Magnetic field transducer

Abstract

A magnetic field transducer (1) comprising a tunnel magnetoresistance (TMR) sensing arrangement (2) comprising a TMR Wheatstone bridge (6), and a power supply (4) configured to supply power to the TMR sensing arrangement (2) and comprising a current source (5). The current source (5) is configured to set a predefined base current (Is) and a supplementary current (Isup) of the power supply (4). The magnetic field transducer (1) further comprises a signal regulation circuit (3) comprising a bridge resistance measurement section (8) configured to output a signal which is a function of a resistance of the TMR sensing arrangement (5), wherein the signal regulation circuit (3) is connected to the current source (5), configured to control a current output of the supplementary current source Isup.

Description

[0001] P3057PC00

[0002] MAGNETIC FIELD TRANSDUCER

[0003] Field

[0004] The present invention relates to a magnetic field transducer comprising a TMR sensing arrangement.

[0005] Background

[0006] It is known to provide a magnetic field transducer with a tunnel magnetoresistance (TMR) sensing arrangement to detect and measure a magnetic field. In general, when the TMR sensing arrangement is exposed to an external magnetic field, the TMR sensing arrangement changes its resistance in response to the field's strength and direction. These resistance changes can be measured to infer the characteristics of the external magnetic field.

[0007] The response of the TMR sensing arrangement to the external magnetic field typically appears as a magnetization curve of its sensing layer. Since the resistance of the TMR arrangement is related to a magnetization of it sensing element, this curve represents the relationship between the magnetization of the TMR sensing arrangement and the strength of the external magnetic field.

[0008] An advantage of TMR technology is its high magnetoresistive effect. A relative change in resistance of TMR sensing elements upon application of external field can reach several hundreds of percent. High sensitivity of TMR sensing arrangements simplifies noticeably signal conditioning circuit and brings advantage compared to other types of magnetic field sensors.

[0009] Although TMR sensing elements may be provided with a good linearity of response over a certain operating range, for large measurement ranges, higher order distortions may be present in TMR-based transducer due to nonlinear magnetization of the sensing layer. Those distortions become more and more dominant the wider the range of magnetic fields TMR sensing element is meant to work with. At high magnetic fields one observes typical “bending” of the magnetization curve which corresponds to drop of the local sensitivity. This imposes a trade-off between desired working field range and the linearity error.

[0010] A voltage bias is typically required to enable current flow through the TMR sensing arrangement. This voltage bias facilitates spin-dependent tunneling of electrons across the insulating barrier (i.e. TMR effect) within the TMR structure. As the resistance changes due to the TMR effect, the voltage bias generates a measurable voltage drop across the arrangement. P3057PC00

[0011] The magnitude of this voltage drop corresponds to the resistance, allowing the detection of the magnetic field.

[0012] One common method of applying a voltage bias in TMR sensing arrangements is through a constant voltage source. However, the linear error is relatively high due to intrinsic nonlinearity of sensing layer magnetization curve, which negatively affects measurement accuracy.

[0013] An alternative approach is to use a constant current source to bias the TMR sensing arrangement. Compared to the constant voltage approach, a constant current source usually provides better linearity. The reason for that is for the most linear TMR sensors, resistivity of a TMR Wheatstone bridge grows with the magnetic field. Being biased by constant current and exposed to a high magnetic field, a TMR Wheatstone bridge acquires higher bias voltage. Athough the increase in the bias voltage also increases voltage at the TMR Wheatstone bridge output which partially compensates intrinsic nonlinearity of sensing layer magnetization, for large measurement ranges the linear error may still lead to a reduced measurement accuracy.

[0014] Summary of the invention

[0015] In view of the foregoing, it is an object of this invention to provide a magnetic field transducer comprising a TMR sensing arrangement which is accurate over a large measurement range.

[0016] It is advantageous to provide a magnetic field transducer that is economical to produce and operate.

[0017] It is advantageous to provide a magnetic field transducer that is stable and reliable.

[0018] It is advantageous to provide a magnetic field transducer that is easy to implement.

[0019] Objects of this invention have been achieved by providing a system according to claim 1. Dependent claims set forth various advantageous features of embodiments of the invention.

[0020] Disclosed herein is a magnetic field transducer comprising a tunnel magnetoresistance (TMR) sensing arrangement comprising a TMR Wheatstone bridge, and a power supply configured to supply power to the TMR sensing arrangement and comprising a current source. The current source is configured to set a predefined base current and a supplementary current of the power supply. The magnetic field transducer further comprises a signal regulation circuit comprising a bridge resistance measurement section configured to output a supplementary current regulation signal based on a resistance of the TMR sensing arrangement, the signal regulation P3057PC00 circuit being connected to the current source to regulate said supplementary current with said supplementary current regulation signal. The supplementary current provides a correction for non-linearity, especially non-linearity occurring at high magnetic field strengths.

[0021] In embodiments, the TMR Wheatstone bridge comprises two (half bridge configuration) or four (full bridge configuration) TMR sensing branches, each TMR sensing branch comprising a plurality of magnetic tunnel junction elements.

[0022] In an embodiment, the TMR Wheatstone bridge comprises two said TMR sensing branches and two sensing branches comprising fixed resistors.

