JPH07169101A - Phase change optical disk only for high density reproduction - Google Patents

Abstract

PURPOSE:To make it possible to store information in a high density by succes sively forming a 1st protective film, a phase change film, a 2nd protective film, a 1st reflecting film, a 3rd protective film and a 2nd reflecting film on a substrate for an optical disk. CONSTITUTION:A 1st protective film made of a ZnS-SiO2 composite film is formed on a substrate for an optical disk and a phase change film made of a material whose crystal structure is varied by heat when irradiated with laser light is formed on the 1st protective film. The crystal structure of the phase change film is an amorphous structure. A 2nd protective film, 1st reflecting film made of Al, etc., in accordance with information to be recorded, a 3rd protective film and a 2nd reflecting film are successively formed on the phase change film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel read-only phase change optical disc and a reproducing method thereof.

[0002]

2. Description of the Related Art In the case of a conventional optical disc in which information is recorded in reproduction-only concave and convex pits as shown in FIG. 3, laser light is applied to the optical disc and the information in the spot narrowed down on the optical disc is recorded. Is a method for reading the difference in the reflectance and the like caused by the difference in the phase difference of the pits. This spot depends on the wavelength of the laser light and cannot be made smaller than the spot diameter determined from the diffraction limit. Therefore, the size of the pit that can be read has a limit depending on the wavelength of the laser beam, and the pit cannot be made smaller than a certain size.
The recording density of optical discs such as D has a limit.

In an optical disc using a phase change material as a recording medium, only the spot portion of the recording layer irradiated with laser light is heated to change the crystal structure of the recording layer (crystal phase → amorphous) for recording. When reproducing, this is a method in which the reflectance changes at the portion where the crystal structure has changed, and that portion is read as one pit. For this reason, even if fine pits are formed by a method such as writing with a writing tip, there is a limit to the size of the pits that can be reproduced as in the case of the above-mentioned optical disc, and thus there is a limit to the recording density.

For the optical disk using the magneto-optical recording medium shown in FIG. 4, the difference between the spot irradiated with the laser beam and the heated area of the rotating optical disk is used. , There is a method of high-density reproduction (publication 3-88156: Sony, etc.).

[0005]

According to this method, it is possible to perform high density reproduction which is 2 to 6 times higher than the conventional one.
Because it is not a method to reproduce the signal by the change in the amount of reflected light,
Since the magneto-optical signal in the minute area is reproduced, a decrease in CN and the like cannot be avoided, and the structure of the optical pickup becomes complicated. Therefore, so far, there is no method of reproducing at high density by changing the amount of reflected light.

[0006]

The structure of the optical disk of the present invention will be described below with reference to FIG. Glass, PMMA,
A first protective film composed of a composite film of ZnS and SiO ₂ is formed on an optical disk substrate (which may have a groove serving as a guide for tracking) made of polycarbonate or the like, and a laser beam is formed thereon. A phase change film made of a material such as TeO _X , InSe, GeTe, Ge ₂ Sb ₂ Te ₅ whose crystal structure is changed by heat upon irradiation is formed. The crystal structure of the phase change film formed by sputtering or the like is an amorphous structure.

A second protective film is formed on this, and a first reflective film made of Al or the like is formed on the second protective film corresponding to the information to be recorded. In this case, the size of the pit to be formed is the size of 1/4 to 1/2 of the spot diameter of the laser to be irradiated (for example, the first reflection is applied only to the portion corresponding to 1 of digital information). A film is formed, and the first reflective film is not formed on other portions).

Thereafter, in some cases, reverse sputtering is performed to etch the surface, and then a third protective film is further formed, and a second reflective film is formed thereon. In this case, the previously formed phase change film has a crystallization structure (hereinafter, single crystal,
The difference in reflectance with respect to the wavelength of the irradiated laser light when a polycrystal is formed or when it is in a high temperature state (crystallized state) regardless of the presence or absence of the first reflective film. Of the second protective film and the third protective film are formed so as to be within 5% (claim 2).

