JP2000149330A - Optical recording medium - Google Patents

Abstract

(57) Abstract: An optical recording medium having a land / groove structure capable of accurately obtaining address information even in an unrecorded state and after recording is provided. A substrate has a land / groove structure. In an optical recording medium, a notch-shaped prepit adjacent to a groove is formed on at least one edge of a land between grooves, and the width of the prepit is １ ／ of the land width.
An optical recording medium as described below, wherein the length of the prepit is longer than the longest recording pit length of the recording pit formed in the groove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to an optical recording medium for recording information by light, such as a tape, a card and a disk having a land / groove structure, and in particular, a compact disk in the form of a disk (hereinafter referred to as a compact disk). , A CD) and a digital video disk (hereinafter, also referred to as a DVD).

[0002]

2. Description of the Related Art In recent years, with the spread of CDs, write-once optical disks (hereinafter, also referred to as CD-Rs) complying with the CD standard have been developed.
VD-R) and rewritable DVD (hereinafter also referred to as DVD-RW) are being developed. A general structure of a write-once or rewritable optical recording medium is as shown in FIG. 1, and a transparent resin substrate (1) having lands (peaks) (7) and grooves (valleys) (6) is formed on a transparent resin substrate (1).
A recording layer (2), a reflective layer (3), and a protective layer (or an adhesive layer) (4) are formed in this order, and a transparent substrate (5) is further provided thereon in some cases.

[0003] In recording and reproducing such an optical recording medium,
It is necessary to accurately obtain address information, and optical recording media having various structures have been proposed to satisfy such demands. One example is an optical recording medium described in JP-A-9-326138. This optical recording medium has wobbled grooves, and prepits are formed at predetermined intervals in an area between the grooves (ie, land areas). The pits are, for example, a land portion connecting the grooves. It is formed as a notch. Then, address information can be obtained by a pre-pit signal detected from the pre-pit. This optical recording medium has an advantage that address information can be obtained accurately even when its track pitch is narrow.

[0004]

The above-mentioned optical recording medium is
In the unrecorded state, that is, before the recording pit is formed on the recording layer of the groove, the pre-pit signal, that is, the output from the pre-pit is large, and the address information can be obtained accurately. However, when a recording pit is formed in a groove on the side of the prepit, the prepit signal after the formation of the recording pit tends to be small. As a result, it is difficult to accurately obtain the prepit signal, and a signal error has not been recorded. There is a problem that the address information increases more than in the case of the state and it is difficult to obtain address information accurately.

The present invention has been made in view of such circumstances, and has as its object to provide an optical recording medium capable of accurately obtaining address information even in an unrecorded state and after recording.

[0006]

To achieve the above object, an optical recording medium according to the present invention is an optical recording medium whose substrate has a land / groove structure, wherein at least one of lands between the grooves is provided. A notch-shaped prepit adjacent to the groove is formed at the edge, and the width of the prepit is equal to or less than 1/2 of the land width, and the length of the prepit is the longest recording pit length of the recording pit formed in the groove. Longer. Here, the “land edge” means that the running direction of the land / groove is the longitudinal direction, and the direction perpendicular to the longitudinal direction and parallel to the main surface of the recording medium is the width direction. It means the side edge in the width direction. "Length" refers to the dimension of the land / groove in the direction in which the running direction is defined as the longitudinal direction, and "width" refers to the dimension perpendicular to the longitudinal direction and parallel to the main surface of the recording medium. Means With this structure,
Even when information is recorded by forming recording pits in the groove of the optical recording medium, an increase in errors of the pre-pit signal is suppressed, and address information can be stably obtained.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An optical recording medium according to the present invention in which a substrate has a land / groove structure and at least one edge of a groove between lands is formed with a prepit adjacent to the groove, the recording pit is formed in the groove. Will be described.

[0008] The optical recording medium referred to in the present invention includes all optical recording media for recording information by light, such as tapes, cards, and disks. DV that can record
It is preferably applied to DR and DVD-RW.

