Domain Wall Movement in Undoped Ferroelectric HfO2: A Rayleigh Analysis

The discovery of ferroelectricity in doped HfO₂ in 2011 gave rise to quite a stir in the scientific world that persists up to this day. The complementary metal oxide semiconductor compatibility, as well as good scalability, enables versatile applications ranging from ferroelectric field effect transistors to ferroelectric tunnel junctions and neuromorphic devices. Stabilizing the metastable polar orthorhombic phase with space group Pca2₁-phase, which is responsible for the ferroelectricity in HfO₂, is still challenging. We demonstrate for the first time a sputter deposition of undoped ferroelectric HfO₂ on superconducting NbN electrodes, with a remanent polarization of 6.4 μC/cm². Grazing incident X-ray diffraction on the layer structure, dynamic hysteresis measurements, and electron energy loss spectroscopy on fabricated devices indicate a HfO₂ layer with low oxygen deficiency. Furthermore, no evidence of interdiffusion of oxygen or nitrogen at the interfaces is found. A sudden “wake-up” for the transition from the dielectric state to the ferroelectric state as well as no classical fatigue effect for the degradation of the ferroelectric performance are observed. These analyses are extended by an investigation of Rayleigh behavior using impedance spectroscopy. In that way, the domain wall flexibility is quantified and classified within different regimes of the various domain wall motions.