WO2023168996A1 - Structured superconducting-tape single photon detector and preparation method therefor - Google Patents

Abstract

Disclosed in the present invention is a structured superconducting-tape single photon detector. In the present invention, the photon response sensitivity of a superconducting tape is improved by means of structure regulation and control, and the requirements of a conventional superconducting single photon detector regarding the width of a superconducting tape are reduced, such that high-sensitivity single-photon detection can be realized; and the structured superconducting-tape single photon detector is characterized in having a large detection area and a high speed, being simple in terms of preparation, being easily expandable to a large-scale array structure, etc. The single photon detector sequentially comprises, from bottom to top: a substrate, a structured superconducting tape, an electrode, an optical dielectric layer and an optical reflection layer. The preparation method mainly comprises: depositing a superconducting thin film on a surface of a substrate by means of magnetron sputtering; preparing a metal electrode on the superconducting thin film by means of photolithography and stripping technology; preparing on the superconducting thin film a structured superconducting tape shape by means of electron beam lithography technology and reactive ion etching technology; and respectively depositing an optical dielectric layer and a metal reflection layer on the surface of the structured superconducting tape by means of chemical vapor deposition technology and electron beam evaporation technology, which optical dielectric layer and metal reflection layer serve as optical cavities.

Description

Structured superconducting strip single-photon detector and preparation method thereof Technical field

The invention relates to the field of light detection technology, and specifically to a structured superconducting strip single photon detector and a preparation method thereof.

Background technique

Superconducting Nanowire Single Photon Detector (SNSPD) is a powerful tool for light limit detection. After more than 20 years of rapid development, SNSPD has high detection efficiency, ultra-low dark count, and ultra-low dark count. High temporal resolution and wide response spectrum. These excellent properties make it stand out among many single photon detectors and have good application prospects in fields such as deep space optical communications, quantum optics, biofluorescence imaging, lidar, and dark matter detection.

Traditional SNSPDs usually fill a 20 μm × 20 μm area with meandering nanowire structures with a width of 80 to 100 nm as the photosensitive surface of the detector, and use single-mode optical fibers to optically couple the SNSPDs. In practical applications, detectors require larger photosensitive surfaces to effectively perform free space coupling or multimode fiber coupling (core diameter greater than 50 μm), and conventional small-area SNSPDs can no longer meet application needs. Therefore, the preparation of SNSPD with large photosensitive area and high performance has become an inevitable trend in the future.

Currently, methods to increase the photosensitive area of SNSPD include: on the one hand, expanding the area of a single pixel detector by increasing the length of the nanowire. However, the dynamic inductance of the detector will increase as the length of the nanowire increases, which will affect The recovery time and maximum count rate of the device. On the other hand, array SNSPD is used to increase the area of the detector. However, as the number of arrays increases, it poses a huge challenge to the SNSPD readout circuit. In these methods, as the SNSPD area expands, geometric defects of the nanowires during the preparation process are inevitable, which will affect the uniformity and yield of the detector, and ultimately all aspects of the detector's performance will be reduced. How to prepare large-area, high-efficiency, high-speed array superconducting single-photon detectors while reducing related negative effects has become an urgent problem to be solved.

Contents of the invention

Purpose of the invention: In order to prepare a large-area superconducting single-photon detector and to improve the uniformity and yield of the detector during the preparation process, the present invention proposes a structured superconducting strip single-photon detector and a preparation method thereof.

Technical solution: a structured superconducting strip single photon detector, including from bottom to top: a substrate, a structured superconducting strip located on the surface of the substrate, an electrode located at the tail end connection of the structured superconducting strip, The optical medium layer on the surface of the structured superconducting tape and the optical reflective layer on the surface of the optical medium layer; wherein the structured superconducting tape is designed with a micro-nano structure pattern on the superconducting tape, and the Patterns with micro-nano structures include multiple micro-nano pore structures, and the micro-nano pore structures are closed hole structures. The closed hole structures include but are not limited to round holes, elliptical holes, square holes, rectangular holes, and machine holes. Wing holes.

