**Alessandro S. Spinelli \*, Gerardo Malavena, Andrea L. Lacaita and Christian Monzio Compagnoni**

Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milan, Italy; gerardo.malavena@polimi.it (G.M.); andrea.lacaita@polimi.it (A.L.L.); christian.monzio@polimi.it (C.M.C.) **\*** Correspondence: alessandro.spinelli@polimi.it; Tel.: +39-02-2399-4001

**Abstract:** In this paper, we review the phenomenology of random telegraph noise (RTN) in 3D NAND Flash arrays. The main features of such arrays resulting from their mainstream integration scheme are first discussed, pointing out the relevant role played by the polycrystalline nature of the string silicon channels on current transport. Starting from that, experimental data for RTN in 3D arrays are presented and explained via theoretical and simulation models. The attention is drawn, in particular, to the changes in the RTN dependences on the array working conditions that resulted from the transition from planar to 3D architectures. Such changes are explained by considering the impact of highly-defective grain boundaries on percolative current transport in cell channels in combination with the localized nature of the RTN traps.

**Keywords:** 3D NAND Flash memories; random telegraph noise; Flash memory reliability
