Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1998-03-31
2000-05-30
Strecker, Gerard
Electricity: measuring and testing
Magnetic
Magnetometers
324225, 338 32R, G01R 3309, H01L 4308
Patent
active
060694769
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic field sensor having a magnetoresistance bridge. It can be used in the measurement of magnetic fields, particularly weak fields, i.e. of a few dozen Oersteds.
2. Discussion of the Background
Field sensors are known formed by four magnetoresistances connected as a WHEATSTONE bridge. FIG. 1 shows an example thereof. Each of the four magnetoresistances is shaped like an elongated bar and are pairwise connected in electrical opposition in the bridge (respectively R1 and R2), terminals being respectively located between the magnetoresistances. The input or supply voltage applied between two terminals of the bridge is designated Ve and the output or measuring voltage between the two other terminals is designated Vs.
In such a connection, only two of the magnetoresistances have to be sensitive to the magnetic field to be measured (e.g. the magnetoresistances R2), otherwise the bridge would be balanced in all circumstances. One of the solutions consists of placing a magnetic shield in front of two of the magnetoresistances, namely the magnetoresistances R1 in FIG. 2, where the shield carries the reference Ec.
Such a sensor is e.g. described in the article by J. DAUGHTON et al entitled "Magnetic Field Sensors Using GMR Multilayer", published in "IEEE Trans on Magnetics", vol. 30, No. 2, March 1994.
Although satisfactory in certain respects, such sensors remain complex due to the means intended to render passive two of the magnetoresistances,
SUMMARY OF THE INVENTION
The object of the present invention is to obviate this disadvantage by avoiding having to have recourse to such a shield.
For this purpose the present invention recommends the longitudinal orientation of two of the magnetoresistances and the transverse orientation of the two others, the orientations being relative to the direction of the field to be measured. Under certain conditions defined hereinafter, the two transversely connected magnetoresistances are insensitive to the variation of the field applied and are consequently neutralized. Only the longitudinally connected magnetoresistances are sensitive to the field applied. Thus, the sought neutralization function is indeed obtained solely through the orientation of the magnetoresistances and without using any supplementary means.
More specifically, the present invention relates to a magnetic field sensor comprising on the one hand at least four magnetoresistances connected to a WHEATSTONE bridge, each magnetoresistance having on at least one part the shape of an elongated bar with a longitudinal direction and a transverse direction, the four magnetoresistances being in pairwise electrical opposition in said bridge, and on the other hand means for supplying voltage to the bridge and means for measuring the asymmetrical voltage of the bridge, said sensor being characterized in that the magnetoresistances are of the multilayer type and that two of the opposing magnetoresistances in the bridge have their longitudinal direction oriented parallel to a direction which is that of the field to be measured, the two others having their transverse direction oriented parallel to said same direction.
The term magnetoresistances of the multilayer type is understood to mean magnetoresistances constituted by a stack of several bilayers, a bilayer having a ferromagnetic layer and a non-magnetic layer, the first and last layers of the stack being in each case ferromagnetic.
The longitudinal magnetoresistances are said to be active and the transverse magnetoresistances are said to be passive.
Advantageously, the sensor also comprises a polarizing means able to apply to at least two magnetoresistances oriented in longitudinal manner a magnetic polarization field. This polarizing means can be a winding or a conductor through which flows a polarizing current, or a permanent magnet.
The winding can surround the two longitudinal magnetoresistances or can surround all the magnetoresistances.
Advantageously, the sensor also co
REFERENCES:
patent: 4079360 (1978-03-01), Ookubo et al.
patent: 4447781 (1984-05-01), van Dyke
patent: 4533872 (1985-08-01), Boord et al.
patent: 5287238 (1994-02-01), Baumgart et al.
patent: 5351005 (1994-09-01), Rouse et al.
patent: 5561368 (1996-10-01), Dovek et al.
patent: 5617071 (1997-04-01), Daughton
patent: 5686837 (1997-11-01), Coehoorn et al.
Miles J J et al: "Micromagnetic Modelling of Spin Valve and GMR Read Heads" IEEE Transactions on Magnetics, vol. 32, No. 5, pp. 4597-4602.
Publication Entitled: "Magnetoresistance of microscopic strips of thin (NiFe/Ag) multilayers with large bi-quadratic coupling" by S. Young, et al, published in "Journal of Magnetism and Magnetic Materials", 162, 1996, pp. 38-42.
Cuchet Robert
Fedeli Jean-Marc
Vieux-Rochaz Line
Commissariat a l''Energie Atomique
Strecker Gerard
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