Magnetomechanical accelerometer

Abstract

The magnetomechanical accelerometer (10) comprises a first magnetic tunnel junction (11) mounted in a fixed manner and a magnetic component mounted in a movable manner relative to the first junction (11) so as to be able to approach / move away from the first junction (11) during an acceleration phase experienced by the accelerometer. The magnetic component is a further magnetic tunnel junction (12) or permanent magnet. The first junction (11) is mechanically and magnetically coupled with the magnetic component. The accelerometer also includes processing circuitry.

Description

Technical Field

[0001] The present invention relates to an accelerometer based on spintronic technology and a method for measuring acceleration by using such an accelerometer. Background Art

[0002] Accelerometers are currently used in many devices to monitor acceleration.

[0003] Generally, it is desirable that the acceleration measured by an accelerometer provide useful input for identifying events in the environment in which the accelerometer is used. For example, an airbag may be activated once a certain acceleration threshold is reached, or a display in a portable device may be oriented based on how the user moves it.

[0004] Currently, the main types of accelerometers include MEMS (micro-electromechanical systems)-based capacitive devices, which generate a voltage when the distance between the plates of a capacitor changes due to acceleration, and piezoelectric displacement transducers, which generate a voltage after deformation caused by acceleration.

[0005] Known accelerometers including MEMS-based capacitive devices suffer from problems with electromagnetic interference and are not easily scalable to sub-micron dimensions, while accelerometers including piezoelectric displacement transducers are mechanically weak.

[0006] An object of the present invention is to provide an accelerometer that overcomes the disadvantages of the prior art.

[0007] Another object of the present invention is to provide a highly sensitive accelerometer.

[0008] Another object of the present invention is to provide an accelerometer that is easily scalable and can be integrated with current high-density technologies such as CMOS (Complementary Metal Oxide Semiconductor).

[0009] These and other objects are achieved by means of a magnetomechanical accelerometer as claimed in the appended claims. Summary of the Invention

[0010] The magnetomechanical accelerometer according to the invention comprises at least one first magnetic tunnel junction mounted in a fixed manner, the first magnetic tunnel junction comprising a free ferromagnetic layer and a reference ferromagnetic layer.

[0011] The accelerometer further comprises a magnetic component mounted in a movable manner relative to the aforementioned at least one first magnetic tunnel junction so as to be able to approach / move away from the at least one first magnetic tunnel junction during the acceleration phases experienced by the accelerometer.

[0012] The magnetic component is another magnetic tunnel junction or a permanent magnet.

[0013] The at least one first magnetic tunnel junction and the magnetic component are mechanically coupled via elastic means and magnetically coupled via a dipole interaction caused by a static magnetic field generated by the at least one first magnetic tunnel junction and the magnetic component.

[0014] The accelerometer also includes processing circuitry configured to:

[0015] - applying a voltage and / or a direct current to the at least one first magnetic tunnel junction, the voltage and / or the direct current being sufficient to activate a self-oscillating operating mode of the magnetization of the free ferromagnetic layer of the at least one first magnetic tunnel junction;

[0016] - applying an alternating current to the at least one first magnetic tunnel junction so as to induce an injection-locked state in the at least one first magnetic tunnel junction and induce a rectified voltage at ends of the at least one first magnetic tunnel junction due to a spintronic diode effect;

[0017] - measuring a rectified voltage at the end of at least one first magnetic tunnel junction; and

[0018] - Determining the acceleration based on the measured rectified voltage.

[0019] The processing circuit is configured to determine acceleration based on the rectified voltage, preferably by comparing a change in the rectified voltage relative to a reference rectified voltage measured in the absence of acceleration.

[0020] Preferably, in at least one first magnetic tunnel junction, the reference ferromagnetic layer has a fixed magnetization parallel to the same reference ferromagnetic layer, and the free ferromagnetic layer has a stable magnetization responsive to an external stimulus in a direction perpendicular to the same free and variable ferromagnetic layer.

[0021] If the magnetic component is a further magnetic tunnel junction, then in such further magnetic tunnel junction, preferably, the reference ferromagnetic layer has a fixed magnetization parallel to the same reference ferromagnetic layer, and the free ferromagnetic layer has a stable magnetization in response to an external stimulus in a direction perpendicular to the same free and variable ferromagnetic layer.

[0022] Furthermore, the processing circuit is configured to apply a voltage and / or a direct current to the further magnetic tunnel junction that is sufficient to activate a self-oscillating operating mode of the magnetization of the free ferromagnetic layer of the further magnetic tunnel junction and to induce a mutual injection locked state in which the oscillations of the magnetization of the free ferromagnetic layer of the further magnetic tunnel junction are synchronized with the oscillations of the magnetization of the free ferromagnetic layer of the at least one first magnetic tunnel junction.

