Methods of Planarization
1.) Niobium trilayer technique with "Spin-on-Glass" planarization
This technique uses large area Nb/AlOx/Nb-trilayers. Small patterns are created by etching processes and subsequently planarized.
SEM-micrograph of a Nb/AlOx/Nb-transistor in SOG-technique
2.) Niobium trilayer technique with "CMP" planarization
This technique uses SiO2 to replace the "Spin-on-Glass". The circuit is planarized by chemical-mechanical polishing (CMP).
SEM-micrograph of a Nb/AlOx/Nb-transistor in CMP-technique
Literature:
A. B. Pavolotsky, T. Weimann, H. Scherer, J. Niemeyer, and A. B. Zorin, "Novel Method for Fabricating Deep Submicron Nb/AlOx/Nb Tunnel Junctions Based on Spin-on Glass Planarization", IEEE Trans. Appl. Supercond. 9 (2), 3251 (1999).
R. Dolata, H. Scherer, A. B. Zorin and J. Niemeyer, "Single-charge devices with ultrasmall Nb/AlOx/Nb trilayer Josephson junctions", J. Appl. Phys. 97, 054501 (2005).