JPH04205938A - Optical recording method - Google Patents

Abstract

PURPOSE:To allow recording with the same power even if the linear speed at the point on a track increases from the inner periphery to the outer periphery of a disk by continuously increasing or decreasing the film thickness of any of a light incident side protective layer, recording film and reflection side protective layer from the inner periphery to the outer periphery. CONSTITUTION:For example, a reflection film 11 of an information recording medium is formed to the thickness increasing from the outer periphery of a substrate 9 toward the inner peripheral direction. There is a relation of the successive increase in the film thickness and the successive decrease in the transmittance between the film thickness and transmittance of the reflection film 11. Then, the transmittance of the reflection film 11 is lower on the inner periphery than on the outer periphery when this film is formed thicker from the inner periphery to the outer periphery of the substrate 9 and, therefore, the laser beam 13 transmitted through the reflection film 11 has the smaller laser power as the radius R of the substrate 9 is smaller. The reflection film 11 is formed to such film thickness as to optimize the laser power at respective radii in such a manner, by which the recording and reproducing of information are executed at the optimum power even if the laser power over the entire surface from the inner periphery to the outer periphery.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to FM modulated analog signals such as video and audio using a light beam such as a laser beam, computer data, digital audio signals, etc. The present invention relates to an optical recording method capable of recording and reproducing digital information in real time.

[Conventional technology]

There are two types of principles for recording on a thin film using a light beam such as a laser beam: a phase change type, a magneto-optical type, etc., but in both cases, recording is performed using heat generated by light absorption.

Therefore, when recording is performed at the same rotational speed on the outer and inner peripheries of a disk-shaped recording medium, the linear velocity of a point on the recording track is greater on the outer periphery, so if the optimum optical power is set on the inner periphery, the outer periphery This will result in a lack of power. To prevent this, it is necessary to change the pulse width of the light beam power depending on the radius of the recording track. It is not easy to change the power accurately in a short time, so efforts are being made to change the pulse width, but it is difficult to change it significantly without reducing the recording density, so the power still changes slightly. The reality is that we must do so. This may cause an increase in equipment price and a decrease in reliability.

[Problem to be solved by the invention]

Therefore, in the above-mentioned conventional technology, the cost of the device increases and the reliability decreases.

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art described above and provides an optical recording method and an optical disc that make an optical disc device inexpensive and highly reliable.

[Means to solve the problem]

In order to achieve the above object, in the optical recording method and optical disc of the present invention, recording is performed with the same laser power regardless of the radius of the recording track on the optical disc.

Further, by using a recording medium or a magnet for applying an external magnetic field as described below, it is also possible to record with the same laser power and the same pulse waveform.

First, in a magneto-optical disk that uses a magnetic recording film with perpendicular magnetic anisotropy and has two or more laminated magnetic layers with different Curie temperatures, an initialization magnet located away from the optical head is used to direct the magnetization. The thickness of the auxiliary layer that is reversed is
Make the disc thinner from the inner circumference to the outer circumference.

In addition, while keeping the ratio of the recording layer thickness and the auxiliary layer thickness of the magneto-optical disk constant, the recording layer thickness is decreased from the inner circumference to the outer circumference of the disk, and the recording layer The interfacial domain wall energy between the disk and the auxiliary layer is decreased from the inner circumference to the outer circumference of the disk.

Furthermore, in other optical disks such as phase change optical disks and magneto-optical disks, the thickness of the recording layer is made thinner from the inner circumference to the outer circumference of the disk.

Further, a metal protective layer is formed on the optical disk, and the thickness of the metal protective layer is made thinner from the inner circumference to the outer circumference of the disk.

Further, the thickness of the protective layer on the light incident side of the optical disc is made thinner from the inner circumference to the outer circumference of the disk.

This method does not have a metal reflective layer or the thermal conductivity of the metal reflective layer is 0.5 W/C! Ni-Cr lower than It-deg
The effect is great when the film is made of an alloy or the dielectric layer between the metal reflective layer and the recording film has a thickness of 150 nm or more.

This is particularly effective if the recording film has low thermal conductivity, such as a phase change recording film.

It is also effective to reduce the thickness of the protective layer on the side opposite to the light incident side from the inner circumference toward the outer circumference.

