Performance degradation due to extrinsic base encroachment in advanced narrow-emitter bipolar circuits—part I: Basic inverter

Abstract

This paper presents a detailed two-dimensional numerical simulation study on the performance degradation caused by the extrinsic base encroachment in advanced narrow-emitter bipolar circuits. It is shown that, depending on the circuit families used, the extrinsic base encroachment results in distinct effects on the operation and performance of the circuits. The design considerations and scaling implications, using a basic inverter as an example for saturating circuit, are discussed in Part I. It is shown that while the extrinsic base encroachment causes increases in the delay time, fall time, and rise time of a basic BJT inverter, the saturation time of the inverter actually decreases since the transistor is driven less deep into saturation due to reduced collector current (reduced current gain). The decrease in the saturation time, however, is accompanied by the reduced noise margin, especially for narrow emitter stripes. The cases for nonsaturating circuits are discussed in Part II using non-threshold logic as an example. © 1989 IEEE