JPH06274938A - Optical information recording medium - Google Patents

Abstract

(57) [Summary] [Object] It is an object of the present invention to provide an optical information recording medium that is rewritable by overwriting, has a large reflectance, and is easily compatible with a duplication plate. [Structure] A thin film material whose optical constant changes by laser light irradiation is provided on the base material, and the phase of the reflected light of the incident light changes before and after the change, and the total reflection reaching the reproduction system due to this phase change The configuration is such that a change in light amount is detected, and a change in light absorption is small before and after the change. [Effect] Since the change in reflectance is not required, the difference in absorptance is small, and distortion in the recording state due to the difference in temperature rise condition during overwriting recording in the recorded area and the unrecorded area is suppressed, and the overwrite is performed even at high reflectance. Rewriting is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium for recording / reproducing information with high density by using a laser beam.

[0002]

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 wavelength of the light 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 optical information recording medium uses this for recording / reproducing information.

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, a flat plate-shaped medium is moved by, for example, a rotating unit such as a motor or a translation unit, and a laser beam 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 light spot having an output sufficiently lower than the threshold value to the recording portion, and it is detected that the optical characteristics are different between the recording portion and the unrecorded portion, and the signal is reproduced.

Among the optical information recording media, there is a recording medium called a phase change type which makes an optical change with almost no change in shape. This is a recording medium that uses a change in optical constant due to a change in crystallinity of a recording thin film material. That is, the thin film material is changed between an amorphous state and a crystalline state by laser light irradiation, and at least one of the extinction coefficient and the refractive index of the thin film material is changed for recording, and the reflectance, in other words, the reflectivity at this portion. The signal is reproduced by detecting that the amplitude of the reflected light changes and, as a result, the amount of reflected light reaching the detection system changes. Since the phase change type recording medium hardly changes its shape, there is no need to use a complicated air sandwich structure like a perforated type medium, and a simple adhesion protection structure can be used and the medium is easy to manufacture and is a low cost medium. is there.

An amorphous chalcogenide thin film is known as a recording thin film material. For example, there is an oxide-based thin film mainly comprising Te-TeO ₂ consisting of tellurium and tellurium oxide (JP-B 54-3725, JP-reference U.S. Patent Publication No. 3,971,874). In addition, Te-TeO ₂ -
A thin film containing Pd as a main component is also known (Japanese Patent Publication No. 2-9).
955, U.S. Pat. No. 4,624,914).
Further, a thin film containing Ge-Sb-Te as a main component is also known (JP-A-62-209742 and JP-A-62-2).
25934 and "" High speed overwritable pha
se change optical disk material ", Japanese Journal
of Applied Physics, vol. 26 (1987) suppl. 26-4 ”).

When recording a signal, the phase change type optical recording medium modulates the power level of the laser light between two laser powers, a recording power and an erasing power, to erase a signal already recorded and to generate a new signal. It is possible to use so-called overwrite recording for recording (Japanese Patent Publication No. 2-58).
690). Amorphization can be obtained by heating the thin film material above its melting point by recording power and then quenching it.
Crystallization is realized by raising the temperature to the crystallization temperature with weak erase power. Therefore, no matter what the state before recording, the portion irradiated with the recording power becomes amorphous and the portion irradiated with the erasing power becomes crystallized, so that one laser beam can be passed once. Write recording can be realized.

In a phase change type optical recording medium, generally, 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 further provided thereon. A structure in which a transparent layer is provided and a reflective layer is provided thereon is used. A high melting point inorganic dielectric is used for the transparent layer, and a metal is used for the reflective layer. By using such a structure, the shape of the recording thin film layer hardly changes even when it goes through a molten state when the recording thin film layer changes in phase, particularly when it becomes amorphous. Further, it is usual that the thickness of each layer is selected and designed so that the reflectance change is large and the light absorption is large during the phase change.

[0008]

Since the phase change optical recording medium can reproduce a signal by changing the reflected light amount, if the absolute value of the reflectance is large, a video disk (trade name laser disk) or a digital audio disk (trade name compact disk). There is a possibility that it can be compatible with a recording medium (reproduction disc) in which a signal is recorded in advance by the uneven pits such as the above). That is, it is possible to reproduce the signal with a device for exclusively reproducing them. Since a replica disk is usually provided with a metal thin film having a high reflectance such as aluminum (Al) on a resin substrate having concave and convex pits, it is 70
It has a reflectance of at least%. The closer the reflectance is to this value, the easier it is to achieve compatibility.

