Magnetic field sensing device

Abstract

A magnetic field sensing apparatus and method for measuring a magnetic field distribution are described, including a predetermined region of a diamond nitrogen vacancy center substrate and a controller. The predetermined region has a plurality of magnetic sensing elements that can be selectively activated and read out. In order to enable a magnetic sensing element to sense a magnetic field while generating a local electric field, the sensing element is exposed to light of a predetermined wavelength or range of wavelengths, the magnetic element is irradiated with microwaves of a predetermined frequency or range of frequencies, and the generated light current is collected and measured to allow the sensed magnetic field value to be extracted therefrom.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Belgian application No. 2022 / 5385 (“Magnetic fieldsensing device”), filed on May 19, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the field of devices and methods for sensing magnetic field distribution. Background Art

[0004] Devices for measuring the magnetic field distribution of any permanent magnet and magnet assembly are known in the art. These devices are called magnetic field sensing devices, sometimes also called magnetic field cameras, which consist of a plurality of magnetic field sensing elements to allow local measurements to be made so that the spatial distribution of the magnetic field in the sensing area of ​​the magnetic field sensing device can be determined with appropriate resolution. These magnetic field sensing elements can be arranged in a one-dimensional or two-dimensional array in the form of a matrix or grid.

[0005] An example of such a magnetic field sensing device is disclosed in EP1720026A1. The magnetic field sensing elements used are Hall sensors arranged in a matrix. In order to be able to address each Hall sensor in the matrix individually, switches in the form of transistors are used. The Hall sensors and switches are made of semiconductor materials.

[0006] In recent years, methods for measuring magnetic fields using diamond nitrogen vacancy (NV) center materials have been studied. For example, "Bourgeois, E., Jarmola, A., Siyushev, P. et al. Photoelectric detection of electron spin resonance of nitrogen-vacancy centres in diamond. Nat Commun 6, 8577 (2015)" describes two such methods: optical detection of magnetic resonance (ODMR) and photocurrent detection of magnetic resonance (PDMR).

[0007] Existing magnetic field sensing devices consisting of Hall sensors and transistor switches made of semiconductor materials have their advantages in measuring magnetic field distribution.

[0008] US10,901,054B1 discloses an integrated optical waveguide and electronics using quantum defect centers. Like many current designs, a pair of electrodes are arranged relative to each other in a more or less symmetrical manner. However, this arrangement results in the generation of an inhomogeneous electric field (especially at the ends). As a result, the magnetic fields of adjacent sensing devices may interfere with each other, leading to inaccurate results.

[0009] However, an object of the present invention is to provide an alternative magnetic field sensing device and method so that the measurement results are more accurate.

[0010] Another object of the present invention is to integrate such a magnetic field sensing device on a diamond NV center substrate to obtain higher spatial resolution of the magnetic field sensing element and to improve measurement sensitivity and overall measurement time. Summary of the invention

[0011] To achieve these objectives in one aspect of the present invention, a magnetic field sensing device for determining a magnetic field distribution in a region is provided, comprising a predetermined region of a diamond NV center substrate and a controller. The predetermined region has a plurality of magnetic sensing elements, each of the plurality of sensing elements having a first contact and a second contact in electrical contact with a surface of the diamond NV center substrate. Each second contact is electrically isolated from each first contact.

[0012] The diamond NV centre substrate may constitute a diamond material in the form of a thin plate containing nitrogen vacancy (NV) centres.

[0013] According to the present invention, the controller is configured to control:

[0014] - a biasing element to apply a bias voltage to the first contacts of the selected plurality of sensing elements so as to generate a local external electric field in each of the selected sensing elements, while the selected sensing elements are illuminated by at least one light source so as to induce a photocurrent in each of the selected sensing elements and illuminated by at least one microwave source so as to affect the photocurrent generated in each of the selected sensing elements;

[0015] - a measuring unit to measure the photocurrent detected by each of the second contacts of the selected sensing elements and to extract therefrom the sensed magnetic field value of each of the selected sensing elements;

[0016] -Adjusting the selection of a plurality of sensing elements to allow obtaining a sensed magnetic field value for each selectable sensing element of a predetermined area. It will be appreciated that the number of sensing elements in a predetermined area determines the maximum resolution. Thus, in the case of a measurement at maximum resolution, all selectable sensing elements are controlled as described and the magnetic field value for each sensing element in the predetermined area is extracted. However, it may be decided to measure at a lower resolution, so that only part of the available sensing elements in the predetermined area are used for measurement over the entire predetermined area, or in other words, only part of the sensing elements in the predetermined area can be selected. Alternatively, at a lower resolution, all sensing elements are used for measurement, but only the sensed magnetic field values ​​of the sensing element combinations are extracted according to the desired resolution.

[0017] The measuring unit usually comprises an amplifier, equipment for measuring current and / or voltage, signal processing means and a data processing unit.

