Terahertz superconducting dynamic inductance detector based on silicon nitride film and preparation method thereof

Abstract

The application discloses a terahertz superconducting dynamic inductance detector based on a silicon nitride film and a preparation method thereof. The detector comprises a substrate, a terahertz superconducting dynamic inductance detector pixel array and a substrate hole array. The substrate is a silicon substrate with a silicon nitride film on the upper and lower surfaces. The substrate hole array is arranged on the lower surface of the substrate and is obtained by removing the silicon substrate and the silicon nitride film on the lower surface of the silicon substrate. The silicon nitride film on the upper surface of the substrate is arranged between the substrate hole array and the terahertz superconducting dynamic inductance detector pixel array. The resonant frequencies of each unit of the terahertz superconducting dynamic inductance detector pixel array are different, which facilitates frequency division multiplexing technology to read out. The substrate hole array is arranged below the position of the meander inductance of each unit of the terahertz superconducting dynamic inductance detector pixel array, which can improve the responsivity to photons and further improve the detection sensitivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detectors, in particular to a terahertz superconducting dynamic inductance detector based on a silicon nitride film and a preparation method thereof. BACKGROUND

[0002] The terahertz wave band is located between the microwave wave band and the visible light wave band, and the corresponding frequency range is generally defined as 0.1 THz to 10 THz. Since the peak value of the cosmic microwave background radiation (CMB) and the photon energy of a large part of the cosmic space are in the terahertz wave band, the terahertz wave band contains rich astronomical information, and is of great significance for studying the evolution of the universe, the formation of stars and planets.

[0003] The lumped element KID (LEKID) has made great progress in the fields of astronomical imaging and single-photon detection due to its simple preparation process and the adoption of frequency division multiplexing readout technology, which is convenient for large array readout. However, the existing superconducting dynamic inductance detectors generally have defects such as low detection sensitivity and large noise. SUMMARY

[0004] The purpose of the present application is to provide a terahertz superconducting dynamic inductance detector based on a silicon nitride film which can improve the detection sensitivity, and another purpose of the present application is to provide a preparation method of the terahertz superconducting dynamic inductance detector.

[0005] The technical scheme of the present application is as follows: the terahertz superconducting dynamic inductance detector based on a silicon nitride film comprises: a substrate, which is a silicon substrate with a silicon nitride film on the upper and lower surfaces; a terahertz superconducting dynamic inductance detector pixel array deposited on the upper surface of the substrate; and a substrate hole array, which is provided on the lower surface of the substrate with the terahertz superconducting dynamic inductance detector pixel array as a reference, and is obtained by removing the silicon substrate and the silicon nitride film on the lower surface of the silicon substrate, and the silicon nitride film on the upper surface of the substrate between the substrate hole array and the terahertz superconducting dynamic inductance detector pixel array.

[0006] Further, each detector pixel unit of the terahertz superconducting dynamic inductance detector pixel array comprises: a resonator circuit, which changes the resonant frequency by receiving incident light, thereby characterizing the detection of the incident light signal; and a coplanar waveguide feed line, which is composed of a center feed line and a ground plane, and is coupled with the resonator circuit to frequency-division multiplex the resonant frequency of the resonator circuit to an external frequency detection device, so as to detect the change of the resonant frequency by the external frequency detection device, thereby characterizing the detection of the incident light signal by the resonator circuit.

[0007] Further, the resonator circuit comprises: a meander inductor, which breaks Cooper pairs to generate quasi-particles by receiving incident light energy at terahertz frequency, thereby generating a change in dynamic inductance; and a forked-toe capacitor, which is connected with the meander inductor, and together with the meander inductor, forms the resonator circuit, which is coupled with the coplanar waveguide feed line, and the change in dynamic inductance of the resonator circuit causes a change in resonant frequency of the resonator circuit, and the change in resonant frequency is transmitted to an external frequency detection device through the coplanar waveguide feed line. Wherein, modifying the number of forked-toe capacitors changes the resonant frequency of the resonator circuit.

[0008] Further, the superconducting metal used in the terahertz superconducting dynamic inductance detector pixel array includes tantalum, aluminum or niobium.

[0009] Preferably, the material used in the meander inductor part is aluminum, and the materials used in the remaining parts are tantalum.

[0010] Further, the thickness of the silicon substrate is 300-500 um; the thickness of the silicon nitride film is 100-300 nm, the depth of the hole array of the silicon substrate is 300-500 um; and the thickness of the terahertz superconducting dynamic inductance detector pixel array is 40-200 nm.

