JPH06103609A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the optical recording medium having high rewriting resistance by suppressing the deformation of recording marks at the time of repeating many times of overwriting in the rewritable optical recording medium of a phase transition type. CONSTITUTION:Second grooves 30 are further formed on lands 10 constituting recording tracks 11 of the optical disk to introduce a pair of level differences 30a, b. As a result, the deformation, etc., of protective layers 2, 4 and recording material layer 3 considered to be the cause for formation of the slender recording marks are suppressed and the optical disk having the high rewriting resistance is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording material layer whose characteristics such as optical or magnetic change due to a change in reflectance, a change in refractive index or a change in shape due to a phase change of an optical recording material. The present invention relates to a write-once or rewritable optical recording medium as recording means, and more specifically to the structure of the optical recording material layer.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for high density and large capacity information recording, and the research has been actively conducted in Japan and overseas. Particularly, the optical recording medium has a recording density 10 to 100 times higher than that of the conventional magnetic recording medium, and further,
Since information can be recorded and reproduced in a non-contact state between the reproducing head and the recording medium, the recording medium is less damaged and has a long service life. Therefore, it is regarded as a promising high-density, large-capacity recording method for recording and reproducing a huge amount of information.

This optical recording medium is a read-only type depending on the application.
The write-once type and the rewritable type can be roughly classified.
The read-only type is a read-only recording medium that can only read information, while the write-once type is an optical recording that can record and reproduce information as needed, but cannot erase recorded information. It is a medium. On the other hand, the rewritable type is an optical recording medium capable of recording and reproducing information, and further erasing recorded information to rewrite it, and is the most promising one for use as a data file for computers. Is.

Regarding the rewritable optical recording medium, two recording systems, a magneto-optical system and a phase change system, are being developed, and both systems still have room for improvement in terms of recording material and writing mechanism. is there. Among the above methods, in the phase change method, generally, a laser beam whose pulse output and pulse width are controlled is focused on the recording surface of the medium and heated. The optical recording material of the optical recording medium irradiated with laser light or the like causes a phase change due to heating of the laser light, and a transition from a crystalline state to an amorphous state or a phase transition occurs,
Recording marks are formed on the optical recording material. The optical recording medium is
Information is recorded and erased by the difference in the reflectance of the recording mark in each state of the phase-changed state, for example, the crystalline state and the amorphous state.

The normal structure of this phase change type optical recording medium is that many tracking grooves 2 as shown in FIGS.
On the transparent substrate surface 1 such as polycarbonate provided with 0,
Forming a protective layer 2 made of ceramics such as ZnS,
The recording material layer 3 is provided on the protective layer 2. Further, a protective layer 4 made of ceramic or the like is formed again on the recording material layer 3, and a surface protective layer 6 made of an organic material is sequentially deposited. A between the protective layer and the surface protective layer of the organic material
Providing a reflection / cooling layer 5 such as 1 is also performed. The reflection / cooling layer 5 reflects the laser light incident from the substrate to improve the utilization efficiency of the laser light and the like, and is designed to prevent the recording material layer 3 from being melted when it changes from a crystalline state to an amorphous state. It has the purpose of increasing the cooling rate.
When the recording material layer 3 is in a molten state, the ceramic protective layers 2 and 4 act as heat insulating layers.

In a normal optical disk, the optical recording material is in a crystalline state in the initial state, and at the time of information recording, a laser beam is irradiated onto the recording material to melt the irradiated portion, followed by rapid cooling, and a spot having a diameter of about 1 μm in an amorphous state. To form. Since the amorphous spot has a lower reflectance than the crystalline spot, information can be read by detecting the spot as a recording mark. On the other hand, in erasing information, the recording mark is erased by irradiating a spot in an amorphous state, which is a recording mark, with light and annealing it to return it to a crystalline state.

In order to form such a recording mark, it is necessary to focus the laser light on the recording material layer 3 as a spot of about 1 μm as described above. Therefore, the substrate 1 of the recording medium is formed with the groove 20 for obtaining the diffracted light for tracking, and this groove is called a groove. Then, the laser light is focused on the recording material layer 3 in the hill portion called the land 10 sandwiched between the grooves, and the recording mark is formed.

