Extrinsic ferroelectricity originated from oxygen vacancy drift in HfO2-based films

TL;DR

This paper demonstrates that the ferroelectricity observed in HfO2-based films is extrinsic, caused by oxygen vacancy drift under electric pulses, which mimics true ferroelectric behavior and explains various device phenomena.

Contribution

It reveals that oxygen vacancy drift induces extrinsic ferroelectric-like hysteresis in HfO2 films, providing a new understanding of the underlying mechanism.

Findings

Oxygen vacancies oscillate under electric pulses, creating nonlinear currents.

The hysteresis loop mimics intrinsic ferroelectric polarization.

This mechanism explains wake-up, split-up, and endurance effects.

Abstract

It is generally accepted that oxygen vacancies play a central role in the emergence of ferroelectricity for HfO2-based materials, but the underlying mechanism still remains elusive. Herein, starting from the basic characterization circuit, we propose that the observed ferroelectricity is extrinsic. A key finding is that charged oxygen vacancies oscillate within the sample under repeated electric pulses, yielding a nonlinear current which behaves similarly to the polarization current for a normal ferroelectric. This unwanted current signal results in a ferroelectric-like hysteresis loop with both remnant polarization and coercive field in good agreements with experimental values, given a charged oxygen vacancy concentration in the vicinity of 1*10^20/cm^3. Moreover, it is possible to exploit this mechanism to reproduce the effects of wake-up, split-up and limited endurance that are of crucial relevance for the device applications.