Role of Emitter Area in Neutron-Hardened Transistor Design

Using Hauser´s equation for the current dependence of effective emitter area in Hahn´s epitaxial transistor model, it is predicted that emitter debiasing appreciably increases the equilibrium collector resistance of a transistor having a structure typical of neutron-hardened transistors. To experimentally determine whether debiasing is as severe as predicted, a small transistor and an adjacent emitter-shaped resistor were fabricated on the same chip. Near coincidence of the emitter-shaped resistor I-V characteristic with the transistor saturation locus, before and after irradiation to neutron fluences up to 5× 1014 n/cm2 (E > 10 KeV), demonstrates that emitter debiasing is not important in determining the saturation locus (onset of hFE falloff with collector current) in transistors having a moderate emitter stripe width (2 mils). It is concluded that extremely narrow emitter stripe widths are not needed for neutron-hardened transistors.