JPH0883426A - Optical information recording method and medium therefor - Google Patents

Abstract

PURPOSE: To obtain a satisfactory signal amplitude by realizing a stable tracking characteristic. CONSTITUTION: When the depth of a groove 12 is in the range of (1) with respect to the wavelength λ of a reflected laser light reproducing information of the inside of a recording thin film 15 and a difference Δϕ1 ,2 between the phase ϕ1 of a reflected light 18 from an unrecorded part and the phase ϕ2 of a reflected light from a recording part is in the range of (2), information is recorded in a groove part 13 and when the Δϕ1 ,2 is in the range of (3), information is recorded in a land part 14. Here, (1) is (1/16 to 1/8)λ+0.5Nλ, where N is an integer equal to or larger than zero, (2) is (0.3 to 0.5)π+(2πn-1)π, where n is an integer and (3) is (0.5 to 0.7)π+2nπ, where n is an integer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium and an optical information recording method capable of recording / reproducing information with high density by using a laser beam, and more particularly to a rewritable optical disk and its information recording. Regarding the method.

[0002]

2. Description of the Related Art As an optical disc capable of recording / reproducing signals and erasing signals, a phase change type optical disc using a chalcogenide as a recording thin film material is known. Generally, a signal is recorded by setting the recording thin film material in a crystalline state to an unrecorded state, irradiating a laser beam, and melting and quenching the recording thin film material to an amorphous state. On the other hand, in the case of erasing a signal, the recording thin film material is heated to a crystalline state by irradiating a laser beam having a power lower than that at the time of recording.

Recording thin film materials include, for example, Te and I
It is general to use a material containing n, Sb, Se or the like as a main component, which undergoes a phase change between amorphous and crystalline, or a substance which causes a reversible phase change between two different crystal structures.

One of the merits of phase change recording is that an information signal can be overwritten by using only a single laser beam as a recording means. That is, a laser output is modulated between two levels, a recording level and an erasing level, according to an information signal and irradiated onto a recorded information track to record a new signal while erasing an existing information signal. (JP-A-56-145530).

Further, in order to improve the recording density, it has been proposed to determine the structure of the disc so that a phase difference occurs between the unrecorded portion and the recorded portion with respect to the wavelength λ of the reproducing laser light. (JP-A-3-41638, JP-A-3-157830). When the recording portion (recording mark) is read by the change in reflectance, a large reproduction signal cannot be obtained unless the area of the recording state is sufficiently larger than the size of the laser beam used for reproduction. Because the light intensity of the reproducing beam generally has a Gaussian distribution and spreads outside the phase-changed recording mark, the amount of reflected light depends on the reflectance of the recording mark and the reflectance of the surrounding unrecorded area. This is because it is proportional to the value obtained by weighting each area and the light intensity distribution and averaging them. On the other hand, in the case of the phase change reproducing structure, it is utilized that the phases from the recorded portion and the unrecorded portion are different and they interfere with each other to change the reflected light amount. Therefore, when the phase difference between the reflected light in the recorded portion and the unrecorded portion is (1 + 2n) π (n is an integer), the change in the reflected light amount is the largest, and it is desirable to be close to this value. In the intensity distribution of the reproducing beam, the effect of interference is greatest when the intensity of incident light on the recording portion is equal to the intensity of incident light on the surrounding unrecorded portion, and thus the intensity change of reflected light is large. That is, when the recording mark is smaller than the size of the reproduction beam, the reproduction signal can be increased. From the above, when reproducing with the same reproducing beam, a larger signal can be obtained with a recording mark having a smaller area in the phase change reproduction than in the reflectance change reproduction.

[0006]

Generally, a recordable optical disc has a groove for tracking. In this case, the push-pull method is generally used to obtain the tracking error signal. Then, in order to realize stable tracking characteristics, it is common to adopt a groove depth λ / 8 at which the tracking error signal becomes maximum.

However, in the case of the above-mentioned optical disk having the phase change reproduction structure, since the phase difference between the recording mark and the reflected light at the peripheral portion is used for reproduction, the tracking error signal is not reproduced as the reproduction signal unless special consideration is given. It is expected to be strongly affected. That is, a tracking error signal is different between the unrecorded state and the recorded state, and stable tracking characteristics cannot be obtained. In the prior art, no consideration has been given to this point.

In order to solve the above problems in the prior art, it is an object of the present invention to provide an optical information recording method and an optical information recording medium which can obtain stable tracking characteristics.

[0009]

In order to achieve the above object, the first structure of the optical information recording method according to the present invention comprises a substrate having a groove for tracking and a laser beam formed on the substrate. An optical information recording method for performing recording by irradiating a laser beam having a predetermined wavelength on an optical information recording medium including at least a recording thin film capable of causing a phase change by irradiation and shifting to a state having different optical constants, Wavelength λ of laser light for reproducing information recorded on the recording thin film
On the other hand, the optical groove depth of the substrate is in the range of the above (Formula 1), and the reflectances in the unrecorded area and the recorded mark area of the optical information recording medium are substantially equal to each other. If the difference Δφ _1,2 between the phase φ ₁ of the reflected light from the unrecorded area and the phase φ ₂ of the reflected light from the recording mark area is within the range of (Equation 2) above, recording is performed in the groove. And

A second structure of the optical information recording method according to the present invention has a substrate having a tracking groove and a substrate formed on the substrate, which causes a phase change by irradiation of laser light and has different optical constants. A method for recording information on an optical information recording medium having at least a recording thin film capable of transitioning to a state by irradiating a laser beam having a predetermined wavelength, wherein the laser reproduces information recorded on the recording thin film. With respect to the wavelength λ of light, the optical groove depth of the substrate is within the range of (Formula 1), and the reflectance in the unrecorded area and the recorded mark area of the optical information recording medium is substantially equal, If the difference Δφ _1,2 between the phase φ ₁ of the reflected light from the unrecorded area of the information recording medium and the phase φ ₂ of the reflected light from the recording mark area is within the range of (Equation 3) above, the land portion between the grooves To record To.

