JP3830045B2 - Optical information recording medium and optical information recording / reproducing apparatus - Google Patents

Description

  The present invention relates to an optical information recording medium for recording by changing the reflectance or optical phase of a recording film by irradiating a laser beam, and more particularly to a phase change optical disk, and optical information using the optical information recording medium. The present invention relates to an optical information recording / reproducing apparatus for recording / reproducing data.

  In a phase change optical disc, information is recorded / reproduced by irradiating a recording film that causes a reversible state change between crystal and amorphous by changing the reflectance or optical phase of the recording film. Is called. When recording information, the recording film that is in an amorphous state immediately after manufacturing the disk is crystallized by irradiating it with laser light (this process is called initialization), and then irradiating the laser light for recording. Recording is performed by making the film amorphous. As typical examples of the recording film, GeTe, SbTe, GeSbTe, InSbTe, AgInSbTe and the like are well known.

  As technology for increasing the recording capacity of phase change optical discs, signal processing technology, land / groove recording technology for recording both in and between guide grooves for substrate tracking, or optical diffraction limit in recent years. In addition, super-resolution reproduction technology that enables reproduction of minute marks has been attempted. In addition to these techniques, a multi-layer disc that increases the number of recording surfaces while keeping the same laser incident surface is one option for increasing the recording capacity. In particular, a two-layer disc using two recording films can greatly increase the capacity per disc, and therefore, research and development has been actively conducted.

  With this two-layer disc, there is a possibility that the capacity can be increased up to twice as much as that of a single-layer disc. In fact, a DVD-ROM using a red semiconductor laser has been commercialized as a single-layer 4.7 GB, double-layer 9 GB disk.

  In a two-layer disc having the same laser incident surface, as shown in FIG. 2, the disc closer to the incident surface is defined as L0 disc 10, and the disc farther from the incident surface is defined as L1 disc 20. Hereinafter, the L0 disk and the L1 disk may be referred to as layers. In these layers 10 (20), a dielectric film 12 (22), a recording film 13a (23a), a dielectric film 14 (24), and a reflective film 15 (25) are provided on (under) the substrate 11 (21). ing. The layer 10 and the layer 20 are obtained by bonding the reflective film 15 in the layer L0 and the dielectric film 22 in the layer L1 through the intermediate layer 16.

In order to reproduce the information recorded in the layer L1, the layer L0 needs to have a certain transmittance with respect to the semiconductor laser used for reproducing the information. Assuming that the transmittance of the layer L0 is T0 and the reflectance of the layer L1 alone is R1, the effective reflectance of the layer L1 when reproducing the disk L1 in a dual-layer disc is reduced to T0 ² × R1. If T0 is 0.3 (30%), the effective reflectivity of the layer L1 is reduced to 9% of the reflectivity of the disk L1 alone.

  In order to ensure the effective reflectance of the disk L1, the transmittance of the disk L0 needs to be about 0.5 (50%). If the transmittance of the disk L0 is excessively increased, the reflectance of the disk L0 is lowered and the quality of the signal recorded on the disk L0 is deteriorated. Therefore, in order to ensure sufficient characteristics for both the disks L0 and L1, the disk L0 The transmittance is preferably about 0.5.

As a combination of the recording film constituent elements, the InGeSbTe recording film is described in, for example, Patent Document 1 for the purpose of improving the number of rewrites. It is added in the form of replacing the part, ie, (GeSbTe) _1-y In _y (see, for example, Patent Document 1). Furthermore, in Patent Document 1, the range of 0.03 ≦ y ≦ 0.3 is preferable, but as described later, when a part of Sb is replaced with In, a smaller amount of In is used. The recording characteristics can be remarkably improved by addition.
JP-A-7-223372

  Since the recording film 13a (23a) used in the phase change optical disk has a constant absorption rate with respect to the laser beam for recording and reproducing information, in order to ensure a transmittance of about 0.5. Needs to reduce the thickness of the recording film 13a (23a). In a phase change recording film used as a single layer, the thickness of the recording film is generally set in a range of 13 to 25 nm. On the other hand, in order to ensure a transmittance of about 0.5, conventionally, the thickness of the recording film 13a (23a) had to be reduced to about 6 nm. However, when the film thickness of the recording film is reduced to about 6 nm, the crystallization speed is lowered, so that the erasing performance is deteriorated or the number of repetitions of information rewriting is reduced. Occurs.