The specific land / groove structure of the optical recording medium can be determined according to the performance required for the optical recording medium. For example, the present invention relates to an optical recording medium having wobbled grooves and an optical recording medium having non-wobbled grooves, for example, light in the form of a disk in which the grooves describe a smooth curve along the circumferential direction. It can be applied to recording media.

In the optical recording medium of the present invention, a signal from a prepit formed on a land, that is, a prepit signal is detected to obtain address information. Therefore, the pre-pit arrangement method can be appropriately selected according to the type of the optical recording medium.

In the optical recording medium according to the present invention, the prepit is formed in at least one edge of the land of the substrate in a notch shape adjacent to the groove. FIG. 2 schematically shows an example of a part of a substrate constituting the optical recording medium of the present invention. The substrate (1) of the optical recording medium shown in FIG.
It has a groove structure, and an elongated notch occupying a part of the width of the land (7) is formed as a pre-pit (8) only at one edge of the land (7). In FIG. 2, the pre-pit (8) is formed only on the right side of the groove (6), that is, on the left edge of the land (7) when viewed from the direction of arrow A. In this drawing and the drawings described later, an optical recording medium in which prepits are formed only on one edge of a land is shown. However, in the optical recording medium of the present invention, the prepits have both lands. It may be formed on the edge.

Although the present invention is not limited by any theory, it is presumed that the reason why the error of the pre-pit signal obtained from the optical recording medium of the present invention is reduced is as follows.

FIG. 3 shows an optical recording medium in an unrecorded optical recording medium in which notched pre-pits (8 ') connecting grooves (6) are formed on lands (7). A state where the beam spot (9) of the pickup is applied is schematically shown. In this case, in the beam spot (9), the prepit (8 ') and the groove (6) are on the prepit (8') side of the groove (6).
Are almost the same, the resulting phase difference is small,
On the other hand, on the land (7) side of the groove (6),
The phase difference generated due to the step between the lands is large. This state is schematically shown in the graph of FIG. FIG. 6A shows the relationship between the recording depth and the magnitude of the phase difference. Curve E shows the change in the phase difference on the prepit side, and curve F shows the change in the phase difference on the land side. ing. The phase difference on both sides in the unrecorded state corresponds to the phase difference in A of FIG. 6A, and a difference C between a large phase difference on the land side and a small phase difference on the prepit side is detected as a prepit signal.

Next, FIG. 4 shows a state in which recording pits (10) are formed on the sides of the pre-pits of the optical recording medium of FIG. When the beam spot is hit on the pre-pits as in FIG. 3, the recording pits on the pre-pit (8 ') side of the groove (6) are changed due to the deterioration and decomposition of the recording layer due to the formation of the recording pits. The phase difference between the pre-pit and the pre-pit becomes large, while the phase difference becomes small on the land (7) side of the groove (6) due to the deterioration or decomposition of the recording layer due to the formation of the recording pit. Therefore, as shown in FIG. 6A, as the degree of alteration or decomposition of the recording layer increases, that is, as the recording depth increases, the phase difference on the pre-pit side increases due to the influence of the recording pits. Since the phase difference on the land side is small, the difference D in the phase difference on both sides after recording B is small, and the detected pre-pit signal is small.

Therefore, by increasing the length of the prepit and providing a portion which is not affected by the recording pit, it is possible to secure the output of the prepit signal of a certain value or more, thereby suppressing a decrease in the output of the prepit signal. Can also be considered. However, according to this method, when the length of the prepit is longer than the pit length of the recording pit, the recording pit may be adjacent to the prepit over its entire length. In the groove adjacent to the prepit, the groove is widened, that is, the groove surface is large. Therefore, the reflection level is increased by the prepit, and the reflection level is increased as the width of the prepit adjacent to the groove is increased. Therefore, higher power is required to form recording pits having the same reflection characteristics as recording pits formed in other portions in grooves adjacent to the pre-pits. In other words, when recording pits are formed with a constant recording power as usual, the recording pits adjacent to the pre-pit area over the entire length are recorded pits that are not adjacent to the pre-pits or only a part of the recording pits are The recording is “shallow” as compared with the recording pit adjacent to the recording pit. Such influences are more susceptible to smaller recording pits, and as a result, data errors from the reproduced signal increase.

