Current sensor and current detection device

Abstract

A current sensor (10) comprises a diamond substrate (11), a first layer (12) disposed on at least a surface (11a) side of the diamond substrate (11) and including a diamond crystal in which an NV center (13) is disposed, a second layer (14) disposed on at least the surface (11a) side of the diamond substrate (11) and including a diamond crystal having a lower refractive index than the first layer (12), a transparent electroconductive layer (15) disposed on at least the surface (11a) side of the diamond substrate (11) and having a lower refractive index than the first layer (12), and a radiation body (16) that is disposed on at least the surface (11a) side of the diamond substrate (11) and radiates microwaves for generating electron spin resonance, the second layer (14), the first layer (12), and the transparent electroconductive layer (15) being arranged in the stated order on at least the surface (11a) of the diamond substrate (11).

Description

Technical Field

[0001] The present disclosure relates to a current sensor and a current detection device.

Background Art

[0002] Patent Document 1 discloses a sensor that measures a magnetic field using a diamond element having an NV center.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] A current sensor according to one aspect includes a substrate, a first layer including a diamond crystal in which NV centers are arranged, the first layer being disposed on at least one surface side of the substrate, a second layer including a diamond crystal having a refractive index lower than that of the first layer, the second layer being disposed on at least one surface side of the substrate, a transparent conductive layer having a refractive index lower than that of the first layer, the transparent conductive layer being disposed on at least one surface side of the substrate, and a radiator that emits microwaves for generating electron spin resonance, the radiator being disposed on at least one surface of the substrate. On at least one surface of the substrate, the second layer, the first layer, and the transparent conductive layer are arranged in this order.

[0005] A current detection device according to one aspect is a detection device including the above-described current sensor, a light-emitting element, a light-receiving element, and an oscillation element. The light-emitting element irradiates excitation light to the NV centers, and the light-receiving element receives fluorescence of the NV centers.

Brief Description of the Drawings

[0006] [Figure 1] FIG. 1 is a cross-sectional view for explaining an outline of a current sensor according to a first embodiment. [Figure 2]Figure 2 is a block diagram illustrating an example of a current detection device. [Figure 3] Figure 3 is a cross-sectional view illustrating the schematic of the current sensor according to the second embodiment. [Figure 4] Figure 4 shows an example of a dispersion curve for a three-layer slab waveguide. [Figure 5] Figure 5 shows an example of the boundary distribution of a three-layer slab waveguide. [Modes for carrying out the invention]

[0007] The following describes a current sensor and current detection device according to an embodiment. The current sensor and current detection device are for detecting a magnetic field generated in a target object. Figure 1 is a cross-sectional view illustrating the schematic of a current sensor according to the first embodiment. Figure 2 is a block diagram illustrating an example of a current detection device.

[0008] [First Embodiment] (Current sensor) The current sensor 10 uses an NV center to detect undetected currents generated in the target object from changes in the magnetic field at the NV center. The current sensor 10 is a so-called diamond sensor.

[0009] The current sensor 10 includes a diamond substrate (substrate) 11, a first layer 12, a second layer 14, a transparent conductive layer 15, and a radiator 16. On at least one surface 11a of the diamond substrate 11, the current sensor 10 is arranged in the order of the second layer 14, the first layer 12, and the transparent conductive layer 15.

[0010] The diamond substrate 11 is a substrate containing diamond. The diamond substrate 11 has a second layer 14 on surface 11a. The diamond substrate 11 has an antenna conductor 16 on surface 11b facing the opposite side of surface 11a. The thickness of the diamond substrate 11 is selected, for example, in the range of 100 μm to 500 μm.

[0011] The first layer 12 is a layer containing a diamond crystal in which NV centers are located. The first layer 12 is located on at least one side 11a of the diamond substrate 11. The first layer 12 is located on the second layer 14, which is located on the side 11a of the diamond substrate 11. A transparent conductive layer 15 is bonded to the first layer 12 on the side opposite to the side in contact with the second layer 14.