The structured superconducting strip is composed of a superconducting film, and its structure is a meandering structure connected end to end.

The width of the structured superconducting strip is 0.1-20 μm, and the filling rate of the superconducting strip is 0.1-0.9.

The characteristic of the micro-nano structure is that the lateral width along the direction of the superconducting strip is 3% to 95% of the width of the superconducting strip.

In the present invention, the filling rate of the detector is improved by designing the structured superconducting strip into a meandering shape connected end to end. The structured superconducting strip is controlled by designing a micro-nanohole array structure with a certain size on the superconducting strip. The generation and passage of magnetic flux in the superconducting ribbon contributes to the detector's response to single photons. The existence of the optical medium layer and the optical reflection layer can increase the absorption rate of single photons by the structured superconducting strip, thereby improving the detection efficiency of the structured superconducting strip single photon detector. Since the width of structured superconducting strips is on the order of micrometers, it is easier to prepare large-area structured superconducting strip single-photon detectors with good uniformity than traditional nanowires.

The invention also discloses a method for preparing a structured superconducting strip single photon detector, which includes the following steps:

Step 1: Use magnetron sputtering technology to grow a layer of superconducting film on the substrate;

Step 2: Grow electrodes on the superconducting film;

Step 3: Use electron beam exposure technology and reactive ion etching technology to transfer the micro-nano structure pattern to the superconducting film to obtain the superconducting strip shape with micro-nano structure.

Step 4: According to step 3, it is characterized in that, after using electron beam exposure technology and reactive ion etching technology to transfer the pattern of the micro-nanopore structure to the superconducting film to obtain the structured superconducting strip shape, it also includes Following steps:

A chemical vapor deposition method is used to deposit a layer of silicon dioxide as an optical medium layer on the surface of a superconducting strip with a micro-nano structure;

Electron beam evaporation and lift-off techniques are used to grow a layer of gold on the surface of the optical medium layer as an optical reflective layer.

Step 5: According to step 3, it is characterized in that the use of electron beam exposure technology and reactive ion etching technology to transfer the pattern of the micro-nanopore structure to the superconducting film to obtain the shape of the structured superconducting strip specifically includes:

Spin-coating the positive electron beam etching resist on the superconducting film with the electrode as the electron beam etching resisting layer;

Electron beam exposure technology is used to expose the film with an electron beam etching-resistant layer according to the pattern of the micro-nano structure, and development and fixing processes are used to obtain the pattern of the micro-nano structure on the electron beam etching-resistant layer;

Reactive ion etching technology is used to transfer the pattern of micro-nanopore structure to the film to obtain a structured superconducting strip shape;

N-methylpyrrolidone solution water bath ultrasonic was used to remove the positive electron beam etching resist remaining on the surface of the structured superconducting tape, and finally a structured superconducting tape with a clean surface was obtained.

Step 6: According to step 5, it is characterized in that: in the electron beam exposure technology, an electron beam current of 2nA is used to draw the pattern of the micro-nano structure on the film with an electron beam etching resistant layer, and the exposure dose is 600 μC/cm ² .

Beneficial effects: Compared with the existing technology, the present invention has the following advantages:

(1) The present invention provides an idea of structured superconducting strips to prepare large-area superconducting strip single-photon detectors. Through structural regulation, the sensitivity of the superconducting strips to photons is increased, and the cost of conventional superconducting single-photon detectors is reduced. Regarding the requirements for the width of superconducting strips, micron-wide structured superconducting strips allow the preparation of large photosensitive area detectors, which can achieve single photon detection while reducing the difficulty of process preparation. It has the characteristics of low preparation difficulty and high coupling efficiency. Large photosensitive The advantage of the area will expand the practical application of the detector; that is to say, the single-photon detector of the present invention can realize highly sensitive single-photon detection, and has the characteristics of large detection area, fast speed, simple preparation, and easy expansion to large-scale arrays Structural and other characteristics;

(2) Compared with superconducting nanowire single-photon detectors with the same photosensitive area, micron-wide structured superconducting strip single-photon detectors have smaller dynamic inductance and recovery time; under the same superconducting wire width, this The effective cross-sectional area of the structured superconducting strip in the invention is smaller, which helps to improve the response ability of the detector to single photons; the micron-wide structured superconducting strip in the invention has a larger current carrying capacity, which helps It has a large signal-to-noise ratio at the readout end;

(3) Micron-wide structured superconducting strips have lower dark counting capabilities, which is beneficial to the application of superconducting strip single-photon detectors in the field of astronomy, such as the detection of dark matter.

