| Lead-free BiFeO3 (BFO) ferroelectric thin film, with a rhombohedrally distorted perovskite structure with space group R3c (a = 5.36 (A|°) andα= 59.348°), is the only one that exhibits both ferroelectricity and G-type antiferromagnetism at room temperature, and possesses a giant remanent polarization and high Curie temperature (TC = 1103 K) and high Neel temperature (TN = 643 K), which make itself a candidate material for high-density nonvolatile ferroelectric random access memory and other potentially interesting applications, such as actuators, sensors, and tunable microwave devices.In this work, we prepared Bi0.9La0.1Fe0.95Mn0.05O3 (BLFMO) thin films on Pt(111)/Ti/SiO2/Si(100) substrates by chemical solution deposition (CSD) method. Different experimental parameters of Ferroelectric thin films such as precursor solution, doping, annealing mode, pyrolysis temperatures and heating rates were considered. And the microstructure, remanent polarization, leakage current density of these thin film samples was measured.Through the analysis of the test results of BLFMO ferroelectric thin films, we get a better preparation. The solutes are iron nitrate and bismuth nitrate, etc., and solvents are 2-methoxyethanol, ethylene glycol and acetic anhydride, whose volume ratio is 12:6:1. The BLFMO precursor solution was spin coated on Pt(111)/Ti/SiO2/Si(100) substrates, pyrolyzed at 420℃for 5 min, and annealed at 550℃for 10 min. These processes were repeated 9 times until the thickness of the film approaches about 300 nm, and then conducted the final annealing for 20 min so as to fully crystallized.The results show that thin films have a better crystallinity, no impurity phase, a large remnant polarization value (21μC/cm2 @ 266 kV/cm) and the relatively large leakage current (7×10-3 A/cm2 @ 6 V). The comparison of ferroelectric properties with different technological parameter of thin films are shown below. The thin films of La doping BFO are better than the pure BFO thin films, the thin films using sequential layer annealing (SLA) are better than conventional annealing (CA), the thin films pyrolyzing at 420℃are better than 350℃and 400℃, the thin films using 6℃/s heating rate is better than 55℃/s.To reduce the leakage current and enhance the remnant polarization of films, we also prepared Bi3.4Ce0.6Ti3O12 (BCT) film and BLFMO/BCT composite thin film. Through the discussion of microstructure and ferroelectric properties of BCT thin films, it is shown that BCT ferroelectric thin films with (117) and (00l) double-preferred orientation and good crystallinity, and have a large remanent polarization (13μC/cm2 @ 333 kV/cm) and a low leakage current density (2.5×10-5 A/cm2 @ 6 V). In addition, BLFMO/BCT composite thin films have all the characteristic peaks of both BLFMO and BCT thin films, greatly enhance the ferroelectric properties (24μC/cm2 @ 333 kV/cm) relative to BLFMO, and obviously reduce the leakage current (1.8×10-4 A/cm2 @ 6 V), which makes it close to the application requirements. |
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