Kavli Affiliate: Gary A. Steele
| First 5 Authors: Roudy Hanna, Roudy Hanna, , ,
| Summary:
Improvements in circuit design and more recently in materials and surface
cleaning have contributed to a rapid development of coherent superconducting
qubits. However, organic resists commonly used for shadow evaporation of
Josephson junctions (JJs) pose limitations due to residual contamination, poor
thermal stability and compatibility under typical surface-cleaning conditions.
To provide an alternative, we developed an inorganic SiO$_2$/Si$_3$N$_4$
on-chip stencil lithography mask for JJ fabrication. The stencil mask is
resilient to aggressive cleaning agents and it withstands high temperatures up
to 1200textdegreeC, thereby opening new avenues for JJ material exploration
and interface optimization. To validate the concept, we performed shadow
evaporation of Al-based transmon qubits followed by stencil mask lift-off using
vapor hydrofluoric acid, which selectively etches SiO$_2$. We demonstrate
average $T_1 approx 75 pm 11~SImicrosecond$ over a 200 MHz frequency
range in multiple cool-downs for one device, and $T_1 approx 44pm
8~SImicrosecond$ for a second device. These results confirm the
compatibility of stencil lithography with state-of-the-art superconducting
quantum devices and motivate further investigations into materials engineering,
film deposition and surface cleaning techniques.
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