[0012] The first layer 12 includes, for example, a first diamond layer 121 which is a non-doped diamond layer, and a second diamond layer 122 which includes NV centers. The first diamond layer 121 and the second diamond layer 122 which includes NV centers are arranged in that order from the side closer to the substrate 11.

[0013] The thickness of the first diamond layer 121 and the second diamond layer 122, which includes the NV center, is selected, for example, in a range of approximately 1 μm to 10 μm.

[0014] The NV centers are located in the first layer 12 on the side opposite to the surface in contact with the second layer 14. The NV centers may be arranged individually or in multiples in the diamond crystal. The NV centers may be aligned in one direction. The NV centers may be crystals with multiple different orientations.

[0015] An NV center is a complex defect in a diamond crystal where nitrogen replaces a carbon atom that should be present, and there is a vacancy in an adjacent location. An NV center is a defect in which a portion of a degenerate shared electron pair is missing. In a zero magnetic field, an NV center has electrons with orbital angular momentum at two energy levels: m=0 and m=±1. Because the m=±1 electrons have a magnetic moment, they are affected by an external magnetic field, and the degeneracy of m=±1 is lifted, resulting in two additional energy levels. By detecting the electron spin resonance resulting from these phenomena using light waves and microwaves, the strength of the external magnetic field (the magnetic field being detected) can be detected.

[0016] Electrons in the NV center are excited by light with a wavelength of 532 nm and emit fluorescence with a wavelength of 638 nm during the relaxation process. This fluorescence process is unlikely to occur at the electron spin resonance frequency. Therefore, by using this property, the electron state at m=±1 can be observed. In the NV center of the second diamond layer 122, the electron spin resonance frequency at zero magnetic field is known to be approximately 2.87 GHz. When microwaves at the frequency of this resonance point (resonance frequency) are irradiated, the fluorescence at a wavelength of 638 nm is extinguished. Furthermore, the microwave resonance frequency changes due to changes in the electron state at m=±1 depending on the magnitude of the external magnetic field, etc. By capturing this change as a frequency change in fluorescence intensity, the magnetic field and current can be detected. Light with a wavelength of 532 nm is incident from surface 12c, which is the side surface of the first layer 12, and is reflected by surface 12d, and the fluorescence at a wavelength of 638 nm is emitted towards the transparent conductive layer 15.

[0017] The second layer 14 contains a low refractive index diamond crystal. The second layer 14 contains a diamond crystal with a lower refractive index than the first layer.

[0018] The second layer 14 is disposed on the surface 11a of the diamond substrate 11. The second layer 14 is a low refractive index layer made of boron-doped diamond. The refractive index of the boron-doped diamond is designed to be lower than that of undoped diamond by, for example, 0.5% to 1.5%. The boron concentration in the boron-doped diamond is, for example, 1.0 × 10⁻⁶. 16 atoms / cm 3 The above 1.0 × 10 21 atoms / cm 3 The following ranges are selected. The thickness of the second layer 14 is selected, for example, in a range of approximately 10 μm to 100 μm. The second layer 14 functions as a low refractive index layer provided inside the diamond substrate 11, beyond the second diamond layer 122 which contains the NV center.

[0019] The transparent conductive layer 15 is bonded to the surface of the first layer 12 opposite to the surface in contact with the second layer 14. The transparent conductive layer 15 is made of a transparent material that has conductivity. The transparent conductive layer 15 has a lower refractive index than the first layer 12.

[0020] The transparent conductive layer 15 is a low refractive index transparent conductive layer. The transparent conductive layer 15 is formed of ITO (Indium Tin Oxide), etc. The refractive index of the transparent conductive layer 15 is designed to be lower than that of diamond and higher than that of air. The conductivity of the transparent conductive layer 15 is designed to be, for example, less than 10 mΩ·cm. The thickness of the transparent conductive layer 15 is selected, for example, in the range of 1 μm or more and 10 μm or less. The transparent conductive layer 15 is transparent to visible light including the vicinity of a wavelength of 637 nm. The transparent conductive layer 15 transmits the fluorescence of the NV center.

[0021] The first electrode 24 and the second electrode 25 are joined to both end sides of the transparent conductive layer 15. One side of this conductive layer serves as an input side and the other side serves as an output side, and it operates as a conductor for drawing in the measured current.

