110-GHz Through-Substrate-Via Transition Based on Copper Nanowires in Alumina Membrane

A new through-substrate via (TSV) for millimeter-wave frequencies is proposed. The via is formed by copper nanowires connecting the bottom and top surfaces of a porous alumina membrane. It is shown here that the nanowire via is simple to fabricate using a low-cost technology. The nanowire vias were tested as coplanar waveguide transitions and characterized up to 110 GHz. The results show insertion loss better than 0.37 dB and return loss better than 14 dB per transition at 110 GHz. An electrical model for the vias was derived to give a design tool for circuit designers. These TSVs, along with the high-performance transmission lines already developed on the porous alumina membranes, contribute to a powerful platform for the design of high-performance circuits on this innovative interposer.