JPH08329528A - Optical recording medium and recording and reproducing method - Google Patents

Abstract

PURPOSE: To obtain an optical information recording medium for making recording, reproducing and erasing of information in both of the groove parts and between the grooves of a substrate by irradiation with a laser beam and a recording and reproducing method using the same. CONSTITUTION: This optical recording medium is constituted by successively laminating a lower dielectric protective layer, phase transition type recording layer, upper dielectric protective layer and material reflection layer on a transparent substrate 1 formed with the grooves. Both of the parts on the grooves and between the grooves are used as recording regions and the recording, erasing and reproducing of the information are made by irradiation with the laser beam of a wavelength of <=700nm. The width of the grooves is specified to 0.1 to 0.7μm, the spacing between the grooves to 0.1 to 0.7μm and the depth (d) of the grooves to λ/7n<d<λ/5n (where, λ: the wavelength of irradiating light, n: the refractive index of the substrate, d: the depth of the grooves). The phase difference α of the reflected light from the unrecorded regions and the reflected light from the recorded regions is specified to (m-0.1)π<=α<=(m+0.1)π (m 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 recording medium and a recording / reproducing method.
The present invention relates to an optical information recording medium for recording, reproducing, and erasing information on both the groove and the groove of a substrate, and a recording / reproducing method using the same.

[0002]

2. Description of the Related Art In recent years, a recording medium capable of recording and reproducing a large amount of data at high density and at high speed has been demanded as the amount of information has increased. Optical discs are expected to meet such applications. There is. The demand for higher capacity and higher density in such a recording medium is inevitable in the era when the recording medium and the recording device were imposed in handling a huge amount of image information and audio signals, and digital modulation technology and data compression technology. Keeping pace with the progress of, the progress is just progressing.

As a specific means of increasing the density, in an optical disc, the wavelength of the light source is shortened and the lens has a high NA (Numeric).
MCAV (constant recording density on the inner and outer circumferences) by increasing the recording frequency toward the outer circumference under a constant number of rotations by reducing the convergent beam diameter of the irradiation light due to al. Modified Constant Angular Velocity), mark edge recording that puts information on the beginning and end of the mark, etc. have been developed and used, and the current situation is that further densification methods are being sought for the future.

In a recordable optical disc, a guide groove is preliminarily formed on the disc to form a so-called track. Normally, by recording laser light between the guide grooves or in the guide grooves, information signals are recorded,
Playback or deletion is performed. In general optical discs currently on the market, information signals are usually recorded either between the guide grooves or in the guide grooves, and the other is a boundary for separating adjacent tracks to prevent signal leakage. It only plays the role of.

If it is possible to record information at this boundary portion, for example, in the guide groove when recording between the guide grooves, or between the guide grooves when recording in the guide groove. The recording density is doubled, and a large improvement in recording capacity can be expected. Hereinafter, a method of recording a guide groove in a groove, a space between the guide grooves and a land, and recording information in both the land portion and the groove portion is abbreviated as L & G recording.

As a proposal for L & G recording, Japanese Patent Publication No. 63-
No. 57859 is available, but when such a technique is used, it is necessary to pay great attention to reducing crosstalk. That is, in the L & G recording described in Japanese Patent Publication No. 63-57859, since the distance between the recording mark train of a certain track and the recording mark train of the adjacent track is half the convergent beam diameter, the recording mark train to be reproduced is The convergent beam diameters overlap to the adjacent recording mark row.

Therefore, there is a problem that the crosstalk during reproduction becomes large and the reproduction S / N deteriorates. In order to reduce this crosstalk, for example, SPIE Vo
l. 1316, Optical Data Storage
ge (1990) pp. 35, there is a method for reducing crosstalk by providing a special optical system and a crosstalk cancel circuit in the optical disc reproducing apparatus.

However, this method has a demerit that the optical system and the signal processing system of the apparatus become more complicated. As a method for reducing crosstalk without providing a special optical system or signal processing circuit for reducing playback crosstalk, equalize the width of the groove (guide groove) and the land (between guide grooves). There is a proposal that it is effective to set the groove depth within a certain range corresponding to the reproduction light wavelength. (Jpn. J. Appl. Phy
s. Vol 32 (1993) pp. 5324-532
8).

According to this, the crosstalk is reduced when the land width = the groove width and the groove depth is λ / 7n to λ / 5n (λ: reproducing light wavelength, n: refractive index of the substrate). Are shown as calculated and experimental facts. This is also described in Japanese Patent Application Laid-Open No. 5-282755.

According to the CN ratio (carrier / noise ratio) and the groove depth dependence of crosstalk described in this paper, the effect of reducing crosstalk can be seen by setting the groove depth to the optimum value. The CN ratio in the land portion and the groove portion is unbalanced.

