reflectance with light having the same or different wavelength as the excitation light. Recording / reproducing method for the optical disk.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The optical disc of the present invention has, as a recording medium, an aggregate of luminescent fine particles having a function of reducing or decreasing and storing the reflectance as a function of the irradiation time or the irradiation intensity of the excitation light (TDRM). For example, when a thin film having an aggregate of luminescent fine particles (hereinafter sometimes referred to as “nanoparticles”) is used, the TDRM function is performed on the nanoparticle thin film at room temperature and in contact with air. The reflectance of the area irradiated with the excitation light decreases as a function of the irradiation time (irradiation amount). This change in reflectivity is reversible and different from the change in reflectivity caused by melting or phase change due to heat as in the conventional recording method described above. Thus, a recording pit having an arbitrary shape can be formed on the nanoparticle thin film based on the difference in reflectance between the excitation light irradiation region and the non-irradiation region on the nanoparticle thin film.

[0010] Such an optical memory effect is an essential physical property of a multi-particle system in which nanoparticles are close to each other in a nano-particle thin film formed on a solid substrate by various coating methods.
It is possible to control the reflectance of the nanoparticle thin film by changing the thickness of the nanoparticle thin film, the material of the solid substrate, the intensity of excitation light, the irradiation method (continuous or intermittent), and the like.

In the present invention, the time for reducing the reflectance is usually 3 hours or less, preferably about 1 × 10 ^-9 seconds to 1 minute, and the reduction rate of the reflectance (reduced reflectance / initial reflectance) Is usually 0.9 times or less, preferably 0.01 to
It is about 0.7 times. In addition, the duration of holding, holding or storing the reflectance is 1 second or more, preferably 1 hour or more, and more preferably 24 hours or more at a temperature of 77K or more.

The size of the luminescent fine particles having a TDRM function, which is the subject of the present invention, is usually 0.5 to 0.5 μm.
An aggregate of fine particles of 100 nm, preferably 0.5 to 50 nm, and more preferably 1 to 10 nm, may be mentioned. If the particle size is too large, it becomes bulky, and if it is too small, it becomes atoms or molecules themselves. The type of nanoparticles forming the TDRM material is not particularly limited, and may be fine particles having the above-mentioned predetermined size. For example, I-VII compound semiconductors such as CuCl, CdS, C
II-VI compound semiconductors such as dSe, III- such as InAs
Semiconductor crystal such as Group V compound semiconductor and Group IV semiconductor, TiO
₂ , metal oxides such as SiO and SiO ₂ , phosphors, inorganic compounds such as fullerenes and dendrimers, organic compounds such as phthalocyanines and azo compounds, and composite materials thereof.

[0013] Incidentally, within a range not to impair the object of the present invention,
The surface of these nanoparticles may be chemically or physically modified, and additives such as a surfactant, a dispersion stabilizer and an antioxidant may be added. Such nanoparticles can be obtained by colloidal chemistry, such as the reverse micelle method (Lianos, P. et a).
l., Chem. Phys. Lett., 125, 299 (1986)) and the hot soap method (Peng, X. et al., J. Am. Chem. Soc., 119,
7019 (1997)).

As an example of an embodiment of the optical disk and the recording / reproducing method of the present invention, an optical disk in which a film made of an aggregate of the luminescent fine particles is formed on a disk-shaped solid substrate is used as a recording thin film of the optical disk. When the recording thin film is irradiated with excitation light (light on the shorter wavelength side than the absorption edge of the film made of the aggregate of the luminescent fine particles), the reflectance of the excitation light irradiation region in a specific wavelength range decreases or decreases due to the TDRM function. Therefore, the area where the reflectance is reduced or reduced is treated as a recording pit. Information recorded on the recording thin film is reproduced by detecting a difference in reflectance using light having an appropriate wavelength different from the excitation light.

