Investigation of the role of oxygen vacancies on polarization fatigue in ferroelectric thin films

The role of oxygen vacancies in ferroelectric thin films is investigated using numerical simulation. In a perovskite cell, the octahedral cage surrounded by oxygen ions is distorted in the presence of oxygen vacancy. Consequently, it results in an asymmetric double-well potential profile along the c-axis of the cell. Ti4+ prefers to stay at the lower minimum on one side of the cell than the other side having a higher local minimum. This asymmetric potential profile affects the flipping probability of a dipole in Ising Model. On the other hand, oxygen also traps a hole, resulting in a space charge. The accumulation of space charge suppresses the electric field inside the film. Thus the switching of dipoles is impeded. Both the vacancy and space charge distributions are included to simulate fatigue, imprint and thickness effect.