[0023] In an embodiment, the TMR Wheatstone bridge comprises a voltage bias terminal, a voltage bias output terminal, a negative output terminal, and a positive output terminal, wherein each terminal is a junction or node where two adjacent sensing branches are electrically connected.

[0024] In an embodiment, the current source comprises a main current source and a supplementary current source, wherein the main current source is configured to set the base current and the supplementary current source is configured to set the supplementary current.

[0025] In an embodiment, the supplementary current source is directly electrically connected to the main current source.

[0026] In an embodiment, the current source or at least the main current source is a voltage driven current source.

[0027] In an embodiment, the signal regulation circuit is electrically connected to a base current section and a resistor section, wherein the resistor section is configured to provide a predefined reference resistance to at least one of the signal regulation circuit or the power supply and the base current section is configured to provide a predefined current to the signal regulation circuit.

[0028] In an embodiment, the signal regulation circuit comprises the base current section and the resistor section.

[0029] In an embodiment, the base current section is directly electrically connected to the supplementary current source. P3057PC00

[0030] In an embodiment, the resistor section comprises a thermoresistor configured to compensate variation of TMR Wheatstone bridge resistance caused by temperature change.

[0031] In an embodiment, a resistance of the resistor section is based on a resistance of the TMR Wheatstone bridge in an absence of an external magnetic field.

[0032] In an embodiment, the resistor section is connected to a component to control a temperature of the resistor section based on the thermoresistor and the resistance of the TMR Wheatstone bridge in the absence of the external magnetic field.

[0033] In an embodiment, the TMR Wheatstone bridge comprises vortex based TMR sensing elements or hard-bias TMR sensing elements.

[0034] In an embodiment, the TMR Wheatstone bridge comprises in-plane magnetic anisotropy in a sensing layer with an easy axis oriented essentially perpendicular to a sensitivity axis, or wherein the TMR Wheatstone bridge comprises an out-of-plane magnetic anisotropy in a sensing layer with an easy axis oriented essentially parallel to a sensitivity axis.

[0035] Further objects and advantageous features of the invention will be apparent from the claims, from the detailed description, and annexed drawings.

[0036] Brief description of the drawings

[0037] Figure 1 is a schematic circuit diagram of a magnetic field transducer according to an embodiment of the invention;

[0038] Figure 2a is a schematic perspective view of a TMR Wheatstone bridge of a magnetic field transducer according to an embodiment of the invention;

[0039] Figure 2b is a schematic circuit diagram of a TMR Wheatstone bridge ;

[0040] Figure 2c is a plot depicting a resistance of a TMR Wheatstone bridge changes in response so an applied external magnetic field.

[0041] Figure 2d is a plot depicting an output voltage of a hard-bias TMR Wheatstone bridge according to a prior art in response to an applied external magnetic field;

[0042] Figure 2e is a linear error plot illustrating a linear fit error of the output voltage of the hard-bias TMR Wheatstone bridge in Figure 2e;

[0043] Figure 2f is a resistance-magnetic field plot of the hard-bias TMR Wheatstone bridge in Figure 2e;

[0044] Figure 2g is a graph depicting an output magnetization of a vortex TMR Wheatstone bridge in response to an applied magnetic field; P3057PC00

[0045] Figure 2h is a linear error plot illustrating a linear fit error of the vortex TMR Wheatstone bridge in Figure 2f;

[0046] Figure 3a is a schematic circuit diagram of an embodiment of a magnetic field transducer according to the invention;

[0047] Figure 3b is a plot of a TMR Wheatstone bridge output voltage and its bias current over time for the embodiment of figure 3a and two variants of the prior art;

[0048] Figure 4a is a schematic circuit diagram of another embodiment of the magnetic field transducer according to the invention;

[0049] Figure 4b is a schematic circuit diagram of yet another embodiment of a magnetic field transducer according to the invention.

[0050] Figure 5 is a time-voltage graph of the magnetic field transducer according to all the embodiments and two variants of the prior art; and

[0051] Detailed description of embodiments of the invention

[0052] Referring to the figures, a magnetic field transducer 1 according to embodiments of the application comprises a tunnel magnetoresistance (TMR) Wheatstone bridge 2, a signal regulation circuit 3, and a power supply 4. For instance, the TMR Wheatstone bridge 2, the signal regulation circuit 3, and the power supply 4 are electrically connected to each other through wiring or conductive pathways.

[0053] The power supply 4 comprises a voltage supply Vsand a current source 5. The current source comprises a main current source lsand according to an aspect of the invention, further comprises a supplementary current source lSUp. The main current source and supplementary current source are depicted as separate elements in Figure 1 , however it is to be understood that the current source 5 may be formed as a single circuit entity, which has a variable current component represented by the supplementary current source. For instance, the current source 5 of the magnetic field transducer 1 can be understood as a voltage driven current source (VDCS), in which the base current and the supplementary current are added up at the input or added in the adder circuit.

[0054] The power supply 4 is connected to a voltage bias terminal Vbias of the vortex TMR sensing arrangement 2 and provides power to the TMR Wheatstone bridge 2. Further details with respect to the vortex TMR Wheatstone bridge 2 are provided below in relation to Figure 2a and 2c. P3057PC00

[0055] The signal regulation circuit 3 is connected to the voltage bias terminal Vbias and is connected in a control loop to the supplementary current source lSUp, configured to control the current output of the supplementary current source lSUp.

