JPH07130006A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a difference in recording sensitivity between the groove and land of an optical disk in recording or reproduction with an optical information recording medium for recording in both the groove and land of the optical disk. CONSTITUTION:The thickness of a reflecting layer 5 in a land 8 on a substrate 1 is made smaller than that in a groove 7, the thickness of a recording thin film 3 in the groove 7 is made larger than that in the land 8 or the thickness of a 2nd dielectric layer 4 in the land 8 is made larger than that in the groove 7. By this means, heat is radiated from the land 8 and the groove 7 under the same conditions and the same recording or erasing sensitivity is ensured for both the land 8 and the groove 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium which records and reproduces information at high speed and high density by using light, heat and the like.

[0002]

2. Description of the Related Art In recent years, optical discs capable of recording and reproducing information signals such as data, video and audio have been actively developed.

One of the optical discs is a so-called phase change recording medium in which the state and optical constants of the recording film material are changed by laser light irradiation, and a change in reflectance due to the change is detected to record / reproduce a signal. The phase change recording medium has been actively researched because the signal can be rewritten by reversibly changing the state of the recording film material.

As a phase change recording material, a chalcogen alloy is well known, for example, GeSbTe system, InSb.
There are Te-based, GeSnTe-based, InSe-based, SbTe-based, and other materials. Irradiation of these materials with a relatively high power laser beam brings them into an amorphous state, and irradiation of a laser beam with a relatively weak power brings them into a crystallized state. Since the amorphous state and the crystalline state have different optical constants, the recording signal can be reproduced as a change in the amount of reflected light due to laser irradiation.

In a recordable optical disc, a guide groove is previously formed on a substrate of the optical disc to form a track. Information signals are recorded or reproduced by focusing the laser light on the convex portions or the flat portions of the concave portions of the tracks. In a general optical disk currently on the market, an information signal is usually recorded on only one of a convex portion and a concave portion, and the other is a guard band for separating adjacent tracks. Further, generally, in an optical disc used for information processing, information is exchanged with the outside in units of a fixed length in the track direction called a sector composed of a data area and an address area.

On the other hand, research and development aiming at high-density recording are also under way. For example, not only on a guide groove for signal recording of an optical disk but also on a guide groove (a concave portion of a track carved on a substrate (hereinafter, simply referred to as a groove). )) And the guide groove (a convex portion of a track carved on the substrate (hereinafter simply referred to as a land)) to record a signal to increase the recording density (for example, JP-B-63-57859). Issue). Further, in this case, the groove depth is set to λ / (7n) or more and 5λ / (14n) or less (n is the refractive index of the substrate) of the wavelength λ of the recording and / or reproducing light, and if the groove width is limited, the adjacent track It has been reported that crosstalk from signals (because signals are recorded on both grooves and lands, both are recording tracks) can be made extremely small (for example, Proceedings of the 1992 Autumn Meeting of Applied Physics, P. 94).
8, lecture number 18a-T-3. Furthermore, Japanese Patent Application No. 4-79
483). It is considered that the present method is a very effective technique because the recording density can be doubled even by the conventional technique by recording the signal on both the land and the groove.

[0007]

However, the recording sensitivity may be different between the land and the groove. It is considered that this is because the heat radiation conditions are different between the land and the groove. Consider a case where a signal is recorded in the groove 7 in FIG. The recording layer 3 on the groove 7 irradiated with the laser beam 9 rises in temperature with time and eventually exceeds the melting point and melts. After that, when the irradiation of the laser beam 9 is finished, the melted portion is cooled and becomes amorphous. At this time, the heat dissipation from the recording layer 3 is much larger than that of the recording layer 3 because the heat transfer coefficient of the reflective layer 5 made of metal is much larger than that of the recording layer 3. It is considered that the heat flow 11 diffuses to the reflective layer 5 via Next, land 8
However, since the geometrical relationship between the recording layer 3 and the reflective layer 5 is different from that of the groove 7, the temperature rising / cooling conditions are also different. Since the land 8 is convex on the side opposite to the side where the laser light 10 is input, the heat diffusion from both ends of the land 8 to the reflection layer 5 is not only upward in FIG. Also done to. That is, it is considered that the land 8 is more likely to be thermally diffused than the groove 7, so that it is difficult to raise the temperature of the recording layer 3 and the cooling rate after melting is high. It is considered that the difference in the temperature rising / cooling process of the recording layer 3 causes the difference in the recording characteristics of the optical disc. If there is a difference in recording sensitivity between the land 8 and the groove 7 as described above, it is necessary to change the recording power between the land 8 and the groove 7, which complicates the apparatus.

The present invention solves the above-mentioned problems of the conventional optical information recording medium, in which the groove portion and the land portion have the same temperature rising condition or the same cooling condition, and the same recording and erasing sensitivity is obtained in both the land and the groove. It is an object of the present invention to provide an optical information recording medium obtained.

