Grid-control superconducting nanowire low-temperature thermometer and preparation method thereof

Abstract

The invention discloses a grid-control superconducting nanowire low-temperature thermometer and a preparation method thereof, and relates to the technical field of superconducting electronics and low-temperature detection. Comprising a substrate and a superconducting layer, and the superconducting layer comprises a grid electrode, a superconducting nanowire and an inductor; the grid electrode is vertical to the superconductive nanowire, has a distance from the superconductive nanowire and is used for electric field regulation and control; the superconducting nanowire is connected with the inductor and is used for responding to particles injected into the grid electrode and outputting a pulse signal; the inductor is connected with the superconducting nanowire and is used for inhibiting a latch-up effect under high bias current; the superconducting layer material is a superconducting thin film material with a superconducting transition temperature Tc exceeding a measurement temperature zone; according to the invention, (quasi) particle injection in the critical current process of the superconducting nanowire is regulated and controlled through the grid electric field, high-precision measurement of the low temperature is realized in combination with nonlinear response of the pulse counting rate and the temperature, and the device and the method have the advantages of wide temperature zone measurement, low noise, high sensitivity, low power consumption, small self-heating, simple measurement system and low cost.

Description

Technical Field

[0001] This invention relates to the fields of superconducting electronics and cryogenic detection technology, specifically to a gated superconducting nanowire cryogenic thermometer and its preparation method. Background Technology

[0002] In fields such as quantum physics, cryogenic physics, and space exploration, high-precision measurement of minute temperature fluctuations in cryogenic environments is crucial. For example, in cosmic microwave background radiation, dark matter detection, and other space exploration missions, the detected signals are extremely weak, requiring thermometers to not only operate at low temperatures but also provide extremely high sensitivity and low noise characteristics. Meanwhile, the operation of cryogenic devices such as qubits and quantum sensors depends on a strictly temperature-controlled environment, requiring real-time and accurate temperature feedback to ensure the stability and high precision of quantum systems.

[0003] Traditional thermometers struggle to meet the sensitivity and stability requirements of experiments in low-temperature regions. For example, traditional Pt resistive temperature sensors and silicon / gallium arsenide diode temperature sensors suffer from insufficient measurement range and significant heat leakage. Low-temperature thermometers based on superconducting materials include superconducting transition-edge sensors (TES), superconducting quantum interference devices (SQUID), and resonators. However, these thermometers exhibit various challenges such as narrow temperature range, complex measurement systems, high cost, complex fabrication processes, poor noise control, limited dynamic range, and poor system integration. Further improvements and optimizations are needed in materials engineering, micro / nano manufacturing, and electronic system design.

[0004] Based on this, the present invention proposes a gated superconducting nanowire cryogenic thermometer and its preparation method. Summary of the Invention

[0005] This invention aims to address the technical problems of existing cryogenic thermometers, such as high self-heating, narrow dynamic range, poor noise control, high cost, and complex measurement system. The goal is to provide a gate-controlled superconducting nanowire cryogenic thermometer and its fabrication method. By controlling the (quasi)particle injection during the critical current process of the superconducting nanowire through a gate electric field, and combining this with the nonlinear response of pulse count rate and temperature, high-precision measurement of cryogenic temperatures is achieved. This thermometer offers advantages such as wide temperature range measurement, low noise, high sensitivity, low power consumption, low self-heating, simple measurement system, and low cost.

[0006] The present invention is achieved through the following technical solution.

[0007] The first objective of this invention is to provide a gate-controlled superconducting nanowire cryogenic thermometer, comprising a substrate and a superconducting layer, wherein the substrate is disposed at the bottom of the superconducting layer to provide support for the superconducting layer, and the superconducting layer comprises a gate, a superconducting nanowire, and an inductor; The gate is perpendicular to the superconducting nanowire and has a spacing for electric field modulation. The superconducting nanowires are connected to an inductor to respond to particles injected through the gate and output pulse signals. The inductor is connected to the superconducting nanowire to suppress latch-up under high bias current. The superconducting layer material has a superconducting transition temperature T that exceeds the measured temperature range. c Superconducting thin film materials.

[0008] Furthermore, the spacing between the gate and the superconducting nanowire is 10 nm to 500 nm.

