JP4231434B2 - Information recording medium - Google Patents

Description

  The present invention relates to an information recording medium on which information is recorded by irradiation with an energy beam. In particular, the present invention relates to a phase change optical disc compatible with a red laser such as DVD-RAM, DVD-RW, DVD + RW, and Blu-ray, HD (High Density). The present invention relates to a phase change type optical disc compatible with a blue laser such as DVD.

  In recent years, the market for read-only optical disks such as DVD-ROM and DVD-Video has been expanded. Following this, the market for rewritable DVDs such as DVD-RAM, DVD-RW, DVD + RW, etc., is rapidly expanding as a computer backup medium and a video recording medium replacing VTR. With the expansion of this market, in recent years, there has been an increasing demand for improvement in transfer rate and access speed and increase in capacity for recordable DVDs.

  In recordable erasable DVDs such as DVD-RAM and DVD-RW, a phase change recording method using a phase change material for a recording layer on which information is recorded is employed. In the phase change recording method, information of “0” and “1” is basically recorded in correspondence with the crystalline state and the amorphous state of the phase change material. In addition, since the refractive index of the phase change material is different between the crystalline state and the amorphous state, each layer constituting the recording type DVD is configured so that the difference in reflectance between the portion changed into the crystal and the portion changed into the amorphous is maximized. The refractive index, film thickness, etc. are designed. The crystallized part and the amorphous part are irradiated with laser light, and the difference in the amount of light reflected from each part of the optical disk is detected to detect “0” and “1” recorded in the recording layer.

  In addition, in order to make the predetermined position amorphous (usually, this operation is called “recording”), a relatively high power laser beam is irradiated and the temperature of the recording layer becomes equal to or higher than the melting point of the recording layer material. To heat. On the other hand, in order to crystallize a predetermined position (usually, this operation is called “erasing”), a crystal having a temperature of the recording layer equal to or lower than the melting point of the recording layer material is irradiated with a relatively low power laser beam. Heat to a temperature near the conversion temperature. In this way, by adjusting the power of the laser light applied to the predetermined portion of the recording layer, the state of the predetermined portion can be reversibly changed between the amorphous state and the crystalline state.

  As described above, the phase change material used for the recording layer of the information recording medium of the phase change recording method has a large difference in refractive index between the amorphous state and the crystalline state, and the amorphous crystallizes in an erasing operation in a very short time. The material to be preferred is preferred. In addition, a material that is less deteriorated by repeated recording and erasing is preferable. From such a viewpoint, conventionally, various phase change materials have been studied.

  For example, in Japanese Patent Laid-Open No. 2001-322357, high-density recording is possible by using a material in which a metal such as Ag, Al, Cr, or Mn is added to a Ge—Sn—Sb—Te-based material as a recording material. It is disclosed that an information recording medium excellent in repeated rewritability and having little deterioration over time in crystallization sensitivity can be obtained. JP-A-2-14289 discloses a Ge—Sb—Sn—Te recording layer material.

  Japanese Patent Application Laid-Open No. 62-209741 discloses a Bi-Ge-Te phase change recording material, and a practical composition range of the material is defined. Japanese Patent Laid-Open No. 1-287836 discloses a practical range of a Bi—Ge—Sb—Te phase change recording material. Further, a Bi-Ge-Se-Te phase change recording material has been proposed as a recording layer forming material, and its practical range is disclosed (for example, see Patent Documents 1 and 2).

  Furthermore, PCOS2001 reports a Ge—Sn—Sb—Te-based material as a recording material that can cope with the double to quadruple speed of DVD-RAM. In ISO / ODS2002, an information recording medium capable of supporting 2 × and 5 × speeds of DVD-RAM has been reported, and this 5 × speed medium achieves 5 × speed by adopting an 8-layer structure with a new nucleation layer added. is doing.

  As a technology for increasing the capacity of a recordable DVD, the laser spot diameter is further reduced by reducing the wavelength of the laser light to 405 nm and increasing the objective lens NA to 0.85. A method for recording information is known (for example, Jpn. J. Appl. Phys. Vol. 39 (2000), pp. 756-761, Part 1, No. 2B, Feb. 2000). This method is used as a main technology of the so-called Blu-ray Disc, and the influence on the disc tilt is reduced by adopting a substrate having a thickness of 0.1 mm thinner than that of a conventional DVD. A 0.1 mm thick substrate used for Blu-ray Disc plays important roles such as mechanical protection and electrochemical protection (corrosion prevention) of the recording layer.

  The basic structure of a rewritable optical disk such as a conventional DVD-RAM or DVD-RW is that a first dielectric layer, a phase change recording layer, a second dielectric layer and a reflection are formed on a polycarbonate (PC) substrate having a thickness of 0.6 mm. It has a four-layer structure in which layers are sequentially stacked, and is manufactured by bonding a 0.6 mm thick substrate from the reflective layer side. However, in the above-described Blu-ray Disc, if the substrate is manufactured with a laminated structure similar to that of a conventional optical disc, the thickness of the substrate is as thin as 0.1 mm, so that it is difficult to maintain the rigidity of the substrate. Therefore, the Blu-ray Disc is formed by sequentially stacking a reflective layer, a second dielectric layer, a phase change recording layer, and a first dielectric layer on a thick substrate, for example, a 1.1 mm thick PC substrate (conventional rewriting). Finally, the substrate is manufactured by forming a substrate having a thickness of 0.1 mm from the first dielectric side as a cover layer. The cover layer of the Blu-ray Disc is formed by attaching a 0.1 mm thick sheet on the first dielectric layer with an ultraviolet curable resin adhesive, and spinning the ultraviolet curable resin on the first dielectric layer. A method of forming a cover layer by applying uniformly by a coating method and curing an ultraviolet curable resin by ultraviolet irradiation has been proposed.

  As a material for forming a recording layer of Blu-ray Disc, for example, an Ag—In—Sb—Te recording material disclosed in Japanese Patent No. 2941848 can be used. This document also discloses in detail the composition of a material obtained by adding a fifth element and a sixth element to an Ag—In—Sb—Te recording material.

  Also, as a method for increasing the capacity of a recordable DVD, an optical disk in which each layer is laminated on a 0.6 mm-thick substrate in the same order as in the past, the laser light wavelength is 405 nm, and the objective lens NA is 0.65. A method of recording information has also been proposed. This method has a larger laser spot diameter and a lower recording density because the objective lens NA is smaller than a method using a cover layer having a thickness of 0.1 mm such as the aforementioned Blu-ray Disc. However, there is an advantage that the rigidity of the substrate can be easily maintained and the recording layer can be easily multi-layered. There is also an advantage that the influence of dust and scratches on the medium can be reduced.

JP 62-73439 A (first page, FIG. 1) JP-A-1-220236 (first page, FIG. 1)

  By the way, in a replaceable information recording medium such as the optical disk described above, compatibility with various information recording apparatuses is extremely important. For example, DVD-RAM media already have DVD-RAM drives compatible with double speed recording (transfer rate: 22 Mbps) by CLV rotation control, but DVD-RAM media for CAV control recording (22 to 55 Mbps) are available. It is important from the viewpoint of the consumer's benefit to ensure that recording / reproduction is performed with this double speed CLV compatible drive. On the other hand, it is of course very important to ensure that the CAV compatible DVD-RAM medium recorded by the double speed CLV compatible drive can be recorded and reproduced by the CAV compatible drive.

  In the near future, a blue laser drive (HD DVD) that follows the DVD-RAM drive recording method (method of recording by irradiating laser light from the substrate side) will be introduced to the market. Drive demand is expected to grow steadily. In addition, with the widespread use of 1x speed recording drives equipped with blue lasers, as with DVD-RAM drives using red lasers, demand for 2x and 3x speed compatible drives capable of recording at higher speeds will arise. Easy to predict. In such a situation, it is important to maintain compatibility between the 1 × speed recording drive and the 2 × and 3 × speed compatible drives capable of high-speed recording.

  The object of the present invention is to have high durability against repeated data recording and high-speed recording even when information recording is performed with a blue laser in an information recording medium using a Bi-Ge-Te phase change material as a recording layer. In addition, an information recording medium having a wide range of recording linear velocities that can be handled is provided.

Before explaining the information recording medium of the present invention, the background to the present invention will be described. Among the above-described conventional phase change materials, the present inventors use a Bi—Ge—Te phase change material as a recording layer, and set the composition ratio of Bi, Ge, and Te in the recording layer to Bi, Ge, and Te. It was found by a verification experiment that an information recording medium with high reliability of recorded data and high durability against repeated recording of data can be obtained by making the composition range surrounded by the following points on the triangular composition diagram.
_{B2 (Bi 2, Ge 47,} Te 51)
C2 (Bi ₃ , Ge ₄₇ , Te ₅₀ )
D2 (Bi ₄ , Ge ₄₇ , Te ₄₉ )
_{D6 (Bi 16, Ge 37,} Te 47)
C8 (Bi ₃₀ , Ge ₂₂ , Te ₄₈ )
B7 (Bi ₁₉ , Ge ₂₆ , Te ₅₅ )
The composition range surrounded by the above points on the triangular composition diagram of Bi, Ge, and Te is shown in FIG. The composition range surrounded by the thick line in FIG. 3 is the optimum composition range of the recording layer in order to obtain an information recording medium with high reliability of recording data and high durability against repeated recording of data.

In the conventional example (Japanese Patent Laid-Open No. 62-209741), the practical composition range of the Bi-Ge-Te phase change material is GeTe and Bi ₂ Te ₃ on the triangular composition diagram with Bi, Ge and Te as vertices. It exists in existing in the area | region on the line which connects. However, according to the present inventors' verification experiment, a Bi-Ge-Te phase change material having a composition of a region where Ge is excessively added to the line connecting GeTe and Bi ₂ Te ₃ is used as the recording layer. Thus, it was found that the signal quality was good and the durability against repeated recording was excellent.

This is thought to be due to the following reasons. Bi-Ge-Te phase change materials include compounds of GeTe, Bi ₂ Te ₃ , Bi ₂ Ge ₃ Te ₆ , Bi ₂ GeTe ₄ and Bi ₄ GeTe _{7 to} the extent that has been clarified so far. To do. When a part of the melted region is recrystallized immediately after being melted by irradiating a light beam to record (amorphize) information in a predetermined part of the recording layer, it depends on the composition of the recording layer. It is considered that the compound, Bi, Ge and Te mentioned above are recrystallized from the outer edge of the melting region in order from the material having the highest melting point. When these substances are arranged in descending order of melting point, they are as follows.
Ge: about 937 ° C
GeTe: about 725 ° C
Bi ₂ Ge ₃ Te ₆ : about 650 ° C.
Bi ₂ Te ₃ : about 590 ° C
Bi ₂ GeTe ₄ : about 584 ° C
Bi ₄ GeTe ₇ : about 564 ° C.
Te: about 450 ° C.
Bi: about 271 ° C

Since the melting point of Ge is the highest as described above, the phase change material in which Ge is excessively added is recorded from the composition material on the line connecting GeTe and Bi ₂ Te ₃ in the triangular composition diagram with Bi, Ge and Te as vertices. In the information recording medium used as the layer, it is considered that Ge is easily segregated at the outer edge of the melted region. When Ge is excessively present at the outer edge portion of the melting region, the crystallization speed of the outer edge portion of the melting region is reduced, and recrystallization from the outer edge portion can be suppressed. Therefore, it is possible to suppress the occurrence of recrystallization “bands” caused by rewriting many times. At the same time, the crystallization speed is high near the track center (the center of the melted region), and good erasing performance can be obtained even during high-speed recording. However, if the amount of Ge added is too large, the crystallization speed of the entire recording film decreases, so it is important to set the amount of Ge added excessively to an appropriate amount.

  If recrystallization from the outer edge of the melting area can be suppressed, it is not necessary to increase the laser power in order to improve the reproduction signal amplitude, and it is not necessary to melt a wide area, and the recording mark recorded on the adjacent track is erased. The problem (cross erase) can be solved.

In addition, as a phase change material used for a recording layer of an information recording medium of a phase change recording method, from the viewpoint of the storage life of a recording mark in an amorphous state, a plurality of phases in an amorphous state do not exist, and the crystallization temperature of the material is It is important that the activation energy is high when the amorphous material is crystallized. The present inventors have found through a verification experiment that the above condition is satisfied in the vicinity of Ge ₅₀ Te _{50 in} a triangular composition diagram having Bi, Ge, and Te as vertices. As described in the conventional example, this is one of the causes that the crystallization temperature of GeTe is as high as about 200 ° C., and the crystallization temperature is lowered as the composition approaches Bi ₂ Te _3. It is believed that there is. In addition, the present inventors have found through a verification experiment that the composition in the vicinity of Ge ₅₀ Te ₅₀ hardly changes the amorphous state even after long-term storage and that good erasing characteristics can be obtained. However, if the amount of GeTe is too large, the crystallization speed decreases and high-speed recording becomes impossible. On the other hand, if the amount of Bi ₂ Te ₃ is too large, the crystallization temperature is lowered and the storage life is deteriorated. Therefore, the optimum composition of the Bi-Ge-Te phase change material is a composition in which an appropriate amount of Bi ₂ Te ₃ is added to Ge ₅₀ Te ₅₀ and a composition in a region where excess Ge is present. is there.

