KR20010029133A - Phase change optical disc - Google Patents

Abstract

PURPOSE: An optical disk is provided to reduce jitter value while overwriting and to prevent cross-erase occurrence through increasing light absorbing ratio between a crystalloid and an amorphous material on a recording layer. CONSTITUTION: A phase changing optical disk(100) is formed by a transparent substrate(110), a first dielectric layer(120), a recording layer(130), and a second dielectric layer(140). Herein, the recording layer is formed by alloy of Ge2Sb2Te5 and Sb, alloy of GeSb2Te4 and Sb, or alloy of GeSb4Te7 and Sb. The first dielectric layer and the second dielectric layer are formed by TiO2, ZnO, CeO2, or AnS having refracting rate over 2.5. Herein, the first dielectric layer improves light absorbing ratio between crystalloid and amorphous material in the recording layer. Moreover, the first dielectric layer adjusts reflecting rate according to thickness. Herein, the light absorbing ratio is improved by increasing light absorbing rate of the crystalloid through destructive interfering waves reflected on the recording layer and reflected on the first dielectric layer.

Description

Phase change optical disc

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change optical disc in which the optical characteristics of the recording layer are changed by irradiation of a laser beam. In particular, when a blue wavelength laser beam is used as a light source, the overwrite characteristic is excellent and cross-erasure is performed. The present invention relates to a phase change optical disk having a layer structure capable of suppressing the occurrence of a cross-erase phenomenon.

As a non-contact information recording medium used in an optical disc player, an optical disc is developing in a high capacity, high speed, and high density direction in accordance with the progress of the information society. Accordingly, technologies related to optical discs capable of recording / reproducing high-density information such as DVD (Digital Versatile Disc) RAMs and the like in connection with recording / reproducing video information on multimedia or high-quality TV are actively being developed. In particular, the phase change optical disk is an optical information recording medium for recording, reproducing, and erasing information by irradiation of a laser beam, and the optical head is relatively easy to construct, and so-called, overwriting is easy to simultaneously perform recording and erasing. Due to such characteristics, research for increasing the density is being actively conducted.

The phase change optical disc records and reproduces information using a property in which the recording layer of the portion irradiated with the laser beam becomes crystalline or amorphous depending on the power and cooling speed of the incident laser beam, thereby changing its optical characteristics. do. That is, in the case of recording, it is possible to melt a recording layer initialized to a crystalline phase by irradiation of a laser beam with short power to high power recording pulses, and then amorphous by quenching to generate a recording mark. In the reproduction of information on the recording mark, since the light reflectance in the crystalline and amorphous states is different when the laser beam incident on the optical disk is reflected from the recording layer, the difference in reflectance is detected by the photodetector and reproduced as an electrical signal. do. In the case of erasing the recording mark, the recording mark of the amorphous layer is crystallized by the erasing pulse of low power at long pulse to erase the recording mark.

Such a phase change optical disc has a so-called cross-erase phenomenon in which the track interval becomes narrower as the recording density increases, so that the marks of the adjacent tracks are partially erased during recording. The lower the light absorption rate (Aa) in the amorphous recording layer is, the better. That is, the larger the ratio (Ac / Aa) of the light absorption rate Ac in the crystalline state of the recording layer to the light absorption rate Aa in the amorphous state, the better.

In addition, in order to not change the size of the recording mark during overwriting in which recording pulses are superimposed on the erase pulses to simultaneously perform recording and erasing, the light absorption ratio (Ac / Aa) in the crystalline and amorphous states of the recording layer is 1.1 to It is well known that it should have a value of about 1.2.

Therefore, the high density phase change optical disk must satisfy the essential condition that the light absorption ratio (Ac / Aa) in the crystalline and amorphous state of the recording layer should have a value of 1.2 or more.

In a phase change optical disc using a conventional red or near-infrared laser beam as a light source, the optical absorption ratio (Ac / Aa) in the crystalline and amorphous states of the recording layer is shown in FIGS. 1 and 2 so as to have a value of 1.2 or more. It is formed into a multilayer structure as shown.

1 is a vertical cross-sectional structural view schematically showing an example of a conventional phase change optical disk.

