JP4308866B2 - Information recording medium - Google Patents

Description

  The present invention relates to an information recording medium, and more particularly to an information recording medium capable of recording or rewriting information by phase change of a recording layer by light irradiation.

One of the rewritable information recording media is a phase change type optical recording medium. A phase change optical recording medium includes a recording layer in which an atomic arrangement reversibly changes between two different states (amorphous phase-crystalline phase) by irradiation with a light beam. Depending on the two different atomic arrangement states of the recording layer, Information is recorded or information is rewritten.
In recent years, BD-RE (Blu-ray Disk Rewritable), which records or rewrites information with laser light in the blue wavelength region, transfers data in addition to recording capacity compared to DVD-RAM (Digital Versatile Disk Random Access Memory). It is known to be fast. The double-speed data transfer speed of BD-RE is 72 MBps, while the double-speed data transfer speed of DVD-RAM is 22 MBps. That is, the data writing speed of the BD-RE is about three times that of the DVD-RAM. Therefore, the study of the phase change recording material required for the BD-RE compatible with 1 × to 2 × speed is considered to be equivalent to the phase change recording material used for the DVD-RAM compatible with about 3 × to about 6 × speed. The phase change recording material used for the RE recording layer requires a material suitable for high speed. Furthermore, in order to increase the amount of information, a multilayer BD-RE having a plurality of information layers is also being studied.

As the phase change recording material for forming the recording layer of the phase change type optical recording medium, a high melting point Ge—Sb—Te alloy or the like is generally used. For this reason, in order to reduce thermal damage to the resin substrate such as polycarbonate during the phase change between the “amorphous phase and the crystalline phase” due to the irradiation of the light beam, a protection including a dielectric material on both sides of the recording layer is performed. In many cases, a layer is formed (see Patent Document 1).
According to our study, a BiGeTe-based material has been reported as a phase change recording material suitable for high speed (see Patent Document 2).

JP 2005-056545 A JP 2004-155177 A

  By the way, in the case of a multilayer type information recording medium having two or more information layers, light transmitted through an information layer closer to the side where recording / reproducing light is incident (hereinafter referred to as an information layer on the closer side) is used. Therefore, it is necessary to record information in an information layer far from the incident side of the recording / reproducing light (hereinafter, information layer on the far side). For this reason, when the laminated structure of the information layer on the near side becomes complicated, the light transmittance of the information layer on the near side is lowered, and the recording characteristics of the information layer on the far side cannot be sufficiently exhibited.

On the other hand, according to our study, it has been found that a BiGeTe phase change recording material suitable for higher speed has a higher melting point than that of a Ge—Sb—Te alloy and is at least 700 ° C. or higher. . Therefore, the reflective layer is configured using an Ag alloy having high thermal conductivity in the blue wavelength region. Further, in order to reduce thermal damage due to the phase change of the phase change recording material, a protective layer using ZnS—SiO ₂ or the like having a small extinction coefficient in the blue wavelength region is often provided adjacent to the reflective layer.
However, it is known that the Ag alloy has the property of being easily corroded by the S element in the ZnS—SiO ₂ layer. Furthermore, the corrosion by the S element of the Ag alloy tends to proceed in a high humidity environment. For this reason, there is a problem in that the recording characteristics of the information layer deteriorate if the information layer is repeatedly rewritten a plurality of times.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an information recording medium which is excellent in rewriting performance many times and does not deteriorate recording characteristics in a high humidity environment, in a multilayer information recording medium using a phase change recording material having a high melting point. There is to do.

As a result of diligent study, the present inventor has provided a three-layer structure of a reflective layer / a protective layer / recording layer containing a Cr—Ta—O-based material on the information layer closer to the recording / reproducing light incident side. As a result, it was found that the rewriting performance of the information recording medium using the phase change recording layer material was improved, and the present invention was completed based on such knowledge.
Thus, according to the present invention, it comprises a substrate, a plurality of information layers formed on the substrate and capable of recording and rewriting information by light irradiation, and an intermediate layer formed between the information layers, The information layer on the side closer to the light irradiation side includes a recording layer containing a Bi—Ge—Te phase change recording material, and a Cr element, a Ta element and an O element formed in contact with the recording layer. There is provided an information recording medium comprising: a protective layer including: a reflective layer including an Ag element formed in contact with the protective layer.

That is, in a multilayer type information recording medium using a high melting point Bi—Ge—Te phase change recording material, a recording layer and an Ag alloy are formed on the information layer closer to the recording / reproducing light irradiation side. By forming a three-layer structure in which a protective layer containing a Cr—Ta—O-based material is provided between the reflective layer and the reflective layer, information can be recorded / reproduced and rewritten many times at high speed and high density.
Here, the thickness of the protective layer is preferably 8 nm to 25 nm.
Further, the composition of the Cr element and the Ta element included in the protective layer _(Cr X Ta _Y) is preferably 0.05 to 1.7 in the range of (Y / X).

Further, the composition ratios of the Bi element, Ge element and Te element contained in the recording layer are the following A, B on the triangular composition diagram having the Bi element, the Ge element and the Te element as vertices. It is preferable to be within the range surrounded by the points C and D.
A (Bi3, Ge46.2, Te50.8)
B (Bi5, Ge46, Te49)
C (Bi13, Ge38, Te49)
D (Bi10, Ge38, Te52)
(However, the composition of each element is atomic%.)
Moreover, it is preferable that the said reflection layer contains an Ag-Ca-Cu alloy.
Furthermore, the light is preferably blue laser light having a wavelength of 410 nm or less. An information recording medium to which the present invention is applied is useful as a BD-RE or the like that records or rewrites information with a laser beam in a blue wavelength region.

