JP2007141455A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absolutely imperative technique for reducing cross-erase when performing a high density recording so that a track pitch is ≤70% of a laser beam spot diameter in an information recording medium used for recording of information through radiation of an energy beam. <P>SOLUTION: An optical disk 15 has a lower protective layer 2: (ZnS)<SB>80</SB>(SiO<SB>2</SB>)<SB>20</SB>(100 nm), a lower interface layer 12: Cr<SB>2</SB>O<SB>3</SB>(5 nm), a recording layer 3: Ag<SB>6</SB>Ge<SB>16</SB>Sb<SB>22</SB>Te<SB>55</SB>phase transition recording layer (10 nm), an upper interface layer 13 (5 nm), a heat diffusion control layer 4: (ZnS)<SB>80</SB>(SiO<SB>2</SB>)<SB>20</SB>(140 nm), a heat buffer layer 14: Cr<SB>40</SB>(Cr<SB>2</SB>O<SB>3</SB>)<SB>60</SB>(35 nm), and a heat diffusion layer 5: Al (80 nm), on a substrate 1 made of a polycarbonate. Even when the optical disk 15 is used for high density recording wherein the track pitch is 70% of the laser beam spot diameter or less, cross-erase is not produced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an information recording medium on which information is recorded by irradiation with an energy beam, and more particularly to a rewritable optical disk such as a phase change optical disk or a magneto-optical disk. Further, the present invention relates to an information recording apparatus that satisfactorily reproduces or records the information recording medium.

  In the description of the present invention, the information recording medium may be expressed as a phase change optical disk, a magneto-optical disk, or simply an optical disk. In addition, the present invention is applicable to an information recording medium in which information is recorded by generating heat by irradiation of an energy beam and changing the atomic arrangement or magnetic moment by this heat. In particular, the present invention is also effective for 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 addition, the energy beam described above may be expressed as a laser beam or simply a laser beam. As described above, the present invention is an electron beam as long as it is an energy beam capable of generating heat on an information recording medium. The present invention can also be applied to an information recording medium that is recorded by an energy beam that is not generally regarded as light, such as a beam or an ion beam.

  In a rewritable optical disk, a step having an uneven shape (groove shape) is provided on a plastic substrate for tracking a laser beam, and a method of recording information in a concave portion or a convex portion is generally used. However, for the purpose of improving the recording density (narrow track pitch), in recent years, a method of recording information on each of the concave and convex portions using the above-described concave and convex shape has been developed. Here, the concavo-convex convex portion is called a land, and the concavo-convex concave portion is defined as a groove. Generally, when the track pitch of the information recording medium is narrowed to about 80% of the laser beam spot and information is recorded on both the land and the groove, the adjacent information recording track (the groove for the land or the land for the groove) From the playback signal. For example, when information recorded on the land is reproduced, a reproduction signal from the information recorded on the groove leaks, and there is a problem that the information recorded on the land cannot be reproduced accurately. This leakage of the reproduction signal from the information recorded on the adjacent information recording track is called crosstalk.

  In order to solve this problem, a method is known in which a plurality of magnetic layers are provided as recording layers, and the temperature distribution of the recording layer when irradiated with a laser beam is used to reproduce information only in the high temperature part (Patent Document 1, Patent Document 2). According to these methods, since the temperature of the recording layer of the adjacent information recording track is lower than the temperature of the recording layer of the center track, the reproduction signal leaks from the information recorded on the adjacent information recording track. Does not occur. However, in this recording method, there is a method for suppressing a phenomenon (so-called cross erase) of erasing information (record mark) recorded on an adjacent information recording track (adjacent groove at land recording or adjacent land at groove recording). Is not considered enough. For example, in Patent Document 1, a thermal diffusion layer having a high thermal conductivity is provided on the side opposite to the laser beam incident side of the magnetic layer, but since the distance between the magnetic layer and the thermal diffusion layer is as small as 20 nm or less, Heat easily diffuses to the adjacent information recording track via the heat diffusion layer. In Patent Document 2, although the distance between the magnetic layer and the thermal diffusion layer is relatively thick at 80 nm, the recording layer is a metal magnetic layer (in the present invention, the function of changing atomic arrangement or electronic state by laser beam irradiation). The thin film is called a recording layer.), And the total thickness of these three layers is as extremely large as 145 nm. For this reason, it has been found that heat diffuses in the recording layer and information recorded on the adjacent information recording track is erased. Therefore, it is a big problem to develop a technique for reducing cross erase.

By the way, the level difference (groove depth) between the center of the concave portion and the convex portion is usually set to λ / 8 where λ is the wavelength of the laser that forms the laser beam. This is because the largest tracking error signal is obtained when the groove depth is λ / 8. However, in recent years, since the land groove recording method has been devised, the groove depth may be set to λ / 7 or more and λ / 5 or less (Patent Document 3). The feature of this method is that even when the track pitch is narrowed to about 60% of the laser beam spot, the crosstalk from the adjacent information recording track (the leakage of the signal from the adjacent information recording track) can be canceled. However, in this recording method, a method for suppressing the phenomenon of erasing a recording mark (so-called cross erase) recorded on an adjacent information recording track (adjacent groove during land recording or adjacent land during groove recording) is sufficiently provided. Not considered. For example, in Patent Document 3, a GeSbTe-based phase change recording material having a lower thermal conductivity than a metal is used as a recording layer, and the recording layer has a thickness of 5 to 50 nm. Since the distance to the diffusion layer (reflection layer) is as small as 180 m, there is a problem that heat is diffused to the adjacent information recording track via the thermal diffusion layer during information recording, and cross erasure is likely to occur. all right.
For example, in the standard of 2.6 GB / surface DVD-RAM, a laser having a laser wavelength (λ) of 645 to 660 nm is narrowed down by a lens having a lens numerical aperture (NA) of 0.6, and therefore approximately 0.97. Recording and reproduction can be performed using a laser beam spot of ˜0.99 μm (0.9λ / NA). For this reason, crosstalk can be canceled even when the track pitch is 0.7 μm or less. On the other hand, the track pitch is 0.74 μm in the 2.6 GB / plane DVD-RAM standard. This is because cross erase occurs if the track pitch is further narrowed. Therefore, it is a big problem to develop a technique for reducing cross erase.

The film structure of the rewritable optical disc is such that a dielectric protective layer such as Si ₃ N ₄ or ZnS—SiO 2 (hereinafter referred to as a lower protective layer), a TbFeCo magnetic film, or a GeSbTe film is formed on the plastic transparent substrate. A recording layer typified by a chalcogenide phase change film, etc., and a dielectric protective layer similar to the lower protective layer (hereinafter referred to as a thermal diffusion control layer) are sequentially laminated, and a metal such as an Al alloy or an Au alloy. This is a multiple interference structure provided with a reflective film (hereinafter referred to as a heat diffusion layer). The feature of this structure is to emphasize the change in the optical properties of the recording layer by setting the refractive index and thickness of the lower protective layer, recording layer, thermal diffusion control layer, and thermal diffusion layer to appropriate values. Thus, by reflecting the light, a large carrier-to-noise ratio is obtained.

  The role of the thermal diffusion layer is to reflect the light transmitted through the lower protective layer, the recording layer, and the thermal diffusion control layer and return it to the light incident side. Therefore, optically, a high reflectance is required. However, since the heat conductivity of high reflectivity metals such as Al, Au, Pd, Pt, Cu, and Ag is generally very large, the following problems occur.

  When the thermal diffusion layer has a high thermal conductivity, it means that the heat generated in the recording layer is easily diffused into the thermal diffusion layer, so that the temperature of the recording layer is difficult to rise and the laser power required for recording is reduced. There is a problem that it increases (recording sensitivity decreases) (recording sensitivity problem).

  In order to solve the above problems, two thermal diffusion layers are provided, the thermal conductivity of the thermal diffusion layer closer to the recording layer is set to a low thermal conductivity, and the side opposite to the recording layer side of the thermal diffusion layer A method of providing a thermal diffusion layer having a relatively high thermal conductivity is known (Patent Document 4).

  However, since the reflectance of the low thermal conductivity metal satisfying the above thermal condition is as low as 60% or less, the low thermal conductivity metal film cannot sufficiently satisfy the optical characteristics as the reflective film as described above. Therefore, it has been difficult to make the signal modulation degree, CNR (carrier-to-noise ratio) of the reproduced signal, the overall reflectivity of the multiple interference structure, etc. sufficiently large (low CNR problem).

