JPH0449665B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a thin film magnetic sensor capable of detecting changes in an external magnetic field, particularly changes in a minute magnetic field. Conventional Structure and Problems Conventionally, many sensors using semiconductor materials, magnetic materials, etc. have been developed and put into practical use as magnetic sensors for detecting the amount of change or change in an external magnetic field.
For example, in devices using semiconductor materials, Hall elements,
There are field effect transistor elements and the like. these are
- group compounds such as InSb and GaAs, Si, Ge, etc. are mainly used. Items using magnetic materials include memory elements, magnetoresistive elements, ring-type magnetic heads, etc., including permalloy, sendust, Ni-Zn, and Mn.
-Zn ferrite etc. are used. In addition, U.S. Patent No. 3,820,090 describes that a linear magnetic material is mechanically and
Heat treatment is applied to change the coercive force of the layer near the surface of the magnetic wire (second magnetic part), making it larger than the coercive force of the inside (first magnetic part), and the magnetic wire is wound around this. The device is listed. This is the second
The coercive force of the first magnetic part is larger than the coercive force of the first magnetic part, and the structure is Fe-Co-
The inside of the magnetic wire consists of a part with a small coercive force, and the part near the outer surface is a thin wire with a part with a large coercive force. For example, in this magnetic device, when the direction and magnitude of the external magnetic field are changed in the longitudinal direction of a thin wire, the part with a large coercive force interacts magnetically with the part with a small coercive force, so the direction of magnetization of both changes. When the magnetic field is in the same direction but opposite to the external magnetic field, magnetization reversal in the portion with low coercive force occurs with an external magnetic field that is greater than the coercive force Hc ₁ and smaller than the coercive force Hc ₂ in the portion with high coercive force.
Also, if the external magnetic field and the magnetization direction of the part with high coercive force are the same, and only the magnetization direction of the part with low coercive force is opposite to them, the external magnetic field will gradually increase and the magnetization direction of the part with low coercive force will be the same. When the coercive force is about the same as that of Hc, the magnetization reversal of the part with a small coercive force (reversal in the same direction as the external magnetic field) is assisted by the part with a large coercive force, and it occurs more sharply in a magnetic field of about Hc ₁ . An electromagnetic induction phenomenon occurs due to magnetization reversal due to the influence of an external magnetic field in the part with low coercive force, and a current is generated in the pick-up coil wound around a thin wire. A large pulse voltage can be obtained. The magnitude and steepness of this pulse voltage are far superior to those using magnetization reversal of a single magnetic material. Furthermore, in the case of a single magnet, the pulse width generated in the pickup coil depends on the alternating frequency of the external magnetic field; if the change is slow, the width is wide, and if it is not fast, the pulse width is narrow. In contrast, the U.S. patent
In the case of the device described in the specification of No. 3820090, it is induced by the large Barkhausen jump,
A steep pulse voltage with a constant width can be obtained without depending on the alternating frequency of the external magnetic field. Although the device described in US Pat. No. 3,820,090 has excellent characteristics as described above, the manufacturing method thereof is complicated and it is difficult to manufacture it with a high yield. Also diameter 250
Although micron-thin wires are used, it is extremely difficult to create smaller devices. The magnitude of the external magnetic field required to generate a more steep induced pulse is approximately 15 Oersteds, and the magnetic field requires a weaker external magnetic field or a minute magnetic field, such as an external magnetic field of 1 Oersteds or less, to generate an induced pulse. The heads described in US Pat. No. 3,820,090 are not used. OBJECTS OF THE INVENTION It is an object of the present invention to provide a magnetic sensor having a thin film structure that can significantly solve the above-mentioned conventional problems and difficulties. Structure of the Invention In order to achieve the above object, the thin film magnetic sensor of the present invention is produced by stacking two cobalt-zirconium amorphous magnetic thin films having cobalt as the main component and having different coercive forces on a non-magnetic substrate. It is equipped with a pick-up coil. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. First, using a cobalt (Co)-zirconium (Zr) alloy target, two layers of cobalt (Co)-zirconium (Zr) amorphous magnetic thin films with different coercive forces are formed on a nonmagnetic substrate by sputtering. The coercivity of the two magnetic thin films can be made different by changing the sputtering conditions, for example, the argon (Ar) gas pressure during sputtering. When approximately 5 at% of zirconium (Zr) is added to cobalt (Co), the coercive force of the magnetic thin film decreases rapidly. It is known that this is due to progress of amorphization.
