Design and Characterization of Novel Barium Strontium Titanate Thick Films for Sub-6 GHz RF Applications


In this article, a novel study of the design and characterization of barium strontium titanate (BST) thick films produced by electrophoretic deposition (EPD) on flexible platinum foils is reported. Intended for sub-6 GHz radio frequency (RF) applications, a study on film and electrode thickness is conducted. First, a comparison of tunability and quality factor between different film thicknesses regarding frequency is performed. The $Ba_{0.7}Sr_{0.3}TiO_{3}$ varactors demonstrate variable capacitance between 49% and 55% for frequencies from 500 MHz to 5 GHz. Afterward, the influence of electrode thickness on the capacitance and quality factor of the films are studied. The variable capacitance and the quality factor present a tradeoff regarding the parametric studies of film and electrode thicknesses. Lastly, a microstrip line is deposited over the BST thick film to simulate and measure the phase-shifting capabilities of the device. Using a one-tone measurement setup, the small-signal S-parameter measurements of the phase shifter are also presented, and the linearity is analyzed considering two different bias voltages, 0 and 10 V. For the first time, the BST thick films fabricated by EPD process are implemented and measured in the RF regime as a metal-insulator-metal capacitor and as a phase shifter circuit.






Bouca, P; Figueiredo, R; Wlodarkiewicz, A; Tkach, A; Matos, JN; Vilarinho, PM; de Carvalho, NB

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This work was supported in part by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Lisbon (POR LISBOA 2020) and the Competitiveness and Internationalization Operational Programme (COMPETE 2020) of the Portugal 2020 framework [Project CoViS with Nr. 070090 (POCI-01-02B7-FEDER-070090)]; and in part by the Project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by National Funds through the Portuguese FCT/MCTES. The work of Patricia Bouca was supported by the Fundacao para a Ciencia e Tecnologia (F.C.T.) under Ph.D. Grant 2020.05679.BD. This article is an expanded version from the IEEE MTT-S International Microwave Symposium, Atlanta, GA, USA, June 20-25, 2021.

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