JP3376807B2 - 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.
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 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 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 Vol. 1316, Optical D
ata Storage (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 of reducing crosstalk without providing a special optical system or a signal processing circuit for reducing the reproduction crosstalk, the width of the groove (guide groove) and the land (between the guide grooves) is reduced. There is a proposal that it is effective to make the grooves equal to each other and 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.
These proposals are based on the assumption that the widths of the grooves and lands are equal, and based on that, we show the crosstalk reduction effect by computer simulation, show an example of actually making and evaluating a disk, and show its effectiveness. Mention sex.

However, as a result of further diligent studies, when the groove width is narrowed while keeping the groove and land widths to 1: 1 to increase the density by narrowing the track pitch, after repeated overwriting. The characteristics of the land are significantly deteriorated in terms of the unerased mark before the mark and the deterioration of the jitter of the record mark, and conversely, even if the track pitch is narrowed in the groove, the erasure property and the jitter after the repeated recording overwrite are not easily deteriorated. There was found.

[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 beam as a light source, whichever the land portion or the groove portion is used as a recording area, It is an object of the present invention to provide a highly reliable high-density optical disc, in which both the repeated overwrite characteristics are kept at a high level.

[0012]

The present invention has been made as a result of repeated studies on the regulation of the groove depth and the influence of the groove width and the land width on the repetitive recording / erasing characteristics. On the formed transparent substrate, the lower dielectric protective layer, the phase change recording layer, the upper dielectric protective layer,
An optical recording medium having a structure in which metal reflective layers are sequentially stacked, and recording and erasing and reproducing information by irradiating a laser beam using both of the above-mentioned groove and the space between the grooves as recording areas, The depth d of the groove satisfies the following inequality,

[0013]

## EQU6 ## λ / 7n <d <λ / 5n (where λ: wavelength of irradiation light, n: refractive index of substrate, d:
Groove depth)

(2) The width of the groove is GW, and the width between the grooves is LW
And both are larger than 0.1 μm, and

[0015]

[Equation 7] GW <LW and

[0016]

## EQU8 ## 0.62 × (λ / NA) ≤ LW ≤ 0.
The optical recording medium is characterized by satisfying 80 × (λ / NA) (NA is the numerical aperture of the lens).

With the above-described structure, in the optical disc of the present invention, it is possible to prevent a significant reduction in the erase ratio at the land portion, regardless of whether recording or erasing is repeated a number of times on either the land portion or the groove portion. It is possible to obtain a high-quality reproduced signal with low recording mark jitter in both the land portion and the groove portion.

By taking advantage of the wide margin even if the groove width is narrowed in terms of the repetitive overwrite characteristic, the groove width is defined to be narrower than the land width, so that the track pitch is narrowed to the same extent. It is possible to achieve the same or higher density as the L & G recording optical disc having the same land width and groove width. The present invention will be described in detail with reference to specific examples.

FIG. 1 is an enlarged perspective view schematically showing a part of the optical disc of the present invention. 3 and 4 respectively
The land portion and the groove portion are formed on the disk substrate in advance, and the widths of the land portion and the groove portion are drawn larger than they actually are. However, the width of the land portion 3 is larger than that of the groove portion 4 according to the present invention. It is wide in the range described in claim 1.

Although the recording layer 2 is actually protected by a dielectric layer or the like, layers other than the recording layer 2 are omitted for the sake of easy understanding of the drawing. The recording layer 2 is formed of a material that causes a reversible phase change, and information is recorded, erased, and reproduced by utilizing the fact that the reflected light amount of the irradiation laser light changes between a crystalline state and an amorphous state. .

FIG. 1 shows an example in which an unrecorded area on the land portion 3 of the L & G optical disk is irradiated with a reproduction light beam. Reference numeral 5 denotes a laser beam focused by using an objective lens or the like, which is irradiated onto the disc from the substrate 1 side and used for recording, erasing and reproducing.
Since the convergent beam 5 is emitted from the substrate side, it is incident from the other side of the paper surface and reflected.

Therefore, when viewed from the light source side, the land portion 3
Is concave, while the groove portion 4 is convex. The step d between the land 3 and the groove 4 may be any value within the range of λ / 7n to λ / 5n, where λ is the wavelength of the convergent beam 5 and n is the refractive index of the substrate 1.

This is described in Jpn. J. Appl. Phys.
Vol 32 (1993) pp. As described in 5324-5328, the groove depth is λ / 7n to λ / 5.
This is because crosstalk from adjacent tracks is reduced when n (λ: wavelength of reproduction light, n: refractive index of substrate).
In the present invention, the width of the land is in the range of 0.62 × (λ / NA) to 0.80 × (λ / NA).

