JPH052733A - Magnetic disk - Google Patents

Abstract

PURPOSE:To provide the magnetic disk formed by using a titanium substrate having an extremely good noise characteristic. CONSTITUTION:This magnetic disk has the nonmagnetic substrate, a substrate film formed thereon and further the magnetic film formed thereon. The nonmagnetic substrate is constituted of titanium or an alloy essentially consisting of the titanium and the substrate film is constituted of films including >=2 layers of chromium films. Two or more layers of the chromium films consist of the same compsn. and the thin film forming temp. varies. The film on the extreme substrate side of the substrate films has 30 to 1000Angstrom film thickness and is constituted of one kind selected from titanium oxide, titanium carbide and titanium nitride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention uses titanium as a substrate,
The present invention relates to a magnetic disk having excellent noise characteristics.

[0002]

2. Description of the Related Art Magnetic disks have been increasing in capacity and recording density year by year, and not only improvements and developments of magnetic thin films and underlayers, but also non-magnetic disks. Various studies have also been conducted on substrates.

As such a magnetic disk substrate, at present, a Ni-P layer is plated on the surface of an Al alloy and the treated layer is processed to have a predetermined surface precision.

The problems with the Al alloy substrate are, firstly, that the rigidity is low, so that it is not possible to meet the demand for thinning in the future, and secondly, because the high temperature strength is low, there is a future demand for magnetic films formed by high temperature sputtering. The point is that it cannot be applied as a substrate during film formation.

As a metal-based nonmagnetic substrate for solving the above problems, it has been attempted to use titanium and titanium alloys as described in JP-A-52-105804. Japanese Patent Application Laid-Open No. 56-71821 proposes a method of using titanium and a titanium alloy as a magnetic disk substrate, forming a thin film on the magnetic disk substrate, and further performing anodic oxidation to prevent defects of the substrate from being transmitted to the upper laminated film. Further, JP-A-59-151335 proposes an α-type titanium alloy substrate on which a Co-Cr film can be directly formed on the substrate. Further, JP-A 1-112521 proposes to use a hard titanium alloy having a good surface roughness as a magnetic disk substrate.

By the way, a process using an Al alloy substrate that is most commonly used at present on a titanium substrate, that is, a process of plating an Al alloy with Ni-P and laminating a chromium layer and a magnetic layer on the Ni-P plating is carried out. When applied, there is a problem in that electromagnetic characteristics similar to conventional ones cannot be obtained.
This is because a titanium substrate has Ni on top of it like an Al substrate.
This is because the P plating is hard to be attached.

Therefore, the present inventors formed a disc by forming a nonmagnetic film of Cr or the like on a titanium substrate and further forming a protective film and a lubricating film on the titanium substrate without performing Ni-P plating, The electromagnetic characteristics of this disk were evaluated. However, as a result, it was confirmed that the noise characteristics were poor.

Such problems have not been taken into consideration in the conventional magnetic disk using the titanium substrate, and therefore, the underlying film and the magnetic film on the titanium substrate have hardly been studied. The inventions of the base film and the magnetic film that have been made so far are those using an Al-based substrate or those not depending on the substrate.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic disk using a titanium substrate having extremely good noise characteristics.

[0010]

In order to solve the above-mentioned problems, the present invention comprises a non-magnetic substrate, an underlayer formed thereon, and a magnetic film formed thereon. A magnetic disk, wherein the non-magnetic substrate is made of titanium or an alloy containing titanium as a main component, and the underlayer is made of a film of two or more layers. .

As a result of various investigations by the inventors of the present invention to obtain a disk having good noise characteristics using a titanium substrate, the noise characteristics of a conventional magnetic disk in which a Cr underlayer and a magnetic film are laminated on a titanium substrate What is bad is that the crystal defects of the titanium substrate are inherited by the Cr underlayer, and Ti itself and other impurities in the titanium substrate diffuse into the Cr underlayer, which adversely affects the magnetic film. I found out. As a result of further research based on such knowledge, it was found that the noise characteristics are improved by using two or more non-magnetic underlayers. That is,
By making the underlayer film into two or more layers, it is possible to prevent crystal defects of the titanium substrate from affecting the magnetic film and to prevent diffusion of Ti itself and other impurities in the titanium substrate from affecting the magnetic film. . In other words, by forming the base film in two or more layers, crystal defects of the substrate and element diffusion from the substrate can be sufficiently absorbed.

