Magnetic sensor including bridge circuit having fixed resistance like structure of element

A magnetic sensor uses a magnetoresistance element which can be driven in a stable manner with a dipole irrespective of a polarity of an external magnetic field. A resistance value R of first magnetoresistance elements varies, and a resistance value of second magnetoresistance elements does not vary with a variation in magnetic field magnitude of the external magnetic field H1 in the positive direction. A resistance value R of second magnetoresistance elements varies and a resistance value of first magnetoresistance elements does not vary with a variation in magnetic field magnitude of the external magnetic field H2 in the negative direction. Accordingly, the magnetic sensor can be driven in a stable manner with a dipole irrespective of the polarity of the external magnetic field.

This patent document claims the benefit of Japanese Patent Application No. 2006-203716 filed on Jul. 26, 2006, which is hereby incorporated by reference.

BACKGROUND

The present embodiments relate to a non-contact magnetic sensor including a magnetoresistance element, and more particularly, to a magnetoresistance element which can be driven in a stable manner with a dipole irrespective of a polarity of an external magnetic field.

2. Related Art

A hall element, a magnetoresistance element, or the like are used in a non-contact magnetic sensor Since in the hall element, power consumption is high and hysteresis does not exist, it is required to install a hysteresis circuit or it is difficult to minimize a size of an element. Accordingly, a magnetic sensor using the magnetoresistance element is noticeable.

Magnetic sensors are used for detecting an open and close states of a foldable cellular phone and the like. For example, in related art, a magnetoresistance element and a fixed resistance element are coupled in series to output a potential, and an on-off switching signal is outputted according to a variation in output on the basis of a variation in magnetic field magnitude of an external magnetic field. When it is detected that the foldable cellular phone opens by outputting an on signal, for example, a backlight under a display is controlled so that the backlight emits light. The related art is disclosed in JP-A-8-17311 and JP-A-2003-60256.

However, in the method for detecting opening and closing, there is a following problem. That is, since a variation in resistance of the magnetoresistance element depends on a polarity of an external magnetic field, a direction of a magnet opposed to the magnetic sensor is limited. When the magnet is disposed in a direction opposite to a positive direction, the polarity of the external magnetic field is inverted and thus the resistance value of the magnetoresistance element is not changed according to the magnetic field magnitude of the external magnetic field in which the polarity is inverted. Accordingly, the open and close detection can not be properly performed.

SUMMARY

The present embodiments may solve the above-mentioned problems, and particularly, an object of the invention is to provide a magnetic sensor using a magnetoresistance element which can be driven in a stable manner with a dipole irrespective of a polarity of an external magnetic field.

In order to accomplish the above-mentioned object, according to an aspect of the invention, there is provided a magnetic sensor comprising a series circuit having a first magnetoresistance element and a second magnetoresistance element connected to each other, of which resistance values vary with a variation in magnetic field magnitude of an external magnetic field, in series and outputting a potential of a connecting portion between the first magnetoresistance element and the second magnetoresistance element. When a direction of the external magnetic field is in a positive direction and a direction opposite to the positive direction is a negative direction, a resistance value of the first magnetoresistance element varies, and the resistance value of the second magnetoresistance element does not vary with a variation in magnetic field magnitude of the external magnetic field in the positive direction. The resistance value of the second magnetoresistance element varies and a resistance value of the first magnetoresistance does not vary with a variation in magnetic field magnitude of the external magnetic field in the negative direction.

In the invention, a magnetic sensor adapted for both magnetic field directions, may be formed irrespective of a polarity of an external magnetic field. Accordingly, the magnetic sensor removes design difficulties, for example associated with a configuration of a magnet generating an external magnetic field.

In the invention, it is preferable that an increasing or decreasing tendency of the resistance variation of the first magnetoresistance element with the variation in magnetic field magnitude in the positive direction may be opposite to an increasing or decreasing tendency of the resistance variation of the second magnetoresistance element with the variation in magnetic field magnitude in the negative direction with respect to a non-magnetic field state of the external magnetic field.

As mentioned above, since the opposite tendency is presented, a variation in potential from the connecting portion may have the same tendency when the external magnetic field is in the positive direction and the negative direction. That is, when the potential from the connecting portion has a tendency to decrease according to increasing a magnetic field magnitude in the positive direction of the external magnetic field, the potential may have the same tendency to decrease according to increasing a magnetic field magnitude in the negative direction of the external magnetic field. Accordingly, a change in circuit or a change in control of a control unit is not specially required.

In the invention, when the external magnetic field is in the positive direction, a fixed resistance value X1of the second magnetoresistance element may be lager than a minimum resistance value X2of the first magnetoresistance element varying with a variation in magnetic field magnitude in the positive direction, and may be smaller than a maximum resistance value X3. When the external magnetic field is in the negative direction, a fixed resistance value X4of the first magnetoresistance element may be lager than a minimum resistance value X5of the second magnetoresistance element varying with a variation in magnetic field magnitude in the negative direction, and may be smaller than a maximum resistance value X6, and wherein a ratio of ‘fixed resistance value X1—minimum resistance value X2to maximum resistance value X3—fixed resistance value X1’ may be equal to a ratio of ‘maximum resistance value X6—fixed resistance value X4to fixed resistance value X4—minimum resistance value X5’. Wherein the fixed resistance value X1may be a value between the minimum resistance value X2and the maximum resistance value X3, and the fixed resistance value X4may be a value between the minimum resistance value X5and the maximum resistance value X6.

