JP3087433B2 - Optical information recording medium and structure design method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can overwrite an information signal having a high signal quality by irradiating a high energy beam such as a laser beam to a phase change material thin film formed on a substrate. The present invention relates to a configuration of a rewritable optical information recording medium and a configuration method thereof.

[0002]

2. Description of the Related Art The ability to locally change the optical properties (refractive index) of a minute portion by irradiating a laser beam to a chalcogenide thin film formed on a substrate is a light-induced phase change. It is already known as a phenomenon. That is, if the irradiation condition of the laser beam is selected, the irradiated part is rapidly changed from a state in which the atomic bonding state is relatively disordered (amorphous phase) to a state in which the atom bonding state is relatively adjusted (crystalline phase), and conversely, from a crystalline phase to an amorphous phase. It can be changed, and application development has been performed as one of methods for performing high-density information recording.

One of the advantages of the phase change recording is that an information signal can be overwritten using only a single laser beam as recording means. That is, when the laser output is modulated according to the information signal between the recording level and the erasing level according to the information signal and irradiated onto the recorded information track, a new signal can be recorded while erasing the existing information signal. (JP-A-56-145530). This method is advantageous for recording video and audio signals because the head can be simplified because no magnetic circuit components are required unlike magneto-optical recording, and the rewriting time can be reduced because no erasing operation is required. The research and development of recording media is underway.

[0004] Problems specific to overwriting have also been extracted, and solutions have been proposed. For example, there is a problem that the erasing rate at the time of overwriting is lower than the erasing rate when only the erasing operation is performed. To solve this problem, we have disclosed in JP-A-1-149238 a recording medium in which the optical absorptance in a recording mark portion in an amorphous state is equal to the optical absorptance in an unrecorded portion in a crystalline state, and a crystalline state portion. A recording medium was proposed in which the light absorptance of the recording medium was higher than that of the amorphous state portion. That is, as shown in FIG.
And a medium in which a recording layer 2 sandwiched by a dielectric 3 is formed on the medium and a medium in which a light reflection layer 4 is further provided on the dielectric 3 and a protective plate 5 is attached. It has been disclosed that an optical recording medium that satisfies the condition regarding the light absorption rate is formed by appropriately selecting the optical recording medium, and that the erasing rate at the time of overwriting is improved in this medium.

[0005] However, in the case of the medium according to the prior art, the change in reflectance was not sufficiently large. For example, in Table 2 of the embodiment on page 3, the medium N whose absorptivity in the amorphous state is larger than that in the crystalline state
o. 1, No. Medium No. 4 shows a change in reflectance of 19.1% and 16.4%, whereas medium No. 4 has a higher absorptance in the crystalline state than in the amorphous state. 3, No. No. 6 showed only a small change in reflectivity of 9.7% and 11.2%. In particular, when the recording film is 40 nm, the value is less than half. FIG. 6 is a graph of the results of the examples described in JP-A-1-149238, in which the light absorptance in the crystal part is A (cry) and the light absorptivity in the amorphous part is A. (amo), the difference ΔA (= A (cry) −A (amo)) between the light absorptivity in the two states before and after recording and C / N
Also shows the relationship between the erasure rate. According to this, it can be seen that the erasing rate is improved as the difference ΔA in the light absorption rate increases in the positive direction, while the C / N is reduced, though slightly. The cause of the C / N reduction in this case is apparent from FIG.

FIG. 7 is the same as FIG.
38 is a graph of the results of the examples described in Japanese Patent Publication No. 38, where the light absorption in the crystal part is A (cry), and the reflectance is R.
(cry), the light absorptance in the amorphous portion is A (amo), and the reflectivity is R (amo), and the difference ΔA (= A (cry) −A (amo)) in the two states before and after recording ) And the reflectance change ΔR
(= R (cry) -R (amo)). According to this, in the recording medium of the conventional example, the reflectance change amount ΔR decreases in one direction as the difference ΔA in the light absorptivity increases, and the erasing rate and the signal amplitude at the time of overwriting are opposite. It turns out that they were in a relationship.

