JPH07105064B2 - Optical information recording medium - Google Patents

Description

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

2. Description of the Related Art When a laser beam is focused by a lens system, a light spot whose diameter is on the order of the long wave of the light beam can be formed. Therefore, it is possible to form a light spot having a high energy density per unit area even from a light source having a small output. Therefore, it is possible to change a minute area of the substance, and it is also possible to read out the change of the minute area. An engineering information recording medium uses this for recording / reproducing information. Hereinafter, "optical recording medium"
Or simply described as "medium".

The basic structure of an optical recording medium is that a recording thin film layer whose state is changed by laser spot light irradiation is provided on a substrate having a flat surface. The following methods are used for recording / reproducing signals. That is, the planographic medium is moved by rotating means or translation means such as a motor, and laser light is converged and irradiated onto the recording thin film surface of this medium. The recording thin film absorbs laser light and heats up. When the output of laser light is increased above a certain threshold value, the state of the recording thin film changes and information is recorded. This threshold value is an amount that depends on the thermal characteristics of the substrate, the relative speed to the light spot of the medium, and the like in addition to the characteristics of the recording thin film itself. The recorded information is irradiated with a laser beam spot whose output is sufficiently lower than the threshold value, and some optical characteristics such as transmitted light intensity, reflected light intensity or their polarization direction are different between the recorded part and the unrecorded part. It detects that and reproduces.

Therefore, materials and structures that change state with low laser power and exhibit large optical changes are desired.

As the recording thin film, Bi, Te, a metal thin film containing them as a main component, or a compound thin film containing Te is known. These perform punching type recording in which a thin film is melted or vaporized by laser light irradiation to form small holes, and the phases of reflected light or transmitted light from this recording part and its peripheral part are different, so they cancel each other out by interference, Alternatively, reproduction is performed by detecting a change in the amount of reflected light or the amount of transmitted light that is diffracted and reaches the detection system. In addition, there is also a recording medium called a phase change type which changes optically without changing its shape. The material is oxide thin film amorphous chalcogen compound thin film, a Te-TeO ₂ consisting of tellurium and tellurium oxide as a main component (JP-B 54-3725 Patent Publication). In addition, Te-TeO ₂
A thin film containing pd as a main component is also known (Japanese Patent Laid-Open No. 61-6829).
No. 6). At least one of the extinction coefficient and the refractive index of the thin film changes due to laser light irradiation for recording, and the amplitude of transmitted light or reflected light changes at this portion, and as a result, the maximum amount of transmitted light passes through the detection system. Alternatively, the signal is reproduced by detecting that the amount of reflected light changes.

Light is a wave and is described by its amplitude and phase. As described above, the signal reproduction is detected by the change in the transmitted light amount or the reflected light amount. The cause is that the transmitted light amplitude or the reflected light amplitude in the minute area of the film itself changes (amplitude change recording). There is a case where the phase of light or reflected light changes (phase change recording).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Among the above optical recording media, the perforated type has a large change in the amount of reflected light, and since it is phase change recording, recording with a high recording density can be performed, but a clear hole is formed. It is difficult and the noise during playback is large. Further, it is necessary to take a complicated hollow structure, which is a so-called air sandwich structure, because a protective structure in close contact cannot be obtained, which makes manufacturing difficult and costly. In addition, since it is a modified recording, it cannot be erased and rewritten.

Compared to this, the phase-change recording medium is a medium with a simple structure that is easy to manufacture because it does not change the shape, and it is a low-cost medium. There is a problem of low density. Further, there is a problem in that it is difficult to achieve compatibility with a duplication board (audio disk, video disk, etc.) due to the concave-convex pit which is a phase change type recording medium.

Means for solving the problem By providing a thin film material whose optical constant is changed by laser light irradiation on the base material, the phase of the reflected light or the transmitted light of the incident light changes before and after the change, and The configuration is such that a change in the amount of reflected light or the amount of transmitted light is detected. Further, at that time, the reflected light amplitude or the transmitted light amplitude does not change or is small before and after the change.

Operation With the above-mentioned configuration, optically equivalent recording to phase change recording by unevenness can be performed. Therefore, although it is a phase change recording, recording with a high recording density can be performed, and a duplication board (audio disc, video disc, etc.) with uneven pits
It is easy to take compatibility with. Further, in the phase change recording, the recorded state can be returned to the original state by selecting a material without changing the shape, that is, erasing / rewriting is possible, and rewritable phase change recording can be realized.

