JPS61153856A - Information recording medium - Google Patents

Abstract

PURPOSE:To obtain an information recording medium having especially improved corrosion resistance by forming a recording layer of a magnetic alloy having an axis of easy magnetization in a direction perpendicular to the surface of the layer and by anodically oxidizing the surface of the recording layer in a vapor phase to form a thin metallic oxide film as a protective layer. CONSTITUTION:A thin film of an amorphous alloy of rare earth and transition metals such as Tb-Fe or Gd-Tb-Fe is formed on a substrate 1 of glass or the like as a recording layer 2 having an axis of easy magnetization in a direction perpendicular to the surface of the layer. The atmosphere in an apparatus used to form the recording layer is replaced with an atmosphere of a gaseous Ar-O2 mixture, and oxygen radicals or ions are made incident on the surface of the recording layer 2 by plasma excitation to oxidize the surface of the layer 2. An anodic oxide film of about 300Angstrom thickness is formed as a protective layer 3 by the oxidation, and a photo- and thermomagnetic recording medium whose recording layer 2 has improved corrosion resistance is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an information recording medium having a recording layer made of a magnetic alloy thin film, and particularly to an information recording medium with improved corrosion resistance.

[Technical background of the invention and its problems]

□Recording of information by irradiation with a light beam such as a laser beam,
2. Description of the Related Art Photothermal magnetic recording media that utilize the -effect as much as possible are attracting attention as optical discs that can be reproduced and erased. This photothermal magnetic recording medium has a structure in which a recording layer made of a magnetic alloy thin film with an axis of easy magnetization perpendicular to the film surface is formed on a substrate, and records are recorded by irradiation with a light beam modulated according to an information signal. By locally heating the layer near the Curie point, information is recorded in the form of magnetization reversal. On the other hand, to reproduce recorded information, a light beam is irradiated onto a recording layer where magnetization reversal occurs locally, and the rotation of the plane of polarization reflected from the surface of the recording layer at that time, that is, the effect is utilized as much as possible. It is done.

The recording layer of a photothermal magnetic recording medium that utilizes such an effect as much as possible includes TbFe, GdFe, GdTbFe, and TbFe.
Rare earth-transition metal amorphous alloy thin films such as bFeCo and GdTbFeCo are known. All of these amorphous alloy thin films have a large Kerr rotation angle θK and a relatively low Curie point. In addition, these amorphous alloys have advantages in terms of ease of creating a large-area and uniform recording layer, that is, film formability, recording efficiency for writing information with small photothermal energy, and reproduction output S/distance. 1i111 is excellent as a recording layer of a photothermal magnetic recording medium.

However, these opto-thermal magnetic recording media with rare earth-transition metal amorphous alloy thin films as the recording layer generally have extremely poor corrosion resistance, and this is a major obstacle to the practical application of magneto-optical recording. It has become. 'For this reason, attempts have been made to improve the corrosion resistance by forming a transparent dielectric film on the recording layer. However, since thin films such as SiO2 and SiO used as dielectric films are formed by high frequency sputtering, defects such as pinholes are likely to occur inside the film due to the effects of radiant heat and dust during sputtering.

Therefore, over a long period of time, moisture in the atmosphere will enter through these defects, causing corrosion of the recording layer, and forming a dielectric film is not very effective in improving corrosion resistance. Ta. Also, in magnetic recording media for normal magnetic recording, not for magneto-optical recording, especially magnetic alloy 1i11
In the case where No. 1 is used as a recording layer, a dielectric film is similarly formed on the surface as a protective layer, so there is a problem similar to that described above.

[Purpose of the invention]

An object of the present invention is to provide an information recording medium in which a recording layer made of a magnetic alloy in has improved corrosion resistance. Here, a protective layer for improving corrosion resistance is formed on a recording layer made of a thin film of a magnetic alloy such as rare earth-transition metal amorphous alloy 3111g1, which has an axis of easy magnetization perpendicular to the film surface.
．． By anodizing the surface of the recording layer in the gas phase! It is characterized in that it is realized by the formed oxide WIII.