Furthermore, it is also preferable to vary the thickness of the layers other than the light incident side protective layer in the radial direction of the disk so that the change in light reflectance is 10% or less over the entire recording/reproducing area of the disk. In this way, the difference in recording sensitivity between the inner and outer circumferences is small, and the difference in reflectance is also small, making it easy to detect servo and playback signals for autofocus and tracking.

In addition, the thickness of either the light incident side protective layer or the recording film 2 reflective layer side protective layer is increased stepwise or continuously or thinned stepwise or continuously from the inner circumference to the outer circumference of the disk. By doing so, the light reflectance decreases from the inner circumference to the outer circumference due to the light interference effect.

This increases light absorption at the outer periphery.

In addition, by providing a light-absorbing or light-reflecting layer on the light incident side of the substrate, or by mixing a light-absorbing or light-reflecting material into the substrate, the rate at which the recording or reproducing light beam reaches the recording film can be increased from the inner circumference of the disk. Increase gradually towards the outer periphery. As the light-absorbing or light-reflecting material, for example, an inorganic material containing a metal element or an organic dye can be considered.

In addition, if the optical disk is a magneto-optical disk having a magneto-optical recording film, the magnet that generates the recording magnetic field is shaped to become thicker from the inner circumference toward the outer circumference, so that the strength of the recording magnetic field increases toward the outer circumference. do.

Although one of the above means may be used, even better effects can be expected if two or more are used simultaneously.

[Effect]

When the auxiliary layer is made thinner at the outer periphery of a magneto-optical disk, and when the protective layer on the light incident side is made thinner at the outer periphery of a phase-change optical disk or magneto-optical disk, the generated heat is transferred to the surrounding area due to thermal conduction. Escape is suppressed and recording sensitivity is improved.

Additionally, if a light absorber is mixed into the light incident side or inside the substrate, the amount of light absorbed by the recording film will decrease, so by reducing the amount mixed into the outer periphery of the disk, the amount of light absorbed by the recording film will be reduced. This increases recording sensitivity. The same holds true when the reflectance at the outer periphery is lowered using a magneto-optical recording film or the like.

When the magnetic field at the outer periphery is made stronger by the shape of the magnet for applying an external magnetic field in magneto-optical recording, the laser light sensitivity is improved at the outer periphery due to the characteristics of the magneto-optical recording film.

Due to these effects, even though the linear velocity of points on the track increases from the inner circumference to the outer circumference, it is possible to record with the same power and with the same waveform.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

Example 1 A magneto-optical recording medium 1 is a disc-shaped polycarbonate substrate 2
First, a silicon nitride film 3 with a thickness of 85 nm is formed thereon. On top of this is Tb24FeG8C as a memory layer.
The os amorphous magnetic layer 4 has Tb, , D y1 as an auxiliary layer.
□F e, 2Co2. The amorphous magnetic layer 5 is provided with a film thickness ratio of 4:15. Both magnetic layers have outer peripheral side film thickness hM,
A film thickness gradient is provided in which hs□ is thinner than the inner peripheral side film thickness hM2゜hs2, in this case, hM = 20 nm
, hs, = 75 nm, hMz = 40 nm, hs, = 15
It is 0 nm. The top layer is a silicon nitride film 1 with a thickness of 80 nm.
It is a provision. The L plate is a cross-sectional view of an apparatus for producing this recording medium. The substrate 2 is held by a substrate holder 7 and rotated about a central axis 6. On the other hand, a target 9 for forming a silicon nitride film or a magnetic layer by sputtering is placed facing the substrate 2, and a mask 8 for controlling the thickness of the recording layer is placed between the target 9 and the substrate 2. ing. As shown in FIG. 4, which is a view from A in FIG.
and a movable shielding mask 8c. Silicon nitride film 3
In forming this, silicon was placed as a target 9, and sputtering was performed using a mixed gas containing Ar and 10% N2 with the opening 8b fully open. In forming the magnetic layer, T b − is used as the target 9.
A Fe-Co or Tb-DyFe-Co alloy target was placed, and using Ar gas, the movable shielding mask 8C was moved in the direction of arrow B to shield a part of the target 9, and sputtering was performed.

