JP3376806B2 - Optical recording medium and recording / reproducing method - Google Patents

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, and an optical information recording for recording, reproducing and erasing information on both the groove portion and the groove portion of a substrate by irradiating a laser beam. The present invention relates to a medium and a recording / reproducing method.

[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 normally recorded only 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 information on both the groove and the guide groove, the land between the guide grooves, and both the land portion and the groove portion will be described as L & G recording.

As a proposal for L & G recording, Japanese Patent Publication No. 63-5
7859, etc., but when such a technique is used, it is necessary to pay great attention to the reduction of 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 dependency of crosstalk described in this paper, the effect of reducing crosstalk can be seen by optimizing the groove depth. And the CN ratio in the groove 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.

[0011]

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.

[0012]

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, a dielectric layer, a phase change recording layer, a dielectric layer, and a metal reflective layer are sequentially laminated, and both the groove and the groove are used as a recording area.
An optical recording medium for recording, erasing and reproducing information by irradiating a laser beam having a wavelength of 00 nm or less, wherein (1) the groove width is 0.1 μm or more and 0.7 μm or less, and the width between grooves <br / > Is 0.1 μm or more and 0.7 μm or less, the groove width and the width between the grooves are
And the groove depth d satisfies the following inequalities,

[0013]

## EQU5 ## λ / 7n <d <λ / 5n (λ: wavelength of irradiation light, n: refractive index of substrate, d: depth of groove)

(2) Of the reflected light from the unrecorded area and the reflected light from the recorded area defined below, the one with the higher reflectance is R _high (%), and the one with the lower reflectance is R _low (%), If the phase difference between the reflected light from the unrecorded area and the recorded area is 2πα ,

[0015]

(6) 10 ≤ R _high ≤ 40

[0016]

## EQU00007 ## Rlow / Rhigh.ltoreq.0.15 m.pi..noteq.2.pi..alpha. ( M is an integer) where 2.pi..alpha. = (Phase of reflected light from unrecorded area)-(phase of reflected light from recording area) Fill and irradiate laser light of wavelength λ
Then, the absorption rate of the recording layer is determined by the recording layer.
A _a when the phase is a phase and when the recording layer is in a crystalline state
Absolute rate in crystalline and amorphous states, where A _c
The ratio A _c / A _a of

An optical recording medium, wherein the Equation 8 is a _{0.84 ≦ A c / A a <} 1.01.

With the above-described structure, 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 guaranteeing 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 phase of the reflected light from the land portion lags 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 by 2πα from the reflected light from the crystalline region.

In the following, the amplitude reflectance of the convergent beam will be formulated using the phase difference 2πα 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]

[Formula 9] φ ₁ = R _c1 · exp [−2πi · 2nd / λ] + R _c2 · exp [−2πi · 0] (a)

Where R _c1 is the amount of reflected light from the region 6 of the land portion irradiated with the convergent beam, 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
Indicates an imaginary unit. As shown in FIG. 2, the amplitude reflectance φ ₂ when the convergent beam 5 is on the land portion having the amorphous recording mark can be expressed by the following equation.

[0026]

Equation 10] _{φ 2 = R a1 · exp [} -2πi (2nd / λ + α)] + R c2 · exp [-2πi · 0] (b) provided that, R _a1 is the region 6 of land portions converging beam is irradiated , R _c2 indicates the amount of reflected light from the region 7 of the groove portion irradiated with the convergent beam.

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]

Equation 11] _{φ 3 = R c1 · exp [} -2πi · 0] + R c2 · exp [-2πi (2nd / λ)] (c) provided that, R _c1 is from the region 7 of the groove portions converging beam is irradiated , 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]

Equation 12] _{φ 4 = R a1 · exp [} -2πiα] + R c2 · exp [-2πi (2nd / λ)] (d) where the reflection from the region 7 of the R _a1 is a groove portion converging beam is irradiated The amount of light, R _c2 , indicates the amount of light reflected from the region 6 of the land portion irradiated with the convergent beam.

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]

[ Equation 13] R _c2 = βR _c1 (e)

[0033]

## EQU00004 ## Multiply 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]

Equation 15] _{R c1 = R c / (1} + β) (g)

[0035]

[Number 16] _{R c2 = βR c / (1} + β) (h)

[0036]

[Number 17] _{R a1 = R a / (1} + β) (i)

[0037]

## EQU16 ## R _a2 = βR _a / (1 + β) (j) Substituting equations (g) to (j) into equations (a) to (d) and rearranging,

[0038]

[Number 19] _{φ 1 = [R c / (} 1 + β)] [β + exp [-4πind / λ]] (k)

[0039]

