Extension of impact-ionization multiplication coefficientmeasurements to high electric fields in advanced Si BJT's

Measurements of the impact-ionization multiplication coefficient M-1 in advanced Si BJTs 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 on collector-base voltages close to BV_CBO requires that the contribution of holes to impact ionization be properly accounted for