Air-Gap Transmission Lines on Organic Substrates for Low-Loss Interconnects

The fabrication of low-loss transmission line structures with an air dielectric layer is described. The channels are characterized at low frequency (10 and 100 kHz) using capacitance and loss tangent and at high frequency (500 MHz to 10 GHz) using -parameter measurements. The incorporation of an air gap resulted in structures with effective dielectric constants between 1.5-1.8 and significantly lower loss tangents. The fabrication technique could be used to create more complicated air gap transmission line structures for use in monolithic microwave integrated circuits.