[0023] Preferably, the accelerometer includes, in addition to the first magnetic tunnel junction, a second magnetic tunnel junction mounted in a fixed manner. In this case, the movable magnetic component is arranged between the first and second magnetic tunnel junctions such that the first and second magnetic tunnel junctions and the magnetic component are substantially aligned, and the magnetic component can be moved in a direction connecting the first and second magnetic tunnel junctions during an acceleration phase experienced by the accelerometer.

[0024] Preferably, in addition to the first magnetic tunnel junction, the accelerometer further comprises a second magnetic tunnel junction mounted in a fixed manner, a third magnetic tunnel junction mounted in a fixed manner, and a fourth magnetic tunnel junction mounted in a fixed manner. The first magnetic tunnel junction, the second magnetic tunnel junction, the third magnetic tunnel junction, and the fourth magnetic tunnel junction are arranged in pairs aligned along two mutually orthogonal directions. The magnetic component is arranged in a central position relative to the first magnetic tunnel junction, the second magnetic tunnel junction, the third magnetic tunnel junction, and the fourth magnetic tunnel junction, so that the magnetic component can move in a plane along the two mutually orthogonal directions connecting the first magnetic tunnel junction and the second magnetic tunnel junction and connecting the third magnetic tunnel junction and the fourth magnetic tunnel junction during the acceleration phase experienced by the accelerometer.

[0025] Preferably, in addition to the first magnetic tunnel junction, the accelerometer further comprises a second magnetic tunnel junction mounted in a fixed manner, a third magnetic tunnel junction mounted in a fixed manner, a fourth magnetic tunnel junction mounted in a fixed manner, a fifth magnetic tunnel junction mounted in a fixed manner, and a sixth magnetic tunnel junction mounted in a fixed manner. The first magnetic tunnel junction, the second magnetic tunnel junction, the third magnetic tunnel junction, the fourth magnetic tunnel junction, the fifth magnetic tunnel junction, and the sixth magnetic tunnel junction are arranged in pairs aligned along three mutually orthogonal directions. The magnetic component is arranged at a central position relative to the first magnetic tunnel junction, the second magnetic tunnel junction, the third magnetic tunnel junction, the fourth magnetic tunnel junction, the fifth magnetic tunnel junction, and the sixth magnetic tunnel junction, so that the magnetic component can move in space along the three mutually orthogonal directions connecting the first magnetic tunnel junction and the second magnetic tunnel junction, connecting the third magnetic tunnel junction and the fourth magnetic tunnel junction, and connecting the fifth magnetic tunnel junction and the sixth magnetic tunnel junction during the acceleration phase experienced by the accelerometer.

[0026] Preferably, the magnetic tunnel junctions of the accelerometer are connected to separate electrodes.

[0027] The method for measuring acceleration using the magnetomechanical accelerometer as described above comprises the following steps:

[0028] - applying a voltage and / or a direct current to at least one first magnetic tunnel junction, the voltage and / or the direct current being sufficient to activate a self-oscillating operating mode of the magnetization of the free ferromagnetic layer of the at least one first magnetic tunnel junction;

[0029] - applying an alternating current to the at least one first magnetic tunnel junction so as to induce an injection-locked state in the at least one first magnetic tunnel junction and induce a rectified voltage in ends of the at least one first magnetic tunnel junction due to a spintronic diode effect;

[0030] - during an acceleration phase experienced by the accelerometer, bringing the magnetic component closer to / away from said at least one first magnetic tunnel junction;

[0031] - measuring a rectified voltage at the end of the at least one first magnetic tunnel junction;

[0032] - Determining the acceleration based on the measured rectified voltage.

[0033] Preferably, the step of determining the acceleration based on the rectified voltage comprises comparing a change in the rectified voltage relative to a reference rectified voltage measured in the absence of acceleration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] These and other features and advantages of the present invention will become apparent from the following description of preferred embodiments, which is given by way of example and not limitation, with reference to the accompanying drawings, in which elements denoted by the same or similar reference numerals represent elements having the same or similar function and structure, and in which:

[0035] Figure 1 A schematic diagram illustrating a magnetomechanical accelerometer according to an embodiment of the present invention;

[0036] Figure 2a Schematic diagrams showing examples of tunnel junctions that may be used in magnetomechanical accelerometers according to various embodiments of the present invention;

[0037] Figure 2b Schematic diagrams showing additional examples of tunnel junctions that may be used in magnetomechanical accelerometers according to various embodiments of the present invention;

[0038] Figure 3 Shown Figure 1 a graph of the tension measured at the end of a fixed knot and the relative displacement of a movable knot with respect to the fixed knot in an accelerometer in response to a time-varying external acceleration, both varying as a function of time;

[0039] Figure 4 Shown Figure 1 a graph showing the variation of the tension measured at the end of a fixed knot as a function of the distance between the fixed knot and the movable knot in an accelerometer;

[0040] Figure 5 A schematic diagram showing a magnetomechanical accelerometer according to another embodiment of the present invention;

[0041] Figure 6 Schematic diagram showing a magnetomechanical accelerometer according to another embodiment of the present invention. DETAILED DESCRIPTION

[0042] Reference below Figure 1 、 Figure 2a and Figure 2b A magnetomechanical accelerometer 10 according to a first embodiment of the present invention is described.

