Josephson junctions generate, when subjected to microwave irradiation, voltages with a very high precision and are used in metrology applications. So-called PJVS (programmable Josephson voltage-standards) are capable of generating both AC and DC voltages of up to 10 V. Our work addresses a full fabrication scenario for 10 V PJVS arrays driven at 70 GHz to be used in low microwave-power conditions as in, but not limited to GUNN diodes or cryocooler applications. Nb x Si1−x in its function as a barrier material was characterised with AFM, RBS and reflectometry in order to establish a reliable technological foundation. A 10 V PJVS array driven with microwave power below 50 mW is further presented, which was achieved by optimising the fabrication technology regarding the degree of homogeneity of the Josephson junctions composition and thickness. Control over these parameters is crucial in choosing a stable and well-suited characteristic voltage (I c R n product) and critical current density j c. With this, a low-power operation of a PJVS array is possible without the need for liquid helium cooling, which is currently limiting the availability of PJVS based metrology.

AC Josephson voltage standards are typically based on series arrays of overdamped Josephson junctions, which are presently realized using an NbxSi1-x barrier at PTB. The characteristic parameters of these SNS-like junctions can be tuned by the Nb content and the thickness of the barrier over a wide range for operation from 10 GHz to 70 GHz. Based on these junctions, we developed binary-divided 10 V arrays as well as pulse-driven arrays for 1 V output voltages.

The PTB Josephson Arbitrary Waveform Synthesizer (JAWS) enables the generation of arbitrary waveforms up to voltages of 70 mV RMS (199 mV PP ) using two Josephson arrays in series containing 4000 Josephson junctions each.The SNS-like double-stacked junctions are based on Nb x Si 1-x as barrier material.While the JAWS system is typically operated using a Dewar with liquid helium, the operation in a closed-cycle pulse-tube cryocooler at temperatures around 4.2 K range was here investigated and successfully demonstrated.For this purpose a special designed cryoprobe was used to provide high quality pulses to the Josephson arrays.

Essential applications of terahertz technology are urgently in need of compact, tunable solid-state continuous wave radiation sources. However, no satisfactory solution is yet available for the frequency range of up to approximately 1.0 THz. Here, we present coherent radiation from large series arrays of Josephson junctions between 0.1 and 0.25 THz with off-chip radiation power of 7 μW. Niobium junctions oscillate at 4.2 K and the detection has been done at room temperature. The well-known obstacle to impedance matching is overcome by utilizing the excited resonances in the junction substrates serving as dielectric resonator antennae.