Method for measuring an external magnetic field using at least one magnetic storage point

Abstract

One aspect of the invention relates to a method for measuring the strength of an external magnetic field 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 the 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); the method is characterized in that it comprises at least: - the step of continuously applying a plurality of currents or voltages of different amplitudes to at least one storage point until a switch of the magnetization direction of the storage layer exists to determine a minimum current value or a minimum voltage value for switching the magnetization direction of the storage layer; - the step of determining the external magnetic field strength to be measured based on the minimum switching current value or the minimum switching voltage value.

Description

Technical Field

[0001] The technical field of this invention is spintronics, and more specifically, magnetic sensors and memories that operate using the tunneling magnetoresistance principle.

[0002] This invention relates to a method for obtaining the functionality of a linear magnetic field sensor based on the use of at least one magnetic random access memory element, such as an MRAM (Magnetic Random Access Memory) type memory. As an example of such an MRAM type memory, a tunnel junction with perpendicular magnetic anisotropy can be mentioned. Background Technology

[0003] A vertically anisotropic MRAM device with a spin-torque-based write mechanism comprises three elements in its simplest form. Figure 1A The image shows one such MRAM device.

[0004] [ Figure 1A The MRAM device 1 shown in the figure includes a magnetic tunnel junction 10, which includes a reference layer 107 with a fixed magnetization direction 106, a so-called "free" or "storage" layer 101 with a variable magnetization direction 102 between two states, and a tunnel barrier layer 105 separating the two layers 101 and 107, thereby forming a magnetic tunnel junction.

[0005] In an advantageous embodiment of this MRAM, magnetic layers 101 and 107 have perpendicular magnetic anisotropy, such that the advantageous magnetization direction is orthogonal to the substrate surface. The most common operating principle of this MRAM device 1 is that the reference layer 107 has a much higher magnetic anisotropy relative to the storage layer 101, such 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 can be considered fixed, for example, in […]. Figure 1A The magnetization 102 of the storage layer 101 can take either of two preferred directions—upward or downward, as shown in […]. Figure 1A As shown in the image.

[0006] The resistance state of MRAM device 1 can be measured by measuring the resistance of magnetic tunnel junction 10. The resistance measured as a function of the magnetic field varies between the minimum resistance state when magnetization 106 and 102 are in the same direction and the maximum resistance state when they are in opposite directions.

[0007] A favorable method for transitioning from one resistive state to another is by applying a current through this magnetic tunnel junction 10. At the threshold of current flow, the magnetic moment transmitted by the spin bias current is large enough to reverse the magnetization direction 102 of the storage layer 101. The threshold current density jc can be estimated as follows:

[0008]

[0009] Where e is the electron charge, η is the spin bias, μ0 is the free permeability, h-bar is the reduced Planck constant, Ms is the 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 storage layer 101 is generated by the sum of the dipole field generated by reference layer 107 and the external field. Therefore, for memory operation, the magnetic tunnel junction 10 of MRAM device 1 will typically have a reference layer 107 designed to reduce this dipole field. For example, this can be done by dividing reference layer 107 into two magnetic sublayers with opposite magnetization directions, such as […]. Figure 1B As indicated in [].

[0010] exist[ Figure 1B In the MRAM device 1b, a magnetic tunnel junction 10b is included. The magnetic tunnel junction 10b includes a storage layer 101 with 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 with a fixed magnetization direction 106 (such as the magnetic sublayer 107 of the MRAM device 10 in [Figure 1]), a magnetic sublayer 109 with a magnetization direction 110, and an antiferromagnetic coupling sublayer 108 for coupling the magnetic sublayers 107 and 109 to each other according to RKKY (“Ruderman-Kittel-Kasuya-Yosida”). RKKY (“Ruderman-Kittel-Kasuya-Yosida”) coupling is the interaction between the magnetic moments of two magnetic layers separated by a non-magnetic layer. This antiferromagnetic RKKY coupling is ensured by the presence of a non-magnetic spacer layer between the two coupled magnetic layers. By varying the thickness of the nonmagnetic spacer layer, the RKKY coupling oscillation between the two magnetic layers transitions from ferromagnetic to antiferromagnetic. This phenomenon is described in the following literature: Parkin et al., Physical Review Letters (Vol. 67, p. 3598, 1991). A synthetic antiferromagnetic structure (“SAF”) is generated by introducing an antiferromagnetic coupling layer 108 (made of, for example, Ru, Ir, Ta, or Mo) between the two magnetic sublayers 107 and 109, such that the two sublayers have opposite magnetization directions. This magnetic tunnel junction 10b has a higher […]. Figure 1A The dipole field of the magnetic tunnel junction 10 in the image is lower.

[0011] The aforementioned MRAM devices 1 and 1b store information about the magnetization direction 102, which can be read through the resistance states of magnetic tunnel junctions 10 and 10b, respectively. Switching from one state to another can be performed by applying a field or current above a threshold. The characteristics of the transfer curve are those of the hysteresis curve, where high-resistance and low-resistance states are possible within certain field or current ranges, and only one resistance state is possible above the field or current switching threshold. A “single resistance state” refers to a high, medium, or low state; each resistance state is not defined by a single resistance value but by a set of resistance values, such as a resistance range.

