1. Field of the Invention
The present invention relates to a magnetic sensor as a device for a sensitive micro magnetic sensor such as a magnetic head of audio visual (AV) equipment, control equipment, a computer and others or a magnetic impedance effect device, a magnetic inductance device and others respectively suitable for a direction finder and others.
2. Description of the Related Art
Recently, the need for miniaturization and sensitization of a magnetic sensor has increased. As a result, a magnetoresistance effect device (magnetoresistance device or MR) that detects magnetic flux, not the change in time of the magnetic flux, has been actively researched for use as a head. Such an MR device utilizes a phenomenon in which the electrical resistance due to the interaction between the magnetization of a ferromagnetic body and the conduction electrons of a DC current varies by an external magnetic field. This MR device is effective for the promotion of miniaturization. However, until now, since the rate of change of electrical resistance of the MR device has been very small, the signal-to-noise ratio (S/N ratio) is not sufficient. Therefore, there is a problem in that it is difficult to obtain the desired detection sensitivity.
Also recently, the research of a giant magnetoresistance effect device (GMR device) which detects the change of an external magnetic field utilizing a phenomenon called giant magnetoresistance effect is also widely conducted, however, in the case of such a GMR device, the rate of change of electric resistance is also not sufficient and as there is also a problem of hysteresis, giant magnetoresistance effect is not a technique suitable for the acceleration of miniaturization.
As a sensitive micro magnetic sensor which can solve the problems of the above MR device and GMR device, such a magnetic impedance effect device (hereinafter called an MI device) as disclosed in Japanese Published Unexamined Patent Application No. Hei 7-181239 is proposed. Such an MI device utilizes an electromagnetic phenomenon that when high frequency current is fed to a magnetic wire composed of a magnetic substance with high permeability, impedance by skin effect is greatly varied by an external magnetic field. For example, as a change of 50% or more of impedance can be obtained by a magnetic field of a few gauss when an amorphous wire 1 to 3 mm long and approximately 30 .mu.m in diameter is used for a magnetic wire, a compact and sensitive magnetic sensor can be provided.
FIG. 20 is a characteristic drawing showing correlation between voltage generated between both ends of an amorphous magnetic wire when frequency current of a sine wave of 100 kHz or more is applied in such an MI device and an external magnetic field and shows a state in which voltage between both ends of the magnetic wire varies according to the intensity of the external magnetic field. However, as shown in FIG. 20, as the change of voltage between both ends of the magnetic wire (a sensing part which serves the detection of an external magnetic field) is symmetrical based upon when an external magnetic field is zero gauss, an operating point (coordinates showing a state in which an external magnetic field is zero) is required to be shifted to a suitable position in which the linearity of a graph can be secured such as a point A in FIG. 20 in case the above MI device is used for a sensor which can detect not only the intensity of an external magnetic field but the direction as well.
Therefore, in such a case, heretofore, a magnetic wire 2 is inserted into a tube 1 composed of a non-magnetic substance such as vinyl as shown in FIG. 21, a biased magnetic field Hb is applied to the magnetic wire 2 by feeding direct current to a coil 3 wound by a predetermined number of turns on the peripheral surface of the tube 1 and an operating point is set. Both ends of the magnetic wire 2 are soldered to a conductor, a soldering land or others, the magnetic wire 2 between a pair of solder connections 4 becomes a sensing part which serves the detection of an external magnetic field and the intensity and the direction of an external magnetic field can be detected by measuring voltage in the sensing part.
However, as the shape of a graph showing correlation between voltage in the sensing part of the magnetic wire 2 and an external magnetic field varies when a biased magnetic field Hb is applied to the magnetic wire 2 by the coil 3, a conventional type MI device has a problem that a desired operating point cannot be set. That is, assuming that a uniform biased magnetic field Hb is applied to the whole sensing part of the magnetic wire 2, correlation between voltage and an external magnetic field is shown as a characteristic curve obtained by shifting the graph shown in FIG. 20 by Hb to the left as shown by a chain line in FIG. 22 and the shape itself of the graph should be unchanged. However, in fact, as shown by a full line in FIG. 22, it is clear from experiments by the inventors of the present invention that the shape of the graph is a characteristic curve different from the shape of the graph shown in FIG. 20. The reason is thought to be that the coil 3 for applying a biased magnetic field does not generate a desired magnetic field at both ends of the wound part.
That is, the intensity of a magnetic field generated by feeding direct current to the coil for applying a biased magnetic field is approximately uniform in a part except both ends of the wound part as shown in FIG. 23, however, it is known that a generated magnetic field is rapidly decreased near both ends of the wound part. Therefore, when the sensing part of the magnetic wire is influenced by a magnetic field generated at both ends of the wound part of the coil, the intensity of a biased magnetic field applied to the sensing part is dispersed in the longitudinal direction and this is thought to change the shape of the graph showing correlation between voltage and an external magnetic field when a biased magnetic field is applied.
As shown in FIG. 22, when a biased magnetic field uneven in the longitudinal direction is applied to the sensing part of the magnetic wire, an error occurs even if voltage in the sensing part is measured and an external magnetic field is detected. This is because the linearity of a graph showing correlation between voltage and an external magnetic field is not satisfactory in the vicinity of an operating point B at which a biased magnetic field is set to Hb, and the precision of detection is deteriorated.
Further, in the above conventional type MI device, the coil 3 for applying a biased magnetic field is wound on the tube 1 made of vinyl and others, however, as the outside diameter of the tube 1 is set to approximately 0.5 mm, the length is set to approximately 1 to 3 mm and the tube 1 is small, assembly operation that the coil 3 is wound on the peripheral surface by a few tens of turns or more is not easy and handleability is unsatisfactory.
In such a conventional type MI device, the end of the magnetic wire 2 is electrically and mechanically connected to a conductor and others by soldering, however, as the wettability of the magnetic wire 2 composed of an amorphous wire and other materials is low, sufficient attachment strength and the reliability of conduction in the solder connection 4 which solders the end cannot be expected.