In this case, when the phase change film is in an amorphous state, the difference between the reflectance of the portion where the first reflection film is present and the reflectance when the phase change film is in a high temperature state (crystallized state) is 5
When it is within%, the reflectance changes only in the portion where the phase change film is in the amorphous state and the first reflection film is not present. (Claim 3) Further, when the phase change film is in an amorphous state, the difference between the reflectance of the portion without the first reflection film and the reflectance when the phase change film is in a high temperature state (crystallized state) is When it is within 5%, the reflectance changes only in the portion where the phase change film is in the amorphous state and the first reflection film is present (claim 4).

Referring to FIG. 13, which is a case where ZnS; SiO ₂ is used as the second protective film in the case of claim 3, it will be described with reference to FIG.
When using a semiconductor laser with an emission wavelength of
When information is reproduced with or without a reflective film, ZnS; SiO ₂ (ZnS: SiO ₂ = 4: 1) is used as the protective film, and Ge ₂ Sb ₂ Te ₅ is used as the phase change film. The thickness of the film is 160 to 180 nm, and the thickness of the third protective film is 10 to 70 n.
m or 180 to 250 nm, when the phase change film has a crystallized structure, the reflectance is almost the same regardless of the presence or absence of the first reflective film, and the phase change film has an amorphous structure. In that case, the reflectance of the portion where the first reflective film is present becomes almost the same as the reflectance when the phase change film has a crystallized structure. Therefore, the reflectance changes and the information can be reproduced only when the portion without the first reflective film is in the amorphous state.

Further, in the case of claim 4, which is the case where ZnS; SiO ₂ is used as the second protective film, the same will be described with reference to FIG. Thickness 0 to 50 nm, or 180 to 230 nm, third
The thickness of the protective film is 30 to 150 nm or 220 to 33
Similarly, when the phase change film has a crystallized structure even when it is formed to a thickness of 0 nm, the reflectivity shows a close value regardless of the presence or absence of the first reflective film, and the phase change film has an amorphous structure. In this case, the reflectance of the portion without the first reflection film is almost the same as the reflectance when the phase change film has a crystallization structure. Therefore, unlike the cases of claims 3 and 5, the reflectance changes and information can be reproduced only when the portion having the first reflective film is in an amorphous state (claim 6).

In the opposite case of claim 2, the phase change film is in an amorphous state and the reflectance is the same or reflected with respect to the wavelength of the irradiated laser light regardless of the presence or absence of the first reflection film. Even when the rate difference is within 5%, high density reproduction can be achieved as in the case of claim 2 (claim 7). Next, the optical disk described in claim 9 will be described with reference to FIG. The optical disc according to claim 9 is provided with a thin portion and a thick portion of the recording layer corresponding to information to be recorded, whereby the third protective film and the first reflection film according to claim 1 are provided. It is not necessary to form a film, and an optical disc capable of high density reproduction can be obtained.

Referring to FIG. 14, for example, when a semiconductor laser having an emission wavelength of 780 nm is used as a light source and the material used for the recording layer is Ge ₂ Sb ₂ Te ₅ , the thin portion The film thickness of 50 to 70 nm and the thick portion of 90 to 110 nm are formed,
An optical disc for high density reproduction can be produced by a method similar to the method described in (17).

The forming method in this case is to form a thin film (about 100 nm) over the entire surface of the phase change film on the optical disk having the first protective film formed up to the first protective film. After that, a resist is applied, and patterning is performed by an exposure device so that the resist remains only in the region where the film thickness is increased, and the resist is developed. After that, by RIE, ion beam etching, etc., the thickness of the thin portion of the phase change film is reduced to 63
Etching is performed up to nm. A second protective film and a reflective film are formed on this.

In the optical disc of the tenth aspect, when the phase change film is in a high temperature state (crystallized state), the same reflectance is exhibited regardless of the difference in the film thickness of the phase change film. However, when the phase change film remains in the amorphous state at low temperature, the reflectance in the thin portion of the phase change film shows a relatively high reflectance, but the reflectance in the thick portion of the phase change film decreases. (See FIG. 14). Therefore, since the reflectance of the high temperature portion of the laser light irradiated portion becomes constant, the information is erased, and only the information of the low temperature amorphous portion of the laser light irradiated portion is erased. Can be played.

In this case, the thin portion of the phase change film is in an amorphous state or the thick portion of the phase change film is in an amorphous state, and the reflectance when the phase change film is at a high temperature. When the ratio is the same or the difference is within 5%, the reflectance changes only when either the thick part or the thin part of the phase change film is in an amorphous state. (Claim 12).