The width of the land is a general-purpose semiconductor laser (wavelength 830 nm) used in a tracking optical system.
It is necessary to have a wavelength of about 1 μm, and if it is less than this, tracking becomes impossible using the above-mentioned general-purpose semiconductor laser. Note that, contrary to the above-mentioned optical recording medium, it is possible to use a groove as a recording area and a land for tracking. In this way, the optical recording medium is formed by sequentially depositing the above-mentioned protective layer, recording material layer and the like on the transparent substrate on which these lands and grooves are formed.

Among recording methods for an optical recording medium having a recording material layer that changes in phase, a recording method called overwrite is drawing attention as a rewritable recording method.

In this method, as shown in FIG. 8, the output of the laser light to be irradiated is modulated into two levels, high and low. In the high level irradiation of the peak power P _P level which is the highest power, regardless of whether the state before irradiation is crystalline or amorphous, it is melted and rapidly cooled to form an amorphous recording mark. Therefore, the high level becomes the level for writing. On the other hand, in the irradiation of the bias power P _B level which is a low power, the irradiated place is annealed,
Be crystallized. Therefore, the low level is a level for erasing. Further, the reading power is lower than this, and reading is performed by irradiation with the reproducing power P _R level.

[0011]

When the recording method as described above is used, it is possible to rewrite the recording on the optical recording medium many times. Therefore, it is possible to realize a recording medium with high recording density and free input and output. However, under the present circumstances, the CN ratio and the erasing ratio are lowered due to the flow and the segregation of the recording material as the overwriting is repeated many times, and the number of rewritable times is limited.

FIG. 9 shows an outline of the state of recording marks when overwriting is repeated. In the overwrite, recording and erasing of the recording mark on the land 10 are repeated. Therefore, in the land 10,
An erase bit 42 from which the recording mark is erased and a recording bit 41 which is a recording mark are formed continuously or in an overlapping manner. It has been found that the recording bit 41 and the erasing bit 42 become slender as shown in FIG. 9 when overwriting is repeated many times. That is,
In the optical recording medium overwritten many times, elongated recording bits 41 and erasing bits 42 are formed,
A coarse crystal band 44 is formed at the boundary between these and the surrounding crystal region 43 due to the slow annealing speed. The width of the elongated recording bit 31 is approximately 0.5 μm.

FIG. 10 shows changes in the CN ratio (carrier-noise ratio) and the erasing ratio measured when the land, which is a recording track, is repeatedly overwritten.
In this measurement, a protective layer was formed on the surface of a transparent polycarbonate disk substrate having a diameter of 90 mm with a ceramic layer having a layer thickness of 10 nm made of a mixture of ZnS and SiO ₂ , and further a layer thickness made of Ge ₂ Sb ₂ Te _2. 20 nm
Recording material layer, ceramic protective layer having a layer thickness of 120 nm, A
An optical disk is used in which a reflective cooling layer made of 1 or Al alloy is sequentially applied by a sputtering method, and an ultraviolet curable resin is applied as an organic protective layer thereon by a spin coating method. The light reflectance of the optical disk after film formation is about 5%. The scanning linear velocity of the laser used for overwriting was 9.0 m / s, the peak power was 17 mW,
Pulse width 52.5n under the condition of bias power 8mW
s, a signal having a frequency of 5.80 MHz was repeatedly overwritten, and changes in the CN ratio and the erase ratio were measured.

As can be seen in FIG. 10, 100,000
When overwriting is repeated approximately, both the CN ratio and the erase ratio decrease. Observing the recording track at this time with a transmission electron microscope, as shown in FIG.
It is observed that the recorded bits are elongated and deformed. The cause of this is not clear at present, but deformation of the protective layer and recording material layer is conceivable.When investigating the film component in the direction perpendicular to the recording track, it was found that the side surface of the elongated recording bit was the recording material. It is observed that the composition of the layer is low and the composition of the ceramic layer material that is the protective layer is high.
Therefore, it is assumed that the layer thickness of the protective layer on the side surface of the recording mark becomes relatively thick, while the layer thickness of the recording material layer becomes thin, so that the portion melted in the longitudinal direction of the recording track. It is conceivable that elongated recording marks may be formed due to the extruding or the high thermal conductivity in the longitudinal direction. As described above, it is considered that some non-uniformity occurs due to repeated overwriting a number of times in the state of the recording material layer of the land 10 of the recording track, which should be originally uniform, and therefore an elongated recording mark is formed. Get In such an elongated recording mark, the length of the recording track in the longitudinal direction is larger than the diameter of the laser spot, and an unerasable portion is generated, so that the erasing ratio is reduced, and at the same time, the CN ratio is also reduced.

