Terahertz single-photon detection unit and array type detection device

Abstract

The invention discloses a terahertz single-photon detection unit and an array type detection device, the terahertz single-photon detection unit comprises a resonator, a superconductive tunnel junction and a terahertz photon absorber, and the resonator and the terahertz photon absorber are connected through a gate capacitor and the superconductive tunnel junction; the resonator comprises a circular spiral inductor and an interdigital capacitor, and a circular spiral inductor connecting part is led out from the extension position of the outer periphery of the circular spiral inductor and connected with the top of the interdigital capacitor. According to the invention, a circular spiral inductor structure is adopted, the quality factor of the resonator is effectively improved, and the sensitivity of a detector to signals causing phase shift is enhanced. The array type detection device comprises a plurality of detection units with different resonant frequencies, signals of the detection units are coupled to a central feeder line, and a reading system is simple. According to the terahertz array type detection device disclosed by the invention, terahertz detection in a wide frequency band range can be realized; the detection sensitivity is extremely high, and terahertz single photons can be detected and counted.

Description

Technical Field

[0001] The present invention relates to the field of terahertz single-photon signal detection, and in particular to a terahertz single-photon detection unit and an array detection device. Background Art

[0002] Terahertz waves generally refer to electromagnetic waves with a frequency range of 0.1-10THz, corresponding to photon energy of 0.4-41.4meV, which is between millimeter waves and far infrared, and is at the intersection of microelectronics and photonics technology. Based on the non-destructive, penetrating, fingerprint characteristics, and wide bandwidth characteristics of terahertz waves, terahertz technology has important application prospects in biomedicine, deep space communications, national defense and security inspection, material science and other fields. High-performance detectors are one of the key components for the development of terahertz technology. Since the photon energy in the terahertz band is low and the propagation in the atmosphere will be greatly attenuated due to the absorption of water vapor, high-sensitivity detectors based on low-temperature superconducting technology are currently the hot spots in terahertz detector research.

[0003] Common superconducting terahertz detectors include superconducting tunnel junction detectors (SIS), superconducting transition edge junction detectors (TES), superconducting hot electron thermal bolometers (HEB), and superconducting microwave dynamic inductance detectors (MKID). However, as the requirements for detector imaging quality, spectral resolution, and other indicators continue to increase, the development of new detectors with single-photon detection capabilities has become the current development direction. The superconducting quantum capacitance detector (QCD) has demonstrated excellent performance in terahertz single-photon detection and is the most sensitive superconducting terahertz detector verified to date. At present, research on QCD is in its infancy, and the performance of terahertz single-photon counting and imaging using QCD needs to be further improved. Summary of the invention

[0004] Purpose of the invention: The present invention aims to provide a terahertz single-photon detection unit that improves the performance of a superconducting quantum capacitance detector in counting and imaging terahertz single photons; another purpose of the present invention is to provide an array detection device comprising the terahertz single-photon detection unit.

[0005] Technical solution: The terahertz single-photon detection unit described in the present invention includes a resonator and a terahertz photon absorber, and the resonator and the terahertz photon absorber are connected through a gate capacitor and a superconducting tunnel junction; the resonator includes a circular spiral inductor and a forked-finger capacitor, and a circular spiral inductor connection part extends from the outer circumference of the circular spiral inductor and is connected to the top of the forked-finger capacitor.

[0006] Furthermore, the circular spiral inductor starts from the center of the circle and expands outward in a clockwise direction upward and downward respectively, and the two spiral lines are parallel, the line widths of the spiral lines are consistent, and the line spacing remains unchanged.

[0007] Furthermore, the circular spiral inductor connecting portion is formed by vertically extending two parallel lines with the same line width and line spacing from the end of the outermost circle of the circular spiral inductor, and connected to the interdigital capacitor portion after being vertically bent twice.

[0008] Furthermore, the number of circular spiral coils of the circular spiral inductor is determined by the resonant frequency of the resonator.