The exchange coupling force acting between the magnetic layers is greater in the thinner outer peripheral portion of the magnetic layer than in the thicker inner peripheral portion of the magnetic layer. If this continues, it will fall within the override characteristic.

Differences occur at the outer periphery. After sputtering, the magneto-optical recording medium 1 was heated to 200°C in vacuum for 30 minutes.
Annealing treatment was performed for 0 minutes. By this treatment, the interfacial domain wall energy is more significantly reduced at the inner circumference because the film thickness is thicker, so that the exchange coupling force becomes almost the same at the inner and outer circumferences.

The annealing temperature is preferably in the range of 150 to 300°C, and the annealing time is preferably 10 minutes to 1 hour.

Example 2 In Example 1, the memory layer T b -F e-
After forming the Co magnetic layer 4 with a film thickness gradient, Tb-D
The y-Fe-Co magnetic layer 5 was formed to have the same thickness on the inner and outer peripheries. In this case, the magneto-optical recording medium 1
The annealing process for Example 1 may be performed at a lower temperature and/or for a shorter time than in Example 1. For example, 150°C for 20 minutes is appropriate.

Example 3 In Example 1, the Tb-Fe-Co magnetic layer 4 serving as the memory layer was formed so that the film thickness was the same on the inner and outer peripheries. In this case, the annealing treatment of the magneto-optical recording medium 11 may be performed at a lower temperature and/or for a shorter time than in the second embodiment. For example, 100° C. for 10 minutes is appropriate.

Note that an amorphous film of rare earth and transition metal, such as Tb-Gd-Fe or Gd-Dy-Fe-Co, is used for the magnetic layer. Inner peripheral side film thickness (hs.

+hM2) is 770-200n, outer peripheral side film thickness (h st
+hMx) is preferably formed in a range of 50 to 100 nm.

Further, the films provided on both sides of the magnetic layers 4 and 5 may be dielectric films such as aluminum nitride, silicon oxide, and aluminum nitride.

Example 4 Gd-Tb-Fe was applied to the memory layer using the apparatus shown in FIG.
The magnetic layer (memory layer) was hM, ~4 Q nm.

After forming hM2=60 nm, N2 gas containing 10% O2 gas was introduced into the device, the surface of the Gd-Tb-Fe magnetic layer was exposed to this mixed gas for 30 seconds, and the inside of the device was again placed in a high vacuum. After evacuation to Gd-Tb-Fe-Ce
The magnetic layer (auxiliary layer) hM2=60nm, hM2:90n
m, and an AQN film was formed as a protective film at 110 m.
Only 0n was provided on the top layer. By flowing the mixed gas of 02 and N2, an oxide layer of about 20 oxides was formed on the top layer of the Gd-Tb-Fe-Co magnetic layer. This oxide layer has the effect of weakening the magnetic coupling between the memory layer and the auxiliary layer.
The effect is more pronounced as the thickness of the magnetic layer becomes thinner. Therefore, there was no difference in the override characteristics between the inner and outer circumferences.

Embodiment 5 FIG. 5 shows an embodiment of the information recording medium of the present invention. A recording film 1o is formed on one side of the substrate 9. Also,
A reflective film 11 is formed on the opposite surface. The reflective film 11 includes AQ and Si.

Ti, Cr, Co, Ni, Cu, Zn, Pt.

At least one metal such as Au is used.

Recording and reproduction are performed using a laser beam 13 that passes through the reflective film 11 and the substrate 9 using a lens 14 to form a minute spot on the surface of the recording film. At this time, the thickness of the reflective film 11 is
The substrate 9 is formed thicker from the outer periphery toward the inner periphery. There is a relationship between the film thickness and transmittance of the reflective film 11, as shown in FIG. 6(a), where the transmittance decreases as the film thickness increases at the wavelength of the laser beam 13. When the substrate 9 is formed thicker from the outer circumference toward the inner circumference, the transmittance of the reflective film 11 is lower at the inner circumference than at the outer circumference.

Here, the laser power of the laser beam 13 transmitted through the reflective film 11 decreases as the radius R of the substrate 9 decreases. The optimum laser power for substrate 9 is a function of radius. For example, it is a function of 5.

