Magnetic Field Sensing Device

Abstract

Magnetic field sensing device. A magnetic field sensing device and method for measuring a magnetic field distribution is described, the magnetic field sensing device comprising a predetermined area of ​​a diamond NV center substrate and a controller. The predetermined area comprises a plurality of magnetic sensing elements that can be selectively activated and read out. To enable the magnetic sensing elements to sense a magnetic field, simultaneously a local electric field is generated, the sensing elements are exposed to light of a predetermined wavelength or range of wavelengths, the magnetic elements are illuminated with microwaves of a predetermined frequency or range of frequencies, and the generated photocurrents are collected and measured, allowing the value of the magnetic field sensed from the magnetic sensing elements to be extracted.

Description

[Technical field]

[0001] This application claims priority to and the benefit of Belgian Patent Application No. 2022 / 5385 ("Magnetic field sensing device"), filed May 19, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the field of devices and methods for sensing magnetic field distributions. [Background technology]

[0003] Devices for measuring the magnetic field distribution of any permanent magnet and magnet assembly are known in the art. Such devices are called magnetic field sensing devices, sometimes called magnetic field cameras, and consist of a number of magnetic field sensing elements, allowing for example local measurements that allow the spatial distribution of the magnetic field in the area sensed by the magnetic field sensing device with an appropriate resolution to be determined. These magnetic field sensing elements may be arranged in a one-dimensional array or in a two-dimensional array in a matrix or grid.

[0004] An example of such a magnetic field sensing device is disclosed in EP 1 720 026 A1. The magnetic field sensing elements used are Hall sensors arranged in a matrix. To be able to individually address each of the Hall sensors in the matrix, switches in the form of transistors are used. The Hall sensors and the switches are made of semiconductor material.

[0005] In recent years, techniques for measuring magnetic fields using nitrogen vacancy (NV) centres in diamond 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 techniques: Optical Detection of Magnetic Resonance (ODMR) and Photocurrent Detection of Magnetic Resonance (PDMR).

[0006] Existing magnetic field sensing devices, consisting of Hall sensors and transistor switches made of semiconductor materials, have advantages for measuring magnetic field distribution.

[0007] US Patent No. 10,901,054 B1 discloses an integrated optical waveguide and electronic device using quantum defect centers. As in many current designs, a pair of electrodes therein are arranged facing each other in a nearly symmetrical manner. However, such an arrangement results in non-uniform electric fields, especially at the ends. Thus, the magnetic fields of adjacent sensing devices may interfere with each other, resulting in inaccurate results. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. 1720026A1 [Patent Document 2] U.S. Patent No. 10,901,054B1 [Non-patent literature]

[0009] [Non-Patent Document 1] Bourgeois, E., Jarmola, A., Siyushev, P. et al., Photoelectric detection of electron spin resonance of nitrogen-vacancy centers in diamond, Nat Commun6, 8577 (2015) Summary of the Invention [Problem to be solved by the invention]

[0010] However, it is an object of the present invention to provide an alternative magnetic field sensing device and method which makes the measurement results more accurate.

[0011] Another object of the present invention is to integrate such a magnetic field sensing device onto a diamond NV centre substrate to achieve higher spatial resolution of the magnetic field sensing element, improving measurement sensitivity and overall measurement time. [Means for solving the problem]

[0012] To achieve these objects, in one aspect of the present invention, a magnetic field sensing device is provided for determining a magnetic field distribution in a predetermined area of ​​a diamond NV center substrate, the magnetic field sensing device comprising a controller. The predetermined area has a plurality of magnetic sensing elements, each of the plurality of sensing elements having a first contact and a second contact that electrically contact a surface of the diamond NV center substrate. Each second contact is electrically insulated from each first contact.

[0013] The diamond NV centre substrate may comprise a diamond material containing nitrogen vacancy (NV) centres in the form of a thin plate.

[0014] According to the present invention, the controller comprises: - a biasing element for applying a bias voltage to first contacts of selected sensing elements of the plurality of sensing elements, thereby generating a localized 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 a biasing element for irradiating by at least one microwave source, thereby influencing the photocurrent generated in each of the selected sensing elements; - a measurement unit for measuring the photocurrent detected at each of the second contacts of the selected sensing elements and extracting therefrom a value of the sensed magnetic field for each sensing element of the selected plurality of sensing elements; - means for adjusting the selection of the plurality of detector elements, making it possible to obtain a value of the detected magnetic field for each selectable detector element of a given area; It should be understood that the number of sensing elements in a given area determines the maximum resolution. Thus, when a measurement is performed with the maximum resolution, all selectable sensing elements are controlled as described and a value of the magnetic field is extracted for each sensing element in the given area. However, it may be decided to measure with a lower resolution and thus use only a portion of the available sensing elements in the given area and perform the measurement over the entire given area, in other words only a portion of the sensing elements in the given area are selectable. Alternatively, with a lower resolution, all sensing elements are used for the measurement, but the values ​​of the sensed magnetic field are extracted only for the combination of sensing elements according to the desired resolution.

