JP4506680B2 - Optical recording medium - Google Patents

Description

  The present invention relates to an optical recording medium on which data is recorded by optically changing a recording layer when irradiated with laser light.

  Optical recording media such as CD (Compact Disc) and DVD (Digital Versatile Disc) are widely used as information recording media. Furthermore, in recent years, attention has been focused on optical recording media capable of recording information with higher density and larger capacity by using blue or blue-violet laser light as irradiation light. In order to unify the specifications, it has been proposed to use a blue-violet laser beam having a wavelength of about 405 nm, and an optical recording medium corresponding to this is becoming widespread. When blue or blue-violet laser light is used as irradiation light, tracks are formed on the optical recording medium with a track pitch in the range of 0.1 to 0.5 μm. Note that the recording capacity can be further increased if a multi-layer recording type in which a plurality of recording layers are formed with a light-transmitting spacer interposed therebetween.

  Optical recording media are roughly classified into ROM (Read Only Memory) type in which data cannot be additionally written or rewritten, R (Recordable) type in which data can be additionally written only once, and RW (Rewritable) type in which data can be rewritten. . Regarding the recording layer of the R-type optical recording medium, it is important that the optical characteristics change when irradiated with laser light, and that the recording layer hardly deteriorates even when stored for a long period of time and has excellent durability. Conventionally, an organic dye has been widely used as a material for a recording layer of an R-type optical recording medium. Such a conventional organic dye is a material that hardly absorbs ultraviolet rays, blue, and blue-violet visible light having a short wavelength that easily promotes a chemical reaction, and this property contributes to suppression of alteration.

  However, since conventional organic dyes hardly absorb blue or blue-violet short-wavelength visible light, when using blue or blue-violet laser light as irradiation light, a sufficient change in optical properties cannot be obtained, and data Could not be recorded. Further, it has been difficult to develop an organic dye that can sufficiently change the optical characteristics even when a blue or blue-violet laser beam is used as the irradiation light, and hardly changes in quality even when stored for a long period of time.

  On the other hand, an R-type optical recording medium using an inorganic material containing Bi and O as a material for the recording layer is known (see, for example, Patent Document 1 and Patent Document 2).

JP 2003-48375 A Japanese Patent Laid-Open No. 10-334507

  However, even with an inorganic material containing Bi and O, when blue or blue-violet laser light is used as irradiation light, a change in desired optical characteristics may not be obtained.

  In addition, such an inorganic material containing Bi and O changes its light transmittance as well as its reflectance when irradiated with laser light. Therefore, when an inorganic material containing Bi and O is used as the material of the recording layer of the multilayer recording type optical recording medium, the recording mark is formed by irradiating the upper recording layer (cover layer side) with laser light. Since the amount of laser light reaching the lower (substrate side) recording layer varies when no recording mark is formed, the data recording accuracy to the lower recording layer and the lower recording layer There was a problem that the reproduction accuracy of the data was low.

  The present invention has been made in view of the above problems, and provides an optical recording medium on which data can be reliably recorded / reproduced even when blue or blue-violet laser light is used as irradiation light. With the goal.

  In the present invention, a blue or blue-violet laser is used as the irradiation light by using a material mainly containing Bi (bismuth) and O (oxygen) as the recording layer material and having a ratio of the number of O atoms of 63% or more. Even when light is used, an optical recording medium on which data is reliably recorded / reproduced is realized.

Since the conventional inorganic material containing Bi and O is mainly composed of Bi ₂ O ₃ , the ratio of the number of O atoms in the recording layer is about 60%. On the other hand, in the course of reaching the present invention, the inventor formed various recording layers having different composition ratios of Bi and O and examined their optical characteristics. As a result, the number of O atoms in the recording layer was determined. When the ratio is 63% or more, the reflectance of the portion of the recording mark formed by irradiation with blue or blue-violet laser light (wavelength of about 380 to 450 nm), the reflectance of the unrecorded portion, It was found that the difference between the two increases and that data can be reliably recorded / reproduced. Further, the inventor has found that when the ratio of the number of O atoms in the recording layer is 63% or more, the light transmittance is remarkably increased, the light transmittance of the portion where the recording mark is formed, and the light of the unrecorded portion. It has been found that the difference between the transmittance and the transmittance is small, and that it is suitable as a recording layer material for a multilayer recording type optical recording medium.