[0022] The radiator 16 is located on the surface 11b of the diamond substrate 11 opposite to the surface 11a where the second layer 14 is formed. The radiator 16 emits microwaves that generate electron spin resonance. The radiator 16 transmits and emits microwaves that irradiate the NV centers of the second diamond layer 122. The radiator 16 is, for example, an antenna conductor such as a loop antenna formed of a conductor thin film. The frequency of the radiator 16 is, for example, 2.8 GHz or more and 2.9 GHz or less. The input power of the radiator 16 is, for example, -20 dBm or more and +20 dBm or less. The film thickness of the conductor thin film of the radiator 16 is selected, for example, in the range of 0.2 μm or more and 2 μm or less.

[0023] An oscillation element 31 is electrically connected to the input side of the radiator 16. The radiator 16 may include a capacitance forming portion such as an IDT (Interdigital Transducer).

[0024] (Current detection device) The current detection device 1 includes a device substrate 2, a current sensor 10, a light-emitting element 21 and a light-receiving element 22 that input and output light to the NV center of the second diamond layer 122, and an oscillating element 31. In this embodiment, the current sensor 10 and the light-emitting element 21 and light-receiving element 22 that input and output light to the NV center of the second diamond layer 122 are arranged on the device substrate 2.

[0025] The device substrate 2 is a substrate that supports the current detection device 1. A current sensor 10, a light-emitting element 21, and a light-receiving element 22 are arranged on the device substrate 2.

[0026] The light-emitting element 21 and the light-receiving element 22 function as detectors that detect the magnetism of the object to be detected. The light-emitting element 21 and the light-receiving element 22 input and output light to the NV center of the second diamond layer 122. The light-emitting element 21 and the light-receiving element 22 are controlled by the control unit 201 of the signal control unit 200. The control unit 201 controls the emission of light in the light-emitting element 21. The control unit 201 controls the reception of light in the light-receiving element 22. The control unit 201 processes the red fluorescence signal received by the light-receiving element 22. The control unit 201 outputs the current to be measured as the detection result.

[0027] The light-emitting element 21 is, for example, a light source such as a semiconductor laser. The light-emitting element 21 emits excitation light that irradiates the diamond crystal. The light-emitting element 21 irradiates the NV centers of the second diamond layer 122 with excitation light.

[0028] The light-emitting element 21 is a laser diode. The light-emitting element 21 emits green excitation light. Based on the control of the control unit 201, the light-emitting element 21 emits laser light with a wavelength of, for example, 532 nm. The polarization direction of the light source may be in TE (Transverse Electric) mode. As the light-emitting element 21, for example, a green light-emitting diode (LED), a green vertical cavity surface-emitting laser diode (VCSEL), and a green laser diode (LD) can be used. Power is supplied to the light-emitting element 21 from wiring arranged on the device substrate 2. The light-emitting element 21 can also be substituted with a light-emitting diode (LED) that includes a center wavelength of 532 nm.

[0029] The light-emitting element 21 is positioned on the device substrate 2, spaced apart from the current sensor 10 in the X-axis direction. The light-emitting element 21 is positioned a certain distance away from the surface 12c of the first layer 12 in the X-axis direction.

[0030] The light-emitting element 21 emits excitation light that is incident on one side surface 11c of the first layer 12 and excites the NV center of the second diamond layer 122. The light-emitting element 21 irradiates light onto the surface 12c of the first layer 12. The excitation light emitted from the light-emitting element 21 is irradiated from the side surface 12c of the first layer 12.

[0031] The light-emitting element 21 may include one or more reflective surfaces with adjusted reflectivity on the other side surface 11d of the first layer 12. Between the light-emitting element 21 and the diamond substrate 11, at least one of, for example, an isolator and a lens may be included.

[0032] The incident end face of the light-emitting element 21 may be coated with, for example, an AR (Anti-Reflection) coating or beveled polishing.

