Impact of depolarization electric-field and charge trapping on the coercive voltage of an Si:HfO2-based ferroelectric capacitor

Abstract

The shift of coercive voltage (V c) during cycling is investigated on ferroelectric (FE) silicon-doped hafnium oxide thin films with different (i) Si concentrations in HfO2, (ii) thickness of the ferroelectric layer (T FE), and (iii) thickness of the interface layer (T IL). We find that the depolarization field (E dep) and charge trapping are two major root-causes for the shift of coercive voltage. The increased remanent polarization (P r) with cycling of up to 105 causes a strong E dep, which leads to a higher voltage for polarization switching. On the other hand, the trapped charge improves the charge compensation, and then it suppresses the V c shift due to E dep: in the case of Si doping content, TFE, and TIL, the difference in the magnitude of Vc increases by 4.5%, 0.5% and 3% while the difference in E dep increases by 5%, 8% and 15%, respectively. To investigate the rate of charge trapping, the defect band energy level is extracted by two-state NMP theory incorporated into a ‘Comphy’ tool. These results suggest that the strategy discussed above is a promising approach to designing FE-HfO2 devices.