Accordingly, when the external magnetic field acts in the positive direction, there is a time when a varying resistance value of the first magnetoresistance element becomes equal to the fixed resistance value X1of the second magnetoresistance element. When the external magnetic field acts in the negative direction, there is a time when a varying resistance value of the second magnetoresistance element becomes equal to the fixed resistance value X4of the first magnetoresistance element. A potential at this time may be a threshold potential for switching the switching signal. In the invention, since the time when the external magnetic field is in the positive direction may be the time when the external magnetic field is in the negative direction, an offset does not exist, and a threshold potential of the magnetic sensor adapting for both the positive and negative magnetic fields is easily controlled, and thus the magnetic sensor can be driven in a stable manner.

In the invention, the first magnetoresistance element and the second magnetoresistance element may have the same film configuration having an anti-ferromagnetic layer, a fixed magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer. An R-H curve in which a abscissa denotes an external magnetic field and a ordinate denotes a resistance value of a magnetoresistance element, a first interlayer-coupling magnetic field Hin1acting between the fixed magnetic layer and free magnetic layer of the first magnetoresistance element, may be shifted in the positive direction of the external magnetic field, and a second interlayer-coupling magnetic field Hin2acting between the fixed magnetic layer and the free magnetic layer of the second magnetoresistance element, may be shifted in the negative direction.

As controlled above, a so-called hysteresis loop can be formed in a region in which the external magnetic field is positive in the first magnetoresistance element, and can be formed in a region in which the external magnetic field is negative in the second magnetoresistance element. Accordingly, the magnetic sensor adapting for both the positive and negative magnetic fields can be simply and properly formed in which a resistance value of the first magnetoresistance element varies, and a resistance value of the second magnetoresistance element does not vary with a variation in magnetic field magnitude of the external magnetic field in the positive direction and in which a resistance value of the second magnetoresistance element varies and a resistance value of the first magnetoresistance does not vary with a variation in magnetic field magnitude of the external magnetic field in the negative direction.

In the invention, the first interlayer-coupling magnetic field Hin1and the second interlayer-coupling magnetic field Hin2(absolute value) may have the same magnitude.

Accordingly, a resistance value of the magnetoresistance element can be varied at the same time when the external magnetic field is positive and when the external magnetic field is negative, whereby the magnetic sensor is adapted for both the positive and negative field directions can be driven in a stable manner.

By adjusting the interlayer coupling magnetic field described above, in the non-magnetic state of the external magnetic field, a magnetization of the fixed magnetic layer and a magnetization of a free magnetic layer of one of the first magnetoresistance element and the second magnetoresistance element may be in the same direction. A magnetization of the fixed magnetic layer and a magnetization of the free magnetic layer of the other may be in an anti-parallel state, and a magnetization of the fixed magnetic layer of the first magnetoresistance element and a magnetization of the fixed magnetic layer of the second magnetoresistance element may be in the same direction.

In the invention, two first magnetoresistance elements and two first magnetoresistance elements may be provided. The first magnetoresistance element and second magnetoresistance element may constitute a first series circuit, and the other first magnetoresistance element and the other second magnetoresistance element may constitute a second series circuit, wherein the first magnetoresistance element of the first series circuit and the second magnetoresistance element of the second series circuit may be connected in parallel to each other, and the second magnetoresistance element of the first series circuit and the first magnetoresistance element of the second series circuit may be connected in parallel to each other, and wherein a difference between a potential of the connecting portion in the first series circuit and a potential of the connecting portion in the second series circuit may be outputted as a differential voltage.

Accordingly, since a change in potential with a variation in magnetic magnitude of the external magnetic field can increase, a sensitivity of the magnetic sensor is excellent.

In the invention, the magnetic sensor adapted to handle both the positive and negative magnetic fields can be formed irrespective of a polarity of an external magnetic field. Accordingly, a disposition of a magnet generating an external magnetic field is less limited than in the related art and thus the assembly is easier,

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 4are a partial schematic views illustrating a foldable cellular phone including a non-contact magnetic sensor of the embodiment.FIGS. 5 and 7are a partial plan views illustrating a non-contact magnetic sensor of the embodiment.FIGS. 6 and 8are a circuit diagram of a magnetic sensor.FIG. 9is a partial sectional view illustrating the non-contact magnetic sensor as viewed from a direction taken along Line A-A inFIG. 5.FIG. 10Ais a graph (R-H curve) illustrating a hysteresis characteristic of a first magnetoresistance element.FIG. 10Bis a graph (R-H curve) illustrating a hysteresis characteristic of a second magnetoresistance element.FIG. 10Cis a graph (R-H curve) in whichFIG. 10Ais coupled withFIG. 10B.FIG. 11is a graph illustrating a relation between an external magnetic field H and a differential potential, andFIG. 12is a graph illustrating a relation among a gas pressure and power and an interlayer-coupling magnetic field Hin during a plasma treatment.

As shown inFIG. 1, a foldable cellular phone1includes a first member2and a second member3. The first member2is screen display portion and the second member3is a manipulation portion. A liquid crystal display or a receiver or the like is provided on a surface of the first member2opposite the second member3. Various buttons, a microphone, and the like are provided on a surface of the second member3opposite the first member2.FIG. 1illustrates a closing state of the foldable cellular phone1. As shown inFIG. 1, a magnet5is built in the first member2and a magnetic sensor4is built in the second member3. The magnet5and the magnetic sensor4face each other in the closing state shown inFIG. 1. Alternatively, the magnetic sensor4may be disposed at a position departing from the direction parallel to an application direction of the external magnetic field other than the position facing the magnet5.

