JPH0450651B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a magnetic recording medium suitable for perpendicular recording.

Conventional structure and its problems In the conventional longitudinal recording, as the recording wavelength becomes shorter, the demagnetizing field becomes larger and it becomes impossible to obtain a large residual magnetization.
The so-called perpendicular recording method, in which recording is performed antiparallel to each other in a direction perpendicular to the surface of the magnetic recording medium, is attracting attention as a high-density recording method because the shorter the wavelength, the smaller the demagnetizing field, making it possible to obtain a large residual magnetization. . To realize this recording method, the magnetic recording layer requires a so-called perpendicular magnetization film, in which the magnetic recording layer is magnetized perpendicularly to the film surface, and currently a sputtered film of Co-Cr (about 20wt% Cr) has the best crystal orientation. It is known that there is.

In addition, some Co-M (M is Cr, W, Mo, Ti, Ru,
It shows atoms added to dilute the saturation magnetization of Co such as V and weaken the demagnetizing field. ) alloys, all of which have good crystal orientation in their sputtered films.

Forming these perpendicularly magnetized films on a moving substrate is important for the practical application of perpendicular recording. FIG. 1 is an enlarged cross-sectional view of a typical magnetic recording medium for perpendicular recording. Soft magnetic layer 2 on substrate 1
A perpendicular magnetization film 3 is disposed thereon, and a surface protective layer, a back coating layer, etc. are disposed as appropriate. FIG. 2 is a schematic diagram of the sputtering method, in which a target 4 is placed in a vacuum facing the substrate 1, and a high frequency power source 5 is applied to the target 4 by adjusting a matching circuit 6 at a certain pressure. is supplied to generate a high-frequency glow discharge.

Ions A ⁺ generated by the discharge impact the target 4 and knock out atoms B forming the target 4. 7 is a substrate holder, and 8 is a target holder. For example, target 4 is Co-containing 20% Cr.
It is possible to obtain perpendicularly magnetized films with various perpendicular coercive forces by making the film from a Cr alloy, using argon as the discharge gas, and using a high frequency of 13.56 MHz. (In this case, the substrate holder 7 shall be replaced with a cylindrical can often used for roll-up deposition.) When attempting to obtain a perpendicularly magnetized film, the coercive force becomes extremely large as shown by curve D in Figure 3. I had a problem with it becoming smaller.

A possible cause of this is gas released from the substrate. In particular, when a soft magnetic layer is not provided, new substrate surfaces enter the sputtering atmosphere one after another, so it can be seen as a continuous gas source. Even if a perpendicularly magnetized film was formed on a pretreated soft magnetic layer, the perpendicular coercive force only increased slightly and no clear improvement was observed.

Purpose of the invention The present invention solves the above-mentioned conventional problems.
The present invention provides a method for manufacturing a magnetic recording medium that can form a perpendicularly magnetized film having a large perpendicular coercive force on a moving polymer substrate using a sputtering method.

Structure of the Invention The present invention uses a glow discharge in which the sputtering speed of Co atoms is higher than the sputtering speed of M atoms when forming a perpendicularly magnetized film made of a Co-M alloy on a moving polymer substrate by a sputtering method. This method is characterized by the ability to continuously form a perpendicularly magnetized film with a large perpendicular coercive force.

DESCRIPTION OF EMBODIMENTS The present invention was completed by determining that the selection of glow discharge conditions is extremely important in forming a perpendicularly magnetized film having a large perpendicular coercive force on a moving polymer substrate by a sputtering method. Something,
Examples will be described below with reference to the drawings.

As the polymer substrate 1 in FIG. 1, polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose diacetate and nitrocellulose,
Polycarbonate, polyvinyl chloride, polyamideimide, polyhydantoin, polyparapanic acid, polyimide, etc. are used.

A typical example of the soft magnetic layer 2 is a permalloy thin film, but it can also be replaced with Co, Fe, Ni, or the like.

Perpendicular magnetization films include Co-Cr, Co-Ti, Co-Mo,
In the case of ternary alloys such as Co-W, Co-Ru, Co-Mn, and Co-Cr-Rh, there are two elements represented by M. The sputtering speed between the element and Co shall be selected so as to satisfy the conditions of the present invention.

In addition, in the case of Co-Ni-Cr, Co-Ni-V, Co-Ni-Ti, etc., treat them as if Co has replaced Co-Ni. However, let us focus on the relationship between Co and M atoms.

