Information recording medium and method for manufacturing the same

An information recording medium includes a substrate and an information layer formed on the substrate. The information layer includes a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy; a Cr-containing layer including at least Cr and O, arranged in contact with a first surface of the recording layer; and a Ga-containing layer including at least Ga and O, arranged in contact with a second surface of the recording layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording medium that is capable of recording, erasing, rewriting and reproducing information optically or electrically, as well as to a method for manufacturing the same.

2. Related Background Art

As conventional information recording media, phase-changing information recording media are known that record, erase and rewrite information using the phenomenon that a phase change between a crystalline phase and an amorphous phase occurs in a recording layer (phase-changing material layer) that is made of a phase-changing material. Among such phase-changing information recording media, there are optical phase-changing information recording media, with which information can be recorded, erased, rewritten and reproduced using a laser beam. In these optical phase-changing information recording media heat generated by irradiation of a laser beam causes a phase change between the crystalline phase and the amorphous phase in the phase-changing material of the recording layer, and differences in the reflectance of the crystalline phase and the amorphous phase are detected and read out as information. In rewritable optical phase-changing information recording media, which allow the erasing and rewriting of information, the initial state of the recording layer is ordinarily the crystalline phase, and to record information, the recording layer is melted through irradiation of a laser beam of high power (recording power) and rapidly cooled down, turning the portions on which the laser beam was irradiated (laser beam irradiation portions) into the amorphous phase. On the other hand, to erase information, the recording layer is heated by irradiating a laser beam of a power that is lower than during recording (erasing power) and slowly cooled, thus turning the laser beam irradiation portions into the crystalline phase. Consequently, in rewritable optical phase-changing information recording media, it is possible to record new information while erasing recorded information, that is, to rewrite information, by irradiating onto the recording layer a laser beam whose power is modulated between a high power level and a low power level. Moreover, in write-once optical phase-change information recording media in which information can be recorded once, but cannot be erased or rewritten, the recording layer is generally in the amorphous phase in its initial state. To record information on such a recording medium, the recording layer is heated by irradiating a laser beam with high power (recording power), and then slowly cooled, thus turning the laser beam irradiation portions into the crystalline phase.

There are also electrical phase-change information recording media, in which information is recorded by phase-changing the phase-changing material of the recording layer through joule heat that is generated by applying electric energy (for example an electric current) instead of irradiating a laser beam. In such electrical phase-change information recording media, the phase-changing material of the recording layer undergoes a phase change between a crystalline phase (low resistance) and an amorphous phase (high resistance) due to joule heat that is generated by applying a current, for example, and information is read out by detecting the difference in electric resistance between the crystalline phase and the amorphous phase.

An example of optical phase-change information recording media is the 4.7 GB DVD-RAM (digital versatile disk—random access memory) proposed by the inventors (see for example JP H10-275360A). Like the information recording medium12shown inFIG. 12, this 4.7 GB DVD-RAM includes, from the side from which a laser beam11is irradiated, a substrate1, and an information layer100having a seven-layer structure including a first dielectric layer2, a first interface layer3, a recording layer4, a second interface layer5, a second dielectric layer6, a light-absorbing correction layer7, and a reflective layer8, layered in this order on top of the substrate1.

The first dielectric layer2and the second dielectric layer6have the optical function of increasing the optical absorption efficiency by adjusting the optical distance and increasing the signal intensity by increasing the change of the reflectance between when the recording layer4is in the crystalline phase and when it is in the amorphous phase, and furthermore have the thermal function of thermally insulating the recording layer4, which becomes hot during recording, from the substrate1and the dummy substrate10, which are easily damaged by heat. Conventionally, a mixture of 80 mol % ZnS and 20 mol % SiO2(referred to below as (ZnS)80(SiO2)20(mol %) or (ZnS)80(SiO2)20; the same notation also is used for other mixtures) is used for the dielectric layers. This mixture is a superior dielectric material, which is transparent, has a high refractive index, a low thermal conductivity, and a good thermal insulation, and has favorable mechanical characteristics and moisture resistance. It should be noted that the film thickness of the first dielectric layer2and the second dielectric layer6can be determined strictly by calculation with the matrix method, such that the following conditions are satisfied: the change of the reflected light amount between the crystalline phase and the amorphous phase of the recording layer4is large, and the optical absorption at the recording layer4is large. By using for the recording layer4a high-speed crystallizing material including Ge—Sn—Sb—Te, in which some of the Ge in the pseudo-binary system phase-changing material GeTe—Sb2Te3obtained by mixing the compounds GeTe and Sb2Te3, is substituted with Sn, it is possible to realize not only initial recording/rewriting properties, but also excellent archival characteristics (indicating whether a recorded signal can be reproduced after storage for a long time), and archival overwrite characteristics (indicating whether a recorded signal can be erased or rewritten after storage for a long time).

The first interface layer3and the second interface layer5have the function of preventing substance migration that otherwise may occur between the first dielectric layer2and the recording layer4or between the second dielectric layer6and the recording layer4. Here, “substance migration” refers to the phenomenon that if (ZnS)80(SiO2)20(mol %) is used for the first dielectric layer2and the second dielectric layer6, sulfur in the (ZnS)80(SiO2)20(mol %) diffuses into the recording layer when repeatedly writing/rewriting the recording layer4through irradiation of the laser beam11. When sulfur diffuses into the recording layer, the repeated rewriting properties deteriorate. In order to prevent this deterioration of the repeated rewriting properties, it is advantageous to use a nitride including Ge for the first interface layer3and the second interface layer5.

With the above-described technology, excellent repeated rewriting properties and high reliability were achieved, and a 4.7 GB DVD-RAM was proposed and brought to market.

Various technologies have been studied to increase the capacity of information recording media even further. For example, for optical phase-changing information recording media, a technology has been studied in which high-density recording is performed by reducing the spot diameter of the laser beam by using a bluish-purple laser having a wavelength that is shorter than that of conventional red lasers, or by making the substrate on the side from which the laser beam is irradiated thin and using an objective lens having a large numerical aperture (NA). When recording with smaller spot diameters, the time for which the laser beam is irradiated onto the recording layer becomes relatively short. Therefore, in order to enable crystallization with shorter times, it is necessary to make the recording layer from a more readily crystallizing material, or to provide a layer with a high crystallization enhancing effect adjacent to the recording layer.

Furthermore, technologies have been studied by which the recording capacity is doubled by using optical phase-changing information recording media having two information layers (in the following also referred to as “double-layer optical phase-changing information recording media”) and recording and reproducing information on two information layers with a laser beam that is irradiated from one side (see for example JP 2000-36130A and JP 2002-144736A). In double-layer optical phase-changing information recording media, in order to record/reproduce the information layer that is located further away from the side from which the laser beam is incident (referred to as “second information layer” in the following), a laser beam is used that passes through the information layer located closer to the side from which the laser beam is incident (referred to as “first information layer” in the following), so that in the first information layer, the recording layer is made thin and its transmittance is increased. However, when the recording layer becomes thin, the number of crystal nuclei that are formed when the recording layer is crystallized is reduced, and the distance over which atoms can move is shortened. Therefore, the thinner the recording layer is, the more difficult it becomes to form the crystalline phase becomes (i.e. the crystallization speed decreases). Consequently, in a first information layer having a thin recording layer, it is necessary to make the recording layer from a material with better crystallization capability or to provide a layer with a high crystallization enhancing effect adjacent to the recording layer.

Furthermore, when the time it takes to record information on the information recording medium is shortened and the information transfer rate is increased, the time for crystallization also becomes short. Therefore, also in order to realize phase-changing information recording media for high transfer rates, it is again necessary to make the recording layer from a material with better crystallization capability or to provide a layer with a high crystallization enhancing effect adjacent to the recording layer.

Conventionally, in order to address this problem, and realize a medium with high capacity and suitable for high transfer rates, a material with high crystallization capability is used for the recording layer, and interface layers made of a nitride including Ge, as in the 4.7 GB DVD-RAM, are arranged on both sides of the recording layer.

However, when using a material in which the crystallization capability is increased in order to improve the crystallization speed of the optical phase-changing information recording medium, then the amorphous phase becomes difficult to form in particular in rewritable optical phase-changing information recording media. Therefore, it becomes necessary to heat the recording layer to a higher temperature, widen the melting region of the recording layer, and quickly cool the recording layer. Thus, a higher energy (laser power) becomes necessary to record information, and there is the problem that the recording sensitivity decreases. Moreover, when interface layers made of a nitride including Ge are used as in the conventional case, then there is the problem that the interface layers may be damaged by the heat generated in the recording layer by applying a large energy, considerably deteriorating the repeated rewriting properties.

Furthermore, since the thermal conductivity of nitrides including Ge is high, heat tends to diffuse in particular when the interface layer is thick. Also due to this reason, there is the problem that the recording sensitivity is decreased.

Moreover, when the interface layers are made of a nitride including Ge, then the extinction coefficient of the interface layers becomes large, so that light is absorbed more easily by the interface layers. When more light is absorbed by the interface layers, then there is the problem that the difference between the reflectance in the crystalline phase and the reflectance in the amorphous phase of the optical phase-changing information recording medium becomes small, and the signal intensity decreases. Moreover, more light is absorbed by the interface layers, so that there is the problem that the recording sensitivity decreases even further.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a phase-changing information recording medium with which the crystallization speed of the recording layer is increased while suppressing a decrease in recording sensitivity, repeated rewriting properties and signal intensity.

A first information recording medium according to the present invention comprises a substrate and an information layer provided on the substrate; the information layer comprising a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy; a Cr-containing layer comprising at least Cr and O, arranged in contact with a first surface of the recording layer; and a Ga-containing layer comprising at least Ga and O, arranged in contact with a second surface of the recording layer.

A second information recording medium according to the present invention comprises a substrate and an information layer provided on the substrate, the information layer comprising a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy; a first Ga-containing layer comprising at least Ga and O, arranged in contact with a first surface of the recording layer; and a second Ga-containing layer comprising at least Ga and O, arranged in contact with a second surface of the recording layer.

A third information recording medium according to the present invention comprises a substrate and an information layer provided on the substrate, the information layer comprising a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy; a first Cr-containing layer comprising at least Cr and O, arranged in contact with a first surface of the recording layer; a second Cr-containing layer comprising at least Cr and O, arranged in contact with a second surface of the recording layer; and a Ga-containing layer comprising at least Ga and O, arranged in contact with the second Cr-containing layer.

A fourth information recording medium according to the present invention comprises a substrate and an information layer provided on the substrate, the information layer comprising a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy; a Cr-containing layer comprising at least Cr and O, arranged on a side of a first surface of the recording layer; a Ga-containing layer comprising at least Ga and O, arranged on a side of a second surface of the recording layer; and a C-containing layer containing C as its principal component and arranged in contact with the recording layer between the recording layer and the Cr-containing layer and/or between recording layer and the Ga-containing layer.

A first information recording medium manufacturing method according to the present invention comprises:

(a) a step of forming a Cr-containing layer using a Cr-containing sputtering target comprising at least Cr and O;

(b) a step of forming a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy;

(c) a step of forming a Ga-containing layer using a Ga-containing sputtering target comprising at least Ga and O;

wherein the steps (a) to (c) are carried out in the order of step (a), step (b), step (c) or in the order of step (c), step (b), step (a).

A second information recording medium manufacturing method according to the present invention comprises:

(a) a step of forming a first Ga-containing layer using a first Ga-containing sputtering target comprising at least Ga and O;

(b) a step of forming a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy;

(c) a step of forming a second Ga-containing layer using a second Ga-containing sputtering target comprising at least Ga and O;

wherein the steps (a) to (c) are carried out in the order of step (a), step (b), step (c) or in the order of step (c), step (b), step (a).

A third information recording medium manufacturing method according to the present invention comprises:

(a) a step of forming a first Cr-containing layer using a first Cr-containing sputtering target comprising at least Cr and O;

(b) a step of forming a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy;

(c) a step of forming a second Cr-containing layer using a second Cr-containing sputtering target comprising at least Cr and O;

(d) a step of forming a Ga-containing layer using a second Ga-containing sputtering target comprising at least Ga and O;

wherein the steps (a) to (d) are carried out in the order of step (a), step (b), step (c), step (d) or in the order of step (d), step (c), step (b), step (a).

A fourth information recording medium manufacturing method according to the present invention comprises:

(a) a step of forming a Cr-containing layer using a Cr-containing sputtering target comprising at least Cr and O;

(b) a step of forming a recording layer whose phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam or application of electric energy;

(c) a step of forming a Ga-containing layer using a Ga-containing sputtering target comprising at least Ga and O;

wherein the steps (a) to (c) are carried out in the order of step (a), step (b), step (c) or in the order of step (c), step (b), step (a); and

further comprising a step of forming a C-containing layer using a C-containing sputtering target comprising C as its principal component between step (a) and step (b) and/or between step (b) and step (c).

DETAILED DESCRIPTION OF THE INVENTION

With the first to fourth information recording media, it is possible to provide phase-changing information recording media with a decrease in recording sensitivity, repeated rewriting properties and signal intensity suppressed and the crystallization speed of the recording layer increased.

If the first information recording medium is an optical information recording medium wherein the recording layer's phase can be changed between the crystalline phase and the amorphous phase by irradiation with a laser beam, then it is preferable that the Cr-containing layer, the recording layer and the Ga-containing layer are arranged in this order from a side from which the laser beam is incident. By arranging the Cr-containing layer closer to the side from which the laser beam is incident, it is possible to attain higher crystallization speed. By arranging the Ga-containing layer further away from the side from which the laser beam is incident, it is possible to suppress the thermal conduction from the recording layer and attain higher recording sensitivity. Accordingly, by arranging the Cr-containing layer and the Ga-containing layer in this way, it is possible to attain higher recording sensitivity, signal intensity and repeated rewriting properties. Moreover, in the case of an optical information recording medium, the information layer further may comprise at least one of a first dielectric layer arranged closer to the side from which the laser beam is incident than the Cr-containing layer, and a second dielectric layer arranged further away from the side from which the laser beam is incident than the Ga-containing layer. The information layer further may comprise a reflective layer arranged further away from the side from which the laser beam is incident than the Ga-containing layer. By providing at least one of the first and the second dielectric layer, or the reflective layer, the effect of increasing the optical absorption efficiency of the recording layer or the signal intensity or the like can be attained as well. It should be noted that in this specification, in order to distinguish dielectric layers or interface layers that are included in the same information layer, “first” and “second” is used in conjunction with the names of the dielectric layers and interface layers, where “first” means arranged on the side of the recording layer that is closer to the side from which the laser beam is irradiated and “second” means arranged on the side of the recording layer that is further away from the side from which the laser beam is irradiated.

The first information recording medium of the present invention also may be a multi-layer information recording medium comprising first to N-th information layers (where N is an integer of 2 or more), and wherein at least one of the first to N-th information layers is said information layer. In this case, it is preferable that at least one of the first to N-th information layers has the same film configuration as the information layer included in the above-described first information recording medium of the present invention. Thus, also in an information recording medium provided with a plurality of information layers, the crystallization speed of the recording layer can be increased while suppressing a decrease in recording sensitivity, repeated rewriting properties and signal intensity. It is preferable that the first information recording medium of the present invention comprises first to N-th information layers, and is an optical information recording medium wherein the recording layer's phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam; that the first to N-th information layers are arranged in that order from the side from which the laser beam is incident; that at least the first information layer has the same film configuration as the information layer included in the above-described first information recording medium of the present invention; and that the first information layer comprises a first dielectric layer, a Cr-containing layer, a recording layer, a Ga-containing layer, a reflective layer and a transmittance adjusting layer arranged in that order from the side from which the laser beam is incident.

In the first information recording medium of the present invention, the Cr-containing layer further may comprise at least one element selected from Zr, Hf, Y and Si. Preferably, the Cr-containing layer comprises Cr2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. It should be noted that in this case, it is preferable that the Cr content concentration in the Cr-containing layer is 5 to 40 atom %, and it is preferable that the O content concentration is 55 to 75 atom %. Moreover, it is preferable that the Cr2O3content concentration in the Cr-containing layer is 10 to 90 mol %.