  That is, the above object can be achieved by the following invention.

(1) A substrate and a recording layer formed on the substrate and having optical characteristics that change when irradiated with laser light. The recording layer contains Bi and O, and the recording layer The total number of Bi and O atoms in the recording layer with respect to the number of all atoms constituting the recording layer is 80% or more, and the ratio of the number of O atoms in the recording layer is 63% or more. An optical recording medium characterized by the above.

(2) The optical recording medium according to (1), wherein the ratio of the number of O atoms in the recording layer is 73% or less.

(3) In (1) or (2), the recording layer is characterized in that a ratio of the number of O atoms to the total number of Bi and O atoms constituting the recording layer is 63% or more. Optical recording medium.

(4) In any one of (1) to (3), the recording layer includes Mg, Ca, Y, Dy, Ce, Tb, Ti, Zr, V, Nb, Ta, Mo, W, Mn, Fe, Does not contain Zn, Al, In, Si, Ge, Sn, Sb, Li, Na, K, Sr, Ba, Sc, La, Nd, Sm, Gd, Ho, Cr, Co, Ni, Cu, Ga, Pb An optical recording medium characterized by the above.

(5) The optical recording medium according to any one of (1) to (4), wherein the recording layer is substantially made of Bi and O.

(6) The optical recording medium according to any one of (1) to (5), wherein tracks for forming recording marks are formed at a track pitch in the range of 0.1 to 0.5 μm.

(7) The optical recording according to any one of (1) to (6), wherein a light-transmitting spacer layer is provided, and a plurality of the recording layers are formed with the spacer layer interposed therebetween. Medium.

  The total value of the number of Bi and O atoms in the recording layer with respect to the number of all atoms constituting the recording layer is preferably 90% or more.

  In the present application, the term “track pitch” means that in the case of a groove type optical recording medium in which the groove portion is a track, the pitch between the groove and the groove adjacent to the groove, and the land and groove portions are tracks. In the case of a land / groove type optical recording medium, the pitch is defined as the pitch between a land and a groove adjacent to the land.

  According to the present invention, data can be reliably recorded / reproduced using blue or blue-violet laser light as irradiation light. Even in the case of a multilayer recording type, data can be recorded / reproduced with certainty.

  Hereinafter, preferred embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the optical recording medium 10 according to the first embodiment of the present invention includes a reflective layer 14, a dielectric layer 16, a recording layer 18, a dielectric layer 20, and a cover layer 22 on one surface of a substrate 12. This is an R type optical disc that is formed in this order and changes the optical characteristics of the recording layer 18 when irradiated with laser light, and is characterized by the material of the recording layer 18. The optical recording medium 10 has a disk shape with an outer diameter of about 120 mm and a thickness of about 1.2 mm.

  The substrate 12 has a thickness of about 1.1 mm, and tracks 13 are formed on the surface on the reflective layer 14 side as a groove portion with a track pitch of 0.1 to 0.5 μm. The term “groove” is generally used to mean a concave portion serving as a track, but the term “groove” is also used for convenience in the present application for the convex portion serving as a track. In the present embodiment, the groove is a convex portion protruding toward the cover layer 22 side. As the material of the substrate 12, polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, or the like can be used.

  The reflective layer 14, the dielectric layer 16, the recording layer 18, and the dielectric layer 20 are formed in a concavo-convex pattern following the concavo-convex pattern of the substrate 12.

  As the material of the reflective layer 14, Al, Ag, Au, Cu, Mg, Ti, Cr, Fe, Co, Ni, Zn, Ge, Ag, Pt, or the like can be used. Of these, it is preferable to use Al, Ag, Au, or Cu in that a high reflectance can be obtained.

Examples of the material of the dielectric layer 16 and the dielectric layer 20 include oxides such as SiO ₂ , Al ₂ O ₃ , ZnO, CeO ₂ , and Ta ₂ O ₅ , nitrides such as SiN, AlN, GeN, and GeCrN, A material whose main component is a sulfide such as ZnS or a combination thereof can be used.

