Compared to other energy storage devices,the dielectric capacitors exhibit many advantages such as high power density,fast charge/discharge rates,and stable performance.With the miniaturization of integrated circuits and the development of pulse power technology,thin-film capacitors have emerged due to their small size and low dielectric absorption.However,the unsatisfactory energy storage density is a major obstacle hindering the development of dielectric energy storage materials.To obtain dielectric materials with ideal energy storage density,large polarization differences and high breakdown strength are needed simultaneously.Traditional methods of simply mixing inorganic fillers with large dielectric constant into high breakdown strength polymer matrix fail to adjust performance due to interfacial effects and different polarization mechanisms between the matrix and fillers.Moreover,the uneven distribution of small-size fillers and surface agglomeration phenomenon also affect the practical application of capacitors.In this study,Sr Ti O3-Bi Fe O3(STO-BFO)dielectric thin films were prepared by a sol-gel method.By controlling the preparation process,amorphous-microcrystalline coexisted STO-BFO films with the same composition were obtained,avoiding interfacial mismatch issues.The main research content is as follows:(1)Sr Ti O3-Bi Fe O3 thin films regulated by nano-microcrystalline structure.STO-BFO thin films were prepared on Pt/Si substrates using a sol-gel method,and the effects of heat treatment temperature(450℃to 600℃)on the microstructure,dielectric,and energy storage properties of the thin films were investigated.High-resolution transmission electron microscopy was used to analyze the thin films heat-treated at 550℃,revealing the presence of unevenly sized,locally ordered nano-polar regions in the film.Selected area electron diffraction shows broad diffraction rings,indicating the amorphous structure of the film.Under different heat treatment conditions,the grain content changes,the film surface shows no obvious defects,the thickness is uniform,and the interface structure with the substrate was clear without diffusion phenomena.The dielectric constant and leakage current of all films are stable.With increasing temperature,the dielectric constant increases from 30.9 to 58.4,and the leakage current improves from 1.03×10-6 A/cm2 to 7.89×10-6A/cm2.At annealing temperatures of 450℃,500℃,and 550℃,the thin films demonstrate fewer crystalline grains and defects,and the breakdown strength remains within a relatively high range.The temperature coefficient of capacitance of the films from room temperature to 230°C is within 15%,which is favorable for application in practical scenarios.Among them,the thin film sample heat-treated at 550℃shows the optimal energy storage properties,achieving a maximum discharge energy density of 64.9 J/cm3with an efficiency of 74.6%.Furthermore,the energy storage performance shows excellent fatigue endurance,temperature and frequency stability.(2)Sr Ti O3-Bi Fe O3thin films tailoring by substrate orientation.La Ni O3(LNO)thin films were deposited on Si substrates by magnetron sputtering technology and the crystal orientations of LNO films with modulated by controlling the heat treatment conditions.The surface of LNO is relatively smooth,the thickness is about 130 nm,and the resistivity is about 10-4Ω·cm,which is suitable for use as electrodes.STO-BFO thin films were prepared on LNO buffered Si substrates.The effect of LNO orientations on the dielectric and energy storage properties of dielectric thin films were studied.The results show that,compared with the film grown on LNO(110)orientated substrate,the dielectric film grown on LNO(100)orientated substrate shows a smaller maximum polarization value(20.2μC/cm2).However,the remnant polarization is small(1.4μC/cm2)and the breakdown strength is high(4301 k V/cm),which result in an ultrahigh energy storage density of 90.9 J/cm3with an efficiency of 77.8%,indicating a significant advantage over other samples.Meanwhile,the thin film shows insignificant changes after 105fatigue cycles,indicating good fatigue endurance. |