Another conventional example is disclosed in JP-A-3-11384.
No. 4 discloses a medium having a medium structure without a reflective layer and having a recording film having a large thickness of 80 nm (Table 1, page 3). In this case, however, there is no disclosure of a medium condition under which the light absorption of the crystal part is sufficiently larger than the absorption of the amorphous part in this case. For example, although there is a disclosure of a configuration in which the absorptance of the amorphous portion is 10% or more higher than that of the crystalline portion, the difference is at most 2.1% in a medium in which the absorptance of the crystalline portion is larger than the amorphous portion, and the difference is at most 2.1%. It was not enough to cancel the difference.

[0008]

The prior art (Japanese Patent Application Laid-Open No. 1-149238) in which attention was paid to the difference in light absorptivity .DELTA.A between both the recording mark portion in the amorphous state and the non-recording mark portion in the crystalline state. In the disclosed recording medium, an improvement in the erasing rate in overwrite mode recording was realized, but on the other hand, as shown in FIG. 7, the reflectance change ΔR before and after recording was small. Reflectance change Δ
Since R is the magnitude of the signal itself, basically ΔR
Becomes smaller, the C / N also decreases. At this time, as in the case of the conventional example, the recording mark pitch is 2 μm or more (linear velocity 1).
Under the recording conditions such as 5 m / s and a recording frequency of 7 MHz), the area of the formed recording mark portion is sufficiently large as compared with the laser spot. The resulting large C / N can be obtained, but this is not the case when the mark pitch is further reduced to increase the recording density. In this case, since the size of the recording mark becomes smaller than or equal to the size of the laser spot, if ΔR is smaller, only a smaller change in the reflected light amount can be obtained.
The effect of the decrease in ΔR appears as a large decrease in C / N. In other words, on the premise that high-density recording is performed, it can be said that a recording medium that can simultaneously satisfy the C / N and the erasure rate during overwriting has not been realized yet.

Another problem is that mark position recording (or PPM recording) conventionally used for a phase change recording medium is performed.
In order to replace the method with the mark edge recording (or PWM recording) method, a higher erasing rate is required. In the mark position recording, even if the shape of the recording mark is slightly distorted, no error occurs as long as the peak position can be detected, but in the mark position recording, the distortion of the shape becomes an error as it is. In this case, for example, as in the case of magnetic recording,
It is necessary to clear an erasing rate of about 26 dB.

An object of the present invention is that even when overwrite recording of a high-density signal whose recording mark length is close to the size of a laser spot is performed, both the C / N and the erasing rate are large, or it is suitable for mark edge recording. An object of the present invention is to provide a recording medium in which both ΔA and ΔR are sufficiently large and simultaneously satisfy at least ΔA ≧ 5% and ΔR ≧ 15% with the aim of obtaining a large erasing rate. Another object of the present invention is to provide a method for configuring the recording medium.

[0011]

According to the present invention, at least a first dielectric thin film layer is formed on a substrate by irradiating a laser beam.
There the phase and the recording layer whose optical characteristics of phase change material thin film which changes reversibly between an amorphous phase, a second dielectric thin film layer, and the optical information recording medium having a reflective layer
The reflective layer is made of Au or an alloy thin film layer containing Au as a main component, and has a thickness of 15 nm or less.

Then, assuming that the thickness d0 of the recording layer and the thicknesses d1 and d2 of the first and second dielectric thin film layers are independently and variously varied, the recording film is made amorphous by a matrix method. In some cases, the reflectance and the absorptance in the crystalline state are calculated, and d0,
The combination of d1 and d2 is determined.

[0013]

In the optical information recording medium having the four-layer structure, the incident light I travels in a portion (A) where it is absorbed by the recording layer and turns into heat, a portion (L) where it is absorbed in the reflection layer and turns into heat, It can be roughly divided into four parts: a part (R) reflected by the surface and a part (T) that passes through the medium. Here, the amount of light absorbed by the recording layer differs between when the recording layer is in an amorphous state and when it is in a crystalline state.
= I- [L (amo) + R (amo) + T (amo)], A (cry) = I-
[L (cry) + R (cry) + T (cry)]. That is, the difference in light absorptivity between the amorphous part and the crystalline part is ΔA = A (cry)
−A (amo) = [R (amo) −R (cry)] + [L (amo) −L (cr
y)] + [T (amo) −T (cry)], that is, ΔA = ΔL + ΔT−
ΔR (ΔL = L (amo) −L (cry), ΔT = T (amo) −T (cr
y), ΔR = R (cry) −R (amo)). here,
For example, in order to ensure ΔR ≧ 15% and ΔA ≧ 5%, a difference of 20% or more in total of the first term (absorptivity difference in the reflective layer) and the second term (transmittance difference) on the right side. Should be secured.