Further, by setting the composition in the vicinity of Ge ₅₀ Te ₅₀ in the triangular composition diagram with Bi, Ge, and Te as vertices, the Ge—Sb—Sn—Te system, the Ge—Sb—Te system, the Ag— Compared with the In-Sb-Te recording material, the difference in optical constant (Δn, Δk) between the crystal part and the amorphous part in the blue region having a wavelength of 405 nm is large, so the difference in reflectance between the recorded part and the unrecorded part (contrast) ) Can be increased, and the reproduction signal amplitude can be increased.

In addition, when recording is performed using a blue laser with a wavelength of 405 nm in order to further increase the density of information, the composition of the Bi-Ge-Te phase change material is the triangular composition with Bi, Ge, and Te as vertices. It has been found that the following problems can be solved by using a composition in which Ge is added in excess of the composition on the line connecting GeTe and Bi ₂ Te ₃ in the figure.

  (1) It is generally known that the spot diameter of a laser beam is proportional to λ / NA when the laser wavelength is λ and the lens numerical aperture is NA. When using a semiconductor laser with a wavelength of 405 nm and an objective lens with a numerical aperture NA of 0.85, the laser spot diameter is a semiconductor laser with a wavelength of 650 nm (red laser) used in a conventional DVD and an objective lens with a numerical aperture of NA 0.60. The diameter is about half of the laser spot diameter when using. Even when a semiconductor laser with a wavelength of 405 nm and an objective lens with a numerical aperture NA of 0.65 are used, the laser spot diameter is about 60% of the laser spot diameter in the case of a conventional DVD. Therefore, when overwriting is attempted using a blue laser beam at the same linear velocity as that of a conventional DVD, the spot diameter becomes smaller, so the time for heating a point on the recording track is shorter than that of the conventional DVD. Become. As a result, when information is overwritten, the remaining information is likely to remain.

  (2) Generally, when the wavelength of a laser beam is shortened, the difference (Δn, Δk) in the optical constant between the crystal part (unrecorded part) and the amorphous part (recorded part) in the recording layer becomes small. Therefore, the difference in reflectance (contrast) between the recorded portion and the unrecorded portion is reduced, and the reproduction signal amplitude is reduced.

  (3) When a blue laser is used, the beam diameter is further narrowed, so that the energy intensity at the center of the beam is higher than that in the case of a red laser. As a result, damage to the recording layer due to rewriting many times increases.

  (4) Deterioration of information due to a large number of reproductions also increases.

  (5) When the track pitch is narrowed in order to increase the recording density, or when both the groove (groove) and the groove (land) provided on the substrate are used as the recording track, the data is recorded on the adjacent track. Cross erase that crystallizes a part of the mark becomes remarkable. When the problem of cross erase occurs, it becomes difficult to reduce the track pitch, and the effect of reducing the beam diameter by the blue laser cannot be fully utilized.

  As described above, the Bi-Ge-Te recording material having the composition range as described above is an excellent recording material as a material for recording information using a blue laser. However, according to the verification experiment of the present inventors, it is clear that some problems may occur when recording information with a blue laser on a recording layer formed of a Bi—Ge—Te recording material. became. The problem will be described below.

(1) The first problem is that the number of times information can be rewritten by the blue laser may be reduced. Bi-Ge having a composition in which Ge is added in an appropriate amount over the line connecting GeTe and Bi ₂ Te ₃ on the triangular composition diagram of Bi, Ge, and Te of the Bi—Ge—Te recording material of the Bi—Ge—Te recording material. When the Te recording material was used and information was rewritten many times using a blue laser, the number of rewritable times was about 1000 times. This rewritable number of times is considered to be a sufficient number of times when considering the rewritable number of times defined in the standards of the next-generation product Blu-ray disc and HD DVD and the energy intensity of the blue laser. However, when considering use in an actual drive, for example, a high power top pulse is applied to the same part of the track every time rewriting, or only a part of the area in the track is repeatedly written at the same starting position. It can be rewritten as Therefore, it is assumed that a predetermined portion of the disk can be rewritten many times with a high-power blue laser, and in practice, it is desirable to have a rewriting durability of 1000 times or more.

The reason why the number of rewritable times becomes about 1000 times with the composition of the Bi-Ge-Te recording material is estimated as follows. Generally, when overwriting is repeated at the same place on a recording medium, the recording layer material repeats melting and solidification. Melting begins from the center of the melting region and solidification begins from the periphery of the melting region. In the solidification, among the elements or compounds constituting the recording layer material, Ge and the like are solidified first, and Bi, Te, Bi ₄ GeTe _{7 and the} like are solidified later. In this case, components that solidify later (Bi, Te, Bi ₄ GeTe _{7 and the} like) move to the central portion as the solidification progresses from the peripheral portion to the central portion of the molten region. It decreases at the periphery and increases and segregates at the center. At this time, the concentration of the component (such as Ge) that solidifies first increases at the outer edge of the melting region and decreases as it goes to the center of the melting region.

On the other hand, at the time of melting, components solidified later (Bi, Te, Bi ₄ GeTe ₇ etc.) are melted first, and due to the concentration gradient of Bi, Te, Bi ₄ GeTe ₇ etc. produced during the solidification. It diffuses from the center to the periphery of the melting region. In general, when a concentration gradient occurs in each element and compound, each element and compound diffuses from a high concentration to a low concentration so as to eliminate the concentration gradient. However, even if Bi, Te, Bi ₄ GeTe ₇ or the like diffuses from the central part to the peripheral part of the molten region, the concentration gradient of Bi, Te, Bi ₄ GeTe ₇ or the like generated in the recording layer during solidification is completely eliminated. It doesn't go away. Therefore, if overwriting is repeated many times at the same location, the increase in segregation components such as Ge at the outer edge of the melting region that occurs during solidification will be canceled by diffusion due to the concentration gradient of each element and each compound in the melting region during melting. The segregation of each element and each compound proceeds until. As the segregation of Ge or the like progresses at the outer edge of the melting region, the dispersion of the reflectance from the recording mark increases, and the noise increases due to factors such as the disappearance of the recording mark.

  In addition, the following causes can be considered as a cause of a decrease in the number of rewritable times. This is presumably because Ge atoms have a relatively large atomic radius and the diffusion rate at the time of melting is slow or difficult to diffuse, so that the segregation of Ge atoms is likely to proceed. In addition, it is considered that the reason why Ge atoms cannot be segregated by Ge alone by rewriting many times, and the effect of suppressing recrystallization at the outer edge of the molten region is reduced.

(2) The second problem is that when recording information with a blue laser, the range of recording linear velocities that can be handled is narrow, and high-speed recording may be difficult. The above-mentioned Bi-Ge-Te phase change material is a recording layer material developed for CAV (Constant Angular Velocity) recording of DVD-RAM using a red laser, and is double the speed of current DVD-RAM. Good recording / reproducing characteristics can be realized in a recording linear velocity range from recording (transfer speed 22 Mbps) to 5 × speed recording (55 Mbps). This recording speed is in the range of 8.2 m / sec to 21.0 m / sec when converted to a recording linear speed of CLV (Constant Linear Velocity).

  In order to perform information recording corresponding to the recording linear velocity using a blue laser, it is necessary to further increase the crystallization speed of the recording layer material and further improve the erasure ratio during high-speed recording. This is because the spot diameter of the blue laser is about half of the spot diameter of the red laser, so when overwriting at the same linear velocity, a certain point on the recording track is compared to when recording with the red laser. This is because the passing time is shortened to about half, and the remaining information is easily lost due to overwriting of previously recorded information.

  The recording linear velocity of the next-generation optical disc (HD DVD) using a blue laser, which is currently under deliberation on standards, is 5.64 m / sec to 6.01 m / sec (transfer rate 36 Mbps). At this recording speed, a Bi—Ge—Te phase change material can be used sufficiently. However, assuming 2 × speed recording and 3 × speed recording, the erasure ratio is insufficient in such a high recording speed range, and rewriting may be difficult. In particular, in the case of triple speed recording, there is a high possibility that the erasure ratio will be insufficient. In addition, when performing high-speed recording, higher recording power is required, and there is a possibility that recording sensitivity is deteriorated.

The present invention has been made to solve the above-described problems. According to the first aspect of the present invention, there is provided an information recording medium, which is provided on a substrate, Bi, Ge, A recording layer formed of a phase change material containing Te and an element MA other than these elements, wherein a part of Ge is replaced by the element MA, and Bi, (Ge + MA), and Te in the recording layer The composition ratio is in the composition range surrounded by the following points on the triangular composition diagram of Bi, (Ge + MA) and Te,
B2 ′ (Bi ₂ , (Ge + MA) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA) ₂₆ , Te ₅₅ )
An information recording medium is provided in which the element MA is Si and the content of the element MA in the recording layer is in the range of 1 to 20 atomic%.

According to the first reference aspect, there is provided an information recording medium, a substrate, a recording layer provided on the substrate and formed of a phase change material including Bi, Ge, Te, and an element MA other than these elements, A part of Ge is replaced by the element MA, and the composition ratio of Bi, (Ge + MA) and Te in the recording layer is determined by the following points on the triangular composition diagram of Bi, (Ge + MA) and Te: In the enclosed composition range,
B2 ′ (Bi ₂ , (Ge + MA) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA) ₂₆ , Te ₅₅ )
An information recording medium is provided in which the element MA is B and the content of the element MA in the recording layer is in the range of 1 to 10 atomic%.

The inventors of the present invention used a Bi—Ge—Te phase change material, and the composition ratio of Bi, Ge, and Te in the recording layer was surrounded by the following points on the triangular composition diagram of Bi, Ge, and Te. By using a phase change material having a composition range as a forming base material, and using a phase change material in which a part of Ge of the forming base material is replaced with at least one element (substitution element MA) of Si and B as a recording layer material. The present inventors have found that even when information is recorded with a blue laser, recrystallization of the molten region is suppressed, and the durability of rewriting many times is improved.
_{B2 (Bi 2, Ge 47,} Te 51)
C2 (Bi ₃ , Ge ₄₇ , Te ₅₀ )
D2 (Bi ₄ , Ge ₄₇ , Te ₄₉ )
_{D6 (Bi 16, Ge 37,} Te 47)
C8 (Bi ₃₀ , Ge ₂₂ , Te ₄₈ )
B7 (Bi ₁₉ , Ge ₂₆ , Te ₅₅ )

  When a part of Ge of the base material for forming the recording layer is replaced with Si, Si has a higher melting point than Ge and GeTe. Crystallization is suppressed. Further, since the atomic radius of Si atoms is small, SiTe segregates quickly when solidified and diffuses rapidly when melted. Furthermore, since Si is difficult to form a compound with constituent elements in the recording layer material other than Te, that is, Bi and Ge, SiTe exists stably even if rewritten many times, and the recrystallization suppression effect is inhibited. It is unlikely to be done.

  When a part of Ge in the base material for forming the recording layer is replaced with B, since B atoms have a small atomic radius of 1.2 mm or less, B atoms are segregated quickly to the outer edge of the molten region during solidification. Furthermore, since B atoms diffuse relatively quickly during melting, an increase in the segregation of Ge atoms at the outer edge of the melting region can be suppressed even if rewriting is performed many times.

  However, when the content of the substitution element MA (Si and / or B) increases, the difference (Δn, Δk) between the optical constants of the crystal part and the amorphous part in the recording layer material becomes small. In some cases, the Si content needs to be in the range of 1 to 20 atomic%. When the substitution element MA is B, the B content needs to be in the range of 1 to 10 atomic%. In addition, when the total content of the substitution element MA is less than 1 atomic%, the above-described effects (such as a recrystallization suppressing effect) by the substitution element MA cannot be obtained.

According to the second reference aspect, there is provided an information recording medium, a substrate, a recording layer provided on the substrate and formed of a phase change material containing Bi, Ge, Te, and an element MB other than these elements; A part of Ge is replaced by the element MB, and the composition ratio of Bi, (Ge + MB) and Te in the recording layer is as follows on the triangular composition diagram of Bi, (Ge + MB) and Te: In the enclosed composition range,
B2 ′ (Bi ₂ , (Ge + MB) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MB) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MB) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MB) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MB) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MB) ₂₆ , Te ₅₅ )
An information recording medium is provided in which the element MB is at least one element of Sn and Pb, and the content of the element MB in the recording layer is in the range of 1 to 20 atomic%.

