Method for manufacturing a device for detecting a magnetic field

Abstract

The present invention relates to a method for manufacturing a device for detecting a magnetic field, which consists in selectively irradiating a plurality of magnetoresistive elements having identical physical parameters, deposited on the same semiconductor chip, with light ions in order to modulate the magnetic properties of the free magnetic layer of each of the magnetoresistive elements, thereby making it possible to integrate a plurality of magnetoresistive elements on the same semiconductor chip, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges, and connecting the magnetoresistive elements together in series so that the assembly provides an overall response made up of a plurality of linear portions, each of the linear portions being the average of the linear responses of all the magnetoresistive elements.

Description

Description Title: Manufacturing process for a magnetic field detection device. Technical field.

[0001] This disclosure relates to the field of magnetoresistive or magnetic field sensors, which utilize the change in electrical resistance of a magnetic material induced by a change in an applied external magnetic field. Specifically, this disclosure concerns a method for manufacturing a magnetic field sensing device capable of generating a plurality of linear responses, each corresponding to an applied external magnetic field within a corresponding range of external magnetic fields, thereby providing the sensing device with a plurality of magnetic sensitivities while simultaneously expanding the range of external magnetic fields.

[0002] This disclosure also relates to such a magnetic field detection device comprising a plurality of magnetoresistive elements deposited on a single semiconductor chip. Previous technique

[0003] A magnetoristic sensor or magnetic field sensor refers to a sensor that exploits the variation in electrical resistance of a magnetoresistive element as a function of the amplitude and direction of the applied magnetic field.

[0004] Figure 1 shows a perspective view of a conventional three-layer stacking used to obtain such a magnetic field sensor using magnetoresistance.

[0005] The stack includes a first magnetic layer 101 which has an easily orientable direction of magnetization. This first layer 101 is made of a magnetic material. It is the free layer whose magnetization is sensitive to the external magnetic field.

[0006] A second magnetic layer 102 has a fixed magnetization direction. This second layer is made of a magnetic material that may have a different composition than that of the first magnetic layer 101. It is the reference layer.

[0007] A third layer 103 made of a non-magnetic material is arranged between the first and second magnetic layers 101, 102.

[0008] When the separation layer is electrically conductive, the sensor exploits giant magnetoresistance (GMR), which reflects the dependence of the electric current on the relative orientation of the magnetizations of the magnetic layers located on either side of the non-magnetic metallic layer.

[0009] When the separation layer is electrically insulating, the sensor exploits tunnel magnetoresistance (TMR), which reflects the dependence of the current in a tunnel junction on the relative orientation of the magnetizations located on either side of the non-magnetic insulating layer.

[0010] In order to obtain a measurement signal that varies with the external magnetic field, the magnetic stack must be in a perpendicular magnetic configuration where the easy magnetization direction of the two magnetic layers is perpendicular to each other in zero magnetic field. This requires controlling the anisotropies in the two magnetic layers to create an easy magnetization direction in each layer that is perpendicular to that of the other layer, allowing for a linear and reversible variation of the electrical resistance value as a function of the applied external magnetic field.

[0011] When the magnetoresistive stack 100 is subjected to a magnetic field whose direction is perpendicular to the easy magnetization direction of the free layer, and whose amplitude varies, the magnetization in the free layer 101 deviates from the direction when the field is zero, forming an angle with respect to the easy magnetization direction. The magnetization of the reference layer remains fixed and is oriented along the easy magnetization direction of the reference layer. The relative angle between the magnetizations of the two layers is therefore modulated by the applied magnetic field, resulting in a reversible variation of the magnetoresistance of the sensing element, and consequently of the signal obtained by measuring the resistance.

[0012] The variation in resistance is substantially linear when the applied magnetic field is less than the anisotropy field of the first free layer 101.

[0013] When the applied magnetic field is greater than the anisotropic field of the first free layer 101 but less than the anisotropic field of the second reference layer 102, the applied field is strong enough to saturate the first free layer. Under these conditions, a maximum response is obtained. In other words, the resistance no longer changes.

[0014] Figure 2 schematically represents the shape of a transfer curve 20 representative of an example of the response generated by a magnetoresistive sensor from Figure 1 when exposed to a magnetic field of varying amplitude. In Figure 2, the intensity of the external magnetic field is represented on the x-axis and the resistance on the y-axis.

[0015] Curve 20 includes a linear region 20a between an upper saturation point 20e and a lower saturation point 20d in which the electrical resistance of the sensor varies linearly with the applied magnetic field. This is the region in which the magnetoresistive sensor can provide an indicative signal of the intensity of the applied magnetic field and be used as a magnetic field sensor.

[0016] Curve 20 comprises two saturation regions 20c, 20b extending from saturation points 20e, 20d, in which the resistance no longer changes with respect to the external magnetic field. In other words, the resistance remains essentially constant regardless of variations in the magnetic field.

[0017] The operation of a magnetoresistive element or magnetoresistive sensor is therefore mainly limited to the linear region 20a. The two characteristic parameters of a magnetic field sensor are thus the sensitivity of the magnetoresistive sensor, which depends on the variation of resistance per unit of magnetic field, and the magnetic field range in which the signal remains linear.

[0018] To obtain a high-performance magnetoresistive sensor, it is necessary to control the orientation of the magnetic moments of the magnetic structures, so as to be able to correlate the linear variation of electrical resistance with the magnetic field to be measured, to obtain a linear response over the widest possible range of magnetic fields, while having a large variation of resistance per unit field.

[0019] As stated above, to obtain a linear response, the easy magnetization direction of the free magnetic layer 101 must be perpendicular to the magnetization direction of the reference layer 102 when the applied external field is zero.

[0020] However, it is known that magnetoresistive elements generally have a relatively limited operating range, and usually for low intensity magnetic fields.

