Superconductor-insulator-superconductor mixer devices for 1.1 THz

Superconducting frequency mixers are a crucial component of high spectral resolution heterodyne receivers for radio astronomy. Superconductor-Insulator-Superconductor (SIS) mixers are the established highest sensitivity choice in the submillimeter wavelength range. There is great interest in using SIS-mixers also for THz-frequencies since they offer a higher intermediate frequency bandwidth and potentially higher sensitivity and stability than superconducting hot electron bolometer mixers which are currently used in this regime. A possible junction design for 1.1 THz would consist of a niobium-based SIS-junction embedded in NbTiN top and bottom wiring layers. It has been shown that such a junction exhibits strong DC heating effects due to quasiparticle trapping, the absence of diffusion cooling, and a slow electron-phonon interaction time. The heating substantially reduces the mixer performance. We investigate the possibility of adding a gold layer between the junction's Nb top electrode and the NbTiN top wiring in order to increase the heat transport coefficient. This and some additional challenges concerning the fabrication of these devices are discussed in this talk.