JPH0414414B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a magnetic recording medium having a magnetic thin film used as a high-density magnetic recording medium, and in particular to a magnetic recording medium having a surface protective film layer with excellent wear resistance. It's about the medium.

(Prior Art) In recent years, there has been an increasing demand for higher density magnetic recording media, and continuous thin film media are attracting attention. As the continuous thin film media, γ-Fe ₂ O ₃ based oxide ferrite film media, Co-Ni based metal thin film media, etc. are known, but these so-called in-plane magnetization type media have a high retention capacity of the magnetic film. High-density recording has been achieved by increasing the magnetic force, increasing the residual magnetic flux density, and making the magnetic film thinner.

In contrast to the above-mentioned in-plane magnetization type media, perpendicular magnetization type metal thin film media such as Co-Cr are attracting attention as media that can achieve higher density. In such a continuous thin film medium, it is essential to form a lubricating layer or a protective film and a lubricating layer on the surface of the magnetic film in order to ensure the durability of the medium.

As the lubricating layer, fluorine-based or silicone-based oils, as well as solid lubricating layers such as carbon films, are in practical use. In addition, as a protective film, SiO ₂ , Al ₂ O ₃ ,
Oxides, nitrides, and carbides of metals or metalloids such as AlN, TiN, and SiC are known. In particular, for media in which a magnetic film and the above-mentioned protective film are formed on a flexible polymer substrate, unlike hard disks, the head and the medium are in a sliding state during use, so it is difficult to maintain the necessary durability. Extremely difficult.

On the other hand, since extremely high recording density is required for perpendicular magnetization media such as Co-Cr, the gap between the head and the medium must be made as small as possible, and the thickness of the protective film layer must be 500 Å or less. , preferably 300 Å or less.

By the way, floppy media are usually used in jackets or cartridges. In such usage, if oil is used as a lubricating layer, not only will the oil layer be depleted due to head sliding, but also the liner used in the jacket or cartridge has the function of wiping off the oil. , the liner dries the oil even faster.

(Problems to be Solved by the Invention) In order to prevent the oil layer from depleting, a proposal has been made to form fine irregularities on the protective film layer and form an oil layer thereon. According to JP-A No. 58-200431, a resin is used as a protective film, and after the resin mixed with liquid paraffin is formed in a thin layer on the protective film, the liquid paraffin is evaporated by heating. As a result, unevenness is formed on the resin layer. However, in order to remove the fluid by evaporation from the thin layer of the resin and liquid paraffin mixture, the temperature must be at least 250°C.
However, in the case of a medium using a flexible polymer substrate, there is a drawback that using such high temperature to evaporate the fluid causes other adverse effects and cannot be applied.

Furthermore, Japanese Patent Application Laid-Open No. 127230/1983 discloses a method in which a protective film layer of SiO ₂ with a thickness of 500 Å is formed using a high-frequency magnetron device, and then unevenness is formed by plasma treatment.

However, in order to form irregularities on the surface of the protective film layer by plasma treatment, a process of forming a non-magnetic insulating thin film layer and a process of plasma treating this thin film layer are required, so the media manufacturing apparatus is The problem was that it became complicated and expensive, and the cost also increased.

(Means for Solving the Problems) The present invention provides a magnetic recording medium that can eliminate and improve the problems and drawbacks of conventional protective films and manufacturing methods, that is, an expensive device,
The object of the present invention is to provide a magnetic recording medium having a protective film layer that can be formed without a complicated process and that can effectively reduce oil depletion when used in combination with an oil lubricating layer. The above object can be achieved by providing the medium described in the claims. That is, in a magnetic recording medium in which a magnetic thin film is formed on a non-magnetic substrate, a non-magnetic protective film is formed on the magnetic thin film, and an oil lubricating layer is further formed on the protective film, the protective film is generally To provide a magnetic recording medium having a silicon oxide film produced so as to have an apparent density in the range of 1.70 g/cm ³ to 2.05 g/cm ³ using a high frequency sputtering device using an SiO ₂ target. The above objective can be achieved by the following.

