What does occur in W/HZO/W capacitors upon ac electrical cycling: a structural phase transition or a structural phase transformation?

With this proposal we aim to understand whether Hf0.5Zr0.5O2 thin films - sandwiched between W electrodes – undergo a structural phase transition (tetragonal to polar orthorhombic) or a structural phase transformation (weakly-developed to fully-developed polar orthorhombic) upon ac electric field cycling. Electric field cycling results indeed in an unconventional piezoelectric behaviour of Hf0.5Zr0.5O2: the dynamic change of its d33 piezoelectric coefficient, from positive to negative. Building on the success of previous investigations at XMaS, the structural evolution of Hf0.5Zr0.5O2 will be measured by wide-angle small angle scattering (WAXS) and X-ray diffraction (XRD) performed on W/Hf0.5Zr0.5O2/W capacitors in the pristine state and after ex-situ electrical cycling. The role of Hf0.5Zr0.5O2 thickness in the structural change will also be explored.