  In addition, when the thermal diffusion layer has high thermal conductivity, heat tends to spread in the plane direction of the thermal diffusion layer, and the information recorded on the adjacent information recording track is erased due to the influence of this heat (cross erase). Happens (cross erase problem).

  In addition, when the recording film of the rewritable optical disc is a phase change recording material, these information recording media usually have a configuration of a protective layer, a GeSbTe-based recording film, a protective layer, and a reflective layer on a substrate. Is higher in the crystalline state than in the amorphous state. Thereby, the absorptance in the recording film becomes larger in the amorphous state. When overwriting in this state, the recorded mark part in the amorphous state is more likely to absorb light than the crystalline state part, so it is easy to raise the temperature, so the newly recorded mark becomes larger than the normal size, The playback signal is distorted.

  In order to prevent this, attempts have been made to make the absorption rate of the crystalline state in the recording film larger than that of the amorphous state. For example, by providing a very thin Au reflection layer of 10 nm, the relationship between the absorption rate in the crystalline state and the absorption rate in the amorphous state is reversed (Non-patent Document 1), or 65 nm Si is used in the reflection layer. There are examples in which the relationship between the absorption rate in the crystalline state and the absorption rate in the amorphous state is reversed (Non-Patent Document 2).

  However, since neither method has a sufficiently thick heat diffusion layer, the recording film cannot be quickly cooled after the recording film is melted. For this reason, there arises a problem that the recording film deteriorates after rewriting many times (recording film deterioration problem at the time of rewriting many times).

  In order to solve this problem, two reflective layers are provided on the side opposite to the laser beam incident side of the recording film, the reflective layer closer to the recording film is Si, and the other reflective layer (thermal diffusion layer) There is a method of reversing the relationship between the absorptivity in the crystalline state and the absorptivity in the amorphous state by using Al as an alloy (Non-patent Document 3). Although this method is an excellent method, the thickness of the Si thin film is limited to 50 nm to 100 nm in order to make the inversion of the absorptance sufficient and to obtain an optically good multiple interference structure. Therefore, the degree of freedom in design is reduced when performing thermal design, and there is no sufficiently thick thermal diffusion control layer (a protective layer existing between the recording layer and the Si thin film). Therefore, there arises a problem that heat is diffused to the adjacent information recording track through the Si thin film having a high thermal conductivity and the thermal diffusion layer (Al alloy) to cause cross erase. In addition, since a semiconductor thin film such as Si usually has a low film formation rate, it cannot be said that productivity is good and there is a problem in mass production.

JP-A-8-249737 JP-A-9-293286 JP-A-6-338064 Japanese Patent Laid-Open No. 3-272032 IEICE Technical Report MR92-71, CPM92-148 (1992-12) P.I. 37 IEICE Technical Report MR93-53, CPM93-105 (1993-12) P.I. 1 Proceeding of International Symposium on Optical Memory 1995, pp151-152

  As described in detail above, various problems occur when performing high density recording. In particular, when performing high-density recording such that the track pitch is 70% or less of the laser beam spot diameter, a technique for dramatically reducing cross erase is indispensable.

  All of the above methods are excellent methods, but none of the above methods sufficiently assumes high-density recording in which the track pitch is 70% or less of the laser beam spot diameter. The erase could not be reduced. Needless to say, the structure in which cross erase is likely to occur is a structure in which a heat flow from the land to the groove or from the groove to the land is large. In addition, when the flow of heat between the land and groove is large in this way, as described later, when information is recorded on both the land and the groove, the laser power required for recording is recorded on the land and on the groove. The problem that it is different from the case occurs.

  An object of the present invention is to provide an information recording medium in which CNR, overwrite characteristics, and recording sensitivity are not deteriorated even in high-density recording in which the track pitch is 70% or less of the laser beam spot diameter, and no cross erase occurs. It is to provide.

  Furthermore, the object of the present invention is to realize a narrow track pitch without degrading CNR, overwrite characteristics and recording sensitivity even in high density recording in which the track pitch is 70% or less of the laser beam spot diameter. Moreover, it is to realize an information recording medium having a high recording density corresponding to an information recording / reproducing apparatus using an inexpensive semiconductor laser.

  Further, an object of the present invention is to realize a narrow track pitch without reducing the CNR and recording sensitivity even in high density recording in which the track pitch is 70% or less of the laser beam spot diameter. An object of the present invention is to provide an information recording medium capable of realizing good overwrite characteristics even in high-density recording in which the length is half or less of the energy beam spot diameter.

  Furthermore, the object of the present invention is to realize a narrow track pitch without degrading CNR, overwrite characteristics and recording sensitivity even in high density recording in which the track pitch is 70% or less of the laser beam spot diameter. Moreover, it is an object to provide an information recording medium in which a reproduction signal does not deteriorate after rewriting many times about 100,000 times.

  Furthermore, the object of the present invention is to realize a narrow track pitch without degrading CNR, overwrite characteristics and recording sensitivity even in high density recording in which the track pitch is 70% or less of the laser beam spot diameter. Moreover, it is an object to provide an information recording medium in which a difference in recording sensitivity does not occur when information is recorded on a land and when information is recorded on a groove.