Next, the present invention will be explained in detail.

Among the methods for manufacturing magnetic recording media, a high frequency sputtering method is usually used as a means for forming a silicon oxide protective film.

In the present invention, a silicon oxide protective film formed on a magnetic thin film by a high-frequency sputtering method has an apparent density of
The magnetic recording medium is characterized in that it is within the range of 1.70 g/cm ³ to 2.05 g/cm ³ . The apparent density is 1.70g/cm ³ to 2.05g/cm ³ using commonly used high frequency sputtering equipment targeting SiO ₂ .
In the magnetic recording medium of the present invention having a silicon oxide protective film in the range of 1 to 2, the silicon oxide protective film is porous and is therefore impregnated with a large amount of lubricating oil. Therefore, after forming the SiO ₂ protective film disclosed in JP-A No. 59-127230, silicon can be used for the medium of the present invention without going through complicated steps such as plasma treatment using expensive equipment. The present inventors have discovered that since the lubricating oil applied to the surface of the protective film is impregnated into the inside of the silicon oxide protective film, depletion of the lubricating oil is suppressed and the durability of the medium is significantly improved. The present invention was completed based on this knowledge.

In order to obtain a silicon oxide protective film suitable as a protective film containing lubricating oil, the present inventors will explain in detail experimental data obtained by various studies on the dependence of the film quality of a silicon oxide film on sputtering conditions during high-frequency sputtering.

The sputtering conditions other than the argon gas pressure and target voltage during sputtering are as follows.

Ultimate pressure: 4 to 6 × 10 ^-7 Torr Vacuum degree before gas introduction: 2 to 4 × 10 ^-6 Torr Distance between electrodes: 75 mm Target material: SiO ₂ shape: φ8 inches Platform: water cooling Also, various sputtering conditions The film quality of the silicon oxide film prepared was evaluated by measuring the relative etching rate and apparent density. The relative etching rate was determined by assuming that the etching rate of a silicon oxide film formed on a glass substrate was 1 at an argon gas pressure of 24 mTorr during sputtering and a target voltage of 1.2 KV. The etching solution is hydrofluoric acid,
A mixed solution of ammonium fluoride and ethylene glycol was used, and the apparent density was determined by measuring the weight and volume of a silicon oxide film formed on a glass substrate.

FIGS. 1 and 2 are diagrams showing the dependence of the relative etching rate and apparent density of a silicon oxide film on argon gas pressure, respectively. The target voltage is
It is 1.2KV.

As can be seen from Figures 1 and 2, when the argon gas pressure is in the range of 8mTorr to 34mTorr,
The apparent density decreases as the argon gas pressure increases, and the etching rate decreases as the argon gas pressure increases.
In the range of mTorr to 24 mTorr, the etching rate increases as the argon gas pressure becomes higher, but in the range of argon gas pressure of 24 mTorr to 34 mTorr, the etching rate hardly increases even if the argon gas pressure is increased. It is believed that the etching rate depends on the area of the film surface in contact with the etching solution, and the etching rate increases as the surface area increases. That is, an increase in the surface area of the SiO ₂ film indicates that the denseness of the film becomes lower and the porosity of the film increases. Therefore, from Figure 1, the argon gas pressure is from 8 mTorr to 24 mTorr.
In this range, it can be said that as the argon gas pressure increases, the porosity of the silicon oxide film that is formed increases. When the argon gas pressure exceeds 24 mTorr, the etching rate of the silicon oxide film hardly increases even if the argon gas pressure increases.
When the temperature exceeds mTorr, the quality of the silicon oxide film hardly changes. On the other hand, according to Figure 2, the apparent density is 24mTorr when the argon gas pressure is 24mTorr.
Even if it is above, it decreases as the argon gas pressure increases. A low apparent density means that the formed silicon oxide film has a high porosity, so according to the apparent density measurement results, the argon gas pressure ranges from 8 mTorr to 34 mTorr.
As the argon gas pressure increases in the range of
This means that the porosity of the silicon oxide film formed has increased, which clearly contradicts the above-mentioned result of the dependence of the etching rate on argon gas pressure.

