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CN-116324457-B - Method for measuring an external magnetic field using at least one magnetic storage point

CN116324457BCN 116324457 BCN116324457 BCN 116324457BCN-116324457-B

Abstract

One aspect of the invention relates to a method for measuring an external magnetic field strength by using at least one magnetic storage point, the at least one magnetic storage point comprising-a storage layer (101) having a magnetization (102) switchable between two magnetization directions substantially perpendicular to a layer plane, -a reference layer (107) having a fixed magnetization (106) perpendicular to the layer plane, and-a tunnel barrier layer (105) separating the storage layer (101) and the reference layer (107), characterized in that it comprises at least the steps of continuously applying a plurality of currents or voltages of different magnitudes to the at least one storage point until a switching of the magnetization directions of the storage layer is present to determine a minimum current value for switching the magnetization directions of the storage layer or a minimum voltage value for switching the magnetization directions of the storage layer, -determining the external magnetic field strength to be measured from the minimum switching current value or the minimum switching voltage value.

Inventors

  • RICARDO SOUSA
  • Ivan Lucien Pr e zhbianu

Assignees

  • 法国原子能及替代能源委员会
  • 国家科学研究中心CNRS

Dates

Publication Date
20260505
Application Date
20210824
Priority Date
20200824

Claims (15)

