KR100617203B1 - optical recording medium - Google Patents

Abstract

The present invention relates to an optical recording medium capable of high-sensitivity recording, wherein a third-order nonlinear material having a positive imaginary part of the nonlinear coefficients is disposed at the rear of the recording film, so that the absorption rate increases as the light intensity increases. By using, it is possible to implement an optical disk of a new structure having high sensitivity and low jitter.

Inverse supersaturated absorption layer

Description

Optical recording medium

1 is a structural cross-sectional view showing an optical recording medium according to the prior art.

2 to 5 are structural cross-sectional views showing an optical recording medium according to the first to fourth embodiments of the present invention.

6A is a graph showing the temperature distribution of a recording film of a general four-layer film structure.

6B is a graph showing the temperature distribution of the recording film of the structure according to the present invention;

The present invention relates to an optical recording medium capable of high sensitivity recording.

In general, optical disk technology, which started with compact disk-read only memory (CD-ROM), is currently evolving.

As a result, a digital versatile disk-read only memory (DVD-ROM) having a capacity of 4.7 GB was commercialized for playback only, and a 2.6 GB recording capacity was commercialized for a rewritable DVD-ROM. The next version, which will have a recording capacity of GB, is expected to be commercialized soon.

The field currently being studied in phase change type optical discs is also focused on increasing the data transfer rate in order to increase the recording density and high-speed recording.

However, in the case of high density recording, the size of the laser beam spot used due to the diffraction limit cannot be reduced to less than the wavelength length, which shows a limitation of densification.

Therefore, researches to find a short wavelength laser light source are in progress, and the development of a laser in the blue band is currently in progress.

In the case of high-speed recording, there is a tendency that overwrite jitter, which occurs due to large absorption of amorphous and the like, is larger than absorption of the crystalline layer.

In consideration of the latent heat during melting of the crystalline layer, more energy is required when melting the crystalline part. Therefore, in order to solve this overwrite jitter, the absorption rate of the crystalline layer is made larger than that of the amorphous layer, that is, the absorption rate. You need to create a reverse structure.

For this reason, an absorption rate reversal structure in which an optical interference layer is inserted between a substrate and a lower dielectric or in the middle of a lower dielectric is used for a conventional four-layer film, that is, a substrate, a lower dielectric, a recording film, an upper dielectric, and a reflective film.

However, in this case, energy absorption is caused by the optical interference layer, and the energy absorbed by the recording film layer is reduced.

Therefore, stronger recording and erasing power is required, and the sensitivity of the entire disc becomes smaller.

In addition, the limit of jitter required by high density is becoming more and more stringent in terms of time.

This tends to follow naturally as the mark size decreases with higher density.

Another technique applied to optical discs for high density recording is high density recording using third-order nonlinear effects.

This nonlinear optics means that the properties of a material react nonlinearly with the intensity of light, rather than being linearly proportional to its intensity.

Examples of this are changes in the refractive index and absorption of materials when the intensity of the light is changed, the refractive index of the medium changes with the intensity of light when strong light is incident on the medium, so that the path of light gathers as it passes through the lens, Spreading phenomenon.

The theoretical background of nonlinear optics is as follows.

When an electric field (light) is applied to a material, it is P (polarization) indicating a change state of the electric field inside the material, and P is expressed as follows.

값이 선형계수이고,

값이 3차 비선형성의 정도를 나타내는 계수이다.here,

The value is a linear coefficient,

The value is a coefficient representing the degree of third order nonlinearity.

는 자체가 복소수(complex number)로서 물질의 복소 굴절률(complex refractive index)과 관련이 있다.This third order nonlinear coefficient

Is itself a complex number and is related to the complex refractive index of the material.

That is, the complex refractive index of the material considering the nonlinearity is expressed as follows.

here,

to be.

값과 비례하는 관계임을 알 수 있다.Looking at the above equation, the change in refractive index due to third-order nonlinearity

It can be seen that the relationship is proportional to the value.

If the real part of the nonlinear coefficient is positive, the tertiary nonlinear material acts as a convex lens and shows a self-focusing effect in which light passing through the tertiary nonlinear material is focused, and when the real part is negative The third nonlinear material acts as a concave lens, and the light passing through the third nonlinear material is defocused.

In the case where the imaginary part of the nonlinear coefficient is positive, the absorption rate increases as the intensity of light increases, and in the case where the imaginary part is negative, the absorption rate decreases as the intensity of the light increases.

In other words, if the coefficient is negative, the self-focusing effect exhibits a saturable absorption property, and if the coefficient is positive, the defocusing effect is shown.

By using this magnetic focusing effect of nonlinear materials, the beam can be focused below the diffraction limit and applied to high density recording.

As described above, the structure of a conventional phase change optical disk using a tertiary nonlinear material is shown in FIG. 1.

