JPH11112058A - Manufacture of magnetic field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a magnetic field sensor having a very high magnetoresistance change ratio and great magnetoresistance effect multilayer film provided by laminating layers of 10 nm or less with suppressing the mutual, diffusion between the layers on a flexible resin substrate originally difficult for use as a substrate and then doing the device processing. SOLUTION: The method comprises setting on a substrate fixing table a flexible resin substrate having a κ/L value of 1.5×10<3> W/m<2> K or more where κ, and L are thermal conductivity and thickness of the substrate, and laminating layers of 10 nm or less with cooling the substrate from the substrate fixing table to form a great magnetoresistance effect multilayer film by the vacuum film forming method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a magnetic field sensor for converting a change in an external magnetic field into an electric signal.

[0002]

2. Description of the Related Art A magnetic field sensor is a device for converting a change in an external magnetic field into an electric signal. The magnetic field sensor is used to pattern a magnetic field detecting thin film such as a ferromagnetic material or a semiconductor thin film. It converts changes in the magnetic field into electric signals.

For example, a ferromagnetic magnetoresistive sensor is a device that measures a magnetic field intensity using a phenomenon (magnetic resistance effect, MR effect) in which the electric resistance of a ferromagnetic metal changes due to an external magnetic field.

[0004] In a magnetic film consisting of a single layer, the magnetic anisotropy magnetoresistance effect of a ferromagnetic metal film which has been known for a long time has been used, but recently, for example, Japanese Patent Application Laid-Open No. 5-259530.
A magnetic field sensor using a coupled giant magnetoresistance effect (GMR effect) using a magnetic film having a multilayer structure has also been developed, as disclosed in Japanese Patent Application Laid-Open No. 7-77531.

[0005] In addition, the National Technical Report, 4
Vol. 2, No. 4, pp. 465, (NiFeCo / C
u) VTR using multilayer film as giant magnetoresistive element
A capstan motor rotation detection sensor is introduced.

[0006] These giant magnetoresistive films are generally formed on a hard substrate such as silicon or glass. Phys. Lett. (69) 3092
As described in U.S. Pat. No. 3,094,1996 (1996), attempts have been made to form a spin-valve structure film exhibiting a giant magnetoresistance effect on an organic film. The organic film is advantageous in that it is inexpensive as compared with a hard substrate, is easy to cut or separate when forming an element form, and greatly contributes to lowering the price of a product.

Incidentally, the giant magnetoresistive films known at present are generally of an antiferro (coupling) type having a (ferromagnetic / non-magnetic conductor) structure, and (high coercivity ferromagnetic / non-magnetic conductor). Inductive ferri (non-coupling) type with low coercivity ferromagnetic structure, (antiferromagnetic material / ferromagnetic material / nonmagnetic conductor /
It is roughly classified into a spin valve type having a (ferromagnetic material) structure, and a non-solid solution type granular type of Co / Ag type.

These giant magnetoresistive films have the following structures:
The detectable magnetic field strength, that is, the saturation magnetic field strength of the magnetoresistive effect greatly differs depending on the composition. Therefore, when designing an actual giant magnetoresistive film, select a basic form from various giant magnetoresistive films so as to obtain the highest magnetic field sensitivity depending on the magnetic field strength to be detected, and further change the composition system, It is necessary to optimize the detailed structure.

In the giant magnetoresistive film, an antiferro (coupling) type having a (ferromagnetic / non-magnetic conductor) structure,
And the induction ferri (non-coupling) type of (high coercivity ferromagnetic material / non-magnetic conductor / low coercivity ferromagnetic) structure is called a giant magnetoresistive multilayer film,
A large magnetoresistance effect can be obtained only by stacking 10 to 100 extremely thin layers having a thickness of 10 nm or less.

On the other hand, in the above-mentioned spin valve type, the thickness of one layer constituting the magnetic layer exceeds 10 nm in order to utilize the resistance change due to the spin direction between the two magnetic layers. It is also called a sandwich type because of the small number of layers. The above Appl. Phys. Lett. (6
9) The giant magnetoresistive film disclosed in 3092 to 3094 (1996) is a spin valve type.

[0011]

The giant magnetoresistive multilayer films of the coupling type and the inductive ferrimagnetic type described above and above are suitably used as a magnetic field sensor because the detection magnetic field is an appropriate value of several hundred Oe. Is often done. As described above, use of an organic film as a substrate has begun to be considered.