  Conventionally, when the recording film thickness is reduced, it is represented by GeN or SiN between the recording film 13a (23a) and the dielectric films 12, 14 (22, 24) in order to prevent the erasing performance from being lowered. An interfacial layer was added. However, the addition of such an interface layer complicates the disc manufacturing process and increases the disc manufacturing cost.

  Accordingly, an object of the present invention is to provide an optical information recording medium having excellent erasing performance and excellent repeatability while ensuring a certain transmittance in a two-layer disc without adding an interface layer. It is in.

One embodiment of the present invention is an optical information recording medium for performing recording by changing the reflectance or optical phase of a recording film by laser light irradiation, and the composition of the recording film is (GeTe) _x Sb _2-y. In _y Te ₃ is used, and a component whose composition ratio of the recording film is in the range of 0.04 ≦ y <2, 4 ≦ x ≦ 8 is a main component.

  In this embodiment, the thickness of the recording film can be 6 nm or more and 13 nm or less. The information recording layer is formed by sandwiching a recording film between dielectric films. This information recording layer is formed on a transparent substrate. By providing a reflective film on the side of the information recording layer opposite to the incident light, an optical information recording medium having one information recording layer is formed.

An optical information recording medium having two information recording layers is configured as follows. That is, this two-layer optical information recording medium is
A transparent first substrate on which laser light is incident;
A first information recording layer provided on the transparent first substrate;
A first reflective film provided on the first information recording layer;
An intermediate layer provided on the first reflective film;
A second information recording layer provided on the intermediate layer;
An optical information recording medium comprising a second reflective film provided on the second information recording layer;
Each of the first and second information recording layers is configured such that the recording film is sandwiched between the first dielectric layer and the second dielectric layer,
The first recording layer of the second information recording layer has a composition represented by _{(GeTe) x Sb 2-y} In y Te 3, the composition ratio is 0.04 ≦ y <2, 4 ≦ x ≦ The main component is a component shown in the range of 8.

In the optical information recording medium of the present invention, for example, polycarbonate or glass can be used as the substrate. As the first and second dielectric films, SiN, SiO ₂ , TaO _x , Al ₂ O ₃ , AlN, ZnS—SiO ₂ or the like, or a laminated film thereof can be used. As the reflective film, Ag or Au having a film thickness of about 10 nm and 8 to 12 nm can be used.

  The configuration of the optical information recording / reproducing apparatus of the present invention is characterized in that optical information is recorded or reproduced by a semiconductor laser having a wavelength of 400 to 430 nm using any one of the optical information recording media described above. And

  By using the optical information recording medium according to the present invention, when the recording film thickness is reduced, it is excellent in erasing performance and repetitive characteristics while ensuring a certain transmittance without adding an interface layer. It is possible to provide an excellent optical information recording medium. In particular, even when the recording film thickness is 8 nm, it is possible to ensure a transmittance of 50% or more. In addition, by using the optical information recording medium according to the present invention, a high C / N can be obtained for recording and reproducing optical information using a semiconductor laser having a wavelength of 400 to 430 nm. Furthermore, by using the optical information recording medium according to the present invention, it is possible to improve the cross erasing characteristics and improve the recording density.

  FIG. 1 is a sectional view showing a configuration of an optical information recording medium according to an embodiment of the present invention. As shown in the figure, the two-layer optical information recording medium according to the present invention includes a layer L0 (10) and a layer L1 (20), and an intermediate layer 16 for bonding the layers L0 and L1. In the present invention, the layer L0 alone can be used as a single-layer optical information recording medium, but in the following description, the description will focus on a two-layer optical recording information medium.

  As the substrate 11 (21), a polycarbonate (PC) substrate or a glass substrate can be used. On the substrate 11 (21), a guide groove for tracking laser light for recording / reproducing information is usually formed (not shown). The L0 disk 10 has a structure in which a dielectric film 12, a recording film 13, a dielectric film 14, and a reflective film 15 are sequentially laminated on a substrate 11.

