Engineering ferroelectric switching dynamics

Abstract

The word dynamics roots from the Greek word δύναμις (dynamis) which means "power" 1. Consequently, this branch of science deals with the effects of forces on motion such as aerodynamics which deals with the motion of gas, and thermodynamics which describes the relationship between thermal and mechanical energy etc. In ferroelectrics, switching dynamics deals with the study of domain wall motion under an applied electric field 2-4. But in order to understand a physical system fully it is not only important to understand the dynamical behaviour of the system, but also the degrees of freedom of the system which determine the number of independent ways in which a system can move. For an ensemble the degrees of freedom are determined by its stochastic variables. Apropos, within systems at real device scale (present day ferroelectric based devices are 130 nm in lateral dimension), it is pertinent to treat them as an ensemble rather than as a single entity. Ferroelectrics, because of their non-volatility and bi-stability and, most importantly, their switchability between the two states using an applied electric field, have found applications such as non-volatile random access memory (NVRAM) devices 3, 5. Ferroelectric RAM (FeRAM) devices were first proposed by Dudley Allen Buck in his master's thesis in 1952 at MIT 6. It was shown that ferroelectrics can not only be used for storing memory but also for logic operations. Field effect transistors based on ferroelectrics (FeFET), as well as ferroelectric tunnel junctions (FTJ) based devices in recent years have also been realized for the realization of non-destructive read out memories 7-12. Even though the crystal structure and internal chemical environment renders the bi-stability in ferroelectrics 13, 14 , the actual switching in ferroelectrics takes place through nucleation and growth mechanisms 3, 4, 15, 16 of ferroelectric domains. In FeRAM and FeFET, the device performance characterised by the switching speed, remnant polarization, coercive voltages, leakage current, reliability and stability, is of paramount importance. For the above devices, since domain wall switching dynamics determines the switching speed, coercive voltages, operating voltages and energy consumption etc., it gave rise to a plethora of research into the domain wall switching dynamics and statistics treating the ferroelectrics as ideal insulators. On the other hand, ferroelectrics were also treated as semiconductors to explain