JP5029280B2 - Optical recording medium and method for manufacturing optical recording medium - Google Patents

Description

The present invention relates to an optical recording medium capable of multi-value recording of two or more values and a method for manufacturing the optical recording medium.

  Currently available optical recording media include a read-only type, a write-once type, and a rewritable type. Read-only types include CD-ROMs and DVD-ROMs, write-once types include CD-Rs, and rewritable types include phase change recording methods such as CD-RW, or light like MO. There is a magnetic recording type.

In each optical recording medium, information is recorded by irradiating the recording layer with light having a predetermined wavelength to form recording pits. In addition, information is reproduced by utilizing the difference in reflection intensity between the recording pit and other portions when light is irradiated (see Patent Document 1).
JP 2003-77174 A

  Since optical recording media have different wavelengths of light used for recording / reproduction depending on the type, the optical band gap of the material constituting the recording layer also differs depending on the type. Conventionally, in order to make the optical band gap of the recording layer different, it is necessary to change the material itself constituting the recording layer, and it has been difficult to make different types of optical recording media.

The present invention has been made in view of the above points, and an object thereof is to easily provide an optical recording medium having a different optical band gap in a recording layer and a method for manufacturing the optical recording medium.

( 1 ) The optical recording medium according to claim 1 includes a first recording layer and a second recording layer each made of carbon and / or a carbon compound, and the ratio of sp ² bonds to sp ³ bonds is the first The recording layer is different from the second recording layer.

The first recording layer and the second recording layer have different optical band gaps due to different ratios of sp ² bonds and sp ³ bonds. Therefore, if the wavelength of the laser used for recording is properly used, a recording pit can be formed in only one of the first recording layer and the second recording layer, or a recording pit can be formed in both of them. You can also. A portion where a recording pit is formed only on one of the first recording layer and the second recording layer, a portion where a recording pit is formed on both of them, and a portion where no recording pit is formed are respectively reproduced. As a result, multi-value recording can be realized since the reflectance when the laser for irradiation is different is different.

If multilevel recording is used, the recording density will be much higher than in the case of binarization. For example, when 16 bits are one word, the amount of information that can be expressed by binarization is 216 = 6.55 × 10 ⁴ , but in the case of ternarization, 316 = 4.305 × 10 ⁷ .

The optical recording medium of the present invention is characterized in that the recording state is stable, the recording margin is wide, and errors are not likely to occur.
( 2 ) In the optical recording medium of claim 2 , each of the first recording layer and the second recording layer contains C _{x Hy} and H ₂ as essential components and N ₂ and / or NH ₃ as optional components, respectively. It is formed by plasma reaction film formation using a mixed gas containing. The mixed gas used for forming the first recording layer and the mixed gas used for forming the second recording layer have different mixing ratios of H ₂ and / or optional components. In the present invention, by changing the composition of the mixed gas, the ratio of sp ² bonds and sp ³ bonds can be made different between the first recording layer and the second recording layer.
( 3 ) Since the optical recording medium of claim 3 has a protective layer adjacent to at least one of the first recording layer and the second recording layer, it can prevent heat and mechanical damage. .
( 4 ) Since the optical recording medium of claim 4 has a reflective layer, it is possible to improve the contrast of recorded and unrecorded portions during reproduction.
( 5 ) Since the invention of claim 5 has a heat insulating layer between the first recording layer and the second recording layer, thermal interference during recording can be prevented.
( 6 ) In the manufacturing method of claim 6 , the mixing ratio of H ₂ and / or an arbitrary component is used for the mixed gas used for forming the first recording layer and the mixed gas used for forming the second recording layer. Different. As a result, the optical band gap differs between the first recording layer and the second recording layer in the optical recording medium manufactured according to the present invention. Therefore, if the wavelength of the laser used for recording is properly used, a recording pit can be formed in only one of the first recording layer and the second recording layer, or a recording pit can be formed in both of them. You can also. A portion where a recording pit is formed only on one of the first recording layer and the second recording layer, a portion where a recording pit is formed on both of them, and a portion where no recording pit is formed are respectively reproduced. As a result, multi-value recording can be realized since the reflectance when the laser for irradiation is different is different.
As the mixed gas, for example, those made of C _x H _y and H _2, which consists of C _x H _y, H _2, and N _2, which consists of C _x H _y, H _2, and NH _3, C _x H _y, are those composed of H _2, N _2, and NH _3. In C _x H _y , x is a natural number from 1 to 5, and y is a natural number from 2 to 10. Examples of C _x H _y include CH ₄ , C ₂ H ₂ , C ₂ H ₄ , C ₃ H ₆ , C ₄ H ₆ , C ₄ H ₈ , C ₄ H ₁₀ , C ₅ H _{8 and the} like. .
When the ratio of H _{2 in} the mixed gas is increased, the ratio of sp ² bonds / sp ³ bonds in the recording layer is decreased, and the optical band gap is increased. In addition, when the mixed gas contains at least one of N ₂ and NH ₃ , increasing the ratio increases the sp ² bond / sp ³ bond ratio in the recording layer and decreases the optical band gap. Become.

