Development and testing of Band 10 receivers for the ALMA project

• The ALMA Band 10 (787–950 GHz) SIS receivers have been developed.
• The complex conductivity of NbTiN was measured by a THz-TDS for the mixer design.
• Tens of Band 10 receivers have been produced and their performance was quite well.
• The best achieved receiver noise temperature was 125 K corresponding to 3hf/kB.
• Band 10 receiver installed in the ALMA antenna captured astronomical signals.

The production model of a dual polarization heterodyne receiver for the Atacama Large Millimeter/submillimteter Array (ALMA) telescope has been developed to operate in the 787–950 GHz frequency band. The receiver uses two double sideband (DSB) waveguide mixers with Nb/AlOx/Nb tunnel junctions and NbTiN/SiO2/Al microstrip tuning circuits on quartz substrate. A terahertz time domain spectrometer was used to characterize our NbTiN film for the tuning circuit design, which revealed that the complex conductivity of the film is described by the Mattis-Bardeen theory including a finite scattering time of 15 fs and a superconducting gap with a gap ratio 2Δ/kBTC ∼ 4.0. Tens of these receivers (out of the total production number of 73) have been successfully produced, and their performance is well within the stringent ALMA requirements. The best achieved DSB receiver noise temperature is 125 K, corresponding to about 3hf/kB for 4 K operation. One of Band 10 receivers has successfully been installed in the ALMA antenna for a test observation.