JP2003121522A - Thin-film magnetic field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film magnetic field sensor, using a large magnetic field resistance thin-film that eliminates measurement errors by residual magnetization, and accurately concurrently measure the strength and the direction of magnetic field. SOLUTION: The large magnetic field resistance thin-film 12 is formed between the terminals of two pieces of sensor base elements 3 via a conductor film 11. Each of soft magnetic thin films 1 is connected to the terminals 13, 14, 15, 16. A constant voltage is applied to the terminals 13, 15 in these terminals as input terminals, and then a voltage is measured with terminals 14, 16 as an output terminal. That is, a bridge circuit, that electrically forms the sensor base element 3 and the large magnetic field resistance thin-film 12 as arms, is formed. The large magnetic field resistance thin-film 12 is magnetically separated from the soft magnetic thin films 1, and then the variation of a resistance value between the sensor basic elements 3 appears, as it is, as the voltage variance between the output terminals 14, 16. A coil 7 and a terminal 8 are formed with spiraling these sensor base elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field sensor for measuring a magnetic field in space, which is used for precisely measuring the magnitude and direction of a magnetic field using a giant magnetoresistive thin film, for example, a nano-granular giant magnetoresistive thin film. The present invention relates to a thin film magnetic field sensor.

[0002]

2. Description of the Related Art FIG. 1 is a patent application filed by the present inventors.
1-87804 and JP-A-11-274599.
2 shows a thin film magnetic field sensor disclosed in Japanese Patent Publication No. In the figure, a portion written as a giant magnetoresistive thin film is a metal-insulator nanogranular giant magnetoresistive thin film that exhibits a large electric resistance change of about 10% when a magnetic field of 10 kOe is applied. As in this example, in the case of a giant magnetoresistive thin film, the change width of the electric resistance value with respect to the applied magnetic field is larger than that of a general magnetoresistive material, but as described above, the application for causing the electric resistance change occurs. Since the magnetic field is large, when only the giant magnetoresistive thin film is used alone, it is not possible to expect a change in the electric resistance value in a small magnetic field of 100 Oe or less, which is generally used as a magnetic field sensor. The configuration of FIG. 1 supplements it. That is, the soft magnetic thin film plays a role of collecting magnetic flux in the periphery, and by selecting an appropriate size of the soft magnetic thin film, in principle, regardless of the magnitude of the magnetic field around the soft magnetic thin film, the giant magnetic resistance It is possible to apply a high magnetic flux density to the thin film portion within the saturation magnetic flux density of the soft magnetic thin film. From the viewpoint of electric resistance in the configuration of FIG. 1, the electric resistance value between the soft magnetic thin films is the sum of the electric resistance values of the soft magnetic thin film portion and the giant magnetoresistive thin film portion. Since the electric resistivity of the thin film is 100 times or more larger than that of the soft magnetic thin film, the electric resistance value between the soft magnetic thin films is substantially equal to the value of the giant magnetoresistive thin film portion. That is, a large change in the electric resistance of the giant magnetoresistive thin film directly appears in the electric resistance between the soft magnetic thin films. FIG. 2 shows an example of the electric resistance change of the structure of FIG. 1 as described above, which realizes an electric resistance value change of about 6% in a small magnetic field of several Oe, which is an anisotropic material which is a conventional material. It is more than twice as large as the magnetoresistive material.

[0003]

However, in the case of realizing a magnetic field sensor for measuring the absolute value and the direction of the applied magnetic field based on the measured electric resistance value of the giant magnetoresistive thin film, the method shown in FIG. The configuration turned out to be a big problem.

The first problem is that the electric resistance change of the giant magnetoresistive thin film does not depend on the direction of the magnetic field and has isotropic characteristics. That is, as shown in FIG. 2, in the configuration of FIG. 1, the same electric resistance change is shown in two positive and negative directions of the magnetic field, and the direction of the magnetic field cannot be specified.
The configuration shown in FIG. 1 can be used as a sensor that detects only the magnitude of a magnetic field, but it is necessary to specify the direction of the magnetic field. A direction sensor that reads the direction of the geomagnetism and a relative angle of the magnetized magnetic body It cannot be used as an angle sensor for reading.

