High-energy electron local injection in top-gated metallic superconductor switch

Abstract

The gate-tunable superconductivity in metallic superconductors has recently attracted significant attention due to its rich physics and potential applications in next-generation superconducting electronics. Although the operating principles of these devices have been attributed to the small leakage currents of high-energy electrons in recent experiments, the generated phonons can spread over considerable distances in the substrate, which may limit their further applications. Here, we utilize a top gate structure with monocrystalline h-BN as a gate dielectric and demonstrate the gate-adjustable supercurrent in a metallic Nb microbridge. The gate current of the devices perfectly follows the Fowler-Nordheim law of field emission, indicating that the injection of high-energy electrons presumably causes the suppression of the supercurrent. Our devices reduce the distance between the gate and the microbridge to a few nanometers or less, significantly minimizing the generated phonons’ spreading distance and power dissipation in the substrate or surrounding environment. These observations demonstrate that top-gated metallic superconducting switches with local electron injection can improve the device integration density, providing us with more versatile and practical opportunities to explore superconducting circuit architecture.

High-Performance Gate-Controlled Superconducting Switches: Large Output Voltage and Reproducibility

“…We note that there is only one report to date about the observation of a GCS in micrometer-wide Nb bridges (i.e., with w S ≫ ξ), but these devices have a top-gate other than a side-gate geometry, unlike the ones investigate in the present study. In a device with a top gate, the most relevant dimension for the GCS is not w S but the S thickness, which in ref is ∼6 nm and hence still comparable to ξ (<15 nm; ref ).…”

“…The control of a superconducting current (supercurrent) via the application of a gate voltage ( V G ), currently known as gate-controlled supercurrent (GCS), has become a subject of great interest, as evidenced by the number of experimental − and theoretical studies − reported on it. Among the main motivations behind the interest in the GCS is its potential for the development of voltage-controlled superconducting logics that would intrinsically have low-energy dissipation (since based on superconductors) and better performance than other superconducting logics already available. − Compared to these, GCS-based logics would offer several advantages including higher device density (due to the smaller device size), larger number of devices connectable in series (i.e., higher fan out), stronger resilience to magnetic noise and easier interfacing with conventional metal-oxide semiconductor (CMOS) circuits to form hybrid superconducting/semiconducting computing architectures .…”

“…Some of these mechanisms ascribe the GCS to phenomena triggered by the finite leakage current ( I leak ) that flows in most device realizations between the gate and the superconductor (S) constriction under an applied V G . These phenomena include tunneling of high-energy electrons between the gate and the S, − ,, phonons induced by I leak in the substrate heating the S constriction, and high-energy electrons or phonons induced by I leak which drive the S into an out-of-equilibrium state characterized by phase fluctuations but without heating. , In addition to these I leak -related mechanisms, it has also been suggested that the electric field (associated with the applied V G ) can induce effects responsible for a GCS. − ,,, …”