At around 10 at%, it becomes almost completely amorphous, and when zirconium (Zr) is further increased, microcrystals become mixed in the amorphous. However, the coercive force is much smaller than that of cobalt (Co) alone. Saturation magnetization gradually decreases as the amount of zirconium (Zr) added increases; for example, when adding 30 at%, it becomes approximately
It becomes 1K Gauss. When the saturation magnetization becomes small, the induced pulse voltage value generated in the pickup coil due to magnetization reversal does not become large. Therefore, the appropriate amount of zirconium (Zr) to be added is 5 at% to 20 at%. Figure 1 shows the relationship between the coercive force and saturation magnetization of a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film and the amount of zirconium (Zr) added.
In FIG. 1, 1 is a graph showing changes in coercive force, and 2 is a graph showing changes in saturation magnetization. The coercive force of a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film can be changed by using targets with different amounts of zirconium (Zr), but the targets must be changed each time the film is formed. Alternatively, there are problems with workability and equipment, such as the need to use equipment that permanently installs a plurality of targets. In this respect, it is easier to create magnetic thin films with different coercive forces by simply changing the sputtering conditions. Second
The figure is a graph showing changes in coercive force and saturation magnetization of a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film due to argon (Ar) gas pressure during sputtering. In FIG. 2, 3 is a graph showing changes in coercive force, and 4 is a graph showing saturation magnetization. A cobalt (Co)-zirconium (Zr) amorphous magnetic thin film formed on a nonmagnetic substrate by the sputtering method exhibits magnetic anisotropy in the film plane. In other words, it becomes a magnetic thin film with an easy axis in a particular direction. Since the thin film magnetic sensor of the present invention causes magnetization reversal of the magnetic thin film in the direction of an external alternating magnetic field, if the easy axis is aligned in this method, a steeper magnetization reversal will occur and the induced pulse voltage will also increase. FIG. 3 shows the M-H curves of the cobalt (Co)-zirconium (Zr) amorphous magnetic thin film in the easy axis direction and the hard axis direction. 5 is an MH curve in the easy axis direction, and 6 is an MH curve in the hard axis direction. Two layers of cobalt (Co) with different coercive forces according to the present invention
-The order in which a zirconium (Zr) amorphous magnetic thin film is formed on a non-magnetic substrate is that cobalt (Co), which has a small coercive force that causes the magnetization reversal that generates the induced pulse, ) - It is best to first form a zirconium (Zr)/amorphous magnetic thin film on a non-magnetic substrate, and then form a cobalt (Co) - zirconium (Zr)/amorphous magnetic thin film with a large coercive force on top of it. . When formed in this order, the variation in coercive force of the magnetic thin film formed below is reduced,
It is stable. That is, as shown in FIG. 4, a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film 8 having a small coercive force is first formed on a non-magnetic substrate 7, and then argon (Ar) gas pressure is applied during sputtering. Instead, a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film 9 having a large coercive force is formed. Next, as shown in FIG. 5, two layers of cobalt (Co)-zirconium (Zr) amorphous magnetic thin films 8 and 9 formed overlappingly on the non-magnetic substrate 7 are coated with hydrofluoric acid, nitric acid and water using photolithography technology. Etch it with a mixed solution to make it into strips 10. At this time, the longitudinal direction of the strip is made to coincide with the easy axis direction of the magnetic thin film. As shown in FIG. 6, the nonmagnetic substrate 7 is cut into strips, and the pick-up coil 11 is wound around the longitudinal direction of the strip to form a thin film magnetic sensor. The thin film magnetic sensor thus produced is placed in a uniform external alternating magnetic field, and the alternating magnetic field