Patent Application
20050280934
The present invention relates to various thin-film magnetic heads, such as MR (Magnetoresistive) head, GMR (Giant Magnetoresistive) head, TMR (Tunneling Junction Magnetoresistive) type head and CPP (Current Perpendicular to plane) type head, and a method for producing the same.
Recently, in the field of magnetic recording, demand for higher density has been increased and development has been made to meet such demand. With the increase of the density, several types of heads for hard disks have been studied and developed, such as a thin-film magnetic head in which a soft magnetic thin film is used as magnetic poles.
There are different types of thin-film magnetic head, including MR head, GMR head, and TMR type or CPP type head.
Typically, the thin-film head adopts the CSS (Contact Start Stop) type in which the thin-film head is floated above the recording medium by bearing effect of air. The head is generally held at a distance (about 1-10 nm) slightly above the magnetic disc rotating at a high speed. Therefore, surface strength and abrasion resistance, that provide tolerance to head crash and CSS abrasion, are important. Various studies have been made to improve the abrasion resistance, as disclosed, for example, in Japanese Patent Application Kokai No. 4-276,367, in which a protective film is formed on a rail of a magnetic head slider. This protective film consists of a silicon layer having a thickness of 250 Å (25 nm) or less, exhibiting low strength. In addition, when such a silicon layer is applied to the magnetic thin-film head structure containing a sintered substrate made of alumina and titanium carbide, an alumina insulation layer, a thin film made of a soft magnetic material (e.g. permalloy, Sendust, iron nitride and the like) and the like, cohesion or adhesiveness between the thin-film head and the protective film becomes poor, leading to problems such as peeling of the film and insufficient abrasion resistance.
For protective layer to improve the abrasion resistance, thin-film made of TiN or TiCN, diamond-like carbonaceous film (DLC) and the like have been known. However, use of these films on the thin-film magnetic head cannot attain sufficient durability.
Japanese Patent No. 2,571,957 discloses that a buffer layer consisting of amorphous silicon and amorphous silicon carbide is formed on the surface of an oxide, and then a film of carbon or a film mainly composed of carbon is further formed thereon. However, even though the protective layer with the buffer layer is applied to the thin-film head, sufficient durability cannot be attained. In addition, it has disadvantages in that the extra step is required to form the buffer layer, in addition to the step to form the protective film, leading to a longer production period and a higher production cost. Moreover, the buffer layer makes the film thicker, which contradicts the demands on the magnetic head for hard disk, such as cost-effectiveness, mass-productivity, and larger packing density.
Under these circumstances, the present applicant has proposed an Si—C protective film formed by vapor deposition from predetermined compositions (see Japanese Patent Application Kokai Nos. 10-289419 and 10-275308).
The storage capacity of hard disc depends on the performance of the head, and the future market will demand the capacity of 120 GB or more. Therefore, the thickness of the protective film covering the head is demanded to be 3 nm (30 Å) or less.
On the other hand, the above-disclosed protective film realizes a thickness of approximately 7 nm (70 Å), due to the limitation in the technical level at that time, and thus sufficient durability cannot be obtained if the film is used as it is. Especially, corrosion resistance against water is important, since the problem of water condensation may occur in the device.
The object of the present invention is to provide a thin-film head which comprises a thin film exhibiting strong coherence to the components of the head and excellent durability, and a method for producing the same.
Another object is to provide a method for producing the thin-film head in which a thinner film can be obtained with less production steps and lower costs.
The above-mentioned objects can be attained by any one of the following (1)-(10):
(1) A thin-film head wherein a protective film is formed at least on the surface facing a recording medium,
(2) The thin-film head according to the (1) above, wherein end faces of an oxide substrate, an oxide insulation layer and a layer made of soft magnetic metal are present on said surface facing the recording medium.
(3) The thin-film head according to (1) above, wherein said head is selected from an MR head, a GMR head and a TMR type or CPP type head.
