JPH0544737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium on which information can be recorded and reproduced using laser light.

(Prior Art) A write-once optical disk memory that records and reproduces information on a medium using a laser beam has an excellent feature as a large-capacity recording device because of its high recording density. As a recording medium for such a write-once optical disk memory, semimetal thin films such as Te and Bi, and organic thin films are used. Organic thin films have thermal properties superior to semimetallic thin films, that is, low thermal conductivity and small heat capacity, so that the temperature rise of the film per absorbed energy density is large, and high recording sensitivity can be expected. However, organic thin films do not exhibit as large a reflectance as semimetallic thin films in the wavelength range of semiconductor lasers (~800 nm), so when using semiconductor lasers as light sources for reproduction, there may be problems with the quality of reproduction signals and servo signals. arise.

As a method to improve this, a media configuration in which a reflective film such as A1 is provided between the organic thin film and the substrate is known. By adopting this configuration and adjusting the thickness of the organic thin film, the change in reflectance before and after recording, that is, the amount of modulation, can be made as large as in the case of a semimetallic thin film. However, this configuration has a limitation in that the direction of incidence of the recording and reproducing light is limited to the surface side of the medium.

(Objective of the Invention) An object of the present invention is to provide an optical recording medium with a high reproduction output using a novel medium configuration capable of improving the drawbacks of the prior art described above.

(Structure of the Invention) That is, the present invention provides an optical recording medium in which information is recorded and read by irradiation with a laser beam. and has a refractive index of 2.0 or more at the wavelength of the laser beam.
a second spacer layer that is substantially transparent to the laser beam and has a smaller refractive index at the wavelength of the laser beam than the first spacer layer, and a recording layer that absorbs the laser beam. It is characterized by laminating at least three layers.

(Detailed explanation of the structure) For a medium in which a recording layer is formed on a transparent substrate, the medium reflectance when the substrate is incident on the substrate depends on the optical constants (complex refractive index) of the recording layer and the substrate and the thickness of the recording layer. do. Glass or various synthetic resins are usually used as the transparent substrate. The refractive index n in the range from visible light to near-infrared light is approximately 1.5, and is almost independent of wavelengths in this range. Therefore, the reflectance of the medium is determined by the optical constants and thickness of the recording layer. When using an organic dye film or a resin film in which an organic dye is dispersed as a recording layer, the complex refractive index (n-ik) of these films falls within the semiconductor laser wavelength range (~
800nm) at most 2.5−i1.0.

For example, if the complex refractive index of the recording layer is 2.3-i0.8 and the refractive index of the substrate is 1.5, the medium reflectance at a wavelength of 830 nm incident on the substrate will depend on the thickness of the recording layer, as shown in Figure 1. Dependent. From this, the maximum reflectance is obtained when the thickness of the recording layer is approximately 90 nm, and the value is 18
%. For media in which recording is performed by forming holes in the recording layer, the size of the reproduction output (amount of modulation)
is approximately proportional to the difference between the reflectance of the medium when no holes are formed and the reflectance when holes are formed and the thickness of the recording layer is zero, that is, the reflectance of only the substrate. I can do it. In the example shown in Figure 1, if the thickness of the recording layer is 90 nm, the medium reflectance when no holes are formed is 18%, and the substrate reflectance is 4%, so the modulation amount is 14%. .

