Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Deposition condition of (001)-epitaxial K(Ta0.6Nb0.4)O-3 (KTN) films on SrRuO3/SrTiO3 substrates by pulsed laser deposition was optimized. The optimized KTN film showed a saturated ferroelectric hysteresis loop with large withstand electric field, and the paraelectric to ferroelectric phase transition at room temperature (RT). Electro-optic (EO) property was characterized by modulation ellipsometry at RT, showing the maximum EO coefficient rc of 42 pm/V, which is larger than the previously reported value for KTN thin films having the same composition. Our findings show the importance of the precise tuning of deposition condition to achieve the large EO response in KTN films, promoting the potential application as a light modulator in EO devices at ambient temperature in the future. (C) 2022 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.21187

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/admi.202101682

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/admi.202101682

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0056121

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

DOI： 10.35848/1347-4065/ac17e0

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Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/ac17e0/pdf

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

<title>Abstract</title>
Electro-optic (EO) modulators for silicon photonics using CMOS-compatible materials and processes are in great demand. In this study, epitaxial (100)-undoped HfO₂ and Y-doped HfO₂ thin films were fabricated on Sn-doped In₂O₃/yttria-stabilized zirconia(100) substrates at room temperature via magnetron sputtering. EO measurement of the Y-HfO₂ film using modulation ellipsometry showed that the phase was changed by 180° after application of positive and negative poling biases, and the modulation amplitude increased linearly with increasing AC electric field, indicating a linear EO effect based on ferroelectricity. The observed results indicate that ferroelectric HfO₂-based films are viable candidates for CMOS-compatible EO devices.

DOI： 10.35848/1347-4065/ac087d

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Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/ac087d/pdf

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

(001)-epitaxial (Ba0.5Sr0.5)TiO3 (BST) thin films with different magnitudes of compressive strain were fabricated on SrRuO3/SrTiO3 substrates by pulsed laser deposition, and their electro-optic (EO) properties were characterized by modulation ellipsometry at different temperatures. All fabricated films showed an increased paraelectric-to-ferroelectric phase transition temperature upon compressive strain and revealed c-domain structures in the ferroelectric phase. We experimentally clarified that the EO properties of compressively strained BST thin films are enhanced toward the phase transition temperature modified by the strain. The experimental results were compared with the theoretical prediction based on a phenomenological thermodynamic model. Although the measured EO coefficient r(c) was less than that theoretically predicted, the experimentally observed strain effect on the EO properties is in good qualitative agreement. Published under license by AIP Publishing.

DOI： 10.1063/1.5117218

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

The influence of compressive strain on the linear electro-optic (EO) effect in c-domain (BaxSr1-x)TiO3 (BST) thin films was theoretically investigated using a phenomenological thermodynamic model. We considered that the c-domain BST thin films were grown on cubic substrates and an electric field was applied parallel to the direction of spontaneous polarization. To estimate the EO coefficients, we considered not only the intrinsic EO effect but also the elasto-optic effect by converse piezoelectric response. We found that the EO response is mostly determined by the difference in temperature from the ferroelectric-to-paraelectric phase transition boundary modified by the strain, and the elasto-optic effect appreciably affects the overall EO coefficient when the intrinsic EO effect is weak. (C)2019 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.19011

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We demonstrate a significant improvement in the epitaxial growth of perovskite dielectric films on MgO by introducing a SrTiO3 (STO)/TiO2 buffer layer, which enhances their dielectric response. 270-nm-thick (001)-epitaxial (Ba, Sr) TiO3 (BST) films were deposited by pulsed laser deposition on STO/TiO2-buffered MgO with a SrRuO3 (SRO) bottom electrode. The film directly deposited on SRO/MgO grew in a three-dimensional mode, resulting in a rough and poorly crystalline film with an almost relaxed strain. On the other hand, the film with a buffer layer grew in a two-dimensional mode, resulting in a flat and highly crystalline film with a large compressive strain (-0.80%). As a result, the paraelectric-to-ferroelectric phase transition temperature increased by 220 degrees C and an out-of-plane dielectric constant exceeding 1000 was achieved. (C) 2018 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.57.0902B1

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

(001)-epitaxial (Pb0.91La0.09)(Zr0.65Ti0.35)O-3 (PLZT) ferroelectric thin films were fabricated on SrTiO3 and MgO substrates, with an SrRuO3 bottom electrode layer, using pulsed laser deposition. When films were deposited in a single step at a high temperature conventionally used for epitaxial growth, island growth was observed. To suppress the island growth, we used a two-step growth technique. First, a thin initial layer was deposited at a low temperature to promote rapid strain relaxation from the lattice mismatch. Consequently, the island growth was suppressed and when a second layer was deposited at high temperature, a remarkably flatter surface was achieved as compared with that of conventional one-step-grown films. The two-step-grown PLZT films are promising for use in ferroelectric thin film-based plasmonic electro-optic devices. (C) 2016 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.16110

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