In order to optimize the laser power at each radius of the substrate 9, the thickness of the reflective film 11 is formed in accordance with its transmittance. For example, as shown in FIG. 6(b), the transmittance is 70% at the innermost radius of the information recording substrate 9, and the transmittance increases as the radius increases until the transmittance reaches 100% at the outermost radius. Forms film thickness. It is also possible to match the relative relationship between the transmittances of the innermost diameter and the outermost diameter. When information was recorded and reproduced using the same laser power over the entire surface of such an information recording medium, a stable signal with good S/N was obtained over the entire surface of the substrate 9. Therefore, according to the present invention, even if the laser power is the same over the entire surface from the outer circumference to the inner circumference, it is possible to record and reproduce information at the optimum power.

A protective film may be formed to prevent damage to the reflective film 11. Similar results as above are obtained.

By changing the thickness of the absorption film 12, the transmittance of the wavelength of the laser beam 13 changes as shown in FIG. 6(a). Therefore, the same results as above were obtained when the absorbing film 12 was used instead of the reflective film 11.

For example, at least one type of cyanine dye, naphthoquinone, and phthalocyanine compound was formed in the absorption film 12.

As shown in FIG. 8, while changing the thickness of the light reflecting/absorbing film, the thickness of the recording film may also be made thinner at the outer periphery of the disk.

Embodiment 6 FIG. 7 shows an embodiment of the information recording medium of the present invention. A recording film 16 is formed on the substrate 15. Further, the substrate 15 (for example, glass) contains a light absorbing material 17. The light absorbing material 17 contains metal ions (Cr, F
e, Mn), colloidal metals (A u , A g
+ Cu ) colloidal nonmetal (C, S, Se)
etc. are used. When the content of the light-absorbing material 17 increases, it absorbs the laser beam 13 and the transmittance decreases. Therefore, by reducing the content as the radius of the substrate 15 becomes larger, an information recording medium having a transmittance corresponding to the radius of the substrate 15 similar to that shown in FIG. 6(b) can be obtained. When this information recording medium was used to record and reproduce information in the same manner as in Example 5, the same results as in Example 5 were obtained. Therefore, according to the present invention, even if the laser power is the same over the entire surface from the outer circumference to the inner circumference, it is possible to record and reproduce information at the optimum power.

As shown in FIG. 9, the content of the light-absorbing material may be varied in the radial direction, and at the same time, the thickness of the recording film may be made thinner at the outer peripheral portion.

Embodiment 7 FIG. 10 shows an example of a structural cross-sectional view of a conventional disk. First, diameter 13a1. A base layer 25 having tracking grooves was formed on the surface of a disk-shaped chemically strengthened glass plate 24 having a thickness of 1.2 mm using an ultraviolet curing resin. Then, a 5i-N layer 26 was formed thereon using a magnetron sputtering device. Next, this 5i-
Ge1□Sb on the N layer 3. A recording film 27 having a composition of T es'+ was sputtered to a thickness of about 30 nm. Next, a 5i-N protective layer 28 was formed again using a magnetron sputtering device. Furthermore, an 80 nm thick Au layer 29 was formed thereon in the same sputtering apparatus. After that, another disk with the same structure was bonded to this via an adhesive layer 30. In the conventional disk structure, the laser power required for recording increases as the linear velocity increases toward the outer periphery. needs to be made larger. That is, the recording power must be changed depending on the measurement location, which makes the circuit complicated. Therefore, in the present invention, in order to keep the laser power required for recording constant regardless of the location (radius) on the disk, the thickness of the protective layer is changed depending on the radius of the disk, as shown in FIG. I'm letting you do it. That is, the thickness of the lower protective layer is made thinner toward the outer periphery. This is because, as shown in FIG. 12, by reducing the thickness of the lower protective layer, the laser power required for recording can be reduced. For example, 18
When the disk is rotated at 00 rpm, the thickness of the protective layer at a radius of 30 m (linear speed: 5.7 m/s) is 300 nm.
If the recording power at this time is 18 mW, the radius is 6
The recording power at 0wm (linear velocity: 11.3m/s) is also 18
mW, the thickness of the protective film should be 1100 nm.

Further, as shown in FIG. 13, the lower the reflectance of the disk, the greater the amount of absorption, so less laser power is required for recording. Therefore, if the disk structure is determined using the optical interference effect so that the reflectance is lower in areas where the linear velocity is faster than in areas where the linear velocity is slower, it is possible to maintain a constant recording power regardless of the radius of the disk. .

