JP5136235B2 - Optical information recording medium and design method - Google Patents

Description

  The present invention relates to an optical information recording medium and a design method. More specifically, the present invention relates to an optical information recording medium having a phase change layer whose optical characteristics change nonlinearly depending on temperature or light intensity, and such an optical. The present invention relates to a method for designing a dynamic information recording medium.

  An optical disk medium is known as an example of an optical information recording medium that reproduces information by laser light irradiation. Optical discs are classified according to their functions into a reproduction-only type (ROM medium) that only reproduces recorded information, a write-once type that can be recorded only once, and a rewritable type that can rewrite data. Among these, ROM media are widely used as distribution media for images or package software because they can be copied at low cost and at high speed by using a technique called injection molding. In addition, the write-once and rewritable markets have also expanded, driven by the proliferation of ROM media. In consideration of further progress in image quality improvement in the future, it is desired that the optical disk has a larger capacity.

  The capacity of the optical disc depends on the beam diameter of the laser beam used for reproducing information. The smaller the beam diameter, the higher density information can be reproduced without error. In the case of a ROM medium, geometrical irregularities formed on a substrate generally called a pit represent information, and in order to increase the capacity, it is necessary to form smaller pits. The most effective means for accurately reading out information from minute pits is to reduce the beam diameter of the laser beam.

  By the way, even if the light emitted from the laser diode is converged through the objective lens, it does not converge to one point due to the influence of diffraction, but becomes a beam having a finite size. In general, this is called the diffraction limit. When the wavelength of the laser beam is λ and the numerical aperture of the objective lens is NA (Numerical Aperture), λ / (4NA) is the limit of the reproduction resolution. Specifically, when λ = 405 nm and NA = 0.65, λ / (4NA) ≈156 nm, and bits having a length of 156 nm or less cannot be accurately read.

  In order to accurately read out a pit having a length of 156 nm or less under the above conditions, it is necessary to make the wavelength of the laser light shorter than 405 nm or make the NA of the objective lens larger than 0.65. However, current laser technology is limited in providing short wavelength lasers. In addition, a polycarbonate (PC) substrate generally used for optical disks is also problematic in that the substrate is not transparent to light having a wavelength shorter than 405 nm, that is, the light transmittance is reduced. . Regarding the NA, there is a problem that the cost becomes high to manufacture an objective lens having a large NA. Further, the larger the numerical aperture of the objective lens, the shorter the distance between the pickup and the disc. For this reason, when the NA is increased, the risk of collision between the optical head and the disk increases, and the collision between both increases the risk of damaging the disk surface and leading to data loss.

  A medium super-resolution technique is known as a technique for improving the reproduction resolution beyond the diffraction limit. In the medium super-resolution, a medium using a super-resolution layer whose optical characteristics change nonlinearly with temperature or light intensity is used. Patent Document 1 describes an optical information recording medium using a phase change layer as a super-resolution layer. FIG. 12 shows an enlarged view of a pit row formed in advance on a transparent substrate of a super-resolution optical disc. The laser beam that has passed through the objective lens is irradiated as a focused spot on the medium. The super-resolution layer absorbs the irradiated laser light and the temperature rises.

  The super-resolution layer changes from the solid phase state to the liquid phase state in the melted region that exceeds the melting point of the super-resolution layer, in the region where the temperature is increased by laser light irradiation. The region that has changed to the liquid phase state has an increased reflectivity and functions as an opening for reproducing the recording mark. As a result, the size of the aperture that contributes to reproduction can be made smaller than the focused spot size determined by the diffraction limit. Thereby, information on a minute recording mark below the reproduction limit can be read out as a super-resolution reproduction signal.

