Lowering of leakage current density of (Ba, Sr)TiO3 thin films by pulse injection deposition

(Ba, Sr)TiO3 (BST) thin films were prepared on Pt/SiO2/Si substrates by low pressure metallorganic chemical vapor deposition using Ba(C11H19O2)(2) [Ba(TMHD)(2)], Sr(C11H19O2)(2) [Sr(TMHD)(2)], and Ti(O-i-C2H7)(4). The effects of deposition parameters on the film growth characteristics were systematically investigated. With increasing [Ba + Sr]/[Ti] ratio from 0.8 to 1.2, the grain shape of BST thin films was changed from round to triangular, and the grain sizes and surface roughness increased. The dielectric constants of BST thin films deposited by pulse injection in which the vapor of precursors was allowed to flow periodically into the reaction chamber, were slightly higher than those of BST thin films deposited continuously. In addition, the leakage currents were lowered by an order of magnitude. The improvement in the electrical properties of pulse BST thin films seems to originate from better crystallinity and less carbon contamination during the pulse deposition process. A 35 nm thick Ba-0.35 Sr-0.65 TiO3 film deposited by pulse injection at 550 degrees C and postannealed at 600 degrees C in an O-2 atmosphere for 30 min shows an oxide equivalent thickness of 0.64 nm, a leakage current density of 1.0 x 10(-7) A/cm(2) at + 1.5 V, and a dielectric dissipation factor less than 0.5%.