[0012] On the other hand, a magnetic field sensor with linear characteristics is based on a magnetic configuration in which the magnetization of the reference layer 107b and the magnetization of the detection layer 101 are orthogonal to each other. This is in [ Figure 2 As illustrated in the figure, the detection layer 101 may have a magnetization direction 102 that is orthogonal to the magnetization direction of the reference layer 107b in the absence of a field (white arrow). Figure 2 The magnetic field sensor 1c shown in the figure may include only the reference sublayer 107 instead of SAF (a composite antiferromagnet corresponding to the multilayer reference layer 107b).

[0013] For a field applied in the vertical direction, i.e., perpendicular to the plane of the layer, magnetization can rotate between parallel alignment and antiparallel alignment with reference layer 107b. Starting from a direction orthogonal to equilibrium, the conductance of the magnetic tunnel junction 10c of the magnetic field sensor 1c varies with cos(θ), where θ is the relative angle between the magnetization direction of reference layer 107b and the magnetization direction of detection layer 101. For a field applied along the magnetization axis of reference layer 107b, the resistance varies almost linearly with the applied field. Techniques can be used to further linearize the output of the field sensor 1c, for example, by combining several sensors 1c with opposite reference layer 107b orientations in a full Wheatstone bridge or half Wheatstone bridge arrangement. However, when no magnetic field is applied, each sensor always has an orthogonal magnetization direction between detection layer 101 and reference layer 107 or 107b, unlike memories where the magnetization directions of detection layer 101 and reference layer 107 or 107b must be aligned along the same axis.

[0014] Because the alignment requirements for memory and sensor operation differ so much for magnetization with zero external field, the goal of creating sensors and memories from the same material stack necessitates a trade-off between the two functionalities. The result is a degradation in the co-integration of both types of devices on the same substrate, based on the same magnetic stack. Summary of the Invention

[0015] This invention provides a solution to the previously discussed problems by allowing the functionality of storage points with vertical interface anisotropy to be extended beyond their information storage function, in order to also obtain linear magnetic field sensor functionality using the same magnetization optimized for memory operation.

[0016] Therefore, one aspect of the present invention relates to a method for measuring the strength of an external magnetic field using at least one magnetic storage point, the at least one magnetic storage point comprising:

[0017] - A storage layer having magnetization that can be switched between two magnetization directions substantially perpendicular to the layer plane;

[0018] - A reference layer having a fixed magnetization perpendicular to the layer plane; and

[0019] - A tunnel barrier layer that separates the storage layer and the reference layer;

[0020] The method is characterized by including at least:

[0021] - The step of continuously applying multiple currents or voltages of different amplitudes to the at least one storage point until a switching of the magnetization direction of the storage layer occurs to determine the minimum switching current value or the minimum switching voltage value of the magnetization direction of the storage layer, as a function of the initial magnetization direction of the storage layer, wherein the switching of the magnetization direction of the storage layer is a switch 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 a switch from a configuration antiparallel to the magnetization direction of the reference layer to a configuration parallel to the magnetization direction of the reference layer.

[0022] - The steps to determine the strength of the external magnetic field to be measured based on the minimum switching current value or the minimum switching voltage value.

[0023] "Switching" refers to switching the magnetization direction of the storage layer from a configuration parallel to the reference layer to a configuration antiparallel to the reference layer, or vice versa, as a function of the initial magnetization direction.

[0024] Since the magnetization directions of the reference layer and the storage layer are orthogonal to the layer plane, the term "external magnetic field strength" refers to the strength of the vertical component of the external magnetic field, that is, the strength of the component along the axis of the magnetization direction of the reference layer and the storage layer.

[0025] The term "minimum switching current or minimum switching voltage" refers to the minimum current or voltage applied to the magnetic tunnel junction after which the magnetization direction of the storage layer has been switched.

[0026] The present invention allows the strength of the vertical component of an external magnetic field to be obtained from the minimum switching voltage or minimum switching current at the magnetic storage point, which is obtained by continuously applying current or voltage of varying amplitudes. "Continuously applying multiple currents or voltages" means applying currents or voltages sequentially to each other, whether the application is discrete or continuous. Therefore, for example, voltage or current pulses and voltage or current ramps are included in the continuous application of multiple currents or voltages. The present invention advantageously utilizes the fact that the current and voltage vary substantially linearly with respect to the applied external magnetic field, thereby achieving a voltage difference that is substantially linearly proportional to the strength of the external magnetic field.

[0027] Since existing magnetic storage devices already have read and write components, the present invention makes it advantageous to reuse these components to realize the functionality of magnetic field strength sensing.

[0028] With this invention, sensor properties, such as sensitivity and field range, can be adjusted simply by modifying the sensor region (along the plane of the layer) without requiring modification of the material stack.

[0029] Therefore, the present invention enables the realization of both information storage and magnetic field sensing functions in a smaller overall size using the same magnetic stack without compromising storage and sensing functionality.

[0030] Advantageously, the present invention can meet various sensor specifications by simply adjusting the lateral dimensions of the storage points.

[0031] In addition to the features just discussed in the preceding paragraphs, a method for measuring the strength of an external magnetic field according to one aspect of the invention may have one or more of the following supplementary features, considered individually or in combination of all technically possible features:

[0032] - The at least one storage point is a magnetic tunnel junction with out-of-plane magnetization.