A phase change layer is known as one of the super-resolution layers. Since the phase change layer exhibits different optical characteristics between the crystalline state and the molten state, super-resolution reproduction can be realized by using a reversible change between the crystalline state and the molten state. That is, since the optical characteristics change greatly between the crystalline state and the molten state, it is possible to reproduce pits below the diffraction limit.
JP-A-5-89511

  FIG. 13 shows the state of the phase change layer when the super-resolution reproduction operation is performed using the phase change layer. Usually, the super-resolution medium has a laminated structure such as a protective layer, a super-resolution layer, and a reflective layer. Of these, only the super-resolution layer (phase change layer) is illustrated in FIG. 13 for the sake of simplicity. In FIG. 13, the pit row is also not shown. Three phases of phase change layers are mixed in the focused beam irradiation region. That is, (A) a region where heat is held and melted in the vicinity of the center of the laser beam, (B) once held at a high temperature and melted, the temperature decreases as the laser beam moves, and the liquid phase changes to a solid phase. Returned region, (C) Although the temperature rises, there are three types of regions: the region that is the beam edge, the temperature upper layer width is narrow, and the region that remains in the solid phase without reaching the melting point exists.

  Since the optical constants of the phase change layer are different in the above three types of states, the reflectance is not the same. However, there is no conventional example that discloses that three types of states are mixed in the beam during the super-resolution operation, and all three reflectances in the above (A) to (C) have been considered so far. The media design has not been made. For this reason, the S / N (signal-to-noise ratio) of the minute mark reproduction signal is insufficient, and it is difficult to obtain good detection performance (low error rate).

  An object of the present invention is to provide an optical information recording medium having a phase change layer and an optical information recording medium capable of sufficiently ensuring a reproduction signal S / N of a minute mark, and a design method thereof.

In order to achieve the above object, an optical information recording medium of the present invention is a super-resolution medium having a phase change layer, which is a state of the phase change layer when irradiated with laser light used for information reproduction. There are a dissolved state, a crystallized state without dissolution, and a crystallized state after dissolution, and the reflectance of the super-resolution medium in the region where the phase change layer is in a dissolved state is RA, and the phase change layer is RA / (RB + RC) is 1 where RB is the reflectivity of the super-resolution medium in the region crystallized after dissolution, and RC is the reflectivity of the super-resolution medium in the region crystallized without being dissolved. .5 or more.

  A medium configuration design method for an optical information recording medium according to the present invention is a method for designing a medium configuration of a super-resolution medium having a phase change layer, wherein the phase when the laser beam used for information reproduction is irradiated. As the state of the change layer, there are a dissolved state, a state crystallized without being dissolved, and a state crystallized after dissolution, and the reflectivity RA of the super-resolution medium in the region where the phase change layer is in a dissolved state, Based on the reflectivity RB of the super-resolution medium in the region where the phase change layer is crystallized after being dissolved, and the reflectivity RC of the super-resolution medium in the region where it is crystallized without being dissolved The configuration is determined.

  The optical information recording medium of the present invention can sufficiently increase the reproduction signal S / N of a minute mark.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a cross section of an optical information recording medium according to an embodiment of the present invention. The optical information recording medium includes a substrate 101, protective layers 102 and 104, a super-resolution layer 103, and a reflective layer 105. The substrate 101 has recording pits formed in advance as geometric irregularities. The optical information recording medium has a configuration in which a protective layer 102, a super-resolution layer 103, a protective layer 104, and a reflective layer 105 are sequentially stacked on a substrate 101.

For the protective layers 102 and 104, a dielectric such as ZnS—SiO ₂ , SiN, SiO ₂ , SiON, Ta ₂ O ₅ can be used. The protective layer may be formed of only one layer, or may be formed of a multilayer film in which dielectrics are sequentially stacked. The super-resolution layer 103 is a phase change layer. A general phase change material such as InSb, GeBiTe, Bi ₂ Te ₃ , GeSbTe, Sb ₂ Te ₃ , GaSb, or AgInSbTe can be used for the super-resolution layer 103. An interface layer having a thickness of about 3 nm to 5 nm may be appropriately added between the super-resolution layer 103 and the protective layer in order to improve reliability. For the reflective layer 105, an Al alloy, an Ag alloy, or the like can be used.

