JPH10188346A - Optical information recording medium and recording/ reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recording medium capable of performing a recording and a reproducing for a stable mark length. SOLUTION: This recording medium is formed by laminating a third protective layer 11, a first protective layer 12 which has the refractive index and the attenuation coefficient that are different from the ones in the layer 11, a recording layer 13 in which the atomic arrangement is changed by a recording light beam irradiation and the optical characteristic is also changed, a second protective layer 14 and a reflector layer 15 on a transparent substrate 10. The film thickens of each layer and the refractive index and the attenuation coefficient of the layer 11 are selected so that the reflectivity is increased more than 10% by the irradiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of recording and erasing information by causing a recording layer to change its optical characteristics due to a change in atomic arrangement by irradiation with a laser beam, an electron beam or the like. The present invention relates to an information recording medium and a recording / reproducing method for recording and reproducing information by detecting a change in optical characteristics.

[0002]

2. Description of the Related Art A recordable and erasable information recording medium is, for example, as shown in FIG.
It has a structure composed of a recording layer 3, a second protective layer 4, and a reflective layer 5. The substrate 1 is made of glass or a plastic material (for example, polymethyl methacrylate resin or polycarbonate resin), and the first and second protective layers are
It is made of ZnS, SiO ₂ , Al ₂ O ₃ , SiN or a mixture thereof. The recording layer 3 is made of chalcogenite such as GeSbTe.
It can be formed by a deposition method such as sputtering. The reflection layer 4 is made of Al, Au, or an alloy containing these as a base material and containing Ti, Mo, Zr, Cr, or the like.

Using such an information recording medium, information can be recorded / erased in the following manner, for example. First, the information recording medium is heated by irradiating the entire surface thereof with a light beam to bring the recording layer into a state of high crystallinity (a state in which atoms are relatively correctly arranged, hereinafter referred to as a crystalline state). next,
For writing (recording) information, the recording layer is irradiated with short and strong pulsed light, heated and melted, and then rapidly cooled. Then, the pulsed light irradiating part is in a state where crystallinity is reduced (a state in which the atomic arrangement is disordered, hereinafter, referred to as amorphous).

[0004] Since the structure of the atomic arrangement is different between the crystalline state and the amorphous state, the optical properties (transmittance and reflectivity) change, whereby information can be recorded. The information thus written can be erased by irradiating the recording section with long and weak pulsed light and heating and gradually cooling it below the melting point. This is because the recording section returns to the original crystalline state.

[0005] In addition, by using a laser power (recording power) in which a strong and short pulse is superimposed on a weak continuous laser power (bias power) as shown in FIG. The above state can be realized by so-called overwriting, in which a new recording portion is simultaneously formed while erasing (crystallizing) the state).

As described above, in an actual recording medium, the change in the reflectance between crystalline and amorphous is used as a signal. Therefore, the thickness of each of these layers is determined by the protective layer / recording layer and the protective layer / reflective layer. It is designed in consideration of the optical interference effect of the interface. Therefore, there is an optimum film thickness that allows a large change in optical reflectance depending on the optical constant of the material used for the recording medium.

For example, GeSbTe is used as a recording layer material, Al is used as a reflective layer, and ZnS is used as a protective layer.
FIG. 12 shows the calculated reflectance of the recorded state (amorphous) and the unrecorded state (crystal) with respect to the thickness of the second protective layer when SiO ₂ is used. From the results shown in FIG. 12, the film thickness at which the maximum change in reflectance is obtained is 10 nm
The thickness is preferably around 20 nm and 140 nm to 150 nm. When the thickness is 10 nm to 20 nm, the recording is performed in such a direction that the reflectance decreases by recording. When the wavelength is 140 nm to 150 nm, recording is performed in a direction in which the reflectance increases by recording.

However, optically, in such two film thickness ranges, there is a film thickness range in which the change in reflectivity can be large during recording. However, when the film thickness of the protective layer becomes large, the recording layer moves from the recording layer to the reflection layer. It is known that the flow of heat is blocked, sufficient quenching cannot be controlled by modulation of the laser power, and the recording characteristics deteriorate (for example, T.OHT).
A et al. JJAP. VOL 128 (198
9) SUP ULMENT28-3, pp123-1
28).

