magnetic field sensor

Abstract

The differential detection system (1) includes an optically trapping diamond nitrogen-vacancy doped layer (2) with an adjacent microwave resonator (4) having a resonant frequency with an operating bandwidth around the magnetic resonance of the nitrogen vacancy center. The microwave resonator (4) includes a suppressed portion (4B) and an unsuppressed portion (4A). A sensor photodiode (6A) is positioned distal to the doped layer (2) and aligned with the unsuppressed portion (4A) of the microwave resonator (4). A reference photodiode (6B) is spaced from the sensor photodiode (6A) and is substantially coplanar with the sensor photodiode (6A), while also aligned with the unsuppressed portion (4A) of the microwave resonator (4). The sensor (6A) and reference photodiode (6B) are connected back-to-back to a single transimpedance amplifier.

Description

[Technical Field]

[0001] The present invention relates to magnetic field sensing, and more particularly to magnetometers for measuring magnetic fields. [Background technology]

[0002] The present invention has been developed to provide a magnetometer device and readout substantially disposed on a single chip, and will be described with reference to this application, which may be used as an accelerometer. However, it will be understood that the invention is not limited to this particular application, but is made broadly applicable to detecting small changes in ambient physical conditions, including, for example, magnetic fields and temperature.

[0003] In recent years, the world has been on the brink of major advances in making new quantum technologies available for real-world use. While the benefits of "quantum" approaches are unparalleled, most remain impractical due to the size, weight, and power requirements, primarily of large, expensive, laboratory-based systems. This is not an easy task to address, especially given that many quantum-enabled technologies require cryogenic cooling to operate.

[0004] Existing classical magnetometers have limitations (e.g., thermal noise, drift, large size / weight, high power consumption) that preclude any possibility of navigation using the Earth's magnetic field lines. Quantum-based sensors are promising, but while their sensitivity lies around fT / √Hz, most sensors have limitations. For example, they do not provide directional information (atomic vapor cells) or require large peripheral cooling equipment (superconducting quantum interference devices). They are expensive to build and operate. Each technology has its advantages and disadvantages, so there are few one-size-fits-all solutions. Technologies utilizing the magnetic sensitivity of nitrogen-vacancy (NV) centers in diamond represent a promising new quantum platform that could enable GPS-free navigation capabilities for both civil and military applications.

[0005] This approach relies on optically detecting the magnetic resonance signatures from negatively charged nitrogen-vacancy (NV) centers in diamond. Nitrogen-vacancy NV centers are nitrogen atoms that substitute for carbon atoms in the diamond lattice and are adjacent to "vacant" sites. This generates a strong fluorescence signal when the nitrogen-vacancy NV centers are illuminated with a laser having a subthreshold wavelength, typically between 510 nm and 540 nm. The optical fluorescence measurably changes in response to the surrounding magnetic or microwave fields, at least in part as a result of a phenomenon known as the Zeeman shift or Zeeman effect. This enables a variety of real-world applications, particularly in quantum technologies.

[0006] An attempted device is known from US Pat. No. 5,699,703. Here, an on-chip sensor comprises an RF or microwave generator with a centrally located optical filter. Nitrogen-vacancy (NV) vacancy doped diamond is placed in close proximity to the microwave generator and receives the laser light input thereto. A photodetector is placed underneath with a plasmonic filter intermediate to filter out the incident light, and the photodetector provides an electrical signal output. The incident laser light is split to provide a reference signal to a reference diode. The signal from the on-chip photodiode and the signal from the reference photodiode are sent to respective transimpedance amplifiers (TIAs). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2019 / 0235031 Summary of the Invention [Problem to be solved by the invention]

[0008] In this prior art, the total photocurrent of the on-chip diode array (sensing) is sensed by an off-chip transimpedance amplifier (TIA) and an off-chip reference diode is used. This leads to a mismatch between the two sensing currents and the reference current due to the type (exact material stack), exact dimensions, and parasitic elements on the path of the sensing current to the off-chip transimpedance amplifier (TIA). This is considered to be a significant barrier to fully integrating a diamond quantum sensing system on a single chip, as the prior art is unable to detect extremely low fluorescence currents.