InFIG. 1, the external magnetic field H1emitted from the magnet5acts on the magnetic sensor4, and the magnetic sensor4detects the external magnetic field H1, whereby the closing state of the foldable cellular phone1is detected.

Meanwhile, when the foldable cellular phone1is in an opening position as shown inFIG. 2, the first member2is gradually move apart from the second member3, accordingly the magnitude of the external magnetic field H1which acts on the magnetic sensor4becomes gradually smaller, and thus the magnitude of the external magnetic field H1acting on the magnetic sensor4becomes zero. When the magnitude of the external magnetic field H1acting on the magnetic sensor4is a predetermined value or less, the opening state of the foldable cellular phone1is detected. For example, a control unit built in the foldable cellular phone1controls a backlight in the rear of the liquid crystal display or the manipulation buttons so as to emit light.

The magnetic sensor4of the embodiment is the sensor adapting for both the positive and negative magnetic fields. That is, inFIG. 1, an N pole of the magnet5is located on the left of a figure of the magnet and an S pole is located on the right of a figure. However, as shown inFIG. 3, when the polarity is inversely disposed (N pole is right of figure and S pole is left of figure), a direction of the external magnetic field H2acting on the magnetic sensor4is inverted to a direction of the external magnetic field H1inFIG. 1. In the embodiment, in the above-mentioned case, the opening operation is properly detected when the cellular phone1is opened according toFIG. 4from the closing state according toFIG. 3.

As shown inFIG. 5, the magnetic sensor4of the embodiment is mounted on the circuit board6built in the second member3. In the magnetic sensor4, two first magnetoresistance elements10,11and two second magnetoresistance elements12,13are disposed on a single element base7.

As shown inFIG. 5, the magnetoresistance elements10to13constitute a bridge circuit. The first magnetoresistance element10and the second magnetoresistance12connected in series constitute a first series circuit14. The first magnetoresistance element11and the second magnetoresistance13connected in series constitute a second series circuit15.

The first magnetoresistance element10of the first series circuit14and the second magnetoresistance element13of the second series circuit15are connected in parallel, and the connecting portion is an input terminal16. The second magnetoresistance element12of the first series circuit14and the first magnetoresistance element11of the second series circuit15are connected in parallel and the connecting portion is an earth terminal or ground17.

As shown inFIG. 5, a first connecting portion between the first magnetoresistance element10of the first series circuit14and the second magnetoresistance element12is a first output terminal18, and a second connecting portion between the first magnetoresistance element11of the second series circuit15and the second magnetoresistance element13is a second output terminal19. The terminals16to19are electrically connected to terminals (not shown) on the circuit board6by a wire bonding, a die bonding, or the like.

As shown inFIG. 6, the first output terminal18and the second output terminal19are connected to a differential amplifier (OP-AMP)20, which is connected to a control unit21.

The first magnetoresistance elements10,11and the second magnetoresistance elements12,14have a film configuration as followings.

As shown inFIG. 9, the first magnetoresistance element10(11) and the second magnetoresistance element13(12) are laminated in an order of an underlying layer30, a seed layer31, an anti-ferromagnetic layer32, a fixed magnetic layer33, a non-magnetic intermediate layer34, free magnetic layers35,37(a free magnetic layer of the second magnetoresistance element13denotes reference numeral37), and a protection layer36from the bottom. The underlying layer30, for example, is formed of one or more non-magnetic materials such as Ta, Hf, Nb, Zr, Ti, Mo, and W. The seed layer31is formed of NiFeCr, or Cr, or the like. The anti-ferromagnetic layer32is formed of anti-ferromagnetic materials containing an element α (i.e. α is one or more elements of Pt, Pd, Ir, Rh, Ru, and Os) and Mn or anti-ferromagnetic materials containing an element α, an element α′ (i.e. α′ is one or more elements of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, and rare-earth element), and Mn. For example, the anti-ferromagnetic layer32is formed of IrMn or PtMn. The fixed magnetic layer33and the free magnetic layers35,37are formed of materials such as CoFe alloy, NiFe alloy, and CoFeNi alloy. The non-magnetic intermediate layer34is formed of non-magnetic conductive materials such as Cu. When a Tunnel magnetoresistance element is used, the non-magnetic intermediate layer34is formed of an insulation-barrier layer such as TiOx. The protection layer36is formed of Ta and the like. The fixed magnetic layer33or the free magnetic layers35,37may have a laminated ferri structure (a structure in which a magnetic layer/a non-magnetic layer/a magnetic layer are laminated and a structure in which a non-magnetic layer is interposed between two magnetic layers of which magnetization directions are anti-parallel with each other). The fixed magnetic layer33or the free magnetic layers35,37may be a laminated structure formed of a plurality of magnetic layers with different materials.

In the first magnetoresistance element10and the second magnetoresistance element13, the anti-ferromagnetic layer32and the fixed magnetic layer33are contacted. Accordingly, when a magnetic field acts, a heat treatment is performed, whereby an exchange coupling magnetic field (Hex) is generated on an interface between the anti-ferromagnetic layer32and the fixed magnetic layer33. Therefore, a magnetization direction of the fixed magnetic layer33is fixed in one direction. InFIG. 9, the magnetization direction33aof the fixed magnetic layer33is shown by an arrow. In the first magnetoresistance element10(11) and the second magnetoresistance element13(12), all magnetization directions33aof the fixed magnetic layers33are shown in a direction denoted as X2.