However, since the conventional phase-change type optical recording medium uses the above-mentioned structure, the incident laser light is hardly transmitted, but is partially absorbed and the rest is reflected. Of course, there is absorption in the reflective layer, but it is negligible. In addition, the phase change type optical recording medium reproduces a signal by detecting a change in reflectance, but if an attempt is made to increase the modulation degree of the change in reflectance (the ratio of the change in reflectance due to recording to the reflectance before recording), it will be amorphous. The reflectance of one of the states and the crystalline state must be large and the reflectance of the other must be small. In that case, the light absorption in each state is conversely small in one and large in the other. For example, the reflectance Rc in the unrecorded state (crystalline state), the recorded state (amorphous state)
If the reflectance of Ra is Ra, the light absorptivities are approximately (1-Rc) and (1-Ra), respectively, and the ratio is (1-Rc).
c) / (1-Ra). In a recording medium with a large ratio, when a new signal is overwritten while the signal is being recorded, the temperature reached in the previous state is different due to the difference in absorption even if the same laser power is applied to the amorphous part and the crystalline part. Normal recording cannot be performed because the recording marks have different sizes or the shape of the recording marks is distorted. In the conventional phase change recording medium, the reflectance of the laser light is 20 to 30% in the crystalline state and about 0 to 10% in the amorphous state to obtain a reflectance difference of about 20%. In this case, the absorptance was 70 to 80% in the crystalline state and about 90% or more in the amorphous state, and the ratio was relatively small and the influence on the overwrite characteristics was small. In an unrecorded state, the reflectance was brought close to 70% to increase the modulation degree,
For example, if the reflectance in the recording state is 30% or less, the light absorptance in the crystalline state is 30% or less, the light absorptance in the amorphous state is 70% or more, and the ratio is double or more, so that overwrite cannot be substantially performed. It becomes a state.

In other words, the phase change recording medium has a problem that it is impossible to obtain a recording medium which can be overwritten and which is compatible with the duplication disk because of its large reflectance.

A method for improving the erasing characteristic by selecting the absorption difference of the thin film has already been proposed (Japanese Patent Laid-Open No. 1-1.
(See Japanese Patent Publication No. 49238). It is disclosed that in a phase change recording medium, overwrite characteristics are improved by optical design of a multilayer thin film structure such that absorption of a recording thin film layer is substantially equal in an amorphous state and a crystalline state. In addition, even if the same amount of energy is absorbed in the amorphous state and the crystalline state, the temperature raising conditions differ due to the difference in thermal properties such as the thermal conductivity and the latent heat of fusion of the two, and the amorphous state tends to reach a higher temperature. It is also disclosed that greater absorption in the crystalline state gives better results. However, also in this case, the reflectance change is used for signal reproduction, and it is difficult to obtain a high reflectance change and a large reflectance change or modulation degree.

An object of the present invention is to provide a recording medium in which distortion in a recording state due to a difference in temperature rising condition during overwrite recording in a recorded portion and an unrecorded portion is suppressed, and overwrite rewriting is possible even at a high reflectance. To do.

[0013]

[Means for Solving the Problems] A thin film material whose optical constant is changed by laser light irradiation is provided on a base material, and the phase of reflected light of incident light is changed before and after the change, and a reproducing system by this phase change is provided. The configuration is such that a change in the total amount of reflected light that reaches the light source is detected, and the change in light absorption before and after the change is small.

Specifically, 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 on the first transparent layer, and a second transparent layer is further provided on the first transparent layer. In the structure provided with a reflective layer, the thickness of the first transparent layer, the recording thin film layer, the second transparent layer and the reflective layer, when the recording material changes the optical constants with almost no change in shape, The configuration is selected so that the phase of the reflected light of the incident light changes and the change in the light absorption of the recording thin film material layer before and after the change is small.

[0015]

With the above-described structure, the signal is reproduced not by the reflectance change but by the reflected light amount change caused by the phase change, so that a signal with a large modulation degree is obtained without causing the absorption difference as described above. be able to. Since the change in light absorption between the changed part and the unchanged part is small, when performing new recording on the already recorded state, the same temperature rise condition of the recording thin film can be obtained regardless of the previous state and the same recording state can be obtained. can get. As a result, good overwrite rewriting with little erasure remaining can be performed. Therefore, overwriting is possible even with a medium having a high reflectance.

Further, with such a structure, optically equivalent recording to phase change recording by 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 becomes easier to achieve compatibility with a duplication disk (audio disk, video disk, etc.) due to the uneven pits.

Light is a wave and is described by its amplitude and phase. The light changes its amplitude and phase by being reflected. Here, the case where the amplitude of the reflected light mainly changes is called reflectance change, and the case where the phase changes mainly are called phase change. When light is applied to an uneven pit such as a replica disk, the reflectance is the same in the pit portion and the peripheral portion, but the phase of the reflected light differs depending on the unevenness. As a result, the reflected light from the pit portion and the peripheral portion interfere with each other to cancel each other, and as a result, the amount of light incident on the detection system decreases. On the other hand, in the case of the conventional phase-change type recording medium, the reflectance differs between the recorded portion and the unrecorded portion, and the amplitude of the reflected light differs, resulting in a change in the amount of light incident on the detection system. As described above, both the phase change type medium and the reflectance change type medium reproduce the signal by the difference in the amount of light reaching the detection system, but the principles of changing the amount of light are different.

The phase change type phase change medium has already been proposed by the present inventors. (JP-A-2-73537, JP-A-2-113451, and JP-A-3-
41638 gazette). The phase-change recording medium of phase-change type can perform recording that is optically equivalent to phase-change recording due to unevenness, so that it is possible to perform recording with a high recording density even though it is phase-change recording. , Video discs, etc.) is also easy to obtain. In addition, phase change recording restores the recorded state by selecting the material without changing the shape.
That is, it is disclosed that erasing / rewriting is possible and rewritable phase change recording can be realized.