For practical use of a phase change type optical recording medium, 10
A stable CN ratio and erasing ratio are required even after exceeding 0000 times. Therefore, in order to put the above optical recording medium into practical use, it is necessary to suppress the recording mark from becoming elongated and improve the rewriting resistance.

In view of the above problems, therefore, it is an object of the present invention to prevent the recording marks from being deformed by overwriting many times and to realize an optical recording medium having a high rewriting resistance.

[0017]

In order to solve the above problems, according to the present invention, the recording tracks of the lands or grooves, which are conventionally formed uniformly in the initial stage, are not uniform due to the irradiation of laser light. A step is formed at a place where the state is likely to occur, thereby preventing the recording mark from being deformed beyond the irradiation range of the laser beam. That is, an optical recording material layer capable of recording / erasing a recording mark based on the optical characteristics according to the present invention is provided,
In an optical recording medium in which this optical recording material layer has at least one band-shaped recording track that enables tracking by an optical system, the optical recording material layer is symmetrical with respect to the widthwise center of the recording track. At least one set of steps is formed along this recording track. The step may be a groove recessed from the upper surface of the recording track or a land protruding from the upper surface of the recording track. When a general-purpose laser beam having a wavelength of about 830 nm is used, the width of the recording track is about 1 μm, and about 0.5 μm is selected as the width of the step formed in this recording track.

[0018]

The elongated recording marks whose CN ratio or erase ratio is reduced by a large number of overwrites are considered to be caused by nonuniformity in the recording track due to a large number of overwrites. In particular, it is assumed that the change in the layer thickness of the recording material layer and the protective layer due to the temperature distribution in the recording track due to the laser beam for forming and erasing the recording mark is a problem. Therefore, by forming a land or a groove (second land or groove) in the recording track, a step is introduced to control the heat dissipation at a problematic temperature distribution location, and the layer thickness variation is suppressed. From the temperature distribution that tends to occur, the temperature distribution is such that fluctuations in the layer thickness are less likely to occur. Further, even when the thickness of the protective layer changes, the step introduced in the present invention has a high degree of freedom of deformation, and therefore it is considered that the influence on the thickness of the recording material layer itself is suppressed. Therefore, the nonuniformity of the recording material layer is rarely increased.

Further, in the present invention, the recording track for tracking is the same, and since a step is newly introduced in this recording track, the conventional tracking mechanism can be used. In particular, a general-purpose approximately 830
When a laser beam having a wavelength of nm is used, the width of a conventional recording track is almost the limit for tracking. Therefore, it is desirable to introduce the second land or groove as described above.

As described above, the optical recording medium according to the present invention is
Without changing the recording / reading mechanism side such as tracking,
The rewriting resistance of the optical recording medium can be improved.

[0021]

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

FIG. 1 shows a cross section of an optical disk according to this embodiment, and FIG. 2 shows a perspective view of a transparent substrate 1 used for this optical disk in FIG. The optical disk of the present embodiment also uses a transparent polycarbonate disk substrate 1 having a diameter of 90 mm and a layer thickness of a mixture of ZnS and SiO _{2 on} the surface of the substrate 1 like the conventional optical disk described above. The protective layer 2 is formed of a 10 nm ceramic layer. A recording material layer 3 made of Ge ₂ Sb ₂ Te ₂ and having a layer thickness of 20 nm is further formed on the protective layer 2. On the recording material layer 3, the same material as the protective layer 2 and a protective layer having a layer thickness of 120 nm are formed. Layer 4 is formed. On top of this protective layer 4, Al or A
The reflective cooling layer 5 made of the 1-alloy is formed. Each of the layers 2 to 5 is sequentially formed by a sputtering method, and an ultraviolet curable resin is further applied thereon as an organic protective layer 6 by a spin coating method. The light reflectance of the optical disk after film formation is about 5%.

