NV diamond-based magnetic field sensor

Abstract

The invention relates to a magnetic field sensor (1) having an NV diamond (2), an excitation light source (3), which is designed to emit an excitation beam (4) for exciting electronic states of the NV diamond (2) and which is arranged such that the excitation beam (4) emitted thereby can generate an electric field within the NV diamond (2), a detector (5), which is arranged and designed to detect fluorescence radiation which the NV diamond (2) can emit as a result of irradiation with the excitation radiation (4), a microwave structure (6), which is arranged and designed to generate a microwave field within the NV diamond (2) in order to manipulate spin states of the NV diamond (2), a magnetic field generating device (7), which is designed to generate an internal, static magnetic field within the NV diamond (2) and which comprises at least one permanent magnet (8), and a hood (10) and a base plate (11), which are arranged such that they form a closed chamber (12). The NV diamond (2), the excitation light source (3), the detector (5) and the microwave structure (6) are arranged within the closed chamber (12). The hood (10) has at least one recess (13) for receiving the at least one permanent magnet (8, 9).

Description

[0001] R.415783

[0002] - 1 -

[0003] Description

[0004] title based on an NV diamond

[0005] The present invention relates to a magnetic field sensor based on an NV diamond.

[0006] State of the art

[0007] To detect a magnetic field, so-called NV magnetic field sensors are used. These sensors consist of a diamond whose crystal lattice has defects in the form of NV centers. In an NV center, a nitrogen atom occupies the lattice site of a carbon atom, with a defect located in the immediate vicinity of the nitrogen atom—again occupying the lattice site of a carbon atom. Hereinafter, the term NV center refers to the negatively charged NV center (also called N), which binds an additional electron. If such a crystal lattice is irradiated with excitation radiation with a wavelength between 490 nm and 575 nm, an electronic transition from a ground state occurs in the crystal lattice. 3 A2 into an excited state 3 E induced. From the excited state 3 E relaxes the NV center back to its ground state by emitting fluorescence radiation in a wavelength range between 637 nm and approximately 750 nm.3 A2. The basic state 3 A2 has three magnetic substates with m s =0, m s =±1. The states with m s =0 and m s The values ​​=±1 differ by an energy difference of 2.87 GHz (zero field splitting). The excited state 3 E also has three magnetic substates with m s =0, m s =±1. If the NV center is now in the ground state 3 When A2 is exposed to microwave radiation with a frequency of approximately 2.87 GHz, the NV center oscillates between the m s =0, 3 A2 -ground state and the m s =±1 , 3 A2 ground state. Upon irradiation with the excitation radiation, the NV center is now partially removed from the m s =±1 , 3 A2- R.415783

[0008] - 2 -

[0009] Ground state in the excited m s =±1 , 3The electron is put into an E-state. From there, it relaxes back to the ground state, predominantly without emitting radiation. If the amplitude of the fluorescence radiation is measured as a function of the microwave frequency, a sudden drop in the amplitude of the fluorescence radiation (a so-called dip) occurs at a frequency of 2.87 GHz. The drop in the amplitude of the fluorescence radiation can be explained by the fact that – when irradiated with microwave radiation at a frequency of 2.87 GHz – the s =0, 3 A2 -ground state is occupied with a lower probability compared to the situation without an irradiated microwave.

[0010] In an external magnetic field, the energetically degenerate states split m s =±1 , 3The A2 ground state is energetically degraded. If the amplitude of the fluorescence radiation is measured while changing the frequency of the microwave radiation, two dips are observed. The frequencies at which these dips occur depend on the size of the splitting of the m s =±1 , 3 A2 - ground state and thus depends on the field strength of the external magnetic field (Zeeman effect). In this way, the field strength of an external magnetic field can be determined.

[0011] Such a magnetic field sensor is known, for example, from DE 10 2020 204 732. In this sensor, the excitation radiation is generated using a laser diode arranged in a cavity. The cavity is formed by a recess in a carrier wafer and a glass substrate that hermetically seals the cavity. The excitation radiation is guided through the glass substrate into a lower layer, where it is focused onto a low-voltage diamond. The lower layer has a substrate on which the remaining system components, such as the diamond, a radio frequency device, photodetectors, and other optical components, are arranged. The substrate is sealed with a cap substrate containing an opening through which the excitation radiation can reach the diamond.

[0012] It is an object of the invention to provide a magnetic field sensor that does not have the disadvantages of the prior art.

[0013] Disclosure of invention R.415783

[0014] - 3 -

[0015] The present invention relates to a magnetic field sensor according to claim 1 and a method for manufacturing the magnetic field sensor according to claim 9. Advantageous embodiments of the invention are the subject of the dependent claims and the description.

