Preparation And Properties Study Of Epitaxial Double-layered BTO And BZT Ferroelectric Thin Films

Barium titanate(BaTiO₃,BTO)is one of the most used ferroelectric thin film materials at present.It has a simple structure,low dielectric loss,and good electrical conductivity.Therefore,it is an ideal material for preparing ceramic capacitors.Barium zirconate titanate(Ba(Zr_xTi_1-x)O_3,BZT)has been extensively studied in recent years.It has huge potential application value because of low leakage current strength and strong pressure resistance.In this thesis,a single-layer BTO film and a double-layer BTO/BZT film were prepared by magnetron sputtering technology,and optimized under different parameters.The main contents of this paper are as follows:1.Property characterization of single-layer BTO film grown on Pt/Ti/Si substrate.(1)The effect of different distance between the targets on the structure and crystallinity of BTO film was studied.It is found that when the distance between the targets is 5.5cm,the film has the smallest half-width,the largest grain size,sharp diffraction peaks of multiple orientations, and no obvious impurity peaks.(2)The surface structure of the thin films prepared under different argon/oxygen mixing ratios are obviously different.The(001)phase characteristic peaks crystal are very obvious in the BTO polycrystalline thin film prepared with argon/oxygen ratio of 4:1.The SEM images show that the crystal grains are round and the holes are relatively small,which indicates that the uniformity and stability of the film prepared under this condition are better than others.(3)The effect of the cooling atmosphere on the surface structure and electrical properties of the film was studied.When the temperature of the BTO thin film decreased in the pure oxygen atmosphere,the full width at half maxima of the prepared BTO thin film is the smallest,the crystalline peak is sharpest,the hysteresis loop becomes slender.2.Property characterization of of single-layer BTO film grown on STO/SRO substrate.(1)The effect of the change of the deposition temperature on the BTO film was studied.When the growth temperature reaches 600?,the BTO film becomes continuous and dense with fewer holes.When the growth temperature is above 650?,a high(00l)orientation diffraction peak appears according to the BTO film's XRD pattern.Four adjacent diffraction peak appears in the BTO film's?scanning pattern.It demonstrates the C-axis epitaxial growth of the BTO film on the STO(001)/SRO substrate.(2)The effect of the change of the deposition pressure on the BTO film was studied.When the sputtering pressure is 1Pa,the BTO film has only(001)orientation,indicating that it has good epitaxial characteristics.At this time,the leakage current density drops below 10^-6A/cm².(3)The effect of the change of the deposition power on the BTO film was studied.When the power is 80W,the full width at half maxima of the XRD diffraction peak of the BTO film is only 0.35°,and the electric hysteresis loop is closed,which can withstand the applied electric field pressure above 90V.3.Property characterization of double-layer BTO&BZT film grown on STO/SRO substrate.(1)Different components of BZT were selected as the outer film.It was found that Ba(Zr_0.2Ti_0.8)O₃and BTO had the best combination degree,with the epitaxial growth in the(00l)direction.There was no obvious miscellaneous phase,the boundary of the section is clear,and the film quality is good.Therefore,the Ba(Zr_0.2Ti_0.8)O₃component is selected as the outer layer material of the double-layer film.(2)The total thickness of the double-layer film is fixed to 1.5?m,and the thickness ratio of the BTO layer and the BZT layer is changed.It is found that the thickness ratio has a significant effect on the hysteresis loop.As the thickness of the BZT increases,the dielectric loss gradually decreases and the breakdown strength that can withstand increases.(3)The thickness ratio of BTO and BZT is fixed at 1:2.When the total thickness is 2100nm,the maximum breakdown strength can reach 792k V/cm,and the maximum polarization and residual polarization are 85?C/cm²and 3.6?C/cm²,respectively.The maximum energy storage density is121.6J/cm³,the energy storage efficiency reaches 78.5%,the leakage current density can be reduced to less than 8x10^-7A/cm²,and the dielectric loss is only 0.148,which is better than other thickness films.