JPH03225622A - Production of perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve reproducibility of thickness of the initial oriented layer in the process of forming CoCr films by sputtering on a polymer base film by specifying pressure of Ar gas used for sputtering to higher value for formation of the first layer and to lower value for formation of second layer. CONSTITUTION:For example, the initial oriented layer 4 as the first layer containing 18.5 wt.% Cr is formed on a polyimide base film 5 at the pressure of Ar sputtering gas as high as >=7X10<-3> Torr. Then a perpendicular magnetic recording layer 3 as the second layer having the same composition as that of the layer 4 is formed at the Ar gas pressure as low as <=1X10<-3> Torr. A magnetic head 6 is made to face to the recording layer 3. Thus, by controlling the pressure of Ar gas on sputtering, reproducibility of thickness control for the initial oriented layer is improved. The obtd. medium has large reproduction output and can be used for high density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a perpendicular magnetic recording medium used in floppy disks for still videos and the like.

[Conventional technology]

In recent years, with the demand for higher density magnetic recording, research has been actively conducted on so-called continuous magnetic thin film magnetic recording media (hereinafter referred to as continuous media) in which the magnetic layer is formed only of magnetic materials.

Continuous media manufactured by vacuum evaporation, sputtering, or plating have a continuous magnetic thin film layer, so they can be used not only for longitudinal recording, but also for perpendicular magnetic recording, which can dramatically improve magnetic recording density. There are high expectations for this technology, and progress is being made to apply it to various product forms such as various magnetic tapes for images or OA, or magnetic disks.

On the other hand, with the recent demand for smaller floppy disks and improvements in magnetic recording technology, still image video signals can be recorded while rotating at a cycle of 1760 seconds, which is the time required to display one screen of a television signal. A so-called 2-inch still video floppy disk (hereinafter referred to as Sv FD) has appeared. This 2 inch Sv
The video signal recorded on a commercial FD is, in principle, the same as that used in a VTR, with a color signal recorded in a low frequency region and a luminance signal recorded in a high frequency region. However, since SV, which is a still image, requires higher image quality than VTR with movement, the recording frequency band is set wider than that of VTR, and the horizontal resolution is set to 2 that of standard Beta VTR.
The standard Sv has 357 lines compared to 40 lines. Furthermore, there is a high demand for higher image quality for both Beta VTR and SV, and progress has been made toward high-band recording frequencies that widen the recording frequency band.
D Beta VTR) and high band Sv have been commercialized. However, the horizontal resolution of ED Beta VTR is 5
In contrast, the high band Sv requires approximately the same resolution of 520 lines.

Therefore, in order to further dramatically improve image quality, high-density magnetic recording is expected, and in particular, the use of perpendicular magnetic recording media manufactured by the sputtering method for 2-inch SV FDs is being considered. When performing a high-quality Sv system on a perpendicular magnetic recording medium, it is necessary to maintain compatibility (hereinafter referred to as backward compatibility) with a system with lower resolution than the conventional standard Sv system and high-band Sv system. When considering this, a method of improving image quality may be considered in which only the recording bands of color signals and luminance signals are further widened without making any major changes to the recording method such as digital recording.

However, although the recording characteristics of perpendicular magnetic recording media allow recording and reproduction up to extremely high recording densities, the reproduction output at low recording densities is low. There was a drawback that the C/H value was insufficient and backward compatibility could not be achieved. In view of this, the present inventors have long sought to improve the reproduction output in the low frequency region of perpendicular magnetic recording media by using We have been studying the function of the so-called initial alignment layer, which has not yet achieved sufficient vertical alignment. This initial orientation layer is determined by measuring the magnetostatic properties of the perpendicular magnetic recording medium using a vibrating magnetic property measuring device such as VSM, as shown in FIG.
When a magnetic hysteresis curve is measured in the direction parallel to the film surface (in-plane direction), which is the direction in which magnetization is difficult in the case of perpendicular magnetic recording, the initial alignment layer is a jump in magnetization that occurs in the initial magnetization curve region near the origin of the magnetic hysteresis curve. Part A is referred to as
Among the many perpendicular magnetic recording media made of only a CoCr layer that have been manufactured in the past, there are very few that have a large reproduction output, and when we examined the magnetic hysteresis curve in the in-plane direction of the medium, we found that It has been found that the perpendicular magnetic recording medium is a perpendicular magnetic recording medium with a thick initial orientation layer 4, which is a layer containing many components in the longitudinal magnetization direction of the initial orientation layer, as shown in FIG. This means that the thickness of the initial orientation layer of a CoCr perpendicular magnetic recording medium manufactured using a conventional manufacturing method is approximately 50 angstroms, whereas the thickness of the initial orientation layer of a perpendicular magnetic recording medium with a high reproduction output is approximately 200 angstroms. ~500 angstroms. Although the mechanism of this increase in reproduction output has not yet been fully elucidated, it is thought to be as follows.

