SPICE modelling of a discrete COTS SiGe HBT for digital applications up to MGy dose levels

Future maintenance tasks of the international experimental thermonuclear fusion reactor (ITER) will require communication links between the remotely operated equipment in the reactor vessel and the control room, that are radiation tolerant up to MGy dose levels. We therefore assessed the DC behaviour of a COTS SiGe heterojunction bipolar transistor (HBT) under gamma radiation up to more than 4 MGy. The DC current gain (beta) presents a limited loss of about 30% for a base current of 100 muA. Our in-situ measurements allowed us to adapt the manufacturer´s SPICE model and account for these radiation effects. Circuit-hardened driving electronics for both photonic transmitters and receivers can hence be designed.