JPH0927103A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic sensor for which a magneto-resistive effect is utilized and which is used as an information reading out means of a hard disk device and which is capable of efficiently converting the magnetic fields impressed from outside to electric signals even if the change in the intensity thereof is small. SOLUTION: This magnetic sensor is a magnetic sensor which detects the intensity of the magnetic fields by utilizing the magneto-resistive effect of a magneto-resistive element consisting of magnetic metallic thin films. The magneto-resistive element 1 is disposed between a buffer layer 6 consisting of metal which has the electric resistance higher than the electric resistance of the magnetic metallic thin films and deprives oxygen in the magnetic metallic thin films and a cover layer 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor utilizing a magnetoresistive effect used as information reading means in a hard disk drive, and more particularly to a magnetoresistive element caused by impurities mixed in a magnetic metal thin film forming process. The present invention relates to means for preventing characteristic deterioration of

Since a hard disk device for recording information on a magnetic disk has a relatively large storage capacity and has a high information processing speed, it is used as a means for storing information processing procedures and data in various information processing devices including a computer. Widely used.

In such a hard disk device, a conventional magnetic head has a coil for writing and reading information. For writing information to and reading information from the magnetic disk, a coil included in the magnetic head is used. I was going.

In recent years, the demand for higher recording density and higher information processing speed has increased as the capacity of hard disk devices has further increased, and in order to read information from a magnetic disk, a magnetic sensor is incorporated into a magnetic head to apply magnetism. The method of direct detection is changing.

Among them, a magnetic sensor for detecting the strength of a magnetic field applied by utilizing the magnetoresistive effect of a magnetoresistive element made of a magnetic metal thin film can be downsized / lightweight and is excellent in mass productivity, and thus hard disk. Attention has been paid to the most suitable magnetic sensor for the device.

However, with the increase in recording density of hard disk devices, the area per bit is decreasing and the strength of the magnetic field is becoming weaker. Therefore, there is a demand for realization of a magnetic sensor that can be efficiently converted into an electric signal even if the change in applied magnetic field strength is small.

[0007]

2. Description of the Related Art FIG. 3 is an explanatory view of the principle of a magnetic sensor utilizing the magnetoresistive effect, and FIG. 4 is a schematic view showing a layer structure of a conventional magnetic sensor.

A magnetic sensor utilizing the magnetoresistive effect is shown in FIG.
The magnetoresistive element 1 formed of a magnetic metal thin film of some kind as shown in FIG. 2 has a property that the magnetoresistive element 1 changes its specific resistance in response to a magnetic field applied from the outside by a magnetoresistive effect. .

The magnetoresistive element 1 is arranged so that one side surface thereof faces the recording track 2 of the magnetic disk with a gap, and is supplied to the magnetoresistive element 1 through the conductor patterns 11 connected to both ends. Recording current 2
Flows in a direction parallel to the plane of.

Further, the magnetic sensor comprises a bias layer 3 made of a soft magnetic material which is arranged in parallel with the magnetoresistive element 1 and faces each other with a gap. When the magnetoresistive element 1 is energized, the bias layer 3 is formed by the current magnetic field. A bias magnetic field is applied to the magnetized magnetoresistive element 1.

On the other hand, on the recording track 2 on which information is magnetically recorded, a large number of magnetic domains 21 are arranged in the traveling direction shown by a large arrow, and the magnetic domain 21 is "1" or "1" of the information recorded therein. It is magnetized in the traveling direction or the opposite direction corresponding to 0 ".

When the direction of the magnetic field due to the magnetic domain 21 coincides with the direction of the magnetic field of the bias layer 3, a large magnetic field is applied to the magnetoresistive element 1, and when the direction of the magnetic field due to the magnetic domain 21 is opposite, the magnetic field due to the bias layer 3 is weakened. The magnetic field applied to the magnetoresistive element 1 is weakened.

As a result, the resistance of the magnetoresistive element 1 having the magnetoresistive effect changes in accordance with the direction of the magnetic field applied by the magnetic domain 21, and the potential difference between the conductor patterns 11 of the magnetoresistive element 1 is detected. The information recorded on the recording track 2 can be read.

As described above, in order to simultaneously magnetize in the same direction in response to the applied magnetic field, it is necessary to form a single magnetic domain structure in the magnetoresistive element 1. Therefore, the single domain domainization layers 12 made of a ferromagnetic material for aligning the magnetization directions of the magnetoresistive element 1 are arranged at both ends of the magnetoresistive element 1.