  The inventors of the present invention use the Bi-Ge-Te phase change material and the above-described points (B2, C2, and Bi) in the triangular composition diagram in which the composition ratio of Bi, Ge, and Te in the recording layer is Bi, Ge, and Te. A phase change material having a composition range surrounded by D2, D6, C8, and B7) is used as a forming base material, and a part of Ge in the forming base material is replaced with at least one element (substitution element MB) of Sn and Pb. When the recorded phase change material is used as a recording layer material, SnTe and PbTe are formed as crystal nuclei in the recording layer even when information is recorded with a blue laser, so that the nucleation speed is improved. I found that I could make up for the shortage.

  Further, by replacing a part of Ge of the formation base material with at least one element of Sn and Pb, a large number of SnTe and PbTe crystal nuclei are formed in the recording layer, and crystal growth from the crystal nuclei is suppressed. Therefore, an effect of suppressing recrystallization at the time of low linear velocity recording can be expected.

  Since Sn and Pb are simple elements having a low melting point, information can be recorded at a lower recording power by replacing a part of Ge with at least one element of Sn and Pb. Recording sensitivity deterioration can be suppressed. Further, since the recording power can be reduced even at the time of low linear velocity recording, damage to the recording layer due to rewriting many times can be reduced, and rewriting durability can be improved.

  However, when the content of the substitution element MB (at least one element of Sn and Pb) increases, the difference in optical constant (Δn, Δk) between the crystal part and the amorphous part in the recording layer material becomes small. The total content of MB needs to be in the range of 1-20 atom%. If the total content of the substitution element MB is less than 1 atomic%, the effect of the substitution element MB as described above (such as elimination of insufficient erasure) cannot be obtained.

According to the second aspect of the present invention, there is provided an information recording medium, which is a recording medium formed of a phase change material provided on the substrate and containing Bi, Ge, Te, and an element M other than these elements. And a part of Ge is replaced by the element M, and the composition ratio of Bi, (Ge + M) and Te in the recording layer is as follows on the triangular composition diagram of Bi, (Ge + M) and Te. In the composition range surrounded by dots,
B2 ′ (Bi ₂ , (Ge + M) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + M) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + M) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + M) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + M) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + M) ₂₆ , Te ₅₅ )
The element M includes the element MA and the element MB, the element MA is Si, the element MB is at least one element of Sn and Pb, and the total content of the element MA and the element MB in the recording layer is 1 to Ri 20 atomic percent range der, and the information recording medium, wherein the element MA and the element MB is contained 1 atomic% or more, respectively, are provided.

According to a third reference aspect, there is provided an information recording medium, a substrate, a recording layer provided on the substrate and formed of a phase change material containing Bi, Ge, Te, and an element M other than these elements; A part of Ge is substituted with the element M, and the composition ratio of Bi, (Ge + M) and Te in the recording layer is determined by the following points on the triangular composition diagram of Bi, (Ge + M) and Te: In the enclosed composition range,
B2 ′ (Bi ₂ , (Ge + M) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + M) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + M) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + M) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + M) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + M) ₂₆ , Te ₅₅ )
The element M includes the element MA and the element MB, the element MA is B, the element MB is at least one element of Sn and Pb, and the content of the element MA in the recording layer is 1 to 10 atomic% There is provided an information recording medium characterized in that the total content of element MA and element MB is in the range of 1 to 20 atomic%.

In the information recording medium according to the second aspect and the third reference aspect of the present invention, a Bi—Ge—Te phase change material is used, and the composition ratio of Bi, Ge, and Te in the recording layer is Bi, Ge, and Te. A phase change material having a composition range surrounded by the above points (B2, C2, D2, D6, C8, and B7) on the triangular composition diagram is used as a forming base material, and a part of Ge in the forming base material is replaced as described above. A phase change material substituted with the element MA (Si and / or B) and the substitution element MB (at least one element of Sn and Pb) was used as the recording layer material.

As described above, when Ge of the base material for forming the recording layer is replaced with the substitution element MA (Si and / or B), there is an effect of suppressing recrystallization at the time of low linear velocity recording, and the substitution element MB (Sn and Substitution with at least one element of Pb has the effect of eliminating the lack of erasure ratio during high linear velocity recording. Therefore, as in the information recording medium according to the second aspect and the third reference aspect of the present invention, by replacing a part of Ge in the forming base material with the replacement elements MA and MB, the replacement as described above is performed. An information recording medium having both the effects of the elements MA and MB can be obtained. That is, in the information recording medium according to the second aspect and the third reference aspect of the present invention, the problem of recrystallization at the time of low linear velocity recording is solved and the lack of erasure ratio at the time of high linear velocity recording is eliminated. This makes it possible to widen the recordable linear velocity range.

  However, if the total content of the substitution elements MA and MB in the recording layer increases, the effect of the substitution element MA and the effect of the substitution element MB cancel each other, so the total content of the substitution elements MA and MB is limited. 1 to 20 atomic%. However, when B is used as the substitution element MA, the content of the element MA in the recording layer is in the range of 1 to 10 atom%, and the total content of the substitution elements MA and MB is 1 to 20 atom%. It is necessary to be in the range.

  Further, when the total content of the substitution elements MA and MB exceeds 20 atomic%, the difference in optical constant (Δn, Δk) between the crystal part and the amorphous part of the recording material becomes small, while the substitution elements MA and MB When the total content is less than 1 atomic%, the effects of the substitution elements MA and MB as described above cannot be obtained.

When the recording layer materials used in the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention are put together, the following phase change materials of the composition system are obtained. In the present invention, the applicable linear velocity range can be adjusted by adjusting the content of elements other than Bi, Ge, and Te in the recording layer.
Quaternary recording layer materials: Bi-Ge-Si-Te, B-Bi-Ge-Te, Bi-Ge-Sn-Te, Bi-Ge-Pb-Te
Five-element recording layer materials: B—Bi—Ge—Si—Te, Bi—Ge—Pb—Sn—Te, Bi—Ge—Si—Pb—Te, Bi—Ge—Si—Sn—Te, B—Bi -Ge-Pb-Te, B-Bi-Ge-Sn-Te
6-element recording layer materials: B—Bi—Ge—Pb—Sn—Te, Bi—Ge—Pb—Si—Sn—Te, B—Bi—Ge—Si—Sn—Te, B—Bi—Ge—Pb -Si-Te,
7-element recording layer material: B-Bi-Ge-Pb-Si-Sn-Te
By appropriately adjusting the multi-component composition as described above, the performance of the recording layer material can be controlled more finely.

In the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, it is preferable that the wavelength of the light beam used for information recording of the information recording medium is 390 nm to 420 nm.

  The use of a light beam having a wavelength of 390 nm to 420 nm as the light beam used when recording information on the information recording medium is extremely effective for increasing the capacity because the beam spot diameter is reduced. However, compared with a light beam having a wavelength of about 650 nm to 780 nm generally used for CDs and DVDs, (1) the energy intensity is high and it is difficult to rewrite many times. (2) Refractive index between the amorphous state and the crystalline state There arises a problem that the signal intensity becomes small because the difference is small.

The inventors of the present invention conducted a verification experiment using the phase change material used in the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention as the recording layer, so that the wavelength was 390 nm. It has been found that even if information is recorded by using a light beam of ˜420 nm, an information recording medium having high recording data reliability and high durability with respect to repeated data recording can be obtained.

In the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, concentric or spiral grooves are formed on the substrate, and at least one of the grooves and the grooves is formed. One of these is preferably used as a recording track, and in particular, both the groove and the space between the grooves are preferably used as a recording track.

  The method of using both the groove (groove) and the space between the grooves (land) as the recording track can reduce the track pitch as compared with the case where only one of the groove and the land is used as the recording track. This is an extremely effective method for the conversion. However, when both the groove and the land are used as recording tracks, the thermal history of the groove portion and the land portion of the recording layer is different from the difference in the thermal characteristics between the groove and the land due to the difference in shape between the groove and the land. Different. As a result, there arises a problem that a difference occurs between the groove and the land in the information recording and erasing characteristics, and the above-mentioned cross erase occurs.

However, the inventors have conducted a verification experiment by using the phase change material used in the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention as the recording layer material. It has been found that suitable characteristics can be obtained even when both grooves and lands are used as recording tracks.

In the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, the track pitch TP of the recording track of the information recording medium and the wavelength λ of the light beam used for recording / reproducing information And the numerical aperture NA of the objective lens for condensing the light beam,
0.35 × (λ / NA) ≦ TP ≦ 0.7 × (λ / NA)
It is preferable that this relationship is established.

In order to increase the capacity of information, it is an extremely effective method to reduce the track pitch. However, when the track pitch is narrowed, a phenomenon (so-called cross erase) that a part of the mark recorded on the adjacent track is crystallized at the time of information recording is very likely to appear. However, the inventors have conducted a verification experiment to use the phase change material used in the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention as a recording layer. In the case of a narrow track pitch where the pitch TP is 0.35 × (λ / NA) ≦ TP ≦ 0.7 × (λ / NA) (λ: wavelength of the light beam, NA: numerical aperture of the objective lens) Even if it exists, it discovered that cross erase could be reduced significantly.

In the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, the information recording medium further includes an interface layer, and the interface layer is at least one side of the recording layer. It is preferable to be provided in contact with the surface.

In the information recording medium according to the first and second aspects and the first to third reference aspects described above, the present inventors have performed the number of rewrites by forming an interface layer in contact with at least one interface of the recording layer. And it was found by a verification experiment that the shelf life is drastically improved.

In the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, a nucleation layer containing Bi ₂ Te ₃ , SnTe, PbTe or the like may be provided in contact with the recording layer. . When the nucleation layer is provided in contact with the recording layer, the effect of suppressing recrystallization around the recording mark is further improved. This is presumably because when the rate of increase of crystal nuclei is large, crystals grown from each crystal nucleus collide with crystals grown from the adjacent crystal nuclei immediately and suppress crystal growth. Further, in the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, if the recording layer forming material maintains the above-described composition range relationship, impurities may be present. Even if it is mixed, the effect of the present invention is not lost as long as the atomic percent of impurities is within 1%.

In the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention, heat is generated by the irradiation of the energy beam, and the atomic arrangement is changed by this heat. Therefore, the present invention can be applied to an information recording medium other than a disk-shaped information recording medium such as an optical card, regardless of the shape of the information recording medium. In the present specification, the information recording medium of the present invention may be described as a phase change type optical disc or simply an optical disc. In the present specification, the energy beam described above may be expressed as a light beam or simply a laser beam.

The information recording medium according to the first and second aspects and the first to third reference aspects of the present invention is premised on a configuration in which the substrate is disposed on the light beam incident side of the recording layer. A substrate may be disposed on the side opposite to the light beam incident side of the layer, and a protective material such as a protective sheet thinner than the substrate may be disposed on the light beam incident side.

The energy beam irradiated to the information recording medium according to the first and second aspects and the first to third reference aspects of the present invention is an energy beam capable of generating heat on the information recording medium. Since the same effect can be obtained if there is an energy beam such as an electron beam, it may be used.

  According to the information recording medium of the present invention, part of Ge of the phase change material containing Bi, Ge, and Te is substituted with the above-described substitution element MA and / or substitution element MB, and the total content of substitution elements is set. By using the above-mentioned range (1 to 10 atomic% when only B is used as a substitution element, 1 to 20 atomic% otherwise), even when recording information with a blue laser, durability against repeated recording of data Therefore, an information recording medium that is high in speed, capable of high-speed recording, and has a wide range of recording linear velocities that can be obtained can be obtained.

  Examples of the information recording medium of the present invention will be described below, but the present invention is not limited thereto.

[Information recording medium and manufacturing method thereof]
The information recording medium manufactured in Example 1 is a phase change type optical disc, and a schematic cross-sectional view thereof is shown in FIG. As shown in FIG. 1, an optical disc 10 manufactured in this example has a first protective layer 2, a first interface layer 3, a recording layer 4, a second interface layer 5, a second protective layer 6, a thermal diffusion layer on a substrate 1. The layer 7 and the ultraviolet curable resin layer 8 are sequentially laminated. Next, a method for producing the optical disc 10 of this example will be described. The optical disk 10 manufactured in this example employs a so-called land / groove recording method in which information is recorded on both the groove and the land.

  First, a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.6 mm was used as the substrate 1. The substrate 1 was produced by injection molding, and grooves were formed in the information recording area of the radius of 23.8 mm to 58.6 mm of the substrate 1 so that each track pitch of the land track and groove track was 0.34 μm. The track was wobbled at a cycle of 93 channel bits.

Next, (ZnS) ₈₀ (SiO ₂ ) ₂₀ was formed as a first protective layer 2 on the substrate 1 to a thickness of 60 nm by sputtering. Next, Ge ₈ Cr ₂ —N (relative ratio display) was formed as a first interface layer 3 on the first protective layer 2 by sputtering so as to have a thickness of 2 nm.