[0043] The accelerometer 10 includes a magnetic tunnel junction (MTJ) 11 mounted in a fixed manner, hereinafter referred to as the fixed junction for the sake of simplicity. The fixed junction 11 is mechanically coupled to another magnetic tunnel junction 12 by elastic means (not shown), the other magnetic tunnel junction 12 being mounted in a movable manner relative to the aforementioned fixed junction 11 and, for the sake of simplicity, referred to as the movable junction 12 hereinafter. In particular, the fixed junction 11 is constrained to a support 13 fixedly mounted in an apparatus including the accelerometer 10, while the movable junction 12 is constrained to a support 14 that is movable relative to the aforementioned fixed support 13. The fixed support 13 and the movable support 14 are mechanically connected by the aforementioned elastic means so that the movable support 14 can move in the direction connecting the movable junction 12 and the fixed junction 11 under the action of an external acceleration.

[0044] refer to Figure 2a The magnetic tunnel junction used in the present invention is indicated by 50 and comprises a thin intermediate layer 52 of, for example, an insulating and non-magnetic material (e.g., MgO), defined as a tunnel barrier, between two ferromagnetic outer layers 51, 53 (e.g., CoFeB with different material percentages). Of the two ferromagnetic layers 51, 53, a first layer 51, referred to as the free layer, has a stable magnetization in a direction perpendicular to the same first layer 51, and a second layer 53, referred to as the reference layer, has a fixed magnetization parallel to the same second layer 53. These magnetizations are Figure 2a Schematically indicated by arrows in FIG. The magnetization of the free layer 51 evolves dynamically in response to an external stimulus (e.g., a magnetic field, polarized spin current). Depending on the relative orientation of the magnetizations of the reference layer 53 and the free layer 51, the junction 50 is characterized in a known manner by different levels of electrical resistance: a high resistance level is detected in a configuration with antiparallel magnetizations, and a low resistance level is detected in a configuration with parallel magnetizations. This resistance can be measured based on the voltage at the ends of the junction 50.

[0045] Furthermore, in the magnetic tunnel junction 50, due to the so-called spin transfer torque (STT) effect, the magnetization of the free layer 51 can be induced into a self-induced oscillation state in a known manner when a direct current (IDC) is applied. The frequency of the magnetization oscillation depends on the amplitude of the input current (IDC). Similarly, by simultaneously applying an alternating current (AC), the rate of magnetization oscillation can be varied. For AC frequencies close to the self-oscillation frequency of the magnetization of the free layer 51, coupling can occur between the two excitations, causing the magnetization of the free layer 51 to oscillate at the frequency of the AC current (AC). In this mode, the frequency of the oscillation of the magnetization of the free layer 51 remains constant with changes in the DC current (IDC), and the junction 50 is in a state defined as injection-locked. By varying the DC current (IDC), the amplitude and phase of the oscillation of the magnetization of the free layer 51 can be controlled, generating a rectified voltage (Vdc) that depends on the resistance level of the junction 50 and the amplitude and phase of the oscillation of the magnetization of the free layer 51. This phenomenon is known as the "spintronic diode effect" and only occurs for a small range of DC currents (IDC).

[0046] refer to Figure 2b Another example of a magnetic tunnel junction 60 useful in the present invention includes a thin intermediate layer 62 (referred to as a tunnel barrier), such as an insulating and non-magnetic material (e.g., MgO), interposed between a ferromagnetic outer layer 61 and a composite outer layer 63. The outer ferromagnetic layer 61, defined as a free layer, has a stable magnetization oriented in a direction perpendicular to the free layer 61, which is free to respond to external stimuli. The composite outer layer 63 includes a reference layer 64 (e.g., CoFeB) and a confining layer 66 (e.g., CoFe), which are coupled via a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction via an intervening thin metal layer 65 (e.g., Ru), thereby forming a synthetic antiferromagnetic layer 67. The composite layer 63 also includes an antiferromagnetic layer 68 (e.g., PtMn). The direction of the magnetization of the confining layer 66 can be fixed by coupling the confining layer 66 to the antiferromagnetic layer 68. The synthetic antiferromagnetic state 67 is designed so that its magnetization is oriented in the plane of the layer itself. Figure 2b The arrows in the middle schematically represent the magnetization.

