The influence of Mg doping on the materials properties of Ba1−xSrxTiO3 thin films for tunable device applications

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M. W. Cole^{, , a}, P. C. Joshi^a, M. H. Ervin^a, M. C. Wood^a and R. L. Pfeffer^b

^a US Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005, USA

^b Department of Physics, Rurgers University, Piscataway, NJ 08854, USA

Received 31 March 2000;

revised 7 June 2000;

accepted 9 June 2000.

Available online 13 October 2000.

Abstract

We have investigated the structural, microstructural, interfacial, and surface morphological properties of Ba_0.60Sr_0.40TiO₃ thin films Mg doped from 0 to 20 mol%. A strong correlation was observed between the films materials properties and the prior determined dielectric and insulating characteristics as a function of Mg doping. Non-textured polycrystalline films with a dense microstructure and abrupt film-Pt electrode interface were obtained after annealing at 750°C for 30 min. Single phase solid solution films were achieved at Mg doping levels up to 5 mol%, while multiphased films were obtained for Mg doping levels of 20 mol%. Decreases in the films dielectric constant, dielectric loss, tunability and leakage current characteristics were paralleled by a reduction in grain size as a function of increasing Mg dopant concentration. Our results suggest that Mg doping serves to limit grain growth and is thereby responsible for lowering the dielectric constant from 450 to 205. It is suggested that Mg behaves as an acceptor-type dopant at the grain boundary and is responsible for the doped films low dielectric loss and good leakage current characteristics. Examination of the performance-property trade-offs advocates the 5-mol% Mg doped BST film to be an excellent choice for tunable microwave device applications.

Author Keywords: Dilectric properties; Deposition process; Film miscrostructure