Superconducting interconnects for VLSI multi-chip system integration

Results related to the fabrication and measurement of the propagation constant of superconducting microstrip lines operating at microwave frequencies are presented. The phase velocity and penetration depth measurements lead to several conclusions regarding the use of superconducting transmission lines as off-chip interconnects. First, the line´s phase velocity can be determined from simple formulas, which greatly aids in interconnect design. The magnitude of the phase velocity is determined mostly by the effective dielectric constant, except for lines with dielectric thickness on the order of the penetration depth, for which the phase velocity is degraded. Attenuation constant measurements were also done. The low-temperature attenuation level is 2×10^-4 dB/cm at 2.3 GHz even though a poor-quality film was used. This residual attenuation level at low temperature is probably dominated by dielectric losses since it is proportional to frequency; this suggests that the superconductor losses are less than this level