JPH03157830A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To realize high density recording, erasing and rewriting by forming two layers of thin film materials which show changes in the optical constants with irradiation of laser light on a substrate, and detecting the change in the total reflectance or transmittance due to the phase change of the reflected or transmitted light before and after the optical properties of the thin film layers change. CONSTITUTION:On a substrate 1, there formed are a first transparent layer 2 having different refractive index to the substrate 1, the first recording thin film layer 3, second transparent layer 4, second recording thin film layer 5, third transparent layer 6, and further a reflecting layer 7. Thickness of the first transparent layer 2, first recording thin film layer 3, second transparent layer 4, second recording thin film layer 5, third transparent layer 6, and reflecting layer 7 are determined so as to change the phase of transmitted or reflected light when the medium is irradiated with light after the optical properties of the medium change. Thus, the medium has high recording density although it is a phase-transition recording type and is rewritable for such a recording method using phase changes of light which enable erasing and rewriting.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical information recording/reproducing medium that records and reproduces information at high speed and high density using light, heat, etc.

BACKGROUND ART When laser light is focused by a lens system, it is possible to create a small light spot with a diameter on the order of the wavelength of the light. Therefore, it is possible to create a light spot with high energy density per unit area even from a light source with a small output. Therefore, it is possible to change a minute area of a substance, and it is also possible to read out changes in that minute area. Optical information recording media utilize this for recording and reproducing information. Hereinafter, it will be referred to as an "optical recording medium" or simply "medium."

The basic structure of an optical recording medium is that a recording thin film layer whose state changes in some way by laser spot light irradiation is provided on a base material with a flat surface. The following methods are used to record and reproduce signals. In other words, a plate-like medium is moved by rotation means or translation means such as a motor, and a laser beam is focused and irradiated onto the recording thin film surface of this medium. The recording thin film absorbs the laser light and heats up. When the output of the laser beam is increased above a certain threshold, the state of the recording thin film changes and information is recorded. This threshold value is a quantity that depends on not only the characteristics of the recording thin film itself but also the thermal characteristics of the base material, the relative speed of the medium with respect to the light spot, etc. The recorded information is obtained by irradiating the recording section with a laser beam spot with an output sufficiently lower than the threshold value, and detecting that some optical characteristics such as transmitted light intensity, reflected light intensity, or their polarization direction are different between the recorded section and the unrecorded section. Discover and play.

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

As the recording thin film, a thin metal film containing Bi, Te, or a metal containing these as main components [1LTe-containing compound thin film is known. The thin film is melted or evaporated by laser beam irradiation to form small holes.1. X. Reproduction is performed by detecting changes in the amount of reflected or transmitted light that are reflected or transmitted from the recording section and its surroundings and cancel each other out due to interference, or are diffracted and reach the detection system. conduct. There is also a recording medium called a phase change type that undergoes an optical change without a change in shape. As a material, there is an oxide thin film whose main component is Te-TeO2, which is made of amorphous chalcogenide tellurium and tellurium oxide (Japanese Patent Publication No. 3725/1983). A thin film containing L Te Te02-Pd as a main component is also known (Japanese Unexamined Patent Publication No. 68296/1983). These record by changing at least one of the extinction coefficient or refractive index of the thin film by laser light irradiation (＼ The amplitude of the transmitted light or reflected light changes in this part, and as a result, the amount of transmitted light reaching the detection system Alternatively, a change in the amount of reflected light is detected and the signal is reproduced.

Light is a wave and is described by amplitude and phase.

As mentioned above, signal reproduction depends on the amount of transmitted light or reflected light.
The causes C are when the amplitude of transmitted light or reflected light in a minute area of the film itself changes (amplitude change recording), and when the phase of transmitted light or reflected light changes (phase change). record).

Invention or solution (7) Among the optical recording media mentioned above, those with holes do not allow large changes in the amount of reflected light, and because they are phase change recording, recording with high recording density is possible. The structure is difficult to form and the noise during playback is large. Also, since it is a deformed record, it cannot be erased or rewritten.