In the present invention, the above condition is achieved by making the thickness of the Au reflection layer or the alloy reflection layer containing Au as a main component smaller than 15 nm. The reason is as follows. That is, if the reflective layer is made thick enough not to transmit light, the light transmitted through the medium will be small regardless of the state of the recording layer, and the transmittances T (amo), T (cry) and the difference ΔT between them will be obvious. Approaching zero. Since Au has a high reflectance, the absorption in the reflective layer is 10% or less, and ΔL is naturally less than that. Therefore, if the thickness of the reflective layer is increased in order to increase the absolute amount of the light absorption in the recording layer, it is inevitable that ΔA ≒ −ΔR, and the object of the present invention cannot be achieved. In the optical information recording medium of the present invention, the relationship between the thickness of the reflective layer, the reflectance and the absorptance was examined. If the thickness was 15 nm or less, appropriate transmittance and absorptivity to the reflective layer were obtained. It has been found that the above-mentioned object is satisfied with a practically sufficiently large thickness error tolerance. Au or an alloy containing Au as a main component is chemically much more stable than other metals, and has an advantage that it can sufficiently function as an ultrathin film of 15 nm or less.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical optical information recording medium of the present invention is shown in FIG.
As shown in the figure, the first dielectric thin film layer 7 on the substrate 6 is irradiated with a laser beam having a wavelength λ, and the optical constant (refractive index n, extinction coefficient k) at the wavelength λ is relatively large. A recording layer 8 made of a phase change material thin film that reversibly changes optical characteristics between a crystalline state and an amorphous state that is relatively small, a second dielectric thin film layer 9, and Au or Au as a main component. A light reflecting layer 10 made of an alloy having
A laser beam 11 for recording and reproduction is made incident from the substrate side. In FIG. 1, two sheets are laminated so as to be vertically symmetrical via a hot-melt type adhesive layer 12, but as shown in FIG. 2, a UV resin or the like is placed on the second dielectric thin film layer. A single-plate structure in which the protective layer 13 is formed is also possible. As shown in FIG. 3, a light reflecting layer 10, a second dielectric layer 9, a recording layer 8, and a first dielectric layer 7 are stacked on a substrate, and light is incident from the first dielectric layer side. Is also possible.

The material used for the substrate 6 is a transparent resin plate such as PMMA, polycarbonate, amorphous polyolefin or the like, which is usually used for an optical disk or the like, a glass plate, or the like.
A metal plate such as Al or Cu or an alloy plate based on these is used. When an opaque substrate is used, it is necessary to conform to the configuration shown in FIG. In optical disc applications, concentric or spiral continuous grooves with a submicron width and depth, or pit rows are engraved with irregularities on the surface to guide the laser beam used for recording and reproduction. Is usually the case.

When a resin substrate is used, the upper and lower dielectric layers 7 and 9 serve to suppress thermal damage to the surface of the substrate 6 and to suppress deformation and evaporation of the film by sandwiching the phase change material layer 8. It has properties such as higher melting point than resin and recording film material, being transparent to the laser beam used for recording and reproduction, and having high hardness and being hardly scratched. It is necessary to have. For example, oxides such as SiO ₂ , ZrO ₂ , TiO ₂ and Ta ₂ O ₅ , nitrides such as BN, Si ₃ N ₄ , AlN and TiN, Zn
Sulfides such as S and PbS, carbides such as SiC, fluorides such as CaF ₂ , selenides such as ZnSe, and mixtures of these materials include ZnS—SiO ₂ , SiNO and the like, or diamond thin films and diamond-like carbon. it can.