[0047] Back to Figure 1 In the embodiment shown, the fixed junction 11 and the movable junction 12 are advantageously connected to independent electrodes, which allows independent application of current / voltage and independent reading of the voltage at the ends of the fixed junction 11 .

[0048] The fixed junction 11 and the movable junction 12 are also arranged at a certain distance so as to be magnetically coupled via a dipole interaction caused by the static magnetic field generated by their ferromagnetic layers. During the acceleration phase experienced by the accelerometer 10 (or equivalently, a device including the accelerometer 10), the movable junction 12 can approach or move away from the fixed junction 11.

[0049] The processing circuitry (not shown) of the accelerometer 10 supplies a voltage and / or a DC current sufficient to activate the self-oscillating mode of operation of the magnetization of the free layers thereof in a known manner as described above to both the fixed junction 11 and the movable junction 12 of the accelerometer 10. Thus, both the fixed junction 11 and the movable junction 12 act as spintronic diodes in the active mode.

[0050] The pinned junction 11 is also supplied with an alternating current, so that the pinned junction 11 is in an injection-locked state, and a rectified voltage is generated at its ends due to the spintronic diode effect explained above.

[0051] In particular, according to this embodiment, in the self-oscillating state, the frequency of the oscillation of the magnetization of the free layer of the movable junction 12, induced solely by the introduction of a DC current, differs from the frequency of the oscillation of the magnetization of the free layer of the fixed junction 11 in the injection-locked state. In this case, the distance between the fixed junction 11 and the movable junction 12 allows magnetic coupling to synchronize the oscillation of the magnetization in the movable junction 12 with the oscillation of the magnetization in the fixed junction 11. This state is referred to as a mutual injection-locked state. This synchronization causes the phase and / or amplitude of the oscillation of the magnetization of the free layer of the fixed junction 11 to vary, resulting in a change in the rectified voltage read at the end of the fixed junction 11. Advantageously, the synchronization of the oscillation of the magnetization in the movable junction 12 with the oscillation of the magnetization in the fixed junction 11 allows for the realization of an accelerometer 10 with a high sensitivity, potentially reaching several nanometers, and allows for the miniaturization of the accelerometer, with dimensions scalable to the order of several hundred nanometers. In the absence of external acceleration acting on the device on which the accelerometer 10 is mounted, the rectified voltage read at the end of the fixed junction 11 is constant. When accelerometer 10 experiences acceleration, this causes the distance between fixed junction 11 and movable junction 12 to change, which produces a change in the magnetic coupling between the junctions, which causes a change ΔVdc in the rectified voltage at the ends of fixed junction 11. From the change ΔVdc in the rectified voltage detected by the processing circuit at the ends of fixed junction 11, the acceleration acting on accelerometer 10 can then be determined.

[0052] Figure 3The graph shown shows how the evolution over time of the rectified voltage Vdc read at the end of the fixed junction 11 depends on the variation of the distance d between the two junctions due to the influence of acceleration. This combination is possible due to the fact that the dynamics associated with magnetic transients are much faster than mechanical dynamics.

[0053] Figure 4 The illustrated graph shows the linear dependence of the rectified voltage ΔVdc measured at the end of the fixed junction 11 on the distance d between the fixed junction 11 and the movable junction 12. In the aforementioned graph, the reference voltage used to determine the change ΔVdc is the voltage measured at the end of the fixed junction 11 when the fixed junction 11 is in an injection-locked state and its magnetization is asynchronous with the magnetization of the movable junction 12. The linear dependence of the rectified voltage Vdc on the distance d between the junctions provides an efficient procedure for determining the external acceleration applied to the accelerometer 10 from the measured voltage Vdc. Furthermore, this linear dependence allows the accelerometer 10 according to the present invention to detect acceleration without requiring integration and differentiation operations on the measured signal.

[0054] refer to Figure 5 According to another embodiment of the present invention, an accelerometer 110 includes a first magnetic tunnel junction 111 and a second magnetic tunnel junction 115, both of which are fixedly mounted and, for the sake of simplicity, are hereinafter referred to as the first fixed junction 111 and the second fixed junction 115. These first and second fixed junctions are each mechanically coupled to a further magnetic tunnel junction 112 via respective elastic means (not shown), which is mounted in a movable manner relative to the aforementioned fixed junctions 111 and 115 and, for the sake of simplicity, is hereinafter referred to as the movable junction 112. In particular, the first and second fixed junctions 111 and 115 are constrained to respective supports 113 and 116 fixedly mounted in a device including the accelerometer 110, while the movable junction 112 is constrained to a support 114 that is movable relative to the aforementioned fixed supports 113 and 116. The fixed supports 113 and 116 are each mechanically connected to the movable support 114 via the aforementioned elastic means.

[0055] For a description of the tunnel junction, see the reference above. Figure 2a and Figure 2b The content shown.

