On-chip shielding of signals

Abstract

The conductor for a given signal in an integrated circuit (IC) is shielded from electromagnetic coupling with one or more other, potentially noisy on-chip signals by shielding structure that essentially surrounds the signal conductor in a Faraday cage. In one embodiment, the signal conductor lies in the outermost metal layer in the IC. In that case, the shielding structure is a pair of adjacent shielding conductors lying on either side of the signal conductor within the outermost metal layer and a subtending shielding conductor lying in a metal layer below the signal conductor and the two adjacent conductors, where the subtending conductor is electrically connected to each of the adjacent conductors via interlevel interconnects, but there are no active components in the IC that draw current from the shielding conductors. When configured for signal processing, the three shielding conductors are connected either directly or indirectly to a quiet external reference. Such a shielding configuration effectively isolates the given signal carried by the signal conductor from other signals in the IC, thereby effectively protecting the given signal from being corrupted by coupled or induced noise.