[0009]

In the optical information recording medium of the present invention, the film thickness of the reflective layer in the convex portion on the substrate is made smaller than the film thickness of the reflective layer in the concave portion. Alternatively, the film thickness of the recording layer in the concave portion is made larger than the film thickness of the recording layer in the convex portion. Alternatively, the film thickness of the dielectric layer in the convex portion is made larger than the film thickness of the dielectric layer in the concave portion.

[0010]

In the present invention, the thickness of the reflective layer on the convex portion of the substrate is made thinner than that of the reflective layer on the concave portion, or the thickness of the dielectric layer of the convex portion is made thicker than the thickness of the dielectric layer of the concave portion. By doing so, it is possible to reduce the heat dissipation capability of the convex portion and bring it closer to the concave portion, and therefore it is possible to obtain the same recording / erasing sensitivity for the land and the groove.

Further, by making the recording layer of the concave portion thicker than the recording layer of the convex portion, the heat capacity of the recording layer of the concave portion is increased, and by suppressing the temperature rise, the same temperature rising condition as that of the convex portion is provided. Therefore, it is possible to obtain the same recording / erasing sensitivity for the land and the groove.

[0012]

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

In order to make the explanation easy to understand, an example of the conventional optical disc shown in FIG. 4 will be described first. On board 1,
The first dielectric layer 2, the recording layer 3, the second dielectric layer 4, and the reflective layer 5 are sequentially provided. Further, a transparent and close protective cover 6 is provided thereon. Laser light for recording, reproducing and erasing is incident from the substrate 1 side. The groove 7 is on the convex side of the track and the land 8 is on the concave side as viewed from the laser beam incident direction.

In the conventional structure disk, a substrate made of polycarbonate having a diameter of 130 mm and a groove depth of 800 Å and a guide groove having a land and groove width of 0.8 μm are used as the substrate 1. On top of which the first dielectric layer 2
A ZnS-SiO ₂ mixed film having a thickness of 1300 Å and a recording layer 3 having a Ge ₂₂ Sb ₂₂ Te ₅₆ film having a thickness of 250 Å
A ZnS-SiO ₂ mixed film having a thickness of 20 as the dielectric layer 4 of
An Al film was formed as a 0 Å reflective layer 5 by 1500 Å sputtering. Then, a polycarbonate protective cover 6 was provided thereon.

Next, sectional views of the structure of the optical disk according to the present invention are shown in FIGS. FIG. 1 shows a claim 1 according to the present invention.
In the optical disc, the reflective layer 5 of the land 8 is thinner than the groove 7. FIG. 2 is an optical disk according to a second aspect of the present invention, in which the second dielectric layer 4 of the land 8 is thicker than the groove 7. FIG. 3 shows an optical disc according to a third aspect of the present invention, wherein the recording layer 3 of the groove 7 is provided.
Is thicker than the land 8.

Here, in the disk in which the second dielectric layer 4 of the land 8 in FIG. 2 is thicker than the second dielectric layer 4 of the groove 7, the substrate 1 is located at the recording layer 3 and the position of the sputtering target of the dielectric layer. It was prepared not by directly above but by setting it at a position shifted laterally and performing sputtering. This is because the land 8 on the convex side of the substrate 1 is sputtered obliquely.
The sputtered atoms are disturbed by the groove 7 on the concave side of the substrate 1.
It makes use of the fact that it becomes difficult to reach.

After the recording layer 3 or the reflective layer is formed, the recording layer 3 is formed by obliquely ion-etching the substrate 1 by ionizing an inert gas to scrape away the material to be etched, as shown in FIG. A disk in which the reflective layer of the land 8 is thinner than that of the groove 7 in the land 8 or as shown in FIG. This utilizes that the land 8 on the convex side of the substrate 1 is more easily etched than the groove 7 on the concave side by performing the etching obliquely. The structure of the produced disk is shown in (Table 1).

[0018]

[Table 1]

The evaluation conditions of the optical disk are that the wavelength of the laser beam is 780 nm, the numerical aperture (NA) of the objective lens of the optical head used for recording / reproducing of the recording apparatus is 0.55, the linear velocity of the optical disk is 10 m / sec, and the beam is over. Recording and reproduction were performed with a light. The one-beam overwrite is a method of recording a new signal while erasing an already recorded old signal by irradiating a signal track by modulating laser power between a recording level and an erasing level by a recording signal. is there. The area irradiated at the recording level becomes amorphous because it is cooled after melting regardless of whether the original state is the amorphous state or the crystalline state, and the area irradiated at the erase level rises above the crystallization temperature. It is crystallized regardless of the state and a new signal is overwritten.

The signal recording experiment was conducted as follows.

