Concerning the electron injection through the gate oxide due to Fowler-Nordheim tunneling, i.e., the physical phenomenon used to remove electrons from the floating gate in order to erase the non-volatile memory cell, the experimental characteristics as function of the applied voltages have been reproduced with good agreement using only one fitting parameter. It has been noticed that a small localized variation in the thin-oxide thickness strongly influences the erasing process. Also, the injected current density is uniformly distributed in the thin-oxide region, but its value strongly dependens on the cell geometry, as the capacitive coupling between the control gate and the floating gate changes. Hence, the possibility of using a three-dimensional simulator is essential because it allows for a realistic description of the device geometry. Finally, in the observed devices the band-to-band tunneling phenomenon showed a negligible influence on the erasing curves, due to the high doping values in the source region.
The hot-electron injection phenomenon, that occurs when electrons are able to overcome the potential energy barrier at the Si-SiO2 interface, produces a carrier injection in the floating gate, hence the writing of the non-volatile memory cells. The hot-carrier injection simulations have pointed out the difficulty of a good physical description of this model, and therefore further investigations will be devoted to this issue.
|Microelectronics Group Home Page||Staff|
|Research Activities||Teaching Activity|
|DEIS Home Page||University of Bologna Home Page|