JPH064903A - Optical information recording medium and method for designing its structure - Google Patents

Abstract

(57) [Summary] [Structure] When the recording layer is in an amorphous state, the ratio of absorption in the recording layer by the irradiation laser beam of wavelength λ (hereinafter, absorption ratio) and the ratio of reflection from the recording medium (hereinafter, reflection ratio) are set. And A (amo) and R (amo) respectively, and A (cry) and R (cry) respectively when the recording layer is in a crystalline state,
Absorption rate difference between two states ΔA (= A (cry) -A (am
o)) and the difference in reflectance ΔR (= R (cry) −R (amo)) is Δ
The recording medium is configured under the film thickness condition that simultaneously satisfies the two conditions of A ≧ 3% and ΔR ≧ 15%. [Effect] By selecting the light absorptivity of the recording layer in the crystalline state to be 3% larger than that in the amorphous state, an equivalent temperature rise state can be realized between the two and the recording mark distortion at the time of overwriting can be reduced. In a recording medium having a multi-layered structure, the upper limit of the film thickness of the recording layer, the material forming the reflective layer, and the thickness are limited, so that the absorption difference ΔA ≧ 3% and the reflectance change amount before and after recording ΔR ≧ The condition of 15% is compatible.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is capable of overwriting an information signal having a high signal quality by irradiating a phase change material thin film formed on a substrate with a high energy beam such as a laser beam. The present invention relates to a rewritable optical information recording medium and a method of configuring the same.

[0002]

2. Description of the Related Art A chalcogenide thin film formed on a substrate is irradiated with a laser beam to locally heat it to change the optical characteristics (refractive index) of a minute portion. Already known as. That is, if the irradiation conditions of the laser beam are properly selected, the irradiation part is rapidly changed from a state in which the atomic bonding state is relatively disordered (amorphous phase) to a relatively ordered state (crystalline phase), and vice versa. It is possible to change the phase of the recording medium and the applied development has been performed as one of the methods for high density information recording.

One of the merits of phase change recording is that an information signal can be overwritten by using only a single laser beam as a recording means. That is, when the laser output is modulated between the recording level and the erasing level according to the information signal and applied to 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 in that it can simplify the head because it does not require magnetic circuit parts like magneto-optical recording and can shorten rewriting time because it does not require erasing operation. Research and development of recording media is ongoing (eg K. Nishiuchi et al .: Jpn.J.Appl.Phys.Vol.31 (19
92) pp.653-658).

During this period, problems specific to overwrite have been extracted and solutions have been proposed. For example, there is a problem that the erase rate at the time of overwriting becomes lower than the erase rate when only the erase operation is performed. To solve this problem, we have disclosed in Japanese Unexamined Patent Publication No. 1-149238, a recording medium in which the light absorptance in the recording mark portion in the amorphous state is equal to the light absorptance in the unrecorded portion in the crystalline state, and the crystalline state portion We have proposed a recording medium in which the light absorptivity of the recording medium is larger than that in the amorphous state. That is, as shown in FIG. 1, a recording layer 2 sandwiched by a dielectric 3 on a substrate 1 having a smooth surface.
On the medium on which the film is formed and the dielectric 3, a light reflecting layer 4 is further formed.
And a protective plate 5 is attached to the medium, an optical recording medium satisfying the above-mentioned conditions concerning the light absorptivity is formed mainly by appropriately selecting the thickness of each layer of the dielectric layer. It has been disclosed that the erasing rate of is improved.

However, it cannot be said that the change in reflectance is sufficiently large in the case of the medium of the example of this conventional example. For example, in Table 2 of the embodiment on page 3 of the specification of the conventional example, the medium No. 1 having a larger absorptance in the amorphous state than in the crystalline state. 1, No. 4 is 19.1% each,
While it shows a large reflectance change of 16.4%,
Medium No. with a higher absorption rate in the crystalline state than in the amorphous state 3, No. 6 is 9.7% and 11.2 respectively
It showed only a small reflectance change of%. Particularly, when the recording film is 40 nm, the value is half or less.

FIG. 2 is a graph showing the results of the example described in JP-A-1-149238, in which the light absorption rate in the crystal part is A (cry) and the light absorption in the amorphous part is The ratio is A (amo), and the relationship between the difference ΔA (= A (cry) -A (amo)) in light absorption ratio between the two states before and after recording, C / N, and the erasing ratio is shown. According to this, it can be seen that the erasing rate is improved as the difference ΔA in light absorption rate is increased in the positive direction, while the C / N is gradually decreased although it is small. C in this case
The cause of the decrease in / N is clear from FIG.