Description of the drawings

Figure 1 is a schematic three-dimensional structural diagram of the structured superconducting strip single photon detector of the present invention;

Figure 2 is a global SEM image of the structured superconducting strip single-photon detector with a large photosensitive area of 500×500 μm ² of the present invention;

Figure 3 is a partial SEM detail view of the structured superconducting tape of the present invention;

Figure 4 is a flow chart for the preparation of the structured superconducting strip single photon detector of the present invention;

Figure 5 is a voltage pulse signal diagram of the structured superconducting strip single photon detector of the present invention responding to photons at an operating temperature of 300mK;

Figure 6 is a resistance-temperature curve of the structured superconducting strip single photon detector of the present invention;

Figure 7 is the voltage-current characteristic curve of the structured superconducting strip single photon detector of the present invention at an operating temperature of 300mK;

Figure 8 shows the single photon counting and dark counting of the structured superconducting strip single photon detector of the present invention at a wavelength of 1550 nm at an operating temperature of 300 mK.

Detailed ways

The technical solutions of the embodiments of the present invention will now be further described with reference to the accompanying drawings.

The structured superconducting strip single photon detector proposed in the embodiment of the present invention is similar to the geometric hot spot destroying the superconducting state. The magnetic flux crossing is a method for the phase change of the superconducting film. Typically, magnetic flux is effectively pinned in a uniform current-carrying superconducting film due to the presence of a magnetic flux barrier. Relevant experiments have proven that the detection of single photons by superconducting strips is related to magnetic flux dynamics. Controlling the movement of magnetic flux in superconducting films through geometric structures can help improve the detection of single photons by superconducting strips. The present invention realizes structured superconducting strips by designing micro-nanohole arrays on micron-wide superconducting strips. In this embodiment, the micro-nanohole array takes a circular hole array as an example. A structured superconducting strip with a circular hole array Strips can facilitate the generation and crossing of magnetic flux. When the incident photon is absorbed by the current-biased structured superconducting strip, the thermally excited magnetic flux enters the structured superconducting strip, resulting in local suppression of the superconducting order parameter (Δ). Once the bias current exceeds a threshold, the magnetic flux is prevented. The barrier height traversed by the pass will be reduced to zero. Eventually, the magnetic flux moves through the entire superconducting film, destroying the film's superconductivity and producing a detectable voltage pulse, enabling single-photon detection.

In order to achieve the above purpose, the structured superconducting strip single-photon detector according to the embodiment of the present invention is shown in Figure 1, which includes from bottom to top: substrate 1, structured superconducting strip 2, electrode 3, and optical medium layer 4 and optical reflection layer 5. Among them, the structured superconducting strip 2 is located on the surface of the substrate 1, the electrode 3 is located at the tail end connection of the structured superconducting strip 2, and the optical medium layer 4 is located on the surface of the structured superconducting strip 2 as an increaser for absorbing light. The transparent layer and the optical reflective layer 5 are located on the surface of the optical medium layer 4. The optical reflective layer 5 and the optical medium layer 4 constitute the optical cavity of the detector to improve the detector's absorption efficiency of single photons.