The conventional phase change optical disk 10 shown in FIG. 1 includes, for example, an Au interference layer 12 and a first dielectric layer 13 on a substrate 11 formed of a transparent acrylic resin material, a polycarbonate (PC) material, or the like. When the laser beam is irradiated, the recording layer 14, the second dielectric layer 15, and the reflective layer 16, which are formed of a phase change material whose state changes, are sequentially stacked.

In the multilayer film structure described above, a GeSbTe-based material such as ZnS-SiO ₂ as the first dielectric layer 13 and the second dielectric layer 15 and Ge ₂ Sb ₂ Te ₅ as the recording layer 14, and the reflective layer ( 16) aluminum (Al) or an aluminum alloy material is used.

The conventional phase change optical disk 10 has a light reflection factor when the recording layer 14 is crystalline because the optical wave reflected from the interference layer 12 and the light wave reflected from the crystalline recording layer 14 cause a destructive interference. This greatly decreases the light absorption rate increases. On the other hand, when the recording layer 14 is amorphous, since it has a high reflectance, the light absorption in the amorphous recording layer 14 is reduced.

Therefore, the conventional phase change optical disk 10 shown in FIG. 1 has a light absorption ratio (Ac / Aa) in a crystalline and amorphous state of the recording layer 14 when using a red or near infrared laser beam as a light source. It is possible to have a value of 1.2 or more.

However, when the conventional phase change optical disk 10 shown in FIG. 1 uses blue wavelength light, that is, a 400 nm laser beam, as a light source, the Au interference layer 12 has a light reflectance in near infrared or red wavelength light. While it is 90% or more, it decreases to 40% in blue wavelength light, making it difficult to cancel interference the light waves reflected from the crystalline recording layer 14.

This is because when the blue wavelength light, i.e., 400 nm laser beam is used as the light source, in the phase change optical disk structure of FIG. 1, the light reflectance difference in the crystalline and amorphous state of the recording layer 14 according to the thickness of the first dielectric layer 13 It can be confirmed from FIG. 3 which shows the result of calculating (Rc-Ra), the light absorption ratio (Ac / Aa), and the phase difference.

Therefore, in the case where the phase change optical disk using the blue wavelength light as the light source is formed in the layer structure including the Au interference layer 12 as shown in FIG. 1, as shown in FIG. There is a problem that it is difficult to obtain a value of the light absorption ratio (Ac / Aa) in the amorphous state to 1.05 or more.

2 is a vertical cross-sectional structural view schematically showing another example of a conventional phase change optical disk.

The conventional phase change optical disk 20 shown in FIG. 2 has a first dielectric layer 22, a recording layer 23, a second dielectric layer 24, a heat absorption layer 25 and an interference layer on a transparent substrate 21. (26) has a multi-layer structure in which the layers are sequentially stacked.

Si or Au is used as the heat absorption layer 25, and ZnS-SiO ₂ is used as the interference layer 26. The substrate 21, the first dielectric layer 22, the second dielectric layer 24, and the recording layer 23 are used. Is substantially the same material as the phase change optical disk shown in FIG.

In the structure of the conventional phase change optical disk 20 of FIG. 2, the light wave, the heat absorption layer 25, the interference layer 26, and the interference layer (reflected at the interface between the second dielectric layer 24 and the heat absorption layer 25) The light waves reflected at the interface between the layer 26 and the air layer (or protective layer; not shown) cause an extinction interference with respect to the amorphous recording layer 23, thereby reducing the light absorption rate of the amorphous recording layer 23.

Therefore, the conventional phase change optical disk 20 shown in FIG. 2 has a light absorption ratio (Ac / Aa) in the crystalline and amorphous state of the recording layer 23 when using a red or near infrared laser beam as a light source. It is possible to have a value of 1.2 or more.

However, the conventional phase change optical disk 20 shown in FIG. 2 has a tendency to increase the absorption portion of the refractive index of the amorphous recording layer 23 as the light source moves from the near infrared or red wavelength to the blue wavelength region. When the wavelength light, i.e., a 400 nm laser beam, is used as the light source, the light transmittance of the amorphous recording layer 23 decreases, so that the interference layer 26 is positioned next to the recording layer 23 on the basis of the light incident surface. The layered structure makes it difficult to obtain a sufficient interference effect.

