Fluid Imprint and Inertial Switching in Ferroelectric La:HfO₂ Capacitors

Abstract

Ferroelectric (FE) HfO 2 -based thin films, which are considered as one of the most promising material systems for memory device applications, exhibit an adverse tendency for strong imprint. Manifestation of imprint is a shift of the polarization−voltage (P−V) loops along the voltage axis due to the development of an internal electric bias, which can lead to the failure of the writing and retention functions. Here, to gain insight into the mechanism of the imprint effect in La-doped HfO 2 (La:HfO 2 ) capacitors, we combine the pulse switching technique with high-resolution domain imaging by means of piezoresponse force microscopy. This approach allows us to establish a correlation between the macroscopic switching characteristics and domain time−voltage-dependent behavior. It has been shown that the La:HfO 2 capacitors exhibit a much more pronounced imprint compared to Pb(Zr,Ti)O 3 -based FE capacitors. Also, in addition to conventional imprint, which evolves with time in the poled capacitors, an easily changeable imprint, termed as "fluid imprint", with a strong dependence on the switching prehistory and measurement conditions, has been observed. Visualization of the domain structure reveals a specific signature of fluid imprintcontinuous switching of polarization in the same direction as the previously applied field that continues a long time after the field was turned off. This effect, termed as "inertial switching", is attributed to charge injection and subsequent trapping at defect sites at the film−electrode interface.

High polarization, endurance and retention in sub-5 nm Hf0.5Zr0.5O2 films

“…Note that the polarizations measured by PUND can be underestimated due to saturated loops not being measured because of the observed increase of coercive field when using PUND technique ( Fig. S6, ESI †) due to the fluid imprint field, 30 probably caused by charge injection. On the other hand, Fig.…”

Beyond Expectation: Advanced Materials Design, Synthesis, and Processing to Enable Novel Ferroelectric Properties and Applications

“…In parallel, considerable research and development effort has focused on understanding and utilizing the ferroelectric order reported in binary oxides such as doped HfO2, which are compatible with existing CMOS processes [94,95]. Hafnia-based ferroelectrics (and other similar binary systems) exhibit robust polarization stability (albeit with large coercive fields) and the potential for multi-state function [96].…”

Time‐Dependent Imprint in Hf0.5Zr0.5O2 Ferroelectric Thin Films

“…[ 5–11 ] However, there are still reliability issues for practical use, including insufficient switching endurance [ 12,13 ] and fatigue properties. [ 14–16 ] In the case of HfO 2 ‐based ferroelectric thin films, their large time‐dependent imprint [ 17–22 ] and wake‐up effect [ 16,17,23–27 ] —which distinguish them from conventional ferroelectric materials—play important roles in understanding these critical issues.…”

“…Recently, it was reported that the imprint effect in a HfO 2 ‐based ferroelectric capacitor occurs during polarization retention, even at room temperature. [ 17–19,21,22 ] The time‐dependent imprint also occurs in ferroelectric‐gate field effect transistors. [ 20 ] Zacharaki et al.…”

“…[ 21 ] In addition to charge injection, the imprint is caused by the redistribution of a mobile charge through the film. [ 18 ] It is considered that the depolarization field originates from an imperfect screening of the ferroelectric polarization, and the subsequent large electric field generated at the interfacial layer between the electrode and ferroelectric layer work as the driving forces redistributing the mobile charge and charge injection, respectively. [ 28,29 ] However, the origin of this phenomenon is controversial because there are few reports on the time‐dependent imprint in HfO 2 ‐based thin films.…”