On the relationship between field cycling and imprint in ferroelectric Hf0.5Zr0.5O2

Abstract

Manifold research has been done to understand the detailed mechanisms behind the performance instabilities of ferroelectric capacitors based on hafnia. The wake-up together with the imprint might be the most controversially discussed phenomena so far. Among crystallographic phase change contributions and oxygen vacancy diffusion, electron trapping as the origin has been discussed recently. In this publication, we provide evidence that the imprint is indeed caused by electron trapping into deep states at oxygen vacancies. This impedes the ferroelectric switching and causes a shift of the hysteresis. Moreover, we show that the wake-up mechanism can be caused by a local imprint of the domains in the pristine state by the very same root cause. The various domain orientations together with an electron trapping can cause a constriction of the hysteresis and an internal bias field in the pristine state. Additionally, we show that this local imprint can even cause almost anti-ferroelectric like behavior in ferroelectric films.

Bulk Depolarization Fields as a Major Contributor to the Ferroelectric Reliability Performance in Lanthanum Doped Hf0.5Zr0.5O2 Capacitors

“…Again, a higher polar phase portion results in enhanced trapping in the interfacial layers. This trend is stronger at the top electrode interface due to a stronger oxygen scavenging effect resulting in a higher oxygen vacancy concentration at this interface as reported previously …”

“…For the sake of simplicity, multiple domains having different polarization vectors in a single grain are indicated as a single resultant polarization vector. The concentration of oxygen vacancies at the top electrode interface is higher as compared to the one at the bottom electrode interface . This results in higher imprint toward positive bias.…”

“…The endurance characteristics of a ferroelectric capacitor (FeCAP) can be improved by reducing the generation of defects caused by the field cycling stress in the material. Recent literature has revealed oxygen vacancies as the nature of these defects whereby field cycling causes oxygen vacancies to increase in concentration, leading to an increase in leakage current density followed by hard breakdown . Doping the material with La results in a suppression of the generation of oxygen vacancies due to an increase in the oxygen vacancy formation energy, hence the endurance can be improved by La incorporation .…”

“…The imprint can reflect itself as a retention problem of the opposite state of the ferroelectric or in the extreme case it can even cause a write error of the opposite state. It is linked with internal bias creation due to trapping and/or detrapping of charges either at the top or bottom electrode interface . The imprint can also be improved by La incorporation since it reduces the generation of oxygen vacancies acting as trapping sites in the film.…”

Ferroelectric HfO2 for Memory Applications: Impact of Si Doping Technique and Bias Pulse Engineering on Switching Performance

“…Fig.5 summarizes the evolution of ferroelectric parameters along field cycling. All devices are ferroelectric and show an equivalent behavior: remnant polarization increases in all cases (wake-up effect [6]), while a slight decrease of Ec (known as imprint [7]) is observed regardless the doping technique. Both phenomena are usually explained by a redistribution of oxygen vacancies [3], [4], [6] or field-cycling-induced phase transitions [8].…”