JPH05198022A - Optical recording medium - Google Patents

Abstract

PURPOSE:To increase Kerr effect enhancement and to obtain stable tracking characteristic by working a guide layer to prescribed patterns, etching the substrate exposed in spacings and forming an interference layer of a light transmission material having the refractive index higher than the refractive index of the substrate. CONSTITUTION:The guide layer 14 for tracking is constituted by forming a metallic film consisting of Al, Ta, etc., on the glass substrate 12, applying a resist thereon and removing the resist to a prescribed pattern shape by laser beam exposing, etc. The parts where the resist of the metallic film layer is removed are then removed by etching or plasma etching using an aq. acid or alkaline soln., etc. In succession, the prescribed amt. d1 of the substrate 12 is etched. The interference layer 16 of prescribed thickness D is formed thereon by using a TiO2 film, etc., having the refractive index higher than the refractive index of the substrate 12. A recording layer 18 and a protective layer 20 are successively laminated thereon. Multiple reflections are generated between the substrate 12 and the layer 18, by which the Kerr effect enhancement is maximized and 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 the linearly polarized laser light. Furthermore, to obtain good signal characteristics, the apparent Kerr rotation angle is increased by Kerr effect enhancement, and the signal-to-noise ratio (S / N) is increased.
Therefore, an interference layer 34 having a refractive index higher than that of the substrate is provided between the substrate 32 and the recording layer 37.
The interference effect of multiple reflection was used.

[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, and the magneto-optical recording layer, the thickness of the interference layer 34 is approximately λ. / 4n ₂ and to have it, as shown in FIG. 5, this time against tracking in reflectance in the groove 31 becomes very small required to the increase of the Kerr effect, the thickness of the magneto-optical recording layer in addition However, since the reflectance is set to be approximately the minimum, the push-pull signal becomes close to zero and the tracking servo becomes unstable, so that a stable reproduction output cannot be obtained. Therefore, there is a problem in that it is impossible to maximize the Kerr effect enhancement, and 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 in order to solve the above-mentioned problems, and an object of the present invention is to enhance the Kerr effect enhancement and to obtain stable tracking characteristics. An object is to provide an optical recording medium.

[0005]

To achieve this object, the optical recording medium of the present invention comprises a substrate, a tracking guide layer, and an interference layer for increasing the Kerr rotation angle and improving the signal characteristics. And an optical recording medium in which recording layers are sequentially stacked, the guide layer is processed into a predetermined pattern, the substrate exposed in the gap between the guide layers is etched, and the interference layer is bent more than the substrate. It is characterized by being formed of a highly transparent material.

[0006]

According to the above structure, in the optical recording medium of the present invention, the guide layer for tracking is processed into a predetermined pattern, the substrate exposed in the gap between the guide layers is etched, and the interference layer is formed. It is made of a translucent material having a higher refractive index than the substrate.

Since a part of the substrate is etched, an optical path difference of the laser beam is generated between the portion with the guide layer and the portion without the guide layer. Since it becomes possible to perform tracking by the push-pull method by utilizing this, it is possible to maximize the push-pull signal even when the interference layer is set to a film thickness that maximizes the Kerr effect enhancement.
The relationship between the push-pull signal and the etching amount when the Kerr effect enhancement amount is maximized is as shown in FIG. Therefore, the Kerr effect enhancement shows the maximum and excellent S / N, the decrease of the reflection signal of the tracking guide layer can be prevented, and stable tracking characteristics can be obtained, so that both the Kerr effect and the stable tracking can be obtained. The setting range of the thickness of the interference layer for obtaining the wide range is wide, and the accuracy of the variation of the film thickness is eased.

[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 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 a tracking guide layer 1 on a transparent substrate 12 such as glass.
4, the interference layer 16, the recording layer 18, and the protective layer 20 are sequentially laminated.

The tracking guide layer 14 is made of Al or Ta.
It is formed of a metal or the like and is fixed to the substrate 12 in a pattern shape such as a continuous or discontinuous spiral. The tracking guide layer 14 is manufactured by well-known photolithography. That is,
A metal film of Al, Ta or the like is formed on the substrate 12 by a method such as vacuum deposition or sputtering, and a resist is applied thereon by a spin coating method or the like. Then, the resist is removed into a predetermined pattern shape by a laser exposure method or the like. next,
Etching using an acid or alkaline aqueous solution or plasma etching or the like is performed to etch the portion of the metal film from which the resist has been removed. Then, the glass substrate is
About (λ / 8n ₁ ) + L (λ / 4n ₁ ) etching is performed by etching using an F solution or the like, or plasma etching or the like. Finally, the resist is removed with an organic solvent or the like to form an etched glass substrate with the tracking guide layer 14. The glass substrate etching may be performed by removing the resist and using the guide layer pattern as a mask.

The interference layer 16 is made of SiAl formed by a sputtering method, a sol-gel film forming method by spin coating and baking, or the like.
ON, TiO ₂ film, etc., and the film thickness is about (λ / 4n ₂ ).
+ M (λ / 2n ₂ ). The refractive index is 2.2 when SiAlON is used and 2.7 when TiO ₂ is used, which are both higher than the refractive index of 1.46 of the glass substrate. The surface shape is substantially flat when the sol-gel film is formed.

