Polymer interconnections for 3D-chip stacking technology: Directional volume patterning of flexible substrates with conducting polymer wires

Research in 3D interconnection technology involves the functional modeling of complex biological processing structures with high-density 3D connections (such as the visual cortex). We propose a simple multi-chip stack structure, with through-chip connections and conducting polymer wires between layers. Self-assembled polymer wires based on polypyrrole have been produced by a directional electropolymerization process which permits the directional volume patterning of flexible substrates such as polycarbonate filtration membranes and gel layers. We have designed and fabricated successfully a two-chip stack with a perfect vertical electrical transfer between layers without any appearance of cross-talk. The measured values of conductivity for the polymer-based wires were as high as 0.5 S cm^-1. Furthermore we could demonstrate the feasibility of a three-chip stack by using two intermediate polymer-based patterned layers and a special middle chip with through-chip metal connections.