In comparison, phase-change recording media do not involve shape changes, so they have a simple structure, are easy to manufacture, and are low-cost media. There is a problem that the recording density is small.
There is also the problem that it is difficult to maintain compatibility with reproduction discs (audio discs, video discs, etc.) using Z, a phase change type recording medium (concave/convex recording medium).

Means for solving the problem: At least two thin film material layers whose optical constants change when irradiated with laser light are provided on the base material, and the phase of the reflected light or transmitted light of the incident light changes before and after the change, and this phase changes. It is configured to detect changes in the amount of reflected light from the four bodies or in the transmitted scenes due to changes.

Furthermore, in this case, the reflectance or transmittance is configured to have no change before and after the change, or to have a small IA configuration.

Specifically (:L base material - the first material having a different refractive index from the base material)
A transparent layer is provided (i)l, and a first recording thin film layer is provided thereon (i).
A configuration is used in which a second transparent layer is disposed on top of the second transparent layer, and a second recording thin film layer is disposed on top of the third transparent layer. First transparent layer First recording thin film layer Second recording thin film layer of transparent wind box 2 Third
This can be achieved by selecting the film thicknesses of the recording thin film layer and the reflective layer so that the phase of transmitted light or reflected light of incident light changes when the recording material changes.

Effect: With the above-described configuration, recording optically equivalent to phase change recording using unevenness can be performed. Therefore, it is possible to perform high-density recording even though there is a phase change recording method, and it is possible to perform reproduction discs (audio discs, video discs, etc.) using uneven bits.
Also, by selecting the material without changing the shape, phase change recording can be easily erased and rewritten. It is possible to record changes.

An example of the structure of a conventional phase change optical recording medium is shown in FIG. The complex refractive index of a phase change recording material changes when it is irradiated with 1-noser light to heat up and change its phase. Generally, the change is such that the refractive index and the extinction coefficient change in the same direction.

For example, when an amorphous state changes to a crystalline state, the refractive index and extinction coefficient generally increase. The reflectance of such a recording thin film layer depends on the film thickness t2 of the recording thin film layer 3. The reflectance R of the recording thin film when light is incident from the substrate 1 side is the result of multiple interference between the light reflected from the interface on the light incident side of the recording thin film and the reflected light from the interface on the opposite side. When the film thickness t2 is changed, the reflectance increases or decreases as a result of interference at a period determined by the wavelength and refraction, but as the film thickness increases, the amount of light that reaches the interface opposite to the light incident side and is reflected decreases as the film thickness increases. Therefore, the effect of interference disappears. As a result, a curve is drawn in which the increase and decrease due to interference gradually attenuates as the film thickness increases. When the complex refractive index increases, the film thickness period due to interference becomes smaller due to the increase in the refractive index, and at the same time, the attenuating film thickness shifts toward a smaller value due to the increase in the extinction coefficient. As a result of the above, the reflectance difference △R at the time of phase change (7) also changes depending on the film thickness, but generally it becomes maximum at the film thickness where the reflectance becomes minimum in the phase with a small complex refractive index.On the other hand, in such a configuration The change in the phase of the reflected light before and after the phase change is small (~ In other words, the change in reflectance is due to the change in the amplitude of the reflected light.

Conventionally, phase-change recording media are used with a film thickness that maximizes this change in reflectance. Therefore, reproduction of the recorded state is performed by detecting this difference in reflectance. In the case of recording and reproducing a minute area on the order of microns, the size of the recorded area and the size of the light beam used for reproduction are of the same order.For example, the wavelength is 800.
NAO laser light around nm.

When narrowed down with a lens system of about 5.5, the beam can be narrowed down to a beam with a half-width of about 0.9 μm. When recording is performed using such a beam with strong power, a phase change occurs in a range of approximately 0.5 to 1 μm, resulting in a recorded state. Considering the case where this is read out with the same beam, the light intensity of the readout beam generally has a Gaussian distribution and spreads outward from the recorded state where the phase has changed, so the amount of reflected light is equal to the reflectance of the recorded state. It is proportional to the average value obtained by weighting the surrounding unrecorded reflectance by each area and light intensity distribution. Therefore, unless the area of the recorded state is sufficiently large compared to the size of the read beam, a sufficient reproduced signal cannot be obtained.This size limits the recording density.

