Radiation dose effects in trigate SOI MOS transistors

N-channel trigate SOI MOSFETs have been irradiated with [sup.60]Co gamma rays at doses up to 6 Mrad(Si[O.sub.2]). The threshold voltage shift at 6 Mrad is less than 10 mV in transistors with a gate length of 0.3 [micro]m. At 6 Mrad(Si[O.sub.2]), the current drive reduction in the same devices is 10% if [V.sub.G] = 0 V during irradiation and 20% if [V.sub.G] = 1 V during the irradiation. The generation of positive charges in the BOX increases the electron concentration at the bottom interface of the silicon fins. Inversion electrons at the bottom interface have a higher mobility than the electrons at the (ll0)-oriented fin sidewalls. As a result, an increase of transconductance with dose is observed at moderate doses [ < 1 Mrad(Si[O.sub.2])]. At higher doses, the usual mobility degradation caused by interface trap generation is observed. Index Terms--MOSFETs, semiconductor device radiation effects, silicon on insulator technology.