JPH06231487A - Optical information recording medium and optical information recording and reproducing method - Google Patents

Abstract

PURPOSE:To eliminate the unbalance of absorbance by specifying the reflectivity of unrecorded parts to two wavelengths lambda1, lambda2 and the reflectivity of the recording marks formed by irradiation with a laser beam. CONSTITUTION:The structure to satisfy the following optical characteristics (lambda1<lambda2) for the two wavelengths lambda1, lambda2, is determined: The structure has the reflectivity 20%<= R10 <=50%, 15%<=(R10-R11)<=30%, 58% R2o, 40%<=(R20-R21), where R10 is the reflectivity of the unrecorded part to the wavelength lambda10; R11 is the reflectivity to the wavelength lambda1 of the recording marks formed by the irradiation with the laser beam. Protective layers 2, 9, a recording layer 3, a protective layer 4 and a reflection layer 5 are successively formed on a substrate and further, the same PC disk is stuck as the protective substrate 7 by an adhesive 6 thereto. The optical constants of the respective layers are measured. The reflectivity over the entire part of the recording medium is calculated when the film thicknesses are changed from such data, by which the optimum film thickness constitution is determined. The absorbance of light is determined from the energy balance of light at the respective boundaries, by which the variations are eliminated.

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 using a laser beam, and more particularly to a rewritable optical disc.

[0002]

2. Description of the Related Art As an optical disk capable of recording / erasing / reproducing information by irradiating a laser beam, a phase change type optical disk using a chalcogenide as a recording thin film material is known. In general, when the recording thin film material is in a crystalline state, it is set as an unrecorded state, and the recording thin film is melted and rapidly cooled by laser light irradiation to be in an amorphous state to record a signal. On the other hand, in the case of erasing the signal, the recording thin film is heated to a crystalline state by irradiating a laser beam having lower power than that at the time of recording. As the recording thin film material, for example, a material containing Te, In, Sb, Se or the like as a main component, which undergoes a phase change between amorphous and crystal, or a phase change which reversibly occurs between two different crystal structures. It is common to use substances. In order to improve the recording density of information signals, there are means such as shortening the wavelength of laser light used for recording / reproducing or increasing the numerical aperture (NA) of the objective lens.

One of the merits of phase change recording is that an information signal can be overwritten by using only a single laser beam as a recording means. That is, when the laser output is modulated between the recording level and the erasing level according to the information signal and applied to the recorded information track, a new signal can be recorded while erasing the existing information signal. (JP-A-56-145530).

On the other hand, a so-called ROM type optical information recording medium in which information is recorded in advance and data cannot be written or erased thereafter has already been put to practical use in the information processing and music fields. This kind of optical information recording medium does not have the recording layer as described above, and pits for reproducing recorded data are formed in advance on the substrate by means of a press or the like, and Au, A
A reflective layer made of a metal film of g, Cu, Al or the like is formed, and the reflective layer is covered with a protective layer. Typical examples of this ROM type optical information recording medium are a CD (compact disk), a CD-I (interactive compact disk), an LD (laser disk) and the like. Has been converted.

A write-once type optical information recording medium (WORM) which can be reproduced by a CD reproducing device has been proposed (for example, Japanese Patent Laid-Open No. 42652/1990). This is a recording medium having a recording layer made of an organic thin film, and information can be written and reproduced at any time by laser light irradiation.

[0006]

DISCLOSURE OF THE INVENTION An optical information recording medium which can be reproduced by a reproducing apparatus such as a ROM type optical information recording medium, which is already widely used, for example, a CD, an LD, etc., and which can be repeatedly rewritten, and It is very preferable that the recording / reproducing apparatus used for this can be realized. Consider realizing such an optical information recording medium with a phase change type optical disc. In a typical rewritable phase-change type optical information recording medium, the reflectance in the erased state is as low as about 30%, and the modulation degree of the reproduction signal is small. It cannot be played back on the playback device. In order to solve this point, the reflectance of the erased area is set to a high value of around 70% at the reproduction wavelength of 780 nm, and the reflectance of the amorphous area in the recording thin film corresponding to the recording mark is set to 1%.
It may be set as low as around 0% and the signal modulation degree may be increased.