On the other hand, when the holes are shaped, the recorded state is an uneven shape, and the phase of the reflected light from the peripheral part and the recorded part is different, and the reflected light quantity changes due to interference between them. This is utilized.

Therefore, the phase difference between the reflected light at the periphery and the hole is (1±2n)
The change in the amount of reflected light is greatest when π (n is an integer), and it is desirable that it be close to this value.
In addition, the interference effect is greatest when the intensity distribution of the readout beam is equal to the intensity incident on the hole and the peripheral area, and therefore the reflected light intensity change is thick t°C, that is, recording is smaller than the size of the readout beam. When in this state, the reproduced signal will be large.

From the above, it can be seen that when reproducing with the same reproducing light beam, phase change recording allows a larger signal amount to be obtained with a smaller recording area than reflectance change recording, that is, it is possible to record and reproduce at a higher density.

Therefore, if a phase change can be obtained in phase change recording, a recording density comparable to concave/convex recording can be obtained.Moreover, it is desirable that there be no or small change in reflectance. To construct a phase-change optical recording medium such as If the refractive index of the material in contact with the recording thin film changes, the reflected light at each interface changes.

The reflected light from the recording thin film is the result of multiple interference of the reflected light from the light incident side interface of the recording thin film and the reflected light from the opposite interface. When the recording thin film is sufficiently thin and the size of the light that reaches the interface opposite to the light incident side of the recording thin film is sufficiently large (if the optical constant in the unrecorded state is small, the light reaches the interface opposite to the light incident side). When the reflected light is larger than the reflected light from the interface on the light incident side and the optical constant of the recording state is large, conversely, the reflected light from the interface on the light incident side reaches the interface opposite to the light incident side. There is a condition in which the light is larger than the reflected light.Since the optical path lengths of the two are different, there is a phase difference.If this phase difference is large, it is the result of cancellation due to interference.When the optical constant changes due to recording, the total reflected light It becomes possible for the phase of

Furthermore, if the difference in amplitude between the two is almost the same before and after recording (
Of course, the magnitude relationship is reversed), but it is possible that there is almost no change in the reflected light amplitude.

Further, a first transparent layer having a refractive index different from that of the substrate is provided on the substrate, a first recording thin film layer is provided thereon, and a second transparent layer is provided thereon. A second recording thin film layer is provided on top (
A third transparent layer is provided on top of the third transparent layer, and a reflective layer is provided on top of the third transparent layer.First transparent layer First recording thin film layer Second transparent layer Second recording thin film layer By selecting the thicknesses of the third recording thin film layer and the reflective layer, a more efficient phase change type optical recording medium can be obtained. This is because when a transparent layer exists between the two recording thin film layers, the transmittance is large and the phase change during phase change is also large, so the light that has passed through the two recording thin film layers is reflected by the reflective layer, resulting in the above interference. This is because cancellation is performed efficiently.

On the other hand, in optical recording media such as optical disks, a tracking method using groove-like irregularities of a base material is generally used. (For example, see "Optical Disk Technology" supervised by Morio Onoue, Radio Gijutsusha T'L, Chapter 1 1.2° = 13 = 14-5 p79~) In this case, the uneven grooves also change the phase of the reflected light of the incident light. l. Provide information necessary for racking to the detection system. Therefore, when recording and reproducing a phase change while performing tracking using a groove track, the phase change due to the groove and the phase change due to recording are superimposed.

Therefore, consideration must be given to recording and reproducing phase changes without impairing the tracking function.

