STRUCTURAL, ELECTRICAL, AND LOW-TEMPERATURE DIELECTRIC-PROPERTIES OF SOL-GEL DERIVED SRTIO3 THIN-FILMS

Strontium titanate sol was prepared using strontium ethyl haxanoate an d titanium isopropoxide. The sol was then spin coated on fused silica, p-type single-crystal silicon wafers (100) and stainless-steel substr ates and annealed to give polycrystalline, transparent, and crack-free films. The surface morphology and structural properties of the films were studied using scanning electron microscopy and x-ray diffraction, respectively, and differential thermal analysis was used to observe s tructural transition. The dielectric measurements were conducted on fi lms with metal-insulator-metal and metal-insulator-semiconductor confi gurations. Capacitance-voltage (C-V) measurements were carried out and the effect of the annealing temperature was studied. The dielectric c onstant and loss tangent at 1 MHz at room temperature were found to be 105 and 0.02, respectively, for 1.1 mu m thick films. These measureme nts were also carried out at low temperatures down to 20 K. There are indications for a phase transition from a cubic perovskite to tetragon al perovskite structure at about 100 K where the tan delta shows some fluctuation, a characteristic of such transitions. The absence of a pe ak in the dielectric constant and the absence of hysteresis below the transition temperature have been explained on the basis of the low val ue of the tetragonal distortion (c/a = 1.003) reported on bulk materia l. (C) 1997 American Institute of Physics. [S0021-8979(97)05220-1].