Hole Distributions in Erased NROM Devices: Profiling Method and Effects on Reliability

The NROM-cell concept has been introduced as a promising technology to replace Flash nonvolatile memory devices also in embedded products, owing to its intrinsic 2-b/cell operation and better endurance. However, the presence of physically separated electron and hole distributions generated by program and erase operations is reported to be one of the main causes of the device's retention degradation. Therefore, a deep knowledge of the features and evolution of the nitride-storage charge is crucial for reliability, cell optimization, future scalability, and multilevel operation. In this scenario, the purpose of this paper is twofold, which is as follows: (1) to introduce a combined simulative experimental method allowing profiling hole distribution in devices erased with different bias conditions and (2) to monitor through this technique the evolution of the nitride charge with cycling, correlating it to the degradation of memory reliability after cycling.