[0033] The light-receiving element 22 is a photodetector. The light-receiving element 22 is a detector such as a photodiode. For example, the light-receiving element 22 can be a Si-PIN photodiode (PD) or an InGaAs-PIN photodiode. Based on the control of the control unit 201, the light-receiving element 22 receives the fluorescence of the NV center of the second diamond layer 122 of the first layer 12, transmitted through the transparent conductive layer 15. The light-receiving element 22 receives the fluorescence emitted by the excitation light from the diamond crystal.

[0034] The light-receiving element 22 is bonded to the surface of the transparent conductive layer 15 opposite to the surface that contacts the first layer 12.

[0035] An optical filter 23 is placed between the light-receiving element 22 and the transparent conductive layer 15. The optical filter 23 is a filter that cuts out at least one of the wavelengths longer or shorter than the fluorescence wavelength of the second diamond layer 122, which contains the NV center.

[0036] The first electrode 24 is bonded to the exposed surface of the transparent conductive layer 15. The first electrode 24 is bonded to the surface of the transparent conductive layer 15 opposite to the surface in contact with the first layer 12. The first electrode 24 is spaced apart from the second electrode 25. The first electrode 24 is a conductive layer such as Ti / Au. The first electrode 24 is the power input side.

[0037] The second electrode 25 is bonded to the exposed surface of the transparent conductive layer 15. The second electrode 25 is bonded to the surface of the transparent conductive layer 15 opposite to the surface in contact with the first layer 12. The second electrode 25 is spaced apart from the first electrode 24. The second electrode 25 is a conductive layer such as Ti / Au. The second electrode 25 is the power output side.

[0038] The oscillator 31 is a microwave oscillator that generates microwaves. The oscillator 31 generates microwaves that irradiate the NV center of the second diamond layer 122. The oscillator 31 is, for example, a voltage-controlled oscillator (VCO). The oscillator 31 may be composed of semiconductor elements such as a heterojunction bipolar transistor (HBT), a field-effect transistor (FET), a complementary MOS (Metal-Oxide Semiconductor), or a high-electron-mobility transistor (HEMT). The material of the semiconductor element is, for example, Si, GaAs, or GaN. In Figure 1, the oscillator is not shown.

[0039] (Signal control unit) As shown in Figure 2, the signal control unit 200 is, for example, a microcomputer. The signal control unit 200 controls the light emission operation of the light-emitting element 21. The signal control unit 200 controls the light-receiving operation of the light-receiving element 22. The signal control unit 200 controls the microwave oscillation operation of the oscillating element 31. The signal control unit 200 outputs the optical signal of the fluorescence image captured by the light-receiving element 22. The signal control unit 200 has a signal processing circuit, which is a signal processing unit 202, and a control unit 201, which is a control circuit. The control unit 201 supplies timing signals to the light-receiving element 22, the light-emitting element 21, and the oscillating element 31 to control their operation. The control unit 201 controls the frequency of the microwaves output from the oscillating element 31. The signal processing unit 202 performs image processing of the fluorescence image based on the optical signal input from the light-receiving element 22. The signal control unit 200 and the oscillating element 31 are, for example, semiconductor chips. Figure 2 shows an example where the signal control unit 200 and the oscillator 31 are on different semiconductor chips, but they may also be composed of a single semiconductor chip.

[0040] (Detection method) A method for detecting the target magnetic field and current using the current detection device 1 will be described.

[0041] The detection surface of the object to be detected is brought close to or in contact with the magnetic field surface of the current sensor 10 of the current detection device 1. A spatial change in the direction or magnitude of the magnetic field generated on the object to be detected acts on the NV center of the second diamond layer 122 of the diamond substrate 11 of the current detection device 1.

[0042] Then, the light-emitting element 21 and light-receiving element 22 of the current detection device 1 scan the current sensor 10 with fluorescence and excitation light. As a result, the NV centers of the second diamond layer 122 are irradiated and excited from the surface 12c of the diamond crystal of the first layer 12. The light-emitting element 21 and light-receiving element 22 receive the electron spin resonance signals of the NV centers excited by the excitation light from the surface 12c of the diamond crystal as fluorescence. The light-emitting element 21 and light-receiving element 22 receive fluorescence signals corresponding to changes in the direction or magnitude of the magnetic field.