Therefore, conventionally, GeSbTe has been used as a recording layer.
When a recording material such as described above is used, the thickness of the second protective layer is 10 nm to 20 nm, and recording is generally performed in a direction in which the reflectance decreases by recording.

As a method of recording digital data using such an optical disk, a recording mark having the same shape is formed and information is obtained from a space between the mark centers, and a recording position is obtained by changing the length of the recording mark. Mark length recording is known, in which information is recorded and information is obtained from the length of the recorded mark. FIG. 13 shows an example of the mark position recording (A) and the mark length recording (B).

On the other hand, in the past, recording was performed only on either the groove or the land among the groove grooves formed on the optical disk, but recently, recording is performed on both the land and the groove to reduce the capacity. A land / groove recording method of doubling is also proposed. For example, in the literature (N. Miyagawa et al., JJ Ap.
pl. Phys. Vol. 32 (1993) pp532
4-5328), in a phase change optical disk, by setting the groove depth to an appropriate depth (λ / 6),
It is known that crosstalk from adjacent tracks can be improved. FIG. 14 shows an example of recording on both the land portion and the groove portion.

[0012]

In the conventional film thickness configuration suitable for mark position recording, the recording area (amorphized area) on the disk is smaller than that of other unrecorded areas (crystalline areas). not big. On the other hand, when performing mark length recording, the recording area on the disk is larger than when recording mark position. For example, if the diameter of the recording cook is 0.78
μm, the area ratio of the recording area to the unrecorded area on the disc in the mark position recording and the mark length recording having the same density is 26% in the case of the mark position recording, and is 44% in the case of the mark length recording. %.

When such a recording method is used for a recording medium on which recording is performed in a direction in which the reflectance decreases by conventional recording, the larger the area ratio of the recording area, the greater the average reflectance during reproduction compared to before recording. descend. In the case of mark position recording, which has been used in the past, a certain amount of reflected light can be obtained even if recording is performed in the direction where the reflectance decreases due to recording, and signals can be reproduced by focusing and tracking in a normal optical disk drive. Met.

However, in order to further increase the recording density, in the case where the recording marks are packed in the recording of the mark position or when the reproduction is performed, in the case of the disc whose reflectivity is lowered by such recording, the recording is performed with respect to the entire area. Since the area of the region is increased, the average reflectance is reduced to 60% or less of the conventional case.

For example, when the film thickness at the position A in FIG. 12 is used, the average reflectance is less than 10%. Generally, in order to perform focusing and tracking stably, a reflectance of at least about 10% is required.
In the configuration having the second protective layer having such a film thickness, there is a problem that the amount of reflected light required for focusing and tracking cannot be obtained. In order to increase the reflectance, it is necessary to increase the thickness of the protective layer. In this case, the amount of change in the reflectance cannot be maximized.

Further, when recording is performed on both the land portion and the groove portion as described above, diffraction light from the groove portion as viewed from the land portion or diffraction light from the land portion as viewed from the groove portion cannot be obtained. Makes focusing and tracking more unstable.

In the case where the reflectance is reduced by the conventional recording, if there is no escape of light from the back surface of the reflection layer, the absorptance of the recorded portion is large and the absorptance of the unrecorded portion is small. . For this reason, when the new mark is overwritten on the recorded portion and when the new mark is overwritten on the unrecorded portion, the rate of temperature rise during recording differs due to the difference in the absorptivity.

Furthermore, since the unrecorded portion is crystalline, it requires latent heat to melt it, and when heated with the same laser power, the temperature rises further differently. For this reason,
The size of the recording mark formed by melting and quenching will be different. Therefore, when a recording method having information at an edge portion of a recording mark is used, there is a problem that an edge position fluctuates depending on a place.

The present invention has been made under such circumstances,
It is an object of the present invention to provide an information recording medium capable of obtaining a sufficient amount of reflected light and performing stable focusing and tracking, thereby enabling recording and reproduction of a stable mark length.