As shown in FIG. 2, magnetic lines of force 7 flowing between the magnetic layer and the magnetic head 6 during recording and reproduction flow almost perpendicularly to the base film 5 in the perpendicular magnetic recording layer 3, and horizontally in the initial orientation layer 4. flow in the direction.

At this time, since the initial orientation layer has magnetization in the in-plane direction in the direction of the base film, it performs recording and reproduction of longitudinal recording and serves as a return path for magnetic force NA7, increasing reproduction output.

[Problem to be solved by the invention]

It is known that the thickness of this initial orientation layer changes depending on the gas release conditions from the base film before forming the magnetic recording layer of the base film and changes in the surface condition of the base film. Studies have been conducted to reduce the thickness of the layer, and the mainstream has been to provide an underlayer of germanium, titanium, etc. to facilitate the formation of the perpendicular magnetic recording layer.

Therefore, no method has been established for intentionally increasing the thickness of the initial alignment layer and controlling the thickness with good reproducibility.

The present invention has been made in view of the current situation, and its purpose is to thicken the initial orientation layer on the base film in order to increase the reproduction output during perpendicular magnetic recording.
An object of the present invention is to provide a method for manufacturing a perpendicular magnetic recording medium in which the thickness of an initial alignment layer is controlled in order to improve the recording density during perpendicular magnetic recording and to obtain a perpendicular magnetic recording medium with increased reproduction output.

Structure of the Invention [Means for Solving the Problems] In order to solve the above problems, the present invention provides an initial orientation layer having an easy magnetization direction perpendicular to the easy magnetization direction of the perpendicular magnetic recording layer on a base film. According to the present invention, a perpendicular magnetic recording medium in which the thickness of the initial alignment layer is controlled with good reproducibility can be obtained.

That is, in the present invention, when forming a CoCr film on a polymer base film by a sputtering method, a CoCr first layer is formed at a high argon gas pressure of 7X10-3 Torr or more during sputtering, and then 1×10−
This is a method of manufacturing a perpendicular magnetic recording medium characterized by forming a CoCr second layer at a low pressure of 3 Torr or less.

[Effect]

A CoCr film containing 18.5% by weight of Cr was formed while changing the sputtering pressure, and the jump in the initial magnetization curve region shown in Figure 1 of the magnetic hysteresis curve in the in-plane direction of the base film at various film thicknesses was observed. The results of measuring the amount of width A are shown in FIG.

That is, the horizontal axis shows the total film thickness of the sputtered CoCr film, and the vertical axis shows the value measured by converting the jump amount of the magnetic hysteresis curve corresponding to the initial alignment layer into thickness.

Therefore, Fig. 3 shows the relationship between the thickness of the CoCr layer and the thickness of the initial orientation layer. This indicates that the initial orientation layer is not

Here, the manual power for sputtering is 500 W, and the range of argon gas pressure conditions during sputtering is 1 to 9 Xl0-"
Torr and the total film thickness ranged from 0 to 1000 angstroms. It can be seen from FIG. 3 that an initial orientation layer having a thickness of 200 angstroms or more can be obtained when the sputtering argon gas pressure is 5.times.10@-3 Torr or higher.

Next, at 5 to 9X10-3 Torr, the first CoCr
A sputtered film is formed to a thickness of 200 angstroms, and then 1
A second CoCr sputter film was formed to a thickness of 0.2 μm at ×10 −3 Torr.

The thickness of the initial alignment layer at this time was measured by VSM and the results are shown in FIG.

