Ferroelectric zirconium oxide for piezo- and pyroelectric devices (Zeppelin)

• Applicants: Dr.-Ing. Ulrich Böttger; Professor Dr. Alfred Kersch; Professor Dr.-Ing. Thomas Mikolajick
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Synthesis and Properties of Functional Materials
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433647091

The new ferroelectric material system based on hafnium oxide (HfO2) was discovered in 2007 which is characterized by high remanent polarization and low dielectric constant, and is also lead-free and silicon compatible. However, so far these advantageous properties have mostly been realized only in thin layers of HfO2 around 10 nm. The 2018 completed DFG project INFEROX investigated the production of thin, doped HfO2 films for a variety of dopants and for hafnium-zirconia, characterized the material properties, and calculated the free energies with density functional theory to understand the relationship between simulations and experimental observations. Overall, the project was aimed at researching the fundamentals of materials for novel electronic devices. The piezoelectric and pyroelectric properties of these materials have been found to be promising, but were not systematically studied. This proposal suggests to extend the investigation of HfO2-based layers to ZrO2-based doped layers and to produce thicker layers on the order of 1 μm. CSD, ALD and PVD, both from ceramic and metallic targets, are chosen as the deposition method to study the impact of defects. The focus is on the controllable dielectric, piezoelectric and pyroelectric properties, which can be giant in field-driven phase transitions and lead to particularly high performance figures. The project investigates the origins of the dielectric, piezoelectric and pyroelectric properties, optimizes the properties and determines the performance figures of sensor and actuator devices such as varactors, thin-film acoustic resonators (TFBARs), and IR sensors. For the realization of these devices, thick layers on the order of 1 µm are required. In particular, the ferroelectric phase is to be stabilized in these thick layers or supported by field-driven or temperature-driven processes. According to previous understanding, this phase is impacted by interfacial energy, oxygen vacancies, but in part also by metastable phases. In addition, an important goal of the investigation is to better understand and control the kinetics of phase formation and stabilization. On the theoretical side, it is planned to perform a dopant survey, an analysis of the kinetics of the phase transitions, as well as the calculation of piezo and pyroelectric properties in comparison with experimental results.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Uwe Schröder