Here, λ is the wavelength of the irradiation light, and NA is the numerical aperture of the objective lens. When the width of the land is narrower than this range, when the recording mark is repeatedly overwritten on the land, the unerasure of the previous mark becomes remarkable and the jitter of the recording mark is significantly deteriorated. When the width of the land is within this range, there is no erasure of the previous mark or marked deterioration of the jitter of the recording mark when repeatedly overwritten, and the same characteristics as when recording in the groove are maintained.

When the width of the land is larger than this range, there is no problem in the repetitive overwrite characteristic of the land and good characteristics can be obtained, but from the viewpoint of high density recording, the land width is meaninglessly widened and the recording density is increased. It is not a good idea to reduce the. Here, the measuring method of the groove width and the groove depth will be described. He-Ne laser light (wavelength 633n is measured.
m) is irradiated from the side of the substrate having no groove, and the transmitted light is diffracted by the groove of the substrate to measure the 0th order light intensity I ₀ , the 1st order light intensity I ₁ , the 2nd order term intensity I ₂ and the angle of the diffracted light. By doing. 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,

[0026]

[Equation 9] I ₂ / I ₁ = cos ² (πε)

[0027]

## EQU10 ## I ₁ / I ₀ = {2sin ² (πε) (1-c
osδ)} / [π ² {1-2ε (1−ε) (1-cos
δ)}]

[0028]

(11) ε = w / P, δ = 2 (n-1) πd / λ
(N is the refractive index of the substrate)

[0029]

(12) P = λ / sin θ

Since the relationship of is satisfied, the groove width and the 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 rectangle.

When the above method is actually applied to the calculation, not only a true solution but also an impossible solution may be derived at the same time. In order to prevent mistakes in determination of measured values due to this, SEM is used for surface observation and cross-section observation of the substrate disk.
It is certain that the dimensions of the groove shape are grasped in advance by using the method described above, and that the above measurements and calculations are applied to determine the accurate groove width and groove depth to determine the groove shape. is there.

In the present invention, since the land width is wider than the groove width, the width of the recording mark on the land becomes wider than the width of the recording mark on the groove, and as a result, the reproduction signal amplitude or CN ratio ( The carrier-to-noise ratio) becomes larger than that in the groove, which may cause a difference in signal quality between the two. In such a case, it is effective to select the layer structure so that the reproduced signal amplitude or CN ratio in the groove becomes larger than that in the land.

As a guideline, it may be devised so that the change in the reflected light amount of the reproduction light before and after recording in the groove becomes larger than that in the land. As a concrete measure,
It is effective to pay attention to the phase change of the reflected light before and after recording and to define the phase change within a certain range so as to be advantageous for recording on the groove. As a result of our earnest studies, condition (1): when the reflectance of the recording area of the optical recording medium of the present invention is lower than the reflectance of the unrecorded area, the reflected light from the unrecorded area and the recording area The phase difference α between the reflected lights of the following equation is α = (phase of the reflected light from the unrecorded area) − (phase of the reflected light from the recording area)

[0034]

[Expression 13] −π <α <0 That is, the phase of the reflected light from the unrecorded area is delayed from the phase of the reflected light from the recorded area within the range of 0 to π.

Condition (2): When the reflectance of the recording area of the optical recording medium of the present invention is higher than the reflectance of the unrecorded area, it is between the reflected light from the unrecorded area and the reflected light from the recorded area. The phase difference α is expressed by the following equation α = (phase of light reflected from unrecorded area) − (phase of light reflected from recorded area)

[0036]

0 <α <π That is, the phase of the reflected light from the unrecorded area leads the phase of the reflected light from the recording area within the range of 0 to π.

By satisfying the above condition (1) or condition (2), the reproduced signal amplitude in groove recording can be improved, and a signal of equal quality can be obtained in both recording of land and groove. The amplitude could be obtained.
Furthermore, in the case of the above condition (1),

[0038]

[Equation 15] − (3/4) π <α <− (1/4) π In the case of the above condition (2),

[0039]

## EQU16 ## It is more desirable to be in the range of (1/4) π <α <(3/4) π in order to increase the reproduction signal amplitude of the recording mark on the groove.

In order to design a disk satisfying these conditions, it is necessary to accurately grasp the phase difference between the reflected light before and after the phase change. The phase change of the reflected light before and after the phase change can be measured by a laser interference microscope or the like, but it can be obtained by calculation using the optical constant and film thickness of each layer of the disk, which is effective. The calculation method is “Fundamentals and Methods of Spectroscopy” (Kei Keiei, Ohmsha, 19
85) It is described in detail in Chapter 3.

