Examples of superconducting technology application: Sensing and interfacing

Abstract

Technological processes for the fabrication of low-and high-T c Josephson junctions, aimed for certain applications, are described. On the one hand, the integration of low-T c superconductor digital electronics with superconducting sensor arrays enables input signal processing with quantum limited resolution at millikelvin temperatures. We describe this mixed signal superconductor technology for analogue sensor readout and signal multiplexing for operating temperatures down to 300 mK. On the other hand, by making use of modern high-T c Josephson junction technology, sensitive magnetometers, which require a modest cooling power, can be developed. Examples of the application of the mentioned processes are shown.

Study of Microwave Resonances Induced by Bias Lines of Shunted Josephson Junctions

“…The reported test circuits have been fabricated in the framework of the FLUXONICS Foundry at Leibniz IPHT in Jena (Germany) using the standard process for RSFQ [1] [2]. The layer stack consists of 13 layers, including three wiring layers of niobium (M0,M1,M2), one trilayer packet (TRI) in order to implement the Josephson junctions, two layers for resistors (R1,R2) and seven layers for isolation using either SiO2 (I0B,I0C,I1B,I2,I3) or Nb2O5 (I0A,I1A).…”

“…pplication-specific superconducting circuits based on the Rapid Single Flux Quantum (RSFQ) digital technique are generally fabricated with a multilayered thin-film process which integrates one or more ground plane layers [1], [2], [4]. The ground plane, which often covers most of the chip surface, focuses the magnetic field under the superconducting wiring lines, which drastically lowers magnetic couplings between adjacent wires [5], [6].…”

“…This work aims at predicting resonances and designing resonance-free superconducting circuits, starting from a simple circuit model. An electrical model of a shunted Josephson junc-tion is presented with its bias lines and pads fabricated with the 1 kA/cm² RSFQ niobium process of the European FLUX-ONICS Foundry [1] [2]. Starting from the layout that includes the bias lines and pads shown in Fig.…”

Anodization-free fabrication process for high-quality cross-type Josephson tunnel junctions based on a Nb/Al-AlO x /Nb trilayer

“…Josephson tunnel junctions are key components of any superconductor electronic device. This includes superconducting quantum bits [1], superconducting quantum interference devices (SQUIDs) [2], rapid single flux quantum (RSFQ) circuits [3,4], Josephson voltage standards [5], single electron transistors (SETs) [6,7], Josephson parametric amplifiers [8,9] or superconductor-insulator-superconductor (SIS) mixers [10,11]. Most of these devices are based on refractory Josephson tunnel junctions made of an insitu deposited Nb/Al-AlO x /Nb trilayer, the latter being an excellent choice regarding junction quality, tunability of the critical current density, scalability and run-to-run reproducibility of characteristic junction parameters as well as resilience to thermal cycling.…”