If only the thickness of the lower protective layer is changed in a disk with a conventional structure, the reflectance will also change significantly due to light interference effects. For this reason, recording sensitivity differs depending on location. Therefore, the 11th
As shown in the figure, the upper protective layer was also made thinner toward the area where the linear velocity was faster (the outer periphery). At this time, the thickness of the upper protective layer was determined so that the change in reflectance was 10% or less.

In this example, the thickness of the protective layer was continuously thinned from the area where the disk radius was small to the area where it was large, that is, from the area where the linear velocity was slow to the area where it was fast, but it was divided into several areas. A similar effect was obtained even when the thickness of the protective film was gradually reduced. Example 8 FIG. 15 shows the structure of an example of the present invention. Magnetic field applying means 32 made of a permanent magnet or the like are arranged at appropriate intervals to a disc-shaped magneto-optical recording medium 31.

The interval is far on the inner circumferential side of the magneto-optical recording medium 31, and
It is designed to become smaller on the outer circumference side. The strength of the magnetic field increases as it approaches the magnetic field applying means, so as shown in FIG. 14, the magnetic field becomes weaker at the inner periphery and stronger at the outer periphery. The recording sensitivity of the magneto-optical recording medium 1 increases as the magnetic field becomes stronger, so the sensitivity of the outer peripheral portion is higher. On the other hand, the recording sensitivity increases as the linear velocity decreases. That is, the recording sensitivity on the inner circumference is high. Therefore, these two effects (magnetic field strength and linear velocity) are complementary to each other,
The recording sensitivity of the inner and outer circumferences can be made constant.

In this example, the distance between the magneto-optical recording medium 31 and the magnetic field applying means was 1 m+ at the outer circumference (radius 60a+) and 8 m at the inner circumference (radius 30 m). Here, the cross-sectional shape of the magnetic field applying means 1 in the direction perpendicular to the radius is a square of 5 mm x 5 squares. Therefore, the magnetic field on the inner circumference is 2000e and the magnetic field on the outer circumference (
6000e), and the recording sensitivity is poor. As a result, the recording sensitivity at the innermost periphery, where the linear velocity was slow, was almost the same as that at the outer periphery. Therefore, recording magnetic domains of the same size are formed with the same laser power on the inner and outer circumferences, so there is no need to control the laser power on the inner and outer circumferences, and the configuration of the apparatus becomes easier.

Example 9 In order to change the strength of the magnetic field between the inner and outer peripheries, a permanent magnet 33 having a shape as shown in FIG. 16 was used as a magnetic field applying means. That is, the opposite surface of the recording medium 1 has a rectangular shape with the same width on both the inner and outer circumferences, and the side closer to the recording medium 31 has a trapezoid shape that gradually becomes thinner from the inner circumference to the outer circumference. If this magnet is used, the magnetic flux will be concentrated near the medium at the outer periphery, so the magnetic field strength will be strong. Therefore, effects similar to those of the above embodiment can be obtained.

In addition to the methods described above, the present invention can be implemented in the following manner: (1) The magnetic field is increased when recording on the outer circumference in the magnetic field modulation magneto-optical recording method.

(2) In the override method using an exchange-coupled two-layer film, the strength of the recording magnetic field is set as shown in FIG.

Various methods can be considered. Furthermore, the magneto-optical recording medium is not limited to TbFeCo, but may also be a Pt/Co multilayer film, NdFeCo, or the like.

In any case, magneto-optical (thermomagnetic) recording is performed while applying a bias magnetic field that is weak at the inner circumference and strong at the outer circumference.