However, it is not possible to obtain a high MR ratio by forming a giant magnetoresistive multilayer film in which 10 to 100 extremely thin layers having a thickness of 10 nm or less are stacked on a flexible substrate made of resin. It was extremely difficult. That is, since a resin-made flexible substrate has a very low thermal conductivity as compared with a hard substrate made of silicon or glass, a giant magnetoresistive multilayer film is formed on a resin-made flexible substrate by a sputtering method. When a film is formed by a vacuum film forming method, the temperature of the surface of the substrate on which the multilayer film is actually formed tends to increase, even if the substrate is cooled from the back of the substrate. Therefore, the constituent elements are mutually diffused between the layers of the multilayer film during the film formation, and a clean layer interface cannot be obtained. This is especially true as noted above.
This is a problem that occurs remarkably when a giant magnetoresistive multilayer film is formed by laminating 10 to 100 extremely thin layers having a thickness of 10 nm or less.

[0013] Under such circumstances, the present invention has been devised. The purpose of the present invention is to lay a thin film on a resin-made flexible substrate which was originally difficult to use as a substrate. Are laminated in multiple layers while suppressing interdiffusion between the layers to form a giant magnetoresistive multilayer film having a clean layer interface.
An object of the present invention is to provide a magnetic field sensor having an extremely high magnetoresistance ratio (MR ratio).

[0014]

According to the present invention, there is provided a method for manufacturing a magnetic field sensor having a magnetoresistive film on a substrate, wherein the substrate has a thermal conductivity of κ, When the plate thickness is L, the value of κ / L is
A resin flexible substrate having a size of 1.5 × 10 ³ (W · m ⁻² · K ⁻¹ ) or more is used. While cooling the flexible substrate, a giant magnetoresistive multilayer film in which layers each having a thickness of 10 nm or less are laminated as a magnetoresistive film is formed by a vacuum deposition method.

Further, as a more preferred embodiment of the present invention,
The resin flexible substrate is configured to be a polyimide film having a thickness of 200 μm or less.

In a more preferred embodiment of the present invention,
The vacuum film forming method is configured to be a sputtering method.

Further, as a more preferred embodiment of the present invention,
The giant magnetoresistance effect multilayer film has a deposition rate of 0.005 to 0.005.
It is configured to form a film at 0.2 nm / sec.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a method of manufacturing a magnetic field sensor according to the present invention. In particular, a resin-made flexible substrate 10 is placed on a substrate fixing base 30, and a huge substrate is formed on the resin-made flexible substrate 10 by sputtering. A state where the magnetoresistive multilayer film 20 is formed is shown. Reference numeral 20a is a film-forming molecule schematically drawn. The resin-made flexible substrate 10 is usually fixed by a substrate fixing jig 5. Although not shown, a path for a coolant such as cooling water to pass therethrough is formed inside the substrate fixing base 30, and an inlet 51 for the refrigerant to the above-described path and a lower part of the substrate fixing base 30 are provided. An outlet 55 for the refrigerant from the path is formed. Then, by flowing a coolant from the inlet 51, the giant magnetoresistive multilayer film 2 is formed on the substrate 10 while cooling the resinous flexible substrate 10 from the substrate fixing base 30 side.
0 can be formed. The substrate fixing base 30 is formed of a material having high thermal conductivity, for example, aluminum or copper.

Although the giant magnetoresistive multilayer film 20 is not drawn in a multilayer state due to space in the drawing, it is actually a giant magnetoresistive multilayer film in which layers each having a thickness of 10 nm or less are laminated. is there. The apparatus in FIG. 1 is installed in a vacuum chamber (not shown).

Using one example of such a suitable apparatus, the method of manufacturing a magnetic field sensor of the present invention is carried out as follows.
That is, assuming that the thermal conductivity of the resin-made flexible substrate 10 is κ and the thickness thereof is L (shown in FIG. 1), κ
A resin flexible substrate 10 set so that the value of / L is equal to or more than 1.5 × 10 ³ (W · m ⁻² · K ⁻¹ ) is prepared. Then, the resin-made flexible substrate 10 is placed on the substrate fixing table 3.
0, and the resin-made flexible substrate 1
While cooling 0, the giant magnetoresistive effect multilayer film 20 in which layers each having a thickness of 10 nm or less are laminated as a magnetoresistive effect film 20 is formed by a vacuum film forming method.