Therefore, in the optical recording medium of the present invention,
By increasing the length of the pre-pit, a portion that is not affected by the longest recording pit is secured to prevent the output of the pre-pit signal from lowering after recording, and the width of the pre-pit is reduced to reduce the pre-pit notch. The proportion occupied by the portion having a high reflection level in the width direction is smaller than that in the case where the land extends over the entire width of the land. Therefore, even if a recording pit is formed in a groove adjacent to the pre-pit, the reproduced signal is not significantly affected, and as a result, the occurrence of a data error from the reproduced signal can be suppressed.

FIG. 5 schematically shows an example in which recording pits are formed on the optical recording medium of the present invention. In FIG. 5, portions where the prepit (8) is not adjacent to the recording pit (10) exist at both ends in the longitudinal direction of the prepit. Therefore, the detection of pre-pits is performed exclusively at both ends, but the recording pits are not adjacent to this portion or are only adjacent to a part thereof. The change in the phase difference on the side is relatively small. This is described with reference to the graph of FIG. 6B, which shows the relationship between the phase difference and the recording depth, similarly to FIG. 6A. The change in the phase difference is indicated by a curve J. In the unrecorded state A, since the width of the prepit is small, the phase difference on the prepit side is larger than that in the case of FIG. 3, and as a result, the difference G of the phase difference on both sides is slightly smaller. However, since the phase difference on both sides is not significantly affected by the recording pit, the change in the phase difference is relatively small even when the recording depth is increased. That is, the difference H in the phase difference between the two sides after recording B does not greatly change from the difference G in the unrecorded state A, and therefore, a decrease in the output of the pre-pit signal is relatively suppressed.

As described above, the pre-pits formed on the lands have a predetermined range of width and length in order to achieve both suppression of the output reduction of the pre-pit signal and suppression of the data error from the reproduction signal. Is preferred.

The width of the pre-pit is preferably not more than 1/2 of the width of the land on which the pre-pit is formed.
/ 3 is more preferable. The width is 1 / the width of the land
When the value exceeds 2, the proportion of the portion having a high reflection level in the width direction increases, so that a reproduction signal obtained from the recording pit after the formation of the recording pit is affected, and a data error easily occurs.

The length of the prepit is preferably longer than the pit length of the longest recording pit which can be formed in a groove for recording information, and more preferably,
The length is preferably 1.2 to 1.5 times the pit length of the longest recording pit. If the length of the prepit is shorter than the longest recording pit, the area of the portion for securing the detection of the prepit signal after the formation of the recording pit becomes small. Is located, its area is substantially lost, and a sufficient pre-pit signal output cannot be obtained.
The pit length of the longest recording pit varies depending on the type of optical recording medium. For example, the longest recording pit length of a commercially available 3.95 gigabyte DVD-R is about 2 μm.
In this case, the length of the pre-pit is desirably 2.4 to 3.0 μm.

The level of the bottom surface of the prepit shown in FIG. 2 is the same as that of the bottom surface of the groove, but may be higher or lower than the bottom surface of the groove. In the present invention, it is preferable that the bottom level of the prepit is the same as that of the groove bottom from the viewpoint of manufacturing efficiency.

FIG. 2 schematically shows a substrate of an optical recording medium in which pre-pits having a rectangular shape are formed when viewed from the direction of arrow B, that is, when the main surface of the substrate is viewed from above. Although shown, the pre-pits need not be rectangular, and may have, for example, a curved portion in which both ends are arcs as shown in FIG. When actually forming the pre-pits, it may be difficult to make the shape into a rectangular shape as shown in FIG. 2, and as shown in FIG. 7, the pre-pits having a shape having a curved surface at both ends in the longitudinal direction are formed. It is often easy.
When forming a prepit having such a curved shape, the maximum width of the prepit is referred to as the width in the present invention, and the maximum length of a straight line connecting both ends in the longitudinal direction of the prepit is referred to in the present invention. These lengths may be set so as to satisfy the above conditions.