The first structure of the optical information recording medium according to the present invention is an optical information recording medium used in an apparatus for recording / reproducing information by irradiating a laser beam having a predetermined wavelength, and has a groove for tracking. A laser for reproducing information formed on the recording thin film, and at least a recording thin film formed on the substrate and capable of undergoing a phase change by irradiation with laser light and shifting to a state having different optical constants. With respect to the wavelength λ of light, the optical groove depth of the substrate is in the range of (Formula 1), and the reflectance in the unrecorded area and the recorded mark area of the optical information recording medium is substantially equal to each other. The difference Δφ _1,2 between the phase φ ₁ of the reflected light from the recording area and the phase φ ₂ of the reflected light from the recording mark area is in the range of the above (Formula 2).

The second structure of the optical information recording medium according to the present invention is an optical information recording medium used in an apparatus for recording / reproducing information by irradiating a laser beam having a predetermined wavelength, and has a groove for tracking. A laser for reproducing information formed on the recording thin film, and at least a recording thin film formed on the substrate and capable of undergoing a phase change by irradiation with laser light and shifting to a state having different optical constants. With respect to the wavelength λ of light, the optical groove depth of the substrate is in the range of (Formula 1), and the reflectance in the unrecorded area and the recorded mark area of the optical information recording medium is substantially equal to each other. The difference Δφ _1,2 between the phase φ ₁ of the reflected light from the recording area and the phase φ ₂ of the reflected light from the recording mark area is in the range of the above (Formula 3).

[0013]

According to the first configuration of the optical information recording method of the present invention, a substrate having a groove for tracking and a substrate formed on the substrate and having a different optical constant due to a phase change caused by irradiation with laser light. A method for recording information on an optical information recording medium having at least a recording thin film capable of transitioning to a state by irradiating a laser beam having a predetermined wavelength, wherein the laser reproduces information recorded on the recording thin film. With respect to the wavelength λ of light, the optical groove depth of the substrate is within the range of (Formula 1), and the reflectance in the unrecorded area and the recorded mark area of the optical information recording medium is substantially equal, Phase φ of light reflected from the unrecorded area of the information recording medium
Difference between ₁ and phase φ ₂ of light reflected from the recording mark area Δφ
_{If 1 and 2} are in the range of (Equation 2), the absolute value of the TE signal amplitude during recording is sufficiently large by recording in the groove, and the TE signal amplitude between unrecorded and recorded Difference becomes smaller, and moreover, superiority in signal amplitude is obtained as compared with the case of the reflectance difference reproducing medium. As a result, stable tracking characteristics and signal characteristics with a large reproduction amplitude can be obtained.

According to the second structure of the optical information recording method of the present invention, a substrate having a groove for tracking and a substrate formed on the substrate, which causes a phase change by irradiation of laser light, produces an optical constant. A method for recording information on an optical information recording medium having at least a recording thin film capable of shifting to a different state by irradiating a laser beam having a predetermined wavelength, and reproducing the information recorded on the recording thin film. The optical groove depth of the substrate is within the range of the above (Formula 1) with respect to the wavelength λ of the laser beam, and the reflectance in the unrecorded area and the recorded mark area of the optical information recording medium is substantially equal to each other. Phase φ _{1 of} light reflected from the unrecorded area of the optical information recording medium and phase φ of light reflected from the recording mark area
_If the difference Δφ _{1, 2} of ₂ is within the range of the above (Formula 3), the absolute value of the TE signal amplitude at the time of recording is sufficiently large because recording is performed on the land portion between the grooves, and it is not recorded. , The difference in TE signal amplitude between recordings becomes smaller, and moreover, the signal amplitude is superior to that in the case of the reflectance difference reproducing medium. As a result, stable tracking characteristics and signal characteristics with a large reproduction amplitude can be obtained.

