Superconducting single flux quantum (SFQ) digital circuits can operate at high speed with lower power consumption, whereas complementary metal oxide semiconductor (CMOS) circuits are very compatible with conventional technology. By combining SFQ and CMOS circuits, it is expected to realize super high-performance hybrid devices. However, output from SFQ circuits is too small to drive semiconductor circuits, and therefore, additional devices as interfaces to communicate each other are required.

A superconducting nano-wire cryotron (nTron) which was invented by MIT is a three-terminal device, and its basic operating principle is the current-driven transition from the superconducting state to the normal state. Its applications are expected as the interfaces of superconductor-semiconductor hybrid devices, superconducting detectors, and quantum-computing devices. Although the nTron’s fundamental characteristics are getting clear, we still need to understand its physical mechanism and operation characteristics.

We have developed the numerical technique to simulate the three-terminal operation of the nTron by using the finite element method to solve the time-dependent Ginzburg-Landau (TDGL) equation and thermal diffusion equation. Specifically, we first apply the finite gate current and sweep the channel bias current, and we investigate (channel-bias current)-(channel-voltage) characteristics of the nTron.

The direct-current operation model was successfully reproduced experimental data by MIT, and we made sure that direct-current injection from the gate can control channel voltage to induce the normal state transition. Further, we investigated the pulse-wave response of the nTron to understand the behavior of channel state when a pulse current was injected from the gate.

This work was supported by JSPS KAKENHI Grant Numbers JP20K05314.
We thank N. Yoshikawa for the helpful discussions about the nTron’s operation.

Keywords: superconducting nanowire cryotron, Ginzburg-Landau simulation, hybrid devices