JP3166238B2 - Optical recording medium and method of manufacturing optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source suitable for high-density recording in which, for example, a material layer whose reflectivity changes with temperature is formed on a transparent substrate having phase pits formed thereon. The present invention relates to a method for producing a recording medium and an optical recording medium.

[0002]

2. Description of the Related Art For example, optical discs such as digital audio discs (so-called compact discs) and video discs have an aluminum reflective film formed on a transparent substrate on which phase pits are formed in advance in accordance with an information signal. It is configured by forming a protective film and the like.

In such an optical disk, a signal is read out (reproduced) by irradiating the disk surface with readout light and detecting a large decrease in the amount of reflected light due to diffraction of light at the phase pit formation portion. ing.

[0004] In the above-mentioned optical disk, the resolution of signal reproduction is almost determined by the wavelength λ of the light source of the reproduction optical system and the numerical aperture NA of the objective lens, and the spatial frequency of 2NA / λ is the reproduction limit.

Therefore, in order to realize a high density in such an optical disk, it is necessary to shorten the wavelength λ of the light source (for example, a semiconductor laser) of the reproducing optical system or to increase the numerical aperture NA of the objective lens. Required.

However, there is naturally a limit in improving the wavelength λ of the light source and the numerical aperture NA of the objective lens, and it is actually difficult to dramatically increase the recording density.

Therefore, the present applicant has developed an optical disk which can obtain a resolution higher than the above-mentioned limit by the wavelength λ and the numerical aperture NA by utilizing the reflectance of the reading light due to the partial phase change in the scanning spot. Proposed (Japanese Patent Application No. 2
-94452, Japanese Patent Application No. 3-249511).

FIG. 4 shows a schematic cross-sectional view of one example. The optical disc in the example of FIG. 4 is such that a material layer 3 that can be crystallized after melting is formed on a smooth transparent substrate 2 on which phase pits 1 are formed in accordance with an information signal.

In this case, when the reading light, for example, the reproducing laser light is applied to the material layer 3, a temperature distribution occurs in the scanning spot of the reading light. As a result, the material layer 3 partially changes from a crystalline state to a molten state to lower the reflectance, and returns to a crystalline state in a normal state after reading.

The case of irradiating the optical disk of the example of FIG. 4 with a reproduction laser beam will be described with reference to FIG.

In FIG. 5A, SP is a laser spot, which is scanned in the direction of arrow SC as the disk rotates. In FIG. 5A, the phase pits 1 are arranged in the shortest recording cycle q. However, the arrangement interval and the pit length are changed according to the recording data.

In FIG. 5B, the horizontal axis indicates the position of the laser spot SP in the scanning direction SC. Considering a state in which the optical disk is irradiated with the laser spot SP (see FIG. 5A), the light intensity of the laser spot SP has a distribution indicated by a broken line a. On the other hand, the temperature distribution in the material layer 3 of the optical disk is slightly delayed according to the scanning speed of the laser spot SP as shown by the solid line b.

Here, as described above, the laser spot S
Assuming that P is scanned in the scanning direction SC as shown in FIG. 5A, the temperature of the optical disk gradually increases from the leading end side of the laser spot SP in the scanning direction, and finally reaches a temperature equal to or higher than the melting point MP of the material layer 3. .

At this stage, the material layer 3 changes from the initial crystalline state to the molten state, and the reflectivity decreases. Therefore, in the laser spot SP, there is a region Px (shown by oblique lines in FIG. 5A) where the reflectance is low and the phase pit 1 cannot be read out.
There is a region Pz where the reflectance is high and the phase pit 1 can be read out in order to maintain the crystal state.

Therefore, as shown in FIG. 5A, even when, for example, two phase pits 1 exist in the same laser spot SP, only one phase pit 1 existing in the region Pz having a high reflectance is provided. Reading is performed. Therefore, reading can be performed with ultra-high resolution without being limited by the wavelength λ of the reading light and the numerical aperture NA of the objective lens, thereby enabling high-density recording.

In the above-mentioned optical disk (FAD type), the reflectance is low when the material layer 3 is in a molten state and is high when the material layer 3 is in a crystalline state. But,
By selecting various conditions such as the configuration and thickness of the material layer 3, the material layer 3 is configured to have a high reflectance in a molten state and a low reflectance in a crystalline state. In such an optical disk (RAD type), it is possible to read only the region where the reflectance is increased due to the molten state (see the hatched portion in FIG. 5A). Therefore, even in the case of the RAD type, as in the case of the FAD type, it is possible to perform ultra-high-resolution reading, thereby enabling high-density recording.

[0017]

The material layer 3 is formed on the transparent substrate 2 on which the phase pits 1 are formed as described above.
Optical disk (hereinafter referred to as "SR disk")
It has been proposed to use a three-beam method as a tracking servo when reproducing an information signal.

In the three-beam method, two side spots for obtaining a tracking error signal are formed on a recording surface of an optical disk in addition to a main spot for reproducing an information signal. For example, the light intensity of the side spot is made weaker than that of the main spot, and the state of the material layer 3 is changed by the temperature in the side spot so that the reflectance does not change.