When L & G recording is performed, a difference occurs between the carrier level of the land portion and the carrier level of the groove portion, and as a result, the CN ratio on one side is significantly reduced.
It is not desirable in the signal quality of the disc.

[0012]

SUMMARY OF THE INVENTION The present invention is to solve the above problems, and particularly in an L & G recording type optical disc using a laser light having a wavelength of 700 nm or less as a light source, the carrier level of the recording mark of the land portion and the groove portion. It is an object of the present invention to eliminate the above-mentioned imbalance and to provide a high density optical disc that can obtain the same high signal quality regardless of whether recording is performed on the land portion or the groove portion.

[0013]

The present invention has been made as a result of repeated studies on the regulation of the groove depth and the phase difference of the reflected light from the unrecorded area and the recording mark. On the formed transparent substrate, the lower dielectric protective layer,
A phase-change recording layer, an upper dielectric protection layer, and a metal reflection layer are laminated in this order, and the information is recorded by irradiating a laser beam having a wavelength of 700 nm or less using both the groove and the groove as recording areas. An optical recording medium for recording, erasing, and reproducing, comprising: (1) a groove width of 0.1 μm or more and 0.7 μm or less, an interval between grooves of 0.1 μm or more and 0.7 μm or less, and a groove depth d. Satisfies the inequalities shown below,

[0014]

## EQU4 ## λ / 7n <d <λ / 5n (where λ: wavelength of irradiation light, n: refractive index of substrate, d:
Groove depth)

(2) The phase difference α between the reflected light from the unrecorded area and the reflected light from the recorded area defined below is α = (phase of reflected light from unrecorded area)-(from the recorded area Phase of reflected light) Satisfies the following formula

[0016]

## EQU00005 ## An optical recording medium characterized in that (m-0.1) .pi..ltoreq..alpha..ltoreq. (M + 0.1) .pi. (M is an integer). With the configuration described above, in the optical disc of the present invention, the signal quality (carrier level) of the recording mark is the same regardless of whether recording is performed on the land portion or the groove portion.

Therefore, it is an indispensable rule in ensuring the reliability of the optical disc of the L & G recording system in which a laser beam having a wavelength of 700 nm or less is used as a light source. How the present invention works and effects in the reproducing process of the optical recording medium for land & groove recording will be explained in detail below by using a simple model as to the basis of its effectiveness.

FIGS. 1 to 4 are schematic views showing the case where the reproducing light beam is irradiated onto the land or groove of the L & G optical disk. Layers other than the recording layer 2 are omitted for easy viewing of the drawing. The reproduction light beam is condensed using an objective lens or the like, and is assumed to be irradiated onto the disc from the substrate 1 side, and is hereinafter referred to as a converged beam.

FIGS. 1 and 3 show the case where the convergent beam 5 exists in the unrecorded area, and FIGS. 2 and 4 show the case where the convergent beam 6 exists on the recording mark 8. The assumption is that the recording mark 8 is sufficiently longer than the convergent beam 5 to simplify the calculation. As will be shown later in Examples, there is no problem even if the recording mark is actually shorter than the convergent beam diameter.

Here, the state of the recording layer when unrecorded is defined as a crystalline state, and the state of the recording layer when recorded is defined as an amorphous state. The intensity of the convergent beam has a Gaussian distribution according to an actual model, and the beam diameter is defined as 1 / e ² of the central intensity.
Assuming that the width of the land 3 and the width of the groove 4 are equal and half the beam diameter, the land 3 and the groove 4
The step between them is d.

Since the convergent beam is emitted from the substrate side,
It is incident from the other side of the paper and reflected. Therefore, when viewed from the light source side, the land portion 3 is concave and the groove portion 4 is convex. When the groove surface is used as a phase reference, the reflected light from the land portion lags behind the reflected light from the groove portion by 2π · 2nd / λ.

Here, n is the refractive index of the substrate, d is the depth of the groove, and λ is the wavelength of the convergent beam. The phase change is not caused only by the groove depth, but generally the phase difference also changes by the change in the optical constants before and after the phase change of the recording layer. Here, it is assumed that the reflected light from the amorphous region is delayed in phase from the reflected light from the crystalline region by 2πα (α: phase difference).

In the following, the amplitude reflectance of the convergent beam will be formulated using the phase difference α as necessary, with the groove surface as the phase reference. As shown in FIG. 1, the amplitude reflectance φ ₁ when the convergent beam 5 is on the land portion 3 having no amorphous recording mark can be expressed by the following equation.

