Comparison of BST film microwave tunable devices based on (100) and (111) MgO substrates

Minoru Noda; Tomoaki Yamada; Kousuke Seki; Takafumi Kamo; Kaoru Yamashita; Horoshi Funakubo; Masanori Okuyama

doi:10.1109/TUFFC.2010.1681

Comparison of BST film microwave tunable devices based on (100) and (111) MgO substrates

IEEE Trans Ultrason Ferroelectr Freq Control. 2010 Oct;57(10):2221-7. doi: 10.1109/TUFFC.2010.1681.

Authors

Minoru Noda¹, Tomoaki Yamada, Kousuke Seki, Takafumi Kamo, Kaoru Yamashita, Horoshi Funakubo, Masanori Okuyama

Affiliation

¹ Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto, Japan. noda@kit.ac.jp

PMID: 20889408
DOI: 10.1109/TUFFC.2010.1681

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.