CN104752534B - Superconducting nano-wire single-photon detector and preparation method thereof - Google Patents
Superconducting nano-wire single-photon detector and preparation method thereof Download PDFInfo
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 4
- 238000001755 magnetron sputter deposition Methods 0.000 claims description 4
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Abstract
The invention discloses a kind of superconducting nano-wire single-photon detector, it is made up of the superconducting nano-wire unit of N number of series connection, the parallel resistance of N number of different resistances and optical resonator, the resistance of described N number of different resistances is connected in parallel on the two ends of N number of superconducting nano-wire unit respectively, and described optical resonator covers on the superconducting nano-wire unit upper strata of N number of series connection.The present invention can not only realize number of photons and differentiate, and has been also equipped with the ability of spatial discrimination simultaneously.The invention also discloses a kind of method preparing superconducting nano-wire single-photon detector as above, whole technological process has only to carry out the electron beam exposure of a nano wire figure, effectively reduces the preparation cost of device.
Description
Technical Field
The invention relates to a superconducting nanowire single-photon detector and a preparation method thereof, in particular to a superconducting nanowire single-photon detector which can realize space resolution and photon number resolution simultaneously and has high detection efficiency and a preparation method thereof, belongs to the technical field of single-photon detection and extremely weak light detection, and is suitable for the single-photon detection technology which needs to realize photon resolution in visible light and infrared bands.
Background
The single photon detector is a high-sensitivity ultra-low noise device, and detects an extremely weak target signal by detecting and counting incident single photons. Therefore, the high-performance single photon detector has wide requirements in the application fields of emerging weak light detection technologies such as quantum communication, quantum computation, integrated circuit detection, molecular fluorescence detection and the like.
The traditional single photon detectors comprise photomultiplier tubes, avalanche photodiodes and the like, but the single photon detectors have low detection efficiency in near infrared bands and generally low repetition rate, so that the requirements in the fields of quantum communication and the like cannot be met. With the development of thin film technology and micro-processing technology and the urgent need of single photon detection technology, the superconducting nanowire single photon detection technology comes along, has the advantages of high sensitivity, high repetition rate, low dark count and the like, and shows excellent single photon detection capability in visible light and infrared bands.
However, the conventional superconducting nanowire single photon detector mainly works in a nonlinear mode, that is, the number and the position of incident photons cannot be distinguished when the photons are detected. In order to meet the requirements of special applications requiring spatial resolution and photon number resolution, such as linear optical quantum computation, characterization of non-classical light sources, and the like, the structure of a superconducting nanowire single photon detector needs to be improved.
At present, in order to realize the function of photon number resolution, there are mainly the following three schemes:
the superconducting nanowire single photon detector array. However, the superconducting nanowire single-photon detector array requires a very complex readout circuit system, namely, each superconducting nanowire single-photon detector needs a readout circuit composed of an amplifier, a bias circuit and the like;
and the other is a parallel nanowire photon resolution detector. The reading circuit of the parallel nanowire photon resolution detector is simple, but the leakage current is large, so that the detection efficiency and the maximum number of resolved photons of the device are severely limited;
and thirdly, a photon resolution detector with the nanowires connected in series. The readout circuit of the serial nanowire photon resolution detector is simple, the detection efficiency and the maximum number of resolved photons are not affected by leakage current, but the detection efficiency is not high due to the fact that the detection circuit does not have the spatial resolution capability.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a superconducting nanowire single photon detector and a preparation method thereof, which can realize spatial resolution and photon number resolution at the same time and have high detection efficiency.
In order to achieve the above object, a first technical solution adopted by the present invention is a superconducting nanowire single photon detector, which comprises N superconducting nanowire units connected in series, N parallel resistors with different resistances, and an optical resonant cavity, wherein the N resistors with different resistances are respectively connected in parallel at two ends of the N superconducting nanowire units, and the optical resonant cavity covers an upper layer of the N superconducting nanowire units connected in series.
Further, N is an arbitrary integer value equal to or greater than 2.