[0021] Conventional solutions generally involve modifying the thickness or materials of the various layers forming the magnetoresistive element stack to alter the linear response. While these solutions allow for achieving a desired orthogonal configuration between the magnetic anisotropy axis of the reference magnetic layer and that of the free magnetic layer, they only allow for varying the linear response for a single magnetoresistive element. This is because thickness variations and material changes are implemented during the manufacturing steps of the magnetoresistive elements, and current manufacturing techniques do not allow for the fabrication of different magnetoresistive elements on the same semiconductor chip. Therefore, the conventional solution does not enable the fabrication of a magnetic field detection device with multiple linear responses.

[0022] Document WO208212896 proposes a magnetoresistive sensor capable of generating several different linear responses by stacking multiple magnetoresistive elements on top of each other. Each magnetoresistive element is capable of generating a linear response different from those generated by the other magnetoresistive elements. This type of structure allows the thickness of the free layer or the antiferromagnetic layer to be varied in order to modify the linear response during the sensor manufacturing process.

[0023] This solution is not entirely satisfactory because the thin-film deposition technique does not allow for fine-tuning the anisotropy of the free layer. Furthermore, variations in the free layer thickness, generally less than 1 Angstrom, can alter the RKKY coupling. Stacking multiple magnetoresistive elements on top of each other also introduces roughness at the interfaces, thus limiting the sensor's performance. The manufacturing process for such a sensor remains complex because it is necessary to adapt the fabrication process for each magnetoresistive element. Moreover, the number of elements that can be stacked is also limited by the deposition technique.

[0024] Consequently, it is desirable to propose a method which makes it possible to broaden the operating range of a simple sensor to extend the linear region, i.e. the operating range, while maintaining the sensitivity of the magnetic field sensor, i.e. preserving a linear response.

[0025] The present invention therefore aims to overcome the aforementioned drawbacks by proposing an ion irradiation process which allows the magnetic properties of the free magnetic layer of each of the magnetoresistive elements to be modulated from a plurality of identical magnetoresistive elements previously deposited on the same semiconductor chip, thus allowing the integration of several magnetoresistive elements, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges, on the same semiconductor chip.

[0026] The inventors observed that it is possible to modify the magnetic anisotropy of the free magnetic layer by ion irradiation by selecting appropriate irradiation parameters. In particular, they noted that sensitivity increases as the irradiation dose or fluence increases. Thus, it is possible to modulate the magnetic properties of the magnetoresistive element as a function of the irradiation dose or fluence to obtain the desired linear response and operating range. This ion irradiation technique can therefore be applied to modulate the magnetic properties of multiple identical magnetoresistive elements arranged on the same semiconductor chip as a function of energy, irradiation dose, or fluence, thereby creating a detection device with multiple different linear responses, each associated with a specific operating range.

[0027] Another objective of the present invention is to provide a manufacturing process that is easily adaptable regardless of the type of magnetoresistive element used. It can be a GMR magnetoresistive element or a TMR magnetoresistive element, since the process is based primarily on the same physical phenomenon, namely the modification of the magnetic anisotropy of the free layer by ion irradiation / implantation. Summary

[0028] This disclosure improves the situation.

[0029] A method for manufacturing a magnetic field detection device is proposed, said method comprising the following steps: - providing (E1) a plurality of identical magnetoresistive elements deposited on the same semiconductor chip, said magnetoresistive elements being capable of generating the same linear response associated with a range of applied magnetic field, each magnetoresistive element comprising a free region having a magnetic anisotropy along a first direction of easy magnetization, a reference region having a second magnetic anisotropy along a second direction of easy magnetization perpendicular to the first direction of easy magnetization in zero field, a non-magnetic layer interposed between the free region and the reference region;- to selectively irradiate (E2) each magnetoresistive element with an ion beam using a set of ion irradiation parameters chosen to modify the amplitude of the first magnetic anisotropy of the free region so that each irradiated magnetoresistive element generates a different linear response, each associated with a range of applied magnetic field intensity, said irradiation parameters being the ion acceleration voltage and the irradiation dose; - to connect (E3) said magnetoresistive elements in series to form a magnetic field detection device capable of generating an overall response consisting of a succession of contiguous linear portions, each linear portion corresponding to the average of the linear responses generated by the plurality of irradiated magnetoresistive elements.

[0030] The features described in the following paragraphs may optionally be implemented, independently of each other or in combination with each other:

[0031] According to one embodiment, the ions of the ion beam can be selected from the ions in the list including helium (He + ), of hydrogen (H + ), neon (Ne + ), argon (Ar + ), gallium (Ga + ), krypton (Kr + ) or xenon (Xe + ).

[0032] Preferably, the ions can be emitted with an accelerating voltage between 0.1 keV and 500 keV.

[0033] Preferably, the ions can be emitted with an irradiation dose between 1*10 11 ions / cm 2 and 1*10 17 ions / cm 2 .

[0034] According to another embodiment, the free region may include a free ferromagnetic layer, the first magnetic anisotropy along a first direction of easy magnetization of the free ferromagnetic layer being induced by an interfacial anisotropy.

[0035] According to yet another embodiment, the irradiation parameters can be chosen so that the ions emitted during the irradiation step modify the interfacial anisotropy of the free ferromagnetic layer in order to modify the first magnetic anisotropy.

[0036] According to one embodiment, the free region may comprise a free magnetic layer and an antiferromagnetic layer in contact with the free magnetic layer, the first magnetic anisotropy along a first direction of easy magnetization of the free ferromagnetic layer being induced by an exchange anisotropy with the antiferromagnetic layer.

[0037] According to one embodiment, the irradiation parameters can be chosen so that the ions emitted during the irradiation step modify the common interface between the antiferromagnetic layer and the free ferromagnetic layer to control the exchange anisotropy in order to modify the first magnetic anisotropy of the free ferromagnetic layer.

[0038] According to another embodiment, the free region may comprise a free ferromagnetic layer and an RKKY coupling region comprising a non-magnetic transition metal layer in contact with the free ferromagnetic layer, a ferromagnetic layer and an antiferromagnetic layer, the first magnetic anisotropy along a first easy magnetization direction of the free layer being induced by an RKKY coupling.

