Investigation of Retention Noise for 3-D TLC NAND Flash Memory

In this paper, the retention noise [electron emission statistics (EES)] after program operation of 3-D triple-level program cell (TLC) NAND flash memory is investigated. Three main noise sources, consisting of essential EES (EEES), electron numbers fluctuation, and device parameters fluctuation to broaden the retention Vth distributions are comprehensively considered, and the corresponding analytic models are developed. The impact of device parameters fluctuation is relatively larger than EEES and electron numbers fluctuation for our measured 3-D TLC NAND flash memory devices. Using the proposed models, the calculated Vth distributions after different data retention times have good agreements with the measurements, which validate our proposed models. This paper provides a method to predict the Vth distributions accurately and efficiently, and can help in improving reliability of 3-D TLC and quad-level program cell NAND flash memory.