  Embodiments of the present invention will be described below.

(A) Configuration and Manufacturing Method of Optical Recording Medium 1 As shown in FIG. 1, the optical recording medium 1 has a reflective layer 5, a second recording layer 7, a first recording layer 9, and light incident on the surface of a substrate 3. The protective layer 11 is sequentially laminated.

  The substrate 3 is a plastic substrate such as glass or polycarbonate, and may be provided with a tracking groove for guiding the position of the laser beam, unevenness (not shown), and the like. Actually, a polycarbonate substrate having a thickness of 1.1 mm, a diameter of 12 cm, a depth of 27 nm and a spiral guide groove having a pitch of 0.32 μm was used.

The reflective layer 5 is a layer made of Al, Ag, or the like and formed by a sputtering method. The thickness of the reflective layer 5 is 100 nm.
The second recording layer 7 was formed by a pulse power source plasma CVD method. The film forming conditions are as follows: a gas flow rate of a mixed gas having a CH ₄ concentration of 10% (H ₂ : CH ₄ = 10: 90) is 100 sccm, a gas pressure of 90 torr, a frequency of 800 Hz, a duty of 20%, a voltage of 1100 V, and a current of 0.9 A. did. The thickness of the second recording layer 7 is 100 nm.

The first recording layer 9 is basically formed by the same film forming method as the second recording layer 7, but the composition ratio (volume ratio) of the mixed gas used for film formation is changed to a CH ₄ concentration of 20% (H ₂ : CH ₄ = 20: 80). The thickness of the first recording layer 9 is 20 nm.

The light incident protective layer 11 is formed by bonding a polycarbonate resin sheet using an ultraviolet curable resin adhesive so as to have a thickness of 0.1 mm.
(B) Characteristics of Optical Recording Medium 1 For each of the second recording layer 7 and the first recording layer 9, the ratio of sp ² bond to sp ³ bond (hereinafter referred to as “sp ² / sp ³ ratio”), And the optical band gap was measured.

As shown in FIG. 2, the sp ² / sp ³ ratio was first calculated from the ratio of the peak size or area by detecting the peak of sp ² bond and sp ³ bond by Raman spectroscopy.
The optical band gap was calculated using a known method as follows. First, as shown in FIG. 3, the spectral characteristic of the transmittance in the second recording layer 7 or the first recording layer 9 is obtained, and in the second recording layer 7 or the first recording layer 9, as shown in FIG. The spectral characteristics of reflectance were obtained. Next, the spectral transmittance (T) was measured with a spectrophotometer based on the results shown in FIG. Further, based on the results shown in FIG. 4, the reflectance (R) was measured with a spectrophotometer. Moreover, the film thickness d of the 2nd recording layer 7 and the 1st recording layer 9 was each measured with the stylus type film thickness meter. Next, the light absorption coefficient α of each recording layer was calculated by Equation 1.