[0024]

Φ ₁ = R _c1 · exp [−2πi · 2nd / λ] + R _c2 · exp [−2πi · 0] (a) where R _c1 is from the region 6 of the land portion irradiated with the convergent beam. The amount of reflected light, R _c2 is the amount of reflected light from the region 7 of the groove portion irradiated with the convergent beam, n is the refractive index of the substrate,
d is the depth of the groove, λ is the wavelength of the irradiation light, and i is the imaginary unit.

As shown in FIG. 2, the amplitude reflectance φ ₂ when the convergent beam 5 is present on the land portion having the amorphous recording mark
Can be expressed by the following equation.

[0026]

[Equation 7] φ₂= R_a1-Exp [-2πi (2nd / λ + α)] + R_c2• exp [-2πi · 0] (b) where R_a1Is the land area irradiated by the convergent beam
Amount of reflected light from 6, R _c2Is a group of beams
The amount of reflected light from the region 7 of the wave portion is shown.

As shown in FIG. 3, the amplitude reflectance φ when the convergent beam 5 is present in the groove portion having no amorphous recording mark
₃ can be expressed by the following equation.

[0028]

Φ ₃ = R _c1 · exp [−2πi · 0] + R _c2 · exp [−2πi (2nd / λ)] (c) where R _c1 is from the region 7 of the groove portion irradiated with the convergent beam. , R _c2 represents the amount of reflected light from the region 6 of the land portion irradiated with the convergent beam.

As shown in FIG. 4, the amplitude reflectance φ when the convergent beam 5 is present in the groove portion having the amorphous recording mark
₄ can be expressed by the following equation.

[0030]

(9) φ_Four= R_a1・ Exp [-2πiα)] + R_c2Exp [-2πi (2nd / λ)] (d) where R_a1Is the area of the groove where the convergent beam is emitted.
Amount of light reflected from area 7, R _c2Is a laser beam irradiated by a convergent beam.
The amount of reflected light from the region 6 of the band portion is shown.

Here, it is assumed that land width = groove width, and that width is half the convergent beam diameter, so 0 <β <1.
If you put it

[0032]

## EQU10 ## R _c2 = βR _c1 (e)

[0033]

Multiplying by R _a2 = βR _a1 (f) When R _c = R _c1 + R _c2 and R _a = R _a1 + R _a2, and formula (e) and formula (f) are arranged,

[0034]

## _EQU12 ## R _c1 = R _c / (1 + β) (g)

[0035]

## EQU13 ## R _c2 = βR _c / (1 + β) (h)

[0036]

## _EQU14 ## R _a1 = R _a / (1 + β) (i)

[0037]

## EQU15 ## R _a2 = βR _a / (1 + β) (j) Substituting equations (g) to (j) into equations (a) to (d) and rearranging,

[0038]

Φ ₁ = [R _c / (1 + β)] [β + exp [-4πind / λ]] (k)

[0039]

Φ ₂ = [1 / (1 + β)] · [βR _c + _Ra · exp [-4πind / λ-2πiα]] (l)

[0040]

Φ ₃ = [R _c / (1 + β)] [1 + β · exp [−4πind / λ]] (m)

[0041]

Φ ₄ = [1 / (1 + β)] [R _a · exp [−2πiα] + βR _c · exp [−4πind / λ]] (n) Here, in the case of recording on the land portion, the reproduction carrier Level CL '(L) is

[0042]

[Equation 20] CL '(L) = proportional to | φ ₁ | ² − | φ ₂ | ² (o). Also, when recorded in the groove section in the same manner, the reproduction carrier level is

[0043]

[Equation 21] CL ′ (G) = proportional to | φ ₃ | ² − | φ ₄ | ² (p). The fact that there is no difference in the carrier level between the land portion and the groove portion means that the difference between the equation (o) and the equation (p) becomes zero.

Expressions (k) to (n) are replaced by expressions (o) and (p).
Substituting in, the difference is calculated, and if the necessary condition that the difference becomes 0 is found,

[0045]

## EQU22 ## α = mπ (where m is an integer) (q). The phase difference α does not necessarily have to be exactly mπ, and it is effective if any disc reflectance is within a range of ± 0.1π.

On the contrary, if the phase difference is (m-0.
When it is less than 1π) (however, it is larger than (m-π)), the reproduction signal amplitude of the land is significantly smaller than that of the groove, and the phase difference is (m +
When it exceeds 0.1π (however, it is smaller than (m + π)), it is a bad point that the reproduction signal amplitude of the groove becomes significantly smaller than that of the land.

According to the present invention, high signal quality can be assured regardless of which track is recorded on the land or the groove, and the range of the phase difference between phase transitions required for this purpose is specified by the optical constant of each layer. It can be realized by appropriately selecting the film thickness. For the groove depth of the substrate, see Jpn.
J. Appl. Phys. Vol32 (1993) p
p. As described in 5324-5328, the groove depth is λ / 7n to λ / 5n (λ: reproduction light wavelength, n:
Since the crosstalk from the adjacent track is reduced when the refractive index of the substrate), it is preferable to be within this range.

