FERROELECTRIC E-FIELD SENSORS, A nonlinear dynamic approach to the development of innovative measurement devices

Abstract

The exploitation of nonlinear dynamics behavior in ferroelectric material toward the realization of innovative transducers for the detection of weak and low frequency electric fields is the focus of this thesis. A nonlinear dynamical system based on ferroelectric capacitors coupled into a unidirectional ring circuit is considered with particular interest for developing novel electric field sensors. The focused approach is based on the exploitation of circuits made up by the ring connection of an odd number of elements containing a ferroelectric capacitor, which under particular conditions exhibits an oscillating regime of behavior. For such a device a weak, external, target electric field interacts with the system thus inducing perturbation of the polarization of the ferroelectric material; this, the target signal can be indirectly detected and quantified via its effect on the system response. The conceived devices exploit the synergetic use of bi-stable ferroelectric materials, micromachining technologies that allow us to address charge density amplification, and implement novel sensing strategies based on coupling non-linear elemental cells. Advanced simulation tools have been used for modeling a system including electronic components and non linear elements as the conceived micro-capacitors. Moreover, Finite Element Analysis (FEM) has allowed us to steer the capacitor electrodes design toward optimal geometries and to improve the knowledge of effects of the external target E-field on the electric potential acting on the ferroelectric material. An experimental characterization of the whole circuit, including three cells coupled in a ring configuration has also been carried out.