Using this α, as shown in FIG. 5, an (αhν) ^1/2 -E plot was drawn, and the point where the straight line intersected the horizontal axis (optical energy) was defined as the optical band gap. In the example shown in FIG. 5, the calculated optical band gap value is 4.9 eV.

  The measurement results are shown in Table 1.

From this result, it was confirmed that the optical band gap of the second recording layer 7 and the first recording layer 9 could be adjusted only by adjusting the mixing ratio of H _{2 in} the mixed gas.

Further, it was confirmed that the ratio of sp ² / sp ³ in the second recording layer 7 and the first recording layer 9 was changed only by adjusting the mixing ratio of H _{2 in} the mixed gas.
(C) Recording and Reproducing Method for Optical Recording Medium 1 A method for recording information on the optical recording medium 1 and a method for reproducing the recorded information will be described with reference to FIGS. 1, 6, and 7. FIG. .

  As described above, since the optical band gap of the second recording layer 7 is larger than the optical band gap of the first recording layer 9, the wavelength of incident light and the optical absorptance (optical constant: complex) before recording. The relationship with the refractive index (hereinafter referred to as “light absorption characteristics”) is as shown in FIG. After recording, both the second recording layer 7 and the first recording layer 9 exhibit the light absorption characteristics indicated as “after recording” in FIG.

  Here, the first laser wavelength is 410 nm and the second laser wavelength is 380 nm. As shown in FIG. 6, the first laser wavelength is a wavelength that is absorbed by the second recording layer 7 but not absorbed by the first recording layer 9. On the other hand, the second laser wavelength is a wavelength that is absorbed by both the second recording layer 7 and the first recording layer 9.

  When recording is performed on the optical recording medium 1 with the first laser wavelength, as shown in FIG. 7, no recording pits are formed in the first recording layer 9 that does not absorb light (information is not recorded), and there is light absorption. Recording pits 13 are formed only in the second recording layer 7. When the portion that has been recorded at the first laser wavelength and the portion 15 that has not been recorded are irradiated with a reproducing laser beam (first laser wavelength), the reflectance differs due to the optical interference effect. In particular, when the optical interference between the second recording layer 7 and the first recording layer 9 increases, the reflectance in the portion where recording is performed at the first laser wavelength becomes significant.

  When recording is performed on the optical recording medium 1 with the second laser wavelength, recording pits 17 are formed over both the second recording layer 7 and the first recording layer 9 as shown in FIG. The reflectance of the portion that has been recorded with the second laser wavelength, the portion that has been recorded with the first laser wavelength, and the portion 15 that has not been recorded differ when irradiated with the laser beam for reproduction.

  Actually, the reflectance of the non-recorded portion 15 is 35%, and an optical head having an objective lens numerical aperture of 0.85 is used, and conditions for multipass recording with a first laser wavelength and a linear velocity of 5.3 m / s are used. When 5.5 mW was irradiated, the reflectance was 7%. The reflectance of the portion irradiated with 5.1 mW at the second laser wavelength was 23%.

  If the threshold is subtracted at a reflectance of 21%, the signal irradiated at the second laser wavelength can be read, and if the threshold is subtracted at a reflectance of 29%, the signals recorded at the first laser wavelength and the second laser wavelength can be read. That is, as shown in FIG. 7, a ternary signal can be read by a combination of reproduction laser signals. It was also found that the power margin of the laser beam during random pattern recording was ± 1 mW and the jitter was 8% or less, which was wide.

The recording pit is formed as follows. That is, the second recording layer 7 and the first recording layer 9 contain hydrogen, and the portion where the reflectivity changes (recording pits) due to decomposition of the bond between carbon and hydrogen due to the heat of light absorption to change the optical constant. ) Occurs. This was confirmed by analyzing the recording layer before and after the heat treatment by FT-IR. If the mixed gas contains N ₂ or NH ₃ and the recording layer contains nitrogen, it is considered that the decomposition of the bond between carbon and nitrogen also contributes to the generation of recording pits.

