Kinetic pathway of the ferroelectric phase formation in doped HfO₂ films

The dopant-induced ferroelectric HfO₂ formation has been systematically investigated by using cation (Sc, Y, Nb, Al, Si, Ge, and Zr) and anion (N) dopants. Both differences and similarities are discussed among various dopants by focusing on two major factors, the oxygen vacancy (Vo) and the dopant ionic size. First, the doping concentration dependence of the remanent polarization in 27 (±2) nm HfO₂ films is quantitatively estimated. Then, by comparing the polarization result with the structural transformation in doped HfO₂, the pathway of the dopant-induced HfO₂ phase transition is discussed among monoclinic, ferroelectric orthorhombic, tetragonal, and cubic phases. Finally, it is addressed that a dopant species independent phase transition route may exist in HfO₂ owing to the same kinetic transition process, in which the ferroelectric phase seems to be at an intermediate state between tetragonal and monoclinic phases.