Furthermore, the N parallel resistors with different resistance values are prepared from titanium thin films, the thickness of the titanium thin films is the same, and the resistor junctions are changedThe length-width ratio of the structure obtains parallel resistors with different resistance values, and the resistance values of the resistors meet the following proportional relation: when N takes 2, the resistance value of the resistor is 1/2: 1; when N takes 3, the resistance value of the resistor is 1/4: 1/2: 1; when N takes 4, the resistance value of the resistor is 1/4: 1/2: 1: 2; when N is any integer value greater than or equal to 5, the resistance value of the resistor is 1/4: 3/8: 1/2: 1: 2: 4: …: 2N-4The proportional relationship of (c).
Further, the optical resonant cavity is formed by lower layer of silicon oxide (SiO)x) The light-emitting diode is characterized by comprising a dielectric layer and an upper gold reflecting layer, wherein the thickness of the silicon oxide dielectric layer is in a relation of lambda/(4 η) with the detection wavelength lambda, η is the refractive index of silicon oxide, and further, the thickness of the silicon oxide dielectric layer is 240nm, and the thickness of the gold reflecting layer is 100 nm.
The second technical scheme adopted by the invention is a method for preparing the superconducting nanowire single photon detector, which comprises the following steps:
step one, preparing a niobium nitride film by magnetron sputtering: silica (SiO) with a thickness of 250nm grown on both sides2) Growing a niobium nitride film with the thickness of 6-8nm on the silicon (Si) substrate;
secondly, manufacturing a nanowire graph by electron beam exposure: designing a meandering nanowire pattern, wherein the width of the nanowire is 80nm, the duty ratio is 1/3, and the whole covered by the nanowire is square; spin-coating an electron beam resist, writing a nanowire pattern through electron beam exposure, and then obtaining a nanowire through reactive ion etching, wherein the etching time is 30 s;
thirdly, photoetching to form electrodes: manufacturing a gold electrode mask by double-layer photoresist photoetching, firstly growing a titanium film, then growing a gold film, and finally stripping an electrode;
fourthly, etching redundant niobium nitride: photoetching the single-layer photoresist to form an etching mask, etching the redundant niobium nitride film by reactive ions for 45s, and finally removing the photoresist;
fifthly, photoetching to obtain a titanium resistor: the double-layer photoresist is used for photoetching to make a resistance mask, a titanium film with the square resistance of 100 omega is prepared by controlling the growth time of titanium, and finally the titanium resistance with different resistance values is obtained by stripping;
sixthly, photoetching to form an optical resonant cavity: and double-layer photoresist is used for photoetching to form a mask of the optical resonant cavity, a silicon oxide dielectric layer is prepared by using chemical vapor deposition, a gold reflecting layer is grown on the silicon oxide dielectric layer, and finally the optical resonant cavity is stripped.
Further, the thickness of the titanium thin film is 10nm, and the thickness of the gold thin film is 100 nm.
Further, the resistance values of the titanium resistors with different resistance values satisfy the following proportional relation: when N takes 2, the resistance value of the resistor is 1/2: 1; when N takes 3, the resistance value of the resistor is 1/4: 1/2: 1; when N takes 4, the resistance value of the resistor is 1/4: 1/2: 1: 2; when N is any integer value greater than or equal to 5, the resistance value of the resistor is 1/4: 3/8: 1/2: 1: 2: 4: …: 2N-4The proportional relationship of (c).
Furthermore, the thickness of the silicon oxide dielectric layer is 240nm, and the thickness of the gold reflecting layer is 100 nm.
Further, in the sixth step, a silicon oxide dielectric layer is prepared by using chemical vapor deposition at a low temperature of 50 ℃.
Further, in the fifth step, the growth time of the titanium thin film is 50 s.
Has the advantages that: the invention is properly improved on the basis of the principle of the serial nanowire photon resolution detector, so that the serial nanowire photon resolution detector has the capability of spatial resolution while realizing photon number resolution, and the detection efficiency is effectively improved by adding the optical resonant cavity structure on the upper layer of the device. In addition, the preparation process is optimized, only one electron beam exposure is needed, and other processes can be realized through photoetching, so that the times and time of electron beam exposure are reduced, and the preparation cost of the device is effectively reduced.