[0043] In this way, the light-emitting element 21 and the light-receiving element 22 of the current detection device 1 detect the magnetic charge of the object to be detected. The light-emitting element 21 and the light-receiving element 22 detect the height of the magnetic charge of the object to be detected. The signal control unit 200 then calculates the strength of the magnetic field from the signals obtained from the detection results of the light-emitting element 21 and the light-receiving element 22. The signal control unit 200 then calculates the current to be measured flowing through the object to be detected from the calculated magnetic field strength and outputs the result.

[0044] (effect) As described above, in this embodiment, the diamond substrate 11 is arranged in the following order on at least one surface 11a: the second layer 14, the first layer 12 containing a diamond crystal on which the NV center is located, and the transparent conductive layer 15. In this embodiment, the transparent conductive layer 15, which is a low refractive index transparent conductive layer equivalent to a conventional conductor, is transparent to visible light including wavelengths around 637 nm. In this embodiment, the transparent conductive layer 15 transmits the fluorescence of the NV center, and the fluorescence can be detected by the photodetector 22. According to this embodiment, the current to be measured can be detected with high sensitivity by bringing the current to be measured close to the NV center.

[0045] In an embodiment, the transparent conductive layer 15 has a refractive index lower than that of diamond. According to the embodiment, leakage of light to the air layer side can be reduced.

[0046] In an embodiment, the second layer 14 is a low refractive index layer provided inside the diamond substrate 11 and closer to the diamond substrate 11 than the second diamond layer 122 containing NV centers. According to the embodiment, the second layer 14 can reduce leakage of light to the inside of the diamond substrate 11.

[0047] In an embodiment, when selecting the TE mode for the light source, absorption by the transparent conductive layer 15 can be reduced and propagation loss of the excitation light can be reduced.

[0048] In an embodiment, when providing a reflection surface with adjusted reflectivity on the other end side of the first diamond layer 121, the influence of fluctuations due to temperature etc. of multiple reflections can be reduced.

[0049] In an embodiment, when the radiator 16 includes a capacitance forming portion, the antenna can be miniaturized and thus the device can be made smaller.

[0050] In an embodiment, most of the energy of the excitation light is confined and propagated inside the second diamond layer 122 containing NV centers. According to the embodiment, even if the output of the excitation light is low, the NV centers can be effectively excited.

[0051] Here, assuming that the wavelength λ of the excitation light is 532 nm and the refractive index difference Δ is about 0.5%, the normalized frequency V and the normalized propagation constant k0 in vacuum are calculated by Formula 1 and Formula 2. The radius a of the core is about 2 μm or more and 10 μm or less. n1 is the core refractive index, that is, the refractive index of the first diamond layer 121. n2 (n2 < n1) is the cladding refractive index. From such a refractive index difference and the radius a of the core, it can be seen that propagation modes of about 0th order or more and 3rd order or less can exist. [[ID=​​​​

[0053]

number

[0054] Figure 4 shows an example of a dispersion curve for a three-layer slab waveguide. Figure 5 shows an example of a field distribution for a three-layer slab waveguide. Figures 4 and 5 are based on excitation light wavelength λ = 532 nm, core refractive index n1 = 2.443, cladding refractive index n2 = 2.42, and core radius a = 5.00 × 10⁻⁶. -6 This graph is based on m, non-refractive index Δ=0.0041, and normalized frequency V=13.00.

[0055] In contrast to these, the technology described in Patent Document 1 attempts to bring the NV center and the object being measured as close together as possible, but due to the mechanism, there is a space between them, which affects the detection sensitivity. For use as a sensor, miniaturization is desirable. However, if the performance of the light-emitting element and light-receiving element deteriorates due to miniaturization, the amount of excitation light and fluorescence light may become weak. Thus, in order to miniaturize the sensor, there is room for improvement in the method of irradiating the excitation light and the method of receiving the fluorescence.

[0056] [Second Embodiment] Figure 3 is a cross-sectional view illustrating the schematic of a current sensor according to the second embodiment. In the second embodiment, components similar to those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted. The second embodiment differs from the first embodiment in that the current sensor 10 has a mesa structure. The current sensor 10 includes a diamond substrate 11, a first layer 12, a second layer 14, a transparent conductive layer 15, a radiator 16, and a third layer 17.