  Further, when recording on the optical recording medium 1, recording can be performed by simultaneously irradiating a single wavelength or a plurality of wavelengths with an optical head having a plurality of different recording / reproducing laser beams. In this way, multi-value recording with multiple wavelengths can be realized.

  As shown in FIG. 8, the optical recording medium 1 has a configuration in which a reflective layer 5, a second recording layer 7, a first recording layer 9, a protective layer 19, and a light incident protective layer 11 are sequentially laminated on the surface of a substrate 3. Have The substrate 3 is the same as in the first embodiment, and the reflective layer 5, the second recording layer 7, the first recording layer 9, and the light incident protective layer 11 are formed in the same manner as in the first embodiment. is there.

The protective layer 19 is made of ZnS—SiO ₂ with a thickness of 35 nm by sputtering. The protective layer 19 has an effect of reducing deformation of the recording layers (second recording layer 7 and first recording layer 9) due to the recording laser beam.

  When the optical recording medium 1 was irradiated with 5.7 mW using multipass recording at the first laser wavelength, the reflectance was 7.1%. When the second laser wavelength was irradiated with 5.3 mW, the reflectance was 22%.

  Therefore, when an appropriate reflectance is set as a threshold, a ternary signal can be read by a combination of reproduction laser signals as in the first embodiment. It was also found that the power margin of the laser beam during random pattern recording was ± 1 mW and the jitter was 8% or less, which was wide.

  As shown in FIG. 9, the optical recording medium 1 includes a reflective layer 5, a protective layer 21, a second recording layer 7, a first recording layer 9, a protective layer 19, and a light incident protective layer 11 on the surface of the substrate 3. It has a structure in which the layers are sequentially stacked. The substrate 3 is the same as that in the first embodiment, and the reflective layer 5, the second recording layer 7, the first recording layer 9, the protective layer 19, and the light incident protective layer 11 are formed in the same manner as in the second embodiment. It has been done.

The protective layer 21 is made of ZnS—SiO ₂ with a thickness of 35 nm by sputtering. The protective layer 21 has an effect of reducing deformation of the recording layers (second recording layer 7 and first recording layer 9) due to the recording laser beam.

  When the optical recording medium 1 was irradiated with 5.8 mW using multipass recording at the first laser wavelength, the reflectance was 7.3%. In addition, when 5.9 mW was irradiated at the second laser wavelength, the reflectance was 22.5%.

  Therefore, when an appropriate reflectance is set as a threshold, a ternary signal can be read by a combination of reproduction laser signals as in the first embodiment. It was also found that the power margin of the laser beam during random pattern recording was ± 1 mW and the jitter was 8% or less, which was wide.

  As shown in FIG. 10, the optical recording medium 1 has a reflective layer 5, a protective layer 21, a second recording layer 7, a heat insulating layer 23, a first recording layer 9, a protective layer 19, and light incident on the surface of the substrate 3. The protective layer 11 is sequentially laminated. The substrate 3 is the same as that in Example 1, and the reflective layer 5, the protective layer 21, the second recording layer 7, the first recording layer 9, the protective layer 19, and the light incident protective layer 11 are the same as those in Example 3. Is formed in the same manner.

The heat insulation layer 23 is formed by using a mixed gas (CH ₄ : H ₂ = 3: 97) with a CH ₄ concentration of 3% and forming a film with a thickness of 50 nm by pulse power plasma CVD. The heat insulating layer 23 has an effect of preventing the recording pits from being enlarged due to excessive heat of the recording laser beam.

  When the optical recording medium 1 was irradiated with 5.0 mW using multipass recording at the first laser wavelength, the reflectance was 7.0%. When 5.1 mW was irradiated at the second laser wavelength, the reflectance was 22%.

  Therefore, when an appropriate reflectance is set as a threshold, a ternary signal can be read by a combination of reproduction laser signals as in the first embodiment. It was also found that the power margin of the laser beam during random pattern recording was ± 1 mW and the jitter was 8% or less, which was wide.

