CN114583038A - NbN Josephson junction-based superconducting qubit structure and preparation method thereof - Google Patents

NbN Josephson junction-based superconducting qubit structure and preparation method thereof Download PDF

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CN114583038A
CN114583038A CN202210226252.0A CN202210226252A CN114583038A CN 114583038 A CN114583038 A CN 114583038A CN 202210226252 A CN202210226252 A CN 202210226252A CN 114583038 A CN114583038 A CN 114583038A
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josephson junction
layer
nbn
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张露
陈垒
王镇
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Shanghai Institute of Microsystem and Information Technology of CAS
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Abstract

The invention provides a superconducting qubit structure based on NbN Josephson junctions and a preparation method thereof, the superconducting qubit structure comprises a substrate, a buffer layer, a functional layer, an isolation layer, a first wiring part and a second wiring part, wherein the buffer layer is positioned on the upper surface of the substrate, the functional layer is positioned on the upper surface of the buffer layer and comprises capacitors, first Josephson junctions, second Josephson junctions and resonators which are arranged at intervals, the isolation layer fills gaps in the functional layer and covers the exposed surface of the functional layer and the upper surface of the substrate, a first contact hole and a second contact hole are formed in the isolation layer, the first wiring part is filled in the first contact hole and is in contact with the upper surface of the first Josephson junction, and the second wiring part is filled in the second contact hole and is in contact with the upper surface of the second Josephson junction. The invention reduces charge fluctuation in the substrate and enhances the coherence of superconducting qubits by adopting high-resistivity silicon as the substrate and an insulating TaN film as the junction area of the Josephson junction.

Description

NbN Josephson junction-based superconducting qubit structure and preparation method thereof
Technical Field
The invention belongs to the field of superconducting electronics, and relates to a superconducting qubit structure based on NbN Josephson junctions and a preparation method thereof.
Background
The superconducting qubit is a qubit based on a josephson junction circuit, the main part of which is a superconducting circuit containing one or more josephson junctions. The Josephson junction has the structure that a thin insulating layer is sandwiched between two superconductors, when the thickness of the insulating layer is as thin as a few nanometers, the phases of wave functions of the two superconductors are associated, the insulator also becomes a weak superconductor, and the Cooper pair can tunnel to form superconducting current. In this case, the josephson junction is equivalent to a nonlinear inductor, the inductance value of the josephson junction changes with the change of phase difference between two ends of the junction, and by utilizing the nonlinear inductor of the josephson junction and the macroscopic quantum effect characteristic in the superconductor, system energy levels with unequal intervals can be constructed, so that quantum states related to the lowest two energy levels can be well controlled by an external field. However, the superconducting qubit is greatly influenced by the external environment, so that it is difficult to maintain quantum coherence in long-time operation, and the decoherence time of the superconducting qubit is severely limited.
At present, the mainstream of the superconducting qubit circuit still adopts the traditional Al/AlOxa/Al junction whose de-coherence time is affected by amorphous AlOxSuppression of two-level systems in barrier layers. The NbN/AlN/NbN epitaxial nitride Josephson junction is used as a substitute material of a superconducting quantum circuit, the number of two-level systems in the Josephson junction can be reduced, and the epitaxial NbN Josephson junction has relatively high superconducting transition temperature (16K) and large superconducting energy gap (5.2 meV). But high quality epitaxial NbN/AlN/NbN junctions are generally confined to MgO substrates, whose coherence time is limited by the dielectric loss of the MgO substrate. In addition, when AlN is used as the TaN barrier layer, attention needs to be paid to avoid the piezoelectric property of the AlN barrier layer, and the electric field generated in the junction is prevented from being coupled with the crystal lattice of the bottom layer, so that the decoherence phenomenon is generated through phonon emission.
Therefore, there is an urgent need to find a superconducting qubit structure that extends the coherence time and eliminates quantum-phonon coupling.
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide a superconducting qubit structure based on NbN josephson junctions and a method for fabricating the same, which are used to solve the problems of quantum decoherence caused by quantum-phonon coupling and dielectric loss suppressing coherence time in the prior art.
