Book/Dissertation / PhD Thesis

FZJ-2018-02634

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Tailoring the Electronic Properties of Epitaxial Oxide Films via Strain for SAW and Neuromorphic Applications

Dai, Y. (Corresponding author)FZJ*

2018
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-319-8

Please use a persistent id in citations: http://hdl.handle.net/2128/18465  urn:nbn:de:0001-2018050917

Abstract: In this work the impact of biaxial strain on the electronic properties of epitaxial grown oxide thin films is analyzed and discussed using two perovskite systems, (Ba$_{x}$Sr$_{1-x}$)TiO$_{3}$ and (K$_{x}$Na$_{1-x}$)NbO$_{3}$. We show that the phase transition temperature of the oxide films can be tuned via in-plane biaxial strain. Compressive strain leads to a reduction of the transition temperature, tensile strain increases the transition temperature. As a result, the electronic properties (i.e. dielectric constant, piezoelectric effect, and even conductivity) are modified. Possible applications of this “engineering” of the electronic properties of oxide films are demonstrated. Strain of ±1.7% in perovskites thin films is generated by the mismatch of the lattice parameters of film and substrate. (Ba$_{x}$Sr$_{1-x}$)TiO$_{3}$ (x = 0, 0.125, 0.37, 1) and K$_{0.7}$Na$_{0.3}$NbO$_{3}$ films with a thickness ranging between 5 nm and 200 nm are deposited on various scandites ((110) oriented DyScO$_{3}$, TbScO$_{3}$, GdScO$_{3}$, and SmScO$_{3}$) using either pulse laser deposition or metal-organic chemical vapor deposition. For the characterization metallic electrodes (Pt or Ti/Pt) are prepared on the oxide film using e-beam lithography and lift-off technology. The structural properties of the biaxial strained thin films are carefully examined via X-ray diffraction, Rutherford backscattering spectrometry, time-of-flight secondary ion mass spectroscopy, and scanning electron microscopy. Cryoelectronic measurements are used to analyze the electronic properties in a temperature range of 5 K to 500 K. The major results are: (i) In oxide ferroelectric thin films, both compressive and tensile biaxial strain result in a material and strain dependent shift of the phase transition temperature of up to several 100 K. For instance, 1.2 % tensile strain shifts the transition temperature by ~300 K in SrTiO$_{3}$ while -0.6 % compressive stress leads to a reduction of the phase transition temperature by ~300 K in K$_{0.7}$Na$_{0.3}$NbO$_{3}$. (ii) The dielectric constant can be modified at a desired temperature (typically room temperature) via the shift of the phase transition towards this temperature. For instance in case of SrTiO$_{3}$ the permittivity is enhanced from ~300 (unstrained bulk SrTiO$_{3}$) to ~8000 by moving the phase transition temperature to room temperature. (iii) The piezoelectric properties of the oxide films are also tailored via strain. As a result surface acoustic waves can be generated in strained thin (e.g. 27 nm) K$_{0.7}$Na$_{0.3}$NbO$_{3}$ films. The strength of the surface acoustic wave signal correlates to the phase transition of the films and might be used for extremely sensitive sensor systems. (iv) Finally, the conductivity of strained SrTiO$_{3}$ films is enhanced due to the increased mobility of electrons and oxygen vacancies. Using an adequate electrode design which affects the electric field and thus temperature distribution in the film, memristor behavior and even a plasiticity of the resistive behavior can be obtained. The latter can be used for applications ranging from the simulation of a biological synapsis to neuromorphic engineering.

Note: Universität Köln, Diss., 2017

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Contributing Institute(s):

1. Bioelektronik (ICS-8)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

Appears in the scientific report 2018

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Database coverage:
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