Abstract
Barium strontium titanium oxide (BST) thin films on Pt/Ti/SiO2/Si substrate were prepared by a two-step deposition process using RF magnetron sputtering with different first layer thickness and annealing conditions (time, temperature and oxygen pressure). The total film thickness was kept constant, 180nm, while the thickness of the first layer were 15nm, 30nm and 60nm respectively. The annealing temperature for the first layer were 610℃, 660℃, and 700℃, respectively under 5 mTorr, 50 mTorr or 1 Torr oxygen. The annealing conditions of the main layer were the same as those of the one-step deposited films, which were for comparison, i.e, 600℃ ×60min under 1 atm oxygen. The dielectric constants of one-step and two-step deposited bST films are almost the same at 80∼150, and both met the trouble of Ti out diffusion to form TiO2. The electrical properties of BST thin films were affected by first layer thickness, that is optimum at 30nm, annealed at 610℃ under 1 Torr O2. The optimum two-step deposited BST thin films showed a dielectric constant of 132 at 1kHz, almost the same as that of one-step deposited films; a leakage current density of 9.5×10-9 A/cm2 at 100 kV/cm, much lower than that of one-step deposited films; a dielectric loss of 0.005, also much lower than that of one-step deposited films; and a more stable I-V curve. The leakage current density increased quickly at about 300 kV/cm. Protrusions were found to appear on AFM micrographs of one-step deposited BST film surface. Such protrusions were successfully suppressed by two-step deposition. From the above studies, conclusion can be drawn that the two-step deposition BST thin films had better properties than the one-step deposited ones.