Characterization and Modeling of the Polysilicon Emitter Contact for Circuit Simulation

Abstract

The emitter contact in bipolar transistors with polysilicon emitters has been characterized based on an improved open-collector (OC) method, which allows extraction of the nonlinear I-V characteristics of the resistance presented by the poly-/monocrystalline emitter interface. The nonlinear characteristics of the interfacial polysilicon-emitter resistance at low currents are modeled using an approximate rectangular-barrier tunnel junction model to extract an upperbound estimate for the thickness of the oxide layer at the poly-/monocrystalline contact. Having verified that the extracted data based on the improved OC method are consistent with the first-principles rectangular tunnel junction model, a data-driven model accounting for the bias-dependence of the emitter series resistance is presented, which employs a voltage-controlled resistor (VCR) to enable the efficient simulation of the effect of the interfacial nonlinearity as well as the substrate bias. SPICE simulations indicate that the VCR-based model for the emitter resistance accurately predicts the measured I-V characteristics obtained using the improved OC method. The utility of a subcircuit-based model explaining the experimentally observable effect of the substrate bias on the behavior of the emitter resistance is also evaluated for circuit simulation.