Microwave properties of Ba0.5Sr0.5TiO3 thin film coplanar phase shifters

Abstract

Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba 0.5 Sr 0.5 TiO 3 thin films used for microwave phase shifters in the frequency range 45 MHz-50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications.

Effect of growth defects on microwave properties in epitaxial Ba0.5Sr0.5TiO3thin films grown on (001) MgO by pulsed laser deposition

“…The microwave properties of the BSTO films are summarised in Table 2; a detailed description is reported elsewhere [15]. The highest tunability was obtained for films grown at an oxygen pressure of 10 -1 mbar; when such a film was ex-situ annealed, there was a further 40% increase in dielectric tunability as shown in Table 2.…”

“…Furthermore, in studies which evidenced a correlation between MD's and dielectric response [20], localised charges on the cores of the misfit dislocations were associated with hysteresis in the capacitance-voltage characteristics: no such hysteresis is seen in the present films [15].…”

“…The decrease in TD density due to ex-situ annealing is correlated with an increase in the permittivity, tunability and dielectric loss and also a sharpening of the ferroelectric to paraelectric transition (i.e. a reduction of heterogeneity) [15]. Since the TDs are present throughout the volume of the film, it is more likely that they, rather than the MDs, are influencing the dielectric properties.…”

“…The sample patterning and extraction of the dielectric properties of the films are described in detail elsewhere [15]. The use of co-planar lines means that the measured dielectric response is dominated by the in-plane properties.…”

Coplanar Phase Shifters Based on Ferroelectric Thin Films

“…In addition, the PIN diode phase shifters have high insertion loss and can only handle tens of watts. As a result, the subject of ferroelectric phase shifter has been of high interest during the last decade [1][2][3][4][5][6].…”