Carrier Transport Mechanisms of the Programming and Retention Characteristics for TaN-Al2O3-Si3N4-SiO2-Si Flash Memory Devices

Abstract

Carrier transport mechanisms of the programming and retention characteristics for TaN-Al2O3-Si3N4-SiO2-Si (TANOS) flash memory devices were theoretically investigated by using the one-band model taking into account Shockley-Reed statistics, the continuity equation, and the Poisson equation. The simulation results showed that the dominant tunneling mechanism during the programming operation in the TANOS memory devices was varied from the Fowler-Nordheim (FN) tunneling to the direct tunneling (DT) processes and from the DT to the modified FN tunneling processes. The dominant tunneling mechanism in TANOS memory devices at the retention operation mode without gate bias voltage was DT process. Simulation results showed that the retention time increased with increasing tunneling oxide thickness. The threshold voltage shifts, as determined from the theoretical calculation during the programming and retention process, were in reasonable agreement with the threshold voltage shifts obtained from experimental results.