Air Cavity Transmission Lines for Off-Chip Interconnects Characterized to 40 GHz

In this paper, air cavity transmission lines are integrated into printed circuit boards and packages to enable high-speed low-loss chip-to-chip communication. Microstripline and parallel plate structures with copper conductors separated by an air gap dielectric layer are described. The structures use a sacrificial placeholder material along with conventional microelectronics techniques to create a unique buried copper- air-copper microstripline structure. Transmission lines were characterized by S-parameter measurements to 40 GHz. The capacitance was tracked during fabrication to analyze the impact of the air gap. The effective dielectric constant of the final buried copper-air-copper structure was as low as 1.25.