Further, according to the present invention, a substrate having pits or grooves formed on a surface irradiated with light, a first information layer stacked on the pits or grooves of the substrate, and on the first information layer An intermediate layer formed using a light transmissive material and having the pits or the grooves, a second information layer laminated on the intermediate layer, and a cover layer adhered to the second information layer, The second information layer is a Cr layer formed between and in contact with the recording layer containing the Bi—Ge—Te phase change recording material and the reflective layer containing the Ag—Ca—Cu alloy. An information recording medium having a protective layer containing a Ta—O-based material is provided.
Here, the Bi-Ge-Te phase change recording material of the recording layer of the second information layer is Bi7Ge43Te50 (atomic%), and the thickness range of the protective layer of the second information layer is 9 nm to 15 nm. It is preferable that
The intermediate layer is preferably formed by photopolymerization using a light transmissive stamper having a concavo-convex shape with a photocurable resin applied on the first information layer.
Furthermore, it is preferable that the first information layer has a recording layer containing at least a Ge—Sb—Te phase change recording material.

The information recording medium obtained by the present invention is capable of recording / reproducing information and rewriting a large number of times at a high speed and with a high density as compared with the case where ZnS—SiO ₂ or the like is used for the protective layer. It is useful as a BD-RE or the like that records or rewrites information with a laser beam.
Furthermore, the shelf life of the information recording medium is improved even in a high temperature and high humidity environment.

  The best mode for carrying out the present invention (hereinafter, an embodiment of the present invention) will be described in detail below. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention. The drawings used are for explaining the present embodiment and do not represent the actual size.

FIG. 1 is a diagram for explaining a schematic structure of an information recording medium according to the present embodiment. Here, an information recording medium 100 having two information layers capable of recording and rewriting information by light irradiation will be described as an example.
As shown in FIG. 1, the information recording medium 100 has a reversible change between an amorphous phase and a crystalline phase due to light irradiation on the substrate 1 and the side of the substrate 1 on which the recording / reproducing light L is incident. The first information layer (L0) 2 and the second information layer (L1) 4 having a recording layer containing the resulting phase change recording material, and between the first information layer (L0) 2 and the second information layer (L1) 4 The intermediate layer 3 formed using a light transmissive material and the cover layer 5 made of the light transmissive material are sequentially laminated.
Information was recorded and recorded on the recording layers formed on the first information layer (L0) 2 and the second information layer (L1) 4 by the recording / reproducing light L incident from the cover layer 5 side. Information is rewritten.

A tracking pregroove based on a physical format of a predetermined standard is formed on the surface of the substrate 1 and the surface of the intermediate layer 3. Further, in order to record and rewrite information on the information recording medium 100, for example, laser light having a wavelength of 410 nm or less is used as the recording / reproducing light L.
The two information layers are formed in accordance with the order in which information is recorded by the recording / reproducing light L, and the information layer formed on the side far from the side on which the recording / reproducing light L is incident is the first information layer (L0) 2. The information layer formed on the side closer to the recording / reproducing light L incident side is referred to as a second information layer (L1) 4. In the present embodiment, it is necessary to record information on the first information layer (L0) 2 using light transmitted through the second information layer (L1) 4. For this reason, the thickness of the first information layer (L0) 2 (88 nm in the present embodiment) is made thinner than the thickness of the second information layer (L1) 4 (144 nm in the present embodiment). The two information layers (L1) 4 are designed to improve the balance between the light transmittance and the light reflectance.

(Substrate 1)
The substrate 1 is formed using, for example, plastic, metal, glass or the like having appropriate processability and rigidity. In this embodiment, a polycarbonate resin is used to form a disk having an inner diameter (center hole) of 15 mm, an outer diameter of 120 mm, and a thickness of 1.1 mm.
A spiral pregroove is formed on the surface of the substrate 1 in a physical format based on a predetermined standard (not shown). In the present embodiment, the pregroove has a track pitch of 0.32 μm and a groove depth of 20 nm.

(Intermediate layer 3)
As will be described later, the intermediate layer 3 is coated with a predetermined photo-curing resin precursor on the first information layer (L0) 2, and then placed with a light-transmitting stamper, and then photo-curing. It forms by the photopolymerization method (Photo Polymerization: 2P method) which hardens the precursor of a conductive resin. In addition, it can also form by the nanoprint method using a sheet-like light transmissive resin. In the present embodiment, the thickness of the intermediate layer 3 is usually about 20 μm to 30 μm. In addition, an uneven pattern composed of pits or grooves is formed on the surface of the intermediate layer 3 on the cover layer 5 side, similarly to the substrate 1.

  The photocurable resin used as the material of the intermediate layer 3 is preferably a material that is transparent to the recording / reproducing light L, has a high adhesive force, and has a small shrinkage force at the time of curing adhesion. An example of such a material is a radical ultraviolet curable resin. Examples of the radical ultraviolet curable resin include a composition containing a known ultraviolet curable compound and a photopolymerization initiator as essential components. The ultraviolet curable compound contains a monofunctional acrylate, a monofunctional methacrylate, a polyfunctional acrylate, a polyfunctional methacrylate or the like as a polysynthetic monomer component, and each can be used alone or in combination of two or more. Further, as the radical ultraviolet curable resin, it is preferable to use a resin having a viscosity of 20 mPa · s to 1000 mPa · s in a temperature range of 0 ° C. to 40 ° C. in order to form a predetermined film thickness by spin coating. .

