Tip-Based Proximity Ferroelectric Switching and Piezoelectric Response in Wurtzite Multilayers

TL;DR

This paper investigates how proximity ferroelectricity enables switchable polarization in multilayer wurtzite structures using a tip-based approach, revealing regimes of collective switching and suppression influenced by layer sequence and electric fields.

Contribution

It develops a Landau-Ginzburg-Devonshire model and finite element simulations to analyze local piezoelectric response and polarization reversal in multilayers, introducing the concept of proximity ferroelectricity in tip-induced switching.

Findings

Proximity ferroelectricity can induce switchable polarization in non-ferroelectric layers.

Layer sequence significantly affects hysteresis and response asymmetry.

Two main regimes: collective switching and suppression, governed by depolarizing fields.

Abstract

Proximity ferroelectricity is a novel paradigm for inducing ferroelectricity, where a non-ferroelectric polar material, which is unswitchable with an external field below the dielectric breakdown field, becomes a practically switchable ferroelectric in direct contact with a thin switchable ferroelectric layer. Here, we develop a Landau-Ginzburg-Devonshire approach to study the proximity effect of local piezoelectric response and polarization reversal in wurtzite ferroelectric multilayers under a sharp electrically biased tip. Using finite element modeling we analyze the probe-induced nucleation of nanodomains, the features of local polarization hysteresis loops and coercive fields in the Al1-xScxN/AlN bilayers and three-layers. Similar to the wurtzite multilayers sandwiched between two parallel electrodes, the regimes of "proximity switching" (where the multilayers collectively switch) and the regime of "proximity suppression" (where they collectively do not switch) are the only two possible regimes in the probe-electrode geometry. However, the parameters and asymmetry of the local piezo-response and polarization hysteresis loops depend significantly on the sequence of the layers with respect to the probe. The physical mechanism of the proximity ferroelectricity in the local probe geometry is a depolarizing electric field determined by the polarization of the layers and their relative thickness. The field, whose direction is opposite to the polarization vector in the layer(s) with the larger spontaneous polarization (such as AlN), renormalizes the double-well ferroelectric potential to lower the steepness of the switching barrier in the "otherwise unswitchable" polar layers. Tip-based control of domains in otherwise non-ferroelectric layers using proximity ferroelectricity can provide nanoscale control of domain reversal in memory, actuation, sensing and optical applications.