In this case, however, if a laser beam having a wavelength of 780 nm is used as a recording / erasing beam, the light absorption rate of the recording thin film in the erasing portion is about 30%, which is half that of the conventional 70%, and low recording sensitivity. Recording media can only be realized. This means that it is necessary to remarkably improve the performance of the semiconductor laser for recording / erasing light.

An even more important problem is imbalance of the light absorption rate in the erased area and the area where the recording mark is formed. The optical structure in which the erasure area and the area where the recording mark is formed largely differ in reflectivity means that the light absorptances in both areas are largely different. That is,
When overwrite recording is performed, the light absorptance differs between the area where the recording mark existed and the area where it did not exist the previous time, so the new recording mark placed on it has a large shape depending on the presence or absence of the previous recording mark. Distorted. That is, the erasing property is not preferable and the repetitive property is adversely affected.
As described above, an idea of an optical information recording medium which has good repetitive recording / erasing characteristics and which can be reproduced by a conventional ROM reproducing apparatus, and an idea of a recording / reproducing apparatus used for the optical information recording medium have been proposed so far. Absent.

[0009]

[Means for Solving the Problems] A recording / reproducing apparatus equipped with a laser beam having a wavelength λ ₁ shorter than a wavelength near 780 nm used in CDs, LDs and the like, and a phase change type optical information used in this apparatus. A system consisting of a combination with a recording medium is used. Specifically, this recording / reproducing apparatus is an optical information recording medium capable of recording / erasing / reproducing signals, and when a recording mark written by the recording / reproducing apparatus is reproduced at a wavelength of 780 nm, conventional ROM reproduction is performed. 70 playable on device
The optical structure is such that an output signal with a high degree of modulation, which conforms to the CD standard, etc., can be obtained with a high reflectance of around%. at the same time,
In this optical information recording medium, the difference in light absorption rate between the erased area and the recording mark portion is smaller for wavelength λ ₁ than for 780 nm, and the light absorption rate for the erased portion is longer than wavelength λ ₁ . The optical structure in which the case is larger than that for 780 nm, that is, the structure corresponding to two wavelengths. The recording format is RO
The signal format is the same as that of the M-type optical information recording medium.

[0010]

A signal recorded on an optical information recording medium having a dual wavelength structure has high reflectance and modulation when reproduced at a wavelength of 780 nm, so that the signal can be reproduced by a conventional ROM reproducing device. In addition, the optical absorption coefficient is large for the wavelength λ _{1 of} the recording / erasing / reproducing laser light mounted in the recording / reproducing apparatus used in the recording / reproducing system of the present invention, as compared with the case of the wavelength 780 nm. Moreover, since the difference in light absorption between the erased area and the recording mark area is small, good recording and
Repetitive erase characteristics can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

A typical structure example of the recording medium of the present invention is shown in FIG.
Shown in. The laser light for recording, reproducing, and erasing is the substrate 1
Incident from the side.

As the substrate 1, a resin having a smooth surface such as resin such as PMMA or polycarbonate, or glass is used. In the case of an optical disk, the substrate plane 8 is usually covered with spiral or concentric continuous grooves (tracks) for guiding laser light, or with irregularities such as pit rows.

It is desirable that the materials of the protective layers 2, 4 and 9 are physically and chemically stable, that is, have a melting point and a softening temperature higher than the melting point of the recording material and do not form a solid solution with the recording material. For example, Al2O3, SiOx, Ta2O5, MoO3, W
O3, ZrO2, ZnS, AlNx, BN, SiNx, TiN,
It is made of a dielectric material such as ZrN, PbF2, MgF2 or a suitable combination thereof. The protective layer need not be dielectric or transparent. For example, it may be formed of ZnTe having a light absorbing property for visible light and infrared light. Further, when the protective layers 2 and 4 are made of different materials, there is an advantage that the degree of freedom of thermal and optical disk design is increased. Of course, the same material may be used.

The recording thin film 3 is a substance that reversibly changes its structure between a crystalline state and an amorphous state, such as Te or I.
It is made of a phase change material containing n, Se, etc. as main components. The well-known main components of phase change materials are Te-Sb-Ge and Te-
Ge, Te-Ge-Sn, Te-Ge-Sn-Au, Sb-Se, Sb-T
e, Sb-Se-Te, In-Te, In-Se, In-Se-Tl, In
-Sb, In-Sb-Se, In-Se-Te and the like can be mentioned. These thin films are usually formed in an amorphous state, but they absorb energy of laser light or the like to be crystallized and the optical constants (refractive index n, extinction coefficient k) change.