[0020]

In order to solve the above-mentioned problems, the present invention (claim 1) provides a third protective layer and a refractive index and extinction different from those of the third protective layer on a transparent substrate. A first protective layer having a coefficient, a recording layer in which an atomic arrangement is changed by irradiation of a recording light beam, and optical characteristics can be changed,
A second protective layer and a reflective layer are laminated, and the film thickness of each layer and the refractive index of the third protective layer are adjusted so that the reflectance increases by 10% or more by the recording light beam irradiation. An optical information recording medium characterized in that an extinction coefficient is selected.

The present invention (Claim 2) is characterized in that, in the optical information recording medium (Claim 1), the refractive index n and the extinction coefficient k of the third protective layer satisfy the following equations. And n> the refractive index of the first protective layer, and 0 <k <0.5 or n <the refractive index of the first protective layer, and 0 <k The present invention (claim 3) provides the above-described optical information recording. In the medium (Claim 1), the third protective layer is formed of Si and G.
e, and a mixture or alloy of a semiconductor selected from the group consisting of Au and a metal selected from the group consisting of Au, Cu, and Ag, and having a thickness of 200 nm or less.

According to the present invention (claim 4), in the above-mentioned optical information recording medium (claim 1), the thickness of the recording layer is 3
The thickness is 5 nm or less. The present invention (claim 5) provides the optical information recording medium described above (claim 1), wherein the recording layer is made of GeSbTe, has a thickness of 35 nm or less, and the first and second protective layers are ZnS:
The first protective layer is made of SiO ₂ and has a thickness of 60 nm to 150 n.
m or a film thickness of 230 nm to 320 nm, and the second protective layer has a thickness of 10 nm to 140 nm or 180 nm to
The reflective layer has a thickness of 310 nm, the reflective layer is made of an Al alloy, and has a thickness of 50 nm or more.

The present invention (claim 6) provides a third protective layer on a transparent substrate, a first protective layer having a different refractive index and extinction coefficient from the third protective layer, and a recording light. The beam irradiation causes a change in the atomic arrangement, and a recording layer whose optical characteristics can be changed, a second protective layer, and a reflective layer are laminated. By irradiating the recording layer with light having a recording wavelength, By using a disk-shaped optical information recording medium having a groove and a land shape configured to increase the reflectance, by forming a recording mark having a length and an interval according to the information on both the land and the groove. A recording method is provided, wherein the recording is performed on the optical information recording medium.

The optical information recording medium of the present invention is the same as the conventional optical information recording medium in the layer configuration (substrate / first protective layer / recording layer / second protective layer / reflective layer). And a third protective layer inserted between the protective layers. With such a configuration, in addition to the interference at each layer interface,
Utilizing interference from the third protective layer / first protective layer interface,
Instead of a film thickness configuration that reduces the reflectance by conventional recording,
It is possible to adopt a film thickness configuration in which the reflectance increases by recording.

By adopting such a film thickness configuration, even if mark length recording is performed, the reflectance of the recording portion increases, a sufficient amount of reflected light can be obtained, and stable focusing and tracking can be performed. Note that the increase in reflectance due to recording must be 10% or more. It is also desirable that the reflectance of the unrecorded portion is 10% or more.

Further, since the absorptance of the recorded portion is small and the absorptance of the unrecorded portion is large, the temperature in the case where a new mark is overwritten on the recorded portion and the case where the new mark is overwritten in the unrecorded portion is different. By correcting the rising of the recording marks, recording marks of the same size can be formed. For this reason, it is possible to perform recording while suppressing edge fluctuation.

Further, by using a mixture or alloy of a semiconductor such as Si and Ge and a metal such as Au, Cu and Ag as the third protective layer, the optical constant is controlled by changing the mixing ratio of the semiconductor and the metal. This makes it easier to design the third protective layer.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of the information recording medium according to the first embodiment of the present invention. As shown in FIG. 1, in the recording medium, a third protective layer 11, a first protective layer 12, a recording layer 13, a second protective layer 14, and a reflective layer 15 are sequentially laminated on a substrate 10. Having a structure.