  The recording layer 18 contains Bi and O, the total number of Bi and O atoms in the recording layer 18 with respect to the total number of atoms constituting the recording layer 18 is 80% or more, and the recording layer The ratio of the number of O atoms in 18 is 63% or more and 73% or less. The ratio of the number of O atoms in the recording layer 18 is preferably 63% or more with respect to the total number of Bi and O atoms in the recording layer 18.

  The cover layer 22 has a thickness of about 100 μm. As a material for the cover layer 22, an energy ray curable resin such as an acrylic ultraviolet curable resin or an epoxy ultraviolet curable resin having translucency can be used. Here, the term “energy beam” is used to mean a general term for electromagnetic waves such as ultraviolet rays and electron beams, and particle beams, which have the property of curing a specific resin in a fluid state. In addition, as a material for the cover layer 22, a light-transmitting film may be used.

  Next, the operation of the optical recording medium 10 will be described.

  The optical recording medium 10 is irradiated with blue or blue-violet laser light, whereby a recording mark is formed on the track 13 portion of the recording layer 18. Each recording mark has a reduced reflectance (changed in optical characteristics) with respect to a space portion where no recording mark is formed (detected by a reproducing photodetector). Information is recorded by forming a plurality of recording marks 24 and a plurality of space portions on the track 13. Even when blue or blue-violet laser light is used, a sufficient difference in reflectance occurs between the recording mark and the space, and information is reliably recorded / reproduced.

  Also, since the optical recording medium 10 has the dielectric layer 16 formed on one side of the recording layer 18 and the dielectric layer 20 formed on the other side, the moisture in the substrate 12 and the external moisture are recorded on the recording layer. 18 is difficult to reach, and the effect of suppressing alteration of the recording layer 18 can be obtained.

  Next, an example of a method for manufacturing the optical recording medium 10 will be described with reference to the flowchart shown in FIG.

  First, a disk-shaped substrate 12 having an outer diameter of about 120 mm and a thickness of about 1.1 mm is formed by injection molding (S102). At this time, an uneven pattern of the track 13 is formed on one surface of the substrate 12.

  Next, a reflective layer 14 is formed on the surface of the substrate 12 on which the track 13 is formed by vapor deposition such as sputtering or vapor deposition (S104). Similarly, the reflective layer is formed by sputtering or the like. A dielectric layer 16 is formed on 14 (S106). The reflective layer 14 and the dielectric layer 16 are formed in a concavo-convex pattern shape following the concavo-convex pattern of the track 13.

Next, the recording layer 18 is formed on the dielectric layer 16 by sputtering or the like (S108). Specifically, the substrate 12 is placed in a chamber (not shown) in which a Bi target is disposed, and O ₂ gas is supplied into the chamber. Further, when a sputtering gas such as Ar or Xe is supplied into the chamber and collides with a Bi target, Bi particles are scattered, reacting with O ₂ in the chamber, and being oxidized while being oxidized. Deposit on top. Thereby, the recording layer 18 is formed with a substantially uniform thickness following the uneven pattern of the track 13. By adjusting the sputtering conditions, the ratio of Bi and O in the recording layer 18 can be adjusted. The recording layer 18 is preferably composed mainly of Bi and O, but other atoms, compounds, etc. may be mixed as long as the amount is small.

  Next, the dielectric layer 20 is formed on the recording layer 18 by sputtering, vapor deposition, or the like (S110). The dielectric layer 20 is also formed in a concavo-convex pattern shape following the concavo-convex pattern of the track 13.

  Finally, the cover layer 22 is spread to a thickness of 100 μm on the dielectric layer 20 by spin coating, and cured by irradiating with ultraviolet rays or the like (S112). The cover layer 22 may be formed by adhering a previously manufactured film. Thereby, the optical recording medium 10 is completed.

  Next, a second embodiment of the present invention will be described.

  As shown in FIG. 3, the optical recording medium 50 according to the second embodiment includes a spacer layer 52 having translucency, and two recording layers 18 are formed with the spacer layer 52 interposed therebetween. It is characterized by that. Note that the reflective layer 14 is not formed on the spacer layer 52. Since other configurations are the same as those of the optical recording medium 10 according to the first embodiment, the same reference numerals as those in FIG. Note that the uneven pattern of the track 13 in the two recording layers 18 may be the same pattern or a different pattern depending on the type of the optical recording medium.

