Disentangling stress and strain effects in ferroelectric HfO₂

resumo

Ferroelectric HfO2 films are usually polycrystalline and contain a mixture of polar and nonpolar phases. This challenges the understanding and control of polar phase stabilization and ferroelectric properties. Several factors, such as dopants, oxygen vacancies, or stress, among others, have been investigated and shown to have a crucial role on optimizing the ferroelectric response. Stress generated during deposition or annealing of thin films is a main factor determining the formed crystal phases and influences the lattice strain of the polar orthorhombic phase. It is difficult to discriminate between stress and strain effects on polycrystalline ferroelectric HfO2 films, and the direct impact of orthorhombic lattice strain on ferroelectric polarization has yet to be determined experimentally. Here, we analyze the crystalline phases and lattice strain of several series of doped HfO2 epitaxial films. We conclude that stress has a critical influence on metastable orthorhombic phase stabilization and ferroelectric polarization. On the contrary, the lattice deformation effects are much smaller than those caused by variations in the orthorhombic phase content. The experimental results are confirmed by density functional theory calculations on HfO2 and Hf0.5Zr0.5O2 ferroelectric phases.

palavras-chave

TOTAL-ENERGY CALCULATIONS; THIN-FILMS; GROWTH

categoria

Physics

autores

Song, TF; Lenzi, V; Silva, JPB; Marques, L; Fina, I; Sánchez, F

Grupos

G6 - Materiais Virtuais e Inteligência Artificial

Projectos

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

agradecimentos

Financial support from the Spanish Ministry of Science and Innovation (No. MCIN/AEI/10.13039/501100011033), through the Severo Ochoa FUNFUTURE (No. CEX2019-000917-S), project Nos. PID2020-112548RB-I00 and PID2019-107727RB-I00, from Generalitat de Catalunya (No. 2021 SGR 00804), and from CSIC through the i-LINK (No. LINKA20338) program is acknowledged. We also acknowledge Project No. TED2021-130453B-C21, funded by No. MCIN/AEI/10.13039/501100011033 and the European Union Next Generation EU/PRTR. T.S. is financially supported by China Scholarship Council (CSC) under Grant No. 201807000104. This work was also supported by (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract No. UIDB/04650/2020; (ii) the exploratory research Project No. 2022.01740.PDTC (DOI:10.54499/2022.01740.PTDC), and (iii) the Project No. M-ERA-NET3/0003/2021-NanOx4EStor under Grant Agreement No. 958174 (DOI:10.54499/M-ERA-NET3/0003/2021). J.P.B.S. also thanks FCT for the contract under the Institutional Call to Scientific Employment Stimulus-2021 Call (No. CEECINST/00018/2021). This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, Nos. UIDB/50011/2020, UIDP/50011/2020, and LA/P/0006/2020, financed by national funds through the FCT/MCTES (PIDDAC).