In order to solve the above-described problems in the prior art and achieve the object of the present invention, the following information recording medium may be used.
(1) In an information recording medium on which information (recording marks) is recorded by irradiation of a relatively moving energy beam to change atomic arrangement or / and electronic state, parallel to the relatively moving direction. A plurality of information recording tracks, a step between the information recording tracks, one or more types of information recording thin film as a recording layer, and one or more types of heat on the side opposite to the energy beam incident side of the recording layer. The diffusion control layer and the thermal diffusion control layer include thermal diffusion layers having different compositions, and the sum of the film thicknesses of the one or more recording layers is equal to or less than a step between the information recording tracks. An information recording medium characterized in that the sum of the layer thicknesses is equal to or greater than the level difference between the information recording tracks. Reduces cross erase, increases CNR, and increases without reducing recording sensitivity. There is an information recording medium that can improve durability against rewriting deterioration and that does not greatly differ in the quality of a reproduction signal obtained from the land and the groove even when information is recorded on both the land and the groove. Realize. Even in high-density recording where the track pitch is 70% or less of the laser beam spot diameter, narrow track pitch can be achieved without degrading CNR, overwrite characteristics, and recording sensitivity, and information can be recorded on the land. Thus, an information recording medium that does not cause a difference in recording sensitivity between recording information and a groove when recording information is realized. In particular, when the sum of the film thicknesses of the one or more recording layers is 5 nm or more and 20 nm or less, the laser light can easily pass through the recording layer, so that the optical interference effect between the thermal diffusion layer and the recording layer can be effectively utilized. An information recording medium having a high CNR can be obtained. In addition to the above effect, the sum of the film thicknesses of the one or more types of thermal diffusion control layers is not less than the step between the information recording tracks and not more than 300 nm, more preferably not less than 70 nm and not more than 150 nm. , Improve productivity. further,
(2) The information recording medium according to (1), wherein the step between the information recording tracks is a step having a concavo-convex shape (groove shape), and is adjacent to a concave portion (groove portion) and a convex portion (land portion). An information recording medium characterized by each having an information recording track can realize a narrow track pitch of the information recording track without increasing cross erase. further,
(3) The information recording medium according to any one of (1) and (2), wherein the information recording track is arranged at a certain track pitch (a distance between center lines of the information recording track), and the track An information recording medium, wherein the pitch is 50% to 70% of the energy beam spot diameter, and / or
(4) The information recording medium according to (3), wherein the energy beam is a laser beam, the laser wavelength used for the laser beam is λ, and the lens numerical aperture for forming the laser beam is NA. In this case, the effect of the present invention is most apparent in the information recording medium characterized in that the track pitch is 0.5λ / NA or more and 0.6λ / NA or less. Also,
(5) The information recording medium according to (4), wherein the information recording medium includes a transparent substrate on an energy beam incident side, the energy beam is a laser beam, and the laser wavelength of the laser beam is λ, When the refractive index of the transparent substrate at the wavelength λ is n, the step (groove depth) between the center of the concave portion and the convex portion is not less than λ / (7n) and λ / (6.2n). ) With the information recording medium characterized by the following, not only can crosstalk be reduced, but also cross erase can be reduced without lowering recording sensitivity, CNR, and resistance to multiple rewrites. Also,
(6) The information recording medium according to any one of (4) and (5), wherein the information recording medium includes a transparent substrate on an energy beam incident side, the energy beam is a laser beam, The laser wavelength of the laser beam is 630 to 660 nm, the lens numerical aperture for forming the laser beam is 0.57 to 0.643, and the refractive index of the transparent substrate in the wavelength range is 1.45 to 1.65. An information recording / reproducing apparatus using an inexpensive semiconductor laser by an information recording medium comprising a transparent substrate having a track pitch of 0.615 ± 0.03 μm and a groove depth of 59 to 67 nm. A corresponding information recording medium having a high recording density such as a DVD-RAM having a recording capacity of 4.7 GB can be realized. (7) The information recording medium according to any one of (1) and (2), wherein the one or more types of thermal diffusion control layers contain a metal oxide, carbide, nitride, sulfide, or selenide. And / or the information recording medium according to (8) and (7), wherein at least one of the one or more types of thermal diffusion control layers is provided with S. An information recording medium characterized by containing an element or / and an information recording medium according to (9) and (8), wherein the content of S element is 5% or more and 50% or less. With the characteristic information recording medium, the thermal conductivity of the thermal diffusion control layer is 1 W / m. Since K can be lowered, the phenomenon of heat backflow from the thermal diffusion layer to the recording layer can be reduced, and the cross erase can be reduced without lowering the recording sensitivity, CNR, and resistance to multiple rewrites. Also,
(10) The information recording medium according to any one of (1) and (2), wherein the thermal diffusion layer has a total content of Al, Cu, Ag, Au, Pt, and Pd of 90% or more. An information recording medium characterized by
(11) The information recording medium according to (10), comprising the above thermal diffusion layer having an Al element content of 97% or more, and / or (12) (10 ), Wherein the thermal diffusion layer has a thickness of 30 nm or more and 300 nm or less, and the recording layer is made of Ge, Sb, Te, In, Ag, or the like. Not only the phase change recording layer containing the main component but also, for example, the recording sensitivity, CNR, and the multiple rewriting resistance are reduced in the recording on the magneto-optical recording layer containing Tb, Fe, Co, Dy, Gd, etc. as the main component. Cross erase can be reduced without this.
further,
(13) The information recording medium according to any one of (1) to (12), wherein the information is changed from a crystal to an amorphous state and / or from an amorphous state to a crystal according to the change in the atomic arrangement. By using an information recording medium characterized by recording (record mark), CNR, overwrite characteristics, recording even in high-density recording where the track pitch is 70% or less of the laser beam spot diameter. Narrow track pitch can be realized without lowering the sensitivity, and information excellent in compatibility with read-only optical discs (eg, DVD-ROM) such as DVD-RAM, DVD-RW, and DVD-R. A recording medium can be obtained.
(14) The information recording medium according to (13), wherein the content of S element is smaller than the content of S element present in at least one kind of thermal diffusion control layer among the thermal diffusion control layers, An information recording medium comprising a thermal buffer layer present between the thermal diffusion control layer and the thermal diffusion layer, or / and
(15) The information recording medium according to (14), wherein the thermal buffer layer is a mixture of a metal and a metal oxide, a metal sulfide, a metal nitride, or a metal carbide. Or / and
(16) The information recording medium according to (14), wherein the sum of the thicknesses of the thermal diffusion control layers is equal to or greater than the thickness of the thermal buffer layer, and the track pitch is obtained. Even in high-density recording where the laser beam spot diameter is 70% or less of the laser beam spot diameter, a narrow track pitch can be realized without lowering the CNR and recording sensitivity. In particular, the recording mark length is less than half the energy beam spot diameter. Even in such high-density recording, good overwrite characteristics can be realized. In particular,
(17) The information recording medium according to (14), wherein information is recorded by recording a plurality of length recording marks, and the shortest recording mark among the plurality of length recording marks. The effect of the present invention is remarkably exhibited in an information recording medium characterized in that the length of the recording medium is 40% or more and 50% or less of the energy beam spot diameter. Also,
(18) The information recording medium according to (13), comprising at least a plurality of thermal diffusion control layers, wherein the S element content is at least one thermal diffusion control layer among the other thermal diffusion control layers. The track pitch is 70% or less of the laser beam spot diameter by the information recording medium characterized in that the information recording medium is provided with an interface layer that is smaller than the content of S element present in the recording medium and in contact with the recording layer. Even in high-density recording, it is possible to achieve a narrow track pitch without degrading CNR, overwrite characteristics, and recording sensitivity, and to obtain an information recording medium in which a reproduction signal does not deteriorate after rewriting many times such as 100,000 times. it can.

  In the present invention, a plurality of thin films are laminated and the structure of each thin film is utilized. However, each layer does not necessarily have to be strictly separated. For example, if it is about 5 nm or less, it is near the boundary between the eyebrows. The effect of the present invention is not lost even if the composition ratio of the is continuously changed. In the present invention, the composition of each film is shown in atomic%.

The energy beam spot diameter in the present invention indicates a diameter of a region where the intensity is 1 / e ² or more of the center intensity of the beam spot. The present invention also has the effect of improving the recording density in the direction parallel to the information recording track (the effect of realizing good overwrite characteristics when recording a recording mark having a diameter of 50% or less of the energy beam diameter), and the information recording track. There is an effect of improving the recording density with respect to the vertical direction (an effect of suppressing cross erase and quartoque even when the track pitch is 70% or less of the energy beam diameter). In the present invention, the energy beam spot diameter is, for example, when the beam spot shape is other than a circle such as an ellipse, the intensity is 1 / e ² or more of the center intensity of the beam spot in the direction in which each effect appears. Indicates the width of the region.

  The definitions of the interface layer, the thermal diffusion control layer, the thermal buffer layer, and the thermal diffusion layer in the present invention are summarized below. The interface layer is a layer that exists between the recording layer and the thermal diffusion control layer and stabilizes the interface of the recording layer, and the content of at least one element of the thermal diffusion control layer is at least S element content. And a film thickness of 2 to 10 nm. For example, if the composition is clearly different from the recording layer or the thermal diffusion control layer when the surface of the recording layer is changed by some treatment (nitriding, oxidation, etc.), this is called an interface layer.

  The thermal diffusion control layer has at least a film thickness of more than 10 nm, exists between the recording layer and the thermal diffusion layer, and contains an oxide, carbide, nitride, sulfide, selenide that transmits an energy beam as a main component. It is a layer in which k is at least −0.1 among the complex refractive indexes n and k at the wavelength of the energy beam.

  The thermal buffer layer is present at least between the thermal diffusion control layer and the thermal diffusion layer, and refers to a complex refractive index n, k in which k is less than −0.1 and the film thickness is 100 nm or less.

  According to the present invention, even in high density recording in which the track pitch is 70% or less of the laser beam spot diameter, the information recording medium in which CNR, overwrite characteristics and recording sensitivity do not deteriorate and cross erase does not occur. Can be provided.

  The invention is illustrated by the following examples. First, the superiority of the present invention over cross erase will be described. Cross erase is a phenomenon in which the information recorded on the adjacent information recording track is erased by the heat generated when the recording layer is irradiated with a laser beam to record the recording mark, and is transmitted through the laminated thin film. It is one of the biggest obstacles in high density recording.

The effect of reducing the cross erase of the present invention will be described with reference to FIGS. FIG. 1 shows the basic structure of the information recording medium of the present invention. First information recording member is lower protective layer 2 on the substrate 1 groove depth is provided the information recording track of the groove shape of d _g, recording layer 3, the thermal diffusion control layer 4, the thermal diffusion layer 5 are sequentially laminated It is a structured. Further, an information recording member having a similar structure having a substrate 1 ′, a lower protective layer 2 ′, a recording layer 3 ′, and a thermal diffusion control layer 4 ′ and a thermal diffusion layer 5 ′ is bonded through an adhesive 6.

