Ferroelectric Thin Film Crystallization Kinetics Process

The crystallization behavior of amorphous ferroelectric thin films was studied bymeans of conventional furnace annealing (CFA) and rapid thermal annealing (RTA) inthis thesis, in which those factors such as treated temperature, time and heating rateare changed. The surface morphology was analyzed by atomic from microscopy, andthe crystallization quality was characterized by X-ray diffraction. The evolvementproperties concluded from those experiments were compared with the model of filmcrystallization dynamics.The grain size, surface morphology and interface structure of BST films werecontrolled by change of crystallization conditions such as crystallization temperature,heating rate and crystallization time and annealing methods . With the growth of timeand temperature of annealing the grain size and volume fraction of transformed phasewere improved .The grain size was smaller if increasing heating rate. Compared withCFA, the grain, interface and uniformity of films were improved through RTA.Moreover by annealing of circulation the volume fraction of transformed phase can beincreased and thin film and substrate can avoid diffusion and reaction as a result oflongtime annealing.The activation energy of BST thin film were calculated through the JMAisothermal equation:337kJ/mol,Avrami exponent n increase when temperature ishigher. The two activation energies of BST crystallization during the two differentannealing methods and stages were computed on the ground of the relation of grainsize and annealing temperature: 97kJ/mol and 358 kJ/mol for CFA and 256kJ/mol and847 kJ/mol for RTA. The model of the relation between the grain size and annealingtime can be concluded to conform to exponent equation of D∝tn. N equal to onefourth from one to 600 minutes for CFA. However curve is divided into two parts forRTA .When annealing time is less than 10 seconds,grain size rise quickly and n equalto half .When annealing time is more than 10s, changing rate of grain size slow downand n equal to one twenty-fifth .The crystallization mechanism of BST films is indicated that heterogeneousnucleation is dominant at lower temperature and homogeneous nucleation at highertemperature. Furthermore, the grain growth stage is transited from the independentlygrows to fusion with the increase of annealing time.