[0016] The invention provides a magnetic field sensor comprising a low-voltage (LV) diamond, an excitation light source, a detector, a microwave structure, and a magnetic field generation device. The excitation light source is configured to emit an excitation beam to excite electronic states of the LV diamond. The excitation light source can be, for example, a laser diode. In this case, the excitation beam is a laser beam. The excitation light source is particularly configured to generate an excitation light beam with a wavelength between 490 nm and 575 nm. The excitation light source is further arranged and configured to direct the excitation light beam onto the LV diamond, so that an electric field is generated within the LV diamond. As a result of irradiation with the excitation light beam, the LV diamond emits an optical signal, in particular fluorescence radiation in a wavelength range between 600 nm and 850 nm.An optical element that shapes the beam (e.g., a lens) or guides the beam (e.g., a deflecting mirror) can be arranged between the excitation light source and the NV diamond. The detector is designed and positioned to detect the optical signal emitted by the NV diamond as a result of irradiation with the excitation light beam. In particular, the detector is designed to detect radiation in a wavelength range corresponding to the wavelength range of the fluorescence radiation emitted by the NV diamond, especially between 600 nm and 850 nm.

[0017] Additionally, at least one reference detector can be provided to detect the excitation light beam in order to detect fluctuations in the intensity of the excitation light source and to evaluate the optical signal independently of these fluctuations. An optical filter can be placed upstream of the detector and / or the at least one reference detector, R.415783

[0018] - 4 - which is designed to filter out the wavelength range to be detected from the incoming radiation.

[0019] A microwave source can be provided that is configured to generate an electromagnetic field which is fed into the microwave structure. The microwave structure is arranged and configured to shape the electromagnetic field in such a way as to create a microwave field suitable for manipulating the spin states of the NV diamond. The microwave field has one or more frequencies in a frequency band between 2.5 GHz and 3 GHz.

[0020] The magnetic field sensor further comprises a magnetic field generating device arranged and configured to generate an internal, static magnetic field within the NV diamond. The magnetic field generating device may include at least one permanent magnet. The at least one permanent magnet may be configured as a ring magnet whose magnetization direction changes continuously along its circumference. Alternatively, several individual magnets may be provided as permanent magnets, each with a single magnetization direction.

[0021] The magnetic field sensor further comprises a cover and a base plate arranged to form a sealed chamber. This sealed chamber is designed to be hermetically sealed. The NV diamond, the excitation light source, the detector, and the microwave structure are located within this sealed chamber. This protects these components from environmental influences. The cover has at least one recess for receiving the at least one permanent magnet. This recess is designed as a depression located in one or more side walls of the cover, particularly the cover body. The recess can be located within the cover body. The number of recesses depends on the number of permanent magnets.Thus, if the permanent magnet is designed as a ring magnet, a single ring-shaped recess can be provided to receive the ring magnet. In the case of multiple R.415783.

[0022] - 5 -

[0023] While individual magnets are provided for generating the internal magnetic field, multiple recesses may also be provided.

[0024] In this way, multiple functions can be implemented in a single component. The housing acts as a holding device for the at least one permanent magnet, as well as a cover and enclosure for the components of the magnetic field sensor arranged in the sealed chamber. This saves costs associated with the material, manufacturing, and assembly of multiple parts. Significant cost savings can be achieved, particularly if the housing is made entirely or largely of a ceramic material, which is expensive compared to other materials.

[0025] In a further development of the invention, the at least one recess is arranged such that the at least one permanent magnet can be placed on the base plate. This makes it possible to position the at least one permanent magnet on the base plate with a high degree of accuracy. This is particularly advantageous when several individual magnets are arranged on the base plate that attract or repel each other, thus ensuring precise alignment of the individual magnets with respect to one another.

[0026] The magnetic field generating device can comprise at least two permanent magnets designed as individual magnets, arranged relative to each other in such a way as to generate a homogeneous, static magnetic field in which the NV diamond is located. The internal, static magnetic field thus generated can exhibit increased homogeneity in a volume region, which extends particularly along an axis.

[0027] In a further development of the invention, the magnetic field generating device is designed as a Halbach arrangement with at least three permanent magnets designed as individual magnets. The recesses are specifically designed as depressions and arranged in the side walls of the hood such that the individual magnets can be arranged around the NV diamond, resulting in a largely homogeneous, static magnetic field. (R.415783)

[0028] - 6 - the NV diamond. The individual magnets can be arranged along an imaginary circle around the NV diamond. With a number n of individual magnets, these are arranged in particular at an angle of 360° / n along the circle, whereby the orientation and thus the magnetization direction of the respective individual magnets changes with their position along the circle by twice the angle (Halbach arrangement). The at least three individual magnets are arranged in a plane in which, or parallel to which, the direction of the inner, static magnetic field also runs. The inner, static magnetic field exhibits increased homogeneity in a volume region extending along an axis perpendicular to the direction of the inner, static magnetic field.