[0033] - The steps for determining the strength of the external magnetic field include at least the following sub-steps:

[0034] Calculate the 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 under a reference external magnetic field using the same method, and

[0035] The calculation of the magnetic field strength value includes multiplying the 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 by a proportionality constant, and adding the obtained value to the strength value of the reference field.

[0036] - The proportionality constant is determined by calculating the ratio of the difference between the calibration switching current value or calibration switching voltage value and the reference switching current value or reference switching voltage value to the ratio of the strength value of the calibration magnetic field to the strength value of the reference magnetic field. This makes it particularly advantageous to use the linearity of the ratio of current or voltage to the applied magnetic field strength to determine the value of the applied current external magnetic field.

[0037] The step of continuously applying multiple currents or voltages of varying amplitudes until a switch in the magnetization direction of the storage layer occurs includes the following sub-steps:

[0038] o Determine a first resistance of the at least one magnetic storage point, wherein determining the first resistance includes measuring the current or voltage passing through the magnetic storage point.

[0039] The obtained first resistance value is compared with the reference resistance value to identify the relative initial magnetization direction of the storage layer with respect to the reference layer.

[0040] o applies a current or voltage pulse of predefined amplitude and polarity to the at least one magnetic storage point, the polarity of which causes the storage layer to switch to a direction opposite to the relative initial magnetization direction of the storage layer relative to the reference layer.

[0041] o Determine a second resistance of the at least one magnetic storage point, wherein determining the second resistance includes measuring the current or voltage passing through the magnetic storage point after a current or voltage pulse is applied to the magnetic storage point.

[0042] The obtained second resistance value is compared with the reference resistance value to determine whether a switch in the magnetization direction of the storage layer has occurred.

[0043] o If a switch in the magnetization direction of the storage layer has already occurred:

[0044] -Minimum switching current or minimum switching voltage is the current or voltage applied in the preceding step of applying a current or voltage pulse to the magnetic storage point.

[0045] If the switching of the magnetization direction of the storage layer has not yet occurred, the sub-steps of applying current or voltage pulses to the magnetic storage point, determining the second resistance, and comparing the second resistance with the first resistance are repeated using current or voltage pulses with modified amplitudes that are different from the predefined amplitude, until the switching of the magnetization direction of the storage layer occurs.

[0046] - The predefined amplitude is low, and the modified amplitude is greater than this low amplitude. This allows for lower power consumption compared to, for example, starting with a high amplitude current or voltage and then selecting a lower amplitude. The switching threshold in this case is determined by the first amplitude without switching magnetization.

[0047] The step of continuously applying multiple currents or voltages of varying amplitudes until a switch in the magnetization direction of the storage layer occurs includes the following sub-steps:

[0048] A current or voltage ramp or periodic signal of polarity is applied until a switch in the magnetization direction of the storage layer is detected, which prompts the storage layer to switch to a direction opposite to its relative initial magnetization direction with respect to the reference layer.

[0049] The magnitude of the minimum switching current or minimum switching voltage is determined as a function of the total application time of the current or voltage ramp to obtain the value of the minimum switching current or minimum switching voltage.

[0050] - A method for measuring the strength of an external magnetic field includes an additional step of applying a pulse after detecting a switch in the magnetization direction of the storage layer. This pulse has a polarity that promotes the switching of the storage layer to the relative initial magnetization direction of the storage layer with respect to a reference layer and has an amplitude greater than that of the minimum switching current or minimum switching voltage.

[0051] - The method for measuring the strength of an external magnetic field uses multiple magnetic storage points and performs the steps of continuously applying multiple currents or voltages of different amplitudes in parallel to the magnetic storage points among the multiple magnetic storage points.

[0052] - For each of multiple magnetic storage points, the steps of simultaneously and continuously applying multiple currents or voltages of different amplitudes in parallel are performed, and the minimum switching current value or minimum switching voltage value in the magnetization direction is the minimum switching current value or minimum switching voltage value in the magnetization direction of the storage layer of each of the multiple magnetic storage points. This in particular allows the memory to be reset to its initial state, i.e., the state before measurement, when necessary.

[0053] Another aspect of the invention relates to a magnetic storage point, characterized in that it is configured to implement a method for measuring an external magnetic field according to the invention, and it further includes a controller configured to manage the measurement of the resistance of the magnetic storage point.

[0054] In addition to the features just discussed in the preceding paragraphs, a method for measuring the strength of an external magnetic field according to one aspect of the invention may have one or more of the following supplementary features, considered individually or in combination of all technically possible features:

[0055] - Magnetic storage points include magnetic tunneling structures with out-of-plane magnetization (or perpendicular anisotropy).

[0056] - The magnetic storage point also includes a pulse generator, and the controller is also configured to manage the pulse generator.

[0057] - Magnetic storage points have a lateral dimension of less than 200 nm.

[0058] Another aspect of the invention relates to a method for determining the relative distance between a magnetic storage point according to one aspect of the invention and a magnetic object that generates a magnetic field between 1 mT and 500 mT, the method being characterized by comprising the following steps:

[0059] -The method according to the invention for measuring an external magnetic field measures the vertical component of the magnetic field at multiple points in space to determine the amplitude and direction of the magnetic field.

[0060] - The relative distance between the storage layer of the magnetic storage point and the magnetic object is calculated based on the simulation of the magnetic field generated by the magnetic object.