The reflective layer 5 includes Au, Al, Cu, Ni, Fe,
It is made of a metal element such as Cr or an alloy thereof, and functions to enhance the light absorption efficiency of the recording thin film. However, the reflection layer 6 may not be provided by increasing the thickness of the recording thin film 3 to improve the light absorption efficiency. Alternatively, by alternately stacking the recording thin film and the protective layer a plurality of times, it is possible to improve the light absorption efficiency as a whole even if the thickness of one recording thin film is small.

The protective substrate 7 is formed by spin-coating a resin or laminating a resin plate, a glass plate, a metal plate or the like similar to the substrate using an adhesive 6. Further, a structure capable of recording, reproducing and erasing from both sides may be realized by bonding two sets of recording media with the intermediate substrate or the reflection layer inside by using an adhesive.

The recording thin film, the protective layer and the crystallization control layer are usually formed by an electron beam evaporation method, a sputtering method, an ion plating method, a CVD method, a laser sputtering method and the like.

The thickness of the recording thin film 3 is selected so that a part of the incident light can pass through the recording thin film 3 even when the recording thin film 3 is in a crystalline state. When the components reflected by the reflective layer 5 and re-incident in the recording thin film 3 are eliminated, the light interference effect is reduced,
Even if the film thicknesses of the second dielectric thin film layer 4 and the reflective layer 5 are slightly changed, it becomes difficult to control the optical path length, reflectance, absorption in the recording thin film, etc. of the entire medium.

First, second and third protective layers 2, 9, 4
The film thickness of is determined as follows. First, the complex index of refraction of the substances that make up each layer is calculated by the usual method (for example, a method of forming a thin film on a glass plate and calculating based on the measured values of the film thickness, reflectance, and transmittance, or using an ellipsometer). Method). Next, after fixing the thicknesses of the recording thin film 3 and the reflective layer 5, the first, second, and the third methods are performed by the matrix method (see, for example, "Wave Optics" by Hiro Kubota, Iwanami Shoten, 1971, Chapter 3). The thickness of the protective layer of No. 3 is calculated. Specifically, assuming the film thickness of each layer, the balance of light energy is calculated for all interfaces including the surface based on the energy conservation law. That is, by formulating this energy balance equation for each interface in the multilayer medium and solving the obtained simultaneous equations, the incident light of an arbitrary wavelength (actually, the wavelength λ used for reproducing information) can be obtained. The optical path length, the intensity of transmitted light, the intensity of reflected light, and the amount of absorption in each layer can be obtained. By performing the above calculation both when the recording thin film is in the crystalline state and when it is in the amorphous state, the unrecorded area (usually in the crystalline state) and the recorded mark area for the reproduction light of the wavelength λ. It is possible to know the phase difference of the reflected light (which usually applies an amorphous state), the reflectance change ΔR between both regions, the absorption difference between both regions in the recording layer, and the like. In the present invention, two wavelengths λ ₁ and λ ₂ (λ ₂
Is 780 nm), but for λ ₁ <λ ₂ , a structure that satisfies all the following optical characteristics is selected. 1) The reflectance of the unrecorded area is 20% or more for the wavelength λ ₁ .
50% or less. 2) The difference in reflectance between the unrecorded portion and the recorded mark portion with respect to the wavelength λ ₁ is 10% or more and 30% or less. 3) The reflectance of the unrecorded portion is 55% or more for the wavelength λ ₂ . 4) The difference in reflectance between the unrecorded portion and the recorded mark portion is 40% or more with respect to the wavelength λ ₂ .

As an example, a case where the recording thin film 3 is a thin film of Ge ₄₃ Sb ₈ Te ₄₉ ternary material capable of overwriting recording will be described. As a forming method,
An electron beam co-evaporation method using three evaporation sources of Ge, Sb, and Te was used. The recording thin film is formed in an amorphous state. A recording thin film having the above composition was vapor-deposited on a quartz glass substrate, an optical constant (complex refractive index) at each wavelength was measured, and this was heat-treated at 300 ° C. for 10 minutes in an inert atmosphere to obtain a crystalline state. Optical constants were measured at wavelength. It has been confirmed that the optical constant of the crystalline state obtained by the heat treatment is almost equal to the optical constant of the crystalline state obtained by the irradiation of the laser beam. The measurement results of the optical constants at each wavelength (Table 1)
Shown in.