Drawings
Fig. 1 is a schematic structural diagram of a photon-resolved detector with a series nanowire having 6 resistors.
FIG. 2 is a schematic diagram of a readout circuit of a tandem nanowire photon-resolved detector
Fig. 3 is an equivalent circuit schematic diagram of a serial nanowire photon-resolved detector.
FIG. 4 shows the results of the electrothermal simulation of the equivalent resistance of the photon-resolved detector with 3 serially connected nanowires.
FIG. 5 shows the results of electrothermal simulation of the impulse response of a photon-resolved detector with 3 resistors connected in series.
FIG. 6 shows the results of the electrothermal simulation of the equivalent resistance of the photon-resolved detector with 4 serially connected nanowires.
FIG. 7 shows the results of electrothermal simulation of the impulse response of a 4-resistor series nanowire photon-resolved detector.
Fig. 8 is a process flow diagram of a tandem nanowire photon-resolved detector.
FIG. 9 is a schematic diagram of a measurement system of a tandem nanowire photon-resolved detector.
Detailed Description
The invention discloses a superconducting nanowire single photon detector which can simultaneously realize space resolution and photon number resolution and has high detection efficiency. N resistors with different resistance values are respectively connected in parallel at two ends of the N sections of superconducting nanowire units, wherein N can be any integer value larger than or equal to 2. When the resistance value of the resistor satisfies 1/4: 3/8: 1/2: 1: 2: 4, spatial resolution and photon number resolution of incident photons can be achieved by detecting the amplitude of the output pulse. Therefore, the invention not only can realize photon number resolution, but also has the capability of spatial resolution. In addition, the optical resonant cavity structure is added on the upper layer of the device, and the system detection efficiency can be effectively improved. The invention also provides a process method for preparing the superconducting nanowire single photon detector, the whole process flow only needs to carry out electron beam exposure of the nanowire pattern once, and other processes such as electrode, parallel resistor, optical resonant cavity and other structures can be realized by photoetching, thereby reducing the times and time of electron beam exposure and effectively reducing the preparation cost of devices.
Specifically, the superconducting nanowire single photon detector capable of simultaneously realizing spatial resolution and photon number resolution and high detection efficiency comprises N superconducting nanowire units connected in series, N parallel resistors with different resistance values and an optical resonant cavity. The winding superconducting nanowire is prepared from a niobium nitride superconducting thin film, the line width of each section of superconducting nanowire is 80nm, the duty ratio is 1/3, and the length is 400 microns. The parallel resistor is prepared from a thin film of inert metal titanium, N resistors with different resistance values are respectively connected in parallel at two ends of the N serial superconducting nanowire units, wherein N can be any integer value more than or equal to 2. On the same device, the thickness of the titanium thin film was the same, and the resistors with different resistance values were obtained by changing the aspect ratio of the resistors, as shown in table 1. The optical resonant cavity covers the upper layer of the N serial superconducting nanowire units so as to improve the system detection efficiency of the detector.
In order to realize the spatial resolution and the number resolution of incident photons at the same time, the resistance values of the resistors and the resistance values of the resistors after the resistors are mutually superposed are required to be completely different, and the difference between the resistance values is at least 10 omega, so that the error in the micromachining process can be contained. Taking 3 parallel resistors with different resistances in table 1 as an example, 1 photon (25 Ω, 50 Ω, 100 Ω) and 2 photons (25 Ω +50 Ω, 25 Ω +100 Ω, 50 Ω) need to be ensured+100 Ω), each resistance value corresponding to 3 photons (25 Ω +50 Ω +100 Ω) is different, and each resistance value differs by at least 10 Ω, and the corresponding output pulse amplitude is different, thereby can realize 3 incident photons and 2 incident photons3Resolution of 1= 7 spatial positions. If there are 6 parallel resistors with different resistance values, 6 incident photons and 2 can be realized6-resolution of 1= 63 spatial positions.