The solid substrate used in the optical disk of the present invention is usually an organic solid such as a polymer or an inorganic solid material such as glass, a metal, a metal oxide, an alloy, silicon, or a compound semiconductor. Note that the surface of the solid substrate can be modified to be hydrophobic or hydrophilic as long as the object of the present invention is not impaired. For the purpose of enabling the recording pits stored or held by the TDRM function to be erased, a solid substrate provided with a film made of a photoconductive material may be used as the substrate.

In the present invention, after a film containing an aggregate of luminescent fine particles (hereinafter referred to as a “recording thin film”) is formed on the solid substrate, an insulating material such as SiO ₂ is formed on the recording thin film. May be provided, or one or more of them may be laminated. Although the thickness of the recording thin film is not particularly limited, it is usually not less than the diameter of the luminescent fine particles and not more than 1 mm, preferably from the diameter of the luminescent fine particles to 1 mm.
It is a thin film of 00 μm. Further, it is preferable that the luminescent fine particles exist in the recording thin film at a certain density or more. In that sense, the average interparticle distance between the individual luminescent fine particles in the aggregate of the luminescent fine particles is usually within the range of 10 times the particle diameter, and more preferably within the range of 2 times the particle diameter. . If the average interparticle distance is too large, the luminescent fine particles will not exhibit a collective function.

The recording thin film can be obtained, for example, by applying and drying a suspension in which nanoparticles are dispersed in a solvent on a solid substrate. The application method at this time is casting method, die coating method, spin coating method, dip coating (immersion coating)
Method, a wetting film (liquid film) method, a spray coating method, an inkjet method, a Langmuir-Blodgett (LB) method, or the like can be used.

The concentration of the nanoparticles in the suspension is not particularly limited and depends on the coating method and the desired film (layer) structure or particle arrangement structure and film (layer) thickness. For example, in the case of a spin coating method, the thickness of the nanoparticle thin film can be changed by changing the concentration and the rotation speed of the nanoparticles. The target solvent used here is usually water, methanol,
A liquid such as ethanol, toluene, hexane, pyridine, or chloroform, which has a property capable of dispersing nanoparticles, is preferred. For the purpose of obtaining a dried solid recording thin film, it is desirable that the film is volatile.

In the present invention, it is possible to arbitrarily control the geometric shape of the nanoparticle thin film as described above by performing patterning (for example, a pattern with a hydrophilic / hydrophobic surface) on the solid substrate in advance. is there. In addition, as long as the object of the present invention is not impaired, an additive such as a surfactant, a dispersion stabilizer, or an antioxidant, or a polymer, or a binder such as a material that gels in a coating and drying process may be added to the suspension. good.

Such a patterned or non-patterned (uniform) nanoparticle thin film is formed by T
Shows the DRM effect. By exciting (continuously or intermittently) the nanoparticle thin film with light of the appropriate wavelength,
The reflectivity of the film in a certain wavelength range decreases as a function of the excitation light irradiation time. Without any special treatment, the reduced reflectivity of the excitation light irradiated area on the film is maintained at room temperature for at least several hours. It is also possible to increase (return) the reduced reflectivity by applying a light, thermal, electrical, chemical, magnetic or mechanical external field. The reflectance of the nanoparticle film can be controlled by changing the film thickness, the material of the solid substrate, the intensity of the excitation light, the irradiation method (continuous or intermittent), and the like.

The recording / reproducing method of the optical disk of the present invention comprises:
As described above, a signal is recorded by irradiating the optical disc with excitation light (hereinafter sometimes referred to as “writing light”), and reflection of a signal recording area (recording pit) within a certain wavelength range is performed by the TDRM function. A signal recorded as a difference in reflectance is reproduced by irradiating / scanning the optical disk with light having a wavelength different from that of the excitation light (hereinafter, sometimes referred to as “reproduction light”) by reducing or decreasing the reflectance. can do.

