Multiferroic And Leakage Current Characteristics Of Ferroic Thin Films Growth On The (Ba0.65Sr0.35)TiO3Buffer-layer

Owed to the low leakage current, high dielectric constant and high tunability, Ba1-xSrxTiO3is extensive application in electronic, however, there is low remanent polarization and coercive electric field in BST thin film. Barium zirconium titana Ba(ZrxTi1-x)O3has good dielectric properties, high tunability and higher dieletric constant and has shown great potential for the application in tunable microwave devices. Multiferroic (MF) materials posses both ferroelectric order and ferromagnetic (or antiferromagnetic) order in the same phase. BiFeO3(BFO) is one of the most extensively studied MF materials because of its promising magnetoelectric application at room temperature. Due to high TN and Tc that outclass the room temperature, BFO has been fascinating since it was first synthesized in the late1950s. However, BFO becomes unsuitable for applications owing to its large leakage current due to the oxygen vacancies and Fe2+in the samples. Using Nd3+ions in substitution for larger Bi3+ions in the BFO composition, could improve ferromagenetic propertiesIn this work, the thin films of (Ba0.65Sr0.35)TiO3(BST), Ba(Zr0.20Ti0.80)O3(BZT), and sandwich structure BST/BZT/BST were grown on Pt/Ti/SiO2/Si(100) and Si(100) substrates by rf-sputtering, respectively. And all samples crystallied at temperatures650℃for30min in oxygen atmosphere. The cross-sectional images of the thin films were characterized by an field emission scanning electron microscopy (FE-SEM). The dielectric constant and dissipation factor tanδ of the BZT, BST and BST/BZT/BST thin films are680and0.030,240and0.021,85and0.018, respectively at100kHz. Compared with BST and BZT films, the BST/BZT/BST film has lower dielectric constant and lower dissipation. The remanent polarization (Pr) and the coercive electric field (Er) of sandwich structure BST/BZT/BST thin film are up to9.57μC/cm2and33.51kV/cm, which is higher that those of BST and BZT films. The optical properties (refractive index n and extinction coefficient k) of the BST/BZT/BST film on Si(100) substrate were measured by n&k analyzer2000.A multiferroic trilayered structure composed of a Bi0.875Nd0.125FeO3(BNF) layer and two BST layers and a multiferroic hetero structure BNF/BST are grown on a Pt/TiO2/SiO2/Si substrate by rf-magnetron sputtering. For the comparison, single-layered BNF was also prepared on the same substrates. Ferroelectric tests were conduced using asymmetric device structure with Au top electrodes and Pt bottom electrodes. The trilayered BST/BNF/BST and BNF/BST exhibit quite lower leakage currentand dielectric loss, weak ferromagnetic properties and ferroelectric properties. The remnant polarization and coercive field were2.668μC/cm2and9.137kV/cm, and5.13μC/cm2and16.53kV/cm, respectively. And the remnant magnetization and the coercive magnetic field of the BST/BNF/BST and film are7.89emu/cm3and351.33Oe, and9.84emu/cm3and316.78Oe respectively. We considered that the bismuth’s volatilization was limited by BST layers making the Bi/Fe in good station and the action of BST in the charge transfer between BNF and electrode leaded to the quite low leakage current and enhanced ferromagnetic property.We found that the BST buffer-layer could reduce the leakage current of BNF thin film, the results of our works showed that the leakage current of BNF/BST film was7×10-8A/cm2at300kV/cm electric field, which was much lower than the leakage current density of BNF thin film reported in the literatures, and the leakage current of BST/BNF/BST thin film up to8×10-8A/cm2at300kV/cm. The reducing of second phase in the BNF layer thin film improved the resistance of BNF/BST and BST/BNF/BST film, the BST may play an important role in blocking the charges of transition between BNF and bottom electrode and improving resistance. Moreover, the top BST layer was limited the loss of bismuth improving the resitance of BST/BNF/BST film.In addition, the (1-x)BaTiO3-xBi0.5Na0.5TiO3(abbreviated as BT-100xBNT, with x=0,0.05,0.10,0.15,0.20) and (CaCu3)0.95Sr0.05TiO3(CCSTO) ceramics were prepared by the traditional ceramic processing. The dielectric properties and PTC behaviors of BT-BNT ceramics, and the dielectric relaxation of CCSTO ceramics, were also investigated.