The second problem is that it is necessary to further improve the magnetic field detection accuracy. In order to read the magnetic field strength with the configuration of FIG. 1, it is necessary to read the absolute resistance value between the electric terminals connected to the soft magnetic thin films on both sides and determine the magnetic field strength from that value. Uncertain factors such as temperature changes and changes over time are likely to be included, and as a result, the read magnetic field strength is likely to include errors.

The third problem is that it is necessary to reduce the error due to the magnetization remaining in the soft magnetic thin film. Figure 1
For the soft magnetic thin film used for the magnetic material, a magnetic material with as little remanent magnetization as possible is selected, but when the element is placed in a magnetic field, the remanent magnetization of some degree depends on the magnetic field strength. Will remain. This remanent magnetization has the same effect as if the external magnetic field strength were changed, on the resistance value of the giant magnetoresistive thin film, and as a result, the magnetic field strength corresponding to the remanent magnetization causes a reading error.

Therefore, an object of the present invention is to provide a magnetic field sensor which can eliminate the influence of the residual magnetism of the magnetic field sensor and accurately measure the strength and direction of the magnetic field.

[0008]

In order to solve the above-mentioned problems, the first invention is divided into two parts, a soft magnetic thin film divided by a space, a giant magnetoresistive thin film formed so as to fill the space, and a two-part structure. An electric terminal electrically connected to each of the soft magnetic thin films, a coil wound around the soft magnetic thin film and the giant magnetoresistive thin film, a resistance value measuring means between the electric terminals, and a predetermined coil. And a thin film magnetic field sensor.

A second aspect of the present invention relates to a thin-film magnetic field sensor characterized in that the electric terminals form one arm of a bridge circuit, and the resistance value between the electric terminals is measured by measuring the bridge output voltage. .

A third aspect of the present invention relates to a thin film magnetic field sensor in which a coil is composed of a conductor thin film wound around the soft magnetic thin film and the giant magnetoresistive thin film.

According to a fourth aspect of the present invention, the currents flowing through the coils are two currents whose absolute values are substantially equal to each other in a range in which the magnetization of the soft magnetic thin film does not reach saturation, and whose directions are positive and negative. Resistance value Rp between electrical terminals when a positive current is applied
And the resistance value Rm between the electric terminals when a negative current is applied
The present invention relates to a thin film magnetic field sensor characterized in that the absolute value and the polarity of the magnetic field strength around the magnetic field sensor are determined by the difference (Rp-Rm).

A fifth aspect of the present invention relates to a thin film magnetic field sensor characterized in that the value of the current passed through the coil includes a value of current that substantially saturates the magnetization of the soft magnetic thin film.

According to a sixth aspect of the invention, first, a current is applied to the coil in a positive direction in which the magnetization of the soft magnetic thin film is substantially saturated, and then a predetermined positive current in a range not reaching saturation is applied between the terminals. The resistance value Rpm and the resistance value Rpm between the terminals when a predetermined negative current is applied are measured, and then a current in the negative direction in which the magnetization of the soft magnetic thin film is substantially saturated is applied, and further saturation is not reached. The resistance value Rmm between the terminals when a predetermined negative current in the range is applied and the resistance value Rmp between the terminals when a predetermined positive current is applied are measured, and from these resistance values, ((Rp
p + Rmp) / 2- (Rpm + Rmm) / 2) to determine the absolute value and polarity of the magnetic field strength around the magnetic field sensor.

[0014]

The operation of the present invention is as follows. The configuration of the first invention is provided with a coil that surrounds the magnetic field sensor having the configuration of FIG. 1 and a means for supplying a predetermined current to the coil.