Meanwhile, magnetization directions of the free magnetic layers35,37are different in the first magnetoresistance element10and in the second magnetoresistance element13. As shown inFIG. 7, in the first magnetoresistance element10(11), a magnetization direction35aof the free magnetic layer35is a shown in the direction denoted by X2, and is the same as the magnetization direction33aof the free magnetic layer33. However, in the second magnetoresistance element13(12), a magnetization direction37aof the free magnetic layer37is a shown in the direction denoted by X1, and is anti-parallel to the magnetization direction33aof the free magnetic layer33.

As shown inFIG. 5, the external magnetic field H1shown inFIGS. 1 and 2acts on the magnetic sensor4from the shown X2direction to the shown X1direction. A direction of the external magnetic field H1is “a positive direction (+direction)”. Meanwhile, inFIG. 7, the external magnetic field H2shown inFIGS. 3 and 4acts on the magnetic sensor4shown in the X1to the X2direction, and a direction of the external magnetic field H2is “a negative direction (−direction)”.

As shown inFIG. 5, when the external magnetic field (magnetic field in the positive direction) H1acts on the magnetic sensor4, the magnetization35aof the free magnetic layer35magnetized in a direction opposite to the direction of the external magnetic field H1varies, and thus the resistance values of the first magnetoresistance elements10,11vary.FIG. 10Ais an R-H curve illustrate a hysteresis characteristic of the first magnetoresistance elements10,11. In the graph, a longitudinal axis denotes a resistance value R, but may be a resistance variation rate (%). As shown inFIG. 10A, when the external magnetic field H1gradually increases from the non-magnetic field state (zero) to the positive direction, the resistance value R of the first magnetoresistance elements10,11gradually increases along the curve HR1. A minimum resistance value at a point in which the resistance value R varies is X2. Meanwhile, a maximum resistance value at a point in which the resistance value R varies is X3. When the external magnetic field H1decreases from the maximum resistance value X3, the resistance value R of the first magnetoresistance elements10,11gradually decreases along a curve HR2and finally reaches the minimum resistance value X2. Thus, in the first magnetoresistance elements10,11, with respect to a variation in magnetic field magnitude of the external magnetic field H1in the positive direction, a hysteresis loop (HR-A) depicted with the curve HR1and the curve HR2is formed. A “central point” of the hysteresis loop HR-A is a middle value between the maximum resistance value X3and the minimum resistance value X2and a central value of a spreading width of the hysteresis loop HR-A. The magnitude of the first interlayer coupling magnetic field Hin1is determined by the magnetic field magnitude from the center point of the hysteresis loop HR-A to the external magnetic field H=0 (Oe). In addition, the second interlayer coupling magnetic field Hin2inFIG. 10Bcan be obtained in the same manner. The spreading width passing through the central point of the hysteresis loop HR-A is double the coercive force. When the coercive force is very small, a chattering may be easily generated. Accordingly, it is preferable that the coercive force is large. The coercive force is adjusted at 2.5 Oe or so.

As shown inFIG. 10A, in the first magnetoresistance elements10,11, the first interlayer coupling magnetic field Hin1is shifted in the positive direction of the magnetic field. When the external magnetic field H1in the positive direction increases, the magnetic magnitude of the external magnetic field H1keeps the maximum resistance value X3up to B. However, when the external magnetic field H1further increases, the magnetization33aof the fixed magnetic layer33varies in the direction of the external magnetic field H1and is toward the same direction as the magnetization35aof the free magnetic layer35. Accordingly, the resistance value R becomes gradually smaller. However, in practical use, the magnet5in which the external magnetic field H1becomes lager than the magnetic field magnitude is not used.

Meanwhile, as shown inFIG. 7, when the external magnetic field H2acts in the negative direction, since the direction of the external magnetic field H2is equal to the direction of the magnetization35aof the free magnetic layer35of the first magnetoresistance elements10,11in a non-magnetic field state (the external magnetic field is zero), the free magnetic layer35does not vary in accordance with the external magnetic field H2in the negative direction and the magnetization35aof the free magnetic layer35and the magnetization33aof the fixed magnetic layer33keep the equilibrium state. Consequently, as shown inFIG. 10A, the resistance value R of the first magnetoresistance elements10,11keeps a constant value (fixed resistance value) X4with respective to the external magnetic field H2in the negative direction.

Next, a hysteresis characteristic of the second magnetoresistance elements12,13is described. As shown inFIG. 5, when the external magnetic field (magnetic field in the positive direction) H1acts on the magnetic sensor4, the magnetization37aof the free magnetic layer37magnetized in the same direction as the direction of the external magnetic field H1does not varies. Accordingly, as shown inFIG. 10B, even when the external magnetic field H2increases from zero in the positive direction, the second magnetoresistance elements12,13keep a constant value (fixed resistance value) X1. However, when the magnetic field magnitude of the external magnetic field H1increases by more than C, the magnetization33aof the fixed magnetic layer33of the second magnetoresistance element12,13is inverted in the direction of the external magnetic field H1. Accordingly, the resistance value R of the second magnetoresistance elements12,13decreases. However, as described inFIG. 10A, in practical use, the magnet5in which the external magnetic field H1increases more than the magnetic field magnitude C is not used.