In the first information recording medium of the present invention, the Ga-containing layer further may comprise at least one element selected from Zr, Hf, Y and Si. In this case, it is preferable that the Ga-containing layer comprises a material that can be expressed by the following composition formula:
GaA1MB1O100-A1-B1(atom %)
where M is at least one element selected from Zr, Hf, Y and Si, and A1 and B1 satisfy:
5<A1<40
2<B1<30.
That is to say, it is preferable that the Ga content concentration in the Ga-containing layer is 5 to 40 atom %. Furthermore, it is preferable that the O content concentration is 55 to 75 atom %. In this case, the Ga-containing layer further may comprise Cr, and it is preferable that it contains 3 to 25 atom % Cr.

In the first information recording medium according to the present invention, it is preferable that the Ga-containing layer comprises Ga2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. In this case, it is preferable that the Ga-containing layer comprises a material that can be expressed by the following composition formula:
(Ga2O3)C1(Z1)100-C1(mol %)  (2)
where Z1 is at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2, and C1 satisfies:
10≦C1≦90.
That is to say, it is preferable that the Ga2O3content concentration in the Ga-containing layer is 10 to 90 mol %. In this case, the Ga-containing layer further may comprise Cr2O3, preferably in a content of 5 to 40 mol %.

If the second information recording medium is an optical information recording medium wherein the recording layer's phase can be changed between the crystalline phase and the amorphous phase by irradiation with a laser beam, then it is preferable that the first Ga-containing layer, the recording layer and the second Ga-containing layer are arranged in this order from a side from which the laser beam is incident, and that the information layer further comprises at least one of a first dielectric layer arranged closer to the side from which the laser beam is incident than the first Ga-containing layer, and a second dielectric layer arranged further away from the side from which the laser beam is incident than the second Ga-containing layer. Moreover, the information layer further may comprise a reflective layer arranged further away from the side from which the laser beam is incident than the second Ga-containing layer. By providing at least one of the first and the second dielectric layers or the reflective layer, the effect of increasing the optical absorption efficiency of the recording layer or the signal intensity or the like can be attained as well.

The second information recording medium according to the present invention also may be a multi-layer information recording medium comprising first to N-th information layers (where N is an integer of 2 or more). In this case, it is preferable that at least one of the first to N-th information layers has the same film configuration as the information layer included in the above-described second information recording medium of the present invention. Thus, also in an information recording medium provided with a plurality of information layers, the crystallization speed of the recording layer can be increased while suppressing a decrease in recording sensitivity, repeated rewriting properties and signal intensity. It is preferable that the second information recording medium of the present invention comprises first to N-th information layers, and is an optical information recording medium wherein the recording layer's phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam; that the first to N-th information layers are arranged in that order from the side from which the laser beam is incident; that at least the first information layer has the same film configuration as the information layer included in the above-described second information recording medium of the present invention; and that the first information layer comprises a first dielectric layer, the first Ga-containing layer, the recording layer, the second Ga-containing layer, a reflective layer and a transmittance adjusting layer arranged in that order from the side from which the laser beam is incident.

In the second information recording medium of the present invention, at least one of the first Ga-containing layer and the second Ga-containing layer further may comprise at least one element selected from Zr, Hf, Y and Si. In this case, it is preferable that at least one of the first Ga-containing layer and the second Ga-containing layer comprises a material that can be expressed by the composition formula (1), and that A1 and B1 satisfy 5<A1<40 and 2<B1<30. That is to say, it is preferable that the Ga content concentration in the first and/or second Ga-containing layer is 5 to 40 atom %. It is also preferable that the O content concentration in this case is 55 to 75%. Also, in this case, the Ga-containing layers further may comprise Cr, preferably at a content of 3 to 25%.

In the second information recording medium according to the present invention, it is preferable that at least one of the first Ga-containing layer and the second Ga-containing layer comprise Ga2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. In this case, it is preferable that at least one of the first Ga-containing layer and the second Ga-containing layer comprises a material that can be expressed by the composition formula (2), and that 10≦C1≦90. That is to say, it is preferable that the Ga2O3content concentration in the first and/or the second Ga-containing layer is 10 to 90 mol %. In this case, the first Ga-containing layer or the second Ga-containing layer further may comprise Cr2O3, preferably at a content of 5 to 40 mol %.

If the third information recording medium is an optical information recording medium wherein the recording layer's phase can be changed between the crystalline phase and the amorphous phase by irradiation with a laser beam, then it is preferable that the first Cr-containing layer, the recording layer, the second Cr-containing layer and the Ga-containing layer are arranged in this order from a side from which the laser beam is incident, and that the information layer further comprises at least one of a first dielectric layer arranged closer to the side from which the laser beam is incident than the first Cr-containing layer, and a second dielectric layer arranged further away from the side from which the laser beam is incident than the second Cr-containing layer. Moreover, the information layer further may comprise a reflective layer arranged further away from the side from which the laser beam is incident than the second Cr-containing layer. By providing at least one of the first and the second dielectric layers or the reflective layer, the effect of increasing the optical absorption efficiency of the recording layer or the signal intensity or the like can be attained as well.

The third information recording medium according to the present invention also may be a multi-layer information recording medium comprising first to N-th information layers (where N is an integer of 2 or more). In this case, it is preferable that at least one of the first to N-th information layers has the same film configuration as the information layer included in the above-described third information recording medium of the present invention. Thus, also in an information recording medium provided with a plurality of information layers, the crystallization speed of the recording layer can be increased while suppressing a decrease in recording sensitivity, repeated rewriting properties and signal intensity. It is preferable that the third information recording medium of the present invention comprises first to N-th information layers, and is an optical information recording medium wherein the recording layer's phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam; that the first to N-th information layers are arranged in that order from the side from which the laser beam is incident; that at least the first information layer has the same film configuration as the information layer included in the above-described third information recording medium of the present invention; and that the first information layer comprises a first dielectric layer, the first Cr-containing layer, the recording layer, the second Cr-containing layer, the Ga-containing layer, a reflective layer and a transmittance adjusting layer arranged in that order from the side from which the laser beam is incident.

In the third information recording medium according to the present invention, at least one of the first Cr-containing layer and the second Cr-containing layer further may comprise at least one element selected from Zr, Hf, Y and Si. Preferably, at least one of the first Cr-containing layer and the second Cr-containing layer comprises Cr2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. In this case, it is preferable that the Cr content concentration in the Cr-containing layer is 5 to 40 atom %, and the O content concentration is 55 to 75 atom %. Moreover, it is preferable that the Cr2O3content concentration in the Cr-containing layer is 10 to 90 mol %.

In the third information recording medium according to the present invention, the Ga-containing layer further may comprise at least one element selected from Zr, Hf, Y and Si. In this case, it is preferable that the Ga-containing layer comprises a material that can be expressed by the composition formula (1), and that 5<A1<40 and 2<B1<30. That is to say, it is preferable that the Ga content concentration in the Ga-containing layer is 5 to 40 atom %. Moreover, it is preferable that the 0 content concentration in this case is 55 to 75 atom %. In this case, the Ga-containing layer further may comprise Cr, preferably at a content of 3 to 25 atom %.

It is also preferable that the Ga-containing layer comprises Ga2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. In this case, it is preferable that the Ga-containing layer comprises a material that can be expressed by the composition formula (2), and C1 satisfies 10≦C1≦90. That is to say, it is preferable that the Ga2O3content concentration in the Ga-containing layer is 10 to 90 mol %. In this case, the Ga-containing layer further may comprise Cr2O3, preferably at a content of 5 to 40 mol %.

If the fourth information recording medium is an optical information recording medium wherein the recording layer's phase can be changed between the crystalline phase and the amorphous phase by irradiation with a laser beam, then it is preferable that the Cr-containing layer is arranged closer to the side from which the laser beam is incident than the recording layer and the Ga-containing layer is arranged further away from the side from which the laser beam is incident than the recording layer. By arranging the Cr-containing layer and the Ga-containing layer in this way, it is possible to attain a higher recording sensitivity, signal intensity and repeated rewriting properties. Moreover, in the case of an optical information recording medium, the information layer further may comprise at least one of a first dielectric layer arranged closer to the side from which the laser beam is incident than the Cr-containing layer, and a second dielectric layer arranged further away from the side from which the laser beam is incident than the Ga-containing layer, and a reflective layer arranged further away from the side from which the laser beam is incident than the Ga-containing layer. By providing at least one of the first and the second dielectric layers and/or the reflective layer, the effect of increasing the optical absorption efficiency of the recording layer or the signal intensity or the like can be attained as well. In the fourth information recording medium, the C-containing layer is provided between the Cr-containing layer and the recording layer and/or the Ga-containing layer and the recording layer. Therefore, adhesion between the Cr-containing layer and the recording layer and/or the Ga-containing layer and the recording layer is improved, and high reliability can be attained.

The fourth information recording medium according to the present invention also may be a multi-layer information recording medium comprising first to N-th information layers (where N is an integer of 2 or more). In this case, it is preferable that at least one of the first to N-th information layers has the same film configuration as the information layer included in the above-described fourth information recording medium of the present invention. Thus, also in an information recording medium provided with a plurality of information layers, the crystallization speed of the recording layer can be increased while suppressing a decrease in recording sensitivity, repeated rewriting properties and signal intensity. It is preferable that the fourth information recording medium of the present invention comprises first to N-th information layers, and is an optical information recording medium wherein the recording layer's phase can be changed between a crystalline phase and an amorphous phase by irradiation with a laser beam; that the first to N-th information layers are arranged in that order from the side from which the laser beam is incident; that at least the first information layer has the same film configuration as the information layer included in the above-described fourth information recording medium of the present invention; and that the first information layer comprises a first dielectric arranged closer to the side from which the laser beam is incident than the Cr-containing layer, and a reflective layer and a transmittance adjusting layer arranged further away from the side from which the laser beam is incident than the Ga-containing layer.

In the fourth information recording medium of the present invention, the Ga-containing layer further may comprise at least one element selected from Zr, Hf, Y and Si. In this case, it is preferable that the Ga-containing layer comprises a material that can be expressed by the composition formula (1) and A1 and B1 satisfy 5<A1<40 and 2<B1<30. That is to say, it is preferable that the Ga content concentration in the Ga-containing layer is 5 to 40 atom %. Moreover, it is preferable that the O content concentration in this case is 55 to 75 atom %. The Ga-containing layer further may comprise Cr, preferably at a content of 3 to 25 atom %.

In the fourth information recording medium according to the present invention, it is preferable that the Ga-containing layer comprises Ga2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. In this case, it is preferable that the Ga-containing layer comprises a material that can be expressed by the composition formula (2), and that C1 satisfies 10≦C1≦90. That is to say, it is preferable that the Ga2O3content concentration in the Ga-containing layer is 10 to 90 mol %. The Ga-containing layer further may comprise Cr2O3, preferably at a content of 5 to 40 mol %.

The following is an explanation of first to fourth information recording medium manufacturing methods of the present invention.

With the first to fourth manufacturing methods, it is possible to manufacture the above-described first to fourth information recording media, with which the crystallization speed of the recording layer is increased while suppressing a decrease in recording sensitivity, repeated rewriting properties and signal intensity.

The Cr-containing sputtering target used in the first, third and fourth manufacturing method (in the third manufacturing method, at least one of the first Cr-containing sputtering target and the second Cr-containing sputtering target) further may comprise at least one element selected from Zr, Hf, Y and Si. It is preferable that the Cr-containing sputtering target comprises Cr2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2.

The Ga-containing sputtering target used in the first to fourth manufacturing methods (in the second manufacturing method, at least one of the first Ga-containing sputtering target and the second Ga-containing sputtering target) further may comprise at least one element selected from Zr, Hf, Y and Si. In this case, it is preferable that the Ga-containing sputtering target comprises a material that can be expressed by the following composition formula:
GaA2M1B2O100-A2-B2(atom %)  (3)
where M1 is at least one element selected from Zr, Hf, Y and Si, and A2 and B2 satisfy
3<A2<42
0<B2<32.
The Ga-containing sputtering target further may comprise Cr.

It is preferable that the Ga-containing sputtering target used in the first to fourth manufacturing methods (in the second manufacturing method, at least one of the first Ga-containing sputtering target and the second Ga-containing sputtering target) comprises Ga2O3and at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2. In this case, it is preferable that the Ga-containing sputtering target comprises a material that can be expressed by the following composition formula:
(Ga2O3)C2(Z1)100-C2(mol %)  (4)
where Z1 is at least one oxide selected from ZrO2, HfO2, Y2O3and SiO2, and C2 satisfies:
8≦C2≦92.
The Ga-containing sputtering target further may comprise Cr2O3.

The following is an explanation of embodiments of the present invention, with reference to the accompanying drawings. It should be noted that the following embodiments are mere examples, and that the present invention is not limited to these embodiments. Moreover, in the following embodiments, similar elements may be denoted by like numerals, and their further explanation may be omitted.

In Embodiment 1, an example of an information recording medium according to the present invention is explained.FIG. 1shows a partial cross-sectional view of an information recording medium15according to Embodiment 1. The information recording medium15is an optical information recording medium on which information can be recorded and/or reproduced by irradiating a laser beam11.

The information recording medium15is provided with an information layer16on a substrate14, and furthermore with a transparent layer13on the information layer16. In this information recording medium15, the laser beam11is irradiated from the side of the transparent layer13. The information layer16is made from a first dielectric layer102, a first interface layer103, a recording film104, a second interface layer105, a second dielectric layer106and a reflective layer108, layered in this order from the side from which the laser beam is incident.

The transparent layer13is made from a dielectric or a resin, such as a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin. The transparent layer13preferably has a small optical absorption with respect to the laser beam that is used, and preferably has a small birefringence in the short wavelength region. Furthermore, a transparent disk-shaped resin, such as polycarbonate, amorphous polyolefine or polymethylmethacrylate (PMMA), or glass may be used for the transparent layer13. If such a material is used, then the transparent layer13can be glued to the information layer16with a resin, such as a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin for example.

The wavelength λ of the laser beam11determines the spot size when focusing the laser beam11. The shorter the wavelength λ of the laser beam11, the smaller the spot diameter to which the laser beam11can be focused, so that for the case of high-density recording, it is particularly preferable that the wavelength of the laser beam11is not greater than 450 nm. Moreover, if the wavelength λ is less than 350 nm, then the optical absorption by the transparent layer13for example is increased. Therefore, it is preferable that the wavelength λ of the laser beam11is at least 350 nm. Thus, it is particularly preferable that the wavelength λ of the laser beam11is in the range of 350 to 450 nm.

The substrate14is transparent and disk-shaped. A resin such as polycarbonate, amorphous polyolefin or PMMA, or glass may be used for the substrate14, for example.

If necessary, guide grooves for guiding the laser beam11may be formed on the surface of the substrate14facing the information layer16. It is preferable that the surface of the substrate14on the side facing away from the information layer16is smooth. Polycarbonate is especially advantageous as the material for the substrate14, due to its excellent transfer properties and suitability for mass production, as well as its low cost.

It is preferable that the thickness of the substrate14is in the range of 0.5 mm to 1.2 mm, so that it is sufficiently strong, and the overall thickness of the information recording medium15becomes about 1.2 mm. It should be noted that if the thickness of the transparent layer13is about 0.6 mm (thickness allowing favorable recording and reproduction at a numerical aperture of NA=0.6), then it is preferable that the thickness of the substrate14is in the range of 0.55 mm to 0.65 mm. Moreover, if the thickness of the transparent layer13is about 0.1 mm (thickness allowing favorable recording and reproduction at a numerical aperture of NA=0.85), then it is preferable that the thickness of the substrate14is in the range of 1.05 mm to 1.15 mm.

The following is a more detailed description of the configuration of the information layer16.

As noted above, the information layer16comprises a first dielectric layer102, a first interface layer103, a recording layer104, a second interface layer105, a second dielectric layer106and a reflective layer108, layered in this order from the side from which the laser beam11is incident.