In the case where InSe is used for the phase change film, the thin film portion of the phase change film has a reduced reflectance only in the amorphous state. The thin part of 120-130nm, the thick part 1
There is an optical disc having a thickness of 40 to 160 nm (claim 1
4) (see FIG. 15), and when using Ge ₂ Sb ₂ Te ₅ for the phase change film, it is assumed that the reflectance of the thick portion of the phase change film is reduced only in the amorphous state. The thin part of the phase change film is 20 to 50 nm, and the thick part is 60
There is an optical disc having a thickness of up to 90 nm (claim 16).
(See Figure 14).

In the optical disc of the eleventh aspect, when the phase change film is in an amorphous state (low temperature state), the same reflectance is exhibited regardless of the difference in the film thickness of the phase change film. But,
When the temperature of the phase change film is high (crystallized state), the reflectance is low in the thick portion of the phase change film, but high in the portion of the thin phase change film. (See FIG. 14) Therefore,
The reflectance of the low temperature portion (amorphous state portion) of the portion irradiated with the laser light becomes constant, the information is erased, and the information of the high temperature portion of the portion irradiated with the laser light can be reproduced. it can.

In this case, when the thin part of the phase change film or the thick part of the phase change film is in a high temperature state (crystallized state), and when the phase change film is in an amorphous state If the reflectance is the same or the difference is within 5%, the reflectance changes because the phase-change film has a thick portion or a thin portion, which is in a high temperature state (crystallized state).
Only when it becomes (claim 13).

According to the thirteenth aspect, in the case where InSe is used for the phase change film, assuming that the thin portion of the phase change film has a high reflectance only in the high temperature state (crystallized state),
There is an optical disc in which the thin portion of the phase change film has a thickness of 90 to 110 nm and the thick portion has a thickness of 130 to 160 nm (claim 15) (see FIG. 15). When Ge ₂ Sb ₂ Te ₅ is used as the phase change film , The thickness of the phase change film is 50 to 70
There is an optical disc in which a thick portion of 90 nm to 110 nm is formed (claim 17) (see FIG. 14).

[0021]

Next, a method of reproducing the above-mentioned optical disc will be described. Regarding this regeneration method, the optical constant of the phase change film in the high temperature state and the optical constant of the crystallization state are almost equal (from the experimental results, as shown in FIG. 12, as the phase change film, Ge ₂ Sb ₂ Te ₅ When the optical disk using the optical disk is rotated at 1800 RPM and irradiated with laser light, the change in the reflectivity when the power of the laser light is increased and decreased is small, and the change in the reflectivity when the power is decreased is small.
The high temperature state and the crystallization state show almost the same reflectance. ),
Also, the reflectivity changes like a wave as shown in FIGS. 13, 14 and 15 due to light interference when the film thickness of the second protective film or the phase change film is changed. , Which has been confirmed experimentally or by simulation.

The reproducing method according to claim 8 will be described below. According to FIG. 16 showing the relationship between the film thickness of the second protective film and the reflectance, when the film thickness of the second protective film is 170 nm and 230 nm, the phase change film is crystallized. , About 70, showing almost the same reflectance. Further, the portion of the second protective film having a film thickness of 170 nm is about 70 in the amorphous state, and has the same reflectance as the high temperature state (crystallized state) of the phase change film. When the second protective film thickness of 230 nm is in an amorphous state, the reflectance is about 5
It becomes 5.

Therefore, for a phase change optical disc having two types of film thicknesses of the second protective film, there are two states of the phase change film, and thus there are four states in total. Among them, the one having the above film thickness shows the same reflectance in three of the four states, the phase change film is in the amorphous state, and the second protective film thickness is 230 nm. Only when it shows different reflectance.