The material used for the recording layer 8 in the present invention is a material which undergoes a reversible amorphous-crystal phase transformation upon irradiation with a laser beam among the phase change material thin films, and has a larger refractive index in the crystalline state than in the amorphous state. And an extinction coefficient are used. Typically, Ge-Sb-Te, Ge-T
e, In-Sb-Te, Sb-Te, Ge-Sb-Te
-Pd, Ag-Sb-In-Te, Ge-Bi-Sb-
Te, Ge-Bi-Te, Ge-Sn-Te, Ge-S
b-Te-Se, Ge-Bi-Te-Se, Ge-Te
A system such as -Sn-Au or a system in which an additive such as oxygen or nitrogen is added to these systems can be used. These thin films are usually in an amorphous state when formed,
It absorbs energy of a laser beam or the like and crystallizes to increase the optical density. When actually used as a recording medium, the entire surface of the recording film is crystallized in advance, the laser beam is squeezed finely, and the irradiated portion is made amorphous to change the optical constant. The change is performed by irradiating the recording film with a laser beam weakened to such an extent that no further change is made, detecting the change in the intensity of the reflected light and the change in the intensity of the transmitted light, and reproducing the information.
The present invention aims to improve the overwrite characteristics by configuring the medium so that the relationship between the optical characteristics of the recording portion before and after recording and the optical characteristics of the non-recording portion is kept under a certain condition, and is not originally limited to the composition of the recording layer. Absent. Therefore, if a certain representative composition is applicable to the present invention, a composition obtained by adding some additives to the composition is also applicable.

The thickness of the recording layer 8 is selected so that a part of incident light can pass through the recording layer 8 even when the recording layer 8 is in a crystalline state. For example, the phase change material film (crystal phase) is made of a dielectric layer of the same material as the dielectric thin film layers 7 and 9 (the thickness is assumed to be infinite).
Considering the transmittance when sandwiched between, the value is at least 1%
Or more, preferably about 2 to 3% or more, and the value is preferably about 10% or more as compared with the case where the phase change material film is an amorphous phase. This is very important. When the component reflected by the reflective layer 10 and re-entered into the recording layer 8 disappears, the light interference effect decreases, and even if the thickness of the second dielectric thin film layer 9 and the reflective layer 10 is slightly changed, the entire medium Of the recording layer, absorption in the recording layer and the like cannot be controlled.

FIG. 4 shows Ge ₂ S as a typical recording film composition.
This graph shows the relationship between the film thickness and transmittance (wavelength 780 nm) when b ₂ Te ₅ is sandwiched between ZnS—SiO ₂ mixture (SiO ₂ : 20 mol%) films. From the figure, it can be seen that in the case of the crystalline state, the transmittance is 1% or more when the film thickness is 60 nm or less, 2% or more when the film thickness is 50 nm or less, and 3% or more when the film thickness is 40 nm or less.

The metal thin film used for the reflection layer 10 is Au
Is most suitable, but an alloy obtained by adding an additive to Au can also be used. Al, C as additives
r, Cu, Ge, Co, Ni, Ag, Pt, Pd, C
Using at least one selected from the group consisting of materials such as o, Ta, Ti, Bi, Sb, and Mo, it is possible to fine-tune properties such as thermal conductivity and optical constants. For example, when Cr was added, the reflectance was slightly lowered, but the thermal conductivity was greatly reduced, and the sensitivity could be improved. Further, the addition of Mo, Cr and the like improved the adhesive strength with the dielectric layer.

The thicknesses of the first and second dielectric thin film layers 7, 9 are determined as follows. First, the complex refractive index of the material constituting each layer is determined by a conventional method (for example, a method of forming a thin film on a glass plate and calculating based on the measured values of the film thickness, reflectance, and transmittance, or using an ellipsometer Method). Next, after fixing the thicknesses of the recording layer 7 and the reflective layer 9, the first and second dielectrics are formed by a matrix method (see, for example, Hiroshi Kubota, “Wave Optics”, Iwanami Shoten, 1971, Chapter 3). Is obtained by calculation. Specifically, assuming the thickness of each layer, the balance of light energy is calculated for all interfaces including the surface based on the law of conservation of energy.
That is, the energy balance equation is set for each interface in the multilayer medium, and the obtained simultaneous equations are solved to determine the intensity of the transmitted light with respect to the incident light, the intensity of the reflected light, and the amount of absorption in each layer. it can. By performing the above calculation in both the case where the recording film is in the crystalline state and the case where the recording film is in the amorphous state, it is possible to know the reflectance change ΔR and the absorption difference ΔA before and after recording. A film thickness condition is selected in which the difference in reflectance between the two states is as large as possible (≧ 15%) and the absorption in the crystalline state is at least 5% greater than the absorption in the amorphous state.

