JPH08241542A - Optical recording medium - Google Patents

Abstract

PURPOSE: To obtain an optical recording medium capable of recording and reproducing four values at the same position as an optical recording medium used in an external recorder. CONSTITUTION: This optical recording medium has at least a magnetooptical recording film and a phase change type recording film on the substrate. The phase change type recording film has the practically same reflectance and mutually different apparent angles of Kerr rotation when the film has a crystal phase and when it has an amorphous phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can record and reproduce four values at the same position in an optical recording medium used for an external recording device of a computer, and can record and reproduce at high recording density. The present invention relates to an overwritable optical recording medium.

[0002]

2. Description of the Related Art Among optical recording media, magneto-optical recording media and phase change recording media have been put to practical use as rewritable large-capacity recording media, and various attempts have been made to further increase recording density and capacity. There is. A magneto-optical recording medium records in the direction of magnetization of a magnetic film and reads a signal by using the Kerr effect that the plane of polarization rotates when linearly polarized light is applied to a magnetized magnet. In general, a magneto-optical recording medium is provided with a dielectric film or a reflective film for the purpose of increasing the apparent Kerr rotation angle (Kerr rotation angle enhancement), and these films are responsible for protecting the recording film and improving thermal characteristics. Generally, it has a structure of substrate / dielectric film / recording film / dielectric film / reflection film. Generally, a rare earth transition metal alloy film that is easily oxidized is used for the recording film. Therefore, it is said that the nitride film is preferable to the oxide film as the dielectric film. In addition, the recording film is magnetized by heating it to a temperature near the Curie temperature and applying an external magnetic field to the recording film to magnetize the recording film in that direction. The method of changing and recording is called the magnetic field modulation method, and it is put to practical use as a method that can be easily overwritten.

The phase-change recording medium is a method of recording by utilizing two different states of a crystalline phase and an amorphous phase. For recording, the recording film is heated to a temperature higher than the melting point with a high power to make it an amorphous phase and crystallized at a low power. It is a recording medium for recording information by making the intensity of laser power to be a crystal phase by raising the temperature to a binary value, and detecting written information as a difference in reflectance because the optical constants differ between the two states. In order to increase the recording density, the recording area of one recording unit (domain) should be reduced, or conventionally one recording unit is composed of two values. Further high recording density can be expected by performing either method or this combination.

However, in optical recording, the minimum recording unit that can be reproduced depends on the wavelength of the laser, the NA of the condenser lens of the optical head, and the degree of convergence of the light determined by the spatial distribution of the intensity of the laser light. . For this reason, the Ilister is advocated. Regarding multi-valued recording, it is disclosed that the recording position is delicately shifted, the domain is changed in size to make it multi-valued, or the recording film is made multi-layered to make multi-valued recording.
Among them, it is preferable to perform multi-valued recording by using a magneto-optical film and a phase-change recording film because stable recording and reproduction can be performed (Japanese Patent Laid-Open No. Hei 10 (1999) -242242).
4-206054, JP 5-12751, JP 5-1594
(See Japanese Patent No. 10). However, the method disclosed here has a problem that the detection becomes complicated because the detection is performed by the difference between the two quantities of the reflectance and the Kerr rotation angle, and the Kerr ellipticity and the Kerr rotation angle. In particular, when the reflectance changes, there is a problem that it becomes difficult to amplify in signal reproduction. Further, a method of performing multi-valued recording with two magneto-optical recording films is also disclosed, but since three-valued recording is performed with two recording layers, it may be inefficient compared to the number of recording films, or over recording may occur. It cannot write (see JP-A-64-17248, JP-A-1-290143, and JP-A-4-010256).

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and in an optical recording medium having both a magneto-optical recording film and a phase change recording film, the read amount is set to one and the read mechanism is simplified. The purpose is to

[0006]

SUMMARY OF THE INVENTION The present invention is an optical recording medium which solves the above problems, which is an optical recording medium comprising at least a magneto-optical recording film and a phase change recording film on a substrate. The gist of an optical recording medium characterized in that the reflectivity when the variable recording film is in the crystalline phase and that when it is in the amorphous phase show substantially the same value, and the apparent Kerr rotation angle shows different values. To do. The present inventors have found that in an optical recording medium having a magneto-optical recording film and a phase change recording film on a substrate, the reflectance when the phase change recording film is in the crystalline phase and the amorphous phase is substantially equal. The inventors have found that 4-valued recording and reproduction can be performed at the same position by using optical recording media having the same apparent Kerr rotation angles but different values, and various studies have been made to complete the present invention.

In the recording method of the present invention, since the optical recording medium comprises the magneto-optical recording film and the phase-change recording film on the substrate, the incident light is applied to the magneto-optical recording film so that the magneto-optical recording film is not affected by the incident light. The direction of the magnetization of the magneto-optical recording film can be changed by applying an external magnetic field with a magnetic head and changing the direction of the magnetic field. At the same time, by changing the intensity of the incident light in the phase change recording film, when the incident light is strong (when the temperature of the recording film is high), it is in the amorphous phase and when the incident light is weak (when the temperature of the recording film is high). If it is low), it becomes a crystalline phase. Therefore, as shown in Table 1, by irradiating one point of the optical recording medium with strong or weak incident light, one of four states can be recorded at the same position, and four-value recording is possible. It will be possible.