[0061] A better understanding of the invention and its various applications will be gained by reading the following description and reviewing the accompanying drawings. Attached Figure Description

[0062] The accompanying drawings are provided for illustrative purposes and are by no means intended to limit the invention.

[0063] Figures 1a and 1b show schematic representations of MRAM devices according to the prior art.

[0064] - Figure 2 A schematic representation of a TMR magnetic field sensor according to the prior art is shown.

[0065] - Figure 3 A schematic representation of a method for measuring magnetic field strength according to an embodiment of the present invention is shown.

[0066] - Figure 4 A schematic representation of an MRAM device for implementing the method according to the invention is shown.

[0067] - Figure 5 A resistance state diagram of the MRAM device according to the present invention is shown.

[0068] - Figure 6 A diagram showing the boundaries between resistive states in an MRAM device is shown.

[0069] - Figure 7 A graph is shown representing the observed nonlinearity as a function of the lateral dimension of the MRAM device.

[0070] - Figure 8 Multiple resistance state diagrams for different lateral dimensions of MRAM devices are shown.

[0071] - Figure 9 A schematic representation of the magnetic field measurement method according to the present invention is shown.

[0072] - Figure 10A graph is shown representing the current flowing through the MRAM device according to the invention when a periodic signal is applied. Detailed Implementation

[0073] The accompanying drawings are provided for illustrative purposes and are by no means intended to limit the invention.

[0074] Unless otherwise indicated, the same element appearing in different figures has a unique reference numeral.

[0075] [ Figure 3 The diagram illustrates a method for measuring magnetic field strength according to a first embodiment of the present invention.

[0076] The method 3 for measuring the strength of an external magnetic field according to the present invention is performed by using at least one magnetic storage point, which includes a magnetic tunnel junction with out-of-plane magnetization. Reference will be repeated below to the accompanying drawings illustrating a prior art MRAM device. The magnetic tunnel junction of the MRAM device used to implement method 3 includes at least:

[0077] - Storage layer 101, having magnetization 102 that is switchable between two magnetization directions substantially perpendicular to the plane of the layer;

[0078] - Reference layer 107, which has a fixed magnetization 106 perpendicular to the plane of the layer; and

[0079] -Tunnel barrier layer 105 that separates storage layer 101 and reference layer 107.

[0080] "Basically vertical" means a direction that deviates from the direction perpendicular to the plane of the layer by ±15 degrees.

[0081] In a preferred embodiment, the magnetic tunnel junction of the MRAM device used to implement method 3 includes SAF 107b, which has two magnetic layers 107 and 109 that are antiferromagnetically coupled through a coupling spacer layer 108, so as to have less dipole field radiated by the MRAM device and thus less interference to the performance of magnetic field measurements.

[0082] In a first embodiment of the invention, method 3 for measuring the vertical component strength of a magnetic field outside an MRAM device includes a first step 31 of determining a first resistance of a magnetic storage point. This determination can be performed in a conventional manner, for example, by measuring the voltage or current passing through the magnetic storage point.

[0083] Method 3 then includes step 32 of comparing the obtained first resistance with a reference resistance value to identify the relative initial magnetization direction of storage layer 101 relative to reference layer 107 or SAF 107b. Reference layer 107 or SAF 107b will be referred to in the same manner as "reference layer 107".

[0084] Step 32, which compares the measured resistance with at least one reference resistance, allows the initial relative magnetization direction of storage layer 101 with respect to reference layer 107 to be determined; that is, whether the alignment is parallel or antiparallel. A high resistance relative to a resistance threshold is considered an antiparallel alignment of the magnetization directions between storage layer 101 and reference layer 107. Conversely, a low resistance relative to a resistance threshold is considered a parallel alignment of the magnetization directions 102 between storage layer 101 and reference layer 107. Therefore, the magnetization direction 102 of storage layer 101 relative to the magnetization direction 106 of reference layer 107 can be determined.

[0085] In method 3, measuring the first resistance value is used to determine whether the magnetization direction 102 of the storage layer 101 has been switched; that is, whether the magnetization direction 102 of the storage layer 101 has changed from an antiparallel alignment with the magnetization direction 106 of the reference layer 107 to a parallel state, or conversely, from a parallel alignment to an antiparallel state. Determining the relative magnetization direction of the storage layer 101 with respect to the reference layer 107 in another manner does not deviate from the present invention.

[0086] Method 3 includes step 33 of applying a voltage or current pulse of predefined amplitude and polarity to a magnetic storage point, the polarity of which facilitates switching of the storage layer to a direction opposite to the relative initial magnetization direction 102 of the storage layer 101 relative to the reference layer 107. This can be performed in a manner conventionally used for writing to memory. "Facilitates switching of the storage layer to the opposite polarity" means positive or negative polarity as a function of the measured initial magnetization direction 102 (i.e., as a function of the measured initial resistance), and allows switching of the magnetization direction 102 of the storage layer 101. This is in [ Figure 5 [This is represented in the text].

[0087] [ Figure 5 The diagram shows the resistance state of an MRAM device. Specifically, it illustrates the relationship between a pulse voltage in volts and a magnetic field in ohms, as well as the resistance versus these two axes. Therefore, by […] Figure 5 Applying a positive polarity pulse as indicated in [ ] will attempt to make the alignment antiparallel, that is, to switch from low resistance to high resistance. Conversely, by [ ] Figure 5 When a negative polarity pulse is applied as indicated in the diagram, it will attempt to align the components, that is, to switch from high resistance to low resistance.