[0009] (Object of the invention) It is an object of the present invention to provide a magnetometer that overcomes one or more of the drawbacks of the prior art, or to provide a useful alternative. [Means for solving the problem]

[0010] According to a first aspect of the present invention, there is provided a sensor comprising: a diamond layer as a light trapping diamond nitrogen vacancy doped layer having an upper surface and a lower surface; a dielectric coating disposed over a portion of the lower surface of the diamond layer; a microwave resonator disposed adjacent to the dielectric coating and having a resonant frequency with an operating bandwidth around a magnetic resonance of a nitrogen vacancy center, the microwave resonator having a suppressed portion and an unsuppressed portion, the field generated by the unsuppressed portion being greater than the field of the suppressed portion; an optical filter disposed adjacent to the microwave generator; at least one sensor photodiode array positioned adjacent to the optical filter and aligned with the unsuppressed portion of the microwave resonator; and at least one reference photodiode array spaced apart from and substantially in the same plane as the sensor photodiode array, the at least one reference photodiode array being aligned with the suppression portion of the microwave resonator.

[0011] According to a second aspect of the present invention, there is provided a method of providing a magnetic field sensor, the method comprising the steps of: providing a diamond layer as an optically trapping diamond nitrogen-vacancy doped layer having an upper surface and a lower surface, wherein the diamond layer has a dielectric coating disposed over a portion of the lower surface; disposing a microwave resonator adjacent to the dielectric coating; providing the microwave resonator with a suppressed portion and an unsuppressed portion; placing an optical filter adjacent to the microwave generator; positioning at least one sensor photodiode array adjacent to the optical filter and aligned with the unsuppressed portion of the microwave resonator; and positioning at least one reference photodiode array spaced apart from and substantially coplanar with the sensor photodiode array, and aligning the reference photodiode array with the suppression portion of the microwave resonator.

[0012] Another aspect of the differential detection system includes: an optically trapping diamond nitrogen-vacancy doped layer with an adjacent microwave resonator having a resonant frequency with an operating bandwidth around the magnetic resonance of the nitrogen vacancy center, the microwave resonator having a suppressed portion and an unsuppressed portion, the field generated by the unsuppressed portion being greater than the field of the suppressed portion; a sensor photodiode located distal to the light-trapping diamond nitrogen-vacancy doped layer and aligned with a non-suppressed portion of a microwave resonator; and a reference photodiode spaced apart from the sensor photodiode and substantially co-planar with the sensor photodiode, wherein the reference photodiode is aligned with the non-suppressed portion of the microwave resonator and the sensor photodiode and the reference photodiode are connected back-to-back to a single transimpedance amplifier.

[0013] It has therefore been found that a sensor can be advantageously provided with both sensing and reference photodiodes on the same chip, while filtering the excitation laser light along with other non-ideal currents, thereby enabling microwave generation and front-end readout of the device with a single on-chip transimpedance amplifier (TIA) that provides a sufficiently strong signal.

[0014] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an exploded perspective view of a magnetic field sensor according to a preferred embodiment; [Figure 2] FIG. 2 is a schematic cross-sectional side view of the sensor of FIG. 1. [Figure 3] 2 is a representation of the sensor of FIG. 1 disposed on an integrated circuit. [Figure 4] 2 is a schematic diagram of the input signals of the sensor photodiode and the reference photodiode array in the sensor of FIG. 1; [Figure 5] The magnetic field from the resonator is measured across the signals of the array of unsuppressed sensor photodiodes and suppressed reference photodiodes. [Figure 6]2 shows an apparatus for characterizing the sensor of FIG. 1 as an accelerometer. DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring generally to the drawings, it will be understood that like reference numerals are used to indicate like components unless otherwise specified. Figure 1 shows an exploded elevated perspective view of a magnetic field sensor according to a preferred embodiment. Figure 2 is a cutaway side view showing the integration of the sensor 1 of Figure 1 on a CMOS semiconductor chip 10. Figure 3 shows the sensor 1 on the CMOS semiconductor chip 10 mounted on a semiconductor circuit substrate 20.

[0017] The magnetic field sensor (1) comprises an optically trapping diamond nitrogen-vacancy doped layer 2 having an upper surface 2 A and a lower surface 2 B. A dielectric coating 3 is disposed over a portion of the lower surface 2 B of the diamond layer 2.

