Emitter Width Effect on Early Voltage in Bipolar Transistors

Narrow emitters in polysilicon emitter bipolar transistors have been found to result in a larger base width WB, and a larger peak base doping concentration NBPEAK. This in turn cause the VBIC and Mextram Early parameters VER and VEF to increase. This increase with narrow emitters is also true for the Gummel-Poon Early parameters VAR and VAF. The VBIC and Mextram Early parameters, VER or VEF, for an arbitrary emitter width can be modeled as the weighted average of a narrow emitter Early voltage measurement and a wide emitter Early voltage measurement. The weighted average Early voltage is found to be insensitive to the selection of the narrow emitter width as long the selected narrow emitter width encompasses enough of the emitter-base periphery effects.