[0018] In order to enable the magnetic sensing element to sense the magnetic field at the same time, a local electric field is generated by applying a bias voltage between the first contact and the second contact of the sensing element, the sensing element must be exposed to light of a predetermined wavelength or wavelength range, and the magnetic element will be irradiated with microwaves of a predetermined frequency or frequency range. The co-existence of the local electric field and exposure to light induces a photocurrent and enables the collection of the photocurrent. Simultaneous irradiation with microwaves affects the photocurrent, which depends on the presence of a magnetic field. Therefore, by electrically connecting the second contact of the sensing element to the measuring unit, the measuring unit can extract the sensed magnetic field value from the photocurrent detected by the second contact. The above operation can be repeated for each sensing element so that the magnetic field contribution of each individual sensing element is obtained sequentially, or the above operation can be performed in parallel for the selected magnetic sensing elements by connecting the second contact in each selected magnetic sensing element to the measuring unit separately. The ability to extract the sensed magnetic field value of each individual magnetic sensing element, the so-called readout selectivity, can be achieved in a variety of ways without the need to connect each second contact separately. Non-selected magnetic sensing elements that are not applied with a local external field and / or are not exposed to light do not generate photocurrent. Therefore, the readout selectivity of the selected magnetic sensing elements is not affected if their second wires are connected to the second contacts of the selected magnetic sensing elements. Spatial control of the light source and the electric field can create design freedom to allow simpler designs and faster and more accurate measurements. When the second contacts are grouped, readout selectivity can also be achieved by modulating the bias voltage and / or the light source and / or the microwave source, such as exposing different magnetic sensing elements or groups thereof to signals with different modulation frequencies, thereby allowing the use of a multi-frequency lock-in amplifier to separate the contribution of a single magnetic sensing element to the photocurrent detected by the grouped second contacts.

[0019] In an embodiment of the present invention, either one of the first and second contacts of the magnetic sensing element is located inside the other of the first and second contacts. In particular, the arrangement can be such that one of the first and second contacts of the magnetic sensing element substantially surrounds the other of the first and second contacts, i.e. the two contacts have different shapes and one extends around the other (along a closed line or only partially). For example, one contact is a point (of any shape) located in the center of the sensing element, while the other contact is a line arranged towards the periphery of the sensing element. Doing so helps to define the substrate area (between the two contacts) where the electric field is applied and the uniformity of the electric field in the magnetic sensing element. In addition, it improves the shielding of the magnetic sensing element from the influence of neighboring magnetic sensing elements.

[0020] A plurality of sensing elements may be arranged in a one-dimensional or two-dimensional array to define a matrix or grid of magnetic sensing elements forming a magnetic sensing device. A first parallel wire oriented in a first direction may be provided to connect the first contacts, and a second parallel wire oriented in a second direction may be provided to connect the second contacts. This allows connecting the first and second contacts of rows and / or columns of magnetic sensing elements in the matrix.

[0021] The first direction can be selected to be perpendicular to the second direction. Thus, the first conductor can connect the first contact of the row of magnetic sensing elements, while the second conductor can connect the second contact of the column of magnetic sensing elements, and vice versa. This is convenient because the first and second conductors can be easily accessed on different sides of the magnetic sensing device. A multiplexer can be provided, and when the output of the multiplexer is connected to the measurement unit, all second conductors are connected to the multiplexer. Therefore, all second contacts are connected and the measurement unit can read them by row or by column. For example, assume that the first conductor connects the row of magnetic sensing elements, the second conductor (i.e., the readout line) connects the column of magnetic sensing elements, and a single row of magnetic sensing elements is selected and biased so that an electric field exists in each sensing element of the row. When this row of sensing elements is simultaneously exposed to light of a predetermined wavelength and irradiated with microwaves at a predetermined frequency, a photocurrent affected by the magnetic field is generated in each sensing element of the row. In this case, there is only one active sensing element per column, or in other words, each readout line addresses one active sensing element. Therefore, according to the photocurrent measured by the measuring unit, when the readout line is selectively connected to the measuring unit through the multiplexer, the sensed magnetic field value of the single magnetic sensing unit can be extracted.

[0022] In an embodiment of the present invention, when the bias element is controlled to bias the first contact of the selected sensing element, the bias element can be further controlled to ground the first contacts in the unselected sensing elements. Since the second contacts are all grounded, this suppresses potential noise picked up by the second contacts of the unselected sensing elements, which may affect the reliability and accuracy of the measured photocurrent, and thus also affect the reliability and accuracy of the extracted sensed magnetic field value.

[0023] Alternatively, in the case where multiple rows of sensing elements are selected (activated) simultaneously, the biasing element can be controlled to apply a differently modulated bias voltage to each of the associated first conductive lines. The photocurrent measured in the readout line then contains contributions from multiple rows of magnetic sensing elements, but each contribution is modulated differently and can be extracted individually using at least one lock-in amplifier or equipment for analog-to-digital conversion and subsequent fast Fourier transform (FFT) analysis (such as a spectrum analyzer).

[0024] At least one microwave source may be one or more radio frequency (RF) antennas. At least one microwave source may be controlled while irradiating to sweep within a predetermined frequency range. At least one microwave source may be configured to directly irradiate the magnetic sensing element. Alternatively, a set of parallel microwave wires may be provided for carrying microwave signals generated by at least one microwave source, the microwave wires being formed above the first and / or second contacts and being electrically insulated from the first and second contacts and the substrate. The microwave wires may be positioned so that they at least partially cover portions of the substrate that are not covered by the first and / or second contacts. In particular, the microwave wires may be configured to maximize coverage of portions of the substrate that are not covered by the first and / or second contacts, thereby maximizing coupling of the microwaves into the diamond material.