Example An example of the structure of a conventional phase change type optical recording medium is shown in FIG. The complex refractive index of the phase-change recording material changes when the phase of the phase-change recording material is changed by changing the phase by irradiating a laser beam to generate heat. The change generally changes the refractive index and the extinction coefficient in the same direction.
For example, when the amorphous state changes to the crystalline state, the refractive index and the extinction coefficient generally increase. The reflectance of such a recording thin film layer depends on the film thickness t ₂ of the recording thin film layer 3. The reflectance R of the recording thin film when light is incident from the substrate 1 side is the result of multiple interference of the reflected light from the light incident side interface of the recording thin film and the reflected light from the reflective side interface. When the film thickness t ₂ is changed, the reflectance increases or decreases as a result of interference, with the period determined by the wavelength and the refractive index, but as the film thickness increases, the amount of light that reaches the interface opposite to the light incident side and is reflected by absorption increases. Since it decreases, the effect of interference disappears. As a result, a curve is drawn in which the increase / decrease due to interference gradually attenuates as the film thickness increases. When the complex refractive index increases, the film thickness period due to interference decreases due to the increase in the refractive index, and at the same time, the attenuation film thickness shifts toward the smaller direction due to the increase in the extinction coefficient. As a result of the above, the reflectance difference ΔR at the time of phase change also changes depending on the film thickness, but generally it becomes maximum at the film thickness at which the reflectance is minimal in the phase with a small complex refractive index. On the other hand, in such a configuration, the change in the phase of the reflected light before and after the phase change is small. Conventionally, the phase change type recording medium has been used with a film thickness that maximizes this change in reflectance. Therefore, reproduction of the recorded state is performed by detecting this difference in reflectance. In the case of recording / reproducing in a minute area of micron order, the size of the recorded portion is the same as the size of the light beam used for reproducing. For example, if a laser beam with a wavelength of around 800 nm is narrowed down by a lens system with an NA of about 0.5, it will be narrowed down to a beam with a half width of about 0.9 μm. When recording with strong power using such a beam, it is about 0.5-1.
A range of about μm causes a phase change and becomes a recording state. Considering the case of reading this with the same beam, the light intensity of the read beam generally has a glass distribution or a shape distribution close to it, and since the light intensity spreads outside the phase-changed recording state, the reflected light amount is It is proportional to the average of the reflectance in the recorded state and the reflectance in the surrounding unrecorded state, weighted by their respective areas and light intensity distributions. Therefore, a sufficient reproduction signal cannot be obtained unless there is a recording state area that is sufficiently larger than the read beam size. This size limits the recording density.

On the other hand, in the case of the perforated type, the recording state has an uneven shape, and the fact that the reflected light from the peripheral portion interferes with the reflected light and the amount of reflected light changes. Therefore, when the phase difference of the reflected light at the peripheral portion and the hole is (1 ± 2n) π (n is an integer, π is the circular constant), the change in the reflected light amount is the largest, and it is particularly close to this value. It is desirable to be equal. Further, as the intensity distribution of the read beam, when the intensity incident on the hole is equal to the intensity incident on the peripheral portion, the effect of interference is greatest, and thus the change in reflected light intensity is large. That is, the reproduction signal can be large in a recording state smaller than the size of the read beam.

From the above, it is understood that the phase change recording can achieve higher density recording and reproduction than the reflectivity change recording.

Therefore, if the phase change can be obtained in the phase change recording, the recording density comparable to the uneven recording can be obtained. Moreover, it is desirable that the reflectance does not change or is small. In order to configure the above-mentioned phase change type optical recording medium using the phase change type recording thin film material, a base material or a protective layer on at least one side of the recording thin film layer and a refractive index at the wavelength of laser light used This can be achieved by providing different transparent layers. When the refractive index of the material in contact with the recording thin film changes, the reflectance at each interface changes. The reflected light from the recording thin film is the result of multiple interference between the reflected light from the light incident side interface of the recording thin film and the reflected light from the opposite side interface. The recording thin film is thin enough to reach the interface on the opposite side of the light incident side of the recording thin film.If the light intensity is sufficiently large, it reaches the interface on the opposite side of the light incident side when the optical constant in the unrecorded state is small. When the reflected light is larger than the reflected light from the light incident side interface and the optical constant in the recorded state is large, the reflected light from the light incident side interface reaches the interface opposite to the light incident side. There are conditions that make it larger than the reflected light. Both have a phase difference because the optical path lengths are different. If this phase difference is large, as a result of cancellation due to interference, the phase of the entire reflected light can change significantly when the optical constant changes due to recording. Furthermore, if the difference in amplitude between the two is almost equal before and after recording (although the magnitude relationship is reversed, of course), it is possible that there is almost no change in the reflected light amplitude.

