Variability effects on the V<inf>T</inf> distribution of nanoscale NAND Flash memories

A cross-layer approach for new reliability-performance trade-offs in MLC NAND flash memories

“…We developed a compact model partially based on [17], which includes variability effects typical of nanoscaled memories. This allowed to simulate array functionalities during a page-wide programming operation.…”

“…Without loss of generality, we chose to investigate and explore the ISPP full sequence strategy [2] instead of the two-rounds one since it allows reduced simulation time and faster post-processing of the experimental results All these effects contribute to significantly broaden the gaussian distributions related to the programmed threshold voltage levels within the array, negatively impacting the RBER. For the sake of model validation, we were able to perfectly fit experimental data collected from [17] …”

Impact of Neutral Threshold-Voltage Spread and Electron-Emission Statistics on Data Retention of Nanoscale nand Flash

“…V ARIABILITY effects are becoming more and more important for NAND Flash memories, affecting the uniformity and reproducibility of device characteristics and operations as cell dimensions scale down [1]- [4]. In this respect, two main variability sources can be identified: The first is related to cell-to-cell parameter variations, due to process and fundamental reasons [1], and the second accounts for the statistics of fewelectron tunneling and is related to the discrete electron transfer to/from the floating gate (FG) during cell operation [2]- [4].…”

“…In this respect, two main variability sources can be identified: The first is related to cell-to-cell parameter variations, due to process and fundamental reasons [1], and the second accounts for the statistics of fewelectron tunneling and is related to the discrete electron transfer to/from the floating gate (FG) during cell operation [2]- [4]. While this latter variability source appears only when changing the charge state of the FG, fluctuations in cell parameters also Manuscript result into a spread of the neutral threshold voltage (V T,0 ) of the cells in the memory array [1], with atomistic substrate doping representing one of the major spread contributions [5], [6].…”

“…Assuming that W = L = 60 nm, t ox = 8nm, N A = 5 × 10 17 cm −3 and α G = 0.6, the previous expression predicts σ V T,0 = 85 mV, which must be viewed as a lower bound for the real V T,0 spread of a 60-nm NAND array. In fact, despite atomistic doping is one of the main variability sources for V T,0 , many other contributions exist, e.g., due to process-induced tolerances [1]. The effect of the V T,0 spread on data retention was investigated referring to a fresh device at low temperature, where the V T shift from the programmed state only comes from the FG charge loss through the tunnel oxide via direct quantummechanical tunneling, neglecting all the possible detrapping and defect-assisted charge loss processes limiting data retention after cycling.…”