[0039] In this embodiment, the irradiation parameters can be chosen so that the ions emitted during the irradiation step modify the non-magnetic transition metal layer of the RKKY coupling region in order to control the first magnetic anisotropy of the free ferromagnetic layer.

[0040] Preferably, said magnetoresistive elements may be giant magnetoresistance (GMR) elements or tunnel magnetoresistance (TMR) elements.

[0041] In another respect, a magnetic field detection device is proposed, comprising: - a plurality of identical magnetoresistive elements deposited on the same semiconductor chip, each magnetoresistive element comprising a free region having a first magnetic anisotropy along a first direction of easy magnetization, a reference region having a second magnetic anisotropy along a second direction of easy magnetization perpendicular to the first direction of easy magnetization in zero field, an intermediate non-magnetic region interposed between the free region and the reference region;- said magnetoresistive elements being irradiated with a set of irradiation parameters chosen so as to modify the amplitude of the magnetic anisotropy of the first free magnetic region of each magnetoresistive element so that each irradiated magnetoresistive element is capable of generating a different linear response, each associated with a range of applied external magnetic field intensity, said irradiation parameters being the ion acceleration voltage and the irradiation dose; - said magnetoresistive elements being connected in series to form a magnetic field detection device capable of generating an overall response formed of a succession of contiguous linear portions, each linear portion corresponding to the average of the linear responses generated by the plurality of irradiated magnetoresistive elements. Brief description of the drawings

[0042] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, on which: Fig. 1

[0043] [Fig. 1] Figure 1 shows a schematic perspective view of a stack of layers to obtain a known magnetic field sensor. Fig. 2

[0044] [Fig. 2] Figure 2 represents an example of linear response generated by a resistive element of Figure 1 as a function of an applied magnetic field. Fig. 3

[0045] [Fig. 3] Figure 3 represents the main steps of the manufacturing process according to one embodiment.

[0046] [Fig. 4] Figure 4 shows an array of magnetoresistive elements supported by the same semiconductor chip according to an embodiment prior to the ion irradiation step. Fig. 5

[0047] [Fig. 5] Figure 5 shows the network of magnetoresistive elements supported by a semiconductor chip of Figure 4 after the ion irradiation step according to one embodiment, each of the elements having been irradiated with a different set of irradiation parameters. Fig. 6

[0048] [Fig. 6] Figure 6 shows an example of five different linear responses generated by a magnetoresistive element having been irradiated with five different sets of irradiation parameters and the linear response resulting from the series combination of the five linear responses. Fig. 7A

[0049] [Fig. 7A] Figure 7A shows an example of an implementation of a stack of layers forming a magnetoresistive element using interfacial anisotropy to induce magnetic anisotropy in the free layer in order to create the direction of easy magnetization in that layer. Fig. 7B

[0050] [Fig. 7B] Figure 7B shows the same layer stacking as in Figure 7A, but with the free layer and the reference layer of the stack reversed relative to the intermediate layer. Fig. 7C

[0051] [Fig. 7C] Figure 7C shows a curve representing the variation of interfacial anisotropy as a function of irradiation conditions. Fig. 8A

[0052] [Fig. 8A] Figure 8A shows an example of an implementation of a stack of layers forming a magnetoresistive element using exchange anisotropy to induce magnetic anisotropy in the free layer in order to create the direction of easy magnetization in that layer. Fig. 8B

[0053] [Fig. 8B] Figure 8B shows the same layer stacking as in Figure 8A, with the free layer and reference layer of the stacking reversed relative to the intermediate layer, and an example of ion irradiation to modify the exchange anisotropy. Fig. 8C

[0054] [Fig. 8C] Figure 8C shows a curve representing the variation of the exchange anisotropy as a function of irradiation conditions. Fig. 9A

[0055] [Fig. 9A] Figure 9A shows an example of the realization of a stack of layers forming a magnetoresistive element using RKKY coupling (acronym for Ruderman-Kittel-Kasuva-Yoshida) arising from the exchange interaction between two ferromagnetic layers via a transition metal layer to induce magnetic anisotropy in the free layer in order to create the direction of easy magnetization in that layer. Fig. 9B

[0056] [Fig. 9B] Figure 9B shows the same layer stacking as in Figure 9A by reversing the free layer and the reference layer of the stacking with respect to the intermediate layer and an example of ion irradiation to modify the magnetic anisotropy of the free layer. Fig. 9C

[0057] [Fig. 9C] Figure 9C shows a curve representing the variation of RKKY coupling as a function of irradiation conditions. Description of the implementation methods

[0058] For the purposes of this disclosure, a magnetoresistive sensor exploits the change in electrical resistance of a magnetoresistive element induced by a change in an external magnetic field to be measured. The performance of a magnetoresistive sensor is characterized by its magnetic sensitivity, which corresponds to a change in the resistance of a magnetoresistive element in response to an applied magnetic field; the linearity of the sensor's magnetic response to the applied field; and the operating range within which the magnetic response of the magnetoresistive device is linear.

[0059] The linear response of a magnetoresistive element's signal results from a specific magnetic configuration in which the magnetization of the reference layer and the magnetization of the free layer are oriented perpendicularly to each other in a zero-field environment. When the magnetic field to be measured—that is, the external field applied parallel to the easy-magnetization axis of the reference layer—is non-zero, the magnetization of the free layer deviates from the direction of the easy-magnetization axis in a zero-field environment. The relative angle between the two magnetizations of the two layers is modulated by the applied magnetic field, leading to a linear and reversible variation in the sensor's magnetoresistance, and therefore in the signal obtained from the sensor.

[0060] The sensor is therefore defined mainly by the following parameters: - the magnetization of the reference layer whose orientation is defined by the orientation of the easy magnetization axis; - the magnetization of the free layer whose orientation is defined by the orientation of the easy magnetization axis; the magnetization reversal field of the reference layer; - the applied external field, i.e. the one that must be measured, denoted Ha.