The flexible resin substrate 10 used in the present invention
It is preferable to use a thin film that is excellent in flexibility and light even when thin. For example, a substrate similar to a plastic film widely used as a printed wiring board or the like can be used. More specifically, various materials known as plastic film materials, for example, polyimide, polyethylene terephthalate (PET), polyphenylene sulfide, polypropylene (PP), Teflon and the like can be used. In particular, it is preferable to use a polyimide film having high heat resistance in consideration of bonding by soldering, wire bonding, or the like.

As described above, the value of κ / L, which is the ratio of the thermal conductivity κ to the plate thickness L, is 1.5 × 1
0 ³ (W · m ⁻² · K ⁻¹ ) or more. κ / L
The value of means the thermal conductance per unit area,
It is used as an index for determining the degree of heat radiation. When this value is less than 1.5 × 10 ³ (W · m ⁻² · K ⁻¹ ),
The temperature of the surface of the substrate (the side on which the film 20 is formed) rises, and diffusion between the layers of the multilayer film 20 formed on the substrate occurs, and a good giant magnetoresistance effect multilayer film 20 cannot be obtained. As a result, a disadvantage arises in that a high magnetoresistance change rate (MR ratio) cannot be obtained.

The thermal conductivity of the resin-made flexible substrate 10 suitably used in the present invention is shown in Table 1 below. Table 1 also shows the values of the thermal conductivity of alumina, aluminum, brass, paper, copper, silicon, and quartz glass for reference.

[0025]

[Table 1] As shown in Table 1, for example, polyimide is the optimal substrate material, and κ is 0.29 (W · m ⁻¹ · K ⁻¹ ). Therefore, the value of κ / L is set to 1.5 × 10 ³ (W · m ⁻²
-In order to attain K ^-1 ) or more, the plate thickness L needs to be 200 μm or less. Similarly, for example, for polypropylene, the plate thickness L needs to be 80 μm or less. Although the thermal conductivity varies depending on the measurement temperature, a value near room temperature is used in the present invention.

The upper limit of the value of κ / L is not particularly limited. However, if the value is too large, the thickness of the substrate 10 becomes thin, and handling becomes inconvenient. Therefore, it is necessary to use the substrate while setting the plate thickness L in consideration of the convenience of handling the substrate. Usually, the upper limit of the value of κ / L is 80 × 10
³ (Wm- ^2K - ¹ ).

The giant magnetoresistive film to be formed by the production method of the present invention has a layer thickness as introduced on page 347 of a metal artificial lattice (edited by Hiroyasu Fujimori, Agne Technical Center, published in 1995). This is a multilayer film in which a ferromagnetic material and a non-magnetic material of 10 nm or less are laminated. As a specific film structure,
(Co / Cu), (NiFe / Cu), (NiFeCo
/ Cu), (CoFe / Cu), (NiFeCo / Cu)
/ Co / Cu), (NiFe / Cu / Co / Cu),
(CoFe / Cu / NiFe / Cu) or the like may be mentioned as a multilayer film structure formed by repeatedly forming a film five times or more, particularly about 5 to 100 times. Among these, (Co /
Cu), (NiFe / Cu), (NiFeCo / Cu)
Is preferably used.

In the giant magnetoresistive multilayer film 20 having such a multilayer structure, the thickness of each layer is 10 nm or less, particularly preferably 3 nm or less. This is for obtaining a high MR ratio. There is no particular limitation on the lower limit of the layer thickness,
The smaller the layer thickness, the more likely the interlayer diffusion during film formation occurs. Therefore, it is necessary to appropriately set the lower limit of the layer thickness of each layer while taking this point into consideration. Usually, the lower limit of the thickness of each layer is about 0.7 nm.