(Cover layer 5)
The cover layer 5 is formed using a light transmissive material such as polycarbonate resin, for example. In the present embodiment, as the cover layer 5, a polycarbonate resin substrate having a thickness of 75 μm is stuck on the second information layer (L1) 4 with an adhesive.

(First information layer (L0) 2)
Next, the layer structure of each information layer will be described.
FIG. 2 is a diagram for explaining the structure of two information layers of the information recording medium 100 shown in FIG. As shown in FIG. 2, the first information layer (L0) 2 formed on the side far from the side on which the recording / reproducing light L is incident is on the surface side on the substrate 1 where the recording / reproducing light L is incident. , First corrosion prevention layer 6, first reflective layer 7, second corrosion prevention layer 8, first protective layer 9, first recording layer 10 containing phase change recording material, first interface layer 11, second protective layer 12 Are sequentially stacked.

The first corrosion prevention layer 6 is located between the substrate 1 and the first reflective layer 7 and is a layer that prevents corrosion of Ag elements in the first reflective layer 7 described later. In this embodiment, an Nb material film having a thickness of 5 nm is formed using a predetermined sputtering apparatus.
The first reflective layer 7 is incident on the cover layer 5 side, reflects the recording / reproducing light L having a wavelength of 410 nm or less transmitted through the first recording layer 10, and includes a phase change recording material at the time of recording / reproducing information. This is a layer for diffusing heat generated from the first recording layer 10. The first reflective layer 7 is formed of an Ag alloy such as Ag—Ca—Cu, Ag—Nd—Cu, or Ag—Ga—Cu having high thermal conductivity in the blue wavelength region. Among these, an Ag alloy containing 90 mol% or more of Ag is more preferable. In this embodiment, an AgCa (500 ppm) Cu (wt%) film having a thickness of 80 nm is formed by sputtering.

The second corrosion prevention layer 8 is located between the first reflective layer 7 and the first protective layer 9, and corrodes Ag element in the first reflective layer 7 by S element in the first protective layer 9 described later. It is a layer to prevent. In this embodiment, a GeCr—N material film with a thickness of 7 nm is formed by sputtering.
The first protective layer 9 is provided for the purpose of reducing thermal damage to the substrate 1 made of polycarbonate resin, for example, when the phase change of the phase change recording material in the first recording layer 10 occurs. The thickness of the first protective layer 9 is usually 2 nm to 5 nm. In the present embodiment, the first protective layer 9 forms a 3 nm-thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) mixture film by sputtering. In addition, as a material for forming the first protective layer 9, a material in which the mixing ratio of (ZnS) / (SiO ₂ ) is changed, or an oxide or nitride containing an S element can be used.

The first recording layer 10 includes a phase change recording material in which the atomic arrangement reversibly changes between two different states (amorphous phase-crystalline phase) by irradiation of the recording / reproducing light L. Examples of the phase change recording material include SnGeSbTe alloy, GeSbTe alloy, InGeSbTe alloy, and BiGeTe alloy. In the present embodiment, an InGeSbTe alloy target is sputtered in an Ar gas atmosphere to form an InGeSbTe (atomic%) film having a thickness of 14 nm.
The first interface layer 11 is a layer for preventing the constituent elements of both layers from entering, diffusing and chemically reacting between the first recording layer 10 and the second protective layer 12. In the present embodiment, the first interface layer 11 forms a (ZrO) _92- (ZnS) ₈ (mol%) material film having a thickness of 5 nm by sputtering.
The second protective layer 12 is a layer for preventing the constituent elements of both layers from entering, diffusing and chemically reacting between the first interface layer 11 and the intermediate layer 3. In this embodiment, a (ZnS) _80- (SiO ₂ ) ₂₀ (mol%) film having a thickness of 30 nm is formed by sputtering.

(Second information layer (L1) 4)
Next, the second information layer (L1) 4 formed on the side closer to the recording / reproducing light L from the incident side will be described.
As shown in FIG. 2, the second information layer (L1) 4 has a reflectance correction layer 13 and a third corrosion prevention layer 14 on the surface side on which the recording / reproducing light L is incident on the intermediate layer 3.
Further, on the third corrosion prevention layer 14, the second reflective layer 15, the third protective layer 17 formed in contact with the second reflective layer 15, and the second recording formed in contact with the third protective layer 17. A three-layer structure with the layer 19 is provided.
Also, the second interface layer 20 and the fourth protective layer 21 are sequentially laminated on the second recording layer 19.

In the present embodiment, the reflectance correction layer 13 forms a (ZnS) ₈₀ — (SiO ₂ ) ₂₀ (mol%) film having a thickness of 22 nm by sputtering.
The third corrosion prevention layer 14 is located between the reflectance correction layer 13 and the second reflection layer 15, and prevents the Ag element in the second reflection layer 15 from being corroded by the S element in the reflectance correction layer 13. It is. In this embodiment, a Cr ₂₀ Ta ₁₄ O ₆₆ (atomic%) material film having a thickness of 2 nm is formed by sputtering.
The second interface layer 20 is a layer for preventing the constituent elements of both layers from entering, diffusing and chemically reacting between the second recording layer 19 and the fourth protective layer 21. In this embodiment, a ZrCrO (atomic%) material film having a thickness of 3 nm is formed by sputtering.
The fourth protective layer 21 is a layer for preventing the constituent elements of both layers from entering, diffusing and chemically reacting between the second interface layer 20 and the cover layer 5. In this embodiment, a (ZnS) _80- (SiO ₂ ) ₂₀ (mol%) film having a thickness of 38 nm is formed by sputtering.

