JPH10283671A - Phase change type information recording medium - Google Patents

Abstract

(57) [Problem] To enable reproduction of a phase-change type disc on the premise of a push-pull system, such as a DVD-RAM, even in a read-only optical disc apparatus compatible only with the DPD method. . SOLUTION: An interference film 3 for changing a phase difference and a reflectance of a laser beam reflected by a mark and a non-mark of the recording film 3c on a surface of the recording film 3c on a side irradiated with the laser beam.
d is provided. The thickness of the interference film 3d is set so that the phase difference between the reflected light of the mark and the non-mark is in the range of 90 to 120 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type information recording medium in which an information recording medium such as a DVD-RAM capable of recording and reproduction can be reproduced by a reproduction-only optical disk device.

[0002]

2. Description of the Related Art Today, as a next-generation information recording medium having a high information recording density (hereinafter, abbreviated as a disc), a DVD which is a so-called standard is expected. Such a D
The VD includes a DVD-ROM that can perform only reproduction, a DVD-R that can perform additional recording and reproduction, and a DVD-RAM that can perform recording, reproduction, and erasure. There is a read-only optical disk device and an optical disk device capable of recording / reproduction corresponding to each disk.

[0003] A tracking method in a read-only optical disk device is a DPD (Differential) method.
A phase detection (phase difference detection method) is adopted, and a push-pull method is scheduled as a tracking method in an optical disk device capable of recording and reproducing.

In the DPD method, light reflected from a pit (hole) row, which is information, is received by a four-divided light receiving element, and a sum signal of photoelectric conversion signals from two diagonally located light receiving areas is obtained. And a method of obtaining a tracking signal from the phase difference between the respective sum signals (see Japanese Patent Publication No. 2-56734). On the other hand, the push-pull method divides the light receiving element into two parts,
This is a method of obtaining a tracking signal by comparing the symmetry of the photoelectric conversion signals output from the two light receiving regions (see Japanese Patent Publication No. 63-57859).

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

On the other hand, in a phase change type disc such as a DVD-RAM, information is recorded by forming a mark by partially changing a crystal state of a recording layer. Also,
Due to the influence of grooves for tracking in the push-pull method, it is not possible to obtain a clear change in the diffraction pattern due to pits as in DVD-ROM.

[0007]

Therefore, since the tracking method is different between a read-only optical disc device and an optical disc device capable of recording and reproduction, a read-only optical disc device can record and reproduce data on a DVD-RAM and the like. There is a problem that the disc cannot be played.

In this case, the read-only optical disk drive has a D
It is possible to provide the light receiving element so that both the PD method and the push-pull method can be used, but in such a case, there is a problem that the optical disk device becomes expensive.

Accordingly, the present invention is directed to a read-only optical disk device which is compatible only with the DPD method.
-To provide a phase change type information recording medium capable of reproducing a disk such as a RAM.

[0010]

According to the first aspect of the present invention, a recording film is sandwiched between a protective film having a spiral groove and a transparent substrate, and the recording film of the groove is irradiated with laser light. In a phase change type information recording medium in which a mark is formed and information is recorded by the mark and the non-mark, the reflection of the laser light reflected by the mark and the non-mark on the surface of the recording film on the side of the laser light irradiation surface. An interference film for changing the ratio and the phase of the reflected light is provided, and the thickness of the interference film is set so that the phase difference between the reflected light reflected by the non-mark and the mark is in the range of 90 degrees to 120 degrees. It is characterized by having been set as follows.

That is, the phase difference of the laser beam reflected by the mark and the non-mark is taken into consideration in the DPD even in the phase change type information recording medium in consideration of the influence of the phase difference generated by the groove.
In order that the method can be applied, an interference film is provided on the surface of the recording film, and the thickness of the interference film is adjusted so that the phase difference of the reflected light reflected by the mark and the non-mark is in the range of 90 to 120 degrees. Is set.

