| Four kinds of ferroelectric thin films are prepared on Pt?111?/Ti/SiO2/Si substrate by the sol-gel method, there are Bi1-xHoxFe0.97Cr0.03O3?BHxFCO?, Na0.5Bi0.5TiO3?NBT?,?Na0.82K0.18?0.5Bi0.5TiO3?NKBT? and?1-x?NKBT-x BHFCO. The effects of the composition variation on the properties of these films are studied. The main research work and conclusions are as follows:Firstly, the sol-gel method was used to prepare BiFeO3?BFO? and BHx FCO?x=0, 0.05, 0.10, 0.15, 0.20? ferroelectric thin films on Pt/Ti/SiO2/Si substrate annealing at 550 ?. The effects of Ho and Cr co-doping on the microstructure and electrical properties of these thin films were studied, and the results show that the optimum Ho content is 0.15. The BH0.15 FCO film show saturated hysteresis loop, high permittivity??r=270? and small dielectric loss?tan?=0.05?, and the leakage current density of this film is smaller than that of BiFeO3 thin films about three orders of magnitude.Secondly, NBT, NKBT thin films were prepared by sol-gel method at 680 ?, and the microstructure and electrical properties of these films were characterized. The experimental results show that the NKBT thin film is of larger residual polarization?2Pr=25 ?C/cm2?, smaller coercive field?2Ec=9.29 k V/cm? compared with the N BT thin film. The leakage current of NKBT is smaller than that of NBT about one orders of magnitude. The improvement of dielectric properties of NKBT thin films is obviously: the first is t hat the C-V curve has a clear butterfly curve; secondly, ?r of NKBT films greatly increased to about 570, small dielectric loss is about 0.06.Finally, the?1-x?NKBT-x BHFCO?x=0.01,0.03,0.05,0.07? thin films were also prepared by the sol- gel method and annealed at 680 ?. The effect of BHFCO content on the properties of these solid solution were studied, and the optimal doping ratio was also investigated. The results show that the incorporatio n of BHFCO into NKBT does not change the crystal structure of the NKBT. With the increase of BHFCO content, the 2Pr of the?1-x?NKBT-x BHFCO thin films increase firstly, reach the maximum value?2Pr?71.3 ?C/cm2? for x=0.05, while this film also shows the best saturation rectangle degree, the minimum coercive field?2Ec=530 kV/cm?. The leakage current of all the thin films are smaller than that of the pure BHFCO or the NKBT thin film about one to two orders of magnitude. Among them, the leakage current density of 0.95NKBT-0.05 BHFCO thin film is the lowest, which is about 2.1×10-6 A/cm2 at the test field of 300 kV/cm. Additionally, this binary system film is of the maximum ?r?about 493? and the minimum tan??about 0.04?. In addition, it is found that the Curie temperature?Tc? of the solid solution film between 440 ? and 460 ? by testing the dielectric temperature spectra. Then the flexoelectric effect on the dielectric properties of the ferroelectric thin films is analyzed under different film thickness, showing that the flexoelectric effect plays an important role in the reduction of the maximum dielectric constant of the ferroelectric thin films. |
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