Single- and Multi-target Pulsed Laser Deposition of Thin BSTO films: Preparation, Microstructure and Electrical Properti
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Single- and Multi-target Pulsed Laser Deposition of Thin BSTO films: Preparation, Microstructure and Electrical Properties Kumaravinothan Sarma, Peter Kr. Petrov and Neil McN. Alford Centre for Physical Electronics and Materials Centre, Faculty of Engineering, Science and Built Environment, London South Bank University, SE1 0AA, UK.
ABSTRACT A comparative study of microstructure and electrical properties of BaxSr1-xTiO3 films made by single- and multi-target pulsed laser deposition was carried out. The films were epitaxially grown on both LaAlO3 and MgO substrates. The structural properties of all samples were investigated using X-ray diffraction and Raman spectroscopy. The elemental composition of the samples was investigated using energy dispersive X-ray analysis. For electrical properties examination, a simple capacitor structure was patterned on the film surface. Thin films made using both methods exhibit similar structural and electrical properties; however the samples made by a multi-target method underwent phase transition in a broader temperature region. The results prove the possibility of using the multi-target pulse laser deposition as a more flexible method for engineering thin film stoichometry.
INTRODUCTION In recent years BSTO thin films have attracted much research attention as a promising material for electrically controllable microwave devices [1-3]. One of the disadvantages of BSTO films still preventing their wider applications is the strong temperature dependence of their properties. The Curie temperature of a BSTO film is determined mainly by the Ba/Sr ratio. Hence, by altering the stoichiometry ratio, it is possible to tailor a composition with specific properties (relative dielectric constant, tuning ratio and dielectric loss) for specific temperature ranges. The usual way of a BSTO deposition, is using single target with the required stoichiometry. However this approach becomes expensive (in terms of number of targets used) when the need is for a multilayer structure with different Ba/Sr ratio layers or even impossible for BSTO based graded structure. In this paper we present the results of an investigation of thin film fabrication by pulsed laser deposition (PLD) using multi-target, as an alternative to the single-target method. This method enables the engineering of the stoichiometry of the thin film during deposition.
EXPERIMENTAL PROCEDURE A set of BaxSr1-xTiO3 (where x = 0.25, 0.50 and 0.75) thin films were deposited on LaAlO3 and MgO substrates using a single target with corresponding stoichiometry (method 1). Another set of samples with the same stoichiometry were deposited as a periodic structure of
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BaTiO3 (BTO) and SrTiO3 (STO) layers (method 2). The layer thickness was chosen so as to not exceed the critical thickness required for epitaxial growth. In order to obtain a specific Ba/Sr stoichiomeric ratio in the sample, the number of laser pulses shot to BTO and STO targets was adjusted according to the ratio. This enabled a series of STO and BTO layers to be d
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