This is because when the blue wavelength light, i.e., a 400 nm laser beam, is used as the light source, in the phase change optical disk structure of FIG. 2, the difference in the light reflectance in the crystalline and amorphous state of the recording layer 23 according to the thickness of the first dielectric layer 22 ( Rc-Ra) and the light absorption ratio (Ac / Aa) and the phase difference can be confirmed from FIG.

Therefore, when the phase change optical disk using the blue wavelength light as the light source is formed in the layer structure as shown in FIG. 2, as shown in FIG. 4, the light absorption ratio (Ac) in the crystalline and amorphous state of the recording layer 23 is obtained. / Aa) has a problem that it is difficult to obtain a value of 0.85 or more.

SUMMARY OF THE INVENTION The present invention was created to solve the above problems of the prior art, and in particular, in the case of using a blue laser beam as a light source, it is possible to reduce jitter value when overwriting and cross-erase. It is an object of the present invention to provide a phase change optical disk having a layer structure made of suitable materials capable of suppressing the occurrence of a cross-erase phenomenon.

1 is a vertical cross-sectional structural view schematically showing an example of a conventional phase change optical disk,

Figure 2 is a vertical cross-sectional structural view schematically showing another example of a conventional planarizing optical disk,

3 is a graph schematically showing optical characteristics according to a thickness of a first dielectric layer of a conventional phase change optical disk shown in FIG. 1;

4 is a graph schematically showing optical characteristics according to a thickness of a first dielectric layer of the conventional phase change optical disk shown in FIG.

5 is a vertical cross-sectional structural view schematically showing a phase change optical disk according to a first embodiment of the present invention;

FIG. 6 is a graph schematically showing optical characteristics according to a thickness of a first dielectric layer of the phase change optical disk of the present invention shown in FIG. 5;

7 is a vertical cross-sectional structural view schematically showing a phase change optical disk according to a second embodiment of the present invention;

FIG. 8 is a graph schematically showing optical characteristics according to the thickness of the first dielectric layer of the phase change optical disk of the present invention shown in FIG.

9 is a graph showing the optical characteristics of the phase change optical disk in comparison with the conventional case and the present invention.

<Description of the code | symbol about the principal part of drawing>

110 substrate 120 first dielectric layer

130 recording layer 140 second dielectric layer

210 substrate 220 first dielectric layer

230 recording layer 240 second dielectric layer

250 ... reflective layer

In order to achieve the above object, a phase change optical disc according to the present invention comprises: a phase change optical disc having a multilayered film structure comprising at least one dielectric layer formed on a substrate and a recording layer that is irreversibly changed to crystalline and amorphous by irradiation of light. The dielectric layer is characterized in that its refractive index is at least 2.5.

According to the first embodiment of the present invention, the dielectric layer includes a first dielectric layer and a second dielectric layer, and the first dielectric layer, the recording layer, and the second dielectric layer are sequentially stacked on the substrate.

According to a second embodiment of the present invention, the dielectric layer includes a first dielectric layer and a second dielectric layer, and the first dielectric layer, the recording layer, the second dielectric layer, and the reflective layer are sequentially stacked on the substrate.

Here, the dielectric layer is preferably made of at least one material selected from TiO ₂ , ZnO, CeO ₂ and ZnS having a refractive index of 2.5 or more.

The recording layer is preferably made of any one material selected from an alloy of Ge ₂ Sb ₂ Te ₅ and Sb, an alloy of GeSb ₂ Te ₄ and Sb, and an alloy of GeSb ₄ Te ₇ and Sb.

In addition, the recording layer preferably has a light absorption ratio (Ac / Aa) of 1.0 or more in the crystalline and amorphous states, and an optical phase difference of 5 ° or less in the crystalline and amorphous states, and when the amorphous state is more amorphous. It is preferable that the light reflectivity of is large.

The multilayer film structure of the phase change optical disk according to the present invention is applied to an optical disk having a track width of 0.4 µm or less or an optical disk using light having a wavelength of 450 nm or less.

Hereinafter, a phase change optical disk according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

5 is a vertical cross-sectional structural view schematically showing a phase change optical disk according to a first embodiment of the present invention.