As the dielectric films 12 and 14, SiN, SiO ₂ , TaO _x , Al ₂ O ₃ , AlN, ZnS—SiO _{2, or} a laminated film thereof can be used. For the recording film 13, (GeTe) _x Sb _2-y In _y Te ₃ is used as a main component. The ratio of the main component is desirably 95% or more, and elements such as Ge, Sb, Te, Ag, Cr, N ₂ and Co may be added in addition to the main component. Since the reflection film 15 of the disk L0 requires a certain transmittance, Ag, Au or the like having a film thickness of about 8 to 12 nm is generally used. If necessary, a dielectric film may be further added on the reflective film 13 in order to improve the mechanical characteristics and durability of the disk.

  In a two-layer disc, since the laser light incident surface is one, the disc L1 has a configuration in which a reflective film 25, a dielectric film 24, a recording film 23, and a dielectric film 22 are sequentially laminated on a substrate 21. ing. The dielectric films 22 and 24 and the recording film 23 used for the L1 disk 20 can be made of the same material as the disk L0.

  The reflective film 15 of the L1 disc 10 does not require a certain transmittance, and Al having a film thickness of about 100 nm, which is often used in ordinary optical information recording media (DVD-RAM, DVD-RW, etc.), A metal film mainly composed of Ag or Au may be used.

  After the L0 and L1 discs 10 and 20 are respectively produced by sputtering or the like, the intermediate layer 16 is formed using an ultraviolet curable resin or a transparent tape, and the two discs are bonded to form a two-layer disc. The intermediate layer 16 also plays a role of preventing data recorded on the disk L0 from being mixed as noise when the disk L1 is reproduced and data recorded on the disk L1 from being mixed as noise when the disk L0 is reproduced.

  The optical information recording medium according to the present invention has a particularly remarkable effect on recording / reproducing optical information using a semiconductor laser having a wavelength of 400 to 430 nm.

  An example of the configuration of the optical information recording apparatus according to the present invention is shown in FIG. Information to be recorded on the disk 30 (recording information) is sent from the CPU 31 to the laser driving device 32, and the power and pulse width of the laser for recording are controlled by the laser driving device 32 in accordance with the recording information. Further, a selection signal indicating which of the two layers is to be recorded is supplied from the CPU 31, and the light condensing position of the optical head 33 is switched between the layers in accordance with the selection signal. Information emitted from the optical head 33 becomes reproduction data via the reproduction signal 34 and then the data discriminator 35.

Using the PC substrate 11 having a thickness of 0.6 mm, the thickness of the recording film 13 is kept constant at 8 nm, and x and y are changed in different recording film compositions ((GeTe) _x Sb _{2 -y} In _y Te ₃ ). Disc L0) and recording / reproduction evaluation was performed. In any of the disks, the transmittance is 0.5 (50%) or more, and the optical information recording medium according to the present invention can ensure a sufficiently high transmittance even when the recording film thickness is 8 nm. is there. As the PC substrate, a substrate on which guide grooves having a pitch of 0.45 μm and a depth of 25 nm were formed, and recording was performed in the guide grooves. The dielectric films 12 and 14 are made of ZnS—SiO ₂ , and the reflective film 15 is made of Ag having a thickness of 10 nm.

  The disc was rotated at a linear velocity of 5.6 m / s, and the 3T mark was overwritten on the 8T signal at a clock frequency of 60 MHz (T = 15.15 ns), and the erasure rate of the 8T signal was measured. For recording and reproduction, an optical head having a wavelength of 405 nm and an objective lens numerical aperture (NA) of 0.65 was used. The relationship between the recording film composition and the erasure rate is summarized in Table 1 below.

  As can be seen from Table 1, in the range of 4 ≦ x ≦ 8, a high erase rate (25 dB or more) can be obtained even for a recording film as thin as 8 nm when 0.04 ≦ y.

In this example, the thickness of the recording film 13 is kept constant at 8 nm on the same PC substrate 11 as in Example 1, and x and y are changed in different recording film compositions (GeTe) _x Sb _2-y In _y Te ₃ ( Disc L0) and recording / reproduction evaluation was performed. The disk was rotated at a linear velocity of 5.6 m / s, an 8T signal was recorded at a clock frequency of 60 MHz (T = 15.15 ns), and the C / N of the 8T signal was measured.

  For recording and reproduction, an optical head having a wavelength of 405 nm and an objective lens numerical aperture (NA) of 0.65 was used. Table 2 summarizes the relationship between the recording film composition, C / N, and recording power.