Specifically (the depth of the groove track is usually designed to have a convex shape on the incident side of the noser beam 10 and give a phase difference of -π/2, as shown in Fig. 4). Terutahachi
If the phase difference recorded by the phase change is ±π, the two will overlap and the total phase difference will be +π/2 or 1 3/2 × π.
In this case, the polarity of the tracking signal is reversed (see the above-mentioned book for details). It is necessary to prevent the total phase difference from reversing by ensuring that the phase change is 1 to π/2. This can be achieved with the configuration shown in FIG. 5 using the above-mentioned multilayer structure as the recording layer 9. In this case, the total phase difference between the recording phase difference in the recorded area and the phase difference due to the groove is 0, so the polarity of the average phase difference with the unrecorded area remains negative and does not reverse. The fact that the phase difference is O (mu) means that it is equivalent to the state where the groove is no longer present.The advantage is that by cutting off the groove, a signal such as an address can be formed in advance, and a reproduction destination equivalent to the reproduction light from the part can be obtained. There is also.

1. Contrary to Fig. 4, a force may also be considered when the shape of the groove track is concave from the incident side of the laser beam IO (in that case, the phase difference due to the groove is π/2, so the phase change The phase change during recording should be π/2 (°C) The so-called "on-land" method shown in Figure 6 is also known as a groove shape for dragging. (Ibid. (See) In such a case, the tracking signal from the groove is not affected, so it is possible to maximize the phase difference of phase change recording to ±π. This will be explained using an example.

As shown in FIG. 1, the structure of the recording medium of the embodiment includes a transparent layer 2 such as a transparent dielectric material, a recording thin film layer 3, a second transparent layer 4 such as a transparent dielectric material, and a second transparent layer 4, such as a transparent dielectric material. A recording thin film layer 5, a transparent layer 6 such as a third transparent dielectric, and a reflective layer 7 are sequentially provided. Furthermore, a transparent, close-fitting protective layer 8 is provided thereon. Although not shown in the figure, it is also possible to have a configuration without a protective layer.In this case, if air (refractive index 1.0) is used instead of the protective layer 8, it is optically equivalent and the same effect can be obtained. .

The transparent layer 2 is made of a material having a different refractive index from that of the base material 1.

Thicknesses t2 and t4 of these recording thin films, thickness t of the transparent layer
By appropriately selecting lS t3, t5 and the thickness t6 of the reflective layer, a medium with a large phase change can be obtained.

As the base shrine 1, a transparent and smooth flat plate made of glass, resin, etc. is used. Further, the surface of the base material may have groove-like irregularities for tracking guides.

For the protective layers 8 and 17, a material obtained by dissolving resin in a solvent, applying and drying it, or a material obtained by bonding a resin plate with an adhesive, etc. can be used.

The recording thin film material used for the recording thin film layers 3 and 5 is a material that undergoes a phase change between amorphous and crystalline, such as 5bTe&
InTeK GeTe5nKSbSeK Te
5eSb&5nTeSe&InSe&TeGe
5nOX, TeGe5nAuX, TeGe5nSb&
A chalcogen compound such as TeGeSb is used. Te-
TeO2 & Te-Te02-Au & Te-Te02
-Oxide-based materials such as Pd-based materials can also be used. In addition, metal compounds such as AgZnK InSb that undergo crystal-to-crystal phase transition may also be used, but transparent layers 2.4 and 6 may be made of 5i02, SI01Ti0, etc.
2. Oxidized salts such as MgO1G e O2, Si3N4, B
Nitriding such as NS AIN 1$3. ZnS, Zn5e,
Although sulfides such as ZnTe, PbS, or mixtures thereof can be used, the reflective layers 8 and 17 may be made of metallic materials such as Au, AI, Cu, or a dielectric multilayer with high reflectance at a predetermined wavelength. Membrane etc. 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 composite target, and the like can be used.