is applied with the direction of the magnetic field and the longitudinal direction of the magnetic sensor aligned. When this alternating magnetic field reaches a certain strength, the magnetization of the magnetic thin film with a small coercive force is reversed, and an induced pulse is generated in the wound coil 11. The direction of this external magnetic field and the phenomenon of generation of induced pulses are the same as those in US Pat. No. 3,820,090. The height of this induced pulse voltage varies depending on the relative value of the coercive force of the two-layer film formed by the sputtering method. The relative value of this coercive force is also related to the strength of the induced external alternating magnetic field. According to the embodiment of the present invention, the coercive force of the cobalt (Co)-zirconium (Zr) amorphous amorphous magnetic thin film, which has a smaller coercive force, is 2 to 8 times that of the same magnetic thin film, which has a larger coercive force. Evoked pulses were obtained when the value When the coercive force of a magnetic thin film with a small coercive force is greater than 0.6 Oersteds, the strength of the external alternating magnetic field that generates the induced pulse exceeds 1 Oersted when used as a thin film magnetic sensor, and the The sensor does not work when used. Further, a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film having a diameter smaller than 0.05 oersted could not be obtained in the examples of the present invention. Even with a smaller coercive force, if a two-layer film is formed by combining a magnetic thin film with a large coercive force suitable for this, a thin film magnetic sensor that can generate induced pulses can be obtained. If the coercive force of a cobalt (Co)-zirconium (Zr) amorphous magnetic thin film with a large coercive force exceeds eight times the coercive force of a magnetic thin film with a small coercive force, it becomes difficult to obtain an induced pulse voltage. The generation of the induced pulse voltage occurs because the magnetization reversal of the magnetic thin film with a small coercive force of the thin-film magnetic sensor is constrained to an appropriate coercive force of the magnetic thin film with a large coercive force due to changes in the applied external alternating magnetic field. This is thought to be because if the constraint is too strong, that is, if the coercive force of a magnetic thin film with a large coercive force is too large, the two layers will magnetically behave as if they were a single layer. It will be done. On the other hand, if it is too small than twice, the interaction between the two layers will be too weak and the magnetization will be reversed as a single magnetic thin film, making it impossible to obtain the desired steep induced pulse voltage. Next, specific embodiments of the present invention will be described. A 6-inch diameter target made of a cobalt (Co)-zirconium (Zr) alloy whose main component was cobalt (Co) to which 8 at% zirconium (Zr) was added was used. After setting the ultimate vacuum to 2 × 10 ^-7 Torr, we sputtered a cobalt (Co)-zirconium (Zr) alloy by changing the argon (Ar) gas pressure during sputtering. A 5000% (Zr) amorphous magnetic thin film was deposited on a glass substrate. The spatuta power at this time is
It was 400 watts. Next, the argon (Ar) gas pressure during sputtering is set to a condition that provides a coercive force greater than that of the first layer of cobalt (Co)-zirconium (Zr) amorphous magnetic thin film, and the second layer is stacked on top of the first layer. Cobalt (Co) - Zirconium (Zr)
An amorphous magnetic thin film was deposited. The sputter pressure at this time was also 400 watts. The thickness of the second layer is
It was 3500〓. Cobalt (Co)-zirconium (Zr) amorphous magnetic thin films with different coercive forces formed in two layers were masked using photolithography technology into strips with a width of 500 μm and a length of 5 mm (see Figure 5), and then coated with hydrofluoric acid: Etching was performed using an etching solution containing nitric acid:water=5:1:94 (volume %). At this time, the longitudinal direction of the strip was made to coincide with the magnetic easy axis of the cobalt (Co)-zirconium (Zr) amorphous magnetic thin film. Next, the glass substrate was cut into the same shape as the rectangular two-layer film. A thin-film magnetic sensor was created by winding 50 turns of copper wire with a diameter of 60 μm (No. 6