[0011] The preparation method of the above-mentioned terahertz superconducting dynamic inductance detector based on a silicon nitride film comprises the following steps:

[0012] (1) A superconducting metal film is grown on the upper surface of a substrate using a magnetron sputtering device, and a terahertz superconducting dynamic inductance detector pixel array is prepared by laser direct writing technology, reactive ion etching technology, electron beam exposure process and stripping process on the obtained superconducting metal film layer;

[0013] (2) The silicon nitride film at the position corresponding to the terahertz superconducting dynamic inductance detector pixel array on the lower surface of the substrate is removed by laser direct writing technology and reactive ion etching technology; then the position of the silicon substrate exposed by the silicon nitride film on the lower surface of the substrate is exposed by chemical etching of the silicon nitride film on the lower surface of the substrate with potassium hydroxide solution, a hole array of the substrate is obtained by the hole digging process, and finally a terahertz superconducting dynamic inductance detector based on a silicon nitride film is prepared.

[0014] Further, after the reactive ion etching technology treatment, the process of cleaning the residual photoresist with an organic solvent is further included; the organic solvent is N-methyl pyrrolidone, isopropyl alcohol, acetone and anhydrous ethanol.

[0015] Invention principle: The superconducting dynamic inductance detector is a microwave resonator made of superconducting thin film, and its working mechanism is related to the complex impedance change of the superconducting thin film. The present application reads out the complex impedance change of the superconducting thin film with the help of the resonator. When the incident photon energy is higher than twice the superconducting energy gap, the absorbed photons will break the Cooper pairs into quasi-particles, and the increase in the number of quasi-particles in the superconducting thin film will change the surface impedance of the superconducting thin film, resulting in a shift of the resonant frequency of the microwave resonator to low frequency and a decrease in the quality factor (Q value). The detection of the incident photon signal can be realized by detecting the phase shift of the microwave resonant signal.

[0016] When the photons incident on the superconducting thin film destroy the Cooper pairs and generate quasi-particles, phonons will also be released, and the phonons carry part of the energy. If the silicon substrate is directly below the superconducting thin film, the phonons will dissipate into the silicon substrate, and the energy carried by the phonons is lost. In the present application, the area for sensing photons is the meander inductance part of the terahertz superconducting dynamic inductance detector pixel array composed of aluminum metal. The present application realizes the removal of the silicon substrate directly below the meander inductance by means of a substrate hole array, and only a layer of silicon nitride film is retained. Thus, most of the phonons generated by the meander inductance part cannot dissipate into the silicon substrate, and this part of the energy is retained, further improving the responsivity of the device to photons and thus improving the sensitivity of the device.

[0017] In the present application, the terahertz superconducting dynamic inductance detector pixel array is composed of several resonator circuits with different resonant frequencies, and the resonant frequencies are realized by modifying the number of forked capacitors of the resonator circuit. The meander inductance part of the resonator circuit adopts the same period structure and is designed for detecting the same terahertz frequency. The resonator circuit is composed of forked capacitors and meander inductance based on lumped structure. The meander inductance part is composed of a unit period structure, and the appearance outline is approximately a rectangular area of 80um*90um. The terahertz superconducting dynamic inductance detector has high sensitivity in detecting terahertz band signals, and frequency division multiplexing technology is adopted for easy reading out.

[0018] Advantages: Compared with the prior art, the present application has the following advantages: (1) The resonant frequencies of each unit of the terahertz superconducting dynamic inductance detector pixel array are different, which facilitates the use of frequency division multiplexing technology for reading out; (2) The silicon substrate hole structure is realized below the position of the meander inductance of each unit of the terahertz superconducting dynamic inductance detector pixel array, which can improve the responsivity of the superconducting dynamic inductance detector to photons and thus improve its detection sensitivity. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a cross-sectional schematic view of a new terahertz superconducting dynamic inductance detector based on a silicon nitride film in Example 1;

[0020] Figure 2 This is a flowchart of the fabrication method of the novel terahertz superconducting dynamic inductive detector based on silicon nitride thin film in Example 1;

[0021] Figure 3 This is a schematic diagram of the array structure of the novel terahertz superconducting dynamic inductive detector based on silicon nitride thin film in Example 1.

