Hetero-epitaxial Growth of (1, 0, m+1) One Axis-oriented Bismuth Layered Structured Ferroelectrics Thin Films Directly Crystallized by MOCVD

Abstract

Bismuth layered structured ferroelectrics (BLSF) thin films with different number of octahedron number (m-number) were prepared by MOCVD and directly crystallized on the substrates. Directly-crystallized SrBi₂Ta₂O₉ (SBT) (m=2) films on a (111) Pt/Ti/SiO₂/Si substrate were ascertained to have a strong (103) one-axis orientation by the X-ray reciprocal space map** and to be hetero-epitaxially grown on the (111) Pt grains by the TEM observation. Moreover, directly crystallized Bi₂VO_5.5 (m=1) and Bi₄Ti₃O₁₂ (m=3) films deposited on the same substrate showed (102) and (104) one-axis preferred orientations, respectively. These orientations are basically the equal ones with SBT (103) orientation because the tilting angle of c-axis from the substrate surface is also about 55°. Therefore, the direct crystallization is one of the important key techniques for orientation control of BLSF films. Moreover, the directly crystallized SBT film deposited on a (111) Ir/TiO_x/SiO₂/Si substrate at 570 °C by ECR-MOCVD exhibited (103) one-axis orientation, which also originated from the local epitaxial growth on (111)-oriented Ir grains. The remanent polarization (2Pr), and the coercive field (E_c) of this film were 16.1 μC/cm2 and 83 kV/cm at an applied electric field of 360kV/cm, respectively. This Pr value is about 88% of the expected value of (103)-oriented SBT film from both the Pr values of the (116) and (001)-oriented epitaxial films and detailed crystal analysis. Masayuki Fujimoto1