JPH06168481A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve recording density and reliability of information recording by specifying the range of thickness ratio of a recording material layer to an outer protective layer. CONSTITUTION:A transparent substrate 103 on which laser light through a condensor lens 102 is made incident has plural tracking guide grooves 109. On the surface of the transparent substrate 103 where the guide groove 109 is formed, an inner protective layer 104, recording material 105, outer protective layer 106, metal reflecting film layer 107, and disk protective layer 108 are formed. Because it is required that in this film structure, enough temp. rising for recording is obtd. in a narrow area by irradiation of light for recording, the inner and outer protective layers 104, 105 are specified to have 100nm, 200nm thickness, respectively, and the reflecting layer 107 has 100nm thickness. Further, the ratio of thickness of the recording material layer 105 to the outer protective layer 104 is specified to a range between >0.52 and <0.95. Thus, the recording density can be improved.

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 for recording / reproducing information by light.

[0002]

2. Description of the Related Art In an optical disk device, information is recorded on a surface along a spiral or concentric circular track, and a light beam such as a laser beam is irradiated to optically reproduce an information signal. A document file system was initially commercialized as a device that allows the user of the device to record an information signal on an optical disc with a laser, and is a product for use as a peripheral recording device of a computer that requires higher reliability. Has also been put to practical use. Further, a device that can erase the recorded information signal and rewrite it has also been put into practical use. Further, development of an optical card memory device or an optical tape memory device in which the same technique is applied to a card-shaped or tape-shaped recording medium has also been advanced.

In the optical recording medium used in these optical information recording / reproducing apparatuses, a recording mark having a size of about 1 micron has a track pitch of 1. 6
It is formed on a recording line of about micron. As a method of forming the recording mark, various methods have been proposed and put into practical use, such as a method of causing local destruction, deformation, or a change in optical properties due to a phase change in the recording film. Further, as a technique for accurately tracking a recording row with a laser beam, a method is provided in which a track guide groove is provided in advance on an optical disc and a tracking error signal is detected from diffracted light by this, and a method is used in which a slight deviation is made to the left and right of a track There is a method of detecting a tracking error signal by sampling the signals obtained from the marks and comparing them.

As with other recording apparatuses, these optical disk apparatuses are required to have a larger capacity and a smaller size as the applications or fields of application are expanded, and therefore the recording density has been improved. Further, various recording materials and film structures have been developed in order to realize rewriting of information and overwriting.

FIG. 24 is a schematic view showing the structure of a phase change type optical disk. In FIG. 24, an incident beam 601 passes through a condenser lens 602 and then is irradiated from the substrate 603 side. The medium is, in order from the substrate side, the inner protective layer 60.
4. A recording material 605, an outer protective layer 606, a reflective layer 607 made of a metal film, and a disc protective layer 608. The thickness of each of these layers is set to about a dozen to several hundreds of nm, but the optical path length obtained by multiplying this by the refractive index of each layer is a fraction of the order of magnitude of the wavelength of the light used. Therefore, the mutual interference effect of the lights due to the reflection that occurs multiple times at the layer boundary becomes remarkable. At this time, the phase of the reflected light is shifted compared with the phase of the incident light. That is, the amplitude reflectance has an imaginary number component and is expressed as a complex amplitude reflectance.

In recording information, the recording material 605 is changed in its optical properties by irradiating it with a laser beam having an intensity sufficient for recording. This corresponds to a change in the refractive index, extinction coefficient, or both of the numerical values of the recording material 605. Along with this, the light interference effect is greatly changed, and the complex reflectance of the entire multilayer film is increased. It will change.

In the signal reproduction, the complex reflectance of the entire multilayer film is locally changed only in the area of the recording mark, which is detected by the intensity of the reflected light of the laser light. Therefore, the ratio of the complex reflectance of the recorded area to the complex reflectance of the unrecorded area affects the contrast of the reproduced signal. Therefore, the absolute value of the complex reflectance of the entire multilayer film as shown in FIG.
The medium structure has been determined by determining the thickness of each layer under the condition that it greatly changes due to recording.

That is, for example, as a known example of the prior art, "Overwrite characteristic analysis of phase-transition optical recording medium": Nakamura et al., Autumn 1990, 51st Annual Meeting of the Society of Applied Physics, Symposium Digest "Phase Crystallization Mechanism and Erasure Ratio of Modified Optical Disk "(Published by: Japan Society of Applied Physics, October 30, 1990) p. 42-p. 48,
In the recording medium described in, the reflectance is theoretically calculated by changing the thickness of the second layer and the thickness of the fourth layer with respect to the model of the flat multilayer film structure, and the reflectance is set to a desired value. The value of the recording material layer is set to 20 nm and the protective layer is set to 100 nm by a method of setting a proper film thickness.

[0009] As another example, "Characteristics of rewritable phase change optical disk": Obayashi et al., Winter of 1991 (1993), 2nd Phase Change Recording Study Group Symposium Proceedings "Basics of Phase Change Optical Disk" And Application ”(Published by: Phase Change Record Secretary of the Japan Society of Applied Physics, January 31, 1991) p. 20 ~
p. Also in the recording medium described in No. 29, the reflectance is theoretically calculated by changing the thickness of the recording layer and the thickness of the protective layer with respect to the model of the flat multilayer film structure so that the reflectance has a desired value. The thickness of the recording layer is set to a value of 25 to 45 nm by a method of setting the thickness of the recording layer.