[0057] The first layer 12 is a mesa structure. More specifically, the first diamond layer 121 and the second diamond layer 122, which includes the NV center, have a mesa structure that is excavated on both sides.

[0058] Between the second layer 14 and the transparent conductive layer 15 are the first layer 12 and the third layer 17, which is positioned around the first layer 12.

[0059] The third layer 17 includes, for example, a semiconductor material such as Al2O3 or SiO2.

[0060] (effect) As described above, in this embodiment, the current sensor 10 has a mesa structure. According to this embodiment, the mesa structure can more effectively confine the excitation light inside.

[0061] The embodiments disclosed in this application may be modified without departing from the spirit and scope of the invention. Furthermore, the embodiments disclosed in this application and their modifications may be combined as appropriate.

[0062] Furthermore, the current sensor disclosed in this application can be adapted for use as a magnetic field, electric field, and temperature sensor.

[0063] Characteristic embodiments have been described in order to fully and clearly disclose the technology relating to the appended claims. However, the appended claims should not be limited to the above embodiments, but should be configured to embody all modifications and alternative configurations that a person skilled in the art may create within the scope of the fundamental matters presented herein.

[0064] For example, the first diamond layer 12 may be a nitrogen (N) or phosphorus (P) doped diamond layer instead of an undoped diamond layer. By using a nitrogen (N) or phosphorus (P) doped diamond layer, holes or electrons can be injected at the interface with the second layer 14, making it possible to conduct electricity to the first layer 12.

[0065] For example, the transparent conductive layer 15 may be patterned to form an antenna conductor. [Explanation of Symbols]

[0066] 1. Current detection device 2. Device board 10 Current Sensor 11. Diamond substrate (substrate) 12 1st layer 121 The first diamond layer Second diamond layer including 122 NV centers 13 NV Center 14 2nd layer 15 Transparent conductive layer 16 Radiators 21 Light-emitting element 22 Photodetector 23 Optical Filters 24 1st electrode 25 2nd electrode 31 Oscillating element 200 Signal Control Unit 201 Control Unit 202 Signal Processing Unit

Claims

1. circuit board and A first layer comprising a diamond crystal on which an NV center is located, disposed on at least one side of the substrate, A second layer comprising a diamond crystal having a lower refractive index than the first layer, disposed on at least one side of the substrate, A transparent conductive layer having a lower refractive index than the first layer is disposed on at least one side of the substrate, A radiator that emits microwaves that generate electron spin resonance is disposed on at least one side of the substrate, Equipped with, On at least one surface of the substrate, the second layer, the first layer, and the transparent conductive layer are arranged in that order. Current sensor.

2. At least one surface of the substrate is the upper surface of the substrate. The current sensor according to claim 1.

3. The transparent conductive layer is bonded to the first layer. The current sensor according to claim 1.

4. The transparent conductive layer transmits the fluorescence of the NV center. The current sensor according to claim 1.

5. The first layer includes a first diamond layer and a second diamond layer including an NV center. The current sensor according to claim 1.

6. The first diamond layer is a non-doped diamond layer. The current sensor according to claim 5.

7. The first diamond layer has a reflective surface on the side opposite to the incident surface of the excitation light. The current sensor according to claim 6.

8. The aforementioned second layer contains boron-doped diamond, The current sensor according to claim 6.

9. The aforementioned radiator includes a capacitance forming section, The current sensor according to claim 1.

10. One side of the substrate has a mesa structure, The current sensor according to claim 1.

11. A current sensor according to any one of claims 1 to 10, Light-emitting element and A light-receiving element, Oscillating element and A detection device comprising, The light-emitting element irradiates the NV center with excitation light, The light-receiving element receives the fluorescence from the NV center. Current detection device.

12. The excitation light is irradiated from the side of the first layer. The current detection device according to claim 11.

13. The aforementioned oscillator selects the TE mode for the light source. The current detection device according to claim 11.

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