US Patent 7339249 Semiconductor device

An insulating film is provided in a region surrounding a circuit region on a p type silicon substrate, and a frame-shaped electrode is provided to surround the circuit region on the insulating film. The region directly under the electrode at the surface of the p type silicon substrate is formed as a non-doped region with no impurity implanted. Then, a positive power supply potential is applied to the electrode. In this way, a depletion layer is formed directly under the electrode at the surface of the p type silicon substrate. Consequently, the substrate noise is shielded.