Low loss and highly tunable (Ba,Sr)(Ti,Mn)O_3/(Ba,Sr)TiO_3 bilayered films for electrically tunable microwave device applications

摘要

Ba_(0.05)Sr_(0. 95)TiO_3 (BST), 5 mol% Mn-doped BST (Mn-BST) and bilayered Mn-BST/BST films with a thickness of about 100 nm were fabricated by using pulsed laser deposition technique on MgO single crystal substrates, and their microwave dielectric properties were comparatively investigated. It was confirmed that all the BST-based films were crystallized in pure single-oriented perovskite phase. There appeared nanosized pores in the BST film; after addition of Mn, however, the film surface morphology became denser while exhibiting an increased roughness, and ultimately, a smooth and dense morphology was achieved by the design of bilayered Mn-BST/BST film. Coherently, the microwave dielectric properties of BST films were enhanced by Mn doping and more significantly enhanced in the bilayered Mn-BST/BST film. As a result, for the bilayered film, a very low loss tangent of 0.017-0.007 and a high dielectric tunability of 70.9% under £=36 V/|am were simultaneously obtained at 79 K and L-band frequency (1-2 GHz), thereby resulting in an extremely high commutation quality factor of 14492. The excellent microwave dielectric properties obtained in the Mn-BST/BST bilayered film originate not only from the Mn-doping effect, but are also ascribed to the pre-deposition of BST layer, which serves as a good template for the growth of Mn-BST film.