[0029] In a further development of the invention, the excitation light source, the low-voltage diamond, and the magnetic field generation device are aligned with each other such that the electric field generated by the excitation light beam and the internal static magnetic field within the low-voltage diamond at least partially overlap. In particular, the electric field and the internal static magnetic field overlap in a region where the internal static magnetic field has a maximum field strength. Specifically, the electric field and the internal static magnetic field overlap in the volume region where the internal static magnetic field exhibits increased homogeneity. If this volume region extends along an axis, the excitation light beam is aligned along this axis.In this case, the excitation light source, the NV diamond and the magnetic field generating device are aligned to each other in such a way that the excitation light beam is aligned along the axis along which the inner, static magnetic field exhibits increased homogeneity.

[0030] In a further development of the invention, the housing and / or the base plate of the magnetic field sensor comprises a ceramic material. In particular, the housing and / or the base plate consists largely of the ceramic material. The ceramic material offers the advantage over polymers, for example, that it does not damage the components of the magnetic field sensor—especially the excitation light source. Furthermore, the R.415783

[0031] - 7 -

[0032] Magnetic fields are not distorted by the ceramic material, which is an advantage over, for example, metallic materials.

[0033] In a further development of the invention, the excitation light source and the microwave structure are arranged on the base plate.In particular, the NV diamond and the detector are arranged on a surface of the hood opposite the base plate. The detector can be positioned between the NV diamond and the surface of the hood. The distance between the base plate and the surface of the hood opposite the base plate is dimensioned such that the excitation light beam strikes the NV diamond. In this way, a space-saving arrangement of the components and thus a compact design of the magnetic field sensor is enabled, in which the hood acts as a spacer for adjusting the distance between the NV diamond and the excitation light source. It is understood that a mirrored arrangement is also included in the further development of the invention. In such an arrangement, the NV diamond and the detector are arranged on the base plate, while the detector and the microwave structure are arranged on the surface of the hood opposite the base plate.

[0034] Alternatively, the NV diamond, the detector, the reference detector (if applicable), the excitation light source, and the microwave structure can also be arranged on the base plate. A mirrored arrangement is also possible, in which the NV diamond, the detector, the reference detector (if applicable), the excitation light source, and the microwave structure are located on the surface of the hood opposite the base plate. Such an arrangement has the advantage that only the base plate or only the hood needs to be populated. This simplifies the manufacturing process and thus saves costs.

[0035] In a further development of the invention, the magnetic field sensor has a first conductor track that is arranged on or above the surface of the housing opposite the base plate and is operatively connected to the detector. Further conductor tracks can be provided on or within the housing, which can be connected to other components of the magnetic field sensor, such as the reference detector. These conductor tracks R.415783

[0036] - 8 - are routed, in particular, between the receptacles for the permanent magnets, through the hood body to one of the outer sides of the hood. In particular, a second conductor track may also be provided, which is arranged on or below the base plate and is operatively connected to the excitation light source and / or the microwave structure. The arrangement of the first and second conductor tracks in the base plate and in the area opposite the base plate enables a compact and clearly arranged arrangement of the conductor tracks.

[0037] In particular, at least one adhesive joint can be provided on a contact surface of the hood that can be positioned on the base plate. This allows the hood to be easily glued to the base plate and the enclosed chamber to be sealed simply and reproducibly.

[0038] In addition, cooling fins and / or alignment marks may be incorporated on the base plate and / or on one of the outer surfaces of the hood.

[0039] The invention also includes a method for manufacturing the magnetic field sensor comprising the following steps: a. manufacturing the hood using a 3D printing process or an injection molding process, b. providing the base plate, c. arranging the detector, the NV diamond on the hood or on the base plate, d. arranging the at least one permanent magnet on the hood, e. arranging the excitation light source and the microwave structure on the base plate or on the hood, f. joining the hood and the base plate.

[0040] The hood is manufactured using either a ceramic injection molding process or a ceramic 3D printing process. This allows the hood to be produced in its final form – i.e., without any post-processing, R.415783.

[0041] .9. such as the subsequent milling of channels to guide conductor tracks.