Furthermore, a first transparent layer having a refractive index different from that of the substrate is provided on the substrate, a recording thin film layer is provided thereon, a second transparent layer is further provided thereon, and a reflective layer is provided thereon. A more efficient phase change type optical recording medium is obtained by selecting the film thicknesses of the first transparent layer, the recording thin film layer, the second transparent layer and the reflective layer with a structure in which a reflective layer is provided above. You can
This is because the light transmitted through the recording thin film layer is reflected by the reflective layer and the cancellation due to the above interference is efficiently performed.

Next, a specific example will be described.

As the structure of the recording medium, as shown in FIG. 1, an optical layer 2 such as a transparent dielectric is provided on a base material 1, a recording thin film 3 is provided thereon, a transparent dielectric layer 4 is further provided, and a reflective layer 5 is provided. To provide. Further, a transparent protective layer 6 is provided thereon. In addition, although not shown in the figure, a structure in which a protective layer is not provided may be used. In this case, air (refractive index 1.
Considering 0), they are optically equivalent and the same effect can be obtained. A material having a refractive index different from that of the substrate 1 is used for the transparent layer 2.

By appropriately selecting the thickness t ₂ of these recording thin films, the thicknesses t ₁ and t _{3 of the} transparent optical layers, and the thickness t ₄ of the reflective layers, a medium having a large phase change can be obtained.

As the base material, a transparent and flat plate such as glass or resin is used. Further, the surface of the base material may have groove-shaped irregularities for a tracking guide.

As the protective layer, a resin coated with solvent and dried, or a resin plate bonded with an adhesive can be used.

As the recording thin film material, a material that changes the phase between amorphous and crystalline, such as SbTe-based, InTe-based, GeTeSn-based, SbSe
System, TeSeSb system, SnTeSe system, InSe system, TeGeSnO system, TeGeSnA
A chalcogen compound such as u-based or TeGeSnSb-based is used. Te
-TeO ₂ system, Te-TeO ₂ -Au system, even oxide material of ₂ -Pd system such as Te-TeO Chikaeru. In addition, Ag, which has a phase transition between crystals
Metal compounds such as Zn type and InSb type can also be used.

As the transparent optical layer, oxides such as SiO ₂ · SiO, TiO ₂ , MgO and GeO ₂ , nitrides such as Si ₃ N ₄ and BN, and sulfides such as ZnS, ZnTe and PbS can be used.

As the reflection layer, a metal material such as Au, AI, Cu or a dielectric multilayer film having a large reflectance at a predetermined wavelength can be used.

As a method for producing these materials, a vacuum evaporation method using a multi-source evaporation source, a sputtering method using a mosaic-shaped compound target, and the like can be used.

Comparative Example A ternary compound of germanium, antimony and tellurium having a composition of Ge ₂ Sb ₂ Te ₅ which is a phase change material is used as a recording thin film. As a forming method, an electron beam evaporation method using three evaporation sources of Ge, Sb and Te is used. The recording thin film is formed in an amorphous state. Ge ₂ Sb ₂ Te ₅ with the above composition was placed on a glass plate.
When the optical constant of the amorphous state was measured, the complex refractive index n + ki was 4.8 + 1 at the wavelength of 830 nm.
It was 3i. When this is heat-treated at 300 ° C. for 5 minutes to be in a crystalline state, it changes to 5.8 + 3.6i.

This film was vapor-deposited on a polycarbonate resin plate (PC, refractive index 1.58) and coated with resin of the same refractive index material before and after heat treatment in the case of the conventional structure as shown in FIG. 2, that is, in an amorphous state and a crystalline state. The calculated values of the change ΔR in the reflectance R of the light having the wavelength of 830 nm and the film thickness dependence of the phase change in the reflected light are shown in FIGS. 3 (a) and 3 (b).