The first dielectric layer102is made from a dielectric material. The function of this first dielectric layer102is to prevent oxidation, corrosion and deformation of the recording layer104, to adjust the optical distance in order to increase the optical absorption efficiency of the recording layer104, and to increase the carrier level by increasing the change in the amount of reflected light before and after recording. The first dielectric layer102can be made using an oxide such as TiO2, ZrO2, HfO2, ZnO, Nb2O2, Ta2O5, SiO2, Al2O3, Bi2O3, Cr2O3, Ga2O3, or In2O3. It also can be made using a nitride, such as C—N, Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, or Ge—Cr—N. It also can be made using a sulfide, such as ZnS, a carbide, such as SiC, or a fluoride, such as LaF3, or using C. Moreover, it is also possible to use a mixture of the above materials. For example, ZnS—SiO2, which is a mixture of ZnS and SiO2, is particularly excellent as the material of the first dielectric layer102. ZnS—SiO2is an amorphous material, which has a high refractive index, fast film formation speed, and favorable mechanical properties and resistance against moisture.

The film thickness of the first dielectric layer102can be determined strictly by calculation with the matrix method, such that the condition is satisfied that the change of the reflected light amount between the crystalline phase and the amorphous phase of the recording layer104is large.

The function of the first interface layer103is to prevent the migration of substances between the first dielectric layer102and the recording layer104due to repeated recording. It is preferable that the first interface layer103is made of a material whose optical absorption is low, which has a melting point that is so high so that it does not melt during recording, and which has good adhesion to the recording layer104. That it is a material whose melting point is so high that it does not melt during recording is a necessary property in order to ensure that the material of the first interface layer102does not melt and contaminate the recording layer104when a high power laser beam11is irradiated. The reason for this is that, if the material of the first interface layer103contaminates the recording layer104, then the composition of the recording layer104changes, and the rewriting properties deteriorate dramatically. Moreover, that it is a material with good adhesion to the recording layer104is a necessary property for ensuring reliability.

Also the function of the second interface layer105is to prevent the migration of substances between the second dielectric layer106and the recording layer104due to repeated recording, like the first interface layer103. Consequently, it is preferable that is made of a material having the same qualities.

The first interface layer103and the second interface layer105in this embodiment can be made using any of the following four combinations (I) to (IV):

(I) One of the first interface layer103and the second interface layer105is made of a Cr-containing layer containing at least Cr and O, and the other layer is made of a Ga-containing layer containing at least Ga and O.

(II) Both the first interface layer103and the second interface layer105are made of a Ga-containing layer containing at least Ga and O.

(III) One of the first interface layer103and the second interface layer105is made of a Cr-containing layer containing at least Cr and O, and the other layer is made of two layers, namely a Cr-containing layer containing at least Cr and O, and a Ga-containing layer containing at least Ga and O.
(IV) One of the first interface layer103and the second interface layer105is made of a Cr-containing layer containing at least Cr and O, the other layer is made of a Ga-containing layer containing at least Ga and O, and a C-containing layer containing C as its principal component further is provided between the recording layer and the Cr-containing layer and/or between the recording layer and the Ga-containing layer.

The present embodiment is explained for the case in which the first interface layer103and the second interface layer105are made with the combination (I).

In this embodiment, the first interface layer103is made of a material containing Cr and O or a material containing Ga and O. That is to say, the first interface layer103is a Cr-containing layer or a Ga-containing layer. Here, it is preferable that the Cr-containing layer includes the oxide Cr2O3made of Cr and O. And it is preferable that the Ga-containing layer includes the oxide Ga2O3made of Ga and O. Cr2O3and Ga2O3are materials having favorable adhesion to the recording layer104, so that by including these oxides in the first interface layer103, the adhesion to the recording layer104can be improved.

Other than Cr and O or Ga and O, the first interface layer103further may comprise M1 (where M1 is at least one element selected from Zr, Hf, Y and Si.) It is preferable that these elements are comprised as oxides, such as ZrO2, HfO2, Y2O3and SiO2. For example, ZrO2and HfO2are transparent, have a high melting point of about 2700 to 2800° C. and are oxide materials with comparatively low thermal conductivity. Consequently, including these oxides in the first interface layer103improves the repeated rewriting properties. By mixing these two oxides, an information recording medium15can be attained that has superior repeated rewriting properties and high reliability, even when formed in contact with the recording layer104.

If the first interface layer103comprises at least one of ZrO2and HfO2, then it is preferable that the content of Cr2O3included in the Cr2O3—ZrO2or Cr2O3—HfO2or the content of Ga2O3included in the Ga2O3—ZrO2or Ga2O3—HfO2of the first interface layer103is at least 10 mol %, in order to ensure the adhesion to the recording layer104. Moreover, in order to keep the optical absorption low, it is preferable that the content of Cr2O3included in the Cr2O3—ZrO2or Cr2O3—HfO2or the content of Ga2O3included in the Ga2O3—ZrO2or Ga2O3—HfO2is not greater than 90 mol %.

Moreover, if the first interface layer103contains Si as the element M1, then it is preferable that the Si is contained in the form of an oxide, such as SiO2. By including SiO2, it is possible to realize an information layer16with superior recording capabilities, in which the transparency of the first interface layer103is increased. The content of SiO2in the SiO2—Cr2O3or SiO2—Ga2O3is preferably at least 10 mol % and preferably at most 90 mol %. More preferably it is at least 10 mol % and at most 40 mol %.

Moreover, if the first interface layer103contains Y as the element M1, then it is preferable that the Y is contained in the form of an oxide, such as Y2O3. By including Y2O3, it is possible to realize an information layer16with superior repeated rewriting properties. The content of Y2O3in the Y2O3—Cr2O3or Y2O3—Ga2O3is preferably at least 10 mol % and preferably at most 90 mol %.

It is preferable that the film thickness of the first interface layer103is in the range of 0.5 nm to 15 nm, and more preferably in the range of 1 nm to 7 nm, so that the change of the amount of reflected light before and after recording in the information layer16due to optical absorption with the first interface layer103is small.

If the first interface layer103is a Cr-containing layer, then the second interface layer105is formed from a material including Ga and O. That is to say, in this case, the second interface layer105is made of a Ga-containing layer. It is then further preferable that the Ga-containing layer includes the oxide Ga2O3made of Ga and O. If the first interface layer103is a Ga-containing layer, then the second interface layer105is formed from a material including Cr and O. That is to say, in this case, the second interface layer105is made of a Cr-containing layer. It is then further preferable that it includes the oxide Cr2O3made of Cr and O. Like the first interface layer103, it also may include the element M1 in addition to Cr and O or Ga and O. Since the second interface layer105tends to have poorer adhesion to the recording layer104than the first interface layer103, it is preferable that its content of Cr2O3and Ga2O3is at least 20 mol %, which is higher than the content for the first interface layer103.

Like for the first interface layer103, is preferable that the film thickness of the second interface layer105is in the range of 0.5 nm to 15 nm, and even more preferably in the range of 1 nm to 7 nm.

For the second dielectric layer106, the same material system as for the first dielectric layer102can be used. Of these, Bi2O3—SiO2which is a mixture of Bi2O3and SiO2, is a material that is superior as the second dielectric layer106, because it has low thermal conductivity and does not include S.

It is preferable that the film thickness of the second dielectric layer106is in the range of 2 nm to 75 nm, and even more preferably in the range of 2 nm to 40 nm. By choosing the film thickness of the second dielectric layer106from this range, it is possible to disperse heat generated in the recording layer104effectively to the side of the reflective layer108.

The material of the recording layer104is a material whose phase can be changed reversibly between crystalline and amorphous by irradiation with a laser beam11. The recording layer104is made of a material including, for example, Ge, Te and M2 (where M2 is at least one element selected from Sb and Bi), and further may include at least one element of Ga and In. More specifically, the recording layer104can be made of a material expressed by Gea(M2)bTe3+a. In this material, it is preferable that 0<a≦60 and more preferably 4≦a≦40 are satisfied, so that the amorphous phase is stable, the archival characteristics at low transfer rates are good, the rise of the melting point and the decrease of the crystallization speed are low, and the archival overwrite characteristics at high transfer rates are good. Moreover, it is preferable that 1.5≦b≦7 is satisfied and even more preferable that 2≦b≦4 is satisfied, because then the decrease in the crystallization speed is low.

The recording layer104also may be made of the material (Ge-M3)a(M2)bTe3+ain which some of the Ge in Gea(M2)bTe3+ais substituted with at least one element (M3) selected from Sn and Pb. If this material is used, then the element M3 substituting the Ge improves the crystallization capability, so that a sufficiently high erasing ratio can be attained even when the film thickness of the recording layer104is thin. As the element M3, Sn is more preferable, because it is non-toxic. If this material is used, it is preferable that 0<a≦60 (more preferably 4≦a≦40) and that 1.5≦b≦7 (more preferably 2≦b≦4).

Moreover, the recording layer104also may be formed from a material including Sb and M4 (where M4 is at least one element selected from V, Mn, Ga, Ge, Se, Ag, In, Sn, Te, Pb, Bi and Au), for example. More specifically, the recording layer104can be made of a material expressed by Sbx(M4)100-x(in atom %). If x satisfies 50≦x≦95, then the difference in the reflectances of the information recording medium15in the crystalline phase and the amorphous phase of the recording layer104can be made large, and favorable recording/reproducing properties can be attained. In particular if x satisfies 75≦x≦95, then the crystallization speed is particularly fast, and favorable rewriting properties at high transfer rates are attained. Moreover, if x satisfies 50≦x≦75, then the amorphous phase is particularly stable, and favorable recording properties at low transfer rates are attained.

It is preferable that the film thickness of the recording layer104is in the range of 6 nm to 15 nm, in order to ensure a high recording sensitivity of the information layer16. Also, within this range, when the recording layer104is thick, the thermal influence on adjacent regions due to diffusion of heat in the in-plane direction becomes large. If the recording layer104is thin, then the reflectance of the information layer16becomes small. Thus, it is more preferable that the film thickness of the recording layer104is in the range of 8 nm to 13 nm.

The reflective layer108has the optical function increasing the amount of light that is absorbed by the recording layer104. The reflective layer108also has the thermal function to quickly diffuse heat that is generated in the recording layer104, and to make the amorphization of the recording layer104easier. Furthermore, the reflective layer108also has the function of protecting the multi-layer film from the environment in which it is used.

As the material of the reflective layer108, it is possible to use a single metal with a high thermal conductivity, such as Ag, Au, Cu or Al. It is also possible to use an alloy, such as Al—Cr, Al—Ti, Au—Pd, Au—Cr, Ag—Pd, Ag—Pd—Cu, Ag—Pd—Ti, Ag—Ru—Au, Ag—Cu—Ni, Ag—Zn—Al, Ag—Nd—Au, Ag—Nd—Cu or Cu—Si. In particular Ag alloys have a high thermal conductivity, so that they are preferable as the material for the reflective layer108. It is preferable that the film thickness of the reflective layer108is at least 30 nm, to attain sufficient heat diffusion. Within this range, if the reflective layer108is thicker than 200 nm, then its heat diffusion becomes too large, so that the recording sensitivity of the information layer16decreases. Consequently, it is more preferable that the film thickness of the recording layer108is in the range of 30 nm to 200 nm.

It is also possible further to provide a low thermal conductivity layer made of a material with lower thermal conductivity than the reflective layer108between the reflective layer108and the second dielectric layer106. In this case, the low thermal conductivity layer can be formed using a material that has a lower thermal conductivity than the above-noted material of the reflective layer108. For example, if an Ag alloy is used for the reflective layer108, then it is possible to use Al or an Al alloy for this low thermal conductivity layer. The low thermal conductivity layer can be made using Cr, Ni, Si or C or the like alone, or using an oxide such as TiO2, ZrO2, HfO2, ZnO, Nb2O5, Ta2O5, SiO2, SnO2, Al2O3, Bi2O3, Cr2O3or Ga2O3. It also can be made using a nitride, such as C—N, Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, or Ge—Cr—N. It also can be made using a sulfide, such as ZnS, a carbide, such as SiC, or a fluoride, such as LaF3. Moreover, it is also possible to use a mixture of the above materials. It is preferable that the film thickness of the low thermal conductivity layer is in the range of 3 nm to 100 nm (more preferably 10 nm to 50 nm).

It is preferable that reflectance Rc (%) of the information layer16when the recording layer104is in the crystalline phase and the reflectance Ra (%) when the recording layer104is in the amorphous phase satisfy Ra<Rc. Thus, the reflectance is higher in the initial state, in which no information has been recorded, than in the state in which information has been recorded, and a stable recording/reproducing operation can be accomplished. Moreover, it is preferable that Rc and Ra satisfy 0.2≦Ra≦10 and 12≦Rc≦40, more preferably 0.2≦Ra≦5 and 12≦Rc≦30, so that the difference (Rc−Ra) of the reflectances is large, and favorable recording/reproducing properties can be attained.

The information recording medium15can be manufactured by the method explained below.

First, the information layer16is formed on the substrate14(whose thickness is, for example, 1.1 mm). The information layer16is made of a multi-layer film, and the layers are formed in a film-forming device by sputtering in order with sputtering targets of the corresponding materials.

More specifically, first, the reflective layer108is formed on the substrate14. The reflective layer108can be formed by sputtering with a sputtering target made of the metal or alloy serving as the reflective layer108, in an Ar gas atmosphere or a mixed gas atmosphere made of Ar gas and a reactive gas (at least one gas selected from oxygen gas and nitrogen gas).

Subsequently, a low thermal conductivity layer is formed on the reflective layer108, if necessary. The low thermal conductivity layer can be formed by sputtering with a sputtering target made of the element or compound constituting the low thermal conductivity layer, in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.

Subsequently, the second dielectric layer106is formed on the reflective layer108(or on the low thermal conductivity layer if a low thermal conductivity layer has been formed). The second dielectric layer106can be formed by sputtering with a sputtering target made of the compound constituting the second dielectric layer106, in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas. Moreover, the second dielectric layer106also can be formed by reactive sputtering with a sputtering target made of a metal including the element constituting the second dielectric layer106, in a mixed gas atmosphere made of Ar gas and a reactive gas.

Subsequently, the second interface layer105is formed on the second dielectric layer106. The second interface layer105can be formed on the second dielectric layer106by sputtering with a sputtering target made from the compound constituting the second interface layer105(a Cr-containing sputtering target containing Cr and O if the second interface layer105is made of a Cr-containing layer, or a Ga-containing sputtering target if the second interface layer105is made of a Ga-containing layer), in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.

Subsequently, the recording layer104is formed on the second interface layer105. Depending on its composition, the recording layer104can be made by sputtering with a sputtering target made of a Ge—Te-M2 alloy, a sputtering target made of a Ge-M3-Te-M2 alloy or a sputtering target made of a Sb-M4 alloy, using one power source.

For the sputtering gas atmosphere when forming the recording layer104, it is possible to use Ar gas, Kr gas, a mixed gas of Ar gas and reactive gas, or a mixed gas of Kr gas and reactive gas. Moreover, the recording layer104also can be formed by simultaneous sputtering with sputtering targets made of the necessary elementary metals selected from Ge, Te, M2, M3, Sb and M4, using a plurality of power sources. Moreover, the recording layer104also can be formed by simultaneous sputtering with binary or ternary sputtering targets or the like combining the necessary elements selected from Ge, Te, M2, M3, Sb and M4, using a plurality of power sources. Also in these cases, it is possible to perform the sputtering in an Ar gas atmosphere, a Kr gas atmosphere, a mixed gas atmosphere of Ar gas and reactive gas, or a mixed gas atmosphere of Kr gas and reactive gas.

Subsequently, the first interface layer103is formed on the recording layer104. The first interface layer103can be formed by sputtering with a sputtering target made from the compound constituting the first interface layer103(a Cr-containing sputtering target containing Cr and O if the first interface layer103is made of a Cr-containing layer, or a Ga-containing sputtering target if the first interface layer103is made of a Ga-containing layer), in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.

