High Tunable ${\rm Ba}_{0.05}{\rm Sr}_{0.95} {\rm TiO} _{3}$ Thin Films for Microwave Applications at Cryogenic Temperature

La
_0.67
Sr
_0.33
MnO
₃
/Ba
_0.05
Sr
_0.95
TiO
₃
(LSMO/BST) heterostructure thin film was grown on single crystal MgO substrate by pulsed laser deposition. The phase structure and dielectric properties of the film were investigated. The results show that the permittivity of the BST thin film decreased from 1170 to 350 (70% tuning) with the bias voltage increasing from 0 to 80 V at 63 K. The effective loss tangent of the BST thin film is in the range of 0.009-0.017.