Comparative example Recording thin film of gel manila with the composition of Ge2Sb2Te5, which is a phase change material, antimony and tellurium 3
Use the original compound. Formation methods include Ge, Sb, and Te.
Even when electron beam evaporation using two evaporation sources is used, the recording thin film is formed in an amorphous state. The optical constants of an amorphous state in which only Ge2Sb2Te5 of the above composition was deposited on a glass plate were measured. At a wavelength of 830 nm, the complex refractive index n+k i was 4. 8+1. 3i. When this is heat treated at 300°C for 5 minutes in an inert atmosphere to make it into a crystalline state, it becomes 5. 8+3. 6i, this film was placed on a polycarbonate resin plate (PC, refractive index 1.5).
8) Wavelength 83 before and after heat treatment, that is, in the amorphous state and the crystalline state, in the case of the conventional configuration shown in Fig. 2, in which a resin of the same refractive index is deposited on the top and further coated with a resin having the same refractive index.
FIG. 3 shows the calculated values of the film thickness dependence of the change ΔR in the reflectance (amplitude of reflected light) of 0 nm light and the phase change of the reflected light.

The reflectance and phase of reflected light are calculated using the matrix method from the complex refractive index and film thickness of each layer. Assuming that 1 and the adhesion protective layer 6 have infinite film thickness (ignoring the effect of the base material air interface and the adhesion protective layer-air interface), the reflectance R is the reflectance R of the light incident on the base material. The phase is based on the phase at the interface between the base material 1 and the transparent layer 2. Since the phase is equivalent to a period of 2π, this is taken into account in the diagram.

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

9- Addition Example 1 As an example of the present invention, as shown in FIG. As the transparent layer 2, zinc sulfide (ZnS, refractive index 2°20) was deposited to a thickness of t1 by electron beam evaporation, and as the recording thin film layer 3, the recording thin film Ge2Sb2Te5 shown in Example 1 was deposited by the same method as in Example 1. Then, as a transparent layer 4, ZnS was deposited to the same thickness as t3, and then as a recording thin film layer 5, a recording thin film Ge2Sb2 similar to that shown in Example 1 was formed.
Te5 was deposited to a thickness of t4 in the same manner as in Example 1, and ZnS was further deposited to a thickness of t5 as a transparent layer 6. Gold (Au, refractive index 0.20 + 5.04) was deposited thereon as a reflective layer 7.
i) is formed to a thickness t6=50 nm by electron beam evaporation, and is further coated with a resin having the same refractive index as the base material as a protective layer 6. Let the reflectance (amplitude reflectance) of
d-φW) as the film thickness of each layer t1, t2, t3, t4
, calculated by changing t5. As a result, △φ is almost π
Alternatively, it was found that there exists a film thickness condition where ΔR is close to π/2 and ΔR is close to zero.The conditions and calculation results are shown in Table 1.Table 1 shows the thickness of two recording layers as representative ones. This figure shows the results calculated in 5 nm increments under the condition that t2 = t4.

(The following is a blank space) 21 - Skin - Table 1 (t6 = 50 nm) In order to examine the details in more detail, the absorption of each recording thin film layer was calculated, and when the film thicknesses t2 and t4 were 15 nm or more,
It turns out that the absorption of the two recording thin film layers is different, but below ION nm, they are almost equal (-1) If the absorption is different, the magnitude of the recording state of the two layers differs during recording, and the desired reproduction signal cannot be obtained. Therefore, it is desirable that the two be equal, and from the results of L% or more, it can be seen that by appropriately selecting the thickness of the eight layers, a configuration can be obtained in which there is almost no change in reflectance and only the phase of the reflected light changes. Based on this calculation, the following experiment was conducted to make the base H have a thickness of 1. 2rom-i! Using a PC resin disk with a diameter of 200 mm, a ZnS thin film of 165 nm was deposited by the above method while rotating it in a vacuum, and then a recording thin film of Ge was deposited.
2Sb2Te5 was similarly deposited in an amorphous state to a thickness of 5 nm, a ZnS thin film was further deposited to a thickness of 153 nm, and a recording thin film Ge2Sb2Te5 was similarly deposited to a thickness of 5 nm.
Further, a ZnS thin film was evaporated to a thickness of 71 nm, LAU was evaporated to a thickness of 50 nm, and a multilayer thin film with the same structure was formed to a thickness of 18 x 18 mm and a thickness of 0° 2 mm.
Furthermore, the same PC resin disk was pasted with an ultraviolet curable adhesive to form an adhesive protective layer. Formed an optical recording medium (-) A sample formed on a glass substrate was heated at 300°C for 5 minutes in an argon atmosphere to crystallize the entire surface (7) The fouling rate from the substrate side was measured before and after crystallization. There was no change at about 8% in both cases.9 This medium was rotated and a semiconductor laser with a wavelength of 830 nm was heated at a linear velocity of 10 m/sec with a numerical aperture of 0.5.
Focus on the recording thin film using a men's lens and irradiate the recording thin film with an output of 12 mW at medium 6-frequency 5.
The recording thin film was partially crystallized by irradiating variable light with a MHz modulation degree of 50%, and recording was performed by irradiating it with a continuous output of 1 mW and detecting the reflected light with a photodetector (7 The amplitude of the reproduced signal was observed, and since no change in reflectance was observed due to crystallization in the sample on the glass substrate mentioned above, this reproduced signal was determined by the difference in the reflected light between the recorded and unrecorded areas. It can be seen that this is due to the difference in phase.

