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@PHDTHESIS{Dai:845360,
      author       = {Dai, Yang},
      title        = {{T}ailoring the {E}lectronic {P}roperties of {E}pitaxial
                      {O}xide {F}ilms via {S}train for {SAW} and {N}euromorphic
                      {A}pplications},
      volume       = {169},
      school       = {Universität Köln},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-02634},
      isbn         = {978-3-95806-319-8},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {VI, 133 S.},
      year         = {2018},
      note         = {Universität Köln, Diss., 2017},
      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.},
      cin          = {ICS-8},
      cid          = {I:(DE-Juel1)ICS-8-20110106},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2018050917},
      url          = {https://juser.fz-juelich.de/record/845360},
}