JPH0296919A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To relieve the generation of internal stresses by forming a buffer layer formed by alternately laminating Si3N4 films having a compressive stress and tensile stress as well as a nonmagnetic metallic underlying layer, a magnetic layer and a protective lubricating layer successively in this order in a substrate having a prescribed compsn. CONSTITUTION:Plastic is used for the substrate 1a and the buffer layer 6 is interposed between the substrate 1a and the nonmagnetic metallic underlying layer 3. A polyether imide resin is used for the substrate material and is molded by a metallic mold having prescribed surface accuracy to form the substrate 1a. The buffer layer 6 is formed on this substrate 1a by alternately laminating the Si3N4 films (2 to 5X10<9>dyn/cm<2>) 6a having the compressive stress and the Si3N4 films (-1 to -4X10<9>dn/cm<2>) 6b having the tensile stress thereon. The case in which the number of the laminations is 6 layer is shown in the figure, in which both the films 6a, 6b are formed to 50A. The nonmagnetic metallic underlying layer 3 consisting of Cr is formed to 2,000A thickness on this buffer layer 6 and the magnetic layer 4 consisting of a Cr alloy consisting of 30at.% Co and 7.5at.% Ni to 500A thickness, and the protective lubricating layer 5 consisting of carbon to 500A thickness, respectively continuously by sputtering within the same reaction vessel, by which the magnetic recording medium is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic disk used in a magnetic recording device.

[Conventional technology]

The third panel shows a schematic cross-sectional view of the main part of a conventionally used magnetic recording medium. The magnetic recording medium in FIG. 3 has a nonmagnetic metal base layer 2 on an A-6-Mg alloy substrate 1
A magnetic layer 4 of, for example, a Co-Ni-Cr alloy thin film is further coated on the non-magnetic metal base layer 2 via a non-magnetic metal underlayer 3, and a protective lubricant layer 5 is provided on the magnetic layer 4. The structure is such that a nonmagnetic metal base layer 2 to a protective lubricant layer 5 are stacked on a substrate 1 in the order of the numbers.

In the magnetic recording medium configured in this way, the substrate 1 is
The non-magnetic metal substrate layer 2 is preferably formed by electroless plating of N1-P alloy or by alumite treatment of the substrate 1 itself, both of which have a predetermined surface roughness, parallelism and flatness. The surface must be mechanically polished to a specified level of surface accuracy. The non-magnetic metal underlayer 3 is generally formed using Cr, followed by a magnetic layer 4 such as a Co-Ni-Cr alloy. Furthermore, a protective lubricant layer 5 such as carbon or another 02 is continuously applied.
and cover.

The thus obtained a-air recording medium has good mechanical properties such as strength and two-dimensional accuracy, and magnetic properties, such as AJ
-Cr is applied to the N1-P base layer 2 coated on the Mg alloy substrate 1.
200OA of non-magnetic metal underlayer 3.

The Co-30at%Ni-7.5at%Cr film layer 4 was formed by a 500A continuous wave and the carbon protective lubricant layer 5 was formed by a 500A continuous wave, but the coercive force Hc was 9000e as a substitute magnetic property.

As magnetic recording media such as those described above have improved in magnetic properties, there has been an increasing demand for lighter weight and lower costs in recent years.

[Problem to be solved by the invention]

A point to consider in order to reduce the weight and cost of a recording medium is the selection of the substrate material. In other words, since the AJ-Mg alloy is used for the substrate, a hard N1-P layer must be provided on top of the AJ-Mg alloy, and it takes a lot of time to polish the surfaces of the substrate and the N1-P layer. accounts for a large proportion of costs. Therefore, in order to shorten this machining time,
Since the surface must be finished to a specified level of roughness, parallelism, and flatness, it is impossible to significantly reduce man-hours, and there is a limit to cost reduction.As long as AJ-Mg alloy is used, much can be expected. Can not.

-1 Regarding the selection of the substrate material, it is promising to use plastic or a composite material of plastic and ceramic, including reducing the weight of the recording medium.

These materials are lighter than AJ3-Mg alloy and can be formed using a mold, so by processing the surface of the mold with high precision, they can be made in a sufficiently good condition without the need for surface polishing after molding. This is because it has the advantage of providing good surface roughness and parallelism.