Next, the formation position of the pre-pit will be described. In the present invention, the prepit is formed on at least one edge of the land. In the present invention, it is preferable that the pre-pit is formed only on one edge of the land and is always located on the same side with respect to the running direction of the groove. For example, in the optical recording medium of FIG. 2, if the prepits are formed only on the left edge of each land when viewed from the direction of arrow A, the prepits are always located on the same side with respect to the running direction of the groove. Become. Further, for example, in the case of a disk-type optical recording medium, it is preferable to form the prepit only on one of the inner peripheral edge and the outer peripheral edge of the land. Which edge is selected depends on the recording and / or reproducing method of the optical recording medium. That is, when performing recording and / or reproduction on an optical recording medium, usually, a prepit signal is obtained by detecting a prepit formed on one of two lands adjacent to the side of the groove. Therefore, in the present invention, it is preferable that the pre-pit formed on the land to be detected is positioned on the side of the groove so as to be adjacent to the groove.

In other words, the edge of the land where the prepits are formed is determined by the direction in which the optical pickup or the like following the groove of the optical recording medium detects the prepits in the running direction. For example, D
When a reproduction optical pickup or a recording optical pickup follows a groove of a disk-type optical recording medium such as a VD, the optical pickup detects a prepit formed on a land adjacent to the outer periphery of the groove. Are formed so as to be adjacent to the outer peripheral edge of the groove, that is, located at the inner peripheral edge of the land. As described above, when the prepits are formed only on one edge of the land and are arranged so as to be always located on the same side with respect to the running direction of the groove, the prepits are located on both sides of the recording pit formed in the groove. Nothing. Therefore, unlike the case where the notched prepits are formed over the entire width of the land, during recording and / or reproduction, the influence of adjacent prepits that are not to be detected is small, and a high-quality reproduced signal can be obtained.

In the present invention, since the prepits are cutouts occupying a part of the land width, crosstalk from adjacent tracks is reduced. Therefore, the pre-pits may be provided at both edges of the land, depending on the type of the optical recording medium, such as an optical recording medium in which the optical pickup follows the land. In this case, it is desirable that the prepit formed on one edge of the land and the prepit formed on the other edge do not overlap in the longitudinal direction. When the pre-pits formed on both edges of the land overlap, when the optical pickup follows the land to detect the pre-pits,
Prepits may not be detected due to no phase difference.
In other words, it is desirable that the prepits formed on the edges on both sides of the land have no overlapping portions in the longitudinal direction.

When pre-pits are formed on both sides of a certain groove so as to be adjacent to the groove, the pre-pits formed on both sides of the groove do not overlap in the longitudinal direction via the groove. That is, it is desirable that there be no overlapping portions in the longitudinal direction. If prepits overlapping on both sides of the groove are formed, the phase difference on both sides of the groove becomes the same, and when the optical pickup follows the groove, detection of the prepit may be substantially impossible.

The pre-pits formed on the substrate need not all have the same shape and size as long as they satisfy the above requirements, and may have different widths and / or different lengths or different shapes. These may be mixed in one optical recording medium.

The pre-pits can be easily formed, for example, by adding desired pre-pits to a mold or a stamper used for molding a substrate of an optical recording medium. That is, in the process of manufacturing the stamper, when cutting the photoresist by exposure to laser light, the photoresist may be cut so that desired pre-pits are formed. Since the spot of the laser beam used for cutting is round, the starting point and the end point of cutting, that is, both ends in the longitudinal direction of the prepit are likely to be rounded. The desired effect can be obtained without impairing the characteristics of the medium.