The sputtering method can be appropriately selected from known high frequency sputtering, direct current sputtering, magnetron methods, and the like.

Figure 4 shows the relationship between the anode voltage of the oscillator tube and the sputtering rate of Co and Cr using high-frequency (frequency 13.56MHz) two-pole sputtering. It is a normalized relative value.

Co-Cr by changing the operating conditions...
(Cr21w%) was sputtered, and the Co-Cr film thickness was
Adjust the high frequency power so that it is constant at 0.1μm,
A perpendicularly magnetized film was created by varying the moving speed of the polymer substrate, and the coercive force in the vertical direction was measured using a vibrating sample magnetometer.

Example 1 80 μm thick polyethylene terephthalate
A heating medium of °C was moved along a cylindrical can with a diameter of 50 cm, and two Co-Cr targets with a length of 12 cm in the moving direction were placed 10 cm away from the can surface. Then, Co-Cr was sputter deposited. The vacuum chamber was evacuated to 10 ^-6 Torr in advance, and 300W of high-frequency power was applied to the surface of the board.
(Anode voltage 1KV) After glow discharge treatment for 1.2 seconds at Ar9×10 ^-3 Torr, sputter deposition was performed.

Select the operating conditions as shown in Figure 4, change the Ar pressure from 1 x 10 ^-3 Torr to 1 x 10 ^-2 Torr, and change the input power from 560W to 2.2KW per target. The third graph plots the vertical coercive force of the Co-Cr film obtained by changing the moving speed.
It is a diagram.

Satisfying the structural requirements of the present invention, the Co-Cr film formed with the substrate moving a little compared to the vertical coercive force of the Co-Cr film obtained on the stopped substrate.
Although the −Cr film is smaller, the amount of change is suppressed and a large coercive force is obtained. In comparison, there was a rapid decrease in coercive force, and the difference with the present invention is large.

One of the reasons for the difference between the two is that it is known from spectroscopic measurements that the proportion of Cr in the excited state is higher in the glow discharge state that satisfies the requirements of the present invention, but the improvement in crystal orientation due to this is known. Conceivable.

As another example, the same experiment as described above was conducted with the heating medium temperature raised to 120℃, but under the conditions of
950-1050 [Oersted] at 5m/min, then
420 [Ersted].

Example 2 After vacuum drying a 6.8 μm polyamide substrate at 160°C for 24 hours, Ni-Fe was dried at a can surface temperature of 50°C.
(80 wt% Ni) was electron beam evaporated to a thickness of 0.43 μm.

Using the substrate, in the same manner as in Example 1,
Change Co-Cr target to Co-V target
A 0.15μ perpendicularly magnetized film made of Co-V (V24wt%)
m was formed.

The vertical coercivity obtained at a substrate moving speed of 5 m/min was 1020 [Oersted], 990 [Oersted], 950 [Oersted], and 380 [Oersted] depending on the operating conditions.

Effects of the Invention As described above, when forming a perpendicularly magnetized film made of a Co-M alloy by a sputtering method, the present invention uses glow discharge to form a perpendicularly magnetized film made of a Co-M alloy using a glow discharge condition in which the sputtering speed is higher for Co atoms than for M atoms. Even if the polymer substrate moves, a perpendicularly magnetized Co--M alloy film with good crystal orientation and a large perpendicular coercive force can be obtained, and its practical effects are great.

[Brief explanation of the drawing]

Figure 1 is an enlarged cross-sectional view of a magnetic recording medium for perpendicular magnetic recording, Figure 2 is a diagram for explaining the formation of a perpendicularly magnetized film by the sputtering method, and Figure 3 is a diagram for explaining the formation of a perpendicular magnetic film using glow discharge conditions as parameters. FIG. 4 is a characteristic diagram showing the dependence of the coercive force on the moving speed. FIG. 4 is a characteristic diagram showing the relationship between the sputtering speed of each atom and the glow discharge conditions. 1... Polymer substrate, 3... Perpendicular magnetization film.

Claims (1)

[Claims] 1. When forming a perpendicular magnetic film made of Co-M alloy on a moving polymer substrate by sputtering method,
A method for manufacturing a magnetic recording medium, characterized in that a glow discharge is used in which the sputtering speed of Co atoms is higher than the sputtering speed of M atoms.