[0088] Method 3 includes a step 34 of determining a second resistance of the magnetic storage point, which involves measuring the voltage or current passing through the magnetic storage point after a voltage or current pulse is applied to it in step 33. This step can be performed in the same manner as step 31 of Method 3.

[0089] In step 35 of method 3, the second resistor determined in step 34 is compared with the same resistance threshold used in step 32 to determine whether a switch of the magnetization direction 102 of the storage layer 101 has occurred.

[0090] If the switching of the magnetization direction 102 of the storage layer 101 has not yet occurred, then step 37, which modifies the amplitude of the voltage or current applied in step 33, is performed. Then, the method is repeated in step 33, applying a voltage or current pulse with the same polarity as previously determined but with the modified amplitude as defined in step 37, to the magnetic storage point.

[0091] Repeat steps 33 to 35 until the magnetization direction 102 of storage layer 101 is switched.

[0092] Preferably, all pulses have the same time width. In fact, variations in pulse width during the switching sequence degrade field resolution, so the pulse width should not vary significantly throughout the pulse sequence. The pulse width can be the same value used for memory, typically greater than but close to 1 ns. Larger pulse widths are also possible, but this would significantly increase the total time required to perform measurement method 3.

[0093] If a switch in the magnetization direction 102 of the storage layer 101 has been detected in step 35, then the minimum switching current or minimum switching voltage is the current or voltage applied in step 33 prior to applying a voltage or current pulse to the magnetic storage point.

[0094] This is in [ Figure 5 This is represented in [ ], where a series of pulses are applied to the MRAM device. The change in the magnetization direction 102 of the storage layer 101 is detected when the pulses have sufficient amplitude and correct polarity to switch the magnetization direction 102 of the storage layer 101. For example, in [ ] Figure 5 In this context, when the external magnetic field is approximately 300 Oe and the initial alignment of the magnetization directions between storage layer 101 and reference layer 107 is parallel (i.e., when the measured resistance is low), a minimum amplitude of approximately 0.23 volts and a positive polarity are required to switch the magnetization direction 102 of storage layer 101, thus making the alignment antiparallel. Conversely, if the initial alignment of the magnetization directions between storage layer 101 and reference layer 107 is antiparallel (i.e., when the measured resistance is high), a minimum amplitude of approximately 0.38 volts and a negative polarity are required to switch the magnetization direction 102 of storage layer 101, thus making the alignment parallel.

[0095] Preferably, to achieve the lowest power consumption, it will start with a predefined low amplitude (e.g., close to 0), and the amplitude will increase with each new pulse. This allows for the consumption of less energy compared to, for example, starting with a high amplitude current or voltage and then selecting a lower amplitude.

[0096] When a switch in the magnetization direction 102 of the storage layer 101 has been detected in step 35, step 36 is performed to determine the strength of the external magnetic field based on the value of the minimum switching current or minimum switching voltage of the magnetization direction 102 of the storage layer 101. This determination step is achieved by leveraging the fact that the current and voltage vary substantially linearly with respect to the applied external magnetic field. Therefore, the strength of the vertical component of the magnetic field can be determined by calculating the difference between the value of the minimum switching voltage or minimum switching current obtained in step 35 and at least one reference switching current or reference switching voltage value measured under a reference external magnetic field using the same method. This difference is then multiplied by a proportionality constant and added to the strength value of the orthogonal component of the reference field. For example, the reference field can be zero. In this example, the difference between the amplitude of the minimum switching voltage or minimum switching current and the amplitude of the minimum reference voltage or minimum reference current, multiplied by the proportionality constant, equals the strength value of the orthogonal component of the external magnetic field during the measurement.

[0097] The proportionality constant can be determined by calculating the ratio of the difference between the calibration switching voltage or current value and the reference switching voltage or current value to the ratio of the difference between the strength value of the calibration magnetic field and the strength value of the reference magnetic field. Therefore, the proportionality constant is determined using the linearity of the voltage or current change relative to the applied external magnetic field by performing a slope calculation before any measurement. With the aid of this slope calculation, by considering two magnetic fields: the reference field and the calibration field, the proportionality constant is obtained, which then allows the minimum voltage or minimum current of the magnetization direction 102 of the switched storage layer 101 to be correlated with the external magnetic field. Therefore, the strength value of the vertical component of the external magnetic field can be determined based on the value of the minimum switching current or minimum switching voltage.

[0098] Measurement accuracy can be improved by repeatedly applying Method 3 and averaging the continuous minimum switching current or minimum switching voltage values. This can be done by continuously applying Method 3 to determine the minimum switching current or minimum switching voltage values ​​for two switching directions of the storage layer: from low resistance to high resistance and from high resistance to low resistance. By averaging the minimum switching current or minimum switching voltage values ​​in each direction and then subtracting the average of each of the two minimum switching current or minimum switching voltage values ​​under zero external field, a voltage difference is obtained that is substantially linearly proportional to the amplitude of the external field. This improves external magnetic field measurement, but requires a longer time and higher power consumption.