(4) A method for producing a thin-film head including:
vapor-depositing a protective film at least on a surface of the head facing a recording medium while applying a negative bias voltage to the thin-film head, said protective film containing Si, C and H in amounts of 3-9 at %, 61-81 at % and 16-30 at %, respectively, having a film thickness of 1-3 nm and having a refractive index of 2.0 or more.
(5) The method according to (4) above, wherein said bias voltage is applied as self-bias generated by an applied DC voltage or an applied high frequency current.
(6) The method according to (4) above, wherein said protective film is formed by a plasma CVD method.
(7) The method according to (4) above, wherein said protective film is formed by an ionization deposition method.
(8) The method according to (4) above, wherein said protective film is formed by a sputtering method.
(9) The method according to (4) above, wherein said surface facing the recording medium comprises an oxide substrate, an oxide insulation layer, an interlayer thin film and a layer made of soft magnetic metal.
(10) The method according to (4) above, wherein said head is selected from an MR head, a GMR head and a TMR type or CPP type head.
In the present invention, a protective layer comprising Si+ C+H of the predetermined composition ratio is formed at least on the surface facing the recording medium of the thin-film head, i.e., the surface floating above the medium or having a sliding contact with the medium. This protective film can be formed by plasma CVD method, ionization deposition method, sputtering method and the like, while applying DC bias voltage or self-bias on the thin-film magnetic head.
The resulting protective film has a thickness of 1-3 nm and a refractive index of 2.0 or more. Even with this thin structure, the protective film has excellent durability and abrasion resistance, as compared with the thin-films made of TiN or TiCN. In addition, when compared with the diamond-like thin film (DLC) optionally with a buffer layer, the above-obtained film has a higher coherence to the components of the thin-film head, such as alumina, permalloy and Sendust, result in improvement of durability, which in turn renders a longer life to the thin-film head. Moreover, the total thickness of the protective film can be reduced, since there is no need for intermediate layer or buffer layer, and thus cost performance and production efficiency are improved. Since the thickness of the protective film can be reduced to 1-3 nm, packing density can be improved.
The present invention satisfies the demand on the protective film of the head for hard disc of 120 GB or more that the thickness be 3 nm or less. At the same time, the film has a refractive index of 2.0 or more, which gives sufficient durability and especially corrosion resistance against water.
It is preferred that such a protective film be formed by, for example, the plasma CVD method, and the film can be formed under a low film-forming pressure by reducing the amount of gas and under a high bias voltage. In this case, it is preferred that the film-forming pressure is 0.001-0.008 Torr.
The specific embodiment of the thin-film head of the present invention will be explained in detail below.
The thin-film head of the present invention comprises a protective film formed on at least the surface facing the recording medium. The protective film contains Si, C and H in amounts of 3-9 at %, 61-81 at % and 16-30 at %, respectively. Preferably, it contains Si, C and H in amounts of 3-8 at %, 68-81 at % and 16-24 at %, respectively. More preferably, it contains Si, C and H in amounts of 3-8 at %, 70-79 at % and 18-22 at %, respectively.
When the amount of Si is below 3 at/o, the coherence becomes poor, and the durability becomes poor. On the other hand, when the amount of Si is above 9 at %, the film has poor hardness, and the durability at higher temperature and higher humidity becomes low. When the amount of H is below 16 at %, the internal stress becomes large, and the film is susceptible to damage, lowering the durability. On the other hand, when the amount of H is above 30 at %, the hardness of the film becomes poor, lowering the durability.
It is preferred that the composition of the protective film through the thickness be uniform or in the range mentioned above at any part, and the composition of the portion through the thickness of at least ⅓ from the upper surface (opposite to the surface of the thin-film head) and the portion through thickness of ⅔ be uniform or in the range mentioned above.
Optionally, in addition to the above-mentioned main components, 3 wt % or less (relative to the total amount) of at least one element selected from S, B, P and the like, and optionally 1 at % of O, can be contained. The protective film satisfying such conditions is in amorphous state, and the thickness is 1-3 nm. The refractive index at the wavelength of 632.8 nm is 2.0 or more.
