Interconnection coupling on lightly doped substrate for millimeter wave frequencies

A study of the impact of metal guard rings on the coupling between two interconnects is presented. The structure is designed over a bulk silicon substrate with epitaxial layer, so the coupling through the substrate is also involved. A lightly doped profile is adopted and is simulated by means of an electromagnetic simulator for various interconnects' distances and different metal layers, assuming a 65 nm bulk CMOS technology. The impact of various guard ring design (geometrical) parameters is examined. Furthermore, the increase of isolation (resulting in reduction of the noise coupling) between interconnects by cutting the guard rings, or by using multiple rings, is also analyzed. S parameters are used to compare the various structures.