Metal-ferroelectric-insulator-silicon capacitors with a BiFe0.95Mn0.05O3 (BFMO) ferroelectric film and a Bi2Ti2O7 (BTO) insulator have been fabricated. The electrical properties of 300 nm thick BFMO were investigated for different BTO thicknesses. The experimental results show that BFMO/BTO (50 nm) exhibits the largest maximum memory window. Furthermore, the trapped and mobile positive charges initiate at +/- 7 and +/- 8 V, respectively. Compared with BFMO/BTO (30 nm) and BFMO/BTO (70 nm), the BFMO/BTO (50 nm) shows a relatively long retention time.