Fabrication of Sub-Micrometer SIS Junctions for Radio Astronomy

We present a new fabrication scheme for high quality Nb-AlO_x-Nb junctions as used for mm-wave mixers in radio astronomy. The key features of the fabrication process are high-resolution e-beam lithography for junction and contact definition as well as highly selective Niobium and SiO₂ inductively coupled plasma etching. Chemical-mechanical polishing, which is difficult to control for low volume production is not required. We further show that a new type of spin-on glass can be used as a reliable replacement for sputtered SiO₂. We present yield and parameter scattering of these devices.