FIG. 3 is similar to FIG. 2 in Japanese Patent Laid-Open No. 1-1492.
38 is a graph showing the results of the examples described in JP-A No. 38-38, in which the light absorption rate at the crystal part is A (cry) and the reflectance is R.
(cry), the light absorption rate in the amorphous portion is A (amo), and the reflectance is R (amo), the difference ΔA (= A (cry) -A (amo) in the light absorption rate between the two states before and after recording. ) And reflectance change ΔR
It shows a relationship of (= R (cry) -R (amo)). This shows that in the recording medium of the conventional example, the reflectance change amount ΔR decreases unidirectionally as the light absorption difference ΔA increases. It turns out that there was a conflicting relationship with.

Another conventional example, Japanese Patent Laid-Open No. 3-113844
The publication discloses a medium having a medium structure having no reflective layer and a recording film having a large thickness of 80 nm (Table 1).
However, in this case, the condition for obtaining a large ΔA is not disclosed. That is, although there is a disclosure of a structure in which the absorptance of the amorphous part is 10% or more higher than that of the crystal part, in the medium in which the absorptance of the crystal part is larger than that of the amorphous part, the difference in absorptance was at most 2.1%.

[0009]

In the above-mentioned conventional example (JP-A-1-149238), attention is paid to the difference ΔA in light absorption coefficient between the recording mark portion in the amorphous state and the non-recording mark portion in the crystalline state. Although the disclosed recording medium realized the improvement of the erasing rate in the overwrite mode recording, on the other hand, as shown in FIG. 3, the reflectance change amount ΔR before and after the recording tended to be small. Since the reflectance change amount ΔR is a large factor that determines the magnitude of the signal, basically, if ΔR becomes smaller, C
/ N also decreases. A comparatively large C / N was obtained in the conventional example, but it should be noted that this is the result under the recording condition that the recording mark pitch is 2 μm or more (the linear velocity is 15 m / s, the recording frequency can be calculated from 7 MHz). Should be. Under this condition, the size of the recording mark (1 μm at most)
The length is the size of the laser spot (half-value width 0.9 μm)
This is because a large change in the amount of light is detected on the detector as an integrated value, which is sufficiently larger than that in m). However, this is not the case when the mark pitch is further reduced to increase the recording density as in recent years. In this case, the size of the recording mark (diameter of 0.6 in the present embodiment).
5 μm) is as small as or smaller than the size of the laser spot (diameter of 0.9 μm at half width), and if ΔR is small, only a small change in the amount of reflected light can be obtained, and the influence of the decrease in ΔR remains unchanged. It will appear as a large decrease in C / N. That is, the conventional medium has reached the limit of high-density recording. That is, it can be said that a recording medium capable of simultaneously satisfying the C / N and the erasing rate at the time of overwriting has not been realized on the assumption that high density recording is performed.

We have disclosed in Japanese Patent Application No. 4-97606 that an Au reflective layer having a thickness of 15 nm or less can be used as a reflective layer to achieve the same purpose as the present application. However,
Usually, the metal reflection layer also plays a role as a heat sink layer, so that it is not preferable that the upper limit of the reflection layer thickness is determined.

Another problem is to replace the mark position recording (or PPM recording) system used in the conventional phase change recording medium with the mark edge recording (or PWM recording) system, and to further increase the recording density. This means that a high erase rate is required. In mark position recording, even if the shape of the recorded mark is slightly distorted, no error occurs if only the peak position can be detected. However, in mark position recording, since the start and end of the mark are detected, the shape distortion remains an error. In this case, a medium and a recording method in which distortion is less likely to occur are necessary.

It is an object of the present invention to provide an optical recording medium or mark edge recording in which both the C / N and the erasing rate can be large even when overwriting recording of a high density signal whose recording mark length is close to the size of a laser spot is performed. Aiming at an optical recording medium which is less likely to cause distortion, a recording medium satisfying at least ΔA ≧ 3% and ΔR ≧ 15% at the same time by using a metal reflection layer with a small thickness limitation And a specific method of configuring the same.

[0013]

In the rewritable optical information recording medium of the present invention, a reversible structural change is generated by irradiating a substrate with at least a first dielectric thin film layer and a laser beam having a wavelength λ, and Recording layer comprising a thin film of phase-change material whose optical properties are reversibly changed between a crystalline state in which constants (refractive index n, extinction coefficient k) are relatively large and an amorphous state in which they are relatively small. In the optical information recording medium formed by laminating the second dielectric thin film layer and the light reflecting layer, the reflecting layer is made of Al or an alloy thin film containing Al as a main component in this case. The film thickness of each layer is obtained by a matrix method or the like using the thickness d0 of the recording layer, the thickness d3 of the reflective layer and the thicknesses d1 and d2 of the first and second dielectric thin film layers as parameters. The reflectance as a medium and the absorptance in the recording layer in the amorphous state and in the crystalline state are calculated, and it is determined whether or not a predetermined condition is satisfied, and d0, d1, d2 d3
A combination satisfying the above conditions is selected from among the combinations, and the recording medium is constructed under the conditions. A recording device equipped with this recording medium is equipped with a recording / reproducing light source having a wavelength λ.

