JPH07105574A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To obtain a phase shift type optical information recording medium capable of forming a recording mark faithful to an information signal on the recording layer even in the case of overwriting with a single beam. CONSTITUTION:This optical information recording medium is composed of a polycarbonate resin substrate 1, a light absorbing layer 4 of Ti having 10nm thickness, a 1st protective layer 5 of ZnS-20mol% SiO2 mixture having 180nm thickness, a recording layer 2 of an Sb-Te-Ge alloy having 25nm thickness, a 2nd protective layer 6 made of the same material as the 1st protective layer and having 20nm thickness and a reflecting layer 3 of Al different from Ti in heat conductivity. Since the light absorption factor of the recording layer in a crystalline state can be made higher than that in an amorphous state by the presence of the light absorbing layer, a shift in the position of a recording mark and ununiformity in length are hardly caused in the case of overwriting with a single beam. Since the material of the light absorbing layer and that of the reflecting layer are different from each other in heat conductivity, both recording and erasing can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a reversible phase change between a crystalline state and an amorphous state due to light irradiation to record a new optical information recording / erasing / reproducing information. The present invention relates to a medium, and more particularly to an optical information recording medium capable of overwriting information and recording information at a high density.

[0002]

2. Description of the Related Art As an optical information recording medium capable of repeatedly recording information by irradiating a laser beam, a magneto-optical disk utilizing the rotation of the plane of polarization of light reflected by a perpendicular magnetization film or an amorphous state is used. Phase-change type optical discs and the like, which utilize the difference in the optical characteristics of the recording film material in the crystalline state, have already been put into practical use.

These discs record information by heat generated by absorption of irradiated laser light in the film. In addition to this, the state and structure of the recording material is changed by the action of light. As a so-called photon mode recording material to be changed, there are photochromic materials, photochemical hole burning materials and the like, which are being researched as future high density recording materials.

Among such optical information recording media, the phase change type optical disk has a recording layer made of a material in which a phase change between a crystalline state and an amorphous state is reversible by light irradiation. It has an excellent feature that recording and erasing can be performed with a simple optical system, and so-called overwriting of recording new information at the same time while erasing already recorded information can be easily performed.

Generally, in a rewritable phase change type optical disk, the amorphous state in the recording layer is the recorded state and the crystalline state is the erased state. That is, information is recorded by irradiating a recording level laser beam to a temperature higher than the melting point and then rapidly cooling to form an amorphous recording mark according to a signal indicating information, and erasing is performed. The amorphous recording marks are crystallized by raising the temperature to the crystallization-enabling temperature below the melting point by irradiating the erasing level laser beam and then gradually cooling. And
The recorded signal is reproduced by detecting the change in the amount of light reflected from the disk by utilizing the difference in the reflectance between the amorphous part and the crystal part and the difference in the phase of the reflected light.

In a conventional phase change type optical disk, as shown in FIG. 5, a reflection layer 3 made of Al alloy or the like is laminated on the recording layer 2 to utilize the interference effect,
The contrast between the recording mark and the erased portion of the recording layer 2 is increased. Further, recently, as shown in FIG. 6, in order to prevent thermal deformation of the substrate 1, a first protective layer 5 made of a dielectric material is provided between the recording layer 2 and the substrate 1, and the recording layer 2 is provided. In order to prevent the reaction between the reflective layer 3 and the reflective layer 3 and the diffusion of the recording layer material, the recording layer 2 and the reflective layer 3
A four-layer structure in which a similar second protective layer 6 is provided between and is also mainstream because it is suitable in terms of recording / erasing characteristics.

In recent years, the overwrite method has also been changed from the conventional multi-beam method using separate laser beams for recording and erasing to changing the laser power between the recording level and the erasing level according to the information signal. The single-beam method in which a single laser beam modulated in stages is used is the mainstream. In this single-beam method, the portion of the recording layer irradiated with the laser beam having a high recording level power by the laser beam modulated as described above is heated to a temperature higher than the melting point, melted once, and then rapidly cooled. By doing so, an amorphous recording mark is formed. On the other hand, the portion irradiated with the laser beam of the erase level power (power lower than the recording level) is heated to a crystallizable temperature below the melting point and then gradually cooled to form an amorphous recording mark. Be crystallized. According to this method, a new recording mark train is formed by a single laser beam scan regardless of the previously recorded amorphous recording mark train.

