Design and Development of SIS Mixers for ALMA Band 10

摘要

We present the design and preliminary experimental results of Superconductor-Insulator-Superconductor (SIS) mixers for Atacama Large Millimeter Array (ALMA) band 10 (780–950 GHz) receivers. To achieve wide frequency coverage as well as low noise temperature, we integrated high current density (10 ${rm kA/cm}^{2}$) and small-sized (one micrometer in diameter) ${rm Nb/AlO}_{rm x}/{rm Nb}$ SIS junctions with a tuning microstrip line using NbTiN ground plane and Al wiring layers. High quality NbTiN films with Tc reaching 14.5 K and Al films with residual resistivity ratio as large as 15 have been achieved. To minimize the waveguide transmission loss and facilitate the fabrication of mixer block, a full height waveguide was adopted. The waveguide probe was optimized to achieve low input impedance in the frequency range of 780–950 GHz while adopting a backshort cavity of zero depth. Preliminary RF testing with a Nb/Al microstrip tuning circuit demonstrated a DSB receiver noise temperature about 400 K at 832.5 GHz, which promises the accommodation of receiver performance in ALMA specification with low loss NbTiN/Al microstrip lines.