The present invention proposes that in such a phase change type phase change recording medium, the conditions for absorbing the laser light in the recorded portion and the unrecorded portion are further selected so that the temperature rising conditions are the same. is there.

When the phase change of the reflected light is (1 ± 2N) π (N is an integer), the change of the reflected light amount is the largest, and it is preferable that the change is almost equal to this value. This is because when the phase difference is π, the interference effect of the reflected light from each of the recorded portion and the unrecorded portion is the largest. Furthermore (1 ±
If it is within the range of 2N) π ± π / 2, there is sufficient interference effect and it can be used practically. That is, the phase difference Δφ is 3π / 2 ≧ Δφ
It may be ≧ π / 2 or −3π / 2 ≦ Δφ ≦ −π / 2.

The smaller the difference ΔA in absorption of the laser light between the recorded portion and the unrecorded portion, the better it is.
It is sufficient if it is 10% or less (assuming the total amount of incident light is 100%). If the difference in thermal properties such as thermal conductivity or latent heat of fusion between the amorphous state and the crystalline state is not negligible, it may be better to select absorption so that the crystalline state in which the temperature does not rise easily becomes larger. In this case ΔA
= (Crystal absorptivity Ac-amorphous absorptivity Aa), a good range is 10% ≧ ΔA ≧ 0%, and 20%
It is also effective in the range of ≧ ΔA ≧ 0%.

The larger the absolute value of the reflectance is, the larger the signal amplitude is, which is advantageous, and the larger the absolute value of the reflectance, the better it is in consideration of compatibility with the duplicating disk as described above. It is ideal if it is 70% or more, but it is 40 when considering the dynamic range of a normal playback device.
% Or more is sufficient, and 20% or more is sufficient.

The optical constants of the recording thin film layer material are important for obtaining a recording medium having a reflectance of 20% or more and a large phase change. A material having a relatively small extinction coefficient k and a large change in the refractive index n is desirable. It suffices that the extinction coefficient k satisfies k ≦ 1.0 either before or after the change, and the change in the refractive index n is 1.5 times or more.

Furthermore, in order to obtain a recording medium having a reflectance of 40% or more and a large phase change, the extinction coefficient k before and after the change.
Satisfying k ≦ 1.0, the refractive index n satisfying n ≧ 2.0, and the change of n is 1.5 times or more.

Next, a concrete example will be described.

[0026]

EXAMPLE As the construction of a recording medium, as shown in FIG. 1, a transparent layer 2 such as a transparent dielectric material is provided on a substrate 1, a recording thin film layer 3 is provided thereon, and a transparent layer 4 such as a dielectric material is provided. And the reflective layer 5 is further provided. 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, considering air (refractive index 1.0) instead of the protective layer, 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.

The thickness t ₃ of these recording thin film layer 3, large and phase changes in by choosing the thickness t ₅ of the thickness t _2, t ₄ and the reflective layer 5 of the transparent optical layer 2 and 4 appropriately It is possible to obtain a medium having a small change in absorptance.

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, those obtained by dissolving and coating a resin in a solvent and drying and those obtained by adhering a resin plate with an adhesive can be used.

As a material of the phase change type recording thin film layer, a material which changes phase between amorphous and crystalline, such as SbTe.
System, InTe system, GeTeSn system, SbSe system, TeS
eSb system, SnTeSe system, InSe system, TeGeSn
There are O-based, TeGeSnAu-based, TeGeSnSb-based chalcogen compounds and the like. Te-TeO ₂ system,
Te-TeO ₂ -Au system, also known oxide-based material ₂ -Pd system such as Te-TeO. Further, a metal compound such as AgZn-based or InSb-based metal compound that causes a crystal-crystal phase transition is also known.

As a material suitable for the present invention, a material having a relatively small extinction coefficient k and a large change in the refractive index n is desirable. Of these, the compound GeTe of germanium (Ge) and tellurium (Te) is suitable. The fact that this material can be used as a recording thin film layer material is disclosed in, for example, JP-A-62-40648
It is disclosed in the publication. Further, a system containing Se generally has a small extinction coefficient. Among them, the compound Sb ₂ Se _{3 of} antimony (Sb) and selenium (Se) is suitable. The fact that this material can be used as a recording thin film layer material is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 2
It is disclosed in Japanese Patent Publication No.-266978. Further, compounds of germanium (Ge), antimony (Sb) and tellurium (Te) are also suitable.

As the material of the transparent layer, oxides such as SiO ₂ , SiO, TiO ₂ , MgO and GeO ₂ which are high melting point dielectrics, nitrides such as Si ₃ N ₄ and BN, ZnS and ZnT.
e, PbS, and other sulfides or mixtures thereof can be used.

As the material of the reflection layer, a metal material such as Au, Al, 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 composite target, and the like can be used.

Example 1 A compound GeTe of germanium (Ge) and tellurium (Te) was used as a recording thin film layer material. As a forming method, a DC sputtering method using an alloy of Ge and Te as a target is used. The recording thin film is formed in an amorphous state. GeT of the above composition on a glass plate
When the optical constant of a thin film in an amorphous state in which only e was vapor-deposited was measured, the complex refractive index n at a wavelength of 780 nm
The + ki was 4.15 + 0.98i. 300 this
The optical constant was 6.37 + 3.97i as measured by heat treatment in an inert gas atmosphere at 5 ° C for 5 minutes to obtain a crystalline state. Therefore, GeTe has an extinction coefficient k in the amorphous state of k ≦ 1.0 and a change of the refractive index n of 1.5 times or more at a wavelength of 780 nm.

