Effect of K-doping on the dielectric and tunable properties of Ba0.6Sr0.4TiO3 thin films prepared by RF magnetron sputtering

Ba0.6Sr0.4TiO3 (BST) thin films doped by K (0, 5, 10 and 12.5mol%) (BSTK) were deposited by radio frequency (RF) magnetron sputtering on Pt/Ti/SiO2/Si substrates. Atomic force microscopy and X-ray diffraction analysis were used to investigate the structure and morphology of the BST thin films. The dielectric measurements were conducted on metal–insulator–metal capacitors at the frequencies from 1kHz to 1MHz. It was found that the K concentration in BST thin films has a strong influence on the material properties including surface morphology, dielectric, and tunable properties. The surface root-mean-square roughness of the BSTK films decreased when 5mol% K was doped and increased with increasing content of K hereafter. The dielectric constant, dielectric loss and tunability increased when K was doped in the BSTK thin films. The (Ba0.6Sr0.4)95%K5%TiO3 thin film exhibited the highest tunability of dielectric constant of about 62.3% and a figure of merit of 26.1 at a maximum applied bias field at 1MHz.