In this case, when the disk is a FAD type SR disk, since the initial reflectance before the state change is high, an error signal can be stably obtained based on the reflected light from the side spot, and good tracking can be performed. Can control.

However, in the case of a RAD type SR disk, the initial reflectance before the state change is low, so that the amount of reflected light from the side spot is not sufficient, and it has been difficult to perform tracking control.

Therefore, in the present invention, the RAD type S
Even when the R disk is reproduced, the tracking control can be stably performed.

[0022]

An optical recording medium according to the present invention is an optical recording medium in which information and control information for reading out the information are optically readable recorded on a transparent substrate. The transparent substrate includes at least an information recording unit that records the information and a control information recording unit that records the control information, and a material layer whose reflectance changes with temperature is laminated only on the information recording unit. is there. An optical recording medium according to the present invention is an optical recording medium for irradiating a laser beam and reading recorded information, wherein the optical recording medium has at least an information recording section for recording the information and the laser beam arranged at a predetermined position. And a control information recording section including wobble pits, and a material layer whose reflectance decreases as the temperature rises due to laser beam irradiation is laminated on the information recording section and the control information recording section.

According to the method for manufacturing an optical recording medium of the present invention, a step of recording information and control information for reading the information on a transparent substrate so as to be optically readable, and Forming a material layer whose reflectivity changes depending on temperature, and forming a reflective layer corresponding to at least the control information recording portion on the transparent substrate.

[0024]

In the optical disk according to the present invention, for example, the material layer 3 is formed corresponding to the information recording portion of the transparent substrate 2, and the reflection layer 4 is formed corresponding to the control information recording portion. In this case, regardless of the FAD type or the RAD type, when the read light spot scans the control information recording section, a sufficient amount of reflected light can be obtained from the read light spot, and stable tracking control and the like can be performed. Can be performed.

[0025]

An embodiment of the present invention will be described below with reference to the drawings.

In the optical disk 10 of this embodiment, a well-known sample servo system is adopted as a tracking method.
Therefore, in the optical disc 10 of the present example, a plurality of servo areas are provided on one circumference of the track.

FIG. 2 shows the entire optical disc 10 of the present embodiment. As shown in the figure, each track TR is composed of a plurality of segments SG. Each segment SG
Is provided with a servo area SA at the beginning and a data area DA subsequently.

An address segment AD / SG is provided for each predetermined segment SG. Although a detailed description is omitted, a servo area SA is provided at the head of the address segment AD / SG, similarly to the segment SG.

FIG. 3 shows the pit configuration of each segment SG. At the head of the servo area SA, a gray code GC that changes in a cycle of 16 tracks is formed. Following this gray code GC, a clock pit CP for obtaining a synchronization clock and a wobble pit WP for obtaining a tracking error signal are formed. In FIG. 3, S · CLK is a servo clock.

FIG. 1 shows a schematic cross section of a main part of an optical disk 10 of the present embodiment. In FIG. 1, portions corresponding to those in FIG. 4 are denoted by the same reference numerals.

In this example, a gray code GC, a clock pit CP and a wobble pit WP are formed on the transparent substrate 2 corresponding to the servo area SA (the clock pit CP is not shown in FIG. 1). . Further, a recording pit RP corresponding to the information signal is formed corresponding to the data area DA.

On the transparent substrate 2 on which the gray code GC, the clock pits CP, the wobble pits WP and the recording pits RP are formed, the material layer 3 is formed in a layer corresponding to the data area DA. Further, the reflection layer 4 is formed on the entire surface of the transparent substrate 2 on which the material layer 3 is formed.

In this embodiment, a polycarbonate substrate is used as the transparent substrate 2, and the gray code GC, the clock pit CP, the wobble pit WP and the recording pit R
A phase pit was used as P.

In this example, the track pitch P = 1.6 μm, the pit depth Dp ≒ 120 nm, the pit width W1 = RP of the recording pit RP = 0.3 μm, the gray code GC, the clock pit CP and the wobble pit W
The pit width of P was formed under the setting condition of W2 = 0.6 μm.

As a material for the transparent substrate 2, an acrylic resin, a polyolefin resin, glass or the like can be used.

The material layer 3 satisfies the following conditions. That is, due to the heat of the reading light, a state change occurs partially in the reading light spot, the state returns to the initial state after the passage of the reading light, and further, the reflectance changes due to the state change.

The state change referred to here means a change from a crystal to a liquid,
This is a change with the melting point from amorphous to liquid as a boundary. In this case, it is desirable that the crystal becomes a liquid because the change in reflectance is large.

Assuming that the above condition is satisfied, S
e, Te, Bi, Ce, Sb, Pb, Ga, Ge, S
Examples thereof include simple substances such as n and In, and alloys of two or more of these. In this example, a ternary compound of Ge ₂ Sb ₂ Te ₃ was used as the material layer 3.

As described above, in order to prevent the material layer 3 from being laminated on the portion corresponding to the servo area SA, in this embodiment, after forming the material layer 3, the portion corresponding to the servo area SA is formed by using photolithography. Material layer 3 was removed.