  At the time of information reproduction from the optical information recording medium, the laser light is incident from the surface opposite to the protective layer 102 of the substrate 101. The state of the super-resolution layer 103 will be described with reference to FIG. 13. There are three types of super-resolution layers (phase change layers) in the region irradiated with the reproduction laser beam. That is, (A) a region where heat is held and melted in the vicinity of the center of the laser beam, (B) once held at a high temperature and melted, the temperature decreases as the laser beam moves, and the liquid phase changes to a solid phase. Returned region, (C) Although the temperature rises, there are three types of regions: the region that is the beam edge, the temperature upper layer width is narrow, and the region that remains in the solid phase without reaching the melting point exists.

  In the region (A), the phase change layer is in a molten liquid phase state, and the atomic arrangement is randomly disordered as in the amorphous state. However, in the region (A), the film is kept at a higher temperature than in the amorphous state of the solid phase, that is, rapidly cooled from the melted state and returned to the solid phase with disordered arrangement. Atomic motion is more active and the atomic arrangement is different from the amorphous state of the solid phase. As a result, the optical constants are different between the amorphous state and the molten state of the solid phase. In order to perform optical design of a super-resolution medium with high accuracy, an optical constant in a molten state is necessary.

  In the region (B), the phase change layer is in a crystallized state after melting. In the temperature region immediately below the melting point, the crystal nucleation frequency is low and the crystal growth rate is high, so that in the melt crystallization, a crystal state with large crystal grains is formed. On the other hand, the region (C) is a region where crystallization has proceeded in the solid phase without reaching the melting point. When the film is in an amorphous state immediately after film formation and is crystallized by heating from room temperature to a temperature lower than the melting point, crystallization proceeds through a temperature region where the crystal nucleation frequency is high. A crystalline state is formed. Although there are phase change layers that are in a crystalline state immediately after film formation, in such a film, the crystal state in the region (C) is almost the same as the crystal state immediately after film formation. In (B) and (C), since the crystal states are not the same, the optical constant of each crystal state is necessary for the optical design of the super-resolution medium.

  As an example, a super-resolution operation using an increase in reflectivity by melting will be described. The reflectivity in the region (A) is used for reproducing a mark, and is preferably as large as possible. On the other hand, the reflectivity in the region (B) and the region (C) is a disturbance to the reproduction of fine marks, so it is desirable to make it as small as possible. The inventor measures optical constants and reflectances in each of the three states (A), (B), and (C), and calculates the reflectances in both states (B) and (C). It has been found that the reproduction S / N (detection performance) can be improved by making it sufficiently lower than the reflectance in the state of A). That is, the reproduction S / N can be improved by setting the reflectance in the regions (A), (B), and (C) to RA, RB, and RC, respectively, and RA / (RB + RC) to be a predetermined value or more. I found.

  The RA, RB, and RC vary depending on the film thickness of each layer (FIG. 1) constituting the optical information recording medium. The inventor obtained the optical constant of the phase change layer and examined how RA, RB, and RC change with respect to the change in film thickness. Further, the present inventor creates an optical information recording / reproducing medium having RA / (RB + RC) equal to or higher than a predetermined value, measures the reproduction performance, and sets RA / (RB + RC) to be equal to or higher than the predetermined value. It was confirmed that the reproduction S / N could be improved. The ability to improve the reproduction S / N means that information from minute pits below the diffraction limit can be read accurately, and the recording capacity can be greatly improved by adopting the above configuration. .

Hereinafter, description will be made using examples. First, the first embodiment will be described. First, the optical constant of the phase change layer (InSb layer) is obtained. As a sample, a glass substrate having a diameter of 50 mm and a thickness of 350 mm on which ZnS—SiO ₂ : 50 nm, GeN: 5 nm, InSb: 10 nm, GeN: 5 nm, ZnS—SiO ₂ : 50 nm was sequentially laminated by sputtering was used. It was. Note that the reason why the InSb layer is sandwiched between protective layers (ZnS—SiO ₂ layers) is that the InSb layer disappears due to sublimation or evaporation when heated to the melting point in the state of the InSb layer alone.