[0008]

As described above, according to the overwriting by the single beam method, it is possible to record new information at the same time while erasing old information with one scanning of the laser beam. However, there are two types of portions where the recording marks are formed by this scanning, that is, the recording portions in the previous scanning are in an amorphous state and the erased portions are in a crystalline state. . Here, since the crystalline state generally has a higher thermal conductivity than the amorphous state, the heat dissipation in the recording layer is larger in the portion in the crystalline state. In addition, latent heat is required to melt the crystalline portion. From these facts, it takes more energy to form a predetermined recording mark in the crystalline state portion that was the previously erased portion than in forming the equivalent recording mark in the amorphous state portion that was the previous recording portion. Is required.

However, in the conventional phase change type optical disk having the structure shown in FIGS. 5 and 6, the laser light reflectance in the recording layer is higher in the crystalline state portion than in the amorphous state portion, and the absorptivity is higher. The crystalline state portion is lower than the amorphous state portion. That is, as described above, a laser that is converted into heat necessary for forming a recording mark, though the crystalline state portion requires more energy in order to form an equivalent recording mark, The amount of light absorbed in the crystalline state portion is smaller than that in the amorphous state portion. Therefore,
Even if the laser light of the same recording level is applied to the recording portion in this laser light scanning, the temperature of the portion that was in the crystalline state by the previous scanning is higher than the temperature of the portion that was in the amorphous state by the previous scanning. There was a phenomenon that it became too low.

As described above, when the temperature rise degree of the recording layer portion which should be the same recording portion in the current scanning differs depending on the previous recording state, the formed recording marks become uneven in size, There is a problem that a recording mark is formed at a position deviated from the position of, or an unerased portion of previously recorded information occurs.

Such positional deviations and irregular lengths of the recording marks impede the accurate reproduction of information and cause an error in high density recording. Particularly, in a high-density recording / reproducing method called mark edge recording in which the positions of the front end and the rear end of the recording mark are recorded as information, it is necessary to accurately control the length of the recording mark and the front and rear end positions. The present invention has been made in view of the above-mentioned problems of the prior art. Even in the case of overwriting with a single beam, it is possible to form a recording mark faithful to an information signal on a recording layer. The purpose is to provide an information recording medium.

[0012]

In order to achieve the above object, an optical information recording medium according to a first aspect of the present invention, as shown in FIG.
A transparent substrate 1 and formed on one surface of the substrate 1,
A recording layer 2 made of a material in which a phase change between a crystalline state and an amorphous state is reversible by light irradiation, and the recording layer 2
An optical information recording medium comprising at least a reflective layer 3 formed on the surface opposite to the substrate 1.
And a recording layer 2, a light absorbing layer 4 made of a light absorbing material having a thermal conductivity different from that of the reflecting layer is provided.

As a material for the light absorbing layer 4, as described in claim 2, a metal, a semimetal, or a semiconductor is preferable from the viewpoint of durability against repeated recording and erasing. As described in Item 3, Al, T
i, Cr, Ni, Cu, Si, Ge, Ag, Au, P
It is more preferable to use an element selected from the group consisting of d, Ga, Se, In, Sn, Sb, Te, Pb, and Bi, or an alloy containing an element selected from this group.

Regarding the film thickness of the light absorption layer 4,
If it is too thick, most of the incident light is consumed for absorption and reflection in the light absorbing layer, the amount of transmitted light reaching the recording layer 2 becomes small, and not only the recording sensitivity decreases but also the recording layer. The contrast of the reflectance between the recorded portion and the erased portion is also lowered, which is not preferable. Therefore, the thickness of the light absorption layer 4 varies depending on the material used, but is 5 nm.
It is preferably at least 50 nm.

For the substrate 1, a conventionally known material such as polycarbonate resin, PMMA or glass is used. Further, as the material forming the reflective layer 3,
Al, Ti, Cr, Ni, Cu, Si, Ge, Ag, A
Examples of the material include u, Pd, Pt, and the like. Among them, a material having a thermal conductivity different from that of the material forming the light absorption layer 4 is selected and used.