Subsequently, the first dielectric layer102is formed on the first interface layer103. The first dielectric layer102is formed by sputtering with a sputtering target made of the compound constituting the first dielectric layer102, in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas. Moreover, the first dielectric layer102also can be formed by reactive sputtering with a sputtering target made of a metal including the element constituting the first dielectric layer102, in a mixed gas atmosphere made of Ar gas and a reactive gas.

Lastly, the transparent layer13is formed on the first dielectric layer102. The transparent layer13can be made by spin-coating a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin on the first dielectric layer102, and then curing the resin. Furthermore, a transparent disk-shaped resin, such as polycarbonate, amorphous polyolefin or PMMA, or a glass substrate or the like may be used for the transparent layer13. In this case, the transparent layer13can be formed by first applying a resin such as a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin on the first dielectric layer102, adhering the substrate to the first dielectric layer102and spin-coating, followed by curing the resin. Moreover, it is also possible to adhere to the first dielectric layer102a substrate to which an adhesive resin has been applied uniformly beforehand.

It should be noted that, if necessary, it is also possible to perform an initialization step of crystallizing the entire recording layer104, after the first dielectric layer102has been formed or after the transparent layer13has been formed. The crystallization of the recording layer104can be performed by irradiating a laser beam.

Thus, the information recording medium15can be manufactured as described above. It should be noted that in this embodiment, sputtering was used as the film forming method for each of the layers, but there is no limitation to this, and it is also possible to use such methods as vacuum vapor deposition, ion plating, CVD (Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy) or the like.

In Embodiment 2, an example of an information recording medium according to the present invention is explained.FIG. 2shows a partial cross-sectional view of an information recording medium19according to Embodiment 2. The information recording medium19is an optical information recording medium with a multi-layer structure (referred to as “multi-layer optical information recording medium” in the following), which includes a plurality of information layers, and which can record and reproduce information on these information layers by irradiating a laser beam11from one side.

The information recording medium19is provided with a substrate14and, formed thereon, N (N being an integer satisfying N≧2) information layers (N-th information layer18N, . . . , second information layer182, first information layer181) that are layered with optical separation layers17formed between them, and a transparent layer13formed on the first information layer181. It should be noted that in this specification, the first information layer counted from the side from which the laser beam11is incident is referred to as “first information layer181”, and the N-th information layer is referred to as “N-th information layer18N”. Here, the information layers up to the (N-1)th information layer counting from the side from which the laser beam11is irradiated have optical transparency, in order to let the laser beam11reach the N-th information layer18N, which is arranged furthest away from the side from which the laser beam11is irradiated. For the substrate14and the transparent layer13, it is possible to use a similar material as explained for Embodiment 1. Also the shape and function of the substrate14and the transparent layer13are the same as the shape and function described in Embodiment 1.

The optical separation layers17are made from a dielectric or a resin, such as a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin. The optical separation layers17preferably have a small optical absorption with respect to the laser beam11that is used, and preferably have a small optical birefringence in the short wavelength region.

The optical separation layers17are provided in order to differentiate the respective focus positions of the first information layer181, the second information layer182, . . . , to the N-th information layer18Nof the information recording medium19. The thickness of the optical separation layer17should be at least the focus depth (ΔZ), which is determined by the numerical aperture (NA) of the objective lens and the wavelength (λ) of the laser beam11. If the standard optical intensity of the focus is assumed to be 80% for the case that there are no aberrations, then the focus depth (ΔZ) can be approximated by ΔZ=λ/{2(NA)2}. If λ=405 nm and NA=0.85, then ΔZ=0.280 μm, and distances within ±0.3 μm are within the focus depth. Thus, in this case, the thickness of the optical separation layers17should be set to at least 0.6 μm. Moreover, it is desirable that the distances between the information layers are set such that the laser light can be focused using the objective lens. Consequently, it is preferable that the total thickness of the optical separation layers17is within the tolerance (e.g. not greater than 50 μm) allowed by the objective lens.

If necessary, guide grooves for guiding the laser beam11may be formed on the surface of the optical separation layers17on the side where the laser beam11is incident.

In this case, it is possible to record or reproduce the K-th information layer (where K is an integer with 1<K≦N) with a laser beam11that has passed through the first to (K−1)th information layer by only irradiating the laser beam11from one side.

It should be noted that any of the first to N-th information layers may be a read-only (ROM) information layer or a write-once (WO) information layer that can be written only once.

The following is a more detailed description of the configuration of the first information layer181.

The first information layer181comprises a first dielectric layer202, a first interface layer203, a recording layer204, a second interface layer205, a reflective layer208, and a transmittance adjusting layer209, layered in this order from the side from which the laser beam11is incident.

The first dielectric layer202can be made of the same material as the first dielectric layer102described in Embodiment 1 (seeFIG. 1), and has the same function.

The film thickness of the first dielectric layer202can be determined strictly by calculation with the matrix method, such that the following conditions are satisfied: the change of the reflected light amount between the crystalline phase and the amorphous phase of the recording layer204is large, the optical absorption at the recording layer204is large, and the transmittance of the first information layer181is large.

For the first interface layer203, it is possible to use the same material as for the first interface layer103described in Embodiment 1. Also, the function and shape are the same as for the first interface layer103of Embodiment 1.

For the second interface layer205, it is possible to use the same material systems as for the second interface layer105described in Embodiment 1. It is preferable that the film thickness of the second interface layer205is in the range of 0.5 nm to 75 nm, and more preferably in the range of 1 nm to 40 nm. By choosing the film thickness of the second interface layer205from this range, it is possible to disperse heat generated in the recording layer204effectively to the side of the reflective layer208.

It should be noted that it is also possible to arrange a further dielectric layer (second dielectric layer) between the second interface layer205and the reflective layer208. For this second dielectric layer, the same material system as for the first dielectric layer202can be used. Of these, in particular a material including Ga and O is used preferably.

The recording layer204can be formed using the same material as for the recording layer104described in Embodiment 1.

The first information layer181should have a high transmittance, in order to let the necessary amount of laser light reach the information layers that are located further away from the side from which the laser beam11is incident than the first information layer181when recording or reproducing those layers. Thus, it is more preferable that the film thickness of the recording layer204is not greater than 9 nm, and more preferably in the range of 2 nm to 8 nm.

The reflective layer208has the optical function of increasing the amount of light that is absorbed by the recording layer204. The reflective layer208also has the thermal function of quickly diffusing heat that is generated in the recording layer204, and to allow easier amorphization of the recording layer204. Furthermore, the reflective layer208also has the function of protecting the multi-layer film from the environment in which it is used.

For the material of the reflective layer208, it is possible to use the same material as for the reflective layer108in Embodiment 1. Moreover, also its function is the same as for the reflective layer108in Embodiment 1. In particular Ag alloys have high thermal conductivity, so that they are preferable as the material for the reflective layer208. It is preferable that the film thickness of the reflective layer208is in the range of 3 nm to 15 nm, more preferably in the range of 8 nm to 12 nm, in order to increase the transmittance of the first information layer181as much as possible. By setting the film thickness of the reflective layer208to this range, the reflective layer208has sufficient heat diffusion capability, a sufficient reflectance of the first information layer181can be ensured, and also the transmittance of the first information layer181is sufficient.

The transmittance adjusting layer209is made of a dielectric material, and has the function of adjusting the transmittance of the first information layer181. With this transmittance adjusting layer209, it is possible to increase both the transmittance Tc (%) of the first information layer181when the recording layer204is in the crystalline phase and the transmittance Ta (%) of the first information layer181when the recording layer204is in the amorphous phase. More specifically, with the first information layer181including the transmittance adjusting layer209, the transmittances Tc and Ta are increased by 2% to 10% compared to the case that no transmittance adjusting layer209is provided. Moreover, the transmittance adjusting layer209also has the function of effectively dispersing the heat generated in the recording layer204.

It is preferable that the refractive index n and the extinction coefficient k of the transmittance adjusting layer209satisfy 2.0≦n and k≦0.1, more preferably 2.4≦n≦3.0 and k≦0.05, in order to increase the effect of augmenting the transmittances Tc and Ta of the first information layer181.

It is preferable that the film thickness d of the transmittance adjusting layer209is within the range of ( 1/32)λ/n≦d≦( 3/16)λ/n or ( 17/32)λ/n≦d≦( 11/16)λ/n, and more preferably within the range of ( 1/16)λ/n≦d≦( 5/32)λ/n or ( 9/16)λ/n≦d≦( 21/32)λ/n. It should be noted that it is preferable that when the wavelength λ of the laser beam11and the refractive index n of the transmittance adjusting layer209are set to, for example, 350 nm≦λ≦450 nm and 2.0≦n≦3.0, then it is preferable that the film thickness d is in the range of 3 nm≦d≦40 nm or 60 nm≦d≦130 nm, and more preferably in the range of 7 nm≦d≦30 nm or 65 nm≦d≦120 nm. By choosing d from these ranges, both transmittances Tc and Ta of the first information layer181can be augmented.

The transmittance adjusting layer209can be made using an oxide such as TiO2, ZrO2, HfO2, ZnO, Nb2O5, Ta2O5, SiO2, Al2O3, Bi2O3, Cr2O3, or Si—O. It also can be made using a nitride, such as Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, or Ge—Cr—N. It is also possible to use a sulfide, such as ZnS. Moreover, it is also possible to use a mixture of the above materials. Of these, in particular TiO2or a material including TiO2is used preferably. These materials have a high refractive index (n=2.6 . . . 2.8) and a low extinction coefficient (k=0.0 . . . 0.05), so that the effect of augmenting the transmittance of the first information layer181is large.

It is preferable that the transmittances Tc and Ta of the first information layer181satisfy 40<Tc and 40<Ta, more preferably 46<Tc and 46<Ta, so that the necessary amount of laser light reaches the second to N-th information layers182to18Nwhen recording or reproducing.

It is preferable that the transmittances Tc and Ta of the first information layer181satisfy −5≦(Tc−T1)≦5, more preferably −3≦(Tc−Ta)≦3. When transmittances Tc and Ta satisfy this condition, then changes in the transmittances due to the state of the recording layer204in the first information layer181have little influence when recording or reproducing information in the second to N-th information layers182to18Nthat are arranged further away from the side on which the laser beam11is incident than the first information layer181, so that favorable recording and reproducing properties can be attained.

It is preferable that the reflectance Rc1(%) of the first information layer181when the recording layer204is crystalline and the reflectance Ra1(%) of the first information layer181when the recording layer204is amorphous satisfy the relation Ra1<Rc1. Thus, the reflectance is higher in the initial state, in which no information has been recorded, than in the state in which information has been recorded, and a stable recording/reproducing operation can be accomplished. Moreover, it is preferable that Rc1and Ra1satisfy 0.1≦Ra1≦5 and 4≦R1≦15, more preferably 0.1≦Ra1≦3 and 4≦Rc1≦10, so that the reflectance difference (Rc1−Ra1) is large and favorable recording and reproducing properties can be attained.

The information recording medium19can be manufactured by the method explained below.

First, (N−1) layers, namely the N-th information layer18Nto the second information layer182are formed in order on the substrate14(which has a thickness of, for example, 1.1 mm), with optical separation layers17interposed in between. The information layers are made of single-layer films or multi-layer film, and the layers can be formed in a film-forming device by sputtering in order with sputtering targets of the corresponding materials. The optical separation layers17can be formed by applying a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin on the information layers, and then uniformly spreading the resin by rotating the entire disk (spin-coating), and then curing the resin. It should be noted that if guide grooves for the laser beam11are formed in the optical separation layers17, then it is possible to form optical separation layers17in which predetermined guide grooves are formed in the surface by adhering a transfer substrate (mold) whose surface is provided with grooves of predetermined shape with an uncured resin, spin-coating by rotating the substrate14and the transfer substrate, curing the resin, and stripping transfer substrate from the cured resin.

Thus, a disk with (N−1) information layers (N-th information layer to second information layer) layered on the substrate14, and an optical separation layer17formed on the second information layer182is provided.

Subsequently, the first information layer181is formed on the optical separation layer17. More specifically, first, the substrate14on which the (N−1) information layers and the optical separation layers17have been formed is placed in a film-forming device, and then a transmittance adjusting layer209is formed on the uppermost optical separation layer17. The transmittance adjusting layer209is formed by sputtering with a sputtering target made of the compound constituting the transmittance adjusting layer209, in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas. Moreover, the transmittance adjusting layer209also can be formed by reactive sputtering using a sputtering target made of the metal constituting the transmittance adjusting layer209, in a mixed gas atmosphere of Ar gas and a reactive gas.

Subsequently, the reflective layer208is formed on the transmittance adjusting layer209. The reflective layer208can be formed by the same method as the reflective layer108described in Embodiment 1.

If a second dielectric layer is provided between the reflective layer208and the second interface layer205, then this second dielectric layer is formed on the reflective layer208. The second dielectric layer can be formed by the same method as the second dielectric layer106described in Embodiment 1.

Subsequently, the second interface layer205is formed on the reflective layer208(or on the second dielectric layer if a second dielectric layer is provided). The second interface layer205can be formed by the same method as the second interface layer105described in Embodiment 1.

Subsequently, the recording layer204is formed on the second interface layer205. The recording layer204can be formed by the same method as the recording layer104described in Embodiment 1, using a sputtering target with the corresponding composition.

Subsequently, the first interface layer203is formed on the recording layer204. The first interface layer203can be formed by the same method as the first interface layer103in Embodiment 1.

Subsequently, the first dielectric layer202is formed on the first interface layer203. The first dielectric layer202can be formed by the same method as the first dielectric layer102described in Embodiment 1.

Lastly, the transparent layer13is formed on the first dielectric layer202. The transparent layer13can be formed by the method described in Embodiment 1.

It should be noted that it is also possible to perform an initialization step of crystallizing the entire recording layer204, after the first dielectric layer202has been formed or after the transparent layer13has been formed. The crystallization of the recording layer204can be performed by irradiating a laser beam.

Thus, the information recording medium19can be manufactured as described above. It should be noted that in this embodiment, sputtering was used as the film forming method for each of the layers, but there is no limitation to this, and it is also possible to use such methods as vacuum vapor deposition, ion plating, CVD, or MBE or the like.

In Embodiment 3, an example of an information recording medium is explained, in which the multi-layer optical information recording medium in Embodiment 2 is provided with two information layers, that is, N=2.FIG. 3shows a partial cross-sectional view of an information recording medium20according to Embodiment 3. The information recording medium20is a two-layer optical information recording medium in which information can be recorded or reproduced on the information layers by irradiating a laser beam11from one side.

The information recording medium20is made of a substrate14, and a second information layer22, an optical separation layer17, a first information layer21and a transparent layer13layered in this order on the substrate14. For the substrate14, the optical separation layer17and the transparent layer13, it is possible to use the same materials as explained for Embodiments 1 and 2. Also their shape and function are the same as the shape and function described in Embodiments 1 and 2. Like the first information layer181described in Embodiment 2, the first information layer21is formed by layering a first dielectric layer202, a first interface layer203, a recording layer204, a second interface layer205, a reflective layer208and a transmittance adjusting layer209in this order from the side from which the laser beam11is incident.

The following is a more detailed description of the configuration of the second information layer22.

The second information layer22comprises a first dielectric layer302, a first interface layer303, a recording layer304, a second interface layer305, a second dielectric layer306, and a reflective layer308, layered in this order from the side from which the laser beam11is incident. Recording and reproduction of the second information layer22can be performed with a laser beam11that has passed through the transparent layer13, the first information layer21and the optical separation layer17.

For the first dielectric layer302, the same material as for the first dielectric layer102(seeFIG. 1) described in Embodiment 1 can be used, and it also has the same function and shape.

The film thickness of the first dielectric layer302can be determined strictly by calculation with the matrix method, such that the condition is satisfied so that the change of the reflected light amount between the crystalline phase and the amorphous phase of the recording layer304is large.

For the first interface layer303, the same material as for the first interface layer103described in Embodiment 1 can be used, and it also has the same function and shape.

For the second interface layer305, the same material as for the second interface layer105described in Embodiment 1 can be used, and it also has the same function and shape.