[0056] The signal regulation circuit 3 comprises a bridge resistance measurement section 8 configured to access or measure a resistance Rbrd of the TMR Wheatstone bridge 6 of the TMR sensing arrangement 2. For instance, using at least one input terminal coupled to the TMR Wheatstone bridge 6, the bridge resistance measurement section 8 may measure at least one of the resistance Rbrd. The resistance Rbrd of the TMR Wheatstone bridge 6 changes in response to changes in an external magnetic field H and therefore can be also written or understood as a function of the external magnetic field H. The external magnetic field H may change its strength or direction over time.

[0057] The signal regulation circuit 3 further comprises a base current section 12 and a resistor section 24. The resistor section 24 may be adjusted to be equivalent to the resistance of the TMR Wheatstone bridge 6 or proportional to it if the measuring current for the resistor section 24 is only a portion of the base current lsof the current source 5. Bridge resistance measurement section 8 compares instant resistance of the TMR Wheatstone bridge 6 to the reference resistance and generates a voltage at its output which is proportional to that difference. This voltage amplitude is adjusted to the necessary level by the fixed gain amplifier section in and serves as an input signal for voltage driven constant current source VDCS. Voltage driven constant current source establishes a supplementary (constant) current lSUp which is proportional to the input voltage from the amplifier AMP.

[0058] The level of gain for the fixed gain amplifier AMP is selected by minimizing linear error of the TMR Wheatstone bridge 6 output over desired field range.

[0059] The resistor section 24 is configured to create a reference resistance Rref, which may be based on the resistance of the TMR Wheatstone bridge Rbrd in the absence of an external magnetic field H (e.g. (or Rbrd(H = 0)). For instance, the reference resistance Rref may match with the resistance of the TMR Wheatstone bridge Rbrd in the absence of an external magnetic field H (e.g. (or Rbrd(H = 0)). The signal regulation circuit 3 is configured to measure Rbrd and compare Rbrd to Rret. For instance, the bridge resistance measurement section 8 within the signal regulation circuit 3 may measure Rbrd. In an embodiment, the bridge resistance measurement section 8 may comprise the resistor section 24. Alternatively, the bridge resistance measurement section 8 may be electrically connected or coupled to the resistor section 24 and compare Rbrd to Rref. P3057PC00

[0060] In addition, the resistor section may comprise a thermoresistor configured to measure temperature of TMR Wheatstone bridge 6. Thermoresistor can be configured in a such way that variation of resistance 24 with the temperature will follow respective zero-field variation of resistance of the TMR Wheatstone bridge 6. One can reach therefore higher accuracy of the circuit over the working temperature range.

[0061] Within an embodiment of the magnetic field transducer 1 according the application, the voltage bias can be given as follows:

[0062] Vbias=Rbrd(H) ls + (Rbrd(H) - Rref) lsup

[0063] The signal regulation circuit 3 is electrically connected or coupled to the power supply 4. For instance, the signal regulation circuit 3 may be connected to the supplementary current source Isup via corresponding input terminal of the supplementary current source lSUp and an output terminal of the bridge resistance measurement section 8. The supplementary current source may provide a supplementary current, which is proportional to a difference between the resistance of the TMR Wheatstone bridge Rbrd and the reference resistance Rref (e.g. Rbrd - Rret). In other words, the supplementary current source lSUp provides the supplementary current which is dynamically or actively changing depending on the resistance of the TMR Wheatstone bridge Rbrd as the resistance of the TMR Wheatstone bridge Rbrd varies in response to the external magnetic field H.

[0064] Figure 1 illustrates a schematic circuit diagram of the magnetic field transducer 1 according to an embodiment of the application. In Figure 1 , the magnetic field transducer 1 comprises the TMR sensing arrangement 2, the signal regulation circuit 3, and the power supply 4. In this embodiment, the power supply 4 comprises the voltage supply Vs, the current source ls, and the supplementary current source lSUp. The power supply 4 is electrically connected to the voltage bias terminal Vbias of the TMR Wheatstone bridge 6 of the TMR sensing arrangement 2 in order to supply power to the TMR Wheatstone bridge 6. The signal regulation circuit 3 comprises the bridge resistance measurement section 8, the base current section 12, and the resistor section 24. The signal regulation circuit 3 is coupled to the power supply 4 (e.g. the supplementary current source lSUp) in order to provide the resistance difference between the resistance Rbrd and Rref as described above and the supplementary current source lSUp may provide the supplementary current proportional to the resistance difference (e.g. Rbrd - Rref).

[0065] Generally, a voltage bias applied to a TMR sensing arrangement may be required to enable the operation of the TMR sensing arrangement and measure the resistance changes within P3057PC00 the TMR sensing arrangement, as it provides an electrical output corresponding to the detected magnetic field (e.g., the applied external magnetic field H). However, current approaches, such as providing either a single constant voltage or a single constant current to the TMR sensing arrangement, may face challenges depending on the strength of the applied magnetic field. These challenges arise because the resistance of the TMR sensing arrangement varies with the external magnetic field, leading to changes in the output signal when the strength of the external magnetic field is beyond a reliable detection range depending on the design of the TMR sensing arrangement.

