Structural and Electric Characteristics of Two-Layer Bi₄Ti₃O₁₂/(Ba,Sr)TiO₃ Thin Films Deposited on a Silicon Substrate by Radio-Frequency Sputtering at Increased Oxygen Pressures

Abstract

The 400–450-nm-thick Bi₄Ti₃O₁₂ 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_xSr_1 – xTiO₃ sublayer. The use of Ba_0.4Sr_0.6TiO₃ as a sublayer leads to the growth of the Bi₄Ti₃O₁₂ 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_0.8Sr_0.2TiO₃ sublayer is shown to lead to the formation of four crystallite orientations: (111), (117), (100), and (110) and two groups of domains in the Bi₄Ti₃O₁₂ 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°–57° with respect to a normal to the substrate. It is shown that, in the Bi₄Ti₃O₁₂ film with the Ba_0.8Sr_0.2TiO₃ 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).