[0015] The measurement unit typically comprises an amplifier, an instrument for measuring current and / or voltage, signal processing means and a data processing unit.

[0016] To enable the magnetic sensing element to sense the magnetic field, a local electric field must be generated simultaneously by applying a bias voltage between the first and second contacts of the sensing element, the sensing element must be exposed to light of a predetermined wavelength or range of wavelengths, and the magnetic element must be irradiated with microwaves of a predetermined frequency or range of frequencies. The combination of the presence of the local electric field and the exposure to light allows a photocurrent to be induced and collected. The simultaneous irradiation with microwaves affects the photocurrent depending on the presence of the magnetic field. Thus, by electrically connecting the second contact of the sensing element to a measurement unit, the value of the sensed magnetic field can be extracted by the measurement unit from the photocurrent detected at the second contact. The above can be repeated for each sensing element, or can be performed in parallel for selected magnetic sensing elements, by separately connecting the second contact of each selected magnetic sensing element to the measurement unit, in order to obtain the contribution of each individual sensing element to the magnetic field in succession. The ability to extract the value of the sensed magnetic field for each individual magnetic sensing element, the so-called read selectivity, can be realized in several ways, without the need to separately connect each second contact. Unselected magnetic sensing elements, without a local external field applied and / or exposed to light, do not generate photocurrent. Thus, the read selectivity of the selected magnetic sensing elements is not affected even if the second conductive line of the unselected magnetic sensing elements is connected to the second contact of the selected magnetic sensing elements. Spatial control of the light source and electric field creates design freedom, reduces design complexity, and allows faster and more accurate measurements. When grouping the second contacts, read selectivity can still be achieved by modulating the bias voltage, light source, and / or microwave source to expose different magnetic sensing elements or groups thereof to signals with different modulation frequencies, and using a multi-frequency lock-in amplifier to allow separation of the contribution of individual magnetic sensing elements to the photocurrent detected at the grouped second contacts.

[0017] In one embodiment of the invention, either one of the first and second contacts of the magnetic sensing element is arranged inside the other one of the first and second contacts. In particular, either one of the first and second contacts of the magnetic sensing element may be arranged to substantially surround the other one of the first and second contacts, i.e. the two contacts have different shapes and one extends (along a closed line or only partially) around the other. For example, one contact is a point (of any shape) located at the center of the sensing element, while the other contact is a line located relative to the periphery of the sensing element. Doing so not only defines the area of ​​the substrate (between the two contacts) over which the electric field is applied, but also contributes to the uniformity of the electric field within the magnetic sensing element. This also improves the shielding of the magnetic sensing element from the influence of neighboring magnetic sensing elements.

[0018] The plurality of sensing elements may be arranged in a 1D or 2D array to define a matrix or grid of magnetic sensing elements forming a magnetic sensing device. A first parallel conductive line oriented in a first direction may be provided to connect to the first contacts and a second parallel conductive line oriented in a second direction may be provided to connect to the second contacts. This allows for connecting to the first and second contacts of rows and / or columns of magnetic sensing elements in the matrix.

[0019] The first direction may be selected perpendicular to the second direction. Thus, the first conductive line may connect to the first contacts of a row of magnetic sensing elements, while the second conductive line may connect to the second contacts of a column of magnetic sensing elements, or vice versa. This is advantageous since the first and second conductive lines may be easily accessed from different sides of the magnetic sensing device. A multiplexer may be provided to connect all the second conductive lines, while the output of the multiplexer is connected to a measurement unit. This allows all the second contacts to be connected and read out by the measurement unit in rows or columns. For example, assume that the first conductive line connects to the rows of magnetic sensing elements and the second conductive line, the readout line, connects to the columns of magnetic sensing elements, and that a single row of magnetic sensing elements is selected and biased such that an electric field is present in each sensing element of that row. When this row of sensing elements is simultaneously exposed to light of a given wavelength and illuminated with microwaves of a given frequency, a photocurrent is generated in each sensing element of the row, influenced by the magnetic field in the range present. Each column in such a case has only one active sensing element. In other words, each readout line addresses a single active sensing element. Thus, the value of the sensed magnetic field of a single magnetic sensing cell can be extracted from the photocurrent measured by the measurement unit, since the readout lines are selectively connected by a multiplexer to a measurement unit.

[0020] In one embodiment of the present invention, when the biasing element is controlled to bias the first contact of the selected sensing element, the biasing element may be further controlled to connect the first contacts of the unselected sensing elements to ground, which suppresses noise that may be picked up by the second contacts of the unselected sensing elements, which may potentially affect the reliability and accuracy of the measured photocurrent and thus also the reliability and accuracy of the extracted sensed magnetic field value, since all the second contacts are grounded.