The method for anodic oxidation used to form the protective layer made of oxide 1i111 in the present invention is to use a mixed gas of oxygen-based gas such as 02 gas or CO2 gas and rare gas such as Ar at a gas pressure of 1O-3T.・Orr～10 Torr
A method in which the potential of the recording layer is biased to positive lI in an atmosphere in which the pressure is reduced to about r and external power is applied to excite the plasma, and oxygen radicals and oxygen ions in the plasma are effectively made to enter the surface of the recording layer. Alternatively, a method in which the recording layer is simply exposed to oxygen-based gas plasma without applying a particular potential to utilize oxygen radicals in the plasma is suitable.

〔Effect of the invention〕

According to the present invention, since the protective layer of the recording layer is made of a thin film of oxide of the base alloy component that constitutes the recording layer itself,
Unlike conventional recording media in which a protective layer made of an M'R body film is formed by sputtering or the like, defects such as pinholes do not occur inside the Ftrm, and corrosion resistance can be significantly improved. Furthermore, since the protective layer made of the oxide WI film thus formed has the surface portion of the recording layer transformed into an oxide, it also has excellent adhesion to the recording layer.

[Embodiments of the invention]

FIG. 1 is a sectional view of an information recording medium according to an embodiment of the present invention. In the figure, a substrate 1 is, for example, a glass substrate, and has an axis of easy magnetization perpendicular to the film surface on this substrate 1, such as TbFe or GdFe.

GdTbFe, TbFeCo, GdTbFeC.

Records consisting of thin films of rare earth-transition metal amorphous alloys such as
A protective layer 3 is further provided on the recording layer 2, which is formed by anodizing the surface of the recording layer 2 in a gas plasma containing oxygen.

Taking as an example a photothermal magnetic recording medium in which a TbFe layer is formed as the recording material 112, a specific example of its manufacturing process will be described.

! To! To form the recording layer 2, a high-frequency sputtering device was prepared, and a Tt of 10 squares was placed on a 5-inch Fe disk target.
) The pellet is 39% relative to the area of the Fe/disk target.
%, and Ar gas was added to 10 (SCCU).
Sputtering is carried out while maintaining the flowing Ar gas pressure at 5 mTorrk, and TbFe11 is deposited on the glass substrate constituting the base 1.
The recording layer 2 was formed to have a thickness of 1000 mm. Next, exhaust the inside of the device and 02 gas (20%) - Ar (8
0%) mixed gas is introduced and the gas pressure inside the device is 1 Torr.
maintained at r.

Insert a shutter between the target and the substrate and apply RF power to the coil installed above the shutter to generate 02-A.
An r gas plasma was excited on the front side of the substrate with the recording layer applied. At the same time as the plasma was excited, the recording layer was externally biased with +100 V (relative to ground potential). RF
Plasma anodic oxidation was continued for about 5 m1n at an illumination power of 100 W, and an anodic oxide film was formed to a thickness of d-200 mm to form a protective layer 3.

This is #1 shown in Table 1 below. Table 1 also shows examples #2 to #6 of anodic oxidation under other conditions.

TbF anodized by the treatment method number #1 in Table 1
Samples of the TbFe film and the comparative TbFe film that had not been subjected to any anodic oxidation treatment were heated at a constant temperature of 70°C and 85% RH.
The surface condition after being placed in a humidity chamber for 48 hours to conduct an accelerated corrosion resistance experiment is shown in the optical micrographs of Figures 2 and 3.Furthermore, the conventional TbF
The surface condition after the same accelerated test of a sample coated with SiO2 with a thickness of 600 mm as a transparent dielectric film to improve corrosion resistance on the e-film by vapor deposition using electron beam heating is shown in 41i.
! This is shown in the optical micrograph of I. The magnification is 100x in both Figures 2-4.

