Sub-micron superconducting PTLs for SFQ logic circuits

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We have designed and fabricated sub-micron-wide microstrip lines (MSLs) for SFQ circuits. We adopted Al_2O_3 as the insulator of MSLs to realize characteristic impedance of 10 Ω which is equivalent to one of future SFQ VLSI circuits. To evaluate propagation characteristics of MSLs, we measured loaded quality factors of resonance QL. In this measurement, we obtained fundamental resonance peaks around 6 GHz against a design value 5 GHz for each MSL and respective QL is about 100.For the high-density SFQ VLSI circuits, three-dimensional (3-D) integration will be needed. We are trying an Nb electrodeposition from non-aqueous electrolytes, which is suitable for making 3-D wiring through substrates. For the Nb electrodeposition from non-aqueous electrolytes, relatively smooth, metallic colored Nb compound films were obtained from solutions containing LiNbCl_6.