The optical information recording medium of the present invention is
According to the configuration of 1, the irradiation of the laser light of the predetermined wavelength
Optical information recording medium used in devices for recording and reproducing information
A substrate having a groove for tracking,
It is formed on the substrate and undergoes a phase change when irradiated with laser light.
And a recording thin film that can shift to a state with different optical constants.
At least, to reproduce the information formed on the recording thin film
The optical groove depth of the substrate for the wavelength λ of the laser light
Is within the range of (Equation 1) above, and the optical information
The reflectance in the unrecorded area and the recorded mark area of the recording medium is
Approximately the same, the phase φ of the reflected light from the unrecorded area₁And before
Phase φ of light reflected from recording mark area ₂Difference Δφ_{1, 2}
Since it has been configured so that is within the range of (Equation 2) above,
By recording on, the absolute TE signal amplitude during recording is
The value is sufficiently large, and the difference in TE signal amplitude between unrecorded and recorded
Is smaller than that in the case of the reproducing medium with the difference in reflectance.
The advantage is obtained in terms of signal amplitude. As a result, stable
Tracking characteristics and signal characteristics with large playback amplitude
Can be

The optical information recording medium of the present invention is
According to the configuration of 2, the irradiation of the laser light of the predetermined wavelength
Optical information recording medium used in devices for recording and reproducing information
A substrate having a groove for tracking,
It is formed on the substrate and undergoes a phase change when irradiated with laser light.
And a recording thin film that can shift to a state with different optical constants.
At least, to reproduce the information formed on the recording thin film
The optical groove depth of the substrate for the wavelength λ of the laser light
Is within the range of (Equation 1) above, and the optical information
The reflectance in the unrecorded area and the recorded mark area of the recording medium is
Approximately the same, the phase φ of the reflected light from the unrecorded area₁And before
Phase φ of light reflected from recording mark area ₂Difference Δφ_{1, 2}
Since it is configured such that the above is in the range of (Formula 3),
By recording on the land part of the
The absolute value of the amplitude is large enough that the TE signal between unrecorded and recorded
The difference in signal amplitude is small, and the difference in reflectance
In comparison with the above, superiority is obtained in terms of signal amplitude. That conclusion
As a result, it has a stable tracking characteristic and a large reproduction amplitude.
No. characteristics can be obtained.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. First, the results of optical simulation will be described with respect to how the present invention works in signal reproduction of an optical information recording medium to obtain a reproduction signal of high amplitude and stable tracking characteristics.

FIG. 4 shows a state in which the optical disc is irradiated with laser light. As shown in FIG. 4, the optical disc is
Recording which is formed on the substrate 42 provided with the tracking groove 41 and which is formed on the substrate 42 and is capable of shifting to a state in which the optical constants (refractive index n, extinction coefficient k) are different by causing a phase change by irradiation of laser light. And a thin film 49. In order to reproduce the recorded information, first, the recording thin film 49 is irradiated with laser light from the semiconductor laser 43 through the collimator lens 44, the half mirror 45, and the objective lens 46. Then, the reflected light is converted into the objective lens 46 and the half mirror 4.
5, the light is focused on the photodetector 48 through the lens 47. Here, the photo detector 48 is evenly divided into two in the radial direction of the optical disc.

In the optical simulation, the laser light incident on the objective lens 46 is Gaussian distribution light, and a Hopkins model (J. Opt. S) is used.
oc. Am. , Vol. 69, No. 1, Jan. 19
79 p4-24 H. H. (See Hopkins) is used to calculate the beam intensity of the reflected light on the photodetector 48. The amount of reflected light is Photo Detector 4
8, the tracking error signal (hereinafter referred to as "TE signal") is calculated as the difference in the amount of received light in the left and right regions of the photo detector 48 divided into two. When the groove width and the land (flat portion between grooves) are equal, when the incident light is moved in the radial direction of the optical disc, the TE signal is generated near the center on the line connecting the centers of the adjacent grooves 41 and lands. Then, the absolute value becomes the maximum. On the other hand, when the incident light reaches the center of the groove 41 and the land, the TE signal is not detected.

Here, the wavelength of the incident light is 780 nm, the NA (numerical aperture) of the objective lens 46 is 0.55, the track pitch is 1.6 μm, and the groove width (= land width) is 0.8 μm.
(Perpendicular to the groove wall), the mark width is 0.6 μm, the mark period is 1.6 μm, the mark length is 0.8 μm, and the reflectance is equal in the mark portion (recorded portion) and the mark peripheral portion (unrecorded portion). I calculated. The reason why the reflectance is substantially equal in the mark portion and the peripheral portion of the mark is that the amplitude of the reproduction signal can be increased even with a small recording mark and the disc structure can be easily realized ( Japanese Patent Application No. 4-157728).

Reflected light from the mark portion and the mark peripheral portion has a phase difference. Here, the difference between the phase φ ₁ of the reflected light from the unrecorded portion (mark peripheral portion) and the phase φ ₂ of the reflected light from the recorded portion (mark portion) is represented as Δφ _1,2 . The polarities of Δφ _{1 and 2} are such that when a mark is written in an unrecorded portion, the reflection surface in the mark portion is on the beam side (substrate
Seen from the side), it is defined as positive when a phase change occurs as if it goes farther back (on the side of the reflection layer 86), and conversely is defined as negative when a phase change occurs as if it approaches the front. The signal amplitude and TE on the photodetector 48 will be described below with the groove depth and Δφ ₁ , ₂ as parameters.
Evaluate the signal.

FIG. 2 shows the relationship between the groove depth and the TE signal amplitude when the signal recorded in the groove is reproduced. TE on the vertical axis
The signal amplitude indicates a calculated value of the TE signal when the center of the reproduction light approaches the center on the line connecting the centers of the adjacent groove and land. As can be seen from FIG. 2, in the unrecorded state, the optical path length of the groove depth is λ / 8 of the incident light.
At this time, the TE signal amplitude becomes maximum. The groove depth is λ
Even in the case of /8+0.5nλ (n is an integer), it is optically the same. On the other hand, the TE signal amplitude when a mark is recorded differs depending on the value of the phase difference between the unrecorded portion and the recorded portion. As can be seen from FIG. 2, if the phase difference between the unrecorded portion and the recorded portion is in the range of the following (Equation 4), the maximum TE signal amplitude in the unrecorded TE signal amplitude ( It is possible to secure half of the groove depth: λ / 8).