However, other problems arise when using plastic or a composite thereof as the substrate.

This is because there is a large difference in coefficient of thermal expansion between plastic and metal, so cracks are likely to occur in the metal film formed on the plastic substrate. These cracks, depending on their size and quantity, can cause a decrease in the corrosion resistance of the medium and an increase in errors in magnetic recording signals. Therefore 1.
Even when plastic or the like is used for the substrate instead of the Lee-Mg alloy, it is necessary to ensure that the reliability of the recording medium is not impaired.

The present invention has been made in view of the above points, and its purpose is to make magnetic recording media lighter and to reduce costs using plastic or plastic.

It is an object of the present invention to provide a magnetic recording medium that uses a composite material of silica, ceramic, and silica, has good magnetic properties, and has a structure that can prevent cracking and cracking of a metal film.

[Means to solve the problem]

The magnetic recording medium of the present invention has a 5iaN4 film with a pressure line stress and an S film with a tensile stress on a non-magnetic substrate such as plastic.
On this face are sputter-formed a Pa layer, a Fa layer, a non-magnetic metal underlayer, an eiB layer, and an interpolation layer consisting of alternately stacked isNaM layers.

[Effect]

Plastic substrate with a large coefficient of thermal expansion (approx.
℃) and metal II with a significantly smaller coefficient of thermal expansion (
Cr: approx. 8.4 If this buffer layer is formed from a single material, it will require a small thickness (approximately 1000 A).However, the thickness of the buffer layer cannot be made much larger than necessary, so it must be within a predetermined thickness. When the buffer layer is housed, if a single layer is made of a single material, stress will only propagate therein, and it will not be able to absorb or relax the L force.

Therefore, as in the present invention, the buffer layer is formed as a multilayer stack of different films of the same type, which delays stress propagation and shares stress relaxation at the interface of each film, thereby contributing to overall stress relaxation. It becomes possible to do so. Moreover, in view of the manufacturing process of magnetic recording media, these films must not only be easy to form, but also be capable of alternately stacking films of the same type with different shapes depending on the conditions set during film formation. In view of the above, the combination of Si3N4'M, which has compressive stress, and 58aNn 1111, which has tensile stress, is suitable for the buffer layer in terms of the denseness and consistency of both, and these can be used alternately. When laminated, the buffer layer as a whole consists of films of the same type with different shapes stacked every other time within a predetermined thickness.
This buffer layer acts to relieve the internal stress caused by the large difference in coefficient of thermal expansion between the plastic substrate and the metal film, and to prevent the occurrence of cracking in the gold/metal film.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 shows a schematic cross-sectional view of the main parts of a magnetic recording medium obtained according to the present invention, and parts common to those in FIG. 3 are designated by the same reference numerals. The basic configuration of FIG. 1 is the same as that of FIG. 3, but the difference between FIG. 1 and FIG. 3 is that plastic is used for the substrate 1a, and between the substrate 1a and the nonmagnetic metal underlayer 3, There are five cases in which a buffer layer 6 is provided instead of a non-magnetic metal underlayer 2.

This magnetic recording medium is manufactured by first using a polyetherimide resin (trade name Ultem 1000) as a substrate material and molding it with a mold with a predetermined surface accuracy to produce a substrate 1a. (2~5 X
10"dy"/cd) 6a and tensile stress
i3N4711 (-1~-4XIO'""/cd
) 6b A buffer layer 6 is formed by laminating 1c layers alternately.4 In FIG. 1, for convenience, the number of laminated layers of these thin films is 6W.
I is shown in the case of Si3Na with compressive stress.
The film thicknesses of J[[6a and 5iaN4 film 6b with tensile stress are both introduced. Further, on this buffer layer 6, C
r non-magnetic metal underlayer 3 of 2000 A # Co 3
0 at % Nt-7, 5 at % Cr alloy magnetic layer 4
The magnetic recording medium shown in FIG. 1 was constructed by continuously forming a protective lubricant layer 5 of 500i carbon in the same reaction tank.

Here, the Si3Na film 6a having compressive stress and the 5laNa film 6b having tensile stress are formed as follows.