[0009] Furthermore, the gate capacitor includes a lateral gate, a vertical gate and a bottom connection portion of the interdigital capacitor.

[0010] Furthermore, the superconducting tunnel junction includes a bottom layer, a middle layer and a top layer from bottom to top, the bottom layer is a convex structure, and the convex part of the bottom layer is connected to the bottom of the vertical gate. The concave part of the bottom layer is constructed at the center of the upper edge line of the terahertz photon absorber, that is, the concave part of the bottom layer of the superconducting tunnel junction is the terahertz photon absorber film and its extension.

[0011] Preferably, the bottom layer and the top layer are made of superconducting material aluminum, and the middle layer is a thin oxide layer of superconducting material aluminum, with a thickness not exceeding 3 nanometers and a resistance not less than 6.15 kΩ.

[0012] Furthermore, the terahertz photon absorber is composed of a plurality of periodic unit arrays, wherein the periodic unit is two T-shaped structures arranged opposite to each other; a row of half periodic units is mirrored at the top and bottom of the terahertz photon absorber, respectively. The terahertz photon absorber is made of superconducting aluminum.

[0013] The array detection device of the present invention comprises a substrate and a receiving circuit arranged thereon, wherein the receiving circuit comprises a coplanar waveguide, a coplanar waveguide ground plane and the above-mentioned terahertz single-photon detection unit, wherein the coplanar waveguide comprises a central feeder and a feeder connector connected to both ends of the central feeder; the central feeder, the feeder connector and the terahertz single-photon detection unit are surrounded by the coplanar waveguide ground plane and are insulated and separated from the coplanar waveguide ground plane; there are N×M terahertz single-photon detection units, which are arranged in N×M rows and columns to form a resonant detection unit array; the central feeder is arranged in a zigzag shape, interspersed back and forth between rows or columns of the terahertz single-photon detection units, the central feeder portion located outside the circular spiral inductor of the terahertz single-photon detection unit is arc-shaped, and the upper edge of the circular spiral inductor forms a coupling capacitor with the central feeder portion and the coplanar waveguide ground plane.

[0014] Furthermore, the coplanar waveguide ground plane, the wire binding pad of the feeder connector, the central feeder and the resonator all include superconducting niobium thin films.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The present invention adopts a circular spiral inductor structure, which expands the area of ​​coupling between the resonator and the central feeder and enhances the strength of signal coupling; at the same time, the circular spiral inductor structure does not have square corners, so that the surrounding magnetic field distribution is more uniform, which reduces parasitic capacitance and resistance loss; effectively improves the quality factor of the resonator and enhances the sensitivity of the detector to signals causing phase shift; 2. The present invention can flexibly adjust the resonant frequency of the resonator by adjusting the finger length of the resonator interdigital capacitor and the number of windings of the circular spiral inductor, and ensures that the area and coupling strength of each resonator unit are the same; 3. The superconducting The tunnel junction is directly connected to one end of the gate capacitor vertically through the central arm, ensuring that the quantum capacitance change is effectively coupled to the resonator; 4. Compared with the existing grid structure, the T-shaped structure of the terahertz photon absorber can promote a stronger near-field interaction between the terahertz wave and the absorber structure, effectively enhancing the absorption efficiency of photons; 5. Different detection pixels of the detector array of the present invention are designed with different resonant frequencies, coupled to a central feed line, and the signal is read out by frequency division multiplexing. The readout system is simple and easy to array. The terahertz array detection device can realize terahertz detection in a wide bandwidth range; it has extremely high sensitivity and can detect and count terahertz single photons. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the structure of a terahertz single-photon detection unit;

[0017] Figure 2 It is a structural schematic diagram of an array detection device;

[0018] Figure 3 Schematic diagram of the structure of the terahertz photon absorber;

[0019] Figure 4 for Figure 3 Enlarged view of the dotted box;

[0020] Figure 5 Schematic diagram of the cross section of a superconducting tunnel junction. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings.

