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Superconductor digital circuits with π junctions alone
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DOI：10.1063/5.0144604.png)
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Abstract
En 中文
We adopt superconductor/ferromagnet/insulator/superconductor (SFIS) Josephson junctions (JJs) as both switching JJs and intrinsic pi phase shifters in superconductor digital circuits. The critical current density (J(c)) and characteristic voltage (V-c) of the SFIS junctions are about 22 A/cm(2) and 22 mu V, respectively. The intrinsic pi phase shift is confirmed by measuring the suppressed nominal critical current I-cn and half-period-shifted modulation pattern of a pi-pi-pi superconducting quantum interference device (SQUID) that contains three pi-JJs in a super-conducting loop. A single-flux-quantum (SFQ) circuit composed of a DC/SFQ, Josephson transmission line (JTL), and SFQ/DC converter based on SFIS JJs alone is demonstrated at 4.2 K. The energy dissipation of the SFQ/DC converter decreases by 80% because some JJs are self-biased by the pi phase shifter. The intrinsic circulating currents induced by the pi phase shifters lead to a narrow bias margin (+/- 5%) and even error function, which can be solved by parameters optimization or circuit initialization in the future. The half-modulation period (Phi(0)/2) of a half-flux-quantum (HFQ) SQUID (a partial HFQ JTL) exhibits propagation of HFQ between pi-pi-pi SQUIDs, indicating that more complex HFQ circuits can be developed with pi-JJs alone in the future.
Keywords:
JOSEPHSON
FERROMAGNET
FLUX
SUPERCURRENT