Effect of Deposition Parameters on the Microstructural Evolution and Electrical Properties of Charge-Balanced Barium Str
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C11.48.1
Effect of Deposition Parameters on the Microstructural Evolution and Electrical Properties of Charge-Balanced Barium Strontium Titanate Ferroelectric Thin Films Deposited on Ceramic Substrates by Pulsed Laser Deposition Costas G. Fountzoulas1, Steven C. Tidrow2, Michael Hatzistergos3 and Harry Efstathiadis3 1
Weapons Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069, U.S.A. 2 Sensors and Electron Devices Directorate, Army Research Laboratory, Adelphi, MD 207831197, U.S.A. 3 School of Nanoscience and Nanoengineering, University at Albany, SYNY, Albany, NY ABSTRACT Barium strontium titanate (Ba0.60Sr0.40TiO3) thin films are the main materials of interest in tunable phase shifter for microwave antenna applications. Ba0.60Sr0.40Y0.05Ta0.05Ti0.90O3 thin films, of nominal thickness ranging from 1.7 µm to 2.3 µm, were synthesized on MgO (100) substrates, at substrate temperatures ranging from 5000C to 9000C, at oxygen partial pressures 20 and 50 mTorr, at 500 mJ energy fluence on 3 mm x 1 mm spot size and 10 pulses per second using the pulsed laser deposition technique. All film synthesized at temperatures greater than 5000C were crystalline. The effect of the ionic substitution and substrate temperature in conjunction with the effect of the oxygen partial pressure on the microstructure, and mechanical and electrical properties of the thin films have been studied using shallow angle x-ray diffraction, SEM, nanoindentation, atomic force microscopy (AFM), and focused ion beam analysis (FIB) and are reported in detail. We are currently in the process of measuring the capacitance of these films by various methods. INTRODUCTION Ferroelectrics are multicomponent materials with a wealth of interesting and useful properties, such as ferroelectricity, piezoelectricity, and pyroelectricity and above the Curie temperature, paraelectricity. These properties derive from their non-centrosymmetric crystallattice structure in which spontaneous polarization is observed. The most widespread and potentially important use for ferroelectrics exists in the area of nonvolatile random access memories (NVRAM). Ferroelectrics are also of interest above the Curie temperature (Tc), in the paraelectric regime, for voltage-tunable, radio frequency, and microwave phase shifters, filters, and true-time delay devices for electronic scanning antenna technology [1]. The critical material parameters for many microwave device designs are: low dielectric constant, high tunability, lowtemperature Curie peak (Tc), low dielectric loss tangent, low leakage current and small temperature coefficient of permittivity. For electrically tunable microwave devices with a coplanar waveguide structure, BST is used as an active dielectric layer in thin-film form [2]. For phase shifting ceramics, it is desirable to operate the device in the paraelectric region, hence the desire for low Tc [3]. However, in general, the higher the dielectric constant, the more tunable the ceramic will be [4]. By adding 40 mol% SrTiO3 to
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