[0022] The terahertz single photon detection unit 2 of the present invention includes a silicon substrate, a terahertz photon absorber 3, a superconducting tunnel junction 323, and a resonator 20. The resonator 20 is composed of a circular spiral inductor and a forked finger capacitor 24. The circular spiral inductor has a line width of 4 μm, a line spacing of 3 μm, and an isolation section 22 of the coplanar waveguide ground plane 11 between the circular spiral inductor and the center feed line 130 has a line width of 4 μm. The number of winding turns of the circular spiral inductor is adjustable. The upper edge 21 of the circular spiral inductor forms a coupling capacitor with the isolation section 22 of the center feed line 130 and the coplanar waveguide ground plane 11. The line width of the forked finger capacitor 24 is 4 μm, the line length is 400 μm, and the line spacing is 3 μm. The line length of the bottom finger 25 of the forked finger capacitor is adjustable. The distance between the left arm 23 of the forked finger capacitor and the edge of the slot 14 in which it is located is 10 μm.

[0023] The terahertz single-photon detection unit 2 is surrounded by the coplanar waveguide ground plane 11, and the terahertz single-photon detection unit 2 forms an independent closed circuit. The terahertz single-photon detection unit 2 and the coplanar waveguide 13 constructed by the central feed line 130 transmit signals through the coupling relationship between the two. Since the terahertz single-photon detection unit 2 and the central feed line 130 are isolated by the ground isolation section 22, a coupling capacitor is formed. Therefore, there is a weak coupling relationship between the coplanar waveguide 13 and the terahertz single-photon detection unit 2, that is, the coupling coefficient is less than 1.

[0024] In this embodiment, the coplanar waveguide ground plane 11, the wire binding pad 121, the central feed line 130 and the resonator 20 are preferably made of a superconducting thin film niobium film with a thickness of 200 nm, and the superconducting critical transition temperature is about 9.3K.

[0025] like Figure 3 As shown, the area of ​​the entire grid of the terahertz photon absorber 3 is 60×60 μm 2 , consisting of periodic units 31, the longitudinal units are closely connected; the transverse units are separated by a distance 33. The width of all lines constituting the terahertz photon absorber is 100nm. The length of the length 311 of the periodic unit 31 is 6μm, and the length of the width 310 is 5μm. The distance between the left, right and bottom edges of the terahertz photon absorber and the groove 14 is 100nm.

[0026] Figure 4 for Figure 3 The enlarged view of the position 32 in the middle. The gate capacitor is composed of a horizontally elongated horizontal gate 321 and a cross-finger capacitor bottom connection portion 324 parallel to the lower edge of the resonator. A vertical gate 322 extends from the horizontal center of the horizontal gate 321 to form a T-shaped structure. The superconducting tunnel junction 323 connects the vertical gate 322 of the gate capacitor and the upper edge of the absorber respectively.

[0027] Figure 5It is a superconducting tunnel junction 323, including a bottom layer 3233 of the tunnel junction superconductor, a top layer 3231 and an intermediate layer 3232 located between the bottom layer and the top layer. The bottom layer 3234 is connected to the vertical gate 322; the bottom layer 3233 is the film at the center of the upper edge line 34 of the terahertz absorber and its extension. Figure 5 The part within the dotted line box 3233 is Figure 4 The film at the center of the upper edge line 34 of the medium terahertz absorber. The bottom layer and the top layer are preferably aluminum films, and the superconducting critical transition temperature is about 1.2K. The middle layer 3232 is made of aluminum oxide film, which is a non-superconducting material, and its thickness does not exceed the Cooper electron pair coherence length, preferably 1nm. The resistance value of the middle layer 4223 is not less than the quantum resistance 6.15kΩ.

