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
  • G01R33/093—Magnetoresistive devices using multilayer structures, e.g. giant magnetoresistance sensors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance

Definitions

• the present invention relates to a magnetic field sensor with a magnetoresistor bridge. It finds an application in the measurement of magnetic fields, in particular weak fields, that is to say of the order of a few tens of Oersteds.
• Field sensors consist of four magnetoresistors mounted on a WHEATSTONE bridge.
• Figure 1 attached shows an example.
• the four magnetoresistors each have the shape of an elongated bar and are mounted in electrical opposition two by two in the bridge (respectively RI and R2), terminals being located respectively between the magnetoresistors.
• the input voltage (or supply) applied between two terminals of the bridge is denoted Ve, and the output (or measurement) voltage taken between the two other terminals is denoted Vs.
• Ve The input voltage (or supply) applied between two terminals of the bridge
• Vs the output (or measurement) voltage taken between the two other terminals.
• only two of the magnetoresistors must be sensitive to the magnetic field to be measured (for example the R2 magnetoresistors) otherwise the bridge would remain balanced under all circumstances.
• One of the solutions consists in placing a magnetic screen in front of two of the magnetoresistors, the RI magnetoresistors in FIG. 2, where the screen bears the reference Ec.
• a magnetic screen is placed in front of two of the magnetoresistors, the RI magnetoresistors in FIG. 2, where the screen bears the reference Ec.
• Such a sensor is described, for example, in the article by J. DAUGHTON et al. titled "Magnetic
• the present invention recommends orienting two of the magnetoresistors longitudinally and transversely the other two, the orientations being taken with respect to the direction of the field to be measured.
• the two magnetoresistors mounted transversely are insensitive to the variation of the applied field and are therefore neutralized. Only the longitudinally mounted magnetoresistors are sensitive to the applied field. The desired neutralization function is therefore obtained, and this only by the orientation of the magnetoresistors, without recourse to any additional means.
• the present invention relates to a magnetic field sensor comprising, on the one hand, at least four magnetoresistors mounted in bridge of HEATSTONE, each agnoresistor having on at least one part an elongated bar shape with a longitudinal direction and a transverse direction, the four magnetoresistors being in electrical opposition two by two in the bridge, and, on the other hand, means for supplying voltage to the bridge and means for measuring the unbalance voltage of the bridge, this sensor being characterized by the fact that the magnetoresistors are of the multilayer type and that two of the opposite magnetoresistors in the bridge have their longitudinal direction oriented parallel to a direction which is that of the field to be measured, the other two having their transverse direction oriented parallel to this same direction.
• Magnetoresistors of the multilayer type are understood to mean magnetoresistors constituted by a stack of several bilayers, a bilayer comprising a ferromagnetic layer and a non-magnetic layer, the first and last layers of the stack being both ferromagnetic.
• the longitudinal magnetoresistors are said to be active and the transverse magnetoresistors are said to be passive.
• the senor further comprises a polarization means capable of applying at least to the two magnetoresistors oriented longitudinally a magnetic polarization field.
• This polarization means can be a winding or a conductor traversed by a polarization current, or a permanent magnet.
• the winding can surround the two longitudinal magnetoresistors or surround all of the magnetoresistors.
• the sensor further comprises a compensation means capable of applying a compensating magnetic field at least to the two magnetoresistors oriented longitudinally.
• This compensation means may comprise a winding traversed by a compensation current or a conductor traversed by a compensation current.
• the senor can comprise a compensation means capable of applying a field to the two magnetoresistors mounted transversely.
• the multilayer type magnetoresistors are based on FeNi / Ag.
• FIG. 3 shows the resistance variations of a giant effect multilayer magnetoresistor as a function of a magnetic field applied parallel to the longitudinal axis of the magnetoresistance
• - Figure 4 shows the resistance variations of a giant effect multilayer magnetoresistor as a function of a magnetic field applied parallel to the transverse axis of the magnetoresistance;
• - Figure 5 illustrates the general structure of a sensor 1 according to the invention;
• FIG. 8 illustrates an embodiment with double polarization and compensation winding
• FIG. 9a, 9b, 9c illustrate an embodiment of the sensor of the invention.
• FIGs 3 and 4 show the operating principle of the multilayer magnetoresistors used according to the invention. These magnetoresistors are sometimes called "giant effect" ("Giant
• the magnetoresistance can be polarized to operate it around a point M away from the top of the curve.
• FIG. 4 illustrates the behavior of such a magnetoresistance as a function of an applied field perpendicular to the magnetoresistant bar (field note __).
• a tray between two critical values -Hcr and + Hcr plateau along which the resistance does not vary. On either side of this plateau, the resistance decreases almost linearly with the field.
• the magnetoresistors, which are mounted one longitudinally, the other transversely, according to one of the essential characteristics of the invention, will therefore operate differently according to their orientation.
• the point of operation of the bridge will be defined by the point M for the two longitudinal magnetoresistors and by the point P, middle of the plate, for the two transverse magnetoresistors (which are not polarized in this particular case).
• the application of a magnetic field to all four magnetoresistors will therefore reduce or increase the resistance of the two longitudinal magnetoresistors
• the variation in resistance as a function of the applied field, of a multilayer stack of the type in which there is a succession of bilayers (a bilayer comprising a ferromagnetic layer and a non-magnetic layer), the assembly being observed full layer is an isotropic variation, in the sense that, whatever the direction of the applied field, the response is identical and triangular in shape. If we engrave in this full layer of the bars, an anisotropy can appear in the response of the bar according to the direction of the applied field, by appropriately choosing the dimensions of the bar.