[0025] In an embodiment of the present invention, the microwave lines are alternately connected to the ground to define a set of coplanar microwave strips or a set of coplanar waveguides. In another embodiment, dedicated ground electrodes are provided between the microwave lines, for example, each ground electrode is connected to some of the second contacts, so as to obtain a coplanar waveguide structure without alternating the microwave lines with the microwave ground lines.

[0026] In another embodiment of the invention, the set of parallel microwave wires is oriented parallel to the second wires. Referring back to the matrix example above, this means that the microwave wires are parallel to the readout wires, or in other words, parallel to the columns of magnetic sensing elements.

[0027] In another embodiment, at least one microwave source may be controlled to generate a modulated microwave signal.

[0028] In another embodiment of the present invention, the first contact and the second contact are formed on the same surface of the substrate, and light generated by at least one light source is directed to the opposite surface to illuminate the selected sensing element. This is advantageous because the light is not shielded by the contacts, thereby increasing the exposed surface and / or volume of the substrate.

[0029] The illumination is independent of the incident surface and can be continuous throughout the predetermined area. Alternatively, the illumination varies spatially throughout the predetermined area. The spatial variation can be obtained by mechanically moving the light source, or by using one or more reflective elements, such as at least one mirror (e.g., a polygonal mirror), or by using at least one diffractive element, or by using a plurality of light sources that can be selectively addressed. In particular, at least one light source can be a focused laser beam, a linear laser beam, a light-emitting diode (LED), or a one-dimensional or two-dimensional array of lasers, such as a vertical cavity surface emitting laser (VCSEL).

[0030] In another embodiment of the present invention, the measuring unit is configured to extract a sensed temperature value of each of the selected sensing elements from the measured photocurrent.

[0031] In another aspect of the present invention, there is provided a method for determining a magnetic field distribution in a region using a magnetic field sensing device, the magnetic field sensing device comprising a predetermined region of a diamond NV center substrate, the predetermined region having a plurality of sensing elements, each of the plurality of sensing elements having a first contact in electrical contact with a surface of the diamond NV center substrate and a second contact, the second contact being electrically isolated from the first contact; the method comprising the following steps:

[0032] - applying a bias voltage to a selected first contact of the plurality of sensing elements, thereby generating a local external electric field in each of the selected sensing elements, while illuminating the selected sensing elements by at least one light source, thereby inducing a photocurrent in each of the selected sensing elements, and illuminating the selected sensing elements by at least one microwave source, thereby affecting the photocurrent generated in each of the selected sensing elements;

[0033] - measuring the photocurrent detected by each of the second contacts of the selected sensing elements and extracting therefrom the sensed magnetic field value for each of the selected sensing elements, and

[0034] - adjusting the selection of the sensing elements and repeating the steps of the method until the sensed magnetic field value of each selectable sensing element of the predetermined area is obtained.

[0035] The method further comprises placing the object for which the magnetic field distribution has to be determined in the vicinity of the sensing element, preferably at a defined distance from the sensing element.The sensed magnetic field values ​​are then used to calculate the magnetic field distribution, as is known in the art.

[0036] The object to be measured can be of any type and in any technical field. For example, the method of the present invention can be used for biodetection or biosensing in samples of various shapes, sizes or containers. The high sensitivity achieved due to the method of the present invention can, for example, allow the determination of the magnetic field distribution in a microfluidic device, on a chip or wafer, to monitor the function of an electronic system, such as detecting a small current on an integrated circuit. For example, it can also be used for static measurements of quality control in a production environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic top view of an example of a magnetic field sensing device according to the invention is shown.

[0038] Figure 2 A schematic perspective view showing an example of an array of magnetic field sensing elements according to the present invention is shown.

[0039] Figure 3 The embodiment of the present invention is shown Figure 2 Schematic perspective view of the back side of an array of magnetic field sensing elements.

[0040] The figures are produced for illustrative purposes and the members may not be in correct proportion to each other. DETAILED DESCRIPTION

[0041] List of reference symbols used:

[0042] 1: Diamond NV center substrate

[0043] 2: First contact, bias contact

[0044] 3: Second contact, read contact

[0045] 4: First wire, bias line

[0046] 5: Second wire, readout line

[0047] 6: Bias element

[0048] 7: Readout line selection unit, multiplexer

[0049] 8: Transimpedance amplifier, current amplifier

[0050] 9: Lock-in amplifier / frequency analyzer / analog to digital converter (ADC) 10: Microwave line

[0051] 11: Microwave ground wire

[0052] 12: Controller

[0053] 13: Microwave source

[0054] 14: Microwave line selection unit

[0055] 15: Sensing area

[0056] 16: Data processing unit

[0057] 17: Diamond NV center substrate backside

[0058] 18: Back ground electrode

[0059] Examples of the present invention will now be described in more detail with reference to the accompanying drawings.

[0060] It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the spirit and scope of the present invention, the first element, component, region, layer or part discussed below may be referred to as a second element, component, region, layer or part.

