Long-term stability and oxidation of ferroelectric AlScN devices: An operando HAXPES study

TL;DR

This study investigates the long-term oxidation stability of ferroelectric AlScN thin films using operando HAXPES, revealing oxidation mechanisms and the influence of Sc doping on material degradation.

Contribution

It provides a detailed oxidation model for AlScN films and applies operando HAXPES to analyze stability in device-like structures, advancing understanding of ferroelectric material durability.

Findings

Oxygen replaces nitrogen in AlScN, especially favoring Sc oxidation.

Oxygen presence increases with air exposure time.

Operando HAXPES reveals oxidation behavior in device stacks.

Abstract

Aluminum scandium nitride (Al$_{1-x}$Sc$_x$N) is a promising material for ferroelectric devices due to its large remanent polarization, scalability, and compatibility with semiconductor technology. By doping AlN with Sc, the bonds in the polar AlN structure are weakened, which enables ferroelectric switching below the dielectric breakdown field. However, one disadvantage of Sc doping is that it increases the material's tendency towards oxidation. In the present study, the oxidation process of tungsten-capped and uncapped Al$_{0.83}$Sc$_{0.17}$N thin films is investigated by hard X-ray photoelectron spectroscopy (HAXPES). The samples had been exposed to air for either two weeks or 6 months. HAXPES spectra indicate the replacement of nitrogen by oxygen, and the tendency of oxygen to favor oxidation with Sc rather than Al. The appearance of an N$_2$ spectral feature thus can be directly related to the oxidation process. We present an oxidation model that mimics these spectroscopic results of the element-specific oxidation processes within Al$_{1-x}$Sc$_x$N. Finally, in operando HAXPES data of uncapped and capped AlScN-capacitor stacks are interpreted using the proposed model.