As shown inFIG. 7, when the external magnetic field H2acts in the negative direction, since the direction of the external magnetic field H2is anti-parallel to the direction of the magnetization37aof the free magnetic layer37of the second magnetoresistance elements12,13, the magnetization37aof the free magnetic layer37has an influence of the external magnetic field H2, and thus varies. In the non-magnetic field state of the external magnetic field, as shown inFIG. 9, since the magnetization33aof the fixed magnetic layer33of the second magnetoresistance elements12,13is anti-parallel to the magnetization37aof the free magnetic layer37, the resistance value R has a high resistance value. However, when the external magnetic field H2(absolute value) gradually increases, and thus the magnetization37aof the free magnetic layer37is inverted, the magnetization37aof the free magnetic layer37becomes similar to the magnetization33aof the fixed magnetic layer33. Accordingly, the resistance value R of the second magnetoresistance elements12,13gradually decrease along the curve HR3. A minimum resistance value at the portion in which the resistance value R varies is denoted X5and a maximum resistance value at the portion in which the resistance value R varies is denoted by X6. When the external magnetic field H2(absolute value) gradually decreases in the negative direction from the position of the maximum resistance value X5(i.e. when the external magnetic field becomes close to zero), the resistance value R of the second magnetoresistance elements12,13gradually increases along the curve HR4, and thus reaches the maximum resistance value X6. Consequently, a hysteresis loop HR-B surrounded with the curve HR3and the curve HR4is formed.

As shown inFIG. 10B, a second interlayer coupling magnetic field Hin2of the second magnetoresistance elements12,13is shifted in the negative magnetic field.

As mentioned above, in the embodiment, on the R-H curve, the first interlayer coupling magnetic field Hin1of the first magnetoresistance elements10,11is shifted in the positive direction of the external magnetic field, and the second interlayer coupling magnetic field Hin2of the second magnetoresistance elements12,13is shifted in the negative direction of the external magnetic field. Accordingly, since the shift directions are different each other, the magnetic sensor4adapting for both the positive and negative magnetic fields can be made.

The principal is described with reference toFIG. 10C.FIG. 10Cis a graph in which the hysteresis characteristic of the first magnetoresistance elements10,11shown inFIG. 10Aand the hysteresis characteristic of the second magnetoresistance elements12,13shown inFIG. 10B. Both are shown on the same R-H curve.

As shown inFIG. 10C, it is supposed that the magnetic field magnitude of the external magnetic field varies within “use range.”

First of all, as shown inFIG. 10C, in the external magnetic field H, when the external magnetic field H1gradually increases from the non-magnetic field state (zero position) in the positive direction, the resistance value R of the first magnetoresistance elements10,11varies at the position of the hysteresis loop (HR-A). As for the variation in magnitude of the external magnetic field H1in the positive direction in which the resistance value of the first magnetoresistance elements10,11varies, the second magnetoresistance elements12,13do not vary (fixed resistance value) X1. That is, the second magnetoresistance elements12,13function as the fixed resistance element with respect to the external magnetic field H1in the positive direction. Accordingly, as shown in circuit diagram ofFIG. 6, the first magnetoresistance elements10,11function as a variable resistance element with the variation in magnitude of the external magnetic field H1in the positive direction and the second magnetoresistance elements12,13function as a fixed resistance element keeping constant resistance value X1. Accordingly, when the magnitude of the external magnetic field H1varies in the positive direction, a voltage from a first output terminal18of a first series circuit14and a voltage from a second output terminal19of a second series circuit15vary.

Meanwhile, as shown inFIG. 10C, in the external magnetic field H, when the external magnetic field H2(absolute value) gradually increases from the non-magnetic field state (zero position) in the negative direction, the resistance value R of the first magnetoresistance elements10,11varies at the position of the hysteresis loop (HR-A). As for the variation in magnitude of the external magnetic field H2in the negative direction in which the resistance value of the first magnetoresistance elements12,13varies, the first magnetoresistance elements10,11keep a constant resistance value (fixed resistance value) X4. That is, the first magnetoresistance elements10,11function as the fixed resistance element with respect to the external magnetic field H2in the negative direction. Accordingly, as shown in circuit diagram ofFIG. 8, the second magnetoresistance elements12,13function as a variable resistance element with the variation in magnitude of the external magnetic field H2in the negative direction, and the first magnetoresistance elements10,11function as a fixed resistance element keeping constant resistance value X4. Accordingly, when the magnitude of the external magnetic field H2varies in the negative direction, a voltage from a first output terminal18of a first series circuit14and a voltage from a second output terminal19of a second series circuit15vary.

In the embodiment as described above, with respect to the external magnetic field in both of the positive direction and the negative direction, since the output can be obtained from the magnetic sensor4, the magnetic sensor functions as the magnetic sensor adapting for both the positive and negative magnetic fields. Accordingly, although the magnet5generating the external magnetic fields H1, H2is disposed in the direction as shown inFIGS. 1 and 2or is disposed in the opposite direction as shown inFIGS. 3 and 4, both directions may correspond each other. Since the manner of disposition of the magnet5is not limited in comparison with the related art, it is convenient to mount the magnetic sensor4and the magnet5in the apparatus.

In the embodiment, as described inFIG. 10A, the first interlayer coupling magnetic field Hin1of the first magnetoresistance elements10,11is shifted in the positive direction, and as described inFIG. 10B, and the second interlayer coupling magnetic field Hin2is shifted in the negative direction. In the embodiment, as described inFIG. 9, in the first magnetoresistance elements10,11, the magnetization33aof the fixed magnetic layer33and the magnetization33aof the free magnetic layer35are parallel each other and are in the same direction as the external magnetic field H2from the X1direction to the X2direction, that is, in the negative direction. Meanwhile, in the second magnetoresistance elements12,13, the magnetization33aof the fixed magnetic layer33is anti-parallel to the magnetization37aof the free magnetic layer37, the magnetization33aof the fixed magnetic layer33is the same direction as the magnetization33aof the fixed magnetic layer33of the first magnetoresistance elements10,11, and the magnetization37aof the free magnetic layer37is a direction from X2to X1, that is, the same direction as the external magnetic field H1.