Next, the recording layer 4 was formed to a thickness of 11 nm on the first interface layer 3 by sputtering. The recording layer 4 was formed of various materials in which Bi ₃ Ge ₄₇ Te ₅₀ or Bi ₃₀ Ge ₂₂ Te ₄₈ was used as a base material and part of Ge was replaced with Si (added element MA). The method for forming the recording layer 4 is as follows. As a sputtering target, in addition to Ge ₅₀ Te ₅₀ and Bi ₂ Te ₃ targets, a Si ₅₀ Te ₅₀ target was prepared in order to replace part of Ge with Si, and recording layers were simultaneously sputtered with three types of target. Formed. At this time, the sputtering power applied to each target was adjusted so that the composition of the recording layer was a desired composition. In this example, various optical disks were formed in which the content of Si element was changed in the range of 1 to 25 atomic%. For comparison, an optical disk containing no Si element, that is, an optical disk in which the recording layer 4 is formed only from a base material (Bi ₃ Ge ₄₇ Te ₅₀ or Bi ₃₀ Ge ₂₂ Te ₄₈ ) was also produced.

On the recording layer 4 formed by the above method, Ge ₈ Cr ₂ —N (relative ratio display) was formed as the second interface layer 5 to a thickness of 2 nm by sputtering. Next, (ZnS) ₅₀ (SiO ₂ ) ₅₀ was formed as a second protective layer 6 (also referred to as an intermediate layer) with a thickness of 40 nm on the second interface layer 5 by sputtering. Further, Al ₉₉ Ti ₁ was formed as a thermal diffusion layer 7 on the second protective layer 6 by sputtering so as to have a film thickness of 150 nm.

  Next, a UV resin is applied as an ultraviolet curable resin layer 8 on the heat diffusion layer 7, and a polycarbonate transparent substrate (not shown) having a thickness of 0.6 mm is further placed thereon. The transparent substrate was laminated on the ultraviolet curable resin layer 8 by irradiating UV through the transparent substrate and curing the UV resin. The optical disc 10 shown in FIG. 1 was obtained by the above manufacturing method.

  Various optical disks obtained by the above production method were irradiated with an elliptical laser beam having a wavelength of 810 nm, a beam spot major axis of 96 μm, and a minor axis of 1 μm using an initialization apparatus (not shown). Was initialized.

  In this example, as shown in FIG. 1, an optical disc was manufactured with a film configuration similar to that of a conventional product such as a DVD-RAM. However, each layer was laminated on the substrate 1 in the reverse order of FIG. The same effects as those of the present invention can be obtained even with this optical disc. Moreover, you may laminate | stack an absorptance control layer in a predetermined position as needed.

[Information recording / playback device]
FIG. 2 shows a schematic configuration diagram of an information recording / reproducing apparatus for recording and reproducing information with respect to various optical disks produced in this example. As shown in FIG. 2, the information recording / reproducing apparatus 20 used in this example mainly includes a motor 21 for rotating the optical disk 10 manufactured in this example, and an optical head 22 for irradiating the optical disk 10 with laser light. And an L / G servo circuit 23 for tracking control, a reproduction signal processing system 24, and a recording signal processing system 27. As shown in FIG. 2, the reproduction signal processing system 24 includes a preamplifier circuit 25 that adjusts the gain of the reproduction signal, and a 1-7 demodulator 26 that reproduces information based on the reproduction signal. As shown in FIG. 2, the recording signal processing system 27 includes a 1-7 modulator 30 that modulates an input signal using a predetermined modulation method, a recording waveform generation circuit 29 that generates a recording signal waveform, and laser light emission. And a laser drive circuit 28 to be controlled.

The optical head 22 used in this example includes a semiconductor laser having a wavelength of 405 nm and an objective lens having a numerical aperture NA of 0.65 (not shown). Generally, when a laser beam having a wavelength λ is collected by an objective lens having a numerical aperture NA, the spot diameter of the laser beam is approximately 0.9 × λ / NA. Is about 0.6 μm. However, in this example, the polarization of the laser light is circularly polarized. In this example, since the track pitch TP is 0.34 μm, between the track pitch TP, the wavelength λ, and the numerical aperture NA,
TP = 0.55 × (λ / NA)
The relationship is established.

  In addition, since the optical disk manufactured in this example is a land / groove recording type optical disk, the information recording / reproducing apparatus 20 shown in FIG. 2 also supports the land / groove recording system. In the information recording / reproducing apparatus 20 of this example, the tracking for the land and the groove can be arbitrarily selected by the L / G servo circuit 23 in FIG.

  The operation of the information recording / reproducing apparatus 20 will be described below with reference to FIG. As a motor control method for recording / reproducing, a ZCLV method is adopted in which the number of revolutions of the disk is changed for each zone for recording / reproducing. In this example, when recording information, the mark edge method is used and information is recorded on the optical disc 10 by the 1-7 modulation method. In this modulation method, information is recorded with a mark length of 2T to 8T. Here, T represents a clock cycle at the time of recording information, and in this example, T = 15.4 ns. That is, in this example, the shortest 2T mark length is about 0.17 μm, and the longest 8T mark length is about 0.7 μm. In this example, recording was performed at three recording linear speeds of 5.64 m / sec (1 × speed), 11.28 m / sec (2 × speed), and 16.92 m / sec (3 × speed).

  First, a signal necessary for information recording is input to the 1-7 modulator 30 from the outside of the recording apparatus. Next, the signal input to the 1-7 modulator 30 is modulated by the 1-7 modulation method, and 2T to 8T digital signals are output. Next, the 2T to 8T digital signals output from the 1-7 modulator 30 are input to the recording waveform generation circuit 29.

  The recording waveform generation circuit 29 generates a multi-pulse recording waveform necessary for laser light irradiation during information recording based on the input 2T to 8T digital signal. In this example, the high power level region of the multi-pulse recording waveform is composed of a high power pulse having a width of about T / 2 and a low power pulse having a width of about T / 2 formed between the high power pulses. Formed with a series of pulse trains. In addition, the region between the series of pulse trains of the multi-pulse recording waveform was composed of intermediate power level pulses. At this time, the pulse intensity at a high power level for forming (amorphizing) the recording mark on the recording layer and the pulse intensity at the intermediate power level for crystallizing the recording mark are optimal for each optical disc to be recorded and reproduced. Adjusted to value.

  In the recording waveform generation circuit 29, the digital signal waveforms of 2T to 8T are alternately corresponded to “0” and “1” in time series, and in the case of “0”, a laser pulse of an intermediate power level is generated. In the case of “1”, a series of pulse trains composed of the above-described high power pulse and low power pulse was irradiated. At this time, the portion on the optical disk 10 irradiated with the intermediate power level laser pulse becomes a crystal, and the portion irradiated with the series of pulse trains composed of the high power pulse and the low power pulse described above becomes amorphous (mark portion). Change. Further, when forming the series of pulse trains composed of the high power pulse and the low power pulse described above, the recording waveform generation circuit 29 determines the start pulse width and the end pulse of the multi-pulse waveform according to the space length before and after the mark portion. It has a multi-pulse waveform table corresponding to the method of changing the pulse width of the tail (adaptive recording waveform control), so that the multi-pulse recording waveform that can eliminate the influence of thermal interference between marks as much as possible It has occurred.

  Next, the multi-pulse recording waveform generated by the above-described recording waveform generating circuit 29 is transferred to the laser driving circuit 28, and the laser driving circuit 28 stores the multi-pulse recording waveform in the optical head 22 based on the input multi-pulse recording waveform. Controls the emission of the semiconductor laser. Information is recorded by narrowing down the laser light emitted from the semiconductor laser onto the recording layer of the optical disk 10 by the objective lens in the optical head 22 and irradiating the laser light at a timing corresponding to the multi-pulse recording waveform. It was.

  Next, the reproducing operation of the information recorded as described above will be described. First, a laser beam is irradiated onto the recording mark of the optical disk 10 from the optical head 22, and the reflected light from the recording mark and a portion other than the recording mark (unrecorded portion) is detected by the optical head 22 to obtain a reproduction signal. The amplitude of the reproduction signal is amplified with a predetermined gain by the preamplifier circuit 25 and transferred to the 1-7 demodulator 26. The 1-7 demodulator 26 demodulates information based on the input reproduction signal and outputs reproduction data. With the above operation, the reproduction of the recorded mark is completed.

  In the measurement of the error rate described later, a random pattern signal including 2T to 8T was recorded and reproduced.

[Evaluation of recording layer material]
The following measurements were performed on various optical disks in which the content of Si (substitution element MA) contained in the recording layer produced by the above production method was changed and evaluated.

  Various optical discs manufactured by the above manufacturing method are mounted on the information recording / reproducing apparatus shown in FIG. 2, and the error rate at the recording linear velocity of 1 × speed and 2 × speed (however, the error rate after rewriting the random pattern 10 times) (Hereinafter, these evaluation items are referred to as a 1 × speed recording error rate and a 2 × speed recording error rate). From this test result, the recording / erasing performance and signal quality of each optical disk were evaluated. Here, the error rate was measured by recording a random pattern (random pattern of 2T to 8T) in order from the inner periphery to the outer periphery of five consecutive tracks, and then measuring the error rate at the center track of the five tracks.

In this example, in order to evaluate the rewritable life of the recording layer, the error rate after 1000 rewrites in 1 × speed recording and 2 × speed recording was measured (in the following, these evaluation items were rewritten after 1000 rewrites). 1x speed recording error rate and 2x speed recording error rate). The optical disk produced in this example employs land / groove recording, but here, the average value when information is recorded on each land and groove is shown. The target values for each evaluation are as follows.
Error rate (after 10 rewrites): 5 × 10 ⁻⁵ or less Error rate after 1000 rewrites: 1 × 10 ⁻⁴ or less

First, in this example, performance evaluation was performed by performing each of the above tests on an optical disk having a Si element content of 5 atomic% among optical disks manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as a base material for forming a recording layer. went. As a result, the 1 × speed recording error rate is 3.5 × 10 ⁻⁵ , the 2 × speed recording error rate is 4.5 × 10 ⁻⁵ , the 1 × speed recording error rate after 1000 rewrites is 8.0 × 10 ⁻⁵ , The double speed recording error rate after 1000 rewrites was 9.5 × 10 ⁻⁵ , and the target level could be achieved for all evaluation items.

Next, among the optical discs manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as the recording layer forming base material in this example, optical discs having Si element contents of 0, 1, 2, 20 and 25 atomic% are respectively shown. 100 sheets were produced, and the performance was evaluated by performing the above tests on all the produced optical disks. The results are shown in Table 1. However, in this table, out of 100 optical disks produced for each content of Si element, the number of optical disks that achieved the above-mentioned target level of each evaluation item was examined (hereinafter referred to as a pass rate). ). Table 1 shows the pass rate of each evaluation item of the optical disk using Bi ₃ Ge ₄₇ Te ₅₀ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the Si element content. In addition, the notation of the pass rate in Table 1 was represented by (pass number of sheets) / 100 sheets. For example, 50/100 is described when the target level reaches 50 out of 100 sheets.

As is apparent from Table 1, when Bi ₃ Ge ₄₇ Te ₅₀ is used as the base material for forming the recording layer, the optical disc without addition of Si element has a 1 × speed recording error rate, a 2 × speed recording error rate, and 1000 times after rewriting. In the evaluation item of the double speed recording error rate, the pass rate was 100% (passed 100 out of 100 sheets), but at the single speed recording error rate after 1000 rewrites, the pass rate was 25 out of 100 sheets, and the rest 75 sheets did not reach the target level.

  Further, in the optical disc having the Si element content in the recording layer of 1 to 20 atomic%, as is clear from Table 1, the pass rate was 100% in all the evaluation items.

  As is clear from Table 1, the pass rate for both the 1 × speed recording error rate and the 2 × speed recording error rate is 25 out of 100 sheets, and the remaining 75 sheets for the optical disk having the Si element content of 25 atomic% in the recording layer. Did not reach the target level. An optical disc that did not reach the target level had a low signal modulation. Also, in the case of an optical disk having a Si element content of 25 atomic% in the recording layer, the pass rate is 80 out of 100 for both the 1 × speed recording error rate and the 2 × speed recording error rate after 1000 rewrites, and the remaining 20 are The target level was not reached.

Further, when Bi ₂ Ge ₄₇ Te ₅₁ and Bi ₄ Ge ₄₇ Te ₄₉ are used as the forming base material of the recording layer in the optical disc of this example, the same as the case where Bi ₃ Ge ₄₇ Te ₅₀ is used as the forming base material. Characteristics were obtained.