2 and 3 schematically show the state of thermal diffusion in the cross-sectional direction when a laser beam is irradiated from the substrate 1 side and the recording layer 3 is heated. 2 shows the case where the thickness d _hc of the thermal diffusion control layer 4 is thinner than the groove depth d _g (Structure A: equivalent to the conventional example), and FIG. 3 shows the thickness d _hc of the thermal diffusion control layer 4 as the groove depth. The case where the thickness is larger than d _g (structure B: the present invention) is shown. Here, for the sake of simplicity, the relationship of the thermal conductivity of each layer is the thermal conductivity of the thermal diffusion layer> the thermal conductivity of the recording layer> the thermal conductivity of the thermal diffusion control layer = the thermal conductivity of the lower protective layer. And

As described above, in FIG. 2, the thickness d _hc of the thermal diffusion control layer 4 is thinner than the groove depth d _g . The energy beam irradiated to the recording layer 3 by the objective lens 7 generates heat in the recording layer 3. Further, the heat generated in the heat generating portion 9 of the recording layer 3 is diffused through the thermal diffusion layer 5. At the boundary portion 10 with the adjacent information recording track, the shortest distance _drh between the thermal diffusion layer 5 and the recording portion 11 of the adjacent information recording track is small, and there is a thermal diffusion layer so as to surround the recording portion 11 of the adjacent information recording track. Therefore, cross erasure is likely to occur due to the influence of heat diffusing through the thermal diffusion layer 5.

In contrast, in the case of FIG. 3, since the thickness d _hc of the thermal diffusion control layer 4 is thicker than the groove depth d _g , the recording unit 11 of the adjacent information recording track diffuses the thermal diffusion layer 5. Hard to be affected by heat. The shortest distance _drh between the thermal diffusion layer 5 and the recording portion 11 of the adjacent information recording track at the boundary portion 10 with the adjacent information recording track is larger than in the case of FIG. 2, and the thermal diffusion is performed as in FIG. This is because the layer 5 does not exist so as to surround the recording portion 11 of the adjacent information recording track.

As described above, the influence of heat on the recording portion 11 of the adjacent information recording track differs depending on the film thickness d _hc of the thermal diffusion control layer 4. This is extremely important in suppressing cross erase. This is because the cross erase can be suppressed by suppressing the influence of heat on the recording unit 11 of the adjacent information recording track.

FIG. 4 is a calculation example of the relationship between the shortest distance _drh between the recording portion 11 of the adjacent information recording track and the thermal diffusion layer 5 and the film thickness d _hc of the thermal diffusion control layer 4. When the film thickness d _hc of the thermal diffusion control layer 4 is equal to or greater than the groove depth d _g , the shortest distance _drh between the thermal diffusion layer 5 and the recording portion 11 of the adjacent information recording track is rapidly increased.

In the above example, the case where information is recorded on the recording layer of the groove has been described. However, when recording on the land, the shortest distance between the recording portion of the land and the thermal diffusion layer is smaller than the film thickness of the thermal diffusion control layer. Show similar changes. Further, as shown in FIG. 5, when the film thickness d _hc of the thermal diffusion control layer 4 is equal to or smaller than the groove depth d _g , the heat diffusion layer 5 exists so as to surround the heat generating portion 9 of the recording layer 3. The heat generated in the section 9 is easily diffused in the direction of the adjacent information recording track. As a result, the cross erase is likely to occur in the adjacent information recording track.

On the other hand, in the case of FIG. 6, since the thickness d _hc of the thermal diffusion control layer 4 is thicker than the groove depth d _g , the recording unit 11 of the adjacent information recording track diffuses the thermal diffusion layer 5. Hard to be affected by heat. This is because the thermal diffusion layer 5 does not exist so as to surround the recording portion 11 of the adjacent information recording track as in the case of FIG. As described above, the influence of the heat generated in the land on the recording portion of the groove can be explained in the same manner as in the case of recording in the groove. According to the present invention, the flow of heat from the land to the groove, or from the groove to the land. The flow of heat can be suppressed. Thus, the cross erase can be reduced if the film thickness of the thermal diffusion control layer is equal to or greater than the groove depth. However, particularly when the land / groove recording method is employed and information is recorded on both the land and the groove. The effect of reducing the cross erase appears.

Figure 7 is a diagram schematically showing a state of thermal diffusion when the film thickness d _r of the recording layer 3 is irradiated with a laser beam to the groove when thicker than the groove depth d _g. In this case, the distance between the heat generating portion 9 of the groove recording layer 3 and the recording portion 11 of the adjacent information recording track is smaller than in FIGS. 2 and 3, and the recording layer 11 has a relatively high thermal conductivity. As the amount of heat that diffuses increases, cross erase tends to occur.

Figure 8 is a diagram schematically showing a state of thermal diffusion when the film thickness d _r of the recording layer 3 is irradiated with a laser beam to the land when thicker than the groove depth d _g. Also in this case, the distance between the heat generating portion 9 of the land recording layer 3 and the recording portion 11 of the adjacent information recording track is smaller than in FIGS. 5 and 6, and the recording layer has a relatively high thermal conductivity. As the amount of heat that diffuses increases, cross erase tends to occur.

As shown in FIG. 5, when the thickness d _hc of the thermal diffusion control layer 4 is thinner than the groove depth d _g and the land is irradiated with a laser beam, the thermal diffusion control is performed as shown in FIG. The thickness d _hc of the layer 4 is thinner than the groove depth d _g , and the recording sensitivity is lowered as compared with the case where the groove is irradiated with a laser beam. In the case of FIG. 2, the lower protective layer 2 and the substrate 1 having a relatively low thermal conductivity are present on the side surface of the heat generating portion 9 of the recording layer 3, whereas in the case of FIG. This is because a thermal diffusion layer having a relatively large thermal conductivity exists on the side surface of the portion 9. This causes a difference in recording sensitivity between the land and the groove, which is a serious problem in designing the information recording / reproducing apparatus.

  In order to solve this problem, when recording information on the land, a method of irradiating a laser beam with a larger power than when recording information on the groove is conceivable. This is not preferable because a new problem that cross erasure easily occurs.

According to the information recording medium of the present invention, the land and groove recording sensitivity difference can be reduced. When the thickness d _hc of the thermal diffusion control layer 4 is thicker than the groove depth d _g as shown in FIGS. 3 and 6, the heat generating portion 9 of the recording layer 3 is recorded in both the groove and the land. This is because a lower protective layer having a relatively low thermal conductivity or a thermal diffusion control layer exists on the side surface.

  Considering the above phenomenon, the inventors examined the thermal conductivity of the recording layer, the thermal diffusion control layer, and the thermal diffusion layer, the relationship between the film thickness and the cross erase, and the optimum thermal conductivity and film thickness exist for each layer. I found it to be. Moreover, the composition of each layer for realizing the thermal conductivity was determined. Experimental examples are shown below.

A land / groove having a track pitch of 0.4 to 0.75 μm and a groove depth of 62 nm, and address information for recording information on both the land and the groove is 0.6 mm thick provided at the head of each sector. Each thin film (lower protective layer 2: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (100 nm), lower interface layer 12: Cr ₂ O ₃ (5 nm) having the structure shown in FIG. 9 is formed on a polycarbonate substrate 1 for recording. Recording layer 3: Ag ₆ Ge ₁₆ Sb ₂₂ Te ₅₅ phase change recording layer (10 nm), upper interface layer 13 (5 nm), thermal diffusion control layer 4: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (140 nm), thermal buffer Layer 14: Cr ₄₀ (Cr ₂ O ₃ ) ₆₀ (35 nm) and thermal diffusion layer 5: Al (80 nm) were sequentially formed by a sputtering process.

Further, a similar substrate 1 ', lower protective layer 2', lower interface layer 12 ', recording layer 3', upper interface layer 13 ', thermal diffusion control layer 4', thermal buffer layer 14 ', and thermal diffusion layer 5' are provided. The information recording member having the same structure as above was bonded through the adhesive 6. The information recording medium having the above configuration is called an optical disc 15. The refractive index of the polycarbonate substrate was 1.58. (Note that the proper film thickness and composition range of each thin film constituting the optical disk 15 are described later.)
There are 36 user recording zones in the radial direction of the disk, and there are 25 to 60 sectors within one zone. In addition, the track pitch is changed between 0.4 and 0.75 μm for each zone so that the track pitch dependency of cross erase can be measured.

  Information was recorded / reproduced on the optical disk 15 (referred to as 10-1 for convenience in FIG. 10) by the information recording / reproducing apparatus shown in FIG. The operation of the information recording / reproducing apparatus will be described below. As a motor control method for recording / reproducing, a ZCLV (Zone Constant Linear Velocity) method is employed in which the rotational speed of the disk is changed for each zone where recording / reproducing is performed. The disk linear velocity is about 8.3 m / s.