[0056] The movable support 114 is arranged between the two fixed supports 113 and 116 so that the two fixed knots 111 and 115 are substantially aligned with the movable knot 112. In such a configuration, the movable support 114 (and thus the movable knot 112) can be moved in the direction connecting the movable knot 112 and the two fixed knots 111 and 115 under the action of an external acceleration.

[0057] The first and second fixed junctions 111, 115, and the movable junction 112 are advantageously connected to independent electrodes, respectively, which allows independent application of current / voltage and independent reading of the voltage at the ends of the fixed junctions 111, 115. Independent measurement of the voltage at the ends of the fixed junctions 111, 115 ensures natural feedback and improves the sensitivity of the accelerometer 110.

[0058] The first fixed junction 111 and the second fixed junction 115 are also arranged at a certain distance from the movable junction 112 so as to be magnetically coupled to the movable junction 112 through a dipole interaction caused by the static magnetic field generated by their ferromagnetic layers. The movable junction 112 can approach / move away from the first and second fixed junctions 111, 115 in different ways during the acceleration phase, i.e., approach the first fixed junction 111 and move away from the second fixed junction 115, or vice versa.

[0059] The processing circuitry (not shown) of the accelerometer 110 supplies a voltage and / or a DC current sufficient to activate the self-oscillating mode of magnetization of the free layers thereof in a known manner to the first and second fixed junctions 111 and 115, as well as to the movable junction 112. Thus, both the first and second fixed junctions 111 and 115, as well as the movable junction 112, function as active spintronic diodes.

[0060] The two fixed junctions 111 , 115 are also powered by an alternating current, so that the fixed junctions 111 , 115 are in an injection-locked state and a rectified voltage is generated at their ends due to the spintronic diode effect.

[0061] In particular, according to this embodiment, in the self-oscillating state, the frequency of the oscillation of the magnetization of the free layer of the movable junction 112, induced solely by the introduction of a DC current, differs from the frequency of the oscillation of the magnetization of the free layer of the fixed junctions 111 and 115 in the injection-locked state. In this case, the distance between the fixed junctions 111 and 115 and the movable junction 112 allows magnetic coupling to synchronize the magnetization oscillation in the movable junction 112 with the magnetization oscillation in the fixed junctions 111 and 115. This state is referred to as a mutual injection-locked state. This synchronization causes a change in the phase and / or amplitude of the oscillation of the magnetization of the free layer of the fixed junctions 111 and 115, which determines a change in the rectified voltage read at the ends of the fixed junctions 111 and 115.

[0062] When no external acceleration is applied to the device on which accelerometer 110 is mounted, the rectified voltage read at the ends of fixed junctions 111, 115 is constant. When accelerometer 110 experiences acceleration, this causes a change in the distance between fixed junctions 111, 115 and movable junction 112. This changes the magnetic coupling between fixed junctions 111, 115 and movable junction 112, which in turn causes a change in the rectified voltage at the ends of fixed junctions 111, 115 by ΔVdc. Based on this change in rectified voltage ΔVdc detected by the processing circuit at the ends of fixed junctions 111, 115, the acceleration acting on accelerometer 110 can be determined.

[0063] refer to Figure 6 According to another embodiment of the present invention, an accelerometer 210 includes a first magnetic tunnel junction 211, a second magnetic tunnel junction 215, a third magnetic tunnel junction 217, and a fourth magnetic tunnel junction 219, all of which are fixedly mounted and, for the sake of simplicity, are hereinafter referred to as the first fixed junction 211, the second fixed junction 215, the third fixed junction 217, and the fourth fixed junction 219. These first fixed junction 211, the second fixed junction 215, the third fixed junction 217, and the fourth fixed junction 219 are each mechanically coupled to another magnetic tunnel junction 212 via respective elastic devices (not shown). The other magnetic tunnel junction 212 is movably mounted relative to the aforementioned fixed junctions 211, 215, 217, and 219, and is hereinafter referred to as the movable junction 212 for the sake of simplicity. In particular, the first, second, third, and fourth fixed knots 211, 215, 217, and 219 are constrained to respective supports 213, 216, 218, and 220 fixedly mounted in the device including the accelerometer 210, while the movable knot 212 is constrained to a support 214 that is movable relative to the aforementioned fixed supports 213, 216, 218, and 220. The fixed supports 213, 216, 218, and 220 are each mechanically connected to the movable support 214 via the aforementioned elastic means.

[0064] For a description of the tunnel junction, see the reference above. Figure 2a and Figure 2b The content shown.