  As can be seen from Table 2, a high C / N is obtained when x ≧ 4. However, as x increases, the power required for recording increases, and particularly when x> 8, the recording power increases remarkably. Since a high recording power increases the load on the laser and accelerates the deterioration of the quality of the laser, the recording power is preferably low. The composition range of the recording film is preferably in the range of 4 ≦ x ≦ 8.

From Example 1 and Example _{2, (GeTe) x Sb 2} -y In y at Te _3, high erasure rate, high C / N composition range (without a significant increase in the recording power) is obtained, It can be seen that 4 ≦ x ≦ 8 and 0.04 ≦ y <2.

Each disk using the recording film 13 of (x, y) = (3.5, 0.1) and (4, 0.1) shown in Table 2 was recorded by a red semiconductor laser having a wavelength of 660 nm. When C / N was evaluated, almost no difference in C / N was observed between the two disks. Therefore, when the value of x is changed, the C / N is markedly improved when a blue-violet semiconductor laser (wavelength 400 to 430 nm) is used.
[Comparative Example 1]

On the same PC substrate as in Example 1, the thickness of the recording film 13 and the composition of the recording film 13 are changed (y is changed in the (Ge ₆ Sb ₂ Te ₉ ) _1-y In _y recording film 13). A disk L0 was produced and evaluated for recording and reproduction. The dielectric films 12 and 14 are made of ZnS—SiO ₂ , and the reflective film 15 is made of Ag having a thickness of 10 nm.

The mother composition Ge ₆ Sb ₂ Te ₉ before In addition in this comparative example corresponds to the case of x = 6 in the present invention. The disk was rotated at a linear velocity of 5.6 m / s, and the 3T mark was overwritten on the 8T signal at a clock frequency of 60 MHz (T = 15.15 ns), and the erasure rate of the 8T signal was measured. For this recording / playback, an optical head having a wavelength of 405 nm and an objective lens numerical aperture (NA) of 0.65 was used. Table 3 below summarizes the relationship between the recording film composition, the erasure rate, and the transmittance. It can be seen from Table 3 that even if In is added so as to replace a part of GeSbTe, the decrease in erasure rate cannot be suppressed when the recording film thickness is reduced.

In this embodiment, a PC substrate 11 having a thickness of 0.6 mm was used to produce a disk by changing the thickness of the recording film 13 and evaluated for recording and reproduction. The composition of the recording film 13 was (GeTe) _x Sb _2-y In _y Te ₃ where x = 6 and y = 0.1. _ZnS-SiO 2 on the PC board 11 (12), the recording film _{13, ZnS-SiO 2 (14} ), were sequentially laminated Ag reflective film 15. As the PC substrate 11, a substrate on which guide grooves having a pitch of 0.68 μm and a depth of 45 nm were formed, and recording (land / groove recording) was performed on both the guide grooves and the flat portions between the guide grooves. The disc was rotated at a linear velocity of 5.6 m / s, and the 3T mark was overwritten on the 8T signal at a clock frequency of 60 MHz (T = 15.15 ns), and the erasure rate of the 8T signal was measured.

  In another track, the 8T signal was overwritten 10,000 times and the C / N of the 8T signal was measured. Furthermore, after recording the 3T signal in the groove (in the guide groove) on another track, measuring the carrier (C0) of the 3T signal, the 8T signal is overwritten 100 times on the adjacent land (flat portion between the guide grooves). Then, the cross erase (C1-C0) was measured by measuring the carrier (C1) of the 3T signal again in the groove.

  For recording and reproduction, an optical head having a wavelength of 405 nm and an objective lens numerical aperture (NA) of 0.65 was used. Table 4 summarizes the relationship between the recording film thickness, the erasure rate, C / N, and cross erasure. When this recording film thickness is reduced to 5 nm, the erasure rate and the repetitive characteristics (8TC / N after 10,000 overwrites) are significantly deteriorated. Therefore, the recording film thickness is desirably 6 nm or more. Further, in the recording film according to the present invention, when the recording film thickness is increased to 15 nm, the repetitive characteristics deteriorate. Therefore, it can be seen from Table 4 that the preferable recording film thickness range is 6 nm or more and 13 nm or less. .