  The spacer layer 52 has a thickness of about 25 μm and is made of a material mainly composed of an energy ray curable resin having translucency such as an acrylic ultraviolet curable resin or an epoxy ultraviolet curable resin. Can do.

  Since the optical recording medium 50 can record information on the two recording layers 18, the recording capacity is large. Further, in the optical recording medium 50, the recording layer 18 contains Bi and O, and the total number of Bi and O atoms in the recording layer 18 with respect to the total number of atoms constituting the recording layer 18 is 80% or more. And has a high light transmittance of about 70%. Further, in the recording layer 18, even if the reflectance of the recording mark portion (detected by the reproducing photodetector) is lowered, the light transmittance of the blue or blue-violet laser light hardly changes. Therefore, regardless of whether data is recorded on the upper recording layer 18 (cover layer 22 side), the lower recording layer 18 is irradiated with a blue or blue-violet laser beam having a certain intensity. Thus, data can be recorded with high accuracy. Further, the data recorded on the lower recording layer 18 can be reproduced with high accuracy.

  Here, an example of a method for manufacturing the optical recording medium 50 will be briefly described. First, the reflective layer 14, the dielectric layer 16, the recording layer 18, and the dielectric layer 20 are formed on the substrate 12 in the same manner as in the first embodiment. Next, a material for the spacer layer 52 is applied on the dielectric layer 20, and a light-transmitting stamper is brought into contact therewith to form the surface of the spacer layer 52 on the side opposite to the substrate 12 into a concavo-convex pattern shape of the track 13 and 25 μm. The spacer layer 52 is cured by irradiating energy rays through the translucent stamper to peel the translucent stamper. Further, the dielectric layer 16, the recording layer 18, the dielectric layer 20, and the cover layer 22 are formed on the spacer layer 52 in the same manner as in the first embodiment. Thereby, the optical recording medium 50 is obtained.

  In the first embodiment and the second embodiment, the recording layer 18 contains Bi and O, and the number of Bi and O atoms in the recording layer 18 with respect to the total number of atoms constituting the recording layer 18. Is 80% or more, and the ratio of the number of O atoms in the recording layer 18 is 63% or more and 73% or less. For example, the recording layer 18 is 1 as in the first embodiment. When the difference in light transmittance between the recording mark and the space where no recording mark is formed is not a problem, such as when only the layer is formed, the ratio of the number of O atoms in the recording layer 18 is set to 73. It may be larger than%.

  In the first embodiment and the second embodiment, the reflective layer 14 is formed on the substrate 12. However, there is a sufficient difference in optical characteristics such as reflectance between the recording mark portion and the space portion. If obtained, the reflective layer may be omitted.

  In the first and second embodiments, the dielectric layers 16 and 20 are formed on both sides of the recording layer 18. However, the dielectric layer may be formed only on one side of the recording layer 18. In this case, if a dielectric layer is formed on the recording layer 18 on the cover layer 22 side, external moisture can be prevented from reaching the recording layer 18. On the other hand, if the dielectric layer is formed on the recording layer 18 on the substrate 12 side, moisture contained in the substrate 12 or moisture entering the substrate 12 from the outside can be prevented from reaching the recording layer. Further, when a plurality of recording layers are formed with a spacer layer interposed as in the second embodiment, the recording layer closest to the cover layer (the light incident surface side) and the recording layer closest to the substrate By forming the dielectric layer on the substrate side, it is possible to suppress the arrival of moisture from both the cover layer side and the recording layer side to the recording layer, which is preferable.

  Further, when good storage characteristics of the recording layer can be obtained, the dielectric layer may be omitted as in the optical recording medium 60 according to the third embodiment of the present invention shown in FIG.

  The optical recording medium 60 has a configuration in which the dielectric layers 16 and 20 and the reflective layer 18 are omitted from the optical recording medium 10 according to the first embodiment, and the recording layer 18 is in direct contact with the substrate 12 and the cover layer 22. . With this simple configuration, cost reduction can be achieved.