[0009] Furthermore, the gate is connected to a gate input electrode, which is used to provide a gate bias voltage to the gate.

[0010] Furthermore, the linewidth of the superconducting nanowire is 20 nm-200 nm.

[0011] Furthermore, it also includes: The superconducting nanowire input electrode is connected to the end of the superconducting nanowire away from the inductor and is used to provide bias current to the superconducting nanowire. The output electrode is connected to the end of the inductor furthest from the superconducting nanowire and is used to output the signal current or pulse generated by the superconducting nanowire.

[0012] Furthermore, the inductor is of the meandering type with a linewidth greater than 500 nm.

[0013] Furthermore, it also includes a protective layer covering the surface of the superconducting layer to prevent the superconducting layer from being oxidized or contaminated.

[0014] Furthermore, the materials of the superconducting layer include, but are not limited to, NbTiN, NbN, and YBCO.

[0015] The second objective of this invention is to provide a method for preparing a gated superconducting nanowire cryothermometer, comprising the following steps: A superconducting thin film is deposited on the substrate surface; Patterns of gates, superconducting nanowires, and inductors were obtained using electron beam lithography. The structures of the gate, superconducting nanowires, and inductor were obtained by reactive ion etching. The pattern of an auxiliary structure for external electrical connection is obtained by ultraviolet exposure technology. The auxiliary structure includes a gate input electrode, a superconducting nanowire input electrode, and an output electrode. The auxiliary structure is obtained by etching using reactive ion etching technology, thereby forming a superconducting layer on the substrate.

[0016] Furthermore, it also includes: depositing a protective thin film on the superconducting layer.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention utilizes the temperature range below the superconducting transition temperature of nanowires, where the superconducting nanowires are in a superconducting state. Particles injected through a gate electric field can split Cooper pairs in the superconducting state, triggering a superconducting-normal phase transition pulse. The injected energy must be greater than the superconducting band gap, and the particle dynamics and superconducting band gap are temperature-dependent. Therefore, the pulse frequency exhibits a significant nonlinear relationship with temperature. By measuring the count rate of the phase transition pulses induced by gate injection, high-precision measurement of low-temperature temperatures can be achieved. This invention also has the advantages of wide temperature range measurement, low noise, high sensitivity, low power consumption, low self-heating, simple measurement system, and low cost. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a planar schematic diagram of the gated superconducting nanowire cryotherm in Embodiment 1 of the present invention; Figure 2 This is the film structure of the gated superconducting nanowire cryotherm in Embodiment 1 of the present invention; Figure 3 This is a planar schematic diagram of the multi-gate superconducting nanowire cryotherm in Embodiment 1 of the present invention; Figure 4 This is a measurement circuit diagram of Embodiment 1 of the present invention; Figure 5 This is a graph showing the temperature-count rate measurement results of Embodiment 1 of the present invention.

[0019] The attached diagram shows the markings and corresponding component names: 1-Gate input electrode, 2-Gate, 3-Superconducting nanowire input electrode, 4-Superconducting nanowire, 5-Inductor, 6-Output electrode, 7-Substrate, 8-Superconducting layer, 9-Protective layer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0021] The following detailed description of an embodiment of a gated superconducting nanowire cryothermometer and its fabrication method, with appropriate reference to the accompanying drawings, is provided. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art.

[0022] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0023] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0025] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0026] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0027] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0028] It should be noted that, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] Example 1

[0030] A grid-controlled superconducting nanowire cryotherm, such as Figure 1 As shown, it includes a substrate and a superconducting layer. The substrate is disposed at the bottom of the superconducting layer to provide support for the superconducting layer. The superconducting layer includes a gate, a superconducting nanowire, and an inductor. The gate is perpendicular to the superconducting nanowire and has a spacing for electric field modulation. The superconducting nanowires are connected to an inductor to respond to particles injected through the gate and output pulse signals. The inductor is connected to the superconducting nanowire to suppress latch-up under high bias current. The superconducting layer material has a superconducting transition temperature T that exceeds the measured temperature range. c Superconducting thin film materials.