[0021] Alternatively, if multiple rows of sensing elements are selected (activated) at one time, the biasing elements may be controlled to apply different modulated bias voltages to each of the associated first conductive lines. The photocurrent measured on the readout line will in this case include contributions from multiple rows of magnetic sensing elements, but each contribution will be modulated differently and may be extracted separately using at least one lock-in amplifier, or equipment for analog to digital conversion and subsequent FFT analysis, such as a spectrum analyzer.

[0022] The at least one microwave source may be one or more RF antennas. The at least one microwave source may be controlled while irradiating to sweep the frequency within a predetermined frequency range. The at least one microwave source may be configured to irradiate the magnetic sensing element directly. Alternatively, a set of parallel microwave conductive lines for transmitting the microwave signal generated by the at least one microwave source may be provided, the microwave lines being formed above the first contact and / or the second contact and being electrically insulated from the first contact and the second contact and the substrate. The microwave conductive lines may be arranged to at least partially cover the portion of the substrate not covered by the first contact and the second contact. The microwave conductive lines may be particularly configured to maximally cover the portion of the substrate not covered by the first contact and / or the second contact, thereby maximizing the coupling of microwaves to the diamond material.

[0023] In one embodiment of the invention, the microwave lines are alternately connected to 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, e.g. each connected to some of the second contacts, to obtain a coplanar waveguide structure without having to alternate the microwave lines with microwave ground lines.

[0024] In a further embodiment of the invention, a set of parallel microwave conductive lines are oriented parallel to a second conductive line. Referring back to the matrix example above, this would mean that the microwave lines are parallel to the readout lines, in other words the columns of magnetic sensing elements.

[0025] In yet another embodiment, at least one microwave source may be controlled to generate a modulated microwave signal.

[0026] In another embodiment of the invention, the first contact and the second contact are formed on the same surface of the substrate and light generated by the at least one light source is directed to the opposite surface to illuminate selected sensing elements, which is advantageous as in this case the light is not blocked by the contacts, thus increasing the exposed surface and / or volume of the substrate.

[0027] The illumination may be continuous over a given area, independent of the surface on which it is incident. Alternatively, the illumination is spatially varied over a given area. The spatial variation may be obtained by mechanically moving the light source, by using one or more reflective elements, such as at least one mirror, e.g. a polygonal mirror, by using at least one diffractive element, or by using multiple light sources that can be selectively addressed. The at least one light source may in particular be a focused laser light, a line laser light, or a one- or two-dimensional array of LEDs or lasers, e.g. Vertical Cavity Surface Emitting Lasers (VCSELs).

[0028] In a further embodiment of the invention, the measurement unit is adapted to extract sensed temperature values ​​for each of the selected sensing elements from the measured photocurrent.

[0029] In another aspect of the invention there is provided a method of determining a magnetic field distribution in an area using a magnetic field sensing device, the magnetic field sensing device comprising a predetermined area of ​​a diamond NV centre substrate, the predetermined area having a plurality of 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 centre substrate, the second contact being electrically insulated from the first contact, the method comprising: - applying a bias voltage to first contacts of selected sensing elements of the plurality of sensing elements, thereby generating a localized external electric field in each of the selected sensing elements, while illuminating the selected sensing elements with at least one light source, thereby inducing a photocurrent in each of the selected sensing elements, and irradiating the selected sensing elements with at least one microwave source, thereby affecting the photocurrent generated in each of the selected sensing elements; - measuring the photocurrent detected at each of the second contacts of the selected sensing elements and extracting therefrom a value of the sensed magnetic field for each sensing element of the selected plurality of sensing elements; - adjusting the selection of sensing elements and repeating the steps of the method until a sensed magnetic field value is obtained for each selectable sensing element in the given area. Includes.

[0030] The method also includes placing an object whose magnetic field distribution needs to be determined in the vicinity of the sensing element, preferably at a predetermined distance from the sensing element, The sensed magnetic field values ​​are then used to calculate the magnetic field distribution, as known in the art.

[0031] The object to be measured can be of any type and from any technical field. The method of the invention can be used, for example, for biodetection or biosensing in samples of various shapes, sizes or containers. The high sensitivity achieved by the method of the invention can make it possible, for example, to determine the magnetic field distribution in microfluidic devices on chips or wafers, to detect small currents on integrated circuits, and to monitor the functioning of electronic systems. The invention can also be used, for example, for static measurements for quality control on the manufacturing site. [Brief description of the drawings]

[0032] [Figure 1] 1 is a schematic top view of an example of a magnetic field sensing device according to the present invention; [Diagram 2] 1 is a schematic perspective view of an example of an array of magnetic field sensing elements according to the present invention; [Diagram 3] 3 shows a backside view of a schematic perspective view of the array of magnetic field sensing elements of FIG. 2, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The figures are made for illustrative purposes and elements may not be in precise proportion to each other.

