Dielectric, optical and electric studies on nanocrystalline Ba5Nb4O15 thin films deposited by RF magnetron sputtering

Abstract

We report the fabrication of nanocrystalline Ag/BNO/Pt/Ti/SiO2/Si thin film capacitors by RF magnetron sputtering with different film thicknesses. The effect of Ba5Nb4O15 (BNO) thickness on structural, microstructural, electrical, optical and dielectric properties is investigated for the first time. BNO sputtering target prepared is by mechanochemical synthesis method to eliminate the subordinate phases. As deposited thin films were X-ray amorphous and crystallinity is induced after annealing at 700°C. Upon annealing, refractive indices of the films enhanced whereas the bandgap is decreased and are in the range of 1.89–2.16 and 4.07–4.24, respectively. With an increase in thickness, the dielectric properties improved substantially, which is described by the representation of a dead layer connected in series with a bulk region of the BNO film. The extracted values of thickness and dielectric constant for the dead layer found to be 15.21nm and 37.03, correspondingly. The activation energy of the mobile charge carriers obtained using the Arrhenius relation are found to be 0.254, 0.036 and 0.027eV, for the films with 150, 250 and 450nm, respectively. The leakage current density found to decrease with thickness and found to be 2.5×10−6A/cm2 at applied voltage of 50kV/cm. The J–E characteristics of the BNO films show a combined response of grain, grain boundaries and film–electrode interfaces. It is interesting to note that in the negative electric field region, conduction is ohmic in nature whereas in the positive field region BNO films exhibit both ohmic and the space charge-limited current mechanisms. The achieved dielectric, electrical and optical properties make these films suitable for MIC, CMOS and optoelectronic applications.