  Information from the outside of the recording apparatus is transmitted to an 8-16 modulator in units of 8 bits. When recording information on the disc 1, recording was performed using a modulation system that converts 8 bits of information into 16 bits, a so-called 8-16 modulation system. In this modulation method, information having a mark length of 3T to 14T corresponding to 8-bit information is recorded on the medium. The 8-16 modulator 10-8 in the figure performs this modulation. Here, T represents the clock cycle at the time of information recording, and here it was 17.1 ns.

  The digital signal of 3T to 14T converted by the 8-16 modulator 10-8 is transferred to the recording waveform generation circuit 10-6, the width of the high power pulse is set to about T / 2, and the laser power is irradiated between the high power levels. Laser irradiation at a low power level with a width of about T / 2 is performed, and a multi-pulse recording waveform is generated in which laser irradiation at an intermediate power level is performed between the series of high power pulses. At this time, the high power level for forming the recording mark was 11.0 mW, the intermediate power level capable of erasing the recording mark was 4.0 mW, and the low power level lower than the intermediate power level was 3.0 mW. In the recording waveform generation circuit 6, the signals of 3T to 14T are made to correspond to “0” and “1” alternately in time series, and in the case of “0”, laser power of an intermediate power level is irradiated. In the case of “1”, a series of high power pulse trains including high power level pulses are irradiated. At this time, the portion irradiated with the intermediate power level laser beam on the optical disk 1 becomes a crystal (space portion), and the portion irradiated with a series of high power pulse trains including a high power level pulse is amorphous. Changes to (marked part). Further, in the recording waveform generation circuit 10-6, when forming a series of high power pulse trains including a high power level for forming the mark portion, according to the length of the space portion before and after the mark portion, It has a multi-pulse waveform table corresponding to a method (adaptive recording waveform control) that changes the first pulse width and the last pulse width of a multi-pulse waveform, and this affects the effect of thermal interference between marks. The multi-pulse recording waveform that can eliminate as much as possible is generated.

  The recording waveform generated by the recording waveform generation circuit 10-6 is transferred to the laser driving circuit 10-7. The laser 1 driving circuit 10-7 uses the semiconductor waveform in the optical head 10-3 based on the recording waveform. To emit light.

  In the optical head 10-3 mounted on the recording apparatus, a semiconductor laser having an optical wavelength of 655 nm is used as an energy beam for information recording. Information was recorded by squeezing the laser beam onto the recording layer of the optical disk 12 with an objective lens having a lens NA of 0.6 and irradiating a laser beam having an energy corresponding to the recording waveform.

  In general, when laser light having a laser wavelength λ is condensed by a lens having a lens numerical aperture NA, the spot diameter of the laser beam is approximately 0.9 × λ / NA. Therefore, in the case of the above conditions, the spot diameter of the laser beam is about 0.98 microns. At this time, the polarization of the laser beam was circularly polarized.

  The recording apparatus is compatible with a system (so-called land / groove recording system) for recording information on both the groove and the land (area between the grooves). In this recording apparatus, tracking for the land and the groove can be arbitrarily selected by the L / G servo circuit 10-9.

  The recorded information was also reproduced using the optical head 10-3. 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 reproduction signal is increased by the preamplifier circuit 10-4 and transferred to the 8-16 demodulator 10-10. The 8-16 demodulator 10-10 converts the information into 8-bit information every 16 bits. With the above operation, the reproduction of the recorded mark is completed.

  When recording is performed on the optical disc 15 under the above conditions, the mark length of the 3T mark, which is the shortest mark, is approximately 0.42 μm, and the mark length of the 14T mark, which is the longest mark, is approximately 1.96 μm.

  Under the above conditions, after information was recorded in the groove, information was recorded in the adjacent information track (land), and the amount of increase in jitter due to cross erase of the reproduction signal of the groove was measured and is shown in FIG.

  Further, an optical disk 16 having the same structure as that of the optical disk 15 except that the thickness of the thermal diffusion control layer is 15 nm is prepared, and the amount of increase in jitter due to the cross erase of the reproduction signal of the groove is measured and shown in FIG. . At this time, the power required for recording of the optical disk 16 was about 1.3 times that of the optical disk 15. The jitter of the optical disc 15 at a track pitch of 0.7 μm was 8.0% land and groove 8.2%, and the jitter of the optical disc 16 at a track pitch of 0.7 μm was 8.5% land and 8.7% groove. .

  In the case of the optical disk 16 in which the film thickness of the thermal diffusion control layer is thinner than the groove depth, when the track pitch is 0.7 μm or less, an increase in jitter due to cross erase occurs, but the optical disk in which the film thickness of the thermal diffusion control layer is thicker than the groove depth. In the case of 15, the jitter increase due to the cross erase occurred at a track pitch narrower than 0.55 μm, and when the track pitch was 0.55 μm or more, there was no jitter increase due to the cross erase. Therefore, it has been clarified that the effect of the present invention is manifested when the track pitch is between 0.55 μm and 0.65 μm.

  Similarly to the above experiment, after information was recorded on the land, information was recorded on the adjacent information track (groove), and the amount of jitter increase due to cross erase of the reproduction signal of the land was measured. When the pitch was between 0.55 μm and 0.7 μm, the cross erase reduction effect of the present invention was manifested.

  In the following examples, information was recorded / reproduced by the information recording / reproducing apparatus shown in FIG. The following experiment was conducted to clarify the relationship between the present invention and the groove depth. Several types with a track pitch of 0.615 μm, address information for recording information on both lands and grooves provided at the head of each sector, thickness 0.6 mm, and groove depth varied between 50 and 80 nm Each thin film having the structure shown in FIG. 9 was sequentially formed on the land / groove recording polycarbonate substrate 1 by a sputtering process. Further, an information recording member having a similar structure was bonded with an adhesive. The refractive index of the polycarbonate substrate was 1.58. Information was recorded / reproduced on the optical disk by the information recording / reproducing apparatus shown in FIG. Information was recorded and reproduced under the same conditions as in the optical disk 15 of the example.

  When recording is performed under the above conditions, the mark length of the 3T mark which is the shortest mark is about 0.42 μm, and the mark length of the 14T mark which is the longest mark is about 1.96 μm.

  After recording information on the groove of several types of optical discs with different groove depths, information is recorded on the adjacent information track (land), and the groove depth dependence of the jitter rise due to crosstalk of the reproduction signal of the groove Measurements are shown in FIG.

When the groove depth was 59 nm to 67 nm, no increase in jitter due to crosstalk occurred. However, when the groove depth was less than 59 nm or larger than 67 nm, jitter increase due to cross erase or crosstalk occurred. . As described above, when the groove depth is 59 nm or more and 67 nm or less, the effect of the present invention is revealed. The effect of reducing crosstalk is determined by the relationship between the laser wavelength of the laser beam and the groove depth. When the laser wavelength of the laser beam is λ and the refractive index of the substrate at the wavelength λ is n, the groove depth is λ / It may be (7n) or more and λ / (6.2n) or less.
Further, when the land and groove were overwritten 100,000 times on the optical disc having a groove depth of 59 nm or more and 67 nm or less, the increase in jitter was 1% or less, and the rewriting characteristics for many times were very good. all right.

The thermal diffusion control layer that exhibits the effects of the present invention is a material that has an optical refractive index between 1.4 and 3.0 and does not absorb light, and is particularly a metal oxide, carbide, or nitride. It is desirable to contain a product, sulfide, or selenide. A plurality of thermal diffusion control layers having different compositions may be combined. When Zn and S are contained in at least one kind of thermal diffusion control layer among the thermal diffusion control layers, the cross erase reduction effect is particularly prominent. In particular, the thermal diffusion control is (ZnS) ₈₀ (SiO 2 _{2) 20} (mol ratio) or ZnS to that changing the mixing ratio of SiO ₂ (SiO ₂ 5 to 50 mol%), when the composition of the material close to the mixed composition of ZnS and following oxides 5-40 mole% Thermal diffusion control is facilitated because the thermal conductivity is reduced. Oxide mixed is _{SiO 2, SiO, TiO 2,} Al 2 O 3, Y 2 O 3, CeO, La 2 O 3, In 2 O 3, GeO, GeO 2, PbO, SnO, SnO 2, Bi 2 O _{3, TeO 2, WO 2,} WO 3, Sc 2 O 3, Ta 2 O 5, ZrO 2 are preferred. In addition to Si-O-N-based materials, oxidized, such as CoO-based material such as Si-Al-O-N-based material, Cr-O-based material such as _{Cr 2 O 3,, CO 2} O 3, CoO , Nitrides such as Si—N materials such as TaN, AlN, Si ₃ N ₄ , Al—Si—N materials (eg, AlSiN ₂ ), Ge—N materials, ZnS, Sb ₂ S ₃ , CdS, Sulfides such as In ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , PbS, Bi ₂ S ₃ , SnSe ₃ , Sb ₂ S ₃ , CdSe, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe , GeSe ₂ , SnSe, PbSe, Bi ₂ Se ₃ and other selenides, CeF ₃ , MgF ₂ and CaF ₂ fluorides, or a thermal diffusion control layer using a composition close to the above materials Also good. Moreover, the layer of these mixed materials may be sufficient. Further, as in this embodiment, a thermal diffusion control layer of ZnS and an oxide and a multilayered thermal diffusion control layer in which the other layers of the above materials are stacked may be used. In this case, among materials other than the material composed of ZnS and oxide, any of oxide, nitride, and fluoride is more preferable. In particular, when the sum of the film thickness of the thermal diffusion control layer is not less than the step between the information recording tracks and not more than 300 nm, the cross erase is reduced, the CNR is increased, and the number of times of rewriting is deteriorated without lowering the recording sensitivity. In addition, an information recording medium can be realized in which the quality of the reproduction signal obtained from the land and the groove does not greatly differ even when information is recorded on both the land and the groove. . More desirably, when the film thickness of the thermal diffusion control layer is not less than 100 nm and not more than 150 nm, productivity is improved in addition to the above effects.

