A new experimental technique for extracting base resistance and characterizing current crowding phenomena in bipolar transistors

A new DC technique for extracting parasitic base resistance, R/sub B/, of advanced bipolar transistors is described. The technique is based on impact-ionization-induced base current reversal and enables R/sub B/ to be measured as a function of collector-base voltage and of emitter current. To obtain accurate results, the influence of the Early effect on the emitter-base voltage at constant emitter current must be accounted for. Measured values of R/sub B/ are correlated with current crowding phenomena, which can be directly observed by means of emission microscopy.<
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