As shown in Figures 2 and 3, the structured superconducting strip 2 is composed of a superconducting MoSi film. In addition to MoSi, it can also be a MoGe, WSi, NbN, or NbTiN film. The structure of the structured superconducting strip 2 is a meandering structure connected end to end. The meandering micron wires are connected end to end to improve the filling rate of the detector; on the structured superconducting strip 2, the generation and crossing of the magnetic flux of the superconducting strip are controlled by designing a circular hole array structure with a certain size. Contributes to the detection of single photons by structured superconducting strips. Parameters in the circular hole array, such as hole size and spacing, can be adjusted according to needs. In some embodiments, the thickness of the superconducting MoSi film is 4.5 nm, the width of the superconducting strip is 1 to 3 μm, the filling rate of the superconducting strip is 0.3 to 0.7, the diameter of the circular hole is 300 nm, and the hole spacing is 200 nm, and the detector The photosensitive area is 500×500μm ² . Since the width of the superconducting strip is on the order of micrometers, compared with traditional nanowires, it is easier to prepare large-area structured superconducting strip single-photon detectors with good uniformity. While achieving single-photon detection, it reduces the cost Process preparation difficulty.

Compared with superconducting nanowire single-photon detectors, micron-wide structured superconducting strips have a larger current carrying capacity, which contributes to a larger signal-to-noise ratio at the external circuit readout; in addition, in the same Micron-wide structured superconducting strip single-photon detectors have smaller dynamic inductance and recovery time under the photosensitive area. And the existence of the optical medium layer 4 and the optical reflection layer 5 can increase the absorption rate of single photons by the structured superconducting strip, thereby improving the detection efficiency of the superconducting strip single photon detector.

The present invention also proposes a method for preparing a structured superconducting strip single photon detector, as shown in Figure 4, which includes the following steps:

S100: Use magnetron sputtering technology to grow a superconducting MoSi film on substrate 1;

S200: Grow a layer of gold electrode with a certain pattern on the superconducting MoSi film through UV lithography, electron beam evaporation and lift-off technology;

S300: Using electron beam exposure technology and reactive ion etching technology to transfer the structured pattern with a circular hole array to the superconducting MoSi film, a structured superconducting strip with a circular hole array 2 is obtained.

S400: Use chemical vapor deposition technology to deposit a layer of pure silicon dioxide on the surface of a structured superconducting strip with a circular hole array as the optical medium layer 4;

S500: Use electron beam evaporation and stripping technology to generate a layer of metallic gold (purity 99.999%) on the surface of the optical medium layer 4 as the optical reflective layer 5.

The preparation method of the present invention can obtain a 1-3 μm superconducting strip on a superconducting film. The filling rate of the superconducting strip is 0.5. The diameter of the circular hole array designed at the center of the superconducting strip is 250-350 nm, and the hole spacing is 200~300nm, the photosensitive area of the detector is 500×500μm ² . This geometrically controlled superconducting ribbon preparation process is beneficial to reducing the difficulty of preparing large-area superconducting ribbon single-photon detectors and increasing the photosensitive area of the detector. Wider superconducting ribbons have the ability to detect near-infrared single photons.

The preparation method of the present invention will be further described with reference to the examples.

The preparation method of this embodiment includes the following steps:

Step 1: Preprocess the double-polished thermal oxide silicon substrate as the detector substrate. The substrate can also be quartz, magnesium oxide, magnesium fluoride and sapphire substrate. In this embodiment, the thickness is 268nm. Double-polishd thermal oxidation silicon substrate; the preprocessing of this step includes:

First, the double-polished thermally oxidized silicon substrate was ultrasonically cleaned with acetone and ethanol at 80W power for 5 minutes each to remove contaminants on the substrate surface;

Then rinse with deionized water;

Finally, use nitrogen to blow dry the moisture on the surface of the substrate.

Step 2: Use magnetron sputtering technology to grow a superconducting MoSi film with a thickness of 4.5nm on the substrate; the specific implementation steps are:

The substrate is sent into the auxiliary chamber of magnetron sputtering, and the substrate is ion milled. The ion milling conditions are: 15Sccm argon gas flow, 30mA ion beam current, 300V anode voltage, and the ion milling time is 1 minute.

