Effect of a built-in electric field in asymmetric ferroelectric tunnel junctions

TL;DR

This study investigates how a built-in electric field influences phase transitions in asymmetric ferroelectric tunnel junctions, revealing a critical thickness for a unique phase transition and its impact on device operation temperatures.

Contribution

It introduces a multiscale thermodynamic model to analyze the effect of built-in electric fields, identifying a critical thickness and describing a new polar non-ferroelectric phase in asymmetric junctions.

Findings

Existence of a critical thickness for phase transition.

Reduction of transition temperature with decreasing thickness.

Built-in electric field causes phase transition smearing.

Abstract

The contribution of a built-in electric field to ferroelectric phase transition in asymmetric ferroelectric tunnel junctions is studied using a multiscale thermodynamic model. It is demonstrated in details that there exists a critical thickness at which an unusual ferroelectric-\'\' polar non-ferroelectric\rq\rq phase transition occurs in asymmetric ferroelectric tunnel junctions. In the \'\' polar non-ferroelectric\rq\rq phase, there is only one non-switchable polarization which is caused by the competition between the depolarizing field and the built-in field, and closure-like domains are proposed to form to minimize the system energy. The transition temperature is found to decrease monotonically as the ferroelectric barrier thickness is decreased and the reduction becomes more significant for the thinner ferroelectric layers. As a matter of fact, the built-in electric field does not only result in smearing of phase transition but also forces the transition to take place at a reduced temperature. Such findings may impose a fundamental limit on the work temperature and thus should be further taken into account in the future ferroelectric tunnel junction-type or ferroelectric capacitor-type devices.