[0061] For applied magnetic fields lower than the free-layer anisotropy field, the variation remains essentially linear. The sensor's sensitivity, which represents the signal variation per unit field strength, is inversely proportional to the free-layer anisotropy field. Modulating the sensor's magnetic properties therefore amounts to modulating the free-layer anisotropy. This disclosure proposes using the technique of ion irradiation with light ions, which allows for local modification in the free layer of the stack and at the interfaces between layers through local kinetic energy transfer, thus modifying the intensity of the induced or present magnetic anisotropy in the free layer.

[0062] In particular, the inventors observed that it is possible to modify the magnetic anisotropy of the free magnetic layer by ion irradiation by selecting appropriate irradiation parameters. They noted, specifically, that sensitivity increases with increasing irradiation dose or fluence. Thus, it is possible to modulate the magnetic properties of a magnetoresistive element according to irradiation conditions, for example, based on irradiation dose or fluence, in order to obtain the desired linear response and operating range of the magnetoresistive element.

[0063] In order to broaden the operating range while maintaining the magnetic sensitivity of the sensor, the present invention proposes a method for manufacturing a magnetic field detection device which consists of selectively irradiating a plurality of magnetoresistive elements having identical physical parameters deposited on the same semiconductor chip with light ions in order to modulate the magnetic properties of the free magnetic layer of each of the magnetoresistive elements, thus allowing the integration of a plurality of magnetoresistive elements on the same semiconductor chip, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges, and connecting them in series together so that the assembly provides an overall response formed of a plurality of linear portions, each of the linear portions being the average of the linear responses of all the magnetoresistive elements.In other words, instead of having a single linear region corresponding to the operating range of a magnetoresistive element, the irradiation process makes it possible to obtain a magnetic field detection device composed of multiple magnetoresistive elements, each with a linear response associated with a specific range of applied external magnetic field strength. Thus, the magnetic response of such a device is formed by a succession of linear segments, each segment corresponding to the average of the linear responses generated by each irradiated magnetoresistive element. The manufacturing process described in this disclosure therefore allows the sensor's operating range to be broadened, from high magnetic fields of 1T to low magnetic fields, while maintaining the sensor's sensitivity.

[0064] With reference to Figure 3, a manufacturing process for a magnetic field detection device according to one embodiment is described above.

[0065] In a first step (E1), a plurality of identical magnetoresistive elements deposited on the same semiconductor chip is provided.

[0066] The term “identical magnetoresistive elements” refers to elements that are identical stacks, meaning they have the same number of layers, the same materials for each layer, and the same thickness for each layer. Therefore, all magnetoresistive elements can be manufactured using the same lithographic masks to deposit them onto the same chip. Consequently, all identical magnetoresistive elements are configured to generate the same linear response associated with the same range of applied external magnetic fields.

[0067] The term “same semiconductor chip” refers to a wafer of semiconductor material in which electronic circuits are integrated. Therefore, multiple magnetoresistive elements are deposited on a single wafer and can be used by one or more circuits.

[0068] Figure 4 illustrates a schematic top view of an example of twelve identical magnetoresistive elements 200 deposited on a single semiconductor chip 201. In this example, they are arranged at regular intervals, forming an array. According to another example, the magnetoresistive elements may have different intervals and may be arranged in a random distribution.

[0069] The structure of an individual magnetoresistive element is in the form of a stack of layers and is mainly composed of three main regions: - a free region comprising a first free or soft ferromagnetic layer with an axis of easy magnetization which orients itself under the effect of an applied external field; - a reference region comprising a first reference ferromagnetic layer having an axis of easy magnetization whose direction defines the direction of detection of the sensor; - a magnetoresistive region interposed between the reference region and the free region and configured to allow the measurement of a variation in resistance when there is a difference in the direction of magnetization between the reference region and the free region.

[0070] The relative angle between the magnetization of the free layer and the magnetization of the reference layer is modulated by the variation in the amplitude of the applied magnetic field, resulting in a linear and reversible variation in the magnetoresistance of the magnetoresistive element.

[0071] The magnetization direction of the reference layer in the reference region can be fixed by means of the exchange anisotropy induced by the presence of an antiferromagnetic layer. According to another embodiment, the magnetization direction of the reference layer can be fixed by the presence of an RKKY coupling.

[0072] The magnetization direction of the free layer of the free region can be induced by different physical phenomena: an interfacial anisotropy, an exchange coupling between an antiferromagnetic layer and a ferromagnetic layer or an RKKY coupling.

[0073] In a second step of the process of this disclosure (E2), each magnetoresistive element in Figure 4 is selectively irradiated by an ion beam with a set of ion irradiation parameters chosen to modify the amplitude of the magnetic anisotropy of the free region of the magnetoresistive element so that each irradiated magnetoresistive element generates a different linear response associated with each range of applied external magnetic field intensity, thus enabling the integration of a plurality of magnetoresistive elements on the same semiconductor chip, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges.

[0074] Figure 5 shows the supported magnetoresistive element array from Figure 4 after the ion irradiation step, each element having been irradiated with a different set of irradiation parameters. Each of the irradiated elements 201' therefore generates a different linear response over a different magnetic field range.

[0075] The irradiation parameters are the accelerating voltage and the irradiation dose. For each magnetoresistive element, the accelerating voltage and the irradiation dose are therefore chosen to obtain the desired linear response and magnetic field strength range. In the example in Figure 5, the twelve magnetoresistive elements are irradiated with twelve sets of irradiation parameters.

[0076] According to one embodiment, the ions of the ion beam are selected from the ions in the list including helium (He + ), of hydrogen (H + ), neon (Ne +), argon (Ar + ), gallium (Ga + ), krypton (Kr + ) or xenon (Xe + ).

[0077] The ions are emitted with an accelerating voltage between 0.1 keV and 500 keV, and with an irradiation dose between 1*10 11 ions / cm 2 and 1*10 17 ions / cm 2 .

[0078] To selectively irradiate each magnetoresistive element, the irradiation step includes a substep for selecting one magnetoresistive element from among the plurality of magnetoresistive elements. To avoid irradiating the unselected magnetoresistive elements, a mask is placed over them, preventing the modification of their magnetic properties by irradiation. The mask can be made of a metallic or insulating material such as Ta, TaN, SiN, W, or a resin.