In the optical information recording medium of the present invention, as shown in FIG. 2, a first protective layer 5 made of a dielectric material is recorded between the recording layer 2 and the substrate 1 if necessary. A similar second protective layer 6 is provided between the layer 2 and the reflective layer 3 to form a five-layer structure, and the first and second protective layers 5 and 6 are provided as required. As the material, one or a mixture of metal or metalloid selected from oxides, carbides, nitrides, fluorides, and sulfides is used.

Here, the optical absorptance of the recording layer 2 is uniquely determined by the optical constants of the materials forming these layers and the film thickness thereof, and as will be described later, in the present invention, the optical absorptivity of the recording layer 2 is determined. The problem is solved by the action that the absorption rate in the crystalline state is larger than that in the amorphous state. Therefore, in the optical information recording medium of the present invention,
The recording layer 2, the reflective layer 3, the light absorbing layer 4, the first protective layer 5, and the second protective layer so that the light absorption rate in the recording layer 2 is higher in the crystalline state than in the amorphous state. It is necessary to select each material for forming 6 and set the film thickness of each layer.

Further, as a method for forming each layer, a conventionally known vapor deposition method, sputtering method or the like can be mentioned. In the optical information recording medium of the present invention, S is used as the recording layer 2.
A disc provided with a phase-change recording material containing b-Te-Ge as a main component is particularly preferable as an optical disc for high-density recording / reproduction.

[0019]

In the optical information recording medium according to the present invention, since the light absorbing layer is provided between the substrate and the recording layer, the light incident on the disc is multiplexed between the light absorbing layer and the reflecting layer. Since the light is reflected, the light absorption coefficient in the recording layer can be made higher than that in the amorphous state by appropriately selecting the material and film thickness of each layer. Thereby, when the recording layer having the crystalline state portion and the amorphous state portion is irradiated with the laser beam of the same recording level, the crystalline state portion has a higher light absorption rate than the amorphous portion, The crystalline portion absorbs more laser light that is converted into heat. Therefore, in the crystalline state portion, the extra energy required due to the influence of the above-mentioned thermal conductivity and latent heat is offset, so that whether the previous recording state was the crystalline state portion or not by the laser beam of the same recording level. Regardless of whether it is a crystalline state portion, an equivalent new recording mark (amorphous portion) faithful to the information signal is formed.

Further, since the light absorption layer is made of a material having a different thermal conductivity from that of the reflection layer, proper heat dissipation from the recording layer is performed, and high performance is obtained in both recording and erasing. To be That is, when forming the recording mark,
In order for the recording layer to become amorphous, it is necessary to solidify the molten recording layer by quenching so that each atom forming the recording layer does not move freely and give time to form a crystal lattice. is there. On the other hand, in order to crystallize and erase the amorphous portion, the temperature required for crystallization (crystallization temperature) so that each atom that constitutes the recording layer can move freely to form a crystal lattice.
It is necessary to keep the temperature above the melting point for a certain period of time or more. Therefore, if it is too rapidly cooled, the amorphization is promoted, but the crystallization becomes incomplete, and if the cooling rate is too low, the crystallization is completely performed, but the amorphization becomes incomplete. In order to simultaneously perform such contradictory recording and erasing, it is necessary to appropriately release the heat generated in the recording layer.

In the structure of the present invention as shown in FIGS. 1 and 2, the heat generated in the recording layer is radiated by the reflecting layer and the light absorbing layer directly or through the protective layer. Here, if the reflective layer and the light absorption layer are made of a material having the same thermal conductivity, when the thermal conductivity of the material is considerably large, the material is too rapidly cooled and the crystallization tends to be incomplete. When the thermal conductivity is considerably low, the cooling rate is too low and the amorphization tends to be incomplete. On the other hand, by configuring the light absorption layer and the reflection layer with materials having different thermal conductivities, the above-mentioned effect (making the light absorption rate in the recording layer higher in the crystalline state than in the amorphous state) Even if the material of the light-absorbing layer selected to exert the above-mentioned effect has a considerably high or low thermal conductivity, the material having the opposite thermal conductivity to the reflective layer material should be used. By this, heat dissipation and heat retention are supplemented in the reflective layer, and as a result, appropriate heat dissipation from the recording layer is performed.