  1. 1. A method (3) for measuring an external magnetic field strength by using at least one magnetic storage point, the at least one magnetic storage point comprising: -a storage layer (101), the storage layer (101) having a magnetization (102) switchable between two magnetization directions substantially perpendicular to the layer plane; -a reference layer (107), the reference layer (107) having a fixed magnetization (106) perpendicular to the layer plane, and -A tunnel barrier layer (105) separating the storage layer (101) and the reference layer (107); the method is characterized in that it comprises at least: A step of continuously applying a plurality of currents or voltages of different magnitudes to the at least one storage point until a switching of the magnetization direction of the storage layer occurs to determine a minimum switching current value of the magnetization direction of the storage layer or a minimum switching voltage value of the magnetization direction of the storage layer, the switching of the magnetization direction of the storage layer being a function of an initial magnetization direction of the storage layer, the switching of the magnetization direction of the storage layer being a switching of the magnetization direction of the storage layer from a configuration parallel to the magnetization direction of the reference layer to a configuration antiparallel to the magnetization direction of the reference layer or from a configuration antiparallel to the magnetization direction of the reference layer to a configuration parallel to the magnetization direction of the reference layer, -A step of determining the external magnetic field strength to be measured from the minimum switching current value or the minimum switching voltage value.
  2. 2. Method (3) for measuring an external magnetic field strength according to claim 1, characterized in that the at least one storage point is a magnetic tunnel junction with out-of-plane magnetization.
  3. 3. Method (3) for measuring the external magnetic field strength according to claim 1, characterized in that the step (36) of determining the external magnetic field strength further comprises at least the sub-steps of: -calculating a difference between the minimum switching current value or the minimum switching voltage value and at least one reference switching current value or reference switching voltage value measured according to the same method under a reference external magnetic field, and -Calculating a magnetic field strength value comprising multiplying the difference between the minimum switching current value or the minimum switching voltage value and the at least one reference switching current value or the reference switching voltage value by a proportionality constant and adding the obtained value to the reference field strength value.
  4. 4. A method (3) for measuring the strength of an external magnetic field according to claim 3, characterized in that the proportionality constant is determined by calculating the ratio of the difference between the calibration switching current value or the calibration switching voltage value and the reference switching current value or the reference switching voltage value to the difference between the strength value of the calibration magnetic field and the strength value of the reference magnetic field.
  5. 5. Method (3) for measuring the external magnetic field strength according to any of claims 1 to 4, characterized in that the step of applying a plurality of currents or voltages of different magnitudes successively until a switching of the magnetization direction of the storage layer occurs comprises the sub-steps of: determining (31) a first resistance of the at least one magnetic storage point, the determining the first resistance comprising measuring a current or a voltage through the magnetic storage point, Comparing (32) the obtained first resistance with a reference resistance value to identify a relative initial magnetization direction of the storage layer with respect to the reference layer, Applying (33) a current or voltage pulse of predefined amplitude and polarity to the at least one magnetic storage point, the polarity facilitating switching of the storage layer to a direction opposite to the relative initial magnetization direction of the storage layer with respect to the reference layer, Determining (34) a second resistance of the at least one magnetic storage point, the determining the second resistance comprising measuring a current or voltage through the magnetic storage point after applying a current or voltage pulse to the magnetic storage point, Comparing (35) the obtained second resistance with a reference resistance value to determine whether a switching of the magnetization direction of the storage layer has occurred, -If switching of the magnetization direction of the storage layer has occurred: The minimum switching current or minimum switching voltage is the current or voltage applied in the previous step of applying a current or voltage pulse to the magnetic storage point, -If switching of the magnetization direction of the storage layer has not occurred, repeating the sub-steps of applying a current or voltage pulse to the magnetic storage point, determining the second resistance and comparing the second resistance with the first resistance with a current or voltage pulse having a modified amplitude different from the predefined amplitude until switching of the magnetization direction of the storage layer occurs.
  6. 6. Method (3) for measuring the external magnetic field strength according to claim 5, characterized in that the predefined amplitude is a low amplitude and the modified amplitude is larger than the low amplitude.
  7. 7. A method (3) for measuring the strength of an external magnetic field according to any of claims 1 to 3, characterized in that the step of applying a plurality of currents or voltages of different magnitudes successively until switching of the magnetization direction of the storage layer occurs comprises the sub-steps of: Applying a current or voltage ramp or periodic signal of a polarity that facilitates switching of the storage layer to a direction opposite to the relative initial magnetization direction of the storage layer with respect to the reference layer until switching of the magnetization direction of the storage layer is detected, -Determining a minimum switching current or a minimum switching voltage amplitude as a function of the total applied time of the current or voltage ramp to obtain a value of the minimum switching current or the minimum switching voltage.
  8. 8. Method (3) for measuring the strength of an external magnetic field according to any of claims 1 to 4, characterized in that it comprises the further step of applying a pulse after detecting the switching of the magnetization direction of the storage layer, the pulse having a polarity facilitating the switching of the storage layer to the relative initial magnetization direction of the storage layer with respect to the reference layer and having a magnitude that is larger than the magnitude of the minimum switching current or the minimum switching voltage.
  9. 9. Method (3) for measuring the external magnetic field strength according to any of claims 1 to 4, characterized in that it uses a plurality of magnetic storage points and in that the step of applying a plurality of currents or voltages of different magnitudes in succession is performed in parallel for the magnetic storage points of the plurality of magnetic storage points.
  10. 10. The method (3) for measuring the external magnetic field strength according to claim 9, characterized in that the step of applying a plurality of currents or voltages of different magnitudes in parallel and consecutively is performed simultaneously for each of the plurality of magnetic storage points, and the minimum switching current value or the minimum switching voltage value of the magnetization direction is the minimum switching current value or the minimum switching voltage value of the magnetization direction of the storage layer of each of the plurality of magnetic storage points.
  11. 11. A magnetic storage point (2), characterized in that it is configured to implement the method for measuring an external magnetic field according to any of the preceding claims, and that it further comprises a controller configured to manage the measurement of the resistance of the magnetic storage point.
  12. 12. A magnetic storage dot (2) according to claim 11, characterized in that it comprises a magnetic tunnel junction with out-of-plane magnetization (or perpendicular anisotropy).
  13. 13. The magnetic storage dot (2) according to claim 11 or 12, characterized in that it further comprises a pulse generator and in that the controller is further configured to manage the pulse generator.
  14. 14. The magnetic storage dot (2) according to claim 11 or 12, characterized in that it has a lateral dimension of less than 200 nm.
  15. 15. A method for determining the relative distance between a magnetic storage point (2) according to any of claims 11 to 14 and a magnetic object (40) generating a magnetic field between 1 mT and 500 mT, the method being characterized in that it comprises the steps of: Measuring the vertical component of the magnetic field at a plurality of points in space to determine the magnitude and direction of the magnetic field according to the method for measuring an external magnetic field of any one of claims 1 to 10, -Calculating the relative distance between the storage layer of the magnetic storage point and the magnetic object from a simulation of the magnetic field generated by the magnetic object.