[0023]

[Equation 4]

If the phase difference is out of this range, the tracking characteristics are extremely susceptible to the influence of disturbance, and the existing technology is not practical. However, what is important for obtaining stable tracking characteristics is not only that the absolute value of the TE signal amplitude at the time of recording is large, but rather that the rate of change of the TE signal amplitude at the time of recording and at the time of non-recording is small. That is. From this viewpoint, the vertical axis of FIG. 2 is changed to the ratio of the TE signal amplitude at the time of recording and the TE signal amplitude at the time of non-recording, and this is shown in FIG. In the case of groove recording, if the phase difference is set in the range of (Formula 5) below and the optical path length of the groove depth is set in the range of (Formula 6) below, the absolute value of the TE signal amplitude during recording is It becomes large to some extent [more than half of the maximum TE signal amplitude (groove depth: λ / 8) in the case of unrecorded], and the difference in TE signal amplitude between unrecorded and recorded becomes small (variation amount of 50% or less. ). As a result, stable tracking characteristics can be obtained.

[0025]

(Equation 5)

[0026]

(Equation 6)

It will be shown in a specific embodiment described later that the above range is actually necessary and sufficient for obtaining stable tracking characteristics. Incidentally, here, the calculation result in the case where the recording mark interval is fixed to 1.6 μm as described above is shown, but the mark length is 0.5 μm to 2.0 μm.
The recording mark spacing is 1.0 μm
Even when the phase difference and the groove depth are limited to the above range even when the range is changed to 4.0 μm, almost the same result as when the recording mark interval is 1.6 μm can be obtained. It was

Next, the case of recording and reproducing a signal on the land portion between the grooves will be described. FIG. 3 shows the relationship between the groove depth and the TE signal amplitude when the signal recorded in the land portion is reproduced. The TE signal amplitude on the vertical axis indicates the calculated value of the TE signal when the center of the reproduction light approaches the center of the line connecting the centers of the adjacent groove and land. As can be seen from FIG. 3, in the unrecorded state, when the optical path length of the groove depth is λ / 8 (+ 0.5nλ) of incident light (n is an integer), the TE signal amplitude becomes maximum. On the other hand, the TE signal amplitude when a mark is recorded differs depending on the value of the phase difference between the unrecorded portion and the recorded portion. As can be seen from FIG. 3, when the phase difference between the unrecorded portion and the recorded portion is in the range of the following (Equation 7), the maximum TE signal amplitude in the unrecorded TE signal amplitude ( It is possible to secure half of the groove depth: λ / 8).

[0029]

(Equation 7)

If the phase difference is out of this range, the tracking characteristics are extremely susceptible to the influence of disturbance, and the existing technology is not practical. However, what is important for obtaining stable tracking characteristics is not only that the absolute value of the TE signal amplitude at the time of recording is large, but rather that the rate of change of the TE signal amplitude at the time of recording and at the time of non-recording is small. That is. In the case of land recording, if the phase difference is set in the range of (Formula 8) below and the optical path length of the groove depth is set in the range of (Formula 6) above, the absolute value of the TE signal amplitude at the time of recording is It becomes large to some extent, and the difference in TE signal amplitude between unrecorded and recorded becomes small. As a result, stable tracking characteristics can be obtained.

[0031]

[Equation 8]

It will be shown in the following specific examples that the above range is actually necessary and sufficient for obtaining stable tracking characteristics. The conditions for obtaining stable tracking characteristics in each of the groove recording and the land recording have been described above. Below, the results of optical simulation will be described for the conditions for obtaining signal characteristics with a large reproduction amplitude. To do.

FIG. 6 shows the relationship between the groove depth and the reproduced signal amplitude when the signal recorded in the groove is reproduced. The signal amplitude on the vertical axis is the total amount of light received on the photodetector 48 when the center of the reproducing light approaches the center of the mark (the reflected light amount in the unrecorded state on the mirror surface is 1) and the center of the reproducing light is between the marks. The difference from the total amount of received light on the photodetector 48 when it reaches the center of (1) (the reflected light amount in the unrecorded state on the mirror surface is 1) is shown. As described above, FIG. 6 shows the result of the optical simulation when the recording mark interval is 1.6 μm. For comparison, the result of the optical simulation of the reflectance difference reproducing medium is shown by a curve 61 in FIG. In the optical simulation of the reflectance difference reproducing medium, the incident light wavelength is 780 nm, and the N of the objective lens is N.
A 0.55, track pitch 1.6 μm, groove width (= land width) 0.8 μm, mark width 0.6 μm, mark length 0.
The value of 8 μm and the mark period of 1.6 μm are the same as the values used in the optical simulation of the phase difference reproducing medium described above.
However, the phase difference between the reflected light from the mark peripheral part (unrecorded part) and the reflected light from the mark part (recorded part) is 0, the reflectivity of the mark part is 5%, and the reflectivity of the mark peripheral part is 30%. I calculated. As can be seen from FIG. 6, when the phase difference between the mark peripheral portion of the phase difference reproducing medium and the reflected light from the mark portion is in the range of the following (Equation 9) and the groove depth is shallower than λ / 8, Can obtain a larger signal amplitude in the phase difference reproduction than in the reflectance difference reproduction.