In order to achieve the above objects and other related objects, the present invention provides a method for preparing a superconducting qubit structure based on NbN josephson junctions, comprising the steps of:
providing a substrate, and forming a buffer layer on the substrate;
forming a functional material layer on the buffer layer, wherein the functional material layer comprises an NbN bottom layer film, a TaN barrier layer and an NbN top layer film which are stacked upwards;
etching the functional material layer to form a functional layer comprising a resonator, a capacitor, a first Josephson junction and a second Josephson junction, and forming an isolation layer covering the exposed surface of the functional layer and the upper surface of the substrate;
thinning the isolation layer to expose upper surfaces of the first and second josephson junctions, and forming a first contact hole and a second contact hole in the isolation layer, wherein the bottom of the first contact hole exposes the capacitor, and the bottom of the second contact hole exposes the resonator;
forming a first wiring part and a second wiring part on the isolation layer, the first wiring part contacting an upper surface of the first Josephson junction and filling in the first contact hole to be electrically connected with the capacitor, the second wiring part contacting an upper surface of the second Josephson junction and filling in the second contact hole to be electrically connected with the resonator.
Optionally, the substrate comprises a silicon substrate, and the resistivity of the substrate is higher than 20k Ω · cm.
Optionally, the material of the buffer layer includes TiN, and the thickness of the buffer layer is in a range of 40nm to 60 nm.
Optionally, the method for forming the buffer layer includes a direct current reactive magnetron sputtering method.
Optionally, the first and second josephson junctions share a bottom electrode, and the first josephson junction further comprises a first junction barrier layer and a first top electrode on and stacked upward from the bottom electrode, the second josephson junction further comprises a second junction barrier layer and a second top electrode on and stacked upward from the bottom electrode.
Optionally, the atomic proportion of the N element in the TaN barrier layer is higher than that of the Ta element.
Alternatively, the material of the first and second wiring portions includes NbN, and the thickness of the first and second wiring portions is in a range of 250nm to 350 nm.
The invention also provides a superconducting qubit structure of a NbN Josephson junction, comprising:
a substrate;
the buffer layer is positioned on the upper surface of the substrate;
the functional layer is positioned on the upper surface of the buffer layer and comprises a capacitor, a first Josephson junction, a second Josephson junction and a resonator which are arranged at intervals;
an isolation layer filling gaps among the resonator, the capacitor, the first Josephson junction and the second Josephson junction in the functional layer and covering exposed surfaces of the resonator and the capacitor and an upper surface of the substrate, and having a first contact hole and a second contact hole therein.
A first wiring portion filled in the first contact hole and contacting an upper surface of the first Josephson junction, and a second wiring portion filled in the second contact hole and contacting an upper surface of the second Josephson junction.
Optionally, the first and second josephson junctions share a bottom electrode, and the first josephson junction further comprises a first junction barrier layer and a first top electrode on and stacked upward from the bottom electrode, the second josephson junction further comprises a second junction barrier layer and a second top electrode on and stacked upward from the bottom electrode.
Optionally, the substrate includes a silicon substrate, and the material of the buffer layer includes TiN.
As described above, the superconducting qubit structure of NbN Josephson junctions and the method for fabricating the same according to the present invention employ silicon as a substrate for fabricating the superconducting qubit structure, thereby reducing charge fluctuation in the substrate, enhancing coherence of a quantum system, reducing dielectric loss, and facilitating prolongation of coherence time, employ TiN having a small lattice mismatch with a NbN bottom layer film in a functional material layer as a buffer layer material, thereby realizing formation of a high-quality functional material layer on the silicon substrate, employ TaN, which is nitride with the bottom electrode, the first top electrode, and the second top electrode, as materials of the first junction barrier layer and the second junction barrier layer, thereby avoiding formation of an oxide at an interface, reducing charge fluctuation in the superconducting qubit, reducing the number of two-level systems in Josephson junctions, and the TaN film exhibits insulation at low temperature, and thus having no piezoelectric effect, the method effectively eliminates the possible quantum-phonon coupling effect, enhances the coherence of the superconducting quantum bit, adopts NbN superconducting materials as the materials of the bottom electrode, the first top electrode and the second top electrode, has higher transition temperature, can inhibit the excitation of quasi-particles so as to further increase the phase-fading time, and has high industrial utilization value.
