Field and high-temperature dependence of the long term charge loss in erasable programmable read only memories: Measurements and modeling

Abstract

High-temperature charge transport across an oxide-nitride-oxide sandwich of erasable programmable read only memories is mainly governed by the oxide conductivity as experimentally determined. It was verified in the examined devices that charge loss is not due to mobile ions. Since hole injection from the control gate into the nitride can be blocked by a 70-Å-thick top oxide we conjecture that charge loss is due to leakage of electrons; however, the observed leakage current is too large to be explained by pure electrode-limited charge transport (Richardson emission and direct tunneling). It was also verified that field gain on asperities and along edges cannot increase the charge loss current to the required range. Numerical evaluation of trap tunneling and resonant tunneling indicated that both mechanisms are weakly temperature dependent while charge loss has a typical activation energy of 1.2 eV in the range of 250–350 °C. Consequently, a multiphonon-assisted tunneling mechanism is proposed where electrons stored on the floating gate tunnel to oxide traps, then are emitted into the nitride. The coupling of the trap level to oxide phonons results in virtual energy levels in the oxide which allow for more effective transition paths. As a consequence of the electron-phonon coupling, the emission occurs close to the oxide conduction-band edge at temperatures between 250 and 350 °C, producing a strong temperature dependence for the mechanism.

Effect of Radiation Exposure on the Retention of Commercial NAND Flash Memory

“…It is not entirely clear what the mechanism is by which a high temperature bake accelerates charge loss from the floating gate. One possibility, suggested by Herrmann et al, [19] is a multi-phonon assisted tunneling process, by which electrons in the floating gate tunnel to oxide traps.…”

Comprehensive studies on the accuracy of trap characterization by using advanced random telegraph noise simulator

“…We consider energy transitions based on the multiphonon-assisted model. [28][29][30] The model proposed by Herrmann and Schenk 29) reproduces only trapping from the Si substrate and de-trapping to the poly-Si gate in order to calculate the trap-assisted tunneling current. For RTN simulation, we extended the model to reproduce the behavior of de-trapping to the Si substrate and trapping from the poly-Si gate.…”

Kinetic Monte Carlo of transport processes in Al/AlOx/Au-layers: Impact of defects

“…Phonon emission rates are modelled analogically with a c D,El multiplied by 1 − f (E x ) in the argument. Both formulae include the multiphonon transition probability L m (z) calculated by 22,33 …”