| In applications of superconducting electronics, significant performance enhancement is expected by increasing the critical current density and reducing the size of the basic circuit elements: the Josepshon junctions.; A fabrication process has been developed which is capable of producing Nb/AlOx/Nb Josephson junctions of deep-submicron (area < 0.1 μm 2) dimensions and high critical current densities (up to 2.5 mA/μm 2). A novel combination of electron beam lithography (EBL) and optical (DUV) lithography is used for patterning, which gives excellent linewidth control and allows significant design flexibility. Erodible quartz (SiO 2) etch masks and reactive ion etch in SF6 gas is used for defining the junctions. RF sputtered quartz is also used as the dielectric material, which is subsequently planarized using chemical-mechanical polishing. The minimum feature size has been reduced to 0.2 μm for all wiring layers and 0.1 μm for the junctions.; At a Jc of 2.1 mA/μm2 the junctions were ‘self-shunted’ and exhibit non-hysteretic I–V characteristics. Prominent subharmonic gap structured was observed in these junctions. Current transport in presence of magnetic fields and microwave radiation were studied. Low frequency noise measurements were made.; A model based on the scattering theory of multiple Andreev reflections and Bogolyubov - de Gennes equations was used to describe the data. The model uses the Schep-Bauer distribution for transparencies and has excellent agreement with the entire measured I–V characteristics.; Key applications of the developed process to RSFQ electronics and SQUIDs, were demonstrated. |