Equation 20] _{φ 2 = [1 / (1} + β)] · [βR c + R a · exp [-4πind / λ-2πiα]] (l)

[0040]

Equation 21] _{φ 3 = [R c / (} 1 + β)] [1 + β · exp [-4πind / λ]] (m)

[0041]

Equation 22] _{φ 4 = [1 / (1} + β)] [R a · exp [-2πiα] + βR c · exp [-4πind / λ]] (n) Here, when recorded in the land portions, reproduced carrier Level CL '(L) is

[0042]

[Equation 23] 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 24] 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 converted into expressions (m) and (o).
Substituting into, the difference is calculated, and the necessary condition for the difference to be 0 is obtained, 2πα = mπ (where m is an integer). This result shows that when the phase difference between the phase transitions is an integral multiple of π (including 0), the reproduction signal amplitudes of the land portion and the groove portion are equal when the land width = the groove width. .

Contrary to this, we have intentionally made a disc having a layer structure having a phase difference between phase transitions, and conducted intensive studies. As a result, they have found a new condition that the signal amplitudes of the land portion and the groove portion do not differ even if the phase difference between phase transitions takes any arbitrary value. This condition is the reflection of the mirror surface of the disc when the recording layer is in a crystalline state.
Ratio and the mirror surface reflectance of the disk in the amorphous state are limited within a certain range.

In the first place, when land width = groove width,
The difference in the reproduction signal amplitude between the land and the groove is related to the phase difference depending on the groove shape and the phase difference between the phase transitions, but the difference in the reflected light amount between the land and the groove (that is, the difference in the reproduction signal amplitude) is It is also highly dependent on the degree of interference effect depending on the ratio of reflectance between transitions. That is, the mirror surface reflectance of the disk when the recording layer is in the crystalline state and the mirror surface portion of the disk when the recording layer is in the amorphous state
Larger one R _high reflectance of the reflectance, when the smaller reflectivity and R _low, if R _low is sufficiently small compared to R _high, the land by how interference substantially even trying phase difference is about to occur And the difference in the amount of reflected light from the groove is sufficiently small.

For the purpose of actually investigating this, we made a large number of discs having different phase differences between phase transitions and R _high and R _low , and examined the influence on the difference in the reproduced signal amplitude between the land and the groove. As a result, as shown in claim 1 of the present invention, in the disk with a limited range of R _high in the range of 10% to 40%, by R _low / R _high is 0.15 or less, the phase transition Even if the interphase difference is any value,
It has been found that it is possible to equalize the signal quality of land recording and the signal quality of groove recording in L & G recording. The specification of the range R _low / R _high necessary for this purpose can be realized by appropriately selecting the optical constants and the film thickness of each layer.

Regarding the groove depth of the substrate, see Jpn. J. A
ppl. Phys. Vol 32 (1993) pp. 53
24-5328, crosstalk from adjacent tracks is reduced when the groove depth is λ / 7n to λ / 5n (λ: reproducing light wavelength, n: refractive index of substrate). , It is desirable to be in this range. here,
The measuring method of the groove width and the groove depth will be described. The measurement is He
-Ne laser light (wavelength: 630 nm) was irradiated from the side of the substrate having no groove, and the transmitted light was diffracted by the groove of the substrate to obtain 0-th order light intensity I ₀ , first-order light intensity I ₁ , and second-order light intensity I _2. And by measuring the angle of the diffracted light. 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.

[0049]

[ Equation 25] I ₂ / I ₁ = cos ² (πε)

[0050]

Equation 26] _{I 1 / I 0 = {2sin} 2 (πε) (1-cosδ)} / [π 2 {1-2ε (1-ε) (1-cosδ)}]

[0051]

Equation 27] 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 can be applied even when it is deviated from the rectangular shape. In terms of ensuring high signal quality regardless of whether recording on the land or groove tracks, in that respect, not only the phase difference is limited but also the ratio of the optical absorptance before and after the phase change of the recording layer falls within a certain range. The effect is amplified by limiting. In PWM recording, since information of 0 or 1 is assigned to the front end and the rear end of the recording mark,
In particular, 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.

Here, the absorptance in the crystalline state is set as A _c , and the absorptance in the amorphous state is set as A _a . For example,
As described in JP-A-5-298747, in the absorptance of the recording layer, a larger absorptance in the crystalline state than in the amorphous state results in a larger CN ratio, a higher erasing rate and a wider power permissible range ( There is a proposal to get a margin).

However, in our study, it is not necessary to make the absorptance in the crystalline state significantly higher than that in the amorphous state.
In terms of the ratio and the jitter of the recording mark, the ratio of absorptance A _c / A _a
But

[0057]

(29) 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 rotational speed of the disk is within a certain limited range, and the linear velocity is from 1.4 m / s to 1
In the disk having the absorptance ratio within this range over a wide range of 5 m / s, the effect of being excellent was remarkably observed.