In other words, ECR plasma CVD and DC
ECR plasma CVD using equipment capable of sputtering
Using the method, the substrate temperature (material) is below ℃, and the 5IH of the raw material is
a, f'h gas was introduced and the film forming pressure was 0.5 to 5.
It is varied within the range of mTorr. At this time, the film forming pressure was 1
A Si3N4 film 6a having compressive stress is formed at mTorr or less, and an Si, sN4 film 6b having tensile stress can be formed at a film forming pressure of 1 mTorr or more. The buffer layer 6 is obtained by repeating this change in film forming pressure and alternately forming and stacking the films 6a and 6b so that each film has a thickness of 50A.

At this time, in order to confirm the effect of the number of times of changing the film forming pressure to form the Si3N4 film 6a with compressive stress and the 5i3N4 film 6b with tensile stress, that is, the lamination process in which these films are stacked alternately, By repeating each film forming pressure condition 10 times, a combed buffer layer 6 having a laminated number of up to 10/jig was formed. For comparison, Si3 with compressive stress was subjected to a film formation pressure of less than 1 mTorr and a film formation pressure of more than 1 mTorr.
Only N4 film 6a and 5ia N4HA 6 with tensile stress
A buffer layer containing only b was prepared, and a substrate made of a composite material of Boriesder resin and calcium carbonate was also prepared.

Further, Cr for the non-magnetic metal underlayer 3, a co-Nmu-Cr alloy for the at magnetic layer, and carbon for the protective lubricant layer 5, which are sequentially formed on the buffer layer 6, are all formed by DC sputtering under the following conditions. .

Substrate temperature: 80°C or less Raw materials: Cr target, *Co-Nt Cr alloy target, Tow C target, Ar gas film formation pressure 10 mTorr Next, for each magnetic recording medium obtained as described above, metal We compared the number of cracks and cracks that occur in the film and the award resistance performance, and the results are shown in Figure 2 (a) and (b).
Shown below. Figure 2 (ω is the vertical axis of Cr of the non-magnetic metal underlayer 3)
The horizontal axis represents the Si3N4 film 62 with compressive stress and the Si3N4 film 6b with tensile stress, which are formed so as to be alternately stacked in the buffer layer 6, with the number of cracks of 1 pm or more per unit area (-) occurring in the buffer layer 6. The average value obtained by measuring the number of layers at 10 points for each magnetic recording medium is plotted.

In Fig. 2 rb>, the vertical axis is the product value Br - δ of the residual magnetic flux density Br, which is a typical magnetic property of the medium, and the film thickness δ of the magnetic layer 4.
1 left in the precincts at ℃, 80% RH1i.
The reduction rate after the corrosion resistance test is ΔBr・δ, and the horizontal axis is the second
Figure (- represents the number of laminated layers of membrane 6a and membrane 6b,
The scores were the same (10 points were tested and the average value was used).

FIGS. 2(a) and 2(b) both show a case in which a plastic substrate is used to form the buffer layer 6 according to the present invention (
0), which also uses a plastic composite substrate (
0), a single Si3N4 film 6a with compressive stress (mu) and a single 3i3N4 film 6b with tensile stress (×) using a plastic substrate for comparison are also shown.

As can be seen from both FIGS. 2(al) and (b), if the buffer layer 6 is made of only one layer of a single material, the FiX
In both cases of 6 a + film 6 b, 8% Cr is added to the underlayer 3.
A crack of 0m or more occurred, which caused Δ)
13r·δ value reaches 5% or more. This holds true even if the film thickness is varied within the range of this embodiment in the case of a single material. When the ΔBr-a value exceeds 5%, errors due to repeated recording and reproduction of the magnetic recording medium increase, so it is obvious that it is not appropriate to form the buffer 16 using only a single material.

On the other hand, in the magnetic recording medium of the present invention, which has a buffer layer 6 in which a 5iiN4 film 6a having compressive stress and a Si3Na film 6b having compressive stress are alternately layered, the film 6a and i
As the number of laminated layers of 6b increases, the number of cracks occurring in the Or base layer 3 rapidly decreases, and the ΔBr・δ value also decreases (becomes).When the number of laminated layers increases to 4 or more, the conventional ΔBr e δ value of 1.5% in a magnetic recording medium in which a substrate 1 is coated with an N1-P plated nonmagnetic metal underlayer 2
A value approximately equivalent to ~2% is obtained. Furthermore, a magnetic recording medium using a composite material of polyester resin and calcium carbonate as a substrate, which was also produced at the same time, has the same effect as that using a substrate of polyetherimide a (Fig. 2 (ω)).