  In the second embodiment, the optical recording medium 50 is a two-layer recording type in which the two recording layers 18 are formed with the spacer layer 52 sandwiched therebetween, but the two or more spacer layers and the three or more layers are used. The present invention is also suitable for a multilayer recording type optical recording medium in which recording layers are alternately formed.

  In the first to third embodiments, the optical recording media 10, 50 and 60 are of a single-sided recording type capable of recording information on only one side, but a double-sided recording type in which recording layers are formed on both sides. Of course, the present invention can be applied to these optical recording media.

  In the first to third embodiments, the optical recording media 10, 50, 60 are formed as convex grooves when the track 13 is viewed from the cover layer 22 side, but viewed from the cover layer 22 side. The present invention is naturally applicable also to a groove-type optical recording medium in which the concave groove portion is a track. The present invention is naturally applicable to a land / groove type optical recording medium in which the land and groove portions are tracks.

  In the first to third embodiments, the optical recording media 10, 50, 60 have a structure in which the cover layer 22 is thinner than the substrate 12. However, the thickness of the substrate and the cover layer is equal to that of a DVD. The present invention is naturally applicable to an optical recording medium having

[Experimental Example 1]
A plurality of optical recording media were produced by the same method as in the first embodiment. The optical recording medium is configured such that the reflective layer 14 is omitted from the optical recording medium 10 according to the first embodiment. Other configurations are the same as those of the optical recording medium 10. In addition, in the recording layer forming step of each optical recording medium, different sputtering conditions are set as shown in Table 1, and seven types of optical recording media having different Bi and O ratios in the recording layer are produced. did.

  The manufacturing method will be described in detail. First, by injection molding, a plurality of polycarbonate resins in which a convex groove portion having a thickness of 1.1 mm, a diameter of 120 mm, a pitch of 0.32 μm and a step of 20 nm on the surface becomes the track 13 are formed. A substrate 12 was prepared.

Next, these substrates 12 were set in a sputtering apparatus, and first, a dielectric layer 16 was formed so as to have a thickness of 10 nm. The material of the dielectric layer 16 is Al ₂ O ₃ .

Further, these substrates 12 were sequentially set in a sputtering apparatus, and the recording layer 18 was formed so as to have a thickness of 15 nm. At this time, as shown in Table 1, the deposition power of the Bi target, the flow rates of Ar gas and O ₂ gas were set, and the ratio of Bi and O in the recording layer 18 was adjusted.

Next, the dielectric layer 20 was formed on the recording layer 18 by sputtering so as to have a thickness of 20 nm. The material of the dielectric layer 20 is also Al ₂ O ₃ like the dielectric layer 16.

  Finally, an ultraviolet curable acrylic resin was applied on the dielectric layer 20 by spin coating, and spread to a thickness of 100 μm, and then cured by irradiation with ultraviolet rays.

  For the seven types of optical recording media thus obtained, the reflectance and the absorptance were measured, and the light transmittance was calculated.

  Next, seven types of optical recording media are sequentially set in the optical recording medium evaluation apparatus DDU1000 (manufactured by Pulse Tech Industrial Co., Ltd.), and the laser light recording power Pw is gradually increased from 3 mW to 10 mW, and 2T and A recording mark having a length of 8T was formed and data was recorded. Other conditions were set as follows.

Laser wavelength: 405 nm
Numerical aperture NA of the objective lens: 0.85
Modulation method: (1, 7) RLL
Recording linear velocity: 5.3 m / sec
Channel bit length: 0.12 μm
Channel clock: 66 MHz
Recording method: On-groove recording Reproduction power: 0.7 mW
Intermediate power: 2.0mW
Base power: 1.0 mW

  In addition, one track was recorded by using a land groove type substrate for observation. With respect to the seven types of optical recording media on which the recording marks were thus formed, the reflectance and the absorptance were measured, and the light transmittance was calculated.

  Next, using the above-described optical recording medium evaluation apparatus, each optical recording medium is sequentially irradiated with a laser beam under the following conditions to reproduce a recording mark having a length of 8T recorded on the recording layer. The degree of modulation and the C / N ratio were measured. For measurement of the C / N ratio, a spectrum analyzer XK180 (manufactured by Advantest Corporation) was used. The playback conditions were set as follows.