[0028] The arrayed superconducting quantum capacitance detector 1 of the present invention comprises a substrate 10 and a receiving circuit arranged on the substrate. The substrate 10 is made of high-resistance silicon with a resistivity of ≥10 kΩ·cm and a thickness of 500 μm. The detection circuit comprises a coplanar waveguide 13, a coplanar waveguide ground plane 11 and a terahertz single-photon detection unit 2. The coplanar waveguide 13 comprises a central feed line 130 and a feed line connector 12 connected to the end of the central feed line. The central feed line, the feed line connector and the terahertz single-photon detection unit are surrounded by the coplanar waveguide ground plane 11 and are insulated from the coplanar waveguide ground plane.

[0029] Among them, the center feeder 130 is arranged in the center feeder slot 131, and the gap between the center feeder and the edges of the center feeder slot is used to achieve insulation isolation from the coplanar waveguide ground plane 11. The feeder connector 12 includes a wire binding pad 121, which is arranged in a pad slot 122, and the wire binding pad is used to achieve insulation isolation from the coplanar waveguide ground plane through the gap between the wire binding pad and the pad slot edge. The pad slot 122 is connected to the center feeder slot 131, and the wire binding pad 121 is connected to the center feeder 130. There are two feeder connectors 12, and the two feeder connectors 12 are respectively located at the two ends of the center feeder 130. Correspondingly, there are also two wire binding pads 121, wherein the wire binding pad 121 at one end is used for inputting the resonant signal, and the wire binding pad 121 at the other end is used for outputting the detection signal. In this example, the line width of the center feeder 130 is 20μm, and the distance from the edge of the center feeder to the edge of the feeder slot is 12μm.

[0030] The terahertz single photon detection units 2 have MхN (M, N is greater than or equal to 1), which are evenly arranged in MхN rows and columns to form a detector array. The central feed line 130 is arranged in a zigzag pattern, interspersed between the rows and the edges of the columns of the resonant detection unit array. In this embodiment, M is 2, N is 2, that is, a superconducting quantum capacitance detector array with 2 rows and 2 columns.

[0031] The working principle of this embodiment is as follows:

[0032] When the incident terahertz single photon signal within the working frequency band of the terahertz wave absorber 3 is received by the absorber, since the frequency of the received terahertz single photon signal is greater than the superconducting energy gap frequency of the quasiparticle library at the superconducting tunnel junction 323, the Cooper electron pairs in the quasiparticle library are broken up to generate quasiparticles. A quasiparticle tunnels to the superconducting island through the superconducting tunnel junction, changes the number of charges on the superconducting island, and translates the quantum capacitance trajectory e / Cg, and the quantum capacitance is reduced to the minimum at the degenerate point. That is, when a terahertz single photon signal is received, the quantum capacitance of the superconducting quantum capacitance detector will jump. The quantum capacitance is coupled to the resonator through the coupling capacitor. Therefore, if a microwave signal is input from the central feed line, the coupling of the equivalent coupling capacitor between the central feed line 13 and the resonant detection unit 2 causes each resonant detection unit to resonate at its own resonant frequency; when the absorber absorbs a photon, the quantum capacitance jumps, and the resonant frequency of the resonator changes. By measuring the phase change of the microwave transmission signal of the central feed line, the quantum capacitance change signal of the superconducting quantum capacitance detector can be detected. This is used to detect terahertz single-photon signals.

[0033] In this embodiment, the central operating frequency of the terahertz photon absorber is 4.5THz, which can be adjusted by changing the length, width, spacing and length and width of the constituent line segments of the unit 31. There are 7×7 detection units in the array detector device of this embodiment, and the resonant frequency of each detection unit 2 is different, that is, each detection unit has a different number of fingers or finger lengths of the left and right fingers of the interdigital capacitor and the number of spiral windings of the spiral inductor. In this embodiment, the resonant frequency of each detection unit is set between 0.5-4GHz, and the resonant frequency of each detection unit is approximately an arithmetic progression. The resonant frequency of adjacent resonant frequency detection units differs by about 5MHz, and the length and width of the detection unit are much smaller than one twentieth of the wavelength of the resonator resonant frequency. In order to avoid interference between channels, the detection units of adjacent resonant frequencies are arranged as far apart as possible in the detector array.