Here, a method of measuring the groove width and the groove depth will be described. He-Ne laser light (wavelength 630n
m) is radiated from the side of the substrate having no groove, and the 0th-order light intensity I ₀ , the 1st-order light intensity I ₁ , the 2nd-order light intensity I ₂ and the angle of the diffracted light obtained by diffracting the transmitted light by the groove of the substrate This is done by measuring. When P is the groove pitch, w is the groove width, d is the groove depth, λ is the laser wavelength, and θ is the angle between the 0th-order light and the 1st-order light, when the grooves are rectangular,

[0049]

(23) I ₂ / I ₁ = cos ² (πε)

[0050]

I ₂ / I ₁ = {2sin ² (πε) (1-co
sδ)} / [π ² {1-2ε (1-ε) (1-cos
δ)}]

[0051]

[Equation 25] ε = w / P, δ = 2 (n-1) πd / λ (n is the refractive index of the substrate)

[0052]

Since the relationship of P = λ / sin θ holds, the groove width and groove depth are calculated. Although the actual groove shape is not a perfect rectangle, the groove shape in the present invention uses the values that uniquely determine the groove width and groove depth by the above-described measurement method.
Therefore, the groove shape in the present invention is applied even when it is deviated from the rectangular shape.

In order to guarantee a high signal quality regardless of whether the recording is performed on the land or groove tracks, not only the regulation of the phase difference but also the ratio of the light absorptance before and after the phase change of the recording layer falls within a certain range. The effect is amplified by specifying. In PWM recording, 0 or 1 at the front and rear ends of the recording mark
In order to allocate the above information, it is particularly required that the shapes of the front end and the rear end of the mark are not distorted during recording.

An absorptivity of the recording layer is an important parameter related to the melting of the phase-change recording layer when forming the amorphous recording mark. As one of the characteristics of the phase change type optical disk, one-beam overwriting can be mentioned as in Japanese Patent Publication No. 5-32811. In the one-beam overwrite, the heating and cooling processes may become non-uniform due to different thermal conductivity depending on whether the recording layer before recording is in an amorphous state or a crystalline state, and the recording mark may be distorted. It has been pointed out.

Further, for example, as described in JP-A-5-298747, in the absorptance of the recording layer, a larger CN ratio and a higher erase ratio are obtained when the absorptance in the crystalline state is larger than that in the amorphous state. There is a proposal that a rate and a wide power margin (margin) can be obtained. However, in our study, it is not always necessary to make the absorptance in the crystalline state significantly higher than the absorptivity in the amorphous state, and as a result of earnest studies, the absorptance in the crystalline state in terms of the CN ratio and the jitter of the recording mark is shown. the a _c, when the absorptance in the amorphous state and a _a, the ratio _{a c} / a _a in the absorption rate

[0056]

It has been found that the disc is particularly excellent in the disc whose layer structure is designed so that 0.84 ≦ A _c / A _a <1.01. This is not limited to the case where the rotation speed of the disk is within a certain limited range, but in a disk where the absorptance ratio is within this range over a wide range of linear velocities from 1.4 m / s to 15 m / s,
The effect of being excellent was noticeable.

If A _c / A _a is less than 0.84, an imbalance occurs in the temperature rising / cooling process at the time of melting of the recording layer at the time of overwriting, depending on the presence / absence of recording marks existing in advance on the recording track. In addition to the problem of mark shape distortion, the recording sensitivity tends to be poor in a disc in which the initial state (unrecorded state) of the disc has a high reflectance and the recorded state has a low reflectance. _c / A
_It is desirable that _a ≧ 0.84.

In order to obtain a disc having such excellent characteristics, a chalcogen-based phase change material whose recording layer composition is Ge, Sb, and Te as main components is formed to a thickness of 20 ± 5 nm. Is especially desirable. If the thickness is too thick or too thin, the number of times of repeated recording and erasing may be significantly reduced, or the allowable width (margin) of the recording power may be reduced.

Considering sensitivity and stability, the reflective film is preferably an alloy of Al and Ti or Al and Ta. Hopefully, the Ti or Ta content is 0.5 at%
Therefore, it has been clarified by experiments that the loss of the reflectance of the disk is small and that the disk plays an appropriate role as a heat dissipation layer.

Although the L & G optical disk of the present invention is a rewritable optical information recording medium, it can also be used as a write-once type that can be rewritten only once. This can be easily done by recording an information write prohibition signal on the disk on the drive side so that the second recording and erasing cannot be performed. The disk can be prepared by forming a normal optical thin film such as magnetron DC sputtering or RF sputtering on a substrate disk such as resin or glass in which grooves are formed in advance.