[0022]

EXAMPLES The present invention will be described in detail below with reference to examples. In the following examples, the case where a material containing Sb, Te, and Ge as the main components is used for the recording layer will be described, but the present invention is not limited to this. <Reference Example> As shown in FIG. 2, a light absorbing layer 4, a first protective layer 5, a recording layer 2, a second protective layer 6, on a substrate 1 made of a transparent resin material (for example, a polycarbonate resin). Regarding the phase-change type optical disc having a structure in which the reflective layer 3 is sequentially laminated, the first protective layer 5, the recording layer 2, the second protective layer 6, and the reflective layer 3 are shown in Table 1 below with a refractive index n and an extinction coefficient. The light absorption coefficient A _{a in the} amorphous state and the light absorption in the crystalline state when the refractive index n and the extinction coefficient k of the material forming the light absorption layer 4 are changed with the material having the thickness k and the film thickness. The difference between the rates A _c (A _a −A _c ) was calculated.

[0023]

[Table 1]

The above-mentioned refractive index n and extinction coefficient k are values at a wavelength of 830 nm, and the thickness of the light absorption layer 4 was calculated to be 10 nm. The results are shown graphically in FIG. The numbers in the figure are the values showing the difference in light absorptance of the recording layer (A _a −A _c ) in%. In the same four-layer structure phase change optical disk as described above except that the light absorption layer 4 is not provided, the light absorption difference (A _a −A _c ) between the recording layers is 2 by the same calculation as above.
It was 4.5%. On the other hand, when the light absorption layer 4 is provided, as can be seen from the graph of FIG. 3, the light absorption rate of the recording layer is appropriately selected by appropriately selecting the refractive index n and the extinction coefficient k of the light absorption layer. The difference (A _a −A _c ) is, for example, less than “0”, that is, the light absorption coefficient A _c in the crystalline state is changed to the light absorption rate A in the amorphous state.
can be greater than _a . <Example 1> A phase change type optical disc having the layer structure shown in FIG. 2 was produced by the following procedure. First, it has a central hole, a diameter of 130 mm, a thickness of 1.2 mm, and a diameter of 1.6 on one side.
A light absorbing layer 4 made of Ti having a thickness of 10 nm is formed on the groove surface side of a disc-shaped polycarbonate resin substrate 1 having grooves with a pitch of μm, and a mixture of ZnS and SiO ₂ (SiO ₂
18% of the first protective layer 5 composed of
The recording layer 2 made of Sb-Te-Ge alloy having a thickness of 0 nm is 2
5 nm, a second protective layer 6 similar to the first protective layer 5
The reflective layer 3 made of Al and Al having a thickness of 150 nm was sequentially formed by a sputtering method of 150 nm, and a UV curable resin was laminated thereon by a spin coating method. This is designated as Sample No. 1-1. Further, as a comparative example, a phase change type optical disk having the same structure as the above except that the light absorption layer 4 made of Ti was not formed was manufactured. This is designated as sample No. 1-2.

Note that Ti has a refractive index n and a refractive index n that can make the light absorption coefficient A _c in the recording layer in the crystalline state larger than the light absorption coefficient A _a in the amorphous state depending on the layer structure and the film thickness. It has an extinction coefficient k. While rotating each sample of the phase-change optical disk thus obtained, the entire surface of the recording layer 2 was made into a crystalline state by irradiating the substrate with the Ar ion laser beam. After that, a driving device was rotated at 1800 rpm, and a signal of 3 MHz was recorded by a laser beam having a wavelength of 830 nm, which was intensity-modulated between a peak power of 20 mW and a bias power of 10 mW in the waveform shown in FIG. Was overwritten and the jitter of this 8 MHz signal was measured.