[0014]

In the four-layered optical information recording medium, the whereabouts of the incident light I is absorbed by the recording layer and converted into heat (A), the part absorbed by the reflective layer and converted into heat (L), the medium. It can be roughly divided into four parts, a part (R) reflected on the surface and a part (T) passing through the medium. The amount of light absorbed by the recording layer is different when the recording layer is in an amorphous state and when it is in a crystalline state.
mo) = I- [L (amo) + R (amo) + T (amo)], A (cry) =
I- [L (cry) + R (cry) + T (cry)]. That is, the difference in light absorption rate between the amorphous part and the crystalline part is ΔA = A (c
ry) -A (amo) = [R (amo) -R (cry)] + [L (amo) -L
(cry)] + [T (amo) −T (cry)], that is, ΔA = ΔL + Δ
T-ΔR (ΔL = L (amo) -L (cry), ΔT = T (amo)-
It is expressed as T (cry), ΔR = R (cry) −R (amo)). Therefore, for example, ΔR ≧ 15% is secured, and ΔA ≧ 3
In order to secure%, it is sufficient to secure a difference of 18% or more in total of the first term (difference in absorptance in the reflective layer) and the second term (difference in transmittance) on the right side.

Compared with Au, the Al reflection layer or the alloy containing Al as a main component has a wavelength of a semiconductor laser light source (visible light-
It has a low reflectance for near infrared light) and a high absorption rate. When the recording film is amorphous and allows a large amount of light to pass therethrough, the light absorptivity of the reflective layer is about 30%, and when the recording film is in a crystalline state and does not allow much light to pass through, the light absorptivity is around 10%. Is. Therefore, if these are used as the reflective layer, ΔL of about 20% can be obtained regardless of the thickness, and the premise that ΔA ≧ 3% and ΔR ≧ 15% are simultaneously satisfied is satisfied.

In the optical recording medium satisfying the above conditions, the amorphous portion has a smaller absorptivity than the crystalline portion, so that even if both portions are irradiated with the same amount of light, the amorphous portion slightly delays the temperature rise. However, when the temperature reaches the melting point, the temperature rise continues in the amorphous part without exchange of latent heat of fusion, whereas the temperature rise is interrupted while absorbing the latent heat in the crystal part.
The temperature difference with the amorphous part is reduced. After melting, the state difference between the two is eliminated and equal light absorption is obtained.
Therefore, by appropriately setting the absorption difference in advance, it is possible to make the temperatures reached by both parts substantially equal. If the temperatures reached by both are the same, the recorded signal mark is not affected by the state before recording and is always formed with the same size, so that no history (erasure residue) before recording remains. That is, a recording mark with less distortion can be obtained.

[0017]

EXAMPLE A typical optical information recording medium of the present invention is shown in FIG.
As shown in FIG. 2, the first dielectric thin film layer 7 on the substrate 6 and the laser beam having the wavelength λ irradiate the optical constants (refractive index n, extinction coefficient k) at the wavelength λ relatively large. A recording layer 8 composed of a phase change material thin film that reversibly changes optical characteristics between a crystalline state and an amorphous state which is relatively small, a second dielectric thin film layer 9, Al or Al as a main component. A light reflection layer 10 made of an alloy
A laser beam 11 for recording and reproduction is made incident from the substrate side. In FIG. 4, two pieces are laminated so as to be vertically symmetrical with the hot-melt type adhesive layer 12 interposed therebetween, but as shown in FIG. 5, UV resin or the like is formed 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. 6, a light reflecting layer 10, a second dielectric layer 9, a recording layer 8 and a first dielectric layer 7 are laminated 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 optical disks, a glass plate,
A metal plate such as Al or Cu or an alloy plate based on these is used. When using an opaque substrate, it is necessary to conform to the configuration of FIG. In optical disc applications, concentric circles or spiral continuous grooves with a width and depth of submicron size, or pit rows are engraved with irregularities on the surface to guide the laser beam used for recording and reproduction. Is normal.

