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Japanese Journal of Applied Physics

Simulation of a Multi-Josephson Junction Single Flux Quantum Switching Device

Ko Hara, Kobayashi Haruo, Shyuuhei Takagi, Fuyuhiko Shiota

Published Dec 1, 1980• 1 citation
Publisher
DOI
10.1143/jjap.19.2519

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We report on a voltage-state logic family based on shunted Josephson junctions and on the Rapid Single Flux Quantum (RSFQ) concept. Storing information in a voltage-state form makes this Multi-Flux-Quantum Logic (MFQL) easier to match to complementary metal-oxide semiconductor (CMOS) circuits. The switching of MFQL element between the voltage and zero-voltage states takes a minimum of two SFQ pulses, and the switching time of this logic is comparable to that of RSFQ logic. The key logic element is an inverter in the form of an asymmetric interferometer, and the underlying idea is to use a separate superconducting wire to supply a standard dc output voltage for the elements. The asymmetric interferometer, directly coupled to the other elements, is actually a Josephson junction based three-terminal device or transistor. Elements such as NOT, OR, NOR, XOR, XNOR, a toggle flip-flop, and an RS trigger have been simulated, and show margins better than /spl plusmn/24%. The performance of this logic with current circuit fabrication technologies is also discussed.
Flux quantum logic and memory circuits using superconducting Josephson tunnel junctions have high-speed switching times (approximately 1 ps), low power dissipation (< 1 (mu) W per circuit) and low levels of thermally induced electrical noise. Current designs of such circuits employ single trilayer junctions, which impose circuit size and logic threshold limitations. A new design component, the multilayered tunnel junction, consists of a vertically stacked array (a 1D superlattice) of Josephson tunnel junctions. The introduction of multilayered junctions into superconducting electronic circuitry offers a reduction in the current device size, fault tolerances, and new device applications. We present numerical simulations of simple circuits employing multilayered Josephson junctions as design components. Comparison with conventional single flux quantum circuitry is discussed. We also present preliminary measurements of multilayered Josephson junctions fabricated for use in flux quantum devices.
We develop a fast magnetic Josephson junction (MJJ)—a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient single flux quantum (SFQ) circuits. We present experimental results for superconductor-insulator-ferromagnet-superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 μV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ∼30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.