  FIG. 2 shows a test apparatus. The sample is placed on a stage 203 having a diameter of about 10 mm. The sample on the stage 203 is heated by the heating source 204. By controlling the amount of heat supplied from the heating source 204, the amount of temperature rise in the sample can be controlled. After the temperature rise, heating is stopped, natural cooling or cooling with nitrogen gas purge is performed, and the sample is cooled to room temperature. When measuring transmittance and reflectance, the light source 201 emits light, and the sample is irradiated with light from the light source 201 via the polarizing beam splitter 202 and the quarter wavelength plate 207. The light applied to the sample has a diameter of about 1 mm and is parallel light that is not condensed.

  The light transmitted through the sample is incident on the photodetector 205. The photodetector 205 detects the transmitted light of the sample. The light reflected by the sample passes through the quarter-wave plate 207 in the reverse direction, is reflected by the polarization beam splitter 202, and enters the photodetector 206. The photodetector 206 detects the reflected light of the sample. Based on the detection signals of the photodetectors 205 and 206, the transmittance and reflectance of the sample can be obtained.

Here, since the sample includes a layer other than the InSb layer, the transmittance and the reflectance that can be obtained using the test apparatus are the transmittance and the reflectance in the state including the layer other than the InSb layer. . Among the layers constituting the sample, the films other than InSb have sufficiently high melting points for both ZnS—SiO ₂ and GeN, so that the optical constants can be measured separately in a single layer state. The optical constant for InSb alone can be calculated from the transmittance and reflectance of the sample, the known optical constants and film thicknesses of ZnS—SiO ₂ and GeN, and the film thickness of InSb.

  The sample was placed in an optical system as shown in FIG. 2, and the temperature dependence of the reflectance / transmittance in the temperature range from room temperature to 520 ° C. was examined. In FIG. 3, the measurement result of the temperature dependence of a reflectance and a transmittance | permeability is shown. In FIG. 3, (i) corresponds to a molten state, (ii) corresponds to a state cooled to room temperature after melting, and (iii) corresponds to a state immediately after film formation. In FIG. 3, a large hysteresis is observed in the reflectance around 500 ° C., which is due to the influence of overheating / overcooling of melting / solidification.

  When TEM (Transmission Electron Microscope) observation was performed on the samples in the states (ii) and (iii), InSb was in a crystalline state with a particle size of about 300 nm in (ii), and (iii) was about 50 nm in particle size. It was confirmed that this was a crystalline state. In addition, when the TEM observation was performed also about the sample heated and cooled to about 400 degreeC lower than melting | fusing point, the crystal state was equivalent to (iii). Since the states (i) to (iii) correspond to the states (A) to (C) shown in FIG. 13, they will be expressed as (A), (B), and (C) hereinafter. .

From the measurement results, the optical constants of InSb in each of the states (A) to (C) were obtained. Table 1 below shows the optical constants of InSb in the states (A) to (C). Since (A) is in a molten state and (B) and (C) are in a crystallized state, (A) and (B) or (A) and (C) have different optical constants. Although (B) and (C) are both in a crystalline state, the particle diameters are different and the optical constants are different. There has never been disclosed a technique related to the design of a super-resolution medium focusing on the difference in optical constant between (B) and (C), and conventionally, either one of the optical states of (B) or (C) is used. Constants have been used in the design.

Next, the present inventor calculated the reflectance of the super-resolution medium using the obtained optical constant of InSb. As the medium configuration, a configuration was assumed in which ZnS—SiO ₂ , GeN, InSb, GeN, ZnS—SiO ₂ , and an Ag alloy were stacked in this order from the substrate side on which the laser light was incident. Here, InSb corresponds to the super-resolution layer 103 in FIG. 1, and ZnS—SiO ₂ sandwiching InSb corresponds to the protective layers 102 and 104. Further, the Ag alloy corresponds to the reflective layer 105, and GeN corresponds to an interface layer between the protective layers 102 and 104 and the super-resolution layer 103.

