Extension of Impact-Ionization Multiplication Coefficient Measurements to High Electric Fields in Advanced Si BJT’s

Measurements of the impact-ionization multiplication coefficient M — 1 in advanced Si BJT’s up to values in excess of 10 (corresponding to a peak electric field at the base-collector junction of about 9 • 10⁵ V/cm) are presented. The intrinsic limitations affecting M — 1 measurements at high electric fields are discussed. In particular, the fundamental role played by the negative base current and the parasitic base resistance in determining instabilities during M — 1 measurements is pointed out. An accurate theoretical prediction of the M — 1 coefficient at collector-base voltages close to bvcborequires that the contribution of holes to impact ionization be properly accounted for. © 1993 IEEE