[0034]

[Equation 9]

Considering this result and the phase difference in consideration of the tracking characteristic, in the case of groove recording, the phase difference is set within the range of the above (Formula 2) and the optical path length of the groove depth is set. If the range of the above (Formula 1) is set, the absolute value of the TE signal amplitude during recording is sufficiently large, the TE signal amplitude ratio (rate of change) between unrecorded and recorded is small, and the reflectance difference reproducing medium is The advantage is obtained in terms of signal amplitude as compared with the case of. As a result, stable tracking characteristics and signal characteristics with a large reproduction amplitude can be obtained.

Next, the case of recording and reproducing a signal on the land portion between the grooves will be described. FIG. 7 shows the relationship between the groove depth and the reproduced signal amplitude when the signal recorded in the land portion is reproduced. The signal amplitude on the vertical axis is the total amount of light received on the photodetector 48 when the center of the reproduction light approaches the center of the mark (1 is the reflected light amount in the unrecorded state on the mirror surface.
And the total amount of received light on the photodetector 48 when the center of the reproduction light approaches the center between the marks (the reflected light amount in the unrecorded state on the mirror surface is 1). As described above, FIG. 7 shows the result of the optical simulation when the recording mark interval is 1.6 μm. For comparison, the result of the optical simulation of the reflectance difference reproducing medium is shown by a curve 71 in FIG. In the optical simulation of the reflectance difference reproducing medium, the wavelength 78 of the incident light is
0 nm, NA of objective lens 0.55, track pitch 1.6 μm, groove width (= land width) 0.8 μm, mark width 0.6 μm, mark length 0.8 μm, mark period 1.6 μ
m is the same as the value used for the optical simulation of the phase difference reproducing medium. However, the phase difference between the reflected light from the mark peripheral part (unrecorded part) and the reflected light from the mark part (recorded part) is 0, the reflectivity of the mark part is 5%, and the reflectivity of the mark peripheral part is 30%. I calculated. As can be seen from FIG. 7, the phase difference between the mark peripheral portion of the phase difference reproducing medium and the reflected light from the mark portion is in the range of the following (Equation 10), and
When the groove depth is shallower than λ / 8, the phase difference reproduction can obtain a larger signal amplitude than the reflectance difference reproduction.

[0037]

[Equation 10]

Considering this result and the phase difference in consideration of the above tracking characteristics, in the case of land recording, the phase difference is set in the range of (Equation 3) and the optical path length of the groove depth is set. If you set the range of (Equation 1) above, TE during recording
The absolute value of the signal amplitude is sufficiently large that T between unrecorded and recorded
The E signal amplitude ratio (rate of change) becomes small, and moreover, superiority is obtained in terms of signal amplitude as compared with the case of the reflectance difference reproducing medium. As a result, stable tracking characteristics and signal characteristics with a large reproduction amplitude can be obtained.

As described above, in the phase difference reproducing medium in which the optical path length of the groove depth is limited to the range of the above (Formula 1),
If the difference Δφ _1,2 between the phase φ ₁ of the reflected light from the unrecorded area and the phase φ ₂ of the reflected light from the recording mark area is within the range of (Equation 2) above, recording is performed in the groove. , Again, φ
_If the range of _{1 and 2} is within the range of the above (Formula 3), stable tracking characteristics and large reproduced signal amplitude can be obtained by recording on the land portion between the grooves.

In the above description, the groove width and the land width are equal and the groove shape is rectangular for the sake of convenience. However, the groove width and the land width are not necessarily limited to this structure. Alternatively, the present invention can be applied even if it has a U-shaped or V-shaped groove shape.

<Specific Examples> The present invention will be described in more detail with reference to specific examples. FIG. 8 is a sectional view showing an embodiment of the optical information recording medium according to the present invention.
As shown in FIG. 8, the substrate surface 82 of the substrate 81 has spiral continuous grooves (tracks) for guiding laser light.
Is provided. A recording thin film 85 is provided on the surface 82 of the substrate while being sandwiched between the first and second protective layers 83 and 84. Here, the recording thin film 85 can be changed to a state in which the optical constants (refractive index n, extinction coefficient k) are different by causing a phase change by irradiation with laser light. A reflective layer 86 is provided on the second protective layer 84, and a protective substrate 87 is further provided on the reflective layer 86. Here, the track pitch was 1.6 μm, the groove width was 0.8 μm, and the groove depth was variously changed to prepare several kinds of substrates.
The laser light for recording / reproducing is incident from the substrate 81 side.