[0034] Examples of the invention will now be described in more detail with reference to the drawings.

[0035] Terms such as "first", "second", etc. may be used herein to describe various elements, components, regions, layers, and / or sections, but it will be understood that such elements, components, regions, layers, and / or sections should not be limited by such terms. Such terms are used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below may be referred to as a second element, component, region, layer, or section without departing from the spirit and scope of the inventive concept.

[0036] The terms used herein are intended to describe particular embodiments and are not intended to limit the inventive concepts. As used herein, the singular forms "a" and "an" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "include," "including," "comprises," and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term "and / or," when used herein, includes any and all combinations of one or more of the associated listed items. Phrases such as "at least one of," when preceding a list of elements, modify the entire list of elements and not the individual elements of the list. Additionally, the use of "may," when describing an embodiment of the inventive concept, refers to "one or more embodiments of the invention."

[0037] When an element is referred to as being "connected" or "coupled" to another element, it will be understood that the element may be directly connected or coupled to the other element, or there may be one or more intervening elements. When an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0038] The terms "substantially," "approximately," and similar terms, as used herein, are used as terms of approximation rather than as terms of degree and are intended to take into account inherent variations in measured or calculated values ​​that would be recognized by one of ordinary skill in the art.

[0039] The terms "use," "using," and "used," as used herein, may be considered synonymous with the terms "utilize," "utilizing," and "utilized," respectively.

[0040] FIG. 1 shows a magnetic field sensing device comprising a defined area of ​​a diamond NV center substrate (1) shown in the xy plane, the defined 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 NV center substrate (1), the second contact (3) being electrically insulated from the first contact (2).

[0041] The diamond NV centre substrate (1) is a diamond material containing nitrogen vacancy (NV) centres in the form of a thin plate, typically having a surface area (in the xy plane) in the range of 4 mm x 4 mm to 10 mm x 10 mm, and a thickness typically in the range of 100 μm to 500 μm.

[0042] The second or read contact (3) of each of the magnetic sensing elements is disposed inside the first or bias contact (2) of the magnetic sensing element. In operation, a bias voltage is applied between the bias contact (2) and the read contact (3) of a sensing element, thereby generating an electric field within the substrate volume (15) of that sensing element. Thus, proper placement and definition of the contacts not only maximizes the sensing area (15), but also contributes to the uniformity of the electric field within the sensing area of ​​the magnetic sensing element.

[0043] 1, a plurality of sensing elements of the magnetic sensing device are arranged in a 2D array to define a 3x3 matrix or grid of magnetic sensing elements forming the magnetic sensing device. Although a 3x3 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 matrix of sensing elements selected from a range of dimensions including, for example, 1x2, 2x2, 5x5, 5x10, 1x10, 5x1, 10x10, 100x100, 1000x1000.

[0044] Horizontally oriented parallel conductive bias lines (4) connect the bias contacts (2) of rows of magnetic sensor elements, while vertically oriented parallel conductive readout lines (5) connect the readout contacts (3) of columns of magnetic sensor elements.

[0045] The width of the contacts and conductive tracks typically ranges from 1 μm to 10 μm, while the thickness may typically range from 0.1 μm to 1 μm. The minimum distance between the bias contact and the read contact of the same magnetic sensing element typically ranges from 5 μm to 100 μm. The distance between the read contacts of adjacent magnetic sensing elements, or pitch, is a measure of maximum resolution and typically ranges from 10 μm to 200 μm.

[0046] A set of parallel microwave conductive lines (10) is provided for transmitting microwave signals. The microwave lines are formed using known techniques used in semiconductor processing and in the manufacture of integrated circuits and MEMS devices. The microwave lines are arranged (in the z-direction) above the bias contacts (2) and read contacts (3) and the bias lines (4) and read lines (5) and are electrically insulated from them and from the substrate. The microwave conductive lines are arranged to at least partially cover the parts of the substrate not covered by the bias and read contacts. The microwave conductive lines may be specifically configured to maximize coverage of the parts of the substrate not covered by the bias and read contacts, thereby maximizing the coupling of microwaves to the diamond material. The set of parallel microwave conductive lines (10) is oriented parallel to the read lines (5), i.e. the rows of magnetic sensing elements.