(Second reflective layer 15)
The second reflective layer 15 reflects the recording / reproducing light L having a wavelength of 410 nm or less that is incident from the cover layer 5 side and passes through the first recording layer 10, and partially transmits the recording / reproducing light L to the first information layer. (L0) Has a property of transmitting to the 2 side.
The second reflective layer 15 is formed thinner than the thickness (80 nm) of the first reflective layer 7 described above in order to obtain an appropriate light transmittance. In addition, Ag-Ca-Cu, Ag-Nd-Cu, and Ag-Ga- having high thermal conductivity in the blue wavelength region are used to release heat generated from the second recording layer 19 including the high-melting-point phase change recording material. It forms with Ag alloys, such as Cu. Among these, an Ag alloy containing 90 mol% or more of Ag is more preferable. In this embodiment, an AgCa (500 ppm) Cu (wt%) film having a thickness of 8 nm is formed by sputtering.
In addition, it is desirable that the second reflective layer 15 has low light absorption, has a light transmittance of 30% or more, and has an appropriate light reflectance.

(Third protective layer 17)
The third protective layer 17 is provided between the second reflective layer 15 and the second recording layer 19 and is provided for the purpose of reducing thermal damage due to heat generation of the second recording layer 19 containing a phase change recording material having a high melting point. .
The third protective layer 17 is formed of a material (Cr—Ta—O-based material) containing a high melting point Cr element, Ta element, and O element.
In the present embodiment, the second information layer (L1) 4 on the side closer to the recording / reproducing light L incident side is in contact with the second reflective layer 15 and includes a third material containing a Cr—Ta—O-based material. A protective layer 17 is provided, and a second recording layer 19 containing a high melting point Bi—Ge—Te phase change recording material is formed in contact with the third protective layer 17 as will be described later. Thus, the second information layer (L1) 4 employs a three-layer structure in which only the third protective layer 17 is provided between the second reflective layer 15 and the second recording layer 19. For this reason, the rewrite performance of the second recording layer 19 using the high melting point Bi—Ge—Te phase change recording material is improved.

Here, in the present embodiment, the composition ratio (Cr _X Ta _Y ) (atomic%) between the Cr element and the Ta element present in the third protective layer 17 is such that (Y / X) is 0.05 to 1. 7, preferably selected from the range of 0.11 to 0.70. When (Y / X) in the composition ratio of Cr element to Ta element (Cr _X Ta _Y ) (atomic%) is excessively small, the reproduction jitter of information recorded on the information recording medium 100 increases, and the recording / reproduction characteristics are improved. There is a tendency to decrease. On the other hand, if it is excessively large, the recording characteristics tend to deteriorate in a high humidity environment.
Furthermore, in the present embodiment, the thickness of the third protective layer 17 is in the range of 8 nm to 25 nm, preferably in the range of 9 nm to 15 nm. If the thickness of the third protective layer 17 is excessively thin, the distance between the second reflective layer 15 and the second recording layer 19 decreases, and the recording power required to record information on the second recording layer 19 increases. Tend. Further, if the thickness of the third protective layer 17 is excessively large, the recording / reproducing light L is absorbed by the Cr—Ta—O-based material, and therefore the recording / reproducing light L necessary for the first information layer (L0) 2 is obtained. Tend to not reach.

(Second recording layer 19)
Similarly to the first recording layer 10 described above, the second recording layer 19 is a phase change recording in which the atomic arrangement reversibly changes between two different states (amorphous phase-crystalline phase) by irradiation of the recording / reproducing light L. Contains materials. In this embodiment, a Bi-Ge-Te phase change recording material is used as the phase change recording material. The Bi—Ge—Te phase change recording material is obtained as a high melting point (about 700 ° C. or higher) metal material in which the Sb element of the Ge—Sb—Te alloy is replaced with the Bi element. By using a Bi—Ge—Te phase change recording material, excellent recording characteristics can be obtained in a wide range from a low linear velocity to a high linear velocity.

(Composition range of Bi-Ge-Te phase change recording material)
FIG. 3 is a triangular composition diagram of a Bi—Ge—Te phase change recording material. As shown in FIG. 3, the composition range of the Bi—Ge—Te phase change recording material is as follows: Ge50Te50 (atomic%) and Bi2Te3 (atomic) in the triangular composition diagram having the Bi element, Ge element, and Te element as vertices. %), A region where Ge element is excessively added is preferable. Here, in the Bi-Ge-Te phase change recording material, for example, the concentration of Ge element is 50 atomic%, the concentration of Te element is 50 atomic%, and the concentration of Bi element is 0 atomic%. , Ge50Te50.
In this region, the refractive index difference between crystal and non-crystal, which is an advantage of Ge50Te50, is large, the crystallization temperature is high, and the activation energy is large. Furthermore, the crystallization speed is fast, and good erasing characteristics can be obtained even at high linear velocity recording.

