JPH05198021A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve S/N and to stabilize tracking characteristic by working a guide layer to a prescribed pattern, forming an interference layer of a light transmissive material having the refractive index higher than the refractive index of a substrate and etching this material in a prescribed amt. CONSTITUTION:The guide layer 16 for tracking is formed of Al, Ta, etc., and is fixed continuously or discontinuously in spiral or other shapes on the interference layer 14. The interference layer 14 is formed of the light transmissive material, such as SiAlON or TiO2 having the refractive index (n) higher than the refractive index of the glass substrate 12. The film thickness D of the layer 14 is specified nearly to D=(lambda/4n)+M(lambda/2n) in relation to the etching amt. (d). In the formula, lambda denotes a reproducing light wavelength; M denotes an integer. As a result, multiple reflections are generated between the substrate 12 and the recording layer 18 and the max. Kerr effect enhancement and excellent S/N are exhibited; in addition, the decrease in the reflection signals of the layer 16 is prevented and the stable tracking characteristic is obtd.

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. Therefore, the substrate 32 and the recording layer 3 are required.
The interference layer 34 having a refractive index higher than that of the substrate is provided between 7 and the interference effect due to multiple reflection is utilized.

[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, the protective layer, and the reflective layer, the interference layer 34 is used. Film thickness is approximately λ /
However, as shown in FIG. 5, the reflectivity in the groove 31 necessary for tracking becomes very small in contrast to the increase of the Kerr effect at this time, and in addition, the film thickness of the magneto-optical recording layer is also the reflectivity. However, the push-pull signal becomes almost 0, the tracking servo becomes unstable, and 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]

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

[0006]

According to the above structure, in the optical recording medium of the present invention, the tracking guide layer is processed into a predetermined pattern, and the interference layer exposed in the gap between the guide layers has a refractive index higher than that of the substrate. It is made of a highly transparent material and is etched by a predetermined amount.

Since the interference layer is partially 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 the tracking can be performed by the push-pull method by utilizing this, it is possible to prevent the decrease of the push-pull signal even when the interference layer is set to the film thickness that maximizes the Kerr effect enhancement. FIG. 4 shows the relationship between the push-pull signal and the etching amount of the interference layer when the Kerr effect enhancement is maximized.

Therefore, the Kerr effect enhancement shows the maximum S / N at the maximum, and it is possible to prevent the reduction of the reflection signal of the tracking guide layer and obtain a stable tracking characteristic, and the Kerr effect increases and becomes stable. The setting range of the thickness of the interference layer is wide to obtain both tracking characteristics,
Accuracy of variation in film thickness is eased.

[0009]

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 an interference layer 14 and a tracking guide on a transparent substrate 12 such as glass. The layer 16, the recording layer 18, and the protective layer 20 are sequentially laminated.

The interference layer 14 on the substrate is formed by the sputtering method,
SiAlON, TiO ₂ films or the like formed by a sol-gel film formation method by spin coating / baking, etc., and the film thickness D thereof is approximately (λ / 4n) in relation to the etching amount d of the interference layer.
+ M (λ / 2n) (λ = reproducing light wavelength, n = interference layer refractive index, M = integer). The refractive index is 2.2 when SiAlON is used and 2.7 when TiO ₂ is used, which are both larger than the refractive index of the substrate glass of about 1.5.

The tracking guide layer 16 is made of Al or Ta.
It is formed of a metal or the like and is fixed to the interference layer in a spiral shape or the like continuously or discontinuously. The tracking guide layer 16 is manufactured by well-known photolithography. That is, A on the substrate 12
A metal film of l, Ta or the like is formed by means such as vacuum deposition or sputtering, and a resist is applied thereon by a spin coating method or the like. Next, the resist is removed by a laser exposure method or the like into a predetermined shape such as a continuous or discontinuous spiral shape. Further, the exposed metal 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 is etched by using an HF solution or the like, or by plasma etching or the like.
Abbreviation (λ / 8n) + L (λ / 4n) (λ = reproducing light wavelength, n
= Refractive index of interference layer, L = integer) Etching. Finally,
By removing the resist with an organic solvent or the like, a processed substrate is formed in which an interference layer that has been etched is laminated in the same manner as the tracking guide layer 16 that has been etched. The interference layer etching may be performed by removing the resist and using the guide layer pattern as a mask.