  The heat diffusion layer is preferably a metal or alloy having high reflectivity and high thermal conductivity, and the total content of Al, Cu, Ag, Au, Pt, and Pd is desirably 90% or more. In particular, when a thermal diffusion layer containing 95% or more of Al is used, an information recording medium that is inexpensive, excellent in high CNR, high recording sensitivity, excellent in multiple rewritability, and extremely effective in reducing cross erase can be obtained. . In particular, when the composition of the heat diffusion layer contains 95% or more of Al, an inexpensive information recording medium with excellent 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 and C is excellent in terms of corrosion resistance, but when the additive element is Co, Cr, Ti, Ni, Fe, or Cu, there is a great effect in improving corrosion resistance. The film thickness of the thermal diffusion layer is preferably 30 nm or more and 300 nm or less. When the film thickness of the thermal diffusion layer is smaller than 300 m, the heat generated in the recording layer is difficult to diffuse. Therefore, the recording film is likely to deteriorate especially when rewritten about 100,000 times, and cross erase occurs. It may be easier. Further, since light is transmitted, it is difficult to use as a reflective layer, and the reproduction signal amplitude may be reduced.

  When the thickness of the thermal diffusion layer is 300 nm or more, the productivity is poor, and internal warping of the thermal diffusion layer may cause warping of the substrate, and information recording / reproduction may not be performed accurately. Moreover, if the film thickness of the thermal diffusion layer is 70 nm or more and 150 nm or less, it is more desirable in terms of corrosion resistance and productivity.

  In this embodiment, recording is performed on a phase change recording layer mainly composed of Ge, Sb, Te, In, Ag or the like as an optical disk. However, the basis of the present invention is that heat is generated by an energy beam, This is to control the thermal characteristics (temperature distribution, cooling rate distribution) as well as the optical characteristics (reflectance, modulation degree) of the optical disk on which the recording mark is recorded by this heat. In addition, the present invention is also effective in recording on a magneto-optical recording layer mainly composed of Tb, Fe, Co, Dy, Gd and the like. Further, the present invention is not limited to a rewritable information recording medium. Further, in the case of organic dye recording in which recording is performed by changing the shape of the substrate or the recording layer, the change occurs only when a high power laser beam is irradiated, and this change is irreversible. The basis of the present invention is to control heat characteristics (temperature distribution, cooling rate distribution) as well as optical characteristics (reflectance, modulation degree) of an optical disc on which recording marks are recorded by the heat generated by the energy beam. Therefore, the present invention is not limited to a rewritable optical disc, and can be applied to a write-once optical disc.

Further, as the recording film used in the present invention, a phase change recording material is particularly suitable. As a material of the recording film in place of Ag ₆ Ge ₁₆ Sb ₂₂ Te ₅₅ used in the above examples, Ag ₅ Ge ₂₀ Sb ₂₀ Te ₅₅ , Ag ₁ Ge ₂₁ Sb ₂₃ Te ₅₅ , and other materials having different composition ratios such as Ag—Ge—Sb—Te are less likely to be rewritten. When the Ag amount is increased, the recording sensitivity is improved, but the remaining unerased is increased. Further, when the Ag amount is reduced, the erasing characteristics are improved, but the recording sensitivity is lowered. In the Ag-Ge-Sb-Te system, a composition in which Ag is 1 to 5 atomic%, Ge is 17 to 23 atomic%, Sb is 19 to 25 atomic%, and Te is in the range of 53 to 59 atomic% is particularly rewritable. It was found that the decrease in the number of times hardly occurred. In addition, the composition in which the material of AgSbTe ₂ or a material close thereto is 2 to 20% and the remaining material is the material of Ge ₂ Sb ₂ Te ₅ or a material close thereto has a large difference in reflectance between the crystalline state and the amorphous state, and the reproduction signal is large. It turned out to be preferable.

Next, ((Cr ₄ Te ₅ ) ₁₀ (Ge ₂ Sb ₂ Te ₅ ) ₉₀ ) and other Cr—Ge—Sb—Te-based recording films, but the jitter of rewritable more than 30,000 times increases, but many other than that Similar good results were obtained in the characteristics. In the W-Ge-Sb-Te system, a composition in which W is in the range of 1 to 5 atomic%, Ge is in the range of 17 to 23 atomic%, Sb is in the range of 19 to 25 atomic%, and Te is in the range of 53 to 59 atomic% is particularly rewritten. It turns out that the remaining disappearance of.

In general, such a recording film is a recording film to which a phase change component mainly composed of Ge—Sb—Te and a high melting point component having a higher melting point are added. 95% or more of the total number of atoms of the phase change component is a combination of GeTe and Sb ₂ Te _3, and the high melting point component of 95% or more of the total number of atoms is Cr—Te, Cr—Sb, Cr—Ge, Cr— Sb—Te, Cr—Sb—Ge, Cr—Ge—Te, Co—Te, Co—Sb, Co—Ge, Co—Sb—Te, Co—Sb—Ge, Co—Ge—Te, Cu—Te, Cu—Sb, Cu—Ge, Cu—Sb—Te, Cu—Sb—Ge, Cu—Ge—Te, Mn—Te, Mn—Sb, Mn—Ge, Mn—Sb—Te, Mn—Sb—Ge, Mn-Ge-Te, V-Te, V-Sb, V-Ge, V-Sb-Te, V-Sb-Ge, V-Ge-Te, Ni-Te, Ni-Sb, Ni-Ge, Ni- Sb-Te, Ni-Sb-Ge, Ni-Ge-Te, Mo-Te, Mo-Sb, M -Ge, Mo-Sb-Te, Mo-Sb-Ge, Mo-Ge-Te, W-Te, W-Sb, W-Ge, W-Sb-Te, W-Sb-Ge, W-Ge-Te , Ag-Te, Ag-Sb, Ag-Ge, Ag-Sb-Te, Ag-Sb-Ge, Ag-Ge-Te, or a composition close to this, more rewritable times Decline is unlikely. It has been found that Cr-Te, such as Cr ₄ Te ₅ , Cr ₂ Te ₃ , Cr ₅ Te ₈ , etc., has a particularly low jitter of 10 to 10,000 rewrites. W-Te, W-Sb, W-Ge, W-Sb-Te, W-Sb-Ge, and W-Ge-Te were found to be particularly less lost during rewriting. Further, it was found that Ag ₂ Te, AgSbTe _{2 and the} like have high signal intensity even when the light source wavelength is shortened, and Ag-Te and Ag-Sb-Te are particularly good.

When the composition of 95% or more of the total number of atoms of the phase change component is Ge ₂ Sb ₂ Te ₅ , the proportion of the high melting point component atoms in the total number of atoms of the recording film is 5 atomic% or more and 20 atomic% or less. Has good rewriting characteristics. Since the erasing characteristics are good, the rewriting characteristics are better at 5 atomic% or more and 15 atomic% or less.