From FIG. 4, the thickness of the initial alignment layer shows a constant value of 200 angstroms, which is almost the same as the thickness of the first CoCr sputtering film. Therefore, an initial alignment layer is formed at 7X10-3 Torr or more, and a normal 0.8 to 1X1O
It has been confirmed that when forming a perpendicular magnetic recording layer at −3 Torr, the thickness of the initial alignment layer can be approximately the same as the thickness of the first CoCr sputtering film, which is the thickness of the initial alignment layer aimed at in the present invention. It is possible to provide a method for manufacturing a perpendicular magnetic recording medium that can control the following.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) Sputtering power was 500W and sputtering argon gas pressure was 5X10-3T on a polyimide film with a thickness of 30μm.
A CoCr first layer film with a thickness of 200 angstroms and a Cr content of 18.5% by weight was formed using a sputtering method with a sputtering power of 500 W and a sputtering argon gas pressure of 1.
A CoCr second layer having the same composition as the first layer was formed to a thickness of 0.2 μm at ×10−” Torr.

(Example 2) Under the conditions of Example 1, the sputtering pressure for forming the first layer film was 7×10''-3 Torr and the thickness was 300 angstroms, and the second layer film was formed under the same conditions as Example 1.

(Example 3) Under the conditions of Example 1, the sputtering pressure for forming the first layer film was 8×10 −3 Torr and the thickness was 400 angstroms, and the second layer film was formed under the same conditions as Example 1.

(Example 4) Under the conditions of Example 1, the sputtering pressure for forming the first layer film was 9 x 10'-'' Torr, the thickness was 500 angstroms, and the second layer film was formed under the same conditions as Example 1. .

(Example 5) Under the conditions of Example 1, the sputtering pressure for forming the first layer was 9 X1O-3 Torr and the thickness was 200 angstroms, and the second layer was formed under the same conditions as Example 1.

(Example 6) Under the conditions of Example 1, the sputtering pressure for forming the first layer film was 9 Xl0-3 Torr and the thickness was 300 angstroms, and the second layer film was formed under the same conditions as Example 1.

(Example 7) Under the conditions of Example 1, the sputtering pressure for forming the first layer film was 9 Xl0-3 Torr and the thickness was 400 angstroms, and the second layer film was formed under the same conditions as Example 1.

The thickness of the initial alignment layer was measured by VSH for the CoCr magnetic layers produced in Examples 1 to 7, and the results of comparison with the thickness of the first layer film are shown in FIG. 5.6 From FIG. 5, the initial alignment layer thickness It can be seen that the thickness of the first layer and the thickness of the first layer are almost the same.

C1 Effect of the invention [Effect of the invention] As stated above, the Cr according to the present invention is 18.5% by weight.
When forming a perpendicular magnetic recording medium by sputtering a CoCr alloy containing CoCr alloy onto a polyimide film and forming an initial alignment layer on the polyimide film, the argon gas pressure during sputtering is set to a higher pressure than before, and the sputtered layer is By controlling the thickness of the CoCr perpendicular magnetic recording medium, a CoCr perpendicular magnetic recording medium that enables high-density recording with a large reproduction output can be formed by forming an initial orientation layer having an easy magnetization direction perpendicular to the perpendicular magnetic recording layer. Furthermore, by controlling the argon gas pressure during sputtering onto the base film, a CoCr perpendicular magnetic recording medium in which the thickness of the initial alignment layer is controlled with good reproducibility can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram of a magnetic hysteresis curve in the in-plane direction of the base film of a perpendicular magnetic recording medium showing an initial orientation layer on the base film. FIG. 2 is a cross-sectional view showing the recording and reproducing process of a perpendicular magnetic recording medium having a sufficient initial orientation layer. FIG. 3 is a characteristic diagram obtained by measuring the relationship between the overall thickness of the CoCr film and the thickness of its initial alignment layer by changing the argon gas pressure during sputtering. FIG. 4 shows that by changing the sputtering pressure of the first CoCr layer,
FIG. 3 is a characteristic diagram showing the initial orientation thickness when forming a CoCr second layer. FIG. 5 is a characteristic diagram showing the relationship between the thickness of the first CoCr layer and the thickness of the initial alignment layer in an example of the present invention. A... Region of magnetization jumping due to the initial orientation layer, B...
Value of the magnetic flux density of the entire CoCr magnetic layer, 3... Perpendicular magnetic recording layer, 4... Initial orientation layer, 5... Base film, 6... Magnetic head, 7... Lines of magnetic force.

Claims (1)

[Claims] 1. When forming a CoCr film on a polymer base film by the sputtering method, the argon gas pressure during sputtering is set to a high pressure of 7 x 10^-^3 Torr or higher.
Form the first layer of oCr, and further layer 1×10^-^3 on top of it.
A method for manufacturing a perpendicular magnetic recording medium, characterized in that a CoCr second layer is formed at a low pressure of Torr or less.