[0099] In the second embodiment, the value of the minimum switching voltage or minimum switching current is determined by applying a voltage or current ramp (instead of a pulse) of polarity until a switch in the magnetization direction of the storage layer is detected, the polarity of which facilitates the switching of the storage layer to a direction opposite to the relative initial magnetization direction of the storage layer relative to the reference layer. An alternative to this ramp could be any periodic signal comprising a monotonically rising portion followed by a monotonically falling portion. The amplitude of the minimum switching voltage or minimum switching current is then determined as a function of the total application time of the voltage or current ramp to obtain a value of the minimum switching voltage or minimum switching current knowing the ramp slope. In this second embodiment, steps 33, 34, 35, and 37 are replaced by applying a voltage or current ramp and detecting a switch in the magnetization direction 102 of the storage layer 101. Other steps 31, 32, and 36 remain unchanged and are necessary for method 3 according to the second embodiment of the invention.

[0100] A continuous change in the measured voltage is caused by a current ramp or periodic signal. When magnetization is reversed, this change is very rapid, on the order of a nanosecond, due to the change in resistance. To detect the switching of magnetization direction, a high-pass filter can be used, which blocks low-frequency signal changes (ramp changes) and allows high-frequency (magnetization changes) signals to pass through.

[0101] For example,[ Figure 10 The diagram shows the current flowing through the MRAM device when a periodic signal is applied according to a second embodiment of the present invention. Figure 10 In this process, a triangular voltage signal is applied, which includes a monotonically rising part and a monotonically falling part. Figure 10 The image shows an oscilloscope trace representing the current flowing through the MRAM device. The horizontal axis represents time, for example, at... Figure 10 In the graph, each division represents 2 microseconds, while the vertical axis represents voltage, for example, in... Figure 10 In the diagram, each division represents 20 millivolts. The values ​​on the x and y axes are unrestricted. Therefore, the x-axis indirectly represents the current flowing through the MRAM device. For example, in the case where the oscilloscope is configured with an internal impedance of 50 ohms, this current can be calculated as 50 ohms multiplied by the voltage measured at the oscilloscope. The exact current value depends on the resistance of the MRAM device and the applied voltage. Figure 10 The voltage applied to the MRAM device is a triangular wave, which can be adjusted in amplitude and offset to trigger junction switching. Figure 10In part A, the applied external magnetic field promotes a parallel configuration of the storage layer 101, while in part B, the applied external magnetic field promotes an antiparallel configuration of the storage layer 101. The switching thresholds i to l, i.e., the change in resistance state, thus increase or decrease as a function of the applied magnetic field. Note that the monotonically decreasing portion between switching thresholds j and k is greater in part A than in part B, because the switching threshold k in part B is shifted upwards by the slope due to the presence of the magnetic field promoting the antiparallel configuration. Similarly, point j in part B has been shifted upwards by the slope, i.e., it is located higher on the vertical axis. At different voltage thresholds, the device changes its resistance state at each switching point i to k, where the transition interval is indicated by the discontinuity of the slope. Therefore, Figure 10 The resistance state does not change significantly, but there is a transition range at the switching threshold.

[0102] To apply a periodic signal, another method can be used. For example, if... Figure 5 If the switching voltage or current thresholds for magnetization of each polarity, as represented in [ ], are symmetrical (i.e., their norms are equal), then the time taken for high resistance is the same as the time taken for low resistance, and the integral over a complete cycle yields a zero DC voltage. If the switching voltage or current thresholds for each polarity are asymmetrical (i.e., if the absolute values ​​of the voltage or current thresholds for the negative polarity are different from those for the positive polarity), then the DC value obtained for the integral over a complete cycle is non-zero and proportional to the asymmetry of the thresholds for the different polarities, then it is permissible to use, for example, [ ] Figure 5 The external field is calculated using the resistance state diagram in the diagram.

[0103] Method 3 according to the first or second embodiment of the present invention may further include an additional step of applying a pulse after detecting a switch in the magnetization direction 102 of the storage layer 101, the pulse having a polarity that promotes the switching of the storage layer 101 to the relative initial magnetization direction of the storage layer 101 with respect to the reference layer 107, and having an amplitude greater than that of the minimum switching current or minimum switching voltage, so as to restore the initial state of the magnetic storage point without affecting its information storage functionality.

[0104] [ Figure 4 ] indicates the MRAM device 2 used to implement method 3 according to the first embodiment of the present invention.

[0105] MRAM device 2 includes a magnetic tunnel junction 10c as described above, a controller 20, and a pulse generator 30. The controller 20 is configured to manage the measurement of the resistance of the magnetic tunnel junction 10c in steps 31 and 34 of method 3 according to a first embodiment of the invention. "Managing" the resistance measurement means obtaining all the steps required for the resistance measurement via the controller 20, including, for example, depending on the controller used, sending a resistance measurement request signal and receiving a resistance measurement signal, such as receiving the voltage or current value applied to the magnetic tunnel junction. The controller 20 is also configured to manage the pulse generator 30, particularly the amplitude of the voltage or current pulses, and to perform at least some of the calculations included in method 3, such as determining the value of the magnetic field strength, preferably all the calculations included in method 3.