The assumed film thickness of each part in the medium was 13 nm of InSb, 50 nm of Ag alloy, and 5 nm of GeN. The film thickness of the ZiS—SiO ₂ layer (protective layer 104) between the super-resolution layer 103 and the reflective layer 105 was 15 nm. The film thickness of ZnS—SiO ₂ (protective layer 102) on the substrate 101 side was a design parameter, and the RA, RB, and RC at each film thickness were calculated while changing the film thickness.

FIG. 4 shows an example of the calculation result of the reflectance. When the film thickness of ZnS—SiO ₂ on the substrate side is changed, the reflectances RA, RB, and RC in the states (A), (B), and (C) change as shown in FIG. Referring to FIG. 4, it can be seen that RB and RC are almost equal and the difference between them is small until the film thickness of ZnS—SiO ₂ is about 50 nm. However, as the film thickness of ZnS—SiO ₂ becomes thicker than 50 nm, the difference between RB and RC increases. In addition, since RC is related to the servo operation, in order to perform the servo operation stably, it is preferable to have a certain reflectance or more. Specifically, in order to ensure stable servo operation, RC is preferably 5% or more.

  FIG. 5 shows the relationship between the film thickness and RA / (RB + RC) for the film thickness range of RC ≧ 5%. Referring to FIG. 5, it can be seen that when the film thickness is about 45 nm to 50 nm, the value of RA / (RB + RC) is larger than the value for other film thickness ranges. From the viewpoint of super-resolution reproduction performance, it is preferable that the protective layer 102 has a film thickness of about 45 nm to about 50 nm, which can secure a certain RC or more and both RB and RC are sufficiently smaller than RA. It is assumed that there is.

  As a comparative example, let us consider a case where only RA and RC are considered as design parameters and a medium configuration is selected based on RA / RC values. FIG. 6 shows the relationship between the film thickness in the range of RC ≧ 5% and RA / RC. Referring to FIG. 6, when the medium configuration is selected based on RA / RC, RA / RC is maximized at about 85 nm. Therefore, it is considered that the thickness of the protective layer 102 is preferably about 85 nm. However, referring to FIG. 5, since the value of RB increases at a film thickness of about 80 nm, the value of RA / (RB + RC) decreases, and from the viewpoint of super-resolution reproduction performance, it does not become a preferable medium configuration. Conceivable.

  Next, Example 2 will be described. In Example 2, based on the examination of Example 1, an optical information recording medium (Disk 1) in which the thickness of the protective layer 102 is 45 nm and an optical information recording medium (in which the thickness of the protective layer 102 is 85 nm) ( Disk 2) was created and the reproduction performance was compared. That is, the reproduction performance was measured in Disk 1 that selected the media configuration based on RA / (RB + RC) and Disk 2 that selected the media configuration based on RA / RC, and the two were compared.

  The film thickness of the prepared optical information recording medium (Disk1, Disk2) other than the protective layer 102 was the same as the film thickness of each part of the medium assumed in Example 1. That is, the thickness of the super-resolution layer 103 (InSb) was 13 nm, the thickness of the protective layer 104 was 15 nm, and the thickness of the reflective layer 105 (Ag alloy) was 50 nm. The film thicknesses of the interface layer (GeN) between the protective layer 102 and the super-resolution layer 103 and the interface layer (GeN) between the super-resolution layer 103 and the protective layer 104 were 5 nm, respectively.

