Evidence of ferroelectric HfO2 phase transformation induced by electric field cycling observed at a macroscopic scale

Abstract

The phase transformation of ferroelectric (FE) HfO2 induced by electric field cycling was observed at a macroscopic scale using the conventional X-ray diffraction (XRD) technique. We confirmed that the increase in the switchable polarization (Psw) is the result of the phase transformation to increase the amount of the higher symmetric phase of HfO2, both observed at a macroscopic scale. During characterization, we found an anomalous shift difference between the in-plane and the out-of-plane interplanar spacing in every HfO2 film we fabricated. We speculate that this phenomenon is unique to HfO2 and may have played an important role in the phase transformation during the waking-up effect of FE-HfO2.