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

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 into a film having 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.

A resin layer is preferably 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.

Further, 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, recording / erasing / reproduction can be performed simultaneously on both sides without replacing the disc at all. 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. Can be measured, such as by measuring the For laser interference microscope of the phase difference.

Since A _c / A _a is the absorptance ratio of only the recording layer in the multilayer 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 / reproduction of the optical disc of the present invention uses a one-beam laser focused by an objective lens and irradiates from the substrate side of the rotating optical disc.

At the time of recording and erasing, the rotating disk is irradiated with a pulsed laser beam to change the recording layer into two reversible states, a crystalline state and an amorphous state, and a recording state or an erasing state (unrecorded 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, a laser beam having a power lower than the laser power at the time of recording and erasing is applied to the rotating disk. 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.

[0071]

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. The width of the tracking groove (groove width) formed on the substrate and the width between the grooves (land width) are set to be 1 for the purpose of reducing the leakage of the signal from the adjacent track in any case. It is desirable to set it to: 1.

However, from the viewpoint of ensuring the track cross signal or preventing the deterioration of the characteristics when recording and erasing are repeated many times, the groove width and groove width are considered in consideration of the optimum shapes of the land and the groove. If the land width ratio is such that crosstalk does not occur,
You may intentionally deviate slightly from 1: 1.

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. Disks having different layer thicknesses were prepared.

Table 1 shows a list of the film thickness, reflectance, reflectance ratio between phase transitions, phase difference and absorptance ratio of the recording layer.
Both are included in the optical disc of the present invention. The lower dielectric protection layer and the upper dielectric protection layer are made of ZnS and SiO ₂ (4: 1
(Molar ratio).

The recording layer is 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 22:25:53 (atomic ratio).

For the reflective layer, a material containing 2.5 mol% of Ta in Al was used. All thin films are sputtered to lower dielectric protective layer / recording layer / upper dielectric protective layer /
The reflective layer was formed in this order. 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, the recording layer is irradiated with a convergent beam of a high-power laser to change the recording layer to an amorphous state, and the resulting change in the amount of reflected light from the amorphous recording mark causes the recording mark to change. Can be detected. Then, the disk is rotated at a linear velocity of 3 m / s, a 680 nm semiconductor laser beam is focused on the 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 performed as follows. The irradiation pulse is modulated with three values of the recording power of the semiconductor laser, the base power (erasing power), and the reproducing power for the purpose of performing one-beam overwriting, and the recording frequency is 2.2.
The frequency was 4 MHz and the duty ratio was 25%. The reproduction power was fixed at 1.0 mW.

Recording power and base power (erasing power)
First, the base power was fixed at 4.5 mW, only the recording power was changed and recording was performed, the carrier level was measured using a spectrum analyzer, and the power at which the carrier level rises was taken as the optimum recording power.

Next, the recording power is fixed to the optimum recording power, the base power combination is changed, and the base power (erasing power) that minimizes the jitter of the recording power is set as the optimum base power (erasing power). . Table 1 shows the CN ratio after overwriting recording 10 times on the groove and land.
It was shown to. In each case, the quality of the reproduced signal was good in both the land portion and the groove portion.

[0082]

[Table 1]

Example 2 A disk was produced in the same manner as in Example 1 except that the Ge: Sb: Te composition of the recording layer was 2: 2: 5. This recording layer composition has a faster crystallization rate than the recording layer of Example 1, and is suitable for a case where the linear velocity or the rotational velocity of the disc is higher.

These disks were rotated at a linear velocity of 10 m / s, and the same recording / reproducing experiment as in Example 1 was conducted. As a result, although the recording power and the base power (erasing power) are different from those in the first embodiment, in other points, the static characteristics such as the reflectance and the phase difference between phase transitions and the dynamic characteristics such as the CN ratio are almost the same. The experimental results were obtained.

Comparative Example 1 As a comparative example of Example 1, a disk was prepared in which only the film thickness of each layer was changed. The Ge: Sb: Te composition of the recording layer is 2
It is 2:25:53. Table 2 shows a list of the film thickness of each layer, the reflectance, the reflectance ratio between phase transitions, the phase difference, and the absorptance ratio of the recording layer.

Neither disc is included in the scope of the optical disc of the present invention. Signal recording and evaluation were performed in the same manner as in Example 1. The linear velocity of the disk was 3 m / s. The evaluation results are shown in Table 2. As described above, unlike the disc of the first embodiment, there is a large difference in the reproduction signal quality between the land portion and the groove portion.