It is desirable that a resin layer is applied or spin-coated on the metal reflective layer according to the first aspect in order to protect the film. The dielectric used in the dielectric layer of the present invention can be variously combined, and the refractive index, thermal conductivity,
It is determined by paying attention to chemical stability, mechanical strength, adhesion, etc. Generally, Mg and C, which have high transparency and high melting points
a, Sr, Y, La, Ce, Ho, Er, Yb, Ti,
Zr, Hf, V, Nb, Ta, Zn, Al, Si, G
e, Pb and other oxides, sulfides, nitrides, Ca, Mg, L
Fluorides such as i can be used.

Of these, ZnS and SiO ₂ or Y ₂
When a mixed film of at least one of O ₃ is used, if the content of SiO ₂ or Y ₂ O ₃ is preferably 5 to 40 mol%, the storage stability of the recorded disk is excellent. The disk can be used as a single plate specification using only one surface, and the capacity can be doubled by bonding two disks with the surfaces opposite to the substrates facing each other.

In the case of a laminated disc, by adopting a drive having a structure in which optical pickups are set on both sides of the disc, both sides of the disc can be recorded / erased and reproduced at the same time without replacing the disc. This is an important feature that cannot be achieved with a magneto-optical disc that requires a magnet on the side opposite to the laser irradiation side.

In designing the disk of the present invention, it is necessary to accurately grasp the phase difference of the reflected light before and after the phase change. In addition, it is more desirable to accurately grasp the above A _c / A _a and set it within a certain range from the viewpoint of CN ratio and recording mark jitter. The phase difference can be measured with a laser interference microscope or the like.

Since A _c / A _a is the absorptance ratio of only the recording layer in the multi-layer structure, it cannot be determined by direct measurement. However, both the phase difference of the reflected light before and after the phase change and the absorptance ratio A _c / A _a can be calculated by using the optical constant and the film thickness of each layer. The calculation method is described in detail in Chapter 3 of "Fundamentals and Methods of Spectroscopy" (Kei Keiei, Ohmsha, 1985).

The calculated values of the phase difference and the absorptance ratio in this example and the comparative example were calculated based on the method described in this document. The optical constant of each layer may be measured by an ellipsometer or the like after forming a single layer film by a method such as sputtering in advance. Recording / erasing of the optical disc of the present invention
For reproduction, a one-beam laser focused by an objective lens is used, and irradiation is performed from the substrate side of the rotating optical disk.

At the time of recording and erasing, the rotating disk is irradiated with a pulse-modulated laser beam, and the recording layer is phase-changed into two reversible states, that is, a crystalline state or an amorphous state. State). At this time, by overwriting, it is possible to simultaneously erase the marks existing before recording while recording.

At the time of reproduction, the rotating disk is irradiated with laser light having a power lower than that at the time of recording and erasing. At this time, the phase state of the recording layer immediately before reproduction should not be changed. Reproduction is performed by detecting a change in the intensity of reflected light with a photodetector and determining a recorded or unrecorded state.

The width of the tracking groove formed on the substrate (groove width) and the width between the grooves (land width) are set to be small irrespective of whether the leakage of the signal from the adjacent track is recorded. For the purpose, 1: 1 is desirable. However, from the viewpoint of securing the track cross signal or preventing the deterioration of the characteristics when recording and erasing are repeated many times, the optimum shape of the land and the groove is taken into consideration and If the ratio is such that crosstalk does not cause a problem, the ratio is 1:
It may be intentionally slightly shifted from 1.

[0070]

The present invention will be described in more detail with reference to specific examples. The substrate disks used in Examples and Comparative Examples were all the same. Further, under any of the recording conditions shown in Examples and Comparative Examples, the noise level when recording on the land and the noise level when recording on the groove were about the same. Therefore, the comparison of the CN ratio between the land recording and the groove recording is synonymous with the comparison of the recording carrier level in this embodiment.

Example 1 Polycarbonate (refractive index 1.56 for laser light having a wavelength of 680 nm) was used as the substrate material, and the groove width and the land width were both 0.65 μm. The groove depth d is set to about 70 nm, which corresponds to about λ / (6n) when the wavelength λ = 680 nm. The lower dielectric protective layer and the upper dielectric protective layer are ZnS and SiO ₂ (4: 1 molar ratio).
The thickness of the lower dielectric protective layer is 100 nm,
The film thickness of the upper dielectric protection layer was set to 20 nm.

The recording layer Ge, Sb, and T, which undergo a reversible phase change between the amorphous layer and the crystalline phase by laser irradiation.
A material containing e as a main component is used and the composition ratio is Ge: Sb: T.
e was set to about 2: 2: 5 (atomic ratio). The thickness of the recording layer was 25 nm. The reflective layer is made of Al and Ta of 2.5 mo
A material containing 1% was used and the film thickness was 100 nm.