Further, Ge ₂ Sb ₂ Te ₅ , GeSb ₂ Te ₄ , GeSb ₄ Te ₇ , In ₃ SbTe ₂ , In ₃₅ Sb ₃₂ Te ₃₃ , In ₃₁ Sb ₂₆ Te ₄₃ , GeTe, Ag-In-Sb-Te other than the above. , Co—Ge—Sb—Te, V—Ge—Sb—Te, Ni—Ge—Sb—Te, Pt—Ge—Sb—Te, Si—Ge—Sb—Te, Au—Ge—Sb—Te, Cu -Ge-Sb-Te, Mo-Ge-Sb-Te, Mn-Ge-Sb-Te, Fe-Ge-Sb-Te, Ti-Ge-Sb-Te, Bi-Ge-Sb-Te, W-Ge Even if it is replaced with at least one of -Sb-Te and a composition close thereto, even if a part of Ge is replaced with In, characteristics close to this can be obtained.

  When each recording film composition contains 15 atomic% or less of nitrogen, the reproduction signal output is slightly reduced, but there is an advantage in that the recording film flow at the time of many rewrites is suppressed. Further, an impurity element in the recording film, that is, an element not described so far, is preferably 10 atomic percent or less of the recording film component because deterioration in rewriting characteristics can be reduced. It was more preferable that it be 5 atomic% or less.

  When the recording film thickness is at least the level difference (groove depth) between the land and the groove, the cross erase reduction effect is large. Moreover, 5 nm or more and 20 nm or less are preferable because the degree of modulation is large and the flow hardly occurs. If it is 15 nm or less, it is more preferable.

  The recording film in the present invention is recorded by an atomic arrangement change. The atomic arrangement change refers to an atomic arrangement change that hardly accompanies a change in the outer shape of the film such as a phase change.

  The heat buffer layer preferably has a complex refractive index n and k in the range of 1.4 <n <4.5 and −2.5 <k <−0.5, particularly 2 <n <3 and −1.5 <k. A material of <-0.5 is desirable. In order to absorb light in the thermal buffer layer, a thermally stable material is preferable, and it is desirable that the melting point is desirably 1000 ° C. or higher.

  Further, when sulfide is added to the thermal diffusion control layer, there was a particularly large cross erase reduction effect. However, in the case of a thermal buffer layer, the content of sulfide such as ZnS is added to at least the thermal diffusion control layer. Desirably less than the sulfide content. This is because adverse effects such as a decrease in melting point, a decrease in thermal conductivity, and a decrease in absorption rate may appear.

The composition of the thermal buffer layer is preferably a mixture of metal and metal oxide, metal sulfide, metal nitride, or metal carbide, and the mixture of Cr and Cr2O3 showed particularly good overwriting characteristics improvement effect. . Specifically, the metals include Al, Cu, Ag, Au, Pt, Pd, Co, Ti, Cr, Ni, Mg, Si, V, Ca, Fe, Zn, Zr, Nb, Mo, Rh, Sn, A mixture of Sb, Te, Ta, W, Ir, and Pb is desirable. Examples of the metal oxide, metal sulfide, metal nitride, and metal carbide include SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , and CeO. , La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , PbO, SnO, SnO ₂ , Bi ₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ preferable. In addition to Si-O-N-based materials, oxidized, such as CoO-based material such as Si-Al-O-N-based material, Cr-O-based material such as _{Cr 2 O 3,, Co 2} O 3, CoO , Nitrides such as Si—N materials such as TaN, AlN, Si ₃ N ₄ , Al—Si—N materials (eg, AlSiN ₂ ), Ge—N materials, ZnS, Sb ₂ S ₃ , CdS, Sulfides such as In ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , PbS, Bi ₂ S ₃ , SnSe ₃ , Sb ₂ S ₃ , CdSe, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe , GeSe ₂ , SnSe, PbSe, Bi ₂ Se ₃ and other selenides, CeF ₃ , MgF ₂ , and CaF ₂ fluorides, or a thermal buffer layer using a composition close to the above materials may be used. Good.

  Further, the film thickness of the thermal buffer layer is preferably 10 nm or more and 100 nm or less. When the film thickness is 20 nm or more and 50 nm or less, a particularly excellent overwrite characteristic improvement effect appears.

  As described above, the thermal buffer layer has a property of absorbing light. For this reason, the thermal buffer layer also absorbs light and generates heat, as the recording layer absorbs light and generates heat. Further, it is important that the absorptance in the thermal buffer layer is larger when the recording layer is in the amorphous state than when the recording layer is in the crystalline state. Thus, by optical design, the effect of reducing the absorption rate Aa in the recording layer when the recording layer is in an amorphous state is smaller than the absorption rate Ac in the recording layer when the recording layer is in a crystalline state. This effect can greatly improve the overwrite characteristics. In order to obtain the above characteristics, it is necessary to increase the absorption rate in the thermal buffer layer to about 30 to 40%. The amount of heat generated in the thermal buffer layer varies depending on whether the recording layer is in a crystalline state or an amorphous state. As a result, the flow of heat from the recording layer to the thermal diffusion layer changes depending on the state of the recording layer, and this phenomenon can suppress an increase in jitter due to overwriting.

  The above effects are manifested by the effect of blocking the flow of heat from the recording layer to the thermal diffusion layer when the temperature in the thermal buffer layer rises. In order to make effective use of this effect, the relationship between the film thickness of the thermal diffusion control layer and the thermal buffer layer is important. As a result of diligent research, the inventors have achieved a narrow track pitch without lowering the CNR and recording sensitivity when the sum of the thicknesses of the thermal diffusion control layers is greater than or equal to the thickness of the thermal buffer layer. It was clarified that good overwrite characteristics can be realized even in high-density recording in which the recording mark length is less than half of the energy beam spot diameter. In particular, when the length of the shortest recording mark is 40% or more and 50% or less of the energy beam spot diameter, the effect of the present invention is most noticeable.

  In particular, when the phase change recording material is used as the recording layer as described above, there may be a phenomenon that the reflectance of the crystal decreases when rewriting is performed many times about 100,000 times. This is a phenomenon that occurs when the refractive index of the recording layer changes because the S element in the thermal diffusion control layer has melted into the recording layer when the recording layer is melted by a laser beam of high power level. . In order to suppress this phenomenon, it is preferable to provide an interface layer having an S element content at least smaller than that of the thermal diffusion control layer between the thermal diffusion control layer and the recording layer. By doing so, the long-term storage life can be improved.

Examples of the material for the interface layer include SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , CeO, La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , PbO, SnO, SnO ₂ , Bi ₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ are preferred. In addition to Si-O-N-based materials, oxidized, such as CoO-based material such as Si-Al-O-N-based material, Cr-O-based material such as _{Cr 2 O 3,, Co 2} O 3, CoO , Si—N materials such as TaN, AlN, Si ₃ N ₄ , Al—Si—N materials (eg, AlSiN ₂ ), nitrides such as Ge—N materials, CeF ₃ , MgF ₂ , CaF _2, etc. Alternatively, an interface layer using a fluoride or a composition close to the above material may be used. Moreover, the layer of these mixed materials may be sufficient. Further, when the interface layer is made of a mixed material of ZnS and the oxide, nitride, and fluoride, it is excellent in that the recording sensitivity is improved.

Next, in order to obtain the optimum film thickness and thermal conductivity of the thermal diffusion control layer and the thermal diffusion layer, the following thermal simulation was performed.
For example, the layout of marks and grooves in a high-density information recording medium of a land-groove recording system such as 4.7 GB DVD-RAM is almost as shown in FIG. That is, the width of each land and groove is about 0.6 μm, and the mark width (width of the melted portion) is about 0.4 μm. The melting point of the recording film is about 600 ° C. Therefore, in order to realize a mark width of 0.4 μm, it is necessary to heat a point 0.2 μm away from the track center 19 to 600 ° C. In such a layout, the recording mark 17 of the adjacent information recording track exists at a position 0.4 μm away from the track center 19 of the center track 18. A phenomenon in which the recording mark 17 of the adjacent information recording track is crystallized is cross erase. The condition that the cross erase does not occur even after recording 100,000 times is determined by a function of the temperature and time at the recording mark 17 of the adjacent information recording track when the center track 18 is irradiated with the laser beam 20.

