JP2005216484A - Phase change type information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable even a read only optical disk unit corresponding to only a DPD method to play back a phase change type disk premised on a push pull system such as a DVD-RAM. <P>SOLUTION: An interference film 3d changing the reflectance and the phase of a laser beam reflected by a mark and a non-mark is provided on the surface on the surface side irradiated with the laser beam of a recording film 3c. The phase difference generated in all reflection light beams caused by the phase difference between reflection light beam reflected by the non-mark and reflection light beam reflected by the mark both depending on the thickness of the interference film 3d and the phase difference between reflection light beam reflected by regions between grooves and reflection light beam reflected by the grooves both depending on the depth of the grooves is set so as to be in the range of 180 to 210°. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a phase change information recording medium in which an information recording medium capable of recording / reproducing such as a DVD-RAM can be reproduced by a reproduction-only optical disc apparatus.

  Nowadays, a so-called standard DVD has been expected as a next-generation information recording medium (hereinafter abbreviated as a disk) having a high information recording density. Such DVDs include a DVD-ROM that can only be played back, a DVD-R that can be added to and played back, and a DVD-RAM that can be recorded, played back and erased. There is a reproduction-only optical disk device corresponding to each disk and an optical disk device capable of recording and reproduction.

  As a tracking method in a reproduction-only optical disc apparatus, a DPD method (Differentialia Phase Detection) is adopted, and a push-pull method is planned as a tracking method in an optical disc apparatus capable of recording / reproduction and the like.

  In the DPD method, reflected light from a pit (hole) row as information is received by a light receiving element divided into four parts, and a sum signal of photoelectric conversion signals from two light receiving regions located on a diagonal line is obtained. This is a method of obtaining a tracking signal from the phase difference of the sum signal (see Patent Document 1). On the other hand, the push-pull method is a method of obtaining a tracking signal by dividing a light receiving element into two and comparing the symmetry of photoelectric conversion signals output from the two light receiving regions (see Patent Document 2).

  That is, information is recorded on a read-only disk such as a DVD-ROM by forming pits in the recording layer. The depth of the pit is set so that the phase difference between the laser beams reflected by the peripheral portion and the inside of the pit is approximately 180 degrees. In the DPD method, a tracking signal is detected from a change in the diffraction pattern from the pit.

On the other hand, in a phase change disk such as a DVD-RAM, information is recorded by forming marks by partially changing the crystal state of a recording layer. Further, due to the influence of the groove for tracking in the push-pull method, a clear change of the diffraction pattern due to the pits cannot be obtained as in the DVD-ROM.
Japanese Examined Patent Publication No. 2-56734 Japanese Examined Patent Publication No. 63-57859

  Therefore, since the tracking method is different between the read-only optical disk device and the recordable / reproducing optical disk device, there is a problem that the read-only optical disk device cannot reproduce a disc that can be recorded / reproduced such as a DVD-RAM.

  In this case, it is possible to provide a light receiving element so that both the DPD method and the push-pull method can be used in a read-only optical disc device, but in this case, there is a problem that the optical disc device becomes expensive.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a phase change information recording medium in which a disc such as a DVD-RAM can be reproduced even in a read-only optical disc apparatus that supports only the DPD method.

  The invention according to claim 1 has a spiral groove, a recording film is sandwiched between a protective film and a transparent substrate, and a mark is formed by irradiating the recording film of the groove with laser light. In the phase-change type information recording medium in which information is recorded by the mark and the non-mark, the reflectance of the laser beam reflected by the mark and the non-mark and the reflected light on the surface of the recording film on the laser beam irradiation surface side And an area between the grooves depending on the phase difference of the reflected light reflected by the non-mark and the mark depending on the thickness of the interference film and the depth of the groove The phase difference generated in the entire reflected light due to the phase difference of the reflected light reflected by the groove is set to be in the range of 180 degrees to 210 degrees.

  That is, an interference film is provided on the surface of the recording film on the laser light irradiation surface side, and the reflectance of the laser light reflected by the mark and the non-mark and the phase of the reflected light are changed by the interference film. At that time, the reflection between the groove and the groove depending on the phase difference of the reflected light reflected by the non-mark and the mark depending on the thickness of the interference film and the depth of the groove. The phase difference generated in the entire reflected light due to the phase difference of light is set to be in a range of 180 degrees to 210 degrees.

  In the invention according to claim 2, the thickness of the interference film is set so that the reflectance of the reflected light reflected by the mark is in the range of 40% to 60% with reference to the reflectance of the reflected light reflected by the non-mark. It is characterized by being set to.

  That is, in order to consider the influence of the groove on the phase difference between the non-mark and the mark, and to make the reflectivity appropriate at that time, the interference film so that the reflectivity of the mark with respect to the non-mark is in the range of 40% to 60% The thickness is set.