All the thin films were formed by sputtering in the order of lower dielectric protective layer / recording layer / upper dielectric protective layer / reflection layer. Since the recording layer is in an amorphous state immediately after film formation by sputtering, the entire surface was annealed by laser light to change the phase to a crystalline state, which was set to an initial (unrecorded) state.

Therefore, for recording, a focused beam of a high-power laser is irradiated onto the track to change the recording layer into an amorphous state, and the resulting change in the amount of reflected light from the amorphous recording mark causes the recording mark to be changed. Detection can be performed. Then, the disk is rotated at a linear velocity of 10 m / s, a 680 nm semiconductor laser beam is focused on a recording film by an objective lens with a numerical aperture of 0.55, and a signal is recorded and reproduced while tracking control is performed by a push-pull method. I went.

Signal recording was carried out as follows. First, select an arbitrary groove and record the 7.47 MHz signal. The optimum recording power is from 10mW to 12mW 1
It was changed in mW increments. The erase power (= base power) was fixed at 6 mW for the purpose of performing 1-beam overwrite.

As a result, when measured with a spectrum analyzer at a resolution bandwidth of 30 kHz, the CN ratio was 54 to
A good value of 55 dB was obtained. Next, an arbitrary land was selected, the same recording was performed and the CN ratio was measured. As a result, a CN ratio of 54 to 55 dB which was exactly the same as that of the groove was obtained. By calculation, the phase difference of the reflected light when the recording layer is in the crystalline state and the amorphous state is 0.01π ahead of the reflected light in the amorphous state. The absorptance ratio A _c / A _a of the recording layer of this disc was calculated to be 0.85.

Example 2 A disc was prepared in the same manner as in Example 1 except that the Ge: Sb: Te composition of the recording layer was 22:25:53. Next, rotate the disk at a linear velocity of 3 m / s,
First, an arbitrary groove was selected, and a signal having a frequency of 2.24 MHz was recorded using the same signal recording device as in Example 1. The optimum recording power was from 8.5 mW to 10.5 mW, and was changed in 0.5 mW steps.

The erase power (= base power) was fixed at 4.5 mW for the purpose of performing one-beam overwriting. As a result, when the resolution bandwidth was measured at 10 kHz, the CN ratio was 57 to 59 dB, which was a good value. Next, when an arbitrary land was selected next time and the same recording was performed and the CN ratio was measured, the CN ratio 57-
59 dB was obtained.

At this time, the jitter of the recording mark was 8 ns measured from the beginning to the end of the mark by detecting the zero-cross point of the second derivative of the signal waveform. The phase difference of the reflected light when the recording layer is in the crystalline state and the amorphous state is calculated,
The reflected light in the amorphous state was advanced by 0.01π. The absorptance ratio A _c / A _a of the recording layer of this disc was calculated to be 0.85. FIG. 5 shows the relationship between the recording power and the CN ratio obtained in this example.

Example 3 The same disk as in Example 1 was rotated at 15 m / s, an arbitrary groove was first selected, and a signal having a frequency of 11 MHz was recorded. The optimum recording power was 12 mW, and the erasing power was fixed at 7 mW for the purpose of performing 1-beam overwriting.

As a result, a CN ratio of 52 dB was obtained by measuring the resolution bandwidth of 30 kHz. DC at 7mW after recording
When the recording track was irradiated with light, the carrier level decreased by 25 dB, and the erasing ratio was 25 dB, which was a good erasing characteristic. Next, when an arbitrary land was selected next time and the same recording was performed and the CN ratio was measured, a CN ratio of 52 dB which was completely equal to that of the groove was obtained. As for the erasing ratio, a value of 24 dB equivalent to that of the groove was obtained.

Comparative Example 1 A disk was manufactured in the same manner as in Example 2 except that the lower dielectric protective layer had a film thickness of 100 nm and the recording layer had a film thickness of 20 nm. Next, the disk was rotated at a linear velocity of 3 m / s, an arbitrary groove was first selected, and a signal having a frequency of 2.24 MHz was recorded using the same signal recording device as in Example 1.

The optimum recording power is up to 10 mW and 1 m
It was changed in increments of W. The erase power (= base power) was fixed at 4.5 mW for the purpose of performing 1-beam overwrite. As a result, when the resolution bandwidth was measured at 10 kHz, C
The N ratio was 56 dB, which was a good value.

Next, when an arbitrary land was selected and the same recording was performed and the CN ratio was measured, a CN ratio of 53 dB, which was exactly the same as that of the groove, was obtained. In this way, the signal quality of the land and the groove are not equal, and C
There was a difference of 3 dB in the N ratio. By calculation, the phase difference between the reflected light when the recording layer is in the crystalline state and the amorphous state is 0.20π ahead of the reflected light in the amorphous state.