The problem of such a small amount of modulation is the second problem.
The problem is solved by one example of the media configuration of the present invention shown in the figure. That is, by providing the first spacer layer 30 and the second spacer layer 40 between the substrate 10 and the recording layer 20, the amount of modulation of the medium can be increased. However, the materials and thicknesses of the first spacer layer 30 and the second spacer layer 40 must be selected so as to satisfy the following conditions. First, consider a configuration as shown in FIG. 3 in which only the first spacer layer 30 is formed on the substrate 10. Substrate 10
The light 100 incident through the interface between the substrate 10 and the first spacer layer 30 and the first spacer layer 3
A part of the light is reflected at the interface between the light beam 0 and the air and becomes reflected light 200. Size of reflected light 200 (reflectance)
depends on the refractive index and thickness of the first spacer layer 30. First spacer layer 30 used in the invention
The material and thickness of are chosen to increase this reflected light 200. That is, the first spacer layer 30
The larger the refractive index of the substrate 10 is, the better. Therefore, the first spacer layer 3
The refractive index of zero is preferably 2.0 or more, and the most desirable thickness is such that the magnitude of the reflected light 200 is maximized. Next, a first spacer layer 30 is formed on the substrate 10.
Consider a configuration as shown in FIG. 4, in which a second spacer layer 40 is provided to increase the reflected light 200 as described above, and a second spacer layer 40 is formed thereon. The light 100 incident through the substrate 10 is transmitted to the interface between the substrate 10 and the first spacer layer 30, the interface between the first spacer layer 30 and the second spacer layer 40, and the interface between the second spacer layer 40 and air. A part of the light is reflected at the interface and becomes reflected light 300. The magnitude (reflectance) of the reflected light 300 depends on the refractive index and thickness of the second spacer layer 40. The second used in the present invention
The material and thickness of the spacer layer 40 are chosen to reduce this reflected light 300. That is, the second
The refractive index of the spacer layer 40 is the same as that of the first spacer layer 3.
It is necessary that the refractive index be smaller than zero. Second
The most desirable thickness of the spacer layer 40 is such that the magnitude of the reflected light 300 is minimized.

By providing the first spacer layer and the second spacer layer under the above conditions and providing the recording layer thereon, the small reproduction output can be improved.

In FIG. 5, a first spacer layer 30 (refractive index 2.0) is formed with a thickness of 100 nm on a substrate 10 (refractive index 1.5), and a second spacer layer 40 (refractive index 1.4) is formed on top of the first spacer layer 30 (refractive index 2.0).
is formed with a thickness of 150 nm and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

In FIG. 6, a first spacer layer 30 (refractive index 2.0) is formed with a thickness of 100 nm on a substrate 10 (refractive index 1.5), and a second spacer layer 40 (refractive index 1.5) is formed on top of the first spacer layer 30 (refractive index 2.0).
The substrate incidence (wavelength
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

In FIG. 7, a first spacer layer 30 (refractive index 2.0) is formed with a thickness of 100 nm on a substrate 10 (refractive index 1.5), and a second spacer layer 40 (refractive index 1.7) is formed on top of the first spacer layer 30 (refractive index 2.0).
is formed with a thickness of 120 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

In FIG. 8, a first spacer layer 30 (refractive index 2.0) is formed with a thickness of 100 nm on a substrate 10 (refractive index 1.5), and a second spacer layer 40 (refractive index 1.8) is formed on top of the first spacer layer 30 (refractive index 2.0).
is formed with a thickness of 120 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

In FIG. 9, a first spacer layer 30 (refractive index 2.3) is formed with a thickness of 90 nm on a substrate 10 (refractive index 1.5), and a second spacer layer 40 (refractive index 1.4) is formed on top of the first spacer layer 30 (refractive index 2.3).
is formed with a thickness of 150 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on it.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 10 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.3) is formed with a thickness of 90 nm, and a second spacer layer 40 (refractive index 1.5) is formed thereon.
The substrate incidence (wavelength
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 11 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.3) is formed with a thickness of 90 nm, and a second spacer layer 40 (refractive index 1.7) is formed thereon.
is formed with a thickness of 120 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 12 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.3) with a thickness of 90 nm is formed, and a second spacer layer 40 (refractive index 1.8) is formed thereon.
is formed with a thickness of 115 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate incident (wavelength).
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 13 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.3) is formed with a thickness of 90 nm, and a second spacer layer 40 (refractive index 2.0) is formed thereon.
The substrate incidence (wavelength
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 14 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.7) is formed with a thickness of 80 nm, and a second spacer layer 40 (refractive index 1.4) is formed thereon.
is formed with a thickness of 150 nm and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 15 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.7) is formed with a thickness of 80 nm, and a second spacer layer 40 (refractive index 1.5) is formed thereon.
The substrate incidence (wavelength
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 16 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.7) is formed with a thickness of 80 nm, and a second spacer layer 40 (refractive index 1.7) is formed thereon.
is formed with a thickness of 120 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 17 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.7) with a thickness of 80 nm is formed, and a second spacer layer 40 (refractive index 1.8) is formed thereon.
is formed with a thickness of 110 nm, and the recording layer 20 (complex refractive index 2.3-i0.8) is provided on the substrate incident (wavelength).
830 nm) shows the dependence of reflection on the recording layer thickness. By comparing with FIG. 1, it can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 18 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.7) with a thickness of 80 nm is formed, and a second spacer layer 40 (refractive index 2.0) is formed thereon.
is formed with a thickness of 100 nm, and the recording layer 20 (complex refractive index 2.3−i0.8) is provided on the substrate incident (wavelength).
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