It can be confirmed from

Si3N4 film 6a with compressive stress and Si with tensile stress
When the 3N4 film 6b is used alone as the buffer layer 6, it is thought that the film thickness needs to be 1000 A or more, but in the present invention, a Si3N4 film with a tensile stress that matches well with the 5iaN4 film 6a, which has a compressive stress, is used. Since the buffer layer 6 is formed as a laminate with the film 6a and the film 6b,
Since the thickness of each buffer layer 6 is 50A, even if 10 layers are stacked, the thickness of the buffer layer 6 is only 500A.

As described above, the magnetic recording medium of the present invention has the buffer layer 6 in which SisN41m 6 a having compressive stress and Si3Na film 6b having tensile stress are alternately laminated.
The films 6a and U6b work at their respective interfaces to absorb or relax the internal stress caused by the large difference in coefficient of thermal expansion between a and Cr of the nonmagnetic metal underlayer 3, and as a result, the metal underlayer 3 It is possible to prevent cracks from occurring in the Cr.

Furthermore, as a result of conducting a C8S test by incorporating the magnetic recording medium of the present invention into a magnetic recording device, it was found that even after 20,000 contact start-stops, no -
No occurrence of this phenomenon was observed, and there was almost no decrease in playback output, confirming that the device had sufficient durability.

In addition, since the magnetic recording medium of the present invention uses plastic or a composite material thereof for the substrate, it is different from the conventional PanorM.
The advantage is that it is about 60% lighter than an alloy substrate, does not require a complicated polishing process, and that each layer deposited on the substrate, including the buffer layer according to the present invention, can be formed sequentially in the same reaction tank. There is also.

〔Effect of the invention〕

As magnetic recording media age, it is desired to reduce costs, and instead of the conventional A2 alloy substrate, which requires many processing steps, plastic or its composite material, which can obtain high surface precision without post-processing, is used. However, the substrates made of these plastic thread materials have thicker (different) thermal expansion coefficients than the metal film (Cr) formed on it, which causes cracks and slag in the metal film after film formation. As a result, the corrosion resistance performance of the medium is significantly reduced.On the other hand, the magnetic recording medium of the present invention, as described in the embodiment, uses a method that changes the film formation pressure between the plastic substrate and the metal film. By interposing a buffer layer in which Si3N4 films with compressive stress and 5i3Ni films with tensile stress are alternately stacked, the internal stress caused by the difference in thermal expansion coefficient between the substrate and the metal film can be reduced. It is now possible to share stress absorption or relaxation at the interface of each stacked film, and this makes it possible to achieve stress relaxation with a buffer layer with a thickness of 500A or less, which was impossible with a buffer layer made of a single material. As a result, it is possible to prevent cracks and scratches from occurring in the metal film.

From the above, it can be concluded that the magnetic recording medium of the present invention eliminates the essential drawbacks that occur when using an aluminum-based substrate, and is superior to conventional magnetic recording media. It maintains the same corrosion resistance and reliability as media using alloy substrates.

[Brief explanation of drawings]

The first factor is shown in FIG. 2, which is a schematic cross-sectional view showing the main structure of the magnetic recording medium of the present invention (at is the number of laminated layers in the buffer layer of the magnetic recording medium of the present invention and the number of cracks occurring in the non-magnetic metal underlayer). Figure 2 (b) is the same (relationship diagram between the number of laminated layers in the buffer layer and ΔBr and δ). Figure 3 is a schematic cross-sectional view showing the main part configuration of a conventional magnetic recording medium. 1. la...substrate, 2... nonmagnetic metal base layer%3.
...Nonmagnetic metal underlayer, 4...Magnetic layer, 5...Main @
Self-sliding layer, 6... Buffer layer, 6a... Si3N4 film with compressive stress, 6b... 3i with tensile stress 3
N41A. Figure 1 Figure 3

Claims (1)

[Claims] 1) Si_3N_4 with compressive stress on a substrate made of plastic or a composite material of plastic and ceramic
1. A magnetic recording medium comprising a buffer layer in which Si_3N_4 films having tensile stress are alternately stacked, a nonmagnetic metal underlayer, a magnetic layer, and a protective lubricant layer formed in this order.