Pull-down transient-imposed extrinsic base consideration in BiNMOS transistors

A detailed two-dimensional numerical simulation study of the bipolar devices in the BiCMOS circuit environment during pull-down transients is presented. The charge buildup and removal phenomenon in the bipolar device determines the switching speed of the BiNMOS devices. The tradeoffs in designing the extrinsic base in terms of the switching behavior are also described. It is shown that the structure with the extrinsic base p⁺ area farthest from the intrinsic base area has the best switching speed owing to the largest initial overshoot in the base voltage and the lateral base effects