Drawings
Fig. 1 shows a flow chart of a method for preparing a superconducting qubit structure for NbN josephson junctions in accordance with the present invention.
Fig. 2 is a schematic cross-sectional view showing a buffer layer formed by the method for preparing a superconducting qubit structure of a NbN josephson junction of the present invention.
Fig. 3 is a schematic cross-sectional structure diagram showing the functional material layer formed by the method for preparing the superconducting qubit structure of the NbN josephson junction of the present invention.
Fig. 4 is a schematic cross-sectional view showing the first josephson junction region and the second josephson junction region formed by the method for preparing the superconducting qubit structure of the NbN josephson junction of the present invention.
Fig. 5 is a schematic cross-sectional view showing a capacitor and a resonator formed by the method for manufacturing the superconducting qubit structure of the NbN josephson junction of the present invention.
Fig. 6 is a schematic cross-sectional view showing the separation layer formed by the method for preparing the superconducting qubit structure of the NbN josephson junction of the present invention.
Fig. 7 is a schematic cross-sectional structure view showing the separation layer thinned by the method for preparing the superconducting qubit structure of the NbN josephson junction of the present invention.
Fig. 8 is a schematic cross-sectional view showing the first contact hole and the second contact hole after the formation of the method for preparing the superconducting qubit structure of the NbN josephson junction of the present invention.
Fig. 9 is a schematic cross-sectional view showing a wiring layer after a method for manufacturing a superconducting qubit structure of a NbN josephson junction according to the present invention.
Fig. 10 is a schematic cross-sectional view of a superconducting qubit structure of the NbN josephson junction of the present invention.
Description of the element reference numerals
1 substrate
11 buffer layer
12 functional material layer
121 NbN underlayer film
122 TaN barrier layer
1221 first Josephson junction region
1222 second Josephson junction region
123 NbN top layer film
124 resonator
125 capacitor
126 first josephson junction
127 second Josephson junction
13 functional layer
131 bottom electrode
132 first junction barrier layer
133 first top electrode
134 second junction barrier layer
135 second top electrode
2 isolating layer
21 first contact hole
22 second contact hole
3 wiring layer
31 first wiring part
32 second wiring part
Detailed Description
The following embodiments of the present invention are provided by way of specific examples, and other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 10. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Example one
This embodiment provides a method for preparing a NbN josephson junction-based superconducting qubit structure, as shown in fig. 1, in order to form the NbN josephson junction-based superconducting qubit structure, the method includes the following steps:
s1: providing a substrate, and forming a buffer layer on the substrate;
s2: forming a functional material layer on the buffer layer, wherein the functional material layer comprises an NbN bottom layer film, a TaN barrier layer and an NbN top layer film which are stacked upwards;
s3: etching the functional material layer to form a functional layer including a resonator, a capacitor, a first Josephson junction and a second Josephson junction, and forming an isolation layer covering an exposed surface of the functional layer and an upper surface of the substrate;
s4: thinning the isolation layer to expose upper surfaces of the first and second josephson junctions, and forming a first contact hole and a second contact hole in the isolation layer, wherein the bottom of the first contact hole exposes the capacitor, and the bottom of the second contact hole exposes the resonator;
s5: forming a first wiring part and a second wiring part on the isolation layer, the first wiring part contacting an upper surface of the first Josephson junction and filling in the first contact hole to be electrically connected with the capacitor, the second wiring part contacting an upper surface of the second Josephson junction and filling in the second contact hole to be electrically connected with the resonator.
Referring to fig. 2, the step S1 is executed: a substrate 1 is provided, and a buffer layer 11 is formed on the substrate 1.
As an example, the substrate 1 comprises a silicon substrate or other suitable material, the resistivity of the substrate 1 being higher than 20k Ω · cm. In this embodiment, silicon with high resistivity (greater than 20k Ω · cm) is selected as the substrate 1, and since silicon has high resistivity (greater than 20k Ω · cm), dielectric loss in the substrate 1 is reduced, and the decoherence time is prolonged, and the preparation process of the device on the silicon substrate is mature, which is beneficial to the processing and large-scale integration of quantum devices.