The substrate having the land / groove structure in which the prepits are formed can be used as an optical recording medium by using a conventional method. For example, when manufacturing a CD-R or DVD-R, as shown in FIG. 1, a recording layer (2) and a reflective layer (3) are sequentially provided on a substrate (1), and a protective film (4) is formed thereon. May be formed, or a substrate (5) may be further provided thereon as required. In this case, the recording layer (2) includes, for example, a metal-containing azo dye, a polymethine dye (cyanine dye, merocyanine dye, styryl dye,
Squarylium dye, aminovinyl dye), triphenyl metal dye, fluoran dye, quinone dye,
One or more grooves selected from a group consisting of cationic dyes, macrocyclic azaannulene dyes (phthalocyanine dyes, naphthalocyanine dyes, porphyrin dyes, subphthalocyanine dyes), indophenol dyes and condensed ring dyes such as perylene The pigment can be formed by vapor deposition or coating.

The reflection layer (3) is made of gold, silver, aluminum,
Copper, chromium, platinum, nickel, titanium, or an alloy thereof can be formed by sputtering or vacuum evaporation. In addition, a protective film (or an adhesive layer) (4)
May be formed of an ultraviolet curable resin (for example, an epoxy resin, a urethane-based resin, a silicon-based resin, or the like) made of a polymer material. The substrate (5) laminated on the protective film (4)
The same ones as described above can be used.

In the optical recording medium of the present invention obtained in this way, by increasing the length of the prepit, the output of the prepit signal is suppressed from being reduced even after the recording pit is formed in the groove, and the error of the prepit output signal is reduced. Deterioration is suppressed. Also, by reducing the width of the pre-pit,
The error from the reproduced signal due to the formation of the prepit is suppressed. Therefore, according to the optical recording medium of the present invention,
Even after the formation of the recording pit, the pre-pit signal can be reliably detected to obtain stable address information, and a high-quality signal can be obtained during reproduction.

[0032]

(Example 1) Using a polycarbonate resin, a track pitch of 0.74 μm and a groove width of 0.3 were used.
μm, groove depth 50 nm, land width 0.44 μ
m, radius 120mm, thickness 0.6mm disk,
Prepits having a width of 0.14 μm and a length of 2.6 μm and having the same bottom surface level as the groove bottom surface were formed on the inner peripheral edge of the land.

This substrate is coated with a metal-containing azo dye at 10 ^-4 To
rr or less in a vacuum to form a recording layer having a thickness of 110 nm, and sputtering gold thereon to form a recording layer having a thickness of 100 nm.
Was formed, and a protective layer of an ultraviolet-curable acrylic resin and a polycarbonate resin having a thickness of 0.6 mm were laminated in this order to produce a write-once optical recording medium.

The obtained optical recording medium is unrecorded,
Next, in a state after recording in which recording pits including the longest recording pit having a pit length of about 1.87 μm were formed, an error rate of a prepit signal and a data error from a reproduction signal were measured. The recording pits were formed by converting a video signal from a formatter into a pulse-like recording signal using an optical disc evaluation device DDU-1000 manufactured by Pulstec Industrial Co., and irradiating a 638 nm laser beam to the recording layer. went. Also, the error rate of the pre-pit signal and the data error from the reproduced signal are the optical disk evaluation devices DR-3330 and DR-334 manufactured by Kenwood, respectively.
Measured using 0.

(Embodiment 2) The width of the prepit is set to 0.12.
An optical recording medium was manufactured in the same manner as in Example 1 except that the length was set to 2.8 μm and the length was set to 2.8 μm. Data error was measured.

(Comparative Example 1) The pre-pit is a notch in a land connecting the grooves, and the length of the notch is set to 0.
An optical recording medium was manufactured in the same manner as in Example 1 except that the thickness was 2 μm, and the unrecorded state, the error rate of the pre-pit signal after recording, and the data error from the reproduced signal were measured in the same manner as in Example 1.

(Comparative Example 2) The length of the pre-pit was 2.0 μm.
An optical recording medium was manufactured in the same manner as in Comparative Example 1 except that m was used, and the unrecorded state, the error rate of the pre-pit signal after recording, and the data error from the reproduced signal were measured in the same manner as in Example 1.

