Electrical/thermal properties of nonplanar polyoxides and the consequent effects for EEPROM cell operation

The electrical/thermal properties of nonplanar polyoxides and the resulting effects for EEPROM operational margins are reported. The polyoxide between floating gate (FG) and control gate (CG) of FLOTOX-type EEPROM cells is no nplanar because it always contains edges, where CG wraps over PG, At such e dges a highly stable electrical passivation of Fowler-Nordheim (FN) leakage currents occurs, which can cause a degradation of EEPROM operational margi ns, due to an electron discharge mechanism from the FG of charged EEPROM ce lls during the first charging operation after conventional baking. The EEPR OM cell study includes the dependence on repeated passivation/depassivation of the polyoxide, on baking temperature and baking time. It is found that the average magnitude of the electron discharge is reduced after each passi vation/depassivation cycle, which points to a progressive increase of the n umber of electrons captured in deep neutral electron traps at the polyoxide edges. Analysis of the temperature dependence Leads to an activation energ y (thermal detrapping energy of the electrons) of 1.3 eV for the degradatio n mechanism of EEPROM cell operational margins as well as the nonplanar pol yoxide depassivation.