Therefore, as described in claim 5, the first protective film made of Al or the like is formed on the second protective film having a thickness of 170 nm formed thereon according to the information to be recorded, and the first reflective film is formed thereon. 60 nm thick protective film of No. 3 is formed, and the second
In an optical disc having a reflective film formed on the entire surface, a portion with the first reflective film is a thin portion (170 nm) of the second protective film, and a portion without the first reflective film is a thick portion of the second protective film (second protective film). And the third protective film, the film thickness is 230 nm),
The optical disc conforms to the above case. Therefore, the first
The signal intensity changes and the information is reproduced only when the phase change film is in the amorphous state in the portion where there is no reflection film (claim 5).
(As described above, the amount of reflected light differs depending on the presence / absence of the first reflection film because of the interference between the phase change film and the first reflection film (FIG. 5a), and the interference between the phase change film and the second reflection film ( 5b) .. As described above, the reflectivity changes because the optical constant changes due to the change of the crystal structure of the phase change film. The reproducing method described in 8 will be described by taking the case of using the optical disc described in claim 5 as an example.

While the optical disc having information recorded on the first reflection film is rotated, the focused laser beam is irradiated onto the optical disc. The diameter of the pit (first reflection film) recorded on this disc is about half the spot diameter of the laser light. In this case, in the conventional optical disc, when two or more signals were included in the spot, the information could not be reproduced due to the difference in the amount of light reflected from the spot. For example, the signals included are 10 and 01.
In the case of, it could not be distinguished. However, in the rotating optical disc, by utilizing the difference between the part irradiated with light and the part actually heated, and reproducing only the information of the "and" part, the optical disc of the present invention can be obtained. It can be reproduced at high density.

For example, in the optical disc according to the fifth aspect, in the heated region of the portion irradiated with the laser beam, the temperature becomes high and becomes almost the same as the crystallized state, and the reflectance becomes high. In the crystallized state of this phase change film, the first
It exhibits the same reflectance regardless of the presence or absence of a reflective film. this is,
This is because the irradiated laser light has the same influence due to the interference between the reflection film and the phase change film, and the wavelengths of the laser light sources used are different, so that the second protective film and the third protective film have different wavelengths. The film thickness is different. Therefore, in the portion where the temperature becomes high, the information of the first reflective film in which the information is recorded can be erased.

Of the portion irradiated with laser light,
Since the crystal structure of the phase change film in the unheated part remains the amorphous structure, the part where the first reflective film is present (the part where the back protective film thickness is 170 nm) is as shown in FIG. 5a. Shows the same reflectance as the heated portion due to the interference between the phase change layer and the first reflection film, but in the portion without the first reflection film (the portion where the back surface protective film thickness is 230 nm), 5b, the phase change layer and the second
The reflectance decreases due to the interference with the reflection layer (see FIGS. 5 and 1).
3).

As described above, in the information recorded on the first reflective film, the information of the high temperature region of the portion irradiated with the laser beam is erased, and the low temperature portion (the portion where the phase change film is in the amorphous state) is erased. Only information can be played. Therefore, since the area smaller than the spot irradiated with the laser light is reproduced, high density reproduction is possible. Also, the first
When the reflective film is made of Al or the like, the heat in that part may be diffused to give a thermal contrast, but the third protective film is formed on the reflective film, and the thermal conductivity of Al or the like. Is large and the thermal capacity is also small, the influence of heat diffusion due to the presence or absence of the first reflective film does not occur.

After the information is reproduced, the power and irradiation time of the laser light to be irradiated may be optimized or the laser light for erasing may be irradiated in order to make the phase change layer have an amorphous structure. (Claim 19). Furthermore, by optimizing the "deviation" between the light spot and the high temperature part,
You can also play smaller pits.