Laser wavelength: 405 nm
Reproduction power Pr: 0.7 mW
Numerical aperture NA of the objective lens: 0.85

  FIG. 4 is a graph showing the relationship between the ratio of the number of O atoms in the recording layer and the C / N ratio of the reproduction signal of the recording mark having a length of 8T. As shown in FIG. 4, when the ratio of the number of O atoms is 60%, the C / N ratio is 35 dB or less, and it is difficult to reliably reproduce the recorded data. When the ratio of the number of atoms is 62% or more, the C / N ratio is remarkably increased to 45 dB or more, and recorded data can be reproduced satisfactorily. Furthermore, when the ratio of the number of O atoms in the recording layer is 63% or more, the C / N ratio is remarkably increased to 50 dB or more, so that recorded data can be reproduced more satisfactorily. The C / N ratio of the reproduction signal of the recording mark was measured again after being held for about 50 hours in a high temperature and high humidity environment with a temperature of 80 ° C. and a relative humidity of 85%, but no change was observed. That is, it was confirmed that the data storage characteristics were good.

  Further, the relationship between the wavelength of irradiated light and the absorptance was measured for three types of optical recording media in which the ratio of the number of O atoms to the total value in the recording layer was 60%, 66%, and 77%. However, the results shown in FIG. 5 were obtained. In FIG. 5, the curve with the symbol A has a ratio of the number of O atoms in the recording layer of 60%, the curve with the symbol B has a ratio of the number of O atoms in the recording layer of 66%, and the symbol C The curve attached with indicates the measurement result of the optical recording medium in which the ratio of the number of O atoms in the recording layer is 77%. In order to function as a recording layer, the absorptance needs to be at least 5% or more, and if the absorptance is 8% or more, a recording mark can be reliably formed. Therefore, an optical recording medium in which the ratio of the number of O atoms in the recording layer is 77% needs to use laser light with a wavelength of 450 nm or less as irradiation light, and preferably uses laser light with 420 nm or less. Further, an optical recording medium having a ratio of the number of O atoms in the recording layer of 66% needs to use laser light having a wavelength of 550 nm or less as irradiation light, and preferably uses laser light having a wavelength of 500 nm or less. An optical recording medium having a ratio of the number of O atoms in the recording layer of 60% exhibits a high absorption rate of 20% or more with respect to irradiation light of all wavelengths, but as described above, the wavelength of irradiation light is 405 nm. When this laser beam is used, the C / N ratio is insufficient, so that it cannot be used as a recording layer.

  In other words, an optical recording medium in which the ratio of the number of O atoms in the recording layer is 77% is suitable as an optical recording medium when laser light having a wavelength of 450 nm or less is used as irradiation light. An optical recording medium having an atomic ratio of 66% is suitable as an optical recording medium when laser light having a wavelength of 550 nm or less is used as irradiation light.

  FIG. 6 is a graph showing the relationship between the ratio of the number of O atoms in the recording layer and the light transmittance before the recording mark is formed, and FIG. 7 shows the number of O atoms in the recording layer. It is a graph which shows the relationship between a ratio and the difference of the light transmittance before and after formation of a recording mark. As shown in FIG. 6, the recording layer of the optical recording medium in which the ratio of the number of O atoms in the recording layer is 60% has a light transmittance of about 60%, whereas the O atom in the recording layer is The recording layers of the six types of optical recording media having a number ratio of 62% or more have a light transmittance higher than 65%. Furthermore, the recording layers of the five types of optical recording media in which the ratio of the number of O atoms in the recording layer is 66% or more have a high light transmittance of about 80%. Further, in the recording layer in which the ratio of the number of O atoms in the recording layer is 62 to 73%, the difference in light transmittance before and after the formation of the recording mark is suppressed to about 2%. Therefore, it can be seen that the recording layer having a ratio of the number of O atoms in the recording layer of 62 to 73% is suitable as a recording layer of an optical recording medium of, for example, three or four layers.

[Experimental example 2]
With the same configuration as the optical recording medium 60 according to the third embodiment, a plurality of types of optical recording media in which the recording layer is in direct contact with the substrate and the cover layer 22 were produced. The thickness of each recording layer 18 was 45 nm, and the other configuration was the same as that of the optical recording medium manufactured in Experimental Example 1.