[0047] For a magnetic sensing element to be able to sense a magnetic field, simultaneously a local electric field must be generated, the sensing element must be exposed to light of a given wavelength or range of wavelengths, the magnetic element must be illuminated with microwaves of a given frequency or range of frequencies, and the generated photocurrent must be collected and measured, allowing the value of the magnetic field sensed from the magnetic sensing element to be extracted. This may be possible as follows: 1. The diamond substrate is illuminated with light of an appropriate wavelength (typically green, but blue light and even combinations of different colors such as green and red, or green and yellow can be used) to excite charge carriers into the conduction band, up to the excited NV state. 2. Charge carriers are transported to the ground state ( 3 A 2 )0 state to degenerate ( 3 A 2 ) + / - 1NV state, the NV center is supplied with microwave electromagnetic radiation at around 2.87 GHz. This allows more charge carriers to be excited ( 3 E) Two metastable states from + / -1NV state 1 A 1 and 1 E NV states and back to the ground NV state, which causes an associated change in the electrical photocurrent, since the charge carriers decaying through these metastable NV states do not contribute to the photocurrent. A constant frequency may be selected. This may be done if the resonant frequency is known, for example if it has been determined in a previous calibration step. The microwave radiation may be supplied while sweeping the microwave frequency over 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, for example in steps of 1 MHz. 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 read contact on the diamond surface. This bias voltage is set to 10 V between the bias contact and the read contact at the diamond. 2 V / cm to 10 5An electric field having a magnitude in the range of V / cm is generated, which collects the generated charge carriers in the conduction band towards one of the contacts. The collected photocurrent is then measured at a constant frequency or at each frequency within a given frequency range. When the photocurrent is collected and measured while the frequency of the microwave field is swept over a range around 2.87 GHz, a decrease in the photocurrent is observed at a specific resonant frequency. These absorption minima occur in pairs around a common center frequency. The location of this center frequency is typically 2.87 GHz, but can shift 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. Measuring the distance between the minima therefore gives information about the sensed magnetic field, allowing the value of the sensed magnetic field to be extracted from the measured photocurrent. Furthermore, the common center frequency of all pairs of minima is temperature dependent, so that the local temperature at the measurement location can be extracted from the photocurrent spectrum. The sensor described in this invention can therefore also be used as a temperature sensor array or as a combined magnetic field and temperature sensor array.

[0048] As shown in Figure 1, the controller (12) is connected to the bias element (6), the measurement unit's readout line selection unit (7), 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 the microwave line selection unit. The readout line (5) is connected to the readout line selection unit (7). In an operational mode, the controller (12) is - a bias element (6) for applying a bias voltage to the bias contact (2) of a selected one of the nine detector elements while the selected detector element is illuminated with light and irradiated with microwaves; - a measurement unit for measuring the photocurrent detected at each of the read contacts (3) of the selected sensing elements and for extracting therefrom, for each sensing element of the selected plurality of sensing elements, a value of the sensed magnetic field; - means for adjusting the selection of the detector elements and for repeating the aforementioned control steps until, when measuring with full resolution, a value of the detected magnetic field has been obtained for each selectable detector element, i.e. for all nine detector elements; The device is configured to control

[0049] The readout procedure of the matrix of magnetic sensing elements may be as follows. A bias voltage is applied to a selected one of the bias lines, while the other bias line may be simultaneously connected to ground. At least the sensing area (15) of a selected magnetic sensing element (in this example, the sensing element in a selected row, in other words the sensing element associated with a selected bias line (4)) is illuminated with light of a suitable wavelength or wavelength range. A microwave signal is generated by a microwave source (13) while sweeping the microwave frequency over a range around 2.87 GHz, e.g., from 2.80 GHz to 2.94 GHz, or from 2.70 GHz to 3.04 GHz, e.g., in steps of 1 MHz, and the generated signal is transmitted using microwave line (10) to at least the sensing areas (15) of selected sensing elements such that microwaves can be coupled to the substrate at these sensing areas (15). For each microwave frequency, the photocurrent detected via the readout line (5) is measured. The readout lines may be selectively read out by the measurement unit using a multiplexer (7). Alternatively, this may be done simultaneously using parallel current measurement equipment. The photocurrent of each readout line substantially only includes the photocurrent detected at the readout contact of the selected sensing element. The other sensing elements of the readout line are not active. Furthermore, the bias contacts of the other sensing elements are connected to ground potential, so that the effect of noise picked up at the readout contacts of these other inactive sensing elements is suppressed. The measurement unit comprises 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 may be used instead of the transimpedance amplifier (8). The resulting signal may then be further processed by the measurement unit using signal processing means, such as, for example, a lock-in amplifier, an analog-to-digital converter, a spectrum analyzer, and / or other electrical measurement and / or analysis equipment (9). The acquired measurements are therefore associated with a selected individual sensing element, in other words with a single sensing area 15. A data processing unit 16 extracts from the measurements the value of the magnetic field sensed by that single magnetic sensing element. Once results have been obtained for each sensing element in the selected row, a bias voltage may then be applied to another bias line (4), whereupon the procedure described above may be repeated until all bias lines have been selected.