The optical discs described in claims 1 to 4, 6 and 7 are also reproduced by the same method as described above.
The reproducing method according to claim 18 will be described below. According to FIG. 17 showing the relationship between the film thickness of the phase change film (Ge ₂ Sb ₂ Te ₅ ), and the reflectivity, the phase change is observed between the part where the film thickness of the phase change film is 63 nm and the part where the film thickness is 100 nm. When the film is in an amorphous state, it is about 56, and the reflectance is almost the same. Further, in the state where the portion of the phase change film having a thickness of 100 nm is crystallized (high temperature state), the reflectance is about 57, which is almost the same as when the phase change film is in the amorphous state. At this time, when the thickness of the phase change film is 63 nm and the phase change film is in the crystallized state (high temperature state), the reflectance is about 89. Therefore, in a phase change optical disc having two types of phase change film thicknesses, there are two types of phase change film states, and therefore there are four states in total. Of these, in the case of the above configuration, 4
Three of the three states show almost the same reflectance, the phase change film is in a high temperature state, and the thickness of the phase change film is 63 nm.
Shows the different reflectance only. Therefore, by forming a thin portion of the phase change film with a thickness of 63 nm and a thick portion with a thickness of 100 nm as in the optical disc according to claim 17, the thickness of the phase change film is 63 nm, The signal strength changes and the information is reproduced only when the temperature becomes high temperature (crystallized state). (As described above, the reflectivity varies depending on the film thickness of the phase change film, because the interference between the phase change film and the reflective film causes
This is because the optical path difference is different depending on the film thickness of the phase change film. ) Hereinafter, based on the above matters, the reproducing method described in claim 18 will be described by taking the case of using the optical disc described in claim 17 as an example.

An optical disc in which portions of the phase change film having film thicknesses of 63 nm and 100 nm are formed corresponding to 1 and 0 of recorded digital information is reproduced by a method similar to the method described in claim 8. At this time, the phase change film is in an amorphous state in the part which is not in the high temperature state in the part irradiated with the laser beam, and the reflectance of the thick part and the thin part of the phase change film are almost the same. Therefore, the recorded information cannot be read due to the difference in the thickness of the phase change film.

However, when the phase change film in the portion irradiated with the laser beam is in a high temperature state (crystallized state), the reflectance varies depending on the film thickness of the phase change film, and the thick portion of the phase change film is amorphous. The reflectance is almost the same as in the case of the state, but the reflectance is high in the portion where the phase change film is thin, and the information can be read. Therefore, the information can be read out only in the high temperature region of the portion irradiated with the laser beam, and the information recorded due to the difference in the film thickness of the phase change film is
It will be reproduced while being exposed to heat. Therefore, the information is reproduced only in the portion irradiated with the laser beam and having a high temperature, so that high-density reproduction is possible.

The optical discs described in claims 9 to 16 can be reproduced by the same method as above. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0034]

Embodiment 1 Hereinafter, an example of the invention described in claim 5 among the inventions described in claims 1 to 7 will be shown. Diameter 130
A circular glass substrate of mm is prepared. The first layer made of ZnS; SiO _{2 on} this substrate by RF magnetron sputtering.
A protective film is formed to a thickness of about 100 nm. At this time, ZnS; SiO ₂ was used as a target, and after evacuating the chamber of the sputtering apparatus to 1 × 10 ⁻⁶ Torr or less, Ar gas was introduced to make the gas pressure in the chamber 5 × 10 ^−3. As Torr,
Sputtering is performed.

Next, a phase change film made of Ge ₂ Sb ₂ Te _{5 is formed} on the surface of the same by RF magnetron sputtering in the same amount as about ₂₅ n.
m. The target used in this case is Ge ₂ Sb ₂ Te.
_5, and the conditions of the sputtering apparatus, ZnS; are the same as in the case of SiO _2. The phase change film immediately after being formed has an amorphous structure, although it depends on the conditions and the like.

On top of this, as a second protective film, ZnS; SiO
_A film of _{2 is} formed to a thickness of about 170 nm. The formation conditions are the same as those for the first protective film. Further, a first reflective layer is formed on the first reflective layer corresponding to the information to be recorded. In this case, the first reflection film is formed on the portion corresponding to 1 of the recorded digital information, and the first reflection film is not formed on the portion corresponding to 0. The method for forming the first reflective film is as follows:
After forming the Al film by sputtering, applying photoresist, exposing and developing,
The resist of the portion corresponding to is left. The pattern of this resist is such that a resist having a diameter of 0.4 μm is formed with a minimum interval of 0.4 μm.
After that, the Al film in the portion without the resist is removed by dry etching such as RIE, and then the resist is removed with an organic solvent such as acetone. The Al film is formed using an Al target and sputtering with Ar gas. The other forming conditions are the same as in the previous case.

A third protective film made of ZnS; SiO _{2 is} formed thereon to a thickness of about 60 nm, and a second reflective film made of Al is formed thereon to a thickness of about 50 nm. It is formed by hardening it on this with an ultraviolet curable resin or the like.

