Effect of Laser Energy and Laser Pulses on the Microstructure, Composition and Properties of Barium Strontium Titanate T
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Effect of Laser Energy and Laser Pulses on the Microstructure, Composition and Properties of Barium Strontium Titanate Thin Films Synthesized by Pulsed Laser Deposition Costas G. Fountzoulas, J. D. Demaree and Steven H. McKnight Weapons and Materials Research Directorate, Army Research Laboratory, APG, MD, 210055069. ABSTRACT Barium strontium titanate (BSTO) films were synthesized by the pulsed laser deposition technique (PLD) on silicon substrates at room temperature. The thin films were synthesized at ambient temperature and 30 mT oxygen partial pressure, with 300, 400 and 500 mJ/cm2 laser fluence at 5, 10 and 20 pulses per second on silicon wafer substrates. All films were subsequently post-annealed at 750°C in a continuous oxygen stream. The microstructure, crystallinity and lattice constant of the BSTO films were studied with the aid of atomic force microscopy (FEM) and Glancing Angle X-ray Diffraction analysis (GAXRD). The hardness and modulus of elasticity of the films were studied with the aid of a nanohardness indenter. The film stoichiometry was determined with the aid of Rutherford Backscattering Spectrometry (RBS). The results of this research will be combined with the results of our previous work [1, 2] on the effect of substrate temperature and oxygen partial pressure on the microstructure and properties of the BSTO films in order to construct a structural zone model (SZM) of the BSTO films synthesized by PLD. INTRODUCTION Thin films of barium strontium titanate (BSTO) deposited by the pulsed laser deposition (PLD) technique exhibit excellent electronic properties including tunable dielectric constants and low electronic loss. The dielectric constant of the BSTO depends on the applied electric field. This variable dielectric constant results in a change in phase velocity in the device allowing it to be tuned, in real time, for a particular application. The dielectric requirements for a tunable BSTO thin film are (a) loss less than 0.01; (b) high tunability; (c) dielectric constant between 30 and 100; (d) low leakage current; and (e) good frequency and temperature stability of dielectric properties [1]. A tunable BSTO film must be single phase and crystalline. It must also have a smooth, defect free surface, uniform microstructure, and exhibit good thermal stability with the substrate. The microstructure of the film influences the electronic and mechanical properties (internal stresses and adhesion). These important factors affect the mechanical integrity and reliability of a device made of these thin films. For several decades ferroelectric memory has attempted unsuccessfully to compete with semiconductor and magnetic memory. Niche markets have developed around the advantages of ferroelectric memory such as radiation hardness and non-volatility. Among the features holding back ferroelectric memory have been cost, fatigue, and large switching voltages. The use of epitaxial structures, and the metallization of the ferroelectric with oxides such as YBCO, La-SrCo-O, and Sr-Ru-O in place of Pt or Au has cre
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