By analogy, if N parallel resistors with different resistance values are provided, the resolution of the number of N photons can be realized at most (2)N-1) resolution of the incident positions of the species of photons.
The invention also provides a process method for preparing the superconducting nanowire single photon detector which simultaneously realizes the spatial resolution and the photon number resolution and has high detection efficiency. Only the nanowire patterns in the whole process flow need to be exposed by adopting electron beams, and structures such as electrodes, resistors, optical resonant cavities and the like can be completed by photoetching, so that the times and time of electron beam exposure are reduced, and the preparation cost of devices is effectively reduced. The whole process flow mainly comprises the following six steps.
Firstly, preparing a niobium nitride film by magnetron sputtering. Silica (SiO) with a thickness of 250nm grown on both sides2) The niobium nitride film grows on the silicon (Si) substrate, the thickness of the film is 6-8nm, the superconducting critical temperature Tc is approximately equal to 7.0-7.5K, and the sheet resistance Rsquare≈250-300Ω。
And secondly, manufacturing a nanowire pattern by electron beam exposure. A serpentine nanowire pattern was designed with a line width of 80nm, a duty cycle of 1/3, a nanowire core region of 25 μm x 25 μm, and a nanowire exposure region of 180 μm x 60 μm. Spin-coating an electron beam resist, writing a nanowire pattern through electron beam exposure, and then obtaining the nanowire through reactive ion etching. The etching time is 30s to ensure that the influence of electron beam exposure residual glue is eliminated. The thickness of the etched lines is required to be uniform, and the edges of the lines are free of burrs.
And thirdly, photoetching to form a gold electrode. And (3) manufacturing a gold electrode mask through double-layer photoresist photoetching so as to facilitate later stripping, firstly growing a 10nm titanium film, then growing a 100nm gold film and finally stripping the gold electrode in order to enhance the adhesion of the gold film.
And fourthly, etching redundant niobium nitride. And (4) photoetching the single-layer photoresist to form an etching mask, removing the redundant niobium nitride film by reactive ion etching for 45s, and finally removing the photoresist.
And fifthly, photoetching to manufacture the titanium resistor. And (3) photoetching a double-layer photoresist to form a resistor mask, preparing a titanium film with the square resistance of 100 omega by controlling the growth time of titanium, and finally peeling to obtain the titanium resistors with different resistance values, wherein the resistance value proportion of the titanium resistors meets the proportional relation shown in the table 1.
And sixthly, photoetching to form an optical resonant cavity. Double-layer photoresist is used for photoetching as a mask of an optical resonant cavity, and silicon oxide (SiO) with the thickness of 240nm is prepared by chemical vapor deposition at the low temperature of 50 DEG Cx) And (3) growing a gold reflecting layer with the thickness of 100nm on the dielectric layer, and finally stripping the optical resonant cavity. The optical resonant cavity can effectively enhance the absorption efficiency of the serial nanowire photon resolution detector, so that the system detection efficiency can be greatly improved.
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, it is a schematic structural diagram of a superconducting nanowire single photon detector capable of simultaneously realizing spatial resolution and photon number resolution with high detection efficiency. The superconducting nanowire unit is formed by connecting 6 (namely the aforementioned N = 6) superconducting nanowire units (called nanowire units for short) 2 with the line width of 80nm in series, and two ends of each nanowire unit are connected with a resistor in parallel. The resistance values of the 6 resistors satisfy the proportional relationship described in table 1. The superconducting nanowire is made of an ultrathin niobium nitride film with the thickness of 6nm, and the parallel resistance of the superconducting nanowire is a titanium film with the square resistance of 100 omega. Each superconducting nanowire unit works based on the heat island effect principle. The optical resonant cavity 1 covers the upper layer of the N serial superconducting nanowire units to improve the system detection efficiency of the detector.