의 실수부가 양이어서 자기 집속에 의해 자체 렌즈역할을 하는 물질이거나,

의 허수부가 음이어서 과포화 흡수(saturable absorption)에 의한 수퍼-분해능(super-resolution)효과를 나타내는 물질을 사용하였다.Where the cubic nonlinear material is a cubic nonlinear coefficient

The real part of is a substance that acts as its own lens by magnetic focus,

The imaginary part of was negative, and a material showing a super-resolution effect by saturable absorption was used.

의 실수부가 양이어서 자기 집속을 나타내는 물질로는 InSb, a-As₂S₃, a-Si 등이 알려져 있다.

InSb, a-As ₂ S ₃ , a-Si, and the like are known as materials showing a positive focus due to the positive part of.

In addition, several organic substances are known.

의 실수부가 음이어서 과포화 흡수를 나타내는 물질은 대개 포토 블리처블 다이(Photo-Bleachable-Dye : PBD)로 알려져 있는 유기색소들이다.

Substances that exhibit a supersaturated absorption with negative real parts of are usually organic pigments known as Photo-Bleachable-Dye (PBD).

In addition, Sb thin films have recently been reported to be capable of super-resolution on a similar principle to supersaturation absorption.

In this manner, conventionally, small recording marks are recorded on the recording film by making a beam profile that is sharper than the beam profile of the original laser beam, whether magnetic focusing or supersaturation absorption by PBD or the like is used.

An object of the present invention is to provide an optical recording medium having a new structure which can have high sensitivity and low jitter.

의 허수부가 양이어서 빛의 세기가 클수록 빛의 흡수율이 높아지는 물질로 이루어진 역과포화흡수막으로 구성되는데 있다.Features of the optical recording medium according to the present invention include a protective film formed on a substrate, a recording film formed on the protective film for recording information, and formed on the recording film.

Since the imaginary part of is positive, the greater the intensity of light, the higher the absorption of light.

Another feature of the present invention is that the reverse supersaturated absorption film is formed of any one of a-Si, azobenzene dye, As ₂ S ₃ , Ge ₁₀ As ₁₀ Se ₈₀ , and ZnSe.

Referring to the accompanying drawings, an optical recording medium according to the present invention having the above characteristics is as follows.

First of all, the concept of the present invention is to realize a new optical disk having a high sensitivity and low jitter by arranging a tertiary nonlinear material having a positive imaginary part of the nonlinear coefficient among the tertiary nonlinear effects behind the recording film.

That is, the conventional optical disk using the third-order nonlinear effect is intended to record high density above the diffraction limit by using magnetic focusing or supersaturation absorption, whereas in the present invention, the imaginary part of the nonlinear coefficient is positive among the third-order nonlinear effects. The greater the luminance of light, the more the reverse saturable absorption.

This reverse supersaturation absorption property exhibits a defocusing effect of light, so that in the conventional method, unfavorable results such as the size of the recording mark become larger or the sensitivity is lowered.

However, in the present invention, unlike the conventional disc structure, by placing the third nonlinear material having a positive imaginary part on the back of the recording film, an effect of increasing sensitivity and reducing jitter can be obtained.

The reason is that the central portion of the laser passing through the recording film has a higher temperature than the edge portion of the laser, so that the central portion of the laser is absorbed more by the nonlinear material than the edge portion of the laser.

That is, since the center portion of the laser is absorbed more by the nonlinear material, the temperature of the nonlinear material toward the center portion of the laser increases, so that the temperature of the recording film near the laser center portion is relatively higher than that of the recording film near the laser edge portion. As a result, the recording mark can be recorded at a high density.

FIG. 2 is a structural cross-sectional view showing a phase change type optical disk according to a first embodiment of the present invention, wherein a first protective film, a recording film, a second protective film, a reverse supersaturation absorption film, and a third protective film are formed on a substrate as shown in FIG. A protective film and a reflective film are formed in this order.

The manufacturing process of the first embodiment is as follows.

In the present invention, a thin film is deposited on a substrate made of a transparent material such as polycarbonate, PMMA, glass, etc. to manufacture a disk. The thin film deposition method includes sputtering, CVD (chemical vapor deposition), and e. Various thin film deposition apparatuses such as e-beam deposition can be used.

First, a first protective film is coated on the substrate.

In this case, a transparent dielectric material is used in the wavelength range of the laser used as the protective film, and ZnS-SiO ₂ , SiO ₂ , Si ₃ N ₄ , Al ₂ O _3, and the like.

Next, a recording film is formed over the first protective film.

Here, the recording film is a material having a large difference in the reflective index between amorphous and crystalline, such as Ge ₂ Sb ₂ Te ₅ , Ge ₁ Sb ₄ Te ₇ , Ge ₁ Sb ₂ Te ₄ , AgInSbTe alloy, GeTe alloy, and SbTe alloy. Can be used

Then, a second protective film is coated on the recording film with the same material as or different from the first protective film.

The thickness of the second passivation film should be such that the heat transfer between the recording film under the second passivation film and the reverse supersaturation absorption film on the second passivation film is not excessively prevented.