Disk 1 and Disk 2 were ROM substrates in which a pit having a depth of 45 nm and a minimum length of 100 nm was formed on a PC substrate having a thickness of 0.6 mm. The pit train was recorded by (1-7) modulation, and the shortest pit length was 100 nm and the longest pit length was 400 nm. The created Disk 1 and Disk 2 were evaluated using an optical head with a wavelength of 405 nm and NA = 0.65 at a linear velocity of 6.6 m / s while changing the reproduction power. In the range of 7 mW to 3.3 mW, a good error rate of about 10 ⁻⁶ was obtained. On the other hand, in Disk 2, an error rate lower (good) than 10 ⁻⁴ could not be obtained.

The inventor measured the reflectance corresponding to RA, RB, and RC in Disk 1 and Disk 2, and verified RA, RB, and RC in the created Disk 1 and Disk 2. This verification was performed according to the following procedure.
(1) In the mirror region of Disk 1 and Disk 2 (with a radius of about 22 mm), 0.5 mW power laser light (wavelength 405 nm) that does not change the state of the super-resolution layer 103 (InSb) is irradiated and the reflectance is measured. . This reflectance corresponds to RC. The reason for using the mirror region is that the mirror region is not affected by diffraction due to pits and is suitable for reflectance measurement.
(2) In the mirror region of Disk 1 and Disk 2, after irradiating the laser beam (wavelength 405 nm) of 3 mW power that melts the excess image layer 103 (InSb), the optical head is moved by 0.5 mm in the radial direction. A 0.5 mW power laser beam (wavelength of 405 nm) is irradiated near the center of a 0.5 mm wide region where melt crystallization has occurred, and the reflectance is measured. This reflectance corresponds to RB.
(3) In the mirror region of Disk 1 and Disk 2, a laser beam having a large beam diameter of about 2 μm is irradiated with high power to form a melting region. The laser wavelength at this time was 1600 nm. The same area as the melting area is irradiated with 0.5 mW power laser light (wavelength 405 nm), and the reflectance is measured. The laser beam with a wavelength of 405 nm used for information reproduction is condensed to about 0.5 mm, and since it can be considered that the entire condensed beam is melted, the reflectance measured by this procedure is equivalent to RA. To do.

  When the difference between the reflectance measured by the above procedure and the design values of RA, RB, and RC was determined, the difference was 1% or less for both Disk1 and Disk2. That is, it was confirmed that the reflectivity as designed was obtained at the Disk 1 and the Disk 2.

  Next, Example 3 will be described. In Example 3, in addition to the optical information recording medium in which the thickness of the protective layer 102 used in Example 2 is 45 nm, the optical information recording in which the thickness of the protective layer 102 is 55 nm, 65 nm, 75 nm, and 85 nm. Media were created, RA / (RB + RC) and error rate were determined for each of them, and the relationship between the two was examined. The film other than the protective layer 102 and other measurement conditions were the same as those in Example 2.

FIG. 7 shows the relationship between RA / (RB + RC) and error rate. When the relationship between RA / (RB + RC) and the error rate is obtained from the relationship between the film thickness and RA / (RB + RC) and the relationship between the film thickness and error rate, the graph shown in FIG. 7 is obtained. Referring to FIG. 7, it can be seen that there is a clear correlation between RA / (RB + RC) and the error rate, and the error rate decreases as the value of RA / (RB + RC) increases. That is, it can be seen that a better error rate can be obtained as the value of RA / (RB + RC) increases. It can also be seen that RA / (RB + RC) should be 1.5 or more in order to obtain an error rate of 10 ⁻⁴ or less that can be regarded as an allowable limit of the apparatus.

  In the optical information recording medium having a large value of RA / (RB + RC), RB and RC are substantially equal. Therefore, when designing the medium (selecting the medium configuration), it is possible to set the design policy to make RB and RC substantially the same. For example, an optical information recording medium in which RA / (RB + RC) is equal to or greater than a predetermined value can be obtained by adopting a medium configuration in which the difference in reflectance between RB and RC is within 2%.