  According to the first aspect of the present invention, the non-mark that depends on the thickness of the interference film is reflected by the groove and the region between the grooves that depends on the phase difference of the reflected light reflected by the mark and the depth of the groove. Since the phase difference generated in the entire reflected light due to the phase difference of the reflected light is set to be in the range of 180 degrees to 210 degrees, the DPD method can be applied to the phase change type information recording medium, and the read-only optical disk apparatus However, it is possible to reproduce the phase change information recording medium.

  According to the invention of claim 2, since the thickness of the interference film is set to be in the range of 40% to 60% of the reflectance of the mark and the non-mark, the phase change is performed without deteriorating the quality of the reproduction signal. The DPD method can be applied to the type information recording medium, and the phase change type information recording medium can be reproduced even by the reproduction-only optical disc apparatus.

  The best mode of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a phase change type disc capable of recording, reproducing and erasing according to the present invention. FIG. 1A is a cross-sectional view of the phase change disk, and FIG. 1B is a plan view of the recording layer. FIG. 2 is a partial cross-sectional view showing in detail the configuration of the recording layer shown in FIG.

  In the phase change disk 1 according to the present invention, the recording layer 3 is sandwiched between the protective film 2 and the transparent substrate 4, and the groove 9 having a predetermined depth is directed from the center of the phase change disk 1 toward the outer periphery. It is formed in a spiral shape. The space between the grooves 9 is called a land 8.

  The recording layer 3 includes a heat radiation film 3a made of AITi, a heat retaining film 3b made of ZnSSio2, a recording film 3c made of Gesb, and an interference film 3d made of ZnSSio2.

  For recording and erasing information, the laser beam condensed by the objective lens is incident on the recording layer 3 from the transparent substrate 4 side, and the mark 6 is formed on the recording layer 3 of the groove 9 and has already been formed. This is done by forming the non-mark 7 by erasing the mark 6. Information is reproduced from a change in light intensity of reflected light by the mark 6 and the non-mark 7.

  At this time, if the temperature of the recording film 3c rises more than necessary due to laser light irradiation, the recording characteristics of the recording film 3c may fluctuate, and proper recording may not be performed. In order to prevent such a situation, the heat dissipation film 3a and the heat retaining film 3b are provided. The heat dissipation film 3a promotes heat dissipation or thermal diffusion, and the heat retaining film 3b controls the heat dissipation amount by the heat dissipation film 3 so that the recording temperature of the recording film 3c falls within an appropriate temperature range.

  As described above, information recording or the like is performed by condensing a laser beam on the recording layer 3 to form the mark 6 and the non-mark 7 on the recording layer 3, and the mark 6 and the non-mark 7 are crystals. The state is different. That is, when the recording film 3c is heated with laser light and then rapidly cooled, the recording film 3d becomes amorphous to form the mark 6, and when the cooling rate is slower than that, the recording film 3 crystallizes and the non-mark 7 is formed. Is done. The reflectance of the mark 6 and the non-mark 7 varies depending on the crystal state, and the reflectance is lower in the amorphous state.

  It is an object of the present invention to make it possible to apply both the DPD method and the push-pull method to the phase change type disk 1 having such a configuration. The push-pull method is a method that utilizes the asymmetry of the light intensity in the reflected light. Therefore, in the phase change type disk 1, the groove 9 as described above is formed, and the groove 9 and the land 8 are formed so as to have a predetermined height. Therefore, when a part of the laser beam condensed by the objective lens is irradiated on the land 8 with a deviation from the groove 9, a large asymmetry occurs in the light intensity distribution of the reflected light.

  Therefore, in the present invention, the optical depth of the groove 9 is set according to the characteristics shown in FIG. FIG. 3 shows the push-pull signal sensitivity with respect to the optical depth of the groove 9. The horizontal axis shows the optical depth of the groove 9 when the wavelength of the laser beam is λ, and the vertical axis shows the push-pull signal at that time. Shows sensitivity. The actual depth d of the groove 9 can be obtained by dividing the optical depth by the refractive index n of the transparent substrate 4 because the laser light passes through the transparent substrate 4. That is, the depth d of the groove 9 is given by d = λ / n / 8. For example, when the wavelength λ is λ = 64 nm and the refractive index n is n = 1.58, the depth d of the groove 9 is d = 50.6 nm.

  In the present invention, the optical depth of the groove 9 is set to λ / 8 so that the push-pull signal sensitivity is the highest, so that the push-pull method can be applied. By setting the depth of the groove 9 in this way, the phase difference between the land 8 and the groove 9 is shifted by 90 degrees, and the quality of the received light signal can be increased.