[0008]

[Table 1]

In the present invention, the method of recording on the magneto-optical recording film is the same as the magnetic field modulation method of a normal magneto-optical device, and the phase change recording film can be overwritten by optical modulation. The state of the subsequent recording film does not depend on the state before recording. Therefore, it is possible to overwrite.

In the present invention, in terms of recording and reproduction, the states 1 and 4 and the states 2 and 3 have the same apparent Kerr rotation angle and different polarization directions. However, in the states 1 and 2 and the states 3 and 4, the directions of rotation of the polarization planes are the same, but the apparent Kerr rotation angles are different. The intensity ratio of the signals read out from the states 1 to 4 due to the difference in the Kerr rotation angle is preferably the intensity ratio of relative intensities 1 or 2 shown in Table 2 from the viewpoint of ease of recording and reproduction.

[0011]

[Table 2]

The reproducing method may be a reproducing system of an ordinary magneto-optical recording device for detecting the Kerr rotation angle, and noise can be reduced by using a differential detecting system.

In order to set the reflectances when the phase-change recording film is in the crystalline phase and when it is in the amorphous phase to be substantially the same and the apparent Kerr rotation angle shows different values, the thickness of each film is set. It can be done by adjusting. That is, the virtual complex refractive index of the entire film is N _c ^* when the phase change recording film is in the crystalline phase and N _a ^* when it is in the amorphous phase. virtual complex refractive index n _c ^{* +,} and n _a ^{* +,} n _c ^* virtual complex refractive index with respect to left-circularly polarized light -, n _a ^{* -} and then, further virtual complex refractive index of the substrate and the n ^* Then, the thickness of each film may be set so that the virtual complex refractive indices have the relationship of the expression (1) and the relationship of the expression (2). ^{_{| (n * -N c *)}} / (n * + N c *) | 2 ≒ | (n * -N a *) / (n * + N a *) | 2 ... (1) N c * + ≠ N a ^{* +} Or N _c ^*- ≠ N _a ^*- (2) Here, the value that the reflectance is substantially the same means that the value in the crystalline phase is different from the value in the reflectance when the phase change recording film is in the amorphous phase. The reflectance value at a given value means a value in the range of 90 to 110%.

As the film constitution, a polycarbonate resin (P
It is sufficient that the magneto-optical recording film and the phase-change recording film are both provided on a transparent substrate such as plastic or glass such as C) or polymethylmethacrylate (PMMA). However, since the writing temperature is generally higher in the phase change recording film, it is preferable to sandwich a dielectric film between the phase change recording film and the magneto-optical recording film. In addition, it is preferable to provide a dielectric film between the substrate and the recording film to improve the corrosion resistance of the recording film and prevent the substrate from being deformed by heat. Furthermore, a reflective film is provided to enhance the Kerr rotation angle. It is also effective to provide. As an example of the film structure, for example, a film structure in which the light incident side is laminated in the following order: substrate / dielectric film (1) / phase change recording film / dielectric film (2) / magneto-optical recording film / dielectric Body membrane
(3) / consisting of reflective film, substrate / dielectric film (1) / magneto-optical recording film / dielectric film (2) / phase change recording film / dielectric film
(2) / consisting of a reflective film, further substrate / dielectric film (1) /
Examples include phase change type recording film / dielectric film (2) / magneto-optical type recording film / reflection film.

The thickness of each layer is determined by the above-described method so that the medium reflectivity is constant and the apparent Kerr rotation angle is different depending on the thermal conditions, the phase change film is in the amorphous phase and the crystalline phase. Set. Depending on the film thickness, the Kerr rotation angle may become the same when the medium reflectance is made equal when the phase change film is in the amorphous phase and when the crystal is in the crystal phase. For example, in the film structure 2, the virtual refractive index of the dielectric film (2) / phase change recording film / dielectric film (3) / reflection film is as follows when the phase change recording film is in the amorphous phase and in the crystalline phase. You can choose to be the same. However, at this time, the apparent car rotation angle also becomes the same, so four-value recording cannot be performed.

In order for the phase-change recording film to show substantially the same reflectivity in the crystalline phase and the amorphous phase and different apparent Kerr rotation angles, the phase-change recording film is made of, for example, a known chalcogen compound. The composition of the film may be a known one, for example Ge-Te, Sb-Te, In-Sb, Sb-Ge-Te, In
-Se-Tl-Co, Ag-In-Te-Sb, In-Sb-Te, etc. are exemplified. If the thickness of the phase change film is less than 5 nm, it is difficult to obtain a uniform film with good reproducibility, and if it exceeds 50 nm, the amount of light passing through the phase change film in the crystalline phase becomes too small. , Preferably 5 to 20 nm.

