FLEET seminar – Stability of Ferroelectric Bubble Domains

Dr Peggy Qi Zhang School of Materials Science and Engineering, The University of New South Wales

Venue: Seminar room G29, New Horizons Bld, Monash University, Clayton

Topological structures in ferroelectric systems have recently drawn immense attention. For example, topological configurations such as skyrmions, flux closures, or nanoscale bubble domains have led to emergent properties including high conductivity, chirality, negative capacitance, and giant electromechanical response. These attributes make polar topologies promising candidates for various low-energy device applications, especially where they can be deterministically controlled.

A new type of nanoscale ferroelectric domain, termed “bubble domains”, has been observed in ultrathin epitaxial PbZr_0.2Ti_0.8O₃/SrTiO₃/PbZr_0.2Ti_0.8O₃ ferroelectric sandwich structures. These bubble domains are laterally confined spheroids of sub-10 nm size with local dipoles opposite to the macroscopic polarization of their surrounding ferroelectric matrix.

This ferroelectric topology is stabilized in thin films by a delicate balance of both mechanical and electrical boundary conditions. Our study has established a systematic understanding of the phase stability of bubble domains. In this seminar, the deterministic control of bubble domain transitions will be demonstrated through designing of the heterostructures configuration, and tuning mechanical/ electric field /temperature conditions.

• Design of the heterostructures configuration: Interface effects have been further exploited to engineer topological defect transitions. Varying the thickness of the ferroelectric and/or dielectric layer in a ferroelectric/dielectric/ferroelectric heterostructure modifies the strain, screening conditions as well as the bare depolarization field and thus plays a significant role in the resulting domains. Under varying thicknesses of these layers, a transition from labyrinthine to bubble domains can be triggered. A similar domain transition occurs upon milling through the ferroelectric layer.
• Mechanical/electric field control: Local mechanical pressure has been exploited to trigger topological defect transitions; the sequence of phase stability goes from labyrinth→bubbles→monodomain under a compressive strain applied along the polarization direction. Under the influence of mechanical pressure, as-grown bubbles can be erased to form a monodomain state, analogous to mechanical writing of polarization. The bubble domains can be created again under pulsed bias at the erased regions. In a slightly different system, mechanical pressure can also trigger the breakdown of as-grown labyrinthine domains into bubbles.
• Temperature/electric field control: Thermal quenching is a route to capture non-equilibrium states. It leads to either configuration depending on the strength of the applied or built-in electric fields. For example, it results into labyrinthine domains (or bubbles) under the absence (or presence) of an electric field.

The results provide a systematic understanding of phase stability and demonstrate controlled manipulation of nanoscale ferroelectric bubble domains that may be exploited for emergent devices.

Dr Zhang will also present this seminar in-person and online at RMIT on Friday 18 November.

Dr Zhang’s research interests include the following:

• Topological phase transitions in ferroic materials including topological defects, domain walls and Skyrmion structures.
• Development of new synthesis techniques for novel ferroelectric oxides with topological properties
• New nanolithography techniques to fabricate ferroelectric domain wall memory devices
• Investigation of nanoscale domains and topological transitions in ultrathin ferroelectric films
• Characterization using scanning probe microscopy (including piezoresponse force microscopy, conductive atomic force microscopy, Kelvin probe force microscopy, electrostatic force microscopy, etc.).