The calculation of a flat multilayer film model is relatively easy, and it is simple and effective for rough estimation. In the past, we designed the medium structure from such an estimate,
After that, this was applied to a substrate having a groove which is a groove for tracking guide.

A conventional media structure design by calculation of a flat multilayer film model will be specifically described. FIG. 25 is a diagram showing the calculation result of the reproduction signal amplitude by the flat multilayer film model. The medium is a polycarbonate resin substrate with an inner protective layer of 10
0 nm ZnSiO ₂ , GeSbTe as recording material layer
System phase change recording material, 20 nm ZnS as outer protective layer
Each layer of iO ₂ and Al as a reflective layer is sequentially laminated. In FIG. 25, the horizontal axis represents the thickness of the recording material layer, and the vertical axis represents the difference in reflected light intensity before and after recording. The intensity of the reflected light obtained by the mirror surface having a reflectance of 1 was set to 100%. As can be seen from the figure, the maximum signal amplitude is realized at the film thickness of 19.5 nm. One design method was to set the film thickness to this value. On the other hand, there is an idea that the quality of the reproduced signal is not determined only by the amplitude. For example, noise generated when reflected light returns to the laser and noise such as shot noise in the detector increase as the amount of reflected light increases. Therefore,
A value obtained by dividing the signal amplitude by the reflected light intensity of the recorded portion, a value obtained by dividing the signal amplitude by the reflected light intensity of the unrecorded portion, and a signal amplitude divided by the average value of the reflected light intensity of the recorded portion and the unrecorded portion. There is also a method of defining a value such as a value as a modulation factor and setting it to a film thickness that maximizes it. FIG. 26 is a diagram showing the calculation result of the modulation degree by the flat multilayer film model. The modulation degree was defined as a value obtained by dividing the signal amplitude by the reflected light intensity of the recorded portion. As can be seen from the figure, a sharper peak than that in FIG.
The maximum is around nm. Conventionally, the medium structure designed by these methods has been adopted to optimize the reproduction signal quality.

[0012]

However, there is a problem in that even if a medium having a structure determined in this way is actually produced, the expected reproduction signal modulation degree cannot be obtained. This is because interference with the phase change of the reflected light generated by the tracking guide groove occurs and the signal deteriorates. For this reason, a desired signal-to-noise ratio cannot be obtained, which has been an obstacle to improving recording density or reliability.

Therefore, the present invention has been made in view of such circumstances, and an object thereof is to make it possible to design a medium structure relatively easily and effectively realize a sufficiently large reproduction signal modulation degree. To provide.

[0014]

In order to achieve the above object, a first optical recording medium of the present invention is a transparent substrate, an inner protective layer formed on the transparent substrate, and the inner protective layer. A recording material layer formed on the recording material layer, an outer protective layer formed on the recording material layer, and a reflective layer formed on the outer protective layer, and light for recording at least information on them. An optical recording medium is provided in which a guide groove for guiding a beam is provided, and the information is recorded in the guide groove, wherein a ratio of the thickness of the recording material layer to the thickness of the outer protective layer is 0.52 or more. It is characterized by being set within the range of 0.95 or less.

The second optical recording medium of the present invention is a transparent substrate, an inner protective layer formed on the transparent substrate, a recording material layer formed on the inner protective layer, and the recording material. A guide groove for guiding a light beam for recording at least information is provided on the outer protective layer and the reflective layer formed on the outer protective layer. An optical recording medium for recording the information in a groove, wherein the ratio of the thickness of the recording material layer to the thickness of the inner protective layer is set in the range of 0.053 or more and 0.098 or less. It is a feature.

Further, a third optical recording medium of the present invention comprises a transparent substrate, an inner protective layer formed on the transparent substrate,
The recording material layer is formed on the inner protective layer, the outer protective layer is formed on the recording material layer, and the reflective layer is formed on the outer protective layer. At least information is recorded on these. An optical recording medium is provided in which a guide groove for guiding a light beam for recording is provided, and the information is recorded between the guide grooves, and a ratio of the thickness of the recording material layer to the thickness of the outer protective layer is 0. It is characterized in that it is set within the range of 0.32 or more and 0.6 or less.

In addition to the above, the fourth optical recording medium of the present invention comprises a transparent substrate, an inner protective layer formed on the transparent substrate,
The recording material layer is formed on the inner protective layer, the outer protective layer is formed on the recording material layer, and the reflective layer is formed on the outer protective layer. At least information is recorded on these. An optical recording medium having a guide groove for guiding a light beam for recording, for recording the information between the guide grooves, wherein a ratio of a thickness of the recording material layer to a thickness of the inner protective layer is 0. It is characterized in that it is set within the range of 0.033 or more and 0.063 or less.

[0018]

With the configuration of the present invention, an efficient medium structure in which a larger reproduction signal modulation degree can be obtained by the synergistic effect of the phase shift due to the change in complex reflectance due to recording and the phase shift due to the groove The layer thickness is set so that As a result, even if the same recording material as the conventional one is used, higher signal quality than the conventional one can be obtained, and the recording density and the reliability of information recording can be improved. This also applies to the protective layer.