By realizing such film thickness and refractive index, the demand for higher density can be satisfied and sufficient durability or and other properties can be provided as well. On the other hand, when the thickness is below 1 nm, durability and other properties become poor, and when the thickness is above 3=m, the spacing from the recording medium becomes large, which does not meet the demand for higher density. In addition, when the refractive index is below 2.0, the durability and the like become poor.
With respect to the refractive index, there is no upper limitation, but in general, it is approximately 2.8. In general, the Vickers hardness of the protective layer is approximately 600-400.
Next, the thin-film head of the present invention will be explained below.
The thin-film head illustrated in the figure is a so-called MR induction type combined head, having both an MR head portion for reproducing and an induction type head portion for recording. The induction type head portion for recording is composed of the upper magnetic pole layer 3, the lower magnetic pole layer 5, the gap 4 and the conductive coil 12 sandwiched therebetween. The MR head portion is composed of the upper shield layer 7, the lower shield layer 9, and the insulation layer 13 and the MR element 8 sandwiched therebetween. In the Figure, the induction type head portion is located on the trailing side, and the MR head portion on the leading side.
In general, a nonmagnetic material (e.g. alumina) is used for the protective layer 2, a soft magnetic material (e.g. permalloy and the like) for the upper and the lower magnetic pole layers 3 and 5, a soft magnetic material (e.g. permalloy, Sendust, iron nitride and the like) for the upper and the lower shield layers 7 and 9, and nonmagnetic material (e.g. alumina) for the base layer 10.
For the MR element, various materials having magnetoresistance can be used, besides permalloy or Ni—Co alloy. Some of them can lower the temperature of heat treatment, and thus are especially preferred when the MR element film comprises multiple layers. Examples of the MR film comprising multiple layers include a spin-valve type artificial lattice multiple-layered film (e.g. NiFe/Cu/NiFe/FeMn and Co/Cu/Co/FeMn) and antiferromagnetic artificial lattice multiple-layered film (e.g. NiFe/Ag and Co/Ag).
For the lead connected to the MR element, materials that do not diffuse into the MR film, such as Ta, W and the like, are preferably used. For the insulation layers 6 and 13, general insulation materials can be used, such as various ceramics including Al2O3 and SiO2. The substrate 11 formed from altic (calcined substrate made of alumina and titanium carbide) is usually fixed to the slider of the magnetic head, and alternatively, the substrate 11 itself can be used as a slider.
The thin-film head unit is formed by laminating these structures, and the protective film 1 of the present invention is formed at least on the surface of the unit which runs along or slides in contact with the magnetic recording medium (magnetic disk), In other words, on the surface facing the recording medium (in the figure, on the left side of the drawing and on the plane perpendicular to the plane of the paper). It should be noted that there is no limitation with respect to the part on which the protective film 1 is formed, as long as the film is formed at least on the surface of the thin-film head unit which runs along the medium or slides in contact with the medium, while it is not necessary to form the protective film on the other portions of the thin-film head. However, the protective film may be formed on or attached to the other parts depending on the conditions in the forming method of the protective film or the forming method of the thin-film head, or the protective film may be formed on the other parts for the purpose of, for example, improving the strength of the entire thin-film head.
There is also no limitation with respect to the size of the various parts, and they should be appropriately selected depending on the structure of the magnetic recording media to be used together. In general, the shield layers 7 and 9 have a thickness of 1-5 μm and a width of 30-200 μm; the MR element (magnetoresistive film) 8 has a thickness of 5-60 nm and a width of 1-10 μm; the distance between the shield layers 7 and 9 and the MR element 8 is 0.03-1.0 μm; the magnetic pole layers 3 and 5 of the induction type head portion has a thickness of 1-5 μm and a width of 0.5-10 μm; the shield layer 7 on the trailing side and the lower magnetic pole layer 5 of the induction type head portion is 1-10 nm.
In the magnetic head of the present invention, there is no limitation with respect to the method of linearization of the MR element, and any appropriate method can be selected, such as current bias method, hard film bias method, soft film bias method and shape bias method.