According to a second aspect of the present invention, the thickness of the interference film is set such that the reflectance of the light reflected by the mark is 40% to 60% based on the reflectance of the light reflected by the non-mark.
%.

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 reflectance at that time appropriate, the reflectivity of the mark with respect to the non-mark is 4
The thickness of the interference film is set so as to be in the range of 0% to 60%.

According to a third aspect of the present invention, the depth of the groove is set such that the phase difference between the light reflected by the groove and the region between the grooves is approximately 90 degrees.

That is, the depth of the groove is set to be approximately 90 degrees so that the phase difference of the reflected light between the groove and the land between the groove can be favorably applied to the push-pull method. It is characterized by.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a phase-change disk capable of recording, reproducing and erasing according to the present invention. FIG. 1 (a)
FIG. 1B is a cross-sectional view of the phase change type disc, and FIG.
Shows a plan view of the recording layer. Also, FIG.
FIG. 3 is a partial cross-sectional view illustrating a configuration of a recording layer illustrated 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 formed from the center to the outer periphery of the phase change disk 1. Are formed spirally. The space between the grooves 9 is called a land 8.

The recording layer 3 is a heat radiation film 3 made of AlTi or the like.
a, insulation film 3b made of ZnSSiO _2, etc., the recording layer 3c made of GeSb like, interference film 3d of _two like ZnSSiO is constituted by sequentially stacking.

For recording and erasing of 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. This is performed by forming the non-mark 7 by erasing the formed mark 6. Reproduction of information is performed from a change in light intensity of reflected light by the mark 6 and the non-mark 7.

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

As described above, information is recorded on the recording layer 3.
Is formed by forming a mark 6 and a non-mark 7 on the recording layer 3 by condensing a laser beam on the recording layer 3. The mark 6 and the non-mark 7 have different crystal states. That is, when the recording film 3c is heated by the laser beam and then rapidly cooled, the recording film 3c becomes amorphous and the mark 6 is formed. At a slower cooling rate, the recording film 3 is crystallized and the non-mark 7 is formed. Is done. The reflectivity of the mark 6 and the non-mark 7 changes depending on the crystalline state, and the reflectivity is lower in the amorphous state.

It is an object of the present invention to enable both the DPD method and the push-pull method to be applied to the phase change type disc 1 having such a configuration. The push-pull method is a method that utilizes the asymmetry of light intensity in reflected light. For this reason, 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.
Are formed to have a predetermined height. Therefore,
When a part of the laser light condensed by the objective lens deviates from the groove 9 and irradiates the land 8, 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 the sensitivity. The actual depth d of the groove 9 is
Since the laser beam passes through the transparent substrate 4, the optical depth can be obtained by dividing the optical depth by the refractive index n of the transparent substrate 4.
That is, the depth d of the groove 9 is given by d = λ / n / 8. For example, if the wavelength λ is λ = 640 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 maximized, so that the push-pull method can be applied. By setting the depth of the groove 9 in this manner, 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 improved.

On the other hand, in the case of the DPD method, the change in the diffraction pattern of the reflected light is used. In the case of a disk having a groove, such as the phase change type disk 1 according to the present invention, the groove is formed in the groove. The effects need to be considered.

That is, when a hole (pit) is formed in a recording film and information is recorded as in a DVD-ROM, a change in the diffraction pattern of only the pit is detected. Quality is higher. However, in the case of the phase change type disc 1, such holes do not exist, and information is recorded on the grooved disc by 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 determined. 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 phase and the reflectance of the reflected light from the mark 6 and the non-mark 7 are changed by changing the thickness of the interference film 3d. Is optimized for a grooved disk.

FIG. 4 shows the thickness of the interference film 3d.
FIG. 7 is a diagram illustrating changes in the phase of the reflected light reflected by the mark 6 and the reflectance between the non-mark 7 and the mark 6 with reference to the phase of the reflected light reflected by the non-mark 7.

