Free-standing silicon shadow masks for transmon qubit fabrication

Abstract

Nanofabrication techniques for superconducting qubits rely on resist-based masks patterned by electron-beam or optical lithography. We have developed an alternative nanofabrication technique based on free-standing silicon shadow masks fabricated from silicon-on-insulator wafers. These silicon shadow masks not only eliminate organic residues associated with resist-based lithography, but also provide a pathway to better understand and control surface-dielectric losses in superconducting qubits by decoupling mask fabrication from substrate preparation. We have successfully fabricated aluminum 3D transmon superconducting qubits with these shadow masks and found coherence quality factors comparable to those fabricated with standard techniques.

Material matters in superconducting qubits

“…However, a similar degradation in performance was not found from freestanding Al qubits, in which Bosch etching generated over 60 micron deep trenches in the underlying Si substrate, possibly because the participation of the SA surfaces in such a structure was sufficiently small to mitigate loss due to oxide formation [70]. Nevertheless, approaches have been pursued to eliminate damage induced by residue or subtractive etching by employing an inorganic hardmask to evaporate Al features on sapphire substrates [202].…”

An Integrated Quantum Material Testbed with Multi-Resolution Photoemission Spectroscopy

“…The MBE system features up to seven effusion cells, as well as a manipulator providing radiative heating up to 1100 • C or direct current heating up to ∼ 1500 • C. Notably, we implement laser-cut stainless-steel shadow masks to perform patterned growth. This shadow mask technique allows us to print micron-scale patterns without the need of exposing thin films to ambient or harsh environments for lithographic processing 28,29 and is thus termed µMBE. The printing resolution is currently limited by the laser cutting precision ∼ 5 µm.…”

The superconducting circuit companion -- an introduction with worked examples

“…A particularly prominent platform for scalable quantum technology is superconducting circuits used for implementing qubits or even higher dimensional qudits. Compared to other quantum technology schemes, such as trapped ions [15][16][17][18][19][20], ultra cold atoms [21][22][23][24][25], electron spins in silicon [26][27][28][29][30][31] and quantum dots [32][33][34][35][36], nitrogen-vacancies in diamonds [37,38], or polarized photons [39][40][41][42], which all encode quantum information in microscopic systems, such as ions, atoms, electrons, or photons, superconducting circuits are quite different as they are macroscopic in size and printed lithographically on plates much similar to classical computer chips [43][44][45][46][47]. The fact that these system exhibit microscopic behavior, i.e., quantum mechanical effects, while being macroscopic in size has led to the notion of mesoscopic physics in order to describe this intermediate scale [48][49][50].…”