[0038]

[Embodiment 2] Hereinafter, an example of the invention described in claim 17 will be shown among the inventions described in claims 9 to 17. Diameter 13
A 0 mm glass circular substrate is prepared. A first protective film of ZnS; SiO _{2 is} formed to a thickness of about 100 nm on this substrate by RF magnetron sputtering. At this time, ZnS; SiO ₂ was used as a target, and after evacuating the chamber of the sputtering apparatus to 1 × 10 ⁻⁶ Torr or less, Ar gas was introduced to make the gas pressure in the chamber 5 × 10 ^−3. As Torr,
Sputtering is performed. Next, similarly, a phase change film made of Ge ₂ Sb ₂ Te _{5 is} formed to a thickness of about 100 nm by RF magnetron sputtering. The target used in this case was Ge ₂ Sb ₂ Te ₅ , and the conditions in the sputtering system were Zn.
S: The same as in the case of SiO ₂ .

The phase change film immediately after being formed has an amorphous structure, depending on the conditions and the like. After this,
Photoresist is applied, and exposure and development are performed so that the resist remains in the portion where the phase change film becomes thicker, corresponding to the information information to be recorded. The pattern of this resist is
A resist having a diameter of 0.4 μm is formed with a minimum interval of 0.4 μm.

Next, by RIE, ion beam etching, etc., the thickness of the phase change film in the resist-free portion is 63 n.
Etch to m. Then, after removing the resist with an organic solvent such as acetone, a second protective film made of ZnS; SiO _{2 is formed} to a thickness of about 100 nm, and a reflective film made of Al is formed to a thickness of about 50 nm. The method of forming the reflective film is the same as that of the first embodiment. Further, an optical disc is formed by hardening it on this with an ultraviolet curable resin.

[0041]

[Embodiment 3] The invention of the reproducing method described in claim 8 will be explained by taking the case of reproducing the optical disk described in the embodiment 1 as an example. Light source is λ = 780 nm, aperture ratio (NA)
= 0.55, and a semiconductor laser and an optical system such as a lens.

The reproducing system is composed of a detector such as a photodiode and an optical system for sending light to the detector. The optical disk described in Example 1 is rotated by a rotating system, and laser light is emitted from a light source. Since the optical disc is recorded at a constant linear velocity, the rotating system
The number of rotations is low when reading a portion away from the central portion. The laser light is focused on the recording layer of the optical disc by passing through the optical system,
The spot diameter was determined from the diffraction limit and was about 1.4 μm. In the high temperature region of this spot, there is no difference in reflectance due to the presence or absence of the first reflective film, and the recorded information is erased. Further, in the region where the temperature is not high, the phase change film is in an amorphous state and the reflectance differs depending on the presence or absence of the first reflective film. At this time, the reflectance of the portion without the first reflection film is almost the same as the reflectance when the phase change film is in a high temperature state (crystallized state).

Therefore, when there is a portion having the first reflection film in a region of the spot where the temperature is not high, the reflectance of the entire spot is lowered, and in other cases, the reflectance is changed. There is no. Therefore, due to this difference in reflectance,
It is possible to read only the information of the region in the spot where the phase change film is in the amorphous state.

The difference in the reflectance of the optical disk within this spot is converted into an electric signal by passing through a detector. Depending on the magnitude of this electric signal, one of the digital signals,
It is possible to judge 0. As described above, the information recorded on the optical disc of Example 1 is determined by the presence or absence of the first reflective film, and the diameter of the portion where the first reflective film is formed and the portion where the first reflective film is not formed are smaller than the spot diameter of the laser light. Therefore, the region where the crystal state of the phase change film changes within the spot is smaller than the spot, and it is possible to reproduce pits that are sufficiently smaller than the spot of laser light that could not be reproduced conventionally.

[0045]

As described above, according to the read-only phase change optical disk of the present invention, it is possible to reproduce a pit smaller than the spot diameter of the laser beam, which cannot be reproduced conventionally. Therefore, the recording density per unit area can be increased. Further, since the portion to be reproduced is the "and" portion of the portion irradiated with laser light and the portion heated by it, a high SN and cross is achieved for the optical disc having the same recording density as the conventional one. A reproduced signal with less talk can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a phase change optical disc according to the first aspect of the invention.