For the second dielectric layer306, the same material as for the second dielectric layer106described in Embodiment 1 can be used, and it also has the same function and shape.

The recording layer304can be formed using the same material as for the recording layer104described in Embodiment 1. It is preferable that the film thickness of the recording layer304is in the range of 6 nm to 15 nm, in order to ensure a high recording sensitivity of the second information layer22. Also, within this range, when the recording layer304is thick, the thermal influence on adjacent regions due to diffusion of heat in the in-plane direction becomes large. If the recording layer304is thin, then the reflectance of the second information layer25becomes small. Thus, it is more preferable that the film thickness of the recording layer304is in the range of 8 nm to 13 nm.

For the reflective layer308, the same material as for the reflective layer108described in Embodiment 1 can be used, and it also has the same function and shape.

As in Embodiment 1, it is also possible to provide a low thermal conductivity layer made of a material with lower thermal conductivity than the reflective layer308between the reflective layer308and the second dielectric layer306. The materials that can be used for such a low thermal conductivity layer are as explained in Embodiment 1, and also its film thickness is as explained in Embodiment 1.

The information recording medium20can be manufactured by the method explained below.

First, the second information layer22is formed. More specifically, first, the substrate14(having a thickness of, for example, 1.1 mm) is prepared, and placed in a film-forming device.

Subsequently, the reflective layer308is formed on the substrate14. If guide grooves for guiding the laser beam11are formed in the substrate14, then the reflective layer308is formed on the side on which the guide grooves are formed. The reflective layer308can be formed by the same method as the reflective layer108described in Embodiment 1.

Subsequently, a low thermal conductivity layer is formed on the reflective layer308, if necessary. The method for forming the low thermal conductivity layer is as explained in Embodiment 1.

Subsequently, the second dielectric layer306is formed on the reflective layer308(or on the low thermal conductivity layer if a low thermal conductivity layer has been formed). The second dielectric layer306can be formed by the same method as the second dielectric layer106described in Embodiment 1.

Subsequently, the second interface layer305is formed on the second dielectric layer306. The second interface layer305can be formed by the same method as the second interface layer105described in Embodiment 1.

Subsequently, the recording layer304is formed on the second interface layer305. The recording layer304can be formed by the same method as the recording layer104described in Embodiment 1, using a sputtering target with the corresponding composition.

Subsequently, the first interface layer303is formed on the recording layer304. The first interface layer303can be formed by the same method as the first interface layer103in Embodiment 1.

Subsequently, the first dielectric layer302is formed on the first interface layer303. The first dielectric layer302can be formed by the same method as the second dielectric layer106described in Embodiment 1.

Thus, the second information layer22is formed.

Subsequently, the optical separation layer17is formed on the first dielectric layer302of the second information layer22. The optical separation layer17can be made by applying and spin-coating a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin on the first dielectric layer302, and then curing the resin. It should be noted that if the optical separation layer17is provided with guide grooves for the laser beam11, then it is possible to form guide grooves in the surface by adhering with an uncured resin a transfer substrate (mold) whose surface is provided with grooves, spin-coating by rotating the substrate14and the transfer substrate, curing the resin, and then stripping the transfer substrate from the resin.

It should be noted that it is also possible to perform an initialization step of crystallizing the entire recording layer304, after the first dielectric layer302has been formed or after the optical separation layer17has been formed. The crystallization of the recording layer304can be performed by irradiating a laser beam.

Subsequently, the first information layer21is formed on the optical separation layer17. More specifically, first, the transmittance adjusting layer209, the reflective layer208, the second interface layer205, the recording layer204, the first interface layer203and the first dielectric layer202are formed in this order on the optical separation layer17. It is also possible to form a second dielectric layer between the reflective layer208and the second interface layer205. These layers can be formed by the method described in Embodiment 2.

Lastly, the transparent layer13is formed on the first dielectric layer202. The transparent layer13can be formed by the method described in Embodiment 1.

It should be noted that it is also possible to perform an initialization step of crystallizing the entire recording layer204, after the first dielectric layer202has been formed or after the transparent layer13has been formed. The crystallization of the recording layer204can be performed by irradiating a laser beam.

Moreover, it is possible to perform an initialization step of crystallizing the entire recording layer304of the second information layer22and the entire recording layer204of the first information layer21after forming the first dielectric layer202or after the transparent layer13has been formed. In this case, if the crystallization of the recording layer204of the first information layer21is performed first, then the laser power that is necessary for crystallizing the recording layer304of the second information layer22tends to become large, so that it is preferable to crystallize the recording layer304of the second information layer22first.

Thus, the information recording medium20can be manufactured as described above. It should be noted that in this embodiment, sputtering was used as the film forming method for each of the layers, but there is no limitation to this, and it is also possible to use such methods as vacuum vapor deposition, ion plating, CVD, or MBE or the like.

In Embodiment 4, another example of an information recording medium according to the present invention is explained.FIG. 4shows a partial cross-sectional view of an information recording medium23according to Embodiment 4. Like the information recording medium15explained in Embodiment 1, the information recording medium23is an optical information recording medium with which information can be recorded and reproduced by irradiating a laser beam11.

In the information recording medium23, different to the information recording media15,19and20explained in Embodiments 1 to 3, a substrate24is arranged on the side from which the laser beam is incident. The information recording medium23is formed by layering an information layer25on the substrate24, and adhering a dummy substrate27on the information layer25, with an adhesive layer26interposed between the information layer25and the dummy substrate27.

The substrate24and the dummy substrate27are transparent and disk-shaped. For the substrate24and the dummy substrate27, it is possible to use, for example, a resin such as polycarbonate, amorphous polyolefin or PMMA, or glass, as for the substrate14described in Embodiment 1.

It is also possible to form guide grooves for guiding the laser beam11in the surface of the substrate24on the side of the first dielectric layer102. It is preferable that the surface of the substrate24that faces away from the first dielectric layer102and the surface of the dummy substrate27that faces away from the adhesive layer26are smooth. Polycarbonate is especially advantageous as the material for the substrate24and the dummy substrate27, due to its excellent transfer properties and suitability for mass production, as well as its low cost. It is preferable that the thickness of the substrate24and the dummy substrate27is in the range of 0.3 mm to 0.9 mm, so that they are sufficiently strong, and the overall thickness of the information recording medium23becomes about 1.2 mm.

The adhesive layer26is made from a resin, such as a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin. The adhesive layer26preferably has a small optical absorption with respect to the laser beam11that is used, and preferably has a small birefringence in the short wavelength region. It should be noted that it is preferable that the thickness of the adhesive layer26is in the range of 0.6 μm to 50 μm, due to the same reasons as for the optical separation layer17.

The information layer25has the same film constitution as the information layer16described in Embodiment 1, and explanations for portions that are labeled by the same numerals as in Embodiment 1 have been omitted.

The information recording medium23can be manufactured by the method explained below.

First, the information layer25is formed on the substrate24(whose thickness is 0.6 mm, for example). If guide grooves for guiding the laser beam11are formed in the substrate24, then the information layer25is formed on the side on which the guide grooves are formed. More specifically, the substrate24is placed in a film-forming device, and the first dielectric layer102, the first interface layer103, the recording layer104, the second interface layer105, the second dielectric layer106and the reflective layer108are layered in this order. It should be noted that a low thermal conductivity layer made of a material whose thermal conductivity is lower than that of the reflective layer108may be formed between the second dielectric layer106and the reflective layer108. The method for forming the various layers is as explained in Embodiment 1.

Next, the substrate24on which the information layer25is layered and the dummy substrate27(whose thickness is 0.6 mm, for example) are glued together using an adhesive layer26. More specifically, a light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin is applied on the dummy substrate27, the substrate24on which the information layer25is layered is adhered to the dummy substrate28and spin-coating is performed, and then the resin is cured. Moreover, it is also possible to apply an adhesive resin uniformly to the dummy substrate27and adhere it to the substrate24on which the information layer25has been formed.

It should be noted that it is also possible to perform an initialization step of crystallizing the entire recording layer104after adhering the dummy substrate27to the substrate24on which the information layer25has been layered. The crystallization of the recording layer104can be performed by irradiating a laser beam.

Thus, the information recording medium23can be manufactured as described above. It should be noted that in this embodiment, sputtering was used as the film forming method for each of the layers, but there is no limitation to this, and it is also possible to use such methods as vacuum vapor deposition, ion plating, CVD, or MBE or the like.

The information recording medium23in which the substrate24is arranged on the side from which the laser beam is irradiated, as described above, has the same effects as the information recording media described in Embodiments 1 to 3.

In Embodiment 5, another example of an information recording medium according to the present invention is explained.FIG. 5shows a partial cross-sectional view of an information recording medium28according to Embodiment 5. Like the information recording medium19of Embodiment 2, the information recording medium28is a multi-layer optical information recording medium, which includes a plurality of information layers and with which information can be recorded and reproduced on the information layers by irradiating a laser beam11from one side.

The information recording medium28is made by adhering (N−1) information layers (first information layer291, second information layer292, . . . , (N−1)th information layer29N-1) layered in that order with optical separation layers17interposed in between on the substrate24, to an information layer (N-th information layer29N) formed on the substrate30, with an adhesive layer26.

The substrate30is transparent and disk-shaped. For the substrate30, it is possible to use, for example, a resin such as polycarbonate, amorphous polyolefin or PMMA, or glass, as for the substrate14described in Embodiment 1.

It is also possible to form guide grooves for guiding the laser beam11in the surface of the substrate30on the side of the N-th information layer29N. It is preferable that the surface of the substrate30on the side facing away from the N-th information layer29Nis smooth. Polycarbonate is especially advantageous as the material for the substrate30, due to its excellent transfer properties and suitability for mass production, as well as its low cost. It is preferable that the thickness of the substrate30is in the range of 0.3 mm to 0.9 mm, so that it is sufficiently strong, and the thickness of the information recording medium23becomes about 1.2 mm.

The first information layer291has the same film configuration as the first information layer181explained in Embodiment 2, so that further explanations thereof have been omitted. Also further explanations of the other portions labeled with the same numerals as in Embodiments 2 to 4 have been omitted.

The information recording medium28can be manufactured by the method explained below.

First, the first information layer291is formed on the substrate24(whose thickness is 0.6 mm, for example). If guide grooves for guiding the laser beam11are formed in the substrate24, then the first information layer291is formed on the side on which the guide grooves are formed. More specifically, the substrate24is placed in a film-forming device, and the first dielectric layer202, the first interface layer203, the recording layer204, the second interface layer205, the reflective layer208and the transmittance adjusting layer209are layered in this order. It should be noted that it is also possible to form a further dielectric layer (second dielectric layer) between the second interface layer205and the reflective layer208, if necessary. The method for forming the various layers is the same in Embodiment 2. After this, the second to (N−1)th information layer (i.e. (N−2) information layers) are layered in order, with optical separation layers interposed between them.

Moreover, the N-th information layer29Nis formed on the substrate30(whose thickness is 0.6 mm, for example). As in the Embodiments 1 to 4, the information layers are made of single-layer films or multi-layer films, and the layers can be formed in a film-forming device by sputtering in order with a sputtering target of the corresponding material.

Finally, the substrate24and the substrate30on which the respective information layers have been layered are glued together with the adhesive layer27. More specifically, a resin such as light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin may be applied on the N-th information layer, the substrate24on which the second to (N−1)th information layers are layered may be adhered to the N-th information layer and spin-coating may be performed, and then the resin may be cured. Moreover, it is also possible to apply an adhesive resin uniformly to the N-th information layer formed on the substrate30and adhere it to the (N−1)th information layer formed on the substrate24.

It should be noted that after the substrate24and the substrate30have been joined together, it is possible to perform an initialization step of crystallizing the entire recording layer204included in the first information layer291. The crystallization of the recording layer204can be performed by irradiating a laser beam.

Thus, the information recording medium28can be manufactured as described above. It should be noted that in this embodiment, sputtering was used as the film forming method for each of the layers, but there is no limitation to this, and it is also possible to use such methods as vacuum vapor deposition, ion plating, CVD, or MBE or the like.

In Embodiment 6, an example of an information recording medium is explained, in which the multi-layer optical information recording medium in Embodiment 5 is provided with two information layers, that is, N=2.FIG. 6shows a partial cross-sectional view of an information recording medium31according to Embodiment 6. Like the information recording medium20of Embodiment 3, the information recording medium31is a two-layer optical information recording medium, with which information can be recorded and reproduced on the information layers by irradiating a laser beam11from one side.

The information recording medium31includes a substrate24on which a first information layer21is formed, and a substrate30on which a second information layer22is formed, and is made by joining the first information layer21and the second information layer22together via an adhesive layer26. It should be noted that the first information layer21and the second information layer22respectively have the same film configuration as the two information layers provided in the information recording medium explained in Embodiment 3, so that a further explanation of the various layers included in the first information layer21and the second information layer22has been omitted. Also the substrate24, the substrate30and the adhesive layer26are as explained in Embodiments 4 and 5, so that their further explanation has been omitted.

The information recording medium31can be manufactured by the method explained below.

First, the first information layer21is formed on the substrate24(whose thickness is for example 0.6 mm) by the same method as explained in Embodiment 4.

If necessary, it is possible to perform an initialization step of crystallizing the entire recording layer204after the first dielectric layer202to the transmittance adjusting layer209have been formed. The crystallization of the recording layer204can be performed by irradiating a laser beam.

Moreover, the second information layer22is formed on the substrate30(whose thickness is 0.6 mm, for example). If guide grooves for guiding the laser beam11are formed in the substrate30, then the second information layer22is formed on the side on which the guide grooves are formed. More specifically, the substrate30is placed in a film-forming device, and the reflective layer308, the second dielectric layer306, the second interface layer305, the recording layer304, the first interface layer303, and the first dielectric layer302are layered in this order. It should be noted that a low thermal conductivity layer made of a material whose thermal conductivity is lower than that of the reflective layer308may be formed between the reflective layer308and the second dielectric layer306. The method for forming the various layers is the same as the method explained in Embodiment 3.

It should be noted that it is also possible to perform an initialization step of crystallizing the entire recording layer304after the first dielectric layer302has been formed. The crystallization of the recording layer304can be performed by irradiating a laser beam.

Lastly, the substrate24on which the first information layer21has been formed and the substrate30on which the second information layer22has been formed are glued together using the adhesive layer26. More specifically, a resin such as light-curing resin (in particular a UV-curing resin) or a delayed action type thermosetting resin may be applied on the first information layer21or the second information layer22, the substrate24on which the first information layer21is formed may be adhered to the substrate30on which the second information layer22is formed and spin-coating may be performed, and then the resin may be cured. Moreover, it is also possible to apply an adhesive resin uniformly to the first information layer21or the second information layer22and adhere the substrate24provided with the first information layer21to the substrate30provided with the second information layer22.

Moreover, if the recording layers204and304have not been initialized at the step of providing the first information layer21on the substrate24and the second information layer22on the substrate30, then it is possible to perform an initializing step of crystallizing the entire recording layers204and304after the gluing step. In this case, it is preferable that the recording layer304included in the second information layer22is crystallized first, for the same reasons as described in Embodiment 3.

Thus, the information recording medium31can be manufactured as described above. It should be noted that in this embodiment, sputtering was used as the film forming method for each of the layers, but there is no limitation to this, and it is also possible to use such methods as vacuum vapor deposition, ion plating, CVD, or MBE or the like.

In Embodiment 7, an example of a method for recording and reproducing information with an optical information recording medium as explained in Embodiments 1 to 6 is described.

FIG. 7diagrammatically shows the configuration of a portion of a recording/reproducing apparatus32used for an information recording/reproducing method according to the present embodiment. The recording/reproducing apparatus32includes a spindle motor33for rotating an information recording medium37, and an optical head36provided with a semiconductor laser35and an objective lens34for focusing a laser beam11emitted from the semiconductor laser35. The information recording medium37can be any of the information recording media explained in Embodiments 1 to 6, and is provided with a single information layer (for example the information layer16of the information recording medium15explained in Embodiment 1) or a plurality of information layers (for example the first information layer21and the second information layer22in the information recording medium20explained in Embodiment 3). The objective lens34focuses the laser beam11onto the information layer(s) of the information recording medium37.