Description

Method for measuring an external magnetic field using at least one magnetic storage point Technical Field The technical field of the present invention is the field of spintronics, and more particularly magnetic sensors and memories operating using the tunnel magnetoresistance principle. The present invention relates to a method for obtaining linear magnetic field sensor functionality based on the use of at least one magnetic random access memory element, such as, for example, an MRAM (magnetic random access memory) memory. As an example of such an MRAM-type memory, a tunnel junction having perpendicular magnetic anisotropy may be mentioned. Background A perpendicular anisotropic MRAM device with a spin transfer torque based writing mechanism comprises three elements in its simplest form. One such MRAM device is shown in fig. 1A. The MRAM device 1 shown in fig. 1A comprises a magnetic tunnel junction 10, the magnetic tunnel junction 10 comprising a reference layer 107 with a fixed magnetization direction 106, a so-called "free" or "storage" layer 101 with a magnetization direction 102 that is variable between the two states, and a tunnel barrier layer 105 separating the two layers 101 and 107, thereby forming a magnetic tunnel junction. In an advantageous embodiment of the MRAM, the magnetic layers 101 and 107 have perpendicular magnetic anisotropy such that the advantageous magnetization direction is orthogonal to the substrate surface. The most common principle of operation of such an MRAM device 1 is to have a much higher magnetic anisotropy of the reference layer 107 relative to the storage layer 101, so that the magnetic field required to reverse the magnetization direction of the storage layer 101 is much lower than that of the reference layer 107. The magnetization 106 of the reference layer 107 may be considered fixed, e.g. pointing upwards in [ fig. 1A ], while the magnetization 102 of the storage layer 101 may take either of two preferred directions-up or down, as shown in [ fig. 1A ]. The resistive state of MRAM device 1 may be measured by measuring the resistance of magnetic tunnel junction 10. The resistance measured as a function of the magnetic field varies between a minimum resistance when magnetizations 106 and 102 are pointing in the same direction and a maximum resistance state in the opposite direction. An advantageous way to transition from one resistive state to another is to apply a current through such a magnetic tunnel junction 10. At the threshold of current flow, the magnetic moment transferred by the spin bias current is large enough to reverse the magnetization direction 102 of the storage layer 101. The threshold current density jc may be estimated as follows: Where e is electron charge, η is spin bias, μ 0 is vacuum permeability, h-bar is an approximated Planck constant, ms is saturation magnetization, t is the thickness of storage layer 101, and Hk is the magnetic anisotropy of storage layer 101. The magnetic field Heff acting on the reservoir 101 is generated by the sum of the dipole field generated by the reference layer 107 and the external field. Thus, for operation of the memory, the magnetic tunnel junction 10 of the MRAM device 1 will typically have a reference layer 107 designed to reduce this dipole field. This may be performed, for example, by dividing the reference layer 107 into two magnetic sublayers with opposite magnetization directions, as represented in fig. 1B. In [ FIG. 1B ], MRAM device 1B includes a magnetic tunnel junction 10B, the magnetic tunnel junction 10B including a storage layer 101 having a magnetization direction 102, a tunnel barrier layer 105, and a reference layer 107B. The reference layer 107b includes three sublayers, a magnetic sublayer 107 having a fixed magnetization direction 106 (such as the magnetic sublayer 107 of MRAM device 10 of fig. 1), a magnetic sublayer 109 having a magnetization direction 110, and an antiferromagnetically coupling sublayer 108 for coupling the magnetic sublayers 107 and 109 to each other according to RKKY ("Ruderman-Kittel-Kasuya-Yosida" coupling). RKKY ("Ruderman-Kittel-Kasuya-Yosida") coupling is the interaction between the magnetic moments of two magnetic layers separated by a nonmagnetic layer. This antiferromagnetic RKKY coupling is ensured by the presence of a nonmagnetic spacer layer between the two coupling magnetic layers. By varying the thickness of the nonmagnetic spacer layer, the RKKY coupling between the two magnetic layers oscillates and changes from ferromagnetic to antiferromagnetic. This phenomenon is described in Parkinson et al, physical review bulletins (Phys. Rev. Lett.) (Vol 67, page 3598, 1991). By introducing an antiferromagnetic coupling layer 108 (e.g., made of Ru, ir, ta or Mo) between the two magnetic sublayers 107 and 109 such that the two sublayers have opposite magnetization directions, a synthetic antiferromagnetic structure ("SAF") is created. Such a magnetic tunnel junction 1