Experimental and simulation results of a symmetrical pad to reduce a stray ground current in superconducting integrated circuits

29th International Symposium on Superconductivity

Suzuki, H.^1 ; Ono, T.^1 ; Yoshikawa, N.^1

Yokohama National University, 79-1, Tokiwadai, Hodogaya-ku, Yokohama

240-8501, Japan^1

关键词: Asymmetric structures;    Ground currents;    Harmful effects;    Operating margins;    Stray magnetic fields;    Superconducting circuit;    Superconducting integrated circuits;    Symmetrical structure;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/871/1/012067/pdf
DOI  :  10.1088/1742-6596/871/1/012067

来源: IOP

【 摘 要 】

The method of extracting bias current is widely used in large scale SFQ circuits to avoid harmful effect by spreading the bias return current on a ground plane, which causes malfunction or degrading the operating margin by the stray magnetic field. Although extracting the bias current is effective, we found that the extraction using a normal pad structure with a bias pad and a current extracting pad still produces a large stray ground current (magnetic field) for its asymmetric structure. We proposed a bilaterally symmetrical pad structure, which can reduce the stray ground current significantly in superconducting circuits. The bias current is extracted from a nearby ground pad of a bias pad in usual method, whereas the bias current is extracted from two of the symmetrical ground pads which are arranged both sides of the bias pad in the symmetrical structure. Then, the bias current is extracted on halves from each of the two pads symmetrically, reducing the stray ground current. First, we have simulated the ground current by using FastHenry program. The results showed that the symmetrical pad structure outside of ground plane reduced spread of the ground return current significantly. Next, we have designed a test chip and confirmed the effectiveness of the symmetrical structure experimentally.