Radiation Dose Effects in Trigate SOI MOS Transistors

N-channel trigate SOI MOSFETs have been irradiated with ⁶⁰ Co gamma rays at doses up to 6 Mrad(SiO₂). The threshold voltage shift at 6 Mrad is less than 10 mV in transistors with a gate length of 0.3 mum. At 6 Mrad(SiO₂), the current drive reduction in the same devices is 10% if V_G=0 V during irradiation and 20% if V_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 (110)-oriented fin sidewalls. As a result, an increase of transconductance with dose is observed at moderate doses [<1 Mrad(SiO₂)]. At higher doses, the usual mobility degradation caused by interface trap generation is observed