As one embodiment of the present invention, as shown in FIG. 1, as a base material 1, a polycarbonate resin plate (PC, refractive index of 1.58) is used as a transparent layer 2, and a mixture of zinc sulfide and silicon dioxide (ZnS-) is used as a transparent layer 2. SiO ₂ , molar ratio 4: 1, refractive index 2.
10) is deposited by magnetron sputtering to a thickness of t ₂ , GeTe is formed as the recording thin film layer 3 to a thickness of t ₃ by the above-described method, and ZnS—Si is formed as the transparent layer 4.
A film of O ₂ having a thickness t ₄ was similarly formed by the sputtering method. On top of this, as a reflection layer 5, gold (Au, refractive index 0.18 + 4.64)
i) was formed to a thickness of t _{5 by the} DC sputtering method, and the protective layer 6 was coated with a resin material having the same refractive index as the base material.

In the case of such a structure, the reflectances Ra and Rc in the amorphous state and the crystalline state and the reflectance change ΔR
(= Rc-Ra), the absorptances Aa and Ac of the recording thin film layer and the absorptance change ΔA (= Ac-Aa), and the phase change Δφ of the reflected light are the film thickness t ₂ of each layer 2, 3, 4 and 5, respectively. t
Calculations were performed by changing ₃ , t ₄ and t ₅ .

The reflectance, the absorptance, and the phase of the reflected light can be calculated by the matrix method from the complex refractive index and the film thickness of each layer. (For example, Hiro Wave Kubota, "Wave Optics," Iwanami Shoten, Chapter 3, 1971, or Leo Levi, Applied O.
ptics II. p62-72, see John Wiley & Sons, Inc., (1968)) Further, the base material 1 and the adhesion protection layer 6 have an infinite film thickness (base material-air interface, adhesion protection layer). -Ignore the effect of the air interface), the reflectance R is determined as the ratio of the light incident from the base material to be emitted into the base material, and the phase is determined based on the phase at the interface between the base material 1 and the transparent layer 2. It was Phase is 1
Since it is equivalent to the period of 2π corresponding to the wavelength λ, in the figures described below, the range of λ / 2 (corresponding to one wavelength λ in the case of reflected light in a round trip) is shown in consideration of this. There is

In FIG. 2, the film thickness t ₃ of the recording thin film layer is 5 nm and the film thickness t _{5 of the} reflective layer is 50 nm at the wavelength λ = 780 nm.
The calculation results of the thickness changes t ₂ and t ₄ of the transparent layers 2 and 4 of the phase change Δφ, the absorption rate change ΔA, and the reflectance change ΔR of the reflected light in the case of are shown. In the figure, the thicknesses t ₂ and t of the transparent layers 2 and 4 are
₄ indicates the optical length (refractive index × physical length) on the scale of wavelength λ. In this case, the refractive index of the transparent layers 2 and 4 is n = 2.1.
Therefore, λ / 2 corresponds to 780 / 2.1 / 2/2 = 185.7 nm. In FIG. 2, the absolute value of the absorption difference ΔA is 10% or less between the line (wavy line) with the absorption difference ΔA = 10% and the line with ΔA = −10%. Further, a region between the line of ΔR = 10% (thin solid line) and the line of ΔR = −10% is a region where the absolute value of ΔR is 10% or less and the change in reflectance is small. Further, the phase difference is large between the curve of Δφ = −π / 2 (thick solid line) and the curve of Δφ = −3π / 2. Therefore, under the conditions of t ₃ = 5 nm and t ₅ = 50 nm, the region where the absorption difference is small has a small reflectance difference and a small phase difference. Therefore, there is no area where overwriting is possible and the signal is large.

Similarly, in FIG. 3, the film thickness t ₃ = 10 nm of the recording thin film layer and the film thickness t ₅ = of the reflective layer at the wavelength λ = 780 nm.
Phase change Δφ and absorptance change Δ of reflected light in the case of 50 nm
A and the thicknesses t ₂ and t of the transparent layers 2 and 4 having the reflectance change ΔR
₄ shows the calculation results of the dependence. The shaded region in the drawing is a region where the absolute value of the absorption difference ΔA is 10% or less and the phase difference is smaller than −π / 2 and larger than −3π / 2 (the absolute value of the phase difference is large). Further, in this region, the absolute value of the reflectance difference ΔR is as small as 10% or less. Although not shown in the figure, the absolute value of the reflectance in this region was about 20%.

Similarly, FIG. 4 shows that the recording thin film layer has a thickness t ₃ = 20 nm and the reflective layer has a thickness t ₅ = at a wavelength λ = 780 nm.
Phase change Δφ and absorptance change Δ of reflected light in the case of 50 nm
A and the thicknesses t ₂ and t of the transparent layers 2 and 4 having the reflectance change ΔR
₄ shows the calculation results of the dependence. In the region shown by the broken line in the figure, the absolute value of the absorption difference ΔA is 10% or less and the phase difference is −π / 2.
It is shown that the region that is smaller and is larger than −3π / 2 (the absolute value of the phase difference is large) is considerably large. Similarly, this area is included in a small area where the absolute value of the reflectance difference ΔR is 10% or less. The absolute value of reflectance was about 25%.