Table 1 shows the measurement results of Examples 1 and 2 and Comparative Examples 1 and 2.

[0039]

[Table 1]

From Table 1, it can be seen that the optical recording media of Examples 1 and 2 corresponding to the optical recording medium of the present invention have a low error rate of the pre-pit signal even in an unrecorded state and after recording, and a data error from a reproduced signal after recording. Was also less. On the other hand, in the optical recording medium of Comparative Example 1, the data error from the reproduced signal was small because the length of the pre-pit was small, but the error rate of the pre-pit signal after recording was high and was not practical. Further, in the optical recording medium of Comparative Example 2, although the pre-pit length was long, the error rate of the pre-pit error signal after recording was small, but the data error from the reproduced signal was large and not practical.

[0041]

According to the optical recording medium of the present invention, in which the substrate has a land / groove structure and is provided with elongated notched prepits occupying a part of the width of the land, the recording pits are formed in the recording layer. Thereafter, it is possible to obtain a relatively high output of the pre-pit signal, and the data error from the reproduced signal is suppressed. Therefore, according to the optical recording medium of the present invention, a high-quality reproduction signal can be obtained while obtaining address information stably, so that a write-once or rewritable optical recording medium having excellent performance can be obtained. Is possible.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a general write-once optical recording medium.

FIG. 2 is a schematic perspective view of an example of a substrate of the optical recording medium of the present invention.

FIG. 3 is a plan view schematically showing a state in which a beam spot of an optical pickup is applied to an optical recording medium in which notched prepits connecting grooves are formed on lands.

FIG. 4 is a plan view schematically showing a state in which recording pits are formed on the optical recording medium of FIG.

FIG. 5 is a plan view schematically showing a state where recording pits are formed on the optical recording medium of the present invention.

6A is a graph showing the concept of the relationship between the recording depth and the phase difference of the optical recording medium of FIG. 3, and FIG. 6B is a graph showing the concept of the recording depth and the phase difference of the optical recording medium of FIG. 6 is a graph showing the concept of the relationship with.

FIG. 7 is a schematic perspective view of an example of the substrate of the optical recording medium of the present invention.

[Explanation of symbols]

1 ... substrate, 2 ... recording layer, 3 ... reflective layer, 4 ... protective layer (or adhesive layer), 5 ... substrate, 6 ... groove, 7 ...
Land, 8 ... Pre-pit, 9 ... Beam spot, 1
0 ... Record pit.

Continued on the front page (72) Inventor Toshiaki Kunieda 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Tsutomu Kai 1006 Kadoma Kadoma, Osaka Pref. Person Ueno Bunko 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F term (reference) 5D029 WA20 WA33 WA34 WB11 WC03 WC10 WD13

Claims (6)

[Claims] An optical recording medium in which a substrate has a land / groove structure, wherein at least one edge of a land between grooves has a cutout prepit adjacent to the groove, and the width of the prepit is smaller than the land. 1/2 of width
An optical recording medium as described below, wherein the length of the prepit is longer than the longest recording pit length of the recording pit formed in the groove. 2. The light according to claim 1, wherein the notch-shaped prepit is formed only at one edge of the land and is always located on the same side with respect to the running direction of the groove. recoding media. 3. A notch-shaped prepit is formed on both edges of a land so that a prepit formed on one edge of the land and a prepit formed on the other edge do not overlap with each other. The optical recording medium according to claim 1, wherein: 4. A notch-shaped prepit is formed adjacent to a groove at an edge of a land located on both sides of the groove so as not to overlap with the groove. Item 4. The optical recording medium according to Item 3. 5. The method according to claim 1, wherein the width of the pre-pit is 1/5 to the width of the land.
The optical recording medium according to any one of claims 1 to 4, wherein the ratio is 1/3. 6. The optical recording according to claim 1, wherein the length of the pre-pit is 1.2 to 1.5 times the length of the longest recording pit formed in the groove. Medium.