In general, the magnetic head of the present invention is formed by thin-film production and pattern formation. For the formation of the films, vapor deposition method, such as sputtering method and vacuum evaporation method, and plating method or the like may be used. Pattern formation can be conducted by selective etching or selective deposition.
The thin-film head of the present invention can be applied to not only the above-mentioned embodiment shown in the Figure, but also thin-film heads having different structures. Examples include a head in which the lower magnetic pole and the upper shield are integrated; a head without MR element thus solely induction type head (hereinafter, the head with MR element is sometimes referred to as “MR thin-film head”, and the simple induction type head as “induction thin-film head”). The preferable effect of the present invention can be attained especially when the thin-film head uses a composite material comprising at least one member selected from a calcined substrate made of alumina and titanium carbide, alumina, permalloy, Sendust and iron nitride.
It is preferred that the thin-film head of the present invention be especially MR head, GMR head, and TMR or CPP type head. The magnetic head of the present invention is used in combination with the known assembly, such as arms.
Next, the method for producing the thin-film head will be explained below. In the present invention, it is especially preferred that the protective film be formed by a plasma CVD method. With respect to the plasma CVD method, reference can be made to, for example, Japanese Patent Application Kokai No. 4-41672. The plasma to be used in the plasma CVD method may be either direct current or alternating current, but alternating current is preferred. Alternating current can range from a few hertz to microwave. In addition, ECR plasma described in, for example, “Diamond thin-film technique” (published by Technology Center) can be used.
In the present invention, bias-applied plasma CVD method is preferably used as the plasma CVD method. In the bias-applied plasma CVD method, a negative bias voltage is applied to the thin-film head. Detailed description is found in, for example, M. Nakayama et al. Journal of the Ceramic Society of Japan Int. Edition Vol. 98, pp 607-609 (1990). Alternatively, self-bias can be utilized, instead of applying a bias voltage. When a plasma power source, which is an alternating-current power supply, is connected to the electrode of the device, plasma is generated. This plasma contains electrons, ions and radicals, and is neutral as a whole. However, when the frequency of the plasma power source is audio frequency (AF), radiofrequency (RF) or microwave (MW), the difference in mobility is generated between ions and electrons, and as a result, negative voltage state is generated on the side of the applied electrode (typically the side that is not grounded). This voltage is called a self-bias voltage. The above-mentioned bias voltage is preferably −10˜−2000 V, and more preferably −50˜−1000 V.
When the protective film is formed using the plasma CVD method, the material gas is preferably selected from the following group of compounds. Examples of the compounds containing Si, C and H include methysilane, dimethylsilane, trimethylsilane, tetramethylsilane, diethylsilane, tetraethylsilane, tetrabutylsilane, dimethyldiethylsilane, tetraphenylsilane, methyltriphenylsilane, dimehtyldiphenylsilane, trimethylphenylsilane, trimethylsilyl-trimethylsilane and trimethylsilylmethyl-trimethylsilane.
Examples of the compounds containing Si, C, H and N include 3-aminopropyldiethoxymethylsilane, 2-cyanoethyltriethoxysilane, 3-allylaminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane. These can be used in combination, or used together with silane compounds and hydrocarbons.
In addition, as the C+H sources, hydrocarbons, such as CH4, C2H4, C2H6, C3H8 and C6H6, can be used. As Si+H sources, SiH4 can be used, and as H sources, H2 can be used.
The flow rate of the above-mentioned material gas can be selected depending on the types of the material gas. In general, it is preferred that the operating pressure be 0.001-0.008 Torr and the input power be 10 W-5 kW.
In the present invention, the ionization deposition method can be used for forming the protective film. With respect to ionization deposition method, reference can be made to, for example, Japanese Patent Application Kokai Nos. 58-174507 and 59-174508. It should be noted that the methods and the devices are not limited to the disclosed ones, and other types of ionization deposition technique can be applied, if it is possible to accelerate the material ionization gas of the protective film.
In this case, as one example of the preferred device, rectilinear ion type or deflection ion type device described in Japanese Patent Application Kokai No. 59-174508 can be mentioned.