Bias power of 10 m is applied to the land and the groove of the conventional structure and to the land and the groove of which the temperature is increased or the heat radiation conditions are different.
The recording power was changed from 11 mW to 25 mW with W, and the recording power (recording sensitivity) at which the C / N value exceeded 40 dB was examined. The results are shown in (Table 2).

[0022]

[Table 2]

In the conventional structure disc, the recording sensitivity is different by 10% or more between the land and the groove, but the heat dissipation conditions are the same by changing the film thicknesses of the reflective layer, the recording layer and the second dielectric layer between the land and the groove. The recording sensitivities of lands and grooves of the discs with the same value were almost equal.

In this embodiment, polycarbonate is used as the substrate 1, but glass, quartz, polymethylmethacrylate, or the like may be used. Polycarbonate is used as the protective cover 6, but the protective cover 6 uses a resin as a solvent. It may be melted, applied and dried, or a resin plate bonded with an adhesive, or the recording layer 3 may be G
Although the eSbTe-based material is used, the recording layer 3 is SbTe-based, G
eSbTeSe system, GeSbTePd system, TeGeSn
Au system, AgSbTe system, GeTe system, GaSb system, I
nSe system, InSb system, InSbTe system, InSbSe
System, InSbTeAg system material may be used, and ZnS—SiO ₂ mixed film is used as the dielectric layers 2 and 4, but Si is used.
O ₂ , SiO, TiO ₂ , MgO, Ta ₂ O ₅ , Al ₂ O ₃ ,
GeO ₂ , Si ₃ N ₄ , BN, AlN, SiC, ZnS,
ZnSe, ZnTe, PbS, or the like or a mixture thereof may be used, and Al is used as the reflective layer 5, but Au,
Needless to say, a material containing a metal material such as Cu, Cr, Ni, or Ti as a main component or a mixture thereof, or a dielectric multilayer film having a large reflectance at a predetermined wavelength may be used.

Further, although the structure having the protective cover 6 is adopted in the present embodiment, it goes without saying that the present invention is also effective for a recording medium having a structure without the protective cover 6.

[0026]

As is apparent from the above description,
The present invention, the film thickness of the reflective layer of the convex portion formed on the substrate is thinner than the film thickness of the reflective layer of the concave portion, the film thickness of the recording thin film layer of the concave portion is thicker than the film thickness of the recording thin film layer of the convex portion, Alternatively, the film thickness of the second dielectric layer of the convex portion is thicker than the film thickness of the dielectric layer of the concave portion,
The same good recording and erasing sensitivity can be obtained in both the land and the groove by setting the land portion and the groove portion to the same heat radiation condition by any of the above means, thereby reducing the cost of complicating the recording / reproducing apparatus. It is possible to reduce the recording density and double the recording density.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining an optical information recording medium according to an embodiment of the present invention.

FIG. 2 is a sectional view illustrating an optical information recording medium according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining an optical information recording medium according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view for explaining heat dissipation conditions of a conventional optical disc.

[Explanation of symbols]

 1 Substrate 2 First Dielectric Layer 3 Recording Layer 4 Second Dielectric Layer 5 Reflective Layer 6 Protective Cover 7 Groove 8 Land 9 Laser Light 10 Laser Light 11 Heat Flow 12 Heat Flow

Front page continued (72) Inventor Nobuo Akabira 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A projection and a recess provided as guide grooves on a substrate are used as recording tracks, and a change which can be optically detected by irradiation of a first dielectric layer and laser light on the substrate. In the optical information recording medium provided with the recording thin film layer, the second dielectric layer, and the reflection layer, the thickness of the reflection layer in the convex portion is smaller than the thickness of the reflection layer in the concave portion. A characteristic optical information recording medium. 2. A projection and recess provided on the substrate as guide grooves are both recording tracks, and the first dielectric layer on the substrate and a change which can be optically detected by irradiation with laser light. In the optical information recording medium provided with the recording thin film layer, the second dielectric layer, and the reflective layer, the film thickness of the second dielectric layer in the convex portion is the film of the dielectric layer in the concave portion. An optical information recording medium characterized by being thicker than the thickness. 3. A projection track and a recess provided as guide grooves on a substrate are used as recording tracks, and a change which can be optically detected by irradiation of a first dielectric layer and laser light on the substrate is provided. In an optical information recording medium provided with a recording thin film layer, a second dielectric layer, and a reflective layer which occur, the thickness of the recording thin film layer in the concave portion is larger than the thickness of the recording thin film layer in the convex portion. An optical information recording medium characterized by: 4. The optical information recording medium according to claim 1, 2 or 3, wherein the recording thin film layer is made of a phase change recording material that reversibly changes its state between amorphous and crystalline. 5. The depth of the guide groove on the substrate is not less than λ / (7n) of the wavelength λ of the recording and / or reproducing light and is 5λ / (14).
5. The optical information recording medium according to claim 4, wherein n) or less (n is the refractive index of the substrate).