[0022]

[Table 1]

As a base material, a groove track having a width of 1.5 μm and a depth of 62 nm was previously formed, and the heat was 1.2 mm and the diameter was 120 mm.
A C (polycarbonate resin, refractive index 1.58) plate was used. A protective layer 2, a protective layer 9, a recording layer 3, a protective layer 4, and a reflective layer 5 are sequentially formed on this substrate by an electron beam vapor deposition method, and the same PC disk as a protective substrate 7 is glued. An optical recording medium having the combined structure (FIG. 1) is formed. Both protective layer 2 and protective layer 4 are ZnS-20 mol%
SiO _2, protective layer 9 is SiO _2, the reflective layer 5 were formed by Au. When the optical constants of the thin films forming each layer were measured, the results shown in Table 2 were obtained.

[0024]

[Table 2]

When the film thickness of each layer is changed from the data of (Table 1) and (Table 2), the optimum film thickness constitution can be obtained by calculating the reflectance and light absorptance of the entire recording medium. it can. The matrix method was used for the calculation of the complex refractive index of each layer from the film thickness. Further, assuming that the substrate 1 and the protective substrate 7 have infinite film thickness (ignoring the effects of the substrate-air interface and the protective substrate-air interface), the reflectance R is the intensity of light incident from the substrate side and the reflection. Then, it was determined as a ratio with the intensity of light emitted into the substrate. The light absorption rate can be obtained from the energy balance of light at each interface.

Here, two wavelengths λ ₁ and λ ₂ (λ ₂ is 78
0 nm), where λ ₁ <λ ₂ was searched for a structure that satisfies all the following optical characteristics. 1) The reflectance of the unrecorded area is 20% or more for the wavelength λ ₁ .
50% or less. 2) The difference in reflectance between the unrecorded portion and the recorded mark portion with respect to the wavelength λ ₁ is 10% or more and 30% or less. 3) The reflectance of the unrecorded portion is 55% or more for the wavelength λ ₂ . 4) The difference in reflectance between the unrecorded portion and the recorded mark portion is 40% or more with respect to the wavelength λ ₂ .

Assuming that the wavelength λ ₁ is 680 nm and the wavelength λ ₂ is 780 nm, the optimum structure is searched. As a result, one of the solutions is the protective layer 2, the protective layer 9, the recording layer 3, the protective layer 4 , The thickness of the reflective layer 5 is 93 nm, 120 nm, 1 respectively
The cases of 7.5 nm, 12 nm, and 50 nm were obtained (Structure 1). FIG. 2 shows the relationship between the film thickness of the protective layer 2 and the light reflectance in the amorphous and crystalline states when only the film thickness of the protective layer 2 is changed in the recording medium having the above structure. As shown in FIG. 2, when the thickness of the protective layer 2 is about 90 nm,
It turns out that all the conditions are met. A sample was prepared based on this calculation, and the optical characteristics at each wavelength were measured using a spectrophotometer. The measurement results are shown in (Table 3).
However, the crystalline state was obtained by heat treatment at 300 ° C. for 10 minutes in an inert atmosphere. Also, the reflectance at the substrate interface is subtracted. From Table 3, it can be seen that the recording medium is almost as designed.

[0028]

[Table 3]

