Stability of 180° domain in ferroelectric thin films

Abstract

Ferroelectric random access memory (FRAM) has attracted much attention in the last two decades due to its ideal properties such as nonvolatility, high speed, and low power consumption. There is a strong incentive to develop high-density FRAMs, in which the switched domains, developed under low voltage or short pulses, are necessarily very small, and are therefore usually unstable and suffer from significant backswitching upon removal of the external voltage. In this investigation, a general form of energy expression for a ferroelectric material containing 180° domains is derived, from which evolution equations of the domain are established. By choosing the change in internal energy as the Liapunov function, a general formulation is developed to determine the stability conditions of the switched domain. This is applied to the case of an ellipsoidal 180° domain and yields a criterion for the stability of switched domains. We note that our approach is generally applicable to many other fields, including phase transformation, nucleation, expansion of dislocation loops in thin films, etc.