Current Dependence of the Neutron Damage Factor

The current dependence of the neutron damage factor for transistor beta degradation was correlated with the carrier transit time across both the emitter-base junction and the base region of a transistor. An electrical measurement related to this transit time was used to generate current-independent damage factors for 100 devices of 16 types. The use of the junction delay in addition to the base transit time was based on recent work which indicated the importance of this region in transistor beta degradation. From this work it appears that a graphical method can be used to separate the components of damage occuring in the base and in the emitter-base depletion region. Because the damage factor is independent of current, a single value can be determined for a given transistor type and used as a figure-of-merit for hardness assurance when divided by the gain-bandwidth product, fT, of the transistor at the operating current. This new damage "constant" should be more effective than the present damage factor in hardness assurance screens because its coefficient of variation is smaller at low currents.