STRUCTURAL AND ELECTRICAL CHARACTERIZATION OF SPUTTER-DEPOSITED SRTIO3 THIN-FILMS

Thin films of ferroelectrics in combination with superconducting YBa2C u3O7-delta (YBCO) find application in tuneable microwave components. T he crystalline quality of the ferroelectric films directly affects the tunability and microwave losses of these components. In the present w ork, SrTiO3 thin films less than or equal to 300 nm in thickness were deposited by rf sputtering in an Ar + O-2 + N2O gas mixture at tempera tures ranging from room temperature to 845 degrees C on LaAlO3 rhomboh edral (110) substrates. The influence of the discharge plasma anisotro py on the film deposition rate and elemental composition was studied b y depositing films on substrates placed both in on- and off- axes. X-r ay diffraction (XRD) showed all films deposited at greater than or equ al to 685 degrees C to be epitaxial (001) SrTiO3 with an enlarged unit cell in the c-direction. The unit cell lattice parameter decreased wi th increasing deposition temperature and often again after annealing i n an oxygen ambient at 800 or 850 degrees C. Using a planar capacitor with a top electrode composed of Au on Ni-Cr, the dielectric propertie s of the SrTiO3 thin films evaluated as a function of de voltage bias and temperature. At 1 MHz the best films were found to have dielectric constant of similar to 500 and a loss Increases in the tunability of the dielectric constant were positively correlated to changes in the l attice parameter toward the bulk value of 0.3905 nm. The epitaxial ori entation relationships of (001) SrTiO3 // (110) LaAlO3 and (101) SrTiO 3 // (121) LaAlO3 were determined by TEM and the former relationship w as verified by XRD. Misfit between the substrate and film gave rise to dislocations positioned 35 unit cells of SrTiO3 apart.