The optical constants of the respective layers may be measured by an ellipsometer or the like after forming a monolayer film by a method such as sputtering in advance. The influence of the reflectance change and the phase change before and after the recording when the land recording or the groove recording is applied is described in detail in JP-A-5-128589 using mathematical expressions.

However, Japanese Unexamined Patent Publication No. 5-128589 does not mention that both the land and the groove are used for the recording area. In addition, there is no regulation concerning the width of the land and the groove, and the C in the groove having a narrow width with respect to the wide land as introduced in the present invention.
It is not an improvement in N ratio.

Although a phase change material can be applied to the recording layer, a chalcogen phase change material having a composition of Ge, Sb and Te as main components can be formed to a thickness of 20 ± 5 nm. 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.

As the reflective film, a metal material containing Al as a main component can be applied. Particularly, in consideration of recording sensitivity and stability, an alloy of Al and Ti or Al and Ta is preferable. Hopefully, the content of Ti or Ta is preferably 0.5 at% to 3.5 at%,
At this time, the loss of the reflectance of the disk is small, and it functions as an appropriate heat dissipation layer.

The L & G optical disk of the present invention is a rewritable optical information recording medium, but 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 an ordinary optical thin film such as magnetron DC sputtering or RF sputtering on a substrate disk such as resin or glass in which a groove is formed in advance. It is desirable that a resin layer is applied or spin-coated on the metal reflection layer to protect the film.

The dielectrics used in the dielectric layer in the present invention can be combined in various ways and are determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion and the like. . Generally, Mg, Ca, which has high transparency and high melting point,
Sr, Y, La, Ce, Ho, Er, Yb, Ti, Z
r, Hf, V, Nb, Ta, Zn, Al, Si, Ge,
Oxides such as Pb, sulfides, nitrides, carbides, Ca, M
Fluorides such as g and Li can be used.

Alternatively, when a mixed film containing at least one of ZnS and ZnSe and at least one of the above compounds is used, good repetitive overwrite characteristics and stability over time can be obtained. In this case, when the content of the metal compound is 5 to 40 mol%, the storage stability of the recorded disc is particularly 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 so that the surfaces on the opposite sides of the substrates face each other. 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.

Recording / erasing / reproduction of the optical disk of the present invention uses a one-beam laser focused by an objective lens and irradiates from the substrate side of the rotating optical disk. At the time of recording and erasing, a rotating disk is irradiated with a pulsed laser beam to change the recording layer into two reversible states, a crystalline state or an amorphous state, and a recording state or an erasing state (unrecorded state). To do.

At this time, by overwriting, it is possible to simultaneously erase the marks existing before recording while recording. At the time of reproduction, laser light 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 the reflected light with a photodetector and determining the recorded or unrecorded state.

[0053]

EXAMPLES The present invention will be described in more detail below with reference to examples. The disk substrates used in the examples and comparative examples were preliminarily formed with tracks having various groove widths and land widths, and a plurality of disk substrates having slightly different groove shapes were prepared. A film having the same layer structure including a recording layer was formed on these substrates.

Example 1 Polycarbonate (refractive index 1.56 for laser light having a wavelength of 680 nm) was used as a substrate material. The repeated overwrite characteristics were compared using a plurality of regions having different land widths and groove widths. Each area (area 1
3) and the land width and groove width are shown in Table 1.

[0055]

[Table 1]

The lower dielectric protective layer and the upper dielectric protective layer are made of a mixture of ZnS and SiO ₂ (4: 1 molar ratio), and the thickness of the lower dielectric protective layer is 100 nm and the thickness of the upper dielectric protective layer is 100 nm. It 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.
Using a material whose main component is e, the composition ratio is Ge: Sb:
Te was set to about 22:25:53 (atomic ratio). The thickness of the recording layer was 25 nm. A material containing 2.5 mol% of Ta in Al is used for the reflective layer, and the film thickness is 100 n.
m.

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 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. Detection can be performed. 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 carried out as follows. A land or groove is selected as a recording area, and a long recording mark of 2.7 μm (mark length: length between marks = 1: 1)
Is repeatedly overwritten a predetermined number of times, and finally 0.
Evaluation was performed by overwriting the short recording mark of 67 μm and measuring the jitter of the recording mark.

When a long 2.7 μm mark was recorded as the input pulse, a divided pulse as shown in FIG. 2 was used to prevent the recording mark from deforming into a tear shape due to thermal interference during recording. When recording a short mark of 0.67 μm, a pulse of 2.24 MHz and a duty ratio of 25% was input.