Furthermore, as a practical composition range when the Bi—Ge—Te phase change recording material having such excellent characteristics is used for the second recording layer 19 of the information recording medium 100, the following is shown on the triangular composition diagram. It is preferable that it exists in the range enclosed by each point of A, B, C, and D.
A (Bi3, Ge46.2, Te50.8)
B (Bi5, Ge46, Te49)
C (Bi13, Ge38, Te49)
D (Bi10, Ge38, Te52)
(However, the composition of each element is atomic%.)

In the present embodiment, a BiGeTe target is sputtered on the third protective layer 17 in an Ar gas atmosphere to form a Bi—Ge—Te film having a predetermined thickness. The thickness of the second recording layer 19 is usually 10 nm or less, preferably 4 nm to 8 nm.
In the present embodiment, in the second information layer (L1) 4, by adopting a three-layer structure in which only the third protective layer 17 is provided between the second reflective layer 15 and the second recording layer 19, the first information layer (L1) 4 The rewriting performance of the second recording layer 19 is improved, and the recording / reproducing light L necessary for recording on the first information layer (L0) 2 can be obtained.

Hereinafter, the present embodiment will be described in more detail based on examples. Note that the present embodiment is not limited to the following examples.
In the following examples, for the information recording medium 100 having the layer structure shown in FIG. 1, the composition of the Cr element and the Ta element (Cr _X Ta _Y ) in the third protective layer 17, the thickness of the third protective layer 17, Each of the results will be described. The optimum composition range of the Bi—Ge—Te phase change recording material contained in the second recording layer 19 will be described.

(1) Evaluation of recording / reproduction characteristics of information recording medium 100 An information recording apparatus used for evaluating the recording / reproduction characteristics of the information recording medium 100 is a semiconductor laser (wavelength 405 nm, numerical aperture 0.85) for irradiating the information recording medium 100 with light. A laser driver that controls the output of a semiconductor laser, a waveform generator that generates a recording pulse generated according to recording information, a waveform equivalent circuit, and a binarization circuit are provided.
In the information recording apparatus used in this embodiment, 1-7 modulation is used, and a mark edge recording type recording mark is formed on the information recording medium 100 to record information. The mark length of the 2T mark which is the shortest mark is about 0.149 μm. The information recording medium 100 is rotated at a predetermined recording linear velocity, and a semiconductor laser beam having a wavelength of 405 nm is condensed by an objective lens having a numerical aperture (NA) of 0.85, and the first recording layer 10 and the second recording are recorded through the cover layer 5. Irradiation on the layer 19 performs recording and reproduction.

  Next, the process of recording and reproduction is shown below. First, information from the outside of the information recording apparatus is transmitted to the 1-7 modulator in units of 2 bits. When information is recorded on the information recording medium 100, recording is performed by a modulation method that converts 2 bits of information into 3 bits, a so-called 1-7 modulation method. Here, 1-7 modulation is a method in which the number of “0” s between “1” and “1” of the modulated bit pattern is limited to 1 to 7. In this modulation method, information having a mark length of 2T to 8T corresponding to 2-bit information is recorded on the information recording medium 100. Here, T represents a clock cycle during information recording. In this example, when the disk linear velocity was 9.84 m / s, it was set to 7.58 ns.

  The 2T to 8T digital signal converted by the 1-7 modulator is transferred to the recording waveform generation circuit, and a multi-pulse recording waveform is generated by dividing the section corresponding to the recording mark into a plurality of short pulses. The multi-pulse recording waveform is subjected to laser irradiation controlled so as not to accumulate heat at the end of writing. At this time, in order to form a recording mark, each pulse is adjusted to an optimum value for each information recording medium 100 to be measured. Further, the recording waveform generating circuit has a multi-pulse waveform table for forming a mark portion. The multi-pulse waveform table supports a method (adaptive recording waveform control) that changes the first pulse width and the last pulse width of the multi-pulse waveform according to the space length before and after the mark part when forming a pulse train. To do. With the multipulse waveform table, a multipulse recording waveform that can eliminate the influence of inter-mark thermal interference between marks as much as possible can be obtained.

The recording waveform generated by the recording waveform generation circuit is transferred to the laser driving circuit, and the laser driving circuit causes the semiconductor laser in the optical head to emit light based on the recording waveform. A semiconductor laser having an optical wavelength of 405 nm is used as an information recording laser beam in the optical head mounted on the information recording apparatus used in this example. Further, the laser beam is focused on the recording layer of the information recording medium 100 by an objective lens having a lens numerical aperture (NA) of 0.85, and information is recorded by irradiating a laser beam corresponding to the recording waveform. It was.
In general, when laser light having a laser wavelength λ is condensed by a lens having a predetermined lens numerical aperture (NA), the spot diameter of the laser beam is approximately 0.9 × λ / NA. In this embodiment, the spot diameter of the laser beam is about 0.43 μm. The polarization of the laser beam was circularly polarized.

A reproduction signal is obtained by irradiating a laser beam onto a recorded mark and detecting reflected light from the mark and a portion other than the mark. The amplitude of the obtained reproduction signal is limited by the limit equalizer, and then the amplitude of the short mark is increased, and the composite of the channel is performed to convert the information into 2 bits every 3 bits. With the above operation, the reproduction of the recorded mark is completed. When information is recorded on the information recording medium 100 under the above conditions, the mark length of the 2T mark, which is the shortest mark, is approximately 0.149 μm, and the mark length of the 8T mark, which is the longest mark, is approximately 0.6 μm.
When performing jitter measurement, a random pattern signal including 2T to 8T was recorded and reproduced, and the reproduced signal was subjected to waveform equalization, binarization, and PLL (Phase Locked Loop) processing to measure jitter.