  On the other hand, in the case of the DPD method, a change in the diffraction pattern of reflected light is used. In the case of a disk with a groove such as the phase change disk 1 according to the present invention, the influence of the groove is taken into consideration. There is a need to.

  That is, when a hole (pit) is formed in a recording film as in a DVD-ROM and information is recorded, a change in the diffraction pattern of only the pit is detected, so the quality of the received light signal is high. Become. However, in the case of the phase change type disk 1, such holes do not exist, and information is recorded on the grooved disk due to the difference in crystal state between the mark 6 and the non-mark 7, so that the change in the diffraction pattern can be accurately detected. It is difficult to detect.

  Therefore, in the present invention, the interference film 3d is provided so as to cover the recording film 3c, and the thickness and thickness of the interference film 3d are changed so that the phase and reflectance of the reflected light from the mark 6 and the non-mark 7 are grooved. Try to be optimal for discs.

  FIG. 4 shows the phase of the reflected light reflected by the mark 6 and the relationship between the non-mark 7 and the mark 6 with respect to the film thickness of the interference film 3d. It is a figure which shows a reflectance change.

  In the figure, for example, it is understood that the thickness of the interference film 3d may be set to 70 nm or 220 nm in order to set the phase difference 6 of the mark 6 with respect to the non-mark 7 to 6 = 100 degrees. At that time, the reflectance Rc of the non-mark 7 is Rc = 10%, and the reflectance Ra of the mark 6 is Ra = 5%.

  5 to 7 show a state in which the phase difference (δ) of the mark 6 with respect to the non-mark 7 is changed by changing the thickness d of the interference film 3d in a state where the optical depth of the groove 9 is set to λ / 8. It is the figure which showed the relationship of DPD signal sensitivity (FIG. 5), 3T signal (FIG. 6), and 14T signal (FIG. 7).

  In each country, the reflectance (R) of reflected light from the mark 6 with respect to the reflectance of reflected light from the non-mark 7 is shown as a subparameter. For example, when the reflectance R is R = 50% and the reflectance of the actual non-mark 7 is 20%, the reflectance of the actual mark 6 is 20% × 50% = 10. %.

  Further, the 3T signal is a signal obtained from the shortest mark 6 in the phase change type disc 1, and the shortest mark can be detected with higher sensitivity when the signal is larger. On the other hand, the 14T signal is a signal obtained from the longest mark 6 on the disc and requires a certain level of magnitude.

  From FIG. 5, it can be seen that the DPD signal sensitivity is maximized when the phase difference 6 is 6 = 90 degrees, and the value increases as the reflectance R increases.

  Further, it can be seen from FIG. 6 that the 3T signal amplitude becomes the largest when the phase difference δ is in the vicinity of δ = 120 degrees, but is not so dependent on the reflectance R.

  Further, FIG. 7 shows that the phase difference δ has the largest 14T signal amplitude in the vicinity of δ = 90 degrees, and the 14T signal amplitude is relatively high when the reflectance R is R = 0% to 60%.

  From the above, in order to increase both the DPD signal sensitivity, the 3T signal amplitude, and the 14T signal amplitude when the reflected light phase difference between the groove 9 and the land 8 is set to 90 degrees, the mark 6 and It can be seen that the phase difference δ of the reflected light with the non-mark 7 may be set in the range of δ = 90 degrees to 120 degrees. That is, the DPD method and the push-pull method can be performed in the optimum state when the phase difference generated in the entire reflected light is in the range of 180 degrees to 210 degrees.

  The optimum phase difference of the reflected light between the mark 6 and the non-mark 7 and the phase difference of the reflected light between the groove 9 and the land 8 are deeply related, so that the phase difference generated in the entire reflected light when the groove depth is changed. It is preferable to change the phase difference of the mark so that the angle is 180 degrees to 210 degrees.

  On the other hand, the reflectivity should be large in order to determine the quality of the reproduction signal and the like. From this point of view, in FIGS. 5 and 6, the DPD signal sensitivity and the 3T signal amplitude are larger when the reflectance is larger. In FIG. 7, a good 14T signal amplitude is obtained around 0 to 60%. Therefore, it is understood that the condition of the reflectance R for increasing the DPD signal sensitivity, the 3T signal amplitude, and the 14T signal amplitude while suppressing the decrease in the reflectance is in the range of R = 40 to 60%.

  If the thickness d of the interference film 3d is set so as to be in such a range, the tracking signal can be detected by the push-pull method and the DPD method. Accordingly, it becomes possible to reproduce a phase change type disc such as a DVD-RAM that can be recorded and reproduced by a reproduction-only optical disc apparatus.