Further, in the disc having the absorptance ratio of the recording layer outside the range of the present invention, the jitter of the recording mark was worse than that of the disc of Example 1.

[0088]

[Table 2]

Comparative Example 2 As a comparative example of Example 2, a disk was prepared in which only the film thickness of each layer was changed. The Ge: Sb: Te composition of the recording layer is 2:
A disk was produced in the same manner as in Comparative Example 1 except for 2: 5. Neither disc is included in the scope of the optical disc of the present invention.

The linear velocity of the disk is 10 as in the second embodiment.
m / s, and signal recording and evaluation were performed in the same manner as in Example 2. As a result, although the recording power and the base power (erasing power) are different from those in Comparative Example 1, the static characteristics such as the reflectance and the phase difference between phase transitions and the dynamic characteristics such as the CN ratio are almost the same in other points. The experimental results were obtained.

That is, there is a large difference in the reproduced signal quality between the land portion and the groove portion. Further, in the disc having the absorptance ratio of the recording layer outside the range of the present invention, the recording mark jitter was worse than that of the disc of Example 2.

[0092]

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 ratio of the reflectance of the reflected light from the unrecorded area to the coherent light having the same wavelength as the reproduction light and the reflectance of the reflected light from the recording area 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 made on 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 Aa is the case where the recording layer is in the amorphous phase and Ac is the case where the recording layer is in the crystalline state, the ratio of the absorption rate between the crystalline state and the amorphous state, A _c / A _a ,

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 disc 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 is recorded, erased, and reproduced by one-beam overwrite of a laser having a wavelength of 700 nm or less. It is possible to provide a recording / reproducing method characterized in that

[Brief description of drawings]

FIG. 1 is an enlarged perspective view for explaining a positional relationship between a groove shape of an optical disk and a converged beam of irradiation laser light in an example.

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 example.

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 example.

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 example.

[Explanation of symbols]

1 substrate 2 recording layers 3 land section 4 Groove part 5 Focused beam Area of convergent beam irradiated on 6 lands 7 Area of convergent beam irradiated on the groove 8 record marks

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI G11B 7/00 B41M 5/26 X (56) References JP-A-7-311980 (JP, A) JP-A-7-287872 ( JP, A) JP 6-215415 (JP, A) JP 5-159360 (JP, A) JP 3-113844 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24

Claims (5)

(57) [Claims] 1. A transparent substrate on which a groove is formed, and a dielectric layer, a phase-change recording layer, a dielectric layer, and a metal reflective layer are sequentially laminated on the transparent substrate. as used, the recording of information by irradiating a laser beam having a wavelength of not more than 700 nm, erase, an optical recording medium to reproduce, (1) the groove width is 0.1μm or more 0.7μm or less, the width between the grooves is 0.1 μm or more and 0.7 μm or less, the groove width and the width between the grooves are
Almost equal and the groove depth d satisfies the following inequality: λ / 7n <d <λ / 5n (λ: wavelength of irradiation light, n: refractive index of substrate, d: depth of groove (2) Of the reflected light from the unrecorded area and the reflected light from the recorded area defined below, the one with the higher reflectance is R
_high (%), lower the the R _low (%), the unrecorded area and When 2πα the phase difference between the reflected light from the recording area, Equation 2] 10 ≦ R _high ≦ 40 Equation 3] R _low / R _high ≦ 0.15 mπ ≠ 2πα (m is an integer) where 2πα = (phase of reflected light from unrecorded area) − (phase of reflected light from recording area) is satisfied, and Of the irradiated laser light, it is absorbed in the recording layer
That when the recording layer is amorphous phase ratio A _a, serial
When the recording layer is in the crystalline state, A _c is the crystalline state.
An optical recording medium, wherein the ratio _{A c} / A _a in the absorption rate of the amorphous state Equation 4 is a _{0.84 ≦ A c / A a <} 1.01. Wherein the recording layer is made of an alloy mainly Ge, Sb, and Te, claim thickness of 20 ± 5 nm 1
The optical recording medium according to 1. 3. The reflection layer is an alloy of Al and Ti or Ta, and the content of Ti or Ta is 0.5 to 3.5 at%.
The optical recording medium according to claim 1 or 2 , wherein 4. One or both of the lower dielectric protective layer and the upper dielectric protective layer comprises ZnS and SiO ₂ or Y.
SiO 2 is a mixed film with one of ₂ O ₃ and
The optical recording medium according to claim 1 , wherein the content of ₂ or Y ₂ O ₃ is 5 to 40 mol%. 5. The optical recording medium according to claim 1, wherein both the groove and the groove are used as recording areas, and recording and erasing in both areas by one-beam overwriting with a laser having a wavelength of 700 nm or less, A recording / reproducing method characterized by reproducing.