JPH05198002A - Optical recording medium - Google Patents

Abstract

PURPOSE:To exhibit excellent S/N and to obtain stable tracking characteristics by forming an interference layer of a light transmissive material having the refractive index higher than the refractive index of a substrate and etching a part thereof. CONSTITUTION:This optical recording medium 10 is constituted by successively laminating an interference layer 14, a recording layer 16, a guide layer 18 for tracking and a protective layer 20 on the transparent substrate 12. The interference layer 14 is SiAlON, TiO2 films, etc., formed by a sputtering method, spin coating, sol-gel film forming method by firing, etc., and has the refractive index higher than the refractive index of the substrate 12. The recording layer 16 is fixed continuously or discontinuously fixed in spiral or other shapes onto the interference layer 14. The interference layer 14 of the optical recording medium 10 having such constitution is the light transparent material having the high refractive index and generates multiple reflections between the substrate 12 and the recording layer 16. The Kerr effect enhancement of the recording layer 16 is maximized and the S/N is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium such as an optical disk memory and an optical card for recording / reproducing information with a laser beam.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, an optical recording medium 30 of this type has an interference layer of SiAlON, AlN or the like on a transparent substrate 32 of acrylic, polycarbonate, glass or the like provided with a guide groove 31 for tracking. 34 and GdTbF
e, a magneto-optical recording layer 37 such as TbFeCo, and SiAlO
The protective layer 38 made of N, AlN or the like and the reflective layer 40 made of Al or the like were sequentially laminated. In such a magneto-optical recording medium 30, information is recorded by irradiating the magneto-optical recording layer 37 with a laser beam to heat it to a Curie temperature or a compensation temperature or higher and at the same time applying a magnetic field from the outside to magnetize the magneto-optical recording layer 37. It was done by inverting. Recording and reproduction have been performed by utilizing the Kerr effect that the rotation of the polarization plane of the reflected light is reversed depending on the direction of magnetization when the magneto-optical disk is irradiated with linearly polarized laser light. Furthermore, in order to obtain good signal characteristics, it is necessary to increase the apparent Kerr rotation angle by Kerr effect enhancement and improve the noise ratio (S / N) with the signal, and therefore interference with a higher refractive index than the substrate. The layer 34 is provided between the substrate 32 and the magneto-optical recording layer 37 to utilize the interference effect due to multiple reflection.

[0003]

However, in the conventional magneto-optical disk, in order to increase the Kerr effect enhancement due to the interference effect in the substrate, the interference layer, the magneto-optical recording layer, and the reflective layer, the film thickness of the interference layer 34 is increased. Is approximately λ / 4n ₂ , but as shown in FIG. 5, at this time, the reflectivity in the groove 31 necessary for tracking, which is opposite to the increase in the Kerr effect, becomes very small. Since the reflectance of the film thickness is also set to the minimum, the push-pull signal becomes almost 0, the tracking servo becomes unstable, and stable reproduction output cannot be obtained. Therefore it is impossible to maximize the Kerr effect enhancement,
In addition, there is a problem that the film thickness setting range of the interference layer for stabilizing tracking is narrow and the accuracy of film thickness variation is strictly required. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a high quality optical recording medium capable of increasing Kerr effect enhancement and obtaining stable tracking characteristics. To provide.

[0004]

In order to achieve this object, an optical recording medium of the present invention has an interference layer for increasing the Kerr rotation angle on a substrate and improving signal characteristics, a recording layer, and a tracking layer. A guide layer, the recording layer is processed into a predetermined pattern, and the interference layer exposed in the gap between the recording layers is formed of a translucent material having a refractive index higher than that of the substrate, and a predetermined amount. It has been etched.

[0005]

According to the above construction, in the optical recording medium of the present invention, the recording layer is processed into a predetermined pattern shape, and the interference layer exposed in the gap between the recording layers has a higher light transmission than the substrate. Formed of a conductive material and etched by a predetermined amount.

By etching a part of the interference layer, an optical path difference of the laser beam is generated between the portion with the recording layer and the portion without the recording layer. By utilizing this, tracking can be performed by the push-pull method, so that it is possible to prevent the push-pull signal from decreasing even when the interference layer is set to a film thickness that maximizes the Kerr effect enhancement. Push-pull signal and interference layer when maximizing Kerr effect enhancement,
The relationship with the etching amount is shown in FIG.

