Effect of Strain on the Tunability of Highly (100) Oriented Mn-doped Barium Strontium Stannate Titanate Thin Films
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Effect of Strain on the Tunability of Highly (100) Oriented Mn-doped Barium Strontium Stannate Titanate Thin Films Shengbo Lu, Ngai Wing Li, and Zhengkui Xu Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China, People's Republic of
Effect of strain on the tunability of highly (100) oriented Mn-doped barium strontium stannate titanate thin films S.B.Lua), Ngai Wing Li and Z.K.Xu Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong ABSTRACT
Highly (100)-oriented Mn-doped barium strontium stannate titanate thin films of a nominal composition (Ba0.7Sr0.3)(Sn0.2Ti0.8-xMnx)O3 (Mn-BSSnT) (x=0, 0.002, 0.004, 0.006 and 0.01), were fabricated on (La0.7Sr0.3)O3/LaAlO3 substrates by pulsed laser deposition. Both elastic strain and inhomogeneous strain were measured by x-ray diffraction techniques. Effect of strain on dielectric properties of the Mn-BSSnT thin films was systematically investigated as a function of the Mn content. Our results show that the tunability is dependent upon not only the elastic strain induced by thermal expansion coefficient and lattice mismatch between the thin film and the substrate but also inhomogeneous strain induced by Mn doping. The tunability decreases with increasing inhomogeneous strain and can be easily manipulated by changing Mn doping content, which is beneficial to real tunable device applications.
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INTRODUCTION Over the last decade, the continuous need for improved, more compact, and multifrequency satellite, radar, and communication systems has driven the investigation of better materials and investigation schemes for key elements of these systems[1-3]. Of the possible oxide candidates, (BaxSr1-x)TiO3 (BST) has been thoroughly studied because of its high permittivity, its lead-free composition, and relative ease of processing. Recently, much work has focused on optimizing the properties of the BST thin films via doping. Mn2+, Ni2+, Mg2+, Zr4+ and Sn4+ etc were doped into BST thin films to develop thin films that possess low dielectric loss and high tunability[4-7]. All though much success has been achieved in optimizing these two material properties, less attention has been devoted to reveal the detailed strain evolution in the doped thin films which is a dominant factor on the property of the thin films and up to date, it is still unclear.
In this work, the strain development in the Mn-BSSnT thin films and their relationship with the dielectric property of the thin film were systemically studied.
EXPERIMENT
The undoped and 0.002, 0.004, 0.006, 0.01 mol Mn-doped (Ba0.7Sr0.3)(Sn0.2Ti0.8)O3 (Mn-BSSnT) targets were prepared by a conventional mixed oxide method. 300nm-thick Mn-BSSnT films and 150nm-thick La0.7Sr0.3CoO3 bottom electrode were deposited on LaAlO3 (LAO) (100) substrates by pulsed laser deposition (PLD) with a KrF excimer laser (λ=248nm). The laser power, repetition rate, oxygen ambient pressure, and growth temperature were 300mJ, 5Hz,
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