[0031] The principle of this low-temperature thermometer is based on the temperature dependence of the Cooper pair splitting rate induced by gate injection. Specifically, particles injected through the gate electric field can split Cooper pairs in the superconducting state, triggering a superconducting-normal phase transition pulse. The injected energy must be greater than the superconducting band gap, and the particle dynamics and the superconducting band gap are temperature-dependent. Therefore, the pulse frequency exhibits a significantly nonlinear relationship with temperature. By measuring the phase transition pulse count rate induced by gate injection, the current temperature can be measured.

[0032] In one specific embodiment, the gate is connected to a gate input electrode, which provides a gate bias voltage to the gate. The gate acts as an electric field regulator, has a width of 5 nm to 5 μm, and is vertically arranged on the side of the superconducting nanowire, maintaining a spacing of 10 nm to 500 nm. Specifically, the end of the gate closest to the superconducting nanowire can be rectangular, pointed, or other configurations, and different geometric dimensions paired with the nanowire can meet different performance requirements, thereby achieving a balance in terms of power consumption, resolution, and operating speed.

[0033] As a preferred implementation method, such as Figure 3 As shown, not only one gate is provided, but multiple gates are arranged in parallel on the side of the superconducting nanowire. This increases the gate count rate when the temperature is low or the device count rate is low, thereby expanding the temperature measurement range of the device or improving its measurement speed and stability.

[0034] In one specific embodiment, one end of the superconducting nanowire is connected to the superconducting nanowire input electrode, which is used to provide bias current to the superconducting nanowire. One end of the superconducting nanowire is connected to an inductor, which is then connected to an output electrode. The output motor outputs the signal current or pulse generated by the superconducting nanowire. The superconducting nanowire is the core sensitive element, which can respond to the (quasi)particles injected into the gate and output a pulse signal.

[0035] In one preferred embodiment, the linewidth of the superconducting nanowire is 20 nm-200 nm. A suitable linewidth results in a smaller operating current and gate bias voltage for the device, and a higher operating speed. The operating speed can also be increased by reducing the linewidth of the superconducting nanowire to improve the gate count rate at the same temperature. However, excessively narrow linewidth should be avoided to prevent unnecessary dark counting that could lead to an increase in noise levels.

[0036] In one specific implementation, the inductor is of the meandering type to prevent the device from latching up under high bias. At the same time, the linewidth should be large enough, generally greater than 500 nm, to avoid it generating large dark count pulses under high bias, which would exceed the gate count and affect the device's temperature measurement performance.

[0037] In this invention, the material of the superconducting layer is selected from materials having a superconducting transition temperature T that exceeds the measured temperature range. c Superconducting thin film materials, such as any one of NbTiN, NbN, and YBCO, are used with silicon substrates or thermally oxidized substrates to achieve lower device power consumption, reduce the heat dissipation of the device itself, and reduce the impact on the measured environment.

[0038] As a preferred embodiment, the gated superconducting nanowire cryothermometer of the present invention further includes a protective layer, such as... Figure 2 As shown, a protective layer covers the surface of the superconducting layer to prevent the superconducting layer from being oxidized or contaminated, thereby improving the long-term stability and reliability of the device.

[0039] This embodiment also provides a measurement circuit based on the gated superconducting nanowire cryotherm of the present invention, such as... Figure 4 As shown, it mainly includes current source I. b0 Bias-Tee, Low Noise Amplifier (LNA), Time-to-Digital Converter (TDC), Voltage Source (V g0 The specific connection relationships are as follows: Current source: Connected to the DC terminal of the bias-Tee to provide a stable DC bias current I to the superconducting nanowires. b0 ; Bias-Tee: The DC+RF terminal is connected to the output electrode of the thermometer, and the other terminal is divided into two paths: the DC terminal is connected to the bias power supply to apply DC bias current; the AC (RF) terminal is connected to the subsequent amplifier to separate and transmit the nanosecond-level pulse signal generated by the device. Low-noise amplifier (LNA): Connected to the AC (RF) terminal of the Bias-Tee, it amplifies the weak output pulse signal to the order of hundreds of mV so that the subsequent circuitry can read it reliably. Time-to-digital converter (TDC): Connected after the LNA, it is used to count and time-resolve the amplified pulse signal, ultimately obtaining the pulse count rate, and combining it with calibration data to achieve temperature readout; Voltage source: Connected to the gate input electrode of the thermometer, used to apply the gate bias voltage V. g0 To regulate the critical current and pulse generation characteristics of superconducting nanowires.

