Asymmetric capacitance-voltage characteristics of (Bi3.25La0.75)Ti3O12 thin films grown on Si

Electrical properties of La modified bismuth titanate (B3.25La0.75Ti3O12) thin films for a metal-ferroelectric-insulator-semiconductor (MFIS) structure were investigated with capacitance-voltage (C-V). The MRIS structure exhibits progressively increasing C-V memory window with a sweep voltage due to ferroelectric polarization with suppressed charge injection. Moreover, the asymmetric shift of threshold voltage with a sweep voltage was observed. The flat-band voltage (V-tb2) at the negative sweep was gradually increased with a sweep voltage. The flat-band voltage (V-fbl) at the positive sweep decreased at low sweep voltages and then increased at further high voltages (i.e., V-fbl shift toward the positive direction rather than the negative direction). The asymmetric behavior of C-V characteristics was attributed to negative trapped charges by electron injection from Si.