Fabrication and characterization of low-loss Al/Si/Al parallel plate capacitors for superconducting quantum information applications

TL;DR

This paper demonstrates that aluminum-contacted crystalline silicon fin capacitors can achieve low-loss, high-performance in superconducting circuits, enabling more compact quantum computing components with minimal energy loss.

Contribution

It introduces a novel fabrication of high aspect ratio Si-fin capacitors integrated into superconducting circuits, showing superior microwave performance and qubit coherence.

Findings

High quality factor (>500k) in lumped element resonators

Qubit T1 times exceeding 25 microseconds

Low loss and compact design suitable for quantum applications

Abstract

Increasing the density of superconducting circuits requires compact components, however, superconductor-based capacitors typically perform worse as dimensions are reduced due to loss at surfaces and interfaces. Here, parallel plate capacitors composed of aluminum-contacted, crystalline silicon fins are shown to be a promising technology for use in superconducting circuits by evaluating the performance of lumped element resonators and transmon qubits. High aspect ratio Si-fin capacitors having widths below $300nm$ with an approximate total height of 3$\mu$m are fabricated using anisotropic wet etching of Si(110) substrates followed by aluminum metallization. The single-crystal Si capacitors are incorporated in lumped element resonators and transmons by shunting them with lithographically patterned aluminum inductors and conventional $Al/AlO_x/Al$ Josephson junctions respectively. Microwave characterization of these devices suggests state-of-the-art performance for superconducting parallel plate capacitors with low power internal quality factor of lumped element resonators greater than 500k and qubit $T_1$ times greater than 25$\mu$s. These results suggest that Si-Fins are a promising technology for applications that require low loss, compact, superconductor-based capacitors with minimal stray capacitance.