Patent ID: 8664723

Claim:
An integrated circuit structure comprising: a substrate; an isolation ring extending from a top surface of the substrate into the substrate; a well region of a first conductivity type in a surface portion of the substrate, wherein the well region comprises: a first portion comprising a top portion encircled by the isolation ring; and a second portion comprising a top portion encircling the isolation ring; and a base resistance tuning ring comprising a first portion overlapped by the isolation ring, wherein the base resistance tuning ring is between the first portion and the second portion of the well region, and wherein the base resistance tuning ring is selected from the group consisting essentially of: a ring of the first conductivity type, with a net impurity concentration of the base resistance tuning ring being lower than a net impurity concentration of the well region; a substantially neutral ring; and a ring of a second conductivity type opposite the first conductivity type.