Field-induced instabilities in polyimide passivated lateral pnp transistors

Stress-induced shifts in the gain of lateral pnp transistors with different dielectric compositions over the base region are discussed. Two separate degradation mechanisms are analyzed. The first and predominant mechanism is the shift in current gain induced by the collector fringe-field in the presence and 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 those of two-dimensional simulations