As the substrate 81, here, the thickness is 1.2 m.
m polycarbonate disk was used. First and second protection
Physically and chemically stable materials for the protective layers 83 and 84
That is, the melting point and softness
It has a high crystallization temperature and does not form a solid solution with the recording material.
Just do it. Here, ZnS-20 mol% SiO₂To
Using. The recording thin film 85 has a crystalline state and an amorphous state.
A substance that causes a structural change between and is used. Here, G
e₂Sb₂Te_FiveWas used. Ge₂Sb₂Te _FiveIs good
It is possible to obtain good recording / erasing characteristics and repeat characteristics.
Generally known as a phase change recording material
62-209742). The reflective layer 86 is a recording thin film
It functions to increase the efficiency of light absorption to 85. Here, A
u was used. In addition, for example, by increasing the film thickness of the recording thin film 85,
The reflective layer 8 by improving the light absorption efficiency.
It is also possible to adopt a configuration in which 6 is not provided. Protective substrate 8
Here, 7 was formed by spin coating a resin. Place
Depending on the case, two sets of recording media may be used as an intermediate substrate or a reflective layer.
By sticking together with an adhesive on the inside,
The structure may be such that recording, reproduction, and erasing can be performed from the surface. Record
Thin film 85, first and second protective layers 83, 84, reflective layer 8
6 was formed by the sputtering method.

The thickness of the recording thin film 85 is selected so that a part of the incident light beam can be transmitted even when the recording thin film 85 is in a crystalline state. Because, if the recording thin film 85 is too thick,
The component reflected by the reflective layer 86 and re-incident in the recording thin film 85 is eliminated, and the light interference effect is reduced.
Even if the film thicknesses of the second protective layers 83 and 84 and the reflective layer 86 are slightly changed, the degree of freedom in designing the optical characteristics such as the reflectance of the entire medium is narrowed.

The film thickness of the first and second protective layers 83, 84 can be determined as follows. That is, first, the complex refractive index of the material constituting each layer, a normal method (for example, a thin film is formed on a glass plate, the film thickness and reflectance, a method of calculating based on the measured values of the transmittance, or Method using an ellipsometer). Then, with the thickness of the recording thin film 85 and the reflective layer 86 fixed, the first and second protections are performed by a matrix method (see, for example, "Wave Optics" by Hiro Kubota, Iwanami Shoten, 1971, Chapter 3). The film thickness of the layers 83 and 84 is calculated. Specifically, assuming the film thickness of each layer, the balance of light energy is calculated for all interfaces including the surface based on the energy conservation law. That is, by formulating this energy balance equation for each interface in the multilayer medium and solving the simultaneous equations obtained, the optical path length for incident light of any wavelength (actually, wavelength λ used for reproducing information) The intensity of transmitted light, the intensity of reflected light, and the amount of absorption in each layer can be obtained. Whether the recording thin film is in a crystalline state or in an amorphous state, the above calculation is performed to record an unrecorded area (usually in a crystalline state) with respect to the reproduction light of wavelength λ. It is possible to obtain the phase difference of the reflected light in the mark area (usually in an amorphous state), the reflectance of both areas, and the like. As described above, the film thickness composition and the optical characteristics (reflectance of crystals and amorphous materials, amount of absorbed light, phase, etc.) can be determined, so that the film thickness of each layer can be obtained so as to obtain desired optical characteristics. Should be decided. Whether or not the recording medium is formed as designed can be estimated by measuring the reflectance and the transmittance of the formed medium using a spectrum meter or the like and comparing them with the values calculated in advance. in this case,
The estimation accuracy can be improved by performing the same comparison with two or more wavelengths. The amount of phase change between the recorded part and the unrecorded part can be determined by using an interference film thickness meter or the like to determine how the interference fringes of the light of the same wavelength as the reproduction light are deviated between the recorded part and the unrecorded part. It can be determined by observing.

The following (Table 1) shows the optical constants for the wavelength of 780 nm of each layer used for the optical design.

[0046]

[Table 1]

Regarding the sample used in the experiment, the film thickness of the first protective layer 83 on the substrate 81 side, the film thickness of the second protective layer 84 on the reflective layer 86 side, the reflectance R1 in the amorphous state.
The measured values of the reflectance R2 in the crystalline state and the phase difference between the two states are shown below (Table 2).

[0048]

[Table 2]

However, the optical characteristics are values for a wavelength of 780 nm. The thicknesses of the recording thin film 85 and the reflective layer 86 are fixed to 15 nm and 50 nm, respectively. The actual measurement value of the reflectance was obtained using a spectrophotometer. Crystallization is 250 ℃
By heat treatment in nitrogen for 10 minutes. Further, a partial region of the sample piece was crystallized by a semiconductor laser to form an amorphous region and a crystalline region side by side, and this portion was observed using an interference film thickness meter. And
The phase difference was calculated from the amount of shift between the two regions of the interference fringe having a wavelength of 780 nm.