The substrate 10 is made of glass or a plastic material (for example, polymethyl methacrylate resin, polycarbonate resin, etc.), and the third protective layer 11 is made of Si,
It is composed of a mixture of a semiconductor such as Ge and a metal such as Au, Cu and Ag. The first protective layer 12 and the second protective layer 14 are made of ZnS, SiO ₂ , Al ₂ O ₃ , SiN, or a mixture thereof.

The recording layer 13 is made of chalcogenite such as GeSbTe, and these can be formed by a vapor deposition method such as vacuum evaporation and sputtering. The reflection layer 14 is made of a metal such as Al or Au, or an alloy containing these metals as a base material and containing Ti, Mo, Zr, Cr, or the like. The reflective layer 14 has a role of effectively radiating heat generated in the recording layer in addition to the purpose of optical reflection, and therefore, the thickness thereof is desirably 50 nm or more.

FIG. 2 shows the case where the film thickness is simultaneously changed while changing the optical constants (refractive index n and extinction coefficient k) of the third protective layer 11 of the recording medium having such a layer structure. FIG. 9 is a characteristic diagram illustrating a maximum change amount of a reflectance between a recorded portion and an unrecorded portion. At this time, a ZnS: SiO ₂ layer having a film thickness of 110 nm and a refractive index of 2 was used as the first protective layer, a GeSbTe layer having a film thickness of 10 nm as the recording layer, and a film thickness of 230 nm as the second protective layer. 2 ZnS: Si
An Al layer having a thickness of 100 nm was used as the O ₂ layer and the reflection layer.

Since the light incident from the substrate side causes multiple reflections at the interface between the layers, the manner in which the reflectance changes between the recorded portion and the unrecorded portion depends on the change in the refractive index and the extinction coefficient of the third protective layer. different. In order to obtain the effect of the present invention, an increase in reflectance of 10% or more is required. Therefore, the refractive index of the third protective layer and the refractive index of the third protective layer are adjusted so as to achieve such an increase in reflectance. What is necessary is just to select the decay coefficient.

That is, as shown in FIG. 2, when the refractive index n and the extinction coefficient k of the third protective layer are n> the refractive index of the first protective layer (= 2), and 0 <k <0. When 5, or n <the refractive index (= 2) of the first protective layer, and 0 <k, it is possible to adopt a layer configuration in which recording increases the reflectance by about 10% or more by recording. Therefore, stable focusing and tracking can be performed without a decrease in reflectance due to recording.

FIG. 3 shows an example of a recording medium having this layer structure, in which the third protective layer has a refractive index of 3.5 and an extinction coefficient of 0.2.
15, the reflectance of the recorded portion and the unrecorded portion when the film thickness of the first protective layer was changed to 75 nm, and the amount of change in the reflectance. For the recording layer, a film thickness of 10 nm
The thickness of the GeSbTe layer and the second protective layer is 2
A 30 nm ZnS: SiO ₂ layer, and a 100 nm thick Al layer were used as the reflective layer.

In the case of FIG. 3, the thickness of the first protective layer is 70 n.
When recording is performed in the range of m to 165 nm and 250 to 330 nm, the reflectance is increased. In this configuration,
In particular, the thickness of the first protective layer is set to 120 nm or 295 n.
When m is set, the amount of change in reflectance is 19%, which is the maximum.
At this time, the reflectance of the unrecorded portion is 14%, and the reflectance is greatly increased by recording. Therefore, stable focusing and tracking can be performed, and the maximum change in reflectance can be obtained.

FIG. 4 shows that the refractive index of the third protective layer is 3.5,
The change in reflectance with respect to the thickness of the third protective layer when the extinction coefficient is set to 0.15 is similarly shown. As the first protective layer, a 110 nm-thick ZnS: SiO ₂ film is used.
A 10 nm-thick GeSbTe layer as a layer and a recording layer;
As the second protective layer, a 230 nm-thick ZnS: Si
An Al layer having a thickness of 100 nm was used as the O ₂ layer and the reflection layer. As shown in FIG. 4, the thickness of the third protective layer is 40 n.
It can be seen that recording in the range of m to 95 nm and 140 to 195 nm increases the reflectance.