Furthermore, when recording and reproducing were performed by changing the frequency of the recorded signal, it was confirmed that the frequency characteristics extended toward higher frequencies compared to the conventional recording thin film configuration with a film thickness of 85 nm as shown in Figure 2. kAlso record the signal and set the linear velocity to 10m.
Similarly, the output of 18 mW was 1 at the thin film surface recorded at 1/sec.
It was confirmed that when the norther was continuously irradiated, the recording thin film melted and changed to an amorphous state, erasing the previously recorded signal.

Example 2 As shown in Fig. 12, the base material has a width of 0°6 μm.
Thickness l, 2 mm, with groove tracks 65 nm deep.
- Using a PC resin disk with a diameter of 200 mm and rotating it in a vacuum, a ZnS thin film of 94 nm was deposited using the above method - Furthermore, a recording thin film of 10 nm was deposited in the same manner as Ge2Sb2Te5.
Z nS was deposited in an amorphous state with a film thickness of m.
A thin film was deposited to a thickness of 177 nm, and a recording thin film Gc2S was added.
Similarly, b2Te5 was formed in an amorphous state with a thickness of 10 nm. Furthermore, a ZnS thin film was evaporated to a thickness of 47 nm. A thin film of LAu was deposited to a thickness of 50 nm. A multilayer thin film with the same structure was formed into a film of 18 x 18 mm and a thickness of 0.2 mm. The same P film was also formed on the glass substrate.
An optical recording medium is formed by pasting C resin disks with an ultraviolet curable adhesive to form an adhesive protective layer.9 The sample formed on the glass substrate is heated at 300°C for 5 minutes in an argon atmosphere to crystallize the entire surface. When the reflectance from the substrate side was measured before and after crystallization, it was approximately 15% and remained unchanged.The medium formed on the resin disk was rotated at a linear velocity of 10 m/s.
A semiconductor laser with a wavelength of 830 nm is focused at a linear velocity of ee using a lens system with a numerical aperture of 0.5, focused on the recording thin film, and irradiated with tracking control on the groove track to generate a circular output of 8.5 mW on the recording thin film surface. Single frequency 5M with output of
Recording was performed by irradiating light modulated with a Hz modulation degree of 50% to partially crystallize the recording thin film.9 Tracking control remained stable even after recording, and the reflected light was further irradiated with a continuous output of 1 mW. When detected by a photodetector and reproduced, the amplitude of the reproduced signal was observed, and since no change in reflectance was observed due to crystallization in the sample on the glass base material described above, this reproduced signal was detected in the recorded area and in the unrecorded area. It can be seen that this is due to the fact that the phase of the reflected light differs depending on the area. It is also confirmed that the phase difference is within a range that does not adversely affect tracking control.