[0050] As an alternative to the above readout procedure, a bias voltage may be applied simultaneously to multiple selected bias lines (4), with said bias voltage being amplitude modulated to have different modulation frequencies for the different selected bias lines. The photocurrent detected on the readout line includes contributions from multiple selected sensing elements. A transimpedance amplifier (8) converts the electrical photocurrent into a voltage. The resulting readout line signals are further analyzed using multiple lock-in amplifiers (9) or spectrum analyzers and / or subjected to Fourier analysis to determine the contribution at each of the different modulation frequencies, each corresponding to a single different bias line. A set of spectra is then obtained, from each of which the local magnetic field of a single sensing element can be extracted. Instead of modulating the bias voltage so that each row of sensing elements receives a signal with a different modulation frequency, one may choose to modulate the illumination signal with different modulation frequencies for the different rows, or modulate the microwave signal with different modulation frequencies for the different microwave lines (rows) if the microwave lines are parallel to the bias lines.

[0051] The modulations may be applied simultaneously to the signal sources, one of which is applied to the rows of the sensing elements and the other to the columns of the sensing elements. For example, in the configuration shown in FIG. 1, one may choose to modulate the bias voltage at different frequencies for different bias lines (associated with the rows) and the microwave signal at different frequencies for different microwave lines (columns). In that way, each sensing element can receive a different unique combination of bias voltage modulation frequency and microwave modulation frequency. In this case, the readout lines of selected sensing areas of the sensing areas can be connected together and measured as a single photocurrent signal. The frequency spectrum of said single photocurrent signal then contains frequency components corresponding to all combinations of bias voltage modulation frequencies and microwave modulation frequencies. Since these combinations are uniquely selected, the magnetic field in each individual sensing area can be measured by extracting the corresponding composite frequency of the individual sensing areas from the photocurrent spectrum.

[0052] For example, the modulation frequency fb of the bias voltage can be chosen in the range of 1 kHz to 5 kHz, and the modulation frequency fm of the microwave line can be chosen in the range of 10 kHz to 100 kHz. The composite frequency, in this case, is in the range of 11 kHz to 105 kHz, so that a series of lower frequencies repeats around each higher frequency, thus forming a number of frequency components corresponding to each combination of bias voltage frequency and microwave frequency. These frequencies can further be extracted from the photocurrent signal using a number of lock-in amplifiers, spectrum analyzers, or Fourier analysis, as explained above.

[0053] When selecting the modulation frequencies, care is taken to avoid compound frequencies at the same position in the spectrum, since some folded frequencies around a particular frequency may coincide with some frequencies around the lower modulation frequency. Therefore, the distance between subsequent higher frequencies, for example between fm1 and fm2, should be at least twice the range of the lower frequencies fb1 to fbn.

[0054] The multiple unique composite frequencies simultaneously present in the measured photocurrent signal can be further separated using spectral techniques such as lock-in amplification, spectral analysis, FFT analysis, and the like.

[0055] As previously discussed, to extract the value of the magnetic field from the measured photocurrent, the photocurrent is measured at multiple microwave frequencies, which results in the observation of absorption minima (peaks) at specific 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 crystallographic axes of the diamond lattice in the diamond NV center substrate. Each NV center is oriented along one of the four crystallographic axes of the diamond lattice and is sensitive only to the local magnetic field component along that crystallographic direction. The multiple NV centers in the diamond NV substrate are randomly distributed in the four crystallographic orientations, resulting in each of these orientations having approximately equal sensitivity.

[0056] A magnetic field oriented to have a component along each of the four lattice orientations will thereby give rise to four pairs of resonant peaks (minima) in the photocurrent spectrum, as each orientation sees a non-zero magnetic field along the lattice orientation.

[0057] To resolve the magnetic field components along different crystallographic orientations, a bias field may be applied to offset each pair of minima so that the magnetic field components can be separated and individually detected. The bias field may be applied to the sensing device using one or more permanent magnets, or one or more electromagnets, such as Helmholtz coils.

[0058] Since space is three-dimensional, measurements along three of the four crystal orientations are sufficient to fully resolve the applied magnetic field into its Cartesian components. To examine only the three pairs of resonant peaks (minima) in the photocurrent spectrum, the applied bias field may be oriented perpendicular to one of the four crystal orientations. That orientation is insensitive to magnetic fields in this case, and only the three pairs of resonant peaks appear in the spectrum, along with a single peak in the fourth orientation (not split, since there is no magnetic field along that direction). The spectrum thus consists of seven peaks, only six of which are used to determine the magnetic field components along the three sensitive crystal orientations.

[0059] A transformation can then be performed to convert the measured magnetic field components along the crystal orientations into a Cartesian coordinate system. This can be done if the magnetic sensing device has first been calibrated by applying a magnetic field along each of the Cartesian dimensions and recording the response of each pair of resonant peaks. This procedure results in a transformation equation that converts between the crystal orientation components and the Cartesian components. This makes it possible, during the actual measurement, to apply a (constant) bias field perpendicular to one of the crystal orientations (thereby exciting only the three crystal orientations) and record the difference therefrom.