Next, in this example, each of the above tests was performed on an optical disk having a Si element content of 5 atomic% from among optical disks manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as a base material for forming a recording layer. Performance evaluation was performed. As a result, the 1 × speed recording error rate is 4.8 × 10 ⁻⁵ , the 2 × speed recording error rate is 3.5 × 10 ⁻⁵ , and the 1 × speed recording error rate after 1000 rewrites is 9.5 × 10 ⁻⁵ , The double speed recording error rate after 1000 rewrites was 8.8 × 10 ⁻⁵ , and the target level could be achieved for all evaluation items.

In this example, among the optical disks manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, 100 optical disks each having a Si element content of 0, 1, 2, 20, and 25 atomic% were obtained. Each of the manufactured optical disks was subjected to the above tests, and performance evaluation was performed. The results are shown in Table 2. Table 2 shows the pass rate of each evaluation item of the optical disk manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer in this example, and shows the pass rate of each evaluation item with respect to the content of Si element. .

As is apparent from Table 2, when Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer, the optical disk not containing Si element has a 1 × speed recording error rate, a 2 × speed recording error rate, and 1000 times after rewriting. The pass rate was 100% (100 out of 100 passes) in the evaluation item of 2 × speed recording error rate, but the pass rate was 50 out of 100 copies at the 1 × speed recording error rate after 1000 rewrites, and the rest 50 sheets did not reach the target level.

  Further, in the optical disk having the Si element content of 1 to 20 atomic% in the recording layer, as is clear from Table 2, the pass rate was 100% in all evaluation items.

  As can be seen from Table 2, the optical disk with the Si element content of 25 atomic% in the recording layer has a pass rate of 20 out of 100 for both the 1x recording error rate and the 2x recording error rate, and the remaining 80 discs. Did not reach the target level. An optical disc that did not reach the target level had a low signal modulation. In addition, as is apparent from Table 2, in the case of an optical disc in which the Si element content in the recording layer is 25 atomic%, the pass rate is 100 out of 100 for both the 1 × speed recording error rate and the 2 × speed recording error rate after 1000 rewrites. 80 sheets, and the remaining 20 sheets did not reach the target level.

Further, when Bi ₁₆ Ge ₃₇ Te ₄₇ and Bi ₁₉ Ge ₂₆ Te ₅₅ are used as the base material for forming the recording layer in the optical disc of this example, Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer. The same characteristics as the optical disk were obtained.

From the above results, Bi ₂ Ge ₄₇ Te ₅₁ , Bi ₄ Ge ₄₇ Te ₄₉ , Bi ₃ Ge ₄₇ Te ₅₀ , Bi ₁₆ Ge ₃₇ Te ₄₇ , Bi ₁₉ Ge ₂₆ Te ₅₅ and Bi ₃₀ Ge ₂₂ Te ₄₈ are recorded. In the optical disk in which the recording layer is formed with a material in which a part of Ge in each base material is replaced with Si (substitution element MA) as a forming base material, the content of the substitution element MA in the recording layer is 1 to 20 atomic%. As a result, target values were achieved for all evaluation items.

That is, when Si is used as the additive element MA in the recording layer, the composition ratios of Bi, (Ge + MA), and Te in the recording layer are set as follows on the triangular composition diagrams of Bi, (Ge + MA), and Te. Set the composition range surrounded by dots,
B2 ′ (Bi ₂ , (Ge + MA) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA) ₂₆ , Te ₅₅ )
In addition, by setting the content of the additive element MA (Si) in the recording layer to 1 to 20 atomic%, even when information is recorded with a blue laser, durability against repeated data recording is high and high-speed recording is possible. It was also found that an information recording medium having a wide range of recording linear velocities that can be handled can be obtained .

[Reference Example 1]
In the optical disc of Reference Example 1 , Bi ₃ Ge ₄₇ Te ₅₀ and Bi ₃₀ Ge ₂₂ Te ₄₈ are used as the base material for forming the recording layer, and a part of Ge in each base material is replaced with B (substitution element MA). A recording layer was formed. The method for forming the recording layer in the optical disc of this example is as follows.

Ge ₅₀ Te ₅₀ and Bi ₂ Te ₃ targets were prepared, and simultaneous recording was performed to form the recording layer 4. At this time, in order to replace a part of Ge with B, film formation was performed by attaching a B chip on the sputtering target. Further, the sputtering power applied to each target was adjusted so that the composition of the recording layer 4 was a desired composition. In this example, various optical disks were manufactured by changing the B content in the recording layer in the range of 1 to 15 atomic%. For comparison, an optical disk that does not contain B, that is, an optical disk in which the recording layer is formed only with a forming base material (Bi ₃ Ge ₄₇ Te ₅₀ or Bi ₃₀ Ge ₂₂ Te ₄₈ ) was also manufactured. An optical disk was manufactured in the same manner as in Example 1 except for the recording layer.

  Further, in this example, 100 optical discs having B contents of 0, 1, 2, 10 and 15 atomic% were produced, respectively, and a 1 × speed recording error was applied to all the produced optical discs as in Example 1. The rate and the double speed recording error rate, and the single speed recording error rate and double speed recording error rate after 1000 rewrites were measured and evaluated. In addition, the target value of each evaluation item was the same as that of Example 1.

Table 3 shows the evaluation results of the above test performed on an optical disk manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as a base material for forming the recording layer in this example. Table 3 shows the pass rate of each evaluation item of the optical disk using Bi ₃ Ge ₄₇ Te ₅₀ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the B content.

As is apparent from Table 3, when Bi ₃ Ge ₄₇ Te ₅₀ is used as the base material for forming the recording layer, the optical disc without addition of the B element has a 1 × speed recording error rate, a 2 × speed recording error rate, and 1000 times after rewriting. In the evaluation item of the double speed recording error rate, the pass rate was 100% (passed 100 out of 100 sheets), but at the single speed recording error rate after 1000 rewrites, the pass rate was 25 out of 100 sheets, and the rest 75 sheets did not reach the target level.

  Further, in the optical disk having the B element content in the recording layer of 1 to 10 atomic%, as is apparent from Table 3, the pass rate was 100% for all the evaluation items.

  As is apparent from Table 3, in the optical disk having the B element content of 15 atomic% in the recording layer, the pass rate was 25 out of 100 for both the 1x recording error rate and the 2x recording error rate, and the remaining 75 discs. Did not reach the target level. An optical disc that did not reach the target level had a low signal modulation. In addition, in the case of an optical disk having a B element content of 15 atomic% in the recording layer, the pass rate is 80 out of 100 for both the 1 × speed recording error rate and the 2 × speed recording error rate after 1000 rewrites, and the remaining 20 are The target level was not reached.

Further, when Bi ₂ Ge ₄₇ Te ₅₁ and Bi ₄ Ge ₄₇ Te ₄₉ are used as the formation base material of the recording layer in the optical disc of this example, the same as when Bi ₃ Ge ₄₇ Te ₅₀ is used as the formation base material. The characteristics were obtained.

Next, Table 4 shows the evaluation results of the above test performed on the optical disk manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer in this example. Table 4 shows the pass rate of each evaluation item of the optical disk using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the content of B element.

As is apparent from Table 4, when Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer, the optical disc without the addition of B element has a 1 × speed recording error rate, a 2 × speed recording error rate, and 1000 times after rewriting. The pass rate was 100% (100 out of 100 passes) in the evaluation item of 2 × speed recording error rate, but the pass rate was 50 out of 100 copies at the 1 × speed recording error rate after 1000 rewrites, and the rest 50 sheets did not reach the target level.

  Further, in the optical disk having the B element content in the recording layer of 1 to 10 atomic%, as is clear from Table 4, the pass rate was 100% for all the evaluation items.

  As is apparent from Table 4, in the optical disk having the B element content of 15 atomic% in the recording layer, the pass rate was 20 out of 100 for both the 1 × speed recording error rate and the 2 × speed recording error rate, and the remaining 80 sheets. Did not reach the target level. An optical disc that did not reach the target level had a low signal modulation. Further, in the case of an optical disc having a B element content of 15 atomic% in the recording layer, as is clear from Table 4, the pass rate is 100 out of 100 for both the 1 × speed recording error rate and the 2 × speed recording error rate after 1000 rewrites. 80 sheets, and the remaining 20 sheets did not reach the target level.

Further, when Bi ₁₆ Ge ₃₇ Te ₄₇ and Bi ₁₉ Ge ₂₆ Te ₅₅ are used as the base material for forming the recording layer in the optical disc of this example, Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer. The same characteristics as the optical disk were obtained.

From the above results, Bi ₂ Ge ₄₇ Te ₅₁ , Bi ₄ Ge ₄₇ Te ₄₉ , Bi ₃ Ge ₄₇ Te ₅₀ , Bi ₁₆ Ge ₃₇ Te ₄₇ , Bi ₁₉ Ge ₂₆ Te ₅₅ and Bi ₃₀ Ge ₂₂ Te ₄₈ are recorded. In the optical disk in which the recording layer is formed with a material in which a part of Ge in each base material is replaced with B (substitution element MA) as a forming base material, the content of B in the recording layer is 1 to 10 atomic%. As a result, target values were achieved for all evaluation items.

That is, when B is used as the additive element MA in the recording layer, the composition ratios of Bi, (Ge + MA), and Te in the recording layer are set to the following triangular composition diagrams of Bi, (Ge + MA), and Te. Set the composition range surrounded by dots,
B2 ′ (Bi ₂ , (Ge + MA) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA) ₂₆ , Te ₅₅ )
In addition, by setting the content of the additive element MA (B) in the recording layer to 1 to 10 atomic%, even when information is recorded with a blue laser, durability against repeated data recording is high and high-speed recording is possible. It was also found that an information recording medium having a wide range of recording linear velocities that can be handled can be obtained .

[Reference Example 2]
In the optical disk of Reference Example 2 , Bi ₃ Ge ₄₇ Te ₅₀ and Bi ₃₀ Ge ₂₂ Te ₄₈ are used as the base material for forming the recording layer, and a part of Ge in each base material is replaced with Sn (substitution element MB). A recording layer was formed. The method for forming the recording layer in the optical disc of this example is as follows.

In this example, in addition to the Ge ₅₀ Te ₅₀ and Bi ₂ Te ₃ targets, in order to replace a part of Ge with Sn, an Sn ₅₀ Te ₅₀ target is further prepared, and the recording layer is formed by simultaneous sputtering with three types of target. Formed. At this time, the sputtering power applied to each target was adjusted so that the composition of the recording layer was a desired composition. In this example, various optical disks were manufactured by changing the Sn content in the recording layer in the range of 1 to 25 atomic%. For comparison, an optical disk that does not contain Sn, that is, an optical disk in which the recording layer is formed only with a forming base material (Bi ₃ Ge ₄₇ Te ₅₀ or Bi ₃₀ Ge ₂₂ Te ₄₈ ) was also manufactured. An optical disk was manufactured in the same manner as in Example 1 except for the recording layer.

  In this example, for the various optical discs produced in this example, error rates at 1 × and 3 × recording linear velocities (hereinafter, these evaluation items are referred to as 1 × speed recording error rate and 3 × speed recording error rate), The error rate after 1000 rewrites in 1 × speed recording and 3 × speed recording (hereinafter, these evaluation items are referred to as 1 × speed recording error rate and 3 × speed recording error rate after 1000 times rewriting) and evaluated. In addition, the target value of each evaluation item was the same as that of Example 1.

First, in this example, performance evaluation is performed by performing each of the above tests on an optical disk having a Sn content of 10 atomic% from among optical disks manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as a base material for forming a recording layer. Went. As a result, the 1 × speed recording error rate is 4.5 × 10 ⁻⁵ , the 3 × speed recording error rate is 3.4 × 10 ⁻⁵ , the 1 × speed recording error rate after 1000 rewrites is 8.8 × 10 ⁻⁵ , The triple speed recording error rate after 1000 rewrites was 9.4 × 10 ⁻⁵ , and the target level could be achieved for all evaluation items.

Next, among the optical disks manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as the recording layer forming base material in this example, 100 optical disks with Sn contents of 0, 1, 2, 20, and 25 atomic% were respectively obtained. Each of the manufactured optical disks was subjected to the above tests, and performance evaluation was performed. The results are shown in Table 5. Table 5 shows the pass rate of each evaluation item of the optical disk using Bi ₃ Ge ₄₇ Te ₅₀ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the Sn content.

As can be seen from Table 5, when Bi ₃ Ge ₄₇ Te ₅₀ was used as the base material for forming the recording layer, the pass rate was 100% at the single-speed recording error rate in the optical disk not containing Sn. The double speed recording error rate was 25 out of 100 sheets, and the remaining 75 sheets did not reach the target level. Further, as is clear from Table 5, in the evaluation items of the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewritings, the pass rate was 20 out of 100 sheets, and the remaining 80 sheets reached the target level. There wasn't.

  Moreover, in the optical disc having the Sn content of 1 to 20 atomic% in the recording layer, as is clear from Table 5, the pass rate was 100% for all the evaluation items.