The recording layer 18 is formed by sputtering, vacuum deposition or the like using a magneto-optical material which is an amorphous alloy mainly containing a rare earth and a transition metal, that is, TbFeCo (terbium iron cobalt alloy) or the like. The protective film 20 protects the recording layer 18 from chemical changes, and is made of SiAlON, TiO ₂ or the like, and is formed by sputtering, vacuum evaporation or the like. When the recording layer 18 is irradiated with the laser light through the substrate 12, the optical recording medium 10 has the recording layer 1 due to the magneto-optical effect.
The Kerr rotation angle of the reflected light is changed in relation to the local magnetization direction in 8, and based on the Kerr rotation angle of the reflected light,
The information is read. When writing information, the recording layer 18 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 having the above structure, the interference layer is a translucent material having a high refractive index, and multiple reflection occurs between the substrate 12 and the recording layer 18. Assuming that the amount of phase change due to the interference layer is A and the thickness of the interference layer is D, one formula is established, and the Kerr effect enhancement becomes maximum when A = π + 2Mπ. From equation 1, D = (λ / 4n ₂ ) + M (λ / 2
In the case of n ₂ ), A = π + 2Mπ, and the Kerr effect enhancement in the recording layer is maximized and the S / N is improved.

In the structure of the present invention, the push-pull signal for tracking has a value obtained by subtracting the amount of phase change corresponding to the amount of substrate etching from the amount of phase change by the interference layer is π / 2 + Nπ (N is an integer). It becomes maximum at one time,
It becomes zero when π + Nπ. When the phase change amount corresponding to the substrate etching amount d ₁ is B, the phase difference is A−B
And B is expressed by the equation (2), and the relationship between the push-pull signal and the phase difference AB is as shown in FIG. Here, A = π + 2Mπ which maximizes the Kerr effect enhancement, and AB = (π / which maximizes the tracking signal.
2) + Nπ, d ₁ = (λ / 8n ₁ ) + L (λ /
4n ₁ ) and (L = 2m−N = integer). Further, the Kerr effect enhancement is maximum, and the tracking signal is zero, that is, AB = π + Nπ is d ₁ =
(Λ / 4n ₁ ) + L (λ / 4n ₁ ). Therefore, in the optical recording medium of the present invention, the etching amount d ₁ is (λ / 8n ₁ ) + L
By approaching (λ / 4n ₁ ), it is possible to prevent the push-pull signal for tracking from decreasing and to achieve stable tracking servo, and d ₁ is (λ / 4n ₁ ) + L (λ / 4n ₁ ).
The push-pull signal gradually decreases as the value approaches d ₁ = (λ
/ 4n ₁ ) + L (λ / 4n ₁ ), the push-pull signal finally becomes zero and tracking becomes impossible, but d ₁
In the case of = λ / 6n ₁ + Lλ / 4n ₁ , 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, the Kerr effect enhancement is maximized to improve the S / N, the tracking characteristics are stable and a high quality product is obtained, and the Kerr effect is increased and the stable tracking characteristics are obtained. In addition, the setting range of the thickness of the interference layer for obtaining the above is widened, and the required accuracy of the film thickness is relaxed.

A = (2π / λ) * n ₂ * D * 2 (λ:
Reproduction light wavelength in vacuum, n ₂ : Refractive index of interference layer, D: Interference layer thickness) ... 1 equation B = (2π / λ) * n ₁ * d ₁ * 2 (λ: Reproduction light in vacuum Wavelength, n ₁ : substrate refractive index, d ₁ : substrate etching amount)
-Formula 2 Above, one embodiment of the present invention has been described in detail based on FIG. 1, but the present invention can be implemented in other modes.

For example, as shown in FIG. 2, the recording 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 is transmitted through the magnetic thin film, is then reflected by the reflective layer, and is transmitted through the magnetic thin film again. As a result, not only the Kerr effect but also the Faraday effect is added, so that even greater Kerr effect enhancement occurs. Also in this case, a decrease in reflectance of the tracking guide layer 14 is prevented, and stable tracking characteristics can be obtained.

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

Further, not only the magneto-optical material but also 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.

[0020]

As is apparent from the above description, in the optical recording medium of the present invention, the interference layer is formed of a translucent material having a higher refractive index than the substrate, and a part of the substrate is etched. As a result, multiple reflections occur in the interference layer, the Kerr effect enhancement is maximum and the S / N is excellent, and the reduction of the reflection signal of the tracking guide layer is prevented.
A stable tracking characteristic can be obtained, and the setting range of the thickness of the interference layer for widening both the Kerr effect and stable tracking is wide, and the precision of the variation of the film thickness is eased to produce a high-quality optical recording medium. it can.

[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 push-pull signal for tracking and an 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 guide layer 16 interference layer 18 recording layer

Claims (1)

[Claims] 1. An optical recording medium in which a substrate, a tracking guide layer, an interference layer for increasing the Kerr rotation angle and improving signal characteristics, and a recording layer are sequentially laminated, wherein the guide layer is An optical recording medium characterized by being processed into a predetermined pattern, etching the substrate exposed in the gap between the guide layers, and forming the interference layer from a translucent material having a higher refractive index than the substrate. ..