The giant magnetoresistive multilayer film 20 is formed by a vacuum film forming method such as a sputtering method, an evaporation method, a molecular beam epitaxy method (MBE method) or the like. Among them, it is preferable to form a film by a sputtering method. The sputtering method has an advantage that the film forming speed can be set over a wide range and has a relatively low film forming cost. Therefore, the sputtering method is particularly suitable for forming a multilayer film. When a multilayer film having a thickness of each layer of 10 nm or less is formed, it is necessary to control the film thickness on the order of angstroms. Therefore, it is usually advantageous to set the film formation speed to a small value, but the productivity is also low. Must be taken into account. However,
In the sputtering method, since the average energy of sputtered atoms is as high as about 10 eV, when the deposition rate is extremely high, the temperature of the substrate surface increases, and interlayer diffusion of the multilayer film occurs, and a high-quality laminated film is formed. There is a tendency that it cannot be formed. Therefore, in the present invention, the deposition rate of the sputtered atoms is preferably set to 0.005 to 0.2 nm / sec, more preferably 0.01 to 0.1 nm / sec. Within this range, the productivity is good and a good laminated film can be formed. In the evaporation method, the average energy of atoms is about 1 eV.
Because of the lower temperature, the temperature rise on the substrate surface during film formation is not as remarkable as the sputtering method when compared at the same film formation rate.

In the vapor deposition method, a film having an island shape or a column shape is easily grown, and it is difficult to form a layered structure having a flat interface. In addition, the molecular beam epitaxy method tends to take a long time for film formation because an ultra-high vacuum is required. Equipment costs are also high.

The cooling of the resin-made flexible substrate 10 from the substrate fixing base 30 side in the present invention is shown in FIG. 1 and a coolant such as water is continuously supplied into the substrate fixing base 30 as described above. It is done by flowing. At this time, the cooling operation of the substrate 10 is desirably performed such that the temperature difference ΔT between the front surface and the back surface of the substrate 10 is as large as possible.

The giant magnetoresistive multilayer film 20 formed on the substrate 10 in this manner is usually processed into a predetermined pattern shape, and further subjected to post-processing such as known wiring, to provide a magnetic field sensor. Take the form.

[0033]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention.

(Experimental Example 1) As a resin-made flexible substrate, 3
A polyimide film having an inch diameter and a plate thickness of 50 μm was prepared, and this substrate was mounted on an aluminum substrate fixing base. After that, 200Å-Ti (15Å-NiFeCo / 20Å) was deposited on the substrate by a dual ion beam sputtering apparatus.
-Cu) A multilayer film having a 30 structure was formed. The substrate fixing table was cooled by circulating cooling water (flow rate: 5 liter / min) controlled at a temperature of 25 ° C. The structure of the multilayer film is initially 20
A multilayer film having a total thickness of 1250 ° was formed by sequentially stacking 30 layers each of 0 ° Ti, then 15 ° NiFeCo alloy and 20 ° Cu. A (NiFeCo / Cu) 30-layer laminate structure has the function of a magnetoresistive film,
Is a base layer, which functions to promote crystallization of the magnetic layer laminated thereon and to improve the adhesion. In addition,
To improve the adhesion, before forming the multilayer film,
Ion milling of the substrate surface was performed with argon ions. The composition of each of the targets used was 99.9 in purity.
%, And the ultimate pressure was reduced to 4 × 10 ⁻⁷ Torr, and then argon gas was introduced. The degree of vacuum during the film formation was 1.4 × 10 ⁻⁴ Torr. The accelerating voltage of argon ions during film formation was 300 V, the beam current (proportional to the amount of argon ions) was 30 mA, and the average film forming speed of the NiFeCo film and the Cu film was 0.03 nm / sec.

After the formation of the multilayer film (magnetic film) in this manner, exposure and development were performed by a photoresist operation to form a pattern of the magnetic film. The pattern is 15 μm wide, 900
A 500 μm square electrode portion having a length of 0 μm was formed at the end of the pattern. Then, the unnecessary portion of the magnetic film not masked with the photoresist is removed by ion milling,
A magneto-sensitive pattern (magnetoresistive film) was formed. A tin-plated copper wire is joined to the electrode by soldering, and an insulating adhesive layer with good heat conductivity such as silicon resin is placed on the magnetic film to prevent self-heating of the element during use. Then, a 5000 μm square Cu member was bonded to assist heat radiation. Thus, a magnetic field sensor was completed, and a sample of Example 1 was obtained.

Next, only the plate thickness of the resin-made flexible substrate was changed variously as shown in Table 2 below, and the other conditions were the same as in the method of manufacturing the sample of Example 1, except for the samples of Example 2. Three samples, one comparative example, and two comparative examples were produced. The MR ratio (%) of each of these samples was measured in the following manner.