This recording medium was rotated at a linear velocity of 6 m / s, a semiconductor laser beam having a wavelength of 680 nm was focused by a lens system having a numerical aperture of 0.45, and the groove track was irradiated with tracking control. Focus is intentionally 1 μm from recording thin film
I shifted it. First, the recording thin film surface was irradiated with laser light with a continuous output of 6.5 mW to uniformly crystallize the recording thin film on the track. Laser light output of 11mW on this track
The recording thin film was partially amorphized by irradiating while being modulated at 3.3 MHz between 5 mW and 5 mW to form marks for recording. 1mW continuous output (playback power)
And the reflected light is detected by a photo detector,
When the obtained reproduced signal was measured with a spectrum analyzer, a CN ratio of 53 dB (frequency resolution of 30 kHz, the same applies hereinafter) was obtained. A signal modulated to 0.92 MHz with the same power was recorded on this track, and a new signal was overwritten. When the reproduced signal was measured in this state, a CN ratio of 22 dB at 3.3 MHz was obtained. If 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, the erase rate in this case is -25 dB.
Becomes CN when recording both frequencies alternately and repeatedly
The ratio and the erasing rate were measured, but the change after 1000 times of repeated recording remained at 2 dB or less. Next, a track recorded at a linear velocity of 6 m / s, a wavelength of 680 nm and a recording frequency of 3.3 MHz was set at a linear velocity of 1.3 m / s, and a wavelength of 7
Playback was performed with just focus using an optical pickup with 80 nm and a numerical aperture of 0.45. Linear velocity 1.3m / s is C
At a linear velocity within the standard of D, at this time, the interval between the previously recorded recording marks is 1.8 μm, and the frequency is 0.72 MHz.
(Equal to the frequency of the 3T signal in the CD standard).
The CN ratio at the frequency of 0.72 MHz was 52 dB.

Next, a laser having a wavelength of 780 nm is used for an unrecorded track to change the linear velocity, the recording power, etc. to 1.8.
A signal with a period of μm was recorded, and its recording / erasing / repeating characteristics were examined. As a result, even when the best recording / erasing characteristics are shown, the CN ratio of the first recording mark is 53.
Although it exceeded dB, the first erasure rate was only 18 dB.
Also, there was no recording condition (linear velocity, power, focal position of laser light, etc.) that kept the decrease of the CN ratio of the signal of 1.8 μm period to less than 3 dB after 100 times of repeated recording. . This is useless as a rewritable recording medium. This means that 1) At a wavelength of 680 nm, the difference in reflectance between amorphous and crystalline is small (26% by actual measurement), that is, the difference in light absorption rate in the recording thin film is small (26 by analogy from actual measurement and calculation results).
%), Good erasure / repetition characteristics can be obtained. 2) At a wavelength of 780 nm, the difference in reflectance between amorphous and crystalline is large (49% in actual measurement), that is, the difference in light absorptivity in the recording thin film is large. (By analogy with actual measurement and calculation results, 49
%), It can be explained that good erasing / repeating characteristics cannot be obtained. In practice, it is necessary to discuss the difference in light absorption rate between the amorphous and crystalline recording thin films, but it is difficult to measure the light absorption rate of the recording thin film.
However, when the transmittance of the recording medium is small and the light absorptance of the reflective layer is small, the light absorptance of the recording thin film in each state can be expressed by about (100−reflectance)%, and therefore the light absorptivity of It is reasonable to replace the difference with a difference in reflectance.

The reason why the laser beam is slightly focused on the recording thin film when recording / erasing at a wavelength of 680 nm will be described below. This is because when recording with just focus at a wavelength of 680 nm, the recording mark width becomes narrow, and when reproducing at a wavelength of 780 nm, a sufficient amplitude modulation degree cannot be obtained, and a signal reproduction error remarkably increases. As a result of studying formation of a wide recording mark even when recording at a wavelength λ ₁ (here, 680 nm), the focus of laser light is electrically shifted by means, or the aperture ratio is small (4. It was effective to use an objective lens (smaller than 5) or to restrict the aperture of the objective lens to reduce the substantial numerical aperture, or a combination thereof. At this time,
It is desirable that the recording mark can be formed with a width equal to or wider than the case of recording with just focus at 780 nm and a numerical aperture of 4.5.

Next, music information was recorded on the above recording medium at a wavelength of 680 nm so as to be in the CD format by using a CD encoder. Attempts were made to play this on various commercially available CD players. As a result, about 60% of the CD reproducing devices could reproduce the music information, but the remaining devices were difficult to reproduce. It is considered that this is because the reflectance defined by the CD standard does not reach 70% to 90%. However, for the time being, it was confirmed that an optical information recording medium which can be reproduced by a commercially available CD reproducing apparatus and which can be repeatedly recorded by using another wavelength can be obtained.