The first advantage of passing a predetermined current through the coil in this manner is that an accurate magnetic field can be applied to the soft magnetic thin film and the giant magnetoresistive thin film. That is, as in the first invention, the magnetic field generated by the current flowing in the air-core coil only follows the Biot-Savart law, and as long as the coil shape is stable, it always has a constant value including temperature and aging. It is possible to apply a magnetic field. Based on this accurate value of the magnetic field, it is possible to determine the surrounding magnetic field strength by referring to this. in this case,
The coil may be a linear conductor or a thin film conductor.

The second advantage is that the direction of the magnetic field acting on the soft magnetic thin film and the giant magnetoresistive thin film can be selected by changing the direction of the current to positive or negative. It is possible to determine the direction of the peripheral magnetic field with reference to this.

The third advantage is elimination of errors due to residual magnetization. By setting the current flowing through the coil to a value that substantially saturates the magnetization of the soft magnetic thin film, the value of the residual magnetic field can be forcibly determined.

According to the second aspect of the present invention, as a means for measuring the resistance value between the electric terminals, the electric terminal is placed on one arm of the bridge circuit and the bridge output voltage is measured without directly measuring the resistance value. It replaces resistance measurement with easier voltage measurement.

The third invention applies a conductor thin film technique in which a soft magnetic thin film and a giant magnetoresistive thin film are wound around a coil as a method for realizing a coil. By applying such conductor thin film technology, it is possible to realize a coil close to the soft magnetic thin film and the giant magnetoresistive thin film. Since the magnetic field strength generated when a certain current is applied to the coil is inversely proportional to the distance from the coil, the value of the current required to give a predetermined magnetic field strength to the soft magnetic thin film and the giant magnetoresistive thin film is The number of people approaching is small. The power consumption as a sensor is dominated by the current flowing through the coil, so this coil technology reduces power consumption.
A small magnetic field sensor can be realized.

The fourth aspect of the present invention represents a specific configuration for determining the accurate value and direction of the magnetic field. In other words, as the current value, the resistance value when two currents having positive and negative directions in which absolute values are substantially equal to each other in a range in which the soft magnetic thin film and the giant magnetoresistive thin film do not reach saturation The magnetic field strength and the direction are determined based on the difference of. With such a configuration, fluctuations in the absolute value of the resistance value are excluded by the difference in the resistance value. Further, since the sign of this difference in resistance value matches the sign of the magnetic field applied from the outside, the direction of the magnetic field can be easily determined.

The fifth aspect of the present invention shows a specific configuration for eliminating an error due to residual magnetization. That is, the value of the residual magnetic field can be forcibly determined by setting the current flowing in the coil to a value that substantially saturates the soft magnetic thin film and the giant magnetoresistive thin film.

