Integrated circuit high voltage protection

Claim 1

A transistor formed on a substrate of a first conductivity type of an integrated circuit for protecting the circuit from high static discharge voltages that can be introduced through an electrically conductive wire bonding pad formed thereon with a defined perimeter, said transistor comprising: a first elongated diffusion in said substrate having a second conductivity type doping opposite to that of said substrate and having its width entirely under said pad for a first portion of its length, an outside edge of said first diffusion length portion being adjacent to and substantially parallel with a defined segment of the pad perimeter, said first diffusion being electrically connected to said pad and additionally having a second portion of its length extending outside of said pad perimeter to the integrated circuit to be protected against high static discharge voltages, a second elongated diffusion in said substrate having said second conductivity type and having only a portion of its width under said pad along its said defined perimeter segment and electrically insulated therefrom, an inside edge thereof under said pad being substantially parallel with and spaced apart from the outside edge of the first diffusion in order to form a channel in the substrate therebetween along said defined pad perimeter segment, said second diffusion having its width extending from under the pad along its said defined perimeter segment, and an electrically conductive bus layer formed over the portion of the second diffusion width that extends outside of said pad perimeter, said layer being electrically isolated from said pad and having an edge that is parallel with and extends along substantially the entire length of said defined pad perimeter, said conductive layer being electrically connected with said second diffusion and to a common voltage circuit point, whereby a drain and a source of a protective transistor are formed by the first and second diffusions, and a gate is formed by the defined perimeter segment of the pad positioned over the channel between the first and second diffusions.