As shown, the phase change optical disk 100 according to the first embodiment of the present invention, the first dielectric layer 120, the recording layer 130 and the second dielectric layer 140 on the transparent substrate 110 It has a multilayer film structure which is laminated | stacked sequentially.

The substrate 110 may be formed of a material substantially the same as a material used for a conventional phase change optical disk, and the recording layer 130 may be an alloy of Ge ₂ Sb ₂ Te ₅ and Sb and an alloy of GeSb ₂ Te ₄ and Sb. And GeSb ₄ Te ₇ and Sb.

The first dielectric layer 120 is used to increase the light absorption ratio (Ac / Aa) between the crystalline and amorphous phases of the recording layer 130 and to adjust the reflectance according to the thickness thereof. In an embodiment, the first dielectric layer 120 and the second dielectric layer 140 may be formed of at least one material selected from among TiO ₂ , ZnO, CeO _2, and ZnS having refractive indices of 2.5 or more.

In the conventional phase change optical disc shown in FIG. 1, the Au interference layer absorbs light and decreases reflectance, making it difficult to cancel interference of light waves reflected from the crystalline recording layer. In the case of using a dielectric layer having a high refractive index such as TiO ₂ , the reflectance is large enough to cause a destructive interference and light absorption is not generated.

According to the multi-layered film structure of the phase change optical disk 100 according to the present invention, the optical wave reflected from the crystalline recording layer 130 and the optical wave reflected from the first dielectric layer 120 having a high refractive index cancel each other. By increasing the absorption rate, the light absorption ratio (Ac / Aa) between the crystalline and amorphous phases of the recording layer 130 can be increased.

FIG. 6 illustrates that the recording layer 130 has Ge ₂ Sb ₂ Te ₅ having a thickness of 12 nm in the multilayer structure of the phase change optical disk 100 according to the first embodiment of the present invention illustrated in FIG. 5. The second dielectric layer 140 is formed with TiO ₂ having a thickness of 135 nm, while varying the thickness of the first dielectric layer 120, the light reflectance difference (Rc-Ra) between crystalline and amorphous phases of the recording layer 130 and The graph shows the result of calculating the light absorption ratio (Ac / Aa).

Here, referring to FIG. 6, the light reflectance difference Rc-Ra and the light absorption ratio Ac / Aa are periodically changed according to the thickness of the first dielectric layer 120, and the thickness of the first dielectric layer 120 is 75 nm. Alternatively, it can be seen that the light absorption ratio (Ac / Aa) is 1.1 or more at 135 nm, and the light reflectance difference (Rc-Ra) is approximately -0.13.

As described above, when the phase change optical disk using the blue wavelength light as the light source is formed into a layer structure including a dielectric film having a high refractive index as shown in FIG. 5, the above two optical characteristics are both phase change having a conventional multilayer film structure. It is superior to the disk. Therefore, according to the thickness of the first dielectric layer 120, the light reflectance Ra in amorphous phase can be made larger than the crystalline light reflectance Rc of the recording layer 130, and the light absorption ratio (Ac / Aa) is also 1.1 or more. Since it can be adjusted, the jitter value can be reduced when overwriting, and the occurrence of cross-erase phenomenon can be suppressed.

7 is a vertical cross-sectional structural view schematically showing a phase change optical disk according to a second embodiment of the present invention.

As shown, the phase change optical disk 200 according to the second embodiment of the present invention includes a first dielectric layer 220, a recording layer 230, and a second dielectric layer 240 on a transparent substrate 210. And a reflective layer 250 in which the reflective layers 250 are sequentially stacked.

Each layer from the substrate 210 to the second dielectric layer 240 is made of the same material as that of the corresponding layer of the phase change optical disk 100 according to the first embodiment of the present invention shown in FIG. The detailed description is omitted.

However, in the phase change optical disc 200 according to the second embodiment of the present invention, a reflection layer 250 is further formed as compared to the phase change optical disc 100 according to the first embodiment of the present invention, and the reflection layer 250 The high thermal conductivity metal material, for example, aluminum (Al) or aluminum alloy material is used. Accordingly, there is an advantage in that the mark boundary becomes clear by quenching the molten recording layer 230 during recording and the amplitude of the reproduction signal is increased.

