Properties Of BaZr_xTi_2-xO₅Thin Films Prepared By Sol-Gel Method

Barium dititanate (BaTi2O5), a new lead-free ferroelectric material, has ferroelectric, piezoelectric, pyroelectric, electro-optical, acousto-optic and nonlinear optical properties, which has significant potential application in microelectronic and optoelectronic fields. However, the remnant polarization (Pr) of BaTi2O5is too small for its practical application. The ferroelectric properties of BaTi2O5ceramics were improved by element doping. Due to the demand of device miniaturization, it is necessary to prepare element-doped BaTi2O5thin films. In the present study, the Zr-doped BaTi2O5(BaZrxTi2-xO5, x=0-0.04, BZT) thin films were prepared on Pt/Ti/SiO2/Si substrates by the sol-gel method. The effects of preparation process, Zr content and compositionally graded structure on microstructure, dielectric and ferroelectric properties of BaTi2O5thin films were investigated. The main results and conclusions are performed as follows:The BZT precursors were prepared, and then these precursors were baked and calcined at different temperatures to obtain the BZT powders. With increasing the Zr content, the lattice parameters of a-, b-and c-axes increased.The BaTi2O5thin films were prepared on the Pt/Ti/SiO2/Si substrates by the sol-gel method. The BaTi2O5phase already formed at700℃. With increasing the annealint temperature, the grain size gradually increased. At higher annealing temperature (more than900℃), the Ba6Ti17O40phase was formed with BaTi2O5phase in the films. The BaTi2O5thin film, which was annealed at800℃, had the better electrical properties with2Pr of2.25μC cm-2, coercive field (2Ec) of113.4kV cm-1, dielectric constant (εr) of55and dielectric loss (tanδ) of0.063(at1MHz).The BZT thin films were prepared on Pt/Ti/SiO2/Si substrates by the sol-gel method. With increasing the Zr content, the crystallization temperature of BZT films increased. The dielectric and ferroelectric properties were improved due to the Zr doping. The BZT thin film with x=0.02had the maximum εr of53at1MHz, and the BZT thin film with x=0.01had the maximum2Pr of1.37μC cm-2under applied electric field (E) of636kV cm-1.The compositionally graded BZT thin films were prepared on Pt/Ti/SiO2/Si substrates by the sol-gel method. The polarization enhancement of the compositionally graded BZT thin films was observed. The upgraded BZT thin film had better dielectric property (εr=75, at1MHz) and ferroelectric property (2Pr=0.66μC cm-2, at E=200kV cm-1).