The sixth aspect of the present invention shows a specific structure for determining an accurate value and direction of the external magnetic field and, at the same time, eliminating an error due to residual magnetization. That is, first, the coil is supplied with a positive current so that the soft magnetic thin film and the giant magnetoresistive thin film are substantially saturated. By this operation, the magnetization existing in the soft magnetic thin film and the giant magnetoresistive thin film is canceled to forcibly give the magnetization in one direction. Then, the current is continuously reduced from the saturated current to a predetermined positive current in the non-saturated range, and the resistance value between terminals in this state is set to Rpp. Subsequently, the current is continuously changed to a predetermined negative current, and the inter-terminal resistance value Rpm in that state is measured. Then, a negative current is applied so that the soft magnetic thin film and the giant magnetoresistive thin film are substantially saturated. By this operation, the magnetization is canceled in the soft magnetic thin film and the giant magnetoresistive thin film to forcibly give the magnetization in the opposite direction. Then, a predetermined negative current in a range that does not reach saturation is applied, and the inter-terminal resistance value Rm in that state is given.
Measure m. Further, the current value is continuously changed up to a predetermined positive current, and the inter-terminal resistance value Rmp in this state is measured. From these resistance values, ((Rpp + Rmp)
/ 2- (Rpm + Rmm) / 2) determines the absolute value and the polarity of the magnetic field strength around the magnetic field sensor, thereby eliminating the influence of magnetization and determining the exact value and direction of the external magnetic field. Is.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows the first embodiment. Reference _numeral 1 is, for example, a soft magnetic thin film having a composition of Co ₇₇ Fe ₅ Si ₉ B ₈ . This material has an extremely high saturation magnetic flux density of 12 kG, while the coercive force is 0.07 Oe.
And has extremely small features. A thin slit is provided between the soft magnetic thin films, and a giant magnetoresistive thin film 2 having a component of, for example, Co ₃₉ Y ₁₄ O ₄₇ is formed so as to fill the slit. The sensor element 3 is a part formed by the soft magnetic thin film 1 and the giant magnetoresistive thin film 2.
Call. Since the value of the specific resistance of the soft magnetic thin film 1 is lower than the specific resistance of the giant magnetoresistive thin film 1/100 or less, it was measured between the terminals 5 and 5 ′ attached to the soft magnetic thin film 1. The electric resistance value is substantially equal to the resistance value of the giant magnetoresistive thin film 2. 6 is a measuring unit for this resistance value, which is measured by measuring the voltage generated between the terminals when a constant current is applied.

A coil 7 is formed around the sensor basic element 3. Both ends of the coil 7 are joined to the terminals 8 and 8 '. Reference numeral 9 is a current generator (constant current source) for supplying a predetermined current.

FIG. 4 shows a second embodiment. The two basic soft magnetic thin films 1 sandwich the giant magnetoresistive thin film 2 to form the sensor basic element 3 as a whole. Sensor basic element 3
The conductor thin film 7 made of, for example, copper is formed by wrapping around.
These are formed by a series of thin film processes.

For example, on the substrate 10, first, the conductive thin film 7 in the lower portion of the sensor basic element is formed in a sleeper shape by using photoresist and sputtering appropriately. An insulating film (not shown) such as SiO ₂ is formed by sputtering so as to fill the space between the sleepers and cover the sleepers. Si
While O ₂ is formed, the upper surface of the SiO ₂ because remains uneven remains of sleepers pattern, the surface of SiO ₂ is planarized by lapping. A soft magnetic thin film 1 and a giant magnetoresistive thin film 2 are formed thereon by photoresist and sputtering. At the end of the conductor thin film 7, a conductor film is stacked in a columnar shape by sputtering. An insulating film (not shown) is again formed by sputtering from above. Further, the upper portion of the conductor thin film 7 is sputtered thereon.

FIG. 5 shows a third embodiment. In this case, two sensor basic elements 3 are used. A giant magnetoresistive thin film 12 is formed between terminals of these sensor basic elements via a conductor film 11. Terminals 13, 14, 15, and 16 are connected to each soft magnetic thin film. Among these terminals, a constant voltage is applied as an input terminal between the terminals 13 and 15, and a voltage is measured as an output terminal between the terminals 14 and 16. That is, electrically, a bridge circuit having the sensor basic element 3 and an element in which the giant magnetoresistive thin film 12 is sandwiched between the conductor films 11 as an arm is formed.

The giant magnetoresistive thin film 12 is magnetically separated from the soft magnetic thin film 1, and the change in resistance between the sensor basic elements appears as it is as a change in voltage between the output terminals 14 and 16. A coil 7 and terminals 8 and 8'are formed around these sensor basic elements. Coil 7 in FIG.
Is a thin film coil, but is shown by a solid line for simplicity.

The fourth embodiment will be described with reference to FIGS. FIG. 6 shows an example of how the electric resistance value changes depending on the external magnetic field strength when the coil current is zero in the configuration of FIG.

In the example of FIG. 6, the resistance value when the magnetic field strength is zero is about 250 kΩ, and the resistance value is temporarily reduced as the magnetic field strength is increased, and becomes about 240 kΩ in the case of 5 Oe.

