Fabrication of Superconductor Integrated Circuits of D-Band Dual-Polarization Balanced SIS Mixers
We have fabricated prototype superconductor integrated circuits (ICs), which accommodate planar orthomode transducer (OMT) and balanced superconductor-insulator-superconductor (SIS) mixers operating at D-band (125–163 GHz). The fabrication of the ICs is different from the conventional SIS mixer fabrication process in several aspects because of new features and components being introduced and incorporated. In particular, very flat silicon membranes that mechanically support the planar OMT and the waveguide probes for local oscillator coupling were formed with a combination of dry and wet etching methods to completely remove the handle layer and the buried oxide layer of the silicon on insulator substrates. We also applied an anodization passivation of the surface of the ground plane and a via-hole etching process with an i-line stepper in the formation of low-leakage SIS junctions. The SIS junctions of moderately good quality have been fabricated with an average quality factor as high as 18, which indicate the integrity of the junction definition with the complex fabrication of ICs.