Working Group Ferroelectric Oxide Layers - Summary

Owing to its excellent ferro- and piezoelectric properties, still nowadays lead-zirconium-titanate (PZT) is used in electronic devices (for instance pressure sensors, ultrasonic devices, non-volatile memory devices). However, lead pose a permanent hazard for our environment and health. A promising lead-free alternative is provided by potassium-sodium-niobate, (K,Na)NbO3, based materials, which exhibit likewise a perovskite structure. On the one hand, control of the structure and the composition of (K,Na)NbO3 is challenging due to the high volatility of the alkaline oxides and several phase transitions. But on the other hand, this offers the opportunity for improved or novel material properties.

At IKZ, (K,Na)NbO3 thin films are successfully deposited by the metal-organic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD) techniques. By the application of a chemical and a physical deposition method, a large range of deposition parameters are available in order to investigate and optimize their influence on film composition, defect formation, interface and functional film properties. For instance, in order to reduce the leakage current in thin films, (K,Na)NbO3 thin films, especially those grown by PLD, are systematically doped by foreign atoms (like Cu, Ba, Mn). By means of a FE Tester, the ferroelectric behavior can be analyzed.

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The inherent coupling between lattice strain and electrical polarization in epitaxial ferroelectric thin films allows the targeted manipulation of the functional film properties. For the so-called “strain engineering” this can be achieved by the adequate choice of film composition and substrate material. For the latter, a unique variety of oxide substrates is provided at IKZ. In this respect, of particular interest is the deposition of strained thin films with induced, monoclinic symmetry, since this is related to very high piezoelectric properties. Relevant film-substrate combinations are predicted by means of a strain-phase diagram, which is calculated within the framework of the Landau-Ginzburg-Devonshire theory.

An especially intriguing aspect of ferroelectric films is the formation of domains. Size and orientation of the domains are crucially determined by the lattice mismatch between film and substrate material as well as by the film thickness and the anisotropy of the lattice strain. These properties and the nature of the intermediate domain walls have a large influence on the macroscopic, ferro- and piezoelectric characteristics of the films. Consequently, understanding and control of the domains are essential for further applications in electronic devices, for example in successfully realized surface acoustic wave (SAW) devices. For a detailed characterization, on the one hand the piezoresponse force mode (PFM) of the well-known atomic force microscope is applied. The result is presented by a space-resolved mapping of the domain walls und by the relative orientation of the electrical polarization in adjacent domains. For the determination of the macroscopic piezoelectric coefficients, a double interferometer is used.

Year to date within the scope of a “Senatsausschuss Wettbewerb” (SAW) project of the Leibniz Association, additionally, thin niobium oxide and strontium-titanate (SrTiO3) thin films are investigated with regard to their application in adaptive electronics. The project is aimed at characterizing and controlling of incorporated defects.

In addition to the intentionally incorporated anisotropic lattice strain, an adjusted off-stoichiometry provides the possibility to influence the electrical properties of perovskite materials. Besides the above mentioned alkaline-niobates, fundamental research is performed in this regard for SrTiO3. In particular, the use of two fundamentally different growth methods provides a broad range of deposition parameters.

key publications

B. Cai, J. Schwarzkopf, E. Hollmann, D. Braun, M. Schmidbauer, T. Grellmann, R. Wördenweber
Electronic Characterization of Polar Nanoregions in Relaxor-Type Ferroelectric NaNbO3 Films.
PHYS REV B 93 (2016) 224107
doi: 10.1103/PhysRevB.93.224107

 J. Schwarzkopf,  M. Schmidbauer, A. Duk, R. Wördenweber
Ferroelectric Domain Structure of Anisotropically Strained NaNbO3 Epitaxial Thin Films.
J APPL PHYS 115 (2014) 204105
doi:10.1063/1.4876906

J. Sellmann, J. Schwarzkopf, A. Kwasniewski, M. Schmidbauer, D. Braun, A. Duk
Strained Ferroelectric NaNbO3 Thin Films: Impact of Pulsed Laser Deposition Growth Conditions on Structural Properties.
THIN SOLID FILMS 570 Part A (2014),  107 - 113
doi:10.1016/j.tsf.2014.09.016 

A. Duk, M. Schmidbauer and J. Schwarzkopf
Anisotropic One-Dimensional Domain Pattern in NaNbO3 Epitaxial Thin Films Grown on (110) TbScO3.
APPL PHYS LETT 102 (2013) 091903
doi:10.1063/1.4794405

Working Group Ferroelectric Oxide Layers - Methods

Deposition Methods:
  • Metal-organic chemical vapor deposition (MOCVD)
  • Pulsed laser deposition (PLD)
Characterization Methods:
(in collaboration with working group Physical Characterization)
  • AFM, PFM, CAFM
  • Spectroscopic ellipsometry
  • FE tester