As shown in FIG. 4, the conventional magnetic sensor is composed of two conductor patterns 11 made of Ta and Fe-Mn alloy, which are laminated on a substrate 4 made of alumina (Al ₂ O ₃ ). The magnetoresistive element 1 has two single domain layers 12 and a magnetoresistive element 1 made of permalloy (Ni—Fe alloy).
A buffer layer 13 made of Ta, a bias layer 3 made of a Ni—Fe—Rh alloy, and a protective film layer 5 made of Al ₂ O ₃ are further formed thereon in layers.

[0016]

With the increase in recording density of hard disk devices, each magnetic domain of a recording track is becoming smaller and the applied magnetic field is becoming weaker. Therefore, there is a strong demand for realization of a magnetic sensor that can efficiently convert an electric signal even if the change in the applied magnetic field strength is small.

However, a sputtering method is generally used as a film forming means for a magnetoresistive element in the process of manufacturing the above-mentioned magnetic sensor, and a small amount of an adsorbed substance in the chamber or impurities contained in the sputtering target is generated. It is taken into the magnetoresistive element.

Impurities are taken into the magnetoresistive element in the film forming process, which has various adverse effects on the characteristics of the magnetic sensor. Above all, when oxygen is present inside the magnetoresistive element, the magnetic characteristics are deteriorated and the SN of the magnetic sensor is deteriorated. There was a problem that the ratio decreased.

An object of the present invention is to provide a magnetic sensor that can efficiently convert an electric signal even if the change in the magnetic field strength applied from the outside is small.

[0020]

FIG. 1 is a schematic view showing the layer structure of a magnetic sensor according to the present invention. Note that the same object is denoted by the same symbol throughout the drawings.

The above problem is a magnetic sensor for detecting the strength of a magnetic field applied from the outside by utilizing the magnetoresistive effect of a magnetoresistive element made of a magnetic metal thin film. This is achieved by the magnetic sensor of the present invention which is disposed between the buffer layer 6 and the cover layer 7 which are made of a metal that deprives oxygen of the magnetic metal thin film to a greater extent than the magnetic metal thin film.

[0022]

In FIG. 1, a buffer layer and a cover layer made of a metal that deprives the magnetic metal thin film of oxygen are provided on both surfaces of the magnetoresistive element, so that oxygen in the magnetoresistive element can be converted into oxygen in the buffer layer by heat treatment after film formation. The amount of oxygen in the magnetoresistive element decreases by moving to the cover layer.

As a result, oxygen in the magnetoresistive element which deteriorates the magnetic characteristics is reduced, and a magnetic sensor having a high SN ratio can be realized. That is, it is possible to realize a magnetic sensor that can be efficiently converted into an electric signal even if the change in the magnetic field strength applied from the outside is small.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that FIG. 2 is a schematic diagram showing a layer structure in another embodiment of the present invention.

The magnetic sensor according to the present invention has a buffer layer 6 and a cover layer 7 which are laminated and formed on an alumina substrate 4 as shown in FIG. 1. The magnetoresistive element 1 and two conductor patterns 11 and The single domain layer 12 is provided between the buffer layer 6 and the cover layer 7.

The magnetoresistive element 1 is made of Ni--Fe alloy, the conductor pattern 11 is made of Ta or W, the single domain domain layer 12 is made of Fe--Mn alloy, and the buffer layer 6 and the cover layer 7 are made of Ni. −
For example, Ti which is more easily oxidized than a magnetic metal thin film such as Fe alloy or Fe-Mn alloy is used.

Although the magnetoresistive effect of the magnetoresistive element 1 is usually impaired by providing the buffer layer 6 and the cover layer 7 made of metal on both sides, the ratio of Ti is higher than that of the specific resistance of Ni—Fe alloy of about 25 μΩ · cm. The resistance of 55 μΩ · cm is much larger and the magnetoresistive effect is not impaired.

[0028] Alternatively thickness using a glass substrate having the Al ₂ O ₃ film was formed on the surface of 1500Å on the alumina substrate for confirming the effect of the present invention, the film thickness on the Al ₂ O ₃ film is 70 Å Ti A buffer layer made of a film, a magnetoresistive element made of a Ni-Fe alloy film having a film thickness of 200Å, and a cover layer made of a Ti film having a film thickness of 70Å were formed.

As a product for comparison of characteristics, an Al ₂ O ₃ film excluding a buffer layer and a cover layer and a magnetoresistive element were formed on a glass substrate, and both were left in a vacuum at 300 ° C. for 1 hour. After heat treatment, the BH tracer was used to measure the magnetic properties.

The present invention in Table 1 shows the measurement results of the former having the layer constitution, and the conventional product shows the measurement results of the latter having the layer constitution. The electric resistance of the magnetoresistive element is 4
The resistance change rate was measured by the terminal method and calculated by the following equation (where ρ ₀ is the resistance value when the coercive force is 0 Oersted, ρ ₂₀
Indicates the resistance value when the coercive force is 20 Oersted).

Resistance change rate (%) = (ρ ₀ −ρ ₂₀ ) / ρ ₂₀ × 100

[0032]

[Table 1]

From Table 1, by adding a Ti film having a film thickness of 70Å as a buffer layer and a cover layer, the magnetic characteristics of the magnetoresistive element are improved, and at the same time, the rate of change in resistance is increased to improve the magnetoresistive effect of the magnetoresistive element. S in the magnetic sensor used
The improvement of the N ratio is clear.

The optimum film thicknesses of the buffer layer and the cover layer differ depending on the change of the conditions during film formation, that is, the change of the oxygen content in the Ni-Fe alloy film. When both thicknesses are less than 50Å, the oxygen adsorption effect is small and improvement in magnetic properties cannot be expected.

However, it is not necessary that the film thickness of each layer is 50 Å or more. If at least one of the buffer layer and the cover layer has a film thickness of 50 Å or more, even if the other film thickness is 0, The magnetic characteristics can be improved as will be apparent from the experimental examples described later.

Further, when the total value of the film thicknesses of the buffer layer and the cover layer, or one of the film thicknesses exceeds 200Å, the resistance value decreases and the current flowing through the buffer layer and the cover layer increases. Therefore, there arises a problem that the resistance change rate of the magnetoresistive element is reduced.

That is, when at least one of the buffer layer and the cover layer has a film thickness of 50Å or more, and the total film thickness of the buffer layer and the cover layer is in the range of 50 to 200Å, the magnetoresistive element is formed. It is possible to improve the magnetic characteristics of and improve the rate of resistance change.

Further, in order to confirm the effect of the present invention, the same experiment was conducted by replacing the material of the buffer layer and the cover layer with the Ti film from the Mg film. As a result, it was confirmed that even if the Ti film was replaced with the Mg film, the magnetic characteristics of the magnetoresistive element were similarly improved and the resistance change rate was increased.

However, the Mg film is different from the Ti film when one of the buffer layer and the cover layer has a film thickness of 50 Å or more and the total film thickness of the buffer layer and the cover layer is in the range of 50 to 100 Å. The magnetic characteristics of the magnetoresistive element can be improved and the rate of resistance change can be increased.

The material of the buffer layer and the cover layer is Ti or
Any metal other than Mg, which has a larger electric resistance and is more easily oxidized than a magnetic metal, can be obtained even if the buffer layer and the cover layer are different metals, provided that the above conditions are satisfied. .

Another embodiment of the magnetic sensor according to the present invention comprises a buffer layer 6 formed on an alumina substrate 4 as shown in FIG. 2, and a magnetic resistance is provided between the alumina substrate 4 and the buffer layer 6. The element 1, two conductor patterns 11 and a single magnetic domain layer 12 are formed.

The magnetoresistive element 1 is made of Ni--
Fe alloy, conductor pattern 11 is Ta or W, and single domain domain layer 12 is Fe-
The buffer layer 6 is made of Mn alloy, and the buffer layer 6 is made of Ni-Fe alloy or Fe-
Metals that are more easily oxidized than magnetic metal thin films such as Mn alloys, for example
A thin film of Ti is used.

[0043] After the film thickness on a glass substrate in order to confirm the effect of the present embodiment as in the case of the embodiment was formed an Al ₂ O ₃ film of 1500 Å, film thickness on the Al ₂ O ₃ film A buffer layer made of a 100 Å Ti film and a magnetoresistive element made of a Ni-Fe alloy film having a film thickness of 200 Å were formed.

As a product for comparison of characteristics, an Al ₂ O ₃ film and a magnetoresistive element excluding a Ti film buffer layer were formed on a glass substrate, and both were left in a vacuum at 300 ° C. for 1 hour. After heat treatment, the BH tracer was used to measure the magnetic properties.

The present invention in Table 2 shows the measurement results of the former having the layer constitution, and the conventional product shows the measurement results of the latter having the layer constitution.

[0046]

[Table 2]

From Table 2, by adding a Ti film having a film thickness of 100Å as a buffer layer, the magnetic characteristics are improved as compared with the conventional magnetoresistive element, and at the same time, the rate of change in resistance is increased to increase the magnetoresistive effect of the magnetoresistive element. In a magnetic sensor using
The improvement of the N ratio is clear.

The optimum value of the film thickness of the buffer layer varies depending on the change in conditions when the magnetoresistive element is formed, but if it is less than 50 Å, the magnetic characteristics cannot be improved, and if it exceeds 200 Å, the current flowing through the buffer layer is increased. Is increased and the resistance change rate of the magnetoresistive element is decreased. That is, when the thickness of the buffer layer is in the range of 50 to 200Å, the magnetic characteristics of the magnetoresistive element can be improved and the rate of resistance change can be increased.

In order to confirm the effect of another embodiment of the present invention, the same experiment was conducted by changing the material of the buffer layer from the Ti film to the Mg film. As a result, even if the Ti film is replaced with the Mg film, the magnetic characteristics of the magnetoresistive element are similarly improved, and the resistance change rate is increased. However, unlike the case of the Ti film, the Mg film can improve the magnetic characteristics of the magnetoresistive element and increase the resistance change rate when the thickness of the buffer layer is 50 to 100 Å.

By thus disposing the buffer layer and the cover layer made of a metal that deprives oxygen in the magnetic metal thin film on both sides of the magnetoresistive element, oxygen in the magnetoresistive element is buffered by heat treatment after film formation. The oxygen in the magnetoresistive element is lowered by moving to the layer or the cover layer.

As a result, oxygen in the magnetoresistive element is reduced, magnetic characteristics are improved, and a magnetic sensor having a high SN ratio can be realized. That is, it is possible to realize a magnetic sensor that can be efficiently converted into an electric signal even if the change in the magnetic field strength applied from the outside is small.

[0052]

As described above, according to the present invention, it is possible to provide a magnetic sensor which can be efficiently converted into an electric signal even if the change in the magnetic field strength applied from the outside is small.

[Brief description of drawings]

FIG. 1 is a schematic view showing a layer structure of a magnetic sensor according to the present invention.

FIG. 2 is a schematic view showing a layer structure in another example of the present invention.

FIG. 3 is an explanatory view of the principle of a magnetic sensor utilizing the magnetoresistive effect.

FIG. 4 is a schematic diagram showing a layer structure of a conventional magnetic sensor.

[Explanation of symbols]

 1 Magnetoresistive Element 3 Bias Layer 4 Substrate 5 Protective Layer 6 Buffer Layer 7 Cover Layer 11 Conductor Pattern 12 Single Domain Domain Layer

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Yutaka Shimizu Inventor Yutaka Shimizu 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Makoto Iijima 1015 Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor Masashige Sato 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (5)

[Claims] 1. A magnetic sensor for detecting the strength of a magnetic field applied from the outside by utilizing the magnetoresistive effect of a magnetoresistive element made of a magnetic metal thin film, wherein the magnetoresistive element has an electric resistance of the magnetic metal. A magnetic sensor, which is disposed between a cover layer and a buffer layer made of a metal that deprives oxygen of the magnetic metal thin film to a greater extent than the thin film. 2. The buffer layer and the cover layer are made of Ti, and at least one of the buffer layer and the cover layer is
The magnetic sensor according to claim 1, wherein the magnetic sensor has a film thickness of 50 Å or more, and a total film thickness of the buffer layer and the cover layer is in a range of 50 to 200 Å. 3. The buffer layer and the cover layer are made of Mg, and at least one of the buffer layer and the cover layer is
The magnetic sensor according to claim 1, which has a film thickness of 50 Å or more, and a total film thickness of the buffer layer and the cover layer is in a range of 50 to 100 Å. 4. The magnetic sensor according to claim 1, wherein the magnetoresistive element is provided without a cover layer, and the magnetoresistive element is attached to a buffer made of a metal whose electric resistance is larger than that of the magnetic metal thin film and deprives oxygen in the magnetic metal thin film. Magnetic sensor characterized by. 5. The magnetic sensor according to claim 4, wherein the buffer layer is made of Ti having a film thickness of 50 to 200Å or Mg having a film thickness of 50 to 100Å.