TID Effects in Highly Scaled Gate-All-Around Si Nanowire CMOS Transistors Irradiated to Ultra-High Doses

Total-ionizing-dose (TID) effects are investigated in a highly-scaled Gate-All-Around FET technology using Si nano-wire channels of 8 nm diameter. n− and p-FETs are irradiated up to 300 Mrad(SiO2) and annealed at room temperature. TID effects are negligible up to 10 Mrad(SiO2). At ultra-high doses the TID degradation depends on the irradiation bias condition, with more severe effects observed in longer channel devices. The worst-case irradiation condition is when positive bias is applied to the gate. Threshold-voltage shifts are caused by H+-driven generation of in-terface traps at the oxide/channel interface. In contrast, FETs ir-radiated under negative gate bias are dominated by transconduct-ance loss and increases of low-frequency noise, suggesting activa-tion of border traps. Enhanced off-leakage current is observed in n-FETs due to charge trapping in shallow-trench isolation, and in p-FETs due to trap-assisted recombination at STI sidewalls and/or spacer dielectrics at drain/bulk junctions.