For each of the above 11 types of structures, the substrate has a groove depth of 10 nm to 100 nm in 10 nm increments.
A type was prepared, and a disc was prepared and evaluated. FIG. 1 is a sectional view of a disk for explaining the present embodiment. FIG.
FIG. 1A shows a case where recording is performed in the groove portion.
(B) shows a case where recording is performed on the land portion. On the surface of the substrate 11, a recording area including a groove portion 13 and a land portion 14 is formed. The recording mark 16 written in the recording thin film 15 is reproduced by reproducing light. In this embodiment, the value of the groove depth 12 (10 nm to 100 n
m) and the value of the phase difference (−0.8π to + 1.0π) between the reflected light 17 from the recording mark and the reflected light 18 from the periphery of the recording mark when the reproducing light is irradiated, are independently changed. , Reproduction amplitude and tracking characteristics were investigated. These media are preliminarily initialized (crystallized) on the entire surface of the recording thin film 15 by an initialization device using an argon laser.
Treated. After that, this medium is rotated at a linear velocity of 12 m / s, the semiconductor laser light having a wavelength of 780 nm is narrowed down by a lens system having a numerical aperture of 0.55, and the groove portion 13 on the recording thin film 15 is formed.
Alternatively, the land portion 14 between the grooves is focused and irradiated. 7.5M single frequency with various powers on the surface of the recording thin film 15.
The recording thin film 1 is irradiated with light modulated at 30 Hz and a modulation degree of 30%.
5 was partially amorphized for recording (mark pitch 1.6 μm). Then, continuous light of 1 mW was irradiated, and the reflected light was detected by a photodetector to observe the reproduced signal amplitude and the second harmonic distortion. It is considered that when the signal is recorded with a power that minimizes the second harmonic distortion, the recording mark length is about 50% duty and 0.8 μm. Therefore, the following signal recording is performed with a power that minimizes the second harmonic distortion, and the result will be described. Also, as the disturbance, an acceleration of 1 G and a frequency of 3 in the vertical direction of the disk.
It was investigated whether or not the laser beam could stably follow the track when a vibration of 0 Hz was applied. 1G,
If stable tracking can be realized at a value of 30 Hz, it is considered that there will be no practical problem when considering the normal drive usage situation.

In this way, the phase difference between the reflected light 18 from the mark peripheral portion of the recording medium and the reflected light 17 from the mark portion, the groove depth 12 of the substrate 11 and the amplitude of the reproduced signal, and the tracking characteristics were examined. However, the following became clear.

(1) When performing groove recording, the groove depth is 60 n.
Sample number (disk No.) is 1 for substrates of m or less,
For discs 2, 3, 10, and 11, all C
A large value of 50 dB or more was obtained as the NR (carrier to noise ratio).

(2) In the case of groove recording, among the combinations of phase difference and groove depth that can obtain good CNR as in (1), stable tracking characteristics with respect to vibration with an acceleration of 1 G and a frequency of 30 Hz are obtained. The groove depth is 30n
Sample numbers were part of 2, 3 and 1 on substrates from m to 60 nm. The results of the vibration test are shown below (Table 3).

[0054]

[Table 3]

In the above (Table 3), ∘ indicates a disc that can be tracked under a vibration test, and x indicates a disc that cannot be tracked. λ / 16 is about 30 nm, λ / 8
Corresponds to a groove depth of about 60 nm. FIG. 9 shows the relationship between the groove depth and the TE signal amplitude during groove recording, arranged for each phase difference due to recording. The TE signal amplitude was obtained by turning off the tracking servo after recording and observing the TE signal on an oscilloscope. TE
The signal amplitude was plotted with the maximum TE signal amplitude at the time of unrecorded being 1.

(3) When land recording is performed, the groove depth is 6
Substrates of 0 nm or less with sample numbers 1, 8, 9, 10,
For the 11 discs, each has a CNR of 50.
A large value of dB or more was obtained.

(4) In the case of land recording, among the combinations of phase difference and groove depth that can obtain good CNR as in (3), stable tracking characteristics with respect to vibration of acceleration 1 G and frequency 30 Hz are realized. What can be done is a substrate having a groove depth of 30 nm to 60 nm and a sample number of 8,
It was part of 9 and 10. The results of the vibration test are shown below (Table 4).

[0058]

[Table 4]

In the above (Table 4), ◯ indicates a disc that can be tracked under a vibration test, and x indicates a non-trackable disc. FIG. 10 shows the relationship between the groove depth and the TE signal amplitude during land recording, arranged for each phase difference due to recording. The TE signal amplitude was plotted with the maximum TE signal amplitude at the time of unrecorded being 1.

The above is the experimental result, but the optical equivalence is maintained even if rewritten as follows. That is, in the case of groove recording, good CNR can be obtained and stable tracking characteristics can be obtained only when the phase difference between the recorded portion and the unrecorded portion is in the range of the above (Formula 2), and , Where the groove depth is in the range of the above (Equation 1). Further, in the case of land recording, good amplitude can be obtained and stable tracking characteristics can be obtained because the phase difference between the recorded portion and the unrecorded portion is in the range of the above (Formula 3), and , Where the groove depth is in the range of the above (Equation 1). Even when random data in which the mark length and the mark interval are mixed between 1.2 μm and 4.4 μm is recorded, the same as in the case where the marks are recorded at a single frequency with a period of 1.6 μm, In the combination of the phase difference and the groove depth,
It was possible to obtain stable tracking characteristics.

Although the above results show the experimental results for the substrate having the same groove width and land width, even if the ratio of the groove width to the land width is in the range of 0.8 to 1.2. Similar results can be obtained. Further, in the above-mentioned embodiment, the case of the rewritable type optical disk has been described as an example, but the present invention is not necessarily limited to this, and the present invention is equally effective in the write-once type.