In the rewritable optical information recording medium of the present invention, each layer is sequentially stacked by a method such as vacuum evaporation, magnetron sputtering, DC sputtering, ion beam sputtering, or ion plating as in the case of forming an ordinary optical thin film. Can be formed in a cascading manner. Whether the recording medium is as designed can be verified by measuring the reflectance and transmittance of the completed medium using a spectrum meter and comparing the measured values with values calculated in advance. In this case, it is not possible to directly measure the absorption in the recording film and the absorption in the reflection layer, but the accuracy can be improved by performing the same comparison at two or more wavelengths. Hereinafter, the present invention will be described in more detail with reference to specific examples.

(Example 1) Five recording media corresponding to a laser wavelength of 780 nm were prepared based on the above calculation using a sputtering apparatus provided with four cathodes corresponding to a 100 mm diameter target in one vacuum chamber. . The material of the substrate is polycarbonate and the size is outside diameter 300m
m, the inner diameter was 35 mm, and the thickness was 1.2 mm. The surface of the substrate is covered with a continuous groove having a pitch of 1.3 μm, a depth of 60 nm, and a width of 0.6 μm. A dielectric film and a phase change recording film were formed on the grooved surface as follows.

Each medium has substantially the same configuration except for the thickness of the second dielectric layer. The first dielectric layer has a thickness of 93 nm.
A ZnS—SiO ₂ (SiO ₂ : 20 mol%) mixture film of
Ge ₂ Sb ₂ Te ₅ film of the recording layer thickness 40 nm, the reflective layer is Au having a thickness of 10 nm. The second dielectric layer is ZnS-
It is a SiO ₂ (SiO ₂ : 20 mol%) mixture film having a thickness of 128 nm, 139 nm, 151 nm, 162 nm,
174 nm. The media have different absorptivity differences ΔA and reflectance differences ΔR (Table 1). Each value was calculated.

[0026]

[Table 1]

As the sputtering gas, argon was used for all
The gas pressure was 3 mTorr. The dielectric was formed by RF sputtering at a power of 300 W and a deposition rate of 10 nm per minute. For the recording layer, DC sputtering was used and 100 W
The film was formed at a power of 10 nm at a rate of 10 nm per minute.

Table 2 shows the results obtained by examining the reflectance and the transmittance of the above five types of media for both the case where the recording layer is a crystalline layer and the case where the recording layer is an amorphous phase. It shows the measured values. It can be seen that the calculated value and the measured value are in good agreement in any medium. Further, the value of ΔR obtained from the upper and lower evaluations was in good agreement with the calculated value, and it was confirmed that the prototype recording medium had optical characteristics almost as designed. From this, No. 2 and 3 can be regarded as recording media within the scope of the present invention.

[0029]

[Table 2]

Example 2 Two disks of Example 1 were prepared and bonded together with a hot-melt adhesive so that the surface with the film was inside. Each disk was rotated at 1800 rpm, and the overwrite characteristics were evaluated at the outermost periphery (linear velocity 27 m / s). The recording signal is a single frequency signal of 17.5 MH (f1) and 6.5 MH (f2) assuming mark edge recording. A. Recording was performed using a 0.55 objective lens (duty: 50%). The measurement procedure is as follows. First, f1 is recorded and the CN ratio is measured, and then f2 is overwritten and f1
The decay rate was measured by measuring the attenuation ratio of the components.
Table 2 shows the peak power at which the CN ratio reaches 50 dB (measurement limit: 30 mW), the saturation value of the CN ratio, the maximum value of the erase ratio, and the bias power region where the erase ratio exceeds 26 dB. From Table 3 and Table 1, the following was found.