[0019]

FIG. 1 shows an optical system of an optical recording / reproducing apparatus. According to this figure, an optical head 110 is provided below the optical recording medium, that is, the optical disc 100, facing the optical disc 100. The optical head 110 includes a condenser lens 102 facing the optical disc 100, a laser element 111 for generating a laser beam, and the laser element 1.
Collimator lens 112 that collimates the laser light from 11, beam splitter 113 into which the parallel laser light from collimator lens 112 is incident, and condenser lens 102 that collects the laser light through this beam splitter 113
Reflected by the optical disc 100 and reflected by the condensing lens 102.
A reflection mirror 114 having a reflection surface that reflects in the direction of, a lens 115 that focuses the reflected light deflected by the beam splitter 113, and a photodetector 116 that converts the reflected light focused by the lens 115 into an electrical signal. It is composed of

The optical disc 100 is constructed as shown in FIGS. That is, a plurality of tracking guide grooves 109 are formed in the transparent substrate 103 on which the laser light that has passed through the condenser lens 102 is incident, and the inner protective layer 104 is formed on the transparent substrate 103 on the guide groove side.
A recording material 105, an outer protective layer 106, a reflective layer 107 made of a metal film, and a disc protective layer 108 are sequentially stacked. As a material for each layer, a polycarbonate resin is used for the transparent substrate 103, ZnSiO ₂ is used for the inner protective layer 104 and the outer protective layer 106, and G is used for the recording material layer 105.
An eSbTe-based phase change recording material is used for the reflective layer 107.
1 (aluminum), and an ultraviolet effect resin is used for the disk protective layer 108. The thickness of these material layers is
There are restrictions from the request for the recording characteristics of the recording medium to be appropriate. That is, one of the preconditions is to obtain a film structure in which a temperature rise sufficient for recording is realized in a narrow area to be recorded by irradiating the recording medium with light during recording. In this embodiment, the thicknesses of the inner protective layer 104 and the outer protective layer 106 are 100 nm and 20 nm, respectively.
And the thickness of the reflective layer 107 is set to 100 nm. Since the extinction coefficient of Al as a material is relatively large, the thickness of the reflective layer 107 is not strictly limited, and
Even if the thickness is thicker than 100 nm, the optical characteristics do not change so much.

In order to realize a medium in which the recording characteristics are within the practical range as set as described above and the reproducing characteristics are good, reproduction is performed when the film thickness of the recording material is changed. It is calculated how the signal changes. This calculation is based on the method of analyzing the propagation of light in consideration of the interference effect of the multilayer thin film. FIG. 4 created based on the calculation result shows the calculation result of the reproduction signal level when the groove is not formed in the recording medium. In FIG. 4, the reflectance of the recording medium when the various layers as described above are formed on the flat substrate is calculated by changing the thickness of the recording material, and the reflectance of the recording material in the crystalline state and in the amorphous state is calculated. Two curves 201 and 202 are shown, where the horizontal axis represents the thickness of the recording material and the vertical axis represents the reflectance. A curve 201 shows the reflectance in the crystalline state, and a curve 202 shows the reflectance in the amorphous state. The crystalline state corresponds to the state of the recording medium before recording, and the Armophas state corresponds to the state of the recording medium after recording.
When the thickness of the layer is set to the thickness around the area where the level difference between these two curves is large, the amplitude of the reproduced signal can be increased and a good signal can be obtained. To obtain a high degree of modulation of the playback signal, the playback signal level (reflectance) after recording
The thickness of the layer may be set to a smaller thickness. However, this calculation does not consider the size of the mark or the guide groove of the track, so that the calculation result deviates from the actual optimum value.

FIG. 5 shows the calculation result of the reproduction signal level when the recording medium has a groove. FIG. 5 shows the calculation result of the reproduction signal level obtained before and after forming a mark on a medium having a groove having a track pitch of 1.2 μm and a groove width of 0.6 μm. In the figure, a curve 301 shows the reflectance before recording, and this reflectance has the same value both inside the groove and between the grooves. This is because a groove having a rectangular cross section whose groove width is half the track pitch is formed. Regarding the reproduction signal level after recording, the calculation result in the case of in-groove recording in which recording light is irradiated into the groove to form a mark in the groove is the curve 302.
, The calculation result in the case of on-land recording in which recording light is irradiated between the grooves to form marks between the grooves is a curve 303.
, And two recording schemes are shown.
In this analysis, the interference effect of the multi-layer thin film, the phase shift due to the groove, the diffraction effect generated in the condensing optical system, and the like are considered. As can be seen from comparison with FIG. 4, the optimum film structure is slightly different from the layer structure expected from FIG. 4 due to the influence of the phase shift due to the groove. Also, the optimum film structure for each of the two recording methods is still slightly different.

The behavior of the signal amplitude for viewing the above relationship will be described in detail. FIG. 6 shows the film thickness dependence of the signal amplitude, and curves 401 and 402 show the calculation results for in-groove recording and on-land recording, respectively. According to this figure, the peak of the amplitude in the case of in-groove recording is near the film thickness of 23.5 nm, and the peak of the amplitude in the case of on-land recording is near the film thickness of 16 nm. As can be seen from the figure, if the film thickness at the peak is 100% and the film thickness is in the range of 80% to 120%,
A sufficiently large signal amplitude can be realized.

