# ALD-Derived WO3–x Leads to Nearly Wake-Up-Free Ferroelectric Hf0.5Zr0.5O2 at Elevated Temperatures

## TL;DR

A new method using tungsten oxide helps make a memory material stable at high temperatures, improving its performance in advanced computing.

## Contribution

Introducing a WO3–x layer to suppress the wake-up effect in Hf0.5Zr0.5O2 at elevated temperatures.

## Key findings

- Adding WO3–x reduces wake-up cycles from 105 to 10 at 125°C.
- DFT calculations show WO3 stabilizes the ferroelectric phase at high temperatures.

## Abstract

Breaking the memory wall in advanced computing architectures
will
require complex 3D integration of emerging memory materials such as
ferroelectricseither within the back-end-of-line (BEOL) of
CMOS front-end processes or through advanced 3D packaging technologies.
Achieving this integration demands that memory materials exhibit high
thermal resilience, with the capability to operate reliably at elevated
temperatures, such as 125°C, due to the substantial heat generated
by front-end transistors. However, silicon-compatible HfO2-based ferroelectrics tend to exhibit antiferroelectric-like behavior
in this temperature range, accompanied by a more pronounced wake-up
effect, posing significant challenges to their thermal reliability.
Here, we report that by introducing a thin tungsten oxide (WO3–x
) layerknown as an oxygen
reservoirand carefully tuning its oxygen content, ultrathin
Hf0.5Zr0.5O2 (5 nm) films can be
made robust against the ferroelectric-to-antiferroelectric transition
at elevated temperatures. This approach not only minimizes polarization
loss in the pristine state but also effectively suppresses the wake-up
effect, reducing the required wake-up cycles from 105 to
only 10 at 125°C, a qualifying temperature for back-end memory
integrated with front-end logic, as defined by the JEDEC standard.
First-principles density functional theory (DFT) calculations reveal
that WO3 enhances the stability of the ferroelectric orthorhombic
phase (o-phase) at elevated temperatures by increasing the tetragonal-to-orthorhombic
phase energy gap and promoting favorable phonon mode evolution, thereby
supporting o-phase formation under both thermodynamic and kinetic
constraints.