Reliability and reproducibility of Josephson junction fabrication - Steps towards an optimized process
Typ
Examensarbete för masterexamen
Program
Publicerad
2019
Författare
Osman, Amr
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
We investigated the reliability and reproducibility of the fabrication process of
Al/AlOx/Al Josephson junctions with varying sizes using the cross-type lithography
technique. Room temperature resistance measurements on thousands of junctions
showed a standard deviation varying from 0.8% and 5.5% depending on the junction
size, and a fabrication yield higher than 97%. Additionally, we investigated two steps
towards optimizing the fabrication process. Firstly, the Ar-ion milling duration was
reduced, whose e ect on the junction quality remains to be investigated. Secondly, a
one-step fabrication technique of Josephson junction is proposed in this thesis. Such
a technique reduces the number of lithography steps needed, and in addition, Arion
milling of the substrate is avoided. This technique proves to be very reliable for
small JJ sizes, with a fabrication yield also higher than 97%. However, further work
is needed in order to reduce its standard deviation, in addition to low temperature
measurements to investigate the quality of qubits fabricated using these JJs. Finally,
a tentative study for the ageing of Josephson junctions was investigated over the
course of 180 days showing an average increase in the resistance of only 5%.