(see figure). A uniform external alternating magnetic field was applied to this sensor, and the induced pulse voltage generated in the coil was investigated. Nos. 1 to 16 in the following table show the coercive force of the magnetic thin films of the examples of the present invention, the external alternating magnetic field and the induced pulse voltage necessary to generate induced pulses. The induced pulse voltage value obtained was constant regardless of the frequency of the external alternating magnetic field. In addition, the longitudinal direction of the strip was made to match the difficult axis direction of the magnetic thin film. In the thin film magnetic sensor, induced pulses could not be obtained even if the external alternating magnetic field was changed. This seems to be because the magnetic interaction between the two layers does not become a condition that can generate an induced pulse. Nos. 17 and 18 in the table show those outside the invention. Effects of the Invention As described above, the present invention consists of two layers of cobalt (Co)-zirconium (Zr) amorphous magnetic thin films having different coercive forces stacked on a non-magnetic substrate, and a pick-up coil wound around this. So, the outside is small, less than 1 oersted.

[Table] A steep and large induced pulse voltage can be obtained in response to an alternating magnetic field. Moreover, the value is excellent in that it does not depend on the frequency of the external alternating magnetic field. The ability to respond to a minute magnetic field in this way makes it an effective sensor, as it can also reproduce minute signals recorded on a magnetic recording medium, for example. Furthermore, since it has a thin film structure, it has the advantage that a smaller sensor or a group of integrated sensors can be made using photolithography technology.

[Brief explanation of drawings]

The drawings show examples of the present invention. Figure 1 is a graph showing changes in coercive force and saturation magnetization depending on the amount of zirconium (Zr) added, and Figure 2 is a graph showing changes in coercive force and saturation magnetization due to argon (Ar) gas pressure during sputtering. A graph showing changes in saturation magnetization, FIG. 3 is a graph showing M-H curves in the easy axis direction and hard axis direction of the magnetic thin film, and FIGS. 4 to 6 are explanations showing the manufacturing order of the thin film magnetic sensor of the present invention. It is a diagram. 7... Nonmagnetic substrate, 8, 9... Cobalt-tantalum amorphous magnetic thin film, 11... Coil.

Claims (1)

[Claims] 1. A cobalt-zirconium amorphous magnetic thin film whose main component is cobalt with different coercivity.
A thin film magnetic sensor that is formed by stacking layers on a non-magnetic substrate and has a pick-up coil attached to it. 2. The thin film magnetic sensor according to claim 1, wherein the amount of zirconium added to the cobalt-zirconium amorphous magnetic thin film is 5 at% to 20 at%. 3. The thin film magnetic sensor according to claim 1, which is formed by forming a cobalt-zirconium amorphous magnetic thin film by a sputtering method. 4. Claim 1, in which a cobalt-zirconium amorphous magnetic thin film with a low coercive force is first formed on a non-magnetic substrate, and then a cobalt-zirconium amorphous magnetic thin film with a large coercive force is overlaid thereon. Thin film magnetic sensor described in Section 1. 5 The ratio of the coercive force of the two types of cobalt-zirconium amorphous magnetic thin films is 1:2 to 1:
8. The thin film magnetic sensor according to claim 1. 6. The thin film magnetic sensor according to claim 1, wherein the cobalt-zirconium amorphous magnetic thin film having a small coercive force has a coercive force value of 0.05 to 0.7 oersteds. 7. The thin film magnetic sensor according to claim 1, wherein the longitudinal direction of the strip made of two types of cobalt-zirconium amorphous magnetic thin films having different coercive forces coincides with the easy axis direction of the cobalt-zirconium amorphous magnetic thin film.