Next, a reverse supersaturated absorption film is formed on the second protective film.

의 허수부가 양인 물질로서 빛의 세기가 셀수록 비선형적으로 흡수율이 증가하는 물질을 사용한다.Here, as the material of the reverse superabsorption membrane, the third nonlinear coefficient

A material with a positive imaginary part of is used as the light intensity increases and the absorption rate increases nonlinearly.

As the nonlinear countersaturated material, semiconductor materials such as a-Si, azobenzene dye, As ₂ S ₃ , Ge ₁₀ As ₁₀ Se ₈₀ glass, and ZnSe, which have multiphoton absorption, are used.

The third passivation film is formed on the reverse supersaturated absorption film by the same or different dielectric material as the material of the first or second passivation film, and the reflective film is formed on the third passivation film layer to complete the fabrication of the disk.

Here, the reflective film uses a metal material having high thermal conductivity and high reflectivity such as Al alloy, Au, Ag, Cu, or the like.

In addition to such a structure, the present invention may have a structure in which only the second passivation layer is omitted, as shown in FIG. 3, and the second and third passivation layers and the reflection layer may be simultaneously omitted as shown in FIG. 4. 5, only the second and third passivation layers may be omitted.

In this case, the material of each layer uses the same material as in the first embodiment.

The recording and reproducing method of the present invention having such a structure is as follows.

First, when the recording laser is incident from the substrate toward the recording film during recording, the central portion of the laser passing through the recording film is higher in temperature than the edge portion of the laser, so that the central portion of the laser is absorbed more by the nonlinear material than the edge portion of the laser.

As a result, the temperature of the nonlinear material toward the center of the laser is raised, so that the temperature of the recording film toward the center of the laser becomes relatively higher than that of the recording film toward the edge of the laser.

In this case, the recording sensitivity of the recording film is increased to enable recording at lower power during recording.

In the third nonlinear phenomena, only the part where the intensity of light is more than a certain amount has a substantial effect, so the strongest part of the light intensity, that is, the central part of the laser, has a high absorption rate in the third nonlinear layer, but the peripheral portion thereof has a relatively low absorption rate. .

FIG. 6A is a graph showing a temperature distribution when there is no tertiary nonlinear film, and FIG. 6B is a graph showing a temperature distribution when the tertiary nonlinear film (reverse supersaturation film) is behind the recording film.

6A and 6B, it can be seen that when the tertiary nonlinear film is behind the recording film, the recording film temperature at the center of the laser is relatively higher at the same power than when the tertiary nonlinear film is not present.

The reason for this is that since the reflective film is a heat sink in the optical disk and the recording film is a heat source, heat is transferred from the recording film to the reflective film.

In this case, if there is a reverse supersaturation absorption layer behind the recording film, the reverse supersaturation absorption layer absorbs heat only at the center of the laser, and thus the reverse supersaturation absorption layer becomes a secondary heat source.

In this case, the reverse supersaturation absorption layer at the center of the laser rises, so that the heat of the recording film at the center of the laser does not move well toward the reflective film, unlike the recording film at the periphery of the laser. Relatively higher.

Therefore, the recording sensitivity of the recording film is improved.

In addition, since only the recording film temperature of the laser center is increased and the recording film temperature of the laser periphery does not rise, the recording film of the laser periphery has a quench structure relatively.

Therefore, the heat flow increases in the inter-plane direction of the recording film rather than in-plane direction of the recording film, so that the shape of the recording mark is constant.

That is, jitter is reduced.

In this way, the information can be recorded in a high density on the disk due to the effect of increasing sensitivity and decreasing jitter value.

In the case of reproduction, the same procedure as in recording may be performed.

As described above, the present invention significantly increases the recording sensitivity at the same power, so that not only recording is possible at low power, but also the jitter can be reduced by making the peripheral portion of the recording mark relatively quenched.

The above two effects are particularly useful for high density phase change discs.

The reason is that in the case of a high density disc, since the size of the recording mark is very small, low jitter values and high sensitivity are further required.

Therefore, the present invention can be said to be one of the technologies necessary for the practical use of high density phase change disks.

Claims (5)

A protective film formed on the substrate; A recording film formed on the protective film to record information; A reflective film formed on the recording film; And a reverse supersaturation absorption film formed between the recording film and the reflective film and made of a material having a higher light intensity to absorb light, and absorbing heat transferred from the recording film to the reflective film. The optical recording medium according to claim 1, wherein the reverse supersaturated absorption film is any one of a-Si, azobenzene dye, As ₂ S ₃ , Ge ₁₀ As ₁₀ Se ₈₀ , and ZnSe. The optical recording medium according to claim 1, wherein a protective film is formed between the recording film and the reverse supersaturation absorption film. delete The optical recording medium according to claim 1, wherein a protective film is formed between the reverse supersaturated absorption film and the reflective film.

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