Dielectric materials

Dielectric materials can be used based on their dielectric ferroelectric, piezoelectric or pyroelectric properties. All four topics were covered in different projects during the last years. The main focus of developing ferroelectric HfO₂-based materials is the detailed understanding of the ferroelectric properties in thin doped HfO₂ layers. A variety of dopant materials were studied in addition to a mixed Hf_1-xZr_xO₂. Deposition techniques included atomic layer deposition and physical vapor deposition. The ferroelectric orthorhombic Pca2₁ phase of HfO₂ is formed when the material is crystallized with a certain dopant or oxygen concentration at the phase boundary between the monoclinic and the tetragonal/cubic phase and is enhanced through mechanical confinement. Scanning transmission electron microscopy and electron diffraction methods confirmed the structure. Continuous research aims to understand the root cause of this previously unknown phase. Here, dopant and oxygen content, which are directly related to stress and strain in the layer, play an essential role in phase stabilization. A linear relation between strain and the coercive field of the phase transition field was found.
Wurtzite-structured ferroelectric nitrides, such as cation-substituted aluminium nitride, are being developed as a second ferroelectric material for use in devices.

Our competences thereby cover the value chain, from material development to device engineering, structural and electrical characterization, device reliability. The target applications are ferroelectric films for ferroelectric and dynamic random access memory cells (FeRAM and DRAM), high dielectric constant materials for power devices, and diffusion barriers.