WO2006067100A1 - Procede de mesure d'un champ magnetique faible et capteur de champ magnetique a sensibilite amelioree - Google Patents
Procede de mesure d'un champ magnetique faible et capteur de champ magnetique a sensibilite amelioree Download PDFInfo
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- WO2006067100A1 WO2006067100A1 PCT/EP2005/056890 EP2005056890W WO2006067100A1 WO 2006067100 A1 WO2006067100 A1 WO 2006067100A1 EP 2005056890 W EP2005056890 W EP 2005056890W WO 2006067100 A1 WO2006067100 A1 WO 2006067100A1
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- magnetic field
- magnetoresistive element
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- 230000005291 magnetic effect Effects 0.000 title claims abstract description 65
- 238000000034 method Methods 0.000 title claims description 13
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- 229910015136 FeMn Inorganic materials 0.000 description 1
- 229910002555 FeNi Inorganic materials 0.000 description 1
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 1
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
- G01R33/09—Magnetoresistive devices
Definitions
- the present invention relates to magnetic field sensors in weak fields, and more particularly to magnetoresistive sensors used for the measurement of weak fields, that is to say less than or equal to the Earth's magnetic field. It should be noted that the notion of weak field may be related to the distance between the magnetic source and the sensor or the size of the magnetic source itself.
- a magnetoresistive sensor uses the magnetoresistance of ferromagnetic materials and nanostructures, that is to say the variation of the electrical resistance of a conductor under the effect of the magnetic field applied to it.
- a bias current i In practice such a sensor requires the application of a bias current i.
- the output voltage Vs obtained is a function of the bias current i and the magnetoresistance and thus allows the reading of the value of the applied magnetic field.
- this voltage measurement is longitudinal, that is to say in the same direction as the current i, or transverse, that is to say in an orthogonal direction.
- sensors using GMR giant magnetoresistance or TMR tunnel magnetoresistance are widely used in all areas of the industry for detection or measurement.
- Magnetometers, altitude sensors, heading detection, mines, current sensors, magnetic signatures are all examples of use.
- a GMR sensor comprises at least two separate ferromagnetic layers, whose magnetization vectors can have different orientations in the plane according to the external magnetic field.
- Multilayer structures including a repetition of an alternation of ferromagnetic conductive layers and non-ferromagnetic conductive layers, which have a large giant magnetoresistance effect, are known in particular.
- This GMR giant magnetoresistance effect reflects the spin dependence of the resistance of this artificial magnetic structure.
- the total exploitable effect is of the order of ten per cent of the resistance of the sensitive zone (where the magnetic effects occur) of the magnetic structure.
- An exemplary embodiment of such a sensor is illustrated in Figure 1. It corresponds to a structure described in French Patent No. 98 15697.
- the 1/3/2 stack may be of the Co / Cu / FeNi type.
- the bias current i flows in all the conductive layers 1, 2 and 3.
- the voltage measurement Vs follows in the example a longitudinal geometry.
- TMR sensor described in French patent N 0 00 06453 is illustrated in Figure 2. It comprises a stack of layers FM1 / I / FM2 / AF, where FM1 and FM2 are two ferromagnetic metal layers (Co, Fe or NiFe for example), I, a thin insulating layer and AF, a layer of antiferromagnetic material (for example an antiferromagnetic such as FeMn or IrMn).
- FM1 and FM2 are two ferromagnetic metal layers (Co, Fe or NiFe for example)
- I a thin insulating layer
- AF a layer of antiferromagnetic material
- TMR tunnel magnetoresistance or SDT
- This phenomenon corresponds to the conservation of the spin of the electrons when they cross the insulating barrier by tunnel effect.
- the current i flows between the conductive layers FM 1 and FM 2, through the insulating barrier I.
- the voltage Vs is measured across the FM 1 and FM 2 layers.
- a problem common to these magnetoresistive sensors is that in low-field measurement applications, for which the sensor operates at a low frequency, typically less than 1 kilohertz, the accuracy of the output signal provided by these sensors is mainly limited by drifting. thermal signal.
- the thermal drift of the output signal is indeed the main component of low frequency noise (around 1 Hz) of these sensors. This is particularly troublesome especially for the measurement of weak fields or null fields.
- a magnetoresistive sensor receives a bias current i, and in response, provides at its terminals a voltage signal Vs representative of the external field H ext applied on the sensitive area of the sensor.
- a voltage signal Vs representative of the external field H ext applied on the sensitive area of the sensor.