[0061] The terms used herein are used to describe specific embodiments and are not intended to limit the inventive concept. Unless the context clearly indicates otherwise, the singular forms "a" and "an" used herein also include plural forms. It should also be understood that the terms "include", "including", "comprises" and / or "comprising" when used in this specification specify the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or their combinations. As used herein, the term "and / or" includes any and all combinations of one or more related listed items. Before the element list, expressions such as "at least one" will modify the entire element list without modifying the individual elements in the list. In addition, "may" is used when describing the embodiments of the inventive concept to refer to "one or more embodiments of the present invention".

[0062] It will be understood that when an element is referred to as being "connected to" or "coupled to" another element, it may be directly connected to or coupled to another element, or one or more intermediate elements may be present. When an element is referred to as being "directly connected to" or "directly coupled to" another element, there are no intermediate elements.

[0063] As used herein, the terms "substantially," "approximately," and similar terms are used as terms of approximation, rather than terms of degree, and are intended to account for the inherent variations in measured or calculated values ​​that those of ordinary skill in the art would recognize.

[0064] As used herein, the terms "use," "using," and "used" may be considered synonymous with the terms "utilize," "utilizing," and "utilized," respectively.

[0065] Figure 1 A magnetic field sensing device is shown, which includes a predetermined area of ​​a diamond NV center substrate (1) shown in an xy plane, the predetermined area having a plurality of sensing elements, each of the plurality of sensing elements having a first contact (2) electrically contacting the diamond NV center substrate (1) and a second contact (3), the second contact (3) being electrically isolated from the first contact (2).

[0066] The diamond NV center substrate (1) is a thin plate-like diamond material containing nitrogen vacancy (NV) centers, with a surface area (in the xy plane) typically in the range of 4 mm by 4 mm to 10 mm by 10 mm, and a thickness typically in the range of 100 μm to 500 μm.

[0067] The second or read contact (3) of each magnetic sensing element is located inboard of its first or bias contact (2). In operation, a bias voltage will be applied between the bias contact (2) and the read contact (3) of the sensing element, thereby generating an electric field in the substrate volume (15) in the sensing element. Therefore, properly positioning and defining the contacts helps to maximize the sensing area (15) and the uniformity of the electric field in the sensing area of ​​the magnetic sensing element.

[0068] like Figure 1 As shown, a plurality of sensing elements of the magnetic sensing device are arranged in a two-dimensional array to define a 3 by 3 matrix or grid of magnetic sensing elements forming the magnetic sensing device. Although a 3 by 3 matrix is ​​used as an example, other configurations may be selected depending on the shape and geometry of the area to be sensed, such as a sensing element matrix selected from a range of sizes including 1x2, 2x2, 5x5, 5x10, 1x10, 5x1, 10x10, 100x100, 1000x1000.

[0069] Horizontally oriented parallel conductive bias lines (4) connect the bias contacts (2) of the magnetic sensing element rows. Vertically oriented parallel conductive readout lines (5) connect the readout contacts (3) of the magnetic sensing element columns.

[0070] The width of the contacts and wires is typically between 1 μm and 10 μm, while the thickness is typically between 0.1 μm and 1 μm. The closest distance between the bias contacts and readout contacts of the same magnetic sensing element is typically in the range of 5 μm to 100 μm. The distance or pitch between the readout contacts of adjacent magnetic sensing elements represents the maximum resolution and is typically in the range of 10 μm to 200 μm.

[0071] A set of parallel microwave wires (10) is provided for carrying microwave signals. The microwave wires are formed using known techniques used in semiconductor processing and manufacturing integrated circuits and micro-electro-mechanical system (MEMS) devices. The microwave wires are located above the bias contacts (2) and readout contacts (3) and the bias lines (4) and readout lines (5) (in the z direction) and are electrically insulated from the bias contacts, readout contacts, bias lines and readout lines and from the substrate. The microwave wires are positioned so that they at least partially cover portions of the substrate not covered by the bias and readout contacts. In particular, the microwave wires can be configured to maximize coverage of portions of the substrate not covered by the bias and readout contacts, thereby maximizing microwave coupling into the diamond material. The set of parallel microwave wires (10) is parallel to the readout lines (5), or in other words, parallel to the columns of magnetic sensing elements.

[0072] In order for a magnetic sensing element to be able to sense a magnetic field while generating a local electric field, the sensing element must be exposed to light of a predetermined wavelength or wavelength range, irradiate the magnetic element with microwaves of a predetermined frequency or frequency range, and collect and measure the resulting photocurrent from which the sensed magnetic field value is extracted. This can be enabled as follows:

[0073] 1. Illuminate the diamond substrate with light of an appropriate wavelength (usually green light, but blue light can also be used, or even a combination of different colors, such as green and red, or green and yellow) to excite charge carriers into the conduction band and excited NV states.

[0074] 2. Microwave electromagnetic radiation at around 2.87 GHz is applied to the NV center to resonantly excite charge carriers from the ground ( 3 A2)0 state to degenerate ( 3 A2) + / -1NV state. This allows more charge carriers to pass through the two metastable states 1 A1 and 1 ENV state from excited ( 3E) The + / -1 NV state falls back to the ground NV state, resulting in an associated electro-photocurrent change, since the charge carriers decaying through these metastable NV states do not contribute to the photocurrent. A fixed frequency can be selected. This can be done when the resonant frequency is known, for example determined in a previous calibration step. The microwave radiation can also be applied while sweeping the microwave frequency through a predetermined range around 2.87 GHz, for example from 2.80 GHz to 2.94 GHz or from 2.70 GHz to 3.04 GHz in steps of 1 MHz.