Jitter measurement results were obtained with a light absorption layer.
It was 3 nsec for the disk of No. 1-1 and 10 nsec for the disk of the comparative example (No. 1-2) without the light absorption layer.
It was sec. Since the jitter value is proportional to the variation in the length of the recording mark and the amount of misalignment, this result shows that the presence of the light absorption layer significantly reduces the variation in the length of the recording mark and the amount of misalignment. <Example 2> A light absorbing layer 4 made of Au having a thickness of 10 nm was formed on the groove surface side of the polycarbonate resin substrate 1 similar to Example 1.
Mixture of ZnS and SiO ₂ (abundance ratio of SiO ₂ 20mo
1%) with a first protective layer 5 of 110 nm, Sb-T
The recording layer 2 made of an e-Ge alloy is 11 nm, the second protective layer 6 similar to the first protective layer 5 is 20 nm, and Al-Ti.
The reflective layer 3 made of (Ti abundance ratio of 40 atom%)
nm sequential sputtering method, and then UV
By stacking the cured resin by spin coating,
A phase change type optical disc having the layer structure shown in FIG. 2 was produced. This is designated as Sample No. 2-1.

As a comparative example, the reflective layer 3 is made of Al-T.
A phase change type optical disk having the same structure as that described above was manufactured except that the same film thickness (150 nm) made of Au was used instead of i (the abundance ratio of Ti was 40 atomic%). This is designated as Sample No. 2-2. Furthermore, as a comparative example, the first protective layer 5, the recording layer 2, the second protective layer 6, and the reflective layer 3 were made of the same material as No. 2-1 without forming the light absorption layer 4 made of Au. However, the thickness of the first protective layer 5 is 60 n
m, the recording layer 2 is 25 nm, the second protective layer 6 is 12 nm,
A phase change type optical disc having a reflection layer 3 of 150 nm was manufactured in the same manner as described above. This is sample No. 2
-3.

Regarding the thermal conductivity of the material forming each of the light absorption layer 4 and the reflection layer 3, Au and Al--Ti are used.
When thin films of (Ti abundance ratio 40 atomic%) were formed on glass substrates and measured, Au was about 300 W / (m
・ K) and Al-Ti (abundance ratio of Ti: 40 atomic%)
Was about 4.5 W / (m · k). These samples
For the No. 2-1 to No. 2-3 phase-change optical disks, the light absorption rate in the recording film was measured at the incident light wavelength of 680 nm.
Was calculated by optical calculation. The results are shown in Table 2 below. In Table 2, A _C represents the light absorptance of the recording layer in the crystalline state, and A _a represents the light absorptance of the recording layer in the amorphous state.

[0029]

[Table 2]

As can be seen from Table 2, in No. 2-1 and No. 2-2 provided with the light absorption layer 4, the light absorption rate in the recording layer is less than the value A _{C in} the crystalline state. It is larger than the value A _a in the crystalline state. In contrast, in the No. 2-3 not provided a light-absorbing layer 4, it is larger towards the value A _a in the amorphous state than the value A _C of the light absorption rate in the crystalline state of the recording layer Has become.

Further, after making the entire surface of the recording layer 2 in a crystalline state in the same manner as in Example 1, the respective samples were rotated by a driving device at 1800 rpm, and a peak power of 20 mW and a bias power were obtained in the waveform shown in FIG. A 3 MHz signal was recorded by a laser beam having a wavelength of 680 nm and intensity-modulated between 10 mW, and then an 8 MHz signal was overwritten, and the jitter of the 8 MHz signal was measured.

The jitter measurement result is 3 nsec for the disk No. 2-1 corresponding to the embodiment of the present invention.
The disk No. 2-2 corresponding to the comparative example has 15 nse.
c, which was 10 nsec for the disks No. 2-3, which also corresponded to the comparative example. Also, for each sample, the C of the reproduced signal of 8 MHz recorded by overwriting
When the N / N ratio (carrier-to-noise ratio) and the erasing ratio of the erased 3 MHz signal were examined, it was found that in the No. 2-1 disk, the C / N ratio of the 8 MHz signal was 53 dB and that of the 3 MHz signal was 3 MHz. The erasing ratio was 40 dB, which were both high values.
Further, in the No. 2-2 disc, the erasing ratio of the signal of 3 MHz was a low value of 10 dB. Furthermore, No. 2-3
In case of the disk, the C / N ratio of 8MHz signal is 50d.
B, the erasing ratio of the 3 MHz signal was 30 dB.

