Microwave Properties of Mn Doped (Ba_{1 - x},Sr_x)TiO₃Thin Films for Tunable Phase Shifter

Abstract

Ferroelectric Mn doped Ba 0.5 Sr 0.5 TiO 3 (Mn-BST) films with/without BaTiO 3 (BT) buffer layer have been grown on (001) MgO substrates by a pulsed laser deposition to investigate electrical tunability at microwave frequencies. Structural properties and surface morphologies of the films were investigated using an X-ray diffractometer and a scanning electron microscope, respectively. Microwave dielectric properties of Mn-BST thin films with BT buffer were studied for reduction of dielectric loss and improvement of electrical tunability. Distributed analog phase shifters have been designed and fabricated on Mn-BST films with/without BT buffer layer to understand microwave dielectric properties. The differential phase shift of the phase shifter fabricated on Mn-BST film was 22 • at 10 GHz with 80 V of applied dc bias voltage. In comparison, phase shifter fabricated on Mn-BST/BT multilayers exhibit 41 • of differential phase shift at the same condition. This suggests that a BT buffer layer is for microwave tunable device applications. The phase shifter fabricated on Mn-BST/BT multilayers exhibit a low insertion loss (S 21 ) of −1.1 dB, and a low return loss (S 11 ) of −14 dB with a bias voltage of 80 V.