  As shown in FIG. 11, the optical recording medium 1 has a structure in which a first recording layer 9, a second recording layer 7, a reflective layer 5, and a UV curable resin protective layer 25 are sequentially laminated on the lower surface of a substrate 3. The substrate 3 is the same as that in Example 1, and the first recording layer 9, the second recording layer 7, and the reflective layer 5 are formed in the same manner as in Example 1. The UV curable resin protective layer 25 was formed by spin coating and UV irradiation curing.

  When performing recording and reproduction on the optical recording medium 1, laser light is incident from the substrate 3 side. The relationship between the laser power and the reflectance was the same as in Example 1. That is, as in the first embodiment, it is possible to read a ternary signal by a combination of reproduction laser signals.

  As shown in FIG. 12, the optical recording medium 1 has a structure in which a protective layer 19, a first recording layer 9, a second recording layer 7, a reflective layer 5, and a UV curable resin protective layer 25 are sequentially laminated on the lower surface of the substrate 3. Have The substrate 3 is the same as in Example 1, and the first recording layer 9, the second recording layer 7, the reflective layer 5, and the UV curable resin protective layer 25 are formed in the same manner as in Example 5. It is.

The protective layer 19 is made of ZnS—SiO ₂ with a thickness of 35 nm by sputtering. The protective layer 19 has an effect of reducing deformation of the recording layers (second recording layer 7 and first recording layer 9) due to the recording laser beam.

  When performing recording and reproduction on the optical recording medium 1, laser light is incident from the substrate 3 side. The relationship between the laser power and the reflectance was the same as in Example 2. That is, in the same manner as in the second embodiment, it is possible to read a ternary signal by a combination of reproduction laser signals.

  As shown in FIG. 13, the optical recording medium 1 includes a protective layer 19, a first recording layer 9, a second recording layer 7, a protective layer 21, a reflective layer 5, and a UV curable resin protective layer 25 on the lower surface of the substrate 3. It has a stacked structure. The substrate 3 is the same as in Example 1, and the protective layer 19, the first recording layer 9, the second recording layer 7, the reflective layer 5, and the UV curable resin protective layer 25 are the same as in Example 6. It is formed.

The protective layer 21 is made of ZnS—SiO ₂ with a thickness of 35 nm by sputtering. The protective layer 21 has an effect of reducing deformation of the recording layers (second recording layer 7 and first recording layer 9) due to the recording laser beam.

  When performing recording and reproduction on the optical recording medium 1, laser light is incident from the substrate 3 side. The relationship between the laser power and the reflectance was the same as in Example 3. That is, as in the third embodiment, a ternary signal can be read by a combination of reproduction laser signals.

  As shown in FIG. 14, the optical recording medium 1 has a protective layer 19, a first recording layer 9, a heat insulating layer 23, a second recording layer 7, a protective layer 21, a reflective layer 5, a UV curable resin on the lower surface of the substrate 3. The protective layer 25 is sequentially stacked. The substrate 3 is the same as that in Example 1, and the protective layer 19, the first recording layer 9, the second recording layer 7, the protective layer 21, the reflective layer 5, and the UV curable resin protective layer 25 are the same as those in the above example. 7 is formed.

The heat insulation layer 23 is formed by using a mixed gas (CH ₄ : H ₂ = 3: 97) with a CH ₄ concentration of 3% and forming a film with a thickness of 50 nm by pulse power plasma CVD. The heat insulating layer 23 has an effect of preventing the recording pits from being enlarged due to excessive heat of the recording laser beam.

  When performing recording and reproduction on the optical recording medium 1, laser light is incident from the substrate 3 side. When the optical recording medium 1 was irradiated with 5.0 mW using multipass recording at the first laser wavelength, the reflectance was 7.0%. When 5.1 mW was irradiated at the second laser wavelength, the reflectance was 22%. That is, when an appropriate reflectance is set as a threshold, a ternary signal can be read by a combination of reproduction laser signals as in the first embodiment.