  Furthermore, it can be seen from Table 4 that the recording film according to the present invention has very good cross erasing characteristics. Therefore, the recording film according to the present invention is not limited to the application to the disk L0 of a two-layer disc, and even when used as a recording film of a conventional single-layer type optical information recording medium, due to its excellent cross erasing characteristics, It has a remarkable effect that the recording density can be improved.

FIG. 4 shows a configuration example of the optical information recording medium in the case of the single layer type. A transparent substrate 41 on which laser light is incident; and an information recording layer formed on the transparent substrate 41. The information recording layer includes a first dielectric film 42 formed on the transparent substrate 41 and the first dielectric film 42. A recording film 43 formed on one dielectric layer 42 and a second dielectric film 44 formed on the recording film 43, and a reflective film 45 on the second dielectric film 44. Is an optical information recording medium. The composition of the recording film, the main component is represented by _{(GeTe) x Sb 2-y} In y Te 3, the composition ratio of the main component is in the range of 0.04 ≦ y <2,4 ≦ x ≦ 8. When a substrate having a thickness of 0.6 mm is used as a substrate, it is usually attached to a substrate 47 on which an information recording layer is not formed via an intermediate layer 46 made of an ultraviolet curable resin layer or a transparent tape, as shown in FIG. Take a composition to match.

  When the recording film according to the present invention is applied to a two-layer disc, the recording film having a thickness of about 8 nm according to the present invention is used as the recording film of the disk L0 requiring a certain transmittance, and the transmittance is restricted. By using the recording film having a film thickness of about 12 nm according to the present invention as the recording film of the disk L1 having no defect, it becomes possible to easily realize a two-layer disk having excellent repetitive characteristics and capable of high density recording. Since the recording film according to the present invention is less dependent on the film thickness of the erasure rate, the disks L0 and L1 can be manufactured by simply using the recording film having the same composition and changing the film thickness.

In order to examine the effect of reducing the cross erase by adding In in more detail, the same measurement as in Example 3 was performed. In this measurement, the same substrate, protective film, and reflective film as in Example 3 were used. The recording film had a constant film thickness of 12 nm, and the composition was changed in the range of y = 0.02 to 0.3 in (GeTe) ₆ Sb _{2 -y} In _y Te ₃ . Table 5 shows the results of measurement of cross erasure in the same manner as in Example 3.

  As can be seen from Table 5, the cross erase can be greatly reduced by adding a predetermined amount (specifically, y ≧ 0.04) in the form of replacing Sb with In. In Example 1 where the film thickness of the recording film was 8 nm, as shown in Table 1, the erasure rate was about 26 dB at y = 0.3, but the film thickness of the recording film was 12 nm. In this example, even if the amount of In added was large, the erasure rate did not deteriorate so much, and even when y = 0.4, the erasure rate was as high as about 28 dB.

  In addition, although the Example using the 0.6-mm-thick board | substrate (light transmission layer) was described as a form of the optical information recording medium based on this invention, the optical information recording medium based on this invention differs in thickness. For example, the present invention can also be applied to a disc using a light transmission layer having a thickness of 0.1 mm, for example.

It is sectional drawing explaining the structure of the optical information recording medium of one Embodiment of this invention. It is sectional drawing explaining the structural example of the optical information recording medium of a prior art example. It is a figure which shows one example of a structure of the optical information recording device concerning this invention. It is a figure which shows the structural example of the optical information recording medium in the case of 1 layer type.

Explanation of symbols

10, 20, 30 Disc 11, 21 Substrate 12, 14, 22, 24 Dielectric film 13, 13a, 23, 23a Recording film 15, 25 Reflective film 16 Intermediate layer 31 CPU
32 Laser driving device 33 Optical head 34 Reproduction signal 35 Data identifier 41 Transparent substrate 42 First dielectric film 43 Recording film 44 Second dielectric film 45 Reflective film 46 Intermediate layer 47 Substrate on which no information recording layer is formed

Claims (11)