In this case, the wavelength of the writing light needs to be higher than the excitation energy of the nanoparticle thin film, that is, shorter than the absorption edge of the nanoparticle thin film.
For example, as a storage thin film material, CdSe having a particle size of 3.7 nm is used.
Is used, the light has a wavelength of 550 nm or less. Further, the wavelength of the reproduction light needs to be a wavelength within a range in which the reflectance changes due to the TDRM function, and is an energy smaller than the excitation energy of the nanoparticle thin film, that is, a wavelength longer than the absorption edge of the nanoparticle thin film. Is preferred. The range of the wavelengths of the writing light and the reproducing light can be changed (adjusted) by changing the particle size and the material of the luminescent fine particles forming the memory thin film.

According to the optical disk recording / reproducing method of the present invention as described above, the wavelengths of the writing light and the reproducing light can be shortened, and the decrease in the reflectivity can be reduced by the excitation light irradiation time or intensity. Since it becomes a function, one recording pit signal can be given a gradation, so that extremely high-density recording becomes possible. Further, since the TDRM function is reversible, it can be erased (eraseable) many times in principle. Further, the optical disk of this recording / reproducing method can be manufactured by coating all the steps, so that low cost can be realized.

[0024]

EXAMPLES Specific examples of the present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention. Example 1 CdSe nanoparticles having an average particle size of 3.4 nm were dispersed in toluene, a suspension having a concentration of 5 wt% was prepared, and 1 ml of the suspension was spin-coated on a glass substrate to form a thin film. Spin coating is 300 rpm
It was performed at 0 rpm. The spin coating time (time during which the substrate was rotating) was 10 minutes. Drying was performed by air drying for 24 hours and drying under reduced pressure for 48 hours (room temperature).

C on the glass substrate thus obtained
The transmission and reflection spectra of the dSe nanoparticle thin film were measured with a spectrophotometer. An integrating sphere was used for spectrum measurement. The measurement wavelength range is 220 to 2000 nm. In order to minimize the measurement error, the spectrophotometer was warmed up for one hour from the start-up, and the baseline was measured before all measurements.

As described above, the transmission of the CdSe nanoparticle thin film
And one hour after measuring the reflection spectrum
UV light (as writing light) (wavelength 365 nm, 150 μW
/ Cm ^Two) Was applied to the nanoparticle thin film. Then the nano
When the transmission and reflection spectra of the particle thin film were measured again
At this time, there is no difference in the transmission spectrum before and after UV irradiation.
Although the reflection spectrum did not show
There was a significant decrease in the long region (FIGS. 1a, b). This C
The absorption edge of the dSe nanoparticles is about 600 nm,
There is no absorption at the upper long wavelengths (FIG. 2). Therefore 600-7
If light in the range of 50 nm is used as reproduction light, the nanoparticles
Write light without affecting the reflectivity of the thin film
The recorded signal can be read. Also the reflectivity
Since the decrease is a function of the writing light irradiation time or intensity,
One recording pit signal can have gradation.
Thus, extremely high-density recording becomes possible.

Application Example 1 FIG. 3 shows an example of a recording / reproducing method of an optical disk capable of reproducing a signal or information by detecting a signal or information recorded or stored by the TDRM effect as a difference in reflectance. The principle is shown. FIG.
In FIG. 1, an excitation light (writing light) 5 corresponding to a signal to be recorded is applied to an optical disk in which a nanoparticle thin film 1 is coated on a solid substrate 2 and a protective film 3 such as SiO ₂ is formed on the nanoparticle thin film 1. Irradiation reduces the reflectance of the irradiated area on the nanoparticle thin film 1 to form recording pits 4. To reproduce the recorded signal, the reproduction light 6 is made incident on the optical disc, the reflected light 7 is detected, and the reproduction is performed by reading the difference in the reflectance between the recording pit and the portion other than the recording pit. The recording method may be mark position recording (signal 8 is placed at the center of recording pit 4) shown in FIG. 3B, or mark edge recording (signal 9 is placed at the end of recording pit 4) shown in FIG. 3c. good.

