Impact of self-heating effect on the retention of 3-D NAND flash memory

The three-dimensional (3-D) NAND flash memory technology has been considered as a promising candidate for future memory solutions, because it overcomes the scaling limitation and reliability issues faced by conventional planar memory. Even though 3-D NAND flash memory structures have many merits, self-heating effect is aggravated seriously due to the poor thermal conductivity of some of the materials in nanoscale used in 3-D NAND fabrication and gate-all-around (GAA) geometry. In this work, the local temperatures in a 3-D NAND flash memory with different operation modes are evaluated. The average temperature can be heated to 400K for the 48-layer stacked cells during the continuous PAGE READ operation. The self-heating effect will cause severe degradation of retention due to the thermal enhanced charge diffusion along the 3-D NAND vertical structure. The impact of self-heating effect on the retention of a string of three cells is simulated by electro-thermal simulation, and three different programmed patterns are considered. The most severe retention degradation by up to 1.6V of the 5.6 V programmed voltage after 10
⁷
s retention time. The results can be useful to the design and optimization for the new generation of 3-D NAND flash memory.