[0075] 3. The generated photocurrent is collected by applying a bias voltage, for example in the range of 1 V to 50 V, between the bias contact and the readout contact on the diamond surface. This bias voltage generates an electric field in the diamond with a magnitude between the bias voltage and the readout contact of 10 2 V / cm to 10 5 V / cm range, the electric field collects the charge carriers generated in the conduction band to one of the contacts. The collected photocurrent is further measured at each frequency in a fixed frequency or a predetermined frequency range. When the frequency of the microwave field is swept in the range near 2.87 GHz, the photocurrent is collected and measured, and a decrease in the photocurrent at certain resonant frequencies is observed. These absorption minima appear in pairs, centered on a common center frequency. The position of this center frequency is typically 2.87 GHz, but varies with temperature. The distance between each pair of minima expressed in units of microwave frequency is proportional to the magnetic field along one of the crystal axes. Therefore, measuring the distance between the minima can provide information about the sensed magnetic field, so that the sensed magnetic field value can be extracted from the measured photocurrent. In addition, the common center frequency of all pairs of minimum values ​​is related to temperature, so the local temperature of the measurement location can be extracted from the photocurrent spectrum. Therefore, the sensor described in the present invention can also be used as a temperature sensor array, or as a combined array of magnetic field and temperature sensors.

[0076] like Figure 1 As shown, the controller (12) is connected to the bias element (6), the readout line selection unit (7) of the measurement unit, the microwave source (13) and the microwave line selection unit (14). The bias element (6) is connected to each row of bias contacts (2) via an associated bias line (4). The microwave source (generator) (13) is connected to the microwave line (10) via a microwave line selection unit. The readout line (5) is connected to the readout line selection unit (7). In the operating mode, the controller (12) is configured to control:

[0077] - a biasing element (6) for applying a bias voltage to the biasing contacts (2) in the selected nine sensing elements while the selected sensing elements are irradiated with light and irradiated with microwaves,

[0078] - a measuring unit for measuring the photocurrent detected by each read-out contact (3) of the selected sensing element and extracting therefrom the value of the magnetic field sensed by each of the selected sensing elements,

[0079] - Adjust the selection of sensing elements and repeat the above control steps until the sensed magnetic field value of each selectable sensing element (ie, all nine sensing elements when measuring with maximum resolution) is obtained.

[0080] The readout process of the magnetic sensing element matrix is ​​as follows:

[0081] A bias voltage is applied to a selected bias line. At the same time, the other bias lines can be connected to ground.

[0082] At least the sensing area (15) of the selected magnetic sensing elements (in this example the sensing elements of the selected row, or in other words the sensing elements associated with the selected bias line (4)) is illuminated with light of an appropriate wavelength or wavelength band.

[0083] A microwave source (13) is used to generate a microwave signal while sweeping the microwave frequency in a range of about 2.87 GHz (e.g., from 2.80 GHz to 2.94 GHz or from 2.70 GHz to 3.04 GHz) in steps of 1 MHz, and a microwave line (10) is used to transmit the generated signal to at least the sensing regions (15) of the selected sensing elements, so that the microwaves can be coupled into the substrate at these sensing regions (15).

[0084] For each microwave frequency, the photocurrent detected by the readout line (5) is measured. The readout line can be selectively read out by the measurement unit using a multiplexer (7). Alternatively, this can be done simultaneously using parallel current measurement equipment. The photocurrent in each readout line essentially only includes the photocurrent detected by the readout contact of the selected sensing element. The other sensing elements of the readout line are not activated. In addition, since their bias contacts are connected to ground potential, the influence of noise picked up by the readout contacts of these other passive sensing elements is suppressed. The measurement unit includes a transimpedance amplifier (8) and a data processing unit (16). The transimpedance amplifier converts the electrical photocurrent into a voltage. Alternatively, a (low-noise) current amplifier can be used instead of the transimpedance amplifier (8). The measurement unit can then further process the resulting signal using a signal processing device (such as a lock-in amplifier, an analog-to-digital converter, a spectrum analyzer and / or other electrical measurement and / or analysis equipment (9)). Therefore, the measurement result obtained is associated with a single selected sensing element, or in other words, with a single sensing area (15). The data processing unit (16) extracts the magnetic field value sensed by the single magnetic sensing element from the measurement result.

[0085] When the results for each sensing element in the selected row are obtained, a bias voltage may then be applied to another bias line (4), and the above process may be repeated until all bias lines are selected.