In such a configuration, particularly when the thickness of the first protective layer is 75 nm and 175 nm, the amount of change in reflectance becomes the maximum. At this time, the reflectance of the unrecorded portion is 14%, and the reflectance is greatly increased by recording.
Therefore, stable focusing and tracking can be performed, and the maximum reflectance change amount can be obtained.

FIG. 5 shows the reflectance and the amount of change in the reflectance of the recorded portion and the unrecorded portion when the thickness of the second protective layer is changed. The configuration is such that the reflectivity increases by recording in almost the entire area with respect to the thickness of the second protective layer. The thickness of the second protective layer is 20 nm to 150 nm, 190 to 32
In the range of 0 nm, the reflectance increases by recording. When the thickness of the second protective layer is 80 nm or 250 nm, a maximum reflectance change of about 20% is obtained.

As described above, in the recording medium of the present invention, the second
Even if the thickness of the protective layer is as thin as 40 nm, a sufficient amount of change in reflectance can be obtained, so that rapid cooling can be controlled by modulating the laser power, which is a problem in the conventional configuration.

FIG. 6 shows the reflectance and the amount of change in the reflectance of the recorded portion and the unrecorded portion when the thickness of the recording layer is changed. From this figure, it can be seen that the reflectance change can be obtained if the thickness of the recording layer is 50 nm or less, but it is particularly desirable that the thickness be 35 nm or less.

FIG. 7 shows another example of a recording medium in which the refractive index of the third protective layer is 0.2, the extinction coefficient is 3, and the film thickness is 20 n.
m represents the reflectance of the recorded portion and the unrecorded portion and the amount of change in the reflectance when the film thickness of the first protective layer (ZnS: SiO ₂ ) is changed. At this time, a GeSbTe layer with a thickness of 10 nm was used as the recording layer, a ZnS: SiO ₂ layer with a thickness of 230 nm as the second protective layer, and an Al layer with a thickness of 200 nm as the reflective layer. Since the light incident from the substrate side causes multiple reflection at the interface of each layer, it can be seen that the manner of change in the reflectance differs depending on the film thickness.

As shown in FIG. 7, the protective layer has a thickness of 60 nm.
In the range of 140 to 140 nm and 220 to 320 nm, the reflectance is increased by recording. In this configuration,
Particularly, the thickness of the first protective layer is set to 110 nm and 280 nm.
In this case, the reflectance change amount is 22%, which is the maximum. At this time, the reflectance of the unrecorded portion is 20%, and the reflectance is greatly increased by recording. Therefore, stable focusing,
Tracking becomes possible, and the maximum amount of change in reflectance can be obtained.

FIG. 8 shows that the refractive index of the third protective layer is 0.2,
The change in reflectance with respect to the thickness of the third protective layer when the extinction coefficient is set to 3 is similarly shown. From this figure, it can be seen that, when the film thickness is 80 nm or less, the reflectivity is increased by recording. Further, the maximum change in reflectance is obtained at 20 nm, but when it exceeds 40 nm, the change becomes 50% or less of the maximum change. The third is that the reflectance of the unrecorded portion is 10% or more, stable focusing and tracking are possible, and a large change in reflectance is obtained.
Is limited to 40 nm or less.

FIG. 9 shows that the refractive index of the third protective layer is 0.2,
It shows the reflectance of the recorded portion and the unrecorded portion when the thickness of the second protective layer is changed when the extinction coefficient is 3, and the amount of change in the reflectance. With respect to the thickness of the third protective layer, the reflectance is increased by recording in almost all areas. The film thickness is 0 nm to 140 nm, 180 to 320 nm
In the range, the reflectance increases by recording. As in FIG. 6, the change in the amount of change in the reflectance with respect to the change in the film thickness of the second protective layer is small, so that the film thickness can be controlled.