[0040] The principle is as follows: In the temperature range below the superconducting transition temperature of the nanowire, the superconducting nanowire is in a superconducting state when a DC voltage V is applied to the gate. g0 A bias current I is applied to the superconducting nanowire. b0 Particles injected through the gate cause Cooper pairs in the superconducting nanowires to break apart, generating pulse signals on the nanowires. These AC pulse signals are separated by a bias-Tee, initially at an amplitude in the mV range. After amplification by a low-noise amplifier, the signal reaches hundreds of mV. The amplified signal is then processed by a time-to-digital converter (TDC) to read the temperature corresponding to the pulse count rate, thus achieving temperature measurement. By appropriately controlling the gate voltage and nanowire bias current, the dark count of the nanowires can be kept below 100 Hz, ensuring that the measurement noise remains within a controllable range. Adjusting the gate bias voltage and nanowire bias current allows for a wider range of temperature measurements or reduces device power consumption.

[0041] In summary, compared with existing thermometers that rely on resistance-temperature relationships or noise characteristics, the low-temperature thermometer of the present invention has the following technical advantages: 1. Simple fabrication process; compared to SQUID-based superconducting thermometers, it only requires a single-layer process. 2. Wide temperature range coverage: By adjusting the gate voltage and bias current, high-precision temperature measurement can be achieved in the temperature range below the superconducting transition temperature of the material, with a dynamic range that is more than three orders of magnitude higher than that of traditional TES thermometers. 3. Low noise and high sensitivity: It adopts a superconducting nanowire pulse counting mechanism, and the dark counting can be lower than 1 Hz. Compared with SQUID, it does not require a strict magnetic shielding environment. 4. It can be integrated on-chip, and the device structure is compatible with CMOS technology, adapting to the integration needs of chips such as quantum computing; 5. Low power consumption design: By optimizing the nanowire linewidth and gate structure, the device power consumption is below 1nW. Compared with silicon diode type thermometers, it significantly reduces the thermal interference caused by the temperature measurement device itself, and can measure the temperature of the cold stage of the refrigerator at 20 mK and above.

[0042] Therefore, the technology of this invention provides a new solution for low-temperature measurement in fields such as quantum computing, low-temperature electronic circuits, and low-temperature physics research.

[0043] Example 2

[0044] Based on Example 1, this embodiment designs the superconducting nanowire into a meandering structure and changes the gate to an interdigitated gate structure, which eliminates the need for a series inductor and improves the measurement speed of the device.

[0045] Example 3

[0046] A method for fabricating a gated superconducting nanowire cryothermometer includes the following steps: (1) The silicon substrate is cleaned and dried to obtain a clean silicon substrate suitable for thin film deposition; (2) A superconducting NbTiN thin film with a thickness of 7 nm was deposited on the surface of a silicon substrate using DC magnetron sputtering technology; (3) By using electron beam exposure technology, patterns of gate, superconducting nanowire and inductor are obtained on electron beam photoresist to define the subsequent etching area; (4) The structures of the gate, superconducting nanowire and inductor were obtained by reactive ion etching; (5) Using ultraviolet exposure technology, patterns such as auxiliary structures are transferred onto photoresist, wherein the auxiliary structures include a gate input electrode, a superconducting nanowire input electrode, and an output electrode; (6) Superconducting nanowire input electrodes, output electrodes, and gate input electrodes are etched on the superconducting layer using reactive ion etching technology to obtain auxiliary structures for external electrical connection. (7) After dicing, discrete components are obtained, and the components are packaged to obtain a package that can be used independently.

[0047] Preferably, a protective thin film can also be deposited on the superconducting layer.

[0048] Test case The thermometer in this embodiment adopts the structure of Embodiment 1, wherein the specific structural parameters are: the thickness of the superconducting thin film is 7 nm; the gate width is 200 nm and the spacing between it and the nanowire is 80 nm; the width of the superconducting nanowire is 80 nm, the length is 2 μm, and the inductance linewidth is 500 nm.

