Analysis of detrap current due to oxide traps to improve flash memory retention

Abstract

To improve flash memory retention characteristics, we study detrap current due to oxide traps in metal-oxide-semiconductor structures (MOS capacitors and MOSFETs). We show that threshold voltage shift due to detrap current in flash memories can reach 0.6 V for 1 year. This value is detrimental for flash memory retention. Next, we analyze the two types of conduction mechanism of the detrap current, which are direct tunneling to the anode from deeper traps and thermally excited electron tunneling to the oxide conduction band from shallower traps. The deeper traps are generated by electron injection during Fowler-Nordheim stressing, while the shallower traps are generated by hole injection.