FIG. 7 shows the film thickness dependence of the signal modulation degree. The signal modulation degree is a value obtained by dividing the signal amplitude by the reflected light intensity of the recording area. Curve 501 in the figure shows the calculation results for in-group recording and on-land recording, respectively.
According to this figure, in in-groove recording, the peak of the modulation degree is near the film thickness of 18 nm, and in on-land recording,
The peak of the modulation degree is near 13 nm in film thickness. As can be seen from the figure, 80% when the peak film thickness is 100%
Within a range of from 120% to 120%, a sufficiently large signal modulation degree can be realized.

As can be seen from the above calculation results, the characteristics are improved by increasing the recording material film thickness in the case of in-groove recording in which a mark is formed in the groove and by making it thinner than in the case of on-land recording. be able to. In the case of this embodiment, the recording material film thickness d is 15 nm <d
By setting the range to be <23 nm, the characteristics of the recording medium are optimized. In the case of on-land recording in which marks are formed between the grooves, the recording material film thickness d is set to 10 n.
The characteristics of the recording medium are optimized by setting the range of m <d <17 nm.

Next, a second embodiment will be described. The layer structure of the optical recording medium is the same as that shown in FIG. That is, the medium is an inner protective layer 104, a recording material layer 105, an outer protective layer 106, and a reflective layer 1 made of a metal film, which are sequentially stacked from the transparent substrate 103.
07 and the disc protection layer 108. Further, the substrate 103 has a tracking guide groove 109.
Is formed. As the material of each layer, the substrate 103 is a polycarbonate resin, the inner protective layer 104 and the outer protective layer 1
06 is ZnS—SiO ₂ , and the recording material layer 105 is GeSb.
The Te-based phase change recording material, the reflective layer 107 is made of Al, and the disk protective layer 108 is made of an ultraviolet curable resin. The ratio of the elements Ge, Sb and Te forming the recording material layer 105 is set to 2: 2: 5, for example.

Further, in the second embodiment, the inner protective layer 104 and the outer protective layer 106 have thicknesses of 100 nm and 20 nm, respectively, and the reflective layer 107 has a thickness of 100 nm. Regarding the thickness of the reflective layer 107, since the extinction coefficient of Al, which is the material, is relatively large, the thickness is not strictly limited, and even if the thickness is set to 100 nm or more, the optical characteristics of the recording medium are too large. does not change. Further, the track pitch is set to 1.0 micron, and the mark is formed on the medium in which the groove having the groove width of 0.5 micron is formed. At this time, when the thickness of the recording material layer 105 is changed, the reproduction signal is calculated and compared with the calculation result of the first embodiment. In the second embodiment, the composition ratio of the recording material and Since the optical constant is different from that of the first embodiment, the optimum film thickness setting value is slightly different from that of the first embodiment.

The calculation result of the reproduction signal amplitude in the recording medium of the second embodiment shown in FIG. 8 corresponds to the calculation result of the first embodiment shown in FIG.
2 shows the calculation results for in-groove recording and on-land recording, respectively. According to this figure, the peak of the amplitude appears at a plurality of points, which is caused by the interference effect of the thin film. Since the recording material layer 105 has an absorption characteristic, the peak of the amplitude approaches a constant value as the film thickness increases. If you select the film thickness where the amplitude peak takes the maximum value,
Although the highest level signal can be obtained, if the recording characteristics, the manufacturability of the medium, and other conditions are inconvenient, the thickness of the recording material layer 105 can be set to a value near the second and third peaks. Good.

FIG. 9 is a plot of the signal modulation degree obtained from the recording medium of the second embodiment. This drawing corresponds to FIG. 7 in the first embodiment. The modulation degree of the signal is a value obtained by dividing the signal amplitude by the reflection intensity of the recorded area.
In FIG. 9, curves 501 and 502 show the calculation results for in-groove recording and on-land recording, respectively. According to FIG. 9, the degree of modulation is small in the film thickness near the second and third peaks, and this film thickness is not very advantageous from the viewpoint of reproduction characteristics.

FIGS. 10 and 11 show in detail the behavior near the peak of the signal amplitude in FIGS. 8 and 9. In FIG. 10, curves 401 and 402 show the calculation results in the case of in-groove recording and on-groove recording, where the peak in in-groove recording is near the film thickness of 27.5 nm, and the peak in on-land groove recording is 15 nm. It is near the film thickness. As can be seen from the figure, in each case, if the peak film thickness is 100%, and within the range of 50% to 150%, a sufficient signal modulation degree can be realized. Thickness is effective.

In FIG. 11, curves 501 and 502 show the calculation results in the case of in-groove recording and on-groove recording, respectively. The peak in in-groove recording is near the film thickness of 22 nm, and the peak in on-land recording is near the film thickness of 14 nm. As can be seen from the figure, the peak film thickness is 100 in each case.
When the percentage is within the range of 50% to 150%, a sufficiently large signal modulation degree can be realized, and this film thickness is effective. From these results, the optimum range of the film thickness is determined. In the second embodiment, in the case of in-groove recording, the thickness d of the recording material layer 105 is 18 nm <d <30.
By setting the thickness in the range of nm, the characteristics of the recording medium are further improved. Further, in the case of on-land recording in which marks are formed between the grooves, the thickness d of the recording material layer 105 is set to 10
By setting the range of nm <d <19 nm, the characteristics of the recording medium are further improved.