(2) Multiple rewrite performance The multiple rewrite performance (rewrite life) of the first recording layer 10 and the second recording layer 19 is 2T to 8T as information on the information recording medium 100 at a linear velocity of 9.84 m / s. A random pattern is overwritten and recorded 1000 times, and jitter is measured when the random pattern is reproduced at a linear velocity of 4.92 m / s. The smaller the jitter value, the better the rewriting performance for many times.

(3) Archival reproduction jitter The archival reproduction jitter (storage life) is recorded on the information recording medium 100 by overwriting a random pattern of 2T to 8T as information 10 times. Jitter at the time of reproduction after standing for 48 hours (acceleration test) in an environment of ° C. × 80 RH% atmosphere is measured and displayed as an increase in jitter (δ jitter). The smaller the value of the amount of increase in jitter, the better the shelf life in a humid environment.

(Example 1 to Example 5, Comparative Example 1 to Comparative Example 2)
(Preparation of information recording medium 100)
The information recording medium 100 is prepared by the following procedure. The layer structure of the information recording medium 100 is the same as that shown in FIG. The second recording layer 19 of the second information layer (L1) 4 was formed using Bi7Ge43Te50 (atomic t%) as a phase change recording material considered to be suitable for high-speed recording.
The composition of the Cr element and the Ta element contained in the third protective layer 17 is shown in Table 1. The thickness of the third protective layer 17 is 9 nm. Each layer of the first information layer (L0) 2 and the second information layer (L1) 4 in the information recording medium 100 has a plurality of sputtering chambers and is formed by using a sputtering apparatus having a small film thickness distribution and high reproducibility. .

First, the first information layer (L0) 2 is formed. A first corrosion prevention layer 6 was formed by sputtering a 5 nm thick Nb material film on a polycarbonate substrate 1 having a diameter of 120 mm and a thickness of 1.1 mm. Subsequently, an AgCa (500 pm) Cu (wt%) film having a thickness of 80 nm was formed as the first reflective layer 7. A GeCr—N material film having a thickness of 7 nm was formed thereon as the second corrosion prevention layer 8. Next, a (ZnS) _80- (SiO ₂ ) ₂₀ (mol%) material film having a thickness of 3 nm was formed as the first protective layer 9. Subsequently, an In—Ge—Sb—Te material film having a thickness of 14 nm was formed as the first recording layer 10. A (ZrO) _92- (ZnS) ₈ (mol%) material film having a thickness of 5 nm was formed thereon as the first interface layer 11. Next, a (ZnS) ₈₀ — (SiO ₂ ) ₂₀ (mol%) material film having a thickness of 30 nm was formed as the second protective layer 12.

  The substrate 1 on which the first information layer (L0) 2 was formed was once taken out of the sputtering chamber, and the intermediate layer 3 was formed. A stamper in which a signal track for the second information layer (L1) 4 is formed on the first information layer (L0) 2 is bonded with an ultraviolet curable resin, and then cured, and then the stamper is peeled off. An intermediate layer 3 having a guide groove for the second information layer (L1) 4 was formed on (L0) 2.

Next, the second information layer (L1) 4 is formed. On the intermediate layer 3, a (ZnS) _80- (SiO 2) ₂₀ (mol%) material film having a thickness of 22 nm was formed as the reflectance correction layer 13. Subsequently, a Cr ₂₀ Ta ₁₄ O ₆₆ (atomic%) material film having a thickness of 2 nm was formed as the third corrosion prevention layer 14.
Next, an AgCa (500 pm) Cu (1 wt%) material film having a thickness of 8 nm was formed as the second reflective layer 15 on the third corrosion prevention layer 14. Subsequently, a 9 nm thick Cr—Ta—O material film was formed as the third protective layer 17.
Here, the composition of the Cr element and the Ta element contained in the Cr—Ta—O film (Cr _X Ta _Y ) is set in a Cr ₂ O ₃ target, Cr ₂ O ₃ (40) -Ta ₂ O ₅ ( 60) A (mol%) target was mounted, and these two targets were simultaneously sputtered and adjusted by changing the sputtering power of each target. Table 1 shows the composition of Cr element and Ta element (Cr _X Ta _Y ).
Subsequently, a Bi7Ge43Te50 (atomic%) material film having a thickness of 6 nm was formed as the second recording layer 19 on the third protective layer 17.

Next, a ZrCrO (atomic%) material film having a thickness of 3 nm was formed as the second interface layer 20 on the second recording layer 19. Subsequently, a (ZnS) _80- (SiO ₂ ) ₂₀ material film having a thickness of 38 nm was formed as the fourth protective layer 21. Further, a 75 μm-thick polycarbonate cover layer 5 is bonded onto the fourth protective layer 21 with an adhesive, and as shown in Table 1, the composition of the Cr element and the Ta element contained in the third protective layer 17 ( cr _X Ta _Y) were prepared seven different types of information recording medium 100.

(Initialization of information recording medium 100)
The information recording medium 100 prepared by the above operation was irradiated with laser light having an elliptical beam with a laser spot size of 95 μm from a semiconductor laser (wavelength: 810 nm), and the entire disk surface was initially crystallized.