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

FIGS. 5 to 7 show that the optical depth of the groove 9 is λ.
/ 8, the DPD signal sensitivity (FIG. 5) and the 3T signal (FIG. 6) when 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. 8) and 14T signals (FIG. 7).

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

The 3T signal is a phase change type disc 1
Is the signal obtained from the shortest mark 6 in, and the larger the signal, the more sensitive the shortest mark can be detected. On the other hand, the 14T signal is a signal obtained from the longest mark 6 on the disk, and requires a certain magnitude.

FIG. 5 shows that when the phase difference δ is δ = 90 degrees, D
It can be seen that the PD signal sensitivity is maximized and its value increases as the reflectance R increases.

FIG. 6 shows that the 3T signal amplitude becomes largest when the phase difference δ is near δ = 120 degrees, but does not depend much on the reflectance R.

Further, from FIG. 7, the phase difference δ has a maximum 14T signal amplitude in the vicinity of δ = 90 degrees, and the reflectance R is R
= 0% to 60% indicates a relatively high 14T signal amplitude.

As described above, when the phase difference of reflected light between the groove 9 and the land 8 is set to be 90 degrees,
In order to increase the DPD signal sensitivity, the 3T signal amplitude, and the 14T signal amplitude to high values, the phase difference δ of the reflected light between the mark 6 and the non-mark 7 should be set in the range of δ = 90 degrees to 120 degrees. I understand. That is, the phase difference occurring in the entire reflected light is 1
In the range of 80 degrees to 210 degrees, both the DPD method and the push-pull method can be performed in an optimum state.

Since 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 due to the groove 9 and the land 8 are deeply related, when the depth of the groove is changed, the entire reflected light is changed. It is preferable to change the phase difference of the mark so that the generated phase difference becomes 180 degrees to 210 degrees.

On the other hand, it is better that the reflectance is large in order to determine the quality of a reproduced signal or the like. From these viewpoints, in FIGS. 5 and 6, the higher the reflectance, the higher the DPD signal sensitivity and the 3T signal amplitude. Also, in FIG.
A good 14T signal amplitude per% is obtained. 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%.

The interference film 3d is set in such a range.
If the thickness d is set, the tracking signal can be detected by the push-pull method and the DPD method. Therefore, it becomes possible to reproduce a phase-change type disc such as a DVD-RAM capable of recording and reproduction with a read-only optical disk device.

FIG. 8 shows a conceptual configuration diagram of a general optical disk device. The optical disk device includes a laser source 21 for generating and emitting a laser beam,
Laser beam from the disk and the phase-change disk 1
The mirror light reflected by the half mirror 22 to form a laser spot on the phase-change disk 1, and converged by the objective lens 23 to form the half mirror 22. Light-receiving element 24 that receives reflected light from phase-change disk 1 that has passed through the optical disk 1, and performs photoelectric conversion, detects a photoelectric conversion signal output from light-receiving element 24, and detects a tracking signal, a servo signal of a focus signal, and a reproduction signal. A servo circuit 26 for receiving a servo signal from the detection circuit 25 and controlling a servo mechanism 29 such as a tracking motor or a tracking coil and a focus coil;
An information reproducing circuit 27 that receives a reproduction signal from the detection circuit 25 and reproduces information is provided.

The laser light emitted from the laser source 21 is reflected by the half mirror 22 and is reflected by the objective lens 23.
And is condensed by the objective lens 23 and irradiates 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 manner, the photoelectric conversion signal output from the light receiving element 24 is input to the detection circuit 25, and the detection circuit 25 supplies the servo signal supplied to the servo circuit 26 and the information reproduction circuit supplied to the information reproduction circuit 27. A signal is output.

At this time, if the optical disk device is a reproduction-only device, the light receiving element 24 is divided into four parts.
According to the DPD method, the detection circuit 25 is located on a diagonal line.
The sum signal of the photoelectric conversion signals from the two light receiving areas is obtained, the tracking signal is detected from the phase difference between the sum signals, and the tracking signal is output to the servo circuit 26.