[0022] Figure 4 yes Figure 3 Enlarged view of a single unit 13 of the middle detector pixel array;

[0023] Figure 5 yes Figure 4 Enlarged view of the meandering inductor section 24 of the resonator circuit;

[0024] Figure 6 These are images of the detector taken under an optical microscope at different magnifications. Detailed Implementation

[0025] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0026] Example 1: As Figure 1 As shown, the novel terahertz superconducting dynamic inductor detector based on silicon nitride thin film provided in this embodiment includes a substrate, a terahertz superconducting dynamic inductor detector pixel array deposited on the upper surface of the substrate, and a substrate hole array 6. The substrate includes, from top to bottom, an upper silicon nitride thin film 1 disposed on the upper surface of a silicon substrate 2, a silicon substrate 2, and a lower silicon nitride thin film 3 disposed on the lower surface of the silicon substrate 2. The terahertz superconducting dynamic inductor detector pixel array includes a tantalum metal thin film 4 and an aluminum metal thin film 5. The upper silicon nitride thin film 1 on the upper surface of the silicon substrate is located between the substrate hole array 6 and the terahertz superconducting dynamic inductor detector pixel array.

[0027] Each detector pixel unit of the aforementioned terahertz superconducting dynamic inductive detector pixel array includes: a resonator circuit, which receives incident light and causes a change in its resonant frequency, thereby characterizing the detection of the incident light signal; and a coplanar waveguide feed line, which consists of a center feed line and a ground plane. The coplanar waveguide feed line is coupled to the resonator circuit, and the resonant frequency of the resonator circuit is frequency-division multiplexed to an external frequency detection device. The external frequency detection device detects the change in the resonant frequency, thereby characterizing the resonator circuit's detection of the incident light signal.

[0028] The resonator circuit comprises: a meander inductance which, by receiving incident light energy at terahertz frequency, destroys Cooper pairs to generate quasi-particles, thereby generating a change in dynamic inductance; and a forked capacitor which is connected with the meander inductance, both of which together constitute a resonator circuit which is coupled with a coplanar waveguide feed line, the change in dynamic inductance of the resonator circuit causes a change in resonator frequency, and the resonator frequency change information is transmitted to an external frequency detection device through the coplanar waveguide feed line. Wherein, modifying the number of forked capacitors will change the resonant frequency of the resonator circuit.

[0029] As shown in Figure 2 , the preparation method of the above-mentioned new type of terahertz superconducting dynamic inductance detector based on silicon nitride film is as follows:

[0030] (a) The original silicon wafer with a silicon substrate thickness of 300-500um and a silicon nitride film thickness of 100-300nm on the upper and lower surfaces of the silicon substrate is cleaned by N-methyl pyrrolidone and isopropyl alcohol to remove impurities on the surface of the original silicon wafer;

[0031] (b) A tantalum metal film with a thickness of 100-200nm is grown on the surface of the silicon nitride film on the upper surface of the silicon substrate by magnetron sputtering;

[0032] (c) A photoresist is uniformly coated on the surface of the silicon nitride film on the lower surface of the silicon substrate, a corresponding pattern is left on the silicon nitride film on the lower surface of the silicon substrate by using laser direct writing technology and development technology, and the silicon nitride film in the corresponding area is removed by reactive ion etching technology, so that the silicon substrate is exposed;

[0033] (d) A photoresist is uniformly coated on the surface of the tantalum metal film, and a pattern of a terahertz superconducting dynamic inductance detector pixel array is left on the tantalum metal film by using photoetching, development and reactive ion etching technology, the pattern structure is as shown in Figure 3 and Figure 4 , the Figure 3 is an array structure diagram of the new type of terahertz superconducting dynamic inductance detector based on silicon nitride film, 11 is a coplanar waveguide feed line of the terahertz superconducting dynamic inductance detector pixel array, 12 is a square mark on the layout, and 13 is a single unit of the detector pixel array, Figure 4 is an enlarged view of the single unit 13 of the detector pixel array, in which 21 is a ground plane of the terahertz superconducting dynamic inductance detector pixel array, 22 is a forked capacitor part of the resonator circuit, 23 is a center feed line of the coplanar waveguide feed line, 24 is a meander inductance part of the resonator circuit, and 25 is a position of a silicon substrate hole array unit relative to the terahertz superconducting dynamic inductance detector pixel array unit, the structure of a single detector pixel unit is as shown in Figure 4 , at this time Figure 4 , the structures of 24 and 25 in Figure 4The center 23 is the center feed line of the coplanar waveguide, with a width of 16 um; Figure 4 The ground plane 21 is the ground plane, and the gap between the center feed line and the two sides of the ground plane is 10 um. Figure 5 The center 22 is the forked-toe capacitance part of the resonator circuit, with a length of 1000 um and a width of 4 um, and the two sides are longitudinally distributed with a gap of 10 um between each other. The width of the rest of the forked-toe capacitance is 10 um;