That is, ΔR and ΔA in (Table 1) have strong correlations with the CN ratio, erasure rate and bias power margin in (Table 3), respectively. When ΔA is less than 5%, erasure is performed. It was shown that there was no bias power region exceeding the rate of 26 dB. This means that in order to achieve the same temperature rise in the crystal part and the amorphous part, the crystal part needs more energy than the amorphous part by an amount corresponding to the latent heat of fusion, which is ΔA. This would indicate that it corresponds to about 5%. In addition, the CN ratio is 50
It was shown that ΔR is required to be 15% or more in order to obtain dB or more.

That is, the recording medium of the present invention (No. 2, N
o. 3) was shown to have a CN ratio exceeding 50 dB and a wide power range exceeding an erasure ratio of 26 dB.

[0033]

[Table 3]

Example 3 As in Examples 1 and 2, a polycarbonate substrate, a ZnS-SiO ₂ mixture thin film, and Ge ₂ S
Various recording media fabricated assumes wavelength 780nm with b ₂ Te ₅ thin film, and its characteristics were evaluated. The thickness of the recording film is 2
0 nm to 80 nm, and the thickness of the reflective layer is 3 nm to 50 n.
m. Table 4 shows the characteristic evaluation results for the designed and manufactured recording medium. In the table, a circle indicates that the thickness conditions of the upper and lower dielectric layers satisfying ΔR ≧ 15% and ΔA ≧ 5% exist in a sufficiently wide film thickness range (for example, ± 5% or more). There is a dielectric layer thickness condition that satisfies ΔR ≧ 15% and ΔA ≧ 5%, and a cross indicates that the above condition is not satisfied.

[0035]

[Table 4]

From this evaluation, it was found that the thickness of the Au reflective layer was 15 n
It was shown that a recording medium intended for the present invention can be constituted by selecting m or less.

Example 4 The same operations as in Examples 1, 2, and 3 were performed on a glass substrate, and similar results were obtained.

Example 5 The same evaluation as in Example 2 was performed on the inner peripheral portion (linear velocity: 10 m / s). The frequencies are 6.5 MHz (f1) and 2.4 MHz (f2).
No. like the outer peripheral part. 2, No. 3 is 50dB or more CN
The ratio and the wide power width exceeding 26 dB were exhibited. Also, N
o. The medium No. 3 also exhibited a CN ratio of 50 dB or more and an erasing rate exceeding 26 dB, but had a narrow power width.

(Example 6) Ge-Sb-Te ternary alloy
The composition is expressed as Ge on the triangular composition coordinates of Ge-Sb-Te. _TwoSb_Two
Te_FiveComposition and GeSb_FourTe₇Connecting composition and Sb simple composition
Investigate the optical constants with various changes in the range, based on this
Calculation and trial production evaluation were performed, but the Sb concentration was 40% or less.
The above Ge_TwoSb_TwoTe_FiveIs almost the same as when
It is found that the recording medium of the present invention can be configured in the region.
Was.

[0040]

According to the present invention, a recording medium having a large CN ratio, a high erasing rate, and a wide power allowance (margin), and a design method thereof have been provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of one embodiment of an optical information recording medium of the present invention.

FIG. 2 is a diagram showing the configuration of one embodiment of the optical information recording medium of the present invention.

FIG. 3 is a diagram showing a configuration of an embodiment of the optical information recording medium of the present invention.

FIG. 4 shows an embodiment of the present invention. Diagram showing the relationship between the thickness of the recording layer constituting the recording medium and the transmittance

FIG. 5 is a sectional view showing a configuration of a conventional phase change optical recording medium.

FIG. 6 is a graph showing a relationship between a CN ratio and an erasing rate of a recording medium described in an example of a conventional example and a light absorption rate difference ΔA.

