Field-induced instabilities in polyimide passivated lateral PNP transistors

Abstract

ABstroct-Stress-induced shifts in the gain of lateral p-n-p transistors with different dielectric compositions over the base region are discussed. Two separate degradation mechanisms are analyzed. The first and predominant mechanism is the collector fringe-field induced shift in current gain in the presence of polyimide over the base. The shift is dramatically reduced by covering the base with the emitter metal lead which acts as a “field-shield.’’ It is found that in optimized devices, the field-shield need not cover the entire base to suppress punch-through and surface inversion. The second mechanism is related to hot electron injection and trapping under the large two-dimensional field at the collector boundary covered by the field-shield. Experimental results are compared with two-dimensional simulations.