Here, comparing No. 2-1 and No. 2-3, as described above, the value of the jitter is proportional to the variation in the length of the recording mark and the amount of positional deviation. -3
No. 2-1 has a large jitter of 10 nsec because it does not have the light absorbing layer 4, and No. 2-1 has a small jitter because it has the light absorbing layer 4. Due to the presence of the light absorbing layer, the length of the recording mark becomes longer. It can be seen that the variation and the amount of positional deviation are significantly reduced.

The disc No. 2-2 is No. 2-
Despite having the light absorption layer 4 as in No. 1, the erasing ratio of the signal of 3 MHz was as low as 10 dB, and the jitter was also as large as 15 nsec. This is because the disk No. 2 is different from the disk No. 2-1 in that the reflective layer 3 is the same as the light absorption layer 4 and is Au having a considerably large thermal conductivity. That is, the recording layer 2
The heat generated in 2) is radiated from the light absorption layer 4 made of Au and the reflection layer 3 through the first and second protective layers 5 and 6 fairly rapidly, so that the temperature required for crystallization is sufficiently high. It is considered that the erasure is not sufficient because it is not retained in. It is considered that the incomplete erasing in this way resulted in a large jitter value.

As described above, from the result of the second embodiment,
The presence of the light absorbing layer significantly reduces the irregularity of the recording marks, and the light absorbing layer and the reflecting layer are formed of an appropriate combination having different thermal conductivities to increase both the C / N ratio and the erasing ratio. It can be seen that both recording and erasing can be achieved. <Example 3> On the groove surface side of the polycarbonate resin substrate 1 similar to Example 1, the light absorption layer 4 made of Ge is 40 nm,
Mixture of ZnS and SiO ₂ (abundance ratio of SiO ₂ 20mo
1% of the first protective layer 5 with a thickness of 150 nm, Sb-T
A recording layer 2 made of an e-Ge alloy is formed to have a thickness of 15 nm, a second protective layer 6 similar to the first protective layer 5 is formed to have a thickness of 40 nm, and a reflective layer 3 made of Al is formed to have a thickness of 150 nm in this order by a sputtering method. A phase-change type optical disc having a layer structure shown in FIG. 2 was produced by laminating cured resins by spin coating. This is designated as Sample No. 3-1.

Further, as a comparative example, a phase change type optical disk having the same structure as described above was manufactured except that the reflection layer 3 was made of Ge instead of Al and had the same film thickness (150 nm). This is designated as Sample No. 3-2. Further, as a comparative example, a phase change type optical disk having the same configuration as No. 3-1 except that the light absorption layer 4 made of Ge was not formed was produced in the same manner as described above. This is designated as Sample No. 3-3.

The thermal conductivity, which is a material forming each of the light absorption layer 4 and the reflection layer 3, is about 60 W / Ge in the literature value.
(M · k) and Al was about 200 W / (m · k). With respect to each of these samples, after the entire surface of the recording layer 2 was crystallized in the same manner as in Example 1, a signal of 3 MHz was recorded by a laser beam having a wavelength of 680 nm and then 8 MHz was recorded in the same manner as in Example 2. The signals were overwritten and the jitter of this 8 MHz signal was measured. 8M recorded by overwriting for each sample
The C / N ratio (carrier-to-noise ratio) of the reproduced signal of Hz and the erase ratio of the erased 3 MHz signal were examined.

The measurement result of the jitter is 3 nsec for the disk No. 3-1 corresponding to the embodiment of the present invention.
The disk No. 3-2 corresponding to the comparative example is 25 nse.
c, which was 10 nsec for the disk No. 3-3 corresponding to the comparative example. In the case of No. 3-1 disc, the C / N ratio of 8 MHz signal is 50 dB, 3M.
The elimination ratio of the Hz signal was 40 dB, which were both high values. Further, in the disk of No. 3-2, the C / N ratio of the 8 MHz signal was a low value of 30 dB. Furthermore, N
In the disk No. 3-3, the C / N ratio of the 8 MHz signal was 50 dB and the erasing ratio of the 3 MHz signal was 28 dB.

