Retention Reliability Improvement Using Nitride with Varying Trap Density in SONOS Type Non-volatile Memory

A new SONOS type structure employing bi-layered nitride with varying trap density and high-k blocking oxide is proposed for NAND Flash memory applications. The bi-layered silicon nitride with varying trap density is composed of a SiNx/Si3N4 stack and Al2O3 was used for the high-k blocking oxide. Compared with conventional SONOS structures, the proposed structure shows remarkable improvement of charge retention reliability while maintaining good programming/erase performance.