Figure 19 shows the first layer on the substrate 10 (refractive index 1.5).
A spacer layer 30 (refractive index 2.7) is formed with a thickness of 80 nm, and a second spacer layer 40 (refractive index 2.3) is formed thereon.
is formed with a thickness of 90 nm and the recording layer 20 (complex refractive index 2.3-i0.8) is provided on the substrate.
830 nm) shows the dependence of the reflectance on the recording layer thickness. By comparing with Figure 1,
It can be seen that the amount of modulation is improved by inserting the first spacer layer and the second spacer layer.

The first and second spacer layers used in the present invention are preferably substantially transparent at the readout laser wavelength. The first spacer layer is preferably one with a large refractive index of 2.0 or more.
Various oxides and semiconductors can be used. As oxides, Cr ₂ O ₃ , MoO ₃ , SnO ₂ , TiO ₂ , TeO ₂ and various lower oxides and various magnetic garnets are effective, and as semiconductors, Si, Se, Ge, B and their compounds are effective. Can be used. Moreover, various nitrides, carbides, and sulfides can also be used. The second spacer layer may have a refractive index smaller than that of the first spacer layer. for example,
_AlF3 , _BaF2 , CaF, _CeF3 , _DyF3 , _ErF3 ,
EuF ₃ , GdF ₃ , HfF ₄ , HoF ₃ , LaF ₃ , LiF,
MgF ₂ , NaF, NaF ₃ , PrF ₃ , SmF ₃ , SrF ₂ ,
Various fluorides such as YF ₃ , YbF _{3 ,} Al ₂ O ₃ , CeO ₂ ,
_{Cr2O3 , Dy2O3 , Er2O3 , Eu2O3 , Fe2O3 , Fe3O4 ,}
Gd ₂ O ₃ , GeO ₂ , HfO ₂ , Ho ₂ O ₃ , In ₂ O ₃ , Lu ₂ O ₃ ,
MgO, _MnO2 , _MoO3 , _Nb2O5 , _NiO , SiO,
_{SiO2 , Sm2O3 , SnO2 , Ta2O5} , _TiO2 , _V2O5 ,
Various oxides such as WO ₃ , Y ₂ O ₃ , ZrO, ZrO ₂ , ZrN
Various nitrides such as, various carbides such as ZrC, GeS,
Various sulfides such as ZnS, cobalt phthalocyanine,
Copper phthalocyanine, molybthene phthalocyanine,
Various organic dyes such as magnesium phthalocyanine, nickel phthalocyanine, zinc phthalocyanine, and Sudan Black B, various photoresists, various electron beam resists, and various organic substances such as polystyrene can be used.

The recording layer is preferably one containing an organic substance as a main component, and more preferably one that can be formed by vapor deposition or sputtering. Specifically, various squarylium dyes, various 5-amino-2 _, 3
- various phthalocyanine dyes such as dicyano _- 1,4-naphthoquinone dye, vanadyl phthalocyanine, titanyl phthalocyanine, aluminum phthalocyanine, aluminum chloride phthalocyanine, titanium phthalocyanine, lead phthalocyanine, platinum phthalocyanine, plasma polymerized organic film containing Te;
An organic film in which Te is surrounded by alkyl groups, an organic material in which Te is surrounded by fluorocarbon, etc. can be used. From the viewpoint of weather resistance, 5-amino-2 _, 3-dicyano-8-(substituted anilino)-1
_, 4-naphthoquinone dyes are superior. As the substituent, an alkoxyl group or an alkyl group having 4 or less carbon atoms is most desirable.