Further, under the film thickness condition near the intersection of the curves 401 and 402 in FIG. 9 or the intersection of the curves 501 and 502 in FIG. 10, almost the same signal quality can be obtained in both in-groove recording and on-land recording. . The recording medium having such a structure can be applied to both of the recording methods and can be applied to a mixture of both methods. When used in this way, the recording material layer 105 is formed particularly near 14 nm.
A large effect can be obtained by setting the thickness of the. In this way, it is similarly effective in the third and fourth embodiments to be described later to obtain the conditions under which substantially equal signal qualities are obtained in both in-groove recording and on-land recording. .

Next, in-groove recording is considered to be effective in improving the track density, and the film thickness setting conditions in this case will be described. Here, an example in which the second embodiment is examined from another viewpoint will be described, but the layer structure of the optical recording medium is the same as in FIG.

Then, in this embodiment, the inner protective layer 10
4 and the outer protective layer 106 have a thickness of 240 nm and 2
The reflection layer 107 has a thickness of 10 nm.
It is set to 0 nm. Regarding the thickness of the reflective layer 107, since the extinction coefficient of Al, which is a material, is relatively large, the thickness is not strictly limited, and even if the thickness is set to 100 nm or more, the optical characteristics of the recording medium are too large. does not change. Further, the track pitch is set to 1.0 micron, and the mark is formed on the medium in which the groove having the groove width of 0.5 micron is formed. At this time, the thickness of the inner protective layer 104 is d1, the thickness of the recording material layer 105 is d2, and the thickness of the outer protective layer 106 is d3. FIG. 12 shows the change in the modulation factor when the value of d2 / d3 is changed. S / N
In order to secure the ratio and sufficiently achieve the performance of the recording / reproducing apparatus, the modulation factor needs to be 2 or more. For that purpose, it is necessary that the value of d2 / d3 is within the range of 0.52 or more and 0.95 or less. Moreover, when the value of d2 / d1 is changed, the modulation degree changes as shown in FIG. Also in this case, in order to secure the S / N ratio and sufficiently achieve the performance of the recording / reproducing apparatus, the modulation degree needs to be 2 or more. Therefore, the value of d2 / d1 is 0.053
Above, it is necessary to be within the range of 0.098 or less.

Next, the film thickness setting conditions for on-land recording will be described with reference to FIGS. 14 and 15. in this case,
FIG. 14 shows the change in the modulation factor when the value of d2 / d3 is changed. According to FIG. 14, in order to obtain a modulation factor of 2 or more, the value of d2 / d3 needs to be in the range of 0.32 or more and 0.6 or less. Also,
When the value of d2 / d1 is changed, the value of d2 / d1 needs to be within the range of 0.033 or more and 0.063 or less in order to obtain the modulation degree of 2 or more.

The above d2 / d3 and d2 / d1 are
For example, Mansuripur, et al. "Laser-induced local hea
ting of multilayess "AppliedOptics vol.21, No6, 15
Computation of multilayer film from light field calculation by March 1982
xHayness of Hopkins "Diffraction The
ory of Laser Read-Out Systems for Optical VideoDis
ks, "Journal of Optical Society of America 69 4 (1
979) Alternatively, Motomiya (y.Honguh), "Diffraction analysis on optical disks" Optics 20 Vol.4, pp.210-215 (199)
It is calculated by the diffraction model disclosed in 1).

Next, the third embodiment will be described. The layer structure of the optical recording medium is the same as that of the second embodiment. That is, the medium is the inner protective layer 10 that is sequentially stacked from the transparent substrate 103.
4, a recording material layer 105, an outer protective layer 106, a reflective layer 107 made of a metal film, and a disc protective layer 108, and a tracking guide groove 109 is formed in the substrate 103. As the material of each layer, the substrate 103 is a polycarbonate resin, the inner protective layer 104 and the outer protective layer 106.
Is ZnS-SiO ₂ , and the recording material layer 105 is GeSbTe.
The phase change recording material, the reflective layer 107 is made of Al, and the disk protective layer 108 is made of an ultraviolet effect resin.
The ratio of the elements Ge, Sb and Te forming the recording material layer 105 is set to 2: 2: 5, for example.

In the third embodiment, the thickness of the inner protective layer 104 is set to 100 nm and the recording / recording material layer 105 is formed.
Is set to 22 nm, and the thickness of the reflective layer 107 is 1
It is set to 00 nm. Further, a mark is formed on the medium in which the track pitch is set to 1.0 micron and a groove having a groove width of 0.5 micron is formed. At this time, what happens to the reproduced signal when the thickness of the outer protective layer 106 is changed is calculated.