[0079] In Figure 5, as an example, the magnetoresistive element 200' is selected for irradiation, and the other elements are defined as not to be irradiated. A mask 206 is deposited over these unselected elements to prevent ions from irradiating their layers. The masks are deposited using a known process involving UV lithography followed by ion etching. The masks typically have a thickness between 10 nm and 1500 nm.

[0080] The irradiation step is thus repeated for all magnetoresistive elements. After each irradiation step of a magnetoresistive element, the mask is removed in order to replace it with another mask, thus exposing the next magnetoresistive element to be irradiated.

[0081] After irradiation of all the elements, the process includes a connection step in which the irradiated magnetoresistive elements 200' are connected in series to form a magnetic field detection device capable of generating a main response consisting of a succession of contiguous linear portions, each linear portion being the average of the linear responses generated by each of the irradiated magnetoresistive elements.

[0082] Figure 6 shows the schematic profile of five curves 301, 302, 303, 304, and 305, representing five responses generated by five irradiated magnetoresistive elements from Figure 5 when subjected to a magnetic field of intensity in a direction perpendicular to the magnetization direction of the free layer. Each of the five elements is irradiated with a different set of irradiation parameters. In Figure 6, the intensity of the external magnetic field is represented on the x-axis and the resistance on the y-axis.

[0083] Curves 301, 302, 303, 304, 305 each have a substantially linear region associated with a different magnetic field range 301a, 302a, 303a, 304a, 305a.

[0084] The process includes a third step E3 in which the magnetoresistive elements are connected in series to form a magnetic field detection device capable of generating an overall response consisting of a succession of contiguous linear portions, each linear portion corresponding to the average of the linear responses generated by the plurality of irradiated magnetoresistive elements.

[0085] In Figure 6, curve 300 represents the main response generated by the five irradiated magnetoresistive elements connected in series. The main response 300 results from the average of the five generated responses 301, 302, 303, 304, 305. The main response is formed from a succession of linear portions 300a, 300b, 300c, 300d, 300e, 300f, 300g, 300h, 300i.

[0086] For example, in the first linear portion 300a, the five connected elements generate a first substantially linear response over a first range of magnetic field intensity 301a.

[0087] In the second linear portion 300b, the five connected elements generate a second substantially linear response over a second magnetic field intensity range 303b.

[0088] In the third linear portion 300c, the five connected elements generate a third substantially linear response over a third magnetic field intensity range 303c.

[0089] In the fourth linear portion 300d, the five connected elements generate a fourth substantially linear response over a third magnetic field intensity range 303d.

[0090] In the fifth linear portion 300e, the five connected elements generate a fifth substantially linear response over a fifth range of magnetic field intensity 303e.

[0091] In the sixth linear portion 300f, the five connected elements generate a sixth substantially linear response over a sixth magnetic field intensity range 303f.

[0092] In the seventh linear portion 300g, the five connected elements generate a seventh substantially linear response over a seventh magnetic field intensity range of 303g.

[0093] In the eighth linear portion 300h, the five connected elements generate an eighth substantially linear response over an eighth magnetic field intensity range 303h.

[0094] In the ninth linear portion 300i, the five connected elements generate a ninth substantially linear response over a ninth magnetic field intensity range 303i.

[0095] The process described in this disclosure thus makes it possible to obtain a magnetic field detection device that has a plurality of different sensitivities corresponding to a change in the device's resistance in response to an applied magnetic field. In the example shown in Figure 6, the device, which is formed of five magnetoresistive elements, has nine sensitivities, each corresponding to a linear portion associated with a range of applied magnetic fields. In other words, the magnetic field detection device fabricated according to the process described in this disclosure consists of a plurality of irradiated magnetoresistive elements comprising a plurality of substantially linear regions, each of the linear regions corresponding to a linear response to the applied magnetic field, thus making it possible to broaden the range of magnetic fields in which the response remains linear while maintaining the sensitivity.In prior art, the sensor has a single operating range with a single linear region.

[0096] Three examples of multilayer structures of a magnetoresistive element used in the process of this disclosure are described above with reference to Figures 7A-9C.

[0097] Figures 7A-7B represent a cross-sectional view of an example of an individual 500 magnetoresistive element whose free layer magnetization is induced by an interfacial anisotropy.

[0098] The magnetoresistive element 500 comprises a stack of thin layers deposited on the semiconductor chip 506. The layers are stacked in a direction orthogonal to the plane of the chip 506.

[0099] With reference to Figure 7A, the stack comprises successively from the semiconductor chip 506 a first conductive electrode layer 507, a reference region 510, a non-magnetic region 530, a free region 520 and a second conductive electrode layer 508.

[0100] In the example illustrated in Figures 7A and 7B, the reference region 510 comprises a first magnetic antiferromagnetic layer 512 and a reference ferromagnetic layer 511 whose easy magnetization axis direction is induced by a coupling effect with the first antiferromagnetic layer 512.

[0101] In the example shown in Figure 7A, the free region 520 comprises a free ferromagnetic layer. The direction of easy magnetization is induced by the interfacial anisotropy. According to another embodiment, the free region may comprise several free ferromagnetic layers. The free layer is the layer with the weakest anisotropy field, that is, the one whose magnetization is easily oriented under the influence of an applied external field.

[0102] The reference region is configured to exhibit a higher coercive field than the magnetic field being measured. Thus, by applying a magnetic field, it is possible to induce a change in the orientation of the magnetization of the free region without changing the magnetization of the reference region.

[0103] The non-magnetic region 530 comprises a non-magnetic layer interposed between the free layer 520 and the reference layer 511. This layer can be made of a non-magnetic conductive material, for example, metal-based such as copper or semiconductor-based. The magnetoresistive element utilizes the GMR effect of the "spin valve" formed by the two magnetic regions separated by the conductive region.