In the ionization deposition method, the inside of the vacuum container is kept under the high-vacuum of approximately 10−6 Torr. This vacuum container is equipped with a filament therein which generates thermoelectrons when heated by the alternating-current power supply. This filament is sandwiched by an electrode couple, and voltage Vd is applied to the filament. In addition, an electromagnetic coil which generates a magnetic field for capturing ionized gas is placed in such manner that it surrounds the filament and the electrode couple. The material gas collides with the thermoelectrons from the filament, and generates positive thermolytic ions and electrons. This positive ion is accelerated by negative potential Va applied to the grid. By adjusting Vd, Va and the magnetic field of the coil, the composition and the quality of the film can be altered. In the present invention, it is preferred that Vd=10˜500 V and Va=−10˜−500 V. In this case also, a negative bias voltage is used for applying bias to the thin-film head. The bias voltage is preferably direct current. Alternatively, self-bias can be utilized instead of applying bias voltage. As mentioned above, the bias voltage is preferably −10˜−2000 V, more preferably −50˜−1000 V.
When the protective film is formed by the ionization deposition method, the same material gas as in the case of the plasma CVD method can be used. The flow rate of the material gas can be selected depending on the type of the gas. In general, the operating pressure is preferably 0.001-0.008 Torr.
It is also possible to form the protective film by the sputtering method. In this case, gases such as hydrocarbon (e.g. H2 and CH4) and SiH4 can be introduced as reactive gas, in addition to sputter gas, such as Ar and Kr. In addition, C, Si, SiC or the like may be used as a target, or mixed target containing C, Si and SiC may be used as a target, or more than two targets selected from the group containing C and Si may be used. Polymer can be used as a target. With the use of such targets, a high frequency power is applied, thereby sputtering the target; and the sputter is accumulated on the thin-film head placed on the substrate, thereby forming a protective film. In this case also, a negative bias voltage is used for applying bias to the substrate or the thin-film head. The bias voltage is preferably direct current. Alternatively, self-bias can be utilized instead of applying bias voltage. The bias voltage mentioned above is preferably −10˜−2000V, more preferably −50˜−1000 V. The high frequency sputter power is generally 50 W-2 kW. In general, the operating pressure is preferably 10−5-10−3 Torr.
The present invention will be explained in detail with reference to the specific Examples. In the following Examples, the film is formed on GMR head, by plasma CVD method.
Si(CH3)4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 3 SCCM and 20 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma, and the operating pressure of 0.005 Torr and the self-bias of −800 V were applied on the running surface or sliding surface of the GMR thin-film head, thereby forming a film of 2 nm. This film is referred to as Sample 1. Samples 2-4 were prepared in substantially the same manner as in the case of Sample 1, except that the thickness of the protective film is changed to those shown in Table 1.
Sample 5 was prepared in substantially the same manner as in the case of Sample 1, except that the operating pressure was changed to 0.05 Torr and the self-bias to −400 V.
For comparison, Si(CH3)4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 2 SCCM and 30 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma, and the operating pressure of 0.005 Torr and the self-bias of −800 V were applied on the running surface or sliding surface of the GMR thin-film head, thereby forming a film of 2 nm. This film is referred to as Sample 6.
For another comparison, Si(CH3)4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 15 SCCM and 10 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma, and the operating pressure of 0.005 Torr and the self-bias of −800 V were applied on the running surface or sliding surface of the GMR thin-film head, thereby forming a film of 2 nm (Sample 7).
In addition, Si(CH3)4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 30 SCCM and 2 SCCM, respectively. RF of 1200 W was applied as alternating current for generating plasma, and the operating pressure of 0.005 Torr and the self-bias of −800 V were applied on the running surface or sliding surface of the GMR thin-film head, thereby forming a film of 2 nm (Sample 8).
Further, SiH4 and C2H4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 10 SCCM and 70 SCCM, respectively. RF of 100 W was applied as alternating current for generating plasma, and the operating pressure of 0.05 Torr and the self-bias of −800 V were applied on the running surface or sliding surface of the GMR thin-film head, thereby forming a film of 2 nm (Sample 9).
