Leakage-current characteristics of sol–gel-derived Ba1-xSrxTiO3 (BST) thin films

Thin films of Ba0.5Sr0.5TiO3 (BST) were fabricated on RuO2/Ru/SiO2/Si substrates by spin coating multicomponent sol prepared using metal alkoxides. To analyze the surface effect of the dielectric film on the leakage current characteristics required for DRAM applications, post-annealing was carried out under O2 or Ar atmosphere. Based on AES and RBS data, we have concluded that doubly ionized oxygen vacancies are readily generated on the outermost surface of the BST thin film post-annealed under Ar atmosphere. The leakage current densities of the BST thin film post-annealed with O2 and with Ar gases are approximately 1×10−6 A/cm2 and 4.6×10−6 A/cm2 at 1V, respectively. This observation was interpreted in terms of (i) the increase in the tunneling current caused by the decrease in the depletion width at the surface region under Ar atmosphere and (ii) the effect from the bottom electrode under oxidative environment.