  Using the information recording apparatus described above, the multiple rewriting performance of the first recording layer 10 in the first information layer (L0) 2 of the seven types of information recording media 100 described above was evaluated, and the second information layer (L1) 4 The second recording layer 19 was evaluated for multiple rewriting performance and archival reproduction jitter. The results are shown in Table 1.

From the results shown in Table 1, in the second information layer (L1) 4 on the side closer to the recording / reproducing light L incident side, the second reflective layer 15 containing an Ag-based alloy and the Cr—Ta—O-based material. By providing a three-layer structure formed by contacting a third protective layer 17 containing Ni and a second recording layer 19 containing a Bi-Ge-Te phase change recording material (Example 1 to Example 5), the second It can be seen that the multiple rewriting performance and archival reproduction jitter of the recording layer 19 are improved. At this time, the composition ratio (Cr _X Ta _Y ) (atomic%) between the Cr element and the Ta element present in the third protective layer 17 is within the range of (Y / X) of 0.05 to 1.7. is there.
It can also be seen that the multiple rewriting performance of the first recording layer 10 in the first information layer (L0) 2 on the side far from the side on which the recording / reproducing light L is incident is improved.
In particular, the composition ratio (Cr _X Ta _Y ) (atomic%) between the Cr element and the Ta element present in the third protective layer 17 is (Y / X) in the range of 0.11 to 0.7 ( In Examples 2 to 4, it can be seen that the multiple rewriting performance and archival reproduction jitter of the second recording layer 19 and the multiple rewriting performance of the first recording layer 10 are improved in a well-balanced manner.

On the other hand, when the concentration of Ta element present in the third protective layer 17 is 0 atomic% (Comparative Example 1), the multiple rewriting performance of the second recording layer 19 is deteriorated. It can be seen that the rewrite performance of many times also deteriorates. This is because the amount of Cr ₂ O ₃ present in the third protective layer 17 is large, so that the light transmittance of the second information layer 19 is lowered and sufficient recording / reproducing light L is obtained in the first information layer 10. It is thought that there is not.
In addition, when the concentration of Cr element present in the third protective layer 17 is 0 atomic% (Comparative Example 2), the archival reproduction jitter of the second recording layer 19 is increased, and the shelf life in a humidified environment is increased. It turns out that falls. When the information recording medium 100 used in Comparative Example 2 was observed with an optical microscope, film peeling was observed.

(Examples 6 to 14, Comparative Examples 3 to 9)
16 types of information recording media in which the thickness of the third protective layer 17 made of the Cr—Ta—O material film of the second information layer (L1) 4 was changed between 0 and 30 nm by the same operation as in Example 1. And the rewriting performance of the second recording layer 19 in the second information layer (L1) 4 and the first recording layer 10 in the first information layer (L0) 2 of each information recording medium was evaluated many times. The results are shown in Table 2.
The composition (Cr _X Ta _Y ) of Cr element and Ta element contained in the Cr—Ta—O material film of the third protective layer 17 is Cr ₂ O ₃ target, Cr ₂ O ₃ (40) -Ta ₂ O _5. (60) (Mole%) Co-sputtering with a target was performed to adjust to Cr ₂₀ Ta ₁₄ O ₆₆ (atomic%). (Y / X) is 0.7.

From the results shown in Table 2, the second information layer (L1) 4 includes a second reflective layer 15 containing an Ag-based alloy, a third protective layer 17 containing a Cr-Ta-O-based material, and a Bi-Ge-Te-based phase. In the information recording medium having a three-layer structure formed in contact with the second recording layer 19 including the change recording material, the thickness of the third protective layer 17 including the Cr—Ta—O-based material is 8 nm to 25 nm. In Examples 6 to 14, it can be seen that the multiple rewriting performance of the second recording layer 19 is improved.
In particular, when the thickness of the third protective layer 17 is 9 nm to 15 nm (Examples 7 to 10), the multiple rewriting performance of both the second recording layer 19 and the first recording layer 10 is improved. I understand.

On the other hand, when the third protective layer 17 is not provided (Comparative Example 1) and when the thickness of the third protective layer 17 is 7 nm or less (Comparative Examples 2 to 7), the second recording layer 19 is rewritten many times. It turns out that performance falls. In particular, when the thickness of the third protective layer 17 is 7 nm or less (Comparative Examples 2 to 7), the Bi—Ge—Te phase change recording material film of the second recording layer 19 is obtained by repeating the rewriting operation. It is considered that the Cr—Ta—O-based material of the third protective layer 17 diffuses therein, and the reproduction signal is deteriorated.
In addition, it can be seen that the multiple rewriting performance of the second recording layer 19 also decreases when the thickness of the third protective layer 17 is 27 nm or more (Comparative Example 8 and Comparative Example 9). This is because the Cr—Ta—O-based material constituting the third protective layer 17 has a large coefficient of thermal expansion, so that a crack is formed between the portion thermally irradiated with the recording / reproducing light L and the other portion. As a result, it is considered that the Cr—Ta—O-based material diffuses into the second recording layer 19.
Furthermore, if the thickness of the third protective layer 17 is excessively large, the light transmittance of the second information layer (L1) 4 is lowered, and therefore the amount of light necessary for recording cannot be obtained in the first information layer (L0) 2. It is considered that the jitter of the first information layer (L0) 2 is lowered.