[0104] In another example, the non-magnetic region 530 may include a layer made of an electrically insulating, non-magnetic material, for example, based on oxidized and / or nitro-oxidized aluminum, oxidized gallium, oxidized tantalum, or oxidized magnesium. The magnetoresistive element utilizes the TMR effect of the junction formed by the two magnetic regions, separated by the insulating layer 530. This layer is sufficiently thin to allow electrons to tunnel through it. For example, its thickness could be between 0.5 nm and 6 nm.

[0105] The stacking order of the three regions 510, 520, and 530 interposed between the upper electrode layer 508 and the lower electrode layer 507 can be reversed. In Figure 7B, the stacking successively comprises, starting from the semiconductor chip 506, a free region 520, a non-magnetic region 530, a reference region 510, and a second conductive electrode layer 508.

[0106] In both cases, the magnetoresistive effect leads to a variation in the electrical resistance of the 500 stack as a function of the magnetic field to be measured.

[0107] In both of these designs, the irradiation process is similar and can be used to modify the magnetic anisotropy of the free layer of the free region.

[0108] The first electrode layer and second electrode layer 507, 508 are for example made of an electrically conductive material, forming two electrical terminals to inject a current perpendicular to the plane of the layers.

[0109] The magnetization of the reference region is perpendicular to the magnetization of the free region.

[0110] Instead of modulating the physical parameters of magnetoresistive elements—that is, the thicknesses of the different layers, the dimensions, and the nature of the materials, which require precise local control—as in the case of the magnetoresistive element in Figures 7A and 7B, which uses interfacial anisotropy to induce the magnetization direction of the free layer, the solution presented here consists of modifying the interfacial anisotropy of the free layer 520 by ion irradiation, controlling only the irradiation parameters, namely the accelerating voltage and the irradiation dose. This irradiation process thus allows for a smooth and controlled modification of the interfacial anisotropy.

[0111] Figure 7C represents a C1 curve showing the evolution of the amplitude of the interfacial anisotropy obtained on a magnetoresistive element of Figure 7A or 7B as a function of irradiation conditions, for example, the irradiation dose. The stack of layers is irradiated by a beam of light He ions + for different intensities of ionic flux, i.e., different fluences. The experimental results, illustrated in Figure 7C, show that the magnetic anisotropy gradually decreases as the irradiation dose increases. Ion irradiation tests on a magnetoresistive element demonstrate that it is possible to precisely modulate the amplitude of the interfacial anisotropy with very fine control by varying the irradiation dose. It is therefore possible to modify the detection sensitivity of the magnetoresistive element and the magnetic field range within which the response remains linear.

[0112] In the case where the plurality of magnetoresistive elements of Figure 4 are formed by the magnetoresistive element of Figure 7A or 7B, the irradiation step of the process of this disclosure consists of selectively irradiating the free layer 520 of the free region of each of the elements in order to modify the interfacial anisotropy of each of the free regions in order to modulate the magnetic properties of the free magnetic layer of each of the magnetoresistive elements, thus allowing the integration of a plurality of magnetoresistive elements on the same semiconductor chip, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges.

[0113] Figures 8A-8B represent a cross-sectional view of a second example of an individual 600 magnetoresistive element whose free layer magnetization is induced by an exchange anisotropy.

[0114] The magnetoresistive element 600 comprises a stack of thin layers deposited on the semiconductor chip 606. The layers are stacked in a direction orthogonal to the plane of the chip 606.

[0115] With reference to Figure 8A, the stack comprises successively from the semiconductor chip 606 a first conductive electrode layer 607, a reference region 610, a non-magnetic region 630, a free region 620 and a second conductive electrode layer 608.

[0116] In the example illustrated in Figures 8A and 8B, as in the example in Figures 7A and 7B, the reference region 610 comprises a first magnetic antiferromagnetic layer 612 and a reference ferromagnetic layer 611 whose easy magnetization axis direction is induced by a coupling effect with the antiferromagnetic layer 612.

[0117] In the example of Figure 8A, the magnetic anisotropy along an easy magnetization direction of the free ferromagnetic layer 621 of the free region is induced by an exchange bias anisotropy. The free region 620 comprises a second antiferromagnetic layer 622 in contact with the free ferromagnetic layer 621 to induce said first exchange bias anisotropy. For example, the materials of the second antiferromagnetic layer can be based on IrMn, FeMn, PtMn, NiMn, or other manganese-based compounds.

[0118] As in the example in Figure 7A, the non-magnetic region 630 comprises a non-magnetic layer interposed between the free ferromagnetic layer 621 and the reference layer 611. This layer may be made of a non-magnetic conductive material, and the magnetoresistive element may be a GMR element. Alternatively, it may be made of a non-magnetic insulating material, and the magnetoresistive element may be a TMR element.

[0119] Thus and with reference to Figure 8A, the stack comprises successively from the semiconductor chip 606, a first conductive electrode layer 607, a magnetic antiferromagnetic layer 612, a reference ferromagnetic layer 611, a non-magnetic layer 630, a free ferromagnetic layer 621, an antiferromagnetic layer 622 and a second conductive electrode layer 608.

[0120] The stacking order of the three regions 610, 620, and 630 interposed between the upper electrode layer 608 and the lower electrode layer 607 can be reversed. In Figure 8B, the stacking consists successively, starting from the semiconductor chip 606, of a first conductive electrode layer 607, a free region 620, a non-magnetic region 630, a reference region 610, and a second conductive electrode layer 608.

[0121] The first electrode layer and second electrode layer 607, 608 are for example made of an electrically conductive material, forming two electrical terminals to inject a current perpendicular to the plane of the layers.

[0122] When a ferromagnetic material and an antiferromagnetic material share a common interface, an effect called "exchange bias" can be observed, manifesting primarily as a shift in the magnetic field of the hysteresis loop. The free ferromagnetic layer 621 then exhibits an anisotropy direction imposed by the antiferromagnetic material.