The recording, erasing and overwriting of information on the information recording medium is performed by modulating the power of the laser beam11between a peak power (Pp(mW)) of high power and a bias power (Pb(mW)) of low power. By irradiating a laser beam11with the peak power, an amorphous phase is formed in a local portion of the recording layer, and this amorphous phase serves as a recording mark. Between recording marks, a laser beam11of the bias power is irradiated, and a crystalline phase (erased portion) is formed. It should be noted that if the laser beam11is irradiated with the peak power, then so-called multi-pulses are common, in which a pulse train is formed. The multi-pulses may be formed by modulating only with the power levels of the peak power and the bias power, or they may be formed by modulating with power levels in the range of 0 . . . Pp(mW).

Moreover, information signals are reproduced by setting as the reproduction power (Pr(mW)) a power that is lower than the power level of the peak power and the bias power, which does not influence the optical state of the recording marks when irradiating the laser beam11with this power level, and with which a sufficient amount of reflected light for the reproduction of the recording marks from the information recording medium can be attained. The signals from the information recording medium37obtained by irradiating a laser beam11with this reproduction power are read with a detector, thus reproducing the information signal.

The numerical aperture of the objective lens34is adjusted so that the spot diameter of the laser beam is within the range of 0.4 μm and 0.7 μm, preferably within the range of 0.5 and 1.1 μm (more preferably within the range of 0.6 and 0.9 μm). It is preferable that the wavelength of the laser beam is not greater than 450 nm (more preferably in the range of 350 nm to 450 nm). It is preferable that the linear speed of the information recording medium37when recording information is in the range of 1 m/sec to 20 m/sec (more preferably in the range of 2 m/sec to 15 m/sec), because in this range crystallization due to the reproduction light tends not to occur and a sufficient erasing capability is attained.

If, for example, the information recording medium37is the information recording medium20provided with two information layers (seeFIG. 3), then when recording on the first information layer21, the laser beam11is focused onto the recording layer204of the first information layer21, and information is recorded on the recording layer204with the laser beam11, which has passed through the transparent layer13. The reproduction of information is performed using the laser beam11that has been reflected by the recording layer204and passed through the transparent layer13. On the other hand, to record information on the second information layer22, the laser beam11is focused on the recording layer304of the second information layer22, and information is recorded with the laser beam11, which has passed through the transparent layer13, the first information layer21and the optical separation layer17. The reproduction of information is performed using the laser beam11that has been reflected by the recording layer304and passed through the optical separation layer17, the first information layer21and the transparent layer13.

It should be noted that if guide grooves for guiding the laser beam11are formed in the surface of the substrate14and the optical separation layer17of the information recording medium20, then the information may be recorded in the groove surfaces (grooves) that are closer to the side from which the laser beam11is irradiated, or in the groove surface (lands) that is further away therefrom. It is also possible to record information in both grooves and lands.

The following is an explanation of yet another embodiment of the information recording medium of the present invention.FIG. 8is a diagram schematically showing a partial cross section of an information recording medium38and the schematic configuration of an electric information recording/reproducing apparatus according to the present embodiment. The information recording medium38according to the present embodiment is an electrical information recording medium with which information can be recorded and reproduced through the application of electrical energy (for example a current).

The information recording medium38of the present embodiment includes a substrate39, and a lower electrode40, a first information layer41, a second information layer42and an upper electrode43layered in this order on the substrate39. The first information layer41is made of a first interface layer411, a recording layer412and a second interface layer413arranged in this order from the side of the substrate39. The second information layer42is made of a first interface layer421, a recording layer422and a second interface layer423arranged in this order from the side of the substrate39.

For the material of the substrate39, a resin such as polycarbonate, glass, a ceramic such as Al2O3, a semiconductor such as Si, or a metal such as Cu may be used. The following explanation is for the case that a Si substrate is used for the substrate39.

The lower electrode40and the upper electrode43are provided for applying a current to the recording layer412of the first information layer41and the recording layer422of the second information layer42.

The recording layers412and422are made of a material in which a reversible phase change between a crystalline phase and an amorphous phase can be induced by the Joule heat generated through the application of the current, and the recording of information utilizes the phenomenon that the specific resistance changes between the crystalline phase and the amorphous phase. For the material of the recording layers412and413, the same materials as for the recording layers in the information recording media explained in Embodiments 1 to 6 can be used, and the recording layers412and413can be formed by the same method.

In the first information layer41, the first interface layer411and the second interface layer413are provided in order to adjust the crystallization time of the recording layer412. In the second information layer42, the first interface layer421and the second interface layer423are provided in order to adjust the crystallization time of the recording layer422.

For the material of the first interface layers411and421and the second interface layers413and423, it is possible to use the same materials as for the first interface layer103and the second interface layer105in Embodiment 1, respectively.

For the lower electrode40and the upper electrode43, it is possible to use a single metal, such as Al, Au, Ag, Cu, Pt or the like, or an alloy material having one or a plurality of these as its principal component, or an alloy material to which one or more other elements have been added in order to increase moisture resistance or to adjust the thermal conductivity. The lower electrode40and the upper electrode43can be formed in an Ar gas atmosphere by sputtering with a sputtering target of the metal material or the alloy material serving as the electrode material. It should be noted that it is also possible to form the layers by vacuum vapor deposition, ion-plating, CVD or MBE.

The following is an explanation of the electrical information recording/reproducing apparatus44that is used for recording and reproducing information on the information recording medium38. The electrical information recording/reproducing apparatus44according to this embodiment is electrically connected to the information recording medium38via application portions45. This electrical information recording/reproducing apparatus44is provided with a pulse power source48for applying electrical pulses to the recording layers412and422that are arranged between the lower electrode40and the upper electrode43of the information recording medium38. The pulse power source48is connected to a switch47, and current pulses can be applied between the electrodes of the information recording medium38by closing this switch47. The electrical information recording/reproducing apparatus44further is provided with a resistance measuring device46for detecting resistance changes due to phase changes in the recording layers412and422. The resistance measuring device46is connected to a switch49, and the resistance measuring device46can be connected to the information recording medium38by closing this switch49. In order to change at least one of the recording layers412and422from the amorphous phase (high-resistance state) to the crystalline phase (low-resistance state), the switch47is closed (and the switch49is opened) to apply a current pulse between the electrodes, and the temperature of the portion to which the current pulse is applied, and the temperature of the portion to which the current is applied is kept, for the crystallization time, at a temperature that is higher than the crystallization temperature of the material and lower than its melting point. To change the recording layer back from the crystalline phase to the amorphous phase, a current pulse that is higher than during crystallization is applied for a short time, and the recording layer is set to a temperature that is higher than its melting point and melted, after which it is cooled rapidly.FIG. 11shows an example of recording and erasing pulses waveforms that are output from the pulse current source48of the electric information recording/reproducing apparatus44. These recording and erasing pulses waveforms are explained in more detail in the following working examples.

Let ra1be the resistance when the recording layer412of the first information layer41is in the amorphous phase, rc1be the resistance when the recording layer412is in the crystalline phase, ra2be the resistance when the recording layer422of the second information layer42is in the amorphous phase and rc2be the resistance when the recording layer422is in the crystalline phase. The sums of the resistances of the recording layer412and the recording layer422can be set to the four different values ra1+ra2, ra1+rc2, ra2+rc1and rc1+rc2, if rc1≦rc2≦ra1<ra2or rc1≦rc2≦ra2<ra1or rc2≦rc1<ra1<ra2or rc2≦rc1<ra2<ra1. Consequently, it is possible to detect four different states, that is two bits of information, by measuring the resistance between the electrodes with the resistance measuring device46.

By arranging a multitude of these information recording media38in a matrix, it is possible to configure an electric information recording medium50with large capacity, as shown inFIG. 9. Each of the memory cells51of this electric information recording medium50is formed in a tiny region and with the same configuration as the information recording medium38. The recording and reproducing of information in these memory cells51is performed by assigning one word line52and one bit line53to each of the memory cells51.

FIG. 10shows a configuration example of an information recording system using the electric information recording medium50. A storage device54includes the electric information recording medium50and an address specifying circuit55. A word line52and a bit line53of the electric information recording medium50are specified by the address specifying circuit55, and information can be recorded and reproduced with respect to each of the memory cells51. Moreover, by electrically connecting the storage device54to an external circuit56including at least a pulse power source57and a resistance measuring device58, it is possible to record and reproduce information in this electric information recording medium50.

The information recording media of the foregoing Embodiments 1 to 9 were explained using examples in which (I) of the above-described materials (I) to (IV) was used as the material for the first interface layer and the second interface layer, but there is no limitation to this, and it is also possible to use any of the materials represented by (II) to (IV), thereby attaining the same effects.

WORKING EXAMPLES

The following is a more detailed explanation of the present invention using working examples.

Working Example 1

In Working Example 1, the information recording medium15inFIG. 1was fabricated, and the relation between the materials of the first interface layer103and the second interface layer105to the recording sensitivity, signal strength and the repeated rewriting properties of the information layer16was determined. More specifically, a plurality of samples (1-1 to 1-5) with different materials for the first interface layer103and the second interface layer105were fabricated, and the recording sensitivity, the signal strength and the repeated rewriting properties of the information layer16were measured for each of these samples.

The samples were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 1.1 mm) provided with guide grooves (depth: 20 nm; track pitch: 0.32 μm) for guiding the laser beam11was prepared as the substrate14. Then, an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer108, a (Bi2O3)80(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer106, a second interface layer105(thickness: 5 nm), a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer104, a first interface layer103(thickness: 5 nm), a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer102were formed in this order by sputtering on this polycarbonate substrate.

Lastly, a UV-curing resin was applied to the first dielectric layer102, a polycarbonate sheet (diameter: 120 mm; thickness: 90 μm) was adhered to the first dielectric layer102, and a uniform resin layer was formed by rotating the entire disk. After this, a transparent layer13of 100 μm thickness was formed by curing the UV-curing resin by irradiating UV light onto this resin layer. Thereafter, an initialization step of crystallizing was performed by irradiating a laser beam onto the recording layer104. In this manner, a plurality of samples with different materials for the first interface layer103and the second interface layer105were manufactured.

Using the recording/reproducing apparatus32shown inFIG. 7, the recording sensitivity, signal strength and number of times of repeated rewriting of the information layer16in the information recording medium15was measured for the thus obtained samples. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.85, the linear speed of the samples during measurement was set to 4.9 m/s and 9.8 m/s, and the shortest mark length (2 T) was set to 0.149 μm. The information was recorded in grooves. The following is an explanation of the method for measuring the recording sensitivity, signal strength and number of times of repeated rewriting.

The recording sensitivity was evaluated by modulating the power of the laser beam11between 0 and Pp(mW), recording random signals from a mark length of 0.149 μm (2 T) to 0.596 μm (8 T) with the (1-7) modulation method, and measuring, with a time interval analyzer, the front end jitter of the recording marks (jitter (discrepancy of the mark position) at the front end portion of the recording marks) and the rear end jitter of the recording marks (jitter (discrepancy of the mark position) at the rear end portion of the recording marks). It should be noted that the recording properties are better, the smaller the jitter. Moreover, Ppand Pbare set such that the average jitter (average value of the front end jitter and the rear end jitter) becomes minimal, and the optimum Ppfor this was taken as the recording sensitivity.

The signal strength was evaluated by modulating the power of the laser beam11between 0 and Pp(mW), alternately recording signals with a mark length of 0.149 μm (2 T) and 0.671 μm (9 T) consecutively for 10 times in the same groove, and finally measuring with a spectrum analyzer the CNR (carrier-to-noise ratio) of the carrier level and the noise level at the frequency of the 2 T signal for overwriting with a 2 T signal. This CNR value was taken as the signal strength. It should be noted that the signal strength is stronger with larger CNR value.

The number of times of repeated rewriting was evaluated by modulating the power of the laser beam11between 0 and Pp(mW) and consecutively recording random signals with mark lengths of 0.149 μm (2 T) to 0.596 μm (8 T) in the same grooves, and measuring the front end jitter and the rear end jitter at each of the recording rewriting cycles with a time interval analyzer. The number of rewriting cycles at which there was an increase of 3% with respect to the average jitter of the first time was taken as the upper limit of the number of times of repeated rewriting. It should be noted that Ppand Pbwere determined such that the average jitter becomes minimal.

Tables 1 and 2 list the materials for the first interface layer103and the second interface layer105in the samples and the evaluation results regarding the recording sensitivity, signal strength and the repeated rewriting properties of the information layer16. Table 1 shows the results for a linear speed of 4.9 m/s (1×) and Table 2 shows the results for a linear speed of 9.8 m/s (2×). In the tables, Zr—Ga—O means (ZrO2)50(Ga2O3)50and Zr—Cr—O means (ZrO2)50(Cr2O3)50. In this table, Zr—Cr—O/Zr—Ga—O means that the interface layer is formed using a (ZrO2)50(Cr2O3)50layer and a (ZrO2)50(Ga2O3)50layer, and that the (ZrO2)50(Cr2O3)50layer is arranged on the side on which the recording layer is formed. For the recording sensitivity at 1× speed, a value of less than 5.2 mW was taken to be “good”, a value of at least 5.2 mW and less than 6 mW was taken to be “fair” and a value of 6 mW or more was taken to be “poor.” For the recording sensitivity at 2× speed, a value of less than 6 mW was taken to be “good”, a value of at least 6 mW and less than 7 mW was taken to be “fair” and a value of 7 mW or more was taken to be “poor.” For the signal strength at both 1× speed and 2× speed, a value of at least 48 dB was taken to be “good”, a value of at least 45 dB and less than 48 dB was taken to be “fair” and a value of less than 45 dB was taken to be “poor.” As for the repeated rewriting properties, at both 1× speed and 2× speed, a number of times of repeated rewriting of at least 1000 was taken to be “good”, a number of at least 500 and less than 1000 was taken to be “fair” and a number of less than 500 was taken to be “poor.”

As a result, it was found that in the sample 1-1 using Ge—N for the first interface layer103and the second interface layer105(comparative example), the repeated rewriting properties at 1× speed are insufficient. Moreover, it was found that in the samples 1-2, 1-3, 1-4 and 1-5 using the above-noted compositions (I) to (IV) for the first interface layer103and the second interface layer105, the recording sensitivity, the signal strength and the repeated rewriting properties are good. It was found that in particular in the sample 1-5, in which (ZrO2)50(Cr2O3)50is used for the first interface layer103and (ZrO2)50(Ga2O3)50is used for the second interface layer105, the recording sensitivity, the signal strength and the repeated rewriting properties are all particularly good.

Additional Examples

Working Example 2

In Working Example 2, information recording media15as shown inFIG. 1was fabricated, and the relation between the material of the second interface layer105and the repeated rewriting properties of the information layer16was examined. More specifically, a plurality of samples (2-1 to 2-17) with different materials for the second interface layer105were fabricated, and the number of times of repeated rewriting of the information layer16was measured for each of these samples.

The samples were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 1.1 mm) provided with guide grooves (depth: 20 nm; track pitch: 0.32 μm) for guiding the laser beam11was prepared as the substrate14. Then, an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer108, a (Bi2O3)50(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer106, a second interface layer105(thickness: 5 nm), a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer104, a (ZrO2)50(Ga2O3)50layer (thickness: 5 nm) serving as the first interface layer103, a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer102were formed in this order by sputtering on this polycarbonate substrate.

Lastly, a UV-curing resin was applied to the first dielectric layer102, a polycarbonate sheet (diameter: 120 mm; thickness: 90 μm) was adhered to the first dielectric layer102, and a uniform resin layer was formed by rotating the entire disk. Next, the UV-curing resin was cured by irradiating UV light on this resin layer. Thus, a transparent layer13of 100 μm thickness was formed.