FIG. 8 illustrates that the recording layer 230 has Ge ₂ Sb ₂ Te ₅ having a thickness of 14 nm in the multilayer structure of the phase change optical disk 200 according to the second embodiment of the present invention shown in FIG. 7. The second dielectric layer 240 is formed of TiO ₂ with a thickness of 90 nm, and the reflective layer 250 is formed with Al having a thickness of 100 nm, while changing the thickness of the first dielectric layer 220 while recording layer 230 is formed. The graph shows the results of calculating the light reflectance difference (Rc-Ra) and the light absorption ratio (Ac / Aa) between crystalline and amorphous.

Here, referring to FIG. 8, when the thickness of the first dielectric layer 220 is about 75 nm or 135 nm, the light absorption ratio (Ac / Aa) is 1.27, and the light reflectance difference (Rc-Ra) is approximately −0.2. It can be seen that the optical characteristics of the phase change optical disk 100 according to the first embodiment of the present invention is superior to that of the multilayer structure of FIG. 5.

As described above, when the phase change optical disk using the blue wavelength light as the light source is formed into a layer structure including a dielectric film having a high refractive index as shown in FIG. 7, the jitter value can be reduced at the time of overwriting and cross It is possible to suppress the occurrence of cross-erase phenomenon.

9 is a graph showing the optical characteristics of the phase change optical disk in comparison with the conventional case and the present invention.

A, B, C, and D symbols shown on the graph X-axis of FIG. 9 indicate the multilayer film structures shown in FIGS. 1, 2, 5, and 7, respectively.

Here, referring to FIG. 9, a phase change optical disk according to the present invention having a multilayer film structure (C, D) having a dielectric layer having a high refractive index formed between a substrate and a recording layer has an image having a conventional multilayer film structure (A, B). It can be seen that the light reflectance difference and the light absorption ratio are significantly improved compared to the change optical disk. In particular, it can be seen that the light absorption is improved by about 30%, which means that the effect of significantly suppressing the cross-erase phenomenon can be obtained.

Although the present invention has been described with reference to the disclosed embodiments, these are merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

As described above, according to the phase change optical disk according to the present invention, the optical absorption ratio (Ac / Aa) in the crystalline and amorphous phases of the recording layer is increased, so that the blue wavelength light is used as a light source. The jitter value can be reduced while suppressing the occurrence of cross-erase.

Claims (10)

In a phase change optical disc of a multilayer film structure comprising at least one dielectric layer formed on a substrate and a recording layer reversibly changed crystalline and amorphous by irradiation of light, And said dielectric layer has a refractive index of at least 2.5. The method of claim 1, And the dielectric layer includes a first dielectric layer and a second dielectric layer, and has a multilayer structure in which the first dielectric layer, the recording layer, and the second dielectric layer are sequentially stacked on the substrate. The method of claim 1, And the dielectric layer includes a first dielectric layer and a second dielectric layer, and has a multilayered film structure in which the first dielectric layer, the recording layer, the second dielectric layer, and the reflective layer are sequentially stacked on the substrate. The method of claim 1, The dielectric layer is a phase change optical disk, characterized in that made of at least one material selected from TiO ₂ , ZnO, CeO ₂ and ZnS having a refractive index of 2.5 or more. The method of claim 1, And the recording layer is made of any one selected from an alloy of Ge ₂ Sb ₂ Te ₅ and Sb, an alloy of GeSb ₂ Te ₄ and Sb, and an alloy of GeSb ₄ Te ₇ and Sb. The method of claim 1, And the recording layer has a light absorption ratio (Ac / Aa) of 1.0 or more in a crystalline and amorphous state. The method of claim 1, And the recording layer has a phase difference of 5 ° or less in a crystalline and amorphous state. The method of claim 1, And the recording layer has a larger light reflectance in an amorphous state than in a crystalline state. The method according to claim 2 or 3, The multilayer film structure is a phase change optical disk, characterized in that applied to the optical disk having a track width of 0.4㎛ or less. The method according to claim 2 or 3, And the multilayer film structure is applied to an optical disk using light having a wavelength of 450 nm or less.