- the output signal Vs is illustrated in FIG. 3b, and represents the variation of voltage as a function of the applied field H ext .
- Vs V 0 + vs.
- the corresponding normalized response curve as a function of the applied field H ext is that illustrated in FIG. 3b.
- On the ordinate, there is the variation vs of the output voltage Vs, related to the maximum voltage variation vs c that can be measured, obtained for H ext H c .
- This response curve has two saturation elbows, for a characteristic field value H c , which corresponds to the value VS 0 , and for a characteristic field value -H c .
- the characteristic value H c depends on the properties specific to the structure of the sensor considered. It is understood that the value of H c may be greater or smaller, allowing the measurement of a field of greater or lesser amplitude.
- the field measurement signal comes from the second term of the equation (ie SH ext ) and in practice leads to a variation of a few fractions of percents per oersteds. But at the same time, R 0 , the isotropic part of the resistance, varies with the temperature of a few fractions of percents per degree. Which means in other words, that if we want to make a precise sensor to a millioersted, we must provide that the ambient temperature in the sensor environment is stable to better than 1 millikelvin, which is a problem whose resolution seems particularly difficult.
- the object of the invention is to improve the sensitivity of the magnetoresistive sensors, more particularly the GMR or TMR sensors.
- the output voltage measured at the terminals of the magnetoresistive element is a function of the external field to be measured and the modulated field: it is the image of the variations of the magnetoresistance with the total magnetic field applied. It is shown that this modulation makes it possible, at the output, to overcome the offset R0 of the magnetoresistance, so that the sensitivity of the sensor is improved.
- the amplitude of the odd harmonics of the output signal thus obtained is linear around the zero field, in a certain measurement range.
- the extraction of an odd harmonic from the output signal, at the modulation frequency, therefore gives a measurement of the external field which is independent of the offset value R 0 of the sensor, and therefore of its thermal drift.
- this field modulation is applicable for measuring a small field H ext in front of the amplitude H 3 of the modulated field.
- H 3 is determined in an appropriate manner, in particular as a function of the saturation value H c of the sensor in question.
- the extraction of the third harmonic gives a direct measurement of the external field.
- the associated measurement range corresponding to the linear zone of the amplitude of this harmonic as a function of the field, is reduced.
- the modulated field comprises a continuous component H 0 , which can be varied in stages, so as to extend the measurement zone of the sensor, in ranges.
- the value of this component H 0 can also be controlled by a feedback loop to impose a zero field on the sensitive area of the sensor. The value of the external field is then deduced from the value of the DC component H 0 .
- the invention therefore relates to a method for measuring a weak magnetic field, comprising the use of a current-polarized magnetoresistive element, characterized in that it comprises the application of a modulation field in a sensitive zone of the magnetoresistive element, the extraction of an odd harmonic from an output signal of said magnetoresistive element, to provide a measurement of said weak magnetic field from the amplitude of said harmonic.
- the invention also relates to a magnetic field sensor, for measuring a weak external magnetic field, comprising a magnetoresistive element and current biasing means of said element, characterized in that it further comprises application means a frequency and amplitude controlled modulation magnetic field and a synchronous detection device of an output signal of said element for measuring the amplitude of an odd harmonic of the output signal.
- FIG. 1 schematically illustrates a GMR sensor of the state of the art
- FIG. 2 schematically illustrates a TMR sensor of the state of the art
- FIGS. 3a and 3b respectively represent a device for measuring an external magnetic field applied in a sensitive zone of a magnetoresistive element, and the associated response curve as a function of the amplitude of the applied external field;
- FIG. 4 schematically illustrates a magnetic field measuring device according to the invention
- FIG. 5 represents another embodiment of a magnetic field measuring device according to the invention, comprising external means for generating a modulation field in a sensitive zone of a magnetoresistive element;
- FIG. 6 diagrammatically illustrates a first embodiment of a measuring device according to the invention, comprising a conducting layer able to generate a modulation field in the sensitive zone of the magnetoresistive element according to the invention
- FIG. 7 gives the output voltage variation curves of a magnetoresistive element as a function of an applied external field, and as a function of the amplitude of the modulation field applied according to the invention
- FIG. 8 represents the amplitudes of the first four harmonics of the signal, as a function of an external field, for a given amplitude modulation field
- FIG. 9 details the amplitudes of the harmonics 1 and 3, and the associated linear measurement zone
- FIG. 10 illustrates the variation of amplitude of the harmonic 1, in the case where the DC component of the modulation field is taken substantially equal to the characteristic value H c of saturation of the magnetoresistive element,
- FIG 11 is a block diagram of a measuring range selection circuit that can be used in the sensor according to the invention
- FIG 12 is a block diagram of a sensor according to the invention, with a feedback loop for controlling the value of the DC component of the modulation field to the amplitude measured at the output.