[0086] As an alternative to the above-described readout process, a bias voltage may be applied simultaneously to a plurality of selected bias lines (4), whereby the bias voltage is amplitude modulated at different modulation frequencies for different selected bias lines. The photocurrent detected by the readout line comprises contributions from a plurality of selected sensing elements. A transimpedance amplifier (8) converts the electro-photocurrent into a voltage. The resulting signals of the readout lines are further analyzed using a plurality of lock-in amplifiers (9) or a spectrum analyzer, and / or a Fourier analysis is performed to determine the contribution at each different modulation frequency, each modulation frequency corresponding to a different bias line. Thus, a set of spectra is obtained, from each of which the local magnetic field of a single sensing element may be extracted. Instead of modulating the bias voltage so that each row of sensing elements is subjected to a signal with a different modulation frequency, it may be chosen to modulate the illumination signal with different modulation frequencies for different rows, or, in the case where the microwave lines are parallel to the bias lines, it may be chosen to modulate the microwave signal with different modulation frequencies for different microwave lines (rows).

[0087] Modulation can be applied to the signal sources simultaneously, with one source applied to the rows of sensing elements and the other to the columns. Figure 1 In the configuration shown, the bias voltages of different bias lines (associated with rows) can be selected to be modulated at different frequencies, and the microwave signals of different microwave lines (columns) can be modulated at different frequencies. By doing so, each sensing element can be subjected to a different and unique combination of bias voltage modulation and microwave modulation frequency. In this case, the readout lines selected by the sensing area can be connected together and measured as a single photocurrent signal. The spectrum of the single photocurrent signal then contains frequency components corresponding to the combinations of all bias voltages and microwave modulation frequencies. Since these combinations are selected to be unique, the magnetic field of each individual sensing area can be measured by extracting its corresponding combination frequency from the photocurrent spectrum.

[0088] For example, the modulation frequency fb of the bias voltage can be selected in the range between 1kHz and 5kHz, and the modulation frequency fm of the microwave line can be selected in the range between 10kHz and 100kHz. The combined frequency will then be in the range between 11kHz and 105kHz, whereby a series of lower frequencies are repeated around each higher frequency, thereby forming a plurality of frequency components corresponding to each combination of bias voltage and microwave frequency. Furthermore, as described above, these frequencies can be extracted from the photocurrent signal using a plurality of lock-in amplifiers, a spectrum analyzer, or Fourier analysis.

[0089] When choosing the modulation frequencies, care should be taken not to have combination frequencies at the same position in the spectrum, since some foldback frequencies around a certain frequency may coincide with some frequencies around the lower modulation frequency. Therefore, the distance between subsequent higher frequencies (such as fm1 and fm2) should be at least twice the range of the lower bit frequencies fb1 to fbn.

[0090] The numerous unique combination frequencies that exist simultaneously in the measured photocurrent signal can be further separated using spectral techniques such as lock-in amplification, spectrum analysis, and FFT analysis.

[0091] As mentioned before, in order to extract the magnetic field value from the measured photocurrent, the photocurrent is measured at multiple microwave frequencies, so that absorption minima (peaks) are observed at certain frequencies. These minima occur in pairs, centered around a common center frequency. The distance between each pair of minima, expressed in units of microwave frequency, is proportional to the magnetic field along one of the crystal axes of the diamond lattice of the diamond NV center substrate. Each NV center is oriented along one of the four crystal axes of the diamond lattice and is sensitive only to the local magnetic field component along that crystal direction. Since the multiple NV centers of the diamond NV substrate are randomly distributed in the four crystallographic orientations, each of these orientations will have more or less equal sensitivity.

[0092] The magnetic field is oriented so that it has a component along each of the four lattice orientations, and will therefore produce four pairs of resonant peaks (minima) in the photocurrent spectrum, since each orientation senses a non-zero magnetic field along its direction.

[0093] To resolve magnetic field components along different crystallographic orientations, a bias magnetic field can be applied to offset each minimum pair so that they are separated and can be detected individually. The bias magnetic field can be applied to the sensing device using one or more permanent magnets or one or more electromagnets (such as Helmholz coils).

[0094] Since space is three-dimensional, it is sufficient to measure along three of the four crystallographic orientations in order to completely decompose the applied magnetic field into its Cartesian components. In order to see only three pairs of resonance peaks (minima) in the photocurrent spectrum, the applied bias magnetic field can be oriented perpendicular to one of the four crystallographic orientations. This direction is then insensitive to the magnetic field and only three pairs of resonance peaks will appear in the spectrum, as well as a single peak in the fourth direction (there is no splitting since there is no magnetic field along this direction). The spectrum will therefore consist of seven peaks, of which only six are used to determine the magnetic field components along the three sensitive crystallographic orientations.

[0095] A conversion can then be performed to transform the measured field components along the crystallographic orientations into a Cartesian coordinate system. This can be done if the magnetic sensing device is first calibrated by applying a magnetic field along each Cartesian dimension and recording the response of each pair of resonance peaks. This process produces a conversion formula for converting between the crystallographic orientation components and the Cartesian components. This allows to apply a (constant) bias magnetic field perpendicular to one of the crystallographic orientations during the actual measurement (thus exciting only the three crystallographic orientations), and record any deviations.