Specifically, the thickness of the substrate 1 is related to the process of forming the functional material layer, and can be set according to actual needs. In this embodiment, the thickness of the substrate 1 is 0.625mm to meet the requirement of the subsequent device for forming the functional material layer.
As an example, the material of the buffer layer 11 includes TiN or other suitable materials, the thickness of the buffer layer 11 is in a range of 40nm to 60nm, and preferably, the thickness of the buffer layer 11 is 50 nm. In this embodiment, a TiN layer is used as the buffer layer 11, and the lattice matching between TiN and NbN is small, so that a high-quality functional material layer can be grown on a silicon substrate.
As an example, a method of forming the buffer layer 11 includes a direct current reactive magnetron sputtering method or other suitable methods.
Referring to fig. 3 to 6, the steps S2 and S3 are executed: forming a functional material layer 12 on the buffer layer 11, wherein the functional material layer 12 includes an NbN bottom layer film 121, a TaN barrier layer 122, and an NbN top layer film 123 stacked upward; the functional material layer 12 is etched to form a functional layer 13 including a resonator 124, a capacitor 125, a first josephson junction 126 and a second josephson junction 127, and an isolation layer 2 covering an exposed surface of the functional layer 13 and an upper surface of the substrate 1.
Specifically, as shown in fig. 3, in order to form the functional material layer 12, a cross-sectional structure diagram is shown, first, the NbN underlayer film 121 is formed on the buffer layer 11 by using a dc reactive magnetron sputtering method or other suitable methods, and in the process of forming the NbN underlayer film 121, a stoichiometric ratio of Nb to N is controlled so that the NbN underlayer film 121 exhibits a superconducting property at a low temperature.
Specifically, the process parameters are controlled during the NbN underlayer film 121 formation process to obtain the NbN underlayer film 121 with a suitable thickness.
Specifically, the thickness of the NbN underlayer film 121 is 100nm to 200nm, and preferably, the thickness of the NbN underlayer film 121 is 150 nm.
Specifically, after the NbN underlayer film 121 is formed, the TaN barrier layer 122 is formed on the NbN underlayer film 121 by using dc reactive magnetron sputtering or other suitable methods. In this embodiment, the TaN barrier layer 122 is formed by a dc reactive magnetron sputtering method.
For example, the atomic ratio of the N element is higher than that of the Ta element in the TaN barrier layer 122.
Specifically, in the process of forming the TaN barrier layer 122, the content of N is increased by adjusting the ratio of Ta to N, so as to obtain the TaN barrier layer 122 having insulating properties at low temperature.
Specifically, the thickness of the TaN barrier layer 122 is 1nm to 2nm, and preferably, the thickness of the TaN barrier layer 122 is 1.5 nm.
Specifically, after the TaN barrier layer 122 is formed, the NbN top layer film 123 is formed on the TaN barrier layer 122 by using a dc reactive magnetron sputtering method or other suitable methods, and then the functional material layer 12 is obtained, and the stoichiometric ratio of Nb and N is controlled in the process of forming the NbN top layer film 123 so that the NbN top layer film 123 exhibits a superconducting characteristic at a low temperature.
Specifically, the thickness of the NbN top layer film 123 is 150nm to 250nm, and preferably, the thickness of the NbN top layer film 123 is 200 nm.
Specifically, the TaN barrier layer 122, the NbN bottom layer film 121, and the NbN top layer film 123 are both nitrides, and the TaN barrier layer 122 has chemical stability against oxidation, so that formation of oxides at interfaces between the TaN barrier layer 122, the NbN bottom layer film 121, and the NbN top layer film 123 is avoided, and charge fluctuation in a quantum device can be reduced.