When the optical disk device is a recording / reproducing device, the light receiving element 24 is divided into two parts, and the detection circuit 25 operates in accordance with the push-pull method to symmetrically convert the photoelectric conversion signals output from the two light receiving regions. By comparing the characteristics, the tracking signal is detected and output to the servo circuit 26.

The phase change type disk 1 according to the present invention comprises:
As described above, the interference film 3d is applied so that the DPD method can be applied.
The thickness d of the groove is set and the depth of the groove 9 is set so that the push-pull method can be applied. Becomes possible.

The servo circuit 26 that has received the servo signal from the detection circuit 25 controls the driving of the servo mechanism 29 based on the servo signal. Thereby, tracking control and focus control are performed.

[0048]

According to the first aspect of the present invention, the thickness of the interference film is set so that the phase difference between the laser beams reflected by the marks and the non-marks is in the range of 90 to 120 degrees. The DPD method can be applied to the phase change type information recording medium, and the reproduction of the phase change type information recording medium can be performed even with a read-only optical disk device.

According to the second aspect of the present invention, since the thickness of the interference film is set so as to be in the range of 40% to 60% of the reflectance between the mark and the non-mark, the quality of the reproduced signal is degraded. DPD even in phase change type information recording media
The method can be applied, and the reproduction of the phase-change type information recording medium can be performed even in a read-only optical disk device.

According to the third aspect of the present invention, the depth of the groove is set so that the phase difference of the reflected light between the groove and the land between the groove is approximately 90 degrees.
Push-pull method can be applied.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a phase change type information recording medium applied to the description of an embodiment of the present invention, wherein FIG.
(B) is a partial plan view.

FIG. 2 is a schematic cross-sectional view showing an enlarged main part of the invention.

FIG. 3 is a diagram illustrating a change in push-pull signal sensitivity with respect to a groove depth.

FIG. 4 is a diagram showing the phase and reflectance of a mark and a non-mark with respect to the thickness of an interference film.

FIG. 5 is a diagram showing the DPD signal sensitivity when the phase difference of the reflected light of the mark with respect to the non-mark is changed, using the reflectance of the reflected light of the mark with respect to the non-mark as a sub-parameter.

FIG. 6 is a diagram showing, as sub-parameters, the 3T signal amplitude when the phase difference of the reflected light of the mark with respect to the non-mark is changed, and the reflectance of the reflected light of the mark with respect to the non-mark.

FIG. 7 is a diagram showing, as sub-parameters, a 14T signal amplitude when the phase difference of the reflected light of the mark with respect to the non-mark is changed, and the reflectance of the reflected light of the mark with respect to the non-mark.

FIG. 8 is a diagram showing a configuration of a general optical disk device.

[Explanation of symbols]

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

Claims (3)

[Claims] A recording film is sandwiched between a protective film having a spiral groove and a transparent substrate, and a mark is formed by irradiating the recording film of the groove with laser light, and the mark and the non-mark are formed. In a phase change type information recording medium on which information is recorded, the reflectance of the laser light reflected by the mark and the non-mark and the phase of the reflected light are changed on the surface of the recording film on the laser light irradiation surface side. An interference film to be provided, and a thickness of the interference film is set so that a phase difference between light reflected by the non-mark and the mark is in a range of 90 degrees to 120 degrees. Phase-change type information recording medium. 2. The thickness of the interference film is set such that the reflectance of the light reflected by the mark is in the range of 40% to 60% based on the reflectance of the light reflected by the non-mark. 2. The phase change type information recording medium according to claim 1, wherein 3. The groove according to claim 1, wherein a depth of the groove is set such that a phase difference between light reflected by the region between the groove and the groove is substantially 90 degrees. 2. The phase change type information recording medium according to item 2.