The reflectance and the phase of the reflected light were calculated by the matrix method from the complex refractive index and the film thickness of each layer (see, for example, Hiro Kubota "Wave Optics" Iwanami Shoten, 1971 Chapter 3).
Assuming that the base material 1 and the adhesion protection layer 6 have infinite film thickness (ignoring the effects of the base material-air interface and the adhesion protection layer-air interface), the reflectance R is the base of the light incident from the base material. The phase was determined as the ratio of light emitted into the material, and the phase was determined based on the phase at the interface between the base material 1 and the transparent layer 2. Since the phase is equivalent to a period of 2π, this is taken into consideration in the figure.

The reflectance difference ΔR between the amorphous state and the crystalline state is a film thickness of 15 nm.
It becomes maximum at and 85 nm and becomes 14% and 24% respectively, but there is almost no phase change and it is π / 6 or less.

Example 1 As one example of the present invention, as shown in FIG. 1, zinc sulfide (ZnS, refractive index 2.10) was electron beam evaporated as a transparent layer 2 on a polycarbonate resin plate (PC, refractive index 1.58) as a substrate 1. The recording thin film Ge ₂ Sb ₂ Te ₅ shown in the comparative example was formed as the recording thin film layer 3 by the same method as the comparative example, and ZnS was formed as the transparent layer 4 with the thickness t ₁ = 142 nm by the method. ₃ = 235nm It vapor-deposited similarly. On this, gold (Au, refractive index 0.20 + 5.04i) is formed as a reflective layer 5 by an electron beam vapor deposition method with a thickness t ₄ = 20 nm, and a resin having the same refractive index as the base material is coated as a protective layer 6. did.

FIG. 4 shows the calculated values of the dependence of the reflectance R on the thickness t ₂ of the recording thin film layer before and after the heat treatment in such a structure, that is, in the amorphous state and the crystalline state, and the reflectance change ΔR and the phase change of the reflected light. Figure 5 (a) shows the calculated value of the film thickness t ₂ dependence of
It shows in (b). When the film thickness t ₂ of the recording thin film layer is 10 nm, there is no change in reflectance and a phase change of reflected light of approximately −0.9π is obtained, which is approximately π.
It is shown to be close to.

Next, let us consider a case where the thickness of the recording thin film layer is fixed to 10 nm and the thicknesses of other layers are changed in the same configuration.

The thickness t ₂ of the recording thin film layer is 10 nm, and the thickness t ₃ of the transparent layer 4 is 235n.
The calculated values of the reflectance change ΔR and the film thickness t ₁ dependence of the phase change of the reflected light when the thickness t ₄ of the reflective layer 5 is 20 nm are shown in FIGS. 6 (a) and 6 (b). Shown in. Since the transparent layer has no absorption, the thickness gives the same effect in the period corresponding to the phase π. In the case of this embodiment, the same characteristics are given at a period of 198 nm, so that the thickness is shown in the figure, but all the thicknesses can be discussed. Thickness t ₁ is (142 + 198k) nm
It is shown that when (k: integer), there is no reflectance change and a phase change of reflected light of about -0.9π is obtained, which is close to π. It can be seen that for other film thicknesses, the reflectance change is large and the phase change is small.

10n thickness t ₁ of the transparent layer 1 is 142 nm, the thickness t ₂ of the recording thin film layer
m and the calculated values of the reflectance change ΔR when the thickness t ₄ of the reflection layer 5 is 20 nm and the film thickness t ₃ dependency of the phase change of the reflected light on the thickness t ₃ of the transparent layer 2 are shown in FIGS. Show. Thickness t ₃ is (37 + 198k)
It is shown that when nm (k: integer), there is no change in reflectance and a phase change of reflected light of about −0.9π is obtained.

From the above results, it can be seen that by appropriately selecting the thickness of each layer, there is almost no change in the reflectance and only the phase of the reflected light changes. The following experiments were performed based on this calculation.

