title: Comparison of BST film microwave tunable devices based on (100) and (111) MgO substrates.
abstract: We have increased the figure-of-merit (FOM) of a (Ba,Sr)TiO₃ (BST) film microwave tunable device by approximately three times for MgO(111) compared with a MgO(100) substrate at a frequency range of 20 GHz. Differences in permittivity and tunability in a BST film may be closely related to the difference in the film strain. The ratio of calculated permittivities of BST(100) and BST(111) films nearly corresponds to that of the FOM in the microwave range, which was rather unexpected because a higher permittivity leads to both larger tunability and dielectric loss in ferroelectrics. From a series of results, it is suggested that there are additional influences of orientation (other than the direct influence of strain itself) on the tunable properties in BST films especially in the high-frequency region.
authors.affiliation: Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto, Japan. noda@kit.ac.jp
authors.forename: Minoru
authors.initials: M
authors.lastname: Noda
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Yamada
authors.forename: Kousuke
authors.initials: K
authors.lastname: Seki
authors.forename: Takafumi
authors.initials: T
authors.lastname: Kamo
authors.forename: Kaoru
authors.initials: K
authors.lastname: Yamashita
authors.forename: Horoshi
authors.initials: H
authors.lastname: Funakubo
authors.forename: Masanori
authors.initials: M
authors.lastname: Okuyama