[0018] A microwave resonator (or RF array) 4 is disposed beneath the distal doped layer 2 of the dielectric coating 3. The microwave resonator 4 is configured to excite nitrogen vacancy centers within the doped layer 2. As best shown in Figure 1, the microwave resonator 4 comprises a suppressed portion 4B and an unsuppressed portion 4A. The field adjacent the unsuppressed portion 4A is much greater than the field adjacent the suppressed portion 4B, preferably by at least two orders of magnitude.

[0019] An optical filter 5 in the form of a plasmonic filter is positioned adjacent to the distal doped layer 2 of the microwave generator 4. The filter 5 is adapted to prevent transmission of scattered, non-fluorescent light as described below. Disposed below the distal cavity (4) of the filter 5 is a photodiode array 6 formed from a plurality of substantially equally spaced arrays.

[0020] The photodiode array 6 is formed from two portions, a sensor portion 6A and a reference portion 6B, which preferably share substantially the same physical characteristics. In some preferred embodiments, the photodiode array portions 6A and 6B are integrally formed to form a single photodiode array 6. Advantageously, this allows the signals of either portion 6A or 6B to provide substantially the same response and have substantially the same noise.

[0021] The reference photodiode array 6B is located adjacent to the optical filter 5 and is aligned with the suppressed portion 4B of the microwave resonator 4. The sensor photodiode array 6A is preferably on the same "chip" as portion 6B and is coplanar with it. The sensor photodiode 6A is aligned with the unsuppressed portion 4A of the microwave resonator 4. It is noted herein that the optically detected magnetic resonance (ODMR) effect is suppressed on the RF array where the RF field is suppressed. This provides a reference for the background fluorescence and scattered green light from the laser pump 2. This thus distinguishes between the RF field on the microwave resonator and the microwave resonator itself, and therefore the active effect of current flowing through the wires in the "suppressed" portion of the microwave resonator.

[0022] 2 and 3, the sensor 1 is shown mounted on a CMOS semiconductor chip 10, which in a preferred embodiment is mounted on a semiconductor substrate 20. Herein, the photodiode array 6 (and the sensor 4A photodiodes and reference 4B photodiodes) are integrated into the CMOS chip 10, which is mounted on a circuit board 20. The electrical outputs of the photodiode arrays 6A and 6B (best seen in FIG. 3) are connected to circuitry on the circuit board 20 via the mounted CMOS chip 10.

[0023] 3, the electrical outputs of the sensor photodiode 6A and the reference photodiode 6B are connected back-to-back to a single transimpedance amplifier located on the circuit board 20. This arrangement advantageously overcomes the drawbacks of connecting different sensor and reference diodes to an off-chip transimpedance amplifier.

[0024] In a further preferred embodiment, circuit board 20 further comprises a microwave or RF generator configured to provide a signal to microwave resonator 4, and also houses a phase-locked loop in communication with the output of microwave resonator 4 and the photodiode detector transimpedance amplifier. Ideally, circuit board 20 (although not explicitly shown in FIG. 3) also houses processing circuitry configured to process signals from the sensor photodiode detector in response to fluorescent light, as described below.

[0025] It will be appreciated that in use, the sensor 1 of the preferred embodiment most advantageously rejects background (preferably green) excitation light and other non-ideal currents because, since they reside on the same CMOS chip 10, both photodiode arrays 6A and 6B appear nearly identical and are positioned substantially within a close distance of a few hundred micrometers of each other.

[0026] In a preferred embodiment, the entire microwave generation and front-end readout system is integrated onto a 1.2x1.2mm substrate 20 with an area approximately the size of an Australian 50 cent coin. 2 It will be appreciated that the sensor 1 can be integrated into a CMOS chip 10 of 3x3mm. The sensor 1 overcomes the crucial step of integrating a transimpedance amplifier TIA onto the chip, while generating a powerful amplified signal at the output of the TIA, sufficient to feed a digitization and lock-in amplifier stage (e.g. on an FPGA). As shown in the figure, the entire sensor 1 device is 3x3mm 2The laser can be integrated onto the chip, with only the pump laser and the doped diamond layer 2 remaining as off-chip components.