[0096] exist Figure 1 In the embodiment, a set of microwave lines (10) is provided for transmitting each microwave signal to a corresponding sensing area (15). Figure 2 As shown in the perspective view, for Figure 1 The same 3 by 3 sensing element matrix is ​​provided with a set of parallel microwave wires (10) for carrying microwave signals and a set of microwave ground wires (11) in an alternating coplanar configuration so as to form a coplanar waveguide in each column of the sensing element matrix. The microwave wires (10) of the coplanar waveguide are located above the bias contact (2) and the readout contact (3) and the bias line (4) and the readout line (5) (in the z direction) and are electrically insulated from them and the substrate. The microwave wires are positioned to cover the sensing area (15). The set of parallel microwave wires (10) is parallel to the readout line (5), or in other words, parallel to the columns of magnetic sensing elements. The microwave ground wires (11) are located in a coplanar position between the microwave wires (10) so that each microwave line (11) has a microwave ground wire (10) on each side of its length direction. The microwave ground wires (11) are electrically insulated from the substrate, the bias contact (2) and the readout contact (3) and the microwave wires (10). In the working state of the magnetic sensing device, the microwave ground wires (11) are grounded. This coplanar waveguide topology allows a constant impedance of, for example, 50 ohms to be maintained along the entire trajectory of the microwave line (10), allowing efficient transmission of microwave energy over the diamond surface.

[0097] like Figure 3 As shown, an additional back ground electrode (18) may be provided on the back side (17) of the diamond NV center substrate (i.e., the side of the substrate opposite to the side carrying the microwave line) to optimize exposure of the substrate to microwave radiation. The back ground electrode is preferably designed so that sufficient uncovered substrate surface remains at the back side (17) of the diamond NV center substrate to allow illumination of the substrate from the back side (17).

[0098] Advantageously, the sensing device of the present invention is incorporated into sufficient hardware to allow it to be used to measure the magnetic field distribution of a particular object.

[0099] The method further comprises placing the object for which the magnetic field distribution has to be determined in the vicinity of the sensing element, preferably at a defined distance from the sensing element.The sensed magnetic field values ​​are then used to calculate the magnetic field distribution, as is known in the art.

[0100] The object to be measured can be of any type and in any technical field. For example, in medical imaging and diagnosis, sensor arrays can be used for magnetoencephalography (MEG), a non-invasive technique that can measure the magnetic field generated by neuronal activity in the brain. MEG signals are typically in the range of a few femtotesla to hundreds of femtotesla. The high sensitivity and spatial resolution of the sensor array will improve the detection of brain activity and may lead to better diagnosis and treatment of neurological diseases. The array can also promote the development of high-resolution magnetic resonance imaging (MRI) systems and improve diagnostic capabilities. MRI systems typically use magnetic fields of 0.5T to 3T or higher.

[0101] In nanotechnology and materials science, the sensor arrays can be used in magnetic force microscopy (MFM), a technique used to map the magnetic properties of materials at the nanoscale. The high spatial resolution and sensitivity will enable detailed mapping of magnetic domains in materials, aiding the understanding of magnetism and the development of new materials. In addition, the arrays can be used to characterize magnetic nanoparticles, which typically range in size from 10-100nm and have magnetic fields in the millitesla (mT) range at close distances. Magnetic nanoparticles have applications in drug delivery, hyperthermic cancer treatment, and magnetic separation.

[0102] In biological and chemical sensing, sensor arrays can be used to detect and quantify the presence of magnetically labeled biomolecules (such as proteins or DNA, etc.) in biological samples. The high sensitivity achieved due to the method of the present invention can, for example, allow the determination of the magnetic field distribution within a microfluidic device. This may lead to the development of highly sensitive diagnostic tools and detection methods. The array can also study the changes in the magnetic field caused by chemical reactions, providing insights into the reaction mechanism and kinetics.

[0103] Finally, in electronics and data storage, the high spatial resolution and sensitivity of sensor arrays can be used to read and write magnetic data storage devices, such as magnetic random-access memory (MRAM), thereby improving data density and performance. MRAM devices typically use magnetic fields in the range of 1 picotesla to 1 microtesla, depending on the measurement distance, which is typically between 1 micron and 100 microns. Sensor arrays can also be used to detect and locate defects in magnetic devices or materials, thereby improving quality control and failure analysis.

[0104] The invention can also be used to monitor the function of electronic systems, such as detecting small currents on integrated circuits or printed circuit boards. It can also be used for static measurements of quality control in a production environment, for example.

[0105] In summary, the high sensitivity, spatial resolution, and wide range of detectable magnetic fields of magnetic sensor arrays open up many possibilities in various research and industrial fields such as medical imaging, nanotechnology, biological and chemical sensing, and electronics.

[0106] Although the present invention has been described in detail with particular reference to exemplary embodiments of the present invention, the embodiments described herein are not intended to be exhaustive or to limit the scope of the present invention to the precise forms disclosed. Those skilled in the art and technology to which the present invention belongs will appreciate that changes and modifications may be made to the described structures and assembly and operation methods without significantly departing from the principles, spirit and scope of the present invention, as described in the claims and their equivalents.

