Mesoscale Polarization Dynamics and Nonlinear Permittivity Characterization

The polarization dynamics of ferroelectric materials are important for many applications including filters, phase shifters, non-volatile memory, and new transistor designs that exploit ferroelectric switching to increase power efficiency. In recent years, the ferroelectrics community has made great progress in relating the nanoscale structure of materials to their polarization dynamics. This work has lead to the design of nonlinear dielectric materials with specific electrical properties relevant to applications. These new materials include low-loss tunable superlattices, materials with resonant domain wall hopping, and PbTiO3/SrTiO3 superlattices with tunable polar order. The dynamics of these materials under a microwave-frequency electric field are still difficult to study theoretically so experimental characterization of the dynamics is informative. In this talk, we discuss microwave-frequency linear and nonlinear electrical characterization. Broadly speaking, linear permittivity measurements reveal characteristic timescales associated with different dynamical mechanisms, while nonlinear measurements are sensitive to coupling among these mechanisms. Specifically, our talk will focus on our development of a new method to measure nonlinear permittivity, its validation on a Ba0.5Sr0.5TiO3 (BST) thin film, and measurements of superlattices with toroidal polar order.