Claims

1. A terahertz single photon detection unit, characterized in that: The invention comprises a resonator (20) and a terahertz photon absorber (3), wherein the resonator (20) and the terahertz photon absorber (3) are connected via a gate capacitor and a superconducting tunnel junction (323); the resonator (20) comprises a circular spiral inductor and a forked-finger capacitor, and a circular spiral inductor connection portion is led out from the outer circumference of the circular spiral inductor and connected to the top of the forked-finger capacitor.

2. The terahertz single photon detection unit according to claim 1, characterized in that: The circular spiral inductor starts from the center of the circle and expands outward in a clockwise direction upward and downward respectively. The two spiral lines are parallel, the line widths of the spiral lines are consistent, and the line spacing is unchanged.

3. The terahertz single photon detection unit according to claim 2, characterized in that: The circular spiral inductor connecting portion is two parallel lines with the same line width and line spacing extending vertically from the end of the outermost circle of the circular spiral inductor, and is connected to the interdigital capacitor portion after being vertically bent twice.

4. The terahertz single photon detection unit according to claim 1, characterized in that: The number of the circular spiral coils of the circular spiral inductor is determined by the resonant frequency of the resonator.

5. The terahertz single photon detection unit according to claim 1, characterized in that: The gate capacitor comprises a lateral gate (321), a vertical gate (322) and an interdigital capacitor bottom connection portion (324).

6. The terahertz single photon detection unit according to claim 5, characterized in that: The superconducting tunnel junction (323) comprises a bottom layer (3233), an intermediate layer (3232) and a top layer (3231) in order from bottom to top, the bottom layer (3233) is a convex structure, and the convex portion (3234) of the bottom layer is connected to the bottom of the vertical gate (322).

7. The terahertz single photon detection unit according to claim 6, characterized in that: The bottom layer (3233) and the top layer (3231) are made of superconducting material A, and the middle layer (3232) is a thin oxide layer of superconducting material A with a thickness not exceeding 3 nanometers and a resistance not less than 6.15 kΩ.

8. The terahertz single photon detection unit according to claim 1, characterized in that: The terahertz photon absorber (3) is composed of a plurality of periodic units (31) distributed in an array, wherein the periodic units (31) are two T-shaped structures arranged opposite to each other; a row of half periodic units (31) are respectively mirror-imaged at the top and bottom of the terahertz photon absorber (3).

9. An array detection device, comprising a substrate (10) and a receiving circuit arranged thereon, characterized in that: The receiving circuit comprises a coplanar waveguide (13), a coplanar waveguide ground plane (11) and the terahertz single-photon detection unit according to claims 1 to 8, wherein the coplanar waveguide (13) comprises a central feed line (130) and a feed line connector (12) connected to both ends of the central feed line (130); the central feed line (130), the feed line connector (12) and the terahertz single-photon detection unit (2) are surrounded by the coplanar waveguide ground plane (11) and are connected to the coplanar waveguide ground plane (11). ) are insulated and separated; the terahertz single-photon detection units (2) have N×M numbers, which are arranged in N×M rows and columns to form a resonant detection unit array (130); the central feed line (11) is arranged in a zigzag pattern, interlaced back and forth between the rows or columns of the terahertz single-photon detection units (2); the central feed line portion located outside the circular spiral inductor of the terahertz single-photon detection unit (2) is arc-shaped, and the upper edge of the circular spiral inductor forms a coupling capacitor with the central feed line portion and the coplanar waveguide ground plane.

10. The array detection device according to claim 9, characterized in that: The coplanar waveguide ground plane, the wire binding pad of the feeder joint, the central feeder and the resonator all include superconducting niobium thin films.

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