Specifically, the forming of the functional layer 13 includes the steps of:
forming a first mask layer on the upper surface of the NbN top layer film 123, and patterning the first mask layer;
etching the NbN top layer film 123 and the TaN barrier layer 122 to define a first Josephson junction area 1221 and a second Josephson junction area 1222;
forming a second mask layer on an upper surface of the NbN underlayer film 121 and covering exposed surfaces of the first josephson junction area 1221 and the second josephson junction area 1222, and patterning the second mask layer;
the NbN underlayer film 121 and the buffer layer 11 are etched to obtain the resonator 124, the capacitor 125, the first josephson junction 126 and the second josephson junction 127, and then the functional layer 13 is obtained.
Specifically, as shown in fig. 4, in order to show a schematic cross-sectional structure after etching the NbN top layer film 123 and the TaN barrier layer 122, the method for etching the NbN top layer film 123 and the TaN barrier layer 122 includes step exposure and inductively coupled plasma etching or other suitable methods. In this embodiment, the NbN cap layer film 123 and the TaN barrier layer 122 are etched in one step by using the step-wise exposure and inductively coupled plasma etching method, so that the etching steepness and the uniformity of the sidewall can be ensured, and the verticality can be effectively avoidedThe etching gas may include CF due to the uneven distribution of the size of the junction in the vertical direction4And Ar.
Specifically, as shown in fig. 5, in order to form the schematic cross-sectional structure after the resonator 124, the capacitor 125, the first josephson junction 126 and the second josephson junction 127, the NbN underlayer film 121 and the buffer layer 11 are etched by using step exposure and inductively coupled plasma etching or other suitable methods to obtain the resonator 124, the capacitor 125, the first josephson junction 126 and the second josephson junction 127, and the etching gas may include CF4And Ar.
As an example, the first josephson junction 126 and the second josephson junction 127 share a bottom electrode 131, and the first josephson junction 126 further includes a first junction barrier layer 132 and a first top electrode 133 on the bottom electrode 131 and stacked upward, and the second josephson junction 127 further includes a second junction barrier layer 134 and a second top electrode 135 on the bottom electrode 131 and stacked upward.
Specifically, the shape of the first junction barrier layer 132 includes a circle and the diameter of the first junction barrier layer 132 is 1.0 μm to 3.0 μm, and the shape of the second junction barrier layer 134 includes a circle and the diameter of the second junction barrier layer 134 is 1.0 μm to 3.0 μm.
Specifically, the use of the insulating TaN barrier layer 122 as the first junction barrier layer 132 and the second junction barrier layer 134 can reduce the number of two-level systems in the first josephson junction 126 and the second josephson junction 127, and the first junction barrier layer 132 and the second junction barrier layer 134 do not have a piezoelectric effect, thereby effectively eliminating the quantum-phonon coupling effect and enhancing the coherence of superconducting qubits.
In particular, NbN superconducting materials have relatively high superconducting transition temperature (16K) and large superconducting energy gap (5.2 meV), so that the excitation of quasi-particles can be inhibited, and the phase-losing coherence time is prolonged.
Specifically, as shown in fig. 6, in order to form the isolation layer 2 with a schematic cross-sectional structure, a method for forming the isolation layer 2 includes physical vapor deposition, chemical vapor deposition, or other suitable methods. In this embodiment, the isolation layer 2 covering the exposed surface of the functional layer 13 and the upper surface of the substrate 1 is formed by a chemical vapor deposition method.
Specifically, the material of the isolation layer 2 includes silicon dioxide, silicon nitride, or other suitable insulating materials.
Specifically, the thickness of the isolation layer 2 is 450nm to 550nm, and preferably, the thickness of the isolation layer 2 is 500 nm.
Referring to fig. 7 to 10, the steps S4 and S5 are executed: thinning the isolation layer 2 to expose upper surfaces of the first josephson junction 126 and the second josephson junction 127, and forming a first contact hole 21 and a second contact hole 22 in the isolation layer 2, wherein the bottom of the first contact hole 21 exposes the capacitor 125, and the bottom of the second contact hole 22 exposes the resonator 124; a first wiring portion 31 and a second wiring portion 32 are formed on the isolation layer 2, the first wiring portion 31 being in contact with an upper surface of the first josephson junction 126 and filled in the first contact hole 21 to be electrically connected to the capacitor 125, the second wiring portion 32 being in contact with an upper surface of the second josephson junction 127 and filled in the second contact hole 32 to be electrically connected to the resonator 124.
