A 4-Nb-Layer Cell Library Suitable for LSI Superconductor Digital Circuits
Xiaoping Gao, Yuxuan Feng, Minghui Niu, Xi Gao, Huanli Liu, Bicong Weng, Shucheng Yang, Xue Zhang, Liliang Ying, Wenbo Zhao, Wei Peng, Jie Ren · IEEE Transactions on Applied Superconductivity · 2025
The increase in the single-flux-quantum (SFQ) circuit scale will cause the overall bias current to increase dramatically. The magnetic field interference caused by the current supplied to the SFQ circuit can no longer be ignored. In addition, more complex SFQ circuits require a cell library for more diversified cell types and a more stable operating range to ensure the circuits’ yield. The SIMIT-Nb03P process is then put forward as a tradeoff between process stability and cost. It is compatible with the Nb03 process and does not need an expensive chemical mechanical planarization process. The added new dc power layer is proved to have less interference by simulation. The conversion from Nb03 to Nb03P cell library was very convenient. In addition, some new cells are designed to meet the requirements of complex SFQ circuits. Test circuits of 20 cells of Nb03P were designed and fabricated and were fully verified at low frequencies. The common bias margin of the whole cell library is (–26%, 20%). A variety of large-scale circuits (up to more than 10 000 Josephson junctions) achieve correct function at high frequencies and show good yields on the wafer. It shows that this updated process is cost efficient and suitable for large-scale integration circuits.