Claims

1. A magnetic field sensing device for determining a magnetic field distribution in an area, comprising: A predetermined area of ​​a diamond nitrogen vacancy center substrate (1), the predetermined area having a plurality of sensing elements, each of the plurality of sensing elements having a first contact (2) and a second contact (3) electrically contacting a surface of the diamond nitrogen vacancy center substrate (1), the second contact (3) being electrically isolated from the first contact (2); wherein, in each sensing element, one of the first contact (2) and the second contact (3) is located inside the other of the first contact (2) and the second contact (3), and Controller (12); Wherein, in the operation mode, the controller (12) is configured to control: - a biasing element (6) for applying a bias voltage to the first contacts (2) of the selected plurality of sensing elements, thereby generating a local external electric field in each of the selected sensing elements, while the selected sensing elements are illuminated by at least one light source, thereby inducing a photocurrent in each of the selected sensing elements, and illuminated by at least one microwave source (13), thereby affecting the photocurrent generated in each of the selected sensing elements; - a measuring unit to measure the photocurrent detected by each of the second contacts (3) of the selected sensing elements and to extract therefrom the sensed magnetic field value of each of the selected sensing elements, and - adjusting the selection of the plurality of sensing elements to allow obtaining a sensed magnetic field value for each selectable sensing element of the predetermined area.

2. The magnetic field sensing device according to claim 1, wherein: In each sensing element, one of the first contact (2) and the second contact (3) substantially surrounds the other of the first contact (2) or the second contact (3).

3. A magnetic field sensing device according to any preceding claim, wherein: The plurality of sensing elements are arranged in a one-dimensional or two-dimensional array, wherein first parallel conductive lines (4) oriented along a first direction connect the first contacts (2), and second parallel conductive lines (5) oriented along a second direction connect the second contacts (3).

4. The magnetic field sensing device according to claim 3, wherein: The first direction is perpendicular to the second direction.

5. The magnetic field sensing device according to claim 3 or 4, wherein: The measuring unit is connected to the second conducting line (5) via a multiplexer (7).

6. A magnetic field sensing device according to any preceding claim, wherein: The biasing element (6) is controlled to connect the first contacts (2) of the unselected sensing elements to ground.

7. The magnetic field sensing device according to claims 3 to 5, wherein: The biasing element (6) is controlled to apply a differently modulated bias voltage to each of the first conductive lines (4).

8. The magnetic field sensing device according to claim 7, wherein: The measuring unit comprises at least one lock-in amplifier (9).

9. The magnetic field sensing device according to any of the preceding claims, further comprising a set of parallel microwave wires (10) for carrying microwave signals generated by the at least one microwave source (13), wherein the microwave lines (10) are formed above the first contact (2) and / or the second contact (3) and are electrically insulated from the first contact (2), the second contact (3) and the substrate (1).

10. The magnetic field sensing device according to claim 9, wherein: The microwave lines (10) are alternately connected to ground to define a set of coplanar microwave strips or a set of coplanar waveguides (10; 11).

11. The magnetic field sensing device according to claim 9 or 10, wherein: The set of parallel microwave conductors (10; 11) is oriented parallel to the second conductor (5).

12. The magnetic field sensing device according to claim 10, wherein: The at least one microwave source (13) is controlled to generate a modulated microwave signal.

13. A magnetic field sensing device according to any preceding claim, wherein: While irradiating, the at least one microwave source (13) is controlled to sweep the frequency within a predetermined frequency range.

14. A magnetic field sensing device according to any preceding claim, wherein: The first contact (2) and the second contact (3) are formed on the same surface of the substrate (1), and light generated by the at least one light source is directed to an opposite surface (17) to illuminate a selected sensing element.

15. A magnetic field sensing device according to any preceding claim, wherein: The irradiation is continuous across the predetermined area.

16. The magnetic field sensing device according to claims 1 to 14, wherein: The illumination varies spatially across the predetermined area.

17. The magnetic field sensing device according to claim 16, wherein: The at least one light source is a focused laser beam.

18. The magnetic field sensing device according to claim 16, wherein: The at least one light source is a linear laser beam.

19. The magnetic field sensing device according to claim 16, wherein: The at least one light source is a one-dimensional or two-dimensional array of light emitting diodes or lasers.

20. A magnetic field sensing device according to any preceding claim, wherein: The measuring unit is configured to extract a sensed temperature value of each of the selected sensing elements from the measured photocurrent.

21. A method for determining magnetic field distribution in an area using a magnetic field sensing device, the magnetic field sensing device comprising a predetermined area of ​​a diamond nitrogen vacancy center substrate (1), the predetermined area having a plurality of sensing elements, each of the plurality of sensing elements having a first contact (2) and a second contact (3) in electrical contact with a surface of the diamond nitrogen vacancy center substrate (1), the second contact (3) being electrically isolated from the first contact; wherein, In each sensing element, one of the first contact (2) and the second contact (3) is located inside the other of the first contact (2) or the second contact (3), and the method comprises the following steps: - applying a bias voltage to the first contacts (2) of the selected plurality of sensing elements, thereby generating a local external electric field in each of the selected sensing elements, while illuminating the selected sensing elements by at least one light source, thereby inducing a photocurrent in each of the selected sensing elements, and illuminating the selected sensing elements by at least one microwave source (13), thereby affecting the photocurrent generated in each of the selected sensing elements; - measuring the photocurrent detected by each of the second contacts (3) of the selected sensing elements and extracting therefrom the sensed magnetic field value of each of the selected sensing elements; and The selection of the sensing element is adjusted, and the steps of the method are repeated until the sensed magnetic field value of each selectable sensing element in the predetermined area is obtained.

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