As a comparative example, the relationship between the RA / RC and the error rate was obtained from the RA / RC measurement results and error rates of the optical information recording media of each film thickness. Table 2 shows RA / RC measurement results and error rate measurement results. FIG. 8 shows the relationship between RA / RC and error rate. Referring to FIG. 8, there is no clear correlation between RA / RC and error rate, and it can be seen that RA / RC cannot be an index representing the performance of the medium.

  Example 4 will be described. In Example 4, when selecting a media configuration, it was examined whether or not a suitable media configuration could be selected using only RA / RB as an index. That is, referring to FIG. 4, since RA / (RB + RC) is large in a region where RB is small, a medium configuration suitable for super-resolution reproduction can be selected by paying attention to RA and RB. It seems to be. In view of this, for a medium configuration different from that in Example 1, it was examined whether or not a suitable medium configuration could be selected using only RA / RB as an index.

FIG. 9 shows the relationship between RA, RB, RC and the film thickness of the protective layer 102 (FIG. 1) in an optical information recording medium having a medium configuration different from that of the first embodiment. As a medium configuration, in order from the substrate 101 side, a protective layer 102 (ZnS—SiO ₂ : film thickness is a design parameter), an interface layer (GeN: 5 nm), a super-resolution layer 103 (InSb: 8 nm), and an interface layer (GeN: 5 nm), a protective layer 104 (ZnS—SiO ₂ : 15 nm), and a reflective layer 105 (Ag alloy: 50 nm) were stacked. Even if the RB is low, there is a case where the RC becomes large, and it cannot be said that this medium has a medium configuration suitable for super-resolution reproduction.

  FIG. 10 shows the relationship between RA / (RB + RC) and the thickness of the protective layer 102 in the optical information recording medium having the above configuration. As shown in FIG. 10, the value of RA / (RB + RC) in the optical information recording medium having the above-described structure may exceed 1.5, but the maximum value is lower than that in FIG. Therefore, based on the value of RA / (RB + RC), it can be determined that the above configuration is not a medium configuration suitable for super-resolution reproduction. In this case, the medium configuration may be changed by changing the film thickness other than the protective layer 102.

  FIG. 11 shows the relationship between RA / RB and the thickness of the protective layer 102 in the optical information recording medium having the above configuration. Referring to FIG. 11, the value of RA / RB is large in the range of about 30 nm to 40 nm, and by setting the thickness of the protective layer 102 in that range, a suitable medium configuration can be obtained. I think. That is, it can be seen that only RA and RB cannot correctly determine whether the above configuration is a medium suitable for super-resolution reproduction, and a suitable medium configuration cannot be selected.

In summary, the optical information recording medium has a super-resolution medium RA in the region where the phase change layer is in a dissolved state, and the super-resolution medium in a region where the phase change layer is crystallized after being dissolved. RA / (RB + RC) is equal to or greater than a predetermined value, where RB is the reflectivity of RB, and RC is the reflectivity of the super-resolution medium in the region crystallized without melting. By setting RA / (RB + RC) to a predetermined value or more, the reproduction S / N can be improved and high-density recording becomes possible. In particular, by setting RA / (RB + RC) to 1.5 or more, a good error rate of 10 ⁻⁴ or less can be obtained.

  In designing the medium configuration, the reflectance RA of the super-resolution medium in the region where the phase change layer is in the dissolved state, and the reflectance RB of the super-resolution medium in the region where the phase change layer is crystallized after being dissolved. The medium configuration is determined based on the reflectance RC of the super-resolution medium in a region that is crystallized without being dissolved. Considering separately the reflectivity (RB) of the region crystallized after melting and the reflectivity (RC) of the region crystallized without melting, RB, RC and the region in the melted state By selecting the medium configuration based on the reflectance RA, it is possible to obtain a medium configuration that can improve the reproduction S / N.

