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.
In this paper, 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 300 nm with an approximate total height of 3 μm 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/AlOx/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 500 k and qubit T1 times greater than 25 μs.
These results suggest that Si-Fins are a promising technology for applications that require low-loss, compact, superconductor-based capacitors with minimal stray capacitance.
npj Quantum Information, Published online: 22 January 2025; doi:10.1038/s41534-025-00967-5