Thereafter, an initialization step of crystallizing the recording layer104was performed by irradiating a laser beam onto the recording layer104. In this manner, a plurality of samples were manufactured in which the first interface layer103and the second interface layer105provided on both sides of the recording layer104are Ga-containing layers, and in which different materials are used for the second interface layer105.

The repeated rewriting properties of the information recording media15of the resulting samples were evaluated using the recording/reproducing apparatus32shown inFIG. 7. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.85, the linear speed of the samples during measurement was set to 4.9 m/s and 9.8 m/s, and the shortest mark length (2 T) was set to 0.149 μm. The information was recorded in grooves. The method for measuring the number of times of repeated rewriting is the same as in Working Example 1.

Tables 3 and 4 list the materials for the second interface layer105of the information layer16in the information recording media15and the evaluation results regarding the repeated rewriting properties of the information layer16. Table 3 shows the results for a linear speed of 4.9 m/s (1×) and Table 4 shows the results for a linear speed of 9.8 m/s (2×). As for the evaluation of the repeated rewriting properties, a number of times of repeated rewriting of at least 10000 was taken to be “very good”, a number of at least 1000 and less than 10000 was taken to be “good”.

As a result, it could be confirmed that when a material represented by the composition formula (Ga2O3)C1(Z1)100-C1is used for the second interface layer105, then the repeated rewriting properties are particularly good in the samples in which C1 is in the range of 10≦C1≦90 (samples 2-2 to 2-4 and 2-6 to 2-17).

Working Example 3

In Working Example 3, information recording media20as shown inFIG. 3were fabricated, and the relation between the material of the first interface layer303and the second interface layer305to the recording sensitivity, signal strength and repeated rewriting properties of the second information layer22was examined. More specifically, a plurality of samples (3-1 to 3-5) with different materials for the first interface layer303and the second interface layer305were fabricated, and the recording sensitivity, signal strength and number of times of repeated rewriting of the second information layer22were measured.

The samples were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 1.1 mm) provided with guide grooves (depth: 20 nm; track pitch: 0.32 μm) for guiding the laser beam11was prepared as the substrate14. Then, an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer208, a (Bi2O3)80(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer306, a second interface layer305(thickness: 5 nm), a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer304, a first interface layer303(thickness: 5 nm), and a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer302were formed in this order by sputtering on this polycarbonate substrate.

Next, a UV-curing resin was applied on the first dielectric layer302, a transfer substrate provided with grooves (depth: 20 nm; track pitch: 0.32 μm) was adhered thereon, and a uniform resin layer was formed by rotating the entire disk, and after curing the UV-resin by irradiation of UV light on this resin layer, the transfer substrate was stripped off. Through this step, a 25 μm thick optical separation layer17provided with guide grooves for guiding the laser beam11was formed on the side of the first information layer21.

After this, a TiO2layer (thickness: 20 nm) serving as the transmittance adjusting layer209, an Ag—Pd—Cu layer (thickness: 10 nm) serving as the reflective layer208, a (ZrO2)25(SiO2)25(Ga2O3)50layer (thickness: 10 nm) serving as the second interface layer205, a Ge28Sn3Bi2Te34layer (thickness: 6 nm) serving as the recording layer204, a (ZrO2)25(SiO2)25(Cr2O3)50layer (thickness: 5 nm) serving as the first interface layer203, and a (ZnS)80(SiO2)20layer (thickness: 40 nm) serving as the first dielectric layer202were formed in this order by sputtering on the optical separation layer17.

Lastly, a UV-curing resin was applied to the first dielectric layer202, a polycarbonate sheet (diameter: 120 mm; thickness: 65 μm) was adhered to the first dielectric layer202, and a uniform resin layer was formed by rotating the entire disk. Next, the UV-curing resin was cured by irradiating UV light on this resin layer, thus forming a 75 μm thick transparent layer13. After this, an initialization step of crystallizing the recording layer304of the second information layer22and the recording layer204of the first information layer21was performed by irradiation of a laser beam. In this manner, a plurality of samples with different materials for the first interface layer303and the second interface layer305were manufactured.

The recording sensitivity, signal strength and number of times of repeated rewriting of the second information layer23of the information recording media20of the resulting samples were evaluated using the recording/reproducing apparatus32shown inFIG. 7. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.85, the linear speed of the samples during measurement was set to 4.9 m/s and 9.8 m/s, and the shortest mark length (2 T) was set to 0.149 μm. The information was recorded in grooves. The methods for measuring the recording sensitivity, the signal strength and the number of times of repeated rewriting are the same as in Working Example 1.

Tables 5 and 6 list the materials for the first interface layer303and the second interface layer305of the second information layer22of the information recording media20and the evaluation results regarding the recording sensitivity, signal strength and the repeated rewriting properties of the second information layer22. Table 5 shows the results for a linear speed of 4.9 m/s (1×) and Table 6 shows the results for a linear speed of 9.8 m/s (2×). In the tables, Zr—Ga—O means (ZrO2)50(Ga2O3)50and Zr—Cr—O means (ZrO2)50(Cr2O3)50. In this table, Zr—Cr—O/Zr—Ga—O means that the interface layer is formed using a (ZrO2)50(Cr2O3)50layer and a (ZrO2)50(Ga2O3)50layer, and that the (ZrO2)50(Cr2O3)50layer is arranged the side on which the recording layer is formed. For the recording sensitivity at 1× speed, a value of less than 10.4 mW was taken to be “good”, a value of at least 10.4 mW and less than 12 mW was taken to be “fair” and a value of 12 mW or more was taken to be “poor.” For the recording sensitivity at 2× speed, a value of less than 12 mW was taken to be “good”, a value of at least 12 mW and less than 14 mW was taken to be “fair” and a value of 14 mW or more was taken to be “poor.” For the signal strength at both 1× speed and 2× speed, a value of at least 44 dB was taken to be “good”, a value of at least 41 dB and less than 44 dB was taken to be “fair” and a value of less than 41 dB was taken to be “poor.” As for the repeated rewriting properties, at both 1× speed and 2× speed, a number of times of repeated rewriting of at least 1000 was taken to be “good”, a number of at least 500 and less than 1000 was taken to be “fair” and a number of less than 500 was taken to be “poor.”

As a result, it was found that in the sample 3-1 using Ge—N for the first interface layer303and the second interface layer305(comparative example), the repeated rewriting properties at 1× speed are insufficient. Moreover, it was found that in the samples 3-2, 3-3, 3-4 and 3-5 using the above-noted compositions (I) to (IV) for the first interface layer303and the second interface layer305, the recording sensitivity, the signal strength and the repeated rewriting properties are good. It was found that in particular in the sample 3-5, in which (ZrO2)50(Cr2O3)50is used for the first interface layer303and (ZrO2)50(Ga2O3)50is used for the second interface layer305, the recording sensitivity, the signal strength and the repeated rewriting properties are all particularly good.

Additional Examples

Working Example 4

In Working Example 4, information recording media20as shown inFIG. 3were fabricated, and the relation between the material of the second interface layer305of the second information layer22to the repeated rewriting properties of the second information layer22was examined. More specifically, samples of information recording media20including second information layer22with different materials for the second interface layer305were fabricated, and the number of times of repeated rewriting of the second information layer22was measured for each of these samples. It should be noted that the samples of this working example were fabricated in the same manner as the samples of Working Example 3, except that (ZrO2)50(Ga2O3)50was used for the first interface layer303and the materials listed in Table 3 used in Working Example 2 were used for the second interface layer305.

As a result to evaluating the repeated rewriting properties in the same manner as in Working Example 2, it could be confirmed that when a material represented by the composition formula (Ga2O3)C1(Z1)100-C1is used for the second interface layer305, then the repeated rewriting properties are particularly good in the samples in which C1 is in the range of 10≦C1≦90, which is similar to the result obtained in Working Example 2.

Working Example 5

In Working Example 5, information recording media20as shown inFIG. 3were fabricated, and the relation between the material of the first interface layer203and the second interface layer205in the first information layer21to the recording sensitivity, signal strength and repeated rewriting properties of the first information layer21was examined. More specifically, a plurality of samples (5-1 to 5-5) with different materials for the first interface layer203and the second interface layer205were fabricated, and the recording sensitivity, signal strength and number of times of repeated rewriting of the first information layer21were measured.

The samples were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 1.1 mm) provided with guide grooves (depth: 20 nm; track pitch: 0.32 μm) for guiding the laser beam11was prepared as the substrate14. Then, an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer308, a (Bi2O3)80(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer306, a (ZrO2)25(SiO2)25(Ga2O3)50layer (thickness: 5 nm) serving as the second interface layer305, a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer304, a (ZrO2)25(SiO2)25(Cr2O3)50layer (thickness: 5 nm) serving as the first interface layer303, a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer302were formed in this order by sputtering on this polycarbonate substrate.

Next, a UV-curing resin was applied on the first dielectric layer302, a transfer substrate provided with grooves (depth: 20 nm; track pitch: 0.32 μm) was adhered thereon, and a uniform resin layer was formed by rotating the entire disk. Next, the UV-curing resin was cured by irradiating UV light on this resin layer, and then the transfer substrate was stripped off. Through this step, a 25 μm thick optical separation layer17provided with guide grooves for guiding the laser beam11was formed on the side of the first information layer21.

After this, a TiO2layer (thickness: 20 nm) serving as the transmittance adjusting layer209, an Ag—Pd—Cu layer (thickness: 10 nm) serving as the reflective layer208, a second interface layer205(thickness: 10 nm), a Ge28Sn3Bi2Te34layer (thickness: 6 nm) serving as the recording layer204, a first interface layer203(thickness: 5 nm), and a (ZnS)80(SiO2)20layer (thickness: 40 nm) serving as the first dielectric layer202were formed in this order by sputtering on the optical separation layer17.

Lastly, a UV-curing resin was applied to the first dielectric layer202, a polycarbonate sheet (diameter: 120 mm; thickness: 65 μm) was adhered to the first dielectric layer202, and a uniform resin layer was formed by rotating the entire disk. After this, a transparent layer13of 75 μm thickness was formed by curing the resin through irradiation of UV light. Thereafter, an initialization step of crystallizing the recording layer304and the recording layer204with a laser beam was performed. In this manner, a plurality of samples with different materials for the first interface layer203and the second interface layer205were manufactured.

The recording sensitivity, signal strength and number of times of repeated rewriting of the first information layer21of the information recording media20of the resulting samples were evaluated using the recording/reproducing apparatus32shown inFIG. 7. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.85, the linear speed of the samples during measurement was set to 4.9 m/s and 9.8 m/s, and the shortest mark length (2 T) was set to 0.149 μm. The information was recorded in grooves. The method for measuring the recording sensitivity, the signal strength and the number of times of repeated rewriting is the same as in Working Example 1.

Tables 7 and 8 list the materials for the first interface layer203and the second interface layer205of the first information layer21of the information recording media20and the evaluation results regarding the recording sensitivity, signal strength and the repeated rewriting properties of the first information layer21. Table 7 shows the results for a linear speed of 4.9 m/s (1×) and Table 8 shows the results for a linear speed of 9.8 m/s (2×). In the tables, Zr—Ga—O means (ZrO2)50(Ga2O3)50and Zr—Cr—O means (ZrO2)50(Cr2O3)50. In this table, Zr—Cr—O/Zr—Ga—O means that the interface layer is formed using a (ZrO2)50(Cr2O3)50layer and a (ZrO2)50(Ga2O3)50layer, and that the (ZrO2)50(Cr2O3)50layer is arranged on the side on which the recording layer is formed. For the recording sensitivity at 1× speed, a value of less than 10.4 mW was taken to be “good”, a value of at least 10.4 mW and less than 12 mW was taken to be “fair” and a value of 12 mW or more was taken to be “poor.” For the recording sensitivity at 2× speed, a value of less than 12 mW was taken to be “good”, a value of at least 12 mW and less than 14 mW was taken to be “fair” and a value of 14 mW or more was taken to be “poor.” For the signal strength at both 1× speed and 2× speed, a value of at least 43 dB was taken to be “good”, a value of at least 40 dB and less than 43 dB was taken to be “fair” and a value of less than 40 dB was taken to be “poor.” As for the repeated rewriting properties, at both 1× speed and 2× speed, a number of times of repeated rewriting of at least 1000 was taken to be “good”, a number of at least 500 and less than 1000 was taken to be “fair” and a number of less than 500 was taken to be “poor.”

As a result, it was found that in the sample 5-1 using Ge—N for the first interface layer203and the second interface layer205(comparative example), the recording sensitivity at 1× speed and 2× speed as well as the repeated rewriting properties at 1× speed are insufficient. Moreover, it was found that in the samples 3-2, 3-3, 3-4 and 3-5 using the above-noted compositions (I) to (IV) for the first interface layer203and the second interface layer205, the recording sensitivity, the signal strength and the repeated rewriting properties are good. It was found that in particular in the sample 5-5, in which (ZrO2)50(Cr2O3)50is used for the first interface layer203and (ZrO2)50(Ga2O3)50is used for the second interface layer205, the recording sensitivity, the signal strength and the repeated rewriting properties are all particularly good.

Additional Examples

Working Example 6

In Working Example 6, information recording media20as shown inFIG. 3were fabricated, and the relation between the material of the second interface layer205of the first information layer21to the repeated rewriting properties of the first information layer21was examined. More specifically, samples of information recording media20including first information layers21with different materials for the second interface layer205were fabricated, and the number of times of repeated rewriting of the first information layer21were measured for each of these samples. It should be noted that the samples of this working example were fabricated in the same manner as the samples of Working Example 5, except that (ZrO2)50(Ga2O3)50was used for the first interface layer203and the materials listed in Table 3 used in Working Example 2 were used for the second interface layer205.

As the result of evaluating the repeated rewriting properties in the same manner as in Working Example 2, it could be confirmed that when a material represented by the composition formula (Ga2O3)C1(Z1)100-C1is used for the second interface layer205, then the repeated rewriting properties are particularly good in the samples in which C1 is in the range of 10≦C1≦90, which is similar to the result obtained in Working Example 2.

Working Example 7

In Working Example 7, information recording media23as shown inFIG. 4were manufactured, and the same measurements and evaluation as in Working Example 1 were performed.

The samples in this working example were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 0.6 mm) provided with guide grooves (depth: 40 nm; track pitch: 0.344 μm) for guiding the laser beam11was prepared as the substrate24. Then, a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer102, a first interface layer103(thickness: 5 nm), a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer104, a second interface layer105(thickness: 5 nm), a (Bi2O3)50(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer106, and an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer108were formed in this order by sputtering on this polycarbonate substrate.

After this, a UV-curing resin was applied on a separately prepared dummy substrate27, and a uniform resin layer (thickness: 20 μm) was formed by adhering the reflective layer108of the information layer25formed on the substrate24to the dummy substrate27and rotating the entire disk. Then, the UV-curing resin was cured by irradiating UV light on this resin layer, thus adhering the information layer25to the dummy substrate27via the adhesive layer26. Lastly, an initialization step of crystallizing the entire recording layer104with a laser beam was performed. As in the case of Working Example 1, the materials listed in Table 1 and Table 2 were used for the first interface layer103and the second interface layer105, and five samples were fabricated.

The recording sensitivity, signal strength and number of times of repeated rewriting of the information layer25of the information recording media23of the resulting samples were measured using the same method as in Working Example 1 except the numerical aperture of the objective lens34, the linear speed of the samples, and the shortest mark length. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.65, the linear speed of the samples during measurement was set to 8.6 m/s and 17.2 m/s, and the shortest mark length was set to 0.294 μm. The information was recorded in grooves.

As in Working Example 1, it was found that in particular in information layers25in which (ZrO2)50(Cr2O3)50or (ZrO2)50(Ga2O3)50is used for the first interface layer103and the second interface layer105, the recording sensitivity, the signal strength and the repeated rewriting properties are good. It was found that in particular in the case that (ZrO2)50(Cr2O3)50is used for the first interface layer103and (ZrO2)50(Ga2O3)50is used for the second interface layer105, an information recording medium23was obtained in which the recording sensitivity, the signal strength and the repeated rewriting properties of the information layer25are all particularly good.