Specifically, as shown in fig. 7, in order to obtain a schematic cross-sectional structure after thinning the isolation layer 2, the isolation layer 2 is thinned by chemical mechanical polishing or other suitable methods, and the upper surface of the first josephson junction 126 is the upper surface of the first top electrode 133, and the upper surface of the second josephson junction 127 is the upper surface of the second top electrode 135.
Specifically, as shown in fig. 8, in order to form the cross-sectional structure schematic diagram after the first contact hole 21 and the second contact hole 22 are formed, the first contact hole 21 and the second contact hole 22 are formed in the isolation layer 2 by using a step exposure and a reactive ion etching method or other suitable methods.
Specifically, the wiring layer 3 is formed before the first wiring portion 31 and the second wiring portion 32 are formed.
Specifically, as shown in fig. 9, in order to schematically show a cross-sectional structure after the wiring layer 3 is formed, the wiring layer 3 is formed by dc reactive magnetron sputtering or other suitable method.
Specifically, as shown in fig. 10, in order to form the cross-sectional structural schematic diagram after the first wiring portion 31 and the second wiring portion 32 are formed, the wiring layer 3 is etched by using a step exposure and an inductively coupled plasma etching or other suitable methods to form the first wiring portion 31 and the second wiring portion 32.
As an example, the material of the first and second wiring portions 31 and 32 includes NbN or other suitable low-temperature superconducting material, and the thickness of the first and second wiring portions 31 and 32 is in a range of 250nm to 350nm, and preferably, the thickness of the first and second wiring portions 31 and 32 is 300 nm.
The method for preparing the NbN josephson junction-based superconducting qubit structure of the present embodiment uses high-resistivity silicon as the substrate 1, reduces charge fluctuation in the substrate 1, enhances quantum system coherence, reduces dielectric loss, facilitates prolonging coherence time, forms the buffer layer 11 on the substrate 1 to ensure obtaining the high-quality functional material layer 12, enables the thin TaN barrier layer 122 in the functional material layer 12 to have good interface characteristics with the NbN bottom layer film 121 and the NbN top layer film 123, ensures the quality of the first josephson junction 126 and the second josephson junction 127, uses TaN thin films as the material of the first junction barrier layer 132 and the second junction barrier layer 134, reduces the number of two-level systems in the first josephson junction 126 and the second josephson junction 127, enhancing the coherence of the superconducting qubit. In addition, the NbN superconducting material with higher transition temperature is adopted as the electrode material of the first Josephson junction 126 and the second Josephson junction 127, so that the excitation of quasi-particles is inhibited, and the phase-decoupling time is further prolonged.
Example two
This embodiment provides a superconducting qubit structure based on a NbN josephson junction, as shown in fig. 10, which is a schematic cross-sectional view of the superconducting qubit structure of the NbN josephson junction, including a substrate 1, a buffer layer 11, a functional layer 13, an isolation layer 2, a first wiring part 31 and a second wiring part 32, wherein the buffer layer 11 is located on an upper surface of the substrate 1, the functional layer 13 is located on an upper surface of the buffer layer 11 and includes a capacitor 125, a first josephson junction 126, a second josephson junction 127 and a resonator 124 that are arranged at intervals, the isolation layer 2 fills a gap between the resonator 124, the capacitor 125, the first josephson junction 126 and the second josephson junction 127 in the functional layer 13 and covers exposed surfaces of the resonator 124 and the capacitor 125 and an upper surface of the substrate 1, and a first contact hole 21 and a second contact hole 22 are arranged in the isolation layer 2, the first wiring portion 31 is filled in the first contact hole 21 and contacts with the upper surface of the first josephson junction 126, and the second wiring portion 32 is filled in the second contact hole 22 and contacts with the upper surface of the second josephson junction 127.
As an example, the first josephson junction 126 and the second josephson junction 127 share a bottom electrode 131, and the first josephson junction 126 further includes a first junction barrier layer 132 and a first top electrode 133 on the bottom electrode 131 and stacked upward, and the second josephson junction 127 further includes a second junction barrier layer 134 and a second top electrode 135 on the bottom electrode 131 and stacked upward.
