STRUCTURE DEVELOPMENT STUDIES OF SRBI2(TA1-XNBX)(2)O-9 THIN-FILMS

In this research, two tasks were pursued: (1) determination of the ons et temperature of ferroelectric hysteresis properties of SrBi2Ta2O9 th in films by structure development study, and (2) low temperature proce ssing for thin film fabrication. For task (1), a nondestructive optica l method using spectroscopic ellipsometry was utilized for characteriz ing the structure development of SrBi2Ta2O9 thin films. The optical co nstants and film thickness were measured as a function of annealing te mperature by spectroscopic ellipsometry. By observing the changes in r efractive indices and film thickness, the temperatures of phase transf ormation and grain growth were determined. Consistent results were obt ained from x-ray diffraction measurements. By comparing the results of the structure development study and ferroelectric hysteresis properti es investigation, the onset temperature of the hysteresis curve of SrB i2Ta2O9 with 50% excess Bi was determined to be about 700 degrees C. T he critical factor for the compound to exhibit a well-defined hysteres is curve was found to be the grain size. For task (2), the effects of excess Bi content and Nb/Ta ratio of SrBi2(Ta1-xNbx)(2)O-9 on the ferr oelectric hysteresis properties were studied. It was found that the on set temperature for obtaining well-defined hysteresis properties can b e reduced by adding excess Bi or increasing Nb/Ta ratio. By choosing S rBi2Nb2O9 with 50% excess Bi, the onset temperature of the hysteresis curve was reduced to about 650 degrees C.