FIG. 7 is a graph showing a relationship between a reflectance change ΔR and a light absorption difference ΔA of a recording medium described in an example of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Recording layer 3 Dielectric layer 4 Light reflection layer 5 Protective plate 6 Substrate 7 First dielectric layer 8 Recording layer 9 Second dielectric layer 10 Reflective layer 11 Laser beam 12 Adhesive layer 13 Protective layer

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kenichi Osada 1006 Kadoma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Kenichi Nishiuchi 1006 Odakadoma Kadoma, Osaka Pref. In-company (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/24

Claims (8)

(57) [Claims] To 1. A substrate, at least a first dielectric thin film layer, a recording layer whose optical characteristics between the crystalline phase and the amorphous phase by irradiation with a laser beam formed of a phase change material thin film which changes reversibly, A second dielectric thin film layer and a thickness of 15
A rewritable optical information recording medium, comprising: a reflective layer made of Au or an alloy thin film layer containing Au as a main component and having a thickness of not more than nm. 2. At least a first dielectric thin film on a substrate
Layer, the crystalline phase and the amorphous phase
Phase change thin film whose optical properties change reversibly between layers
Recording layer, a second dielectric thin film layer, and a film thickness of 15
Au or an alloy thin film containing Au as a main component having a thickness of not more than nm
A reflective layer comprising a layer, the absorption of the laser beam by the recording layer and the
The reflectivity of the recording medium, wherein each of the case where the recording layer is an amorphous phase A (amo) and R (amo), also before
When the recording layer is a crystalline phase , the amorphous phase and the crystalline phase of the recording layer are denoted by A (cry) and R (cry), respectively.
Difference in the absorptivity between the phases ΔA (= A (cry) -A
(amo)) and the difference in reflectance ΔR (= R (cry) -R (am
o)) is a .DELTA.A ≧ 5% and [Delta] R ≧ 15%, respectively
An optical information recording medium characterized by the above-mentioned . 3. The reflective layer according to claim 1, wherein said reflective layer contains Au as a main component and Al, C
r, Cu, Ge, Co, Ni, Mo, Ag, Pt, P
3. The optical information recording medium according to claim 1 , wherein the optical information recording medium is an alloy with at least one member selected from the group consisting of d, Co, Ta, Ti, Bi, and Sb. 4. The optical information recording medium according to claim 2 , wherein the difference ΔA in the absorptivity is 10% or more. 5. The optical information recording medium according to claim 2 , wherein the difference ΔR in the reflectance is 20% or more. 6. A method according to claim 1, wherein said first and second dielectric thin film layers are formed of Zn.
S-SiO ₂ mixture, the recording layer Ge-Sb-Te3
Based alloy and then, the optical information recording medium according to thickness of the recording layer to claim 1 or 2 was 40nm or less. 7. The method according to claim 1, wherein the first and second dielectric material thin films are Z
nS-SiO _2, the recording layer is Ge-Sb-Te,
Wherein the thickness of the recording layer was 25nm or less claim 1 or
3. The optical information recording medium according to item 2 . 8. A substrate at least a first dielectric thin film layer, the optical properties between the crystalline phase and the amorphous phase <br/> by irradiation of the laser beam is made of phase change material thin film reversibly changes A recording layer, a second dielectric thin film layer, and a film thickness of 1
When a rewritable optical information recording medium having a reflective layer made of Au or an alloy thin film containing Au as a main component and having a wavelength of 5 nm or less is irradiated with an irradiation laser beam having a wavelength of λ ,
Absorptance of the irradiated laser beam by the recording layer and
The reflectance by the recording medium is A (amo) and R (amo) when the recording layer is in the amorphous phase , and A (cry) and R (respectively) when the recording layer is in the crystalline phase. cry) with the amorphous phase of the recording layer.
Difference in the absorptivity between the phase ΔA (= A (cry) -
Difference A (amo)) and the reflectance ΔR (= R (cry) -R (a
mo)) are designed to simultaneously satisfy the two conditions of ΔA ≧ 5% and ΔR ≧ 15%, respectively , wherein the recording layer and the first and second dielectric thin film layers The optical thickness of each of the optical elements is set to a maximum of λ / 2.
Variously assumed in the range of, by a matrix method, a proportion that is absorbed into the phase change material thin film of the incident light fraction reflected from (the light absorptance A) and the recording medium surface (reflectance R) and if the phase change material thin film is an amorphous state, calculated for both the case where the crystalline state,
A method for designing an optical information recording medium, wherein a combination of d0, d1, and d2 satisfying the two conditions is obtained.