As described above, the calculation result at the wavelength of 690 nm is shown, but this film thickness changes according to the wavelength used for recording.
The optimum film thickness also changes depending on the groove shape provided for tracking the light beam on the substrate, but in any case, the film thickness of each layer is adjusted so that the reflectance increases by 10% or more by recording. Further, if the reflectance of the unrecorded portion is set to 10% or more, there is no departure from the gist of the present invention.

The third protective layer having a refractive index and an extinction coefficient in the above ranges is a mixture of a semiconductor having a high refractive index such as Si and Ge and a metal such as Au, Cu and Ag. Can be obtained. For example, an intermediate refractive index and extinction coefficient between Si and Au can be obtained by using two targets of Si and Au and changing the film formation rate of both targets by a vacuum sputtering method.

Next, a recording / reproducing apparatus using such a recording medium will be described. FIG. 15 shows a recording / reproducing apparatus using the recording medium of the present invention. Recording medium 21 described above
Is fixed to a spindle motor 22 and is rotatable at a predetermined rotation speed. An optical system 23 for condensing the laser light over the substrate of the medium is disposed above the recording medium. The light emitted from the semiconductor laser 29 is converted into parallel light by the collimator lens 31a,
The light is focused on the medium 21 by the objective lens 26 through b.

The reflected light from the medium 21 is split by the beam splitter 31b, passes through the detection lens 30a, enters the light receiver 28, and becomes a detection signal. On the other hand, this signal is also supplied to a servo system 35 for supplying a current to a drive coil 25 for driving the objective lens 26. In this way, it is possible to keep the distance to the medium constant (focusing) and to form an image of the converged spot on the recording medium 21. Also,
The diffracted light from the groove provided in advance on the medium 21 is received by the photodetector 28, and the objective lens 2
6 in the track direction, the recording medium 21 is controlled.
The upper groove can be traced.

The recording medium 21 has a diameter of 120 m.
The refractive index is 3.4, the extinction coefficient is 0.12, and the film thickness is 73n on a grooved polycarbonate disk disk having a thickness of 0.6 mm and a thickness of 0.6 mm by controlling the film formation rates of Si and Au.
m third protective layer, 110 nm thick ZnS: SiO ₂
First protective layer made of GeSbTe having a thickness of 11 nm
(Composition: atomic ratio 2: 2: 5) recording layer, Zn
S: A _second protective layer made of SiO ₂ and a reflective layer made of Al having a thickness of 200 nm were sequentially formed by vacuum sputtering.

This recording medium was crystallized in advance using an argon laser, set in a recording / reproducing apparatus shown in FIG. 15, and a signal was recorded by rotating a spindle motor. The rotation speed is 3000 rpm. The recording signal was such that the shortest mark was 1.6 μm (1,
7) RLL (Run Length Limited) code random data (marks of different lengths) was used. Focusing and tracking were stable before and after recording. At this time, the reflectance of the unrecorded portion was 13%, and the reflectance of the recorded portion was 35%.

Next, a circuit for generating digital data from a detection signal will be described. The signal from the detector is first subjected to current / voltage conversion. It is then amplified to the voltage required for digitization. Thereafter, only the AC component is detected in the preprocessing circuit. This signal is sent to a comparator, compared with the slice level, and becomes digital data. The slice level is detected by smoothing this signal, and feedback is applied so as to always slice approximately the center of the signal amplitude.

FIG. 16 shows the reproduced signal at this time. The midpoint of the signal amplitude is used as the slice level of the digital data, and the digital data is created while comparing the signal with the signal. The digital signal actually reproduced and the (1,7) R used for recording
When the random data of the LL code were compared, they completely matched, and it was confirmed that recording and reproduction of this code was possible.

[0053]

As described above, according to the optical information recording medium of the present invention, the reflectance is increased by irradiating the recording layer with light having the recording wavelength.
Since the third protective layer having a predetermined refractive index and extinction coefficient is disposed between the substrate and the first protective layer, a sufficient amount of reflected light is obtained, and stable focusing and tracking are possible. It became. Further, recording and reproduction of a stable mark length became possible.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a recording medium of the present invention.

