Preparation And Characterization Of Electrical Properties Of Lanthanum Strontium Ferrite Thin Film

As a kind of important functional materials, the perovskite-type oxide of lanthanum strontium fereite (La_1-xSr_xFeO₃, LSF) films, due to their stable crystal structure, unique electromagnetic properties, catalytic properties and sensitivity etc, they can be used as catalyst, in the field of solid oxide fuel cells, gas sensors, high-temperature heating material, magnetic sensor and many other fields. At present, the researches on LSF films are one of frontiers and focuses at home and abroad. In this paper, the LSF films have been preparing by sol-gel method on Si (100) substrate, the influence on film dielectric properties of ingredent of sol, heat treatment process, film thickness, La/Sr ratio and elements substitution were studied.The effects of different sol ingredent on the properties of LSF film, that is the anhydrous alcohol/glacial acetic acid ratio, the dosage of deionized water, diethanolamine and acetyl acetone in sol on film dielectric properties, were investigated by using orthogonal experimental method. It can be found that, the best result was that alcohol/acid ratio was 2:1, the dosage of deionized water, diethanolamine and acetyl acetone was 3ml, 1.5 ml and 0.3 ml respectively, when it was tested at the frenquency of 1kHz, its dielectric constant and dielectric loss were 3215.85 and 1.39 respectively.The influence of heat treatment process on LSF film dielectric properties was studied. The results showed that the best heat treatment process for LSF was that when the preprocessing temperature and annealing temperature were 300℃and 750℃, processing time was 450s, La_0.5Sr_0.5FeO₃ film had maximum dielectric constant for 3446.60 at the frequency of 1kHz, and its dielectric loss was 0.96. And the influence of annealing temperature on film structure and properties was that the dielectric constant of LSF thin film exhibited a trend of increase then decrease with the increasie of annealing temperature, and the film annealed at temperature of 750℃had maximum dielectric constant. XRD and SEM results showed that the La_0.5Sr_0.5FeO₃ film annealed at temperature of 750℃had a good crystallization, the obvious perovskite structure, uniform grain size and no crack defects such as hollow.Using sol-gel method to prepare La_0.5Sr_0.5FeO₃ thin film, and the influence of film thickness on LSF film dielectric properties was studied. From the results, it can be found that along with the increase of film thickness, the dielectric constant of LSF thin film presented a trend of increase then decrease. And the LSF film with the thickness of three-layer (about 450nm) had maximizing dielectric constant for 3357.22 at the frequency of 1 kHz , and the minimum dielectric loss was 0.95.The La_1-xSr_xFeO₃ films were prepared by using sol-gel method, the influence of La/Sr ratio on LSF film dielectric properties was studied, the results found that as Sr content increased, the dielectric constant of the LSF presented a trend of increase and then decrease, and when Sr dosage was 0.5, its dielectric constant reach maximum value of 3521.57 and minimum dielectric loss of 1.20 at the frequency of 1 kHz.The influence of Mn and Gd element replacement on La_0.5Sr_0.5FeO₃ film dielectric properties was systematically studied. Experimental results tested at the frenquency of 1kHz showed that: (1) With the increase of the content of Mn element, the relative dielectric constant of La_0.5Sr_0.5Fe_1-xMn_xO₃ films showed an ascendant trend, and the maximum value is about 3374.75 when x = 0.05; and minimum dielectric loss is 0.82 when the value of x is 0.05. XRD results showed that La_0.5Sr_0.5Fe_0.95Mn_0.05O₃ film still exhibited perovskite structure, good crystal, no defects such as cavity and crack, etc. (2) With the increase of the content of Gd element, the relative dielectric constant of films showed an ascendant trend, when y = 0.4,the maximum dielectric constant value is about 3486.47 and the dielectric loss value is 0.98. XRD and SEM results showed that La_0.1Gd_0.4Sr_0.5FeO₃ film still exhibited perovskite structure, good crystal, no defects such as cavity and crack, etc.