Strain and Interface Design for the Optimization of Ferroelectricity in the Hf1-xZrxO2 Material System (SIDFEM)

• Applicants: Professor Dr. Alfred Kersch; Dr. Uwe Schröder
• Subject Area: Synthesis and Properties of Functional Materials ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560447782

The proposed project uses a capacitor to investigate the effects and mechanisms of mechanical stress or strain effects on ferroelectric phase formation caused by internal or external influences in the Hf1-xZrxO2 material system. Internal influences are deformations due to an oxygen imbalance, dopants of different sizes, or composition gradients, such as nanolaminates. External influences are grain size and thickness, electrode mismatch, and buffer layer. These effects interfere with the chemical effects and should be differentiated. The properties of interest are the structural phase composition, the Curie temperature, and the wake-up behavior. The investigation aims to find the optimal conditions for temperature-stable, ferroelectric Hf1-xZrxO2 films showing low degradation under electric fields. The interest in effects on a larger scale than the unit cell requires the ability to study such systems with high accuracy in simulation. Therefore, the simulation work will focus on developing suitable machine-learned potentials and using these potentials in molecular dynamics simulations of the systems under the influence of voltage and temperature. The work packages ultimately lead to the possibility of specifically optimizing the ferroelectric capacitor. These include the effects of nanolaminates and the dopant and oxygen concentration variation via lattice distortions. In parallel, based on an existing ZrO2 potential model, a generalized potential for Hf1-xZrxO2 is developed in a second version, including oxygen defects. The interface modification is investigated experimentally in two steps: adding interfacial layers to change the lattice mismatch to the ferroelectric and changing the electrode material itself. These investigations are accompanied by simulations using voltage boundary conditions and then with an additional atomistic TiN potential model added to the model for the ferroelectric. The ferroelectric film properties, such as the Curie temperature and the coercive field, are systematically investigated experimentally and in simulation. The model development concludes with constructing an improved density functional beyond PBEsol, which contains barrier heights of the energy landscape in addition to the lattice sizes. The knowledge about the material system gained in the previous investigations is finally used to optimize the relevant overall system, a ferroelectric 3D capacitor.

• DFG Programme: Research Grants
• Co-Investigator: Professor Ney Henrique Moreira, Ph.D.