Although various substrates can be used, glass and synthetic resin are generally preferred. Synthetic resins include polymethyl methacrylate (PMMA),
Examples include polycarbonate, polyetherimide, polysulfone, and nipoxy resin. The shape of the board is
It can be in the form of a disk, sheet, or tape.

Information is recorded on the recording layer by forming holes in the recording layer. In a disk medium using a disk-shaped substrate, holes are recorded to form a large number of concentric or spiral tracks.
In order to accurately record a large number of tracks at regular intervals, light guide grooves are usually provided on the substrate. When light enters a groove approximately the diameter of the beam, the light is diffracted.
As the beam center shifts from the groove, the spatial distribution of the diffracted light intensity changes, and a servo system can be configured to detect this and direct the beam to the center of the groove.
Usually, the width of the groove is set in the range of 0.5 to 1.2 μm, and the depth is set in the range of 1/8 to 1/4 of the recording/reproducing wavelength used. The recording medium of the present invention is formed on the grooved surface of a substrate.
Since it is desirable that the surface shape of the medium be similar to the groove shape, it is preferable to use a method for forming the medium that allows the medium to adhere along the groove shape, such as a vacuum film forming method such as evaporation, sputtering, or ion plating. be.

Examples of the present invention will be described below.

Example 1 On a disc-shaped PMMA substrate with a diameter of 200 mm and a thickness of 1.2 mm.
Si was deposited to a thickness of 800 Å by electron beam heating, and copper phthalocyanine dye and 5-amino-2,3-dicyano-8-(4-ethoxyanilino)-1,4-
Naphthoquinone dye (hereinafter abbreviated as naphthoxynon dye) was heated to 1000 Å and 800 Å, respectively.
Å was deposited. The degree of vacuum during evaporation is 1×10 ^-5 Torr or less, and the evaporation equipment is approximately 5 Å/sec,
It was set to 4 Å/sec and 2 Å/sec.

Si, copper phthalocyanine dye, and naphthoquinone dye are formed individually on the substrate, and the wavelength is 830 μm.
The complex refractive index is 2.7 for Si, 2.0 for copper phthalocyanine dye, and 2.3− for naphthoquinone dye.
It was i0.8.

A laser beam was incident on the above laminated film of Si, copper phthalocyanine dye, and naphthoquinone dye from the PMMA substrate side, and information was recorded and reproduced. Using a semiconductor laser (wavelength 830nm) as the laser,
The beam was focused to a beam diameter of 1.5 μm using an objective lens with NA=0.55. When recording with a recording power of 10 mW and reproducing with a continuous light of 0.7 mW, an output of 1.2 V is obtained, which is higher than the output of 440 mV without the first and second spacer layers of Si and copper phthalocyanine. It was done.

Example 2 On a disc-shaped PMMA substrate with a diameter of 200 mm and a thickness of 1.2 mm.
SnO ₂ was deposited to a thickness of 900 Å using an electron beam heating method, and thereon a copper phthalocyanine dye and the naphthoquinone dye of Example 1 were deposited to a thickness of 1050 Å and 800 Å, respectively, using a resistance heating method. The degree of vacuum during deposition was 1×10 ^-5 or less, and the deposition rates were approximately 3 Å/sec, 4 Å/sec, and 4 Å/sec, respectively.
It was set to 2 Å/sec. When the complex refractive index at a wavelength of 830 nm was determined, they were 2.3, 2.0, and 2.3−i0.8, respectively.

Information was recorded and reproduced by entering a laser beam into the above laminated film of SnO ₂ , copper phthalocyanine dye, and naphthoquinone dye from the PMMA substrate side. A semiconductor laser (wavelength: 830 nm) was used as the laser, and the beam was focused to a beam diameter of 1.5 μm using an objective lens with NA=0.55. Recorded with recording power 10mWD, 0.7m
When reproduced with continuous light of W, an output of 850 mV is obtained, and an output of 440 mV is obtained without the first and second spacer layers.
An output larger than the mW output was obtained.

