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EP-3992655-B1 - MAGNETORESISTIVE SENSOR ELEMENT HAVING A WIDE LINEAR RESPONSE AND ROBUST NOMINAL PERFORMANCE AND MANUFACTURING METHOD THEREOF

EP3992655B1EP 3992655 B1EP3992655 B1EP 3992655B1EP-3992655-B1

Inventors

  • CHILDRESS, JEFFREY
  • Strelkov, Nikita
  • Timopheev, Andrey

Dates

Publication Date
20260513
Application Date
20201103

Claims (5)

  1. A magnetoresistive element (10) for a magnetic sensor, the magnetoresistive element (10) comprising a tunnel barrier layer (22) included between a reference layer (21) having a fixed reference magnetization (210) and a sense layer (23) having a free sense magnetization (230); the sense magnetization (230) comprising a stable vortex configuration in the absence of an applied magnetic field; the magnetoresistive element (10) further comprising a reference pinning layer (24) in contact with the reference layer (21) and pinning the reference magnetization (210) by exchange-bias at a first blocking temperature (Tb1); and a sense pinning layer (25) in contact with the sense layer (23) and pinning the sense magnetization (230) by exchange-bias at a second blocking temperature (Tb2) lower than the first blocking temperature (Tb1); characterized in that the sense layer (23) has a thickness between 15 nm and 80 nm, wherein the sense pinning layer (25) is configured such that the strength of exchange-bias between the sense pinning layer (25) and the sense layer (23) is lower than the strength of exchange-bias between the reference pinning layer (24) and the reference layer (21), and wherein the strength of exchange-bias between the sense pinning layer (25) and the sense layer (23) is between 2x10 -8 J/cm 2 and 4x10 -8 J/cm 2 .
  2. The magnetoresistive element according to claim 1, wherein the sense layer (23) comprises a CoFe, NiFe or CoFeB based alloy.
  3. The magnetoresistive element according to claim 1 or 2, wherein the reference pinning layer (24) are the sense pinning layer (25) comprise, or are formed of, an antiferromagnetic material.
  4. The magnetoresistive element according to claim 3, wherein the reference pinning layer (24) are the sense pinning layer (25) comprise an alloy based on Ir and Mn, Fe and Mn; Pt and Mn, Ni and Mn, Cr, NiO or FeO.
  5. Magnetic sensor comprising a plurality of the magnetoresistive element (2) according to any one of claims 1 to 4.

Description

Technical domain The present invention concerns a magnetoresistive element adapted to sense an external magnetic field and having a wide linear response and a nominal performance that remains substantially unchanged after the magnetoresistive element has been subjected to high magnetic fields. The present invention further concerns a magnetic sensor comprising a plurality of the magnetoresistive element. Related art Fig. 1 shows a cross-section view of a conventional magnetoresistive sensor element 2 comprising a ferromagnetic reference layer 21 having a reference magnetization 210, a ferromagnetic sense layer 23 having an averaged free sense magnetization 230 and a tunnel barrier layer 22 between the reference and sense ferromagnetic layers 21, 23. The sense magnetization 230 can be oriented in an external magnetic field 60 while the reference magnetization 210 remains substantially undisturbed. The external magnetic field 60 can thus be sensed by measuring a resistance of the magnetoresistive sensor element 2. The resistance depends on the orientation and magnitude of the averaged sense magnetization 230 relative to the reference magnetization 210. The reference magnetization 210 can be pinned by exchange coupling between an antiferromagnetic layer 24 and the reference layer 21. Figs. 2a and 2b illustrate a top view of the sense layer 23, wherein the sense magnetization 230 comprises a stable vortex configuration. In the vortex configuration, the magnetization curls in a circular path along the edge of the sense layer 23 and around a core 231 reversibly movable in accordance to the external magnetic field 60. The vortex configuration provides a linear and non-hysteretic behavior in a large magnitude range of the external magnetic field 60, for practical size of the magnetoresistive sensor element 2 and thickness of the sense layer 23. The vortex configuration is thus advantageous for magnetic sensor applications. The obtention of a vortex configuration in the sense layer 23 depends on a number of factors, including materials properties of the sense layer 23. Generally, the vortex configuration is favored (at zero applied field) by varying the aspect ratio of the thickness on the diameter of the sense layer 23. The aspect ratio is still typically much less than 1 (for example 0.01 to 0.5). More particularly, Fig. 2a shows the sense magnetization 230 in absence of the external magnetic field 60 with the core 231 of the vortex configuration being substantially at the center of the sense layer cross-section. In this configuration, the sense layer 23 has a net magnetic moment that is substantially zero (M=0). Fig. 2b shows the sense magnetization 230 in the presence of the external magnetic field 60. The external magnetic field 60 causes the core 231 to move in a direction (shown by the doted arrow) substantially perpendicular to the one of the external magnetic field 60. The displacement of the core 231 results in a net magnetic moment (M ≠ 0) in the sense layer 23. In particular, a displacement of the core 231 towards the right (as shown in Fig. 2b) results in a net magnetic moment M > 0 (positive axis is pointing along the applied field 60) in the sense layer 23, whereas a displacement of the core 231 towards the left (not shown), when the external magnetic field 60 is oriented opposed to the direction shown in Fig. 2b, results in a net magnetic moment M < 0 in the sense layer 23. Fig. 3 shows a hysteresis response (or magnetization curve) to the external magnetic field 60 (Hext, in arbitrary unit) on the sense magnetization 230 (M, in arbitrary unit) of the conventional magnetoresistive sensor element. The full hysteresis loop of a vortex sense magnetization 230 is characterized by a linear increase of magnetization M with the applied magnetic field Hext until the vortex expulsion field is reached at the Hexpl point. At this point the sense magnetization 230 becomes magnetically saturated. To recover the vortex state in the sensing layer 23, one needs to reduce the magnetic field below the nucleation field Hnucl, where the nucleation field Hnucl is the field at which vortex re-forms after high-field vortex expulsion. As long as the applied magnetic field is within the magnitudes corresponding to the expulsion field (+/-Hexpl) of the vortex in the sense magnetization 230, the hysteresis response to the external magnetic field 60 comprises a reversible linear portion corresponding to the movement of the core 231 with the external magnetic field 60. The values and the slope of the linear part of hysteresis loop are strongly dependent on the size of the sense layer 23. The linear and non-hysteretic portion of the magnetization curve facilitates the measurement of small variations of the external magnetic field Hext. In particular, the vortex is characterized by its susceptibility χ, which corresponds to the slope of the linear region of the M(H) loop: χ=∂M/∂Hext The sensitivity S of the magnetoresistive sensor