摘要
Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.
基金
supported by the Portuguese Foundation for Science and Technology(FCT)in the framework of the Strategic Funding Contract UIDB/04650/2020 and by M-ERA.NET NanOx4EStor Contract no.M-ERA-NET3/0003/2021
the Oblivion Supercomputer at university ofévora,funded by the ENGAGE SKA Research Infrastructure(reference POCI-01-0145-FEDER022217-COMPETE 2020 and FCT)
by the BigData@UE project(reference ALT20-03-0246-FEDER-000033-FEDER and the Alentejo 2020 Regional Operational Program),for providing HPC resources in the framework of the advanced computing project CPCA/A1/415075/2021 awarded by FCT IP
the financial support through the contract FEDR-POC No.332/390008/29.122020-SMIS 109522
the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposals 20202037,20202038 and 20192055
supported by the COST Action CA20116-European Network for Innovative and Advanced Epitaxy(OPERA)
the Royal Academy of Engineering grant,CIET1819_24,for funding and the ERC grant,EU-H2020-ERC-ADG#882929,EROS