Example 3 On a disc-shaped PMMA substrate with a diameter of 120 mm and a thickness of 1.2 mm.
SnO ₂ was deposited to a thickness of 900 Å by an electron beam heating method, and Sm ₂ O ₃ and the naphthoquinone dye of Example 1 were deposited thereon to a thickness of 1200 Å and 800 Å, respectively, by a resistance heating method. The degree of vacuum during evaporation was 1×10 ^-5 Torr or less, and the evaporation rates were approximately 3 Å/sec, 2 Å/sec, and 2 Å/sec, respectively.
sec. When the complex refractive index at a wavelength of 830 nm was determined, they were 2.3, 1.7, and 2.3−i0.8, respectively.
Information was recorded and reproduced by entering a laser beam into the above laminated film of SnO ₂ , Sm ₂ O ₃ and naphthoquinone dye from the PMMA substrate side. A semiconductor laser (wavelength: 830 nm) was used as the laser, and the beam was focused to a beam diameter of 1.5 μm using an objective lens with NA=0.55. When recording was performed with a recording power of 10 mW and reproduction was performed with continuous light of 1.1 mW, an output of 2 V was obtained, which was larger than the output of 700 mV in the case without the first and second spacer layers.

Example 4 A copper phthalocyanine dye of 1000 Å was deposited on a 1.2 mm thick disc-shaped PMMA substrate with a diameter of 200 mm, and then
Y ₂ O ₃ and the naphthoquinone dye of Example 1, respectively.
1200 Å and 800 Å were deposited. Vacuum degree during deposition is 1×
10 ^-5 torr or less, and the deposition rate is approximately 4
Å/sec, 2 Å/sec, and 2 Å/sec. wavelength
The complex refractive index at 830 nm was determined to be 2.0, 1.7, and 2.3−i0.8, respectively.

Information was recorded and reproduced by entering a laser beam into the above laminated film of copper phthalocyanine dye, Y ₂ O ₃ and naphthoquinone dye from the PMAA substrate side. A semiconductor laser (wavelength: 830 nm) was used as the laser, and the beam was focused to a beam diameter of 1.5 μm using an objective lens with NA=0.55. Recorded with a recording power of 10mW, 0.7mW
When played with continuous light, an output of 950mV is obtained,
440mV without first and second spacer layers
A larger output was obtained than that of .

As described above, according to the present invention, an optical recording medium with high reproduction output can be obtained. Note that instead of the naphthoquinone dye shown in the above example as the recording layer,
Naphthoquinone dyes with different substituents, various phthalocyanine dyes such as vanadyl phthalocyanine, titanyl phthalocyanine, aluminum phthalocyanine, aluminum chloride phthalocyanine, lead phthalocyanine, various squarylium dyes, plasma polymerized organic membranes containing Te, Te surrounded by alkyl groups It is equally effective to use an organic film in which Te is surrounded by fluorocarbons.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in the reflectance of an optical recording medium depending on the recording layer thickness, FIG. 2 is a schematic diagram of an optical recording medium that is an embodiment of the present invention, and FIGS. 3 and 4 are diagrams according to the present invention. FIGS. 5 to 19 are schematic diagrams for explaining the principle of the optical recording medium according to the present invention, and FIGS. 5 to 19 are diagrams showing changes in the reflectance of the optical recording medium according to the embodiment of the present invention depending on the thickness of the recording layer. In the figure, 10 is a substrate, 20 is a recording layer, 30
is a first spacer layer, 40 is a second spacer layer,
100 indicates incident light, and 200 and 300 indicate reflected light.

Claims (1)

[Scope of Claims] 1. In an optical recording medium in which information is recorded and read by irradiation with a laser beam, a substrate that is substantially transparent to the laser beam and that is a first spacer layer having a refractive index at the wavelength of the laser beam that is greater than the refractive index of the substrate; and a first spacer layer that is substantially transparent to the laser beam and has a refractive index at the wavelength of the laser beam. a second spacer layer smaller than the layer;
At least three of the recording layers that absorb the laser beam
An optical recording medium characterized by having laminated layers. 2. The optical recording medium according to claim 1, wherein the recording layer is a layer containing an organic substance as a main component. 3. The first spacer layer has a thickness that maximizes the substrate incident reflectance in a state where the recording layer and the second spacer layer are not formed, and the second spacer layer has
The optical recording medium according to claim 1 or 2, wherein the optical recording medium has a thickness such that the substrate incidence reflectance is minimal when the first spacer layer is formed and the recording layer is not formed. .