[0027] Referring to FIG. 4, a schematic diagram of the light input to the photodiodes 6A and 6B is shown. As previously mentioned, sensor 1 achieves full integration of the entire key readout system-on-chip by cleverly suppressing the red fluorescence contrast on the two diode arrays (sensing 6A and reference 6B) and the sensing diode 6A. A red light is shown schematically in the central portion of the beam illuminating the photodiode arrays 6A and 6B, with green light surrounding it. It will be appreciated that FIG. 4 is intended to qualitatively illustrate a balanced detection scheme operating with optically detected magnetic resonance (ODMR)-induced fluorescence contrast generated on the sensing photodiode. This is an intentionally exaggerated representation of the balanced detection scheme, and illustrates the relatively small effect of optically detected magnetic resonance (ODMR) contrast, typically a reduction of less than 1% of the red fluorescence signal.

[0028] The sensor 1 of the preferred embodiment generates a magnetic field on the sensing photodiode array 6A, which results in the suppression of the red fluorescence signature.

[0029]

number

[0030] is incident. In the formula, I SD denotes the total photocurrent generated by the sensing diode array 6A. I R is the current generated by red fluorescence. C is the fractional fluorescence contrast. I G is the current generated by the background green excitation light used to excite nitrogen vacancy NV centers in the doped layer. I d and I ndenote dark current and noise current, respectively. In this specification, suppression refers to optically detected magnetic resonance (ODMR) contrast (or red fluorescence suppression) occurring across the unsuppressed RF antenna 4A, but no optically detected magnetic resonance (ODMR) contrast occurring across the suppressed RF antenna 4B (red fluorescence is not suppressed).

[0031] Since both photodiodes 6A and 6B are uniformly exposed to the green background (from the excitation laser), it can be assumed that the noise currents of both diodes are very similar, especially with regard to thermal noise. In this case, the reference photodiode array 6B (I RD ) is the photocurrent generated by

[0032]

number

[0033] This means that the differential current input to the transimpedance amplifier is fluorescent (red).

[0034]

number

[0035] This means that it is possible to properly represent Turning now to FIG. 5, this shows the simulated applied magnetic field amplitude from the microwave resonator 4 across the unsuppressed sensor photodiode 6A signal and the suppressed reference photodiode array 6B signal. It will be understood that the term "applied" magnetic field refers to the applied magnetic field as a temporary field relevant to the measurement technique used in the described preferred embodiment. This is in contrast to the "external" magnetic field measured by the magnetometer 1, which is typically understood to be static or slowly varying. Furthermore, "amplitude" is used as an RF field, which in the preferred embodiment oscillates at approximately 2.87 GHz, as shown in FIG. 5, which shows the amplitude of its oscillation.

[0036] Figures 6(i)-6(ii) illustrate the use of magnetic field sensor (1) based on an accelerometer. Incorporating sensor 1 into an accelerometer provides a compact quantum accelerometer with a hybrid silicon-diamond control and readout chip, based on the above. While the use of sensor 1 can be applied to other quantum technology architectures and applications, the quantum accelerometer shown in Figure 6 is for inertial measurement navigation or guidance. Sensor 1 enables improved sensitivity and miniaturization, as well as a diamond-based quantum magnetometer that operates most advantageously at room temperature.

[0037] In the embodiment of Figure 6, a diamond-based quantum magnetometer 1 is combined with a conventional mass-spring system to provide a highly sensitive, low-drift means of measuring acceleration. Accelerometers based on sensor 1 are believed to be able to achieve sensitivities of 0.1 μg, which is understood to be an order of magnitude improvement over state-of-the-art commercially available devices. Such applications of sensor 1 used as an accelerometer include unmanned aerial vehicles (UAVs), autonomous vehicles, spacecraft, or subsurface and undersea navigation / mapping in the defense and mining industries, among other applications where high accuracy and compact navigation units are required.

[0038] Figure 6 shows a simplified block diagram illustrating the sensor 1 used in the accelerometer. The mass-spring system (i) induces a change in the magnetic field in the diamond sensor 1 (ii), which causes an optically detectable Zeeman shift in the magnetic resonance (iii). Measurement of acceleration (a) can be performed as follows:

[0039]

number

[0040] In this simplified expression, a is the acceleration. s is the magnetic field sensitivity (T / √Hz). dB / dx is the change in magnetic field felt by the sensor as the distance (x) between the sensor and a magnet of mass (m) changes. t is the measurement time.

