WO1990006575A1

WO1990006575A1 - Magnetic recording medium and process for manufacturing it

Info

Publication number: WO1990006575A1
Application number: PCT/EP1989/001223
Authority: WO
Inventors: Franz Josef LÖFFLER; Dietrich Stephani
Original assignee: Siemens Aktiengesellschaft
Priority date: 1988-12-07
Filing date: 1989-10-16
Publication date: 1990-06-14
Also published as: EP0408681A1

Abstract

A recording medium (2) contains a magnetizable storage layer (7) covered with a protective coating (9) of carbon (C) or a carbon (C) compound. An antifriction layer (11) containing a fluorocarbon is a) containing a fluorocarbon is applied to the protective coating. To ensure good wettability of the protective coating, fluorine (F) is incorporated in at least one of the surface regions (9a) of the protective coating (9) facing the antifriction coating (11). The fluorine can be incorporated at the same time as the C or the C compound is deposited; or it may be incorporated later in a temporary coating of C or the C compound from the free surface.

Description

Magnetic recording medium and method for its production

The invention relates to a magnetic recording medium

a plate-shaped carrier body,

at least one agnetizable storage layer on at least one flat side of the carrier body,

a protective layer made of carbon or a carbon compound which covers the at least one storage layer, and

- A layer of a lubricant which contains a fluorine-carbon compound and is applied to the protective layer.

Such a recording medium is e.g. from the publication "Solid State Technology", October 1988, pages 113 to 115. The invention further relates to methods for producing such a recording medium.

Storage of information by perpendicular (vertical) or longitudinal (horizontal) magnetization of corresponding storage layers in a recording medium is generally known. Corresponding recording media can be present, in particular, in the form of rigid magnetic storage disks or flexible individual disks (floppy discs). A magnetic head which is adapted to the respective magnetization principle and which can be constructed in particular in thin-film technology is passed over them. The distance between the magnetic head and the surface of the recording medium should be kept extremely small. they can be below 1 μm, for example in the case of vertical magnetization. However, such short distances can practically only be ensured by designing a substrate carrying the magnetic head as a so-called missile, which aerodynamically slides over the recording medium. For this purpose, the substrate is advantageously equipped on its underside facing the recording medium with corresponding glide or flight skids (cf., for example, EP-A-0 137 051).

The starting and landing phases of the substrate designed as a missile are particularly critical. In order to avoid damage to the recording medium and its aggregates on the one hand and the magnetic head carried by the substrate on the other hand, one is forced to take measures with which a low friction at the common interface of these parts and a protection of the behavior ¬ thin medium storage layer of the medium are to be guaranteed. For this purpose, the storage layer has hitherto been coated with a thin protective layer made of a hard, abrasion-resistant material and, in addition, a thin layer of a friction-reducing lubricant or lubricant has been applied to its surface. As a suitable material for the protective layer, carbon can be found in the publication mentioned at the outset, which is applied, for example, by a sputtering process to the storage layer of a plate-shaped recording medium. Protective silicon nitride layers (cf. EP-A-0 175389) or oxides, nitrides or carbides of cobalt or chromium (cf. for example EP-A-0 186 358) are also provided. Examples of lubricants are silicon dioxide (see, for example, EP-A-0 134412), hydrocarbon compounds (see, for example, DE-A-35 39 724) or fluorocarbon compounds (see, for example, EP-A-0 175) 389, EP-A-0 186 358 or the publication mentioned at the beginning). These lubricants are generally applied to the respective recording 1 medium separated. They are often referred to as Lubrikant.

If you want to provide carbon or a carbon compound as a hard, abrasion-resistant material for the 5. protective layer, it turns out that the surface of this layer is not uniformly wetted with a liquid lubricant from one of the known fluorocarbon compounds is. This applies in particular to extremely smooth surfaces of protective layer 0. In this case, a homogeneous film is not formed, but under certain circumstances only small droplets are obtained which can easily be seen in a microscope. When the magnetic head comes into contact with the plate-shaped recording medium, this leads to high coefficients of friction and, in some cases, to very large adhesive forces. It was recognized that this behavior of the lubricant on the protective layer is primarily due to an adsorption of water molecules on the carbon surface before coating with the lubricant.

The object of the present invention is now to design the recording medium of the type mentioned at the outset in such a way that the increase in the coefficient of friction due to the inhomogeneous wetting of the protective layer is at least largely eliminated.

This object is achieved in that fluorine is incorporated in the protective layer at least in a zone which adjoins the surface of the protective layer facing the lubricant layer.