Working Group Ferroelectric Oxide Layers - Publications

 J. Schwarzkopf, D. Braun, M. Hanke, R. Uecker, M. Schmidbauer
Strain Engineering of Ferrolectric Domains in KxNa1-xNbO3 Epitaxial Layers
FRONTIERS IN MATERIALS 4 (2017) Art. 26
doi: 10.3389/fmats.2017.00026

M. Sander, M. Herzog, J. E. Pudell, M. Bargheer, N. Weinkauf, M. Pedersen, G. Newby, J. Sellmann, J. Schwarzkopf, V. Besse, V. V. Temnov, P. Gaal
Spatiotemporal Coherent Control of Thermal Excitations in Solids
PHYS REV LETT 119 (2017) 075901
doi.10.1103/PhysRevLett.119.075901

D. Braun, M. Schmidbauer, M. Hanke, A. Kwasniewski, J. Schwarzkopf
Tunable ferroelectric domain wall alignment in strained monoclinic KxNa1-xNbO3 epitaxial films
APPL PHYS LETT 110 (2017)  232903
doi.org/10.1063/1.4985191

M. Schmidbauer, D. Braun, T. Markurt, M. Hanke, J. Schwarzkopf
Strain Engineering of Monoclinic Domains in KxNa1-xNbO3 Epitaxial Layers: A Pathway to Enhanced Piezoelectric Properties
NANOTECHNOLOGY 28 (2017)  24LT02
doi.org/10.1088/1361-6528/aa715a

M. Schmidbauer, M. Hanke, A. Kwasniewski, D. Braun, L. von Helden, C. Feldt, S. J. Leake, J. Schwarzkopf
Scanning X-Ray Nanodiffraction from Ferroelectric Domains in Strained K0.75Na0.25NbO3 Epitaxial Films Grown on (110) TbScO3
J APPL CRYST 50 (2017)  519 - 525
doi.org/10.1107/S1600576717000905

M. Sander, A. Koc, C. T. Kwamen, H. Michaels, A. v. Reppert, J. Pudell, F. Zamponi, M. Bargheer, J. Sellmann, J. Schwarzkopf, P. Gaal
Characterization of an Ultrafast Bragg-Switch for Shortening Hard X-Ray Pulses
J APPL PHYS 120 (2016) 193101  
doi: org/10.1063/1.4967835

B. Cai, J. Schwarzkopf, E. Hollmann, D. Braun, M. Schmidbauer, T. Grellmann,R. Wördenweber
Electronic Characterization of Polar Nanoregions in Relaxor-Type Ferroelectric NaNbO3 Films.
PHYS REV B 93 (2016) 224107
doi: 10.1103/PhysRevB.93.224107

J. Schwarzkopf, D. Braun, M. Hanke, A. Kwasniewski, J. Sellmann, M. Schmidbauer 
Monoclinic MA Domains in Anisotropically Strained Ferroelectric K0.75Na0.25NbO3 Films on (110) TbScO3 Grown by MOCVD.
J APPL CRYSTALLOGR 49 (2016) 375 - 384
doi:10.1107/S1600576716000182

S. Bin Anooz, P. Petrik, M. Schmidbauer, T. Remmele, J. Schwarzkopf
Refractive Index and Interband Transitions in Strain Modified NaNbO3 Thin Films Grown by MOCVD.
J PHYS D: APPL PHYS 48 (2015) 385303
doi:10.1088/0022-3727/48/38/385303

M. Schmidbauer, J. Sellmann, D. Braun, A. Kwasniewski, A. Duk, J. Schwarzkopf
Ferroelectric Domain Structure of NaNbO3 Epitaxial Thin Films Grown on (110) DyScO3 Substrates.
PHYS STATUS SOLIDI-RAP RES LETT 8 (2014) 522 - 526
doi:10.1002/pssr.201409012

B. Cai, J. Schwarzkopf, E. Hollmann, M. Schmidbauer, M.O. Abdel-Hamed, R. Wördenweber
Anisotropic Ferroelectric Properties of Anisotropically Strained Epitaxial NaNbO3 Films.
APPL PHYS 115 (2014) 224103 
doi:10.1063/1.4882296

J. Schwarzkopf,  M. Schmidbauer, A. Duk, R. Wördenweber
Ferroelectric Domain Structure of Anisotropically Strained NaNbO3 Epitaxial Thin Films.
J APPL PHYS 115 (2014) 204105 
doi:10.1063/1.4876906

J. Sellmann, J. Schwarzkopf, A. Kwasniewski, M. Schmidbauer, D. Braun, A. Duk
Strained Ferroelectric NaNbO3 Thin Films: Impact of Pulsed Laser Deposition Growth Conditions on Structural Properties.
THIN SOLID FILMS 570 Part A (2014),  107 - 113
doi:10.1016/j.tsf.2014.09.016

D. Braun, V. Scherer, C. Janowitz, Z. Galazka, R. Fornari, R. Manzke
In-gap States of In2O3 Single Crystals Investigated by Scanning Tunneling Spectroscopy.
PHYS STATUS SOLIDI A 211 (2014) 59 - 65
doi:10.1002/pssa.201330089

 

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