When a resin substrate is used, the upper and lower two dielectric layers 7 and 9 serve to suppress the thermal damage on the surface of the substrate 6, and the phase change material layer 8 is sandwiched to suppress the deformation and evaporation of the film. It has a high melting point compared to resin substrate materials and recording film materials, is transparent to the laser beam used for recording and reproduction, and has high hardness and is hard to be 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, Z
Sulfides such as nS and PbS, carbides such as SiC, CaF ₂
For example, a fluoride such as ZnS, a selenide such as ZnSe, or a mixture thereof such as ZnS—SiO ₂ , SiNO, or a diamond thin film or diamond-like carbon can be used.

The material used for the recording layer 8 in the present invention is one that causes reversible phase transformation between amorphous and crystalline upon irradiation with a laser beam among the phase change substance thin films, and has a refractive index larger in the crystalline state than in the amorphous state. , The one showing the extinction coefficient is 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 obtained by adding an additive such as oxygen or nitrogen to these systems can be used. The present invention, by its nature, is not bound by the composition of the recording layer.
Therefore, if a representative composition is applicable to the present invention, a composition obtained by adding some additives to the composition is also applicable.

These thin films are usually in an amorphous state when they are formed, but when they are crystallized by irradiation with a laser beam or the like, the optical density is increased (the optical constant is increased). When used as a recording medium, the entire surface of the recording film is crystallized in advance, the unrecorded state is set, and the laser beam is narrowed and irradiated onto it, and the irradiated part is made amorphous to reduce the optical constant. I do. When reproducing the above change, irradiate a laser beam weakened to the extent that no further change is added to the recording film, and detect the intensity change of the reflected light from the recording medium and the intensity change of the transmitted light passing through the medium. To play the information.

The thickness d 0 of the recording layer 8 is such that even when the recording layer 8 is crystallized and has a high optical density, a part of the incident light beam is transmitted through the recording layer 8 with a sufficiently detectable intensity. The thickness should be less than dmax. For example, considering the transmittance when the above-mentioned phase change material film (crystal phase) is sandwiched between dielectric layers (assuming infinite upper and lower thickness) of the same material as the dielectric thin film layers 7 and 9, its value is At least about 1% or more, preferably 2
It is desirable that the value is about 3% or more, and the value is about 10% or more as compared with the case where the phase change material film has an amorphous phase, and it is important to select each film thickness as much as possible. When the components reflected by the reflective layer 10 and re-incident in the recording layer 8 are eliminated, the light interference effect is reduced,
Even if the film thickness d3 of the second dielectric thin film layer 9 and the reflective layer 10 is slightly changed, a large change in reflectance of the entire medium cannot be secured.

FIG. 7 shows Ge ₂ S as a typical recording film composition.
₃ shows the relationship between the film thickness and the 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 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. That is, in this case, the maximum film thickness dmax of the recording layer is 60 nm.

As the metal thin film used for the reflective layer 10, Al is used.
In addition to a simple metal, an alloy in which an additive is added to Al can be used. As additives, Au, Cr, Cu, Ge,
Co, Ni, Ag, Pt, Pd, Co, Ta, Ti, B
Properties such as chemical stability, thermal conductivity, and optical constants can be finely adjusted by using at least one selected from the group of materials such as i, Sb, and Mo. For example, when Cr or Ta is added, the reflectance is slightly lowered, but the moisture resistance property is improved. When the amount of additive is small (for example, 10% or less), the optical constant of the alloy is not much different from that of Al alone. Therefore, the results obtained with Al or one of the Al alloys are immediately applicable to the other alloys.

First and second constituents of the recording medium of the present invention
The film thicknesses of the dielectric thin film layers 7 and 9 were determined as follows. First, the complex index of refraction of the substances constituting the dielectric layer, recording layer, reflective layer, substrate, etc. was determined. The complex refractive index of a thin film is usually obtained by forming a thin film on a glass plate, obtaining the film thickness with a step meter, and measuring the reflectance and transmittance at the wavelength you want to measure using a spectrophotometer. A method of calculating a complex refractive index that satisfies Although this method is used in the present invention, it can be measured using an ellipsometer. Next, the thickness of the recording layer 8 and the reflective layer 10 is fixed to a certain value, and then the matrix method is performed using the thicknesses of the first and second dielectric thin film layers 7 and 9 as parameters (see, for example, Hiroshi Kubota, " Optics "Iwanami Shoten, 1971, Chapter 3), the reflectance from the medium, the absorptance in the recording layer, and the absorptance in the reflective layer were calculated. Specifically, the light energy balance was calculated based on the energy conservation law for all interfaces including the surface of the multilayer film structure. By forming this energy balance equation for each interface in the multilayer medium and solving the simultaneous equations obtained, the intensity of transmitted light with respect to incident light, the intensity of reflected light, and the amount of absorption in each layer can be obtained. In the present invention, the above calculation is performed both when the recording film is in a crystalline state and when it is in an amorphous state, and the reflectance change ΔR before and after recording is larger than 15% and ΔA is 3%.
(The light absorptance of the recording layer in the crystalline state is 3 than the light absorptivity of the recording layer in the amorphous state.
%, The film thickness conditions of the dielectric thin film layers 7 and 9 were selected. The above-mentioned work was performed by changing the film thicknesses of the recording layer and the reflective layer, and all possibilities were examined within the practicable film thickness range. When the film thickness of the dielectric layers 7 and 9 having the refractive index n is changed, the optical characteristics of the multilayer film structure are repeated with a thickness of λ / (2n) as a unit for a predetermined light wavelength λ. Therefore, the calculation may be performed within this unit thickness range.
Needless to say, this design method is a universal method that does not depend on the type of material used.