[0065] The fixed supports 213, 216, 218, 220 (and thus the fixed knots 211, 215, 217, 219) are arranged in a cross configuration, i.e., arranged in pairs aligned along two mutually orthogonal directions, wherein the movable support 214 (and thus the movable knot 212) is provided at a central position relative to the four fixed supports 213, 216, 218, 220. In such a configuration, the movable support 214 (and thus the movable knot 212) can move in a plane along the two mutually orthogonal directions connecting the movable knot 212 and the four fixed knots 211, 215, 217, 219 under the action of an external acceleration.

[0066] The first, second, third, and fourth fixed junctions 211, 215, 217, and 219, as well as the movable junction 212, are advantageously connected to independent electrodes, which allows independent application of current / voltage and independent reading of the voltage at the ends of the fixed junctions 211, 215, 217, and 219. Independent measurement of the voltage at the ends of the fixed junctions 211, 215, 217, and 219 ensures natural feedback and improves the sensitivity of the accelerometer 210.

[0067] The first, second, third, and fourth fixed junctions 211, 215, 217, and 219 are also arranged at a distance from the movable junction 212 so as to be magnetically coupled to the movable junction 212 via a dipole interaction caused by the static magnetic field generated by their ferromagnetic layers. The movable junction 212 can approach and move away from the fixed junctions 211, 215, 217, and 219 in different ways during the acceleration phase, i.e., approach one or two fixed junctions and move away from the remaining fixed junctions.

[0068] The processing circuitry (not shown) of the accelerometer 210 supplies a voltage and / or a DC current sufficient to activate the self-oscillating operating mode of the magnetization of the free layers of the first, second, third, and fourth fixed junctions 211, 215, 217, and 219, as well as the movable junction 212, in a known manner. Thus, the first, second, third, and fourth fixed junctions 211, 215, 217, and 219, as well as the movable junction 212, all function as active spintronic diodes.

[0069] The first, second, third and fourth fixed junctions 211, 215, 217 and 219 are also powered by AC current, so that the fixed junctions 211, 215, 217 and 219 are in an injection-locked state and generate a rectified voltage at their ends due to the spintronic diode effect.

[0070] In particular, according to this embodiment, in the self-oscillating state, the frequency of the oscillation of the magnetization of the free layer of the movable junction 212, induced solely by the introduction of a DC current, differs from the frequency of the oscillation of the magnetization of the free layer of the fixed junctions 211, 215, 217, 219 in the injection-locked state. In this case, the distance between the fixed junctions 211, 215, 217, 219 and the movable junction 212 allows magnetic coupling to synchronize the magnetization oscillation in the movable junction 212 with the magnetization oscillation in the fixed junctions 211, 215, 217, 219. This state is referred to as a mutual injection-locked state. This synchronization causes a change in the phase and / or amplitude of the oscillation of the magnetization of the free layer of the fixed junctions 211, 215, 217, 219, which determines a change in the rectified voltage read at the ends of the fixed junctions 211, 215, 217, 219.

[0071] When no external acceleration is applied to the device on which the accelerometer 210 is mounted, the rectified voltage read at the ends of the fixed junctions 211, 215, 217, and 219 is constant. When the accelerometer 210 experiences acceleration, this causes the distance between the fixed junctions 211, 215, 217, and 219 and the movable junction 212 to change. This causes the magnetic coupling between the fixed junctions 211, 215, 217, and 219 to change, which in turn causes the rectified voltage at the ends of the fixed junctions 211, 215, 217, and 219 to change by ΔVdc. Based on the change in rectified voltage ΔVdc detected by the processing circuit at the ends of the fixed junctions 211, 215, 217, and 219, the acceleration acting on the accelerometer 210 can be determined.

[0072] According to another embodiment of the present invention (not shown), the accelerometer can be provided with six fixed knots arranged in pairs along three mutually orthogonal directions, with the movable knot positioned centrally. In this configuration, the movable knot can move in space along the three mutually orthogonal directions connecting the movable knot and the six fixed knots under the influence of external acceleration.

[0073] The description of accelerometers with two and four fixed junctions applies mutatis mutandis to the present embodiment.

[0074] According to a further embodiment of the invention (not shown), the accelerometer comprises a permanent magnet (eg, NdFeB) movably mounted relative to one or more fixed junctions, in place of the movable junctions of any of the preceding embodiments.

[0075] For example, consider an embodiment having a single fixed knot, such as Figure 1In the aforementioned embodiment shown, the junction is fabricated on a support member fixedly mounted on the device containing the accelerometer, while the permanent magnet is fabricated on a support member movable relative to the fixed support member. The fixed support member and the movable support member are mechanically connected by an elastic device, allowing the movable support member to move in the direction connecting the permanent magnet and the fixed junction under the influence of an external acceleration.

[0076] The fixed junction can be powered by the accelerometer processing circuitry either with a DC current / voltage sufficient to activate the self-oscillating mode of operation of its free layer magnetization in a known manner, or with an AC current that determines the generation of a rectified voltage in a known manner due to the spintronic diode effect. Thus, the fixed junction acts as a spintronic diode in the active mode. The permanent magnet is mounted so that its magnetization is oriented along the axis connecting the permanent magnet and the fixed junction.

