An extensive study of the influence of dopants on the ferroelectric properties of HfO2

The ferroelectric properties of hafnium oxide based thin films prepared by chemical solution deposition (CSD) are investigated. In this extensive study, a wealth of strongly different dopants (size and valence) and dopant concentrations is used to induce ferroelectricity in 42 nm thin films. Using the same precursors and preparation conditions for all dopants a good comparability is given. In particular, the dopant size appears to have a crucial impact on the resulting ferroelectric properties. For smaller dopants only a small ferroelectric response is observed whereas for larger dopants the remanent polarization is increased significantly. The crystal phase for varying dopant concentrations and dopant sizes is investigated by grazing incidence X-ray diffractions (GI-XRD). A dominating cubic phase is found for doping concentrations showing the highest remanent polarization. Similar to first CSD studies on Y: HfO2, this is reflected in a prominent wake-up behavior, which is attributed to a phase transition from cubic to orthorhombic during field cycling.