  Specifically, one type of optical recording medium having a recording layer composed only of Bi and O as shown in Table 2, and Bi, O and M (M is One type selected from Mg, Y, Dy, Ce, Tb, Ti, Zr, V, Nb, Ta, Mo, W, Mn, Fe, Zn, Al, In, Si, Ge, Sn, Sb An optical recording medium having a recording layer made of (element) was produced. For optical recording media containing M shown in Tables 3 to 23, different sputtering conditions are set for each of the elements of M, and a plurality of types of optical recording in which the composition ratios of Bi, O, and M are different from each other A medium was made. Ten optical recording media of each type were produced.

  Each type of optical recording medium is irradiated with laser light having a wavelength of about 405 nm after manufacturing (without leaving it in a high-temperature and high-humidity environment) to form a recording mark having a length of 8T. N value was measured.

  Next, after holding each type of optical recording medium in a high-temperature and high-humidity environment with a temperature of 80 ° C. and a relative humidity of 85% for about 50 hours, a laser beam having a wavelength of about 405 nm is irradiated to the unrecorded portion, A recording mark having a length of 8T was formed, and its C / N signal was measured. Tables 2 to 23 show the average values of 8TC / N values of 10 optical recording media of each type.

  As shown in Table 2, in the optical recording medium having the recording layer composed only of Bi and O, the 8TC / N value of the recording mark recorded before being held in the high humidity environment exceeds 50 dB. Although the recording characteristics were good, the 8TC / N value of the recording mark formed after being held in a high humidity environment was smaller than 45 dB, and the recording characteristics were insufficient. This is a structure in which the recording layer is in direct contact with the substrate and the cover layer, and there is no dielectric layer having a function of blocking the transmission of moisture on both sides of the recording layer. This is presumably because the recording layer was altered by the permeated moisture.

  On the other hand, as shown in Tables 3 to 23, an optical recording medium having a recording layer containing M has an 8TC / N value of a recording mark formed before being held in a high humidity environment, It was confirmed that the difference between the recording mark formed after being held in a wet environment and the 8TC / N value was small, and the storage characteristics were good.

  As shown in Tables 3 to 23, when a material containing M is used as the recording layer material, if the ratio of M is excessive, the 8TC / N value may be smaller than 45 dB. It can be seen that if the ratio of the total number of Bi and O atoms to the total number of Bi, O and M atoms is 80% or more, an 8TC / N value of 45 dB or more can be reliably obtained.

  Further, in the relationship between Bi and M, the ratio of the number of Bi atoms to the total number of Bi and M atoms is 42% or more when M is a Group 2 element (Mg), and M is a Group 3 element (Y , Dy, Ce, Tb) is 39% or more, M is a Group 4 element (Ti, Zr), 38% or more, and M is a Group 5 or 6 element (V, Nb, Ta, Mo, W). 56% or more in the case of M, 41% or more when M is a Group 7 or 8 element (Mn, Fe), 63% or more when M is a Group 12 element (Zn), M is a Group 13 element (Al, In) Is 65% or more, and when M is a group 14 to 16 element (Si, Ge, Sn, Sb), it is preferably 62% or more.

  Thus, by adding M to Bi and O, the storage characteristics can be improved. Therefore, it is possible to realize an optical recording medium that has a simple structure in which the dielectric layer does not exist on both sides of the recording layer, the recording layer is in direct contact with the substrate and the cover layer, and is low in cost and has good storage characteristics. .

  Here, a method for measuring light transmittance will be briefly described. Specifically, using an optical film thickness measuring device ETA-RT (manufactured by Steag ETA-OPTIK Co., Ltd.), the recording layer is irradiated with laser light to measure the absorption rate, and the light transmittance is calculated from the absorption rate. Calculated. Since there is an influence of surface reflection, the light transmittance value excluding the influence was obtained. That is, the light transmittance was calculated by the following formula.

  Light transmittance = 100-Reflectance-Absorptance (turbulent reflection, refraction)

  The reflectance was measured using the above-described optical recording medium evaluation apparatus DDU1000.