Therefore, the Kerr effect enhancement is maximum and exhibits excellent S / N, and stable tracking characteristics can be obtained, and the film thickness of the interference layer for increasing the Kerr effect and stable tracking characteristics can be obtained. The setting range is wide, and the accuracy of film thickness variation is alleviated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of an essential part of an optical recording medium 10 according to an embodiment of the present invention. The optical recording medium 10 has an interference layer 14 and a recording layer 16 on a transparent substrate 12 such as glass. ,
The tracking guide layer 18 and the protective layer 20 are sequentially laminated.

The interference layer 14 on the substrate is formed by the sputtering method,
A SiAlON film, a TiO ₂ film, etc. formed by a sol-gel film formation method by spin coating / baking, and the film thickness D thereof is approximately (λ / 4n) + M (λ / 2n) (λ = reproducing light wavelength, n =
Interference layer refractive index, M = integer). Refractive index is SiAlO
When N is used, it is 2.2, and when TiO ₂ is used, it is 2.7, both of which are higher than the refractive index of the substrate glass of about 1.5.

The recording layer 16 is made of, for example, a magneto-optical material which is an amorphous alloy containing a rare earth element and a transition metal as main components, that is, TbFeCo (terbium iron cobalt alloy).
It is formed by sputtering, vacuum deposition, or the like, and is fixed to the interference layer 14 in a spiral shape or the like continuously or discontinuously. The recording layer pattern 16 is produced by well-known photolithography. That is, a recording film of TbFeCo or the like is formed on the interference layer 14 by a method such as vacuum deposition or sputtering, and a resist is applied thereon by a spin coating method or the like. Next, the resist is continuously or discontinuously removed into a predetermined shape such as a spiral shape by a laser exposure method or the like. Further, the exposed recording film portion from which the resist has been removed by etching using an acid, an alkaline aqueous solution, or plasma etching is etched.

Subsequently, the interference layer 14 is etched by using an HF solution or the like, or by plasma etching or the like, approximately (λ / 8n) + L (λ / 4n) (λ = reproducing light wavelength, n = interference). Layer refractive index, L = integer) Etching. Finally, by removing the resist with an organic solvent or the like, the recording layer 16 that has been etched and the interference layer 14 that has been similarly etched are laminated. Interference layer 1
The etching of 4 may be performed by removing the resist and using the recording layer pattern as a mask.

The tracking guide layer 18 is made of Al, T
It is made of a metal such as a or TiN, a nitride, or the like, and is formed by means such as vacuum deposition or sputtering.

The protective layer 20 is a recording layer 16 and a guide layer 18.
To protect the Si from chemical changes, SiAlON,
It is a TiO ₂ film or the like and is formed by means such as vacuum deposition and sputtering.

In the optical recording medium 10, when the recording layer 16 is irradiated with the laser beam through the substrate 12, the Kerr rotation angle of the reflected light changes in association with the local magnetization direction in the recording layer 16 due to the magneto-optical effect. The information is read based on the Kerr rotation angle of the reflected light. When writing information, the recording layer 16 is locally heated to the Curie point or the compensation temperature by irradiation with laser light, and the direction of the external magnetic field is controlled to a desired direction when the local portion is cooled, so that the magnetization direction can be dealt with. Record the information.

In the optical recording medium 10 having the above structure,
The interference layer 14 is a translucent material having a high refractive index, and the substrate 12
Multiple reflection occurs between the recording layer 16 and the recording layer 16. The phase change amount A of the reproduction light, which corresponds to the film thickness of the interference layer 14, satisfies one equation when the film thickness of the interference layer 14 is D, and the Kerr effect enhancement becomes maximum when A = π + 2Mπ (M is an integer). .. According to Equation 1, when D = (λ / 4n) + M (λ / 2n), A = π + 2Mπ (M is an integer), and thus the recording layer 16
The maximum car effect enhancement in S / N
Is improved.

