Towards merged-element transmons using silicon fins: the FinMET

TL;DR

This paper proposes a novel silicon fin-based merged-element transmon (FinMET) device that aims to reduce losses and improve scalability in superconducting qubits by utilizing anisotropic etching and epitaxial superconductor contacts.

Contribution

It introduces the concept of FinMET using silicon fins and demonstrates initial fabrication steps, paving the way for scalable, low-loss superconducting qubits.

Findings

Fabrication of silicon fin capacitors on Si(110) substrates.

Integration of these capacitors into microwave resonator circuits.

Initial low-temperature microwave measurements of the fabricated devices.

Abstract

A merged-element transmon (MET) device, based on silicon (Si) fins, is proposed and the first steps to form such a "FinMET" are demonstrated. This new application of fin technology capitalizes on the anisotropic etch of Si(111) relative to Si(110) to define atomically flat, high aspect ratio Si tunnel barriers with epitaxial superconductor contacts on the parallel side-wall surfaces. This process circumvents the challenges associated with the growth of low-loss insulating barriers on lattice matched superconductors. By implementing low-loss, intrinsic float-zone Si as the barrier material rather than commonly used, potentially lossy AlOx, the FinMET is expected to overcome problems with standard transmons by (1) reducing dielectric losses, (2) minimizing the formation of two-level system spectral features, (3) exhibiting greater control over barrier thickness and qubit frequency spread, especially when combined with commercial fin fabrication and atomic-layer digital etching; (4) potentially reducing the footprint by several orders of magnitude; and (5) allowing scalable fabrication. Here, as a first step to making such a device, the fabrication of Si fin capacitors on Si(110) substrates with shadow-deposited Al electrodes is demonstrated. These fin capacitors are then fabricated into lumped element resonator circuits and probed using low-temperature microwave measurements. Further thinning of silicon junctions towards the tunneling regime will enable the scalable fabrication of FinMET devices based on existing silicon technology, while simultaneously avoiding lossy amorphous dielectrics for the tunnel barriers.