Using a PC resin disk with a thickness of 1.2 mm and a diameter of 200 mm as a substrate, a ZnS thin film was deposited to 142 nm by the above method while rotating it in a vacuum, and a recording thin film Ge ₂ Sb ₂ Te ₅ was deposited to the same right as a 10 nm film. It was formed in a thick and amorphous state. Furthermore, a ZnS thin film with a thickness of 235 nm
The Au was vapor-deposited to a thickness of 20 nm. Multi-layer thin film with the same structure
It was also formed on a glass substrate of 18 × 18 mm and a thickness of 0.2 mm. Further, for the film formed on the resin disk, the same PC resin disk was attached with an ultraviolet curable adhesive to provide an adhesion protection layer to form an optical recording medium.

The sample formed on the glass substrate was heated at 300 ° C. for 5 minutes in an argon atmosphere to crystallize the entire surface, and the reflectance from the base material side was measured before and after crystallization.

This medium is rotated and the linear velocity is 10 m / sec and the wavelength is 830 nm.
The semiconductor laser height was squeezed by a lens system with a numerical aperture of 0.5 and focused on the recording thin film for irradiation. 8m on the recording thin film surface
Recording is performed by irradiating light modulated at a single frequency of 5 MHz and a modulation rate of 50% with the output of W to partially crystallize the recording thin film,
When a continuous output of 1 mW was emitted and the reflected light was detected by a photodetector for reproduction, the reproduction signal amplitude was observed.

In the above sample on the glass substrate, no change in reflectance was observed due to crystallization, so it can be seen that this reproduced signal is due to the difference in the phase of the reflected light between the recorded portion and the unrecorded portion.

Further, when the frequency of the signal to be recorded was changed and recording / reproduction was performed, it was confirmed that the frequency characteristic extended to the high frequency side as compared with the conventional recording thin film having a film thickness of 85 nm as shown in FIG. It was

In addition, when a signal was recorded on the recording thin film surface at a linear velocity of 10 m / sec and a laser of 16 mW was continuously irradiated in the same manner, the recording thin film melted and changed to an amorphous state. It was confirmed that was deleted.

EFFECTS OF THE INVENTION According to the present invention, recording that is optically equivalent to phase change recording due to unevenness can be performed. Therefore, it is possible to perform recording with a high recording density even though it is phase change recording, and it is easy to obtain compatibility with a duplication disk (audio disk, video disk, etc.) due to uneven pits. Further, in the phase change recording, the recorded state can be returned to the original state by selecting a material without changing the shape, that is, erasing / rewriting is possible, and rewritable phase change recording can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a schematic diagram showing the configuration of a conventional example, and FIG. 3 is a diagram showing the reflectance change and the phase change of reflected light in the configuration of the conventional example. FIG. 4 is a graph showing the film thickness dependence of the recording thin film, FIG. 4 is a graph showing the film thickness dependence of the reflectance of the embodiment of the present invention, and FIG. 5 is a change of the reflectance of the embodiment of the present invention. And graphs showing the film thickness dependence of the phase change of the reflected light, and FIGS. 6 and 7 are the film thickness dependence of the transparent layer of the reflectance change and the phase change of the reflected light in one embodiment of the present invention. It is a graph which shows. 1 ... Substrate, 2,4 ... Transparent layer, 3 ... Recording thin film layer, 5 ...
… Reflective layer, 6 …… Protective layer.

Claims (4)

[Claims] 1. An optical information recording medium comprising a substrate and a recording thin film material layer which produces a change which can be optically detected by laser light irradiation, wherein the thin film material changes its shape by laser light irradiation. An optical information recording medium characterized in that the optical constant changes without being accompanied, and the detectable change is mainly due to a change in the phase of reflected light or transmitted light of incident light. 2. The optical information recording medium according to claim 1, wherein a change in transmittance or reflectance of incident light before and after the change is small. 3. A first transparent layer having a refractive index different from that of the substrate is provided on a substrate, a recording thin film layer is provided thereon, and a second transparent layer is provided thereon, and a reflective layer is provided thereon. An optical information recording medium having a structure in which the thickness of the first transparent layer, the recording thin film layer, the second transparent layer and the reflective layer is changed in optical constant without changing the shape of the recording material. 3. The optical information recording medium according to claim 1, wherein the optical information recording medium is selected so that the phase of transmitted light or reflected light of incident light is changed. 4. The optical information recording medium according to claim 1, wherein the phase change is approximately (1 ± 2n) π n: an integer.