Pb/Bi/In and Nb/Al junctions for a 345 GHz open structure astronomical receiver

The authors report on the preparation and properties of Pb/Bi/In-oxide-Pb/Bi and Nb-Al oxide-Nb junctions prepared for a 345-GHz open-structure heterodyne receiver. The lowest receiver noise temperature with the Pb/Bi/In junctions is 215 K DSB. In this case, no matching network is integrated to tune out the junction capacitance. For the Nb/Al junctions, a microwave transmission line compensates the capacitance around 345 GHz. With the Nb-Al oxide-Nb two-junction array at 4.2 K, the lowest receiver noise temperature is 80 K at 330 GHz. The receiver is in use at the IRAM (Institut de Radio Astronomie Millimetrique) 30-m radio telescope in Spain.<>