Also in the optical disc of this example, the land 10 and the groove 20 are formed for tracking, and the land 10 serves as the recording area 11. A point to be noted in the optical disc of the present example is that the land (10) is further provided with a groove (second groove) 30. As can be seen in the substrate 1 shown in FIG. 2, the second groove 30 is a recess formed in the upper surface 10a of the land 10 and has a target width at the center line 10b of the land 10 and a center line 10b. Running along.

In such an optical disk, laser light is applied to the recording material layer 3 through the substrate 1 to perform initialization and recording / erasing. For example, in the push-pull servo system, the substrate 1
The laser light is radiated along the track 11. Therefore, the spot diameter irradiated by the laser is determined by the wavelength of the laser light. When a general-purpose semiconductor laser (wavelength of light source is 830 nm) is used, the recording track 11
Has a width of about 1 μm.

On the other hand, it is known that the width of the recording mark when overwritten many times is about 0.5 μm. Therefore, the changing places of the protective layers 2 and 4 which are considered to be the cause of forming the elongated recording marks can also be considered to be the places of the same width and about 0.5 μm. Therefore, in this example, the second groove 30 having a width of about 0.5 μm is formed around the center line 10b of the land 10. As a result, it is assumed that the thermal diffusion on the side walls 30a and 30b of the second groove 30 becomes large. Therefore, conventionally, it is possible to increase the heat dissipation in the portions where the thicknesses of the protective layers 2 and 4 are changed, so that it is possible to adjust the temperature distribution in the recording track and suppress the change in the thickness of the protective layers 2 and 4. It is thought to be possible. In this case, the recording mark has a lateral width of about 0.5 μm, which is the same as the second groove 30, and a length of about 1 μm, which is the same as the conventional one.

FIG. 3 shows the results of measuring the changes in the CN ratio and the erasing ratio by repeating the overwrite using the optical disk according to the present embodiment. Similar to the above-mentioned conventional optical disc, the overwriting condition is that the laser scanning linear velocity is 9.0 m / s, the peak power is 17 mW, the bias power is 8 mW, and the overwriting signal is also pulse width 52.5 ns and frequency 5 It is set to the same as the above condition, which is .80 MHz. As can be seen in this figure, the CN ratio,
Both the erase ratio and the overall tendency and values are the same as those of the conventional optical disc. However, in the conventional optical disc, both the CN ratio and the erasing ratio decreased after the overwrite was repeated about 100,000 times, but in the optical disc of this example, the CN ratio and the erasing ratio did not decrease even after about 500,000 times. can not see. Therefore, it can be said that the rewriting resistance of the optical disk is improved. Also in the shape of the recording mark, the shape of the recording groove is substantially elliptical inside the second groove 30 as in the initial state, and there is no tendency to extend in the direction along the recording track.

As described above, in the optical disc of this example, even when overwriting is repeated a large number of times, the recording mark does not deform in a slender shape, and the CN ratio,
It is possible to prevent the erase ratio from decreasing. Therefore, it is possible to realize an optical disc having high rewriting resistance. The factor that suppresses the deformation of the recording mark is not clear. However, as described above, it is considered that in the past, the thickness of the protective layer was changed to suppress the lateral thermal diffusion and flow of the recording track, and the recording mark was extended in the longitudinal direction.

On the other hand, in this example, by introducing the steps 30a and 30b at positions where the thickness of the protective layer is considered to change, the thermal diffusion can be adjusted and the change in the thickness of the protective layer can be suppressed. it is conceivable that. Furthermore, the step 30a,
Since the portion b is easily deformed, it may be deformed in the direction of absorbing the thickness of the protective layer.

From the above viewpoint, it can be considered that the same effect can be obtained by narrowing the width of the land 10 as a recording track to about 0.5 μm. However, at present, the wavelength of general-purpose laser light is limited to 830 nm, so if the current track width is 1 μm or less, tracking becomes impossible. Therefore, in order to prevent the recording mark from being deformed in an elongated shape, it is considered that the second groove is formed in the land 10, which is a recording track, as in the optical disk according to the present embodiment.