[0060] In Fig. 1, a set of microwave lines (10) is provided to transmit each microwave signal to a corresponding sensing area (15). Alternatively, as shown in Fig. 2, a perspective view of the same 3 x 3 matrix of sensing elements as in Fig. 1, a set of parallel microwave conductive lines (10) for transmitting microwave signals and a set of microwave ground lines (11) are provided in an alternating coplanar configuration to form a coplanar waveguide for each column of the matrix of sensing elements. The microwave lines (10) of the coplanar waveguide are arranged (in the z-direction) above the bias contacts (2) and read contacts (3) and the bias lines (4) and read lines (5) and are electrically insulated from them and from the substrate. The microwave conductive lines are arranged to cover the sensing area (15). The set of parallel microwave conductive lines (10) are oriented parallel to the read lines (5), i.e. the columns of magnetic sensing elements. The microwave ground lines (11) are arranged coplanarly between the microwave lines (10) such that each microwave line (10) is sandwiched between a microwave ground line (11) on each side of the length of the microwave line. The microwave ground lines (11) are electrically isolated from the substrate, the bias contacts (2) and read contacts (3), and the microwave lines (10). In the operational state of the magnetic sensing device, the microwave ground lines (11) are connected to ground. This coplanar waveguide configuration allows a constant impedance, e.g., 50 ohms, to be maintained along the entire trajectory of the microwave lines (10) so that microwave energy is efficiently transferred across the diamond surface.

[0061] As shown in Figure 3, 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 equipped with the microwave lines, in order to optimize the exposure of the substrate to microwave irradiation. The back ground electrode is preferably designed such that sufficient uncovered substrate surface remains on the back side (17) of the diamond NV center substrate to allow illumination of the substrate from the back side (17).

[0062] The sensing device of the present invention is advantageously integrated into suitable hardware to enable use of the sensing device to measure the magnetic field distribution of a particular object.

[0063] The method also includes placing the object, whose magnetic field distribution needs to be determined, in the vicinity of the sensing element, preferably at a predetermined distance from the sensing element, and the sensed magnetic field values ​​are then used to calculate the magnetic field distribution, as known in the art.

[0064] The object to be measured can be of any type and from any technical field. Sensor arrays may be used, for example, in medical imaging and diagnostics for magnetoencephalography (MEG), a non-invasive technique that measures the magnetic fields generated by neuronal activity in the brain. MEG signals typically range from a few femtotesla to hundreds of femtotesla. The high sensitivity and spatial resolution of sensor arrays will improve the detection of brain activity, potentially leading to better diagnosis and treatment of neurological disorders. Arrays may also contribute to the development of high-resolution magnetic resonance imaging (MRI) systems, improving diagnostic capabilities. MRI systems typically use magnetic fields ranging from 0.5T to 3T or more.

[0065] The sensor arrays could be used for magnetic force microscopy (MFM), a technique used in nanotechnology and materials science to map the magnetic properties of materials at the nanoscale. The high spatial resolution and sensitivity would allow detailed mapping of the magnetic domains of materials, contributing to the understanding of magnetic properties and the development of new materials. The arrays could further be used to characterize magnetic nanoparticles, which are typically in the size range of 10-100 nm and have magnetic fields in the millitesla (mT) range when in close proximity. Magnetic nanoparticles have applications in drug delivery, hyperthermia cancer therapy, and magnetic separation.

[0066] Sensor arrays may be utilized in biological and chemical sensing to detect and quantify the presence of magnetically labeled biomolecules, such as proteins or DNA, in biological samples. The high sensitivity achieved by the method of the invention may allow, for example, the determination of magnetic field distribution in microfluidic devices. This may lead to the development of extremely sensitive diagnostic tools and assays. The arrays may also allow the study of magnetic field changes resulting from chemical reactions, which may provide insight into reaction mechanisms and kinetics.

[0067] Finally, in electronics and data storage, the high spatial resolution and sensitivity of sensor arrays may be used to read and write magnetic data storage devices such as magnetic random-access memory (MRAM), increasing 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 may typically range from 1 micrometer to 100 micrometers. Sensor arrays may also be used to detect and localize defects in magnetic devices or materials, allowing for improved quality control and failure analysis.

[0068] The invention may further be used to monitor the functioning of electronic systems, such as detecting small currents on integrated circuits or printed circuit boards. The invention may also be used for static measurements, for example for quality control on the manufacturing floor.

[0069] In summary, the high sensitivity, spatial resolution, and wide range of detectable magnetic fields of magnetic sensor arrays open up many possibilities across various areas of academic research and industry, including medical imaging, nanotechnology, biological and chemical sensing, and electronics.

