Quantitative analysis of random telegraph signals as fluctuations of threshold voltages in scaled flash memory cells

Random telegraph signals (RTS) in fluctuations of threshold voltage are analyzed using massive readout data in scaled flash memories. A novel quantitative analytical method is proposed to evaluate parameters of the RTS, such as amplitudes and mean time spent in individual states. This evaluation gives us a statistical view of parameters of the RTS as well as their correlations. All of the parameters were found to follow log-normal distribution and to show weak mutual dependences. Possible origins of the distributions are discussed. We also studied evolution of RTS during program/erase operations of flash memories and point out its potential similarity with breakdown phenomena in gate oxide.