[0077] When no external acceleration is applied to the device on which the accelerometer is mounted, the rectified voltage read at the ends of the fixed junction is constant. When the accelerometer experiences acceleration, this causes the distance between the fixed junction and the movable magnet to change, which produces a change in the magnetic coupling between the junction and the magnet, which causes a change in the rectified voltage at the ends of the fixed junction by ΔVdc. There are distances for which the rectified voltage has a linear dependence on the distance between the fixed junction and the movable magnet, such that measurement of the change in rectified voltage ΔVdc detected at the ends of the fixed junction by the processing circuitry allows the acceleration acting on the accelerometer to be determined.

[0078] The above description applies mutatis mutandis also to embodiments with two, four and six fixed knots, by replacing the movable knots with movable permanent magnets.

[0079] The magnetomechanical accelerometer without magnetic tunnel junctions having flexible parts according to the illustrated embodiment is mechanically more robust than known spintronic and piezoresistive accelerometers that are based on bending of certain components after acceleration.

[0080] The magnetomechanical accelerometer according to the embodiment shown above is easy to scale and can be integrated at a higher density. Due to the spintronic diode effect, the sensitivity of the accelerometer according to the present invention can be higher than 200kV / W, which is higher than the sensitivity of known MEMS-based accelerometers.

[0081] Furthermore, since the elements forming the basis of the operating principle of the accelerometer are of ferromagnetic origin, the accelerometer is not susceptible to electromagnetic interferences, unlike known MEMS-based accelerometers.

[0082] Finally, the use of magnetic junctions with tunneling effect allows the creation of low-power, radiation-hardened, highly sensitive, and high-frequency miniature accelerometers that are compatible with CMOS.

Claims

1. A magnetomechanical accelerometer (10; 110; 210), comprising: - at least a first magnetic tunnel junction (11; 111; 211) mounted in a fixed manner, said at least first magnetic tunnel junction (11; 111; 211) comprising a free ferromagnetic layer and a reference ferromagnetic layer, - a magnetic component, said magnetic component being arranged relative to said at least first magnetic tunnel junction (11; 111; 211) is mounted in a movable manner so that the magnetic component can be moved towards / away from the at least first magnetic tunnel junction (11; 111; 211) during the acceleration phase experienced by the accelerometer. 211), the magnetic component is another magnetic tunnel junction (12; 112; 212) or a permanent magnet, The at least first magnetic tunnel junction (11; 111; 211) and the magnetic component are mechanically coupled via elastic means, and the at least first magnetic tunnel junction (11; 111; 211) is electrically coupled to the magnetic component. 211) and the dipole interaction caused by the static magnetic field generated by the magnetic component to perform magnetic coupling, the accelerometer further comprising: - a processing circuit configured to: - applying a DC voltage and / or a current to the at least first magnetic tunnel junction (11; 111; 211), said DC voltage and / or current being sufficient to activate a self-oscillating operating mode of the magnetization of the free ferromagnetic layer of the at least first magnetic tunnel junction (11; 111; 211); - applying an alternating current to the at least first magnetic tunnel junction (11; 111; 211), such that the alternating current induces an injection-locked state in the at least first magnetic tunnel junction (11; 111; 211) and induces a rectified voltage at the ends of the at least first magnetic tunnel junction (11; 111; 211) due to a spintronic diode effect; - measuring the rectified voltage at the ends of said at least first magnetic tunnel junction (11; 111; 211), and - determining the acceleration experienced by the accelerometer based on the measured rectified voltage.

2. The accelerometer (10; 110; 210) according to claim 1, wherein The processing circuit is configured to determine the acceleration based on the rectified voltage by comparing a change in the rectified voltage relative to a reference rectified voltage measured in the absence of acceleration.

3. The accelerometer (10; 110; 210) according to claim 1 or 2, wherein: In the at least first magnetic tunnel junction (11; 111; 211), the reference ferromagnetic layer has a fixed magnetization parallel to the reference ferromagnetic layer, and the free ferromagnetic layer has a stable magnetization in a direction perpendicular to the free ferromagnetic layer and changing in response to an external stimulus.

