Study On Electrical Properties Of BCFTO/BNT Multiferroic Heterostructure

Multiferroic materials, which possess two or more types of primary ferroic order, i.e. ferroelasticity, ferroelectricity, ferromagnetism, and ferrotoroidic ity simultaneously, had been used widely recently in data storage, spintronics, sensors, etc.. BiFeO3(BFO), as a typical representative of single-phase multiferroic material, is the only multiferroic material with ferroelectric and antiferromagnetic orderings above room-temperature. By virtue of high ferroelectric C urie point(TC~1103 K), high G-type antiferromagnetic Neel temperature, lead-free nature and large theoretical remanent polarization(Pr~90-100 μC/cm2), BFO has been supposed to be a superior candidate material for next-generation devices. However, BFO has some intrinsic defects, such as large leakage current, ferroelectric reliability and inhomogeneous magnetic spin structure, which hindered its practical applications in devices enormously. The BiFeO3 thin film is investigated in this Master’s thesis, the main work finished is as follows:(1) The fabrication and characteristics of the Bi1-x CexFe1-yTiyO3 ferroelectric thin films;(2) The fabrication and characteristics of the Bi3.15Nd0.85Ti3O12 ferroelectric thin films;(3) Study on fabrication and electrical properties of Bi0.94Ce0.06Fe0.97Ti0.03O3/Bi3.15Nd0.85Ti3O12(BCFTO/BNT) multiferroic heterostructure.(1). The Bi1-xCexFe1-y Tiy O3(x=0.03, 0.06, 0.09; y=0.03, 0.06, 0.09) thin films were fabricatied on Pt/Ti/SiO2/Si substrated by sol- gel process. The effect of Ce and Ti content on the ferroelectric property and leakage current density of BFO were investigated. We found that the Bi0.94Ce0.06Fe0.97Ti0.03O3 thin film has the best ferroelectric property and the minimum leakage current density. Pure BFO, Ce and Ti individual doping BFO thin films were fabricated by the same process for comparison. The Ce and Ti co-doping BFO thin films(BCFTO) exhibited the enhanced ferroelectricity with a large remnant polarization(2Pr) of 130 μC/cm2, and low leakage current density of 9.10×10-6 A/cm2 which is two orders of magnitude lower than that of pure BFO films at 100 kV/cm. The dielectric constant(364 at 1 kHz) of the BCFTO thin films is much larger than that of pure BFO thin films.(2). For further improving the ferroelectric properties and reducing the leakage current of the BCFTO thin films. The Bi3.15Nd0.85Ti3O12(BNT) thin films were used as a b uffer layer between BCFTO thin films and Pt/Ti/SiO2/Si substrated. The BNT thin films were deposited on Pt/Ti/SiO2/Si substrated by sol- gel process, and the microstructure, ferroelectric and dielectric properties of BN T thin films were investigated. The BNT thin films shows well-shaped P–E hysteresis loop with a remanent polarization(Pr) of 42 μC/cm2(at a applied voltage of 13 V) and acceptable dielectric properties with a high dielectric constant of 570 at 1 kHz.(3). Based on the above research results, the BCFTO/BNT multiferroic heterostructures were were fabricated via sol-gel method on Pt/Ti/SiO2/Si substrates. The microstructure and electrical properties of BCFTO/BNT multiferroic heterostructures were investigated in detail by X-ray diffractometer, scanning electron microscopy, semiconductor deviceanalyzer, ferroelectric test systems and vibrating sample magnetometer respectively. These results suggest that insertion a BNT buffer layer can effectively enhance the ferroelectric, dielectric and magnetic properties of BCFTO thin films.