An optical information recording medium for recording by changing the reflectance or optical phase of a recording film by laser light irradiation,
The recording film has a composition represented by (GeTe) _x Sb ₂ -yIn _y Te ₃ , and the composition ratio of 0.04 ≦ y <2, 4 ≦ x ≦ 8 as a main component. An optical information recording medium. An optical information recording medium for performing recording by changing the reflectance or optical phase of the recording film by irradiation with laser light, and a transparent first substrate (11) on which the laser light is incident;
A first information recording layer provided on the transparent first substrate;
A first reflective film (15) provided on the first information recording layer;
An intermediate layer (16) provided on the first reflective film;
A second information recording layer provided on the intermediate layer;
A second reflective film (25) provided on the second information recording layer;
Second substrate (21) provided on the second reflective film
An optical information recording medium consisting of
In each of the first and second information recording layers, the recording film (13; 23) is sandwiched between the first dielectric layer (12; 22) and the second dielectric layer (14; 24). Configured as
The recording films of the first and second information recording layers have a composition represented by (GeTe) _x Sb _{2 -y} In _y Te ₃ and a composition ratio of 0.04 ≦ y <2 and 4 ≦ x. An optical information recording medium comprising a component represented by a range of ≦ 8 as a main component. The optical information recording medium according to claim 2, wherein the recording film has a thickness of 6 nm to 13 nm. The optical information recording medium according to claim 3, wherein the first reflective film has a thickness of 8 nm to 12 nm. An optical information recording medium for recording by changing the reflectance or optical phase of a recording film by laser light irradiation,
A transparent substrate (41) on which the laser beam is incident;
An information recording layer formed on the transparent substrate, and a first dielectric layer (42) formed on the transparent substrate;
An information recording layer including a recording film (43) formed on the first dielectric layer and a second dielectric layer (44) formed on the recording film;
An optical information recording medium comprising a reflective film (45) formed on the second dielectric layer;
The composition of the recording film is represented by _{(GeTe) x Sb 2-y} In y Te 3, the composition ratio is 0. An optical information recording medium comprising a component represented by a range of 04 ≦ y <2 and 4 ≦ x ≦ 8 as a main component. The optical information recording medium according to claim 5, wherein the recording film has a thickness of 6 nm to 13 nm. Optical information recording medium, optical head for irradiating the optical information recording medium with laser light, and driving for driving the optical head so that the laser light is irradiated to a desired position of the optical information recording medium An optical information recording / reproducing apparatus comprising a mechanism,
The optical information recording medium is
A transparent first substrate (11) on which the laser beam is incident;
A first information recording layer provided on the transparent first substrate;
A first reflective film (15) provided on the first information recording layer;
An intermediate layer (16) provided on the first reflective film;
A second information recording layer provided on the intermediate layer;
A second reflective film (25) provided on the second information recording layer;
An optical information recording medium comprising a second substrate (21) formed on the second reflective film;
The first and second information recording layers are configured by sandwiching a recording film (13; 23) between a first dielectric layer (12; 22) and a second dielectric layer (14; 24). ,
The first recording layer of the second information recording layer has a composition represented by _{(GeTe) x Sb 2-y} In y Te 3, the composition ratio is 0.04 ≦ y <2, 4 ≦ x ≦ An optical information recording / reproducing apparatus comprising a component indicated by the range of 8 as a main component. The optical information recording / reproducing apparatus according to claim 7, wherein the recording film has a thickness of 6 nm to 13 nm. 9. The optical information recording / reproducing apparatus according to claim 8, wherein the thickness of the first reflective film is 8 nm or more and 12 nm or less. Optical information recording medium, optical head for irradiating the optical information recording medium with laser light, and driving for driving the optical head so that the laser light is irradiated to a desired position of the optical information recording medium An optical information recording / reproducing apparatus comprising a mechanism,
The optical information recording medium is
A transparent substrate (41) on which the laser beam is incident;
An information recording layer formed on the transparent substrate; a first dielectric layer (42) formed on the transparent substrate;
An information recording layer including a recording film (43) formed on the first dielectric layer and a second dielectric layer (44) formed on the recording film;
An optical information recording medium comprising a reflective film (45) formed on the second dielectric layer;
The composition of the recording film is represented by _{(GeTe) x Sb 2-y} In y Te 3, containing a component the composition ratio indicated by the scope of 0.04 ≦ y <2, 4 ≦ x ≦ 8 as a main component An optical information recording / reproducing apparatus. The optical information recording / reproducing apparatus according to claim 10, wherein the recording film has a thickness of 6 nm to 13 nm.

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