Furthermore, SiH4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 5 SCCM and 10 SCCM, respectively. RF of 1000 W was applied as alternating current for generating plasma, and the operating pressure of 0.005 Torr and the self-bias of −800 V were applied on the running surface or sliding surface of the GMR thin-film head, thereby forming a film of 2 nm (Sample 10).
The properties of the obtained samples were evaluated as explained below, and the results are shown in Table 1. The compositions of the obtained films determined by chemical analysis are also shown, as well as the refractive indexes measured with an ellipsometer.
[Durability in CSS Test]
CSS test was repeatedly run until the head became unreadable, and the number of the test conducted was recorded. The value was rounded off to the nearest 100,000. In the table, the results are shown with the signs ∘ and x.
Friction coefficient was measured after conducting CSS test 10×104 times. In the Table, the results are shown with the signs ∘ and x.
The head was immersed in deoxidized water for 5 minutes, and the degree of corrosion was observed. Fifty samples were tested, and the ratio of the samples that can be used without any problem after immersion (the acceptable heads) to the total 50 samples is determined. In the Table, the results are shown with the signs ◯, Δ and X.
[Table 1]
*out of scope
Si(CH3)4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 5 SCCM and 25 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma. Substantially the same procedures were repeated as in Example 1 to prepare the samples shown in Table 2, by selecting either 0.005 Torr or 0.05 Torr as the operating pressure and −800 V or −400 V as the self-bias applied on the running surface or sliding surface of the GMR thin-film head. The samples were evaluated and the results are shown in Table 2.
[Table 2]
*out of scope
SiH4 and C2H4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 10 SCCM and 40 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma. Substantially the same procedures were repeated as in Example 1 to prepare the samples shown in Table 3, by selecting either 0.005 Torr or 0.05 Torr as the operating pressure and −800 V or −400 V as the self-bias applied on the running surface or sliding surface of the GMR thin-film head. The samples were evaluated and the results are shown in Table 3.
[Table 3]
*out of scope
Si(CH3)4 and C2H4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 8 SCCM and 20 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma. Substantially the same procedures were repeated as in Example 1 to prepare the samples shown in Table 4, by selecting either 0.005 Torr or 0.05 Torr as the operating pressure and −800 V or −400 V as the self-bias applied on the running surface or sliding surface of the GMR thin-film head. The samples were evaluated and the results are shown in Table 4.
[Table 4]
*out of scope
Si(CH3)4 and CH4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 10 SCCM and 30 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma. Substantially the same procedures were repeated as in Example 1 to prepare the samples shown in Table 5, by selecting either 0.005 Torr or 0.05 Torr as the operating pressure and −800 V or −400 V as the self-bias applied on the running surface or sliding surface of the GMR thin-film head. The samples were evaluated and the results are shown in Table 5.
[Table 5]
*out of scope
Si(CH3)4 and C2H4 were introduced as material gases for compounds containing Si, C and H, at the flow rates of 8 SCCM and 20 SCCM, respectively. RF of 500 W was applied as alternating current for generating plasma. Substantially the same procedures were repeated as in Example 1 to prepare the samples shown in Table 6, by selecting either 0.005 Torr or 0.05 Torr as the operating pressure and −800 V or −400 V as the self-bias applied on the running surface or sliding surface of the GMR thin-film head. The samples were evaluated and the results are shown in Table 6.
[Table 6]
*out of scope
As is apparent from the results shown above, the thin-film head of the present invention has an excellent durability in CSS test, durable friction coefficient and corrosion resistance.
Accordingly, the thin-film head of the present invention can be used for large packing density and is suitable for such an application.
It should be noted that when the thickness of the protective film is above 3 nm, the film is not suitable for thin-film head for large packing density.
[Effect of the Invention]
According to the present invention, the thin-film head that has excellent coherence to alumina, permalloy, Sendust, iron nitride and the like and exhibits excellent durability is provided, as well as the method producing the same. Furthermore, it is possible to attain a method for producing the thinner film with less production steps and lower costs.