- a sensor of an external magnetic field H ext comprises, as illustrated schematically in FIG. 4: a magnetoresistive element 10, having a magnetoresistance R, a generator of bias current i, means 12 for generating a modulation field H m at a modulation frequency f derived from a clock signal CIk, provided for example by a local oscillator 13, a signal processing device 14 comprising a synchronous detection device at the frequency of modulation f of the output signal Vs of the magnetoresistive element 10.
- This electronic device provides the result of measurement mes (H ext ) of the external field
- the synchronous detection device is configured to detect the amplitude of an odd harmonic of the output signal.
- This harmonic is preferably the fundamental h1, detected at the modulation frequency f of the field H m .
- it is the third harmonic h3, detected at the frequency 3f.
- the measuring device comprises in practice a frequency generator, typically a local oscillator, which supplies a reference clock signal CIk, to the modulation field generation means 12 and to the electronic processing device 14.
- the modulation means 12 may be external, non-integrated means. Such a configuration is shown diagrammatically in FIG. 5.
- the sensor then comprises a monolithic casing C in which the elements 10, 11 and 14 of FIG. 4 are integrated and for example a pair of electromagnetic coils B1, B2 arranged on both sides. other housing and controlled appropriately, typically by a generator of sinusoidal current to generate the modulation field Hm in the environment of the case C.
- the modulation means 12 can be further integrated into the structure of the magnetoresistive element 10, for example a structure as shown in FIG. 1 or FIG. 2.
- the sensor can then be integrated in a monolithic housing.
- the modulation means 12 comprise a conductive strip 16 suitably arranged above or below the magnetoresistive element 10.
- a modulation current i m is applied on this band, generated by a sinusoidal current generator 17 at the desired frequency f, so as to create the modulation field H m in the environment of the magnetoresistive element.
- a layer 15 of an insulator is provided between the surface of the magnetoresistive element and the conductive strip 16.
- the band 16 is preferably wider than the magnetoresistive element 10, to have a homogeneous modulation field H m on the entire magnetoresistive element.
- the sensitive area refers to the area where magnetoresistance effects occur, the practical definition of which depends on the structure of the magnetoresistive element. It has been seen previously with reference to FIG. 3b that the magnetoresistance R of the magnetoresistive element 10 as a function of the applied external field H ext on the sensitive zone of the sensor can be written:
- the slope changes are made for the characteristic field values -H c and + H C of the applied field: these are the field values for which the magnetoresistive element under consideration is saturated.
- a modulated field H m is applied, which generally comprises a DC component H 0 and a modulated component H 3 , for example a sinusoidally modulated component.
- H a .cos ( ⁇ ) is alternately positive and negative, ⁇ is (2 ⁇ i.ft), where t is the time and f is the frequency.
- Equation 1 Equation 1 becomes:
- the output voltage Vs across the sensor is modulated.
- This modulation is chosen such that one arrives at one of the saturation bends of the variation dR of the resistance R M.
- the modulation field being chosen, the values of H 0 and H 3 being fixed with H 0 > 0, the study is limited to the measurement of an external field whose values are situated in the following interval: H a ⁇ H c and H c -Ho-H a ⁇ H e ⁇ t ⁇ H c -Ho + H a . (Cond.1).
- H 0 has a positive value or zero.
- H 3 is chosen close to or equal to the saturation value H c in order to benefit from a larger measurement range.
- the value of the modulation field is such that the total field H app has excursions on both sides of the value H c , which means that there is a field modulation around the elbow of saturation.
- Each curve corresponds to a different value of the external field H ext to be measured.
- FIG. 9 (same field modulation conditions as in FIG. 8) highlights these linear parts of the variation of the amplitude of the harmonics h1 and h3 with the external field H ext to be measured.
- the same notation h j is used to designate a harmonic and its amplitude.