On the other hand, FIG. 7 shows a change in resistance value when a current is passed through the coil when the external magnetic field strength is zero. 6 and 7 are almost completely the same when the horizontal axis is replaced with 1 Oe = 5 mA. That is, the change in the magnetic field from the outside and the magnetic field generated by the current flowing through the coil are almost equivalent.

Here, FIG. 8 shows a change in resistance value when a current is flown in the external magnetic field strength of 1 Oe. According to FIG. 8, the magnetic field intensity generated when the current is -5 mA is -10 Oe, and in this case, the magnetic field from the outside is just canceled. Therefore, as shown in FIG.
It can be said that the shape has a bias of -5 mA.

Here, if the current Im in the positive and negative directions is assumed.
When (8 mA in this case) is applied, the resistance values become Rp and Rm, respectively. If the difference between Rm and Rp is taken, the amount is proportional to the magnetic field strength when the magnetic field strength applied from the outside is within a certain limit.

For example, FIG. 9 shows the relationship between ΔR = (Rm-Rp) and the external magnetic field strength, and has a linear relationship up to ± 2 Oe. It should be noted that H is ± 2
In the case of Oe, H corresponds to positive and negative (Rm-Rp)
Is positive and negative, and the relationship is linear, including the sign. That is, it is possible to detect the absolute value of the magnetic field strength and the sign, which is the aim of the present invention. here,
For the selection of the current value to flow when detecting the magnetic field strength,
In FIG. 7, the linear portion of the magnetic field strength measurement range can be maximized by aiming at the approximate center of the portion where the current value and the resistance value change linearly.

The fifth embodiment deals with the case where residual magnetization remains in the soft magnetic thin film for some reason. A stable state can be brought about by intentionally magnetizing the soft magnetic material in a certain direction by passing a current through the coil so as to substantially saturate the soft magnetic thin film.
Even if some residual magnetization remains, one stable state is achieved by forcing a current to flow into the coil to saturate it in a certain magnetization direction. Also, if a current that causes saturation is applied in the opposite direction, another stable state is obtained in which the magnet is magnetized in the opposite direction. In other words, flowing a saturation current has the effect of forgetting all past history.

A sixth embodiment is shown in FIG. First, a current Is for saturating the soft magnetic thin film is passed. After flowing Is, the current is lowered to a current + Im that does not reach saturation. This means moving in the direction of the arrow from Is to Im in FIG. Here, the resistance value Rpp is measured. Subsequently, the current value is changed from + Im to −I.
Change continuously up to m. The resistance value there is Rpm. Next, the saturation current Is is passed in the opposite direction. -I
The current value gradually decreases from s to zero,
The resistance value at the current value of Im is Rmm. Furthermore, -Im
Rmp is measured by continuously changing the current from + Im to + Im. This operation is equivalent to moving on the boundary line of the so-called BH curve hysteresis curve, so that the effect of remanent magnetization held by the soft magnetic material before that is all canceled. The resistance value thus obtained is (Rmm + Rpm) / 2 and (Rmp + Rpp)
By taking the difference of / 2, it becomes possible to measure the pure external magnetic field strength by excluding the influence of remanent magnetization.

[0037]

According to the present invention described above, it is possible to determine the accurate value and direction of the external magnetic field and at the same time eliminate the measurement error due to the residual magnetization.

Further, according to the present invention, since the thin film coil that surrounds the soft magnetic thin film and the giant magnetoresistive thin film is used, it is possible to realize a small magnetic field sensor with low power consumption.

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional thin film magnetic field sensor.

FIG. 2 is a graph showing the relationship between the electric resistance change rate and the magnetic field in the conventional thin film magnetic field sensor of FIG.

FIG. 3 is a perspective view of the thin-film magnetic field sensor of the first embodiment.