[0123] Within the framework of the magnetoresistive element in Figures 8A and 8B, which uses exchange bias to induce the magnetization direction of the free layer 621, the solution presented here involves modifying the exchange bias between the free layer 621 and the second antiferromagnetic layer 622 by irradiating the common interface 623 with ions. More specifically, the irradiation parameters, namely the accelerating voltage and the irradiation dose, are chosen so that the ions emitted during the irradiation step modify the common interface 623 between the second antiferromagnetic layer 622 and the free ferromagnetic layer 621 to control the exchange bias and thereby modify the magnetic anisotropy of the free layer 621. The irradiation process thus allows for a smooth and controlled modification of the interfacial anisotropy.

[0124] Figure 8C shows a C2 curve illustrating the evolution of the amplitude of the exchange anisotropy obtained on a magnetoresistive element from Figure 8A or 8B as a function of irradiation conditions, for example, the irradiation dose. The stack of layers is irradiated by a beam of light He ions + for different intensities of ionic flux, i.e., different fluences. The experimental results, illustrated in Figure 8C, show that the amplitude of the exchange anisotropy varies with the irradiation dose. It is therefore possible to modify the detection sensitivity of the magnetoresistive element and the magnetic field range in which the response remains linear.

[0125] In the case where the plurality of magnetoresistive elements of Figure 4 are formed by the magnetoresistive element of Figure 8A or 8B, the irradiation step of the process of the present disclosure-vr- consists of selectively irradiating the common interface 623 between the free ferromagnetic layer 621 and the second antiferromagnetic layer 622 of the free region of each of the elements in order to modify the exchange anisotropy of each of the free regions in order to modulate the magnetic properties of the free magnetic layer of each of the magnetoresistive elements, thus allowing the integration of a plurality of magnetoresistive elements on the same semiconductor chip, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges.

[0126] Figures 9A-9B represent a cross-sectional view of a third example of an individual 700 magnetoresistive element whose free layer magnetization is induced by an RKKY anisotropy.

[0127] The magnetoresistive element 700 comprises a stack of thin layers deposited on the semiconductor chip 706. The layers are stacked in a direction orthogonal to the plane of the chip 706.

[0128] With reference to Figure 9A, the stack comprises successively from the semiconductor chip 706 a first conductive electrode layer 707, a reference region 710, a non-magnetic region 730, a free region 720 and a second conductive electrode layer 708.

[0129] In the context of the example illustrated in Figures 9A and 9B, as in the example of Figures 7A and 7B and the example of Figures 8A and 8B, the reference region 710 comprises a first magnetic antiferromagnetic layer 712 and a reference ferromagnetic layer 711 whose direction of the easy magnetization axis is induced by a coupling effect with the antiferromagnetic layer 712.

[0130] In the example of Figure 9A, the magnetic anisotropy along an easy magnetization direction of the free layer 721 of the free region is induced by an RKKY coupling. The free region 720 comprises an RKKY coupling region and a free ferromagnetic layer 721 in contact with the RKKY coupling region to induce the magnetic anisotropy of the free layer. The RKKY coupling region comprises a non-magnetic transition metal layer, a ferromagnetic layer, and a second antiferromagnetic layer, the free ferromagnetic layer being in contact with the non-magnetic transition metal layer of the RKKY coupling region.

[0131] The RKKY coupling arises from the two ferromagnetic layers 721 and 723 separated by the non-magnetic layer 722. In this configuration, the magnetizations of the two ferromagnetic layers are coupled by an exchange interaction mediated by electrons in the non-magnetic layer. The non-magnetic layer can be one of the 3D, 4D, or 5D transition metals such as Ru, Re, Cu, or Rh. In the prior art, the thickness of the transition metal layer 722 allows for tuning the RKKY coupling anisotropy. The process described in this disclosure proposes irradiating the non-magnetic layer 722 to control the coupling intensity.

[0132] The non-magnetic region 730 comprises a non-magnetic layer interposed between the free layer 721 and the reference layer 711. This layer may be made of a non-magnetic conductive material, and the magnetoresistive element may be a GMR element. Alternatively, it may be made of a non-magnetic insulating material, and the magnetoresistive element may be a TMR element.

[0133] Thus, and with reference to Figure 9A, the stack comprises, successively from the semiconductor chip 706, a first conductive electrode layer 707, a magnetic antiferromagnetic layer 712, a reference ferromagnetic layer 711, a non-magnetic layer 730, a free layer 721, a non-magnetic transition metal layer 722, a ferromagnetic layer 723, an antiferromagnetic layer 724, and a second conductive electrode layer 708. The RKKY coupling region therefore comprises a non-magnetic transition metal layer 722, a ferromagnetic layer 723, and an antiferromagnetic layer 724.

[0134] The stacking order of the three regions 710, 720, and 730 interposed between the upper electrode layer 708 and the lower electrode layer 707 can be reversed. In Figure 9B, the stacking comprises, starting from the semiconductor chip 706, a first conductive electrode layer 707, a free region 720, a non-magnetic region 730, a reference region 710, and a second conductive electrode layer 708.

[0135] The first electrode layer and second electrode layer 707, 708 are for example made of an electrically conductive material, forming two electrical terminals to inject a current perpendicular to the plane of the layers.

[0136] Within the framework of the magnetoresistive element in Figures 9A and 9B, which uses RKKY coupling to induce the magnetization direction of the free layer 721, the solution presented here involves modifying the RKKY coupling intensity between the free ferromagnetic layer 721 and the ferromagnetic layer 723 by irradiating the non-magnetic transition metal layer 722. More specifically, the irradiation parameters, namely the accelerating voltage and the irradiation dose, are chosen so that the ions emitted during the irradiation step modify the non-magnetic transition metal layer 722 in a controlled manner, thereby altering the magnetic anisotropy of the free layer 721. The irradiation process thus allows for a smooth and controlled modification of the RKKY coupling intensity.

[0137] Figure 9C shows a C3 curve illustrating the evolution of the RKKY coupling intensity obtained on a magnetoresistive element from Figure 9A or 9B as a function of irradiation conditions, for example, the irradiation dose. The stack of layers is irradiated by a light He ion beam + for different ion flux intensities, i.e., different fluences. The experimental results, illustrated in Figure 9C, show that the amplitude of the RKKY coupling varies with the irradiation dose. It is therefore possible to modify the detection sensitivity of the magnetoresistive element and the magnetic field range in which the response remains linear.