[0066] For a constant voltage approach, nonlinear magnetic response of the sensing layer results in non-linear current changes within the TMR sensing arrangement, potentially affecting the accuracy and sensitivity of the sensor. In a constant current approach, the voltage output may deviate from an ideal linear response, particularly at high or low magnetic field strengths. In other words, the output voltage of the TMR sensing arrangement does not exhibit a linear relationship with the strength of the external magnetic field if the field exceeds a certain threshold. Further details related to the sensing limitation are provided below in relation to Figures 2b, 2d, 2e and 2f. This can be observed as non-linearity in the magnetization curve, where the relationship between the applied magnetic field and the magnetization deviates from a linear response. These limitations may create a demand for a magnetic field transducer capable of accurately detecting and measuring an external magnetic field across a wide range of magnetic field strengths.

[0067] The magnetic field transducer 1 may provide a way to improve a measurement accuracy of the external magnetic field using the TMR sensing arrangement 2 by providing the supplementary current source lSUp based on the resistance of the TMR Wheatstone bridge Rbrd measured using the signal regulation circuit 3. The supplementary current provided by the supplementary current source lSUp may be capable of compensating for the non-linearity in the sensing layer magnetization curve when the applied magnetic field exceeds a threshold, enabling accurate and consistent sensing across a wide range of magnetic field strengths. In addition, it may be economical and easy to implement to incorporating the supplementary current source lSuPand the signal regulation circuit 3 to the magnetic field transducer 1 without having an additional hardware to improve the sensing accuracy over a wide range of magnetic field.

[0068] Figure 2a illustrates a perspective view (Figure 2a) of an example of the vortex TMR Wheatstone bridge 6 of the magnetic field transducer 1 and exemplary substructures (Figure 2a, middle and right) of the vortex TMR Wheatstone bridge 6. The TMR sensing arrangement P3057PC00

[0069] 2 comprises a TMR Wheatstone bridge 6. In addition, the TMR Wheatstone bridge 6 comprises a plurality of TMR sensing branches 14. For instance, in a full bridge embodiment, the TMR Wheatstone bridge comprises four TMR sensing branches, namely a first, a second, a third, and a fourth TMR sensing branches 14a - 14d. The TMR Wheatstone bridge 6 comprises a voltage bias terminal Vbias, a ground terminal VGND, a positive output terminal V+, and a negative output terminal V-. Vbias is electrically coupled or connected to the power supply 4, which enables the power supply 4 to provide an electrical potential to the TMR Wheatstone bridge 6 and allows current to flow through the TMR Wheatstone bridge 6. In other words, each terminal can be understood as a node which may be electrically connected to or coupled with a power source, circuit, device, or other circuitry to interact with.

[0070] For instance, at least one of the TMR sensing branch 14 may comprises a plurality of magnetoresistor chains 16. The magnetoresistor resistor chain 16 may comprise a plurality of magnetic tunnel junction (MTJ) elements 20. For instance, the MTJ elements 20 may be connected in-series to form the resister chain 16 and a plurality of the resistor chains 16 are arranged and connected in parallel forming a single TMR sensing branch 14. The MTJ elements may have a pillar shape (e.g. cylinder) or pilaster or any shape comprising a stack of layers depending on applications. The MTJ elements 20 may be micron or submicron size. The MTJ elements may be referred to as MTJ dots. Each MTJ element is connected or coupled to each other electrically via a conductive element 18. Analogously, each magnetoresistor chains are connected via the conductive element 18 each other forming the TMR sensing branch 14. Further, each TMR sensing branch 14 is connected to each other via the conductive element 18.

[0071] The TMR Wheatstone bridge 6 may be an electrical circuit in which the four TMR sensing branches 14a - 14d have any other symmetrical quadrilateral shape with four sides. The TMR sensing branches 14a - 14d may be connected at four junctions or nodes. For instance, the first and the second TMR branches 14a, 14b forms a node corresponding to the voltage bias terminal Vbias. The first and the third TMR branches 14a, 14c forms a node corresponding to a negative output terminal V-. The second and the fourth TMR branches 14b, 14d forms a node corresponding to a positive output terminal V+. The third and the fourth TMR branches 14c, 14d form a node corresponding to the ground terminal VGND. The output voltage of the TMR Wheatstone bridge 6 may be measured across the negative and the positive output terminals V-, V+.

[0072] In general, MTJ elements are components used in circuits, electronic devices, or systems that rely on the interaction of magnetic fields in materials to function. An MTJ typically comprises P3057PC00 two layers of magnetic material separated by a thin insulating layer (e.g. tunnel barrier) that enables quantum tunnelling of electrons. The magnetic state in the layers influence the TMR, depending on the relative angle of their mean magnetisation values.

[0073] For instance, as shown in Figure 2a (right) the MTJ element 20 may comprise a plurality of layers. The layers may comprise a senser layer 22a, a tunnelling barrier 22b, a reference layer 22c, a pinned layer 22d, and an antiferromagnetic layer 22e.

