Properties of Josephson array oscillators at the submillimeter wave region

We have developed resistively shunted tunnel junctions with a small parasit ic inductance (congruent to 100 fH) to improve the high frequency performan ce of Josephson array oscillators. Josephson array oscillators with 11 such junctions and Nb microstrip resonators were designed and fabricated to ope rate at 650 GAz. Shapiro steps induced by Josephson oscillation were clearl y observed at the submillimeter frequency region. By comparing the step hei ght with the numerical simulation, we estimated the power of the Josephson oscillator delivered to the load resistor to be about 10 mu W st 625 GHz. T he linewidth of the Josephson array oscillator was also measured using an i ntegrated receiver consisting of two Josephson array oscillators and an SIS mixer. The designed frequency of the receiver was set at 550 GHz. IF outpu t power spectrum was observed when both the oscillators were biased at abou t 1.17 mV which corresponds to 566 GAz, The composite linewidth of Josephso n oscillation was measured about 8 MHz at 4.2 K.