Giant Random Telegraph Signals in Nanoscale Floating-Gate Devices

Abstract

The magnitude of a random telegraph signal (RTS) in nanoscale floating-gate devices has been experimentally investigated as a function of carrier concentration. Discrete current switching, which is caused by a single trap, has been found to be almost one order of magnitude higher with respect to what was predicted by the classical theory of carrier number and correlated mobility fluctuations. Nevertheless, the trap signature well fits the typical SiO 2 trap spectroscopy. In addition, the rigid shift between the transfer curves related to filled-and empty-trap state, together with the normalized current fluctuation dependence on the channel carrier density, suggests that a pure number fluctuation is the correct theoretical interpretative framework. Thus, we propose a possible physical explanation for such a giant RTS on the basis of a quasi-1-D current filamentation.Index Terms-Flash memory, nanoscale device, noise, random telegraph signal (RTS).

Large random telegraph noise in sub-threshold operation of nano-scale nMOSFETs

“…Specifically, in nano-scaled devices a particularly troubling noise phenomenon called random telegraph noise (RTN) [6] has the potential to severely limit sub-V TH circuit design. RTN is a digital fluctuation in device drain current (I D ) which has already been identified as a large obstacle in super-V TH operation of both SRAM and FLASH memory technologies [7][8][9]. However, the impact of RTN on sub-V TH operation is only sporadically debated in the literature with very little consensus.…”

Reliability of NAND Flash Memories: Planar Cells and Emerging Issues in 3D Devices

“…This held true even if unusually large values for the RTN amplitude had been consistently reported on some devices, together with complex time behaviors [79,82,[87][88][89], that seemed to defy Equation (2). When Flash memories made a large quantity of data readily available, making it possible to pinpoint and study anomalous behaviors occurring with extremely low probability, larger and larger fluctuation amplitudes emerged [90,91], and RTN became a serious reliability constraint in static random-access [92][93][94] and Flash memories [90,91,[95][96][97][98][99], prompting an intensive research effort to understand its root cause and impact on memory array operation. An example of the relevance of RTN is shown in Figure 4, where results obtained on a selected decananometer Flash cell are reported [91]: current fluctuations up to 60% were detected, which cannot be explained with the above theory.…”

“…When Flash memories made a large quantity of data readily available, making it possible to pinpoint and study anomalous behaviors occurring with extremely low probability, larger and larger fluctuation amplitudes emerged [90,91], and RTN became a serious reliability constraint in static random-access [92][93][94] and Flash memories [90,91,[95][96][97][98][99], prompting an intensive research effort to understand its root cause and impact on memory array operation. An example of the relevance of RTN is shown in Figure 4, where results obtained on a selected decananometer Flash cell are reported [91]: current fluctuations up to 60% were detected, which cannot be explained with the above theory. Though early explanations pointed to multiple carrier emissions [88,89], change in defect properties [87] or interacting quantum wells [82], a different approach based on the percolative nature of the current conduction around the charged trap site had been mentioned in [100] and thoroughly revisited in [101], exploiting a concept applied to amorphous semiconductors [102].…”

Tunnel Oxide Nitridation Effect on the Evolution of $V_{t}$ Instabilities (RTS/QED) and Defect Characterization for Sub-40-nm Flash Memory

“…On the other hand, in Flash memory, the focusing point of the nitridation has been a reliability improvement against high field Fowler-Nordheim (FN) stress (> 10 MV/cm) or channel hot carrier [2]. Such nitrogen incorporation is reported to generate high density defects in the oxide and results in worse RTS in both conventional MOSFETs [3] and Flash memory cells [4]. In particular, since the realization that multilevel cell in Flash memory is being limited by random telegraph signal (RTS) [5], applying tunnel oxide nitridation (TON) is expected to result in a tradeoff between reliability and RTS.…”