As an example, the thickness of the bottom electrode 131 ranges from 100nm to 200nm, the thickness of the first junction barrier layer 132 ranges from 1nm to 2nm, the thickness of the second junction barrier layer 134 ranges from 1nm to 2nm, the thickness of the first top electrode 133 ranges from 150nm to 250nm, the thickness of the second top electrode 135 ranges from 150nm to 250nm, and preferably, the thickness of the bottom electrode 131 ranges from 150nm, the thickness of the first junction barrier layer 132 ranges from 1.5nm, the thickness of the second junction barrier layer 134 ranges from 1.5nm, the thickness of the first top electrode 133 ranges from 200nm, and the thickness of the second top electrode 135 ranges from 200 nm.
By way of example, the substrate 1 comprises a silicon substrate or other suitable material, and the material of the buffer layer 11 comprises TiN or other suitable material.
Specifically, the first junction barrier layer 132 and the second junction barrier layer 134 in the first josephson junction 126 and the second josephson junction 127 are TaN thin films which are insulating at low temperature, so that the piezoelectric effect is eliminated, the quantum-phonon coupling effect is effectively eliminated, and the coherence of the superconducting qubit is enhanced.
Specifically, the first josephson junction 126 and the second josephson junction 127 are the same josephson junction, and the first josephson junction 126, the second josephson junction 127 and the capacitor 125 constitute a superconducting qubit structure of the josephson junction, wherein the first josephson junction 126, the second josephson junction 127 and the capacitor 125 can be approximately regarded as one two-level system.
Specifically, the first josephson junction 126 and the second josephson junction 127 correspond to a nonlinear inductor having a certain capacitance, and the resonator 124 corresponds to a capacitance having a fixed inductor, wherein the fixed inductor of the resonator 124 is a geometric inductor of the resonator 124, and the first josephson junction 126, the second josephson junction 127 and the capacitor 125 form a nonlinear resonator.
In particular, since the superconducting qubit structure of the josephson junction is susceptible to noise when coupled to the outside, resulting in a short qubit de-coherence time, the resonator 124 may enable coupling of the qubit to the external environment.
Specifically, the first wiring portion 31 and the second wiring portion 32 are configured to regulate a bias current in the superconducting qubit structure, so that only two or three energy levels can be accommodated in a potential well generated by the superconducting qubit, and two lowest energy levels are used as two quantum states of the superconducting qubit, and according to a coherence condition, photons with a frequency equal to an energy level interval of the harmonic oscillator irradiate the first josephson junction 126 and the second josephson junction 127, thereby completing the regulation of the quantum states in the superconducting qubit structure.
Specifically, the resonator 124 is equivalent to a qubit reader, and the coupling of the resonator 124 and the superconducting qubit is used to complete the reading of the qubit information.
In the superconducting qubit structure based on the NbN josephson junction in this embodiment, by setting TaN thin films with insulating property at low temperature in the first josephson junction 126 and the second josephson junction 127 as the first junction barrier layer 132 and the second junction barrier layer 134, the piezoelectric effect is eliminated, the quantum-phonon coupling effect is effectively eliminated, and the coherence of the superconducting qubit is enhanced.