A typical pulse pattern during overwriting is shown in FIG. At the time of recording, the recording layer is melted and rapidly cooled by setting the laser power to P _w to make the recording layer in an amorphous state. Around this time, by lowering the laser power to P _b , the temperature of the recording layer is raised above the crystallization temperature and below the melting point to realize the crystalline state, that is, the unrecorded state, and the previous mark is erased, and the overwriting is performed. Will be realized.

It is realized by setting the laser power to P _r at the time of reproduction and keeping it at a temperature low enough not to cause a phase change of the recording layer. The laser powers P _w and P _e for optimum overwriting were recorded while changing the power in a matrix, and the power at which the jitter of the recording mark was minimized was the optimum value.

The jitter of the recorded mark was measured by detecting the zero-cross point of the second derivative of the signal waveform from the beginning to the end of the mark. FIG. 4 shows the change in jitter of a short mark of 0.67 μm when repetitive overwriting was performed. It can be seen that, in the land as well, as in the case of the groove, good repeating characteristics are obtained.

Comparative Example 1 Unlike Example 1, a plurality of regions (regions 4 to 5) having land widths outside the range of the present invention were used to compare the repetitive overwrite characteristics. Table 2 shows each region, land width, and groove width.

[0066]

[Table 2]

The same evaluation as in Example 1 was performed, and the results are shown in FIG.
It was shown to. Unlike Example 1, the deterioration of the repeating characteristics in the land portion is remarkable.

[0068]

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, by limiting the land width and the groove width to an appropriate range with respect to the convergent beam diameter determined by both the wavelength of the laser light and the numerical aperture of the objective lens, the land and groove using the conventional land width = groove width is used. It is possible to provide a disc that is more excellent in repetitive overwrite characteristics in the land portion than in recording. Also, by adopting a wide land, the reproduction signal amplitude at the land portion becomes larger than that at the groove portion, and as a remedy for the problem that may cause an undesired difference in signal quality between the land and the groove, The range of the phase change of the reflected light before and after the phase change of the recording layer is defined so that the reproduction signal amplitude becomes more advantageous than that of the land, and the workaround for the problem is proposed. Further, by using the optical recording medium of the present invention, both on the groove and between the grooves are used as recording areas, and by any one beam overwriting of the laser,
It is possible to provide a recording / reproducing method characterized by recording, erasing and reproducing at high density.

[Brief description of drawings]

FIG. 1 is an enlarged perspective view schematically showing an optical disc of the present invention.

FIG. 2 is an explanatory diagram showing an example of divided pulses used in Examples and Comparative Examples.

FIG. 3 is an explanatory diagram of an input pulse during overwriting.

FIG. 4 is a diagram showing the relationship between the number of times of repetitive overwriting and the jitter of recording marks in Example 1.

FIG. 5 is a diagram showing the relationship between the number of repeated overwrites and the jitter of recording marks in Comparative Example 1.

[Explanation of symbols]

1 substrate 2 recording layers 3 land section 4 Groove part 5 Focused beam 6 Record mark

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B 7/24

Claims (5)

(57) [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 in which both are used as recording areas and information is recorded, erased, and reproduced by irradiating a laser beam, wherein (1) the depth d of the groove satisfies the following inequality: Λ / 7n <d <λ / 5n (where λ: wavelength of irradiation light, n: refractive index of substrate, d:
(Depth of groove) (2) When the width of the groove is GW and the width between the grooves is LW,
Both are larger than 0.1 μm and the following equations GW <LW and ## EQU3 ## 0.62 × (λ / NA) ≤ LW ≤ 0.80 × (λ / NA) (NA is the lens ( Numerical aperture) is satisfied (however, LW = 0.71 × (λ / NA)
An optical recording medium, characterized in that (except in some cases) . 2. The phase difference α between the reflected light from the unrecorded area and the reflected light from the recorded area of the optical recording medium is expressed by the following equation α = (phase of reflected light from the unrecorded area) − (from the recording area). 2. The optical recording medium according to claim 1, wherein the phase of reflected light satisfies the following expression: −π <α <0 and the reflectance of the recording area is lower than the reflectance of the unrecorded area. 3. The phase difference α between the reflected light from the unrecorded area and the reflected light from the recorded area of the optical recording medium is expressed by the following equation α = (phase of reflected light from the unrecorded area) − (from the recording area). The optical recording medium according to claim 1, wherein the phase of reflected light satisfies the following expression: 0 <α <π, and the reflectance of the recording area is higher than the reflectance of the unrecorded area. 4. The optical recording medium according to claim 1, wherein the recording layer is made of an alloy containing Ge, Sb and Te as main components and has a thickness of 20 ± 5 nm. 5. The optical recording medium according to claim 1, wherein both on and between the grooves are used as recording areas, and any area can be recorded, erased, and reproduced by one-beam overwriting of a laser. Recording and playback method.