[0042] In a further development of the invention, the method comprises the following additional steps, wherein the hood is produced using the injection molding process: g. Inserting a metallic foil into an injection mold, h. Filling the injection mold with ceramic material, i. Sintering the ceramic material and the metallic foil.

[0043] In this process, the metallic foil is placed in the injection mold before the ceramic material is introduced. During the subsequent sintering process, the ceramic material and the metallic foil bond together permanently. This allows the conductive traces and other metallic structures, such as contact pads, to be integrated into the housing without the need for any post-processing.

[0044] Alternatively, the conductor tracks and, for example, other metallic structures, such as contact pads for contacting electronic components, can also be printed onto one of the, for example, ceramic layers during the 3D printing process.

[0045] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0046] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0047] Brief description of the drawings R.415783

[0048] - 10 -

[0049] Figure 1 shows a magnetic field sensor according to an embodiment of the invention;

[0050] Figure 2 shows a section of the magnetic field sensor according to an embodiment of the invention;

[0051] Figure 3 shows a method for manufacturing a magnetic field sensor according to the invention.

[0052] Embodiments of the invention

[0053] Figure 1 shows a magnetic field sensor 1 with a housing 10 and a base plate 11, which form a sealed chamber 12. An NV diamond 2, an excitation light source 3, in particular a laser diode, a detector 5, and a microwave structure 6 are arranged in the sealed chamber 12. The excitation light source 3 is configured to emit an excitation beam 4 to excite electronic states of the NV diamond 2. The excitation light beam 4 emitted by the excitation light source 3 can be guided to the NV diamond 2 via a beam-shaping or beam-guiding optical element, e.g., a lens 9 or a deflecting mirror. The excitation light beam 4 can generate an electric field within the NV diamond 2. The detector 5 is arranged and designed in such a way that it can detect fluorescence radiation which the NV diamond 2 can emit as a result of irradiation with the excitation radiation 4.

[0054] The detector 5 and a reference detector 14 are arranged on a surface 15 of the hood 10, which is opposite the base plate 11. The NV diamond 2 is also arranged on the surface 15 of the hood 10, with the detector 5 being arranged, in particular, between the NV diamond 2 and the surface 15. The microwave structure 6 is arranged and configured within the NV diamond 2 to generate a microwave field for manipulating spin states of the NV diamond 2. The microwave structure 6 comprises at least one conductor, which is arranged, in particular, on the base plate 11 around the NV diamond 2. R.415783

[0055] - 11 -

[0056] The magnetic field sensor 1 further comprises a magnetic field generating device 7, which is configured to generate an internal, static magnetic field within the NV diamond. The magnetic field generating device 7 comprises at least one permanent magnet 8, which is arranged in a recess 13 in a side wall of the hood 10. The recess 13 is designed as a depression that is formed in a part of the hood body of the hood 10, which comprises the side wall of the hood 10. The at least one recess 13 is arranged in the hood 10 such that the at least one permanent magnet 8 can be placed on the base plate 11. Adhesive joints can be provided in a contact surface 16 of the hood 10 so that the hood 10 can be easily connected to the base plate 11 and the enclosed chamber 12 can be hermetically sealed.

[0057] A first conductor track 17 can be arranged on or above surface 15, i.e., within the housing body, through which, for example, the detector 5 is operatively connected to a control or evaluation device 18 located outside the enclosed chamber 12. A second conductor track 19 can be arranged in or on the base plate 11, through which, for example, the microwave structure 6 is operatively connected to a microwave source 20.

[0058] Hood 10 features a ceramic material.

[0059] The permanent magnets 8 can be designed as individual magnets. In this case, the hood 10 has a corresponding number of recesses 13, as shown in Fig. 2. The individual magnets can be arranged in a Halbach arrangement. Fig. 2 shows an embodiment of the hood 10 according to the invention, in which, in this case, eight individual magnets can be arranged in the hood 10.

[0060] The permanent magnets 8, the excitation light source 3, and the NV diamond 2 are aligned such that the internal static magnetic field and the electric field within the NV diamond 2 at least partially overlap. The internal static magnetic field can exhibit increased homogeneity, for example, along an axis. In the case that the magnetization or the magnetic dipole moments of the permanent magnet(s) according to Halbach's principle R.415783

[0061] - 12 - are aligned, this axis runs perpendicular to the direction of the inner, static magnetic field. In this case, the excitation light beam inside the NV diamond 2 is arranged perpendicular to the direction of the inner, static magnetic field.

