The tunable properties of Mn doped (Ba, Sr)TiO3 thin film varactor at low temperature

Mn doped ferroelectric (Ba, Sr)TiO
3
(Ba
0.05
Sr
0.95
Ti
0.95
Mn
0.05
O
3
, BSTM) thin films were prepared on the MgO single crystal substrate by using pulsed laser deposition technique. The dielectric properties of the varactor composed by this thin film was investigated by using a superconductor resonator at the liquid nitrogen temperature. Measurement results indicated that the thin film showed high quality-factor of up to 140, with a tunability of 72% at the bias voltage of 210 V. The loss tangent of the varactor varied from 0.02 to 0.008 with the bias changed from 0 V to 210 V. Both the low dielectric loss and tunable properties of the BSTM thin film varactor are useful for tunable microwave applications.