The recording layer 18 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 or vacuum deposition.

The protective film 20 is for protecting the recording layer 18 from chemical changes, and is made of SiAlON, AlN or the like, and is formed by sputtering or vacuum evaporation.
When the recording layer 18 of the optical recording medium 10 is irradiated with the laser beam through the substrate 12, the Kerr rotation angle of the reflected light is changed in association with the local magnetization direction of the recording layer 18 by the magneto-optical effect. Information is read based on the Kerr rotation angle of the reflected light. When writing information, the recording layer 18 is locally heated to the Curie point or the compensation temperature by irradiation of 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. The phase change amount A of the laser beam corresponding to the film thickness of the interference layer is expressed by the equation 1 where the film thickness of the interference layer is D, and the Kerr effect enhancement is A = π +
It becomes maximum when 2Mπ (M is an integer). From formula 1 D-d
= Λ / 4n + Mλ / 2n, A = π + 2Mπ (M is an integer), so that the Kerr effect enhancement in the recording layer is maximized and the 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 in the portion with and without the guide layer is (π / 2) + Lπ (L is an integer), and becomes zero when π + Lπ, FIG. 4 shows the relationship between the push-pull signal and the phase difference. The phase difference B is expressed by equation 2. Here, the Kerr effect enhancement becomes maximum when A = π + 2Mπ, and the tracking signal becomes maximum B = (π / 2) + L.
When π, d = (λ / 8n) + L (λ / 4n).
Further, when the Kerr effect enhancement is maximum and the tracking signal is zero, that is, B = π + Lπ, d
= (Λ / 4n) + L (λ / 4n).

Therefore, in the optical recording medium of the present invention, the Kerr effect enhancement is maximized and the push-pull signal for tracking is lowered by bringing the etching amount d close to (λ / 8n) + L (λ / 4n). Prevents and enables stable tracking servo, 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 becomes zero, and tracking servo is completely impossible, but when d = (λ / 6n) + L (λ / 4n), the push The drop of the pull signal was small, and tracking servo was possible. As described above, in the optical recording medium of the present invention, the Kerr effect enhancement is maximized and the S / N ratio is increased.
It is possible to obtain a high-quality product while improving tracking performance and preventing the tracking signal from dropping, and to obtain a high-quality product. Also, as the Kerr effect increases, the setting range of the thickness of the interference layer for obtaining stable tracking expands. ,
The accuracy required for film thickness is relaxed.

A = (2π / λ) * n * (D−d) * 2 ... 1 formula B = (2π / λ) * n * d * 2 Formula (λ: wavelength of reproducing light in vacuum, n: refractive index of interference layer, D: film thickness of interference layer, d: etching amount of interference layer) The present invention is limited to the above-described embodiments. Instead, various changes can be made without departing from the spirit of the invention.

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, it is possible to prevent a decrease in the reflectance of the tracking guide layer 16 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.

Further, the recording layer is not limited to the magneto-optical material, but 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.

[0023]

As is apparent from the above description, in the optical recording medium of the present invention, the guide 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 prevent a decrease in the reflection signal of the tracking guide layer and obtain stable tracking characteristics, and further, it is possible to increase the Kerr effect and to obtain a stable tracking film thickness. The setting range is wide, and the accuracy of variation in film thickness is relaxed, so that 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 optical recording medium.

FIG. 4 is a graph showing a relationship between a tracking push-pull signal and a phase difference.

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 guide layer 18 recording layer

Claims (1)

[Claims] 1. An optical recording medium comprising an interference layer for increasing the Kerr rotation angle to improve signal characteristics, a tracking guide layer, and a recording layer on a substrate, wherein the guide layer is provided. Light that is processed into a predetermined pattern, and the interference layer exposed in the gap between the guide layers is formed of a translucent material having a higher refractive index than the substrate, and is etched by a predetermined amount. recoding media.