Extension of impact-ionization multiplication coefficient measurements to high electric fields in advanced Si BJTs

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 . 10(5) 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 BV(CBO) requires that the contribution of holes to impact ionization be properly accounted for.