Here, of the underlayer films, the thickness of the film closest to the substrate is 30 Å or more (hereinafter referred to as A),
It is preferably 1000 A or less. Its thickness is 30
When it is less than A, the effect of absorbing the above-mentioned crystal defects and element diffusion of the underlying film is reduced, and when it is more than 1000 A, the flatness of the film is lowered and the adhesion to the film formed thereon is decreased. It may get worse.

The plurality of base films may have different compositions, and in short, it is sufficient if the thin film formation is discontinuous. In order to make the thin film formation discontinuous with the same composition, for example, the thin film formation temperature may be changed. Typically, chromium, which has been conventionally used as a base film, may be used to form a plurality of layers by changing the film forming temperature. This is because chromium has a great effect as the above-mentioned base layer.

The uppermost layer of the base film is preferably a Cr film. This allows the magnetic film to have positive in-plane anisotropy.

Further, the base film closest to the substrate may be made of one kind selected from the group consisting of titanium oxide, titanium carbide and titanium nitride. These have a large effect as the above-mentioned base film, that is, an effect of absorbing crystal defects of the titanium substrate and element diffusion from the substrate, similar to chromium, and further function as a hardened layer to improve contact characteristics with the head. This is because it has a function.

[0016]

Embodiments of the present invention will be described below.

On a pure titanium substrate having a diameter of 2.5 inches and a thickness of 0.635 mm, a base film under various conditions shown in Table 1 was formed by sputtering or the like, and Co--C was formed on the base film.
An r-Ta magnetic film was formed by sputtering, and a protective layer and a lubrication layer were further formed on the r-Ta magnetic film to prepare a magnetic disk. The substrate temperature during sputtering was kept constant at 300 ° C. when forming the magnetic film, and was set to various temperatures when forming the base film. The titanium nitride, titanium oxide and titanium carbide films used for the underlayer were formed by nitriding, oxidizing and carbonizing the titanium substrate surface, respectively. The electromagnetic characteristics of these magnetic disks were measured. As noise characteristics, SN ratio (signal / noise ratio) at 30 kfci
The higher the value, the better the noise characteristics. The results are shown in Table 1.

[0018]

[Table 1]

As can be seen from this table, the SN ratio of the one-layer underlayer film was 30 dB and the noise characteristics were poor, but it was higher than that of the two-layer underlayer film. The SN ratio was obtained and the effect of the present invention on the noise characteristics was confirmed.

Among the two or more layers of the base film, the one having the film thickness on the most substrate side of 30 to 1000 A is S.
It was confirmed that the N ratio was 35 dB or more and the noise characteristics were good. Further, better noise characteristics were obtained with the chrome 3 layer than with the chrome 2 layer as the underlayer.
Furthermore, it was confirmed that by forming the film closest to the substrate with titanium nitride, titanium oxide, or titanium carbide, the noise characteristics were improved as in the case of using chromium.

It should be noted that such noise characteristics are
It was better than the magnetic disk using the system substrate.

Although the magnetic film is formed at 300 ° C. here, the same effect can be obtained at less than 300 ° C.

[0023]

According to the present invention, there is provided a magnetic disk using a titanium substrate having an excellent noise characteristic.
Since the magnetic disk of the present invention uses the titanium substrate, it has an advantage that it can be made thin and a magnetic film can be formed by high temperature sputtering.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroyoshi Suenaga             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Kenji Morita             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Yoko Okano             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Toshio Sakiyama             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd.

Claims (6)

[Claims] 1. A magnetic disk comprising a non-magnetic substrate, a base film formed thereon, and a magnetic film further formed thereon, wherein the non-magnetic substrate contains titanium or titanium as a main component. A magnetic disk characterized in that the underlayer film is made of two or more layers. 2. The magnetic disk according to claim 1, wherein the film closest to the substrate among the underlying films has a thickness of 30 angstroms or more and 1000 angstroms or less. 3. The magnetic disk according to claim 1, wherein the underlayer film includes two or more layers of chromium film. 4. The magnetic disk according to claim 3, wherein two or more layers of chromium films have the same composition but different thin film formation temperatures. 5. The magnetic disk according to claim 1, wherein the uppermost layer of the underlayer film is a chromium film. 6. The film closest to the substrate among the underlying films is made of one kind selected from the group consisting of titanium oxide, titanium carbide, and titanium nitride.
6. The magnetic disk according to any one of items 1 to 5.