[0062] Fig. 3 shows the inventive method for manufacturing the magnetic field sensor. In a first step S1, the cover is manufactured using a 3D printing process or an injection molding process. The at least one recess 13 is already incorporated in this process. In a second step S2, the base plate 11 is provided. In a third step S3, the detector 5, the NV diamond 2, optionally the reference detector 14, and the at least one permanent magnet 8 are arranged on the cover 10. Alternatively, the detector 5 and the NV diamond 2 can also be arranged on the base plate 11.

[0063] If the detector 5 and the NV diamond 2 are arranged on the hood 11 in step S3, then in a fourth step S4 the microwave structure 6 and the excitation light source 3 can be arranged on the base plate 11. If the detector 5 and the NV diamond 2 are arranged on the base plate 11 in step S3, the microwave structure 6 and the excitation light source 3 can also be arranged on the hood in step S4, in particular on the surface 15 opposite the base plate 11. In a fifth step, the assembled hood 10 and the assembled base plate 11 are joined together, in particular by gluing, so that an airtight, sealed chamber 12 is formed.

[0064] During the production of the cover 10, metallic structures, such as the conductor tracks 17 and 19, can be integrated, eliminating the need for post-processing of the cover 10. For this purpose, a conductor track is inserted into an injection mold before the ceramic material is added. In a subsequent sintering process, the metallic conductor track and the ceramic material then bond firmly together. Alternatively, the metallic conductor tracks can also be printed directly onto the cover during the 3D printing process.

Claims

R.415783 - 13 - Claims 1. Magnetic field sensor (1) with - an NV diamond (2), - an excitation light source (3) configured to emit an excitation beam (4) to excite electronic states of the NV diamond (2), and arranged such that the excitation beam (4) emitted by it can generate an electric field within the NV diamond (2), - a detector (5) which is arranged and designed to detect fluorescence radiation which the NV diamond (2) can emit as a result of irradiation with the excitation radiation (4), - a microwave structure (6) which is arranged and configured to generate a microwave field within the NV diamond (2) for manipulating spin states of the NV diamond (2), - a magnetic field generating device (7) configured to generate an internal, static magnetic field within the NV diamond (2) and comprising at least one permanent magnet (8), - a hood (10) and a base plate (11) arranged to form a closed chamber (12), wherein the NV diamond (2), the excitation light source (3), the detector (5) and the microwave structure (6) are arranged inside the closed chamber (12), characterized in that the hood (10) has at least one recess (13) for receiving the at least one permanent magnet (8, 9).

2. Magnetic field sensor (1) according to claim 1, wherein the at least one recess (13) is arranged in the hood (10) such that the at least one permanent magnet (8) can be arranged on the base plate (11). R.415783 - 14 - 3. Magnetic field sensor (1) according to claim 1 or 2, wherein the magnetic field generating device (7) has at least three permanent magnets (8) designed as individual magnets which are arranged in a Halbach arrangement.

4. Magnetic field sensor (1) according to one of the preceding claims, wherein the hood (10) and / or the base plate (11) comprise a ceramic material.

5. Magnetic field sensor (1) according to one of the preceding claims, wherein the excitation light source (3) and the microwave structure (6) are arranged on the base plate (11) or on one of the surfaces (15) of the hood (10) opposite the base plate (11).

6. Magnetic field sensor (1) according to one of the preceding claims, wherein the NV diamond (2) and the detector (5) are arranged on the surface (15) of the hood (10) or the base plate (11) opposite the base plate (11), wherein the detector (5) is in particular arranged between the NV diamond (2) and the surface (15).

7. Magnetic field sensor (1) according to one of the preceding claims comprising a first conductor track (17) arranged on or above the surface (15) of the hood (10) opposite the base plate (11) and operatively connected to the detector (5).

8. Magnetic field sensor (1) according to one of the preceding claims with a second conductor track (19) which is arranged on or below the base plate (11) and is operatively connected to the excitation light source (3) and / or the microwave structure (6).

9. Method for manufacturing a magnetic field sensor (1) according to one of the preceding claims comprising the following steps: a. manufacturing the hood (10) by means of a 3D printing process or an injection molding process, b. providing the base plate (11), c. arranging the detector (5), the NV diamond (2) and the at least one permanent magnet (8) on the hood (10) or on the base plate (11), R.415783 - 15 - d. Arranging the excitation light source (3) and the microwave structure (6) on the base plate (11) or on the hood (10), e. Joining the hood (10) and the base plate (11).

10. Method for manufacturing a magnetic field sensor (1) according to claim 9, wherein the hood (10) is manufactured by injection molding, comprising the additional steps: a. Inserting a metallic foil into an injection mold, b. Filling the injection mold with ceramic material, c. Sintering the ceramic material and the metallic foil.

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