FIG. 5 similarly shows that the film thickness t ₃ = 35 nm of the recording thin film layer and the film thickness t ₅ = of the reflective layer at the wavelength λ = 780 nm.
Phase change Δφ and absorptance change Δ of reflected light in the case of 50 nm
A and the thicknesses t ₂ and t of the transparent layers 2 and 4 having the reflectance change ΔR
₄ shows the calculation results of the dependence. In the region shown by the broken line in the figure, the absolute value of the absorption difference ΔA is 10% or less and the phase difference is −π / 2.
It is shown that the region that is smaller and is larger than −3π / 2 (the absolute value of the phase difference is large) is considerably large. Similarly, this area is included in a small area where the absolute value of the reflectance difference ΔR is 10% or less. The absolute value of reflectance was about 20%.

Similarly, in FIG. 6, the film thickness of each reflective layer is t _5.
5 shows a calculation result in the case where the film thickness t ₃ of the recording thin film layer is 40 nm and is constant at 50 nm. In this case, there is a region where the absolute value of the absorption difference ΔA is 10% or less, but there is no region where the phase difference is smaller than −π / 2 and larger than −3π / 2 (the absolute value of the phase difference is large). Has been done.
Similarly, when the film thickness of the reflective layer is t ₅ = 50 nm and the film thickness t ₃ of the recording thin film layer is thicker than 40 nm, it is found from the calculation result that there is no film thickness structure having a small absorption difference and a large phase difference. .

FIG. 7 shows a calculation result when the thickness t ₅ of the reflective layer is thinned to 10 nm. The thickness of the recording thin film layer is t ₃ = 20.
nm. In the region shown by the broken line in the figure, the absolute value of the absorption difference ΔA is 10% or less and the phase difference is smaller than −π / 2 −3
It is shown that the region larger than π / 2 (the absolute value of the phase difference is large) is considerably large. In this case, since the reflection layer is thin and the transmittance is high, the region where the absolute value of the reflectance difference ΔR is 10% or less does not necessarily coincide with the region where the absorption difference is small. The absolute value of reflectance was about 25% in the unrecorded state and 7% or less in the recorded state.

When the calculation was carried out while the thickness t ₅ of the reflective layer was reduced to 10 nm and the thickness t ₃ of the recording layer was further changed, it was found that t ₃ = 10 nm or less or 30 nm or more. It turns out that there is no such condition. Therefore, the above conditions are also influenced by the film thickness of the reflective layer, and therefore the film thickness of the reflective layer must be appropriately selected.

The following experiment was conducted based on the above results. As a base material, on a polycarbonate resin plate (PC, refractive index 1.58) having a thickness of 1.2 mm and a diameter of 130 mm, a mixed dielectric of zinc sulfide and silicon dioxide (Z
nS-SiO ₂ ) by magnetron sputtering to a thickness t ₂ =
After forming a film having a thickness of 46 nm (equivalent to λ / 8), a recording thin film GeTe as the recording thin film layer 3 was similarly formed by a magnetron sputtering method to a thickness t ₃ = 20 nm, and a Zn transparent layer 4 was formed.
S-SiO ₂ was vapor-deposited in the same manner as the thickness t ₄ = 81 nm (corresponding to 7λ / 32). Aluminum (Al) was formed thereon as the reflective layer 5 in the same manner as the thickness t ₅ = 50 nm, and the same PC disk as the base material was bonded as the protective material 6 with an adhesive to form an optical recording medium.

By rotating this recording medium, a linear velocity of 8 m / se
A semiconductor laser beam having a wavelength of 780 nm at a linear velocity of c was focused by a lens system having a numerical aperture of 0.55 and focused on the recording thin film for irradiation. First, the recording thin film on the track was uniformly crystallized by irradiating the recording thin film surface with laser light at a continuous output of 10 mW. When this track was irradiated with a continuous output (reproduction power) of 1 mW and the reflected light was detected by a photodetector, it was confirmed that the reflectance was equivalent to 25%. The laser light output on this track is 22 mW (recording power) and 11 mW (erasing power) on the surface of the recording film.
The recording thin film was partially amorphized by irradiating light modulated with a single frequency of 5 MHz and a modulation degree (duty) of 50% between the recording and recording, and recording was performed. Furthermore, when reproducing light of 1 mW was radiated and the reflected light was detected by a photodetector and reproduced, a 1 MHz reproduction signal was obtained. When this reproduction signal was measured by a spectrum analyzer, the CN ratio (signal to noise ratio) was obtained. 54 dB (frequency resolution 30 k
Hz, and so on). Similarly, laser light output of 22 mW (recording power) and 11 W was applied to this track.
Overwrite recording was performed by irradiating light modulated at a single frequency of 2 MHz and a modulation degree (duty) of 50%, which was different from (erasing power). The portion irradiated with the recording power is made amorphous, and the portion irradiated with the erasing power is crystallized, so that the already recorded mark is erased and a new mark is formed. When the reproduction signal was measured with the same reproduction power in this state, the CN ratio of the 2 MHz signal was 55d.
It was B. Also, as a frequency component of 5 MHz, the CN ratio is 1
6 dB was obtained. This was already recorded 1MH
This shows that the z signal is attenuated by 38 dB. Generally, the difference between the CN ratio of the reproduced signal in the recorded state and the unerased reproduced signal in the erased state is defined as the erase rate. In this case, the erase rate is 38 dB. Generally, if the erasing rate is 26 dB or more, it is practically sufficient, and the above result can be said to be practically sufficient. Therefore, it can be said that the recording medium of this embodiment is a recording medium having a high reflectance and excellent overwrite characteristics.

