Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

The polarity of aluminum scandium nitride (Al_1-xSc_xN) thin films with different Sc contents deposited on transparent indium tin oxide (ITO) electrode-covered yttria-stabilized zirconia (YSZ) (111) substrates using radio frequency-magnetron sputtering was investigated. The Al_1-xSc_xN (x=0), i.e., pure AlN, film on ITO/YSZ(111) exhibited Al polar. By comparing with the polarity of AlN films deposited on different substrates, including Al₂O₃(0001), Pt/YSZ(111), YSZ(111), Pt(111)/TiO_y/SiO₂/Si(100) and Si(100), it was found that the polarity is affected by the degree of epitaxy. In addition, for the Al_1-xSc_xN films on ITO/YSZ(111), the transition from Al polar to N polar occurred with increasing Sc content, x, whereas the degree of epitaxy almost unchanged. These findings offer important insights into the mechanisms governing the self-poling in Al_1-xSc_xN thin films and pave the way for their use in electro-optic devices.

DOI： 10.35848/1347-4065/adf7b2

Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/adf7b2/pdf

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Epitaxial rhombohedral Pb(Zr_xTi_1−x)O₃ (PZT) thin films with different compositions (x = 0.7–0.55) were fabricated on SrRuO₃/SrTiO₃(111) substrates by chemical solution deposition. The domain volume fraction and lattice constants of the thin films varied systematically with the PZT composition. All films exhibited strong ferroelectricity, with remnant polarization values comparable to theoretically estimated values. The effective electro-optic (EO) coefficient (r _c) was not constant with respect to the applied field but varied with the magnitude of AC field due to dynamic domain motion, reaching its maximum value at a certain electric field. The rate of change in r _c due to the reversible ferroelastic domain motion, as well as the electric field at which r _c peaked, were dependent on the PZT composition. These results indicate that precise control of domain structure and composition is essential to enhance the EO response of thin films.

DOI： 10.35848/1347-4065/adf4f0

Open Access

Web of Science

Scopus

Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/adf4f0/pdf

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

We investigated the dependence of the electro-optic (EO) properties of (111)-epitaxial Hf0.5Zr0.5O2 (HZO) thin films on their thickness in the range of 3–30 nm. HZO films were deposited on (La, Sr)MnO3-bufferred SrTiO3(001) substrates using pulsed laser deposition. Both the ferroelectric orthorhombic and paraelectric monoclinic phases were found to coexist in the 30 nm thick film, and the fraction of the former phase increased with the decrease in thickness down to 5 nm. Although the effective EO coefficient, reff, remained almost unchanged down to 10 nm and decreased with a further decrease in thickness, the evident EO response was observed down to 3 nm, which agrees with the fact that HZO films can maintain ferroelectric properties down to a few monolayers in thickness. The small reff in the HZO films with thickness below 5 nm was attributed to the stabilization of the ferroelectric rhombohedral-like phase.

DOI： 10.1063/5.0267559

Web of Science

Scopus

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

The electrocaloric effect (ECE)-induced temperature change (ΔT) in (Ba, Sr)TiO3-based ferroelectrics under unipolar electric fields was analyzed from the separate contributions of the dielectric constant (ε) and remanent polarization (Pr) based on the Maxwell relation. Consideration of the contributions of both ε and Pr is particularly important in a unipolar electric field operation, such as on/off field switching used in device applications. Direct ΔT measurements were also performed based on the lock-in thermography technique to verify the accuracy of the ΔT intensity estimated by the indirect method. The indirect and direct ΔT values were largely consistent. The ΔT intensity near the peak temperature of ΔT was dominated by the Pr contribution; a large ∂Pr/∂T was necessary to increase the overall ΔT magnitude. In contrast, a large ∂ε/∂T was essential to expand the operating temperature range of ΔT at temperatures higher than the dielectric maximum temperature. Quantitative understanding of the contributions of both ε and Pr to ΔT in unipolar electric fields is expected to guide the search for materials with a superior ECE.

DOI： 10.1063/5.0259805

Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Powder and Powder Metallurgy  

DOI： 10.2497/jjspm.15f-t14-02

Open Access