Characterization of quality of BaxSr1−xTiO3 thin film by the commutation quality factor measured at microwaves

Abstract

The loss factor (tan δ) of ferroelectric material at microwaves and the tunability (n) defined as a ratio of the dielectric permittivity at zero dc field to the dielectric permittivity at the given field are strongly connected with the softness of so-called ferroelectric soft mode. The loss factor and the tunability are generalized by the commutation quality factor (CQF). The dielectric response of a ferroelectric material allows one to determine the CQF and to compare it to the theoretical CQF obtained for a perfect ferroelectric sample. In order to compare the theoretical prediction and experimental data, the influence of deposition parameters on microwave properties of BaxSr1−xTiO3 (BSTO) films deposited on sapphire and alumina substrate has been investigated in a wide frequency range (1–30 GHz). The highest CQF at room temperature was obtained for the 30% Ba content target and the deposition temperature 905 °C. The best BSTO films exhibited CQF≅1.6×104 with n=2.1 and tan δ=0.012 at 1 GHz and zero bias. This result is among the best reported for sputtered BSTO films both on sapphire and alumina substrates. Nevertheless the obtained CQF is 3–5 times lower than the upper theoretical limit.

Enhanced electrical properties of ferroelectric thin films by ultraviolet radiation

“…However, recent investigations of thin films of SrTiO 3 , BaTiO 3 , and their solid solution Ba x Sr 1−x TiO 3 ͑BSTO͒, motivated by the prospect of new applications such as electrically controllable microwave devices, 1,2 have uncovered many complexities not previously recognized. The most effort has been aimed at the optimization of thin film fabrication processes, i.e., to the microwave loss reduction ͑microwave loss tangent of ferroelectric thin films is much higher than that of corresponding bulk crystals͒, 3,4 increasing the tunability, 5 and improving the temperature stability. 6,7 These points are now better understood, but the issue of the residual polarization and the hysteresis phenomenon observed under varying bias voltage, resulting in slow relaxation of dielectric constant of ferroelectric films in paraelectric phase ͑above the Curie temperature͒, 8 has not been properly addressed.…”

Conservation of Permittivity and Tunability of Ferroelectrics Over Temperature

“…At the present time, highfrequency devices such as varactors, phase-shifters and tunable filters based on thin and thick (ceramic) films are actively being studied and demonstrate parameters competitive with semiconductor and ferrite analogues [1,2]. One of the main differences of ferroelectric materials in comparison with semiconductors is the stronger temperature dependence of the dielectric constant (ε).…”

Microwave Properties of Thin BSTO Films Based Varactors for High Frequency Applications

“…Investigations of nonlinear dielectric behavior and microwave losses of ferroelectric bulk ceramics and thin films have demonstrated the potential of these materials for microwave applications for frequency range up to 60 GHz [1][2][3]. Today ferroelectric microwave elements operating at room temperature are designed based most of all on BaSrTiO 3 (BSTO) films which have rather high dielectric nonlinearity and low dielectric losses at operating temperature [4,5] in comparison with another ferroelectric materials. However, at present time, BSTO films with combination of high dielectric nonlinearity and low losses in a wide frequency range (at least tan δ ≤ 0.02 at 1 GHz and tan δ ≤ 0.06 at 30 GHz) are needed for room temperature microwave applications.…”