For these reasons, the high-frequency sputtering method
When film formation is performed using a SiO ₂ target,
Argon gas pressure at least 24mTorr to 34m
In the Torr range, the film structure formed is different from the target composition, and it is thought that a film with a composition that is less likely to be corroded by the etching solution is formed.

According to the Institute of Electronics and Communication Engineers technical report CPM68-16,
As a result of investigating the structure of the SiO _x film by determining its radial distribution function from the X-ray diffraction intensity, it has been reported that it is composed of Si and SiO ₂ . On the other hand, it is known that Si is not corroded by the etching solution. Therefore, the argon gas pressure is 8mTorr to 24
In the mTorr range, the membrane porosity uniformly increases as the argon gas pressure increases, but in the argon gas pressure range of 24 mTorr to 34 mTorr, the membrane porosity increases as the argon gas pressure increases. This can be considered to indicate that not only does this increase, but also that the ratio of Si to SiO ₂ in the film increases rapidly.

As can be seen from the above, in the medium of the present invention, the silicon oxide protective film is a SiO ₂ film and
This is a general term for films made of SiO ₂ and Si.

Further, FIGS. 3 and 4 are diagrams showing the target voltage dependence of the relative etching rate and apparent density of a silicon oxide film, respectively. Argon gas pressure is 24 mTorr. As can be seen from Figures 3 and 4, the target voltage ranges from 1.2KV to 0.6KV.
In the range of , the apparent density decreases as the target voltage decreases, and the etching rate increases as the target voltage decreases, but conversely the etching rate decreases as the target voltage decreases below 0.8 KV. ing. Therefore,
When the target voltage ranges from 1.2 KV to about 0.9 KV, the porosity of the membrane uniformly increases as the target voltage decreases, but when the target voltage ranges from about 0.9 KV to 0.6 KV, the porosity of the membrane increases as the target voltage decreases. Therefore, not only does the porosity of the membrane increase, but also the
This indicates that the ratio of Si to SiO ₂ also increases.

Also, from Figures 1, 2, 3, and 4,
When the apparent density of the formed film is reduced by increasing the argon gas pressure and when the apparent density is reduced by decreasing the target voltage, if the apparent density is the same, the apparent density of the formed film is reduced by lowering the target voltage. It is thought that the amount of silicon in the formed film is smaller when the size is smaller. Regarding the durability of the media, when the apparent density of the silicon oxide film was the same, media with a protective film containing a large proportion of Si to SiO ₂ tended to have slightly better durability.

As is clear from the examples below, when the silicon oxide film is formed with an apparent density of 2.05 g/cm ³ or less, the durability of the medium is significantly improved, especially when the apparent density of the silicon oxide protective film is 1.95
From g/cm ³ to 1.80 g/cm ³ , the durability of the medium exceeds 10 million passes as shown in FIG. Furthermore, when the apparent density of the silicon oxide film was less than 1.70 g/cm ³ , scratches due to head sliding tended to occur easily. Therefore, the above-mentioned Japanese Patent Application Laid-open No. 59-
Sputtering conditions can be formed using a high-frequency sputtering device using a SiO ₂ target without the need for plasma treatment, which requires expensive equipment and complicated processes, after forming the SiO ₂ protective film as disclosed in No. 127230. The apparent density of the silicon oxide film is from 1.70g/ ^cm3
If the amount is set within the range of 2.05 g/cm ³ , a silicon oxide film having a quality suitable as a protective film containing lubricating oil can be directly formed by high-frequency sputtering.

Next, the present invention will be explained with reference to examples.