  As is apparent from Table 5, the optical disk having a Sn content of 25 atomic% in the recording layer has a pass rate of 5 out of 100 for both the 1 × recording error rate and the 3 × recording error rate, and the remaining 95 are The target level was not reached. An optical disc that did not reach the target level had a low signal modulation. Further, in the case of an optical disc having a Sn content of 25 atomic% in the recording layer, the pass rate is 80 out of 100 for both the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites, and the remaining 20 are the target. Did not reach the level.

Further, when Bi ₂ Ge ₄₇ Te ₅₁ and Bi ₄ Ge ₄₇ Te ₄₉ are used as the formation base material of the recording layer in the optical disc of this example, the same as when Bi ₃ Ge ₄₇ Te ₅₀ is used as the formation base material. The characteristics were obtained.

Furthermore, the same result as above was obtained when part or all of Sn in the recording layer was replaced with Pb. The recording layer formation method when Pb is used as the substitution element is as follows. In addition to the Ge ₅₀ Te ₅₀ and Bi ₂ Te ₃ targets, a Pb ₅₀ Te ₅₀ target was prepared in order to replace part of Ge with Pb, and a recording layer was formed by simultaneous sputtering with three types of target. At this time, the sputtering power applied to each target was adjusted so that the composition of the recording layer was a desired composition.

Next, in this example, each of the above tests is performed on an optical disk having a Sn content of 10 atomic% among optical disks manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as a base material for forming a recording layer, and performance evaluation is performed. Went. As a result, the 1 × speed recording error rate is 4.9 × 10 ⁻⁵ , the 3 × speed recording error rate is 3.0 × 10 ⁻⁵ , and the 1 × speed recording error rate after 1000 rewrites is 9.6 × 10 ⁻⁵ , The triple speed recording error rate after 1000 rewrites was 8.5 × 10 ⁻⁵ , and the target level could be achieved for all evaluation items.

In this example, among the optical discs manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, 100 optical discs with Sn contents of 0, 1, 2, 20, and 25 atomic% are respectively used. The above tests were performed on all manufactured optical disks, and performance evaluation was performed. The results are shown in Table 6. Table 6 shows the pass rate of each evaluation item of the optical disc using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the Sn content.

As can be seen from Table 6, when Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer, the pass rate is 100% (100 out of 100 sheets) at a single-speed recording error rate in an optical disk not containing Sn. However, at the triple speed recording error rate, the pass rate was 40 out of 100 sheets, and the remaining 60 sheets did not reach the target level. When Sn is not added, the pass rate is 30 out of 100 sheets in the evaluation items of the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites, and the remaining 70 sheets do not reach the target level. It was.

  Further, in the optical disc having the Sn content of 1 to 20 atomic% in the recording layer, as is clear from Table 6, the pass rate was 100% for all the evaluation items.

  As is apparent from Table 6, the optical disk having a Sn content of 25 atomic% in the recording layer has a pass rate of 10 out of 100 for both the 1x recording error rate and the 3x recording error rate, and the remaining 90 are The target level was not reached. An optical disc that did not reach the target level had a low signal modulation. In addition, as is apparent from Table 6, in the optical disk having the Sn content of 25 atomic% in the recording layer, the pass rate is 80 out of 100 for both the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites. The remaining 20 sheets did not reach the target level.

Further, when Bi ₁₆ Ge ₃₇ Te ₄₇ and Bi ₁₉ Ge ₂₆ Te ₅₅ are used as the base material for forming the recording layer in the optical disc of this example, Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer. The same characteristics as the optical disk were obtained. Furthermore, the same result as above was obtained when part or all of Sn in the recording layer was replaced with Pb.

From the above results, Bi ₂ Ge ₄₇ Te ₅₁ , Bi ₄ Ge ₄₇ Te ₄₉ , Bi ₃ Ge ₄₇ Te ₅₀ , Bi ₁₆ Ge ₃₇ Te ₄₇ , Bi ₁₉ Ge ₂₆ Te ₅₅ and Bi ₃₀ Ge ₂₂ Te ₄₈ are recorded. In an optical disk in which a recording layer is formed with a material in which a part of Ge in each base material is replaced with at least one element (substitution element MB) of Sn and Pb as a formation base material, the substitution element MB in the recording layer By setting the total content to 1 to 20 atomic%, target values were achieved for all evaluation items.

That is, the composition ratio of Bi, (Ge + MB) and Te in the recording layer is set to a composition range surrounded by the following points on the triangular composition diagram of Bi, (Ge + MB) and Te,
B2 ′ (Bi ₂ , (Ge + MB) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MB) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MB) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MB) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MB) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MB) ₂₆ , Te ₅₅ )
In addition, by setting the content of the additive element MB in the recording layer to 1 to 20 atomic%, even when information is recorded with a blue laser, durability against repeated recording of data is high, high-speed recording is possible, and It was found that an information recording medium having a wide range of recording linear velocities that can be handled was obtained.

In the optical disk of Example 2 , Bi ₃ Ge ₄₇ Te ₅₀ and Bi ₃₀ Ge ₂₂ Te ₄₈ are used as the base material for forming the recording layer, and part of Ge in each base material is Si (substitution element MA) and Sn (substitution). A recording layer was formed of a material substituted with the element MB). The method for forming the recording layer in the optical disc of this example is as follows.

In this example, in order to replace a part of Ge with Si and Sn, a Ge ₅₀ Te ₅₀ bonded with a Sn ₅₀ Te ₅₀ chip, a Bi ₂ Te ₃ target, and a Si ₅₀ Te ₅₀ target are prepared. A recording layer was formed by co-sputtering. At this time, the sputtering power applied to each target was adjusted so that the composition of the recording layer was a desired composition. In this example, various optical disks were produced by changing the contents of Si and Sn in the recording layer. Specifically, various optical disks were produced in which the Si and Sn contents were changed in the range of 1 to 20 atomic% and the combinations of the Si and Sn contents were changed. For comparison, an optical disk that does not contain Si and Sn, that is, an optical disk in which the recording layer is formed using only a forming base material (Bi ₃ Ge ₄₇ Te ₅₀ or Bi ₃₀ Ge ₂₂ Te ₄₈ ) was also manufactured. An optical disk was manufactured in the same manner as in Example 1 except for the recording layer.

  In this example, with respect to the various optical discs produced in this example, similarly to Example 1, a 1 × speed recording error rate and a 3 × speed recording error rate (error rate after rewriting a random pattern 10 times) and 1000 The 1 × speed recording error rate and the 3 × speed recording error rate after rewriting were measured and evaluated. In addition, the target value of each evaluation item was the same as that of Example 1.

First, in this example, the Si content is 5 atomic% and the Sn content is 10 atomic% from an optical disk manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as the base material for forming the recording layer. The above test was performed on an optical disk and evaluated. As a result, the 1 × speed recording error rate is 2.0 × 10 ⁻⁵ , the 3 × speed recording error rate is 2.5 × 10 ⁻⁵ , and the 1 × speed recording error rate after 1000 rewrites is 6.0 × 10 ⁻⁵ , The triple speed recording error rate after 1000 rewrites was 7.0 × 10 ⁻⁵ , and the target level could be achieved for all evaluation items.

Next, in this example, a combination of Si and Sn contents (hereinafter referred to as [Si, Sn] atomic%) in an optical disk manufactured using Bi ₃ Ge ₄₇ Te ₅₀ as a base material for forming a recording layer is described. [Si, Sn] = [0,0], [1,1], [1,19], [1,20], [19,1], and [20,1] atomic% 100 optical disks, respectively The above tests were performed on all manufactured optical disks, and performance evaluation was performed. The results are shown in Table 7. Table 7 shows the pass rate of each evaluation item of the optical disk using Bi ₃ Ge ₄₇ Te ₅₀ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the combination of the Si and Sn contents. .

As is apparent from Table 7, when Bi ₃ Ge ₄₇ Te ₅₀ is used as the base material for forming the recording layer, an optical disk to which Si and Sn are not added ([Si, Sn] = [0, 0] atomic% optical disk) The pass rate was 100% at the 1 × speed recording error rate, but the 3 × speed recording error rate was 25 out of 100 sheets, and the remaining 75 sheets did not reach the target level. In addition, when Si and Sn are not added, as is clear from Table 7, the pass rate is 20 out of 100 sheets for both the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites. The remaining 80 sheets did not reach the target level.

  Further, in the optical disk having a total content of Si and Sn in the recording layer of 1 to 20 atomic% ([Si, Sn] = [1,1], [1,19] and [19,1] atomic%), As is clear from Table 7, the pass rate was 100% for all evaluation items.

  As is apparent from Table 7, in the case of an optical disk having a total content of Si and Sn in the recording layer of 21 atomic% ([Si, Sn] = [1,20] and [20,1] atomic%) For both the recording error rate and the triple speed recording error rate, the pass rate was 10 out of 100 sheets, and the remaining 90 sheets did not reach the target level. An optical disc that did not reach the target level had a low signal modulation. Further, in the case of an optical disc having a total content of Si and Sn in the recording layer of 21 atomic%, the pass rate is 90 out of 100 for both the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites, and the remaining 10 The sheet did not reach the target level.

Further, when Bi ₂ Ge ₄₇ Te ₅₁ and Bi ₄ Ge ₄₇ Te ₄₉ are used as the formation base material of the recording layer in the optical disc of this example, the same as when Bi ₃ Ge ₄₇ Te ₅₀ is used as the formation base material. The characteristics were obtained. Furthermore, the same result as above was obtained when part or all of Sn in the recording layer was replaced with Pb.

Next, in this example, the Si content is 5 atomic% and the Sn content is 10 atomic% from an optical disk manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as a recording layer forming base material. Each optical disk was evaluated by performing the above tests. As a result, the 1 × speed recording error rate is 2.1 × 10 ⁻⁵ , the 3 × speed recording error rate is 2.3 × 10 ⁻⁵ , and the 1 × speed recording error rate after 1000 rewrites is 5.5 × 10 ⁻⁵ , The triple speed recording error rate after 1000 rewrites was 6.0 × 10 ⁻⁵ , and the target level could be achieved for all evaluation items.

In this example, among the optical disks manufactured using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, the combination of Si and Sn content is [Si, Sn] = [0, 0], [1 , 1], [1, 19], [1, 20], [19, 1], and [20, 1] atomic% optical discs, respectively, 100, and the above tests were performed on all the optical discs produced. The performance was evaluated. The results are shown in Table 8. Table 8 shows the pass rate of each evaluation item of the optical disc using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the combination of the Si and Sn contents. .

As is apparent from Table 8, when Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer, an optical disk to which Si and Sn are not added (an optical disk having [Si, Sn] = [0, 0] atomic%) The pass rate was 100% at the 1 × speed recording error rate, but the 3 × speed recording error rate was 25 out of 100 sheets, and the remaining 75 sheets did not reach the target level. In addition, when B and Sn are not added, as is clear from Table 8, the pass rate is 20 out of 100 for both the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites. The remaining 80 sheets did not reach the target level.

  Further, in the optical disk having a total content of Si and Sn in the recording layer of 1 to 20 atomic% ([Si, Sn] = [1,1], [1,19] and [19,1] atomic%), As is clear from Table 8, the pass rate was 100% for all evaluation items.

  As is clear from Table 8, in the case of an optical disk having a total content of Si and Sn in the recording layer of 21 atomic% ([Si, Sn] = [1,20] and [20,1] atomic%), the speed is 1 ×. For both the recording error rate and the triple speed recording error rate, the pass rate was 20 out of 100 sheets, and the remaining 80 sheets did not reach the target level. An optical disc that did not reach the target level had a low signal modulation. Further, in the case of an optical disc having a total content of Si and Sn in the recording layer of 21 atomic%, the pass rate is 85 out of 100 for both the 1 × speed recording error rate and the 3 × speed recording error rate after 1000 rewrites, and the remaining 15 The sheet did not reach the target level.

Further, when Bi ₁₆ Ge ₃₇ Te ₄₇ and Bi ₁₉ Ge ₂₆ Te ₅₅ are used as the base material for forming the recording layer in the optical disc of this example, Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer. The same characteristics as the optical disk were obtained. Furthermore, the same result as above was obtained when part or all of Sn in the recording layer was replaced with Pb.

From the above results, Bi ₂ Ge ₄₇ Te ₅₁ , Bi ₄ Ge ₄₇ Te ₄₉ , Bi ₃ Ge ₄₇ Te ₅₀ , Bi ₁₆ Ge ₃₇ Te ₄₇ , Bi ₁₉ Ge ₂₆ Te ₅₅ and Bi ₃₀ Ge ₂₂ Te ₄₈ are recorded. In an optical disk in which a recording layer is formed of a material in which a part of Ge in each base material is replaced with Si (substitution element MA) and at least one element of Sn and Pb (substitution element MB) as a formation base material By setting the total content of the substitution elements MA and MB in the recording layer to 1 to 20 atomic%, the target values were achieved for all evaluation items.