- hX H a ⁇ ⁇ arJ y H * - ⁇ H a H * X j ⁇ ⁇ 2 ⁇ l H ⁇ a ⁇ - (H ⁇ - H ⁇ + g lH a
- FIG. 10 (in normalized values) to be measured is shown in FIG. 10 (corresponds to the simulation conditions of FIG. 8). We have a linear portion in the measurement range of -0.4H c - at 0.4H c .
- the demodulated output signal ie the measurement of h1, comprises an offset (the first term of eq.5) and a useful term directly proportional to the desired quantity Hext (the second term of (eq.5).
- H e x t is therefore expressed as a function of the amplitude of the harmonic h1, measured at the output (Vs) of the magnetoresistive element 10, characteristics g1, g2 of the transfer function of the magnetoresistive element 10 and the amplitude H 3 of the applied modulation.
- the measurement of H ext then comprises the subtraction of the offset which depends only on the characteristics g 1, g 2 of the transfer function of the magnetoresistive element 10 and the amplitude H 3 of the modulation applied. This is achieved in practice by an electronic processor adapted to derive the measurement of the external field as a function of G1, G2 and H 3.
- the output voltage of a magnetoresistive sensor is low.
- an output signal Vs is matched to it at a non-zero modulation frequency f.
- Another advantage of the invention is then the frequency translation of the output signal, in the case where the sensor is followed by an amplification electronics. This transposition in frequency facilitates the amplification and contributes to improving the signal-to-noise ratio of the measurement, because the working frequency f is then remote from the zone (about 1 Hz) where the low frequency noise of the electronics exists. amplification.
- the modulation frequency f is of the order of 10 KHz.
- the third harmonic h3 is preferably extracted from the output signal of the magnetoresistive element.
- the device according to the invention comprises a circuit 20 for selecting a range g from n measurement ranges. Depending on the range g selected, a value H 0 (g) is obtained.
- a diagram of a corresponding device is shown in Figure 11.
- H 0 (g) is equal to H c plus or minus a multiple of a quantity ⁇ H 0 .
- H 0 is equal to H c .
- the range selection can in practice be implemented manually or automatically. This selection is interesting to extend the measurement dynamics of a sensor using for measurement, the third harmonic h3. But it also applies to the fundamental h1.
- the change of range is carried out each time one reaches an amplitude of the harmonic h1 which is at the limit of the extent of measurement, towards the point L1 or the point L2.
- the change of range is obtained by modifying the value of H 0 , so as to be in a measurement zone close to the point P.
- this DC component H 0 is controlled by a loop against feedback 200, so that one measurement output a null field on the magnetoresistive element.
- the value of the external field H ext is then deduced from the value of H 0 .
- a practical embodiment of such a feedback loop device 200 is diagrammatically shown in FIG. 12.
- the value of the continuous component H 0 of the modulation field H m is controlled by the output measurement value of the harmonic hj, to be equal to the offset value hj °.
- the output OUT value of the external field measuring device H ext is then calculated as indicated above, based on the value of Ho (t) after stabilization of the loop.
- the invention which has just been described applies to all the fields concerned by weak fields. It is not limited to the use of magnetoresistances GMR, TMR. It applies to any magnetic configuration with a magnetoresistance having a linear and reversible response as a function of the applied field as a function of the applied field, and similar to that illustrated in FIG. 3.B. Thus, the invention can also be applied to AMR anisotropic magnetoresistance elements.
- Modulation, demodulation, servocontrol means of the DC component are made by any suitable electronic device known to those skilled in the art, according to the state of the art.