As described inFIGS. 10A and 10B, the interlayer coupling magnetic fields Hin1, Hin2which are opposite each other are obtained. In order to obtain the magnetization state shown inFIG. 9, a gas flow (gas pressure) or an electric power should be properly adjusted when a plasma treatment (PT) performed on the surface of the non-magnetic intermediate layer23.

As shown inFIG. 12, it can be seen that the interlayer coupling magnetic field Hin varies in accordance with a magnitude of a gas flow (gas pressure) and a magnitude of an electric power. The magnitude of the electric power shown inFIG. 12is W1>W2>W3and in the range of 100W to 300W. As shown inFIG. 12, when the gas flow (gas pressure) and the electric power increases, the interlayer coupling magnetic field Hin can vary from a positive value to a negative value. Accordingly, by adjusting the gas flow or the electric power for the plasma treatment on the first magnetoresistance elements10,11and the gas flow or the electric power for the plasma treatment on the second magnetoresistance elements12,13, the first interlayer coupling magnetic field Hin1of the first magnetoresistance elements10,11may be shifted in the positive direction, and the second interlayer coupling magnetic field Hin2of the second magnetoresistance elements12,13may be shifted in the negative direction.

The magnitude of the interlayer coupling magnetic field Hin varies also in the non-magnetic intermediate layer34. The magnitude of the interlayer coupling magnetic field Hin may be adjusted by changing the film thickness of the anti-ferromagnetic layer when the anti-ferromagnetic layer/the fixed magnetic layer/non-magnetic intermediate layer/free magnetic layer are laminated in an order thereof from bottom.

In the first magnetoresistance element10,11, the first interlayer coupling magnetic field Hin1is the positive value and in this case, an interaction which makes the opposite magnetizations to be parallel acts between the fixed magnetic layer33and the free magnetic layer35. In the second magnetoresistance elements12,13, the second interlayer coupling magnetic field Hin2is the negative value and in this case, an interaction which makes the opposite magnetizations to be anti-parallel act between the fixed magnetic layer33and the free magnetic layer37. By generating the exchange coupling magnetic field in the same direction by heat treatment on the magnetic field between the anti-ferromagnetic layer32and the fixed magnetic layer33of the magnetoresistance elements10to13, the magnetization33aof the fixed magnetic layer33of the magnetoresistance elements10to13can be fixed in the same direction. Further, since the above-mentioned interaction acts between the fixed magnetic layer33and the free magnetic layers35,37, the magnetization state inFIG. 9is formed.

In the embodiment, an increasing or decreasing tendency of the resistance value with the variation in magnetic field magnitude of the external magnetic field H1in the positive direction of the first magnetoresistance element10,11is opposite to an increasing or decreasing tendency of the resistance value with the variation in magnetic field magnitude of the external magnetic field H2in the negative direction of the second magnetoresistance elements12,13with respect to a non-magnetic field state of the external magnetic field. That is, in the first magnetoresistance elements10,11, the resistance value R gradually tends to increase as the external magnetic field H1in the positive direction from the non-magnetic state increases. In the second magnetoresistance elements12,13, the resistance value R gradually tends to decrease as the external magnetic field H2(absolute value) in the negative direction from the non-magnetic state increases.

For the reason, when the external magnetic field H1in the positive direction gradually increases, the potential of the first output terminal18shown inFIG. 6gradually decreases, and the potential of the second output terminal19shown inFIG. 6gradually increases. Likewise, when the external magnetic field H2(absolute value) in the negative direction gradually increases, the potential of the first output terminal18shown inFIG. 8gradually decreases and the potential of the second output terminal19shown inFIG. 8gradually increases. Accordingly, as shown inFIGS. 6 and 8, once a general bridge circuit is formed, the control unit21can perform the same control whether the external magnetic field is in the positive direction or in the negative direction, and particularly, it is not required to change a circuit or a control method in accordance with the polarity of the external magnetic field.

In the embodiment, as shown inFIG. 5, an element length of the first magnetoresistance elements10,11is L1, and an element length of the second magnetoresistance elements12,13is L2. The element length L1is shorter than the element length L2. Accordingly, as shown inFIG. 10C, the resistance value R of the first magnetoresistance elements10,11in the non-magnetic state (zero) of the external magnetic field H is smaller than the resistance value R of the second magnetoresistance elements12,13. The element resistance may vary by varying a cross section, a material, or a film configuration. In order to suppress non-uniform of the temperature coefficient (TCR) by simple manufacturing method, it is proper that the cross section, the material, or the film configuration is equal between the first magnetoresistance elements10,11and the second magnetoresistance elements12,13. Accordingly, film thicknesses or materials of the layers of the first magnetoresistance elements10,11is the same as the second magnetoresistance elements12,13. However, in order to vary the interlayer coupling magnetic field Hin, to vary the film thickness of the non-magnetic intermediate layer34is not excluded. The first magnetoresistance elements10,11and the second magnetoresistance12,13are formed to have the same film configuration. For example, when the fixed magnetic layer33of the first magnetoresistance elements10,11is formed of an artificial ferri structure, the fixed magnetic layer33of the second magnetoresistance elements12,13also is formed of the artificial ferri structure.