FIG. 4 is a perspective view of a thin film magnetic field sensor of a second embodiment including a thin film coil.

FIG. 5 is a perspective view of a third embodiment in which a bridge circuit is formed.

6 is a graph showing the relationship between the electric resistance value and the magnetic field when the coil current is zero in the thin film magnetic field sensor of the first embodiment of FIG.

FIG. 7 is a graph showing the relationship between the electric resistance value and the coil current when the magnetic field is zero in the thin film magnetic field sensor of the first embodiment shown in FIG.

8 is a graph showing the relationship between the electric resistance value and the coil current when the magnetic field is 10 Oe in the thin film magnetic field sensor of the first embodiment of FIG.

FIG. 9 is a graph showing the relationship between ΔR and the magnetic field in the fourth embodiment. Here, ΔR is two currents in which the absolute value of the current flowing through the coil is substantially equal to each other in the range where the magnetization of the soft magnetic thin film does not reach saturation and the directions are positive and negative. Resistance value Rp between the electric terminals when an electric current is applied and resistance value R between the electric terminals when an electric current is applied in the negative direction
It is the difference of m (Rm-Rp).

FIG. 10 is a graph showing a relationship between an electric resistance value and a coil current for explaining a method of measuring pure external magnetic field strength by excluding the influence of 6 remanent magnetization in the sixth embodiment.

[Explanation of symbols]

1, 12; Soft magnetic thin film 2; Giant magnetoresistive thin film 3; Sensor basic element 7; Conductor thin film 8, 8 '; coil terminal 11; Conductor film 13, 14, 15, 16; terminals

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2G017 AA01 AA02 AA03 AD55 AD65                 5D034 BA03 BA08 BB14

Claims (6)

[Claims] 1. A soft magnetic thin film divided into two by a void, a giant magnetoresistive thin film formed so as to fill the void, and an electric terminal electrically connected to each of the two divided soft magnetic thin films. A coil wound around the soft magnetic thin film and the giant magnetoresistive thin film, resistance value measuring means between the electric terminals, and means for supplying a predetermined current value to the coil. Thin film magnetic field sensor. 2. The thin-film magnetic field according to claim 1, wherein the electric terminals form one arm of a bridge circuit, and the resistance value between the electric terminals is measured by measuring the bridge output voltage. Sensor. 3. The thin-film magnetic field sensor according to claim 1, wherein the coil comprises a conductor thin film wound around a soft magnetic thin film and a giant magnetoresistive thin film. 4. The current flowing in the coil is two currents whose absolute values are substantially equal to each other in a range where the magnetization of the soft magnetic thin film does not reach saturation and whose directions are positive and negative. The difference between the resistance value Rp between the electric terminals when the current flows and the resistance value Rm between the electric terminals when the current flows in the negative direction (Rm-Rp) is the absolute value and the polarity of the magnetic field strength around the magnetic field sensor. 2. The method according to claim 1, wherein
4. The thin film magnetic field sensor according to any one of items 1 to 3. 5. The thin-film magnetic field sensor according to claim 1, wherein the current value passed through the coil includes a current value that substantially saturates the magnetization of the soft magnetic thin film. 6. A resistance value Rpp between terminals when a current in the positive direction in which the magnetization of the soft magnetic thin film is substantially saturated is first passed through the coil and then a predetermined positive current in a range not reaching saturation is passed. And a resistance value Rpm between the terminals when a predetermined negative current is flown, and then a current in the negative direction in which the magnetization of the soft magnetic thin film is substantially saturated is flown, and a predetermined range of saturation is not reached. The resistance value Rmm between the terminals when a negative current is applied and the resistance value Rmp between the terminals when a predetermined positive current is applied are measured, and from these resistance values, ((Rpp + Rmp) / 2- (R
6. The thin film magnetic field sensor according to claim 1, wherein the absolute value of the magnetic field strength and the polarity around the magnetic field sensor are determined by pm + Rmm) / 2).