In the rewritable optical information recording medium of the present invention, each layer is sequentially stacked by a method such as vacuum deposition, magnetron sputtering, DC sputtering, ion beam sputtering and ion plating as in the case of forming an ordinary optical thin film. It can be formed in any way. Whether the recording medium is designed or not can be verified by measuring the reflectance and the transmittance of the finished medium with a spectrum meter and comparing them with the values calculated in advance. In this case, the absorption in the recording film and the absorption in the reflective layer cannot be directly measured, but the accuracy can be improved by performing the same comparison at two or more wavelengths.

Whether the finished medium is within the scope of the present invention is determined by examining the layer structure (thickness, optical constant) of the medium and calculating the reflectance of the medium based on the film thickness and optical constant of each layer. It can be confirmed by knowing whether the absorptance of the recording layer is within the range of the present application. Further, since the reflectance and the transmittance of the medium can be easily measured, it is also a proof to compare those values with the transmittance and the reflectance of the medium obtained by the above calculation. If the actual measurement work is performed at two or more wavelengths, more rigorous verification can be performed.

FIG. 8 shows an embodiment of a recording apparatus to which the optical information recording medium of the present invention is applied. The recording apparatus of the embodiment shows the case where a semiconductor laser having a wavelength of λ is used as a light source. The disk 14 is provided with a recording layer made of a phase change material thin film sandwiched by dielectric thin film layers and a reflective layer made of an Al-Cr alloy thin film, and overwrite recording is performed using a light source of wavelength λ. In this case, a high C / N and a high erase rate are realized. The disk 14 is rotated at a constant rotation speed by using a motor 16 as a rotation driving means. Of course, it is also possible to rotate so as to have a constant linear velocity. The optical head 20 can be moved to an arbitrary position on the disk 14 by the transfer mechanism 17. The optical head 20 is equipped with a semiconductor laser light source 15 having a wavelength λ and an optical system (not shown) for converging a laser beam and narrowing it down on a disk. Laser light 19 emitted from the semiconductor laser 15 is applied to the disk 14 through the objective lens 18. Although not shown in the figure, an electric circuit required for a normal optical recording device, for example, a circuit for driving a laser, a focusing electric circuit for controlling a laser beam to be at an optimum position on a disc, It goes without saying that an electric circuit for tracking, a servo circuit, a mechanism, etc. are required. The semiconductor laser is connected to a laser drive circuit and is modulated according to an information signal.
In this device, it is assumed that the signal is overwritten by using a single laser beam. Therefore, the laser output is power-modulated between two values of a relatively high power level (peak power level) sufficient to make the recording layer amorphous and a relatively low power level (bias power level) sufficient to crystallize. Become.

The present invention will be described in more detail with reference to specific examples. (Example 1) Diameter of 100 mm in one vacuum chamber
A recording medium of the present invention was manufactured by using a sputtering apparatus equipped with four targets. In order to design the structure of the recording medium, the optical constant of each layer was first determined. Ge2Sb2Te5
Thin film and ZnS-SiO2 (SiO2: 20mo
1%) thin film and an Al-Cr (Cr: 3 mol%) alloy thin film were formed on a Pyrex glass plate, and the reflectance and transmittance at a wavelength of 780 nm were measured with a spectrophotometer. After the recording film was measured in an amorphous state, it was crystallized in an Ar atmosphere and the reflectance and the transmittance were measured again. Further, each film thickness was measured, and the optical constant of each material satisfying these values was obtained as shown in (Table 1).

[0030]

[Table 1]

Next, the reflectance of the medium and the absorptance at the wavelength of 780 nm in the recording layer are calculated by using the matrix method based on the above optical constants and the thickness of each layer as a parameter, and between the crystal part and the amorphous part. Seven recording media having different absorption differences ΔA were made experimentally. The substrate is a polycarbonate on the disk (refractive index n = 1.58), and the size is 300m outside diameter.
m, inner diameter 35 mm, and thickness 1.2 mm. The surface of the substrate is covered with continuous grooves having a pitch of 1.3 μm, a depth of 60 nm and a width of 0.6 μm. The dielectric film was formed on the grooved surface by RF sputtering of 500 W, and the phase change recording film and the reflection layer film were formed by DC sputtering of 100 W by the sputtering apparatus. Ar is used as the sputtering gas, and is 3 ×
The gas pressure was 10 ⁻³ mmHg.

