Electrical Properties of Sputtered (Ba,Sr)TiO_3. Thin Films Prepared by Two-Step Deposition Method

摘要

The influence of two-step deposition on the electrical propertiesof sputtered (Ba,Sr)TiO_3 thin films was investigated. BST thin filmswith thickness 40 nm were deposited by a simple two-step radiofrequency-magnetron sputtering technique, where the BST thin filmconsisted of a seed layer and a main layer. The dielectric constantwas strongly dependent on the thickness of seed layer, but there wasno dependence on deposition temperature of the seed layer. For a 2 nmseed layer, the dielectric constants were higher by about 29/100 thanthose of single-step BST thin films due to higher crystallinity andthe leakage current was nearly the same as that of a single-stepsample in bias voltage from -2 to 2.5 V. However, an improvement ofthe dielectric constant was not observed for samples having above 4nm thick seed layers. A 40 nm thick BST film with 2 nm thick seedlayer deposited by a two-step method exhibited a SiO_2 equivalentthickness of 0.385 nm and a leakage current density of 2.74 x10~-8A/cm~2 at + 1.5V after post-annealing under an atmosphere offlowing N_2 for 30 min at 750 deg. C.