Hybrid integration of microwave oscillators with Josephson series arrays for the use as voltage standards

Abstract

We have designed and fabricated a new type of Josephson device to be hybrid integrated with microstripline oscillators. For optimum matching of the Josephson series array to the oscillator the samples make use of a new stripline design. The first circuits were fabricated in a simplified NbJA1203INb technology and exhibit excellent dc characteristics and good microwave coupling to the junctions of the array. At 70 GHz constant voltage steps up to 350 mV could be observed. By hybrid integrating different samples with a new 10-GHz oscillator, constant voltage steps were created. For this experiment the Josephson current density had to be low enough to reduce the plasma frequency of the junctions to well below the driving frequency.

A review of Josephson comparison results

“…The first 1 V array had a total of 1474 PbInAu/PbO x /PbAu (B) SIS jj driven at 90 GHz [30]. Junction materials such as NbN/MgO/NbN (C) [31] and Nb/AlO x /Nb (D) [32][33][34][35][36][37][38][39][40][41] were successfully used as well (cf table 2).…”

“…Depending on the type of the Josephson junction, different ranges of frequencies for the RF bias sources have been used from a few hundred kilohertz to 100 GHz. Most of the sources are room-temperature phase-locked oscillator systems, but fully superconducting RF sources based on superconducting monolithic microwave integrated circuits (SMMICs) in GaAs technology have also been successfully operated at 70 GHz [32]. The design of the microwave stripline is also one of the major challenges in fabricating a successful JVS.…”