Working Example 8

In Working Example 8, information recording media31as shown inFIG. 6were fabricated, and the same measurements and evaluation as in Working Example 3 were performed.

The samples in this working example were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 0.6 mm) provided with guide grooves (depth: 40 nm; track pitch: 0.344 μm) for guiding the laser beam11was prepared as the substrate24. Then, a (ZnS)50(SiO2)20layer (thickness: 40 nm) serving as the first dielectric layer202, a (ZrO2)25(SiO2)25(Cr2O3)50layer (thickness: 5 nm) serving as the first interface layer203, a Ge28Sn3Bi2Te34layer (thickness: 6 nm) serving as the recording layer204, a (ZrO2)25(SiO2)25(Ga2O3)50layer (thickness: 10 nm) serving as the second interface layer205, an Ag—Pd—Cu layer (thickness: 10 nm) serving as the reflective layer208, and a TiO2layer (thickness: 20 nm) serving as the transmittance adjusting layer209were formed in this order by sputtering on this polycarbonate substrate.

Moreover, a polycarbonate substrate (diameter: 120 mm; thickness: 0.58 mm) provided with guide grooves (depth: 40 nm; track pitch: 0.344 μm) for guiding the laser beam11was prepared as the substrate30. Then, an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer208, a (Bi2O3)80(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer306, a second interface layer305(thickness: 5 nm), a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer304, a first interface layer303(thickness: 5 nm), and a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer302were formed in this order by sputtering on this polycarbonate substrate.

After this, a UV-curing resin was applied on the first dielectric layer302of the second information layer22formed on this substrate30, and a uniform resin layer (thickness: 20 μm) was formed by adhering this first dielectric layer302to the transmittance adjusting layer209of the first information layer21formed on the substrate24, and rotating the entire disk. Next, the UV-curing resin was cured by irradiating UV light on this resin layer, thus forming an adhesive layer26through which the first information layer21and the second information layer22are glued together. After this, an initialization step of crystallizing the entire recording layer304of the second information layer22and the recording layer204of the first information layer21was performed by irradiation of a laser beam. As in the case of Working Example 3, the materials listed in Table 5 and Table 6 were used for the first interface layer303and the second interface layer305, and five samples were fabricated.

The recording sensitivity, signal strength and number of times of repeated rewriting of the second information layer22of the information recording media31of the resulting samples were measured using the same method as in Working Example 3. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.65, the linear speed of the samples during measurement was set to 8.6 m/s and 17.2 m/s, and the shortest mark length was set to 0.294 μm. The information was recorded in grooves.

As in Working Example 3, it was found that in the second information layers22in which (ZrO2)50(Cr2O3)50or (ZrO2)50(Ga2O3)50is used for the first interface layer303and the second interface layer305, the recording sensitivity, the signal strength and the repeated rewriting properties are good. It was found that in particular in the case that (ZrO2)50(Cr2O3)50is used for the first interface layer303and (ZrO2)50(Ga2O3)50is used for the second interface layer305, an information recording medium31was obtained in which the recording sensitivity, the signal strength and the repeated rewriting properties of the second information layer22are all particularly good.

Working Example 9

In Working Example 9, information recording media31as shown inFIG. 6were fabricated, and the same measurements and evaluation as in Working Example 5 were performed.

The samples in this working example were manufactured as follows. First, a polycarbonate substrate (diameter: 120 mm; thickness: 0.6 mm) provided with guide grooves (depth: 40 nm; track pitch: 0.344 μm) for guiding the laser beam11was prepared as the substrate24. Then, a (ZnS)50(SiO2)20layer (thickness: 40 nm) serving as the first dielectric layer202, a first interface layer203(thickness: 5 nm), a Ge28Sn3Bi2Te34layer (thickness: 6 nm) serving as the recording layer204, a second interface layer205(thickness: 10 nm), an Ag—Pd—Cu layer (thickness: 10 nm) serving as the reflective layer208, and a TiO2layer (thickness: 20 nm) serving as the transmittance adjusting layer209were formed in this order by sputtering on this polycarbonate substrate.

Moreover, a polycarbonate substrate (diameter: 120 mm; thickness: 0.58 mm) provided with guide grooves (depth: 40 nm; track pitch: 0.344 μm) for guiding the laser beam11was prepared as the substrate30. Then, an Ag—Pd—Cu layer (thickness: 80 nm) serving as the reflective layer308, a (Bi2O3)80(SiO2)20layer (thickness: 12 nm) serving as the second dielectric layer306, a (ZrO2)25(SiO2)25(Ga2O3)50layer (thickness: 5 nm) serving as the second interface layer305, a Ge28Sn3Bi2Te34layer (thickness: 10 nm) serving as the recording layer304, a (ZrO2)25(SiO2)25(Cr2O3)50layer (thickness: 5 nm) serving as the first interface layer303, a (ZnS)80(SiO2)20layer (thickness: 60 nm) serving as the first dielectric layer302were formed in this order by sputtering on this polycarbonate substrate.

After this, a UV-curing resin was applied on the first dielectric layer302of the second information layer22formed on this substrate30, and a uniform resin layer (thickness: 20 μm) was formed by adhering this first dielectric layer302to the transmittance adjusting layer209of the first information layer21formed on the substrate24, and rotating the entire disk. Next, the UV-curing resin was cured by irradiating UV light on this resin layer. Thus, an adhesive layer26through which the first information layer21and the second information layer22are glued together was formed. Lastly, an initialization step of crystallizing the entire recording layer304and the recording layer204by irradiation with a laser beam was performed. As in the case of Working Example 5, the materials listed in Table 7 and Table 8 were used for the first interface layer203and the second interface layer205, and five samples were fabricated.

The recording sensitivity, signal strength and number of times of repeated rewriting of the first information layer21of the information recording media31of the resulting samples were measured using the same method as in Working Example 5. For this, the wavelength of the laser beam11was set to 405 nm, the numerical aperture of the objective lens34was set to 0.65, the linear speed of the samples during measurement was set to 8.6 m/s and 17.2 m/s, and the shortest mark length was set to 0.294 μm. The information was recorded in grooves.

As in Working Example 5, it was found that in the first information layer21in which (ZrO2)50(Cr2O3)50or (ZrO2)50(Ga2O3)50is used for the first interface layer203and the second interface layer205, the recording sensitivity, the signal strength and the repeated rewriting properties are good. It was found that in particular in the case that (ZrO2)50(Cr2O3)50is used for the first interface layer203and (ZrO2)50(Ga2O3)50is used for the second interface layer205, an information recording medium31was obtained in which the recording sensitivity, the signal strength and the repeated rewriting properties of the second information layer23are all particularly good.

Working Example 10

Also when in the samples fabricated in Working Example 1 to Working Example 9 a Cr-containing layer was provided between the recording layer and the Ga-containing layer provided as the interface layer, and the same measurements and evaluations were performed, the same results as in Working Example 1 to Working Example 9 were obtained. It should be noted that the composition of the Cr-containing layer that was provided between the recording layer and the Ga-containing layer was (ZrO2)50(Cr2O3)50.

Working Example 11

Also when in the samples fabricated in Working Example 1 to Working Example 9, a C-containing layer containing C as its principal component was provided between the recording layer and the Ga-containing layer provided as the interface layer and/or between the Cr-containing layer and the recording layer, and the same measurements and evaluations were performed, the same results as in Working Example 1 to Working Example 9 were obtained. It should be noted that the C-containing layer used in this Example was a layer made of carbon.

Working Example 12

Also when the Ga-containing layer in Working Example 1 to Working Example 11 further included Si, or when a portion or all of the Zr in the Ga-containing layer was substituted with at least one element selected from Hf and Y, and the same measurements and evaluations were performed, the same results as in Working Example 1 to Working Example 11 were obtained. Also when the Ga-containing layer further comprised Cr, the same results as in Working Example 1 to Working Example 11 were obtained.

Working Example 13

Also when the Cr-containing layer in Working Example 1 to Working Example 12 further included Si, or when a portion or all of the Zr in the Cr-containing layer was substituted with at least one element selected from Hf and Y, and the same experiments were performed, the same results as in Working Example 1 to Working Example 12 were obtained.

Working Example 14

In Working Example 14, the electric information recording medium38shown inFIG. 8was manufactured, and the phase change of the recording layers412and422by application of a current was confirmed.

As the substrate39, an Si substrate was prepared, whose surface was subjected to a nitration process. On this surface, a Pt layer with a surface area of 6 μm×6 μm and a thickness of 0.1 μm serving as the lower electrode40, a first information layer41, a second information layer42and a Pt layer with a surface area of 5 μm×5 μm and a thickness of 0.1 μm serving as the upper electrode43were formed on in this order by sputtering.

The first information layer41was made by forming a (ZrO2)25(SiO2)25(Cr2O3)50layer with a surface area of 4.5 μm×5 μm and a thickness of 0.01 μm serving as the first interface layer411, a Ge22Bi2Te25layer with a surface area of 5 μm×5 μm and a thickness of 0.1 μm serving as the recording layer412, and a (ZrO2)25(SiO2)25(Ga2O3)50layer with a surface area of 4.5 μm×5 μm and a thickness of 0.01 μm serving as the second interface layer413, by sputtering in this order on the lower electrode40.

The second information layer42was made by forming a (ZrO2)25(SiO2)25(Cr2O3)50layer with a surface area of 4.5 μm×5 μm and a thickness of 0.01 μm serving as the second interface layer421, a Sb70Te25Ge5layer with a surface area of 5 μm×5 μm and a thickness of 0.1 μm serving as the recording layer422, and a (ZrO2)25(SiO2)25(Ga2O3)50layer with a surface area of 4.5 μm×5 μm and a thickness of 0.01 μm serving as the second interface layer423, by sputtering in this order on the second interface layer413of the first information layer41.

It should be noted that the first interface layers411and421and the second interface layers413and423formed as above are isolators. Consequently, in order to let a current flow through the recording layers412and422, the first interface layers411and421and the second interface layers413and423are formed with a surface area that is smaller than that of the recording layers412and422, and contacting portions are provided, so that the lower electrode40, the recording layer412of the first information layer41, the recording layer422of the second information layer422and the upper electrode43are electrically connected to one another.

After this, the lower electrode40and the upper electrode43were bonded with Au lead wires, and the electric information recording/reproducing apparatus44was connected to the electric information recording medium38via the application portions45. With this electric information recording/reproducing apparatus44, the pulse power source48was connected via the switch47between the lower electrode40and the upper electrode43, and the change of the resistance due to phase changes of the recording layers412and422was detected with the resistance measuring device46connected via the switch49between the lower electrode40and the upper electrode43.

In this embodiment, the melting point Tm1of the recording layer412of the first information layer41was 630° C., its crystallization temperature Tx1was 170° C., and its crystallization time tx1was 100 ns. Moreover, the recording layer412had an amorphous phase resistance ra1of 500Ω, and a crystalline resistance rc1of 10 Ω.

Also, the melting point Tm2of the recording layer422of the second information layer42was 550° C., its crystallization temperature Tx2was 200° C., and its crystallization time tx2was 50 ns. Furthermore, the recording layer422had an amorphous phase resistance ra2of 800Ω, and a crystalline resistance rc2of 20 Ω.

FIG. 11shows an example of recording and erasing pulse waveforms that are output from the pulse power source48of the electric information recording/reproducing apparatus44. InFIG. 11, Ic1, Ic2, Ia1, Ia2, tc1, tc2, ta1, and ta2represent the following:Ic1, tc1: current and time necessary for letting the recording layer412of the first information layer41make a transition from amorphous to crystalline;Ic2, tc2: current and time necessary for letting the recording layer422of the second information layer42make a transition from amorphous to crystalline;Ia1, ta1: current and time necessary for letting the recording layer412of the first information layer41make a transition from crystalline to amorphous;Ia2, ta2: current and time necessary for letting the recording layer422of the second information layer42make a transition from crystalline to amorphous;

The relation of the current pulses to the recording layer412of the first information layer41(referred to below for convenience's sake as “first recording layer412) and the recording layer422of the second information layer42(referred to below for convenience's sake as “second recording layer422) is explained below.

When the first recording layer412and the second recording layer422are both in the amorphous phase (this referred to as “state 1” below), and a current pulse of Ic1=5 mA, tc1=150 ns was applied with the recording waveform501inFIG. 11between the lower electrode40and the upper electrode43, then only the first recording layer412made a transition from the amorphous phase to the crystalline phase (this is referred to as “state 2” below). When in state 1 a current pulse of Ic2=10 mA, tc2=100 ns was applied with the recording waveform502inFIG. 11between the lower electrode40and the upper electrode43, then only the second recording layer422made a transition from the amorphous phase to the crystalline phase (this is referred to as “state 3” below). When in state 1 a current pulse of Ic2=10 mA, tc1=150 ns was applied with the recording waveform502inFIG. 11between the lower electrode40and the upper electrode43, then both the first recording layer412and the second recording layer422made a transition from the amorphous phase to the crystalline phase (this is referred to as “state 4” below).

Next, when in state 4, in which both the first recording layer412and the second recording layer422are in the crystalline phase, a current pulse of Ia1=20 mA, Ic2=10 mA, tc2=100 ns was applied with the recording waveform504inFIG. 11between the lower electrode40and the upper electrode43, then only the first recording layer412made a transition from the crystalline phase to the amorphous phase (state 3). When in state 4 a current pulse of Ia2=15 mA, ta2=50 ns was applied with the recording waveform505inFIG. 11between the lower electrode40and the upper electrode43, then only the second recording layer422made a transition from the crystalline phase to the amorphous phase (state 2). And when in state 4 a current pulse of Ia1=20 mA, ta1=50 ns was applied with the erasing waveform506inFIG. 11between the lower electrode40and the upper electrode43, then both the first recording layer412and the second recording layer422made a transition from the crystalline phase to the amorphous phase (state 1).

When in state 2 or state 3 a current pulse of Ic2=10 mA, tc1=150 ns was applied with the recording waveform503inFIG. 11, then both the first recording layer412and the second recording layer422made a transition from the amorphous phase to the crystalline phase (state 4). Also, when in state 2 or state 3 a current pulse of Ia1=20 mA, Ic2=10 mA, tc1=150 ns, ta1=50 ns was applied with the erasing waveform507inFIG. 11, then both the first recording layer412and the second recording layer422made a transition from the crystalline phase to the amorphous phase (state 1). When in state 2 a current pulse of Ia1=20 mA, Ic2=10 mA, tc2=100 ns, ta1=50 ns was applied with the recording waveform508inFIG. 11, then the first recording layer412made a transition from the crystalline phase to the amorphous phase and the second recording layer422made a transition from the amorphous phase to the crystalline phase (state 3). Also, when in state 3 a current pulse of Ia2=15 mA, Ic1=5 mA, tc1=150 ns, ta2=50 ns was applied with the recording waveform509inFIG. 11, then the first recording layer412made a transition from the amorphous phase to the crystalline phase and the second recording layer422made a transition from the crystalline phase to the amorphous phase (state 2).

The foregoing results showed that with the electric phase-changing information recording medium38ofFIG. 8, the phases of the first recording layer412and the second recording layer422could be changed electrically between the crystalline phase and the amorphous phase, and four states (state 1: first recording layer412and second recording layer422both amorphous; state 2: first recording layer412crystalline and second recording layer422amorphous; state 3: first recording layer412amorphous and second recording layer422crystalline; state 4: first recording layer412and second recording layer422both crystalline) could be realized.

Moreover, when the number of times of repeated rewriting of the electric phase-changing information recording medium38was measured, it was confirmed that this number was at least ten times higher than in the case where the information layers41and42were not provided with the first interface layer411,421and second interface layers413,423. This is because the first interface layer411,421and second interface layers413,423suppressed the migration of substances from the lower electrode40and the upper electrode43into the first recording layer412and the second recording layer422.

Thus, the information recording medium of the present invention has the quality that recorded information can be retained for a long time (non-volatility) and is suitable for high-density rewritable or write-once optical disks, for example. It can further be applied to electric non-volatile memories.