(Example 2) A compound Sb ₂ Se ₃ of antimony (Sb) and selenium (Se) was used as a recording thin film layer material. As a forming method, a DC sputtering method using an alloy of Sb and Se as a target is used. The recording thin film is formed in an amorphous state. Sb ₂ of the above composition on the glass plate
When the optical constant of the amorphous state in which only Se ₃ was vapor-deposited was measured, the complex refractive index n + was found at a wavelength of 780 nm.
The ki was 3.00 + 0.15i. This is 300 ℃
When heat-treated in an inert gas atmosphere for 5 minutes to obtain a crystalline state, the optical constant was measured and found to be 4.70 + 0.70i.

As one embodiment of the present invention, as shown in FIG. 1, a mixture of zinc sulfide and silicon dioxide (ZnS) is used as a transparent layer 2 on a polycarbonate resin plate (PC, refractive index 1.58) as a substrate 1. -SiO _2, the molar ratio of 4: 1, the refractive index 2.
10) is vapor-deposited by magnetron sputtering to a thickness of t ₂ , Sb ₂ Se ₃ is formed as a recording thin film layer 3 to a thickness of t ₃ by the above method, and ZnS-SiO _{2 is} formed as a transparent layer 4.
Was formed in the same manner as the thickness t ₄ by the sputtering method. On this, gold (Au, refractive index 0.18 + 4.64i) was formed as a reflective layer 5 by a thickness t ₅ DC sputtering method, and a resin having the same refractive index as the base material was coated as a protective layer 6.

The reflectances Ra and Rc and the reflectance change ΔR in the amorphous state and the crystalline state in the case of such a configuration.
(= Rc-Ra), the absorptances Aa and Ac of the recording thin film layer and the absorptance change ΔA (= Ac-Aa), and the phase change Δφ of the reflected light are the film thickness t ₂ of each layer 2, 3, 4 and 5, respectively.
The calculation was performed in the same manner as in Example 1 except that t ₃ , t ₄ and t ₅ were changed.

In FIG. 8, the film thickness t3 of the recording thin film layer is 20 nm and the film thickness t5 of the reflective layer is 50 n at the wavelength λ = 780 nm.
The calculation results of the thicknesses t ₂ and t ₄ of the transparent layers 2 and 4 of the phase change Δφ of the reflected light, the absorption rate change ΔA, and the reflectance change ΔR in the case of m are shown. In FIG. 8, the absorption difference ΔA is 10% or less between the lines (wavy lines) where the absorption difference ΔA = 10%. Also, ΔR ≧ −10% between the lines of ΔR = −10% (dashed line)
This is a region where the reflectance change is small. Also, Δφ = −π / 2
The phase difference inside the curve (solid line) is smaller than -π / 2.
Therefore, under the conditions of t ₃ = 20 nm and t ₅ = 50 nm, the region where the absorption difference is small has a small reflectance difference and a small phase difference. Therefore, there is no area where overwriting is possible and the signal is large.

Similarly, in FIG. 9, the film thickness t3 of the recording thin film layer at the wavelength λ = 780 nm is t3 = 30 nm, and the film thickness of the reflective layer is t ₅ =
Phase change Δφ and absorptance change Δ of reflected light in the case of 50 nm
A and the thicknesses t ₂ and t ₄ of the transparent layers 2 and 4 having the reflectance change ΔR
The calculation result of dependence is shown. The shaded region in the figure is a region where the absorption difference ΔA is 10% or less and the phase difference is smaller than −π / 2 (the absolute value of the phase difference is large). This area is small because the reflectance difference ΔR ≧ −10%. Although not shown in the figure, the absolute value of the reflectance in this region was about 55%.

Similarly, FIG. 10 shows that the recording thin film layer has a thickness t ₃ = 40 nm and the reflective layer has a thickness t ₅ = at a wavelength λ = 780 nm.
Phase change Δφ and absorptance change Δ of reflected light in the case of 50 nm
A and the thicknesses t ₂ and t ₄ of the transparent layers 2 and 4 having the reflectance change ΔR
The calculation result of dependence is shown. It is shown that the region shown by the broken line in the figure has a considerably large region where the absorption difference ΔA is 10% or less and the phase difference is smaller than −π / 2 (the absolute value of the phase difference is large). Similarly, this area has a reflectance difference Δ
It is within a small area with R ≧ −10%. The absolute value of reflectance was about 45%.