[0106] The size of the MRAM device 2 must allow sensor operation to be optimized for sensor linearity and field range. This is made possible by having a lateral dimension of the storage layer 101 of less than 200 nm. "Large dimension" refers to, for example, the diameter of a circle, the major axis of an ellipse, the length or width of the layer plane, as a function of the geometry of the magnetic stack. For these lateral dimensions less than 200 nm, the linearity of the switching voltage relative to the external magnetic field is improved. Lateral dimensions greater than 200 nm show a significant deviation from linear correlation, exhibiting significant nonlinear behavior at 500 nm or higher, such as […]. Figure 8 As indicated in [the document].

[0107] Ideally, the lateral size of the detection layer should be less than 60 nm to ensure that the linearity error rate is less than 5*10. -3 %,like[ Figure 7 As indicated in [the document].

[0108] The minimum switching voltage or minimum switching current is modified as a function of the lateral size of the storage point. This is in [ Figure 6 The figures are shown in the diagram, where two figures represent the minimum switching voltages (in volts) for two different diameters (one 50 nm and one 200 nm). The lower limit size is determined by the area required for magnetization 102 of storage layer 101 perpendicular to the layer plane.

[0109] At measurement time t m The conditions for ensuring the vertical stability of the storage layer (or the detection layer used by the sensor) 102 during this period are as follows:

[0110]

[0111] Where τ0 is the time of the switching attempt (switching pulse), usually estimated to be around 1 ns, and Δ is the thermal stability coefficient, which corresponds to the energy and heat required to reverse the magnetization direction (kJ / T). BThe ratio of T to K. The thermal stability of the storage point can be calculated based on the effective anisotropy Keff, and by convention, Keff has a positive value for perpendicular magnetic anisotropy. In the case of perpendicular magnetic anisotropy to the interface, Keff can be calculated based on the surface anisotropy (Ks), layer thickness (t), and saturation magnetization. For magnetic elements, the thermal stability coefficient can be estimated as follows:

[0112]

[0113] For common values ​​of vertical magnetic interface anisotropy, a typical storage layer 102 is approximately 1 to 2 nm, adjacent to a tunnel barrier providing vertical interface anisotropy. The typical lower limit for the lateral dimension is set at 15 to 20 nm for minimum stability requirements of memory operation. Below 20 nm, the thermal stability of the cell decreases, leading to a reduction in switching voltage, a decrease in linear range, and changes in pulse voltage and sensitivity. Therefore, the lateral dimension can be adjusted to meet different sensor specifications.

[0114] Method 3 according to the first or second embodiment can be used with a plurality of MRAM devices. When method 3 is used with a plurality of MRAM devices, current or voltage pulses, current or voltage ramps, or periodic current or voltage signals are applied in parallel to different MRAM devices. This application can be simultaneous (simultaneously applied to a plurality of MRAM devices in parallel) or sequential (applied individually to each MRAM device). For example, a single controller 20 can manage the application of method 3 to all MRAM devices. In the case of simultaneous application to a plurality of MRAM devices, the amplitude of the current or voltage is modified until switching of all managed MRAM devices is achieved.

[0115] Another object of the present invention relates to using method 3 to measure the magnetic field strength at at least one storage point to determine the relative distance between the storage point and a magnetic object that generates a magnetic field from 1 mT to 500 mT. This is in [ Figure 9 The magnetic storage point 10 is represented in the image, where a magnetic object 40 is placed at a certain distance from the magnetic storage point 10. The magnetic storage point 10 of method 3 is capable of measuring the external magnetic field generated by the magnetic object 40.

[0116] With a general understanding of the geometry of the magnetic object 40, the relative vertical and horizontal distances between the object 40 and the storage layer 102 of the storage point 10 can be determined. For this purpose, it is necessary to determine the vertical component of the magnetic field generated by the relative scanning motion of the magnetic object 40 through the storage layer 102. Method 3 for measuring the magnetic field strength is applied at several points in space, ideally at all points in space, to determine the amplitude and direction of the magnetic field generated by the magnetic object 40. Based on a simulation of the magnetic field generated by the magnetic object 40, the measured values ​​can be used to calculate the relative distance between the storage point 10 and the magnetic object 40. Detection can be performed using one or more storage points 10 arranged with different relative orientations to detect various components of the magnetic field generated by the object 40. Multiple storage points can be arranged as probes to improve detection accuracy through interpolation or by adapting to the expected physical behavior of the system.

Claims

1. A method (3) for measuring the strength of an external magnetic field using at least one magnetic storage point, said at least one magnetic storage point comprising: - Storage layer (101), the storage layer (101) having magnetization (102) that can be switched between two magnetization directions substantially perpendicular to the layer plane. - A reference layer (107) having a fixed magnetization (106) perpendicular to the layer plane; and - A tunnel barrier layer (105) that separates the storage layer (101) and the reference layer (107). The method is characterized in that it includes at least: - The step of continuously applying multiple currents or voltages of different amplitudes to the at least one storage point until a switching of the magnetization direction of the storage layer occurs to determine the minimum switching current value or the minimum switching voltage value of the magnetization direction of the storage layer, as a function of the initial magnetization direction of the storage layer, wherein the switching of the magnetization direction of the storage layer is a switch 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 a switch from a configuration antiparallel to the magnetization direction of the reference layer to a configuration parallel to the magnetization direction of the reference layer. - The steps to determine the strength of the external magnetic field to be measured based on the minimum switching current value or the minimum switching voltage value.