4. The accelerometer (10; 110; 210) according to any one of the preceding claims, wherein In the further magnetic tunnel junction (12; 112; 212), a reference ferromagnetic layer has a fixed magnetization parallel to the reference ferromagnetic layer, and a free ferromagnetic layer has a stable magnetization in a direction perpendicular to the free ferromagnetic layer and which changes in response to an external stimulus, wherein the processing circuit is configured to provide the further magnetic tunnel junction (12; 112; 212) applying a DC voltage and / or current, said DC voltage and / or current being sufficient to activate a self-oscillating operating mode of the magnetization of the free ferromagnetic layer of said further magnetic tunnel junction (12; 112; 212), and causing said DC voltage and / or current to induce a mutual injection locking state, in which the oscillation of the magnetization of the free ferromagnetic layer of said further magnetic tunnel junction (12; 112; 212) is synchronized with the oscillation of the magnetization of the free ferromagnetic layer of said at least first magnetic tunnel junction (11; 111; 211) is synchronized with the oscillation of the magnetization of the free ferromagnetic layer.

5. The accelerometer (110) according to any one of the preceding claims, further comprising a second magnetic tunnel junction (115) mounted in a fixed manner, wherein The magnetic component is disposed between the first magnetic tunnel junction (111) and the second magnetic tunnel junction (115) such that the first magnetic tunnel junction (111) and the second magnetic tunnel junction (115) and the magnetic component are substantially aligned, and the magnetic component is movable in a direction connecting the first magnetic tunnel junction (111) and the second magnetic tunnel junction (115) during an acceleration phase experienced by the accelerometer.

6. The accelerometer (210) according to any one of claims 1 to 4, further comprising a second magnetic tunnel junction (215) mounted in a fixed manner, a third magnetic tunnel junction (217) mounted in a fixed manner, and a fourth magnetic tunnel junction (219) mounted in a fixed manner, wherein: The first magnetic tunnel junction (211), the second magnetic tunnel junction (215), the third magnetic tunnel junction (217) and the fourth magnetic tunnel junction (219) are arranged in a paired aligned manner along two mutually orthogonal directions, and wherein the magnetic component is provided at a central position relative to the first magnetic tunnel junction (211), the second magnetic tunnel junction (215), the third magnetic tunnel junction (217) and the fourth magnetic tunnel junction (219) so that the magnetic component can move within a plane along the two mutually orthogonal directions connecting the first magnetic tunnel junction (211) and the second magnetic tunnel junction (215) and connecting the third magnetic tunnel junction (217) and the fourth magnetic tunnel junction (219) during an acceleration phase experienced by the accelerometer.

7. The accelerometer according to any one of claims 1 to 4, further comprising a second magnetic tunnel junction mounted in a fixed manner, a third magnetic tunnel junction mounted in a fixed manner, a fourth magnetic tunnel junction mounted in a fixed manner, a fifth magnetic tunnel junction mounted in a fixed manner, and a sixth magnetic tunnel junction mounted in a fixed manner, wherein the first magnetic tunnel junction, the second magnetic tunnel junction, the third magnetic tunnel junction, the fourth magnetic tunnel junction, the fifth magnetic tunnel junction, and the sixth magnetic tunnel junction are arranged in pairs along three mutually orthogonal directions, and wherein, The magnetic component is arranged at a central position relative to the first magnetic tunnel junction, the second magnetic tunnel junction, the third magnetic tunnel junction, the fourth magnetic tunnel junction, the fifth magnetic tunnel junction and the sixth magnetic tunnel junction, so that the magnetic component can move in space along three mutually orthogonal directions connecting the first magnetic tunnel junction and the second magnetic tunnel junction, connecting the third magnetic tunnel junction and the fourth magnetic tunnel junction, and connecting the fifth magnetic tunnel junction and the sixth magnetic tunnel junction during the acceleration phase experienced by the accelerometer.

8. An accelerometer according to any one of the preceding claims, wherein The at least first magnetic tunnel junction (11; 111; 211) and the further magnetic tunnel junction (12; 112; 212) are connected to separate electrodes.

9. A magnetomechanical accelerometer (10; 110; 210) A method for measuring acceleration, the method comprising the following steps: - to said at least first magnetic tunnel junction (11; 111; 211) applying a DC voltage and / or current, wherein the DC voltage and / or current is sufficient to activate the at least first magnetic tunnel junction (11; 111; 211) of the self-oscillating working mode of the magnetization of the free ferromagnetic layer; - applying an alternating current to the at least first magnetic tunnel junction (11; 111; 211), such that the alternating current induces an injection-locked state in the at least first magnetic tunnel junction (11; 111; 211) and induces a rectified voltage at the ends of the at least first magnetic tunnel junction (11; 111; 211) due to a spintronic diode effect; - moving the magnetic component closer to / away from the at least first magnetic tunnel junction (11; 111; 211) during an acceleration phase experienced by the accelerometer; - measuring the rectified voltage at the end of the at least first magnetic tunnel junction (11; 111; 211); - determining the acceleration experienced by the accelerometer based on the measured rectified voltage.

10. The method according to claim 9, wherein: The step of determining acceleration based on the rectified voltage includes comparing a change in the rectified voltage relative to a reference rectified voltage measured in the absence of acceleration.

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