Therefore, a phase change type optical information recording medium having a higher reflectance was designed. 630nm as the wavelength λ ₁
As a result of searching for an optimum structure by applying 780 nm to the wavelength λ ₂ , one of the solutions is that the thickness of the protective layer 2, the protective layer 9, the recording layer 3, the protective layer 4, and the reflective layer 5 is 100n each
The cases of m, 120 nm, 25 nm, 12 nm and 50 nm were obtained (structure 2). FIG. 3 shows the relationship between the film thickness of the protective layer 2 and the light reflectance in the amorphous and crystalline states when only the film thickness of the protective layer 2 is changed in the recording medium having the above structure. From FIG. 3, it can be seen that when the thickness of the protective layer 2 is about 100 nm, all of the above four conditions are satisfied. A sample was prepared based on this calculation, and the optical characteristics at each wavelength were measured using a spectrophotometer. The measurement results are shown in (Table 4). However, the crystal state is 300 in an inert atmosphere.
It was obtained by heat treatment at 10 ° C. for 10 minutes. Also, the reflectance at the substrate interface is subtracted. From Table 4, it can be seen that the recording medium is almost as designed.

[0034]

[Table 4]

In the recording medium of (Structure 2), the reflectance of the unrecorded portion (the region where the recording thin film is in the crystalline state) at a wavelength of 780 nm is higher than that of (Structure 1), and is almost 70%. Since the value is a value, it is expected that the ratio compatible with reproduction in a commercially available ROM reproducing device such as a CD reproducing device will further increase compared to (Structure 1). In this case, at the wavelength of 680 nm, the light absorptance of the recording thin film in the unrecorded portion is 50% or less, and therefore the sensitivity of the medium is insufficient, so that the existing evaluation device can sufficiently measure the recording / erasing characteristics. There wasn't. However, since the output of semiconductor lasers is improving day by day, in the near future,
It is a problem that can be overcome, not a principle obstacle. Alternatively, if the wavelength λ ₁ is 630 nm, the light absorptivity is higher, and it is expected that recording can be performed with a smaller output than that using a 680 nm semiconductor laser. here,
Directly on the recording medium of (Structure 2) with a wavelength of 780 nm and an aperture ratio of 4.
Using the pickup of No. 5, the CD format signal was recorded with a just focus and a linear velocity of 6.0 m / s. The signal recorded with the optimum recording power could be reproduced by most commercially available CD reproducing devices. However, in this case, the erase characteristic is not preferable. This is the wavelength 780
In nm, the difference in reflectivity between amorphous and crystalline is large (measured at 4
5%), that is, the light absorption difference in the recording thin film is large (45% by analogy with actual measurement and calculation results), and it can be explained that good erasing / repeating characteristics cannot be obtained. Wavelength 680 nm, in this case, more preferably wavelength 63
When recording / erasing at 0 nm, it is easily expected that better recording / erasing repeating characteristics can be obtained.

As described above, basically, since a signal having a shorter wavelength is recorded / reproduced at a density that can be reproduced at a wavelength of 780 nm, the demand for aberration, noise, etc. of a laser of wavelength λ ₁ is very large. In addition, since the objective lens does not have to have a small aperture ratio, there is an advantage that the optical system can be assembled at low cost.

The structure of the optical information recording medium described so far, the material composition of each layer, the wavelength λ for recording / erasing
_{1. The} recording method and the like are just examples. As long as desired values can be obtained even for optical characteristics, the protective layer between the recording thin film and the substrate may be a single layer, or may be composed of a plurality of layers of three or more layers without any problem. The same applies to the protective layer between the recording thin film and the reflective layer. The material composition of the recording thin film is required to have good recording / erasing repeatability. The wavelength λ ₁ may be selected appropriately,
Also, as the recording linear velocity, a value most suitable for the optical information recording medium may be selected. In order to improve the compatibility with the ROM reproducing device, it is preferable to have a structure in which the reflectance of the unrecorded portion at the wavelength λ ₂ is as high as possible and the reflectance difference is as large as possible. As a result of various studies, if the reflectance of the unrecorded portion at the wavelength λ ₂ is 58% or more and the reflectance difference is 40% or more, it was possible to reproduce with almost half of the CD reproducing apparatuses currently on the market. When the reflectance was 70% or more and the reflectance difference was 50% or more, reproduction was possible with most CD reproducing devices. Further, if the reflectance of the unrecorded portion at the wavelength λ1 is 20% or more and the reflectance difference is 15% or more, a sufficient reproduced signal can be obtained. However, if the reflectance of the unrecorded portion is too high, the recording sensitivity is lowered. Therefore, the reflectance may be at least 50% or less (absorption rate of 50% or more), and desirably 40% or less. It was also found that the difference in reflectance is preferably 30% or less, because the erasing property is deteriorated if the difference in reflectance is too large (that is, the difference in light absorption in the recording thin film is too large).

