Effects of Total Ionizing Dose on the Retention of 41-nm NAND Flash Cells

Flash memories operating in space are subject at the same time to the progressive accumulation of total ionizing dose and to intrinsic aging phenomena. In this work we investigate latent Total Ionizing Dose (TID) effects in 41-nm NAND single level cells that do not display neither floating gate errors nor any apparent kind of degradation after exposure. Retention of irradiated cells is analyzed at room and high temperature as a function of total dose previously received. We found that FG cell retention at room temperature is practically unchanged after a total dose up to 30 krad(Si). On the contrary, TID exposure slightly worsens the cell retention time during high-temperature tests. We attribute this behavior to the removal of compensating electrons from the tunnel oxide at high temperature.