FIG. 2 is a cross-sectional view of a phase change optical disc according to a ninth aspect of the invention.

FIG. 3 is a sectional view of a conventional read-only optical disc.

FIG. 4 is a cross-sectional view of a high-density read-only magneto-optical disk described as a conventional example.

FIG. 5 is a diagram showing how light is reflected in the phase change optical disk of the invention described in claim 5. “A” represents a state of interference between the phase change film and the first reflective film, and “b” represents a state of interference between the phase change film and the second reflective film.

FIG. 6 is a diagram showing how light is reflected in the phase change optical disc of the invention described in claim 17; a is
The state of light interference between the phase change film and the reflection film in the thin portion of the phase change film, and b represents the manner of light interference between the phase change film and the reflection film in the thick portion of the phase change film.

FIG. 7 is a portion of the laser spot in a low temperature state (the phase change film is in an amorphous state) when the phase change optical disk of the invention described in claim 5 is reproduced by the reproduction method described in claim 8. It is explanatory drawing in the case where there is a pit (1st reflective film) in FIG.

FIG. 8 is a description of a case where the phase change optical disk of the invention described in claim 5 is reproduced by the reproduction method described in claim 8 when there is no pit in the low temperature portion of the laser spot. It is a figure.

FIG. 9 is a diagram showing the phase change optical disk of the invention described in claim 17, when reproduced by the reproduction method described in claim 18, wherein pits (areas where information is recorded) are formed in a high temperature area of the laser spot. It is explanatory drawing in a certain case.

FIG. 10 shows a case where a phase change optical disc of the invention described in claim 17 is reproduced by the reproduction method described in claim 18, in which a pit (a region where information is recorded) is formed in a high temperature region of the laser spot. It is explanatory drawing in the case of not being.

FIG. 11 is an explanatory diagram of the invention described in claim 19;

FIG. 12 shows a laser irradiated when a Ge ₂ Sb ₂ Te ₅ is used as a phase change material and ZnS; SiO ₂ is formed as a protective film on both surfaces of the optical disk when the optical disk is rotated at 1800 RPM and irradiated with laser light. It is a figure showing the relationship between the change (rise, fall) of the power of light, and reflectance.

FIG. 13 is a diagram showing the relationship between the film thickness of the second protective film and the reflectance at a wavelength of 780 nm when Ge ₂ Sb ₂ Te ₅ is used as the phase change material and ZnS; SiO ₂ is used as the protective film (Reference) More quote).

FIG. 14 is a diagram showing the relationship between the film thickness of the phase change film and the reflectance at a wavelength of 780 nm when Ge ₂ Sb ₂ Te ₅ is used as the phase change material and ZnS; SiO ₂ is used as the protective film.

FIG. 15 shows the film thickness of the phase change film and the wavelength of 780 n when InSe is used as the phase change material and SiO ₂ is used as the protective film.
It is a figure (quoted from the literature) showing the relationship with the reflectance in m.

FIG. 16 is a diagram for explaining the optical disc of claim 5 described in the operation of claim 8.

FIG. 17 is a diagram for explaining the optical disc of claim 17 described in the operation of claim 18; that's all

Claims (19)