[0049] A bias current of 10 μA and a gate bias voltage of 4 V were applied, and the gate-controlled count rate was recorded over 10 seconds. The temperature-count rate test results within the temperature range of 2.7 K to 4.5 K are as follows: Figure 5 As shown: The device count rate increases with increasing temperature, exhibiting an approximately linear relationship below 4.2 K, while increasing exponentially above 4.2 K. Under these conditions, the device power consumption is ~1 nW, far lower than that of commercial silicon diode thermometers in the same temperature range, and the dark count is 0, demonstrating low power consumption and noise.

[0050] By increasing (decreasing) the gate voltage, the operating range of the device can be dynamically adjusted to the low (high) temperature range, increasing the operating range to 100 mK~5.5K. In addition, by simultaneously adjusting the bias current and gate voltage, the measurable temperature range can be further extended to 50 mK~7.5 K.

[0051] In the region close to and above the superconducting transition temperature of the device, based on the dependence of resistivity on temperature, temperature measurement above the critical temperature is achieved by applying a small bias current and measuring the resistance.

[0052] As can be seen, the low-temperature thermometer provided by the present invention has the advantages of simple preparation, adjustable temperature measurement range, and on-chip integration, and can be applied to fields such as quantum computing, low-temperature electronic circuits, and low-temperature physics research.

[0053] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A gridded superconducting nanowire cryothermometer, characterized in that, It includes a substrate and a superconducting layer, wherein the substrate is disposed at the bottom of the superconducting layer to provide support for the superconducting layer, and the superconducting layer includes a gate, a superconducting nanowire, and an inductor; The gate is perpendicular to the superconducting nanowire and has a spacing for electric field modulation. The superconducting nanowires are connected to an inductor to respond to particles injected through the gate and output pulse signals. The inductor is connected to the superconducting nanowire to suppress latch-up under high bias current. The superconducting layer material has a superconducting transition temperature T that exceeds the measured temperature range. c Superconducting thin film materials.

2. The grid-controlled superconducting nanowire cryotherm according to claim 1, characterized in that, The spacing between the gate and the superconducting nanowire is 10 nm to 500 nm.

3. The grid-controlled superconducting nanowire cryotherm according to claim 1, characterized in that, The gate is connected to a gate input electrode, which is used to provide a gate bias voltage to the gate.

4. A gated superconducting nanowire cryothermometer according to claim 1, characterized in that, The linewidth of the superconducting nanowires is 20 nm-200 nm.

5. The grid-controlled superconducting nanowire cryotherm according to claim 1, characterized in that, Also includes: The superconducting nanowire input electrode is connected to the end of the superconducting nanowire away from the inductor and is used to provide bias current to the superconducting nanowire. The output electrode is connected to the end of the inductor furthest from the superconducting nanowire and is used to output the signal current or pulse generated by the superconducting nanowire.

6. A gated superconducting nanowire cryothermometer according to claim 1, characterized in that, The inductor is of the meandering type with a linewidth greater than 500 nm.

7. A grid-controlled superconducting nanowire cryotherm according to any one of claims 1-6, characterized in that, It also includes a protective layer, which covers the surface of the superconducting layer to prevent it from being oxidized or contaminated.

8. A grid-controlled superconducting nanowire cryotherm according to any one of claims 1-6, characterized in that, The materials of the superconducting layer include, but are not limited to, NbTiN, NbN, and YBCO.

9. A method for preparing a gated superconducting nanowire cryothermometer according to claim 1, characterized in that, Includes the following steps: A superconducting thin film is deposited on the substrate surface; Patterns of gates, superconducting nanowires, and inductors were obtained using electron beam lithography. The structures of the gate, superconducting nanowires, and inductor were obtained by reactive ion etching. The pattern of an auxiliary structure for external electrical connection is obtained by ultraviolet exposure technology. The auxiliary structure includes a gate input electrode, a superconducting nanowire input electrode, and an output electrode. The auxiliary structure is obtained by etching using reactive ion etching technology, thereby forming a superconducting layer on the substrate.

10. The method for preparing a gated superconducting nanowire cryotherm according to claim 9, characterized in that, Also includes: A protective thin film is deposited on the superconducting layer.

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