[0138] In the case where the plurality of magnetoresistive elements of Figure 4 are formed by the magnetoresistive element of Figure 9A or 9B, the irradiation step of the process of this disclosure consists of selectively irradiating the non-magnetic layer 722 of the RKKY coupling region between the free ferromagnetic layer 721 and the second ferromagnetic layer 723 of each of the elements in order to modify the RKKY coupling intensity of each of the free regions in order to modulate the magnetic properties of the free ferromagnetic layer of each of the magnetoresistive elements, thus allowing the integration of a plurality of magnetoresistive elements on the same semiconductor chip, each having different linear responses, i.e. different sensitivities associated with different magnetic field ranges.

[0139] In all three embodiments, it is possible to use the process of this disclosure to fabricate a magnetic field measuring device with an expansion of the magnetic field range to be measured while maintaining the magnetic sensitivity of the device.

Claims

1. Claims

1. A method for manufacturing a magnetic field detection device (10), said method comprising the following steps: provide (E1) a plurality of identical magnetoresistive elements deposited on the same semiconductor chip, said magnetoresistive elements being capable of generating the same linear response associated with a range of applied magnetic field, each magnetoresistive element comprising a free region having magnetic anisotropy along a first easy magnetization direction, a reference region having a second magnetic anisotropy along a second easy magnetization direction perpendicular to the first easy magnetization direction in zero field, a non-magnetic layer interposed between the free region and the reference region; irradiate (E2) selectively with an ion beam each magnetoresistive element with a set of ion irradiation parameters chosen so as to modify the amplitude of the first magnetic anisotropy of the free region so that each irradiated magnetoresistive element generates a different linear response associated each with a range of applied magnetic field intensity, said irradiation parameters being the ion accelerating voltage and the irradiation dose; connect (E3) in series the said magnetoresistive elements to form a magnetic field detection device capable of generating an overall response formed of a succession of contiguous linear portions, each linear portion corresponding to the average of the linear responses generated by the plurality of irradiated magnetoresistive elements.

2. A method according to claim 1, wherein the ions of the ion beam are selected from the ions in the list comprising helium (He + ), of hydrogen (H + ), neon (Ne + ), argon (Ar + ), gallium (Ga + ), krypton (Kr + ) or xenon (Xe + ).

3. A method according to claim 1 or 2, wherein the ions are emitted with an accelerating voltage between 0.1 keV and 500 keV.

4. A method according to any one of the preceding claims, wherein the ions are emitted with an irradiation dose of between 1*10 11 ions / cm 2 and 1*10 17 ions / cm 2 .

5. A method according to any one of the preceding claims, wherein the free region (520) comprises a free ferromagnetic layer (520), the first magnetic anisotropy along a first easy magnetization direction of the free ferromagnetic layer (520) being induced by an interfacial anisotropy.

6. A method according to claim 5, wherein the irradiation parameters are chosen such that the ions emitted during the irradiation step modify the interfacial anisotropy of the free ferromagnetic layer (520) in order to modify the first magnetic anisotropy.

7. A method according to any one of claims 1 to 4, wherein the free region (620) comprises a free magnetic layer (621) and an antiferromagnetic layer (622) in contact with the free magnetic layer (621), the first magnetic anisotropy along a first direction of easy magnetization of the free ferromagnetic layer (621) being induced by an exchange anisotropy with the antiferromagnetic layer (622).

8. A method according to claim 7, wherein the irradiation parameters are chosen so that the ions emitted during the irradiation step modify the common interface (623) between the antiferromagnetic layer (622) and the free ferromagnetic layer (621) to control the exchange anisotropy in order to modify the first magnetic anisotropy of the free ferromagnetic layer (621).

9. A method according to any one of claims 1 to 4, wherein the free region (720) comprises a free ferromagnetic layer (721) and an RKKY coupling region comprising a non-magnetic transition metal layer (722) in contact with the free ferromagnetic layer (721), a ferromagnetic layer (723) and an antiferromagnetic layer (724), the first magnetic anisotropy along a first easy magnetization direction of the free ferromagnetic layer (721) being induced by an RKKY coupling.

10. A method according to claim 9, wherein the irradiation parameters are chosen so that the ions emitted during the irradiation step modify the non-magnetic transition metal layer of the RKKY coupling region in order to control the first magnetic anisotropy of the free ferromagnetic layer (721).

11. A method according to any one of claims 1 to 10, wherein said magnetoresistive elements are giant magnetoresistance (GMR) elements or tunnel magnetoresistance (TMR) elements.

12. Magnetic field detection device (200') comprising: - a plurality of identical magnetoresistive elements deposited on the same semiconductor chip (506, 606, 706), each magnetoresistive element comprising a free region (520, 620, 720) having a first magnetic anisotropy along a first direction of easy magnetization, a reference region (510, 610, 710) having a second magnetic anisotropy along a second direction of easy magnetization perpendicular to the first direction of easy magnetization in zero field, an intermediate non-magnetic region (530, 630, 730) interposed between the free region and the reference region; - said magnetoresistive elements being irradiated with a set of irradiation parameters chosen so as to modify the amplitude of the magnetic anisotropy of the first free magnetic region of each magnetoresistive element so that each irradiated magnetoresistive element is capable of generating a different linear response (301, 302, 303, 304, 305) each associated with a range of applied external magnetic field intensity (301a, 302a, 303a, 304a, 305a), said irradiation parameters being the ion acceleration voltage and the irradiation dose; - said magnetoresistive elements being connected in series to form a magnetic field detection device capable of generating an overall response (300) formed of a succession of linear portions (300a, 300b, 300c, 300e, 300f, 300g, 300h, 300i) contiguous, each linear portion corresponding to the average of the linear responses generated by the plurality of irradiated magnetoresistive elements.

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