Example A Co-Cr perpendicular magnetization film or a double-layer perpendicular magnetization film of permalloy and Co-Cr is formed on a polyethylene terephthalate film or a polyimide film, and a silicon oxide film is formed on the medium by high-frequency sputtering using a SiO ₂ target. was formed to a thickness of 320 Å.

The sputtering conditions during the formation of the silicon oxide film were as described above when examining the dependence of the film quality of the silicon oxide film on the sputtering conditions.
~34mTorr (target voltage 1.2KV), target voltage 0.6~1.2KV (argon gas pressure 24mTorr)
changed within the range. A disk with a diameter of 5.25 inches was punched out from the medium on which the silicon oxide protective film had been formed, and a fluorine oil (Fomblin Z-25 manufactured by Montageson) was applied to the disk to a thickness of about 350 Å by dipping.

This disc was inserted into a floppy disk jacket, recorded and reproduced using a recording and reproducing device, and changes over time in the reproduced output were observed. The head used was a commercially available button-type ring head, the pad pressure was 20 g, and the disc rotation speed was 300 rpm. Durability was evaluated as the number of times the head was slid until the reproduction output decreased to 80% of the initial value.

FIG. 5 is a diagram showing the relationship between the apparent density and durability of a silicon oxide protective film. It can be seen that the durability improves as the apparent density of the silicon oxide protective film decreases, and the degree of increase in durability is particularly large when the apparent density is 2.05 g/cm ³ or less. Furthermore, when the apparent density of the silicon oxide protective film is 1.95 g/cm ³ or less, the durability exceeds 10 million passes, and the apparent density is 1.85 g/cm 3 or less.
cm ³ achieved durability of nearly 20 million passes. When the apparent density of the silicon oxide film becomes 1.80 g/cm ³ or less, the durability of the medium decreases rapidly, and the apparent density becomes 1.70 g/cm ³
If it was less than that, scratches tended to occur easily.

Furthermore, Figure 5 shows that there is a strong correlation between the apparent density and durability of the silicon oxide protective film, and when the apparent density of the silicon oxide protective film is at least 1.80 g/cm ³ or more, It is understood that the increased porosity of the silicon oxide protective film increases the durability of the metal medium with the oil lubricating layer.

(Effects of the Invention) The medium of the present invention has a porous silicon oxide protective film formed in a single process using an ordinary sputtering device without using any special equipment, and this protective film contains a large amount of Because it is impregnated with oil, it is extremely durable.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the argon gas pressure when forming the silicon oxide protective film and the relative etching rate of the silicon oxide protective film, and Figure 2 is a graph showing the relationship between the argon gas pressure when forming the silicon oxide protective film and the relative etching rate of the silicon oxide protective film. Graph showing the relationship with apparent density, 3rd
The figure is a graph showing the relationship between the target voltage when forming a silicon oxide protective film and the relative etching rate of the silicon oxide protective film. Figure 4 shows the relationship between the target voltage when forming a silicon oxide protective film and the apparent density of the silicon oxide protective film. FIG. 5 is a graph showing the relationship between the apparent density of the silicon oxide protective film and the durability of the metal magnetic recording medium.

Claims (1)

[Scope of Claims] 1. In a magnetic recording medium having a magnetic thin film on a non-magnetic substrate, a non-magnetic protective film on the thin film, and an oil lubricating layer on the protective film: the non-magnetic protection The membrane has an apparent density of 1.70g/cm ³ ~
A magnetic recording medium characterized in that the protective film is made of silicon oxide in a range of 2.05 g/cm ³ . 2. The magnetic recording medium according to claim 1, wherein the nonmagnetic substrate is a flexible polymer film. 3. A patent characterized in that the magnetic thin film is at least one magnetic thin film selected from an in-plane magnetization type metal thin film, an in-plane magnetization type oxide thin film, a perpendicular magnetization type metal thin film, and a perpendicular magnetization type oxide thin film. A magnetic recording medium according to claim 1.