Effect of niobium doping on the microstructure and electrical properties of strontium titanate thin films for semiconductor memory application

Niobium doped strontium titanate [Sr(Ti1-xNbx)O-3] thin films (congruent to 40 nm) were deposited on Ir substrates using rf magnetron sputtering. The effect of Nb content (x=0, 0.001, 0.01, and 0.05) on the microstructure, di electric constant, dielectric dispersion, and leakage current was studied. It was found that with increasing Nb content the dielectric constant decrea sed, probably owing to an observed decrease in grain size. The dielectric d ispersion of all the Nb-doped ST films was lower than that of undoped ST fi lm deposited at the same temperature and pressure. For the case of x=0.01, dispersion as low as 0.425% per decade was observed. The leakage current wa s found to increase slightly for x=0.001 and x=0.01, and drastically for th e x=0.05 case. (C) 1999 American Institute of Physics. [S0003-6951(99)00240 -5].