Thermal Stability of Hafnium Zirconium Oxide on Transition Metal Dichalcogenides

TL;DR

This study investigates the thermal stability of hafnium zirconium oxide interfaces with transition metal dichalcogenides, revealing stability depends on surface functionalization and annealing conditions, with implications for ferroelectric device fabrication.

Contribution

It provides new insights into how functionalization and annealing affect the stability and crystallization of HZO on TMDCs, advancing understanding for ferroelectric device integration.

Findings

HZO on non-functionalized MoS2 is unstable upon annealing.

HZO on functionalized MoS2 remains stable between 400-800°C.

HZO/WSe2 interface stable until 700°C, then Se evolves.

Abstract

Ferroelectric oxides interfaced with transition metal dichalcogenides (TMDCs) offer a promising route toward ferroelectric-based devices due to lack of dangling bonds on the TMDC surface leading to a high-quality and abrupt ferroelectric/TMDC interface. In this work, the thermal stability of this interface is explored by first depositing hafnium zirconium oxide (HZO) directly on geological MoS2 and as-grown WSe2, followed by sequential annealing in ultra-high vacuum (UHV) over a range of temperatures (400-800 {\deg}C), and examining the interface through X-ray photoelectron spectroscopy (XPS). We show that the nucleation and stability of HZO grown through atomic layer deposition (ALD) varied depending on functionalization of the TMDC, and the deposition conditions can cause tungsten oxidation in WSe2. It was observed that HZO deposited on non-functionalized MoS2 was unstable and volatile upon annealing, while HZO on functionalized MoS2 was stable in the 400-800 {\deg}C range. The HZO/WSe2 interface was stable until 700 {\deg}C, after which Se began to evolve from the WSe2. In addition, there is evidence of oxygen vacancies in the HZO film being passivated at high temperatures. Lastly, X-ray diffraction (XRD) was used to confirm crystallization of the HZO within the temperature range studied.