As shown in fig. 2, it is a schematic diagram of a superconducting nanowire single photon detector that can simultaneously realize spatial resolution and photon number resolution. During its operation, a DC Bias current close to its critical current (≈ 0.95 Ic) is supplied, which is switched in via the DC terminal (DC) of the Bias tree (Bias-T). The Radio Frequency (RF) end of the Bias-T is connected with a low noise amplifier for signal output. Rp1, Rp2 and Rp Rpn in the figure represent the 1 st, 2 nd, … … th and nth parallel resistors, respectively.
As shown in fig. 3, the equivalent circuit diagram of a superconducting nanowire single photon detector for simultaneously realizing spatial resolution and photon number resolution is shown, each section of superconducting nanowire can be equivalent to an inductor connected in series with a variable resistor, the size of the inductor is determined by the dynamic inductance of the section of nanowire, the dynamic inductance is related to the length, the width, the thickness and the like of the nanowire, the variable resistor is caused by the heat island effect generated by incident photons, and the variable resistor is 0 when no incident photons exist.
When no photon is incident, the nanowire is in a superconducting state, the equivalent resistance is 0, and therefore the output end voltage is 0. When N (N is more than or equal to 1 and less than or equal to 6) photons respectively enter different regions, the nanowires in the corresponding regions absorb the photons to form heat islands, the heat islands are rapidly converted into normal states from superconducting states, and large impedance is generated, so that current is squeezed into the parallel resistors, the pulse amplitudes of output ends are reflected to be different, and the resolution on the number and the positions of the incident photons can be realized.
Corresponding electrical and thermal equations can be established according to the electrical and thermal principles of the circuit shown in fig. 3 and the serial nanowire photon-resolved detector.
The electrical equation is
Wherein,is the current of the bias current and is,is the current that flows through the nanowire or nanowires,is the current flowing through the parallel resistor,is a parallel resistor, and is characterized in that,is the equivalent resistance of the nanowire(s),is the equivalent resistance of the superconducting state nanowire,is a load resistance, and is,is the dynamic inductance of the whole segment of the nanowire,is the dynamic inductance of the nanowire with photon response,is the equivalent capacitance at the output terminal,is composed ofThe value of the voltage across the two terminals,is time.
The thermal equation is
Wherein,in order to be the current density,is the temperature of the nano-wires,is the temperature of the substrate and is,is the thickness of the nano-wire,is the resistivity of the niobium nitride film,is the specific heat capacity of the niobium nitride film,is the boundary heat exchange coefficient between the niobium nitride film and the substrate,in order to obtain the thermal conductivity of the niobium nitride,the distance the thermal island has diffused along the nanowire.
And performing electric heating simulation according to the electric heating equation. Setting initial conditions: superconducting transition temperature T of niobium nitride film with thickness of 6nm and line width of 100nmc=7.0K, sheet resistance Rsquare=300 Ω, dynamic inductance L of each nanowire segmentk=100nH, critical current Ic =14 μ a at absolute zero, bias current 12 μ a at 2.0K, and refrigerator background temperature Tbg=2.0K, the load of the low noise amplifier is equivalently 1M Ω.
When there are 3 parallel resistors, the ratio of the resistance values of the 3 resistors can be taken as Rp1：Rp2：Rp3= 1/4: 1/2: 1, taking the square resistance as 100 Ω, the corresponding resistance value is 25 Ω: 50 Ω: 100 omega. When the number of incident photons is 1-3, the equivalent resistance of the nanowire is as shown in FIG. 4, which is approximately proportional to the number of incident photons; the incident positions of the photons are different, the corresponding output voltages are also different, the corresponding relationship between the resistance and the positions is shown in table 2, and the corresponding output pulse amplitudes when different numbers of photons are incident to different positions are shown in fig. 5. The number of incident photons and their location can be distinguished from the amplitude of the pulse.
When there are 4 parallel resistors, the ratio of the resistance values of the 4 resistors can be taken as Rp1：Rp2：Rp3：Rp4= 1/4: 1/2: 1: 2, taking the square resistance as 100 Ω, the corresponding resistance value is 25 Ω: 50 Ω: 100 Ω: 200 Ω. When the number of incident photons is 1-4, the equivalent resistance of the nanowire is as shown in FIG. 6, which is approximately proportional to the number of incident photons; the incident positions of the photons are different, the corresponding output voltages are also different, the corresponding relationship between the resistance and the positions is shown in table 3, and the corresponding output pulse amplitudes when different numbers of photons are incident to different positions are shown in fig. 7. The number of incident photons and their location can be distinguished from the amplitude of the pulse.