In order to prevent the material layer 3 from being laminated on the servo area SA, in addition to this, a method of attaching a shielding plate at the time of film formation, or providing a lift-off layer in the servo area SA and removing the material layer 3 after the formation is completed. A method or the like can be used.

The reflective layer 4 is made of Al, Au, A
Metals with high reflectivity, such as g and Pt, are used. In this example, Al was used for the reflection layer 4.

When the optical disk 10 thus formed is irradiated with laser light, the temperature rises in the laser spot according to the light intensity distribution. Then, the reflectance increases in the portion exceeding the melting point, and the recording pit R in the data area DA is increased.
Information can be read from P. That is, the optical disk 10 of the present example constitutes a RAD type SR disk.

The material layer 3 is prevented from being laminated on the portion corresponding to the servo area SA, and the reflection layer 4
Are stacked, when the laser spot scans the servo area SA, a sufficient amount of reflected light can be obtained from the laser spot, so that stable tracking control or the like can be performed.

In the example of FIG. 1, the servo area S
Although the material layer 3 is not laminated on the portion corresponding to A, the optical disk 10 can be formed into an FAD type having a high initial reflectance of the material layer 3 by selecting various conditions such as the material configuration and the thickness of the material layer 3. In this case, the material layer 3 may be laminated also on the portion corresponding to the servo area SA, and the reflection by the material layer 3 may be used. In this case, the reflection layer 4 becomes unnecessary.

On the other hand, in the case of the RAD type having a low initial reflectance, the material layer 3 cannot be laminated on the portion corresponding to the servo area SA. in this case,
Although the reflectance increases in the portion exceeding the melting point, the area where the reflectance increases is narrow and distorted, and the amount of reflected light becomes unstable and insufficient, so that it is impossible to perform tracking control or the like satisfactorily. .

In the example of FIG. 1, the servo area SA
An experiment was conducted in which an optical disk was formed by laminating the material layer 3 on a portion corresponding to the above, and an experiment was performed to reproduce the optical disk.

Further, in the example of FIG. 1, the reflection layer 4 is laminated on the entire surface, but it may not be laminated on a portion corresponding to the data area DA.

Further, in the example of FIG. 1, phase pits are used as the recording pits RP and the like, but the invention is not limited to this, and any optically readable one may be used.

[0049]

According to the present invention, for example, a material layer is formed corresponding to an information recording portion of a transparent substrate, and a reflection layer is formed corresponding to a control information recording portion.
Regardless of AD type or RAD type,
When the read light spot scans the control information recording section, a sufficient amount of reflected light can be obtained from the read light spot, and stable tracking control and the like can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part showing a configuration of an embodiment.

FIG. 2 is a diagram illustrating an overall configuration of an embodiment.

FIG. 3 is a diagram showing a pit configuration of a segment.

FIG. 4 is a schematic cross-sectional view illustrating a main part of an example of an optical disc.

FIG. 5 is a diagram showing a relationship between a light intensity distribution of a laser spot and a temperature distribution (reflectance) of an optical disk.

[Explanation of symbols]

 2 Transparent substrate 3 Material layer 4 Reflective layer 10 Optical disk SG segment DA Data area SA Servo area GC Gray code CP Clock pit WP Wobbling pit RP Recording pit

Continuation of the front page (56) References JP-A-5-28498 (JP, A) JP-A-2-96926 (JP, A) JP-A-3-292632 (JP, A) JP-A-4-167237 (JP) JP-A-4-167238 (JP, A) JP-A-5-89511 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24 G11B 7/26

Claims (6)

(57) [Claims] 1. An optical recording medium in which information and control information for reading the information are optically readable recorded on a transparent substrate, wherein the optical recording medium is at least the information for recording the information on the transparent substrate. An optical recording medium comprising: a recording unit; and a control information recording unit for recording the control information, wherein a material layer whose reflectance changes with temperature is laminated only on the information recording unit. 2. The optical recording medium according to claim 1, wherein said information recording section is formed by phase pits. 3. The information recording section includes wobble pits formed for each segment.
An optical recording medium according to claim 1. 4. An optical recording medium for reading recorded information by irradiating a laser beam, wherein the control information recording section includes a material layer on which the information recording section is formed and a control information recording section. 2. The optical recording medium according to claim 1, further comprising a reflection layer disposed at a distant position. 5. An optical recording medium for reading recorded information by irradiating a laser beam, wherein the optical recording medium has at least an information recording section for recording the information and a laser beam for arranging the laser beam at a predetermined position. An optical recording medium, comprising: a control information recording section including wobble pits; and a material layer whose reflectivity decreases with an increase in temperature due to laser beam irradiation is laminated on the information recording section and the control information recording section. . 6. A step of recording information and control information for reading the information on a transparent substrate in an optically readable manner, wherein the reflectance changes depending on the temperature corresponding to the information recording portion on the transparent substrate. A method for producing an optical recording medium, comprising: a step of forming a material layer; and a step of forming a reflective layer corresponding to at least the control information recording section on the transparent substrate.