JPH06111368A - Optical recording medium - Google Patents

Abstract

PURPOSE:To increase the apparent Kerr rotation angle of a recording layer and to obtain a high-grade reproduced output by forming an interference layer having the refractive index higher than the refractive index of a flattening layer on this flattening layer and generating multiple reflections in the interference layer. CONSTITUTION:The interference layer 14 of this optical recording medium 10 is a light transparent material having the refractive index higher than the refractive index of a substrate 11 and the multiple reflections arise between the substrate 11 and the recording layer 15. The Kerr effect enhancement 5 of the recording layer 15 of the optical recording medium 10 is, therefore, increased and the S/N is improved. Even if the film thickness D of the interference layer 14 is not strictly an ideal value, the sufficient Kerr effect enhancement is attained and the high-grade product is obtd, insofar as the interference layer has a thickness of about + or -30% of the ideal value.

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 used in an optical disk memory 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 is a solvent resistant resin material among polyolefins, olefin hydrocarbons, polycarbonates, methyl methacrylate copolymers, or the like, or A tracking metal guide layer 32 is formed on a substrate 11 made of a transparent inorganic material such as glass.
Is formed in a predetermined shape, and is made of an alkoxide such as silicon (Si), titanium (Ti), tantalum (Ta), or zirconia (Zr) as a material, and has a refractive index almost equal to that of the substrate 11. And gadolinium iron cobalt (GdTbFe), terbi iron cobalt alloy (TbFeC
o) etc., and a sialon (Si
A protective layer 16 made of AlON), aluminum nitride (AlN) or the like, and a reflective layer 1 made of aluminum (Al) or the like.
7 and 7 are sequentially laminated.

When recording information in such an optical recording medium 30, when the substrate 11 side of the optical recording medium 30 is irradiated with laser light, the recording layer 15 is heated. Then, when the recording layer 15 is heated to the Curie temperature or the compensation temperature or higher and a magnetic field is applied from the outside at the same time, the magnetization is inverted and information is recorded. When reproducing, the Kerr effect is used in which the rotation of the polarization plane of the reflected light is reversed by irradiating the linearly polarized laser light from the substrate 11 side of the optical recording medium 30 depending on the direction of magnetization. . Furthermore, the multiple reflection and Kerr effect in the protective layer 16 and the reflective layer 17 are utilized.

[0004]

However, in the optical recording medium having the above-described flattening layer, recording layer, protective layer, and reflective layer, the refractive index of the flattening layer and the refractive index of the substrate material are different from each other. Since they are almost equal, the Kerr effect enhancement due to the interference effect cannot be obtained. Therefore, there is a problem that a high reproduction output cannot be obtained.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to form an interference layer having a higher refractive index than the substrate on the upper surface of the flattening layer. An object of the present invention is to provide an optical recording medium capable of obtaining the Kerr effect enhancement.

[0006]

In order to achieve this object, an optical recording medium of the present invention comprises a substrate, a tracking guide layer, and a flattening layer having a refractive index substantially equal to that of the substrate.
An optical recording medium including a recording layer, wherein an interference layer having a refractive index higher than that of the flattening layer is formed on the flattening layer.

In the above optical recording medium, the thickness of the interference layer is (λ / 4n) + (Mλ / 2n; where λ = the wavelength of the reproduction light in vacuum, n = the refractive index of the interference layer, and M = 0. , 1,
2, ...)

[0008]

In the optical recording medium having the above structure, the interference layer is made of a material having a higher refractive index than the substrate, and the interference light causes multiple reflection of reproduction light. Thereby, the Kerr effect enhancement is increased and the S / N is improved.

[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.
A guide layer 12 for tracking, a flattening layer 13, an interference layer 14, and a recording layer are formed on a transparent substrate 11 made of glass or a resin material such as olefin hydrocarbon, polycarbonate ester, and methyl methacrylate copolymer. 15 and protective layer 1
6 and 6 are laminated in that order.

The tracking guide layer 12 is made of tantalum (Ta) and has a concentric circle on the substrate 11.
It is fixed in a continuous or discontinuous manner in a pattern shape such as spiral or straight line. This tracking guide layer 12
Are produced by well-known photolithography. Specifically, a Ta film is vacuum-deposited on the substrate 11,
Alternatively, it is formed by means such as sputtering, and a resist is applied thereon by a spin coating method or the like. Next, the resist is removed in the pattern shape by photolithography such as laser exposure. Further, the portion of the metal film from which the resist has been removed is etched by etching with acid, alkali, or plasma etching.

A flattening layer 13 made of a light-transmissive insulating film is formed on the tracking guide layer 12 by a sputtering method or a sol-gel film forming method by spin coating and baking. The flattening layer 13 is preferably made of an alkoxide such as silicon (Si), titanium (Ti), tantalum (Ta), or zirconia (Zr).