[0070] Although the invention has been described in detail with particular reference to illustrative embodiments thereof, the embodiments described herein are not intended to be exhaustive or to limit the scope of the invention to the precise forms disclosed. Those skilled in the art and techniques to which the invention pertains will recognize that modifications and variations in the structure, assembly methods, and operation described may be practiced without significantly departing from the principles, spirit, and scope of the invention as set forth in the following claims and equivalents thereof. [Explanation of symbols]

[0071] 1. Diamond NV center substrate 2 First contact, bias contact 3 Second contact, read contact 4. First conductive line, bias line 5 Second conductive line, read line 6 Bias element 7 Read line selection unit, multiplexer 8 Transimpedance Amplifiers, Current Amplifiers 9 Lock-in amplifier / frequency analyzer / ADC 10 Microwave lines 11 Microwave ground line 12 Controller 13 Microwave Source 14 Microwave Line Selection Unit 15 Detection Area 16 Data Processing Unit 17 Backside of diamond NV center substrate 18 Backside ground electrode

Claims

1. 1. A magnetic field sensing device for determining a magnetic field distribution in an area, comprising: a predetermined area of ​​a diamond NV central 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 NV central substrate (1), the second contact (3) being electrically insulated from the first contact (2), and in each sensing element, one of the first contact (2) and the second contact (3) being disposed inside the other of the first contact (2) and the second contact (3); A controller (12); In an operational mode, the controller (12) a biasing element (6) for applying a bias voltage to the first contacts (2) of selected detector elements of the plurality of detector elements, thereby generating a local external electric field in each of the selected detector elements, while the selected detector elements are illuminated by at least one light source, thereby inducing a photocurrent in each of the selected detector elements, and are illuminated by at least one microwave source (13), thereby influencing the photocurrent generated in each of the selected detector elements; a measurement unit for measuring the photocurrent detected at each of the second contacts (3) of the selected sensing elements and for extracting therefrom, for each sensing element of the selected plurality of sensing elements, a value of the sensed magnetic field; - means of adjusting the selection of said plurality of detector elements, making it possible to obtain a value of the detected magnetic field for each selectable detector element of said given area; A magnetic field sensing device configured to control the

2. 2. The magnetic field sensing device of 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) and the second contact (3).

3. 3. The magnetic field sensing device of claim 1 or 2, wherein the plurality of sensing elements are arranged in a 1D or 2D array, a first parallel conductive line (4) oriented in a first direction connects to the first contacts (2) and a second parallel conductive line (5) oriented in a second direction connects to the second contacts (3).

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

5. 5. A magnetic field sensing device according to claim 3 or 4, wherein the measurement unit is connected to the second conductive line (5) via a multiplexer (7).

6. 6. A magnetic field sensing device according to claim 1, wherein the biasing element (6) is controlled to connect the first contacts (2) of unselected sensing elements to ground.

7. A magnetic field sensing device according to any one of claims 3 to 5, wherein the biasing element (6) is controlled to apply differently modulated bias voltages to each of the first conductive lines (4).

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

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

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

11. 11. A magnetic field sensing device according to claim 9 or 10, wherein the set of parallel microwave conductive lines (10; 11) are oriented parallel to the second conductive line (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. 13. A magnetic field sensing device according to any one of the preceding claims, wherein the at least one microwave source (13) is controlled to sweep frequencies within a predetermined frequency range while irradiating.

14. 14. The magnetic field sensing device of claim 1, 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 the selected sensing element.

15. A magnetic field sensing device according to claim 1 , wherein the illumination is continuous over the predetermined area.

16. A magnetic field sensing device according to claim 1 , wherein the illumination is spatially varied over the predetermined area.

17. The magnetic field sensing device of claim 16 , wherein the at least one light source is a focused laser light.

18. The magnetic field sensing device of claim 16 , wherein the at least one light source is a linear laser light.

19. 17. The magnetic field sensing device of claim 16, wherein the at least one light source is a one or two dimensional array of LEDs or lasers.

20. 20. A magnetic field sensing device according to claim 1, wherein the measurement unit is configured to extract a sensed temperature value for each sensing element of the selected plurality of sensing elements from the measured photocurrent.

21. 1. A method for determining a magnetic field distribution in an area using a magnetic field sensing device, the magnetic field sensing device comprising a predetermined area of ​​a diamond NV central 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 NV central substrate (1), the second contact (3) being electrically insulated from the first contact, and in each sensing element, one of the first contact (2) and the second contact (3) is disposed inside the other of the first contact (2) and the second contact (3), the method comprising: - applying a bias voltage to the first contacts (2) of selected detector elements of the plurality of detector elements, thereby generating a local external electric field in each of the selected detector elements, while illuminating the selected detector elements by at least one light source, thereby inducing a photocurrent in each of the selected detector elements, and irradiating the selected detector elements by at least one microwave source (13), thereby influencing the photocurrent generated in each of the selected detector elements; - measuring the photocurrent detected at each of the second contacts (3) of the selected sensing elements and extracting therefrom, for each sensing element of the selected plurality of sensing elements, a value of the sensed magnetic field; - adjusting said selection of sensing elements and repeating said steps of the method until a sensed magnetic field value has been obtained for each selectable sensing element of said given area; A method comprising:

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