The ion-milled substrate is sent into the main chamber of magnetron sputtering, and a MoSi film is grown on the substrate when the vacuum degree of the main chamber is below 10 ^-6 mTorr. The growth conditions of the MoSi film are: argon gas flow rate is 30Sccm, sputtering gas pressure is 2mTorr, sputtering current is 0.5A, and sputtering rate is 0.95nm/s.

A layer of Nb ₅ N ₆ film was grown in situ on the MoSi film as a protective layer. The growth conditions of Nb ₅ N ₆ film are: nitrogen and argon flow ratio is 4:1, sputtering pressure is 15mTorr, sputtering power is 400W, and sputtering rate is 0.2nm/s.

Step 3: Grow a layer of gold electrode with a certain pattern on the superconducting MoSi film through UV lithography, electron beam evaporation and lift-off technology. The gold thickness is 120nm; specific operation steps include:

Use a glue spreader to spin-coat positive photoresist AZ1500 on the film surface.

Use a photolithography machine to expose the film according to the pattern of the mask.

The exposed film is developed using a positive developing solution to obtain the electrode pattern.

Electron beam evaporation is used to coat the developed film with a layer of gold.

Use acetone and ethanol to peel off excess gold on an ultrasonic machine.

Step 4: Use electron beam exposure technology and reactive ion etching technology to transfer the geometrically controlled shape of the circular hole array to the superconducting MoSi film; specific operation steps include:

The positive electron beam resist PMMA with a thickness of about 200nm is spin-coated on the surface of the superconducting MoSi film with an electrode shape using a glue leveler. The solute concentration of PMMA used in this embodiment is 4%, the pre-baking temperature of PMMA is 180°C, and the baking time is 4 minutes.

The electron beam exposure machine uses an electron beam current of 2nA to draw the pattern of the structured superconducting strip with a circular hole array; the electron energy of the electron beam exposure machine works at 100keV, the exposure beam current is 2nA, and the scanning step is 0.1~5nm. , the exposure dose is 600μC/cm ² . The pattern of the structured superconducting tape with a round hole array in this embodiment is: round holes are arranged at the center of the superconducting tape to form a superconducting tape with a round hole array. The diameter of the holes is 250-350 nm, and the hole spacing is 200 nm. ~300nm, the effective photosensitive area of the detector is 500×500μm ² .

The exposed sample is developed and fixed using a positive film developer. In this example, a mixture of MIBK:IPA=1:3 is used as the developer, and isopropyl alcohol is used as the fixer. The development time is 2 minutes, the fixing time is 1 minute, and the temperature is 22 degrees Celsius.

Reactive ion etching was used to transfer the developed structured superconducting strip pattern with a circular hole array to the superconducting MoSi film; the chamber pressure was 30mTorr and the etching rate was 1nm/s. The etching time can be adjusted according to the film thickness. In this embodiment, the gas used for reactive ion etching is CF ₄ , the flow rate is 20Sccm, the gas pressure is 1.2Pa, the etching power is 50W, and the etching time is 90s.

Use N-methylpyrrolidone solution in a water bath to remove the electron beam photoresist remaining on the surface of the superconducting strip. The water bath temperature is 80°C and the water bath time is 30 minutes to 1 hour.

Finally, a structured superconducting strip with a circular hole array was obtained, as shown in Figures 2 and 3.

Step 5: Use chemical vapor deposition technology to grow a layer of pure silicon dioxide on the superconducting micron strip as the optical medium layer. The thickness of the silicon dioxide is 268nm, which helps the detector absorb photons.

Step 6: Use photolithography and electron beam evaporation technology to grow a layer of gold as an optical reflective layer on the optical medium layer. The thickness of gold is 200nm.

