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0966-T07-23

Molecular Beam Epitaxial Growth and Dielectric Characterization of Ba0.6Sr0.4TiO3 Films P. Fisher1, M. Skowronski1, P. A. Salvador1, M. Snyder2, J. Xu2, M. Lanagan3, O. Maksimov4, and V. D. Heydemann4 1 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213 2 Pennsylvania State University, Engineering Science and Mechanics, University Park, PA, 16802 3 Pennsylvania State University, Materials Research Institute, University Park, PA, 16802 4 Electro-Optics Center, Pennsylvania State University, 559A Freeport Rd., Freeport, PA, 16229

ABSTRACT Ba0.6Sr0.4TiO3 films were grown by molecular beam epitaxy on MgO(001) and LaAlO3(001) substrates. The growth mode was determined to be two-dimensional by in-situ reflection high-energy electron diffraction. The films were structurally and dielectrically characterized ex-situ using X-ray diffraction, Rutherford backscattering spectrometry, and split cavity resonance mode dielectrometry. The structural and dielectric properties of the Ba0.6Sr0.4TiO3 film grown on MgO were determined to be inferior to the film grown on LaAlO3, as was indicated by the broader rocking curve (0.59 deg. vs. 0.17 deg.) and higher dielectric loss (0.29 vs. 0.12). INTRODUCTION The Ba1-xSrxTiO3 (BST) system is of significant technological interest owing to its nonlinear dielectric properties [1] that make it suitable for a number of microwave applications, including filters, phased arrays, and phase shifters [2-6]. The Curie temperature of the ferroelectric phase of this system decreases in a nearly linear fashion with x, from 400 K for BaTiO3 to 30 K for SrTiO3 [7]. The x = 0.4 composition, or Ba0.6Sr0.4TiO3, is well-studied because its Curie temperature is just below room temperature, allowing extensive tunability without hysteresis under standard operating conditions [7]. Ba0.6Sr0.4TiO3 films were previously grown by a number of techniques, including pulsed laser deposition [1,3,4,6], sputtering [5,8], metal organic chemical vapor deposition [3,9], and sol-gel processing [7,10]. Molecular beam epitaxy (MBE) of Ba0.6Sr0.4TiO3 has been much less studied [11]. Dielectric characterization of BST films is usually performed using capacitor structures that have either co-planar or parallel-plate electrode configurations. In the first case, a capacitor structure is fabricated on the surface of the deposited BST film [5]. In the second case, an underlayer electrode is deposited onto the substrate, followed by the BST film, and then the top electrode. Both of these techniques have significant drawbacks, particularly for measurements in the microwave frequency range. For example, the measured capacitance of the co-planar capacitor structure includes an additional contribution from the substrate; the measured dielectric loss (tan δ) includes contributions both from the electrodes and the substrate. For films measured in the parallel plate geometry, the crystalline quality of the BST film, and therefore the dielectric properties, is always limited by the crystalline quality