Fabrication and Electrical Characterization of Ba (1-x) Sr x TiO 3 Based Thin Films

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Fabrication and Electrical Characterization of Ba(1-x)SrxTiO3 Based Thin Films E. Ngo, W.D. Nothwang, C. Hubbard, M.W. Cole Army Research Laboratory Aberdeen, MD 21005 W. Chang, S. W. Kirchoffer, J. M. Pond Naval Research Laboratory Washington, DC 20375

ABSTRACT Over the past several years there has been a tremendous growth and development of thin film deposition technology in the electronics industry. Ferroelectric thin films have been recognized for their unique dielectric properties and appear to be desirable for tunable microwave device applications. Among the most promising candidates for such applications are Ba(1-x)SrxTiO3[BST] and BST-based thin films. In this work pure BST and acceptor doped BST-based thin films were fabricated on (100) MgO substrates via pulsed laser deposition [PLD]. X-ray diffraction (XRD) in conjunction with the atomic force microscope (AFM) were used to analyze the film crystalinity and surface morphology. The dielectric properties were characterized at both 100 kHz and 20 GHz. The MIM capacitor configuration was used to attain the dielectric properties at 100 kHz and the microwave measurements, S11 reflection parameters, were achieved via interdigitated capacitor design with Au/Ag top electrodes. The parallel resistor-capacitor models were used to determine the microwave capacitance and Q factors and the permittivity was calculated using a modified conformal-mapping partial-capacitance method using the dimension of the capacitors. Our results demonstrated that the low frequency and microwave frequency dielectric properties were strongly influenced by the film composition. Specifically, the Mg doping served to lower the dissipation factor, permittivity, and tunability of the BST based films at both frequencies. This work demonstrates that the BST based thin films possessed excellent microstructural, structural, and dielectric properties. The structure-process-property correlations of the pulsed laser deposited BST and acceptor doped BST-based thin films are discussed in detail. INTRODUCTION In the recent years, there has been a significant increase in the need for, and applications of, microwave circuit technologies. The progress in the communication application area has resulted in a demand for miniaturized components, which are a key

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Figure 1. Diagram of interdigitated capacitors [IDC] with microwave probe in contact. Finger length of the device is 80 micron and finger width spacing is 6 micron.

factor for low power and integratable microwave devices [1-4]. Ferroelectric films have attracted considerable attention for applications in computer memory elements, frequency agile microwave components, pyroelectric sensors, and voltage tunable capacitors [3-8]. For tunable device applications, the ferroelectric material should possess low dielectric loss, low leakage current, and high voltage tunability [4]. A promising candidate material is Ba1-xSrxTiO3 (BST). BST is a continuous solid solution between barium titanate and strontium titanate over the entire range of c