As shown in Table 2, each medium has almost the same structure except the thickness of the second dielectric layer. The first dielectric layer is ZnS—SiO ₂ (SiO ₂ : 2 with a thickness of 82 nm).
0 mol%) mixture film and recording layer are 30 nm thick Ge ₂ S
b ₂ Te ₅ film, reflective layer is Al-Cr alloy film having a thickness of 10 nm. The second dielectric layer ZnS-SiO ₂ (SiO _2:
20 mol%) mixture film with a thickness of 151 nm, 16
2 nm, 168 nm, 174 nm, 180 nm, 186
nm and 197 nm. The absorption difference ΔA and the reflectance difference ΔR are as shown in (Table 2). Each value was calculated.

[0033]

[Table 2]

Table 3 shows the results of actually measuring the reflectance and the transmittance of the above seven types of media by a spectrophotometer and comparing them with the calculated values. When both the case where the recording layer is a crystalline layer and the case where the recording layer is an amorphous phase are investigated, it is shown that the calculated value and the actually measured value are in good agreement with each other. In addition, the value of the reflectance difference ΔR obtained by subtracting the reflectance of the lower table from the reflectance of the upper table is in good agreement with the measured value, and the prototype recording medium has almost the same optical characteristics as designed. Was confirmed to have From this, among the seven media, No. 3, No. 4,
No. It was confirmed that No. 5 can be regarded as a recording medium within the scope of the present invention, as designed.

[0035]

[Table 3]

(Example 2) Two disks each of Example 1 were prepared and laminated with a hot melt adhesive with the surface with the film inside. Each disk was rotated at 1800 rpm with the device shown in FIG.
/ S) was evaluated for overwrite characteristics. In order to perform higher density recording than before, recording was alternately performed at a single frequency of 21 MH (f1) and 8 MH (f2) so that the mark pitch was 1.3 μm. The wavelength of the semiconductor laser beam is 780 nm, and the objective lens is N. A. Of 0.55 was used.

The measurement procedure was such that first, f1 was recorded and the CN ratio was measured, then f2 was overwritten and the attenuation ratio of the f1 component was measured to measure the erase ratio. (Table 4) is C
The peak power at which the N ratio reaches 50 dB (measurement limit of the device: 30 mW), the saturation value of the CN ratio, the maximum value of the erasing rate, and the bias power range in which the erasing rate exceeds 26 dB are shown. From these (Table 4) and (Table 2), the following was found.

That is, ΔR and ΔA in (Table 2) have a strong correlation with the CN ratio, erasure rate and bias power margin in (Table 4) respectively, and when ΔA is 5.9%, a sufficiently large erasure rate is obtained. However, it was shown that when ΔA is about 1.9%, there is no bias power region exceeding the erasing rate of 26 dB.

Further investigation of the relationship between the erasing rate and ΔA revealed that ΔA needs to be at least 3% or more, preferably 5% or more to obtain the erasing 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 requires more energy than the amorphous part by the amount corresponding to the latent heat of fusion. It would indicate that it corresponds to about 3%. Further, it has been shown that ΔR needs to be 15% or more to obtain a CN ratio of 50 dB or more.

When Au was used as the reflective layer before (Japanese Patent Application No. 4-97006), ΔA was 5%.
Although the above was necessary, it was shown that in this case it may be slightly smaller. It is considered that this is because the thermal conductivity of Al—Cr is smaller than that of Au, but it is not clear. In any case, a recording medium (N
o. 3, 4 and 5) were shown to have a CN ratio of over 50 dB and a wide power range over an erasing rate of 26 dB.

[0041]

[Table 4]

(Third Embodiment) The disk of the first embodiment is set to 3 per minute.
It is rotated at a speed of 600 rotations, and the outer peripheral portion (linear velocity 56 m /
In s), recording was performed with a mark pitch of 1.3 μm as in Example 2. At this time, the disc No. 3 and No.
The disk of No. 4 showed a C / N of 50 dB or more and an erasing rate of 26 dB or more. Disk 5 has an erase rate of 26
It did not reach dB. The result shows that ΔA needs to be 10% or more under the high-speed condition exceeding 50 m / s.