Further, the recording format is not limited to the CD format, and it is possible to adapt it to various ROM recording information media such as an LD format. This is not limited to the ROM recording information medium that has already been commercially available or has been put into practical use, and may be the format of the optical information recording medium of ROM that will be put to practical use in the future. Of course, in that case, the wavelength λ ₂ is not limited to 780 nm.

Furthermore, the combination of the optical information recording medium of the present invention and the recording / erasing / reproducing apparatus thereof may be configured to have both a high density recording mode and a low density recording mode. This is because when recording in the low density recording mode, recording is performed in a format that can be reproduced by a desired ROM recording information medium reproducing device, and in the high density recording mode, λ ₁ <
This is a method of recording at a higher density by utilizing λ ₂ . In this case, a recording medium for high-density recording / erasing / reproduction and low-density recording / recording conforming to the conventional ROM standard
Rather than preparing two types of recording media dedicated to erasing / reproducing, the same medium can be used for recording / erasing / reproducing in two modes. In the mode of recording at a relatively low density, the focus of the laser beam is electrically shifted by means, or the objective lens having a smaller aperture ratio (less than 4.5) is switched, or A method of limiting the aperture of the objective lens to reduce the substantial numerical aperture, or a combination thereof is effective. 7 for low-density recording mode
It is preferable to record so that a recording mark can be formed with a width equal to or wider than that when recording with just focus at 80 nm and a numerical aperture of 4.5.

[0040]

EFFECTS OF THE INVENTION A signal recorded on an optical information recording medium having a dual wavelength structure has high reflectance and modulation when reproduced at a wavelength of 780 nm, and therefore can be reproduced by a ROM reproducing device which has been conventionally used. In addition, the optical absorption coefficient is large for the wavelength λ _{1 of} the recording / erasing / reproducing laser light mounted in the recording / reproducing apparatus used in the recording / reproducing system of the present invention, as compared with the case of the wavelength 780 nm. In addition, since the difference in light absorption between the erased area and the recording mark area is small, good recording / erasing repetition characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a recording medium according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the film thickness of the first protective layer constituting the recording medium and the reflectance of the recording medium in the recording medium of (Structure 1) of the example of the invention.

FIG. 3 is a characteristic diagram showing the relationship between the film thickness of the first protective layer constituting the recording medium and the reflectance of the recording medium in the recording medium of (Structure 2) of the example of the invention.

[Explanation of symbols]

 1 Substrate 2 First Protective Layer 3 Recording Thin Film 4 Third Protective Layer 5 Reflective Layer 6 Adhesive Layer 7 Protective Substrate 8 Substrate Plane 9 Second Protective Layer

Claims (9)

