Fabrication of deep-sub-micrometer NbN/AlN/NbN epitaxial junctions on a Si-substrate

Qiu, Wei; Terai, Hirotaka

doi:10.35848/1882-0786/abbfde

Cited by 9 publications

(5 citation statements)

References 29 publications

(54 reference statements)

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“…From measurements of the current-voltage characteristics of test JJs fabricated on the same wafer as the qubits at 4., the Josephson critical current density 𝐽𝐽 𝑐𝑐 , was found to be 40 -48 A/cm 2 . Additionally, we confirmed that there is no change in 𝐽𝐽 𝑐𝑐 between before and after BHF etching of the SiO2 layer, indicating no damage in the JJs by BHF treatment36 .Device parameters. The fabricated qubit-resonator architecture is depicted in Fig.1.…”

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confidence: 67%

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Enhanced-coherence all-nitride superconducting qubit epitaxially grown on Si substrate

Kim

Terai

Yamashita³

et al. 2021

Preprint

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We have developed superconducting qubits based on NbN/AlN/NbN epitaxial Josephson junctions on Si substrates which promise to overcome the drawbacks of qubits based on Al/AlOx/Al junctions. The all-nitride qubits have great advantages such as chemical stability against oxidation (resulting in fewer two-level fluctuators), feasibility for epitaxial tunnel barriers (further reducing energy relaxation and dephasing), and a larger superconducting gap of ~ 5.2 meV for NbN compared to ~ 0.3 meV for Al (suppressing the excitation of quasiparticles). Replacing conventional MgO by a Si substrate with a TiN buffer layer for epitaxial growth of nitride junctions, we demonstrate a qubit energy relaxation time \({T}_{1}=16.3 {\mu }\text{s}\) and a spin-echo dephasing time \({T}_{2}=21.5 {\mu }\text{s}\). These significant improvements in quantum coherence are explained by the reduced dielectric loss compared to previously reported NbN-based qubits with MgO substrates (\({T}_{1}\approx {T}_{2}\approx 0.5 {\mu }\text{s}\)). These results are an important step towards constructing a new platform for superconducting quantum hardware.

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confidence: 67%

“…Fabrication of all-nitride superconducting qubit. Samples were fabricated by using epitaxial growth of NbN/AlN/NbN junctions on Si wafers with TiN buffers and planarization by CMP 27,36 . In brief the fabrication flow is as follows.…”

Section: Methodsmentioning

confidence: 99%

Enhanced-coherence all-nitride superconducting qubit epitaxially grown on Si substrate

Kim

Terai

Yamashita³

et al. 2021

Preprint

Self Cite

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“…Optimizing Models The structure of the atoms was optimized by using DFT based on the projector augmented wave (PAW) method. During relaxation, the Vienna Ab-initio Simulation Package (VASP) [ 21 , 28 , 40 ] was used for calculation. Perdew–Burke–Ernzerhof (PBE) [ 41 ] was used for the exchange–correlation functional between electrons.…”

Section: Appendix A1 System Modelsmentioning

confidence: 99%

“…To date, good experimental results have been achieved by optimizing the substrates and process conditions [ 9 , 12 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. For example, through increasing the buffer layers between the junction and the substrate to reduce the dielectric loss, the energy relaxation time T1 of the all-nitride junctions reaches 16 microseconds (ms), and the phase relaxation time T2 reaches 22 ms [ 13 , 21 ]. However, the results still fall short of expectations.…”

Section: Introductionmentioning

confidence: 99%

Directly Controlling the Transport Properties of All-Nitride Josephson Junctions by N-Vacancy Defects

Qiu¹,

Sun²,

Wang³

et al. 2023

Nanomaterials

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All-nitride Josephson junctions are being actively explored for applications in superconducting quantum chips because of their unique advantages including their antioxidant chemical stability and high crystal quality. However, the theoretical research on their microstructure mechanism that determines transport properties is still absent, especially on the defects. In this paper, we apply the first principles and non-equilibrium Green’s function to calculate the electrical transport characteristics of the yellow preset model. It is first revealed that the N-vacancy defects play a crucial role in determining the conductivity of the NbN-based Josephson junctions, and demonstrate the importance for the uniformity of vacancy distribution. It is found that the uniform number of vacancies can effectively increase the conductance of Josephson junction, but the position distribution of vacancies has little effect on the conductance. The work clarifies the effect of the N-vacancy defects on the conductivity of the NbN-based Josephson junctions, which offers useful guidance for understanding the microscope mechanism of the NbN-based Josephson junction, thus showing a great prospect in the improvement of the yield of superconducting quantum chips in the future.

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“…Superconducting materials grown on Si or Al 2 O 3 substrates may form films of high crystallinity and with inherently low dielectric loss, thus are explored as the materials for building superconducting quantum circuits 1 – 6 . Recently, researchers have made efforts to search for new superconducting films with stable superconducting properties and mature processing used in the quantum computing field, aiming to improve the performance of superconducting qubits, including long coherence time and fast gates 5 , 7 – 12 .…”

Section: Introductionmentioning

confidence: 99%

High-quality superconducting α-Ta film sputtered on the heated silicon substrate

Wu¹,

Ding²,

Xiong

et al. 2023

Sci Rep

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Intrigued by the discovery of the long lifetime in the α-Ta/Al2O3-based Transmon qubit, researchers recently found α-Ta film is a promising platform for fabricating multi-qubits with long coherence time. To meet the requirements for integrating superconducting quantum circuits, the ideal method is to grow α-Ta film on a silicon substrate compatible with industrial manufacturing. Here we report the α-Ta film sputter-grown on Si (100) with a low-loss superconducting TiNx buffer layer. The α-Ta film with a large growth temperature window has a good crystalline character. The superconducting critical transition temperature (Tc) and residual resistivity ratio (RRR) in the α-Ta film grown at 500 °C are higher than that in the α-Ta film grown at room temperature (RT). These results provide crucial experimental clues toward understanding the connection between the superconductivity and the materials' properties in the α-Ta film and open a new route for producing a high-quality α-Ta film on silicon substrate for future industrial superconducting quantum computers.

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Fabrication of deep-sub-micrometer NbN/AlN/NbN epitaxial junctions on a Si-substrate

Cited by 9 publications

References 29 publications

Enhanced-coherence all-nitride superconducting qubit epitaxially grown on Si substrate

Enhanced-coherence all-nitride superconducting qubit epitaxially grown on Si substrate

Directly Controlling the Transport Properties of All-Nitride Josephson Junctions by N-Vacancy Defects

High-quality superconducting α-Ta film sputtered on the heated silicon substrate

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