〔Effect of the invention〕

According to the present invention, recording and reproduction can be performed in the same way on both the inner and outer circumferential portions of a disk rotating at a constant angular velocity, contributing to the simplicity, cost reduction, and high reliability of optical disk devices.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an apparatus for manufacturing an optical disk with a gradient film thickness according to an embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views of an optical disk according to an embodiment of the present invention, and FIG. 5 is a sectional view of an optical disk according to another embodiment of the present invention; FIG. 6 is a relationship between the reflective film thickness and light transmittance in the optical disk of FIG. 5. FIG. 7, FIG. 8, and FIG. 9 are diagrams showing the cross-sectional structure of a disk according to other embodiments of the present invention. FIG. 10 is a diagram showing a conventional disk cross-sectional structure. FIG. A diagram showing a cross-sectional structure of a disk in another embodiment, FIG. 12 is a diagram showing the relationship between the film thickness of the lower protective layer and recording power, and FIG. 13 is a diagram showing the relationship between the reflectance of the disk and recording power. 14 is a diagram showing a preferable magnetic field strength distribution in the radial direction of a magneto-optical recording medium,
FIG. 15 is a diagram showing a conventional method of providing a radial magnetic field strength gradient, and FIG. 16 is a diagram showing the shape of a magnet that produces a radial magnetic field gradient in an embodiment of the present invention. 4... Magneto-optical memory layer, 5... Auxiliary layer, 33...
permanent magnet. vli5 Figure χ 6 times (υ) (b) ¥ mark No. 7 Figure Y: J B Figure No. 9 Hard No. 10 Mouth No. 11 Figure 1 Inner prostitution External use = 71, J Fubushi No. 12 Figure - "Shouting" 1noa 11vS (9m) No. 13
What is 11?

Claims (1)

[Claims] 1. An information recording method in which a recording film is formed on a predetermined disc-shaped substrate directly or through another thin film, and information is recorded by irradiating the recording film with a light beam. , an optical recording method characterized by rotating a disk at a constant angular velocity and recording with approximately the same recording power over the entire recordable range of the disk. 2. The above-mentioned optical disk has perpendicular magnetic anisotropy and has a film in which two or more magnetic layers having different Curie temperatures are laminated, and among these, the thickness of at least the auxiliary layer is set from the inner circumference of the disk. 2. The optical recording method according to claim 1, wherein the optical recording method is made thinner toward the outer periphery. 3. The optical recording method according to claim 2, wherein the thickness of the recording layer of the optical disc is made thinner from the inner circumference to the outer circumference of the disk. 4. While keeping the ratio of the recording layer thickness and the auxiliary layer thickness of the optical disc constant, the thickness of the recording layer is made thinner from the inner circumference to the outer circumference of the disk, and the recording layer and the auxiliary layer are 3. The optical recording method according to claim 2, wherein the interfacial domain wall energy with the disk is decreased from the inner circumference to the outer circumference of the disk. 5. The optical recording method according to claim 1, wherein the optical disc has a metal protective layer, the thickness of which decreases from the inner circumference to the outer circumference of the disk. 6. The optical recording method according to any one of claims 1 to 5, wherein the thickness of the protective layer on the light incident side of the optical disc is made thinner from the inner circumference to the outer circumference of the disk. 7. A claim characterized in that the film thickness of the layers other than the light incident side protective layer is also varied in the radial direction of the disc so that the change in light reflectance is 10% or less over the entire recording/reproducing area of the disc. Item 6. The optical recording method according to item 6. 8. The optical recording method according to any one of claims 1 to 6, wherein the optical reflectance decreases from the inner circumference to the outer circumference of the optical disc due to a light interference effect. 9. The light according to any one of claims 1 to 8, characterized in that the rate at which the light beam reaches the recording film of the optical disc is increased stepwise from the inner circumference to the outer circumference of the disk. Recording method. 10. Claim characterized in that a light reflecting/absorbing film is provided on the side of the substrate of the optical disc that does not have a recording film, and the light transmittance of this film is increased from the inner circumference to the outer circumference of the disk. 9. The optical recording method according to 9. 11. The optical disc according to claim 9, wherein the substrate of the optical disk contains an inorganic material containing a metal element or an organic dye, and the light transmittance of the substrate increases from the inner circumference to the outer circumference of the disk. Recording method. 12. The optical disc according to claim 1, wherein the optical disc has a magneto-optical recording film and is shaped like a magnet so that the strength of the recording magnetic field increases from the inner circumference to the outer circumference of the disk. Recording method. 13. Any one of claims 1 to 12, characterized in that the thickness of the protective layer on the side of the optical disc opposite to the light incident side of the recording film is made thinner from the inner circumference to the outer circumference of the disk. The optical recording method described.