Polarization Switching Kinetics in Ferroelectric/Dielectric Bi-Layer Structures - FeDiBiS

• Applicants: Privatdozent Dr. Martin Schmidbauer; Dr.-Ing. Stefan Slesazeck
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449644906

In ferroelectric layers, the switching of electrical polarization is a fundamental phenomenon that enables a wide range of technological applications. However, the microscopic switching mechanism depends decisively on the ferroelectric properties and the electrostatic boundary conditions. For example, the addition of a nanometer-thin dielectric layer between the ferroelectrics and the electrodes can lead to a ferroelectric tunnel junction (FTJ), which is promising for neuromorphic computing applications. On the other hand, for thicker dielectric layers, the exploitation of the negative capacitance effect (NC) is attractive for extremely low power devices, as this could overcome the fundamental limits of power dissipation in transistors. However, the underlying switching processes in ferroelectric/dielectric bi-layer structures are not yet fully understood. In the present project we want to uncover and understand the fundamental relationship between structural and electrical changes during switching of ferroelectric layers embedded in ferroelectric/dielectric multilayer capacitor structures. We will focus on strained, lead-free potassium-sodium-niobate (KxNa1 xNbO3) films as ferroelectric material grown by metal organic vapor phase epitaxy (MOVPE) close to thermodynamic equilibrium and at comparatively high oxygen partial pressures. This leads to extremely perfect, quasi-defect-free, thin films with almost exact stoichiometric composition, smooth surfaces/interfaces and very regular ferroelectric domain patterns. This perfection enables us to investigate the intrinsic layer properties more precisely. The epitaxy is performed on different rare earth scandate substrates, which allows a specific variation of the epitaxial strain. On the one hand, this leads to the deposition of ferroelectric phases with monoclinic symmetry, which is of high technological interest. On the other hand, extrinsic effects, such as the formation of different domain wall types, can be investigated. The scientific challenge is the deposition of nearly perfect monocrystalline layers with adjustable symmetry and domain arrangement. The kinetics of polarization switching will be further investigated by correlated operando studies using nanoprobe X ray diffraction, which will be performed simultaneously with electrical measurements. In particular, they will help to reveal the correlation of electrical properties, switching behavior and local structural properties of domains and domain walls in a complex material system. The project ideally combines the scientific and technological expertise of both project partners IKZ and NaMLab.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Jutta Schwarzkopf