Low-dropout voltage regulators with various geometries and technological
realisations of serial pnp power transistors were exposed to ionizing
radiation. Although devices with vertical emitters were considered much less
susceptible to the influence of radiation on forward emitter current gain
than circuits with round emitters, the experiment showed a similar
degradation of current gain in both cases. The main reason of high radiation
susceptibility of the examined vertical serial pnp transistor is the
implementation of an interdigitated emitter, with high perimeter-to-area
ratio, causing the great increase of serial transistor?s base current, but a
minor influence on the maximum output current. Transistors with round
emitters with small perimeter-to-area ratio expressed a moderate current gain
degradation, but a rapid fall of the emitter injection efficiency, causing a
significant decrease of the maximum output current. Regardless of the similar
forward emitter current gain degradation, reliability and operational
characteristics of two types of low-dropout voltage regulators were
completely different.
Impact of forward emitter current gain and geometry of pnp power transistors on radiation tolerance of voltage regulators
