Structural, electrical, and low-temperature dielectric properties of sol–gel derived SrTiO3 thin films

Abstract

Strontium titanate sol was prepared using strontium ethyl haxanoate and titanium isopropoxide. The sol was then spin coated on fused silica, p-type single-crystal silicon wafers (100) and stainless-steel substrates 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 structural transition. The dielectric measurements were conducted on films with metal–insulator–metal and metal–insulator–semiconductor configurations. Capacitance–voltage (C–V) measurements were carried out and the effect of the annealing temperature was studied. The dielectric constant and loss tangent at 1 MHz at room temperature were found to be 105 and 0.02, respectively, for 1.1 μm thick films. These measurements were also carried out at low temperatures down to 20 K. There are indications for a phase transition from a cubic perovskite to tetragonal perovskite structure at about 100 K where the tan δ shows some fluctuation, a characteristic of such transitions. The absence of a peak in the dielectric constant and the absence of hysteresis below the transition temperature have been explained on the basis of the low value of the tetragonal distortion (c/a=1.003) reported on bulk material.