Presentation Information
[EDP2-04]Ultra Low Voltage Operation of Half-Flux-Quantum Circuits
*Kenshin Inagaki1, Soma Deguchi1, Feng Li1, Masamitsu Tanaka1, Akira Fujimaki1 (1. Nagoya Univ. (Japan))
Keywords:
π Josephson Junction,Single-Flux-Quantum-Circuits,Half-Flux-Quantum Circuits,Ultra Low Voltage
We are studying half-flux-quantum (HFQ) circuits [1], in which a 0-π SQUID, consisting of a normal Josephson junction (0-junction) and a ferromagnetic Josephson junction (π-junction), is employed as the switching element. In the 0-π SQUID, a circulating current flows to compensate for the π phase shift induced by the π-junction, due to the flux quantization condition. As a result, the 0-π SQUID shows a smaller nominal critical current (Icn) than the critical current Ic of the 0-junction. This characteristic leads to significantly low-power operation.In this work, we evaluated the operating characteristics of HFQ circuits driven by ultra-low bias voltages using numerical simulations. The design guideline of HFQ-based Josephson transmission line (HFQ-JTL) was based on the conventional single-flux-quantum (SFQ) circuits, i.e., LIc=Φ0, considering that the information carrier is a half flux quantum. We designed the loop inductance of the 0-π SQUID , Ljtl, to satisfy the condition (Ljtl/2 + Lloop) = 0.25Φ0. We connected a bias resistor (Rb)such that the bias current was Ib = 0.4Icn. We found that HFQ-JTL can operate at extremely low bias voltages when we set Ic, Lloop, and Icn to 100 µA, 1.27 pH, and 19 µA, respectively. We confirmed stable operation when the bias voltage was lowered from 0.5mV to 3.6 µV. Figure 1 shows the bias voltage dependency of the propagation. The conventional, SFQ-based JTL could not operate in this voltage, and it is attributed to the low-loss switching property of the 0-π SQUIDs used in the HFQ circuits.