Thermal annealing of Nb/Al-AlO/sub x//Nb Josephson junctions

Migacz, Justin; Huber, M. E.

doi:10.1109/tasc.2003.813661

Cited by 13 publications

(7 citation statements)

References 6 publications

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“…Annealing is occasionally used to trim junction resistance and critical current by up to 20%. We found no degradation of junction quality even with 170 anneals, in contrast to expectations based on previous work by others [11]. Most JPL testing in this work was done at room temperature and 4 K. Functional qubit testing has been done at mK temperatures by our collaborators at D-Wave to be reported elsewhere.…”

Section: Discussioncontrasting

confidence: 50%

Submicrometer ${\rm Nb}/{\rm Al}{-}{\rm AlO}_{\rm x}/{\rm Nb}$ Integrated Circuit Fabrication Process for Quantum Computing Applications

Bumble

Fung

Kaul

et al. 2009

IEEE Trans. Appl. Supercond.

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We have developed a low J c (100-1000 A cm 2 ) submicrometer Nb integrated circuit fabrication process for SQUIDbased quantum computing applications. The baseline process consists of 7 masking steps including Pd-Au resistor, Nb/Al-AlOx/Nb trilayer, two Nb wiring layers and two sputtered SiO2 dielectric layers. We have also fabricated wafers with an Nb ground plane. Using deep-UV lithography, inductively coupled plasma etch tools, and self-aligned lift-off for device definition, we routinely achieve micrometer lines and spaces with 400 nm minimum junction dimensions. Room temperature testing is used to select wafers in process and junction annealing has been calibrated for trimming current density. We will describe the process which has been used to produce circuits with over 100 junctions.

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Section: Discussioncontrasting

confidence: 50%

Submicrometer ${\rm Nb}/{\rm Al}{-}{\rm AlO}_{\rm x}/{\rm Nb}$ Integrated Circuit Fabrication Process for Quantum Computing Applications

Bumble

Fung

Kaul

et al. 2009

IEEE Trans. Appl. Supercond.

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“…of a set of junctions versus inverse area, for areas ranging from 0.06 µm 2 to 0.21 µm 2 before and after bridge processing. The dependence is linear and it shows a systematic increase in resistance of approximately 30% that arises from the 5 min of total bake time at 180 • C, consistent with previous studies 24 . We note that the estimated critical current density after the bridge process is 2.6 µA/µm 2 , compatible with flux qubits 25 and larger than typical critical current densities used in transmons.…”

supporting

confidence: 91%

Aluminum air bridges for superconducting quantum devices realized using a single step electron-beam lithography process

Janzen,

Kononenko,

Ren

et al. 2022

Preprint

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In superconducting quantum devices, air bridges enable increased circuit complexity and density as well as mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from 20 µm to 100 µm, with a yield exceeding 99 % for lengths up to 36 µm. When used to connect ground planes in coplanar waveguide resonators, the induced loss contributed to the system is negligible, corresponding to a reduction of the quality factor exceeding 1.0 × 10 8 per bridge. The bridge process is compatible with Josephson junctions and allows for the simultaneous creation of low loss bandages between superconducting layers. Superconducting circuits have emerged as one of the primary candidates for the implementation of quantum computing 1,2 . One of the primary advantages of superconducting circuits is the flexibility in design and scalability resulting from their realization as microfabricated circuits on a chip. As the complexity and scale of superconducting circuits increases, microfabrication methods that enable increased density and quantum coherence are essential. Relevant approaches for scalability include multi-chip fabrication 3-6 and three dimensional wiring integration 7,8 .Air bridges are one of the most relevant components of high-complexity superconducting circuits. They enhance functionality by enabling increased circuit density and by enhancing coherence in distributed resonators and qubits by prevention of mode mixing 9,10 . Several methods have been developed to date to implement air bridge crossovers for superconducting circuits. These processes are carried out using techniques including using a photo resist scaffold followed by etching of the excess aluminum to separate the bridge 10,11 , employing resist stacks that use different resists to define both a scaffold as well as a resist window above the scaffold with an undercut for liftoff 12,13 , and forming a dielectric scaffold that is etched after Al deposition 14 . In this paper, we present a method to fabricate aluminum air bridges that uses a simple single-step fabrication process that relies on gradient exposure electron-beam lithography (EBL). This process produces bridges with lengths ranging from 20 µm to 100 µm, with a yield exceeding 99 % for bridges of lengths up to 36 µm. We characterize coplanar waveguide resonators with integrated air bridges and find that negligible microwave loss is introduced when these bridges are used to connect ground planes. The process is compatible with fabrication of Josephson junctions for superconducting qubits and it has the additional desirable feature a)

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“…The normalized resistance change follows an exponentially plateauing function (red dashed line) that caps at ∆R/R 0 = 1.8%. This trend is similar to that of low temperature (< 150 °C) thermal annealing of JJs demonstrated by [33,[36][37][38]. In order to correlate JJ temperature to laser power, we simulate the temperature (T ) of a JJ directly illuminated by a Gaussian beam with waist 0.81 µm of varying power (P ) using COMSOL Multiphysics.…”

Section: Laser-annealing Mechanismsupporting

confidence: 66%

Effects of Laser-Annealing on Fixed-Frequency Superconducting Qubits

Kim,

Jünger,

Morvan

et al. 2022

Preprint

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As superconducting quantum processors increase in complexity, techniques to overcome constraints on frequency crowding are needed. The recently developed method of laser-annealing provides an effective post-fabrication method to adjust the frequency of superconducting qubits. Here, we present an automated laser-annealing apparatus based on conventional microscopy components and demonstrate preservation of highly coherent transmons. In one case, we observe a two-fold increase in coherence after laser-annealing and perform noise spectroscopy on this qubit to investigate the change in defect features, in particular two-level system defects. Finally, we present a local heating model as well as demonstrate aging stability for laser-annealing on the wafer scale. Our work constitutes an important first step towards both understanding the underlying physical mechanism and scaling up laser-annealing of superconducting qubits.

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Thermal annealing of Nb/Al-AlO/sub x//Nb Josephson junctions

Cited by 13 publications

References 6 publications

Submicrometer ${\rm Nb}/{\rm Al}{-}{\rm AlO}_{\rm x}/{\rm Nb}$ Integrated Circuit Fabrication Process for Quantum Computing Applications

Submicrometer ${\rm Nb}/{\rm Al}{-}{\rm AlO}_{\rm x}/{\rm Nb}$ Integrated Circuit Fabrication Process for Quantum Computing Applications

Aluminum air bridges for superconducting quantum devices realized using a single step electron-beam lithography process

Effects of Laser-Annealing on Fixed-Frequency Superconducting Qubits

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