Do we really need ferroelectrics in paraelectric phase only in electrically controlled microwave devices?

TLDR

Paraelectric materials such as SrTiO₃, KTaO₃, and BaₓSr₁₋ₓTiO₃ are commonly used in tunable microwave devices, but thin films exhibit lower permittivity and a loss tangent around 0.01 at frequencies above 10 GHz, while ceramic ferroelectrics are considered for cost‑effective industrial applications. The study explores, for the first time, the feasibility and advantages of employing ferroelectric materials in their polar phase for electrically controlled microwave devices. The authors investigate the application of ferroelectric materials in the polar phase to electrically tune microwave devices, assessing their performance characteristics. The analysis shows that thin paraelectric films have not achieved significant loss improvement, yet component‑level devices perform well, and ferroelectrics in the polar state (e.g., Na₀.₅K₀.₅NbO₃, SrTiO₃ in antiferroelectric phase) have been successfully used in tunable microwave devices.

Abstract

Typical paraelectric materials (e.g., SrTiO/sub 3/, KTaO/sub 3/, Ba/sub x/Sr/sub 1-x/TiO/sub 3/, x<0.5) and electrically tunable microwave devices based on these materials are briefly reviewed. The analysis shows that in spite of the recent year's extensive efforts, no considerable improvement in the microwave losses in thin paraelectric films has been achieved. Thin films, regardless of fabrication method and substrate type, have much lower dielectric permittivity than bulk single crystals, and the loss tangent at microwave frequencies (f>10 GHz) is of the order of 0.01 (at zero dc-bias field) at room temperature. Nevertheless, quite promising component and subsystem level devices are successfully demonstrated. Use of ceramic (bulk and thick film) ferroelectrics in tunable microwave devices, currently considered for industrial applications, offer cost reduction. In this paper, explicitly for the first time, we consider possibilities and benefits of using ferroelectrics in polar phase in electrically controllable microwave devices. Examples of using ferroelectrics in polar state (e.g., Na/sub 0.5/K/sub 0.5/NbO/sub 3/, SrTiO/sub 3/ in antiferroelectric phase) in electrically tunable devices are reported.