The manufacturing method is basically the same as in the first embodiment, but the composition ratio (volume ratio) of the mixed gas used for forming the second recording layer 7 is set to H ₂ : CH ₄ : N ₂ = 10.8. : 86.6: 2.6, and the composition ratio (volume ratio) of the mixed gas used for forming the first recording layer 9 is H ₂ : CH ₄ : N ₂ = 10.8: 86.1: 3. As 1, an optical recording medium 1 was manufactured.

As in the case of Example 1, the ratio of sp ² / sp ³ and the optical band gap were measured for each of the second recording layer 7 and the first recording layer 9.
The measurement results are shown in Table 2.

From this result, it was confirmed that the optical band gap of the second recording layer 7 and the first recording layer 9 could be adjusted only by adjusting the mixing ratio of N _{2 in} the mixed gas.

Further, it was confirmed that the ratio of sp ² / sp ³ in the second recording layer 7 and the first recording layer 9 was changed only by adjusting the mixing ratio of N _{2 in} the mixed gas.
The relationship between the laser power and the reflectance was the same as in Example 1. That is, as in the first embodiment, it is possible to read a ternary signal by a combination of reproduction laser signals.

In addition, this invention is not limited to the said embodiment at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.
For example, in Example 9, the mixed gas used for forming the second recording layer 7 and the first recording layer 9 is composed of CH ₄ , H ₂ and NH ₃ , or CH ₄ , H ₂ , N _2. And NH ₃ . In these cases, the optical band gap in the recording layer can be reduced by increasing the ratio of NH _{3 in} the mixed gas or the ratio of N ₂ and NH ₃ .

2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. It is a chart showing the result of having measured the recording layer by the Raman spectroscopy. It is a chart showing the result of having measured the transmittance | permeability of the recording layer using the spectrophotometer. It is a chart showing the result of having measured the reflectance of the recording layer using the spectrophotometer. It is explanatory drawing showing the method of calculating an optical band gap. It is a graph showing the light absorption characteristic of a recording layer. FIG. 3 is an explanatory diagram illustrating a method for performing multi-value recording on the optical recording medium 1. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG. 2 is a side sectional view showing the configuration of the optical recording medium 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical recording medium, 3 ... Substrate, 5 ... Reflective layer, 7 ... 2nd recording layer,
9 ... 1st recording layer, 11 ... Light incident protective layer, 13, 17 ... Recording pit,
19, 21 ... protective layer, 23 ... heat insulation layer, 25 ... UV curable resin protective layer,
d: film thickness, α: light absorption coefficient

Claims (6)

A first recording layer and a second recording layer each comprising carbon and / or a carbon compound;
An optical recording medium, wherein a ratio of sp ² bonds to sp ³ bonds is different between the first recording layer and the second recording layer. Each of the first recording layer and the second recording layer has C _x H _y (x is a natural number of 1 to 5, y is a natural number of 2 to 10) and H ₂ as an essential component as essential components. Formed by plasma reaction film formation using a mixed gas containing N ₂ and / or NH ₃ as
The mixed gas used for forming the first recording layer and the mixed gas used for forming the second recording layer have different mixing ratios of H ₂ and / or the optional component. The optical recording medium according to claim 1 . The first recording layer and adjacent to at least one of said second recording layer, according to claim 1 or 2, wherein the optical recording medium characterized by having a protective layer. The optical recording medium according to any one of claims 1 to 3 , further comprising a reflective layer below the first recording layer and the second recording layer. The optical recording medium according to any one of claims 1 to 4, wherein a heat insulating layer between the second recording layer and the first recording layer. Plasma reaction using a mixed gas containing C _x H _y (x is a natural number of 1 to 5 and y is a natural number of 2 to 10) and H ₂ as essential components and N ₂ and / or NH ₃ as optional components Forming the first recording layer and the second recording layer by forming a film,
The mixed gas used for forming the first recording layer and the mixed gas used for forming the second recording layer have different mixing ratios of H ₂ and / or the optional component. Manufacturing method of optical recording medium.