Retention Enhancement in Low Power NOR Flash Array with High-κ-Based Charge-Trapping Memory by Utilizing High Permittivity and High Bandgap of Aluminum Oxide.

For improving retention characteristics in the NOR flash array, aluminum oxide (Al2O3, alumina) is utilized and incorporated as a tunneling layer. The proposed tunneling layers consist of SiO2/Al2O3/SiO2, which take advantage of higher permittivity and higher bandgap of Al2O3 compared to SiO2 and silicon nitride (Si3N4). By adopting the proposed tunneling layers in the NOR flash array, the threshold voltage window after 10 years from programming and erasing (P/E) was improved from 0.57 V to 4.57 V. In order to validate our proposed device structure, it is compared to another stacked-engineered structure with SiO2/Si3N4/SiO2 tunneling layers through technology computer-aided design (TCAD) simulation. In addition, to verify that our proposed structure is suitable for NOR flash array, disturbance issues are also carefully investigated. As a result, it has been demonstrated that the proposed structure can be successfully applied in NOR flash memory with significant retention improvement. Consequently, the possibility of utilizing HfO2 as a charge-trapping layer in NOR flash application is opened.