The invention is based on the knowledge that with such incorporation of fluorine into the carbon material of the protective layer, so-called hydrophobization of the carbon surface, ie resistance to adsorption of Water molecules, is to be achieved. The result of this is that the surface is wetted with a liquid lubricant made from one of the known fluorine-carbon compounds in a much more uniform manner. The previously observed increase in the coefficient of friction when a magnetic head comes into contact with the surface of this recording medium then advantageously no longer occurs.

A method for producing a recording medium according to the invention is characterized in that the carbon or the carbon compound of the protective layer is deposited on the storage layer at the same time as a fluorine-carbon compound. However, it is also possible first to deposit a preliminary layer from the carbon or the carbon compound of the protective layer on the storage layer and then to expose the free surface of this preliminary layer to a fluorine-carbon compound. Both methods have the advantage that they are relatively easy to carry out in order to introduce the fluorine at least into a zone near the surface.

Advantageous refinements of the recording medium according to the invention and the methods for its production are evident from the subclaims.

The invention is explained in more detail below on the basis of an exemplary embodiment, reference being made to the drawing. 1 schematically shows a cross section through an inventive recording medium. FIG. 2 shows the coefficient of friction of this recording medium to be determined in a start-stop test.

FIG. 1 schematically illustrates a cross section through part of a recording medium according to the invention. The recording medium, generally designated 2, can in particular be a rigid magnetic storage disk which is rotationally symmetrical about an axis A and which is a carrier body 3 known per se. The carrier body can be, for example, a hardened glass plate (cf. the

EP-A-0 256 278). On at least one of the two flat sides 4 and 5, for example on the upper flat side 4, a storage layer 7 is applied, which is to be magnetized depending on the magnetization principle provided. In the case of the vertical magnetization principle, the storage layer 7 can have a layer 7a made of a cobalt-chromium alloy, which can be located on a lower layer 7b made of a soft magnetic material. The storage layer 7 is covered with a hard, abrasion-resistant protective layer 9, which consists of carbon (C) or a carbon (C) compound. This protective layer 9 has a thickness d between 5 nm and 100 n, preferably between 10 nm and 50 nm. As indicated by hatching in the figure, according to the invention, this protective layer should be in at least one zone 9a that connects to the Surface 10 adjacent to the protective layer, fluorine (F) must be installed. The depth t of this zone 9a to be measured perpendicular to the flat side 4 should be at least 0.5 nm. However, the entire cross section of the layer 9 can also be provided with F, so that then applies: t '= d. The surface 10 should advantageously be made extremely smooth and have a surface roughness of at most 70 nm, preferably at most 30 nm, based on the maximum roughness depth R _t , based on a measuring distance of 2 mm. The size R. is understood within the predetermined measuring distance to be the distance formed between an upper boundary line touching the surface profile at its highest profile elevation and a lower boundary line parallel to it, touching the surface profile at its deepest profile part (cf. also Draft 1968 to DIN 4762). Finally, a thin layer 11 of a liquid lubricant is applied wet to this smooth surface 10, for example by a dip coating process or by spraying. The lubricant should contain an FC compound and have a kinematic viscosity between 15 cSt and 350 cSt (= 350. 10 m ² / s). Such lubricants are known per se. In particular, they can be oily lubricants made from a perfluorinated ether of the general chemical formula R-CF ₂ 0- (C ₂ F.0) - (CF ₂ 0) -CF ₂ -R. With a corresponding wetting of the surface 10 with such a lubricant, thicknesses d 'of the lubricant layer 11 between 1 and 20 nm, which are to be measured perpendicular to the flat side 4, then result.

In order to produce the recording medium according to the invention, two process routes can be followed in particular to form a protective layer 9 according to the invention on the upper flat side of the at least one storage layer 7: 1) With this process route the C or a C compound such as e.g. TiC, ZrC or WC deposited simultaneously with the F. Known chemical processes such as CVD are used for this purpose

(Chemical Vapor Deposition) or known physical processes such as PVD (Physical Vapor Deposition) can be used. A sputtering process can be used particularly advantageously for this purpose. According to a specific exemplary embodiment for such a sputtering process, at a pressure of 5 to

50. 10 mbar and a power density of 0.5 to 4 W / cm ² an approximately 10 to 50 nm thick C-layer applied. 5 to 40% of a volatile FC compound has already been added to the sputtering gas Ar. FC connections suitable for this are in particular

and CHF ,. The addition can consist of one of these compounds. Mixtures of these compounds can also be added. In addition, these volatile FC compounds can optionally also be used for other gaseous substances, for example be mixed with inert gases. By means of the corresponding sputtering process, a protective layer is obtained in which the F is built in homogeneously over the entire cross section.