The structured superconducting strip with a circular hole array prepared in this embodiment is shown in Figures 2 and 3. The width of the superconducting strip is 1.5 μm, the filling rate is 0.5, and the diameter of the round hole array designed at the center of the superconducting strip is 300nm, pore spacing is 200nm. Figure 5 shows the output voltage pulse diagram of the detector, in which the recovery time of the detector is 149ns and the pulse amplitude is 310mV. Figure 6 shows the change curve of the detector's resistance with temperature. It can be seen from the figure that the superconducting transition temperature of the detector is 3.6K. Figure 7 shows the voltage-current curve of the detector, whose superconducting critical current is 20μA. In order to verify the optical response performance of the detector, the photon count and dark count of the device at the 1550nm single photon level were measured at the detector's operating temperature of 300mK, as shown in Figure 8.

Claims (9)

1. Structured superconducting strip single photon detector, characterized in that the detector includes from bottom to top: a substrate, a structured superconducting strip located on the surface of the substrate, and a tail located at the structured superconducting strip. The electrode at the end connection, the optical medium layer located on the surface of the structured superconducting tape and the optical reflective layer located on the surface of the optical medium layer; wherein, the structured superconducting tape is designed with microstructures on the superconducting tape. Patterns of nanostructures. The patterns with micro-nano structures include multiple micro-nano structures. The micro-nano structures are closed hole structures. The closed hole structures include but are not limited to round holes, elliptical holes, square holes, etc. holes, rectangular holes and wing holes.
2. The structured superconducting strip single photon detector according to claim 1, further comprising: an optical medium layer located on the surface of the structured superconducting strip and an optical reflection layer located on the surface of the optical medium layer.
3. The structured superconducting strip single photon detector according to claim 1, characterized in that the structured superconducting strip is composed of a superconducting film, and its structure is a meandering structure connected end to end.
4. The structured superconducting strip single photon detector according to claim 1, characterized in that the width of the structured superconducting strip is 0.1-20 μm, and the filling rate of the superconducting strip is 0.1-0.9.
5. The structured superconducting strip single photon detector according to claim 1, wherein the micro-nanohole structure is characterized by a lateral width along the superconducting strip direction of 3% to 95% of the superconducting strip width. .
6. A method for preparing a structured superconducting strip single photon detector, which is characterized by including the following steps:

   Using magnetron sputtering technology, a layer of superconducting film is grown on the substrate;

   Growing electrodes on superconducting films;

   Electron beam exposure technology and reactive ion etching technology are used to transfer the pattern of micro-nanopore structure to the superconducting film to obtain the shape of structured superconducting strips.
7. The method for preparing a structured superconducting strip single photon detector according to claim 6, wherein the pattern of the micro-nanopore structure is transferred to the superconducting film using electron beam exposure technology and reactive ion etching technology. After obtaining the structured superconducting strip shape, the following steps are also included:

   A chemical vapor deposition method is used to deposit a layer of silicon dioxide as an optical medium layer on the surface of a superconducting strip with a micro-nano structure;

   Electron beam evaporation and lift-off techniques are used to grow a layer of gold on the surface of the optical medium layer as an optical reflective layer.
8. The method for preparing a structured superconducting strip single photon detector according to claim 6, wherein the pattern of the micro-nano hole structure is transferred to the superconducting film using electron beam exposure technology and reactive ion etching technology. , obtaining the structured superconducting strip shape specifically includes:

   Spin-coating the positive electron beam etching resist on the superconducting film with the electrode as the electron beam etching resisting layer;

   Electron beam exposure technology is used to expose the film with an electron beam etching-resistant layer according to the pattern of the micro-nano structure, and development and fixing processes are used to obtain the pattern of the micro-nano structure on the electron beam etching-resistant layer;

   Reactive ion etching technology is used to transfer the pattern of micro-nanopore structure to the film to obtain a structured superconducting strip shape;

   N-methylpyrrolidone solution water bath ultrasonic was used to remove the positive electron beam etching resist remaining on the surface of the structured superconducting tape, and finally a structured superconducting tape with a clean surface was obtained.
9. The method for preparing a structured superconducting strip single photon detector according to claim 8, characterized in that: in the electron beam exposure technology, an electron beam current of 2nA is used to draw microscopic particles on the film with an electron beam etching resistant layer. For the pattern of nanostructure, the exposure dose is 600μC/cm ² .

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