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Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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DE112005003226T DE112005003226T5 (de) | 2004-12-23 | 2005-12-19 | Verfahren zum Messen eines schwachen Magnetfelds und Magnetfeldsensor mit verbesserter Empfindlichkeit |
US11/722,692 US20080224695A1 (en) | 2004-12-23 | 2005-12-19 | Method of Measuring a Weak Magnetic Field and Magnetic Field Sensor of Improved Sensitivity |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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FR0413831 | 2004-12-23 | ||
FR0413831A FR2880131B1 (fr) | 2004-12-23 | 2004-12-23 | Procede de mesure d'un champ magnetique faible et capteur de champ magnetique a sensibilite amelioree |
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WO2006067100A1 true WO2006067100A1 (fr) | 2006-06-29 |
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Country Status (4)
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US (1) | US20080224695A1 (fr) |
DE (1) | DE112005003226T5 (fr) |
FR (1) | FR2880131B1 (fr) |
WO (1) | WO2006067100A1 (fr) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
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FR2930042A1 (fr) * | 2008-04-15 | 2009-10-16 | Centre Nat Rech Scient | Capteur de champ magnetique. |
FR2930039A1 (fr) * | 2008-04-14 | 2009-10-16 | Centre Nat Rech Scient | Systeme de mesure d'un champ magnetique et procede de suppression du decalage d'un capteur de champ magnetique correspondant. |
EP3467528A1 (fr) | 2017-10-06 | 2019-04-10 | Melexis Technologies NV | Calibrage d'adaptation de sensibilité de capteur magnétique |
US11828827B2 (en) | 2017-10-06 | 2023-11-28 | Melexis Technologies Nv | Magnetic sensor sensitivity matching calibration |
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US8405385B2 (en) * | 2009-03-10 | 2013-03-26 | The Board Of Trustees Of The Leland Stanford Junior University | Temperature and drift compensation in magnetoresistive sensors |
US8975891B2 (en) * | 2011-11-04 | 2015-03-10 | Honeywell International Inc. | Apparatus and method for determining in-plane magnetic field components of a magnetic field using a single magnetoresistive sensor |
US8829901B2 (en) | 2011-11-04 | 2014-09-09 | Honeywell International Inc. | Method of using a magnetoresistive sensor in second harmonic detection mode for sensing weak magnetic fields |
US9869705B2 (en) * | 2013-03-15 | 2018-01-16 | Insight Energy Ventures Llc | Magnetometer sampling to determine an electric power parameter |
US9618588B2 (en) * | 2014-04-25 | 2017-04-11 | Infineon Technologies Ag | Magnetic field current sensors, sensor systems and methods |
FR3067125B1 (fr) * | 2017-06-02 | 2019-07-12 | Commissariat A L'energie Atomique Et Aux Energies Alternatives | Systeme et procede de suppression du bruit basse frequence de capteurs magneto-resistifs |
FR3067116B1 (fr) * | 2017-06-02 | 2019-07-12 | Commissariat A L'energie Atomique Et Aux Energies Alternatives | Systeme et procede de suppression du bruit basse frequence de capteurs magneto-resistifs a magnetoresistence tunnel |
CN108414951B (zh) * | 2018-03-13 | 2023-06-30 | 武汉嘉晨电子技术有限公司 | 周期性调制磁传感器灵敏度降低器件噪声的方法及装置 |
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- 2005-12-19 US US11/722,692 patent/US20080224695A1/en not_active Abandoned
- 2005-12-19 DE DE112005003226T patent/DE112005003226T5/de not_active Withdrawn
- 2005-12-19 WO PCT/EP2005/056890 patent/WO2006067100A1/fr active Application Filing
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Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2930039A1 (fr) * | 2008-04-14 | 2009-10-16 | Centre Nat Rech Scient | Systeme de mesure d'un champ magnetique et procede de suppression du decalage d'un capteur de champ magnetique correspondant. |
WO2009136116A2 (fr) * | 2008-04-14 | 2009-11-12 | Centre National De La Recherche Scientifique (C.N.R.S) | Système de mesure d'un champ magnétique et procédé de suppression du décalage d'un capteur de champ magnétique correspondant |
WO2009136116A3 (fr) * | 2008-04-14 | 2009-12-30 | Centre National De La Recherche Scientifique (C.N.R.S) | Système de mesure d'un champ magnétique et procédé de suppression du décalage d'un capteur de champ magnétique correspondant |
FR2930042A1 (fr) * | 2008-04-15 | 2009-10-16 | Centre Nat Rech Scient | Capteur de champ magnetique. |
WO2009138607A1 (fr) * | 2008-04-15 | 2009-11-19 | Centre National De La Recherche Scientifique (C.N.R.S) | Capteur de champ magnétique |
EP3467528A1 (fr) | 2017-10-06 | 2019-04-10 | Melexis Technologies NV | Calibrage d'adaptation de sensibilité de capteur magnétique |
US10948553B2 (en) | 2017-10-06 | 2021-03-16 | Melexis Technologies Nv | Magnetic sensor sensitivity matching calibration |
US11828827B2 (en) | 2017-10-06 | 2023-11-28 | Melexis Technologies Nv | Magnetic sensor sensitivity matching calibration |
Also Published As
Publication number | Publication date |
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FR2880131B1 (fr) | 2007-03-16 |
DE112005003226T5 (de) | 2007-10-31 |
US20080224695A1 (en) | 2008-09-18 |
FR2880131A1 (fr) | 2006-06-30 |
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