Comparative Example 2 The thickness of the lower dielectric protective layer was 180 nm, the thickness of the recording layer was 20 nm, the thickness of the upper dielectric protective layer was 80 nm, and the thickness of the reflective layer was 100 nm. A disc was prepared in exactly the same manner as in Example 2. Next, the disk is rotated at a linear velocity of 3 m / s, an arbitrary land is first selected, and a frequency of 2.24 MH is obtained using the same signal recording device as in the first embodiment.
The z signal was recorded.

The optimum recording power was set to 8 mW to 9 mW, and was changed in 0.5 mW steps. The erase power (= base power) was fixed at 4.5 mW for the purpose of performing 1-beam overwrite. As a result, the resolution bandwidth is 10 kHz
In the measurement of z, a CN ratio of 50 to 51 dB was taken.

Next, select an arbitrary groove,
When the CN ratio was measured by performing the same recording, the CN ratio was 3
Only 9-40 dB was obtained. In this way, one of the land and groove signal qualities was significantly deteriorated, resulting in a difference of 11 dB in the CN ratio. By calculation, the phase difference of the reflected light when the recording layer is in the crystalline state and the amorphous state was 0.16π behind the reflected light in the amorphous state.

Absorption rate ratio A _c / A of the recording layer of this disc
_{Although a} was calculated to be 1.19, the jitter of the recording mark measured at the land portion was 13 ns, which was inferior to that of Example 2. FIG. 6 shows the relationship between the recording power and the CN ratio obtained in this comparative example.

Comparative Example 3 The lower dielectric protective layer had a thickness of 220 nm, the recording layer had a thickness of 20 nm, the upper dielectric protective layer had a thickness of 80 nm, and the reflective layer had a thickness of 100 nm. A disc was prepared in exactly the same manner as in Example 2.

Next, the disk was rotated at a linear velocity of 3 m / s, an arbitrary land was first selected, and a signal having a frequency of 2.24 MHz was recorded using the same signal recording apparatus as in Example 1. The optimum recording power is 8 mW to 9 mW, and 0.
It was changed in steps of 5 mW. Erase power (= base power) of 4.5 mW for the purpose of performing 1-beam overwrite
It was fixed.

As a result, a CN ratio of 51 to 52 dB was obtained in the measurement with a resolution bandwidth of 10 kHz. Next, when an arbitrary groove was selected next time and the same recording was performed to measure the CN ratio, only a CN ratio of 44 to 45 dB was obtained. In this way, one of the land and groove signal qualities was significantly deteriorated, resulting in a CN ratio difference of 7 dB.

The phase difference between the reflected light when the recording layer is in the crystalline state and the amorphous state is calculated, and the reflected light in the amorphous state is delayed by 0.25π. Although the absorptance ratio A _c / A _a of the recording layer of this disc is 1.21 by calculation, the jitter of the recording mark measured at the land portion is 1
It was 0 ns, which was inferior to that of Example 2.

Comparative Example 4 A disk was manufactured in the same manner as in Example 2 except that the lower dielectric protective layer had a thickness of 150 nm and the recording layer had a thickness of 20 nm. Next, the disk was rotated at a linear velocity of 3 m / s, an arbitrary groove was first selected, and a signal having a frequency of 2.24 MHz was recorded using the same signal recording device as in Example 1.

The optimum recording power was set to 10 mW to 12 mW and changed in 1 mW steps. The erase power (= base power) was fixed at 4.5 mW for the purpose of performing 1-beam overwrite. As a result, the resolution bandwidth is 10 kHz
In the measurement of z, the CN ratio was 54 to 55 dB, which was a good value.

Next, when an arbitrary land was selected and the same recording was carried out and the CN ratio was measured, a CN ratio of 54 to 55 dB which was completely equal to that of the groove was obtained. The CN ratios of the land and the groove are equal and sufficient, so that point is good. However, compared with Example 2, the CN ratio was reduced by about 4 dB and the optimum recording power was about 1.5 mW.
It was needed extra.

The deterioration of the recording sensitivity directly leads to the reduction of the laser light life of the drive used. The phase difference between the reflected light when the recording layer is in the crystalline state and the amorphous state is calculated, and the reflected light in the amorphous state is delayed by 0.03π. The absorptance ratio A _c / A _a of the recording layer of this disc was calculated to be 0.
It was 75.