• the theory provides that if the thickness of the bar increases, the extent of the plate increases, the width of the bar remaining constant otherwise, because the extent of the plate is in fact proportional to t / w or t is the thickness and w the width of the bar.
• this plateau effect is used to make a WHEATSTONE bridge of four magnetoresistors in which two magnetoresistors at least have a t / w ratio giving a plateau effect
• FIG. 5 shows the respective orientation of the magnetoresistive bars.
• the bars GMR1 and GMR2 have their longitudinal axis L parallel to a direction D, which is that of the field H to be measured, while the bars GMR3, GMR4 have their transverse axis T parallel to this direction.
• the applied field H is therefore longitudinal for GMRl and GMR2 and transverse for GMR3 and GMR4.
• FIG 6 shows the electrical connections for building a WHEATSTONE bridge.
• the magnetoresistors are represented by their resistance.
• the resistors R (GMR1) and R (GMR2) are mounted in opposition, as are the resistors R (GMR3) and R (GMR4).
• the measurement voltage Vs is taken between the points SI and S2 located between R (GMR1) and R (GMR4), on the one hand, and R (GMR3) and R (GMR2) on the other hand.
• the supply voltage Ve is applied between on the one hand R (GMR1) and R (GMR3) and on the other hand R (GMR4) and R (GMR2).
• FIG. 6 refers to the electrical resistances and not to the magnetoresistive bars themselves, as for FIG. 5.
• the orientation of the resistors R (GMR1) in the electrical diagram of FIG. 6 therefore has no connection with the orientation of the corresponding bars GMRl ... of FIG. 5.
• the senor is provided with a compensation means constituted by any means and comprising, for example, a winding or a flat conductor traversed by a suitable current.
• FIG. 7 thus schematically shows a comparison and detection circuit 10, the inputs of which receive the unbalance voltage Vs of the bridge, and the output supplies a compensation winding 12.
• the diagram in FIG. 7 also shows a winding 14 which is the polarization winding of the longitudinal magnetoresistors.
• Figure 8 shows a possible practical arrangement.
• the magnetic field to be measured is that which results from the circulation of a current in a flat conductor 20.
• the sensor shown comprises two windings 12 and 14, the first of compensation, the second of polarization. These two windings surround the magnetoresistors GMRl and GMR2.
• the polarization winding can be replaced by a polarization magnet 16 or a planar conductor.
• the bias winding and / or the compensation winding may surround all of the magnetoresistors.
• the sensor of the invention only works correctly if the field applied to the transverse magnetoresistors does not exceed the critical value limiting the plateau along which the resistance of the magnetoresistors remains constant. If this is not the case, provision is made to provide the sensor with a second compensation means comprising, for example, by a winding or a flat conductor traversed by a current.
• the compensation field thus created lowers the total field and makes it possible to bring the latter to a value corresponding to the plateau, or even to a zero value.
• the means for compensating the transverse magnetoresistors can also act on the longitudinal magnetoresistors. It may be, for example, a single flat conductor passing above (or below) the four magnetoresistors and traversed by a current or a single winding surrounding the four magnetoresistors.
• FIG. 9a it can be seen that one starts from a substrate 30, for example made of silicon on which a layer of conductive material, for example gold, copper or the like, is deposited. This layer is etched to form a sheet of lower conductors 32.
• a substrate 30 for example made of silicon on which a layer of conductive material, for example gold, copper or the like, is deposited. This layer is etched to form a sheet of lower conductors 32.
• an insulating layer 34 (see FIG. 9b) is deposited, for example silica, then a layer 36 of conductive material, for example a CrAu alloy. This material is etched so as to leave only two connection tabs on either side of the space reserved for future magnetoresistors. After etching, the sub-assembly therefore comprises eight connection tabs.
• a magnetoresistive multilayer stack is deposited on the assembly and this stack is etched to leave two bars oriented in one direction and two others oriented perpendicular to this direction. That of the bars which is shown in FIG. 9b bears the reference 38. The ends of these bars rest on the connection tabs 36 already produced.
• a layer of insulating material 40 is then deposited. This layer is engraved with openings to the right of the ends of the lower conductors 32 as well as to the right of the rear of the connection tabs.
• a layer of conductive material for example gold or copper, is deposited. This material fills the openings made and thus makes contact with the sheet of lower conductors 32 and the connection tabs 36.
• This conductive layer is then etched to obtain a layer of upper conductors 42 and connections 44 for the magnetoresistors.
• the magnetoresistors which have been described so far are rectangular bars. These bars may have a width less than 40 ⁇ m and a thickness greater than 0.01 ⁇ m so as to have a plateau effect. However, advantageously, the narrower this width, the wider the plate and may give, for example, critical H values of the order of 150 Oe (or even more), for widths of 1 ⁇ m or less.
• the two magnetoresistors GMR1, GMR2 oriented longitudinally can have identical structures and compositions and the two magnetoresistors GMR3, GMR4 oriented transversely can have structures and compositions also identical.

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Nanotechnology (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Measuring Magnetic Variables (AREA)
• Hall/Mr Elements (AREA)

Applications Claiming Priority (3)

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• 1996
  • 1996-08-08 FR FR9610004A patent/FR2752302B1/fr not_active Expired - Fee Related
• 1997
  • 1997-08-07 US US09/043,907 patent/US6069476A/en not_active Expired - Fee Related
  • 1997-08-07 EP EP97936752A patent/EP0853766A1/de not_active Withdrawn
  • 1997-08-07 JP JP10509450A patent/JPH11513128A/ja active Pending
  • 1997-08-07 WO PCT/FR1997/001465 patent/WO1998007042A1/fr not_active Application Discontinuation

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