Measurement of MR Ratio (%) The resistance change was measured while applying a current of 1 mA to each sample shown in Table 2 and applying an external magnetic field of −300 to 300 Oe in the plane. The minimum value ρsat and the maximum value ρmax of the resistance were measured, and the MR ratio ΔR / R was determined from these values. That is, the MR ratio ΔR / R indicates that the maximum resistance is ρmax,
The minimum resistance was ρsat and was calculated by the following equation: ΔR / R
= (Ρmax−ρsat) × 100 / ρsat (%).

The measurement results are shown in Table 2 below.

[0039]

[Table 2] (Experimental Example 2) A 3-inch diameter polyimide film (thickness: 50 μm, 200 μm, 30 μm) was used as a resin flexible substrate.
0 μm), and a multilayer film having a total thickness of 1250 ° was formed by a dual ion beam sputtering apparatus in the same manner as in Experimental Example 1. However, in Experimental Example 2, an experiment was performed by changing the deposition rate in various ways by changing the acceleration voltage and beam current of argon ions. After film formation,
A sample of the magnetic field sensor was manufactured in the same manner as in Experimental Example 1, and an MR ratio was measured by applying a current of 1 mA to the manufactured sample. The results are shown in FIG. As is clear from the graph shown in FIG. 2, if the average deposition rate of the NiFeCo film and the Cu film is 0.005 to 0.2 nm / sec,
A high MR ratio can be obtained by using a polyimide film having a thickness of 00 μm as a substrate. The same applies when a polyimide film having a thickness of 50 μm is used as a substrate. However, when a polyimide film having a thickness of 300 μm is used as a substrate, the NiFeCo film and C
Even if the average film formation rate of the u film was reduced to about 0.03 nm / sec, a film having a high MR ratio could not be obtained.

[0040]

The effects of the present invention are clear from the above results. That is, in the method of manufacturing the magnetic field sensor according to the present invention, when the thermal conductivity of the substrate is κ and the plate thickness is L, the value of κ / L is 1.5 × 10 ³ (W · m ^−2. K ^-1 ) A flexible resin substrate made of resin is used. The resin flexible substrate is set on a substrate fixing base, and the magnetoresistive effect is cooled while cooling the resin flexible substrate from the substrate fixing base side. As a film, thickness 10
A giant magnetoresistive multilayer film in which layers of nm or less are stacked in multiple layers is formed by a vacuum film forming method. Therefore, even if a flexible substrate made of resin, which was originally difficult to use as a substrate, is used, a giant magnetoresistive multilayer film having a clean layer interface can be formed thereon, and an extremely high magnetoresistance A magnetic field sensor having a rate of change (MR ratio) is obtained.

[Brief description of the drawings]

FIG. 1 is a drawing schematically showing a method for manufacturing a magnetic field sensor according to the present invention, in particular, a state in which a giant magnetoresistive multilayer film is formed on a flexible resin substrate by sputtering. .

FIG. 2 is a graph showing a relationship between a film forming rate and an MR ratio, using the thickness of a resin-made flexible substrate as a parameter.

[Explanation of symbols]

 10: flexible substrate made of resin 20: giant magnetoresistive multilayer film

Claims (4)

[Claims] 1. A method of manufacturing a magnetic field sensor having a magnetoresistive film on a substrate, wherein the substrate has a thermal conductivity of κ and a thickness of L of κ / L of 1.5. A resin flexible substrate having a size of × 10 ³ (W · m ⁻² · K ⁻¹ ) or more is used. The resin flexible substrate is set on a substrate fixing base, and the resin flexible substrate is mounted from the substrate fixing base side. A method for manufacturing a magnetic field sensor, comprising: forming a giant magnetoresistive multilayer film in which layers having a thickness of 10 nm or less are laminated as a magnetoresistive film by vacuum deposition while cooling a conductive substrate. . 2. The resin-made flexible substrate has a thickness of 200 μm.
The method for manufacturing a magnetic field sensor according to claim 1, wherein the polyimide film has a thickness of not more than m. 3. The method according to claim 1, wherein the vacuum film forming method is a sputtering method. 4. The method according to claim 1, wherein the giant magnetoresistive multilayer film is formed at a film forming rate of 0.005 to 0.2 nm / sec.