Simulation of the Margins in Single Flux Quantum Circuits Containing π-Shifted Josephson Junctions

Abstract

We designed several single flux quantum (SFQ) flipflops and logic gates composed of Josephson junctions (JJs) and shifted JJs (-JJs) to quantitatively evaluate effectiveness of introduction of -JJs into the SFQ logic circuit. One-output flip-flops and logic gates were designed on the basis of the circuit design methodology we built for the SFQ circuit containing -JJs. The designed flip-flops and logic gates have wide operating margins, the dc bias margins of larger than ±30% and device parameter margins of ±18%, though the static power consumption are reduced compared to conventional ones composed of JJs. We found that the difference in the critical current density between JJs and -JJs does not affect the operating margins of the SFQ flip-flop composed of JJs and -JJs. We devised a circuit structure of the delay flip-flop with complementary outputs composed of JJs and -JJs (-DFFC). The analog circuit simulation shows the dc-bias margin of the -DFFC is larger than ±33%. These results indicate that the large-scale SFQ logic circuit system can be implemented using the flip-flops and logic gates containing -JJs.  Index Terms-Single-flux-quantum (SFQ) circuit, -shifted Josephson junction, flip-flop I. INTRODUCTION NERGY Consumption for Information and Communication Technology (ICT) has drastically increased for decades.Total energy consumption for ICT devices in the world has already reached 1 PWh/year in 2017, which is larger than annual energy consumption in Japan, and is estimated to keep increasing in the future [1]. However, semiconductor integrated circuit technology, which has been supporting the ICT development, is facing several obstacles [2]. Among the obstacles, power consumption is the most serious problem of the semiconductor complementary metal-oxide-semiconductor (CMOS) integrated circuit. In this sort of situation, beyond-CMOS devices that can overcome limitation of CMOS devices, have been studied [3]. Among various beyond-CMOS devices, superconducting digital devices, including single-fluxquantum (SFQ) devices [4,5] and its improved versions have a high-speed operation characteristic with ultra-high energy ef-Manuscript receipt and acceptance dates will be inserted here.

Superconducting Circuits without Inductors Based on Bistable Josephson Junctions

“…The cell inductance can be reduced correspondingly, and the number of JJs in the substituting stack can be decreased down to three, see Figs. 1(c) and 1(d) [20][21][22][23][24][25][26][27][28]. In the RSFQ toggle (T) flip-flop, it is possible even to completely substitute the inductor with a π -JJ [20][21][22].…”

“…The latter is composed of two JJs connected in series, one of which is switched by the clock (clk) pulse, depending on the direction of the measured current, I x . Many widely used cells, such as a delay (D) flip-flop and nondestructive read-out (NDRO) [24], or AND and OR logic cells [25], can be designed within the framework of this approach.…”

Demonstration of an efficient single flux quantum logic circuit by introducing a local magnetic flux biasing

“…By using the phase shift of π, the magnetic flux of approximately ±0.5Φ 0 through the superconductor loop can be used to express two internal logic states. The internal state expression by the half flux quantum is suitable for designing an SFQ flip-flop with complementary outputs [16]. The circuit area can be reduced by inducing a phase shift in the LFB architecture because it does not require a high inductance to store the half flux quantum, whereas a conventional SFQ circuit needs a high inductance i.e., LI C > Φ 0 .…”

Epitaxial growth and superconducting properties of thin-film PdFe/VN and VN/PdFe bilayers on MgO(001) substrates

“…The latter concept was implemented in the US Cryogenic Computing Complexity (C3) Program [11][12][13] with the goal "to demonstrate a small-scale computer based on superconducting logic and cryogenic memory that is energyefficient, scalable and able to solve interesting problems", opening prospects of reaching 100 PFLOPS/s with about 200 kW of electric power consumption including the cryogenic cooling. Niobium-based Josephson junction technology is currently implied to be used for the logics fabrication, however, hybrid Josephson junctions incorporating magnetic components are also considered for the mainframe computation components [9,[14][15][16][17][18][19], and cache and main memories [8,[20][21][22][23][24][25]. It is argued that the use of magnetic Josephson junctions in single-flux quantum electronics significantly reduces the number of junctions and interconnects in the circuits [26] and also has other important advantages such as wide operation margins and low bit-error rate [27].…”