[0074] In the MTJ element 20, the sensor layer 22a (or free layer) interacts with an external magnetic field by altering magnetic state, characterized by mean magnetization. These changes enable precise detection of external magnetic fields, making the MTJ element 20 highly effective for sensing. The tunnelling barrier 22b, typically MgO, separates the sensor layer 22a and the reference layer 22c, allowing electron tunnelling and providing the TMR effect.

[0075] The reference layer 22c has a fixed uniformly magnetized configuration, providing a stable point or reference magnetization of comparison for the sensor layer's state. In other words, the reference layer 22c is pinned uniformly, so that conductance of the MTJ element 20 follows mean magnetization of the sensing layer 22a. The pinned layer 22d stabilizes the reference layer 22c, while the antiferromagnetic layer 22e ensures the magnetization of the pinned layer 22d remains fixed via exchange bias, maintaining reliable operation of the MTJ element 20 and establishing the pinning direction or, in other words, its sensitivity axis.

[0076] Figure 2b illustrates an exemplary circuit diagram of a TMR Wheatstone bridge in connection with Figure 2a, an exemplary pinning direction of individual branches of the vortex TMR Wheatstone bridge 6, and a resistance-magnetic field graph of each branch. Pinning direction referrers to the fixed magnetization direction of the reference layer 22c in each MTJ element 20. The pinning direction may be related to determining the balance of the TMR Wheatstone bridge 6 and response to the external magnetic fields.

[0077] Resistance of a single MTJ element depends on the alignment of the magnetization of the sensor layer 22a (e.g. vortex state) relative to the reference layer. The TMR effect in the MTJ element 20 depends on the relative alignment of the overall magnetization in the senso layer 22a. When the alignment is strong (parallel), the resistance of the MTJ element 20 is low. However, when the magnetizations of the sensor and reference layers 22a, 22c are misaligned (antiparallel), the resistance of the MTJ element 20 increases, resulting in a high-resistance state. The resistance of each sensing TMR branch 14 can be determined by the parallel or series combination of the resistance of individual MTJ elements 20. As the external field P3057PC00 changes, the resistance of the TMR sensing branch 14 reflects the cumulative response of all MTJ elements 20 comprised in the TMR sensing branch 14. When the mean magnetization of the free layer aligns closely with that of the reference layer, the resistance is low due to minimized TMR effect representing a parallel configuration.

[0078] For instance, the pinning directions of the TMR sensing branches 14a - 14d may be assigned in an alternating or symmetric patten. The first branch 14a and a third branch 14c, the pinned layer magnetization may be fixed in one direction (e.g., upward or along a specific axis). For the second branch 14b and the fourth branch 14d, the pinned layer magnetization is fixed in the opposite direction (e.g. downward or along the opposite axis). Alternating the pinning directions ensures that the relative magnetization alignment between the pinned and free layers in each branch creates complementary changes in resistance. This configuration may enhance the differential output signal of the TMR Wheatstone bridge 6 and improves the sensing sensitivity of the TMR sensing arrangement 2.

[0079] For instance, the pinning directions of the TMR sensing branches 14a - 14d may be assigned in an alternating or symmetric patten. As shown in Figure 2c, the first branch 14a and a third branch 14c, the pinned layer magnetization may be fixed in one direction (e.g., upward or along a specific axis). For the second branch 14b and the fourth branch 14d, the pinned layer magnetization is fixed in the opposite direction (e.g. downward or along the opposite axis). Alternating the pinning directions ensures that the relative magnetization alignment between the pinned and free layers in each branch creates complementary changes in resistance when the magnetic state in the free layer 22a is influenced by an external magnetic field. This configuration may enhance the differential output signal of the TMR Wheatstone bridge 6 and improves the sensing sensitivity of the TMR sensing arrangement 2.

[0080] Figure 2c illustrates a plot depicting a resistance of the TMR Wheatstone bridge in response to an applied magnetic field. As described above, the resistance of the TMR Wheatstone bridge generally increases with the increasing strength of the external magnetic field. However, the resistance of the TMR Wheatstone bridge exhibits a parabolic behavior, meaning it does not increase or decrease linearly in response to the applied magnetic field as described in Figure 2c.

[0081] Figures 2d-2h illustrate various examples of TMR Wheatstone bridge configurations employing different mechanisms, demonstrating their responses to changes in the external magnetic field within embodiments of the prior art. P3057PC00

[0082] Figure 2d illustrates a voltage output of a TMR Wheatstone bridge with a hard-bias system in response to an applied magnetic field, which is sweeping linearly and gradually. A constant voltage bias is provided to the TMR Wheatstone bridge. In the hard-bias system, a sense layer is biased by a permanent magnet aligned perpendicular to a sensitivity axis of a MTJ element.

[0083] Figure 2e Illustrates a linear error of the TMR Wheatstone bridge with the hard-bias system described in connection with Figure 2d. The linear error is a residual of a linear fit of the voltage output in Figure 2d. As shown in Figure 2e, although the voltage output of the TMR Wheatstone bridge with the hard-bias system changes proportionally or linearly in response to the applied magnetic field, discrepancies still occur, causing the linearity error.

