Role of holes and electrons during erase of TANOS memories: Evidences for dipole formation and its impact on reliability

The systematic investigation of the role played by electrons and holes during the erase operation of TANOS memories by means of charge separation experiments and physics-based simulations is reported for the first time. We determined a dominance of electrons back-tunneling in the first part of the transient, and dominance of holes in the second part. Good agreement is reached between experimental and simulated data. In addition we demonstrate for the first time the formation of a vertical charge dipole in TANOS devices, whose polarity depends on the P/E operation sequence. This dipole severely affects the program and erase performances and the retention of mild programmed and erased states, which is a concern especially for multilevel applications.