FIG. 16 shows the calculation result of the reproduction signal amplitude based on the recording medium of the third embodiment. Curves 401 and 402 in FIG. 16 show the calculation results for in-groove recording and on-land recording, respectively. From this figure, it can be seen that the characteristics of the signal amplitude differ between in-groove recording and on-land recording. Amplitude peaks appear at multiple locations, which is due to the thin film interference results. Since the material of the outer protective layer 106 has no light absorption, a constant amplitude pattern is periodically repeated as the film thickness increases.
This period corresponds to half the wavelength of light in the outer protective layer 106. It can be seen from the figure that in this constant amplitude pattern, in addition to the maximum peak, smaller peaks may appear, and in this embodiment, such a state appears. If the film thickness showing the maximum amplitude peak is selected first, the largest signal can be obtained with the thinnest film thickness. However, the second and third signals are taken into consideration in consideration of the recording characteristics, the manufacturability of the medium, and the advantages and disadvantages of other conditions. The film thickness corresponding to the peak or near the maximum peak may be set. Further, when a signal of a sufficiently large level can be obtained even if the maximum peak does not exist at a portion where the film thickness is close to 0, a film thickness that can obtain a large signal level may be set. Further, when a signal of a sufficiently large level can be obtained even if the maximum peak does not exist at a portion where the film thickness is close to 0, a film thickness that can obtain a large signal level may be set.

FIG. 17 is a plot of the signal modulation degree obtained based on the recording medium of the third embodiment.
Curves 501 and 502 show the calculation results for in-groove recording and on-land recording, respectively. From this figure, it can be seen that the modulation degree is small in the film thickness near the maximum peak, and this film thickness is not very advantageous in terms of reproduction characteristics.

Further, in consideration of reproducing the recording signal with two or more kinds of wavelengths, the range of the film thickness that can secure good characteristics is further limited. This occurs when it is desired to ensure the compatibility of the recording media in the devices that use different wavelengths. In such a case, a similar calculation is performed for each wavelength using the optical constants corresponding to each wavelength to obtain the signal modulation degree described above, and the film thickness at which the signal amplitude or the signal modulation degree can be sufficiently obtained at both wavelengths. It is necessary to define the range. Specifically, assuming that the film thickness that achieves the peak is 100%, calculation is performed for each wavelength in the range of 50% to 150% of this film thickness, and the film thickness corresponding to the portion where the calculation results overlap is calculated. Just set it. At this time, since the cycle of the modulation degree pattern varies greatly depending on the wavelength, it is more advantageous in terms of the characteristics of the recording medium to set the film thickness at the first peak. It is possible to set the film thickness to the second and subsequent peaks, but the film thickness becomes considerably thicker than usual, so there is a slight disadvantage in terms of effects on manufacturing and other characteristics. Will be needed.

FIGS. 18 and 19 show FIGS. 16 and 1.
7 shows the behavior near the peak of the signal amplitude in detail. In FIG. 18, curves 401 and 402 show calculation results in the case of in-groove recording and on-land recording. The peak in in-groove recording is around 22 nm in thickness of the outer protective layer 106, and the peak in on-land recording is around 2 nm in thickness of the outer protective layer 106. As can be seen, the peak with respect to the film thickness change of the outer protective layer 106 does not appear as a remarkable peak as the film thickness change of the recording material layer 105, but in each case, when the peak film thickness is 100%, Film thickness of 5
Within the range of 0% to 150%, a sufficiently large signal amplitude can be realized, and the film thickness within this range is effective.

In FIG. 19, curves 501 and 502.
Indicates the calculation results for in-groove recording and on-groove recording, respectively. The peak in in-groove recording is near the film thickness of 28 nm, and the peak in on-land recording is near the film thickness of 8 nm. As can be seen from the figure, the peak film thickness is 10 in each case.
If it is within the range of 50% to 150% of this film thickness when 0%, a sufficiently large signal modulation degree can be realized,
This film thickness is effective. From these results, the optimum range of the film thickness is determined, but in the third embodiment, in the case of in-groove recording, the thickness d of the outer protective layer 106 is set to 18 nm.
By setting the range of <d <35 nm, the characteristics of the recording medium are further improved. Further, in the case of on-land recording in which marks are formed between the grooves, the characteristics of the recording medium are further improved by setting the thickness d of the recording material layer 105 within the range of 1 nm <d <12 nm.

Further, the fourth embodiment will be described. Since the layer structure and the material of the optical recording medium are the same as those of the second or third embodiment, the description thereof will be omitted.
In the fourth embodiment, the outer protective layer 106 has a thickness of 20n.
The thickness of the recording / recording material layer 105 is set to 22 n.
m, and the thickness of the reflective layer 107 is set to 100 nm. Further, a mark is formed on a medium in which the track pitch is set to 1.0 micron and a groove having a groove width of 0.5 macron is formed. At this time, what happens to the reproduced signal when the thickness of the inner protective layer 104 is changed is calculated.

FIG. 20 shows the calculation result of the reproduction signal amplitude based on the recording medium of the fourth embodiment. Curves 401 and 402 in FIG. 20 show the calculation results for in-groove recording and on-land recording, respectively. From this figure, it can be seen that the characteristics of the signal amplitude differ between in-groove recording and on-land recording. Amplitude peaks appear at multiple locations, which is due to the thin film interference results. Since the difference in the refractive index between the inner protective layer 104 and the substrate material is smaller than that in the third embodiment of the present invention, this FIG. 20 and FIG.
17 and FIG. 17, the change is gentle,
The signal quality can be changed significantly depending on how the film thickness is set. In this embodiment as well, the amplitude pattern is repeated at a cycle corresponding to half the wavelength of the light in the inner protective layer 104 as in the third embodiment. Therefore, even if the film thickness is set in the vicinity of the peak having the maximum value, there is a degree of freedom that is an integral multiple of the period. In the case of the curve 401 in FIG. 20, it can be seen that a sufficiently large signal can be realized although the maximum peak is not around the film thickness of 0. The film thickness may be set here, or may be set near the peak near 180 nm.
It may be set in the vicinity of the second and third peaks in consideration of the recording characteristics, the manufacturability of the medium, and the advantages and disadvantages of other conditions.

