On the current conduction mechanisms of CeO2/La2O3 stacked gate dielectric

Abstract

It was found that the electrical properties of CeO2/La2O3 stack are much better than a single layer La2O3 film. A thin CeO2 capping layer can effectively suppress the oxygen vacancy formation in the La2O3 film. This work further investigates the current conduction mechanisms of the CeO2 (1nm thick)/La2O3 (4nm thick) stack. Results show that this thin stacked dielectric film still has a large leakage current density; the typical 1−V leakage can exceed 1mA/cm2 at room temperature. The large leakage current should be due to both the oxide defect centers as well as the film structure. Results show that at low electric field (<0.2MV/cm), the thermionic emission induced current conduction in this stacked structure is quite pronounced as a result of interface barrier lowering due to the capping CeO2 film which has a higher k value than that of the La2O3 film. At higher electric fields, the current conduction is governed by Poole–Frenkel (PF) emission via defect centers with an effective energy level of 0.119eV. The temperature dependent current–voltage characteristics further indicate that the dielectric defects may be regenerated as a result of the change of the thermal equilibrium of the redox reaction in CeO2 film at high temperature and the drift of oxygen under the applied electric field.