Structural and electric characteristics of two-layer Bi$_{4}$Ti$_{3}$O$_{12}$/(Ba,Sr)TiO$_{3}$ thin films deposited on a silicon substrate by radio-frequency sputtering at increased oxygen pressures

The 400–450-nm-thick Bi$_{4}$Ti$_{3}$O$_{12}$ thin films with various orientations of crystallites with respect to a normal to the (100)Si substrate plane have been studied. It is established that the crystallite orientation can be controlled by varying the composition of the 4-nm-thick Ba$_{x}$Sr$_{1-x}$TiO$_{3}$ sublayer. The use of Ba$_{0.4}$Sr$_{0.6}$TiO$_{3}$ as a sublayer leads to the growth of the Bi$_{4}$Ti$_{3}$O$_{12}$ film in the single-crystal state with plane (001) parallel to the substrate plane and with a monoclinic distortion of the crystal structure. The Ba$_{0.8}$Sr$_{0.2}$TiO$_{3}$ sublayer is shown to lead to the formation of four crystallite orientations: (111), (117), (100), and (110) and two groups of domains in the Bi$_{4}$Ti$_{3}$O$_{12}$ film; the first group with the polarization direction p-erpendicularly to the substrate and the second group with the polarization directed in the angular range 45.2$^{\circ}$–57$^{\circ}$ with respect to a normal to the substrate. It is shown that, in the Bi$_{4}$Ti$_{3}$O$_{12}$ film with the Ba$_{0.8}$Sr$_{0.2}$TiO$_{3}$ sublayer, the polarization is directed to the substrate and is switched to new stable state with the polarization direction from the substrate when applying an external voltage higher than a critical one (4 V).