  The crystallization time of a Ge-Sb-Te phase change recording material used for a high-density information recording medium such as 4.7 GB DVD-RAM is that activation energy exists between the amorphous state and the crystalline state. It is a function of temperature. The time for the laser beam spot to pass through a certain point on the medium is about 100 ns under the 4.7 GB DVD-RAM condition (8.2 m / s). The crystallization temperature in this time is estimated to be about 300 to 500 ° C. When the adjacent information recording track is irradiated with the laser beam 100,000 times, the integrated value of the time for which the adjacent information recording track is irradiated is about 10 seconds. Therefore, the crystallization temperature in the case of holding for about 10 seconds is a temperature at which cross erase occurs. The crystallization temperature in this time is about 200 ° C. Therefore, from the temperature change at the end of the recording mark 17 of the adjacent information recording track (cross erase observation point 21) when the width of the portion heated to 600 ° C. or more is 0.4 μm by thermal simulation, It is possible to determine whether or not cross erase occurs by calculating a time (cross erase temperature holding time) that is held at or above ° C.

First, the structure shown in FIG. 1 (lower protective layer 2: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (100 nm), recording layer 3: Ag ₆ Ge ₁₆ Sb ₂₂ Te ₅₅ phase change recording layer (10 nm), thermal diffusion control Layer 4: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (140 nm), thermal diffusion layer 5: Al (80 nm)), the thermal conductivity of the thermal diffusion control layer when the thermal conductivity of the thermal diffusion control layer changes And the relationship between the cross erase temperature holding time at the cross erase observation point 21 was calculated and shown in FIG. It was found that there is a thermal conductivity that minimizes the cross-erase temperature holding time and is approximately 0.6 W / mK. Moreover, in order to satisfy the target cross erase temperature holding time of 100 ns or less, it was found that the thermal conductivity should be in the range of 0.1 to 2.3 W / mK. This thermal conductivity is achieved by a dielectric film containing an S element such as (ZnS) ₈₀ (SiO ₂ ) ₂₀ and corresponds to a case where the content of the S element is 5% or more and 50% or less.

  Next, the relationship between the thermal diffusion layer thickness and the cross erase temperature holding time at the adjacent information recording track observation point was calculated, and the result is shown in FIG. In the thin region where the thermal diffusion layer (Al) is 30 nm or less, the cross erase temperature holding time is 100 nm or more. On the other hand, when the thermal diffusion layer thickness is 30 nm or more, the cross erase temperature holding time is 100 ns or less. ing.

  Next, in the case where the film thickness of the thermal diffusion layer is 80 nm, the relationship between the thermal conductivity of the thermal diffusion layer and the cross erase temperature holding time at the cross erase observation point is calculated, and the result is shown in FIG. As shown in the figure, it was found that the longer the thermal conductivity of the thermal diffusion layer, the shorter the cross erase temperature holding time. In particular, it was found that the thermal conductivity of the thermal diffusion layer should be 10 W / mK or higher in order to set the cross erase temperature holding time to 100 ns or less. The substance having a high thermal conductivity is a highly reflective metal such as Au, Al, Cu, Ag, Pd, or Pt, or a high hardness material such as diamond. In particular, when the content of the high reflectance metal is 90% or more, it can be employed as a thermal diffusion layer having a high reflectance and a high thermal conductivity. In particular, considering productivity, cost, corrosion resistance, refractive index, and the like, Al or a metal obtained by adding a metal such as Ti or Cr to Al is the best. In particular, a thermal diffusion layer containing 97% or more of Al is excellent in practicality.

  As described in detail above, the information recording medium of the present invention does not reduce CNR, overwrite characteristics, and recording sensitivity even in high-density recording in which the track pitch is 70% or less of the laser beam spot diameter, In addition, an information recording medium that does not cause cross erase can be realized.

  In addition, the information recording medium of the present invention realizes a narrow track pitch without degrading CNR, overwrite characteristics, and recording sensitivity even in high-density recording where the track pitch is 70% or less of the laser beam spot diameter. In addition, an information recording medium having a high recording density corresponding to an information recording / reproducing apparatus using an inexpensive semiconductor laser can be realized.

  Furthermore, the information recording medium of the present invention can achieve a narrow track pitch without reducing the CNR and recording sensitivity even in high-density recording in which the track pitch is 70% or less of the laser beam spot diameter. It is possible to realize an information recording medium that exhibits good overwrite characteristics even in high-density recording in which the recording mark length is less than half of the energy beam spot diameter.

  In addition, the information recording medium of the present invention realizes a narrow track pitch without degrading CNR, overwrite characteristics, and recording sensitivity even in high-density recording where the track pitch is 70% or less of the laser beam spot diameter. In addition, it is possible to realize an information recording medium in which the reproduction signal does not deteriorate even after rewriting many times about 100,000 times.

  In addition, the information recording medium of the present invention realizes a narrow track pitch without degrading CNR, overwrite characteristics, and recording sensitivity even in high-density recording where the track pitch is 70% or less of the laser beam spot diameter. In addition, it is possible to realize an information recording medium that does not cause a difference in recording sensitivity between when information is recorded on a land and when information is recorded on a groove.

  As described above, the present invention is useful as an information recording medium used for high-density recording in which the track pitch is 70% or less of the laser beam spot diameter.

1 is a structural diagram of an information recording medium of the present invention. It is a schematic diagram which shows the mode of the thermal diffusion of the information recording medium of a comparative example. It is a schematic diagram which shows the mode of the thermal diffusion of the information recording medium by one Example of this invention. It is a figure which shows the relationship between the thermal diffusion control layer film thickness of this invention, and the distance between thermal-diffusion layer-adjacent information recording track recording parts. It is a schematic diagram which shows the mode of the thermal diffusion of the information recording medium of a comparative example. It is a schematic diagram which shows the mode of the thermal diffusion of the information recording medium by one Example of this invention. It is a schematic diagram which shows the mode of the thermal diffusion of the information recording medium of a comparative example. It is a schematic diagram which shows the mode of the thermal diffusion of the information recording medium of a comparative example. 1 is a structural cross-sectional view of an information recording medium according to an embodiment of the present invention. 1 is a block diagram of an information recording / reproducing apparatus using an information recording medium according to an embodiment of the present invention. It is a figure which shows the relationship between the track pitch of the information recording medium in one Example of this invention, and the jitter rise by cross erase. It is a figure which shows the relationship between the groove | channel depth of the information recording medium in one Example of this invention, and the jitter rise by crosstalk. It is a figure which shows the layout of the recording mark and information recording track | truck of the information recording medium in one Example of this invention. It is a figure which shows the relationship between the thermal conductivity of the thermal-diffusion control layer of the information recording medium in one Example of this invention, and cross erase temperature holding time. It is a figure which shows the relationship between the film thickness of the thermal-diffusion layer of the information recording medium in one Example of this invention, and cross erase temperature holding time. It is a figure which shows the relationship between the thermal conductivity of the thermal-diffusion layer of the information recording medium in one Example of this invention, and cross erase temperature holding time.

Explanation of symbols

1, 1 ′: substrate
2, 2 ': lower protective layer,
3, 3 ′: recording layer,
4, 4 ': thermal diffusion control layer,
5, 5 ': thermal diffusion layer,
6: Adhesive,
d _g : groove depth,
7: Objective lens,
8: Energy beam
9: heating part,
10: border with adjacent information recording track,
11: Recording section of adjacent information recording track,
d _hc : film thickness of the thermal diffusion control layer,
_drh : the shortest distance between the recording portion of the adjacent information recording track and the thermal diffusion layer,
d _r : film thickness of the recording layer,
12, 12: Lower interface layer,
13, 13: upper interface layer,
14, 14: thermal buffer layer,
10-1: Optical disc,
10-2: Motor,
10-3: Optical head,
10-4: Preamplifier circuit,
10-6: Recording waveform generation circuit,
10-7: Laser drive circuit,
10-8: 8-16 modulator,
10-9: L / G servo circuit,
10-10: 8-16 demodulator,
15: Optical disc,
16: Optical disc,
17: Recording mark of adjacent information recording track,
18: Central track,
19: Track center,
20: Laser beam,
21: Cross erase observation point.

Claims (3)

In an information recording medium in which information is recorded by atomic arrangement change or / and electronic state change by irradiation of energy beam,
An information recording layer;
The information recording layer includes a thermal diffusion control layer, a thermal buffer layer made of a mixture of Cr and Cr ₂ O _3, and a thermal diffusion layer on the side opposite to the energy beam incident side of the information recording layer. recoding media.   2. The information recording medium according to claim 1, wherein the thermal diffusion layer is made of 97% or more aluminum.   2. The information recording medium according to claim 1, wherein the thermal diffusion layer is made of aluminum to which Ti or Cr is added.

Images