[0062]

As described above, according to the present invention,
An optical information recording medium comprising at least a substrate having a tracking groove and a recording thin film formed on the substrate and capable of shifting to a state having different optical constants by causing a phase change by irradiation of laser light, When recording is performed by irradiating a laser beam having a wavelength, the optical groove depth of the substrate is within the range of (Formula 1) with respect to the wavelength λ of the laser beam for reproducing the information recorded on the recording thin film. , And the reflectances in the unrecorded area and the recording mark area of the optical information recording medium are substantially equal, and the phase φ ₁ of the reflected light from the unrecorded area of the optical information recording medium and the phase of the reflected light from the recording mark area If the difference Δφ _{1, 2} of φ ₂ is in the range of (Equation 2) above, recording is performed in the groove, and Δφ ₁ , ₂ is (Equation 3) above.
Within the range, by recording on the land portion between the grooves, the absolute value of the TE signal amplitude during recording is sufficiently large, and the TE signal amplitude ratio (rate of change) between unrecorded and recorded becomes small. In addition, superiority is obtained in terms of signal amplitude as compared with the case of the reflectance difference reproducing medium. As a result, stable tracking characteristics and good reproduction signal amplitude can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a case where recording is performed on a groove portion or a land portion of a disc in an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a groove depth and a TE signal amplitude when a signal recorded in a groove is reproduced in an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a groove depth and a TE signal amplitude when a signal recorded in a land portion is reproduced in an embodiment of the present invention.

FIG. 4 is a diagram showing a principle of recording / reproducing on an optical disc.

FIG. 5 is a diagram showing a relationship between a groove depth and a TE signal amplitude change before and after recording in groove recording according to an embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between a groove depth and a reproduced signal amplitude when a signal recorded in a groove is reproduced in an embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between a groove depth and a reproduction signal amplitude when a signal recorded in a land portion is reproduced in an embodiment of the present invention.

FIG. 8 is a sectional view showing an embodiment of the optical information recording medium according to the present invention.

FIG. 9 is a diagram showing the relationship between the groove depth and the TE signal amplitude during groove recording according to one embodiment of the present invention, arranged for each phase difference due to recording.

FIG. 10 is a diagram showing the relationship between the groove depth and the TE signal amplitude during land recording according to one embodiment of the present invention, arranged for each phase difference due to recording.

[Explanation of symbols]

 11, 81 substrate 12 groove depth 13 groove portion 14 land portion 15, 85 recording thin film 16 recording mark 17 reflected light from recording mark 18 reflected light from around recording mark 82 substrate surface 83 first protective layer 84 second protection Layer 86 Reflective layer 87 Protective substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Nishiuchi, 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. An optical information recording comprising at least a substrate having a tracking groove, and a recording thin film formed on the substrate and capable of shifting to a state having different optical constants by causing a phase change by irradiation of a laser beam. An optical information recording method for recording on a medium by irradiating a laser beam of a predetermined wavelength, wherein the optical groove depth of the substrate with respect to the wavelength λ of the laser beam for reproducing the information recorded on the recording thin film. Is in the range of the following (Equation 1), the reflectances in the unrecorded area and the recording mark area of the optical information recording medium are substantially equal, and the phase φ ₁ of the reflected light from the unrecorded area of the optical information recording medium is And the difference Δφ _{1, 2} between the phases φ ₂ of the reflected light from the recording mark area is within the range of the following (Equation 2), recording is performed in the groove. [Equation 1] [Equation 2] 2. An optical information recording comprising at least a substrate having a tracking groove and a recording thin film formed on the substrate and capable of changing into a state having different optical constants by causing a phase change by irradiation of laser light. An optical information recording method for recording on a medium by irradiating a laser beam of a predetermined wavelength, wherein the optical groove depth of the substrate with respect to the wavelength λ of the laser beam for reproducing the information recorded on the recording thin film. Is in the range of the above (Formula 1), the reflectances in the unrecorded area and the recording mark area of the optical information recording medium are substantially equal, and the phase φ ₁ of the reflected light from the unrecorded area of the optical information recording medium is And the difference Δφ _{1, 2} of the phase φ ₂ of the reflected light from the recording mark area is within the range of the following (Equation 3), recording is performed on the land portion between the grooves. (Equation 3) 3. An optical information recording medium used in an apparatus for recording / reproducing information by irradiating a laser beam having a predetermined wavelength, the substrate having a groove for tracking, and a laser beam formed on the substrate. At least a recording thin film capable of causing a phase change by irradiation to shift to a state having different optical constants, and the optical groove depth of the substrate with respect to the wavelength λ of the laser beam for reproducing information formed on the recording thin film. Is in the range of the above (Formula 1), the reflectances in the unrecorded area and the recorded mark area of the optical information recording medium are substantially equal, and the phase φ ₁ of the reflected light from the unrecorded area and the recorded mark area An optical information recording medium, characterized in that the difference Δφ _{1,2 in} the phase φ ₂ of the reflected light from is within the range of the above (Formula 2). 4. An optical information recording medium used in an apparatus for recording / reproducing information by irradiating a laser beam having a predetermined wavelength, the substrate having a groove for tracking, and a laser beam formed on the substrate. At least a recording thin film capable of causing a phase change by irradiation to shift to a state having different optical constants, and the optical groove depth of the substrate with respect to the wavelength λ of the laser beam for reproducing information formed on the recording thin film. Is in the range of the above (Formula 1), the reflectances in the unrecorded area and the recorded mark area of the optical information recording medium are substantially equal, and the phase φ ₁ of the reflected light from the unrecorded area and the recorded mark area An optical information recording medium characterized in that the difference Δφ _{1, 2} between the phases φ ₂ of the reflected light from is within the range of the above (Formula 3).