Similarly, FIGS. 11, 12, 13 and 14 show the calculation results when the thickness of the reflective layer is constant at t ₅ = 50 nm and the thickness t ₃ of the recording thin film layer is 80 nm, 120 nm, 160 nm and 320 nm. It is a thing. In each case, there is a region in which the absorption difference ΔA is 10% or less and the phase difference is larger than π / 2 and becomes maximum π in the region indicated by the broken line. Even in these cases, the reflectance difference in the region is approximately 10% ≧ Δ
This matches the region of R ≧ −10%. The absolute values of reflectance were 40%, 40%, 20% and 10%, respectively, and tended to decrease as the recording thin film layer became thicker.
On the contrary, the absolute value of the absorption rate increases as the recording thin film layer increases.

15 and 16 show that the thickness t ₅ of the reflection layer is 1.
The calculation results obtained when the thickness is reduced to 0 nm show that the thickness t ₃ of the recording thin film layer is 20 nm and 40 nm, respectively. In any case, the above condition does not exist. Therefore, the thickness of the reflective layer must be selected appropriately.

The following experiment was conducted based on the above results.
It was. A base material with a thickness of 1.2 mm and a diameter of 130 mm
Transparent on a polycarbonate resin plate (PC, refractive index 1.58)
As the light layer 2, a mixed dielectric of zinc sulfide and silicon dioxide (Z
nS-SiO₂) By magnetron sputtering method₂=
197 nm (equivalent to 17λ / 32) film formation and recording thin
Recording thin film Sb as the film layer 3₂Te₃As well as the magnetron
Thickness t by sputtering method ₃= 40 nm and transparent layer 4
As ZnS-SiO₂The thickness t_Four= 163 nm (7λ /
16 equivalent) was vapor-deposited similarly. A reflective layer 5 is formed on top of this.
Luminium (Al) thickness t_Five= 50nm
In addition, the same PC disk as the base material is glued as the protective material 6.
To form an optical recording medium.

This recording medium was rotated to obtain a linear velocity of 1.3 m /
A semiconductor laser beam having a wavelength of 780 nm was focused at a linear velocity of sec with a lens system having a numerical aperture of 0.55 and focused on the recording thin film for irradiation. First, the recording thin film on the track was uniformly crystallized by irradiating the recording thin film surface with laser light at a continuous output of 8.5 mW. When this track was irradiated with a continuous output (reproduction power) of 1 mW and the reflected light was detected by a photodetector, it was confirmed that the reflectance was equivalent to 45%. The laser light output on this track is a single frequency 1 MHz between the output on the recording film surface of 19 mW (recording power) and 9 mW (erasing power) and the modulation degree (duty) 50%.
The recording thin film was partially amorphized by irradiating the light modulated by the above to form a mark for recording. 1mW
When the reproduction light was irradiated and the reflected light was detected by a photo detector to reproduce, a reproduction signal of 1 MHz was obtained. When the reproduced signal was measured with a spectrum analyzer, a CN ratio of 52 dB (frequency resolution 10 kHz, the same applies hereinafter) was obtained. Similarly, a laser light output of 15 mW (recording power) and 8 mW (erasing power) was applied to this track.
Single frequency 200kHz which is different between and
Overwrite recording was performed by irradiating light modulated at 0%. The part irradiated with the recording power was made amorphous, the part irradiated with the erasing power was crystallized, and the already recorded mark was erased to form a new mark. When the reproduction signal was measured with the same reproduction power in this state, the CN ratio of the 200 kHz signal was 53 dB. A CN ratio of 18 dB was obtained as a frequency component of 1 MHz. That is, the erasing rate was 33 dB, which was a practically sufficient value. Therefore, it can be said that the recording medium of this embodiment is a recording medium having a high reflectance and excellent overwrite characteristics.

As shown in the above examples, the first transparent layer,
By selecting the film thickness of the recording thin film layer, the second transparent layer and the reflective layer, the phase of the reflected light of the incident light changes, and the change in the light absorption of the recording thin film material layer before and after the change is reduced. Then, even under high reflectance, a condition that does not cause a temperature rise condition difference due to an absorption difference is possible.

[0059]

As described above, by using the phase change, a small change in the absorptance that cannot be achieved by the change in the reflectance is possible, and the recording state is caused by the difference in the temperature rising condition during the overwrite recording in the recorded portion and the unrecorded portion. Distortion is suppressed and overwrite rewriting is possible even with high reflectance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 3 is a characteristic diagram showing calculation results for obtaining an optimum area in the embodiment of the present invention.

FIG. 4 is a characteristic diagram showing calculation results for obtaining an optimum area in the embodiment of the present invention.

FIG. 5 is a characteristic diagram showing calculation results for obtaining an optimum area in the embodiment of the present invention.

FIG. 6 is a characteristic diagram illustrating calculation results for obtaining an optimum area in the embodiment of the present invention.

FIG. 7 is a characteristic diagram showing calculation results for obtaining an optimum area in the embodiment of the present invention.

FIG. 8 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 9 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 10 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 11 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 12 is a characteristic diagram illustrating calculation results for obtaining an optimum area in the embodiment of the present invention.

FIG. 13 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 14 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 15 is a characteristic diagram illustrating a calculation result for obtaining an optimum area in the embodiment of the present invention.

FIG. 16 is a characteristic diagram showing calculation results for obtaining an optimum area in the example of the present invention.

