SFQ Propagation Properties in Passive Transmission Lines Based on a 10-Nb-Layer Structure

We have studied single-flux-quantum (SFQ) propagation properties in passive transmission lines (PTLs) based on a 10-Nb-layer device structure (ADP2). In ADP2, we can use the PTLs with a line width about 5 mum, one seventh of conventional line width by adopting a strip line (SL) structure and increasing the characteristic impedance. The evaluation has been conducted on the PTL length and the via-hole structure by using ring oscillators. We found that the decrease in the operating region was larger for longer PTL, compared with that in a conventional device structure (STD2). The results would be caused by the increase in the surface resistance. The via-holes connecting the PTLs on different layers have more complicated structure than those of STD2. We have designed the via-hole structure using the electromagnetic wave simulator HFSS. As a result, we have demonstrated sufficiently large operating margins at any data rates up to 80 Gb/s even for the ring oscillator with 30 via-holes.