Studies of thin film ferroelectrics with charge-compensated substitutions in BST
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Studies of thin film ferroelectrics with charge-compensated substitutions in BST Daniel Potrepka1, Steven Tidrow1, Arthur Tauber1, Kevin Kirchner1, and Bernard Rod1, James Horwitz2, Wontae Chang2, Nissim Navi3,4, and Daniel Bubb2,5 1 Sensors & Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, MD 20783-1197, U.S.A. 2 Naval Research Lab, Washington, DC 20375, U.S.A. 3 School of Engineering and Applied Science, George Washington University, Washington, DC 20052, U.S.A. 4 Permanent Address- Nuclear Research Center- Negev Beer Sheva 9001, Israel 5 Permanent Address- Department of Physics, Seton Hall University, South Orange, NJ 07079, U.S.A. ABSTRACT Thin films were prepared from bulk targets by pulsed-laser deposition techniques. The targets were composed of Ba0.6Sr0.4TiO3 with charge-compensated substitutions for Ti4+. Results of the dielectric characterization measurements will be discussed and compared to the results of similar measurements in bulk materials with the same composition. INTRODUCTION Temperature dependence of thin film dielectric constants for Ba0.6Sr0.4TiO3 (BST) and similar materials are of interest for frequency-agile applications due to the low voltages required to change capacitance and potential for adjustments to impedance for the purpose of matching properties to circuits in microwave devices. The temperature-dependent dielectric constants are typically broadened relative to those for the bulk samples [1]. This paper describes studies of thin films of Ba0.6Sr0.4(YTa)yTi1-2yO3 which build on the successes of reduction in sensitivity to temperature variation for both dielectric constant and tunability in the bulk material Ba0.6Sr0.4(YTa)yTi1-2yO3 compared to BST [1]. Using Ba0.6Sr0.4(YTa)yTi1-2yO3 films deposited by pulsed-laser deposition and characterized by x-ray diffraction analysis, capacitance measurements, and estimated dielectric constants, the potential of these thin-film materials for device applications is studied. EXPERIMENTAL DETAILS Targets of Ba0.6Sr0.4(YTa)yTi1-2yO3, 0 < y < 0.04 and a comparison sample of Ba0.6Sr0.4(AlTa)0.03Ti0.94O3 were synthesized as described in [1] and references therein. Using a KrF laser, the samples were pulsed-laser deposited onto MgO(100) substrates that were heated to 700 oC or 750 oC in 350 mTorr O2. Subsequently, the samples were cooled to room temperature in ~ 700 mTorr O2 atmosphere. For selected samples, a pre-deposition calibration was made using a shadow mask. Then thickness was measured using a Tencor P-10 profilometer which was used, along with the number of laser shots, to calibrate the deposition rate. In this way, the average thickness of deposited films was determined to be 0.5 µm. The θ-2θ x-ray diffraction spectrum for Cu Kα1 radiation was obtained for selected samples. Using the log plot of the results the 200 and 400 peaks for the MgO(100) substrate were identified. Due to the limited H6.3.1 Downloaded from https://www.cambridge.org/core. University of California, Santa Cruz, on 22 Dec 2019 at 09:13:12, subject to th
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