FIG. 2 is a characteristic diagram showing a change in a maximum reflectance change amount depending on a refractive index and an extinction coefficient of a third protective layer.

FIG. 3 is a characteristic diagram showing the reflectance and the amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystalline) with respect to the thickness of a first protective layer.

FIG. 4 is a characteristic diagram showing a reflectance and an amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to a thickness of a third protective layer.

FIG. 5 is a characteristic diagram showing a reflectance and an amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to a film thickness of a second protective layer.

FIG. 6 is a characteristic diagram showing the reflectance and the amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to the thickness of a recording layer.

FIG. 7 is a characteristic diagram showing the reflectance and the amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to the thickness of a first protective layer.

FIG. 8 is a characteristic diagram showing the reflectance and the amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to the thickness of a third protective layer.

FIG. 9 is a characteristic diagram showing a reflectance and an amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to a film thickness of a second protective layer.

FIG. 10 is a sectional view showing a conventional optical information recording medium.

FIG. 11 is a view showing the principle of overwriting.

FIG. 12 shows a configuration of a conventional optical information recording medium.
FIG. 9 is a characteristic diagram showing the reflectance and the amount of change in reflectance in a recorded state (amorphous) and an unrecorded state (crystal) with respect to the thickness of the second protective layer.

FIG. 13 is a diagram showing an example of mark position recording and mark length recording.

FIG. 14 is a diagram showing a state recorded on a land portion and a groove portion.

FIG. 15 is a diagram showing an example of a recording / reproducing device using the optical information recording medium of the present invention.

FIG. 16 is a diagram showing an example of a slice level used for discrimination between a reproduced waveform and digital data.

[Explanation of symbols]

 Reference numerals 1, 10 Substrate 2, 12 First protective layer 3, 13 Recording layer 4, 14 Second protective layer 5, 15 Reflective layer 11 Third protective layer

Claims (6)

[Claims] 1. A third protective layer on a transparent substrate, a first protective layer having a different refractive index and extinction coefficient from the third protective layer, and a change in atomic arrangement caused by irradiation of a recording light beam. Occurs, and a recording layer whose optical characteristics can be changed, a second protective layer, and a reflective layer are laminated. By irradiating the recording layer with a recording light beam, the reflectance increases by 10% or more. The optical information recording medium, wherein the thickness of each layer and the refractive index and extinction coefficient of the third protective layer are selected as described above. 2. The optical information recording medium according to claim 1, wherein the refractive index n and the extinction coefficient k of the third protective layer satisfy the following expression. n> refractive index of the first protective layer, and 0 <k <0.5 or n <refractive index of the first protective layer, and 0 <k 3. The semiconductor device according to claim 1, wherein said third protective layer is made of a semiconductor selected from the group consisting of Si and Ge, and Au, Cu and Ag.
The information recording medium according to claim 1, comprising a mixture or an alloy with a metal selected from the group consisting of: and having a thickness of 200 nm or less. 4. The optical information recording medium according to claim 1, wherein said recording layer has a thickness of 35 nm or less. 5. The recording layer according to claim 3, wherein the recording layer is made of GeSbTe.
The first and second protective layers are made of ZnS: SiO ₂ , and the first protective layer is
The second protective layer has a thickness of 10 to 140 nm or 1 to 150 nm or 230 to 320 nm.
The reflective layer has a thickness of 80 nm to 310 nm;
2. The optical information recording medium according to claim 1, wherein the optical information recording medium is made of an alloy and has a thickness of 50 nm or more. 6. A third protective layer on a transparent substrate, a first protective layer having a different refractive index and extinction coefficient from the third protective layer, and a change in atomic arrangement caused by irradiation of a recording light beam. Is generated, a recording layer whose optical characteristics can be changed, a second protective layer, and a reflective layer are laminated, and the reflectance is increased by irradiating the recording layer with light having a recording wavelength. Done,
Using a disc-shaped optical information recording medium having a groove and a land shape, recording on the optical information recording medium is performed by forming recording marks having a length and an interval corresponding to information on both the land and the groove. A recording method characterized in that: