Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2002-08-22
2003-11-04
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S225000, C338S03200R, C428S692100
Reexamination Certificate
active
06642714
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thin-film magnetic field sensor for measuring a magnetic field in a space, and particularly to a thin-film magnetic field sensor for precisely measuring the degree and direction of a magnetic field, using a giant-magneto-resistant thin-film, such as a nano-granular giant-magneto-resistance effect thin-film.
BACKGROUND ART
FIG. 1
shows a magnetic field sensor disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 11-87804 and 11-274599. In
FIG. 1
, the portion indicated with “Giant-magneto-resistant thin-film” denotes a nano-granular giant-magneto-resistant thin-film of “Metal-Insulator”, which renders an electrical resistance change of about 10% when a magnetic field of 10 k Oe is applied. As in this example, giant-magneto-resistant thin-films have a larger range of change in the electrical resistance value, as compared to ordinary magneto-resistance effect materials. However, as described above, they require a large applied magnetic field to cause an electrical resistance change. Accordingly, where a giant-magneto-resistant thin-film is solely used, hardly any change in the electrical resistance value can be expected with a small magnetic field of about 100 Oe or less, which is generally used in magnetic field sensors.
The structure shown in
FIG. 1
is arranged to compensate for the problem described above. Specifically, there are soft magnetic thin-films, which function as members for gathering magnetic flux around them. Where the dimensions of-the soft magnetic thin-films are appropriately selected, the giant-magneto-resistant thin-film can be supplied with any degree of large magnetic flux density within the saturation magnetic flux density of the soft magnetic thin-films, regardless of the degree of the magnetic field around the soft magnetic thin-films, in principle. Furthermore, seeing the structure shown in
FIG. 1
from the point of view of electrical resistance, although the electrical resistance value between the soft magnetic thin-films is the sum of those of soft magnetic thin-film portions and a giant-magneto-resistant thin-film portion, the resistance value between the soft magnetic thin-films is substantially equal to the resistance value of the giant-magneto-resistant thin-film portion, because the giant-magneto-resistant thin-film has a high electrical resistivity, which is 100 times or more that of the soft magnetic thin-films. In other words, the electrical resistance value of the giant-magneto-resistant thin-film directly takes on the electrical resistance value between the soft magnetic thin-films.
FIG. 2
shows an example of change in electrical resistance in the structure shown in FIG.
1
. As shown in
FIG. 2
, a change of about 6% in the electrical resistance value is realized with a small magnetic field of several Oe. This change is twice or more larger than those of anisotropic magneto-resistance effect materials, which are conventionally used.
However, it has been found that the structure shown in
FIG. 1
brings about a big problem, where it is used to realize a magnetic field sensor for measuring the absolute value of an applied magnetic field on the basis of a measurement value of the electrical resistance of the giant-magneto-resistant thin-film. The problem relates to change in the magneto-resistance value of the giant-magneto-resistant thin-film due to temperature. As described above, in the case of the structure shown in
FIG. 1
, there is freedom of choice in the degree of a magnetic field to be detected. However, even if the sensitivity is increased, it is a choice relative to a magnetic field to respond, and it is impossible to obtain a range of change larger than change in the electrical resistance of the giant-magneto-resistant thin-film, in principal. Actually, in the case of the structure shown in
FIG. 1
, the change value in electrical resistance has been reduced due to other factors as well as that describe above, and becomes about 6%. If a change of the giant-magneto-resistant thin-film due to temperature is added to the change value of about 6% in electrical resistance, the additional change in electrical resistance for that can be a variable in estimating an applied magnetic field.
FIG. 3
shows examples of a temperature characteristic. As shown in
FIG. 3
, change in the resistance value of the giant-magneto-resistant thin-film due to temperature is larger than change in the resistance value due to the applied magnetic field. Accordingly, the structure shown in
FIG. 1
, as it is, can be hardly used as a magnetic field sensor for measuring the absolute value of a magnetic field.
Furthermore, it has also been found that the conventional structure shown in
FIG. 1
brings about a big problem, where it is used to realize a magnetic field sensor for measuring the absolute value and direction of an applied magnetic field. That is, change in the electrical resistance of the giant-magneto-resistant thin-film does not depend on the direction of a magnetic field, but has an isotropic characteristic. Specifically, as shown in
FIG. 2
, the structure shown in
FIG. 1
provides the same change in electrical resistance in positive and negative directions of a magnetic field, and thus the direction of the magnetic field is hardly specified. Accordingly, the structure shown in
FIG. 1
, as it is, can be used as a sensor for only detecting the degree of a magnetic field, but cannot be used as a sensor for specifying the direction of the magnetic field, such as an azimuth sensor for reading the direction of geomagnetism, or a sensor for reading an angle relative to a polarized magnetic material.
An object of the present invention is to provide a thin-film magnetic field sensor, which has a simple structure and a high detecting sensitivity, and reduces measurement errors due to temperature variation or the like, and can measure the intensity and direction of a magnetic field.
DISCLOSURE OF INVENTION
At first, the present invention provides a thin-film magnetic field sensor comprising: a first arm including soft magnetic thin-films, which are separated by a gap having a predetermined gap length, and each have a predetermined film thickness and a predetermined width at a portion in contact with the gap, a giant-magneto-resistant thin-film formed to fill the gap between the soft magnetic thin-films, and terminals respectively and electrically connected to the two separated soft magnetic thin-films; and a second arm including conductive films, which are separated by a gap having a gap length substantially equal to said gap length, and each have a film thickness substantially equal to said film thickness and a width substantially equal to said width at a portion in contact with the gap, a giant-magneto-resistant thin-film formed to fill the gap between the conductive films, and terminals respectively and electrically connected to the two separated conductive films, wherein these arms form two arms of a bridge circuit.
Specifically, according to the present invention, in the electrical resistance value changes of a giant-magneto-resistant thin-film, changes due to temperature, humidity and time-varying are removed, and only a change due to a magnetic field is extracted, so that a magnetic field sensor with a high accuracy is realized. More specifically, a bridge is formed of two lines of elements, which have the same giant-magneto-resistant thin-film and structure, wherein one of the elements includes soft magnetic thin-films one on either side of the giant-magneto-resistant thin-film to increase the sensitivity relative to the magnetic field, and the other element uses the giant-magneto-resistant thin-film as it is to make the sensitivity substantially zero relative to the magnetic field. Since the output of the bridge is in proportion to the difference in the electrical resistance value between the elements, changes of the giant-magneto-resistant thin-film due to temperature, as well as other changes due to humidity, time-varying, etc. are removed from the output voltage, whereby only an electri
Kobayashi Nobukiyo
Masumoto Tsuyoshi
Ohnuma Shigehiro
Shirakawa Kiwamu
Yano Takeshi
Frishauf Holtz Goodman & Chick P.C.
Kinder Darrell
Le N.
The Research Institute for Electric and Magnetic Materials
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