Example 4 As in Examples 1 and 2, a polycarbonate substrate, a ZnS—SiO ₂ mixture thin film, and Ge ₂ S.
Various recording media were prototyped using a b ₂ Te ₅ thin film on the premise of a wavelength of 780 nm, and the characteristics thereof were evaluated. The thickness of the recording film is 2
0 nm to 80 nm, the thickness of the reflective layer from 3 nm to 200 nm
shaken to nm. Table 5 shows the characteristic evaluation results of the designed and manufactured recording media. In the table, ○ indicates ΔR ≧ 15%
In addition, the upper and lower dielectric layers satisfying ΔA ≧ 3% have a wide film thickness margin of ± 3% or more, and Δ indicates ΔR ≧ 15% and ΔA ≧ 3%. Satisfactory dielectric layer film thickness conditions are obtained, and x indicates that there are no film thickness conditions that satisfy the above conditions.

[0044]

[Table 5]

From this evaluation, it was shown that the recording medium intended by the present invention can be constructed by selecting the thickness of the recording layer to be 40 nm or less regardless of the thickness of the Al alloy reflective layer. Also, A
It was shown that a recording medium within the scope of the present invention can be constructed even when the 1-alloy reflective layer is as thick as 200 nm. The thick reflective layer fully functions as a heat sink.

(Example 5) The same experiment as in Example 4 was carried out by selecting the material of Example 1 as the recording layer, ZnS-SiO ₂ and SiO ₂ as the dielectric layer, and Al-Ti as the reflective layer. As a result, when the thickness of the recording film is 25 nm or less and the thickness of the reflective layer is selected to be 15 nm or less, any dielectric material can be used while still achieving the object of the present invention.
It was confirmed that the thickness of the dielectric layer can be made as thin as the thickness of the recording layer (at most 25 nm). That is, it was confirmed that the quenching structure can satisfy the conditions of the present invention regarding ΔA and ΔR. (Table 6) is ZnS-SiO ₂ in the dielectric layer
Is an example using. It was found that this disk can perform overwrite recording with less distortion especially in the region of low linear velocity.

[0047]

[Table 6]

(Example 6) The same results as in Examples 1, 2 and 3 were performed on a glass substrate, and similar results were obtained.

(Example 7) The same evaluation as in Example 2 was performed on the inner peripheral portion of the disk (linear velocity: 10 m / s).
The frequencies were 7.8 MHz (f1) and 3 MHz (f2). As a result, the No. 3, No. 4 and No. 4 5 disk has a CN ratio of 50 dB or more and 26 d
It showed a wide power range exceeding B. Further, in this case, No. The medium of No. 6 also showed a CN ratio of 50 dB or more and an erasing rate of more than 26 dB. However, the power range satisfying the above conditions is No. It was narrower than the 3-5 disc.

(Example 8) Ge-Sb-Te ternary alloy
The composition is Ge on the Ge-Sb-Te triangular composition coordinates. ₂Sb₂
Te_FiveComposition and GeSb_FourTe₇Connecting composition and Sb simple composition
Based on this, we investigated the optical constants with various changes in the range.
A group with Sb concentration of 40% or less was calculated and prototyped.
In the above Ge₂Sb₂Te_FiveIs almost the same as using
It was found that the recording medium of the present invention can be configured in the area.
It was

(Example 9) As a material for the reflective layer, Al-
Instead of Cr, Al-Ta containing 5% of Ta and Au,
The above Examples 1-7 were performed using Al-Au and the like, and similar results were obtained. An alloy having an Al content of 90% or more does not significantly change the optical constant from that of Al, so that similar effects will be obtained.

[0052]

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

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a conventional phase change optical recording medium.

FIG. 2 is a graph showing a relationship between a CN ratio and an erasing rate of a recording medium described in a conventional example and a light absorption difference ΔA.

FIG. 3 is a graph showing a relationship between a reflectance change amount ΔR and a light absorptance difference ΔA of a recording medium described in an example of a conventional example.

FIG. 4 is a diagram showing the configuration of an embodiment of the optical information recording medium of the present invention.

FIG. 5 is a diagram showing the configuration of an embodiment of the optical information recording medium of the present invention.

FIG. 6 is a diagram showing a configuration of an example of an optical information recording medium of the present invention.

FIG. 7 is a diagram showing the relationship between the thickness of a recording layer constituting a recording medium and the transmittance in one example of the present invention.

FIG. 8 is a diagram showing an embodiment of a recording apparatus equipped with a recording medium of the present invention.