On the flattening layer 13, sialon (SiA
1ON), aluminum nitride (AlN), titanium dioxide (TiO ₂ ) or the like is formed by a sputtering method or a sol-gel film formation method by spin coating / firing. The film thickness D of the interference layer 14 is approximately 1 / the wavelength of the reproduction laser light passing through the interference layer 14.
It is about 4. However, when the refractive index of the flattening layer 13 is larger than the refractive index of the substrate 11, the total film thickness of the flattening layer 13 and the interference layer 14 is set to the wavelength of the reproduction laser light. About 1/4 of the above. The refractive index when SiAlON is used as the interference layer 14 is 2.
2. The refractive index when AlN was used was 2.7 when TiO ₂ was used, and the refractive index when silicon nitride (SiN) was used was around 2.0.
As a result, the refractive index becomes larger than 1.46 when glass is used.

The recording layer 15 formed on the interference layer 14 is preferably a magneto-optical material which is an amorphous alloy containing a rare earth and a transition metal as main components, and more preferably,
A terbiiron cobalt alloy (TbFeCo) is used.
Alternatively, platinum cobalt (Pt / Co), garnet-based oxide, or the like may be used. The recording layer 15 is produced by forming these materials on the interference layer 14 by sputtering, vacuum deposition, sintering or the like.

The protective layer 16 protects the recording layer 15 from chemical changes, and is made of sialon (SiAlO).
It is formed by subjecting a material such as N) or aluminum nitride (AlN) to a treatment such as sputtering or vacuum deposition.

In the optical recording medium 10 having the above-described structure, when the recording layer 15 is irradiated with the laser beam through the substrate 11, the reflected light is caused by the magneto-optical effect in relation to the local magnetization direction in the recording layer 15. The Kerr rotation angle is changed, and information is read based on the Kerr rotation angle of the reflected light. In writing information, the recording layer 15 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 10 having the above structure,
The interference layer 14 is a translucent material having a higher refractive index than the substrate 11, and multiple reflection occurs between the substrate 11 and the recording layer 15. In order to maximize the Kerr effect enhancement in the recording layer 15 and increase the apparent Kerr rotation angle, the condition for improving the S / N is that the film thickness of the interference layer 14 is D
Then, D = λ / 4n + Mλ / 2n. That is, the film thickness D of the interference layer 14 is set to about ¼ of the wavelength of the reproduction light in the interference layer 14, or to a value obtained by adding an integral multiple of half the wavelength. Therefore, in the optical recording medium 10 of the present embodiment, the Kerr effect enhancement in the recording layer 15 is increased and the S / N is improved. However, the interference layer 14
Even if the film thickness D is not strictly equal to the above ideal value, the Kerr effect enhancement can be sufficiently obtained as long as the thickness is about ± 30% from the ideal value. As a result of the above-described actions, the optical recording medium 10 of the present embodiment improves the S / N, stabilizes the tracking characteristics, and obtains a high-quality product.

Although one embodiment of the present invention has been described in detail above with reference to FIG. 1, the present invention can be implemented in other modes.

For example, as shown in FIG. 2A, the thickness of the recording layer 15 may be reduced and the reflective layer 17 may be formed on the upper surface of the protective layer 16. According to this structure, the laser light incident from the substrate 11 side passes through the recording layer 15, is reflected by the reflective layer 17, and then passes through the recording layer 15 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 12 can be prevented, and stable tracking characteristics can be obtained.
Further, as shown in FIG. 2B, each layer formed on the substrate 11 may have a step difference of about the film thickness of the guide layer 15. Further, in the configuration shown in FIG.
It can be modified to include the reflection layer 17 as in the configuration shown in FIG.

As the recording layer 15, not only a magneto-optical material but also a perforated type material such as tellurium (Te) or bismuth (Bi), or a phase change type material such as tellurium oxide (TeOx) is used. it can.

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

[0022]

As is apparent from the above description, in the optical recording medium of the present invention, since the interference layer is formed of a translucent material having a higher refractive index than the substrate, When laser light is irradiated, multiple reflection occurs in the interference layer, and the Kerr effect enhancement increases the apparent Kerr rotation angle of the recording layer, thereby improving S / N. As a result, a high-quality reproduction output can be obtained.

[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 an essential part 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.

[Explanation of symbols]

 11 substrate 12 tracking guide layer 13 flattening layer 14 interference layer 15 recording layer

Claims (2)

[Claims] 1. An optical recording medium comprising a substrate, a tracking guide layer, a flattening layer having a refractive index substantially equal to that of the substrate, and a recording layer, wherein a flattening layer is formed on the flattening layer. An optical recording medium comprising an interference layer having a refractive index higher than that of the refractive index. 2. The optical recording medium according to claim 1,
The film thickness of the interference layer is (λ / 4n) + (Mλ / 2n; where λ = wavelength of reproduction light in vacuum, n = refractive index of interference layer,
An optical recording medium characterized in that M = 0, 1, 2, ...