FIG. 21 shows a plot of the signal modulation degree obtained based on the recording medium of the fourth embodiment. Curves 501 and 502 show the calculation results for in-groove recording and on-land recording, respectively. From these results, it is understood that in the case of in-groove recording, the thickness of the inner protective layer 104 may be set to around 180 nm or around 80 nm depending on whether the signal amplitude or the modulation degree is emphasized. Further, the peak in the case of on-land recording is preferably set to have a film thickness near 145 nm or around 115 nm. As can be seen from the figure, the modulation degree pattern is half the wavelength of light in the inner protective layer 104, that is, 191.
The period is 7 nm. Within the error of 1.4 of the period, that is, within the range of the peak film thickness ± 47.9 nm, a sufficiently large signal quality can be realized, and the film thickness within this range is effective. Further, considering the degree of freedom of an integral multiple of the period, it is preferable to set the film thicknesses of the peaks ± 47.9 and ± 191.7 × m (where m is an arbitrary integer) in nm. Signal quality can be realized.

In order to secure the reproducing characteristics at a plurality of wavelengths, the range of the protective layer film thickness is calculated for each wavelength in the same manner as described above in the same manner as in the description of the third embodiment. It may be set in the overlapping part of the range.

Next, a fifth embodiment will be described. According to the research conducted by the inventors, it has been found that the in-groove recording and the on-land recording have different reproduction signal modulation degrees before and after recording. The difference in modulation degree between the two is reflected in the difference in CNR. The CNR during on-land recording is high and the CNR during in-blue recording is low.

In consideration of the above, the fifth embodiment has been achieved. The recording medium 10 is also used in the fifth embodiment.
The layer structure of 0 is the same as that of FIG. Also in this example, the thicknesses of the inner protective layer 104 and the outer protective layer 106 formed of ZnSiO ₂ are fixed to 100 nm and 20 nm, respectively, and the thickness of the reflective layer 107 formed of Al is fixed to 100 nm, and GeSbTe is used. The reflectance inside and between the grooves when the thickness of the recording material layer 105 is changed as shown in FIG. Since the magnitude of the reflectance ratio before and after recording represents the magnitude of the reproduction signal modulation degree, the modulation degree during in-groove recording is the ratio between the pre-recording reflectance 301 and the in-groove recording reflectance 302 and the inter-group recording. The degree of modulation can be evaluated by the ratio of the pre-recording reflectance and the on-land recording reflectance 303. Figure 5
From this, it can be seen that there are separate layer structures in which the degree of modulation increases during in-groove recording and layers in which the degree of modulation increases during on-land recording. In FIG. 5, when the thickness of the recording material layer is 15 nm or less, the degree of modulation during on-land recording is large, and when it is 15 nm or more, the degree of modulation during in-groove recording is large. Therefore, by setting the thickness of the recording material layer 105 of this optical recording medium to 15 nm or more, the CNR is high during in-groove recording, and a reproduced signal of sufficient quality can be obtained. Although FIG. 5 shows the case where the thickness of only the recording material layer 105 is changed, the modulation degree can be adjusted by changing the thickness of the inner protective layer 104 or the outer protective layer 106. Can understand from.

Based on the data shown in FIG. 5, the recording material layer 1
FIG. 23 shows the result of measuring the CNR and the reproduction signal modulation degree by producing a recording medium with the thickness of No. 05 being about 25 nm and the other layers being as described above.

As can be seen from FIG. 23, the modulation degree during in-groove recording is higher than that during on-land recording, and the CNR during in-groove recording at this time is 53.5 dB. This value means that a reproduced signal of sufficient quality can be obtained. In the result of FIG. 23, the CNR during in-groove recording and the CNR during on-land recording have almost the same value. This is because the change in the groove shape of the optical recording medium appears as noise during reproduction and lowers the CNR. During in-groove reproduction, the light intensity applied to the groove end is larger than that during on-land reproduction, so that it is more likely to be affected by the change in groove shape, and noise appears more greatly. Therefore, if the optical recording medium has a small change in groove shape, the CNR during in-groove recording is further improved,
It should have been larger than the CNR at the time of on-land recording.

FIG. 22 shows changes in the degree of modulation with respect to changes in the thickness of the recording material layer 105 in on-land recording and in-groove recording. Curves 601 and 602 represent the recording medium of in-groove recording and on-land recording. The degree of modulation is shown, and the in-groove recording is performed by selectively using the range of the film thickness for the reflectance peak in the in-groove recording and the reflectance peak in the on-land recording with the film thickness corresponding to the intersection of the curves 601 and 602 as a reference. And the optimum film thickness can be set for on-land recording.

