Structure-Property Relationships in W Doped (Ba,Sr)TiO 3 Thin Films Deposited by Pulsed Laser Deposition on (001) Mg O
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Structure-Property Relationships in W Doped (Ba,Sr)TiO3 Thin Films Deposited by Pulsed Laser Deposition on (001) MgO N. Navi1,*, J.S. Horwitz, H.-D. Wu2 and S.B. Qadri, Naval Research Laboratory, Washington DC, 20375 1 G.W. University, Washington, DC 2 SFA, Largo, MD ABSTRACT BaxSr(1-x)TiO3 films (BST) with x=0.5, 0.6, 0.7, containing 1% W, were grown by pulsed laser deposition on MgO (001) substrates in an oxygen pressure from 3 to 500 mTorr, at a substrate temperature of 720 C. The crystal structure of the film, as determined from x-ray diffraction, was fit to a tetragonal distortion of a cubic lattice having two in-plane lattice parameters. The in and out-of-plane lattice parameters c, a, a/, and lattice distortion (a/c and a//c) were calculated from the positions of the measured BST reflections ((004), (024) and (224)). The dielectric properties of the film at 2 GHz were measured using gap capacitors deposited on top of the dielectric film, at room temperature. For all compositions, as a function of the oxygen deposition pressure, a peak in the change in the dielectric constant, as a function of an applied electric field (0 – 80 kV/cm), was observed for films deposited in 50 mTorr of oxygen. Unlike the pure BST, the dielectric Q was insensitive to the oxygen deposition pressure. The largest Kfactor (K=(ε(0)-ε(V)/ε(0) x Q(0)) for films deposited from Ba0.6Sr0.4TiO3 target were observed in a film that had a minimum in-plane strain, where a~a/.
INTRODUCTION The large electric field induced change in dielectric constant of (BaxSr1-x)TiO3 (0 ≤ x ≤ 1), is currently being used to develop a new class low of loss, tunable microwave devices, such as tunable oscillators, delay lines and phase shifters [1]. These devices will reduce the size and the operating power of the current semiconducting and ferrite based devices, and will soon have a significant impact on both radar and wireless communication systems [2]. An issue in the fabrication of these devices is optimizing the processing of the material such that it exhibits a large change in the dielectric constant with an applied bias while minimizing the dielectric loss at microwave frequencies. The dielectric properties of thin films are affected by many factors, such as Ba/Sr ratio, grain size, defect chemistry, oxygen vacancies, strain, and dopants. A strong relationship between structural and dielectric properties of the film has been reported in (BaxSr1-x)TiO3 x=0.4 and x=0.5 films grown by pulsed laser deposition (PLD) with different oxygen deposition pressures [3,4]. As-deposited (Ba, Sr)TiO3 films with minimal stress, grown in a relatively low pressure of O2, exhibited the highest microwave figure of merit (% change ε with DC bias x Q0V) [5-7]. Normally, oxygen deposition pressures around 300 mTorr are used during the PLD of oxide thin films to minimize the formation of oxygen vacancies. The lattice of an oxygen * Permanent address - Nuclear Research Center-Negev (NRCN), Beer Sheva 9001, Israel. H2.6.1 Downloaded from https://www.cambridge.org/core. University of
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