New insights into fully-depleted SOI transistor response after total-dose irradiation

In this work we explore the effects of total-dose ionizing irradiation on f ully-depleted SOI transistors. Closed-geometry and standard transistors fab ricated in two fully-depleted processes were irradiated with 10-keV x rays. Our results show that increases in radiation-induced leakage current are c aused by positive charge trapping in the buried oxide inverting the back-ch annel interface. At moderate levels of trapped charge, the back-channel int erface is slightly inverted causing a small leakage current to flow. This l eakage current may be amplified to considerably higher levels by impact ion ization. At high levels of trapped charge, the back-channel interface is fu lly inverted and the gate bias has little effect on leakage current. Large increases in leakage currents can be obtained with or without impact ioniza tion occurring in the channel region. For these transistors, the worst-case bias configuration was determined to be the "ON" bias configuration for bo th the cases where radiation-induced transistor response was dominated by c harge buildup in the buried oxide and in the trench sidewall isolation. The se results have important implications on hardness assurance.