That is, when Si is used as the substitution element MA, the composition ratio of Bi, (Ge + MA + MB) and Te in the recording layer is surrounded by the following points on the triangular composition diagram of Bi, (Ge + MA + MB) and Te. Set the composition range,
B2 ′ (Bi ₂ , (Ge + MA + MB) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA + MB) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA + MB) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA + MB) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA + MB) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA + MB) ₂₆ , Te ₅₅ )
In addition, by setting the total content of the substitutional elements MA and MB in the recording layer to 1 to 20 atomic%, even when information is recorded with a blue laser, durability against repeated data recording is high and high-speed recording is possible. It was also found that an information recording medium having a wide range of recording linear velocities that can be handled can be obtained .

[Reference Example 3]
In the optical disc of Reference Example 3 , Bi ₃ Ge ₄₇ Te ₅₀ and Bi ₃₀ Ge ₂₂ Te ₄₈ are used as the base material for forming the recording layer, and part of Ge in each base material is B (substitution element MA) and Sn (substitution). A recording layer was formed of a material substituted with the element MB). The method for forming the recording layer in the optical disc of this example is as follows.

In this example, in order to replace a part of Ge with B and Sn, Ge ₅₀ Te ₅₀ with a Sn ₅₀ Te ₅₀ chip attached and a Bi ₂ Te ₃ target are prepared, and the B chip is placed on the sputtering target. The recording layer was formed by pasting and co-sputtering. At this time, the sputtering power applied to each target was adjusted so that the composition of the recording layer was a desired composition. In this example, various optical disks were produced by changing the contents of B and Sn in the recording layer. Specifically, the B content is changed in the range of 1 to 11 atomic%, the Sn content is changed in the range of 1 to 20 atomic%, and the combination of the B and Sn contents is changed. Various optical discs were prepared. For comparison, an optical disk that does not contain B and Sn, that is, an optical disk in which a recording layer is formed only with a forming base material (Bi ₃ Ge ₄₇ Te ₅₀ or Bi ₃₀ Ge ₂₂ Te ₄₈ ) was also produced. An optical disk was manufactured in the same manner as in Example 1 except for the recording layer.

First, in this example, Bi ₃ Ge ₄₇ Te ₅₀ is used as the base material for forming the recording layer, and the combination of the contents of B and Sn is [B, Sn] = [0, 0], [1, 1], [ 1,19], [1,20], [10,1], [10,10], [10,11], and [11,1] atomic% 100 optical disks, respectively, Similar to the first embodiment, the 1 × speed recording error rate and the 3 × speed recording error rate (error rate after rewriting the random pattern 10 times), the 1 × speed recording error rate after rewriting 1000 times, and 3 The double speed recording error rate was measured and evaluated. In addition, the target value of each evaluation item was the same as that of Example 1. The results are shown in Table 9. Table 9 shows the pass rate of each evaluation item of the optical disc using Bi ₃ Ge ₄₇ Te ₅₀ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the combination of B and Sn contents. .

As is apparent from Table 9, when Bi ₃ Ge ₄₇ Te ₅₀ is used as the base material for forming the recording layer, an optical disk to which B and Sn are not added (an optical disk having [B, Sn] = [0, 0] atomic%) The pass rate was 100% at the 1 × speed recording error rate, but the 3 × speed recording error rate was 25 out of 100 sheets, and the remaining 75 sheets did not reach the target level. In addition, when B and Sn are not added, as is clear from Table 9, the pass rate is 20 out of 100 in both the 1 × speed recording error rate and the 3 × speed recording error rate evaluation items after 1000 rewrites. The remaining 80 sheets did not reach the target level.

  Further, when the total content of B and Sn in the recording layer is 1 to 20 atomic% and the content of B is 1 to 10 atomic% ([B, Sn] = [1, 1], As shown in Table 9, the pass rate of all the evaluation items was 100% in the optical discs of [1, 19], [10, 1] and [10, 10] atomic%).

  The total content of B and Sn in the recording layer is 20 atomic% or less, but the optical disk in which the B content exceeds 10 atomic%, that is, [B, Sn] = [11, 1] atoms. As can be seen from Table 9, the% pass rate was 20 out of 100 in all the evaluation items, and the remaining 80 did not reach the target level. An optical disc that did not reach the target level had a low signal modulation.

  Further, as shown in Table 9, when the combination of B and Sn contents in the recording layer is [B, Sn] = [1,20] atomic%, the pass rate is 100 sheets for all evaluation items. 10 in the middle, and the remaining 90 did not reach the target level. In addition, in the case of an optical disc in which the combination of the contents of B and Sn in the recording layer is [B, Sn] = [10, 11] atomic%, as shown in Table 9, the pass rate is 100 for all evaluation items. 20 in the middle, and the remaining 80 did not reach the target level. In the optical disc in which the total content of B and Sn in these recording layers is 21 atomic%, the signal modulation degree is small.

Further, when Bi ₂ Ge ₄₇ Te ₅₁ and Bi ₄ Ge ₄₇ Te ₄₉ are used as the formation base material of the recording layer in the optical disc of this example, the same as when Bi ₃ Ge ₄₇ Te ₅₀ is used as the formation base material. The characteristics were obtained. Furthermore, the same result as above was obtained when part or all of Sn in the recording layer was replaced with Pb.

Next, Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer, and the combination of the contents of B and Sn is [B, Sn] = [0, 0], [1, 1], [1, 19 ], [1,20], [10,1], [10,10], [10,11] and [11,1] atomic% optical discs, respectively, 100, and for all the manufactured optical discs The above tests were performed to evaluate the performance. The results are shown in Table 10. Table 10 shows the pass rate of each evaluation item of the optical disc using Bi ₃₀ Ge ₂₂ Te ₄₈ as the base material for forming the recording layer, and shows the pass rate of each evaluation item with respect to the combination of B and Sn contents. .

As can be seen from Table 10, when Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer, an optical disk to which B and Sn are not added (an optical disk with [B, Sn] = [0, 0] atomic%) The pass rate was 100% at the 1 × speed recording error rate, but the 3 × speed recording error rate was 25 out of 100 sheets, and the remaining 75 sheets did not reach the target level. In addition, when B and Sn are not added, as is clear from Table 10, the pass rate is 20 out of 100 for both the 1 × speed recording error rate and the 3 × speed recording error rate evaluation items after 1000 rewrites. The remaining 80 sheets did not reach the target level.

  Further, when the total content of B and Sn in the recording layer is 1 to 20 atomic% and the content of B is 1 to 10 atomic% ([B, Sn] = [1, 1], As shown in Table 10, the pass rate was 100% for all evaluation items in the optical discs of [1, 19], [10, 1] and [10, 10] atomic%).

  The total content of B and Sn in the recording layer is 20 atomic% or less, but the optical disk in which the B content exceeds 10 atomic%, that is, [B, Sn] = [11, 1] atomic%. As is clear from Table 10, the pass rate was 25 out of 100 for all the evaluation items, and the remaining 75 discs did not reach the target level. An optical disc that did not reach the target level had a low signal modulation.

  Further, as shown in Table 10, the pass rate is 100 sheets for all the evaluation items in the optical disc in which the combination of the B and Sn contents in the recording layer is [B, Sn] = [1,20] atomic%. Of the 15 sheets, the remaining 85 did not reach the target level. In addition, in the optical disc in which the combination of the contents of B and Sn in the recording layer is [B, Sn] = [10, 11] atomic%, as shown in Table 10, the pass rate is 100 sheets for all evaluation items. 30 in the middle and the remaining 70 did not reach the target level. In the optical disc in which the total content of B and Sn in these recording layers is 21 atomic%, the signal modulation degree is small.

Further, when Bi ₁₆ Ge ₃₇ Te ₄₇ and Bi ₁₉ Ge ₂₆ Te ₅₅ are used as the base material for forming the recording layer in the optical disc of this example, Bi ₃₀ Ge ₂₂ Te ₄₈ is used as the base material for forming the recording layer. The same characteristics as the optical disk were obtained. Furthermore, the same result as above was obtained when part or all of Sn in the recording layer was replaced with Pb.

From the above results, Bi ₂ Ge ₄₇ Te ₅₁ , Bi ₄ Ge ₄₇ Te ₄₉ , Bi ₃ Ge ₄₇ Te ₅₀ , Bi ₁₆ Ge ₃₇ Te ₄₇ , Bi ₁₉ Ge ₂₆ Te ₅₅ and Bi ₃₀ Ge ₂₂ Te ₄₈ are recorded. In an optical disk in which a recording layer is formed by a material in which a part of Ge in each base material is replaced with B (substitution element MA) and at least one element of Sn and Pb (substitution element MB) as a formation base material By setting the total content of the substitution elements MA (B) and MB in the recording layer to 1 to 20 atomic% and the content of the substitution element MA (B) to 1 to 10 atomic%, the target values are obtained for all evaluation items. Was achieved.

That is, when B is used as the substitution element MA, the composition ratio of Bi, (Ge + MA + MB) and Te in the recording layer is surrounded by the following points on the triangular composition diagram of Bi, (Ge + MA + MB) and Te. Set the composition range,
B2 ′ (Bi ₂ , (Ge + MA + MB) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA + MB) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA + MB) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA + MB) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA + MB) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA + MB) ₂₆ , Te ₅₅ )
In addition, by recording the total content of the substitution elements MA (B) and MB in the recording layer in the range of 1 to 20 atomic% and the content of the substitution element MA (B) in the range of 1 to 10 atomic%, information recording is performed with a blue laser. Even in this case, it was found that an information recording medium having high durability against repeated data recording, high-speed recording, and a wide range of applicable recording linear speeds can be obtained.

In Examples 1 and 2 and Reference Examples 1 to 3 , an example in which information was recorded / reproduced using a blue laser with a wavelength of 405 nm was described. However, the present invention is not limited to this, and a red laser with a wavelength of 640 nm to 665 nm is used. The same result can be obtained even when information is recorded / reproduced using.

[Optimum configuration]
The optimum composition and optimum film thickness of each layer constituting the information recording medium of the present invention will be described below.

(First protective layer)
The substance present on the light beam incident side of the first protective layer is a plastic substrate such as polycarbonate or an organic substance such as an ultraviolet curable resin. Moreover, these refractive indexes are about 1.4-1.6. In order to effectively cause reflection between the organic material and the first protective layer, the refractive index of the first protective layer is desirably 2.0 or more. The refractive index of the first protective layer is optically larger than the refractive index of the substance (corresponding to the substrate in this embodiment and this reference example ) existing on the light beam incident side, and light absorption does not occur. It is better that the refractive index of the first protective layer is larger in the range. Specifically, the first protective layer has a refractive index n of 2.0 to 3.0 and is formed of a material that does not absorb light, and in particular, a metal oxide, carbide, nitride, sulfide, It is desirable to contain selenide.

The thermal conductivity of the first protective layer is desirably at least 2 W / mk. In particular, a ZnS—SiO ₂ -based compound has a low thermal conductivity, and is optimal as the first protective layer. Furthermore, the material with the addition of SnO ₂ or ZnS to SnO _2, CdS, SnS, GeS, the added material a sulfide such as PbS or SnO ₂ in the _Cr 2 _O 3, _Mo 3 _O transition metal oxides, such as _4, Not only has a low thermal conductivity, but also is more thermally stable than a ZnS—SiO ₂ -based material, and thus exhibits particularly excellent characteristics as the first protective layer.

  When the wavelength of the light beam is about 405 nm, the optimum thickness of the first protective layer is 40 nm to 100 nm in order to effectively use the optical interference between the substrate and the recording layer.

(First interface layer)
Since the melting point of the phase change material used for the recording layer of the information recording medium of the present invention is as high as 650 ° C. or higher, a thermally extremely stable first interface layer may be provided between the first protective layer and the recording layer. desirable. Specifically, as a material for forming the first interface layer, refractory oxides such as Cr ₂ O ₃ , Ge ₃ N ₄ , SiC, refractory nitrides, and refractory carbides are desirable. It is stable and does not deteriorate due to film peeling even after long-term storage.

  In addition, it is more desirable that the first interface layer contains a material such as Bi, Sn, or Pb that promotes crystallization of the recording layer, because an effect of suppressing recrystallization of the recording layer can be obtained. In particular, Te, oxide of Bi, Sn, Pb, Te oxide of Bi, Sn, Pb, a mixture of oxide and germanium, or Te oxide of Bi, Sn, Pb, oxide and transition metal Mixtures with oxides and transition metal nitrides are desirable. Since transition metals easily change their valence, even if elements such as Bi, Sn, Pb, and Te are liberated, the transition metal changes the valence, and the transition metal and Bi, Sn, Pb, Te, etc. This is because bonding occurs between them to produce a thermally stable compound. In particular, Cr, Mo, and W are excellent materials because they have a high melting point, can easily change the valence, and can easily generate a thermally stable compound with the metal.