[Explanation 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 14 Disk 15 Semiconductor laser 16 Motor 17 Transfer mechanism 18 Lens 19 Laser light 20 Optical head

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiaki Furukawa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Kenichi Nishiuchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A rewritable optical information recording medium applied to an optical recording apparatus using a recording / reproducing laser having a predetermined wavelength λ, wherein at least a first dielectric thin film layer is provided on a substrate, and a laser beam having a wavelength λ. Upon irradiation, the optical characteristics are reversibly changed between a crystalline phase having a relatively large optical constant (refractive index n, extinction coefficient k) at the wavelength λ and an amorphous phase having a relatively small optical constant. A recording layer made of a phase change material thin film, a second dielectric thin film layer, and a reflection layer made of Al (aluminum) or an alloy thin film layer containing Al as a main component are laminated, In the case where the recording layer is in the amorphous phase, the ratio of absorption in the recording layer (hereinafter referred to as absorptance) and the ratio of reflection from the recording medium (hereinafter referred to as reflectance) are A (amo) and R (am
o), and when the recording layer is in a crystalline state, A (c
As ry) and R (cry), the difference ΔA (= A (cry) -A (amo)) in the absorptance and the difference ΔR (=
A rewritable optical information recording medium in which the film thickness of each layer is selected so that R (cry) -R (amo)) satisfies two conditions of ΔA ≧ 3% and ΔR ≧ 15% at the same time. 2. The rewritable optical information recording medium according to claim 1, wherein the film thickness of the reflective layer is 15 nm or less. 3. A reflective layer containing Al as a main component, Au, Cr, C
u, Ge, Co, Ni, Mo, Ag, Pt, Pd, C
The optical information recording medium according to claim 1, which is an alloy containing at least one selected from the material group consisting of o, Ta, Ti, Bi, and Sb. 4. The optical information recording medium according to claim 1, wherein ΔA is 10% or more. 5. A rewritable optical information recording medium applied to an optical recording device using a recording / reproducing laser having a predetermined wavelength λ, wherein at least a first dielectric thin film layer is provided on a substrate, and a laser beam having a wavelength λ. Upon irradiation, the optical characteristics are reversibly changed between a crystalline phase having a relatively large optical constant (refractive index n, extinction coefficient k) at the wavelength λ and an amorphous phase having a relatively small optical constant. A recording layer made of a phase change material thin film, a second dielectric thin film layer having a thickness of at most 30 nm, and a reflective layer made of a metal thin film layer are laminated, and the recording is performed in the irradiation laser beam of the wavelength λ. The ratio of absorption in the layer (hereinafter referred to as absorptance) and the ratio of reflection from the recording medium (hereinafter referred to as reflectance) are A (amo) and R (amo), respectively, when the recording layer is in an amorphous phase. ), And if the recording layer is in a crystalline state, As Each A (cry) and R (cry), the difference in absorptivity between the two states ΔA (= A (cry) -
A (amo)) and the difference in reflectance ΔR (= R (cry) −R (am
A rewritable optical information recording medium having a quenching structure in which the film thickness of each layer is selected such that o)) satisfies two conditions of ΔA ≧ 3% and ΔR ≧ 15% at the same time. 6. The dielectric thin film layer is a ZnS—SiO ₂ mixture,
The optical information recording medium according to claim 1, wherein the recording layer is made of a Ge-Sb-Te ternary alloy having a thickness of 40 nm or less. 7. A method of designing a rewritable optical information recording medium applied to an apparatus using a recording / reproducing light source having a predetermined wavelength λ, wherein at least a first dielectric thin film layer and a light beam having a wavelength λ are provided on a substrate. The irradiation reversibly changes the optical characteristics between a crystalline phase having a relatively large optical constant (refractive index n, extinction coefficient k) and an amorphous phase having a relatively small value at the wavelength λ. In order to construct a rewritable optical information recording medium formed by laminating a recording layer composed of a phase change material thin film, a second dielectric thin film layer, and a reflective layer composed of a metal thin film layer, at least the optical constants of the respective layers are Step 1 for determining and Step 2 for determining the maximum value dmax of the thickness d0 of the recording layer
And the thickness d0 of the recording layer, the thicknesses d1 and d2 of the first and second dielectric layers, and the thickness d3 of the reflection layer as parameters, the absorption of the phase change material thin film layer in incident light. Step 3 of calculating the ratio (hereinafter referred to as absorptance A) and the ratio of light reflected from the medium (hereinafter referred to as a reflectance R), and the light absorptivity A (when the phase change material thin film is in an amorphous state) amo) and reflectance R (amo), and light absorption rate A (cry) and reflectance R (cr in the crystalline state
y) and comparing the absorption rate difference between the two states ΔA (= A
(cry) -A (amo)) is equal to or greater than a predetermined value, and the reflectance difference ΔR (= R (cry) -R (amo)) is also equal to or greater than a predetermined value d0, d1 , D2, d3, a method for designing a rewritable optical information recording medium, comprising the step 4 of selecting a combination condition.