Superconducting phase qubits with shadow-evaporated Josephson junctions

Su, Feifan; Liu, Weiyang; Xu, Huikai; Deng, Hui; Li, Zhiyuan; Tian, Ye; Zhu, Xiaobo; Zheng, Dewen; Li, LV; Shen, Zhenxing

doi:10.1088/1674-1056/26/6/060308

Cited by 12 publications

(14 citation statements)

References 30 publications

(39 reference statements)

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“…Epitaxial growth of Al on Si substrates has already been realized by ultrahigh vacuum (UHV)-based deposition techniques like molecular beam epitaxy (MBE) [10] or UHV evaporation [11,12]. However, UHV deposition systems are elaborate to operate and in general not well suited for JJ fabrication because shadow evaporation techniques [13,14] are difficult to implement. Up to now, high-vacuum (HV) electron-beam deposition systems, such as the Plassys MEB 550S system, are mainly used for JJ fabrication.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Al/AlOx/Al-layer systems for Josephson junctions from a microstructure point of view

Fritz

Radtke

Schneider

et al. 2019

Journal of Applied Physics

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Al/AlOx/Al-layer systems are frequently used for Josephson junction-based superconducting devices. Although much work has been devoted to the optimization of the superconducting properties of these devices, systematic studies on influence of deposition conditions combined with structural analyses on the nanoscale are rare up to now. We have focused on the optimization of the structural properties of Al/AlOx/Al-layer systems deposited on Si (111) substrates with a particular focus on the thickness homogeneity of the AlOx-tunnel barrier. A standard high-vacuum electron-beam deposition system was used and the effect of substrate pretreatment, different Al-deposition temperatures and Al-deposition rates was studied. Transmission electron microscopy was applied to analyze the structural properties of the Al/AlOx/Al-layer systems to determine the thickness homogeneity of the AlOx layer, grain size distribution in the Al layers, Al-grain boundary types and the morphology of the Al/AlOx interface. We show that the structural properties of the lower Al layer are decisive for the structural quality of the whole Al/AlOx/Al-layer system. Optimum conditions yield an epitaxial Al(111) layer on a Si(111) substrate with an Al-layer thickness variation of only 1.6 nm over more than 10 m and large lateral grain sizes up to 1 m. Thickness fluctuations of the AlOx-tunnel barrier are minimized on such an Al layer which is essential for the homogeneity of the tunnel current. Systematic variation of the Al-deposition rate and deposition temperature allows to develop an understanding of the growth mechanisms.

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Section: Introductionmentioning

confidence: 99%

Optimization of Al/AlOx/Al-layer systems for Josephson junctions from a microstructure point of view

Fritz

Radtke

Schneider

et al. 2019

Journal of Applied Physics

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“…While experimentally molecular oxygen (O 2 ), 5,26 ozone (O 3 ), 27 and both charged (O + ) 28,29 and neutral atomic oxygen (O) 30,31 can be used, it is known that O 2 has a large dissociation energy which the empirical potentials have not been designed to describe. 32 Campbell et al simulated the oxidation of nanoclusters and found similar behaviour for both neutral atomic oxygen and O 2 molecules excepting a change in the temperature at the surface.…”

Section: A Methodologymentioning

confidence: 99%

Simulating the fabrication of aluminium oxide tunnel junctions

Cyster,

Smith,

Vogt

et al. 2020

Preprint

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Aluminium oxide (AlOx) tunnel junctions are important components in a range of nanoelectric devices including superconducting qubits where they can be used as Josephson junctions. While many improvements in the reproducibility and reliability of qubits have been made possible through new circuit designs, there are still knowledge gaps in the relevant materials science. A better understanding of how fabrication conditions affect the density, uniformity, and elemental composition of the oxide barrier may lead to the development of lower noise and more reliable nanoelectronics and quantum computers. In this paper we use molecular dynamics to develop models of Al-AlOx-Al junctions by iteratively growing the structures with sequential calculations. With this approach we can see how the surface oxide grows and changes during the oxidation simulation. Dynamic processes such as the evolution of a charge gradient across the oxide, the formation of holes in the oxide layer, and changes between amorphous and semi-crystalline phases are observed. Our results are widely in agreement with previous work including reported oxide densities, self-limiting of the oxidation, and increased crystallinity as the simulation temperature is raised. The encapsulation of the oxide with metal evaporation is also studied atom by atom. Low density regions at the metaloxide interfaces are a common feature in the final junction structures which persists for different oxidation parameters, empirical potentials, and crystal orientations of the aluminium substrate.

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“…While experimentally molecular oxygen (O 2 ) 5,26 , ozone (O 3 ) 27 , and both charged (O + ) 28,29 and neutral atomic oxygen (O) 30,31 can be used, fully describing the adsorption of oxygen molecules on aluminium surfaces is an open problem. There is an ongoing discussion in the literature regarding the magnitude of the O 2 dissociation energy [32][33][34][35] and it is not known whether charge or spin dynamics play the dominant role 36 .…”

Section: Oxidation Of Aluminiummentioning

confidence: 99%

Simulating the fabrication of aluminium oxide tunnel junctions

et al. 2021

View full text Add to dashboard Cite

Aluminium oxide (AlOx) tunnel junctions are important components in a range of nanoelectric devices including superconducting qubits where they can be used as Josephson junctions. While many improvements in the reproducibility and reliability of qubits have been made possible through new circuit designs, there are still knowledge gaps in the relevant materials science. A better understanding of how fabrication conditions affect the density, uniformity, and elemental composition of the oxide barrier may lead to the development of lower noise and more reliable nanoelectronics and quantum computers. In this paper, we use molecular dynamics to develop models of Al–AlOx–Al junctions by iteratively growing the structures with sequential calculations. With this approach, we can see how the surface oxide grows and changes during the oxidation simulation. Dynamic processes such as the evolution of a charge gradient across the oxide, the formation of holes in the oxide layer, and changes between amorphous and semi-crystalline phases are observed. Our results are widely in agreement with previous work including reported oxide densities, self-limiting of the oxidation, and increased crystallinity as the simulation temperature is raised. The encapsulation of the oxide with metal evaporation is also studied atom by atom. Low density regions at the metal–oxide interfaces are a common feature in the final junction structures which persists for different oxidation parameters, empirical potentials, and crystal orientations of the aluminium substrate.

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Superconducting phase qubits with shadow-evaporated Josephson junctions

Cited by 12 publications

References 30 publications

Optimization of Al/AlOx/Al-layer systems for Josephson junctions from a microstructure point of view

Optimization of Al/AlOx/Al-layer systems for Josephson junctions from a microstructure point of view

Simulating the fabrication of aluminium oxide tunnel junctions

Simulating the fabrication of aluminium oxide tunnel junctions

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