Multilevel microcoaxial interconnect: a novel technology for VLSI microwave circuits

Interconnects will dictate the high speed microwave operation of future VLSI circuits. Even though Si VLSI devices with f_t in excess of 15 GHz have been reported in the literature, the realization of this performance level is limited. This is due to: (1) the response time and integration density of traditional interconnect technologies (coplanar waveguides, striplines, etc.); and (2) the crosstalk between different interconnect lines, particularly if the metal pitch is decreased to 1 μm or less. A fabrication technique which alleviates this impasse via the construction of multilevel microcoaxial interconnects (M²CI) has been reported. This technology is compatible with existing VLSI processes while maintaining existing interconnect densities. In this paper, the progress to date in developing this technology along with a methodology for the electrical and mechanical characterization of fabricated microcoaxial lines is presented. This includes: (a) the mechanical properties of the microcoaxial lines; (b) the characteristic impedance and its relation to line parameters. Testing to date indicates the successful fabrication of 5 Ω coaxial lines having very small cross sectional areas. Finally, potential VLSI applications of this technology are described