[0041] The above describes only one embodiment of the present invention and modifications obvious to those skilled in the art can be made thereto without departing from the scope of the invention. As used herein, the term "comprises" (and grammatical variations thereof) is used in the inclusive sense of "comprises" or "has" and not in the exclusive sense of "consisting only of."

Claims

1. A sensor, the sensor comprising: a diamond layer as a light trapping diamond nitrogen vacancy doped layer having an upper surface and a lower surface; a dielectric coating disposed over a portion of the lower surface of the diamond layer; a microwave resonator disposed adjacent to the dielectric coating, the microwave resonator having a resonant frequency with an operating bandwidth around a nitrogen vacancy-centered magnetic resonance, the microwave resonator having a suppressed portion and an unsuppressed portion, the field generated by the unsuppressed portion being greater than the field in the suppressed portion; an optical filter disposed adjacent to the microwave generator; at least one sensor photodiode array positioned adjacent to the optical filter, the at least one sensor photodiode array being aligned with the unsuppressed portion of the microwave resonator; at least one reference photodiode array spaced apart from the sensor photodiode array, the at least one reference photodiode array being substantially coplanar with the sensor photodiode array and aligned with the suppression portion of the microwave resonator; The sensor is provided with:

2. the field in the unsuppressed portion of the microwave resonator is at least one or two orders of magnitude greater than the field in the suppressed portion of the microwave resonator; The sensor of claim 1 .

3. The optical filter is a plasmonic filter. The sensor according to claim 1 or 2.

4. the sensor photodiode array and the reference photodiode array are integrally formed or are formed from photodiodes having substantially the same or different physical characteristics; The sensor according to any one of claims 1 to 3.

5. the sensor photodiode array and the reference photodiode array are mounted on a semiconductor integrated circuit or CMOS chip; the sensor photodiode array and the reference photodiode array have outputs connected to the transimpedance amplifier disposed on the semiconductor integrated circuit or CMOS chip having an electrical output for the transimpedance amplifier; The sensor according to any one of claims 1 to 4.

6. the semiconductor integrated circuit or the CMOS chip includes a microwave generator configured to provide a signal to the microwave resonator; The sensor of claim 5.

7. the semiconductor integrated circuit or the CMOS chip includes a phase-locked loop in communication with the microwave resonator and a photodiode detector transimpedance amplifier output; 7. The sensor according to claim 5 or 6.

8. A device comprising a sensor according to any one of claims 1 to 7, the device further comprising a processing circuit configured to process signals from the sensor photodiode detector in response to the fluorescent light; Device.

9. 1. A method of providing a magnetic field sensor, the method comprising: providing a diamond layer as an optically trapping diamond nitrogen-vacancy doped layer having an upper surface and a lower surface, wherein the diamond layer has a dielectric coating disposed over a portion of the lower surface; disposing a microwave resonator adjacent to the dielectric coating; providing the microwave resonator with a suppressed portion and an unsuppressed portion; placing an optical filter adjacent to the microwave generator; positioning at least one sensor photodiode array adjacent to the optical filter and aligned with the unsuppressed portion of the microwave resonator; disposing at least one reference photodiode array spaced apart from and substantially coplanar with the sensor photodiode array and aligning the reference photodiode array with the suppression portion of the microwave resonator; The method comprises:

10. the sensor photodiode array and the reference photodiode array are configured to generate a differential readout corresponding to a measured change in the optical response of nitrogen vacancy diamond fluorescence.

10. The method of claim 9.

11. 1. A differential detection system, comprising: an optically trapping diamond nitrogen-vacancy doped layer with an adjacent microwave resonator having a resonant frequency with an operating bandwidth around the magnetic resonance of a nitrogen vacancy center, the microwave resonator having a suppressed portion and an unsuppressed portion, the field generated by the unsuppressed portion being greater than the field of the suppressed portion; a sensor photodiode located distal to the light-trapping diamond nitrogen-vacancy doped layer, the sensor photodiode aligned with the unsuppressed portion of the microwave resonator; and a reference photodiode spaced apart from the sensor photodiode, the reference photodiode being substantially in the same plane as the sensor photodiode, the reference photodiode being aligned with the unsuppressed portion of the microwave resonator, and the sensor photodiode and the reference photodiode being connected back-to-back to a single transimpedance amplifier. A differential detection system comprising:

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