Nanowire-based through substrate via for millimeter-wave frequencies

A new through substrate via for millimeter-wave frequencies is proposed. The via is formed by copper nanowires connecting the bottom to the top surfaces of a porous alumina membrane. It is shown here that the nanowire-via is simple to fabricate using only six low-cost processing steps. Its dimensions and spacing are only limited by the photolithography process, reaching small sizes, important for high-density interconnections. The nanowire-vias were tested as CPW transitions and characterized up to 40 GHz. The results show low insertion loss of less than 0.035 dB per transitions at 40 GHz.