| Ferroelectric thin films have been studied for many years owing to their interesting electronic and optical properties, which have led to a wide range of technical applications. Bi2VO5.5 (BVO) films, one type of ferroelectric materials belonging to the family of Aurivillius phases, has a variety of excellent properties, such as high Curie temperature, low dielectric constant, good ferroelectric properties and electro-optic properties. There are wide application prospects for BVO films in the volatile ferroelectric memory, the film capacitor, film infrared sensor and lightning device. At present, many researches for the BVO materials are still in the initial stage and mainly focus on two aspects:solid electrolyte body materials and ferroelectric thin films materials. With the development of film preparation technology, BVO ferroelectric thin films materials attracts more and more attention. People are mainly concentrated in the research of ferroelectric and dielectric properties in the field of research, however, research about the optical properties are very few. In addition. People mainly use laser pulse deposition techniques (PLD) and metal organic chemical meteorological deposition (MOCVD) to prepare the BVO films. And, the using of other methods of the preparation of BVO films is rarely reported. As promising ferroelectric thin films materials, BVO films have a great research space and research value. In view of the above reasons, we try to use the sol-gel method to prepare pure and doped BVO films on the different substrates, then, test the structural, electronic and optical properties of these samples. We try to obtain a more comprehensive and in-depth research. Main results are as follows:(1) We successfully obtain the BVO precursor solution and make use of the Sol-gel method to prepare lots of BVO film samples under the different annealing temperatures, which have good surface morphology and internal structure. These samples include BVO/Si, BVO/SiO2/Si, BVO/LNO/Si, Fe and Mg doped BVO films.(2) Using X-ray diffraction (XRD) equipment and atomic force microscope (AFM) to study and observe the micro structure and surface morphology. Then, study the influence of using different substrates and Fe/Mg doping on the BVO structural properties. We found that the introduction of SiO2 layer makes the diffraction peak more strong and obvious. The surface roughness of BVO films is reduced as well. Therefore, the surface morphology and internal structure is improved. But, LNO layer make a different result. The c-orientation diffraction peak intensity appeared weaker, and the AFM pictures tell us that surface morphology and internal structure becomes poor.(3) Raman spectra and Spectroscopic ellipsmetry (SE) measurement are used to study the optical properties of BVO films. The Lorentz model is adopted to fit the measurement data. The refractive index n and extinction coefficient k are obtained finally. The n is 2.35 and k is 0.035 at the 600nm. The optical band gap Eg is about 2.80 eV. The refractive index n and extinction coefficient k decrease with the increase of the thickness of BVO films and increasing with the rising of annealing temperatures. But, when the annealing temperature is above 650℃, the values start to drop.(4) Preparing many Fe and Mg doped BVO thin films. And, we investigate the influences of doping on the ferroelectric property of BVO films. It's found that doping moderate Fe will change the structure, and improve the ferroelectric performance of thin films. When the bias voltage is 18v, the remanent polarization Pr and coercive field Ec are 2.80μC/cm2 and 174kV/cm. Then, Bi2Mg0.08V0.92O5.5 films have the best crystallization properties. And, Bi2Mg0.04V0.96O5.5 films have the best ferroelectric properties.
|
PDF Full Text Request