[0028]

According to the optical disk and the recording / reproducing method of the present invention, the phenomenon that the reflectance decreases when the excitation light is irradiated,
It shows the reflectance before storage even after being stored for a long time in a dark place without light irradiation, that is, it utilizes the function of an aggregate of luminescent fine particles that is stored, and the excitation light is applied to the aggregate. Irradiating a laser beam to cause a change in reflectivity, record information, and then make reproduction light incident on the assembly to detect the reflected light and read the difference in reflectivity between the irradiated portion and the non-irradiated portion of the excitation light. Therefore, information can be recorded at a higher density than before.

[Brief description of the drawings]

FIG. 1A shows transmission and reflection spectra of a CdSe nanoparticle thin film formed on a glass substrate by spin coating. The broken line in the figure is the spectrum before irradiation with UV light (wavelength 365 nm). The solid line in the figure is UV light (wavelength 36
5 nm) Spectrum after irradiation. Although there is almost no difference between the transmission spectrum before and after the irradiation with the UV light, a decrease in the reflectance is observed in the wavelength region of 750 nm or less in the reflection spectrum. The vibration waveform seen in the spectrum near the wavelength of 800 to 900 nm is noise when the detector of the spectrophotometer is replaced. (B) UV of transmission and reflection spectra shown in FIG. 1a
Difference spectrum before and after light irradiation (the spectrum after irradiation is subtracted from the spectrum before UV light irradiation).

FIG. 2 is an absorption spectrum of the CSe nanoparticles shown in FIG. The absorption peak of excitons of the nanoparticles has a wavelength of 564 nm.
It is.

FIG. 3A is a diagram illustrating an optical disk in which a nanoparticle thin film 1 is coated on a solid substrate 2 and a protective film 3 such as SiO ₂ is formed on the nanoparticle thin film 1 and irradiated with excitation light (writing light) 5. Schematically shows the principle of a recording / reproducing method in which a recording pit 4 is formed, a reproducing light 6 is made incident, a reflected light 7 is detected, and a difference in reflectance between a recording pit and a portion other than the recording pit is read to reproduce. FIG. (B) Mark position recording method (signal 8 is placed at the center of recording pit 4). (C) Mark edge recording method (signal 9 is put on the end of recording pit 4).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 nanoparticle thin film 2 solid substrate 3 protective film 4 recording pit 5 excitation light 6 reproduction light 7 reflected light 8, 9 signal

Claims (12)

[Claims] 1. An optical disk comprising, as a recording medium, an aggregate of luminescent fine particles having a function of reducing or reducing and storing the reflectance as a function of the irradiation time or the irradiation intensity of the excitation light. 2. The optical disk according to claim 1, wherein at least one of the solid substrates has a recording layer made of a film containing an aggregate of luminescent fine particles. 3. The optical disc according to claim 1, wherein the time for decreasing the reflectance is 3 hours or less. 4. The optical disk according to claim 1, wherein a reflectance reduction rate is 0.9 times or less of an initial reflectance. 5. The optical disk according to claim 1, wherein the storage time of the reflectance at a temperature of 77 K or more is 1 second or more. 6. The optical memory device according to claim 1, wherein the average distance between the light-emitting fine particles in the aggregate of the light-emitting fine particles is 2 to 10 times the diameter of the fine particles. 7. The optical memory device according to claim 1, wherein the luminescent fine particles have a particle size of 0.5 to 100 nm. 8. The optical memory device according to claim 1, wherein the luminescent fine particles are an inorganic compound. 9. The optical memory device according to claim 1, wherein the luminescent fine particles are an organic compound. 10. The optical memory device according to claim 1, wherein the luminescent fine particles are metal oxides. 11. The light-emitting fine particle is a semiconductor.
8. The optical disk according to any one of items 1 to 7, 12. A signal recorded by reducing the reflectance by irradiating the excitation light, and reproducing the recorded signal by detecting a change in the reflectance with light having the same or different wavelength as the excitation light. 12. An optical disk recording / reproducing method according to any one of 1 to 11.