Fig. 8 is a process flow diagram of the serial nanowire photon-resolved detector. Firstly, preparing a niobium nitride film by magnetron sputtering, and growing silicon dioxide (SiO) with the thickness of 250nm on two sides2) A niobium nitride film is grown on the silicon (Si) substrate as shown in (1).
And secondly, manufacturing a nanowire pattern by electron beam exposure, and designing a meandering nanowire pattern. Spin-coating electron beam resist PMMA (polymethyl methacrylate), writing a nanowire pattern by electron beam exposure as shown in (2), and obtaining the nanowire by reactive ion etching as shown in (3).
And thirdly, photoetching to form a gold electrode mask through double-layer photoresist, growing a 10nm titanium film, then growing a 100nm gold film and finally stripping the gold electrode in order to enhance the adhesion of the gold film, as shown in (4).
And fourthly, etching redundant niobium nitride. And (3) performing single-layer photoresist photoetching to form an etching mask, performing reactive ion etching to remove the redundant niobium nitride film, wherein the etching time is 45s, and finally removing the photoresist, as shown in (5).
And fifthly, photoetching to manufacture the titanium resistor. And (3) performing double-layer photoresist photoetching to prepare a resistance mask, preparing a titanium film with the square resistance of 100 omega by controlling the growth time of titanium, and finally peeling to obtain the titanium resistors with different resistance values, wherein the resistance value proportion of the titanium resistors meets the proportion relation shown in the table 1, as shown in (6).
And sixthly, photoetching to form an optical resonant cavity. Double-layer photoresist is used for photoetching as a mask of an optical resonant cavity, and silicon oxide (SiO) with the thickness of 240nm is prepared by chemical vapor deposition at the low temperature of 50 DEG Cx) And (4) growing a gold reflecting layer with the thickness of 100nm as shown in (7) and finally stripping the optical resonant cavity as shown in (8).
As shown in fig. 9, the measurement system of the serial nanowire photon-resolved detector (PNR-SNSPD) is divided into an optical path system, a circuit system and a GM refrigerator. The coupled optical fiber is used for carrying out light focusing, the series nanowire photon resolution detector after light focusing is arranged in a GM refrigerator, the temperature is reduced to 2.0K, and the series nanowire photon resolution detector can be ensured to continuously work in a low-temperature environment. The optical path system consists of a picosecond pulse laser source, an optical fiber coupler, an optical power meter, an adjustable optical power attenuator, a polarization controller and the like. The picosecond pulse laser source can provide a laser signal with the wavelength of 1550nm, two beams of light with the same power are separated through the optical fiber coupler, one path of light is connected with the optical power meter and used for monitoring the incident light power, and the other path of light is connected with the adjustable optical power attenuator and is connected with the series nanowire photon resolution detector through the polarization controller. The circuit system comprises a constant current source, a Bias-T, a low noise amplifier, a photon counter, a high-speed broadband oscilloscope and the like. The constant current source provides a stable Bias current for the device, the constant current source is formed by connecting a constant voltage source and a resistor of 100k omega in series, the constant current source is connected through a DC end of the Bias-T, and an RF end of the Bias-T is connected with the radio frequency low noise amplifier to amplify an output signal. A photon counter is used to record the number of response pulses over a period of time and an oscilloscope is used to observe the amplitude of the pulses. The photon counter is connected with a computer (PC), and a constant voltage source is controlled by the PC to provide proper bias current for the serial nanowire photon resolution detector.
