We report on the realization of Nb-based all-metallic Dayem nano-bridge gate-controlled transistors (Nb-GCTs). These Josephson devices operate up to a temperature of ∼3 K and exhibit full suppression of the supercurrent thanks to the application of a control gate voltage. The dependence of the kinetic inductance and of the transconductance on gate voltage promises a performance already on par with so far realized metallic Josephson transistors and leads us to foresee the implementation of a superconducting digital logic based on the Nb-GCT. We conclude by showing the practical realization of a scheme implementing an all-metallic gate-tunable half-wave rectifier to be used for either superconducting electronics or photon detection applications.
We report on the realization of Nb-based all-metallic Dayem nano-bridge gate-controlled transistors (Nb-GCTs). These Josephson devices operate up to a temperature of ∼3 K and exhibit full suppression of the supercurrent thanks to the application of a control gate voltage. The dependence of the kinetic inductance and of the transconductance on gate voltage promises a performance already on par with so far realized metallic Josephson transistors and leads us to foresee the implementation of a superconducting digital logic based on the Nb-GCT. We conclude by showing the practical realization of a scheme implementing an all-metallic gate-tunable half-wave rectifier to be used for either superconducting electronics or photon detection applications.
Superconducting field-effect transitor (SuFET) and Josephson field-effect transistor (JoFET) technologies take advantage of electric-field-induced control of charge-carrier concentration to modulate the channel superconducting properties. Despite the fact that the field-effect is believed to be ineffective for superconducting metals, recent experiments showed electric-field-dependent modulation of the critical current ( I C ) in a fully metallic transistor. However, the grounding mechanism of this phenomenon is not completely understood. Here, we show the experimental realization of Ti-based Dayem bridge field-effect transistors (DB–FETs) able to control the I C of the superconducting channel. Our easy fabrication process for DB–FETs show symmetric full suppression of I C for applied critical gate voltages as low as V G C ≃ ±8 V at temperatures reaching about the 85% of the record critical temperature, T C ≃ 550 mK, for titanium. The gate-independent T C and normal-state resistance ( R N ) coupled with the increase of resistance in the superconducting state ( R S ) for gate voltages close to the critical value ( V G C ) suggest the creation of field-effect induced metallic puddles in the superconducting sea. Our devices show extremely high values of transconductance (| g m MAX | ≃ 15 μA/V at V G ≃ ±6.5 V) and variations of Josephson kinetic inductance ( L K ) with V G of 2 orders of magnitude. Therefore, the DB–FET appears as an ideal candidate for the realization of superconducting electronics, superconducting qubits, and tunable interferometers as well as photon detectors.
Recently, the possibility to tune the critical current of conventional metallic superconductors via electrostatic gating was shown in wires, Josephson weak-links, and superconductor-normal metal–superconductor junctions. Here, we exploit such a technique to demonstrate a gate-controlled vanadium-based Dayem nano-bridge operated as a half-wave rectifier at 3 K. Our devices exploit the gate-driven modulation of the critical current of the Josephson junction and the resulting steep variation of its normal-state resistance, to convert an AC signal applied to the gate electrode into a DC one across the junction. All-metallic superconducting gated rectifiers could provide the enabling technology to realize tunable photon detectors and diodes useful for superconducting electronics circuitry.
Local control of superconducting circuits by high-impedance electrical gates offers potential advantages in superconducting logic, quantum processing units, and cryoelectronics. Recent experiments have reported gate-controlled supercurrent in Dayem bridges made of metallic superconductors, mediated by direct current leakage, out-of-equilibrium phonons, or possibly other mechanisms. However, a time-domain characterization of this effect has been lacking. Here, we integrate Dayem bridges made of niobium on silicon into coplanar waveguide resonators and measure the effect of the gate voltage at steady state and during pulsed operation. We consider two types of arrangements for the gate: a side-coupled gate and a remote injector. In both cases, we observe sizable changes in the real and the imaginary part of the constriction's impedance for gate voltages of the order of 1 V. However, we find striking differences in the time-domain dynamics, with the remote injector providing a faster and more controlled response. Our results contribute to our understanding of gate-controlled superconducting devices and their suitability for applications.
The interplay of alternative materials, large-scale integration technologies, and innovative devices plays a pivotal role on the way to fault-tolerant quantum computing. In this context, gate-controlled superconductivity (GCS) emerges as a key enabling technology, promising to advance superconducting logic and quantum electronics, complementing conventional approaches based on Josephson effects and quantum interference. Here, we demonstrate all-metallic superconducting ZrN nanostructures on silicon, fabricated entirely using a subtractive, monolithic dry-etch approach with a 300 mm CMOS-compatible process flow. For Dayem-bridge weak links with decreasing width down to 27 nm, we observe Tc of 7.3 K, width-dependent switching characteristics, and a progressive approach of the tunneling limit. In laterally gated Dayem-bridge and nanowire devices, we observe GCS with full suppression of the critical current, where required gate voltages <5 V promise compatibility with CMOS interfaces. Asymmetries in polarity-dependent power injection via field emission support GCS models that attribute the effect to quasiparticle relaxation through phonon emission. Additional asymmetries in the GCS effect suggest an influence of the substrate condition after dry etching. Field emission features in the gated nanowire device imply superimposed current paths along the gate edge and corners. Finally, we analyze magnetic interference in Dayem-bridge weak links and superconducting quantum interference devices, where quantum interference is governed by Josephson effects and inductance loop asymmetries. Our results contribute to the scaling efforts in hybrid superconducting electronics and quantum-processing units.
Voltage-Tunable Vertical Nb/TiOx/Nb Josephson Junction With High Transconductance and Broad Inductance Modulation
The ability to electrically control the critical current of a Josephson junction is a pivotal capability for developing reconfigurable superconducting electronics and quantum circuits. In this study, we report a voltage-tunable vertical Nb/TiOx/Nb Josephson junction, featuring a top tuning electrode isolated by a 13 nm single-crystal hexagonal boron nitride (h-BN) dielectric. Applying a tuning voltage across this 2D insulator creates a high electric field, enabling the direct injection of high-energy quasi-particles into the junction. This mechanism facilitates the continuous suppression of the critical current to zero, accompanied by a broad modulation of the Josephson inductance. Our superconducting device exhibits a high transconductance ($\sim1mA/V)andallowstheJosephsonkineticinductancetobetunedacrossawiderange(\sim$0.01-1 nH). This voltage-tunable vertical architecture provides a compact device footprint, offering a promising platform for exploring dense, all-metallic superconducting circuits and future active cryogenic applications.
Recent studies have shown that the critical currents of several metallic superconducting nanowires and Dayem bridges can be locally tuned by using a gate voltage ( V g ). Here, we report a gate-tunable Josephson junction structure constructed from a three-dimensional (3D) niobium nanobridge junction (NBJ) with a voltage gate on top. Measurements up to 6 K showed that the critical current of this structure can be tuned to zero by increasing V g . The critical gate voltage was reduced to 16 V and may possibly be reduced further by reducing the thickness of the insulation layer between the gate and the NBJ. Furthermore, the flux modulation generated by Josephson interference of two parallel 3D NBJs can also be tuned by using V g in a similar manner. Therefore, we believe that this gate-tunable Josephson junction structure is promising for superconducting circuit fabrication at high integration levels.