[0084] Figure 2f shows a resistance of the hard-bias TMR Wheatstone bridge in Figure 2d. Similar to the parabolic resistance shape of the (e.g. vortex) TMR Wheatstone bridge above in Figure 2c, the resistance of the hard-bias TMR Wheatstone bridge also exhibits a non-linear dependence on the applied magnetic field. This behavior reflects the influence of the hard-bias field on the magnetization dynamics of the sensing layer, resulting in a characteristic parabolic trend rather than a strictly linear response.

[0085] Figure 2g illustrates a magnetization 41 of a vortex TMR Wheatstone bridge with in response to an applied magnetic field, which is sweeping linearly and gradually. For comparison, a reference linear line 40 and a magnetization 42 of the TMR Wheatstone bridge 6 of the magnetic field transducer 1 according to the application in response to the same applied magnetic field are presented. As shown in Figure 2f, the TMR Wheatstone bridge 6 of the magnetic field transducer 1 outputs more linear response to the applied magnetic field than the output of the TMR Wheatstone bridge without

[0086] Figure 2h illustrates a linearity error of the vortex TMR Wheatstone bridge, as described in Figure 2g. The linearity error shows typical shape of residuals from linear fit in percentage of its full-scale (FS) signal amplitude for a given range of magnetic fields. Similar to the response shown in Figure 2e, the output of the TMR Wheatstone bridge deviates from a linear response, with non-linearity increasing as the applied magnetic field strength increases.

[0087] One potential approach to improve the non-linear response of the vortex TMR Wheatstone bridge involves stabilizing the vortex MTJ element in a thick sensing layer. In this configuration, the diameter or lateral size of the MTJ element is designed to be multiple times larger than its thickness. However, this approach may constrain the design flexibility of the TMR Wheatstone P3057PC00 bridge. Depending on the application, the size of the MTJ element may be restricted by the available space, posing challenges for integration in compact systems.

[0088] As shown in Figure 2d - 2h, regardless of the type of the TMR Wheatstone bridge (e.g. vortex or hard-bias), the output voltage, magnetization, or resistance of a TMR Wheatstone bridge exhibits a dependence on the linearity error, which typically includes a classical cubic term contribution. This cubic term causes deviations from an ideal linear behavior, thereby reducing the local sensitivity of the TMR sensor at higher magnetic fields. However, as shown in Figure 2g (e.g. the line 42), the magnetic field transducer 1 may provide an improved sensing ability at higher external magnetic field by using the signal regulation circuit 3, which enables to dynamically adjust the voltage bias by the supplementary current provided to the TMR sensing arrangement 2 in response to the applied magnetic field. Further, as shown in Figures 2d and 2f, resistance of the (e.g. vortex or hard-bais) TMR Wheatstone bridge generally follows Quasiparabolic shape in response to the applied magnetic field. The magnetic field transducer 1 according to the application can utilize the output of the signal regulation circuit to output a function of the resistance of the TMR sensing arrangement 5 and control the supplementary current based on the function of the resistance of the TMR sensing arrangement 3.

[0089] . Figure 3a - 5 describe several variants of the magnetic field transducer 1 according to an embodiment of the application.

[0090] Figure 3a illustrates a schematic view of a first variant of the magnetic field transducer 1 according to an embodiment of the application.

[0091] Within the first variant of the magnetic field transducer 1 , the power supply 4 comprises the voltage source Vs, the current source ls, and the supplementary current source lSUp. For instance, the supplementary current source lSUp may be connected to the current source ls. In addition, the supplementary current source lSUp may be an add-on current source controlled dynamically by the bridge resistance measurement section 8 of the signal regulation circuit 3 in order to adjust the total current supplied by the power supply 4 to the voltage bias terminal Vbias of the TMR sensing arrangement 2.

[0092] In the variant of figure 3a, the power supply 4 comprises the voltage source Vsand voltage driven current source VDCS connected to the TMR Wheatstone bridge 6 and bridge resistance measurement circuit 8. The bridge resistance measurement circuit comprises of consists of an inverting amplifier which measures the voltage drop over TMR Wheatstone bridge 6. Resistors R7 and R8 define the gain and therefore level of regulation for the supplementary current Isup. A portion of constant bias from voltage source V6 is also admixed to shift the working point to P3057PC00 the desired level. That is to say that the circuit will work in the linear regime. In that case, resistor R10 value is adjusted to provide zero supplementary current then external magnetic field is zero. The output voltage from the bridge resistance measurement circuit 8, which is proportional to the TMR Wheatstone bridge resistance change, is summed up in a block ADD with the constant voltage from the source 6, which defines amplitude of the base current Is. The output of the block ADD drives the VDCS current source 5.

[0093] Figure 3b illustrates a schematic circuit diagram of the prior art with a constant voltage source. Figure 3c illustrates a schematic circuit diagram of another prior art with a constant current source. The TMR Wheatstone bridges presented in Figures 3b and 3c can be understood as analogous to the TMR Wheatstone bridge 6 of embodiments of the magnetic field transducer 1.

[0094] Figure 3d illustrates real-time output waveforms of the TMR Wheatstone bridges from the two prior art examples shown in Figures 3b and 3c, represented by a dash-dot line and a dashed line, respectively. Additionally, it presents the real-time output waveform of the magnetic field transducer 1 , corresponding to the embodiment described in Figure 3a, shown as a solid line.

