Measurement of collector and emitter resistances in bipolar transistors

New DC methods to measure the collector resistance R_C and emitter resistance R_E are presented. These methods are based on monitoring the substrate current of the parasitic vertical p-n-p transistor linked with the n-p-n intrinsic transistor. The p-n-p transistor is operated with either the bottom substrate-collector or the top base-collector p-n junction forward-biased. This allows for a separation of the various components of R_C. R_E is obtained from the measured lateral portion of R_C and the collector-emitter saturation voltage. Examples of measurements on advanced self-aligned transistors with polysilicon contacts are shown. The results show a very strong dependence of R_C on the base-emitter and base-collector voltages of the n-p-n transistor. The bias dependence of R_C is due to the conductivity modulation of the epitaxial collector. From the measured emitter resistance R_E a value for the specific contact resistance for the polysilicon emitter contact of ρ_c≅50 Ω-μm² is obtained