In the embodiment, the manufacturing method is also simple. That is, since conditions for the plasma treatment on the non-magnetic intermediate layer34may vary, at least the first magnetoresistance elements10,11and the second magnetoresistance element12,13can be manufactured in the same process as the non-magnetic intermediate layer34. Since the fixed magnetic layer33of the first magnetoresistance elements10,11and the fixed magnetic layer33of the second magnetoresistance element12,13are fixed in the same magnetization direction33a, the direction of the magnetic field during the heat treatment in a magnetic field can be matched, and the heat treatment in a magnetic field can be simultaneously performed on the first magnetoresistance elements10,11and the second magnetoresistance element12,13.

As shown inFIG. 10C, when the external magnetic field H1in the positive direction acts, the fixed resistance value X1of the second magnetoresistance elements12,13is larger than the minimum resistance value X2of the first magnetoresistance elements10,11varying with the variation in magnetic field magnitude in the positive direction, and is smaller than the maximum resistance value X3thereof. When the external magnetic field H2in the negative direction acts, the fixed resistance value X4of the first magnetoresistance elements10,11is larger than the minimum resistance value X5of the second magnetoresistance elements12,13varying with the variation in magnetic field magnitude in the negative direction, and is smaller than the maximum resistance value X6thereof. As shown inFIG. 10C, a ratio of ‘fixed resistance value X1—minimum resistance value X2to maximum resistance value X3—fixed resistance value X1’ is equal to a ratio of ‘ maximum resistance value X6—fixed resistance value X4to fixed resistance value X4—minimum resistance value X5’.

In the embodiment, the magnitude of the first interlayer coupling magnetic field Hin1is equal to the magnitude (absolute value) of the second interlayer coupling magnetic field Hin2.

In the embodiment, as shown inFIGS. 6 and 8, the output terminals18,19are connected to the differential amplifier20, and a relation between the differential potential from the differential amplifier20and the external magnetic field H is presented as the curves D and F shown inFIG. 11.

As shown inFIG. 11, when the external magnetic field H is in the non-magnetic field state (zero), the differential potential is T1, which, for example, is a positive value (it is possible to be a negative value by the control of the differential amplifier20, but it is described as a positive value). When the external magnetic field H1in the positive direction increases, as shown inFIG. 10c, the resistance value R of the first magnetoresistance elements10,11increases, the second magnetoresistance elements12,13function as the fixed resistance element, and the differential potential gradually decreases as a curve D shown inFIG. 11. In the embodiment, the fixed resistance value X1of the second magnetoresistance elements12,13is in the range of the minimum resistance value X2and the maximum resistance value X3of the first magnetoresistance elements10,11. Accordingly, when the external magnetic field H1increases up to H1-A (refer toFIG. 11), the varying resistance value R of the first magnetoresistance elements10,11is matched with the fixed resistance value X1of the second magnetoresistance elements12,13, whereby the differential potential becomes zero.

When the external magnetic field H2(absolute value) in the negative direction gradually increases, as shown inFIG. 10c, the resistance value R of the second magnetoresistance elements12,13increases, the first magnetoresistance elements10,11function as the fixed resistance element, and the differential potential gradually decreases as a curve F shown inFIG. 11. In the embodiment, the fixed resistance value X4of the first magnetoresistance elements10,11is in the range of the minimum resistance value X5and the maximum resistance value X6of the second magnetoresistance elements12,13. Accordingly, when the external magnetic field H2increases up to H1-B (refer toFIG. 11), the varying resistance value R of the second magnetoresistance elements12,13is matched with the fixed resistance value X4of the first magnetoresistance elements10,11, whereby the differential potential becomes zero.

In the embodiment, when the external magnetic field H1in the positive direction acts, there is a time when a varying resistance value R of the first magnetoresistance elements10,11and the fixed resistance value X1of the second magnetoresistance elements12,13are equal to each other and become zero. Similarly, when the external magnetic field H2in the negative direction acts, there is a time when a varying resistance value R of the second magnetoresistance elements12,13and the fixed resistance value X4of the first magnetoresistance elements10,11are equal to each other and become zero. A potential at this time is a threshold potential. In the control unit21, a comparison unit comparing the threshold potential with the differential potential which changes every moment is provided. When the differential potential is matched with the threshold potential, that is, when the differential potential becomes zero, the control unit21can switch the on-off signals.

In the embodiment, as described above, a ratio of ‘fixed resistance value X1—minimum resistance value X2to maximum resistance value X3—fixed resistance value X1’ is equal to a ratio of ‘maximum resistance value X6—fixed resistance value X4to fixed resistance value X4—minimum resistance value X5’. Since the first interlayer coupling magnetic field Hin1and the second interlayer coupling magnetic field Hin2(absolute value) are the same in magnitude, as shown inFIG. 11, a magnitude H1-A of the external magnetic field H1in the positive direction at the time when the differential potential becomes zero may be equal to a magnitude H2-B of the external magnetic field H2in the negative direction. In addition, when the threshold potential other than zero is used as a threshold potential, as shown inFIG. 11, the magnitude of the external magnetic field with the threshold potential varies between the positive direction and the negative direction. Accordingly, it is preferable that the differential potential with zero is used as a threshold potential.

For example, when the ratios or the magnitudes of the first interlayer coupling magnetic field Hin1and the second interlayer coupling magnetic field Hin2(absolute value) are different from each other and the differential potential is zero, the external magnetic field H1in the positive direction is not equal to the external magnetic field H2in the negative direction. Accordingly, in order to output the switching signal with the same magnitude of the external magnetic field in the positive direction and the negative direction, it is necessary to individually adjust the threshold potentials in the external magnetic fields H1, H2in the positive direction and the negative direction in consideration of an offset.