In each of the above embodiments, an example in which InSb is used for the super-resolution layer (phase change layer) has been described. This is because InSb has a large difference between the optical constant in the molten state and the optical constant in the crystalline state, and it is easy to make RA / | RB + RC | large and it is suitable as a super-resolution layer. . However, the super-resolution layer is not limited to InSb, and Bi ₂ Te ₃ or GeSbTe can also be used. Even in such a case, the reproduction S / N can be improved by selecting a medium configuration based on RA, RB, and RC, and setting RA / (RB + RC) to a predetermined value or more.

  In each of the above embodiments, the medium configuration was obtained in which the RA / (RB + RC) value was equal to or greater than a predetermined value by changing the thickness of the protective layer on the substrate side. However, since RA, RB, and RC change depending on the combination of the film thicknesses of the layers shown in FIG. 1, the film thickness to be changed is not limited to the protective layer on the substrate side, but a film other than the protective layer on the substrate side. A medium configuration in which RA / (RB + RC) is not less than a predetermined value may be obtained by changing the thickness. Further, a medium configuration in which RA / (RB + RC) is a predetermined value or more may be obtained by factors other than the film thickness adjustment of each part.

  Although the present invention has been described based on the preferred embodiments, the optical information recording medium and the design method of the present invention are not limited to the above-described embodiments. Modifications and changes are also included in the scope of the present invention.

1 is a cross-sectional view showing an optical information recording medium according to an embodiment of the present invention. The block diagram which shows the outline | summary of the apparatus which measures a reflectance / transmittance. The graph which shows an example of the change of the reflectance / transmittance observed when the sample which has a phase change layer is heated and cooled. The graph which shows an example of the relationship between the reflectance of a super-resolution medium, and the thickness of a protective layer. The graph which shows the relationship between the film thickness of a protective layer, and RA / (RB + RC). The graph which shows the relationship between the film thickness of a protective layer, and RA / RC. The graph which shows the relationship between RA / (RB + RC) and the error rate characteristic of a super-resolution medium. The graph which shows the relationship between RA / RC and the error rate of a super-resolution medium. The graph which shows another example of the relationship between the reflectance of a super-resolution medium, and the thickness of a protective layer. The graph which shows the relationship between the film thickness of a protective layer, and RA / (RB + RC). The graph which shows the relationship between the film thickness of a protective layer, and RA / RB. The figure which expands and shows the pit row | line | column formed in the super-resolution medium. The figure which shows the state of a phase change layer when performing super-resolution reproduction | regeneration operation | movement using a phase change layer.

Explanation of symbols

101: Substrate 102, 104: Protective layer 103: Super-resolution layer 105: Reflective layer 201: Light source 202: Polarizing beam splitter 203: Stage 204: Heat source 205, 206: Photo detector 207: 1/4 wavelength plate

Claims (4)

A super-resolution medium having a phase change layer,
As the state of the phase change layer when irradiated with laser light used for information reproduction, there are a dissolved state, a crystallized state without dissolution, and a crystallized state after dissolution, and the phase change layer is dissolved. The reflectance of the super-resolution medium in the region in the state is RA, the reflectance of the super-resolution medium in the region in which the phase change layer is crystallized after dissolution is RB, the region in the crystallized state without being dissolved An optical information recording medium in which RA / (RB + RC) is 1.5 or more, where RC is the reflectance of the super-resolution medium. The optical information recording medium according to claim 1 , wherein RC ≧ 5% is satisfied. The optical information recording medium according to claim 1 , wherein RB and RC are substantially the same. A method for designing a medium configuration of a super-resolution medium having a phase change layer, comprising:
As the state of the phase change layer when irradiated with laser light used for information reproduction, there are a dissolved state, a state crystallized without being dissolved, and a state crystallized after dissolution,
Reflectance RA of the super-resolution medium in the region where the phase change layer is in the dissolved state, reflectivity RB of the super-resolution medium in the region where the phase change layer is crystallized after dissolution, and crystallization without dissolution A design method for determining a medium configuration based on a reflectance RC of a super-resolution medium in a region in a finished state.

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