(Example 15)
By the same operation as in Example 1, the composition ratio of Bi element, Ge element and Te element of the second recording layer 19 made of the Bi-Ge-Te film of the second information layer (L1) 4 was changed. An information recording medium was prepared, and for the second recording layer 19 in the second information layer (L1) 4 of each information recording medium, a linear velocity of 4.92 m / sec (1 × speed) and a linear velocity of 9.84 m / sec (2 × speed) ) 10 times rewriting performance (OW10 jitter), archival reproduction jitter and archival OW reproduction jitter were evaluated. The archival OW reproduction jitter is obtained by overwriting after measuring the archival reproduction jitter and evaluating the jitter again. The results are shown in Table 3.

Note that the thickness of the second recording layer 19 made of a Bi—Ge—Te film was 6 nm, and a BiGeTe target was sputtered in an Ar gas atmosphere to change the composition ratio of the Bi element, Ge element, and Te element.
The thickness of the third protective layer 17 made of the Cr—Ta—O material film is 9 nm, and the composition of the Cr element and the Ta element contained in the Cr—Ta—O material film (Cr _X Ta _Y ) is Cr. _{A 2} O ₃ target and a Cr ₂ O ₃ (40) -Ta ₂ O ₅ (60) (mol%) target were simultaneously sputtered to adjust to Cr ₂₀ Ta ₁₄ O ₆₆ (atomic%). (Y / X) is 0.7.

Further, the 10-time rewriting performance (OW10 jitter), archival reproduction jitter, and archival OW reproduction jitter were evaluated according to the following criteria.
a: Jitter ≦ 7%
b: 7% <jitter ≦ 8%
c: 8% <jitter The results are shown in Table 3.

From the results shown in Table 3, sample no. Information recording media of 3, 4, 6, 7, 9, 11 to 13, 17 to 20, 22, and 27 have a linear velocity of 4.92 m / sec (1 × speed) to a linear velocity of 9.84 m / sec (2 × speed). It can be seen that the evaluation results of 10 times rewriting performance (OW10 jitter), archival reproduction jitter, and archival OW reproduction jitter are all a evaluation or b evaluation.
Thus, as a practical composition range when the Bi—Ge—Te phase change recording material is used for the second recording layer 19 of the information recording medium 100, the following A on the triangular composition diagram shown in FIG. It turns out that it exists in the range enclosed by each point of B, C, and D.
A (Bi3, Ge46.2, Te50.8)
B (Bi5, Ge46, Te49)
C (Bi13, Ge38, Te49)
D (Bi10, Ge38, Te52)
(However, the composition of each element is atomic%.)

It is a figure explaining the schematic structure of the information recording medium as this Embodiment. It is a figure explaining the structure of two information layers of the information recording medium shown in FIG. It is a triangular composition diagram of a Bi-Ge-Te phase change recording material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... 1st information layer (L0), 3 ... Intermediate | middle layer, 4 ... 2nd information layer (L1), 5 ... Cover layer, 15 ... 2nd reflective layer, 17 ... 3rd protective layer, 19 ... Second recording layer, 100 ... information recording medium

Claims (10)

A substrate,
A plurality of information layers formed on the substrate and capable of recording and rewriting information by light irradiation;
An intermediate layer formed between the information layers,
The information layer on the side close to the light irradiation side is
A recording layer comprising a Bi-Ge-Te phase change recording material;
A protective layer containing Cr element, Ta element and O element formed in contact with the recording layer;
A reflective layer containing an Ag element formed in contact with the protective layer;
An information recording medium comprising:   The information recording medium according to claim 1, wherein a thickness range of the protective layer is 8 nm to 25 nm. 2. The composition of the Cr element and the Ta element (Cr _X Ta _Y ) contained in the protective layer has a range of (Y / X) from 0.05 to 1.7. Information recording media. The composition ratios of the Bi element, Ge element, and Te element contained in the recording layer are the following A, B, C, and C on the triangular composition diagram having the Bi element, the Ge element, and the Te element as vertices. 2. The information recording medium according to claim 1, wherein the information recording medium is within a range surrounded by each point of D.
A (Bi3, Ge46.2, Te50.8)
B (Bi5, Ge46, Te49)
C (Bi13, Ge38, Te49)
D (Bi10, Ge38, Te52)
(However, the composition of each element is atomic%.)   The information recording medium according to claim 1, wherein the reflective layer contains an Ag—Ca—Cu alloy.   The information recording medium according to claim 1, wherein the light is blue laser light having a wavelength of 410 nm or less. A substrate having pits or grooves formed on a surface irradiated with light;
A first information layer stacked on the pits or grooves of the substrate;
An intermediate layer formed on the first information layer using a light transmissive material and having the pits or the grooves;
A second information layer laminated on the intermediate layer;
A cover layer attached to the second information layer,
The second information layer is a Cr layer formed between and in contact with the recording layer containing the Bi—Ge—Te phase change recording material and the reflective layer containing the Ag—Ca—Cu alloy. An information recording medium having a protective layer containing a Ta—O-based material.   The Bi-Ge-Te phase change recording material of the recording layer of the second information layer is Bi7Ge43Te50 (atomic%), and the thickness range of the protective layer of the second information layer is 9 nm to 15 nm. The information recording medium according to claim 7.   8. The information according to claim 7, wherein the intermediate layer is formed by a photopolymerization method using a light-transmitting stamper having a concavo-convex shape with a photocurable resin applied on the first information layer. recoding media.   The information recording medium according to claim 7, wherein the first information layer has a recording layer containing at least a Ge—Sb—Te phase change recording material.

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