[Claims] _1. An optical information recording medium used in an apparatus for recording / reproducing information by irradiating a laser beam having a predetermined wavelength λ ₁ , wherein the optical information recording medium comprises a substrate and at least a protective layer on the substrate. , A recording thin film capable of causing a phase change by irradiation with laser light and shifting to a state having different optical constants (complex refractive index), and the reflectance of the unrecorded portion of the optical information recording medium with respect to the wavelength λ ₁ . R ₁₀ and the reflectance R _{11 of} the recording mark formed by the laser light irradiation with respect to the wavelength λ ₁ are 20% ≦ R ₁₀ ≦ 50% and 15% ≦ (R ₁₀ −R ₁₁ ) ≦ 3, respectively.
0%, and the reflectance R ₂₀ of the unrecorded portion for the wavelength λ ₂ longer than the wavelength λ ₁ and the reflectance R _{21 of} the recording mark formed by the laser light irradiation for the wavelength λ ₂ are respectively An optical information recording medium, wherein 58% ≦ R ₂₀ and 40% ≦ (R ₂₀ −R ₂₁ ). 2. The optical information recording medium according to claim 1, wherein the wavelength λ ₂ is 780 nm. 3. 70% ≦ R ₂₀ , 50% ≦ (R ₂₀ −R ₂₁ ).
The optical information recording medium according to claim 1, wherein 4. An optical information recording comprising a substrate, at least a protective layer on the substrate, and a recording thin film capable of undergoing a phase change upon irradiation with a laser beam and having a different optical constant (complex refractive index). By irradiating the medium with laser light of wavelength λ ₁ through the objective lens, the recording thin film is partially changed to record information, and the amount of change is optically detected to reproduce information. in the method, the optical information recording medium, the reflectance R ₁₀ of the unrecorded portion with respect to the wavelength lambda _1, the reflectance R ₁₁ for the wavelength lambda ₁ of the recording mark formed by irradiation of laser light, respectively, 20% ≦ R ₁₀ ≦ 50%, 15% ≦ (R ₁₀ −R ₁₁ ) ≦ 3
0%, and the reflectance R ₂₀ of the unrecorded portion for the wavelength λ ₂ longer than the wavelength λ ₁ and the reflectance R _{21 of} the recording mark formed by the laser light irradiation for the wavelength λ ₂ are respectively 58% ≦ R ₂₀ and 40% ≦ (R ₂₀ −R ₂₁ ), and the effective beam diameter of the laser beam on the recording thin film during recording of information is unique from the laser wavelength λ ₁ and the numerical aperture of the objective lens. An optical information recording / reproducing method characterized by irradiating a laser beam so as to be larger than a minimum beam diameter determined by. 5. An optical information recording comprising a substrate, at least a protective layer on the substrate, and a recording thin film capable of undergoing a phase change upon irradiation with a laser beam and having a different optical constant (complex refractive index). By irradiating the medium with laser light of wavelength λ ₁ through the objective lens, the recording thin film is partially changed to record information, and the amount of change is optically detected to reproduce information. in the method, the optical information recording medium, the reflectance R ₁₀ of the unrecorded portion with respect to the wavelength lambda _1, the reflectance R ₁₁ for the wavelength lambda ₁ of the recording mark formed by irradiation of laser light, respectively, 20% ≦ R ₁₀ ≦ 50%, 15% ≦ (R ₁₀ −R ₁₁ ) ≦ 3
0%, and the reflectance R ₂₀ of the unrecorded portion for the wavelength λ ₂ longer than the wavelength λ ₁ and the reflectance R _{21 of} the recording mark formed by the laser light irradiation for the wavelength λ ₂ are respectively 58% ≦ R ₂₀ , 40% ≦ (R ₂₀ −R ₂₁ ), wherein the numerical aperture of the objective lens is smaller than 4.5. 6. The optical information recording / reproducing method according to claim 4, wherein the wavelength λ ₂ is 780 nm. 7. An optical information recording / reproducing method according to claim 4, wherein the information is recorded in a recording format equivalent to that of a compact disc. 8. An optical information recording comprising a substrate, at least a protective layer on the substrate, and a recording thin film capable of undergoing a phase change upon irradiation with laser light and having a different optical constant (complex refractive index). By irradiating the medium with laser light of wavelength λ ₁ through the objective lens, the recording thin film is partially changed to record information, and the amount of change is optically detected to reproduce information. in the method, the optical information recording medium, the reflectance R ₁₀ of the unrecorded portion with respect to the wavelength lambda _1, the reflectance R ₁₁ for the wavelength lambda ₁ of the recording mark formed by irradiation of laser light, respectively, 20% ≦ R ₁₀ ≦ 50%, 15% ≦ (R ₁₀ −R ₁₁ ) ≦ 3
0%, and the reflectance R ₂₀ of the unrecorded portion for the wavelength λ ₂ longer than the wavelength λ ₁ and the reflectance R _{21 of} the recording mark formed by the laser light irradiation for the wavelength λ ₂ are respectively 58% ≦ R ₂₀ and 40% ≦ (R ₂₀ −R ₂₁ ), and the above-mentioned means for switching the numerical aperture of the objective lens into substantially two steps, large and small, is used. The optical information recording / reproducing method is characterized in that the signal is recorded at a relatively high density, and the signal is recorded at a relatively low density when the numerical aperture is reduced. 9. The optical information recording / reproducing method according to claim 8, wherein when recording at a relatively low density at a wavelength λ ₂ of 780 nm, information is recorded in a recording format equivalent to that of a compact disc.