2) This procedure provides for the subsequent incorporation of the F into an already deposited preliminary layer of C or a C compound. The preliminary layer initially formed by known processes is then physically or chemically post-treated such that the F penetrates into the layer from its free surface and is built into at least one zone 9a near the surface. An RF plasma process can advantageously be provided for this, a plasma being formed with a volatile FC compound in accordance with process route 1), such as CF ^. For example, post-treatment is at a pressure of 5 to 100. 10 ^" mbar of this FC connection and a power density of 0.1 to 3 W / cm ^{2 is} possible. In this process, the substrate carrier with the preliminary C-containing layer deposited on it is switched so that it is at a negative potential. Although a small part of the C-containing layer is etched off again, saturation of at least the layer surface with F is achieved.

The surfaces of the protective layers formed according to the two methods are distinguished by the fact that C and F, but no adsorbates with oxygen, can be detected on them during eye electron spectroscopic examinations. It is also advantageously achieved that the layers can be wetted well with perfluoropolyethers and these can be adsorbed well. In a subsequent dip coating process, it is therefore possible to apply a thin, continuous film of the lubricant which has good tribological properties (good sliding values). The determination of the coefficient of friction of a magnetic storage disk designed according to the invention is possible by means of a start-stop test. The results of such a test are recorded in a diagram, as shown in FIG. 2. In this diagram, the count z of the respective new starting process is plotted in the abscissa direction and the friction coefficient μ in the ordinate direction. The disk is driven in accordance with commercially available data storage systems, with a known read / write magnetic head made using thin-film technology being guided over it. The magnetic head can slide aerodynamically over the plate rotating underneath it. When the disk drive starts or stops, the magnetic head comes into contact with the disk. In this phase there is friction and wear. This behavior is tested over several 1000 cycles, the force required for starting being measured and the coefficient of friction being determined in this way. In between, the test is interrupted for a long time, with the magnetic head remaining on the disk. The coefficient of static friction is then recorded. As can be seen from the measurement curve entered in the diagram, the measures according to the invention allow an average value of the coefficient of friction μ to be maintained which is clearly below the value of approximately 0.6 generally required by practice.

Claims

1. Magnetic recording medium with

a plate-shaped carrier body, at least one magnetizable storage layer on at least one flat side of the carrier body,

a protective layer made of carbon or a carbon compound covering the at least one storage layer, and

- A layer of a lubricant which contains a fluorine-carbon compound and is applied to the protective layer, characterized in that in the protective layer (9) at least in one zone (9a) which faces the surface (11) facing the lubricant layer (11). 10) adjacent to the protective layer, fluorine is incorporated.

2. Recording medium according to claim 1, characterized in that the protective layer (9) has a thickness (d) to be measured perpendicular to the flat side (4) of the carrier body (3) between 5 nm and 100 nm, preferably between 10 nm and 50 nm.

3. Recording medium according to claim 1 or 2, so that the depth (t) of the near-surface zone (9) of the protective layer (9) to be measured perpendicular to the flat side (4) of the carrier body (3) is at least 0.5 nm.

4. Recording medium according to one of claims 1 to 3, d a- characterized in that the maximum roughness depth (RA of the measuring layer of 2 mm in length) with the protective layer (9) to be provided on the surface of the memory Layer (7) is at most 70 nm, preferably at most 30 nm.

5. Recording medium according to one of claims 1 to 4, d a- characterized in that the perpendicular to the flat side (4) of the carrier body (3) to be measured thickness (d ¹ ) of the lubricant layer (11) is between 1 nm and 20 nm.

6. Recording medium according to one of claims 1 to 5, d a- characterized in that the lubricant has a viscosity between 15 at room temperature. 10 m ² / s and 350. 10 ^{~ 6} m ² / s.

7. Recording medium according to one of claims 1 to 6, that the lubricant at least contains at least one perfluorinated ether.

8. A method for producing a recording medium according to one of claims 1 to 7, dadurchgekenn¬ characterized in that the carbon or the carbon compound of the protective layer (9) is deposited with a fluorine-carbon compound on the storage layer (7) at the same time .

9. The method according to claim 8, that the carbon or the carbon compound of the protective layer (9) is deposited by means of a sputtering process, a volatile fluorocarbon compound being added to a sputtering gas.

10. A method for producing a recording medium according to any one of claims 1 to 7, dadurchgekenn¬ characterized in that first a preliminary layer the carbon or the carbon compound of the protective layer (9) is deposited on the storage layer (7) and that the free surface of this preliminary layer is subsequently exposed to a fluorine-carbon compound.

11. The method according to claim 10, dadurchgekenn¬ characterized in that the carbon or the carbon compound of the preliminary layer is deposited by means of a sputtering process and that then the free surface of this preliminary layer in a plasma with a volatile fluorocarbon. Connection is treated.

12. The method according to claim 9 or claim 11, characterized in that CF ^ and / or C ₂ F _g and / or C ₃ Fg and / or CHF _{3 is} provided as the volatile fluorine-carbon compound.