Random Telegraph Noise Instability Research Articles

Comprehensive Investigation of Statistical Effects in Nitride Memories—Part II: Scaling Analysis and Impact on Device Performance

This paper presents a scaling analysis of the statistical distribution of the threshold voltage shift <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\Delta V_{T})$</tex></formula> obtained by electron storage in nitride memories, considering both its average and standard deviation. For fixed density of trapped charge, the average <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\Delta V_{T}$</tex></formula> decreases as a consequence of fringing fields, not predictable by any 1-D simulation approach. Moreover, the distribution statistical dispersion increases with technology scaling due to a more sensitive percolative substrate conduction in the presence of atomistic doping and 3-D electrostatics. The impact of these effects on device performance is then highlighted, showing that the accuracy of the staircase programming algorithm can be reduced further from the limitation given by the electron injection statistics during programming. The impact of electron storage in the nitride on random telegraph noise instabilities is also investigated, showing that, despite single cell behavior may be modified, negligible effects result at the statistical level.

Comprehensive Analysis of Random Telegraph Noise Instability and Its Scaling in Deca–Nanometer Flash Memories

This paper presents a comprehensive investigation of random telegraph noise (RTN) in deca-nanometer Flash memories, considering both the nor and the nand architecture. The statistical distribution of the threshold voltage instability is analyzed in detail, evidencing that the slope of its exponential tails is the critical parameter determining the scaling trend for RTN. By means of 3-D TCAD simulations, the slope is shown to be the result of cell geometry, atomistic substrate doping, and random placement of traps over the cell active area. Finally, the slope dependence on cell geometry (width, length, and oxide thickness), doping, and bias conditions is summarized in a powerful formula that is able to predict the RTN instabilities in deca-nanometer Flash memories.

Cycling Effect on the Random Telegraph Noise Instabilities of nor and nand Flash Arrays

The impact of program/erase (P/E) cycling on the random telegraph noise (RTN) threshold voltage instability of NOR and NAND flash memories is studied in detail. RTN is shown to introduce exponential tails in the distribution of the threshold voltage variation between two subsequent read operations on the cells. Tail height is shown to increase as a function of the stress levels, with a larger relative increase for the NAND case. The slope of the distribution instead remains nearly independent of the number of applied P/E cycles. This reveals that trap generation takes place according to the native trap distribution over the active area and means that the tail slope is a basic RTN parameter, depending on the cell process details for a fixed technology. These results are important for the design of the threshold voltage levels in multilevel nor and NAND technologies.

Investigation of the Random Telegraph Noise Instability in Scaled Flash Memory Arrays

This paper investigates the main features of the random telegraph noise statistical instability in Flash memory arrays. The exponential tails introduced in the cumulative distribution of the threshold voltage variation between two subsequent read operations on the cells are shown to be preserved when the available statistics is increased. Large threshold voltage instabilities are therefore to be admitted, requiring the possibility for large random telegraph noise fluctuation amplitudes and the superposition of multi-trap random telegraph noise effects. Moreover, tails drift for increasing elapsed time between the compared read operations due to the activation of slower and slower traps in the random telegraph noise process, whose effect should be carefully considered in drawing reliability projections. Finally, the results for an early and an optimized NOR process are presented, showing non-negligible differences in their exponential tails behavior and revealing the existence of important parameters other than the technology node feature size having a significant impact on the random telegraph noise instability.