[0053]

As described above in detail, according to the optical recording medium of the present invention, the phase shift caused by the change in the complex reflectance due to the recording is larger by the synergistic effect with the phase shift caused by the groove, and thus the reproduced signal modulation is larger. The layer thicknesses are set so that the resulting media structure is efficient. As a result,
Even if the same recording material as the conventional one is used, a higher signal quality than the conventional one can be obtained, and the recording density and the reliability of information recording can be improved. This also applies to the protective layer.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system of an optical recording / reproducing apparatus.

FIG. 2 is a partially cutaway perspective view of an optical recording medium used in the apparatus of FIG. 1 according to an embodiment of the present invention.

3 is a diagram showing a cross-sectional structure of the optical recording medium of FIG.

FIG. 4 is a diagram showing a calculation result of a reproduction signal level when a recording medium has no groove.

FIG. 5 is a diagram showing a calculation result of a reproduction signal level when a recording medium has a groove.

FIG. 6 is a diagram showing film thickness dependence of signal amplitude.

FIG. 7 is a diagram showing a film thickness dependence of a modulation degree of a signal.

FIG. 8 is a diagram showing a calculation result of a reproduction signal amplitude in a recording medium according to a second embodiment of the present invention.

FIG. 9 is a diagram in which the signal modulation degree in the recording medium according to the second embodiment of the present invention is plotted.

10 is a diagram showing in detail the behavior near the peak of the signal amplitude in FIG.

FIG. 11 is a diagram showing in detail the behavior near the peak of the signal modulation degree in FIG. 9.

FIG. 12 is a diagram showing film thickness setting conditions for a recording material layer and an outer protective layer in in-groove recording.

FIG. 13 is a diagram showing film thickness setting conditions for a recording material layer and an inner protective layer in in-groove recording.

FIG. 14 is a diagram showing film thickness setting conditions for a recording material layer and an outer protective layer in on-land recording.

FIG. 15 is a diagram showing film thickness setting conditions for a recording material layer and an inner protective layer in on-land recording.

FIG. 16 is a diagram showing a calculation result of a reproduction signal amplitude in the recording medium according to the third embodiment of the present invention.

FIG. 17 is a diagram in which the signal modulation degree in the recording medium according to the third embodiment is plotted.

FIG. 18 is a diagram showing in detail the behavior near the peak of the signal amplitude in FIG. 16.

FIG. 19 is a diagram showing in detail the behavior near the peak of the modulation degree in FIG.

FIG. 20 is a diagram showing calculation results of reproduction signal amplitude in a recording medium according to the fourth embodiment of the present invention.

FIG. 21 is a diagram in which the signal modulation degree in the recording medium according to the fourth embodiment is plotted.

FIG. 22 is a diagram showing the degree of signal modulation in in-groove recording and on-land recording.

FIG. 23 shows C when the thickness of the recording material layer is 25 nm.
The figure which showed the value of NR and a reproduction signal modulation degree.

FIG. 24 is a schematic diagram showing the configuration of a phase change optical disc.

FIG. 25 is a diagram showing calculation results of reproduction signal amplitude by a flat multilayer film model.

FIG. 26 is a diagram showing a calculation result of a modulation degree by a flat multilayer film model.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Kobayashi 70 Yanagi-cho, Sachi-ku, Kawasaki-shi, Kanagawa, Toshiba Yanagimachi Co., Ltd. (72) Inventor Naoki Morishita 70 Yanagicho, Saiwai-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi factory

Claims (4)

[Claims] 1. A transparent substrate, an inner protective layer formed on the transparent substrate, a recording material layer formed on the inner protective layer, and an outer protective layer formed on the recording material layer, An optical recording comprising a reflection layer formed on the outer protective layer, at least a guide groove for guiding a light beam for recording information is provided in the reflection layer, and the information is recorded in the guide groove. An optical recording medium, wherein the ratio of the thickness of the recording material layer to the thickness of the outer protective layer is set in the range of 0.52 or more and 0.95 or less. 2. A transparent substrate, an inner protective layer formed on the transparent substrate, a recording material layer formed on the inner protective layer, and an outer protective layer formed on the recording material layer, An optical recording comprising a reflection layer formed on the outer protective layer, at least a guide groove for guiding a light beam for recording information is provided in the reflection layer, and the information is recorded in the guide groove. An optical recording medium, wherein the ratio of the thickness of the recording material layer to the thickness of the inner protective layer is set in the range of 0.053 or more and 0.098 or less. 3. A transparent substrate, an inner protective layer formed on the transparent substrate, a recording material layer formed on the inner protective layer, and an outer protective layer formed on the recording material layer. An optical recording comprising a reflection layer formed on the outer protective layer, at which a guide groove for proposing a light beam for recording information is provided, and the information is recorded between the guide grooves. An optical recording medium, wherein the ratio of the thickness of the recording material layer to the thickness of the outer protective layer is set in the range of 0.32 or more and 0.6 or less. 4. A transparent substrate, an inner protective layer formed on the transparent substrate, a recording material layer formed on the inner protective layer, and an outer protective layer formed on the recording material layer, An optical recording comprising a reflection layer formed on the outer protective layer, at least a guide groove for guiding a light beam for recording information is provided in the reflection layer, and the information is recorded between the guide grooves. An optical recording medium, wherein the ratio of the thickness of the recording material layer to the thickness of the inner protective layer is set in the range of 0.033 or more and 0.063 or less.