Blocking of conducting channels widens window for ferroelectric resistive switching in interface-engineered Hf0.5Zr0.5O2 tunnel devices

TL;DR

This study demonstrates that nanometric capping layers on Hf0.5Zr0.5O2 films improve ferroelectric tunnel device performance by blocking conduction channels at grain boundaries, thus widening the operational window and enhancing device endurance.

Contribution

The paper introduces the use of crystalline SrTiO3 and amorphous AlOx capping layers to enhance ferroelectric tunnel devices by blocking conduction channels at grain boundaries.

Findings

Capping layers conformally coat HZO surface.

Capping layers increase device yield and homogeneity.

Capping layers block ionic-like transport channels.

Abstract

Films of Hf0.5Z0.5O2 (HZO) contain a network of grain boundaries. In (111) HZO epitaxial films on (001) SrTiO3, for instance, twinned orthorhombic (o-HZO) ferroelectric crystallites coexist with grain boundaries between o-HZO and a residual paraelectric monoclinic (m-HZO) phase. These grain boundaries contribute to the resistive switching response in addition to the genuine ferroelectric polarization switching and have detrimental effects on device performance. Here, it is shown that, by using suitable nanometric capping layers deposited on HZO film, a radical improvement of the operation window of the tunnel device can be achieved. Crystalline SrTiO3 and amorphous AlOx are explored as capping layers. It is observed that these layers conformally coat the HZO surface and allow to increase the yield and homogeneity of functioning ferroelectric junctions while strengthening endurance. Data show that the capping layers block ionic-like transport channels across grain boundaries. It is suggested that they act as oxygen suppliers to the oxygen-getters grain boundaries in HZO. In this scenario it could be envisaged that these and other oxides could also be explored and tested for fully compatible CMOS technologies.