[0095] In other words, the real-time output waveforms can be understood as a time-voltage graph describing output voltages of the TMR Wheatstone bridge 6 over time when the voltage bias terminal Vbias is connected to the single constant voltage source (Figure 3b, the dash-dot line), the single constant current source (Figure 3c, the dashed line), and the power supply 4 of the embodiment (Figure 3a, the solid line).

[0096] For instance, in the illustrated prior art of Figures 3b and Figure 3c, voltage source V1 provides a sawtooth triangular voltage sweep with the period of 2 sec: that is, for a time period from 0 to 1 second the voltage is changing in a linear manner from its maximum negative to maximum positive value. In this example the TMR Wheatstone bridge 6 is made from four behavioural resistors (QSPICE simulation environment) B1-B4, where its behavioural function emulates change in the resistance of TMR sensing branch using source V1 as input argument.

[0097] Behavioural resistors B2 and B3 have following behaviour function:

[0098] R=2*Rp*(1+TMR) / (2+TMR - TMR*(V1+NL*pow(V1 ,3)))

[0099] Behavioural resistors B1 and B4 have following behaviour function:

[0100] R=2*Rp*(1+TMR) / (2+TMR + TMR*(V1+NL*pow(V1,3))) P3057PC00

[0101] Rp is set 2.5 kOhm and it corresponds to a resistance of TMR branch when it is in low resistive state. TMR is set to 250 % and it corresponds to the size of magnetoresistive effect in each sensing branch B1-B4. A cubic nonlinear term is added to the behavioural function as NL*pow(V1 ,3), where NL is nonlinearity parameter which is set to -0.3. In this way, one emulates reaction of TMR Wheatstone bridge output on external field sweep, where linear voltage sweep from the source V1 works as field sweep and each behavioural resistor changes its resistance accordingly to its function.

[0102] As shown in Figure 3b, the nonlinearity which was introduced into behavioral equations of sensing branches, is visibly seen at the TMR full bridge output. In the example of Figure 3c, constant current biasing regime provides better linearity of the TMR Wheatstone bridge output because an increase of the TMR Wheatstone bridge resistance increases the effective bias voltage on it and partially compensates evident bending of the transfer curve.

[0103] However, according to an aspect of the invention, better linearization is achieved when the current amplitude increases synchronously with the TMR Wheatstone bridge resistance due to the supplementary current supplied to the TMR sensing arrangement 2.

[0104] Figure 3e illustrates a supplementary current provided to the TMR Wheatstone bridge 6 of the embodiment in Figure 3a overtime. Analogous to the resistance graph of the TMR Wheatstone bridge under the influence of the applied magnetic field shown in Figures 2c and 2f, the supplementary current is dynamically adapted due to the applied magnetic field.

[0105] Figure 4a illustrates a schematic circuit diagram of another embodiment of the magnetic field transducer 1 according to an embodiment of the invention. This embodiment is implemented with a grounded TMR Wheatstone bridge, as opposed to the TMR Wheatstone bridge described in Figure 3a which is floating. In this embodiment, the grounded TMR Wheatstone bridge 6 may be provided with further post-processing of the output signal of the TMR Wheatstone bridge signal. For instance, the ground connection provides a stable reference voltage, minimizing drift and improving the stability of the output signal. The layout of the voltage driven current source VDCS 5 is different from the layout of the current source in the embodiment of Figure 3a. In this embodiment, voltage summation, which sets the combination of the base current and the supplementary current, is performed at the input of VDCS current source 5, therefore the adder block may be omitted. Voltage source V5 defines the base bias current ls, while adjustment of resistor R16 allows to scale a magnitude of the supplementary current magnitude Isup. P3057PC00

[0106] Figure 4b illustrates a schematic circuit diagram of yet another embodiment of the magnetic field transducer 1 according to an embodiment of the invention. In this embodiment, the supplementary current source lSUp and the main current source lsare separated and the base current lsand the supplementary current lSUp are set independently. Therefore, changes in the amplitude of the base current lsdoesn’t change the amplitude of supplementary current lSUp. For instance, the supplementary current lSUp is set by resistor R30 while the base current lsis set by voltage source V4.

[0107] Figure 5 illustrates an efficiency of linearisation which can be achieved with embodiments of this invention compared to the prior art. In this example, the initial slope (at t=0.5 s) of TMR Wheatstone bridge output voltage is matched to that of a linear generator signal by scaling the output of the TMR Wheatstone bridge either under constant voltage regime (prior art) or by the embodiments according to the invention such as embodiments of Figure 4a and 4b. Similar to the real-time waveform plot in Figure 3d, the output voltage of the TMR Wheatstone bridge of the embodiments of the magnetic transducer 1 provide a larger range with greater linearity. In other words, sensing stability and reliability of the magnetic transducer 1 is broader than the prior art as it shows improved linearity at higher magnetic field in comparison with the constant voltage bias configuration of Figure 3b.

[0108] It is worth noting that the exemplary embodiments are not limited to the specific configurations described and may be adapted to suit a variety of applications. For instance, the choice between a floating or grounded TMR Wheatstone bridge design, or the coupling between the supplementary current source and the main current source, can vary depending on the specific requirements and operating conditions. These variations demonstrate the flexibility of the embodiments and their potential for broader applicability.

