Barium Strontium Titanate Thin-film Dielectric Nonlinear Characteristics

In order to find path for improving and optimizing the dielectric nonlinearity ofBa_1-xSr_xTiO₃ (where1＞x＞0, shortened name BST) thin films, some important factors inboth the two aspects, interface translation layers and BST layer, (for examples:thickness, dielectric constant, and conductivity of interface translation layers, BST layerthickness, average grain size, grain-boundary shape and so on), were studied in thisthesis, by preparing, testing and analyzing BST thin films. Some work as follows isfinished:Using the model of fiat capacitor with three different dielectric layers, therelationship between electric-field intensity in each layer and time after outside voltageapplied was computed and simulated. It is found that the nagtive effects of interfacetranslation layers bacomemore obvious in higher frequency.The relationship between BST layer thickness and the measured real part ofrelative dielectric constant of the BST capacitor was studied, and several possiblemechanics of BST layer thickness effecting the measured real part of relative dielectricconstant were analyzed. Under the assumption that average grain size in the BST layeris a constant, the main mechanics of film thickness effecting the measured real part ofrelative dielectric constant is that the volume percentage of the interface translationlayer decreases with increasing film thickness.The relationship between average grain size and the measured real part of relativedielectric constant of the BST capacitor was studied, and several possible mechanics ofaverage grain size effecting the measured real part of relative dielectric constant wereanalyzed. Under the assumption that each grain size in the BST layer is single domainparticle and does not contact each other, the main mechanics of average grain sizeeffecting the measured real part of relative dielectric constant of the BST capacitor isthat the volume percentage of the amorphous substance decrease with increasing grainsize.Some phenomena related to ferroelectric hysteresis loop and butterfly loop, such as,the asymmetry phenomena of C-V curves, the horizontal shift of C-V curves andferroelectric hysteresis loops, the vertical shift of ferroelectric hysteresis loops, and the shape changes of ferroelectric hysteresis loops, were analyzed, explained or researchedby experiments.Using traditional ceramic technology, three groups of BST ceramic targets withdifferent percentage of impurity (made of CaO, Al₂O₃ and SiO₂, in certain proportion)were prepared. All the BST ceramic targets were tested and analyzed by XRD, SEM andEDS. Experimental results indicate that: (1) targets with 1mol％doping agent displaygood crystallization and apparent grain-boundary aggregation of doping agent. (2) thecrystallization of BST in targets with 3mol％doping agentwas affected to some extent,(3) the crystallization of BST in targets with 5mol％doping agent was severelydestroyed,BST ceramic targets with 1mol％impurity were used to prepare doped BST thinfilms. Doped BST thin films were tested and analyzed by SEM, XRD, AFM andGAXRD. The testing results of dielectric properties of these doped BST thin films withpreferred orientation indicate: Under the testing frequency of 500 kHz and thetemperature of 12℃, the capacity of one of representative samples can be changed57.3％at a quite low bias voltage 6V while the dielectric loss angle tangent keeps below0.0276.