As a means for producing the same effect, as shown in FIG. 4, the land 10 as a recording track is used.
In addition, the second land 31 protruding upward on the substrate 1
May be introduced. Also in this case, the heat dissipation can be controlled by the steps 31a and 31b, and similarly to the above, the deformation of the recording mark can be suppressed and an optical disc having high rewriting resistance can be realized. Further, as shown in FIG. 5, it is possible to use the groove 20 as a recording track, and in such an optical disc, the same effect can be obtained by forming the second groove 32 in the groove 20. it can. Of course, instead of the second groove 32, a narrow land may be formed in the groove 20.

[0031]

As described above, in the present invention, the land or groove is further formed in the recording track of the optical recording medium having the phase change recording material layer to introduce the step. As a result, it is considered that the temperature distribution in the recording track is adjusted, and it is possible to suppress the cause of the elongated recording marks such as the deformation of the protective layer and the recording material layer, which conventionally occurs when the number of times of rewriting increases. Become. Therefore, it is possible to prevent the recording mark from becoming elongated due to the increase in the number of times of rewriting, and it is possible to realize an optical recording medium in which the CN ratio and the erasing ratio do not decrease even when the number of times of rewriting exceeds 500000 times. Further, in order to improve the rewriting resistance as described above, since the land or groove is further introduced into the recording track, the width of the conventional track and land required for tracking is secured. Therefore, an optical recording medium having high rewriting resistance can be realized without complicating the optical system for recording and reproduction.

As described above, the optical recording medium according to the present invention is
Even if a single recording track is overwritten many times, various recording and reproducing characteristics are not deteriorated, and the number of rewritable times of the optical recording medium can be greatly extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical disc according to an embodiment.

FIG. 2 is a perspective view showing a transparent substrate of the optical disc shown in FIG.

FIG. 3 is a graph showing changes in CN ratio and erase ratio when repetitive overwriting is performed using the optical disc shown in FIG.

FIG. 4 is a perspective view showing a partially cutaway transparent substrate of an optical disc according to another embodiment of the present invention.

FIG. 5 is a perspective view showing a transparent substrate of an optical disc of another embodiment according to the present invention with a part thereof being cut away.

FIG. 6 is a perspective view showing a transparent substrate of a conventional optical disc by partially cutting it out.

FIG. 7 is a cross-sectional view of a conventional optical disc.

FIG. 8 is a graph showing a modulation state of laser light for rewriting and erasing on an optical disc.

FIG. 9 is a plan view showing a state of recording marks formed on recording tracks of the optical disc.

FIG. 10 is a graph showing changes in CN ratio and erasing ratio when repetitive overwriting is performed using a conventional optical disc.

FIG. 11 is an explanatory diagram tracing a transmission electron micrograph showing a state of a recording mark after a conventional optical disc is overwritten many times.

[Explanation of symbols]

1 ... Transparent substrate 2 ... Protective layer 3 ... Optical recording material layer 4 ... Protective layer 5 ... Cooling layer 6 ... Surface protective film 10 ... Land 11 ... Recording track 20 ... Groove 30 ... Second groove 30a, b ... Step difference due to second groove 31 ... Second land 32 ... Second groove (disk having groove as recording track) 41 ... Record bit (record mark) 42 ... Erase bit 43 ... Crystal area 44 ... Coarse crystal band

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kaichi Sato 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Haruo Kawakami 1 Tanabe-taden, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 within Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. Recording of recording marks based on optical characteristics
In an optical recording medium having an erasable optical recording material layer, the optical recording material layer having at least one band-shaped recording track enabling tracking by an optical system, the recording being performed in the recording track. An optical recording medium characterized in that at least one set of steps which are symmetrical with respect to the center of the track in the width direction is formed along the recording track. 2. The optical recording medium according to claim 1, wherein the step is a groove recessed from the upper surface of the recording track. 3. The optical recording medium according to claim 1, wherein the step is a land protruding from an upper surface of the recording track.