[0109] Therefore, the magnetic field transducer 1 according to the exemplary embodiments of the application may be able to provide accurate magnetic field sensing due to the dynamically adapting supplementary current supply to the TMR sensing arrangement by the signal regulation circuit 3 and the supplementary current source lSUp. P3057PC00

[0110] List of references used

[0111] Magnetic field transducer 1

[0112] Tunnel magnetoresistance sensing arrangement 2 TMR Wheatstone bridge 6

[0113] TMR sensing branch 14, 14a, 14b, 14c, 14d Resistor string / chain 16

[0114] Conductive element 18

[0115] Magnetic tunnel junction element 20 Sense layer 22a

[0116] Tunneling barrier 22b Reference layer 22c Pinned layer 22d Antiferromagnetic layer 22e Voltage bias terminal Vbias Bridge Ground terminal VOUT Positive output terminal V+ Negative output terminal V-

[0117] Signal regulation circuit 3

[0118] Bridge resistance measurement section 8 Input terminal Output terminal

[0119] Amplifying section 13 Base current section 12 Resistor section 24

[0120] Power supply 4

[0121] Voltage supply Vs, 30 Output terminal Current source 5

[0122] Main current source ls, 31 Input terminal Output terminal

[0123] Supplementary current source lSUp , 32

[0124] Input terminal

[0125] Output terminal

Claims

P3057PC00Claims1 . A magnetic field transducer (1) comprising: a tunnel magnetoresistance (TMR) sensing arrangement (2) comprising a TMR Wheatstone bridge (6); and a power supply (4) configured to supply power to the TMR sensing arrangement (2) and comprising a current source (5), wherein the current source (5) is configured to set a predefined base current (ls) and a supplementary current (lSUp,), and wherein the magnetic field transducer (1) further comprises a signal regulation circuit (3) comprising a bridge resistance measurement section (8) configured to output a regulation signal based on a resistance of the TMR sensing arrangement (5), the signal regulation circuit being connected to the current source to regulate said supplementary current (lSUp).

2. The magnetic field transducer (1) of claim 1 , wherein the TMR Wheatstone bridge (6) comprises two or four TMR sensing branches (14), each TMR sensing branch comprising a plurality of magnetic tunnel junction elements (20).

3. The magnetic field transducer (1) of the preceding claim, wherein the TMR Wheatstone bridge (6) comprises two said TMR sensing branches (14) and two sensing branches comprising fixed resistors.

4. The magnetic field transducer (1) of any preceding claim, the TMR Wheatstone bridge (6) comprise a voltage bias terminal (Vm), a voltage bias output terminal (Vout), a negative output terminal (V-), and a positive output terminal (V+), wherein each terminal is a junction or node where two adjacent sensing branches (14, 17) are electrically connected.

5. The magnetic field transducer (1) of any preceding claim, wherein the current source (5) comprises a main current source (31) and a supplementary current source (32), wherein the main current source is configured to set the base current (ls) and the supplementary current source is configured to set the supplementary current (lSuP).

6. The magnetic field transducer (1) of any preceding claim, wherein the supplementary current source (lSUp) is directly electrically connected to the current source (ls).

7. The magnetic field transducer (1) of the preceding claim, wherein the current source (5) or at least the main current source (ls) thereof is a voltage driven current source.P3057PC008. The magnetic field transducer (1) of any preceding claim, wherein the base current section (12) is directly electrically connected to the supplementary current source (lSUp).

9. The magnetic field transducer (1) of any preceding claim, wherein the signal regulation circuit (3) is electrically coupled or connected to a base current section (12) and a resistor section (24), wherein the resistor section (24) is configured to provide a predefined reference resistance to at least one of the signal regulation circuit (3) or the power supply (4) and the base current section (12) is configured to provide a predefined current to the signal regulation circuit (3).

10. The magnetic field transducer (1) of the preceding claim, wherein the signal regulation circuit (3) comprises the base current section (12) and the resistor section (24).

11. The magnetic field transducer (1 ) of either of the two directly preceding claims, wherein the resistor section (24) comprises a thermoresistor configured to compensate variation of TMR Wheatstone bridge resistance caused by temperature change.

12. The magnetic field transducer (1) of any one of the three directly preceding claims, wherein a resistance of the resistor section (24) is based on a resistance of the TMR Wheatstone bridge (6) in an absence of an external magnetic field.

13. The magnetic field transducer (1) of any one of the four directly preceding claims, wherein the resistor section (24) is connected to a component to control a temperature of the resistor section (24) based on the thermoresistor and the resistance of the TMR Wheatstone bridge (6) in the absence of the external magnetic field.

14. The magnetic field transducer (1) of any preceding claim, wherein the TMR Wheatstone bridge comprises vortex based TMR sensing elements or hard-bias TMR sensing elements.

15. The magnetic field transducer (1) of any preceding claim, wherein the TMR Wheatstone bridge comprises in-plane magnetic anisotropy in a sensing layer with an easy axis oriented essentially perpendicular to a sensitivity axis, or wherein the TMR Wheatstone bridge comprises an out-of-plane magnetic anisotropy in a sensing layer with an easy axis oriented essentially parallel to a sensitivity axis.

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