Large-Scale SFQ Switches Using Miniaturized 2$\,\times\,$2 Switch Cell

We have developed a miniaturized 2times2 switch cell, a key component of single-flux-quantum switches. The cell was optimized using a full-custom design approach instead of our conventional cell-based design approach. The cell contains 74 Josephson junctions, and its power consumption is 16.8 muW. Its area is significantly reduced to 160 mum times 200 mum, which is 69% smaller than our conventional cell-based switch. We fabricated test chips using our 2.5-kA/cm
²
Nb standard process and confirmed a 40-GHz operation with a bias margin of plusmn8.5% by an on-chip test. We also designed 4times4 and 8times8 cross-bar switches using the 2times2 switch cells. The 40-GHz operation of the 4times4 switch was confirmed with a bias margin of plusmn4% by an on-chip test. The full function of the 8times8 switch was also confirmed with a bias margin of plusmn5% at a low-frequency (10 kHz). The area of these switches was reduced to about half of that of our conventional switches. We discussed large-scale switches using our advanced high- Jc multilayer process. We estimated that area of a 32 times 32 switch designed for the advanced process are reduced by 83% compared to a switch designed for the standard process.