KR930007029B1 - Optical disk - Google Patents

Abstract

The optical disk is manufactured by (a) laminating TbN dielectric layer of 1000 angstroms thickness on the polycarbonate (PC) substrate by the radio frequency sputtering method, (b) laminating TbFeCo recording layer of 700 angstroms thickness on the dielectric layer by the DC sputtering method, and (c) laminating a dielectric protecting layer on the recording layer. The disk has a good oxidation-resistance, a high refractive index and a good SNR.

Description

Optical disc with dielectric layer of TbN

1 is a graph comparing changes in Kerr angle (θk) of a conventional SiN protective film and a TbN protective film according to the present invention.

Fig. 2 is a graph showing a comparison between the SNR and the lifetime of an optical disk having a conventional SiN protective film and an optical disk having a TbN protective film according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly, to an optical disk having a TbN protective film having enhanced oxidation resistance, a high refractive index, an increased θk, and a good SNR (Singal to Noise Ratio). will be.

Conventional optical discs use the following as the protective layer material which serves as a protective role for the disc recording surface, and the structure of the optical disc varies greatly depending on the material used. As a protective film material of a general optical disk, a dielectric material is used a lot. For example, SiC is a nitride dielectric material, Si3N4 is a nitride dielectric material, and SiO2 is an oxide type.

Such a dielectric material is manufactured by electron beam method or sputtering method and generally has a slight difference in thickness, but this thickness is N4n so that almost all energy of the laser beam to be irradiated can be absorbed. Adjust In the second method, a recording material is protected by applying a polymer material or the like on the optical disk substrate material in addition to the dielectric.

In the manufacture of the conventional orphan disk as described above, the disk substrate is made of PC (Poly-Carbonate) or PMMA (Ploy-Methyl-Metacrylate). It was prepared as a coating.

However, the biggest disadvantage of the conventional optical disk having such a protective layer is that oxidation / corrosion is easily caused by changes in the environmental environment and time, and in the case of SiN having good stability, the refractive index is small and the SNR of the output signal is small. It is low. The low SNR of the output signal of the optical disk according to the prior art is caused by the following factors. That is, firstly, in the case of a worm or erasable optical disc, the recording layer material is very weak to the oxidizing and corrosive environment so that the information recording bit material is changed to lower the SNR. Information is lost due to the difference in thermal expansion and humidity expansion coefficients between the substrate and the protective film or between the substrate and the recording layer. Third, Kerr Rotation Angle (θk), which forms SNR in the case of magneto-optical disk, is small. For losing.

Therefore, to solve the disadvantages of the optical disk having a conventional protective coating layer of the present invention, the present invention will be described in more detail below.

The protective film material used in the optical disk of the present invention is a synthetic material of TbN, and since Tb (Terbium) has a strong affinity for oxygen, water vapor / coral particles passed from the outside are trapped and cannot enter the recording layer. Oxidation and corrosion of the layers can be prevented. In addition, since the refractive index of TbN is 2.5, which is considerably higher than that of SiN, 2.0, the effect of improving the θk is doubled compared to that of the SiN protective film. Thus, the SNR (= R.OK2) has a significant increase effect (see also FIG. 1). The reason why θk increases when the refractive index is large is that θk is represented by the ratio of the reflection coefficient Rx of the X component and the reflection coefficient Rx of the Y component, and the three refractive indexes of the protective film reduce the reflection coefficient of the Rx component. Therefore, the size of the Rx component is reduced, so θk = (Ry / Rx) represents a relatively large value.

In addition, an optical disk having a TbN dielectric layer according to the present invention is produced by the following method. That is, a TbN dielectric film material was used on a 5.25 inch poly-Carbonate (PC) substrate and manufactured by RF (Radio Frequency) sputtering method. At this time, the target (Target) was used Tb target, it was carried out by the reactive sputtering method blowing the N2 gas. During the implementation, the total pressure of the N 2 gas was 5 mTorr, and the powder of Ar: N 2 was 4: 1, so that the total thickness was deposited to 1000A (A = angstrom). Thereafter, a recording layer made of TbFeCo was coated by DC sputtering, and the total pressure of Ar was maintained at an isostatic pressure of 3 mTorr and deposited so as to have a total thickness of 700 A (A = Angstrom). In addition, the uppermost dielectric protective film was coated by carrying out the same procedure as the TbN dielectric film manufacturing process.

The performance evaluation of the optical disk having the TbN protective layer (dielectric layer) produced by the present invention as described above is as follows. This evaluation is an SNR strengthening test based on three kinds: corrosion resistance test, durability test, and kerr rotation angle (θk). SNR was measured after 200 hours at 70 degrees Celsius and 97% RH. The measurement was performed. Data for the above experimental results are shown in FIG. In Figure 2 it can be seen that there is no SNR degradation due to the strengthening and corrosion of the SNR.

The optical disk having the TbN protective film (dielectric layer) according to the present invention as described above has the following effects as compared to the conventional optical disk.

First, since the water vapor / oxygen particles cannot enter the recording layer by the Tb component contained in the TbN protective film, the degradation of the recording layer does not occur due to the lapse of time and environmental changes, so the SNR of the output signal does not decrease. The TbN protective film material according to the present invention has good adhesiveness with synthetic resin substrates (e.g. PC, PNMA) to prevent deformation of the disk due to thermal expansion / humidity expansion during recording, and third, because the refractive index is large, It provides the advantage of achieving an increase in the Kerr rotational angle (θk) which can increase the SNR.

Claims (2)

An optical disk having a TbN dielectric layer, comprising a dielectric layer of a TbN material having a high affinity for oxygen on a substrate, and a recording layer and a dielectric protective film laminated on the dielectric layer. The dielectric layer of claim 1, wherein the dielectric layer is stacked by a radio frequency (RF) sputtering method in which N ₂ is injected into a Tb target, and has a dielectric layer of TbN, characterized in that the thickness is 700-1300 Hz (Omstrom). Optical disc.