From these micrographs, anodized TbFem1
No corrosion caused by defects such as pinholes was observed on the surface, and the surface maintained an extremely uniform surface condition, but blisters due to corrosion were clearly observed on the surface of the TbFe film that was not anodized. .

Furthermore, in the TbFe film coated with S+02, deterioration of TbFe1ll from the pinhole portion was also observed.

Next, magnetic alloy ii! that constitutes the recording layer! The coercive force HC and saturation magnetization MS measured as a film using a vibrating sample magnetometer (VSM) are shown in Tables 2 and 3, respectively. These coercive force Hc and saturation magnetization Ms are both obtained when a magnetic field is applied in a direction perpendicular to the film surface of the TbFe film. Note that the acceleration conditions were the same as those used when observing the surface state of TbFem1.

``TbFc1l, which has been oxidized to III polarity in this way, shows almost no change in both Hc and Ms before and after the accelerated test.
ll! In the TbFe film that is not oxidized at the I pole, Hc is 1,,-'
5, and the MS decreased by ~1/3. Also, 5iOz
In T b Fe coated with I, HC is 1
/2, MS decreased by 2/3. It was experimentally confirmed that similar results were obtained with the treatment methods numbered #2 to #6 in Table 1.

As described above, in the information recording medium according to the present invention, T
By using an oxide all formed by anodizing the surface of a recording layer such as bFe111 in a gas phase as a protective layer, the corrosion resistance of the recording layer can be significantly improved. Furthermore, the protective layer thus formed had extremely good adhesion to the recording layer, and in fact, no peeling occurred at all when applied with cellophane tape in a single-pull test. Moreover, since the present invention uses oxidation treatment in the gas phase,
After forming the recording layer by a vapor phase method such as sputtering or vapor deposition,
The process can be performed continuously without breaking the vacuum, and unlike anodizing methods in aqueous solutions, it can be effectively applied to resin-based disk substrates without causing "warpage." There is an advantage.

In addition, the gas phase atmosphere shown in Table 1 is not limited to the TbFe film, but also the GdTbFe film. For anodizing other rare earth-transition metal amorphous alloys such as TbFeCo films,
It can be applied in exactly the same way.

Furthermore, #2 in Table 1. #3. Since it is also possible to apply a low-temperature process as shown in #5, the present invention is effective even when a resin substrate that is practical for optical discs is used.

The invention is not limited to the embodiments described above. For example, in the above explanation, the recording layer is a rare earth-transition metal amorphous alloy thin film for magneto-optical recording, but the recording layer is a Co-Cr based magnetic alloy thin film for normal perpendicular magnetization recording. A similar effect can also be achieved in magnetic recording media by forming a protective layer by anodizing the surface of the recording layer in a gas phase.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an information recording medium according to an embodiment of the present invention, and FIG. 2 is an optical diagram showing the metal structure of the anodized TbFe film after a corrosion resistance test in the information recording medium according to the embodiment. Micrograph, Figure 3 shows Tb without Ili oxidation treatment.
The fourth is an optical micrograph showing the metal structure after the corrosion resistance test on the Fe film surface, and the fourth is an optical microscope photo showing the metal structure after the corrosion resistance test when SiO2 is coated on the 7bFel1 surface that is not anodized. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Recording layer, 3...Protective layer. Applicant's agent Patent attorney Takehiko Suzue Figure 1 2 Le・,1 1:I'shi 3:・1 Da,4

Claims (3)

[Claims] (1) In an information recording medium having a recording layer made of a magnetic alloy thin film having an axis of easy magnetization perpendicular to the film surface, and a protective layer formed on the recording layer, the protective layer is formed on the surface of the recording layer. An information recording medium characterized in that it is an oxide thin film formed by anodic oxidation in a gas phase. (2) The information recording medium according to claim 1, wherein the magnetic alloy thin film constituting the recording layer is a rare earth-transition metal amorphous alloy thin film. (3) The oxide thin film constituting the protective layer is an anodic oxide film obtained by exposing the surface of the recording layer to plasma of a gas containing an oxygen-based gas. Information recording medium described in section.