Controlling ferroelectric hysteresis offsets in PbTiO$_{3}$ based superlattices

TL;DR

This paper investigates the origin of built-in bias in PbTiO3-based ferroelectric superlattices, attributing it to interface defects rather than electrodes, and demonstrates how to control it through compositional design.

Contribution

It reveals the defect-driven origin of bias in ferroelectric superlattices and proposes a method to eliminate it by tuning superlattice composition and periodicity.

Findings

Bias is due to interface defects, not electrodes.

First-principles simulations match experimental bias signs.

Zero bias devices are achievable through compositional control.

Abstract

Ferroelectric materials are characterized by degenerate ground states with multiple polarization directions. In a ferroelectric capacitor this should manifest as equally favourable up and down polarization states. However, this ideal behavior is rarely observed in ferroelectric thin films and superlattice devices, which generally exhibit a built-in bias which favors one polarization state over the other. Often this polarization asymmetry can be attributed to the electrodes. In this study we examine bias in PbTiO$_3$-based ferroelectric superlattices that is not due to the electrodes, but rather to the nature of the defects that form at the interfaces during growth. Using a combination of experiments and first-principles simulations, we are able to explain the sign of the observed built-in bias and its evolution with composition. Our insights allow us to design devices with zero built-in bias by controlling the composition and periodicity of the superlattices.