The magneto-optical recording film may be a generally known and known one, for example, Tb-Fe, Tb-Fe-Co, Gd-Fe, Gd-Fe-Co, Gd-.
Tb-Fe, Gd-Tb-Fe-Co, Dy-Tb-Fe, Dy-Fe, Gd-Co, Tb-Co, Gd-Dy
Rare earth transition metal alloys such as -Tb-Fe, or Co-Pt, Co-P
A superlattice multilayer film such as d, is used. If the thickness of the magneto-optical recording film is less than 5 nm, it is difficult to make a difference in signals, and if it exceeds 50 nm, a large power is required for writing.
The thickness is preferably 50 nm, preferably 5 to 30 nm, particularly preferably 5 to 15 nm.

The dielectric film may be a known one, for example, Si-N, Si-O, Zn-S, Al-N, Si-Al-ON, Zn-S-Si-O, or hydrogen to this. Examples of the inclusion include, each dielectric film 1,
A few may be the same or different. In particular, the dielectric film 2 is 2
The magneto-optical recording film side is preferably a nitride film on the magneto-optical recording film side and the phase-change side is ZnS + SiO because the magneto-optical recording film is oxidized by directly forming an oxide film on the magneto-optical recording film. The thickness of each dielectric film is not particularly limited, but if it is less than 5 nm, it is difficult to form a uniform film, and if it exceeds 500 nm, it takes a long time to form the film.
In addition, the thickness is preferably 5 to 500 nm, and more preferably 5 to 200 nm, because it is easily peeled off.

The reflective film may be a known film, and as is generally used in optical recording media, a film having a high reflectance such as Al, Au, Ag, Pt, and Cu is preferable, but Al is inexpensive and has good corrosion resistance. Therefore, it is preferable. Furthermore, it is preferable to add Ti, Cr, a rare earth or the like to the above metal such as Al because the thermal conductivity is lowered and the corrosion resistance is improved. If the thickness of the reflective film is less than 10 nm, light is transmitted, and if it exceeds 500 nm, it takes a long time to form a film.
The thickness is preferably 500 nm, preferably 10 to 200 nm.

The film forming method is not particularly limited, but a sputtering method which is generally used for manufacturing an optical recording medium may be used.

The reflectance is not particularly limited, but the reflectance is 35%.
If it is set over, the car rotation angle cannot be increased and
If it is less than%, noise increases, so 10 to 35% is preferable. The reflectance of each layer is preferably set to be substantially the same within the range of 10 to 35%.

Although the present invention has been described with respect to the magneto-optical film 1 layer and the phase change film 1 layer, the magneto-optical recording film and the phase change film may be multi-layered to record four or more values in the same recording area. It is also possible to increase the recording density by combining with, such as, Ilister.

[0023]

The present invention provides an optical recording medium having at least a magneto-optical recording film and a phase change recording film on a substrate, and reflection when the phase change recording film is in a crystalline phase and in an amorphous phase. By using an optical recording medium that has substantially the same value and different apparent Kerr rotation angles, two sets of different apparent Kerr rotation angles are recorded at the same position in two different magnetization directions. Since it can be reproduced, 4-level recording and reproduction can be performed at the same position on the medium, and the recording method is also the magnetic field modulation method of the ordinary magneto-optical recording apparatus, and the reproducing method is also the ordinary magneto-optical recording in which the Kerr rotation angle is detected. There is a merit that it can be performed by the device.

[0024]

Embodiments of the present invention will be described below. Example: Dielectric film (1) / phase change recording film / dielectric film (2) / magneto-optical recording film / dielectric film (3) on a glass substrate having a diameter of 86 mm and a thickness of 1.2 mm
/ Reflective film was laminated in this order. Each film was formed by Rf magnetron sputtering. Table 3 shows the film forming conditions for each film. The target was 4 inches, and a single-layer film was formed in advance. The relationship between the time and the film thickness at this time was determined, and the film was formed for a time to obtain a predetermined film thickness.

[0025]

[Table 3]

The result of irradiating this with a laser of 830 mm and measuring the Kerr rotation angle is shown in Table 4.

[0027]

[Table 4]

[0028]

The optical recording medium of the present invention is capable of recording and reproducing two sets of different apparent rotation angles at the same position of the medium in two different directions of magnetization, so that the same on the medium. It is a normal magneto-optical recording device that can perform four-valued recording and reproduction at a position, and that the recording method is also the magnetic field modulation method of the normal magneto-optical recording device, and that the laser power is also binary and the reproduction method also detects the Kerr rotation angle. You can do it. Also, by multi-layering the medium, multi-valued recording and reproduction can be performed, higher density recording can be performed, and overwriting is possible.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Tawara 3-2-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Shin-Etsu Chemical Co., Ltd. Corporate Research Center

Claims (2)

[Claims] 1. An optical recording medium comprising at least a magneto-optical recording film and a phase change recording film on a substrate, and the reflectance when the phase change recording film is in a crystalline phase and in an amorphous phase. Shows substantially the same value, and the apparent Kerr rotation angles show different values. 2. The optical recording medium according to claim 1, wherein a dielectric film is provided between the phase change recording film and the magneto-optical recording film.