Mater. Res. Soc. Symp. Proc. Vol. 1397 © 2012 Materials Research Society DOI: 10.1557/opl.2012.451 Three-Step Deposition Method for Improvement of the Dielectric Properties of BST Thin Films H. Liu 1 , V. Avrutin 1 , C. Zhu 1 , J.H. Leach 1 , E. Rowe 1 , L. Zhou 2 , D. Smith 2 , Ü. Özgür 1 and H. Morkoç 1 1 Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, VA 23284, USA. 2 Physics Department, Arizona State University, Tempe, AZ 85287 USA. ABSTRACT Epitaixal Ba 0.5 Sr 0.5 TiO 3 (BST) thin films were grown on SrTiO 3 (STO) and DyScO 3 substrates by radio-frequency magnetron sputtering system using three-step method which involves a relatively low-temperature (573-773 K) growth of a BST interlayer sandwiched between two BST layers deposited at a high substrate temperature of 1068 K. X-ray diffraction measurement showed different strains on the films with interlayers grown at different temperatures. Post-growth thermal treatment reduced film strain to a great extent (the film strain of a tri-layer film with a 773 K grown interlayer is only -0.001). Comparing with the control films grown at high temperature, three-step technique improved the dielectric properties, especially increased dielectric constant by 60% for BST/STO and 31% for BST/DyScO 3 , respectively. High dielectric constant of 1631.4 and its tuning of 36.7% were achieved on the BST/STO with an interlayer grown on 773 K. INTRODUCTION Ba 0.5 Sr 0.5 TiO 3 (BST) thin film have attracted a considerable attention as a promising material for microwave passive component owing to its high dielectric constant, strong dependence of dielectric permittivity on the applied DC field and relatively low loss [1-3]. Dielectric tunability and dielectric loss are primarily controlled by crystal quality and film strain state of the film. The effect of crystal quality is intuitive: an increase in the quantity of defects in a thin film would tend to yield more centers with which the electromagnetic field could interact, resulting in increased loss. To improve structural perfection, the use of nearly lattice-matched substrates, such as SrTiO 3 (STO) and DyScO 3 , seems desirable. However, the in-plane lattice parameters of the epitaxial BST films grown on nearly (but not perfectly) lattice-matched substrates tend to be “clamped” to the lattice parameters of the substrate, inducing a biaxial strain in the film, which has a strong effect on the dielectric constant and tunability [4, 5]. Therefore, it is important to control the film strain by choosing appropriate substrate and improving growth procedures [6]. In order to enhance the dielectric properties, many approaches such as tailoring the Ar:O 2 ratio during the growth [7] or adding various buffer layer [6, 8], have been investigated recently. In this work, we deposited BST thin film on two different substrates, STO and DyScO 3 , which both have small lattice-mismatch and similar thermal expansion coefficient to BST film [9-11]. For both substrates used, we implemented and tested the three-step growth method in which an interlayer grown at reduced substrate temperature was sandwiched between a thin nucleation layer and a thick top layer both grown at higher substrate temperature in order to