Next, a method for measuring the ratio of the number of Bi, O, and M atoms in the recording layer will be described. The ratio of the number of Bi and O atoms in the recording layer of the optical recording medium was measured by preparing a sample for composition analysis. Specifically, a plurality of Si substrates having a thickness of 0.5 mm are prepared, and these Si substrates are sequentially set in a sputtering apparatus, and Bi target, M target deposition power, Ar gas, O ₂ gas The flow rate was set to the conditions shown in Table 1 and Tables 3 to 23, which were the same as those for producing the plurality of optical recording media, and a recording layer was formed on the Si substrate so that the thickness was 200 nm.

Next, using a fluorescent X-ray apparatus RIX2000 (manufactured by Rigaku Denki Kogyo Co., Ltd.), for Bi measurement, X-rays are generated at a tube voltage of Rh tube = 40 kV and a tube current of 30 mA, and O measurement. X-rays were generated at a tube voltage of the Rh tube = 30 kV and a tube current of 120 mA, and the contents of Bi and O contained in the recording layer were measured by the FP method. At this time, Al was used for the primary X-ray filter, Bi-Lα rays were used as Bi characteristic X-rays, and O-Kα rays were used as O characteristic X-rays. As the characteristic X-ray of the additive element M, an optimum characteristic X-ray was used. The device sensitivity calibration constant of the additive element M was obtained using the bulk as a standard sample. The Bi apparatus sensitivity calibration coefficient required for the FP method was Bi bulk as a standard sample, and the O apparatus sensitivity calibration coefficient was a sample prepared by the briquette method. An Al ring with an inner diameter of 30 mm, a height of 4 mm, and a thickness of 2 mm is used as a protective ring. By placing Bi ₂ O ₃ powder (manufactured by High Purity Chemical Co., Ltd.) in this ring and pressing at about 147000 N, about 2 mm A briquette was prepared. The instrument sensitivity calibration coefficients were 1.20270 for Bi and 0.299447 for O.

  The present invention can be used for an optical recording medium on which data is recorded by irradiating a laser beam to change optical characteristics of a recording layer.

1 is a side sectional view schematically showing the structure of an optical recording medium according to a first embodiment of the invention. Flow chart showing an outline of the manufacturing process of the optical recording medium Side sectional view which shows typically the structure of the optical recording medium based on 2nd Embodiment of this invention. Graph showing the relationship between the ratio of the number of O atoms in the recording layer and the C / N ratio of the reproduction signal of the 8T recording mark in the experimental example Graph showing the relationship between the wavelength of irradiated light and the absorptance in the experimental example The graph which shows the relationship between the ratio of the number of O atoms in the recording layer in the experiment example and the light transmittance before the recording mark is formed A graph showing the relationship between the ratio of the number of O atoms in the recording layer in the experimental example and the difference in light transmittance before and after the formation of the recording mark Sectional drawing which shows typically the structure of the optical recording medium which concerns on 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 50, 60 ... Optical recording medium 12 ... Substrate 13 ... Groove 14 ... Reflective layer 16, 20 ... Dielectric layer 18 ... Recording layer 22 ... Cover layer 52 ... Spacer layer S102 ... Substrate shaping | molding process S104 ... Reflective layer formation process S106 ... Dielectric layer forming step S108 ... Recording layer forming step S110 ... Dielectric layer forming step S112 ... Cover layer forming step

Claims (4)

An optical recording medium in which laser light having a wavelength of 380 to 450 nm is used as irradiation light, a substrate, a recording layer formed on the substrate, and having optical characteristics changed by irradiation with the laser light of the wavelength, becomes a, the recording layer comprises Bi and O, all ratios the number of O atoms of the recording layer against the number of atoms constituting the recording layer is 63% or more An optical recording medium characterized by the above. In claim 1,
An optical recording medium, wherein the ratio of the number of O atoms in the recording layer is 73% or less. In claim 1 or 2 ,
An optical recording medium characterized in that tracks for forming recording marks are formed at a track pitch in the range of 0.1 to 0.5 μm. In any one of Claims 1 thru | or 3 ,
An optical recording medium comprising a light-transmitting spacer layer, and a plurality of the recording layers formed with the spacer layer interposed therebetween.

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