Claims (8)
1. A superconducting nanowire single photon detector is characterized by comprising N superconducting nanowire units connected in series, N parallel resistors with different resistance values and an optical resonant cavity, wherein the N resistors with different resistance values are respectively connected in parallel at two ends of the N superconducting nanowire units, and the optical resonant cavity covers the upper layers of the N superconducting nanowire units connected in series; the N parallel resistors with different resistance values are prepared from titanium thin films, the thickness of the titanium thin films is the same, the parallel resistors with different resistance values are obtained by changing the length-width ratio of the resistor structure, and the resistance values of the resistors meet the following proportional relation: when N is takenAt time 2, the resistance value is 1/2: 1; when N takes 3, the resistance value of the resistor is 1/4: 1/2: 1; when N takes 4, the resistance value of the resistor is 1/4: 1/2: 1: 2; when N is any integer value greater than or equal to 5, the resistance value of the resistor is 1/4: 3/8: 1/2: 1: 2: 4: …: 2N-4The proportional relationship of (c).
2. The superconducting nanowire single photon detector of claim 1, wherein N is any integer value greater than or equal to 2.
3. The superconducting nanowire single photon detector of claim 1, wherein the optical resonant cavity is formed by laminating a lower silicon oxide dielectric layer and an upper gold reflective layer, the thickness of the silicon oxide dielectric layer has a relation λ/(4 η) with the detection wavelength λ, and η is the refractive index of silicon oxide.
4. The superconducting nanowire single photon detector of claim 3, wherein the thickness of the silicon oxide dielectric layer is 240nm, and the thickness of the gold reflective layer is 100 nm.
5. A method of preparing the superconducting nanowire single photon detector of claim 1, comprising the steps of:
step one, preparing a niobium nitride film by magnetron sputtering: growing a niobium nitride film with the thickness of 6-8nm on a silicon substrate with silicon dioxide with the thickness of 250nm growing on the two sides;
secondly, manufacturing a nanowire graph by electron beam exposure: designing a meandering nanowire pattern, wherein the width of the nanowire is 80nm, the duty ratio is 1/3, and the whole covered by the nanowire is square; spin-coating an electron beam resist, writing a nanowire pattern through electron beam exposure, and then obtaining a nanowire through reactive ion etching, wherein the etching time is 30 s;
thirdly, photoetching to form electrodes: manufacturing a gold electrode mask by double-layer photoresist photoetching, firstly growing a titanium film, then growing a gold film, and finally stripping an electrode;
fourthly, etching redundant niobium nitride: photoetching the single-layer photoresist to form an etching mask, etching the redundant niobium nitride film by reactive ions for 45s, and finally removing the photoresist;
fifthly, photoetching to obtain a titanium resistor: the double-layer photoresist is used for photoetching to make a resistance mask, a titanium film with the square resistance of 100 omega is prepared by controlling the growth time of titanium, and finally the titanium resistance with different resistance values is obtained by stripping;
sixthly, photoetching to form an optical resonant cavity: double-layer photoresist is photoetched to be used as a mask of the optical resonant cavity, a silicon oxide dielectric layer is prepared by using chemical vapor deposition, a gold reflecting layer is grown on the silicon oxide dielectric layer, and finally the optical resonant cavity is stripped;
the resistance values of the titanium resistors with different resistance values meet the following proportional relation: when N takes 2, the resistance value of the resistor is 1/2: 1; when N takes 3, the resistance value of the resistor is 1/4: 1/2: 1; when N takes 4, the resistance value of the resistor is 1/4: 1/2: 1: 2; when N is any integer value greater than or equal to 5, the resistance value of the resistor is 1/4: 3/8: 1/2: 1: 2: 4: …: 2N-4The proportional relationship of (c).
6. The method for preparing superconducting nanowire single photon detector according to claim 5, wherein the thickness of the titanium thin film is 10nm and the thickness of the gold thin film is 100 nm.
7. The method for preparing a superconducting nanowire single photon detector as claimed in claim 5, wherein the thickness of the silicon oxide dielectric layer is 240nm, and the thickness of the gold reflective layer is 100 nm.
8. The method for preparing superconducting nanowire single photon detector according to claim 5, wherein in the sixth step, the silicon oxide dielectric layer is prepared by chemical vapor deposition at 50 ℃ in low temperature environment.
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