2. The method (3) for measuring the strength of an external magnetic field according to claim 1, characterized in that, The at least one storage point is a magnetic tunnel junction with out-of-plane magnetization.

3. The method (3) for measuring the strength of an external magnetic field according to claim 1, characterized in that, The step (36) of determining the external magnetic field strength includes at least the following sub-steps: - Calculate the 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 under a reference external magnetic field using the same method, and - Calculate the magnetic field strength value by multiplying the 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 by a proportionality constant, and adding the obtained value to the reference field strength value.

4. The 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 calibration switching voltage value and the reference switching current value or reference switching voltage value to the ratio of the difference between the strength value of the calibration magnetic field and the strength value of the reference magnetic field.

5. The method (3) for measuring the strength of an external magnetic field according to any one of claims 1 to 4, characterized in that, The process of continuously applying multiple currents or voltages of varying amplitudes until a switching of the magnetization direction of the storage layer occurs includes the following sub-steps: - Determine the first resistance of the at least one magnetic storage point (31), wherein determining the first resistance includes measuring the current or voltage passing through the magnetic storage point. - Compare the first resistance value obtained in (32) with the reference resistance value to identify the relative initial magnetization direction of the storage layer relative to the reference layer. - Apply a current or voltage pulse of predefined amplitude and polarity (33) to the at least one magnetic storage point, the polarity of which causes the storage layer to switch to a direction opposite to the relative initial magnetization direction of the storage layer relative to the reference layer. - Determine the second resistance of the at least one magnetic storage point (34), wherein determining the second resistance includes measuring the current or voltage passing through the magnetic storage point after a current or voltage pulse is applied to the magnetic storage point. - Compare the second resistance obtained by (35) with the reference resistance value to determine whether a switch in the magnetization direction of the storage layer has occurred. - If a switch in the magnetization direction of the storage layer has already occurred: The minimum switching current or minimum switching voltage is the current or voltage applied in the preceding step of applying a current or voltage pulse to the magnetic storage point. - If the switching of the magnetization direction of the storage layer has not yet occurred, the sub-steps of applying current or voltage pulses to the magnetic storage point, determining the second resistance, and comparing the second resistance with the first resistance are repeated using current or voltage pulses with modified amplitudes that are different from the predefined amplitudes, until the switching of the magnetization direction of the storage layer occurs.

6. The method (3) for measuring the strength of an external magnetic field according to claim 5, characterized in that, The predefined amplitude is a low amplitude, and the modified amplitude is greater than this low amplitude.

7. The method (3) for measuring the strength of an external magnetic field according to any one of claims 1 to 3, characterized in that, The process of continuously applying multiple currents or voltages of varying amplitudes until a switch in the magnetization direction of the storage layer occurs includes the following sub-steps: - A current or voltage ramp or periodic signal of polarity is applied until a switch in the magnetization direction of the storage layer is detected, which prompts the storage layer to switch to a direction opposite to the relative initial magnetization direction of the storage layer relative to the reference layer. - Determine the minimum switching current or minimum switching voltage amplitude as a function of the total application time of the current or voltage ramp to obtain the value of the minimum switching current or minimum switching voltage.

8. The method (3) for measuring the strength of an external magnetic field according to any one of claims 1 to 4, characterized in that, It includes a further step of applying a pulse after detecting a switch in the magnetization direction of the storage layer, the pulse having a polarity that promotes the switching of the storage layer to the relative initial magnetization direction of the storage layer with respect to the reference layer and having an amplitude greater than that of the minimum switching current or minimum switching voltage.

9. The method (3) for measuring the strength of an external magnetic field according to any one of claims 1 to 4, characterized in that, It uses multiple magnetic storage points and performs the steps of continuously applying multiple currents or voltages of different magnitudes in parallel to the magnetic storage points among the multiple magnetic storage points.

10. The method (3) for measuring the strength of an external magnetic field according to claim 9, characterized in that, The steps of simultaneously and continuously applying multiple currents or voltages of different amplitudes in parallel to each of the multiple magnetic storage points are performed, and the minimum switching current value or minimum switching voltage value in the magnetization direction is the minimum switching current value or minimum switching voltage value in the magnetization direction of the storage layer of each of the multiple magnetic storage points.

11. A magnetic storage point (2), characterized in that, It is configured to implement a method for measuring an external magnetic field according to any one of the preceding claims, and it further includes a controller configured to manage the measurement of the resistance of a magnetic storage point.

12. The magnetic storage point (2) according to claim 11, characterized in that, It includes magnetic tunnel junctions with out-of-plane magnetization (or vertical anisotropy).

13. The magnetic storage point (2) according to claim 11 or 12, characterized in that it further includes a pulse generator and the controller is further configured to manage the pulse generator.

14. The magnetic storage point (2) according to claim 11 or 12, characterized in that, It has a lateral dimension of less than 200 nm.

15. A method for determining the relative distance between a magnetic storage point (2) according to any one of claims 11 to 14 and a magnetic object (40) generating a magnetic field between 1 mT and 500 mT, the method being characterized by comprising the following steps: - At multiple points in space, the vertical component of the magnetic field is measured according to any one of claims 1 to 10 to determine the amplitude and direction of the magnetic field. - The relative distance between the storage layer of the magnetic storage point and the magnetic object is calculated based on the simulation of the magnetic field generated by the magnetic object.

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