On the other hand, the push-pull signal for tracking becomes maximum when the phase difference B of the laser light between the portion with and without the guide layer 18 is (π / 2) + Lπ (L is an integer), and π + Lπ. Sometimes it is zero. The phase difference B
Is expressed by two equations. Here, when A = π + 2Mπ at which the Kerr effect enhancement is maximum and B = (π / 2) + Lπ at which the tracking signal is maximum, d
= (Λ / 8n) + L (λ / 4n). In addition, the Kerr effect enhancement is maximum and the tracking signal is zero, that is, B = π + Lπ, d = (λ / 4
n) + L (λ / 4n). The relationship between the push-pull signal and the etching amount d is shown in FIG.

Therefore, in the optical recording medium of the present invention, by making the etching amount d close to (λ / 8n) + L (λ / 4n), the Kerr effect enhancement is maximized and the push-pull signal for tracking is reduced. Preventing and stable tracking servo becomes possible, and d is (λ / 4n) +
As L (λ / 4n) is approached, the push-pull signal gradually decreases, and tracking servo becomes gradually impossible. d =
When (λ / 4n) + L (λ / 4n), the push-pull signal finally becomes zero, and tracking servo is completely impossible. However, when d = (λ / 6n) + L (λ / 4n), the push-pull signal did not decrease much and tracking servo was possible.

As described above, in the optical recording medium of the present invention, it is possible to maximize the Kerr effect enhancement to improve the S / N, prevent the tracking signal from decreasing, and obtain stable tracking characteristics. Is obtained. In addition, as the Kerr effect increases, the setting range of the interference layer thickness for obtaining stable tracking is also expanded,
The accuracy required for film thickness is relaxed.

A = (2π / λ) * n * D * 2 (1) B = (2π / λ) * n * d * 2 (2) (λ: reproduction light wavelength in vacuum, n : Refractive index of interference layer, D: Thickness of interference layer, d: Etching amount of interference layer) The present invention is not limited to the examples described in detail above, and may be variously modified without departing from the spirit thereof. It is possible to make changes.

For example, as shown in FIG. 2, the recording layer 16 and the guide layer 18 may be thinned, and the reflective layer 22 may be provided on the protective layer 20. That is, the light incident from the substrate 12 side passes through the recording film 16 and the guide layer 18, is then reflected by the reflective layer 22, and again passes through the recording film 16. This allows
Not only the car effect but also the Faraday effect is added, so that even greater car effect enhancement occurs. Also in this case, it is possible to prevent a decrease in the reflectance of the tracking guide layer 18 and obtain stable tracking characteristics.

Instead of glass as the substrate material, acrylic resin, polycarbonate resin, amorphous polyolefin resin or the like can be used.

In addition to the magneto-optical material, the recording layer is not limited to T
A punching type material such as e or Bi, or a phase change material such as TeOx can be used.

Further, the tracking method is not limited to the push-pull method, and the three-beam method can be similarly favorably performed.

[0025]

As is apparent from the above description, in the optical recording medium of the present invention, the recording layer is processed into a predetermined pattern, and the interference layer is a translucent material having a higher refractive index than the substrate. The S-type has maximum Kerr effect enhancement because it is formed by etching and a part of it is etched.
/ N, it is possible to obtain a stable tracking characteristic by preventing a decrease in the reflection signal of the tracking guide layer, and to increase the Kerr effect and to obtain a stable tracking. , And the accuracy of variation in film thickness is alleviated, and a high quality optical recording medium can be manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part of an optical recording medium that is an embodiment of the present invention.

FIG. 2 is a cross-sectional view of essential parts of an optical recording medium that is another embodiment of the present invention.

FIG. 3 is a cross-sectional view of essential parts showing an example of a conventional magneto-optical recording medium.

FIG. 4 is a graph showing a relationship between a tracking push-pull signal and an interference layer etching amount d.

FIG. 5 is a graph showing the relationship between the Kerr effect enhancement amount and push-pull signal, and the interference layer film thickness D.

[Explanation of symbols]

 12 glass substrate 14 interference layer 16 recording layer 18 guide layer

Claims (1)

[Claims] 1. An optical recording medium comprising an interference layer for increasing the Kerr rotation angle and improving the signal characteristics, a recording layer, and a tracking guide layer on a substrate, wherein the recording layer has a predetermined size. The optical recording is characterized in that the interference layer exposed in the gap between the recording layers is formed of a translucent material having a higher refractive index than the substrate and is etched by a predetermined amount while being processed into the pattern Medium.