When the fixed resistance value X1the second magnetoresistance elements12,13in the external magnetic field H1in the positive direction do not intersect the hysteresis loop HR-A of the first magnetoresistance elements10,11, and when the fixed resistance value X4the second magnetoresistance elements10,11in the external magnetic field H2in the negative direction do not intersect the hysteresis loop HR-B of the second magnetoresistance elements12,13, as shown in curves G, H with a dashed-doted line inFIG. 11, a line in which the differential potential is zero can not be used as the threshold potential. Accordingly, it is necessary to individually adjust the threshold potentials in consideration of an offset from the differential potential with zero.

Meanwhile, in the embodiment, since the differential potential with zero is used as the threshold potential, the magnitude H1-A of the external magnetic field in the positive direction with the threshold potential can be equal to the magnitude H2-B of the external magnetic field in the negative direction. Accordingly, it is simple to adjust the threshold potential. That is, in the embodiment, a time for outputting an on-signal by opening the cellular phone shown inFIGS. 1 and 2(or a time for outputting an off-signal by opening the cellular phone) when the external magnetic field H1in the positive direction acts on the magnetic sensor4as shown inFIGS. 1 and 2, may be equal to a time for outputting an on-signal by opening the cellular phone shown inFIGS. 3 and 4(or a time for outputting an off-signal by opening the cellular phone) when the external magnetic field H2in the negative direction acts on the magnetic sensor4as shown inFIGS. 3 and 4. In the embodiment as described above, although the polarities of the external magnetic field H are different each other, the magnetic sensor4which can be driven in a stable manner can be provided by a simple circuit.

In the embodiment, it is further preferable that the fixed resistance value X1is a value between the minimum resistance value X2, and the maximum resistance value X3and the fixed resistance value X4is a value between the minimum resistance value X5and the maximum resistance value X6. Thus, when the on-off signal is switched, the magnitude of the external magnetic field can be adjusted to be the same in the positive direction and the negative direction. Accordingly, the magnetic sensor4adapted for the both positive and negative magnetic fields is driven in a stable manner.

FIG. 13is a plan view illustrating another embodiment ofFIGS. 5 and 6.FIG. 14is a circuit diagram ofFIG. 13.

InFIG. 13, one first magnetoresistance element40and one second magnetoresistance element41are provided, and the first magnetoresistance element40and the second magnetoresistance41are connected in series. An end portion of the first magnetoresistance element40is connected to an input terminal42, an end portion of the second magnetoresistance element41is connected to an earth terminal43, and an output terminal44is connected to the connecting portion between the first magnetoresistance element40and the second magnetoresistance element41.

The first magnetoresistance element40has the hysteresis characteristic shown inFIG. 10Aand the second magnetoresistance element41has the hysteresis characteristic shown inFIG. 10B. Thus, with the variation in magnetic field magnitude of the external magnetic field H1in the positive direction, the first magnetoresistance element40varies in resistance, and the second magnetoresistance element41does not vary. With the variation in magnetic field magnitude of the external magnetic field H2in the negative direction, the second magnetoresistance41varies in resistance and the first magnetoresistance element40does not vary, thereby forming the magnetic sensor adapted for both the positive and negative magnetic fields. Accordingly, assembly is easy.

A preferable film configuration or hysteresis characteristic of the first magnetoresistance40and the second magnetoresistance41is the same as the above-described bridge circuit.

An example of the specific numerical value is described. A length L1of the first magnetoresistance elements10,11, and40is about 1700 μm, a length L2of the second magnetoresistance element12,13, and41is about 1700 μm, a film thickness of the non-magnetic intermediate layer34of the first magnetoresistance elements10,11, and40is in the range of 19 to 23 μm, and a film thickness of the non-magnetic intermediate layer34of the second magnetoresistance elements12,13, and41is in the range of 19 to 23 μm.

A requirement of the plasma treatment, for example, is that an electric power value is about 130 W, an Ar gas pressure is about 45 mTorr (about 6 Pa), and a treatment time is about 60 seconds.

In an adjustment of the interlayer coupling magnetic field Hin, when the plasma treatment is performed on one magnetoresistance element and thus the interlayer coupling magnetic field shifting in the negative direction is obtained, a film thickness of the anti-ferromagnetic layer of the other magnetoresistance element is adjusted in the range of 50 to 200 Å, and thus the interlayer coupling magnetic field shifted in the positive direction is obtained. A surface state varies in accordance with the adjustment for the film thickness of the anti-ferromagnetic layer, whereby the interlayer coupling magnetic field varies.

The first interlayer coupling magnetic field Hin1is in the range of 7.5 to 17.5 Oe, the second interlayer coupling magnetic field Hin2is in the range of −17.5 to −7.5 Oe, and the magnitude of the external magnetic field H in the range for use is in the range of −100 to 100 Oe.

As mentioned above, although the magnetic sensor4in the embodiment is used for the open and close detection of the foldable cellular phone1, the magnetic sensor4may be used for the open and close detection of a portable electronic apparatus such as a game machine. The embodiment, in addition to the open and close detection, may be used in a field for which the magnetic sensor4adapted for the both positive and negative magnetic fields is necessary.

It is optional whether a bias magnetic field is applied to the magnetoresistance element. Although the bias magnetic field may be not supplied to the free magnetic layer constituting the magnetoresistance element, it should be adjusted so as to be in the magnetization state shown inFIG. 9when the bias magnetic is not supplied.

The magnetoresistance element may have a meandering shape in addition to a straight line shape and is not limited in a shape.

Further, a “magnetic sensor” may be one in which the magnetic sensor4and the magnet (external magnetic field generating means)5as a sensor unit are formed in a set or one in which the only magnetic sensor4as a sensor unit is formed.