Here, comparing No. 3-1 and No. 3-3, as described above, the value of jitter is proportional to the variation in the length of the recording mark and the amount of positional deviation, and therefore No. 3 -3
No. 3-1 has a large jitter of 10 nsec because it does not have the light absorbing layer 4, and No. 3-1 has a small jitter because it has the light absorbing layer 4, and the presence of the light absorbing layer reduces the length of the recording mark. It can be seen that the variation and the amount of positional deviation are significantly reduced.

The disk No. 3-2 is No. 3-
Despite having the light absorption layer 4 as in No. 1, the C / N ratio of the signal at 3 MHz was as low as 30 dB, and the jitter was as large as 25 nsec. This is because the disk No. 3-2, unlike the disk No. 3-1, uses Ge, which has the same reflective layer 3 as the light absorption layer 4 and has a considerably small thermal conductivity. That is, the recording layer 2
The heat generated in (1) is radiated from the light absorption layer 4 made of Ge and the reflection layer 3 through the first and second protective layers 5 and 6, but the amount thereof is small. It is considered that the recording was insufficient because the cooling rate was not sufficient to achieve this. Then, it is considered that the jitter became a large value because the recording was incomplete in this way.

As described above, from the results of the third embodiment,
The presence of the light absorbing layer significantly reduces the irregularity of the recording marks, and the light absorbing layer and the reflecting layer are formed of an appropriate combination having different thermal conductivities to increase both the C / N ratio and the erasing ratio. It can be seen that both recording and erasing can be achieved.

[0042]

As described above, according to the present invention, a transparent substrate and one surface of the substrate,
At least a recording layer made of a material in which a phase change between a crystalline state and an amorphous state is reversibly caused by light irradiation, and a reflective layer formed on a surface of the recording layer opposite to the substrate. In the provided optical information recording medium, a light absorbing layer is provided between the substrate and the recording layer, and the material forming the light absorbing layer has a thermal conductivity different from that of the reflecting layer. Even with overwriting by one beam, it is possible to form a recording mark faithful to the information signal in the recording layer, and both recording and erasing can be achieved with high performance, so high density recording is supported. An optical information recording medium capable of being provided can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a layer structure of an optical information recording medium of the present invention.

FIG. 2 is a cross-sectional view showing an example of the layer structure of the optical information recording medium of the present invention.

FIG. 3 relates to <Reference Example>, in which the value of the light absorption difference (A _a −A _c ) of the recording layer between the amorphous state and the crystalline state is compared with the refractive index n of the material forming the light absorption layer. It is a graph shown in relation to the extinction coefficient k.

FIG. 4 is a graph showing an intensity modulation waveform of a laser beam used for recording in <Example 1> to <Example 3>.

FIG. 5 is a sectional view showing an example of a layer structure of a conventional optical information recording medium.

FIG. 6 is a cross-sectional view showing an example of a layer structure of a conventional optical information recording medium.

[Explanation of symbols]

 1 substrate 2 recording layer 3 reflective layer 4 light absorbing layer

Claims (3)

[Claims] 1. A transparent substrate, and a recording layer formed on one surface of the substrate and made of a material capable of reversibly changing a phase between a crystalline state and an amorphous state by light irradiation. In an optical information recording medium having at least a reflective layer formed on the surface of the recording layer opposite to the substrate, a thermal conductivity different from that of the reflective layer is provided between the substrate and the recording layer. An optical information recording medium comprising a light absorbing layer made of a light absorbing material. 2. The optical information recording medium according to claim 1, wherein the light absorption layer is made of a metal, a semimetal, or a semiconductor. 3. The light absorption layer comprises Al, Ti, Cr, N
i, Cu, Si, Ge, Ag, Au, Pd, Ga, S
3. The optical information recording medium according to claim 2, comprising an element selected from the group consisting of e, In, Sn, Sb, Te, Pb, and Bi, or an alloy containing an element selected from this group. .