Furthermore, when recording and reproducing were performed by changing the frequency of the recorded signal, it was confirmed that the frequency characteristics extended toward higher frequencies compared to the conventional recording thin film configuration with a film thickness of 85 nm as shown in Figure 2. In addition to recording the signal, the linear velocity was 10 m.
/see is larger than the output during recording on the recording thin film surface19
When similarly continuously irradiated with a laser with an output of mW, it was confirmed that the recording thin film melted and changed to an amorphous state, erasing the already recorded signal. Effects of the Invention According to the present invention, optical Phase change due to unevenness 27 - - Public - Recording equivalent to recording can be performed. Therefore, it is possible to perform high-density recording even though it is a phase change recording, and it is also easily compatible with reproduction discs (audio discs, video discs, etc.) using uneven bits. The reproduction light and the reproduction light from the phase change recording state are equivalent, and the information signal can be reproduced using the same reproduction optical system and signal processing circuit. It is also possible to restore the recorded state to its original state, that is, erase and rewrite, and rewritable phase change recording can be realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a schematic cross-sectional diagram showing the configuration of a conventional example for comparison. FIG. 3 is a schematic cross-sectional diagram showing the configuration of a conventional example. A graph showing the dependence of the phase change on the thickness of the recording thin film, FIG. 4 is a schematic diagram showing another embodiment of the present invention, and FIG. 5 is a schematic cross-sectional diagram showing the structure of another embodiment of the present invention. It is a schematic diagram. 1... 2, 4, 6, 3, 5... 7... 8...

Claims (9)

[Claims] (1) An optical information recording medium in which a recording thin film layer that causes an optically detectable change upon laser beam irradiation is provided on a base material, the recording thin film layer consisting of at least two layers, and a thin film material An optical information recording medium characterized in that its optical constants change upon irradiation with laser light, and the detectable change is mainly due to a change in the phase of reflected light or transmitted light of the incident light. (2) The optical information recording medium according to claim 1, wherein the change in transmitted light amplitude or reflected light amplitude of the incident light is small before and after the change. (3) A first transparent layer, a first recording thin film layer, a second transparent layer, a second recording thin film layer, a third transparent layer, and a reflective layer each having a different refractive index from the base material on the base material. An optical information recording medium having a structure in which the first transparent layer, the first recording thin film layer, the second transparent layer, the second recording thin film layer, the third recording thin film layer and the reflective layer are sequentially provided. 3. The optical information recording medium according to claim 1, wherein the film thickness of the optical information recording medium is selected so that the phase of transmitted light or reflected light of incident light changes when the recording material changes. (4) The optical information recording medium according to claim 1 or 2, wherein the phase change is approximately (1±2n)πn: an integer. (5) An optical information recording medium in which a recording thin film layer that causes an optically detectable change when irradiated with a laser beam is provided on a base material, in which the light incident on the surface of the base material on which the recording thin film layer is provided is The recording thin film layer is made up of at least two layers, and the optical constants of the thin film material change when irradiated with laser light, so that the detectable change is mainly caused by the change in the incident light. An optical information recording medium characterized by a change in the phase of reflected light or transmitted light. (6) The optical information recording medium according to claim 5, wherein the change in transmitted light amplitude or reflected light amplitude of the incident light is small before and after the change. (7) A first transparent layer, a first recording thin film layer, a second transparent layer, a second recording thin film layer, a third transparent layer, and a reflective layer each having a different refractive index from the base material on the base material. An optical information recording medium having a structure in which the first transparent layer, the first recording thin film layer, the second transparent layer, the second recording thin film layer, the third recording thin film layer and the reflective layer are sequentially provided. 7. The optical information recording medium according to claim 5, wherein the film thickness of the recording material is selected so that the phase of transmitted light or reflected light of the incident light changes when the recording material changes. (8) The optical information recording medium according to claim 5 or 6, wherein the phase change is approximately (±1/2±2n)πn: an integer. (9) The optical information recording medium according to claim 1 or 5, wherein the first recording thin film layer and the second recording thin film layer have approximately the same light absorption.