[0097]

As described above in detail, according to the optical recording medium and the recording / reproducing method of the present invention, even if a signal is recorded on both the land and the groove, the groove depth is limited, so that the adjacent tracks are adjacent. Crosstalk from can be reduced. Further, since the phase difference between the phase of the reflected light from the unrecorded area and the phase of the reflected light from the recording area with respect to the coherent light having the same wavelength as the reproduction light is defined, the recording mark of the land portion The undesired difference between the carrier level and the carrier level of the groove part can be eliminated.

Therefore, a reproduction signal amplitude of the same level can be obtained regardless of whether recording is performed in the land portion or the groove portion, and a high quality and highly reliable land groove recording disk can be provided. Further, the ratio of the irradiation light absorbed by the recording layer when the recording layer of the optical recording medium of the present invention is in the amorphous state, and the irradiation light absorbed by the recording layer when the recording layer is in the crystalline state. Where A _a is the case where the recording layer is in the amorphous phase and A _c is the case where the recording layer is in the crystalline state, the ratio A _c / A _a of the absorptance between the crystalline state and the amorphous state is

[0099]

By defining the range of 0.84 ≦ A _c / A _a <1.01, excellent characteristics with a high CN ratio and low recording mark jitter can be guaranteed, and an excellent disk can be provided. Further, by using the optical recording medium of the present invention, both on and between the grooves are used as recording areas, and any area can be recorded, erased, and reproduced by one-beam overwriting with a laser having a wavelength of 700 nm or less. A characteristic recording / reproducing method can be provided.

[Brief description of drawings]

FIG. 1 is an enlarged perspective view for explaining a groove shape of an optical disc and a positional relationship between a converged beam of an irradiation laser beam and a focused beam of an irradiated laser beam according to the present invention.

FIG. 2 is an enlarged perspective view for explaining the positional relationship between the groove shape of the optical disc and the convergent beam of the irradiation laser light in the present invention.

FIG. 3 is an enlarged perspective view for explaining the positional relationship between the groove shape of the optical disc and the convergent beam of the irradiation laser light in the present invention.

FIG. 4 is an enlarged perspective view for explaining the positional relationship between the groove shape of the optical disc and the convergent beam of the irradiation laser light in the present invention.

FIG. 5 is a diagram showing the relationship between recording power and CN ratio in an example.

FIG. 6 is a diagram showing the relationship between recording power and CN ratio in a comparative example.

[Explanation of symbols]

 1 substrate 2 recording layer 3 land part 4 groove part 5 convergent beam 6 region of convergent beam irradiated on land 7 region of convergent beam irradiated on groove 8 recording mark

Claims (6)

[Claims] 1. A structure in which a lower dielectric protection layer, a phase-change recording layer, an upper dielectric protection layer, and a metal reflection layer are sequentially laminated on a transparent substrate having a groove formed thereon, and between the groove and the groove. An optical recording medium for recording, erasing, and reproducing information by irradiating a laser beam having a wavelength of 700 nm or less, using both as recording areas, wherein (1) a groove width is 0.1 μm or more and 0.7 μm or less, The interval between the grooves is 0.1 μm or more and 0.7 μm or less, and the groove depth d satisfies the following inequality: λ / 7n <d <λ / 5n (where λ: irradiation light Wavelength, n: Refractive index of substrate, d:
Depth of groove) (2) The phase difference α between the reflected light from the unrecorded area and the reflected light from the recorded area defined below is α = (phase of reflected light from unrecorded area) − (recorded area Phase of reflected light from) An optical recording medium characterized by satisfying the following expression: (m−0.1) π ≦ α ≦ (m + 0.1) π (m is an integer). 2. Of the irradiation laser light of wavelength λ, the above-mentioned
The ratio of absorption in the recording layer is the amorphous phase of the recording layer
Case A_a, A when the recording layer is in a crystalline state _cAnd
Then, the ratio A of the absorptance between the crystalline state and the amorphous state_c/
A_aIs the following: 0.84 ≤ A_c/ A_a The optical recording medium according to claim 1, wherein <1.01. 3. The optical recording medium according to claim 1, wherein the recording layer is made of an alloy containing Ge, Sb, and Te as a main component and has a thickness of 20 ± 5 nm. 4. The reflection layer is an alloy of Al and Ti or Ta, and the content of Ti or Ta is 0.5 to 3.5a.
It is t%, The optical recording medium in any one of Claims 1-3. 5. One or both of the lower dielectric protective layer and the upper dielectric protective layer are made of ZnS and SiO _2.
Or a mixed film of either one of Y ₂ O _3, the content of SiO ₂ or Y ₂ O ₃ is 5 to 40 mol%
The optical recording medium according to any one of claims 1 to 4, wherein 6. The optical recording medium according to claim 1, wherein both the groove and the groove are used as a recording region, and recording and erasing are performed in both regions by one-beam overwriting with a laser having a wavelength of 700 nm or less, A recording / reproducing method characterized by reproducing.