Engineered a/c domain patterns in multilayer (110) epitaxial Pb(Zr,Ti)O3 thin films: Impact on domain compliance and piezoelectric properties

M Mtebwa,A Mazzalai,C S Sandu,N Setter,A Crassous

doi:10.1063/1.4948795

Abstract

While there is extensive literature on the influence of both compressive and tensile strain on the domain patterns of (001) tetragonal ferroelectric thin films, little is known regarding domain engineering in (110) films. The primary reason is the absence of suitable substrates that allow the growth of epitaxial films with this orientation. However, recent works emphasized the importance of this orientation with the possibility for e.g. to achieve ultra-high ferroelectric domain density. This work reports the controlled growth of a/c domain patterns in highly tetragonal monocrystalline (110) oriented Pb(Zr0.05, Ti0.95)O3. It is demonstrated that while a/c patterns can easily be realized in the single layer film relaxed under compressive misfit strain, modulation of tensile misfit strain through the use of buffer layers allows for consistent control of domain periodicity, in which case the average domain period was tuned between 630 and 60 nm. The effects of domain density and defects on both switching behavior and piezoelectric properties in single and multilayered structures are also investigated, revealing an optimum composition of the buffer layer for improved domain compliance and piezoelectric properties.

Highlights

Ferroelectric thin films are currently used in applications previously covered by bulk ceramics including dielectric capacitors, sensors and Microelectromechanical systems (MEMs).1,2 Piezoelectric properties of ferroelectric materials such as the most commonly used Pb(Zr,Ti)O3 (PZT) are known to be strongly affected by the domain structures.3,4 the recently discovered and potentially useful functional properties of domain walls such as conductivity5–8 and the photovoltaic effect9,10 have brought more attention on the importance of domain engineering in ferroelectric single crystals and thin films.Theoretical works have established that the ferroelastic domain patterns can be controlled by misfit strain.4,11–14 These predictions have been supported by experimental works mainly conducted on (001) tetragonal films
It is demonstrated that while a/c patterns can be realized in the single layer film relaxed under compressive misfit strain, modulation of tensile misfit strain through the use of buffer layers allows for consistent control of domain periodicity, in which case the average domain period was tuned between 630 and 60 nm
Domain patterns of single and multilayered PZT films were characterized by means of atomic force microscopy (AFM) and piezoresponce force microscopy (PFM)

Summary

INTRODUCTION

Ferroelectric thin films are currently used in applications previously covered by bulk ceramics including dielectric capacitors, sensors and Microelectromechanical systems (MEMs). Piezoelectric properties of ferroelectric materials such as the most commonly used Pb(Zr,Ti)O3 (PZT) are known to be strongly affected by the domain structures. the recently discovered and potentially useful functional properties of domain walls such as conductivity and the photovoltaic effect have brought more attention on the importance of domain engineering in ferroelectric single crystals and thin films. The only reported ferroelastic-ferroelectric domain patterns in single crystalline epitaxial [110] PZT films are those of a/c-type created in relaxed films grown on compressive SrTiO3 (STO) [110] substrates.28,29 This is due to the fact that currently STO[110] is the only readily commercially available perovskite substrate that can support such an orientation and it imposes a compressive misfit strain for all compositions of the most commonly used PZT. Since the Zr content of the film is only 5%, PZT buffer layers with a wide range of Zr content from 6% to 100% can be used to tune the strain level We show this is an efficient way to control the periodicity of ferroelastic domains and create dense a/c domain patterns. The impact of the a/c patterns and the dislocations on both switching behavior and piezoelectric properties is investigated

EXPERIMENTAL

Domain periodicity

SUMMARY AND CONCLUSIONS