[0034] (e) The silicon wafer after the reaction ion etching is cleaned with N-methyl pyrrolidone and isopropyl alcohol, and the tantalum metal thin film surface is uniformly coated with electron beam exposure photoresist. The small size pattern of the meander inductor is left after electron beam exposure, and after development, 40 nm-50 nm aluminum metal thin film is grown by electron beam evaporation technology. Excess aluminum metal thin film is removed by peeling process, leaving only the meander inductor part, as shown in Figure 5 32 in FIG. 3, Figure 5 The center 31 is the connection part of the forked-toe capacitance and the meander inductor of the resonator circuit, 32 is the meander inductor, and 33 and 34 are part of the forked-toe capacitance of the resonator circuit. The width of the meander inductor aluminum line is 90-110 nm, Figure 6 The center 31 is the connection part of the forked-toe capacitance and the meander inductor, with a size of 2 um*4 um;

[0035] (f) Finally, the exposed silicon on the silicon nitride thin film on the lower surface of the silicon substrate is etched clean by potassium hydroxide solution, and a new type of terahertz superconducting dynamic inductance detector based on silicon nitride thin film is obtained. Place it under the optical microscope, light from the bottom, and take pictures at different magnifications, as shown in ​ The red square in the figure is the position of the hole array of the silicon substrate, the silicon nitride thin film is transparent, and the front aluminum metal meander inductor is not made.

Claims

1. A terahertz superconducting dynamic inductive detector based on a silicon nitride thin film, characterized in that, The application relates to a silicon substrate with a silicon nitride film on the upper and lower surfaces, a terahertz superconducting dynamic inductance detector pixel array deposited on the upper surface of the substrate, and a substrate hole array on the lower surface of the substrate, which is obtained by removing the silicon substrate and the silicon nitride film on the lower surface of the silicon substrate, and is referenced to the terahertz superconducting dynamic inductance detector pixel array. Each detector pixel unit of the terahertz superconducting dynamic inductance detector pixel array comprises a resonator circuit which changes the resonant frequency by receiving incident light, thereby representing detection of the incident light signal; and a coplanar waveguide feed line which is composed of a center feed line and a ground plane, is coupled with the resonator circuit, frequency-division multiplexes the resonant frequency of the resonator circuit to an external frequency detection device, detects the change of the resonant frequency by the external frequency detection device, and thereby represents detection of the incident light signal by the resonator circuit. The resonator circuit comprises a meander inductor which generates quasi-particles by destroying Cooper pairs by receiving incident light energy of a terahertz frequency, thereby generating a change of dynamic inductance; and a forked capacitor which is connected with the meander inductor and together forms the resonator circuit, is coupled with the coplanar waveguide feed line, and changes the resonant frequency of the resonator circuit, and transmits the information of the change of the resonant frequency to the external frequency detection device through the coplanar waveguide feed line. The material of the meander inductor is aluminum, and the material of the rest part is tantalum. The material of the terahertz superconducting dynamic inductance detector pixel array is superconducting metal, which comprises tantalum, aluminum or niobium. The thickness of the terahertz superconducting dynamic inductance detector pixel array is 40-200 nm. The thickness of the silicon nitride film is 100-300 nm, and the depth of the silicon substrate hole array is 300-500 um. The thickness of the silicon substrate is 300-500 um. The application comprises the following steps:

2. The terahertz superconducting dynamic inductive probe of claim 1, wherein, (1) growing a superconducting metal film on the upper surface of the substrate by using a magnetron sputtering device, and preparing the terahertz superconducting dynamic inductance detector pixel array by using a laser direct writing technology, a reactive ion etching technology, an electron beam exposure process and a stripping process on the obtained superconducting metal film layer; 3. The terahertz superconducting dynamic inductive probe of claim 1, wherein, (2) removing the silicon nitride film on the lower surface of the substrate corresponding to the position of the terahertz superconducting dynamic inductance detector pixel array by using the laser direct writing technology and the reactive ion etching technology; 4. The terahertz superconducting dynamic inductive probe of claim 1, wherein, and then chemically etching the silicon nitride film on the lower surface of the substrate by using a potassium hydroxide solution to expose the position of the silicon substrate, realizing the substrate hole process, obtaining the substrate hole array, and finally preparing the terahertz superconducting dynamic inductance detector based on the silicon nitride film.

5. The terahertz superconducting dynamic inductive probe of claim 4, wherein, The reactive ion etching technology processing further comprises a cleaning process, and an organic solvent is used to clean residual photoresist; the organic solvent is N-methyl pyrrolidone, isopropyl alcohol, acetone and anhydrous ethanol.

6. A method of fabricating a terahertz superconducting dynamic inductive detector based on a silicon nitride thin film as claimed in claim 1, characterized in that, ​ ​ ​ ​ 7. The production method according to claim 6, wherein ​

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