In summary, according to the NbN josephson junction-based superconducting qubit structure and the preparation method thereof, the high-resistance silicon substrate is used as the substrate, so that charge fluctuation in the substrate is reduced, quantum system coherence is enhanced, dielectric loss is reduced, coherence time is prolonged, the buffer layer is grown on the silicon substrate, and then the functional material layer is grown, so that the high-quality functional material layer is obtained, the TaN film which is insulating at low temperature is used as the first junction barrier layer and the second junction barrier layer, so that the number of two-level systems in the first josephson junction and the second josephson junction is reduced, the coherence of the superconducting qubit is enhanced, and the first junction barrier layer and the second junction barrier layer are insulating, so that piezoelectric effect is eliminated, quantum-phonon coupling effect is effectively eliminated, and the coherence of the superconducting qubit is enhanced. In addition, NbN superconducting materials with higher transition temperature are used as electrode materials of the first Josephson junction and the second Josephson junction, so that the excitation of quasi-particles is inhibited, and the phase-stripping time is further prolonged. Therefore, the present invention effectively overcomes various disadvantages of the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (10)

1. A preparation method of a superconducting qubit structure based on NbN Josephson junctions is characterized by comprising the following steps:
providing a substrate, and forming a buffer layer on the substrate;
forming a functional material layer on the buffer layer, wherein the functional material layer comprises an NbN bottom layer film, a TaN barrier layer and an NbN top layer film which are stacked upwards;
etching the functional material layer to form a functional layer including a resonator, a capacitor, a first Josephson junction and a second Josephson junction, and forming an isolation layer covering an exposed surface of the functional layer and an upper surface of the substrate;
thinning the isolation layer to expose upper surfaces of the first and second josephson junctions, and forming a first contact hole and a second contact hole in the isolation layer, wherein the bottom of the first contact hole exposes the capacitor, and the bottom of the second contact hole exposes the resonator;
forming a first wiring part and a second wiring part on the isolation layer, the first wiring part contacting an upper surface of the first Josephson junction and filling in the first contact hole to be electrically connected with the capacitor, the second wiring part contacting an upper surface of the second Josephson junction and filling in the second contact hole to be electrically connected with the resonator.
2. The method of preparing a NbN josephson junction-based superconducting qubit structure of claim 1, wherein: the substrate comprises a silicon substrate, and the resistivity of the substrate is higher than 20k omega cm.
3. The method of claim 1, wherein the NbN Josephson junction-based superconducting qubit structure comprises: the buffer layer is made of TiN, and the thickness range of the buffer layer is 40 nm-60 nm.
4. The method of preparing a NbN josephson junction-based superconducting qubit structure of claim 1, wherein: the method for forming the buffer layer comprises a direct-current reactive magnetron sputtering method.
5. The method of preparing a NbN josephson junction-based superconducting qubit structure of claim 1, wherein: the first and second josephson junctions share a bottom electrode, and the first josephson junction also includes a first junction barrier layer and a first top electrode overlying the bottom electrode and overlying, the second josephson junction also includes a second junction barrier layer and a second top electrode overlying the bottom electrode and overlying.
6. The method of claim 5, wherein the NbN Josephson junction-based superconducting qubit is prepared by: in the TaN barrier layer, the atomic proportion of an N element is higher than that of a Ta element.
7. The method of preparing a NbN josephson junction-based superconducting qubit structure of claim 1, wherein: the material of the first wiring part and the second wiring part comprises NbN, and the thickness of the first wiring part and the second wiring part is 250 nm-350 nm.
8. A superconducting qubit structure based on NbN josephson junctions, comprising:
a substrate;
the buffer layer is positioned on the upper surface of the substrate;
the functional layer is positioned on the upper surface of the buffer layer and comprises a capacitor, a first Josephson junction, a second Josephson junction and a resonator which are arranged at intervals;
an isolation layer filling gaps among the resonator, the capacitor, the first Josephson junction and the second Josephson junction in the functional layer and covering exposed surfaces of the resonator and the capacitor and an upper surface of the substrate, and the isolation layer being provided therein with a first contact hole and a second contact hole.
A first wiring portion filled in the first contact hole and contacting an upper surface of the first Josephson junction, and a second wiring portion filled in the second contact hole and contacting an upper surface of the second Josephson junction.
9. The NbN josephson junction-based superconducting qubit structure of claim 8, wherein: the first josephson junction and the second josephson junction share a bottom electrode, and the first josephson junction further comprises a first junction barrier layer and a first top electrode on the bottom electrode and stacked upward, the second josephson junction further comprises a second junction barrier layer and a second top electrode on the bottom electrode and stacked upward.
10. The NbN josephson junction-based superconducting qubit structure of claim 9, wherein: the substrate comprises a silicon substrate, and the buffer layer is made of TiN.
CN202210226252.0A 2022-03-09 2022-03-09 NbN Josephson junction-based superconducting qubit structure and preparation method thereof Pending CN114583038A (en)

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