Jeffrey Kessenich

Resolving discrete emission events: A new perspective for detrapping investigation in NAND Flash memories

We report the first experimental evidence of discrete threshold-voltage transients on high-density NAND Flash arrays during post-cycling data retention. Proper choice of experimental conditions eliminates the impact of averaging effects and disturbs on the transients, enabling clear detection of single charge emission events from/to the tunnel oxide of sub-30nm NAND Flash cells. A stochastic model for the discrete emission process was developed from experimental data, demonstrating that number fluctuation of charges trapped in the tunnel oxide and the statistical nature of their emission dynamics strongly affect the post-cycling data retention performance of the arrays. These results pave the way for further analyses of NAND Flash reliability, where the behavior of single electrons and defects can be monitored and facilitate detailed assessments of the fundamental scaling challenges arising from the discrete nature of charge trapping/detrapping.

A new spectral approach to modeling charge trapping/detrapping in NAND Flash memories

We present a semi-analytical model for the description of charge trapping and detrapping phenomena occurring during cycling and idle periods in NAND Flash memories. The model is based on a statistical distribution of detrapping time constants that is affected by the composition of cycles and idle periods and accounts for charge discreteness, statistical charge capture and emission and statistical distribution of the threshold-voltage shift due to single detrapping events. The model can reproduce the experimental data under different conditions and allows to develop and monitor accelerated schemes able to mimic realistic on-field usage of the memory device.