High total dose gamma radiation assessment of commercially available SiGe Heterojunction Bipolar Transistors

Maintenance tasks of the future International Experimental Thermonuclear fusion Reactor (ITER) will require communication links between the remotely operated equipment in the reactor vessel and the control room, some of which need to be radiation tolerant up to MGy dose levels. As a key element of opto -electronic transceivers, we therefore assessed the DC behavior of a commercial-off-the-shelf (COTS) SiGe heterojunction bipolar transistor (HBT) under gamma radiation up to 15 MGy, with dose rates from 160 Gy/h to 27 Gy/h. Our in-situ measurements of the forward DC current gain (hfe) present a limited loss of about 30 % for a base current of 100 µA, with a dependence on the biasing conditions and a thermally activated recovery. These first ever reported results up to MGy levels allow us to design circuit-hardened driving electronics for both photonic transmitters and receivers, enabling high bandwith communications applied in a fusion reactor environment.