  FIG. 8 shows a conceptual configuration diagram of a general optical disc apparatus. The optical disk device includes a laser source 21 that generates and emits laser light, a half mirror 22 that reflects the laser light from the laser source 21, and transmits the reflected light from the phase change disk 1. The reflected laser beam is collected to form a laser spot on the phase change disk 1 and the reflected light from the phase change disk 1 that has been converged by the objective lens 23 and transmitted through the half mirror 22 is received. A light receiving element 24 that performs photoelectric conversion, a detection circuit 25 that detects a photoelectric conversion signal output from the light receiving element 24 and outputs a tracking signal, a servo signal of a focus signal, a reproduction signal, and the like, and a servo signal from the detection circuit 25 That receives the servo and controls the servo mechanism 29 such as the tracking motor or tracking coil and focus coil Road 26 receives a reproduction signal from the detection circuit 25 has information reproducing circuit 27 or the like for reproducing information.

  Then, the laser light emitted from the laser source 21 is reflected by the half mirror 22 and enters the objective lens 23, is condensed by the objective lens 23, and is applied to the recording layer 3 of the phase change disk 1.

  On the other hand, the reflected light from the phase change disk 1 is converged by the objective lens 23, passes through the half mirror 22, and is received by the light receiving element 24.

  In this way, the photoelectric conversion signal output from the light receiving element 24 is input to the detection circuit 25, and the servo signal supplied to the servo circuit 26 by the detection circuit 25 and the information reproduction signal supplied to the information reproduction circuit 27 are output. Is done.

  At this time, when the optical disk device is a read-only device, the light receiving element 24 is divided into four, and the detection circuit 25 follows the DPD method, and the sum of photoelectric conversion signals from two light receiving regions located on diagonal lines. A signal is obtained, a tracking signal is detected from the phase difference of each sum signal, and is output to the servo circuit 26.

  When the optical disc apparatus is a recording / reproducing apparatus, the light receiving element 24 is divided into two parts, and the detection circuit 25 compares the symmetry of photoelectric conversion signals output from the two light receiving areas according to the push-pull method. As a result, the tracking signal is detected and output to the servo circuit 26.

  In the phase change disk 1 according to the present invention, the thickness d of the interference film 3d is set so that the DPD method can be applied as described above, and the depth of the groove 9 is set so that the push-pull method can be applied. Since the setting is made, it is possible to perform reproduction not only on an optical disk apparatus capable of recording and reproduction but also on an optical disk apparatus dedicated to reproduction.

  In this way, the servo circuit 26 that has received the servo signal from the detection circuit 25 drives and controls the servo mechanism 29 based on the servo signal. Thereby, tracking control and focus control are performed.

FIG. 2A is a partial cross-sectional view, and FIG. 2B is a partial plan view of a phase change type information recording medium that is applied to the description of the best mode of the present invention. It is the cross-sectional schematic diagram which expanded and showed the principal part of invention. It is a figure which shows the change of the push pull signal sensitivity with respect to the depth of a groove. It is a figure which shows the phase and reflectance of a mark and a non-mark with respect to the thickness of an interference film. It is the figure which showed the DPD signal sensitivity when changing the phase difference of the reflected light of the mark with respect to a non-mark, using the reflectance of the reflected light of the mark with respect to the non-mark as a subparameter. It is the figure which showed 3T signal amplitude when changing the phase difference of the reflected light of the mark with respect to a non-mark, and the reflectance of the reflected light of the mark with respect to a non-mark as a subparameter. It is the figure which showed as a subparameter the 14T signal amplitude when changing the phase difference of the reflected light of the mark with respect to a non-mark, and the reflectance of the reflected light of the mark with respect to a non-mark. It is a figure which shows the structure of a general optical disk apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Phase change type disk 3 Recording layer 3a Heat dissipation film 3b Thermal insulation film 3c Recording film 3d Interference film 8 Land 9 Groove

Claims (2)

  It has a spiral groove, a recording film is sandwiched between a protective film and a transparent substrate, a mark is formed by irradiating the recording film of the groove with a laser beam, and information is recorded by the mark and non-mark. In the phase change type information recording medium to be performed, an interference film for changing the reflectance of the laser light reflected by the mark and the non-mark and the phase of the reflected light is provided on the surface of the recording film on both sides of the laser light irradiation. The reflected light reflected by the groove and the region between the grooves depending on the phase difference of the reflected light reflected by the non-mark and the mark depending on the thickness of the interference film and the depth of the groove A phase change type information recording medium characterized in that a phase difference generated in the entire reflected light due to the phase difference is set in a range of 180 degrees to 210 degrees. An interference film that changes the reflectance of the laser light reflected by the mark and the non-mark and the phase of the reflected light is provided on the surface on the laser light irradiation surface side of the recording film, and the thickness of the interference film is 2. The reflectance of reflected light reflected by the mark is set in a range of 40% to 60% based on the reflectance of reflected light reflected by the non-mark. Phase change type information recording medium.

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