Ink-jet Printed BaTiO 3 for Photonics
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Ink-jet Printed BaTiO3 for Photonics Petra Lommens, Tom Bruggeman, Glenn Pollefeyt, Melis Arin, Jonas Feys and Isabel Van Driessche SCRiPTS, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281 – S3, 9000 Gent, Belgium. ABSTRACT A water-based BaTiO3 precursor solution, suited for ink-jet printing of hetero-epitaxial BaTiO3 layers on LaAlO3 single-crystal substrates was developed. First, a study on the simultaneous stabilization of Ba2+ and Ti4+ ions in a neutral, aqueous environment was performed. Thermal analysis of the precursor was used to select appropriate temperature programs and the rheology of the solutions is studied to optimize dipcoating and later ink-jet printing parameters. On both substrates, it was possible to obtain epitaxial layers of about 200 nm thickness after sintering at temperatures above 1000 °C. Currently, we are adapting the thermal program and heating atmosphere in order to reduce the sintering temperatures, decrease the surface roughness and increase density. INTRODUCTION Ferro-electric materials find application in capacitors, piezo-electric actuators, DRAM memory devices, electro-optic components etc. Probably the most innovative application for ferroelectrics is their incorporation in photonics. Yet, integration of metaloxides on Si-based components remains an area of research with much room for improvement in terms of materials processing. Theoretically, BaTiO3, having a very high opto-electronic coefficient, remains one of the most promising materials for use as opto-electronic modulator. Yet, there are some important restrictions hindering its’ practical use. To reduce optical losses and ensure high modulating efficiency, we need to integrate quasi single crystalline BaTiO3 (BTO) with perfect epitaxy and extremely smooth surfaces with Si technology. Currently, these requirements can only be fulfilled by other materials with an intrinsic lower opto-electric coefficient such as LiNbO3 and PbZr1-xTixO3 or by using PLD, CVD or MBE to deposit BaTiO3 [1,2]. Chemical solution deposition (CSD) combined with ink-jet printing provides a very valuable alternative, holding the promise of cheap, fast and scalable processing. Patterns can be obtained directly without etching and the approach can be compatible with a whole series of materials and even graded materials [3-7]. Reports on CSD of epitaxial BaTiO3 are scarce [8-11]. Therefore, this work started with the formulation of an environmentally-friendly, aqueous Ba-Ti precursor solution suited for dipcoating on LaAlO3 (LAO) single crystals. Thermal treatment at temperatures above 1000 °C results in epitaxial BTO layers. The precursor rheology and wetting behaviour was studied to confirm compatibility with the inkjet printing devices and printing tests were performed. Similar precursor solutions as the ones used here were used before to produce a complete multiferroic structure of BTO/LSMO on STO by ink plotting [4]. In the future, further optimization of the thermal treatment procedure and wettability of the precurs
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