  The effect is exhibited if the thickness of the first interface layer is 0.5 nm or more. However, when the film thickness of the first interface layer is less than 2 nm, the material for forming the first protective layer may pass through the first interface layer and dissolve in the recording layer, which may deteriorate the reproduction signal quality after many rewrites. Therefore, the film thickness of the first interface layer is desirably 2 nm or more. In addition, when the thickness of the first interface layer is greater than 10 nm, it adversely affects optically, and thus there are adverse effects such as a decrease in reflectivity and a decrease in signal amplitude. Therefore, the film thickness of the first interface layer is desirably 2 nm to 10 nm.

(Recording layer)
The recording layer forming material has already been described in detail in Examples and the like. However, when the recording layer materials used in the information recording medium are put together, the following phase change material is obtained. In the present invention, the applicable linear velocity range can be adjusted by adjusting the content of elements other than Bi, Ge, and Te in the recording layer.
Quaternary recording layer materials: Bi-Ge-Si-Te, B-Bi-Ge-Te, Bi-Ge-Sn-Te, Bi-Ge-Pb-Te
Five-element recording layer materials: B—Bi—Ge—Si—Te, Bi—Ge—Pb—Sn—Te, Bi—Ge—Si—Pb—Te, Bi—Ge—Si—Sn—Te, B—Bi -Ge-Pb-Te, B-Bi-Ge-Sn-Te
6-element recording layer materials: B—Bi—Ge—Pb—Sn—Te, Bi—Ge—Pb—Si—Sn—Te, B—Bi—Ge—Si—Sn—Te, B—Bi—Ge—Pb -Si-Te,
7-element recording layer material: B-Bi-Ge-Pb-Si-Sn-Te
By appropriately adjusting the multi-component composition as described above, the performance of the recording layer material can be controlled more finely.

  In addition, as long as each constituent element of the recording layer material used in the information recording medium of the present invention maintains the relationship of the composition range shown in the above-described examples etc., even if impurities are mixed, If the atomic% of impurities is within 1%, the effect of the present invention is not lost.

  In the structure of the information recording medium of the present invention, it is optically optimal to set the film thickness of the recording layer to 5 nm to 15 nm. In particular, when the recording layer is formed with a film thickness of 7 nm to 11 nm, it is possible to suppress the deterioration of the reproduction signal due to the flow of the recording film at the time of rewriting many times, and to further optimize the modulation degree optically.

(Second interface layer)
Since the melting point of the phase change material used for the recording layer of the information recording medium of the present invention is as high as 650 ° C. or higher, a thermally extremely stable second interface layer is provided between the second protective layer and the recording layer. It is desirable. Specifically, high melting point oxides such as Cr ₂ O ₃ , Ge ₃ N ₄ , SiC, high melting point nitrides, and high melting point carbides are desirable as the second interface layer. These materials are thermally stable and do not deteriorate due to film peeling even after long-term storage.

  In addition, it is more desirable that the second interface layer contains a material such as Bi, Sn, or Pb that promotes crystallization of the recording layer, because an effect of suppressing recrystallization of the recording layer can be obtained. In particular, Te, oxide of Bi, Sn, Pb, Te oxide of Bi, Sn, Pb, a mixture of oxide and germanium, or Te oxide of Bi, Sn, Pb, oxide and transition metal Mixtures with oxides and transition metal nitrides are desirable. Since transition metals easily change their valence, even if elements such as Bi, Sn, Pb, and Te are liberated, the transition metal changes the valence, and between the transition metal and Bi, Sn, Pb, and Te. This is because bonding occurs in order to produce a thermally stable compound. In particular, Cr, Mo, and W are excellent materials because they have a high melting point, easily change their valence, and easily generate a thermally stable compound with the above metal.

  The above effects are exhibited when the thickness of the second interface layer is 0.5 nm or more. However, if the film thickness is thinner than 1 nm, the material for forming the second protective layer may pass through the second interface layer and dissolve in the recording layer, which may deteriorate the reproduction signal quality after many rewrites. Therefore, the film thickness of the second interface layer is preferably 1 nm or more. Further, when the film thickness of the second interface layer is greater than 5 nm, it adversely affects optically, and thus there are problems such as a decrease in reflectivity and a decrease in signal amplitude. Therefore, the film thickness of the second interface layer is desirably 1 nm to 5 nm.

(Second protective layer)
The second protective layer is formed of a material that does not absorb light, and particularly preferably contains a metal oxide, carbide, nitride, sulfide, or selenide. The thermal conductivity of the second protective layer is preferably at least 2 W / mk or less. In particular, a ZnS—SiO ₂ -based compound is optimal as the second protective layer because of its low thermal conductivity. Furthermore, SnO ₂ or, ZnS to SnO _2, CdS, SnS, added GeS, material was added sulfides such as PbS, or a _{Cr 2 O 3, Mo 3 O} 4 or the like transition metal oxides in the SnO ₂ Since the material has not only low thermal conductivity, but is also more thermally stable than the ZnS-SiO ₂ material, even when the thickness of the second interface layer is less than 1 nm, Since the material for forming the second interface layer does not melt, it exhibits particularly excellent characteristics as the second protective layer.

  In addition, when the information recording medium includes an absorptance control layer between the second protective layer and the thermal diffusion layer, and the light beam wavelength is about 405 nm, optical interference between the recording layer and the absorptivity control layer is effective. In order to use this, the optimum film thickness of the second protective layer is 25 nm to 60 nm.

(Thermal diffusion layer)
As a material for forming the thermal diffusion layer, a metal or alloy having high reflectivity and high thermal conductivity is desirable, and a material having a total content of Al, Cu, Ag, Au, Pt, and Pd of 90 atomic% or more is desirable. In addition, a material having a high melting point and high hardness such as Cr, Mo, W and the like and an alloy of these materials are also desirable as a material for forming the heat diffusion layer. It is possible to prevent deterioration due to.

  Specifically, in particular, an information recording medium in which a thermal diffusion layer is formed of a material containing 95 atomic% or more of Al is not only inexpensive, but also has an effect of having high CNR, high recording sensitivity, and excellent resistance to multiple rewriting. The effect of reducing the cross erase is extremely large. In addition, when the thermal diffusion layer is formed of a material containing 95 atomic% or more of Al, an information recording medium that is inexpensive and excellent in corrosion resistance can be realized. As additive elements for Al, Co, Ti, Cr, Ni, Mg, Si, V, Ca, Fe, Zn, Zr, Nb, Mo, Rh, Sn, Sb, Te, Ta, W, Ir, Pb, B, C and the like are excellent in terms of corrosion resistance. However, when Co, Cr, Ti, Ni, or Fe is used as an additive element, there is a great effect in improving corrosion resistance.

  The thickness of the thermal diffusion layer is desirably 30 nm to 100 nm. When the thickness of the thermal diffusion layer is less than 30 nm, the heat generated in the recording layer is difficult to diffuse. Therefore, the recording layer is likely to be deteriorated especially when rewritten about 1000 times with a blue laser, and cross erase is caused. It is likely to occur. Further, when the thickness of the thermal diffusion layer is smaller than 30 nm, light is transmitted, so that it is difficult to use as the thermal diffusion layer, and the reproduction signal amplitude may be reduced. Also, if the thickness of the thermal diffusion layer is greater than 100 nm, the heat applied to the recording layer during information rewriting is likely to diffuse, so the time during which the recording layer is held above the crystallization temperature is shortened, and the recording mark is There is a possibility that it cannot be crystallized sufficiently. Further, when the film thickness of the thermal diffusion layer is 200 nm or more, the productivity is deteriorated, and the substrate is warped due to the internal stress of the thermal diffusion layer, and information recording / reproduction cannot be performed accurately. There is a fear. Moreover, if the film thickness of a thermal-diffusion layer is 30 nm-90 nm, it is excellent in the point of corrosion resistance and productivity, and is more desirable.

In addition, when the information recording medium includes an absorptance control layer between the second protective layer and the thermal diffusion layer, and the metal element contained in the absorptance control layer and the metal element contained in the thermal diffusion layer are the same, the production is There is a big advantage. In this case, two layers of an absorptivity control layer and a thermal diffusion layer can be formed using the same target. That is, when forming an absorptance control layer, sputtering is performed with a mixed gas such as an Ar—O ₂ mixed gas or an Ar—N ₂ mixed gas, and an appropriate refractive index is obtained by reacting a metal element with oxygen or nitrogen during the sputtering. When the thermal diffusion layer is formed, a metal thermal diffusion layer having a high thermal conductivity can be formed by sputtering with Ar gas.

As described above, in the information recording medium of the present invention, a part of Ge of the phase change material containing Bi, Ge, and Te is substituted element MA and / or MB shown in Examples 1 and 2 and Reference Examples 1 to 3. By forming the recording layer with the material replaced with, even when information is recorded with a blue laser, the reliability of the recorded data is high, the durability against repeated recording of data is improved, high-speed recording is possible, and An information recording medium with a wide range of recording linear velocities that can be handled is provided.

FIG. 1 is a schematic cross-sectional view of a phase change recording optical disk manufactured in Example 1. FIG. FIG. 2 is a schematic configuration diagram of the recording / reproducing apparatus used for the evaluation of the optical disk manufactured in Example 1. FIG. 3 is a triangular composition diagram of the Bi—Ge—Te phase change material, and shows the optimum composition range of the Bi—Ge—Te phase change material used in the recording layer of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 1st protective layer 3 1st interface layer 4 Recording layer 5 2nd interface layer 6 2nd protective layer 7 Thermal diffusion layer 8 UV curable resin layer 10 Optical disk

Claims (7)

An information recording medium,
A substrate,
A recording layer provided on a substrate and formed of a phase change material containing Bi, Ge, Te, and an element MA other than these elements;
A part of Ge is replaced by the element MA, and the composition ratio of Bi, (Ge + MA) and Te in the recording layer is surrounded by the following points on the triangular composition diagram of Bi, (Ge + MA) and Te In the composition range,
B2 ′ (Bi ₂ , (Ge + MA) ₄₇ , Te ₅₁ )
C2 ′ (Bi ₃ , (Ge + MA) ₄₇ , Te ₅₀ )
D2 ′ (Bi ₄ , (Ge + MA) ₄₇ , Te ₄₉ )
D6 ′ (Bi ₁₆ , (Ge + MA) ₃₇ , Te ₄₇ )
C8 ′ (Bi ₃₀ , (Ge + MA) ₂₂ , Te ₄₈ )
B7 ′ (Bi ₁₉ , (Ge + MA) ₂₆ , Te ₅₅ )
An information recording medium, wherein the element MA is Si, and the content of the element MA in the recording layer is in the range of 1 to 20 atomic%. An information recording medium,
  A substrate,
  A recording layer provided on a substrate and formed of a phase change material containing Bi, Ge, Te, and an element M other than these elements;
  A part of Ge is substituted with the element M, and the composition ratio of Bi, (Ge + M) and Te in the recording layer is surrounded by the following points on the triangular composition diagram of Bi, (Ge + M) and Te In the composition range,
B2 '(Bi ₂ , (Ge + M) ₄₇ , Te ₅₁ )
C2 '(Bi ₃ , (Ge + M) ₄₇ , Te ₅₀ )
D2 '(Bi ₄ , (Ge + M) ₄₇ , Te ₄₉ )
D6 '(Bi ₁₆ , (Ge + M) ₃₇ , Te ₄₇ )
C8 '(Bi ₃₀ , (Ge + M) ₂₂ , Te ₄₈ )
B7 '(Bi ₁₉ , (Ge + M) ₂₆ , Te ₅₅ )
  The element M includes the element MA and the element MB, the element MA is Si, the element MB is at least one element of Sn and Pb, and the total content of the element MA and the element MB in the recording layer is 1 to An information recording medium, characterized in that it is in the range of 20 atomic% and contains 1 atomic% or more of element MA and element MB. The information recording medium according to claim 1 or 2, wherein a wavelength of a light beam used for information recording of the information recording medium is 390 nm to 420 nm. 4. The concentric or spiral groove is formed on the substrate, and at least one of the groove and the groove is used as a recording track. 5. Information recording medium. 5. The information recording medium according to claim 4, wherein both the groove and the space between the grooves are used as recording tracks. Between the track pitch TP of the recording track of the information recording medium, the wavelength λ of the light beam used for recording / reproducing information, and the numerical aperture NA of the objective lens for condensing the light beam,
0.35 × (λ / NA) ≦ TP ≦ 0.7 × (λ / NA)
The information recording medium according to claim 1, wherein the following relationship is established. The information recording medium further comprises an interface layer, and the interface layer is provided in contact with the surface on at least one side of the recording layer. The information recording medium described.

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