[Claims] 1. A recording is made on a first protective film made of a dielectric material, a phase change film having a different reflectivity due to a difference in crystal structure or a phase structure, and a second protective film laminated on a substrate. Providing the first reflective film corresponding to the information to be
A phase change optical disk comprising a third protective film and a second reflective film formed thereon. 2. When the phase change film is in a crystallized state or in a high temperature state, the reflectance difference is within 5% with respect to the wavelength of the irradiated laser light regardless of the presence or absence of the first reflective film. The phase change optical disc according to claim 1, wherein 3. The reflectance of the phase change film in the crystallized state or the high temperature state with respect to the laser light irradiated,
A difference in reflectance of a portion of the phase change film in the amorphous state where the first reflective film is present is within 5%, and
3. The phase change optical disc according to claim 2, wherein a difference in reflectance difference between the phase change film and a portion without the first reflection film in the amorphous state is 5% or more. 4. The reflectance of the phase change film in the crystallized state or high temperature state and the reflectance of a portion of the phase change film in the amorphous state without the first reflection film with respect to the irradiated laser light. 3. The difference according to claim 2, wherein the difference is within 5%, and the difference in reflectance between the phase change film and a portion where the first reflection film is present in the amorphous state is 5% or more. Phase change optical disc. 5. The second protective film and the third protective film are both Zn.
S; SiO ₂ (ZnS: SiO ₂ = 4: 1), the second protective film has a thickness of 160 to 180 nm, and the third protective film has a thickness of 10 to 70 nm. The phase change optical disk according to claim 3, wherein the optical disk has a thickness of 180 to 250 nm. 6. The second protective film and the third protective film are both Zn.
S; SiO ₂ (ZnS: SiO ₂ = 4: 1), the thickness of the second protective film is 0 to 50 nm or 180 to 230 nm, and the thickness of the third protective film is 30-150 nm or 220
The phase change optical disk according to claim 4, wherein the phase change optical disk has a thickness of ˜330 nm. 7. The phase change film is in an amorphous state, and the difference in reflectance is within 5% with respect to the wavelength of the irradiated laser light regardless of the presence or absence of the first reflective film. The phase change optical disk according to claim 1. 8. A laser beam is irradiated to heat the phase change layer to change from an amorphous state to a high temperature state or a crystallized state, and the reflectance in the heated portion is changed to the first state. The difference in reflectance between the portion with the first reflection film and the portion without the first reflection film in the amorphous portion of the laser spot is measured by the fact that they are almost the same regardless of the presence or absence of the reflection film. 7. The phase change optical disk according to claim 1, which is detected by a detector or the like and converted into an electric signal. 9. The first reflective film and the third protective film are not formed, and the film thickness of the phase change layer is formed to be different depending on the information to be recorded. The phase change optical disk according to claim 1. 10. The difference in reflectance between the thick portion and the thin portion of the phase change film with respect to the irradiated laser light is:
The phase change optical disk according to claim 9, wherein the content is within 5% in a high temperature state (crystallized state). 11. The difference in reflectance between the thick portion and the thin portion of the phase change film with respect to the irradiated laser light is:
The phase change optical disk according to claim 9, wherein the content is within 5% in an amorphous state. 12. The reflectivity when the phase change film is in a crystallized state (crystallized state) and the film thickness of the phase change film is a thick portion or a thin portion with respect to the irradiated laser light. 11. The phase difference according to claim 10, wherein a difference in reflectance when one of the two is in an amorphous state is within 5%, and a difference in reflectance with the other is 5% or more. Change optical disc. 13. With respect to the laser light to be irradiated, the reflectance when the phase change film is in an amorphous state and the thickness of the phase change film is high in either a thick part or a thin part. The difference in reflectance when in the state (crystallized state) is within 5%, and the difference in reflectance with the other is 5%.
The phase change optical disc according to claim 11, wherein the optical disc has a content of at least%. 14. The phase change film is formed of InSe, and the thin part of the phase change film has a thickness of 120 to 130 nm, and the thick part has a thickness of 140 to 160 nm. 13. The phase change optical disc according to claim 10, wherein the optical disc is a phase change optical disc. 15. The phase change film is formed of InSe, the thin part of the phase change film has a thickness of 90 to 110 nm, and the thick part has a thickness of 130 to 160 nm. The phase change optical disk according to claim 11 or 13, characterized in that 16. The phase change film is formed of Ge ₂ Sb ₂ Te ₅ , and the thin part of the phase change film has a thickness of 20 to 50 n.
The phase change optical disk according to claim 10 or 12, wherein the thickness of the thick portion is 60 to 90 nm. 17. The phase change film is formed of Ge ₂ Sb ₂ Te ₅ , and the thin part of the phase change film has a thickness of 50 to 70 n.
The phase change optical disk according to claim 11 or 13, wherein m and the thickness of the thick portion are 90 to 110 nm. 18. A signal is read by a difference in reflectance due to a difference in film thickness of the phase change film when the phase change film is in either a high temperature state (crystallized state) or an amorphous state. And a method for reproducing a phase change optical disc. 19. A method for reproducing a phase-change optical disk, wherein the phase-change film after reproduction is changed from a crystallized state to an amorphous state by irradiating an erasing laser beam after reproduction.