Low temperature direct crystallization of SrBi₂(Ta_1-xNb_x)₂O₉ thin films by thermal metalorganic chemical vapor deposition and their properties

Directly crystallized SrBi₂(Ta_1-xNb_x)₂O₉ (SBTN) films were deposited on (111) Pt/Ti/SiO₂/Si substrates at 585-670°C by thermal metalorganic chemical vapor deposition (MOCVD). The crystalline SBTN film was directly deposited at 670°C irrespective of the deposition rate, but its leakage current markedly decreased when the deposition rate decreased from 5.0 to 2.1 nm/min. When the deposition rate was below 2.1 nm/min, an SBTN film with large ferroelectricity was deposited even at 585°C, and strong (103)-orientation was ascertained by an X-ray reciprocal space mapping method. This orientation is considered to locally epitaxially occur on a (111)-oriented Pt substrate. Twice the remanent polarization (2P_r) and twice the coercive field (2E_c) of the film deposited at 585°C were 12.2 μC/cm² and 160 kV/cm, respectively. When the deposition temperature increased, the film became randomly oriented which was in response to the orientation change in the Pt substrate from single (111) to a mixed orientation of (111) and (100) orientations by heating before starting the film deposition. 2P_r and 2E_c of the film deposited at 670°C increased to 23.8 μC/cm² and 190 kV/cm, respectively.