A step ahead toward a new microscopic picture for charge trapping/detrapping in flash memories

In this work, we present clear experimental results pointing to a new microscopic picture for cycling-induced charge trapping/detrapping in Flash memories. In particular, the evidence gathered from experiments designed to investigate the dependence of charge detrapping on cell threshold-voltage reveals that the simple and widely used model based only on carrier exchange between oxide defects and substrate is not enough to explain the main features of the phenomenon. We then propose a new microscopic description of the detrapping phenomenology, including structural relaxation of oxide defects as a limiting step enabling carrier exchange. This new microscopic picture for the oxide defects is, finally, implemented in a statistical model able to reproduce the charge trapping/detrapping dynamics and the consequent threshold-voltage instabilities along the memory array lifetime.