[Explanation of symbols]

 1 Base Material 2 Transparent Layer 3 Recording Thin Film Layer 4 Transparent Layer 5 Reflective Layer 6 Protective Material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Nagata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yoshitaka Sakagami, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Noboru Yamada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (22)

[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. The optical constant changes with almost no change, and the change that can be detected is mainly due to the change in the phase of the reflected light of the incident light, and the change in the light absorption of the recording thin film material layer before and after the change is small. A characteristic optical information recording medium. 2. The optical information recording medium according to claim 1, wherein a change in reflected light amplitude 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, wherein the film thickness of the first transparent layer, the recording thin film layer, the second transparent layer and the reflective layer is an optical constant with almost no change in the shape of the recording material. 3. The optics according to claim 1 or 2, wherein the phase of the reflected light of the incident light is changed upon the change of the above, and the change of the light absorption of the recording thin film material layer before and after the change is reduced. Information recording medium. 4. The optical information recording medium according to claim 3, wherein the change in light absorption before and after the change is within ± 10%. 5. The optical information recording medium according to claim 1, wherein the phase change Δφ is approximately (1 ± 2N) π N: an integer. 6. The optical information recording according to claim 1, wherein the phase change Δφ is in the range of 3π / 2 ≧ Δφ ≧ π / 2 or −3π / 2 ≦ Δφ ≦ −π / 2. Medium. 7. The optical information recording medium according to claim 2, wherein the reflectance is 40% or more before and after the change. 8. The optical information recording medium according to claim 2, wherein the reflectance is 20% or more before and after the change. 9. 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. The optical constant changes with almost no change, the extinction coefficient k of the thin film material at the wavelength used is in the range of k ≦ 1.0 either before or after the change, and the refractive index n before and after the change. The change is 1.
An optical information recording medium, which is 5 times or more, and a detectable change is mainly due to a change in a phase of reflected light of incident light. 10. An optical information recording medium having a recording thin film material layer provided on a base material, the recording thin film material layer causing a change which can be optically detected by the laser light irradiation, wherein the thin film material changes its shape by the laser light irradiation. The optical constant changes with almost no change, the refractive index n and the extinction coefficient k of the thin film material are within the range of n ≧ 2.0 and k ≦ 1.0 before and after the change, and the change of the refractive index n is 1 or less. An optical information recording medium, which is 5 times or more, and the detectable change is mainly due to the change in the phase of the reflected light of the incident light. 11. 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 further provided thereon, and a reflective layer is provided thereon. An optical information recording medium having a structure, wherein the recording thin film layer is made of a recording material whose optical constant changes without a change in shape due to a phase change, and the first transparent layer, recording thin film layer, The thicknesses of the second transparent layer and the reflective layer are selected so that the phase of the reflected light of the incident light changes when the recording material changes, and the change in the light absorption of the recording thin film material layer before and after the change is small. An optical information recording medium characterized by the above. 12. The optical information recording medium according to claim 11, wherein the change in light absorption before and after the change is within ± 10%. 13. The difference ΔA (= Ac−Aa) between the light absorption Ac in the crystalline state and the light absorption rate Aa in the amorphous state is 20% ≧.
12. The optical information recording medium according to claim 11, wherein ΔA ≧ 0%. 14. The difference between the light absorption Ac in the crystalline state and the light absorption rate Aa in the amorphous state ΔA (= Ac-Aa) is 10% ≧.
The optical information recording medium according to claim 11, wherein ΔA ≧ 0%. 15. The optical information recording medium according to claim 11, wherein the phase change Δφ is approximately (1 ± 2N) π N: integer. 16. A phase change Δφ of 3π / 2 ≧ Δφ ≧ π / 2
Alternatively, the optical information recording medium according to any one of claims 11 to 12, wherein the range is -3π / 2 ≤ Δφ ≤ -π / 2. 17. The optical information recording medium according to claim 11, wherein the reflectance is 40% or more before and after the change. 18. The optical information recording medium according to claim 11, wherein the reflectance is 20% or more before and after the change. 19. An optical information recording medium having a recording thin film material layer provided on a base material, the recording thin film material layer causing a change which can be optically detected by laser light irradiation, wherein the thin film material is formed by a phase change by laser light irradiation. The optical constant changes with almost no change, and the extinction coefficient k of the thin film material at the wavelength used is within the range of k ≦ 1.0 either before or after the change, and refraction before and after the change. The change in the rate n is 1.
An optical information recording medium, which is 5 times or more, and a detectable change is mainly due to a change in a phase of reflected light of incident light. 20. 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 is shaped by a phase change by laser light irradiation. The optical constants change with almost no change, and the refractive index n and the extinction coefficient k of the thin film material are within the range of n ≧ 2.0 and k ≦ 1.0 before and after the change, and the refractive index n An optical information recording medium, wherein the change is 1.5 times or more, and the detectable change is mainly due to a change in the phase of reflected light of incident light. 21. The optical information recording medium according to claim 11, wherein the thin film material contains a material composed of antimony (Sb) and selenium (Se) as main components. 22. The optical information recording medium according to claim 11, wherein the thin film material contains a material composed of germanium (Ge) and tellurium (Te) as main components.